Table of contents

Ceramic electrolytes could potentially enable Li metal anodes, leading to safer and more energy dense solid-state batteries. However, it has been hypothesized that electric field amplification at electrode edges can destabilize the interface and lead to short circuiting during charging. By comparing models of the electric field distribution at the electrode/electrolyte interface for varying electrode geometries with experimental solid-electrolyte systems, we show that areas of high electric field can localize at sharp corners, which may facilitate Li metal penetration at these locations. Symmetric Li/ Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZO) cells were cycled until failure and the spatial distribution of the degradation was analyzed using electron microscopy. We report a decrease in nominal critical current density (CCD) from 1.48 to 1.26 mA cm⁻² due to a 15% increase in electric field from edge effects. Moreover, when considering the CCD locally at spots of high electric field amplification, we find current densities of at least 4 mA cm⁻² can still be sustained. Non-uniform electric field distributions at the Li/LLZO interface could play a major role in determining cycling capabilities and failure modes of solid-state batteries and may also have important implications for the manufacturing of Li metal battery electrodes.

The "sudden death" of a battery because of an abrupt capacity loss is a major cause of concern as it will leave electronic devices inoperable. Existing methodologies predict only the State of Health (SOH), Remaining Useful life (RUL) or detect abrupt capacity loss too close to the actual event, not allowing time for any corrective action. Sudden death does not happen at the same SOH, making the detection crucial. Specialized measurements or extensive number crunching are impractical for online battery health monitoring. Here, a novel lightweight framework, amenable for device implementation, with about 100 cycle advanced prediction has been proposed.

With the widespread application of lithium-ion batteries (LIBs), their applications and transportation in the aviation field are increasing. However, the inherent risk of LIBs and the special operating environment of the aircraft bring new challenges to the fight safety. In this paper, the thermal runaway (TR) characteristics of LIBs with different charging/discharging rates are studied under the pressure of the cruising altitude of civil aircraft (20 kPa). The results show that the increase of charging/discharging rate leads to the advance of the gas release and TR time, and the decrease of TR intensity under both 20 kPa and atmospheric pressures (95 kPa). The decrease of environmental pressure results in the advance of TR time and the decrease of TR intensity. Moreover, at 20 kPa, the TR time differences between batteries with different charging/discharging rates are bigger than that at 95 kPa. The dV/dQ and impedance results show that the loss of cathode materials and the side reactions are the main factors for the decrease of battery safety. The lower external pressure facilitates the open of the safety valve and the oxidation of electrolytes, which further enlarge the safety differences between LIBs with different charging/discharging rates.

Experimental conductivity measurements, obtained on NMC₅₃₂-based electrodes with markedly different porosities and made with percolating and non-percolating CB/PVdF phase, are compared with full-field numerical predictions. These ones are based on segmented nanotomography images and phase bulk properties and contain no tunable parameter. A good agreement between the calculated and measured transport properties is observed. 3D current density fields give insights on the microstructure impacts on the current density distribution. Ionic transport is dominated by low tortuosity micrometric channels. Results also highlight the presence of "dead areas" in porosity that are crossed by a very low ionic current showing that, at high rate, the effective porosity may reduce to the micrometric pore network. For electronic conductivity, the CB/PVdF mixture percolation threshold is evaluated at 6%–7% in volume. Even below this key value threshold, CB/PVdF aggregates significantly improve electronic conductivity by forming gateways between NMC clusters thus minimising the constriction resistances between them. The size of the representative volume element relative to electronic and ionic conductivities is also investigated.

Disk-like micron-sized monocrystalline LiNi_0.5Co_0.2Mn_0.3O₂ is synthesized by the co-precipitation method accompanied with calcination assisted by strontian carbonate without washing process or other complicated treatment. Powder X-ray diffraction, scanning electron microscopy, and transmission electron microscopy are used to characterize the obtained samples. Characterizations reveal that the addition of SrCO₃ help to form monocrystalline LiNi_0.5Co_0.2Mn_0.3O₂ with preferred (104) plane, and the particle is disk-like and in micrometer size. Electrochemical test results indicate that the LiNi_0.5Co_0.2Mn_0.3O₂ exhibits significantly improved capacity retentions of 95.6% and 89.3% after 100 cycles at 1C, for the voltage ranges of 2.8−4.3 V and 2.8−4.5 V, respectively. The excellent cycle performance of the LiNi_0.5Co_0.2Mn_0.3O₂ is ascribed to the unique monocrystalline morphology, high stability of (104) plane and reduced irreversible phase transition.

Enabling fast charging in lithium ion batteries (LIBs) is a key factor to make electric vehicles drive just like gasoline-powered vehicles when the time comes to refuel. However, fast charging to current LIBs (LiNi_xMn_yCo_1−zO₂/graphite) is limited by lithium plating, which is barely reversible and causes LIBs to lose capacity over time. Thus, research to quantify the lithium plating in LIB cells is extremely important in improving our fundamental understanding of lithium plating behavior and enabling fast charging for LIBs. In this study, we precisely quantified the amount of fast-charge-driven lithium plating in a coin-cell composed of LiNi_0.5Mn_0.3Co_0.2O₂ (NMC532)/graphite. We found that the amount of lithium plating gradually increases with the cycle count and reaches 25.59 μmole (26.80 mAh g⁻¹_cathode) by the 100th cycle. The study also reveals that the NMC532 has lost 19% of its original lithium content after 100 fast-charging cycles; this, correspondingly, causes a lattice volumetric strain of 0.59%.

The use of the Blocked-diffusion Warburg (BDW) impedance within electrochemical impedance spectroscopy (EIS) measurements can unveil diffusion properties of the electroactive material of modern batteries at different states-of-charge. The impedance response of the BDW comprises a diffusion response of charge carriers through a short-diffusion distance (e.g. the solid-phase in electroactive material of battery electrodes) and a capacitive response due to accumulation of charge carriers in a blocked-interface (e.g. impermeable current collector of a thin film electrode). This study has developed a mathematical expression based on the Newton-Raphson iteration method to calculate the frequency and time constant during the transition from diffusion to capacitive response in the BDW impedance. The mathematical procedure to calculate the frequency during the diffusion-capacitive transition response in the BDW has been written in a script in Matlab® software and is applied to BDW impedance responses reported in previous studies and extracted from EIS measurements in Li-ion and NiMH batteries. This study demonstrates that the time constant during the transition from diffusion to capacitive response in the BDW differs from the characteristic time constant commonly represented in the BDW mathematical expression. The characteristic time constant represented in the BDW mathematical expression is related to the rate of accumulation of charge carriers in the blocked-interface of the electrode. On the other hand, the time constant during the transition from diffusion to capacitance responses in the BDW impedance can be related to diffusion properties in solid-phase particles with heterogeneous size distribution in the electroactive material of modern battery electrodes.

Here, we present an ingenious approach to convert bio-waste into porous carbon to fabricate a working electrode for the development of sustainable energy storage devices. Carbonization of Borassus Flabellifer fruit skin (BFFS) in an inert atmosphere was followed by KOH activation to synthesize partially graphitic carbon nanosheets attached to the porous carbon. Surface chemistry and porosity were tuned by varying the carbonization and activation temperature to achieve excellent control of the studied physiochemical properties. The as-obtained ABFFS-derived porous carbon exhibited a specific surface area of 1750 m² g⁻¹ with distinctive morphology, showing great prospects for energy storage. The unique content of minerals in BFFS led to a highly porous architecture with a substantial volume fraction having micro- and meso-porosity. Symmetric supercapacitors were fabricated with 1 M H₂SO₄ and EmimBF₄ (ionic liquid) as electrolytes, and the specific capacitance reached values of 202 and 208 F g⁻¹, respectively. The cycling stability of up to 94% at a current density of 2 A g⁻¹ established a fairly stable performance for the supercapacitors based on biomass-derived carbon electrodes, and therefore, confirms the potential of BFFS-derived activated carbon for the advancement of supercapacitors based on bio-waste electrodes.

The ability to track electrode degradation, both spatially and temporally, is fundamental to understand performance loss during operation of lithium batteries. X-ray computed tomography can be used to follow structural and morphological changes in electrodes; however, the direct detection of electrochemical processes related to metallic lithium is difficult due to the low sensitivity to the element. In this work, 4-dimensional neutron computed tomography, which shows high contrast for lithium, is used to directly quantify the lithium diffusion process in spirally wound Li/SOCl₂ primary cells. The neutron dataset enables the quantification of the lithium transport from the anode and the accumulation inside the SOCl₂ cathode to be locally resolved. Complementarity between the collected neutron and X-ray computed tomographies is shown and by applying both methods in concert we have observed lithium diffusion blocking by the LiCl protection layer and identified all cell components which are difficult to distinguish using one of the methods alone.

As the ionic conductivity of solid-state lithium ion conductors rises, knowledge of the detailed conductivity mechanisms is harder to obtain due to the limited frequency resolution of the traditional impedance spectrometers. Moreover, the data is easily affected by the local microstructure (i.e. pores, grain-boundaries) and the preparation conditions. The aim of this work is to demonstrate the feasibility of the coaxial reflection technique as a reliable tool to study fast ionic conductors (i.e. σ > 10⁻⁴ S cm⁻¹). Especially the relative permittivity can be determined more accurately at room temperature. For the first time the electrical performance of LATP and LLZO manufactured via a scalable top-down glass-ceramic route is evaluated. The density turns out to be a key parameter influencing both relative permittivity and resulting conductivities. For a 100% dense LATP sample the coaxial reflection technique reveals a high grain-core conductivity of 6 × 10⁻³ S cm⁻¹ similar to the conductivity of ideal single crystals.

A large and controllable deformation of a cantilever consisting of a MCMB (MesoCarbon MicroBeads) graphite layer on a Cu foil is reported. In the charging process, the insertion of lithium ions causes the expansion of the MCMB layer and generates stress due to the deformation mismatch between the MCMB layer and Cu foil. By controlling the amount of Li ions and thickness ratio, the initially flat MCMB graphite/Cu electrode can bend into circular shape reversibly. A theoretical mechanical model is proposed to analyze the bending deformation. This super deformation driven by electrochemical reactions may be used for real-time control devices.

Combining the use of nickel-rich layered oxide cathode materials with the implementation of aqueous electrode processing can pave the way to cost-reduced and environmentally friendly electrodes and simultaneously increase the energy density of cells. Herein, LiNi_0.33Co_0.33Mn_0.33O₂ (NCM111), LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622), LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) and LiNi_0.8Co_0.15Al_0.05O₂ (NCA) were evaluated in terms of their response to aqueous processing under the same conditions to facilitate a direct comparison. The results illustrate that mainly nickel driven processes lead to lithium leaching which is combined with the increase of the pH value in the alkaline region. For NCA an additional aluminum-involving lithium leaching mechanism is assumed, which could explain the highest amount of leached lithium and the additional detection of aluminum. Electrochemical tests show a reduced capacity for cells containing water-based electrodes compared to reference cells for the NCM-type materials which increases during the first cycles indicating a reversible Li⁺/H⁺-exchange mechanism. In contrast, the NCA cells were completely electrochemically inactive making NCA the most water sensitive material tested in this report. By comparing the cycling performance of cells containing aqueous processed electrodes, a more pronounced capacity fade for nickel-rich cathode materials as compared to their reference cells can be observed.

For many practical applications, fully coupled three-dimensional models describing the behavior of lithium-ion pouch cells are too computationally expensive. However, owing to the small aspect ratio of typical pouch cell designs, such models are well approximated by splitting the problem into a model for through-cell behavior and a model for the transverse behavior. In this paper, we combine different simplifications to through-cell and transverse models to develop a hierarchy of reduced-order pouch cell models. We give a critical numerical comparison of each of these models in both isothermal and thermal settings, and also study their performance on realistic drive cycle data. Finally, we make recommendations regarding model selection, taking into account the available computational resource and the quantities of interest in a particular study.

Al-0.5 wt.% MgO, Al-1 wt.% MgO, Al-1.5 wt.% MgO and pure Al anodes were prepared to investigate the effect of MgO particles addition on the electrochemical performance of aluminum anode for Al-air batteries in alkaline electrolyte. The electrochemical performance of these battery devices, including anodic polarization, corrosion characteristics, hydrogen evolution rate, AC impedance, and discharge behavior was examined and analyzed comparatively in 4 M KOH solution. The results show that Al-0.5 wt.% MgO, Al-1 wt.% MgO composite anodes exhibit a negative shift in the open-circuit potential compared with pure Al anode. Appropriate amount of MgO addition obviously improves the electrochemical activity, corrosion resistance and anode utilization of pure Al anode. These behaviors should be related to the interface characteristic of MgO particles with Al matrix which helps to destroy the integrity and compactness of the oxide layer on anode surface. The influence of MgO addition on the corrosion resistance of composite Al anode is well explained by the energy band and state density calculation based on density functional theory.

A novel method is introduced to simulate the formation of electrochemical double layers on complex electrode particle geometries. Electrochemical double layers play the most crucial role in electrical energy storage of supercapacitors and in capacitive deionization (desalination) devices. The double-layer region usually spans 20 to 50 nanometers, whereas other significant length scales, e.g., particle size or inter-particle space in electrodes, are in tens to hundreds of microns. Thus, a direct numerical simulation in the continuum scale must resolve the ionic concentration and potential gradients in spatial scales across 3 ∼ 4 orders of magnitude difference and is highly challenging. In this paper, we use the smoothed boundary method that defines complex microstructures with a continuous domain-parameter function to reformulate the Nernst-Planck-Poisson equations and solve the reformulated governing equations on adaptively refined meshes. The method allows for accurate simulations of arbitrarily complex geometries with resolutions spanning from nanometers in the double layer to micron/millimeters in the particle/electrode scales. The results show that ions first rapidly adsorb onto or are repelled from the particle surfaces, followed by long-distance diffusion to alleviate the concentration gradient until the system reaches the steady state. The concentration and potential evolutions highly depend on the particle geometries.

Approaches for thermal management of lithium-ion (Li-ion) batteries do not always keep pace with advances in energy storage and power delivering capabilities. Root-cause analysis and empirical evidence indicate that thermal runaway (TR) in cells and cell-to-cell thermal propagation are due to adverse changes in physical and chemical characteristics internal to the cell. However, industry widely uses battery management systems (BMS) originally designed for aqueous-based batteries to manage Li-ion batteries. Even the "best" BMS that monitor both voltage and outside-surface temperature of each cell are not capable of preventing TR or TR propagation, because voltage and surface-mounted temperature sensors do not track fast-emerging adverse events inside a cell. Most BMS typically include a few thermistors mounted on select cells to monitor their surface temperature. Technology to track intra-cell changes that are TR precursors is becoming available. Simultaneously, the complex pathways resulting in cell-to-cell TR propagation are being successfully modelled and mapped. Innovative solutions to prevent TR and thermal propagation are being advanced. These include modern BMS for rapid monitoring the internal health of each individual cell and physical as well as chemical methods to reduce the deleterious effects of rapid cell-to-cell heat and material transport in case of TR.

Development of high-power lithium-ion batteries requires the optimization of the electrode kinetics of lithium-insertion materials to improve the rate capability of these devices. The rate capability of lithium-insertion electrodes is controlled by the concentration overvoltages that arise from changes in the Li⁺ concentration at the electrode/electrolyte interface. Two distinct rate-capability behaviors prevail depending on whether charge transport is limited by Li-ion mass transfer within the solid particles or within the interstitial spaces of the electrode. In this study, the diluted electrode method is employed to characterize the two types of rate-capability behavior exhibited by Li[Ni_1/2Mn_3/2]O₄ (LiNiMO) electrodes. Low-LiNiMO electrodes exhibit better rate capabilities than high-LiNiMO electrodes indicating that lithium-ion transport is more effective (i.e., much faster) in the solid active material than in liquid electrolyte within the electrode pore. The results provide useful insights for understanding the electrode kinetics of lithium-insertion materials and designing electrodes for high-power lithium-ion batteries.

Given the electrochemical modelling and control systems challenges facing lithium-ion batteries in extreme operating conditions, such as low temperature and high C-rate, it is important to understand the transport dynamics in a polarized cell with large electrolyte concentration gradients. To this end, a combination of conventional magnetic resonance imaging (MRI) experiments and MRI experiments coupled with pulsed-field gradient NMR for diffusion measurements were performed on an in situ lithium-ion cell operating at a variety of temperatures and current densities. The aim was to quantify the electrolyte transport parameters with spatial resolution. Some progress was attained towards this aim, and the necessary framework for future studies along this direction was developed; however, it was determined that in order to accurately quantify the transference number, a very accurate measurement of the concentration gradient is necessary when the polarization is large. It was also observed that limiting current behavior in the electrolyte at low temperature arises as a consequence of diffusion limitation on the anodic side, rather than ion depletion on the cathodic side. The framework developed herein may be useful not only for electrochemical model validation, but potentially also comprehensive electrolyte transport characterization, should the identified experimental limitations be overcome.

A dataset is presented containing the rate capability measured for Lithium-ion cells obtained from old notebook batteries. The experimental results show an intersection of rate capabilities, related to degraded cells that exhibit high reversible capacities compared to the rated value and measured at 0.1C discharge rate, but a fast voltage decay and a constrained discharge capacity measured at 1C. With the aid of an electrochemical model it is shown that this intersection is possible if cells containing a lower concentration of Lithium salt in the electrolyte are compared to others that experienced a higher damage in the electrodes during their first use. This article casts doubts on the validity of a state of health determined from the discharge capacity measured at one rate for the classification of Li-ion batteries for a second life, if applied to datasets containing batteries experiencing diverse degradation paths.

Zinc continues to garner immense interest due to its versatility as an anode material in several configurations utilizing either alkaline or mild-pH electrolytes. Current research on using mild-pH electrolytes has improved the rechargeability aspect of Zn-based batteries since Zn²⁺ is solely utilized for plating/stripping of Zn. Several studies have incorporated Zn metal foils, yet, dramatic improvements can be achieved by expressing Zn as a porous structure. Herein, we use a quasi-pulsed electrodeposition process to prepare a conformal Zn coating onto 3D porous copper foam. By tuning the electrodeposition parameters, we achieved an optimal Zn coating that undergoes reversible plating/stripping when tested in symmetric Zn cells, which supported a low overpotential of ∼60 mV for up to 100 cycles. We further investigated changes in the surface morphology by studying the Zn surface of both foil and 3D structure using scanning electron microscopy and X-ray micro-computed tomography. Both techniques showed that the Zn foil undergoes dramatic alterations at the surface, which results in inhomogeneous deposition of Zn, whereas the 3D form exhibited minimal changes. Lastly, we paired both Zn foil and 3D Zn with vanadium oxide and demonstrated that the porous structure supports high rate capability and high specific capacity.

Understanding the impact of repeated fast charging of Li-ion batteries, in particular at low temperatures, is critical in view of the worldwide deployment of EV superchargers. In this study, the effects of fast charging using the conventional CCCV protocol on the performances of a high energy cell were investigated. The fast charging capability was confirmed to be negatively affected by low temperatures. The cell was capable of sustaining repeated fast charging at 23 °C without notable performance degradation, but quickly degraded when the charging temperature was decreased. Post-mortem analysis revealed several failure modes, including lithium plating, graphite exfoliation, jelly-roll deformation, active materials crumbling, aluminum corrosion and an abnormal SEI growth on the anode side. A loss of lithium inventory, mainly due to lithium plating and subsequent SEI growth was identified to be the major cause of performance degradation related to repeated fast charging at low temperatures. These results clearly put in evidence that repeated fast charging can cause significant degradations in Li-ion cells, with detrimental consequences in safety, performance and service life. Gaining insights into the failure modes related to repeated fast charging shall guide battery developers towards the optimization of Li-ion cells for EV application.

All-solid-state lithium-ion batteries (ASSLIBs) without organic liquid electrolytes have attracted considerable attention as a solution to existing safety issues. Si is the most promising anode active material for increasing the energy density of such batteries owing to its high theoretical capacity. However, the stress relaxation of Si with large structural fluctuations is a major challenge to its practical use. In the present study, nanoporous Si particles and a sulfide-based solid electrolyte are composited to accommodate the volumetric expansion. To the best of our knowledge, this is a novel approach in the case of ASSLIBs. We find that the capacity retention of highly dispersed Si composite anodes is 80% up to 150 cycles. Such excellent cyclability is explained by our results, which suggest the following microstructural behavior. The pores in the Si particles act as buffer regions for large volume changes. In addition, the strains arising from the slightly expanded Si particles are relieved by the elasticity of the surrounding sulfide-based solid electrolyte. In summary, this study is a significant step toward the development of high-performance ASSLIBs for various applications.

Organic solvents undergo degradation reactions when in contact with lithium metal. These reactions form a layer of decomposition products that partly prevents further electrolyte decomposition—passivation. Still, the chemical processes in this system are complex and have not yet been fully understood though it is of high relevance for lithium metal batteries. Scanning Electrochemical Microscopy (SECM) in feedback mode as well as GC-MS are used for analyzing the interface as well as soluble decomposition products. SECM data show that the native interface thickness on metallic lithium from ethylene carbonate (EC) and ethyl methyl carbonate (EMC) electrolyte solutions is reduced by approx. 98% by adding 5 wt% vinylene carbonate (VC) to the solution. The addition of VC changed significantly the dynamics of the growth of the deposition layer. GC-MS studies of the EC:EMC electrolyte solution proof an ongoing reaction of the metallic lithium with the electrolyte even after several days. In comparison, the addition of VC appears to stabilize the interface and no decomposition products could be identified. It is concluded that the addition of VC to the electrolyte solution from EC:EMC prevents the trans-esterification of EMC by surface passivation and not by scavenging alkoxides as claimed in literature.

Few-layered reduced graphene oxide (RGO) is prepared from graphite by chemical exfoliation method. In half cell, RGO electrode delivers a specific capacitance value of 41 mF cm⁻² at 0.5 mA cm⁻² in 1.0 M KOH. An attempt is made to improve the capacitance properties of RGO by widening the operating voltage window and improving the charge storage capability through the use of metal oxide nanoparticles as electrolyte additives. The specific capacitance of RGO increases to 62 mF cm⁻² and 87 mF cm⁻² when ZnO and SiO_x nanoparticles were uniformly dispersed in the electrolyte, respectively, at 0.5 mA cm⁻². For a power density of 1.5 mW cm⁻², the symmetric supercapacitor assembled using ZnO and SiO_x nanofluid electrolyte delivers an energy density of 2.6 μWh cm⁻² and 3.03 μWh cm⁻², respectively, which is 2.7 and 3.1 times the value of energy density obtained for symmetric supercapacitor assembled using KOH electrolyte. The nanofluid electrolytes show high stability even after 60 d and the electrochemical performance of RGO is reproducible in the aged nanofluid electrolytes. The RGO electrode shows stable cycling for the tested number of 10000 cycles in all the electrolytes.

The formation and growth mechanism of a solid-electrolyte interphase (SEI) on a graphite-based negative electrode was investigated to enhance the cycle life of lithium ion batteries with a quasi-solid state electrolyte (QSE). In a QSE, liquid constituents including solvate ionic liquid (SIL), diluting solvent, and additives are quasi-solidified on surface of silica particles, which ensures the safety of a 100 Wh class laminated cell. For the SIL, an equimolar complex composed of tetraethylene glycol dimethyl ether (G4) and lithium bis(trifluoromethanesulfonyl)amide (LiTFSA), was utilized. Propylene carbonate (PC) was used as diluting solvent to enhance the ionic conductivity of the SIL. Vinylene carbonate (VC) additive was introduced to form a robust SEI for inhibiting the reductive decomposition of G4 and PC. Nuclear magnetic resonance and hard X-ray photoelectron spectroscopy revealed that the decompositions of LiTFSA, PC, and G4 contributed to the SEI formation at the initial charge. During charge-discharge cycles, continuous decompositions of G4 and PC were a major reason for the SEI growth. To suppress the decomposition, charging at a low rate was introduced at beginning of the initial charge to enhance the VC decomposition and the robust SEI formation. Consequently, the decomposition of the QSE was inhibited, which enhanced its cycle life.

Dual-graphite batteries have emerged as promising candidate for sustainable energy storage due to their potentially low costs and absence of toxic materials. However, the mechanism of anion intercalation and the structures of the resulting graphite intercalation compounds (GICs) are still not well understood. Here, we systematically evaluate the anion intercalation characteristics into graphite for three highly concentrated electrolytes containing LiPF₆, LiTFSI and their equimolar binary mixture. The binary mixture exhibits a significantly enhanced capacity retention and improved intercalation kinetics compared to the single-salt electrolytes in graphite ∣∣ Li metal cells. In situ X-ray diffraction studies prove the formation of stage 1-GICs and a homogeneous distribution of anions within graphite. From ex situ solid-state ¹⁹F magic-angle spinning (MAS) nuclear magnetic resonance (NMR) measurements, GICs can be identified at various states-of-charge (SOCs). The ¹⁹F chemical shifts of intercalated anions indicate no significant charge transfer between anion and graphite. The observed narrow ¹⁹F linewidths of the GIC-signals are most likely caused by a high translational and/or rotational mobility of the intercalates. Furthermore, the ¹⁹F MAS NMR studies allow the identification of the molar ratios for PF₆⁻ and TFSI⁻ anions intercalated into graphite, suggesting a preferred intercalation of PF₆⁻ anions, especially at lower SOCs.

The corrosion behavior and the battery performance of the Aluminum alloy 1050 as an anode in Al/AgO battery in aerated 3.5% NaCl solution, are evaluated in the presence of thiourea as an organic inhibitor, using different approaches, such as potentiodynamic polarization, electrochemical impedance spectroscopy, electrochemical noise analysis, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and galvanostatic discharge. The results indicate that by the addition of inhibitor, the corrosion rate of the aluminum reduces at the initial stages, and by formation of a protective layer on the surface, pits initiation and propagation are controlled. With increasing the immersion time, inhibitor on the surface is provided a situation which aluminum as a battery anode can corrode uniformly and provides needed electron and capacity for battery with a better performance. According to shotnoise and stochastic theory, the probability of formation of pits with a radius of more than 20 μ is reduced significantly in the presence of inhibitor. Also, as it can be seen in the SEM results, aluminum tends to be corroded more uniform, which resulted in an anode efficiency of 91 percent in the galvanostatic discharge test.

Realizing ultra-fast charge and discharge of lithium-ion batteries (LIBs) is one of the effective ways to promote the popularity of electric vehicles, solve energy and environmental problems. A lot of studies have shown that low conductivity and low lithium-ion diffusivity are the major limiting factors for the rate performance of cathode. However, there is no systematic review on the methods to improve the rate performance of cathode for LIBs. Hence this review ground-breakingly summarizes a series of key strategies and their electrochemical mechanisms to increase the rate capacity of cathode materials. The limiting factors for the development of LIBs fast charging are introduced. It analyzes the working mechanisms of the nanostructure and micro-nanostructures. The influences of carbon coating with different carbon sources are introduced and compared in detail. The specific mechanisms and research results of surface coating modification and doping strategies in LiFePO₄, layered structure cathode, and spinel structure cathode are reviewed. Moreover, innovative approaches such as spinel-layered composites preparation, structural-gradient design, and photo-accelerated fast charging are also provided. Finally, some existing challenges and development directions in the future are discussed.

We report a unique solid-state lithium-sulfur cell based on a bilayer electrolyte and composite solid-state cathode. The bilayer electrolyte that contains a layer of mixed conduction membrane and a layer of polymer electrolyte eliminates the use of organic flammable liquid electrolytes and separators. The sulfur electrode is also a unique composite of sulfur with ionically-conducting intercalating nano-particulate material. Unlike many other solid-state batteries, this cell can be cycled at room temperature to utilize 85% of the active material at the sulfur electrode. The low internal resistance of the cell is comparable to that of a liquid electrolyte based lithium-sulfur cell. Impedance studies indicate that the low internal resistance results from the high ionic conductivity of the intercalating nano-particulate materials and the thin layer of polymeric electrolyte. While the volume changes at the cathode result in loss of inter-particle contact with repeated cycling, the addition of alumina to the polymer layer improved the capacity retention. This unique solid-state cell configuration opens a new pathway towards a safer high-energy lithium battery.

Cylindrical lithium-ion batteries are used across a wide range of applications from spacesuits to automotive vehicles. Specifically, many manufacturers are producing cells in the 18650 geometry i.e., a steel cylinder of diameter and length ca. 18 and 65 mm, respectively. One example is the LG Chem INR18650 MJ1 (nominal values: 3.5 Ah, 3.6 V, 12.6 Wh). This article describes the electrochemical performance and microstructural assembly of such cells, where all the under-pinning data is made openly available for the benefit of the wider community. The charge-discharge capacity is reported for 400 operational cycles via the manufacturer's guidelines along with full-cell, individual electrode coating and particle 3D imaging. Within the electrochemical data, the distinction between protocol transition, beginning-of-life (BoL) capacity loss, and prolonged degradation is outlined and, subsequently, each aspect of the microstructural characterization is broken down into key metrics that may aid in understanding such degradation (e.g., electrode assembly layers, coating thickness, areal loading, particle size and shape). All key information is summarized in a quick-access advanced datasheet in order to provide an initial baseline of information to guide research paths, inform experiments and aid computational modellers.

Sb₂S₃ is recognized as a promising anode material for sodium-ion batteries because of its low toxicity and high theoretical capacity of 946 mAh g⁻¹. However, it usually suffers from a severe capacity decay during the charge/discharge processes mainly caused by their inferior electronic conductivities and large volume change. Currently, the preparation of Sb₂S₃-based anode materials is limited to conventional hydrothermal (solvothermal) or solution methods. In this study, a novel vaporization-condensation method is successfully employed to prepare nanocomposites between Sb₂S₃ and active carbon (YP80F carbon). During the vaporization-condensation process, Sb₂S₃ can be reformed and confined within the nanopores of YP80F carbon, obtaining surprising high performance anode materials (Sb₂S₃@YP samples) for Na-ion batteries. the nanopores of carbon can accommodate the large volume of Sb₂S₃ variation during charge/discharge process and enable a fast electron/Na-ion transfer. One of these Sb₂S₃@YP samples delivers a high capacity of 799.5 mAh g⁻¹ at 1162 mA g⁻¹, and maintains at 476.5 mAh g⁻¹ after 1000 cycles (based on the mass of Sb₂S₃). In addition, this vaporization-condensation method provides a significant strategy for preparing Sb₂S₃-based anode materials for long cycle-life sodium-ion batteries.

Adding porosity to battery electrodes is sometimes useful for accommodating volumetric expansion, electrolyte access to active materials, or mitigating poor high-rate performance for thicker electrodes. Ordered macroporous electrode such as inverse opals, are a good model system: binder and conductive additive-free, interconnected electrically, have defined porosity consistent with thickness, good electrolyte wettability and surprisingly good behavior in half-cells and some Li-battery cells at normal rates. We show that at high charge and discharge rates, charge storage in macroporous electrode materials can be completely supressed, and then entirely recovered at low rates. Using a model system of inverse opal V₂O₅ in a flooded Li-battery three-electrode cell electrodes store almost no charge at rates >10 C, but capacity completely recovers when the rate is reduced to <1 C. We show how the IO material is modified under lithiation using X-ray diffraction, Raman scattering and electron microscopy. Chronoamperometric measurements together with a model to fit rate-dependent capacity decay suggests a dependence on the intrinsic out-of-plane conductivity of the electrode. The data show that electrodes with nanoscale dimensions and macroscale porosity are fundamentally limited for high-rate performance if the intrinsic electronic conductivity is poor, even when fully soaked with electrolyte.

A high-performance paper electrode is fabricated through coating polypyrrole (PPy) on ordinary laboratory filter paper via a traditional interfacial polymerization method with perchloric acid (HClO₄) as a dopant. Owing to the superior mechanical flexibility and environmental stability of the free standing PPy paper, the robust electrode displays an ultrahigh capacitance of 1650 mF cm⁻² and remarkable cyclic stability of losing 11.66% after cycling for 10000 times in a three-electrode system. More importantly, the areal specific capacitance has only decreased by 0.08% after five months. Furthermore, by employing the synthesized PPy papers as electrodes and the PVA-H₂SO₄ gel as electrolyte, the assembled all-solid-state supercapacitor with an areal specific capacitance of 566.5 mF cm⁻² is achieved, corresponding to an areal energy density of 38.55 μW h cm⁻² and power density of 0.17 mW cm⁻². These results suggest that the simple synthesis of PPy paper electrode pave a promising way to exploit flexible and durable energy storage applications.

Carbonate-free electrolytes comprising lithium bis(fluorosulfonyl)imide (LiFSI) and sulfolane (SL) (LiFSI/SL) with medium concentrations show excellent cycle stabilities with high Coulombic efficiencies. The high Coulombic efficiencies indicate that there is no corrosion of aluminum current collectors despite the absence of LiPF₆. X-ray photoelectron spectroscopy and electrochemical quartz crystal microbalance measurements show that the passivation layer on the aluminum current collector in LiFSI/SL consists of LiF and sulfurous species. The study findings will expand the applicability range of lithium-ion batteries, the current mainstay of sustainable energy sources.

Aqueous electrode manufacturing of nickel-rich layered oxide cathode materials poses a significant challenge due to their high water sensitivity. LiNi_0.8Co_0.15Al_0.05O₂ (NCA) has been shown to be particularly sensitive not only to water during processing, but also ambient air. In an effort to further clarify the processes that occur when NCA is in contact with water, the active material was investigated after different durations of water exposure. The results show that a differentiation has to been made between the surface impurities already present on NCA in the pristine state, water-induced surface species and water-induced leached species. The results demonstrate that the water-induced surface species can be mainly attributed to chemisorbed CO₂, nickel carbonate and NiOOH-like species but also smaller amounts of newly-formed aluminum and cobalt compounds. The water-induced leached species were assigned to lithium and aluminum-containing species. Water-induced surface species lead to a severe deterioration of the cells due to the resistive nature of these moieties and their involvement in side reactions during cycling. It is essential to find ways to suppress the formation of these species for the successful implementation of aqueous processing for NCA and likely nickel-rich cathode materials in general.

We report on stabilization of Li–S cells cycled with an areal charge/discharge capacity of 2 mAh cm⁻² at current densities of 1–2 mA cm⁻² using ethereal LiTFSI/LiNO₃/DOL/DME electrolyte solution containing 0.1M Li₂S₈. This electrolyte solution enables stable lithium metal stripping−plating both in symmetric Li∣Li and full Li–S cells with composite binder free sulfur impregnated activated carbon fibers cathodes. The addition of Li₂S₈ substantially extends cycling life of these cells due to the formation of smooth non-dendritic Li metal surface protected with an effective SEI enriched with Li sulfides, sulfites and sulfates species. Symmetric Li∣Li could be cycled stably for more than 1000 h at 1–2 mA cm⁻² with Li₂S₈-containing electrolyte solutions. Full Li–S cells demonstrate more than 500 stable cycles (at least 3 times more than with Li₂S₈ free electrolyte solution) at a current density of 1 mA cm⁻² and an areal capacity of 2 mAh cm⁻². The most stable cycling results were achieved for the cells cycled with discharge cut off voltage of 1.9 V preventing the depletion of LiNO₃. The use of electrolyte solutions containing liquid lithium poly-sulfides makes possible considerable decrease in the amount of the electrolyte solution and increases the energy density of the cells.

Highly concentrated electrolytes (HCEs) are attracting interest as safer and more stable alternatives to current lithium-ion battery electrolytes, but their structure, solvation dynamics and ion transport mechanisms are arguably more complex. We here present a novel general method for analyzing both the structure and the dynamics, and ultimately the ion transport mechanism(s), of electrolytes including HCEs. This is based on automated detection of bonds, both covalent and coordination bonds, including how they dynamically change, in molecular dynamics (MD) simulation trajectories. We thereafter classify distinct local structures by their bond topology and characterize their physicochemical properties by statistical mechanics, giving both a qualitative and quantitative description of the structure, solvation and coordination dynamics, and ion transport mechanism(s). We demonstrate the method by in detail analyzing an ab initio MD simulation trajectory of an HCE consisting of the LiTFSI salt dissolved in acetonitrile at a 1:2 molar ratio. We find this electrolyte to form a flexible percolating network which limits vehicular ion transport but enables the Li⁺ ions to move between different TFSI coordination sites along with their first solvation shells. In contrast, the TFSI anions are immobilized in the network, but often free to rotate which further facilitates the Li⁺ hopping mechanism.

A theoretical approach of the insertion/deinsertion of lithium in host materials is proposed to take into account some phenomena not included in classical analyses of lithium battery operation. This is mainly related to the variation of the transport properties in the first atomic layers in the vicinity of the interface which can give rise to rapid storage phenomena. These processes are of great importance in the case of electrodes made of nanoparticles as a result of the considerable development of the interfacial surface. For example, they can be at the origin of the important capacitive behavior of the system. A model based on the numerical integration of transport equations is presented to describe these complex mechanisms. The theoretical analysis is illustrated on the model case of lithium insertion in electrodes made of nanoparticles of anatase and fluorinated anatase.

Transmission line modeling (TLM) has become an important approach for analysis of measured impedance spectra of battery cells. Still, the existing models lack some important features which prevents a full and accurate analysis of measured spectra. Here we present a general physics-based TLM that contains all the processes known from treatments of transport/reaction schemes based on the Newman porous electrode model or the corresponding Poisson-Nernst-Planck framework. Compared to previous TLMs, the present model additionally takes into account the movement of non-active mobile ions in all phases. After detailed description of the individual TLM model elements and their physical background we show, step-by-step, how it can be used to interpret the measured response of NMC cathodes, lithium anodes and full NMC-Li cells. Many details are considered the origin of which is identified by performing carefully designed additional experiments, e.g. electrolytes with variable concentration of salt. Besides identifying all the meaningful impedance features of electrodes and full cells, we also show how various materials parameters such as transport number, diffusion coefficient, conductivity etc can be calculated for various phases appearing in a porous battery electrode system. Finally, we use the findings to analyze the development of impedance response during discharge of a NMC-Li cell.

Graphene quantum dots (GQD) have been used in various potential applications due to their range of attractive properties such as high conductivity, good chemical resistance, very good optical properties and etc. Very first time, in this study, the GQD is used as a molecular catalyst; here the given volume of GQD around 300 μl is dispersed in as prepared vanadium based electrolyte. It is observed that the CV curve of the GQD incorporated electrolyte showed significant variation in the electrochemical activity of VO₂⁺/VO²⁺ redox reaction. The resistive behavior obtained from the EIS analysis of GQD showed highly enhanced values when compared with the bare electrolyte. The addition of GQD in the active electrolyte showed great improvement in the VO₂⁺ to VO²⁺ redox reaction kinetics which is evidenced from the obtained kinetics parameters such as exchange current density, rate constant and etc. The GQD added electrolyte showed excellent improvisation in the exchange current density value of i₀ = 6.175 × 10⁻⁴ A cm⁻² which is two-fold higher than the bare electrolyte (i₀ = 2.365 × 10⁻⁴ A cm⁻²). Thus, the idea of using GQD will play potential effect in various electrochemical applications.

A new strategy for electrochemical interfaces that utilizes multilayer films deposited by atomic layer deposition (ALD) is introduced. Manganese-rich and nickel-rich cathode oxides were coated with a novel bilayer film of metal fluorides. Subsequent exposure to prolonged, high-voltage electrochemical cycling vs graphite electrodes revealed that the bilayer film can greatly enhance the high-voltage stability of cathode oxides. In particular, in manganese-rich cells, capacity fade due to manganese dissolution was substantially reduced and impedance rise was virtually eliminated. Furthermore, in nickel-rich NMC-811 cells, impedance rise was reduced by ∼80%, compared to the NMC-811 baseline, after ∼300 h of high-voltage exposure during cycling. The multilayer film strategy presents an exciting opportunity for tailoring designs and materials for electrochemical interfaces in advanced lithium-ion batteries and beyond.

In efforts to increase the energy density of lithium-ion batteries, researchers have attempted to both increase the thickness of battery electrodes and increase the relative fractions of active material. One system that has both of these attributes are sintered thick electrodes comprised of only active material. Such electrodes have high areal capacities, however, detailed understanding is needed of their transport properties, both electronic and ionic, to better quantify their limitations to cycling at higher current densities. In this report, efforts to improve models of the electrochemical cycling of sintered electrodes are described, in particular incorporation of matrix electronic conductivity which is dependent on the extent of lithiation of the active material and accounting for initial gradients in lithiation of active material in the electrode that develop as a consequence of transport limitations during charging cycles. Adding in these additional considerations to a model of sintered electrode discharge resulted in improved matching of experimental cell measurements.

Fundamental research and practical assembly of rechargeable calcium (Ca) batteries will benefit from an ability to use Ca foil anodes. Given that Ca electrochemistry is considered a surface-film-controlled process, understanding the interface's role is paramount. This study examines electrochemical signatures of several Ca interfaces in a benchmark electrolyte, Ca(BH₄)₂/tetrahydrofuran (THF). Preparation methodologies of Ca foils are presented, along with Ca plating/stripping through either pre-existing, native calcium hydride (CaH₂), or pre-formed calcium fluoride (CaF₂) interfaces. In contrast to earlier work examining Ca foil in other electrolytes, Ca foils are accessible for reversible electrochemistry in Ca(BH₄)₂/THF. However, the first cyclic voltammetry (CV) cycle reflects persistent, history-dependent behavior from prior handling, which manifests as characteristic interface-derived features. This behavior diminishes as Ca is cycled, though formation of a native interface can return the CV to interface-dominated behavior. CaF₂ modification enhances such interface-dominance; however, continued cycling suppresses such features, collectively indicating the dynamic nature of certain Ca interfaces. Cell configuration is also found to significantly influence electrochemistry. With appropriate preparation of Ca foils, the signature of interface-dominated behavior is still present during the first cycle in coin cells, but higher current density compared to three-electrode cells along with moderate cycle life are readily achievable.

This work demonstrates how staged heat release from layered metal oxide cathodes in the presence of organic electrolytes can be predicted from basic thermodynamic properties. These prediction methods for heat release are an advancement compared to typical modeling approaches for thermal runaway in lithium-ion batteries, which tend to rely exclusively on calorimetry measurements of battery components. These calculations generate useful new insights when compared to calorimetry measurements for lithium cobalt oxide (LCO) as well as the most common varieties of nickel manganese cobalt oxide (NMC) and nickel cobalt aluminum oxide (NCA). Accurate trends in heat release with varying state of charge are predicted for all of these cathode materials. These results suggest that thermodynamic calculations utilizing a recently published database of properties are broadly applicable for predicting decomposition behavior of layered metal oxide cathodes. Aspects of literature calorimetry measurements relevant to thermal runaway modeling are identified and classified as thermodynamic or kinetic effects. The calorimetry measurements reviewed in this work will be useful for development of a new generation of thermal runaway models targeting applications where accurate maximum cell temperatures are required to predict cascading cell-to-cell propagation rates.

LiNiO₂ (LNO) is one of the most potential alternatives to LiCoO₂ in Li ion batteries (LIBs). However, it still suffers from poor cyclability. Meanwhile, the recycling processes of LIBs are widely investigated to enable effective recycling for the growing amounts of LIB waste. Cu is one of the dominating impurities in LIB recycling fractions. In this work, LNO and 0.2 mol% Cu-doped LNO are studied. Cu-doping is demonstrated to stabilize the LNO lattice structure, reduce cation mixing and improve the reversibility of phase transitions during electrochemical processes. Consequently, the rate capability of LNO is improved by Cu-doping, especially at high C-rates. The Cu-doped LNO shows much higher capacity retention of 85% than that of 66% for the undoped LNO at the current density of 100 mA·g⁻¹ after 100 cycles in a voltage window of 2.5–4.5 V. Our results show that a possible Cu contamination in the Ni fraction of the LIB material recovery process can be used to enhance the electrochemical properties of newly synthetized Ni-based positive electrode materials.

The mechanism of the spontaneous intercalation of Li metal into graphite electrodes is highly relevant for aging mechanisms and pre-lithiation of Li-ion cells. In the present work, we introduce a method to investigate this mechanism via measuring the open-circuit-potential (OCP). Experiments without electrolyte, with organic solutions without and with LiPF₆ reveal details on the reaction mechanism at 29 °C. The electrodes are investigated by Raman spectroscopy and glow-discharge optical emission spectroscopy (GD-OES) depth profiling to reveal the spatial distribution of the lithiated phases. The analytical information is enriched by simulations with the Battery and Electrochemistry Simulation Tool (BEST). The combination of tools gives interesting insights into the behavior of negative electrodes regarding re-intercalation of deposited Li into graphite and its kinetics, development of inhomogeneities during aging, as well as pre-lithiation and post-mortem analysis methodology.

Lithium-ion cells and batteries pose safety risks along with their favorable characteristics such as high energy and power densities. The numerous differences in chemistries and form-factors along with poor manufacturing quality in some cases, can lead to unpredictable field failures with this battery chemistry. The safety of lithium-ion cells and batteries at various states of charge (SOC) has not been studied comprehensively in the past and the goal of this study was to determine if the result of off-nominal conditions would vary with SOC. The study includes cells and batteries of different form factors, cathode chemistries, and capacities. The off-nominal conditions that the cells were exposed to were high-temperature and low impedance external short. In addition to this, voltage stability for the cells and batteries at various SOC was studied for a period of 9 months. The results demonstrate the differences in the level of safety for the cells and batteries at different SOC.

Mg-air battery is a promising candidate as power supply because of high specific energy, stable discharge voltage, long storage life and friendly environment. However, the corrosion and passivation of Mg remains unresolved as well as oxygen supply, resulting in increase of electrode overpotential. Here, a type of oxygen electrode is present for Mg-oxygen battery, where hydrogen peroxide can directly and indirectly form hydroxide ions by means of nickel foam sandwiched with MnO₂ and Fe/C. In optimization of electrolyte concentration, inhibitor and electrode structure, Na₃VO₄ is superior to Na₃PO₄ and La(CH₃COO)₃ inhibiting Mg corrosion, the optimal NaCl concentration is obtained for Mg-air battery, and the oxygen electrode can effectively improve the performance of Mg-oxygen battery. The results show that the Mg-oxygen battery employing 0.3 wt.% H₂O₂ as oxygen supply and 15.5 wt.% NaCl as the electrolyte can stably run for more than 7 h, and the battery is discharged above 1 V at the current density of 25 mA cm⁻². The findings of Mg-oxygen battery can be available for power supply in the anaerobic or anoxic environment.

Extreme scenarios of high discharge current must be understood for better battery management system design. Physics-based modeling can give a better insight into the battery response but can be challenging due to the large number of parameters. In this work, an electrochemical pseudo-2D model is developed and used in the parameter identification and validated under high current discharge conditions. Commercial 18 650 cells with maximum rated current of 20 A (13.3 C) are characterized with discharge rates up to 40 C under controlled thermal conditions. The proposed three-step parameter identification procedure starts with the open circuit voltage being used to estimate the equilibrium potentials. In a second step, kinetic parameters are identified under high current aided by a parameter sensitivity analysis and parameter optimization with an evolutionary algorithm. The third step is the verification by comparing simulation results with measurements resulting in root main square error under 89 mV for currents until 26.6 C. Limits of the model are explored in the 33.3 C case, where a parameter re-fit shows that polarization effects change for very high current.

The morphology, structure and thermal stability of anode, cathode and separator of lithium-ion batters at different states of health (SOHs: 100%, 91.02%, 83.90% and 71.90%) under 100% state of charge were studied. The morphology analysis showed that the anode material was getting powdery with aging, and the inhomogeneity of lithium in anode increased. The change of cathode was not obvious, while the number and diameter of separator pores decreased, resulting in the increase of impedance. The analysis of structural and thermal stability showed that the grain size of cathode material decreased with aging, while the thermal decomposition temperature did not change significantly. The anode had the greatest impact on the battery safety based on the DSC test. The initial decomposition temperature of solid electrolyte interphase (SEI) decreased from 65.5 °C (100% SOH) to 61.5 °C (71.90% SOH), and the corresponding heat release increased by 59.7%, indicating that the initial self-heating reaction was more serious. The heat released by graphite collapse significantly reduced with aging, which was beneficial to reduce the high temperature hazard after thermal runaway. The research results can provide guidance for the reuse of retired batteries.

Performance and cost requirements for emerging storage applications challenge existing battery technologies and call for substantial improvements in cell energy and rate capability. Convection batteries can reduce mass transport limitations commonly observed during high current operation or with thick electrodes. In prior proof-of-concept work, while convection was shown to improve cell performance, its effectiveness was limited in the select cases studied. To understand the feasibility of the convection battery more comprehensively, we develop a mathematical model to describe convection in a Li-ion cell and evaluate performance as a function of a broad range of cell dimensions, component properties, as well as electrochemical and flow operating conditions. Qualitatively, we find that electrolyte flow enhances accessible capacity for cells with large electrolyte diffusive transport resistance and low initial amounts of electrolyte salt by reducing spatial concentration gradients and, thus, allowing for efficient high current operation. Quantitatively, by leveraging dimensional analysis that lumps >10 physical and cell parameters into representative dimensionless groups, we describe the efficacy, trade-offs, and upper performance bounds of convection in an electrochemical cell. Our analyses suggest that this format has the potential to enable high-power energy-dense storage which, in turn, may offer new application spaces for existing and emerging intercalation chemistries.

Cr was reported to result in a selective dissolution of the Laves phase in 12Cr steel in strong alkaline solutions. However, the current study concludes that Cr does not cause the dissolution of the Laves phase, but plausibly is responsible for the dissolution of Cr carbide at a higher potential. Further, the shoulder of the Laves phase peak resulted from the change of magnetite to hematite on the surface, and the shoulder of the carbide peak resulted from the transpassive behavior of Cr as alloying elements in the matrix.

Sensitized AA5083-H2 aluminum alloy was exposed to chloride-laden thin-film electrolyte at ambient temperature (20%–85% relative humidity) and the local Volta potential measured, in-situ and in real-time, using the Scanning Kelvin Probe Force Microscopy, with the intention to elucidate the earliest stage of localized corrosion. Positive Volta potentials vs alloy matrix were measured for magnesium silicides in ambient air, which, however, underwent a severe nobility loss during corrosion, causing their nobility to invert to active potentials (negative) relative to the alloy matrix. The reason for the nobility inversion was explained by the preferential dissolution of Mg²⁺, which resulted in an electropositive surface. Aluminides, both with and without silicon, were seen to form the main cathodes at all exposure conditions. The local alloy matrix next to closely-separated aluminides were seen to adopt the Volta potential of the neighbor aluminides, which, hence, resulted in local corrosion protection. The phenomenon of nobility adoption introduced in this work raises questions regarding the anode-to-cathode ratio, which was observed to change during corrosion, and the resulting impact to localized micro-galvanic corrosion. This work further demonstrates that it is necessary to measure the Volta potential during corrosion to reflect the true relationship between the Volta potential and corrosion potential or breakdown potential.

In this paper we present a diffusive transport model of alloy 625 crevice corrosion for simulated ocean water. The model uses the empirical electrochemical kinetics (local surface current density) and empirical damage profile to determine the source of cations from surface oxidation reactions and then calculates the total cation concentration in the crevice solution as a function of time. To gain insight into the solution speciation at the calculated cation concentrations, a thermodynamic software package was used. In those calculations, it was assumed that the anodic dissolution products of the individual alloy components form their corresponding metal salts in the crevice solution. The calculations, based on activity, predicted that precipitation occurred in the same time frame as the experimentally observed increase in active area, decrease in surface current density and transition to diffusion control. The salts that precipitated out of the model solution were NaCl, at 5.3 m, and NiCl₂·6H₂O, at 5.7 m. It is shown that the presence of the Cr³⁺, Fe²⁺, Mo³⁺ and Nb⁵⁺ in the model crevice solution increase the cation and chloride activities resulting in precipitation at the same K_sp values as in the pure salts, albeit at lower Na⁺ or Ni²⁺ concentrations. Implications of the speciation results as they relate to actual crevices are discussed.

The microstructures and passivation behavior of selective laser melted 316L stainless steel (SLM SS316L) after various heat treatments (500 °C, 950 °C, and 1100 °C) were investigated. The electrochemical results showed that the SLM SS316L sample that was heat treated at 950 °C exhibited the lowest passive current density. The microstructural characterization analysis indicated that the subgrain structures transformed from dislocation-rich subgrain boundaries into island-like cellular trace structures after heat treatment at 950 °C. This led to improved corrosion resistance due to the elimination of dislocations and the homogenization of the composition. Compositional analyses of the passive film indicated that there was no notable change in the passive film composition after heat treatment at 500 °C and 950 °C. However, heat treatment at 1100 °C promoted the formation of Cr(OH)₃ in the passive film, resulting in a reduced corrosion resistance. Based on these results, heat treatment at 950 °C appears to be an adequate post-process for SLM SS316L to optimize the microstructure, while also improving corrosion resistance.

An environmentally friendly AgInS₂/ZnS nanoparticles (NPs) co-sensitized TiO₂ ultrafine branched nanolawn photoelectrode was constructed by depositing AgInS₂ sensitizer and ZnS passivator on TiO₂ ultrafine nanostructure. This architecture significantly improved the photoelectrochemical conversion efficiency and photoelectrochemical cathodic protection performance for pure copper with a more negative self-corrosion potential under simulated sunlight illumination and in NaCl solution containing no additional hole scavengers. Compared with single AgInS₂ NPs sensitized TiO₂, the design of ZnS passivation layer on TiO₂/AgInS₂ significantly improves the charge generation and separation efficiency, and promotes the consumption of the photogenerated holes. The three-dimensional TiO₂ with porous ultrafine nanobranched structure possesses high-speed electron transmission pathways and facilitates the rapid collection and migration of the photogenerated electrons. Since the conduction band potentials of AgInS₂ and ZnS are more negative, the photogenerated electrons generated by TiO₂/AgInS₂/ZnS will be maintained at a more negative quasi-Fermi level. This ensures that the photogenerated electrons can be transferred to pure copper. The present work provides new ideas for designing nanoheterojunction materials for the protection of pure copper and other metallic materials with more negative self-corrosion potentials exposed in marine environment under simulated sunlight illumination.

This paper describes a systematic study into the role of chromium and chromium (III) oxide thickness in preventing corrosion driven coating disbondment of organically coated packaging steel. A graded wedge of chromium and chromium (III) oxide is applied to steel using physical vapour deposition (PVD). A polyvinyl butyral (PVB) overcoat is applied and corrosion is initiated from an artificial defect using NaCl. Scanning Kelvin probe (SKP) potentiometry is used to monitor coating delamination. Wedge thickness variation allows for high throughput investigations into the effect of both metallic chromium and chromium (III) oxide thickness, on coating disbondment rate. A linear reciprocal relationship is observed between chromium metal thickness and disbondment rate. Increasing chromium (III) oxide thickness (applied over chromium metal) results in a decrease in delamination rate. This work highlights the ability of PVD to produce chromium/chromium (III) oxide corrosion resistant coatings to use as alternatives to hexavalent chromium-based systems.

To clarify the mechanism of localized corrosion on zirconium in chloride environments, corrosion tests of zirconium and its alloys were performed using conventional and micron-scale measurement systems with surface areas of 0.35 cm² and less than 0.04 cm², respectively. The pitting potential significantly dropped by more than 1 V when zirconium was alloyed with over 10 mol% of tin. Zr₄Sn and Zr₅Sn₃ intermetallics hindered the formation of passive films on the substrate. Additionally, tin was found on the surface of a commercially pure zirconium. From the micron-scale measurement results, the inclusion with the highest concentration of tin (at least 0.44 mol%) in the tested area was selected as the preferential initiation site for pitting corrosion. Thus, tin played an important role in determining the corrosion resistance of zirconium in chloride environments.

Grade 2205 Duplex stainless steel (DSS) components were built via selective laser melting (SLM) with gas atomized powder (D₉₀ < 45μm) using a 250 W laser in a nitrogen environment. The relative density was 99.1 ± 0.3%, and the ferrite/austenite phase ratio after annealing was 53.0/47.0 ± 4.8%. Two build orientations (parallel and perpendicular to build direction), as well as as-built SLM (no heat treatment) and annealed conditions, were studied. Corrosion properties were characterized in a 3.5% NaCl electrolyte and compared to 2205 wrought. The charge transfer resistance was > 500 kohm.cm², and the corrosion rate was < 100 nA cm⁻² for all alloys, which suggest passivity. No stable pit formation occurred during cyclic polarization tests although the as-built perpendicular and annealed SLM conditions showed metastable pitting, likely due to surface porosity and/or chemical inhomogeneity. The as-built parallel condition did not show metastable pitting and had the highest average charge transfer resistance, which is evidence of possible improvements from laser melted material, but not conclusive. Ultimately, all SLM DSS 2205 was similar to 2205 wrought, implying that the build orientation and annealing were not as significant of factors as the chemical composition in predicting the passivity and pitting resistance.

Passivation mechanisms and the effects of controlled pre-oxidation, by exposure to oxygen at ultra-low pressure, on Cr and Mo surface enrichments were investigated on polycrystalline AISI 316L stainless steel surfaces with direct transfer between surface preparation and analysis by X-ray photoelectron spectroscopy and electrochemistry. Exposure to sulfuric acid at open circuit potential causes preferential dissolution of oxidized iron species, which promotes Cr³⁺ and Mo^4+/6+ enrichments. Anodic passivation forces oxide film re-growth and Cr³⁺ dehydroxylation with no loss of Mo^4+/6+ pre-enrichment. Ultra-low pressure pre-oxidation promotes Mo^4+/6+ enrichment in the exchange outer hydroxide layer of the passive film, with no Mo⁰ depletion in the modified alloy region underneath the oxide film at open circuit potential, and under anodic passivation. Mo^4+/6+ enrichment improves protectiveness against transient active dissolution during the active/passive transition.

The flow accelerated corrosion (FAC) of EH 36 carbon steel in the oxygen containing flowing electrolyte is studied using multi-electrode array arranged in a jet rig system. The FAC of the working electrodes (WEs) under both uncoupled and coupled conditions are investigated in conjunction with computational fluid dynamics (CFD) simulation. Results show that a higher mass transfer rate would lead to a higher FAC rate when the WEs are uncoupled. The rust layer could retard the oxygen diffusion, resulting in the FAC rate decreasing. The mass transfer process and the distribution of the rust layer are significantly influenced by the fluid hydrodynamics. However, when the WEs are coupled together, serious FAC damage would occur on the WEs where lower mass transfer rates are registered. The macro-cell currents would become the main lead of FAC propagation at coupled conditions.

In this work we introduce a metal-oxide bond-energy model for alloy oxides based on pure-phase bond energies and bond synergy factors that describe the effect of alloying on the bond energy between cations and oxygen, an important quantity to understand the formation of alloy oxides and their composition. This model is parameterized for binary cation-alloy oxides using density-functional theory energies and is shown to be directly transferable to multi-component alloy oxides. We parameterized the model for alloy oxide energies with metal cations that form the basis of corrosion resistant alloys, including Fe, Ni, Cr, Mo, Mn, W, Co, and Ru. We find that isoelectronic solutes allow quantification of pure-phase bond energies in oxides and the calculated bond energy values give sensible results compared to common experience, including the role of Cr as the passive-layer former in Fe–Ni–Cr alloys for corrosion applications. Additionally, the bond synergy factors give insights into the mutual strengthening and weakening effects of alloying on cation-oxygen bonds and can be related to enthalpy of mixing and charge neutrality constraints. We demonstrate how charge neutrality can be identified and achieved by the oxidation states that the different cations assume depending on alloy composition and the presence of defects.

Codeposition of elements is an important phenomenon in the analysis and understanding of mass transfer in electrorefining of pyroprocessing. This study investigated the codeposition of lanthanides in molten salt. Mass transport experiments were conducted to examine the accuracy of the 1D electrorefining model, ERAD. Three lanthanides (La, Ce, and Gd) were selected because their standard reduction potentials are close to each other which facilitates codeposition. For the electrodeposition experiments, six electrochemical cells were used with varying ratios of lanthanides and the electrode potential ranging from 0.00 V to 0.15 V. This controlled the codeposition environment. The resulting electrodeposits were analyzed by ICP-OES and compared with the simulation results from ERAD. The ERAD input parameters were determined through electrochemical studies. Theoretical codeposition ratios were also analyzed using polarization curves. The study indicated that the current density of each element played a major role in its codeposition, as did thermodynamically determined reduction potentials. The overall results were comprehensively investigated and showed that ERAD can reasonably show the tendency of the codeposition results obtained from the experiments. With minor revision, it is expected that this 1D computer code could be effectively utilized for modeling the mass transport of the electrorefining process of pyroprocessing.

Until now, the fabrication of convenient and high-efficient surface enhanced Raman scattering (SERS) substrate has remained challenging. Inspired of the rose petal effect in nature, we develop an effective and facile strategy to localize the trace amount of probe molecules onto SERS-active hot spots using the hydrophobic Ni nanocone supported hydropholic Au nanoball (denoted as Au NB@Ni NC) substrate. The two-step electrodeposited Au NB@Ni NC shows a hierarchical structure with the closely arranged Au nanoballs on the Ni nanocone pinpoints. This unique structure can not only endow the hot spots between the Au nanoballs in SERS, but also contribute to special wettability after natural storage. The results verify that the high contact angle of the probe drops on the Au NB@Ni NC substrate helps concentrate the probe molecules in the hot spots area, leading to an increased SERS intensity. To be specific, this Au NB@Ni NC substrate could test tiny crystal violet droplet of 5 μl volume at 10⁻¹³ M. In practice, we realize the high-sensitive and diverse-analyses SERS detection by simultaneous multiple-spots tests, dispensing with flushing repeatedly. Therefore, this 3D Ni nanocone supported strategy is a promising method for designing applicable SERS substrates.

The electroreduction of HfF₆²⁻ complexes to Hf on a molybdenum electrode in the NaCl-KCl-K₂HfF₆-NaF (5 wt%) melt in the temperature range 973–1123 K was studied by cyclic voltammetry and impedance spectroscopy. It was found that discharge of Hf(IV) complexes to Hf occurs in one step and is irreversible. The diffusion coefficients of Hf(IV) fluoride complexes were determined by cyclic voltammetry. The impedance spectroscopy was used for the determination of the standard rate constants of charge transfer. Electrodeposition of hafnium coatings on a molybdenum substrate was performed in the NaCl-KCl-K₂HfF₆ (10 wt%)-NaF (5 wt%) melt at the cathodic current density 5–100 mA cm⁻² and temperatures 973, 1023 and 1073 K. The influence of the current density and temperature on the roughness of hafnium coatings was studied. It was determined that hafnium coatings with significantly higher purity than that of the hafnium anode were obtained confirming that metal impurities were removed during electrodeposition. The oxidation kinetics data were obtained on a sample with hafnium and a sample of pure molybdenum, which were tested in a water/oxygen mixture at 773 K. The hafnium coating improves the corrosion resistance of coated plates in comparison with that of pure molybdenum.

The electrochemical formation of Dy–Ni alloys was investigated in molten CaCl₂–DyCl₃ (1.0 mol%) at 1123 K. Cyclic voltammetry indicated the formation of Dy–Ni alloys at more negative than 1.0 V vs. Ca²⁺/Ca. Higher cathodic currents were observed from approximately 0.6 V, which indicated the formation of Dy–Ni alloys having higher Dy concentration. An open-circuit potentiometry was carried out with Mo and Ni electrodes before and after the addition of DyCl₃. After the potentiostatic electrolysis of Mo electrode at −0.50 V for 30 s in molten CaCl₂–DyCl₃, only one potential plateau appeared at 0.33 V, which was interpreted as the equilibrium potential of Dy³⁺/Dy. In contrast, four potential plateaus were observed at 0.49, 0.62, 0.87, and 1.04 V for Ni electrode after the potentiostatic electrolysis at 0.25 V for 15 min. According to energy-dispersive X-ray spectroscopy and X-ray diffraction of the electrolyzed samples, the four potential plateaus correspond to the two-phase coexisting states of (DyNi + DyNi₂), (DyNi₂ + DyNi₃), (DyNi₃ + DyNi₅), and (DyNi₅ + Ni). Standard Gibbs energies of formation were calculated for Dy–Ni alloys.

To recover Gd from LiCl-KCl eutectic, the coreduction mechanism of Gd(III) with Pb(II) was investigated using electrochemical methods. The formation potentials related to the formation of three Gd-Pb intermetallics were detected by cyclic voltammetry, square wave voltammetry and chronopotentiometry, and the formation mechanism of Gd-Pb compounds could be described as xPb(II) + 2xe⁻ = xPb. Meanwhile, the electroreduction of Gd on liquid Pb electrode was explored. The diffusion coefficient of Gd metal in liquid metallic Pb was determined by anodic chronopotentiometry. The kinetic parameters of Gd(III)/Gd(in Pb) couple in the temperature range from 723 K to 873 K were determined employing linear polarization (LP) method. Based on the relationship of exchange current density and temperature, the reaction activation energy was estimated to be 23.17 kJ mol⁻¹. In addition, the recovery of Gd from molten salts was performed assisted by liquid Pb electrode by constant potential electrolysis (CPE) and constant current electrolysis (CCE). The products characterized using XRD, SEM with EDS are comprised of GdPb₃ and Pb phases. The concentration change of Gd during CCE process was monitored by ICP-AES, and the recovery rate was estimated. The results showed that Gd concentration decreased and recovery rate increased with the duration.

The present work investigates the application of a Self-Assembled Monolayer (SAM) on the widely used negative photoresist SU-8. (3-Aminopropyl) trimethoxysilane (APTMS) is employed to form SAMs on the surface of the polymer through wet silanization in ethanol. The treatment process of SU-8 resin surface is optimized to achieve a well-formed, high quality SAM. Wettability measurements, atomic force microscopy (AFM) and infrared (IR) spectroscopy are employed to follow and optimize the silanization process. Following silanization, the resulting SAMs are employed as adhesion layers for electroless plated metallic layers. For this purpose, the superior affinity of APTMS amine terminal groups towards Pd²⁺ ions is exploited to activate the surface. Metallic coatings such as Cu, Ni–P or Co–Ni–P are thus deposited by mean of autocatalytic deposition. The surface of metallized samples is analyzed using AFM, scanning electron microscopy (SEM) and glow discharge optical emission spectroscopy (GDOES). Finally, Ni–P is deposited on a micropatterned SU-8 surface to demonstrate the potential of the presented metallization approach for microfabrication.

Copper electroless deposition for the formation of electrically conductive seed layers is important in the manufacturing process of printed circuit boards. As the size of electrical devices decreases, the seed layer also needs to be thinner and its uniformity is highly stressed. In this study, Pd ion adsorption and Cu electroless deposition, which are the most crucial steps in seed layer deposition, were controlled through forced convection. Without forced convection, the seed layers at the top and bottom sides of the microvia are of different thicknesses, which can cause defects. The application of forced convection in Pd ion adsorption uniformly deposited the seed layer by suppressing the adsorption of Pd ions on the top side of the microvia. Furthermore, forced convection on copper electroless deposition enhanced overall mass transfer of reactants such as cupric ions and formaldehyde, and accompanying the deposition rate on the top and bottom sides, which balanced the thickness of the seed layer on the top and bottom sides. Thus, forced convection in Pd ion adsorption and Cu electroless deposition compensated for the suppression of the Pd ion adsorption and improved the uniformity of seed layers on the microvia substrates.

Design and optimization of electrode materials plays the pivotal role on the performance of capacitive deionization (CDI). Activated carbon (AC) has been a workhorse material for electrode fabrication in capacitive technologies. Several modification methods have been reported with enhanced activity and versatility attributes. Undeniably, tuning and tailoring AC properties have opened avenues for broadening the scope of applications, by meeting necessary features of electrodes for a given CDI cell configuration. This review traces the beneficial and also detrimental effects from various modifiers on AC electrodes with respect to CDI performance. Furthermore, a comprehensive classification of CDI cells based on different architectural aspects with a comparative performance is presented. On this basis, the tradeoff between physical, chemical, electrochemical properties in the course of electrode modification and the interdependence between electrode design and CDI cell configuration are discussed with disclosing some prospective guidelines on AC electrode design. It is important to evaluate the electrode materials and modifications in the way of practical including not only the electrode design, but also the cell architecture and operational parameters. This review aims to raise the attention on the rational electrode design by taking into account all necessary features of electrode in a given cell configuration.

Hybrid laser-electrochemical micromachining is a fast and force-free processing technique to machine difficult-to-cut multi-materials with conductivity variations and has the advantage of accelerated material dissolution, oxide layer weakening and surface quality. In this process, the laser can assist electrochemical dissolution or participate in material removal depending on the fluence available on the workpiece surface. The tool-based configuration allows delivery of laser and ECM at higher machining depths and achieves homogeneous application of the two aforementioned processes. The combination of laser and ECM results in high material removal, better surface integrity and processing of advanced materials. On passivating materials, the oxide formation is weakened. In this research, a multidisciplinary model scheme is proposed using a global modelling approach where the model mimics several microscopic physical and chemical phenomena involved in this tool-based hybrid laser-ECM process. The model takes into account electric currents, fluid dynamics, modelling of laser source, hydrogen and oxygen gas generation and heat transfer in solids and fluids. The model allows to study temperature effects on each of the phenomena in the model. Material removal is simulated by using a deformed geometry feature and an automatic remeshing technique generates a new boundary for each subsequent solution step on Comsol^® multiphysics platform. The multiphysics model is presented in detail with a brief description and intuitive explanation of each physics module. The proposed multidisciplinary model scheme can improve the physical understanding of the hybrid laser-ECM process as well as assist in process design for specific applications. The model allows to predict the machined profiles and current density distribution simultaneously. This model also provides insights into several multiphysics phenomena occurring in the interelectrode gap which are difficult to characterize experimentally and therefore the model can act as a virtual sensor. In the later sections of this paper, model based findings are supported experimentally.

Non-biodegradable pharmaceuticals are a group of emerging contaminants that have gained much attention because of their potential risk of inducing adverse ecological and health effects. An efficient Ti/SnO₂-Sb₂O₅-IrO₂-RuO₂ electrode was prepared by Pechini method and employed as the anode for electrochemical degradation of selected pharmaceuticals (i.e., ibuprofen, atenolol, and carbamazepine). Compared its counterparts, Ti/SnO₂-Sb₂O₅-IrO₂-RuO₂ exhibited higher oxygen evolution potential, lower chlorine evolution potential, larger active area, and higher stability. Unlike the negligible effect of solution pH from 4.0 to 10.0, increasing current density favored the target pollutants and COD removal. The removal of IBU was mainly attributed to the reaction with ^•OH, the contribution of which to IBU removal was enhanced with increasing current density. In contrast to IBU, the removal of ATEN and CBZ was mainly ascribed to the reaction with selective radical chlorine species (RCS) mainly in the form of Cl^•, which was produced from direct oxidation of Cl⁻ or indirect oxidation by ^•OH. It was found that the removal of ATEN and CBZ was less affected by dissolved organic matter (DOM) than that of IBU in municipal effluent. This study demonstrates that Ti/SnO₂-Sb-RuO₂-IrO₂ is an attractive electrode for the destruction of pharmaceutical contaminants.

Production of ammonia through coupling renewable energy with electrolysis cells will undoubtedly aid in reducing carbon dioxide emissions from the ammonia production industry. However, if the cost for electrochemical routes does not reach a Haber-Bosch parity point, then it is unlikely that electrochemical ammonia synthesis will become industrially viable. This promotes a strong need for analyses that explore the economics of various system designs and production scales, to assess what systems and scales can attain Haber-Bosch price parity. Here, we aim to define the Haber-Bosch parity targets for various production scales. We then explore the economic considerations for two electrochemical systems for ammonia synthesis. The first system contains a single electrolysis cell where nitrogen and water are the sole reactants. The second system explores a two-staged electrolysis system. The first stage consists of a water electrolysis cell where water serves as the reactant and hydrogen and oxygen are the products. The second stage consists of a nitrogen electrolysis cell where the reactants are nitrogen and hydrogen and ammonia is the product. We emphasize the important role production scale plays in meeting Haber-Bosch price parity, and highlight the key challenges for electrochemical ammonia production.

Deep eutectic solvents (DESs) are emerging as promising electrolytes for electrochemical energy storage applications. Electroactive nitroxide-radical-containing organics can be dissolved in DESs to facilitate redox reactions; however, mechanistic know-how of their charge transfer kinetics at the electrode surface is rather limited. Here, we investigate the mechanism underlying the electrochemical oxidation of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (4-hydroxy-TEMPO). Using polarization measurements on a platinum rotating disk electrode and micro-electrode, we show that the anodic charge transfer coefficient ($\alpha$) for one-electron transfer oxidations of TEMPO and 4-hydroxy-TEMPO approaches 0.9 in DES as well as in aqueous electrolytes, i.e., a significant deviation from α ≈ 0.5 expected for symmetric redox behavior. To explain this observation, a two-step oxidation mechanism is proposed wherein the nitroxide-containing species undergo fast charge transfer at an electrode surface followed by slow rate-limiting desorption of the adsorbed oxidized species. Numerical simulations are reported to characterize how the proposed two-step mechanism manifests in transient cyclic voltammetry behavior of the 4-hydroxy-TEMPO oxidation reaction, and good agreement with experiments is noted.

A novel Ti/PbO₂-Bi-PTh composite electrode was successfully prepared by electrodeposition and applied in electrochemical degradation of phenol. The Ti/PbO₂-Bi-PTh electrode was characterized by XRD, SEM, AFM, LSV, CV and EIS. Results showd that the electrode has a fine and compact surface structure, higher oxygen evolution potential (OEP, 2.42 V) and low charge transfer resistance (51.00 Ω). The electrode also exhibited excellent electrochemical oxidation activity on the degradation of phenol (1000 mg l⁻¹) with degradation efficiency of 100% and TOC removal rate of 93.58% achieved in 60 min and 180 min, respectively. In addition, possible mechanism of phenol degradation on the electrode was proposed by analyzing the intermediate products with GC-MS. Noticeably, the Ti/PbO₂-Bi-PTh electrode displayed excellent stability and high electrocatalytic performance after 10 cycles, indicating its promising application in the phenolic wastewater treatment.

For most core–shell nanostructured Pt-based alloy electrocatalysts, the local environment and configuration of surface Pt layers are randomly generated, which would hinder the further improvement of the utilization, activity and stability of Pt atoms. Herein, we have selected AuCu alloys with different structural ordering as substrates and deposited a Pt shell on their surface via the precise control of replacing Cu with Pt atoms. Various physical and electrochemical characterizations indicate that the structural ordering of an AuCu core could influence the distribution of surface Pt atoms due to the rearrangement of surface atoms. After optimization, the obtained catalysts displayed a high mass activity (0.75 A·mg_Pt⁻¹) and specific activity (0.491 mA·cm_Pt⁻²) for the oxygen reduction reaction (ORR), which were nearly 7.5 times and 3.6 times those of commercial Pt/C, respectively. In addition, the catalysts could also exhibit a high stability with a negligible activity decay after 10,000 cycles of accelerated durability tests (ADTs). The density functional theory (DFT) calculation reveals that the precisely controlled Pt local environment could lower the Gibbs free energy barrier for the rate-determining step of ORR more than a random distribution could, thus enhancing the catalytic performance of the prepared catalysts.

In this work we present a carbon free gas diffusion electrode (GDE) design. It is a first step towards improvement of technologies like alkaline fuel cells, some alkaline electrolyzes and metal-air-batteries by circumventing carbon degradation. A nickel-mesh was made hydrophobic and subsequently electrochemically coated with MnO_x as electrocatalyst. By this, a carbon free GDE was prepared. The contact angle, specific surface area (BET), pore size distribution, crystal phase (XRD) and electrochemical properties were determined. The deposition scan rate (r_scan) during dynamic MnO_x deposition altered the macro surface structure, pore size distribution and deposited mass. High catalyst masses with high specific surface area were achieved by lower r_scan, but hydrophobicity was decreased. Impedance spectroscopy showed that higher MnO_x mass will increase the ohmic resistance, because of the low conductivity of oxides, such as MnO_x. The diffusion of dissolved oxygen is the major contributor to the total resistance. However, the polarization resistance was reduced by increased specific surface area of MnO_x. It was concluded that the ORR and OER are limited by diffusion in this design but nevertheless showed reasonable activity for ±10 mA cm⁻² corresponding to ∼8 Ω cm⁻² while references exhibited ∼3.5 Ω cm⁻².

We show that the coupling effects in non-equilibrium thermodynamics for heat-, mass- and charge- transport in the polymer electrolyte membrane fuel cell (PEMFC) all give significant contributions to local heat effects. The set of equations was solved by modifying an open-source 1D fuel cell algorithm. The entropy balance was used to check for model consistency. The balance was obeyed within 10% error in all PEMFC layers, except for the cathode backing. The Dufour effect/thermal diffusion and the Peltier/Seebeck coefficient are commonly neglected. Here they are included systematically. The model was used to compute heat fluxes out of the cell. A temperature difference of 5 K between the left and right boundary of the system could change the heat fluxes up to 44%. The Dufour effect, for instance, increases the temperature of both anode and cathode, up to 9 K. The possibility to accurately predict local heat effects can be important for the design of fuel cell stacks, where intermediate cooling is central. This work is based on Paper 1484 presented at the Atlanta, Georgia, Meeting of the Society, October 13–17, 2019.

A 3D lattice Boltzmann model is developed to simulate the pore-scale two-phase flow in the porous transport layer (PTL). The PTL, composed of the gas diffusion layer (GDL) and the micro porous layer (MPL), is stochastically reconstructed and validated by comparing the pore size distribution (PSD) with experimental data. This work focuses on the effect of MPL on liquid water transport in terms of hydrophobicity, PSD and structure. It is found that more hydrophobic material and smaller pore size apply higher local capillary force against the water transport. Water can only break through the crack-free MPL under an extremely high inlet pressure (about 400 kPa). Under the real operating conditions of a fuel cell, the PTL with single GDL suffers flooding with a low fraction of dry pore. With the presence of cracked MPL, the fraction of dry pore increases significantly since a large amount of water is constrained in the electrode and only the rest flows into the GDL through the cracks, which can keep the membrane hydrated and avoid flooding. Finally, a systematically designed PTL is proposed with uniformly distributed perforations, which can automatically balance the water content and further optimize the proton conductivity and reactant transport, simultaneously.

Oxygen transport resistivity of the cathode catalyst layer in a low–Pt PEM fuel cell has been determined using two methods: the first one is fitting of our recent physics–based impedance model to the experimental impedance spectra of the cell, and the second is calculation of distribution of relaxation times (DRT) using the same spectra. Comparison of the two methods shows that the DRT peak with the characteristic frequency on the order of 500 to 1000 Hz describes oxygen transport in the open pore and in Nafion film covering Pt/C agglomerates in the catalyst layer. This result makes it possible using experimental impedance spectroscopy and DRT calculation for routine measurements of cathode transport resistivity in low–Pt PEMFCs.

Alkaline pretreatment is perceived as an essential step for high-performance hydroxide exchange membrane fuel cells (HEMFCs), but its exact function is not fully understood. Here we show that alkaline pretreatment is only necessary when carboxylates are generated from platinum- or palladium-catalyzed oxidation of primary alcohol solvents during membrane electrode assembly (MEA) fabrication. When alkaline pretreatment is needed, bicarbonates are a better choice than the most commonly used hydroxide bases. We further demonstrate that MEAs with Pt/Pd-free catalysts, which can be used in HEMFCs, exhibit a better performance without the alkaline pretreatment: a voltage of 0.64 V at 1.0 A cm⁻² and a peak power density of 0.69 W cm⁻² in H₂/O₂. The optimization or elimination of the alkaline pretreatment will simplify the fabrication process for fuel cells and thus reduces their manufacturing costs.

This paper investigates the general performance and durability performance of a high-temperature polymer electrolyte fuel cell (HT-PEFC) with CrN/Cr-coated SS316L as bipolar plates and compares this with the bare SS316L and graphite bipolar plates. Polarization curves are conducted every 200 h during the 1000 h durability tests for evaluating the overall performances of the HT-PEFCs with different types of bipolar plates. An electrochemical model based on polarization curves, combined with electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM), is used for understanding the degradation mechanisms at play. The CrN/Cr-coated SS316L bipolar plates show excellent corrosion resistance and performance in a real HT-PEFC. Thereby, the degradation rate decrease from ca. 16% of the highest output power with the bare metallic bipolar plates and graphite bipolar plates to almost zero with the CrN/Cr-coated steel bipolar plate.

A four-layer solid oxide fuel cell stack consisting of standard anode-supported cells was assembled to investigate long-term stability, but at higher current densities and/or fuel utilization compared to previous investigations. The stack was operated within a furnace temperature range of 700 °C–750 °C with hydrogen fuel at a current density of up to 1 A·cm⁻² and fuel utilization of up to 80% for more than 10,000 h. The average voltage degradation rate was approximately 0.6%kh⁻¹. Increases in the ohmic resistance and anode polarization dominated the degradation behavior. An increase in the current density and fuel utilization under current testing conditions did not fundamentally influence the degradation rate. However, the possible modification in the nickel structure by local higher fuel utilization may have had a long-term impact on the lifetime of the stack. The complexity of the degradation analysis of stacks resulting from an inhomogeneous contact inside the stack was analyzed with the support of impedance measurements and a post-mortem analysis.

The high operation and capital costs of polymer electrolyte water electrolyzers (PEWE) are the major obstacles that have to be tackled for hydrogen to penetrate the market as a solution for renewable energy storage. Commercial stacks often suffer from cationic contamination of catalyst-coated membranes (CCMs) that comes from impure feed water and corrosion of system components, which can result in increasing operation costs and lowered lifetime. This study describes the behavior of the contaminants in the CCMs and their impact on performance under various operating conditions using Gd³⁺ as model contaminant imaged with neutron with a combination of high effective temporal (2 s) and spatial (30 μm) resolutions. The presence of electric field directly affects the position of cations in the CCM leading to their accumulation near the cathode catalyst layer. The cationic impurities trigger multiple loss mechanisms, as the ohmic resistance increase does not scale linearly with the amount of occupied exchange groups in the membrane (10% resistance increase caused by 2.5% exchange groups occupation). A model has been developed that predicts the movement of the ions in the CCM under intermittently operating PEWE and was used as a basis to explain the hysteresis observed in the polarization curve of contaminated PEWEs.

Electrochemical macrokinetics contains the interaction of electrode reactions with transport phenomena. To disentangle the individual processes, dynamic techniques such as electrochemical impedance spectroscopy are widely used. Additional information can be obtained when further quantities besides current and potential are recorded. Here, we present and analyze a method to observe the dynamics of the flux of volatile species, i.e. mass transfer, in porous electrodes during electrochemical reactions with a high time resolution. We call this technique species frequency response analysis (sFRA). It is experimentally demonstrated with electrochemical methanol oxidation reaction on a porous Pt/Ru electrode. The dynamic relationship between current, potential and the flux of the gaseous reaction product CO₂ is measured by differential electrochemical mass spectrometry. The resulting transfer function that relates current density with CO₂ flux is analysed in detail by means of a one-dimensional mathematical model. It is demonstrated how the influence of reaction and transport phenomena can be separated in the sFRA Nyquist plot. Practical aspects such as sensitivity and accessible frequency range are discussed as well as the overall prospects and limitations of the technique.

The spinel oxide, Cu_1.5Mn_1.5O₄ (CMO) is a promising precious group metal-free electrocatalyst (EC) known for acid-mediated oxygen evolution reaction (OER). By employing density functional theory (DFT) based Bader analysis for active sites identification, the effective electronic charges of constituent ions in the ordered-disordered crystal structures were calculated. Accordingly, for DFT result validation, structurally disordered Cu_1.5Mn_1.5O₄ ECs were experimentally synthesized by heat treatment to 200 °C (CMO-200). The disorder—order transitions of CMO related change in surface atomic arrangement and alteration in the Mn³⁺/Mn⁴⁺ and Cu²⁺/Cu¹⁺ states are modulated via corresponding heat treatment (200 °C–800 °C) of CMO, revealing significant influence on OER electrocatalytic activity and durability. The measured higher electrocatalytic activity of disordered CMO-200 contrasted with ordered CMO is attributed to higher Mn³⁺/Mn⁴⁺ and Cu²⁺/Cu¹⁺ states, signifying the beneficial role of Mn³⁺ and Cu²⁺ for facilitating OER. The ordered CMO structures containing lower Mn³⁺/Mn⁴⁺ and Cu²⁺/Cu¹⁺ ratios albeit reveal higher electrochemical stability than the disordered CMO. The present study, thus, provides fundamental insights into the influence of ordered-disordered structures and rearrangement of the oxidation state of active species and their combined synergistic effects on the electrochemical performance for engineering high-performance ECs for acidic OER.

In proton exchange membrane-based electrolysis, cell-level performance and durability is affected not only by individual components, but also by how those components are integrated into membrane electrode assemblies. In this study, several ink and ultrasonic spray parameters are evaluated for their effect on catalyst layer properties, electrolyzer performance, and electrolyzer durability. The relative impact of these variables on kinetic and ohmic loss were revealed and linked to catalyst layer morphology. Ionomer loading and dispersion principally affect kinetics and accelerate kinetic loss over time. Catalyst layer uniformity, however, tends to affect ohmic loss, where poor catalyst-transport layer contact adds resistances, increases ohmic loss, and accelerates ohmic loss over time. These efforts to understand catalyst layer formation and the impact of catalyst layer properties on electrolyzer performance and durability aid in the establishment of robust baselines and better inform component development efforts and manufacturing processes. Separating losses and quantifying how losses change during extended operation are also useful as a diagnostics approach to elucidate why suboptimal performance/durability occurs and develop strategies to mitigate loss.

Over its lifetime in a fuel cell electric vehicle, a polymer electrolyte membrane fuel cell inevitably suffers from certain duration of dry operational conditions, where significant performance losses of the fuel cell take place. In this study, we investigate the activity changes of the fuel cell after a prolonged degradation protocol under dry operational condition, followed by various recovery procedures under wet conditions. The utilization of diluted air on the cathode side is found to be advantageous for the recovery due to the superior heat and water management. This more efficient recovery protocol allows the deconvolution of reversible and irreversible voltages losses after dry operations. A subsequent mechanistic study reveals an irreversible decrease of the effective ionomer coverage on the catalyst particles, while the proton conductivity of the catalyst layer drops. These observations point towards ionomer structural changes caused by the dry conditions. This is confirmed by post-mortem analysis via scanning electron microscope, showing clearly that ionomer redistributes and migrates, an additional mechanism which leads to the performance losses. Overall, the degradation mechanisms seem to be mitigated by higher ionomer content in the catalyst layer, while the investigated surface modification of carbon support shows minor sensitivities.

Two kinds of methane sensors based on lithium-montmorillonite (Li-MMT) or lithium-cyclodextrin (Li-CD) have been developed, and they have been further modified by adding a small amount of carbon nanotubes (CNTs). The sensitivity of the sensors increases linearly with methane content in the concentration range of 50–500 ppm. Other characteristics of the sensors such as response time, gas selectivity, and stability have been investigated as well. The results indicate that all the sensors response quickly, show good sensitivity and selectivity to methane. Li-MMT/CNTs sensor has highest sensitivity towards methane, and Li-CD sensors have certain resistance to dust and humidity, showing great advantages in coal mine safety application.

Graphene, a two-dimensional material consisting of carbon sheets with exceptionally superior mechanical, electrical and thermal properties, presents itself as an effective second phase reinforcement option for composites and functionally graded materials. Although polymer matrix composites reinforced with graphene have been explored extensively, metal/graphene composite is a comparatively new field of research. This perspective article reviews electrochemical deposition as a strategy to fabricate well-dispersed metal/graphene composites for their potential to enhance mechanical and physical characteristics. The recent state of the art research works has been discussed along with the challenges that are being encountered and their possible solutions.

The study of the structure-activity relationship of electrode surfaces is fundamentally important in electrocatalysis research and in situ spatially resolved measurements of catalytic activity at complex surfaces remain challenging. In this study, the electrocatalytic activity of micrometer-sized platinum crystallites for the hydrogen oxidation reaction (e.g. the anode reaction in proton-exchange-membrane fuel cells) is visualized using scanning electrochemical microscopy (SECM). A polycrystalline Pt electrode was galvanically etched to expose the underlying well-defined crystallites which serve as single crystal electrodes in SECM imaging experiments. SECM coupled with electron backscatter diffraction (EBSD) allows correlation of catalytic activity and crystallographic orientation of high-index Pt crystal domains. The structure-reactivity relationship showed that the catalytic activity for hydrogen oxidation reaction (HOR) at potentials near the standard potential for hydrogen increases in the order Pt(100) < Pt(110) < Pt(111), where the Miller index plane represents the terrace orientations of the high-index facets. A clear correlation is observed between increased HOR activity and step-site density on a given base orientation. SECM imaging and localized kinetic measurements at crystal domains from current-potential plots and SECM approach curves show the passivating effect that anion adsorption and oxide growth have on the HOR at more positive potentials.

Here we describe the electrochemical size stability of 1.6, 4.1, and 15.1 nm diameter Au nanoparticles (NPs) supported on indium tin oxide-coated glass electrodes (glass/ITO). Anodic stripping voltammetry (ASV) and the electrochemically-measured total surface area-to-volume ratio (SA/V) provide the NP size following surface oxidation-reduction cycling from −0.2 to 1.6 V (vs Ag wire) in 0.1 M HClO₄. After 1000 oxidation-reduction cyclic voltammetry (CV) scans, the relative size increases by a factor of 12, 7, and 2 for the 1.6, 4.1, and 15.1 nm diameter Au NPs, respectively. The relative size increase is largest for the smallest NPs, also confirmed by electron microscopy, indicating their lower size stability towards surface oxidation-reduction cycling. The size increase is fastest within the first 200 cycles, which decreases with a further increase in the number of cycles until the Au NP diameter stabilizes. The size transformation is more dramatic at higher Au NP electrode coverage and 30%–100% of the Au dissolves during cycling, depending on the coverage and NP size. Various potential cycling and holding profiles show that the Au NP size increases during reduction of the oxide layer, consistent with an electrochemical Ostwald ripening mechanism.

Both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial for metal-air batteries. Achieving a single phase that offers both functionalities is of practical relevance. Here, we report a facile method to couple Fe-N_x moieties and FeNi₃ nanoparticles, and embed these in nitrogen-doped carbon nanotubes (Fe/FeNi₃@NC). The Fe/FeNi₃@NC catalyst demonstrates excellent bifunctional performance in 0.10 molar potassium hydroxide. We observe a half-wave potential of 0.83 V for ORR, and a potential of 1.58 V at a current density of 10 mA cm⁻² for OER. The oxygen electrode fabricated using Fe/FeNi₃@NC exhibits a peak power density of 143 mW cm⁻² for rechargeable Zn-air battery. Over a ∼9 h duration test, the material is also shown to be as stable as the commercial Pt/C + IrO₂ in operating conditions.

For crystalline silicon (c-Si) solar cells, it is useful to measure accurately the thickness of silicon oxide (SiO_x) layer presents on textured c-Si surface to further adapt the fluoride-based etching treatment. Common techniques used to characterize thin films thicknesses, such as ellipsometry or profilometry, are however not suitable for highly textured surfaces. In this work, a methodology based on Electrochemical Impedance Spectroscopy (EIS) has been developed to determine the thickness of anodic SiO_x on n-type textured c-Si surface. EIS measurements have been carried out on bare c-Si surface as well as on c-Si surface with various anodic SiO_x thicknesses grown by photo-oxidation. The as-obtained Nyquist and Bode diagrams enabled to plot the related Mott-Schottky curves and determine the corresponding flatband potentials (V_fb). A reference standard graph giving the anodic SiO_x thickness according to measured V_fb has been therefore established. A shift of Mott-Schottky curves towards higher potential values with increased anodic SiO_x thickness has been shown and explained. Mott-Schottky curves of photo-oxidized silicon surfaces have demonstrated a particular shape related to the different behaviors of Si/SiO_x/electrolyte device depending on the applied overpotential. These results have been used to study the etching rate of anodic SiO_x in NaHF₂ fluoride media.

There is a great interest in the development of advanced electrocatalysts for efficient water splitting. A tantalum iridium oxide (Ta₂O₅-IrO₂) coating is considered to be one of the best electrocatalysts for the oxygen evolution reaction (OER) in acidic media. In the present study, novel Ta₂O₅-IrO₂-rGO coatings with varying loads of reduced graphene oxide (rGO) were designed to investigate the effects of rGO on the catalytic activity and stability of the Ta₂O₅-IrO₂ coating for the OER. Five different electrodes comprised of Ta₂O₅-IrO₂-rGO on a titanium substrate were fabricated with incremental weight percentages of rGO (0.0 wt.%, 1.0 wt.%, 2.0 wt.%, 5.0 wt.% and 7.5 wt.%) using a facile thermal decomposition method. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and energy dispersive X-ray spectroscopy (EDS) were employed to characterize the morphology and composition of the prepared Ta₂O₅-IrO₂-rGO coatings. Longevity tests revealed that the incorporation of rGO into the oxide layer strongly affected the stability of the Ta₂O₅-IrO₂-rGO electrodes. The electrochemical activities of the prepared Ta₂O₅-IrO₂-rGO electrodes were characterized by cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS). The Ta₂O₅-IrO₂-rGO coating containing 1.0 wt.% rGO exhibited the greatest stability, along with enhanced OER activity.

Inspired by the previously published theoretical findings, the present work aims to assess the electrocatalytic activity of molybdenum(IV) sulfide modified with metallic molybdenum for the nitrogen reduction reaction in aqueous electrolyte solution (0.1 M Li₂SO₄; pH 3) and in aprotic [C₄mpyr][eFAP] ionic liquid electrolyte at ambient temperature. The material of interest was synthesized via a high-temperature partial reduction of MoS₂, while electrocatalytic tests followed a previously established robust protocol, which in particular involves strict control over any NH₃ and NO₃⁻/NO₂⁻ contamination at every key step. As expected, no activity was found in aqueous solutions. In aprotic medium, the formation of small amounts of ammonia at low rates was observed and was found to strongly depend on the water concentration and applied potential. However, the amount of electrochemically generated NH₃ always reached a particular limit and did not increase further, even when the N₂ pressure was increased from 1 to 16 bar. The results suggest rapid blockage of the surface of the investigated electromaterial with NH₃, which prevents its operation as a catalyst for the ammonia electrosynthesis.

Thermodynamic and kinetic properties of Mg(II) in LiCl-KCl eutectic melt were investigated by electrochemical techniques. The diffusion coefficients of Mg(II) in the melt at various temperatures were studied by cyclic voltammetry, and the activation energy of Mg(II)/Mg was calculated to be (48.5 ± 3.7) kJ mol⁻¹. The exchange current densities and reaction rate constants of Mg(II)/Mg at different temperatures from 773 K to 873 K were calculated by testing polarization curves on Mo electrode, and results showed that the exchange current densities became larger as the temperature increased. Equilibrium potentials of Mg(II)/Mg on Mo electrode and liquid Zn electrode were also tested by open circuit potential method. Subsequently, the apparent standard potential of Mg(II)/Mg, apparent standard Gibbs energy for the formation of MgCl₂ and activity coefficients of Mg in the liquid Zn were calculated. Finally, metallic Mg was extracted in the form of Zn-Mg alloys by galvanostatic electrolysis on liquid Zn electrode. The deposit was analyzed by X-ray diffraction, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, and Mg₂Zn₁₁ was detected in the deposit.

Developing robust and low-cost electrocatalysts for efficient hydrogen evolution reaction (HER) through facile methods is of great significance to the energy and environment sustainability. Herein, a simple one-pot solvothermal method has been developed to synthesize a hybrid material of nickel@nickel carbide (Ni@Ni₃C) nanochain embedded in a network of single-walled carbon nanotubes (SWCNTs). The electrochemical experiments indicate that the composite of Ni@Ni₃C-SWCNTs has the HER electrocatalytic performance comparable to that of Pt/C in an acidic medium (0.5 M H₂SO₄). The overpotential to reach a current density of 10 mA cm⁻² in 0.5 M H₂SO₄ is only −74 mV with a Tafel slope of 46.9 mV dec⁻¹. Compared to Ni@Ni₃C in the absence of SWCNTs, the enhanced HER performance of Ni@Ni₃C-SWCNTs can be attributed to the increased intrinsic activity, improved electronic conductivity, and the electron coupling effect between Ni@Ni₃C and SWCNTs. The Ni@Ni₃C-SWCNTs composites also show high stability at the overpotential of −0.2 V for 24 h. This work provides guidance for the synthesis of high-performance non-precious metal electrocatalysts for HER.

Pyriproxyfen (PPF) is a juvenile hormone agonist used in agriculture and in combating Aedes aegypti. In this work, for the first time, a study of electrochemical oxidation (EO) of this insecticide is reported, which involved the degradation of a commercial formulation of PPF on boron-doped diamond (BDD) electrode. pH conditions influenced the process; after 360 min of electrolysis the COD removals were 88.1% (pH 3.0), 78.9% (pH 5.0), 65.5% (pH 7.0), 76.7% (pH 9.0) and 80.0% (pH 11.0). The increase in applied current density favored the COD removal and the S₂O₈^2– generation. At 20, 40 and 60 mA cm^–2, the COD removal was 88.1%, 90.0% and 91.0% and the S₂O₈^2– production was 0.15, 0.26 and 0.35 mmol l^–1, respectively. The COD removal process occurred via •OH and other oxidants as S₂O₈²⁻ and SO₄^–•, and it was more efficient at the lowest current density (20 mA cm^–2), which removed 88.1% COD with the lowest energy consumption (25.2 kWh m^–3). Chromatographic (GC-MS and IC) data showed that the EO removed 37% PPF and formed short chain carboxylic acids as final organic by-products. EO with DDB seems to be an appropriate approach to be applied to degrade PPF in contaminated environmental samples.

In this study, a new electrochemical sensor was fabricated and characterized based on a glassy carbon electrode (GCE) modified with ceria (CeO₂) nanoparticles decorated with electrochemical reduced graphene oxide (denoted as Ceria-ErGO/GCE). The results showed that a large number of spherical ceria nanoparticles with a diameter of 20–200 nm are well wrapped by gossamer like ErGO nanosheets. Compared with ceria and ErGO, ceria-ErGO nanocomposites have a synergistic effect on the charge transfer between the electrode and the solution interface. Ultrasensitive and selective determination of dopamine (DA) can be realized at the Ceria-ErGO/GCE. Under the optimum conditions, the calibration curve for the peak current of DA oxidation vs its concentration showed in three fragmented ranges of 6.0 nM–0.1 μM; 0.1 μM–2.0 μM and 2.0 μM–20 μM, respectively. The limit of detection of 3.0 nM (S/N = 3) was obtained under 90 s accumulation. In addition, the advantages of the sensor are easy regeneration of electrode surface, fast and convenient electrode preparation, low cost, sensitive and reliable determination results. This method is particularly suitable for the fast detection of DA in commercial pharmaceuticals and clinical urine as well as serum samples.

It is of great importance to determine the quantification of glucose in human serum. In this work, a novel NiO nanoflower/polymethylene blue (NiO/PMB) modified glassy carbon electrode (GCE) was fabricated and taken as a non-enzymatic glucose biosensor. The composite was characterized by field-emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The electrochemical properties of the modified biosensor were investigated by the cyclic voltammetry (CV) method. This biosensor combined the advantages of NiO nanoflower and PMB, so that a series of characterization results indicated that the composite material exhibiting satisfactory catalytic activity towards glucose. The quantitative determination of glucose was carried out by chronoamperometric measurements (i–t) method and showed linear ranges between 3−50 μM and 50−80 μM, with the limit of detection (LOD) of 2 × 10 ⁻⁷ M (S/N = 3). Under optimal conditions, the sensitivity of the self-assemble biosensor was calculated to be 413.06 μ A cm⁻² mM⁻¹ for glucose. The selectivity, reproducibility, and stability of the glucose biosensor were also confirmed in the study. In addition, this glucose biosensor was successfully applied for the analysis of glucose in real human serum samples.

NiFe layered double hydroxides (NiFe-LDHs) are considered as a promising substitute for noble metal electrocatalysts for oxygen evolution reactions (OER). A three-dimensional NiFe layered double hydroxides nanowire/nanoporous Ni interlayer/nickel foam substrate (NiFe-LDH/Ni/NF) electrocatalyst was designed and prepared on NF by a polystyrene (PS) microsphere template and a two-step in situ electrodeposition method. The electrocatalysts had a high specific surface area, an increased number of electrocatalytic active sites and improved electrochemical stability. In NiFe-LDHs/Ni/NF, the nickel nanoporous interlayer bonded closely with the NF matrix and simultaneously became loaded with the NiFe-LDH nanowires, which accelerated the electron transfer of the electrocatalyst nanowires to the matrix, increased the apparent active area, and promoted the OER. As expected, with a current density of 10 mA cm⁻², NiFe-LDHs/Ni/NF exhibited a smaller overpotential of 247 mV, a smaller Tafel slope of 35.52 mV dec⁻¹ and better durability than those of Ni/NF or NiFe-LDHs/NF. In addition, the overall water splitting system with the anode of NiFe-LDHs/Ni/NF and the cathode of Ni/NF had a small potential of 1.55 V with a current density of 10 mA cm⁻².

Herein, we advance our fundamental understanding of hydrogen electrochemistry as crucial energy technology by challenging the century-long paradigm that Volmer, Heyrovsky, and Tafel reactions are elementary. We identify and resolve the theoretical controversy of this phenomenological model to argue that each reaction must be stepwise not concerted elementarily. The stepwise model provides unprecedented insights as exemplified by resolving current debates on the Tafel analysis and volcano plot based on the controversial concerted model. The stepwise mechanism has not been distinguished from the concerted mechanism experimentally owing to the Laviron–Amatore paradox, which will be overcome by developing transient nanoelectrochemical methods.

Multi-doping strategy plays an important role in improving the properties of carbon nanomaterials for fabricating electrochemical sensor with high performance. In this study, a novel nanohybrid nitrogen coordinated copper co-doped multi-walled carbon nanotubes (MWCNTs@Cu-N-PC) was prepared via a simply green method and used then successfully for the sensitive and selective electrochemical detection of bisphenol A (BPA). The synthesized MWCNTs@Cu-N-PC was characterized through various means including scanning electron microscopy, energy dispersive spectrometer, transmission electron microscopy, X-ray diffraction, Raman spectra and electrochemical methods. As for the electrochemical sensing of BPA based on MWCNTs@Cu-N-PC, the results show that MWCNTs@Cu-N-PC modified electrode can exhibit much better sensing performance than the other related modified electrodes because of the synergistic effects from N and Cu co-doping, and it has a wide linear range (0.01–100 μM) and low limit of detection (5.8 nM) for BPA under the optimized conditions. Furthermore, the MWCNTs@Cu-N-PC electrode shows excellent selectivity, reproducibility, stability and high recovery value for real samples analysis. It's believed that MWCNTs@Cu-N-PC has potential applications in electrochemical sensing, and this work also offers a new and simple way for synthesizing N-coordinated metal co-doped nanomaterials.

A spontaneous modification of glassy carbon electrode (GCE) by reduced graphene oxide (rGO) doped peripherally with gold nanoparticles (AuNPs) was fabricated and characterized by cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS). The electron transfer kinetics of surface materials was evaluated by fitting the charge transfer resistance (R_ct) data in the presence of a redox probe such as [Fe(CN)₆]^3−/4−. The developed sensor (AuNPs.rGO-GCE) exhibited a large enhancement on the electrochemical oxidation of norepinephrine (NOR) than other arrays of surface assemblies. The voltammetric behavior of NOR at the present (AuNPs.rGO-GCE) modified surface was confirmed to follow a quazi-reversible reaction mechanism. Moreover, the apparent diffusion coefficient (D_app) and the heterogeneous rate constant (k_s) parameters of NOR species were collectively calculated using the classical irreversible electrochemical theory. The sensor showed excellent sensitivity and selectivity on NOR quantification in the presence of large concentration of ascorbic acid (AA) and the limit of detection of NOR (DL_3σ) is lowered to 57 nM (10 ppb). The analytical performance of the proposed system was validated successfully for pharmaceutical (injection ampoule) and biological (plasma blood) samples with tolerable recovery percentages.

An electrochemical sensor toward nitrite based on Ni foam supported nickel phosphide (NiP/NF) electrode was successfully fabricated via an in situ electrodeposition strategy. The sensor has exhibited great electrochemical detection ability with a sensitivity of 1.56 × 10⁻⁴ mA μM⁻¹, a linear range from 0.1 to 4000 μM and a detection limit of 0.01 μM (s/n = 3). Moreover, good stability of the electrodeposited electrode can be ascribed to the in situ growth of NiP onto Ni foam to achieve a binder-free electrode. The good recovery achieved for nitrite detection in several water samples also reveals its promising practicality.

Artificial photosynthesis can potentially address the global energy challenges and environmental issues caused by fossil fuels. Photoelectrochemical heterojunction structures of new photonic structures have been developed for efficient sunlight absorption, charge generation and separation and transport, and selective reduction of CO₂ and water splitting. In this review, an overview of several recently developed heterojunction model systems comprised of low-cost photonic materials such as transition metal dichalcogenides (TMDs), perovskite semiconductor nanocrystals, and plasmonic nanostructures is presented to rationalize the potential benefits of utilizing heterojunction structures for efficient and selective CO₂ reduction with renewable energy resources. Recent advances in electroanalytical methods for CO₂ reduction such as scanning electrochemical microscopy (SECM) are reviewed. These techniques can potentially resolve local CO₂ reduction kinetics and their spatial heterogeneities of a heterojunction photoelectrochemical structure.

In this work, a simple synthesis of (silver molybdate) Ag₂MoO₄ nanowires was developed by varying the pH. By adjusting the pH, agglomeration of each Ag₂MoO₄ nanowires were seen and electrochemical performance over each pH was investigated. To construct Ag₂MoO₄ nanowires, this process involves a co-precipitation assisted ultrasound reaction. The as-synthesized Ag₂MoO₄ was physically characterized using SEM, elemental mapping, EDX, and XRD analysis. Ag₂MoO₄ modified GCE was developed to determine a hydrothermal free and urea-free assisted synthesis. H₂O₂ plays a major role in the physiological process and it's an oxidative stress biomarker. Here we develop an electrochemical detection of enzyme-free H₂O₂ by amperometric method. The results obtained by modifying the electrode Ag₂MoO₄@pH-1 (AM@1) showed a good electrochemical reduction over current when compared to the bare electrode and Ag₂MoO₄@pH 2 to 5. LOD was calculated to be 5.42 nM with a linear range from 0.015 to 799.2 μM. The selectivity of sensor was analysed based on AM@1 modified electrode and also, the modified AM@1/GCE sensor has been practically applied in biological samples. Further, AM@1 showed a greater selectivity towards H₂O₂ in presence of some other biochemicals. Moreover, AM@1 exhibits advantages such as good stability, reproducibility, and repeatability.

An economical graphene-carbon paste electrode (GR/CPE) in situ modified with surfactants was used for improvement the sensitivity and selectivity of the electrochemical measurement of itraconazole drug. Among the surfactants, cationic (cetyltrimethyl ammonium bromide, CTAB) and non-ionic (Triton X-100) displayed a decrease in peak current intensity, while anionic (sodium dodecyl sulfate, SDS) exhibited better change in the electrical properties of the electrode-solution interface. The adsorbed-SDS at GR/CPE interacts with itraconazole molecules through hydrophobic and electrostatic attraction which encourages the electron transmission between the drug and electrode surface. Compared with CPE and GR/CPE, SDS-GR/CPE exhibits the enhanced peak current intensity and reduces the over potential toward itraconazole oxidation as a result of the combined effect of GR and SDS. %composition of GR/CPE and SDS concentration were optimized. Wide linear dependence of the current on bulk itraconazole concentration (1.5 × 10⁻⁹–7.0 × 10⁻⁷ M) was achieved in Britton–Robinson buffer, pH 2.0 containing 0.5 mM SDS at 0.3%(w/w) GR/CPE. SDS-GR/CPE presents adequately LOD value (1.36 × 10⁻⁹ ± 1.07 × 10⁻¹⁰ M) for the determination of itraconazole in human plasma. SDS-GR/CPE avoids interference from important common substances in biological and pharmaceutical samples. The fabricated sensor has desirable stability and reproducibility that can be used in routine quality control and pharmacokinetic studies.

Metal-organic frameworks (MOFs) are highly designable porous materials and are recognized for their exceptional selectivity as chemical sensors. However, they are not always suitable for incorporation with existing sensing platforms, especially sensing modes that rely on electronic changes in the sensing material (e.g., work-function response or conductometric response). One way that MOFs can be utilized is by growing them as a porous membrane on a sensing layer and using the MOF to affect the electronic structure of the sensing layer. In this paper, a proof-of-concept for electronic modulation with MOFs is demonstrated. A PdO nanoparticle sensing layer on a chemical-sensitive field-effect-transistor is made more sensitive to a reducing gas, hydrogen, and less sensitive to oxidizng molecules, like H₂S and NO₂, by growing a layer of the MOF "ZIF-8" over the nanoparticles. The proposed mechanism is supported by X-ray photoelectron spectroscopy showing that the ZIF-8 membrane partially reduces the PdO sensing layer.

p-Aminophenol (PAP) is a potentially toxic and mutagenic compound used and/or emitted in industrial, pharmaceutical and agriculture fields. Ion-selective electrode potentiometry (ISE) introduces an effective tool for real-time, portable and direct analysis to overcome lengthy sample preparation, treatment and derivatization steps. The current work aims to develop a portable ISE-potentiometric sensor for direct assay of PAP in industrial, environmental and biological matrices. Sensor assembly included a glassy carbon electrode upon which membrane cocktails were drop-casted. Optimization was carried out using a custom experimental design for the comprehensive evaluation of the main effects of the critical quantitative (percentage of ion-exchanger, PVC to plasticizer ratio and membrane thickness) and qualitative (ionophore type) factors on the sensor performance (Nernstian slope, LOD, LOQ, correlation coefficient). The optimized sensor included 1.20% ion exchanger, PVC: plasticizer ratio 1:4 and calix-[8]-arene as ionophore in 0.07 mm thick PVC membrane. The sensor proved a near-Nernstian slope of 61.9 mV decade⁻¹ within a linear range of 2.99 × 10⁻⁵−1 × 10⁻² M, a LOD of 2.86 × 10⁻⁵ M and rapid response time (1–5 s). The developed method was validated for PAP assay in urine, plasma, water, soil, hair dyes and in paracetamol marketed formulations. Eventually, the developed sensor can have multifarious applications in environmental, clinical and industrial fields.

Fluorescent portable monitoring systems provide real-time and on-site analysis of a sample solution, avoiding transportation delays and solution degradation. However, some applications, such as environmental monitoring of bodies of water with algae pollution, rely on the temperature control that off-site systems provide for adequate solution results. The goal of this research is the development of a temperature stabilization module for a portable fluorescent sensing platform, which is necessary to prevent inaccurate results. Using a Peltier device-based system, the module heats/cools a solution through digital-to-analog control of the current, using three surface-mounted temperature modules attached to a copper cuvette holder, which is directly attached to the Peltier device. This system utilizes an in-house algorithm for control, which effectively minimizes temperature overshooting when a change is enacted. Finally, with the use of a sample fluorescent dye, Rhodamine B, the system's controllability is highlighted through the monitoring of Rhodamine B's fluorescence emission decrease as the solution temperature increases.

Ion-selective membranes (ISMs) are at the core of ion-selective electrode development. Fundamentally, two groups of parameters determine the response of ISMs: selectivity coefficients and diffusion coefficients of mobile species in the membrane. It is possible to assess both by performing a single potentiometric ion-breakthrough experiment. Basically, the ISM is placed between two contacting electrolyte solutions that do not contain the ion that the ISM is selective for (primary ion). After primary ion is added the potential trace carries valuable information about the thermodynamics and the kinetics of the membrane. So far, extracting parameters from the experimental results was possible only after unrealistic simplifications (e.g. assuming all of the diffusion are the same). The state-of-the-art simulation technique the Nernst-Planck-Poisson finite element method is utilized to give insight on how the different physico-chemical processes generate the measured potential. Numerical simulations are used to train a feedforward neural network, in order to learn the connection between the physico-chemical parameters (e.g., thickness, diffusion coefficients, selectivity coefficients, coextraction etc.) and the shape of ion-breakthrough potential trace. By using the trained neural network it was possible to quickly obtain for the first time the diffusion coefficient of all of the mobile species in the ISM.

Hydrogen refueling stations (HRSs) that dispense hydrogen to fuel cell vehicles need to ensure the quality of hydrogen to avoid contamination of the vehicle's expensive fuel cell stacks. Currently, stations verify their fuel quality only periodically to ensure that they meet the strict fuel quality standards specified by either International Organization for Standards (ISO) or Society for Automotive Engineers (SAE). The development of hydrogen contaminant detectors (HCDs) that can provide low cost continuous monitoring at the HRS can be an invaluable asset in protecting fuel cell vehicles from any fuel contamination in-between infrequent expensive analysis of hydrogen fuel quality. An HCD capable of detecting < 200 ppb of CO in hydrogen is presented in this paper. The HCD is based on an electrochemical hydrogen pumping cell whose ultra-low loaded working electrode is poisoned by the contaminant, thus reducing its hydrogen oxidation reaction rate. The hydrogen pumping cell consists of a Nafion® membrane, a sputtered Pt working electrode, a Pt/Ru counter/pseudo-reference electrode and an internal water wicking system that provides humidification to the membrane and electrodes. When this HCD is operated in a pulsed voltammetry mode, it can provide stable CO response for thousands of hours in a HRS.

In this study, the crystallinities, structures, and optical properties of zinc oxide (ZnO) and platinum nanoparticles (Pt NPs)-decorated ZnO nanorods (Pt/ZnO NRs) were investigated by an X-ray diffraction, a field-emission scanning electron microscopy, and a photoluminescence spectrometry. The Pt NPs-decorated ZnO NRs were prepared by direct current (DC) magnetron sputtering for 0 and 30 s. The ZnO and Pt/ZnO NR-based gas sensors are consistent, stable, and repeatable. The sensitivities of the ZnO and Pt/ZnO NR sensors were 1.34% and 121.03%, respectively, at a concentration of 1000 ppm methanol gas and at an operating temperature of 270 °C. The Pt NPs-decorated ZnO NRs exhibit enhanced sensor characteristics of methanol gas.

Modern breath alcohol sensors (BrAS) employ an electrochemical sensor based upon fuel cell technology. These devices closely mimic power generating fuel cell technology from 30 years ago, with each electrode containing massive amounts of Pt black catalyst (∼10−20 mg cm⁻²). Here we report low-loading gas diffusion electrodes (GDE) fabricated using 40% Pt/C and studied the impact of Pt loading on sensor performance. The optimal loading was determined to be ca. 1 mg_Pt cm⁻², which gives the optimal balance between Pt utilization and ethanol sensitivity. The ethanol sensitivity performance achieved with the GDE paired with a Nafion membrane was similar to that achieved with a commercial MEA that employs a Pt loading of 13.7 mg cm⁻² and a PVC membrane. When paired with porous-PVC membranes our GDEs showed even greater sensitivity, readily exceed that of the commercial MEA despite the fact it employs 92% less Pt. The highest sensitivity was achieved when the GDE was paired to a gold-coated PVC membrane (Au-PVC), where the thin layer of gold is believed to enhance the membrane∣electrode interface. Thus, this sensor composition is proposed as a viable lower-cost alternative to the high-loading Pt black electrodes currently used in commercial BrAS technology.

Surface modification of natural clay halloysite with nickel hexacyanoferrate (NiHCF@HNT) have been obtained by chemical deposition of NiHCF at polydimethyldiallyamine pretreated HNT (PDDA/HNT) using positively charged polymer electrolyte as glue as well as nucleation site to grow metal hexacyanoferrate. The deposition of NiHCF on PDDA/HNT was confirmed using FT-IR and FE-SEM images. Cyclic voltammetry and electrochemical impedance spectroscopy techniques were used to study the electrochemical properties of NiHCF modified halloysite nanotubes. The modified sensor showed better electrocatalytic activity in dopamine (DA) oxidation and was used as a DPV sensor. The DA sensor revealed a linear response ranging from 8 to 152 μM (R² = 0.9982) with a sensitivity of 134.4 μA μM⁻¹ cm⁻² and LOD of 0.9 nM. This developed sensor also reveals an excellent catalytic activity, good stability, repeatability, reproducibility, and high sensitivity. Also, the designed sensor exhibited no overlapping signal from other co-existing electroactive species and studied real sample applications like DA injection and serum samples.

In this study, we present a highly responsive room-temperature resistive humidity sensor based on a shellac-derived carbon (SDC) active film deposited on sub-micrometer-sized carbon interdigitated electrodes (cIDEs). This monolithic carbon-based sensor demonstrates an excellent linear relationship with humidity and ohmic contact between the active carbon film and carbon electrodes, which results in low noise and low power consumption (∼1 mW). The active SDC film is synthesized by a single-step thermal process, wherein the temperature is found to control the amount of oxygen functional moieties of the SDC film, thereby providing an efficient means to optimize the sensor response time, recovery time, and sensitivity. This SDC–cIDEs-based humidity sensor exhibits an excellent dynamic range (0%–90% RH), a large dynamic response (50%), and high sensitivity (0.54/% RH). In addition, the two-dimensional feature (thickness ∼10 nm) of the SDC film enables a swift absorption/desorption equilibrium, leading to fast response (∼0.14 s) and recovery (∼1.7 s) under a humidity range of 0%–70% RH. Furthermore, the thin SDC-based sensor exhibited excellent selectivity to humidity from various gases, which in combination with its fast response/recovery promises its application for an instant calibration tool for gas sensors.

In this paper, a microfluidic sensor structure has been proposed for operating frequency reconfiguration purpose. The structure has been designed by using split ring resonator architecture with a transmission line. 0%, 20, 40%, 60%, 80% and 100% ethanol volume content in the ethanol-water mixture have been used as samples to understand sensing characteristic of the proposed structure. After that five sensor structure with different dimension coefficients (1.4, 1.2, 1, 0.8 and 0.6) are designed and manufactured. The ethanol-water mixture samples has been applied to the sensor structure and it is observed that there is a linear relation operating frequency band and the dimension coefficient. The study has been realized both numerically and experimentally and the results are in a good agreement. The proposed structure is a good candidate for microfluidic sensing applications and operating frequency band of the structure can be easily reconfigured any necessary and desired range with respect to electrical characteristics of the samples.

A poly (methylene blue)/copper nanowires modified nano-carbon paste electrode (PMB/CuNWs@nano-CPE) was developed for ultra-sensitive detection of luteolin. The morphology of copper nanowires was characterized by transmission electron microscopy (TEM). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were utilized to investigate the electrochemical properties of the fabricated electrodes. In comparison with bare nano-carbon paste electrodes (nano-CPE), the PMB/CuNWs@nano-CPE presented better electrocatalytic activity towards luteolin, including reduced oxidation peak potential and enhanced oxidation peak current. The influencing factors on sensitivity were discussed, such as instrumental parameters, concentration of methylene blue, electropolymerization cycles, the amount of copper nanowires, pH value, accumulation potential and accumulation time. Under optimal conditions, two linear calibration ranges of 0.5 nM−0.01 μM and 0.01 μM−1 μM and the detection limit (LOD) of 0.1 nM (S/N = 3) were obtained for luteolin. The satisfying results were achieved for the determination of luteolin in Chinese medicine capsule samples.

In the present study we report the design & synthesis of a novel p-n type semiconducting Pd incorporated ZnO: SnO (ZSP) nanocomposite as Hydrogen (H₂) gas sensor, which demonstrates an efficient conductivity and superior stability through nanostructured engineering. The structural characteristics were investigated by X-ray diffraction (XRD), Particle Size Analyzer (PSA), X-ray Photoelectron Spectroscopy (XPS) and morphology by High Resolution Transmission electron microscopy (HRTEM). Gas sensing characteristics of ZnO: SnO nanocomposite towards 500 ppm hydrogen gas exhibited Sensitivity of S = 0.6 whereas ZnO: SnO: Pd nanocomposite exhibited higher Sensitivity of S = 0.91 at a lower operating temperature of 150 °C. The achieved features make the sample ZSP a potential candidate for development of highly Sensitive and Selective H₂ gas sensor.

Carbon dots are fluorescent carbon-based nanoparticles with great potential in bioimaging because they offer multiple imaging windows owing to their excitation-dependent emission features. A recent theoretical study shows that emission of graphene quantum dots responds to external electric field due to Stark effect. Inspired by this work, we have demonstrated here the first experimental study of the Stark effect of fluorescent carbon dots synthesized via a soft-template method. The carbon dots exhibit excitation-dependent emission covering blue to orange emission range. After being encapsulated in artificial lipid bilayers, the carbon dots show voltage-sensitivity of fluorescence. The fluorescence intensity change per mV is comparable with that of commercial membrane potential sensing dyes. Our results demonstrate the great potential of carbon dots in membrane voltage sensing.

Modern diesels employ a particulate filter (DPF) to reduce soot emissions. Additionally, the selective catalytic reduction (SCR) of NOx by NH₃ stored on the SCR catalyst reduces NOx emissions. In some vehicles the functions of these aftertreatment components are combined in the SDPF, a DPF having a SCR washcoat. The RF resonant method has been shown to be an alternative tool for measuring the DPF's soot loading and the SCR's NH₃ loading. For both applications, the transmitted electromagnetic signal between antennae placed on either side of the catalyst change with loading. Here we report the influence of the RF signal on both soot and NH₃ loadings on a SDPF segment. We show that the attenuation of the RF signal by soot is much larger than that caused by saturating it with 400 ppm NH₃. By taking the mean RF signal amplitude measured over a wide range of frequencies, we demonstrate a method for determination of the soot loading even in the presence of stored NH₃. For "light" soot loadings, before the RF attenuation by soot cause the resonant modes to disappear in the spectra, we demonstrate a method for the simultaneous determination of both the soot and NH₃ loadings.

The generation of fast electrochemical response with high sensitivity is a significant parameter for enzymatic biosensors. However, establishing nanocomposite based modified electrode with fast electron shuttling between enzymes and the electrode surface for determination of hydrogen peroxide (H₂O₂) is highly challenging. Herein, the present work aims to develop second generation horseradish peroxidase (HRP) biosensors using Au nanochains dropcasted over electrochemically reduced graphene oxide-chitosan (ERGO-CHIT), a bio-nanocomposite film modified glassy carbon electrode (GCE) for reduction of H₂O₂ is demonstrated. The experimental conditions including effect of pH, loading of enzyme on the electrode surface and concentration of redox mediator as electrolyte were optimized. As a result, the HRP/Au/ERGO-CHIT/GCE electrode shows a larger enhancement in cathodic current signal with sharp peak response for reduction of H₂O₂, which can be attributed to the presence of Au nanochains on the modified electrode which improves the electron transfer between heme (Fe²⁺/Fe³⁺) center of enzymes on the electrode and the redox mediator in the electrolyte solution. The presence of HQ redox mediator in the electrolyte solution have provided stable peak response and offered more beneficiary in lowering the operating potential for the detection of H₂O₂ (−0.1 V), thereby reducing the influence from interference species. From the amperometric measurements, the HRP/Au/ERGO-CHIT/GCE modified electrode revealed high sensitivity (368.01 μA mM⁻¹ cm⁻²) and possesses wide linear range (0.01 to 6.31 mM) which is mainly due to the high surface area and conductivity offered by Au nanochains which are located between ERGO and HRP. The resultant HRP/Au/ERGO-CHIT/GCE was found to possess good operational stability, high reproducibility, repeatability with low detection limits (4 μM), and thus it could be applicable for sensitive and rapid responsive detection of H₂O₂ in biological, clinical and environmental samples.

A simple and label-free aptasensor for rapid determination of ochratoxin A (OTA) has been proposed, which is based on the competitive strategies between single stranded DNA (ssDNA) and methylene blue (MB) on two-dimensional (2D) nitrogen-doped graphene (NGE) surfaces. Compared with the binding force of electrostatic attraction and weak π-π stacking between MB and NGE surfaces, the binding affinity of hydrogen bonding and stronger π-π stacking will contribute to the binding force between ssDNA nucleobases and graphene. As mentioned above, the combination of aptamer with OTA can release complementary DNA (cDNA) to detection system and the single stranded cDNA thus attaches to NGE surfaces through the binding force of hydrogen bonding and strong π-π stacking, causing MB to release from the NGE surfaces. The signal changes of MB could be used to determine OTA concentration. The sensing mechanism has been studied by UV and SWV. The electrochemical processes are characterized by SWV and EIS techniques with low detection-limit (0.71 fg·mL⁻¹) and a wide linear range (1 fg·mL⁻¹–0.1 μg·mL⁻¹). The proposed label-free aptasensor will simplify the detection processes and boost their practical applications to timely prevent OTA exposure to human bodies.

The detection of hazardous gases are essential to protect human health and safety. Nowadays, there is a great demand for the detection of multiple hazardous gases. In this study, a miniaturized electronic nose with SVM recognition models was used for the detection of carbon monoxide, methane, formaldehyde as well as their mixtures. The sensor array consisted of 6 commercial MOS sensors which were cross-sensitive to three kinds of hazardous gases. The SVM models were trained based on the features extracted by two methods in order to recognize the concentration levels of three hazardous gases. The 5-fold cross-validation was used to evaluate and compare the accuracies of different models for all target gases. The results indicated that the wavelet time scattering can extract features more effectively compared with the classic feature extraction method. The models based on the features gained by wavelet time scattering showed the accuracies of 98.73% for CO, 100% for CH₄ and 97.46% for CH₂O. This study provides a practical recognition method and detection platform for multi-gas sensing applications.

Photoluminescence (PL) sensors based on quantum dots (QDs) are difficult to achieve exact detection in sample waters. In this paper, polyvinyl alcohol (PVA) based CdTe/ZnS/CdS QDs and fluorescein isothiocyanate (FITC) fluorophores were used to build a ratiometric PL sensor. Combining with the homemade smartphone-based PL E-eye, the Cd²⁺ exact detection can be achieved. PVA was used to connect QDs and FITC fluorophores without unnecessary ligand exchange and purification. For QDs fluorophore, ethylenediaminetetraaceticacid (EDTA) was used on the surface to induce the specifically Cd²⁺ recognition site. For FITC fluorophore, the PL remains unchanged in this experiment. Thus, the ratio of two fluorophores can be used to provide a built-in correction. The PL changes with the increase of Cd²⁺ concentrations could be displayed as a visual color change on the smartphone. Further quantitative analysis could be carried out by the RGB value of the picture through the App in less than 1 min The ratio of R/G is linear to Cd²⁺ concentration in the range of 1–2000 μg l⁻¹ with a low LOD of 0.057 μg l⁻¹ (S/N). Compared with traditional analysis methods, the PL ratiometric method with PL E-eye is portable, rapid, visible and highly selective especially in discriminate Cd²⁺ from Zn²⁺.