Journal of The Electrochemical Society

Energy storage systems with Li-ion batteries are increasingly deployed to maintain a robust and resilient grid and facilitate the integration of renewable energy resources. However, appropriate selection of cells for different applications is difficult due to limited public data comparing the most commonly used off-the-shelf Li-ion chemistries under the same operating conditions. This article details a multi-year cycling study of commercial LiFePO₄ (LFP), LiNi_xCo_yAl_1−x−yO₂ (NCA), and LiNi_xMn_yCo_1−x−yO₂ (NMC) cells, varying the discharge rate, depth of discharge (DOD), and environment temperature. The capacity and discharge energy retention, as well as the round-trip efficiency, were compared. Even when operated within manufacturer specifications, the range of cycling conditions had a profound effect on cell degradation, with time to reach 80% capacity varying by thousands of hours and cycle counts among cells of each chemistry. The degradation of cells in this study was compared to that of similar cells in previous studies to identify universal trends and to provide a standard deviation for performance. All cycling files have been made publicly available at batteryarchive.org, a recently developed repository for visualization and comparison of battery data, to facilitate future experimental and modeling efforts.

This year, the battery industry celebrates the 25^th anniversary of the introduction of the lithium ion rechargeable battery by Sony Corporation. The discovery of the system dates back to earlier work by Asahi Kasei in Japan, which used a combination of lower temperature carbons for the negative electrode to prevent solvent degradation and lithium cobalt dioxide modified somewhat from Goodenough's earlier work. The development by Sony was carried out within a few years by bringing together technology in film coating from their magnetic tape division and electrochemical technology from their battery division. The past 25 years has shown rapid growth in the sales and in the benefits of lithium ion in comparison to all the earlier rechargeable battery systems. Recent work on new materials shows that there is a good likelihood that the lithium ion battery will continue to improve in cost, energy, safety and power capability and will be a formidable competitor for some years to come.

In this study, the calendar aging of lithium-ion batteries is investigated at different temperatures for 16 states of charge (SoCs) from 0 to 100%. Three types of 18650 lithium-ion cells, containing different cathode materials, have been examined. Our study demonstrates that calendar aging does not increase steadily with the SoC. Instead, plateau regions, covering SoC intervals of more than 20%–30% of the cell capacity, are observed wherein the capacity fade is similar. Differential voltage analyses confirm that the capacity fade is mainly caused by a shift in the electrode balancing. Furthermore, our study reveals the high impact of the graphite electrode on calendar aging. Lower anode potentials, which aggravate electrolyte reduction and thus promote solid electrolyte interphase growth, have been identified as the main driver of capacity fade during storage. In the high SoC regime where the graphite anode is lithiated more than 50%, the low anode potential accelerates the loss of cyclable lithium, which in turn distorts the electrode balancing. Aging mechanisms induced by high cell potential, such as electrolyte oxidation or transition-metal dissolution, seem to play only a minor role. To maximize battery life, high storage SoCs corresponding to low anode potential should be avoided.

Recently, the field of CO₂ electrolysis has experienced rapid scientific and technological progress. This review focuses specifically on the electrochemical conversion of CO₂ into carbon monoxide (CO), an important "building block" for the chemicals industry. CO₂ electrolysis technologies offer potentially carbon-neutral routes for the production of specialty and commodity chemicals. Many different technologies are actively being pursued. Electrochemical CO₂ reduction from aqueous solutions stems from the success of alkaline and polymer electrolyte membrane electrolyzers for water electrolysis and uses performance metrics established within the field of aqueous electrochemistry. High-temperature CO₂ electrolysis systems rely heavily on experience gained from developing molten carbonate and solid oxide fuel cells, where device performance is evaluated using very different parameters, commonly employed in solid-state electrochemistry. In this review, state-of-the-art low-temperature, molten carbonate, and solid oxide electrolyzers for the production of CO are reviewed, followed by a direct comparison of the three technologies using some of the most common figures of merit from each field. Based on the comparison, high-temperature electrolysis of CO₂ in solid oxide electrolysis cells seems to be a particularly attractive method for electrochemical CO production, owing to its high efficiency and proven durability, even at commercially relevant current densities.

Lithium-ion batteries can last many years but sometimes exhibit rapid, nonlinear degradation that severely limits battery lifetime. In this work, we review prior work on "knees" in lithium-ion battery aging trajectories. We first review definitions for knees and three classes of "internal state trajectories" (termed snowball, hidden, and threshold trajectories) that can cause a knee. We then discuss six knee "pathways", including lithium plating, electrode saturation, resistance growth, electrolyte and additive depletion, percolation-limited connectivity, and mechanical deformation—some of which have internal state trajectories with signals that are electrochemically undetectable. We also identify key design and usage sensitivities for knees. Finally, we discuss challenges and opportunities for knee modeling and prediction. Our findings illustrate the complexity and subtlety of lithium-ion battery degradation and can aid both academic and industrial efforts to improve battery lifetime.

What is the best approach for estimating standard electrochemical potentials, E⁽⁰⁾, from voltammograms that exhibit chemical irreversibility? The lifetimes of the oxidized or reduced forms of the majority of known redox species are considerably shorter than the voltammetry acquisition times, resulting in irreversibility and making the answer to this question of outmost importance. Half-wave potentials, E^(1/2), provide the best experimentally obtainable representation of E⁽⁰⁾. Due to irreversible oxidation or reduction, however, the lack of cathodic or anodic peaks in cyclic voltammograms renders E^(1/2) unattainable. Therefore, we evaluate how closely alternative potentials, readily obtainable from irreversible voltammograms, estimate E⁽⁰⁾. Our analysis reveals that, when E^(1/2) is not available, inflection-point potentials provide the best characterization of redox couples. While peak potentials are the most extensively used descriptor for irreversible systems, they deviate significantly from E⁽⁰⁾, especially at high scan rates. Even for partially irreversible systems, when the cathodic peak is not as pronounced as the anodic one, the half-wave potentials still provide the best estimates for E⁽⁰⁾. The importance of these findings extends beyond the realm of electrochemistry and impacts fields, such as materials engineering, photonics, cell biology, solar energy engineering and neuroscience, where cyclic voltammetry is a key tool.

This paper studied the gases release of a graphite//NMC111(LiNi_1/3Mn_1/3Co_1/3O₂) cell during cycle in the voltage ranges of 2.6-4.2V and 2.6-4.8V and the temperatures of at 25°C and 60°C. It was proved that the CO₂, CO, and H₂ gases are released as a result of electrolyte decomposition. And it shows that the CO and H₂ gases evolution is a direct consequence of the electrochemical reaction of electrolyte decomposition, while the CO₂ generation is a consequence of the additional chemical reaction of interaction between the O₂ released from the cathode atomic lattice oxygen and CO released from the same place on the cathode (appearing because of the electrolyte decomposition). That is why at the same electrochemical reaction of electrolyte decomposition, the ratio CO₂/CO varies in the wide range from 0.82 to 2.42 depending on cycling conditions (temperature and cutoff voltage). It was proved that a potential-independent H₂ evolution is a consequence of its adsorption in pores of powdered graphite on anode. There was proposed the mechanism of the electrolyte decomposition and the gases evolution in lithium-ion cells at their cycling, which corresponds quantitatively to all obtained experimental results.

LiFePO₄/graphite (LFP), Li[Ni_0.5Mn_0.3Co_0.2]O₂/graphite (NMC3.8 V, balanced for 3.8 V cut-off), and Li[Ni_0.83Mn_0.06Co_0.11]O₂/graphite (Ni83, balanced for 4.06 V cut-off) cells were tested at 85 °C. Three strategies were used to improve cell lifetime for all positive electrode materials at 85°C. First, low voltage operation (<4.0 V) was used to limit the parasitic reactions at the positive electrode. Second, LiFSI (lithium bis(trifluoromethanesulfonyl)imide) was used as the electrolyte salt for its superior thermal stability over LiPF₆ (lithium hexafluorophosphate). The low voltage operation avoids the aluminum corrosion seen at higher voltages with LiFSI. NMC3.8 V cells were operated at 6 C charge and 6 C discharge without issue for 2500 cycles and then moved to room temperature where normal operation was obtained. Finally, dimethyl-2,5-dioxahexane carboxylate (DMOHC) was used as a sole electrolyte solvent or mixed with dimethyl carbonate. μ-XRF data showed no detectable levels of transition metal deposition on the negative electrode of Ni83 and LFP cells, and DMOHC cells showed less gassing after testing compared to EC-based electrolytes. We found incredible capacity retention and cycle life for Ni83 and NMC3.8 V cells using DMOHC and LiFSI at 70 °C and at 85 °C in tests that ran for more than 6 and 5 months (and are still running), respectively.

Lithium-ion batteries are well-suited for fully electric and hybrid electric vehicles due to their high specific energy and energy density relative to other rechargeable cell chemistries. However, these batteries have not been widely deployed commercially in these vehicles yet due to safety, cost, and poor low temperature performance, which are all challenges related to battery thermal management. In this paper, a critical review of the available literature on the major thermal issues for lithium-ion batteries is presented. Specific attention is paid to the effects of temperature and thermal management on capacity/power fade, thermal runaway, and pack electrical imbalance and to the performance of lithium-ion cells at cold temperatures. Furthermore, insights gained from previous experimental and modeling investigations are elucidated. These include the need for more accurate heat generation measurements, improved modeling of the heat generation rate, and clarity in the relative magnitudes of the various thermal effects observed at high charge and discharge rates seen in electric vehicle applications. From an analysis of the literature, the requirements for lithium-ion thermal management systems for optimal performance in these applications are suggested, and it is clear that no existing thermal management strategy or technology meets all these requirements.

The standard format for cylindrical Li-ion cells is about to change from 18650-type cells (18mm diameter, 65mm height) to 21700-type cells (21mm diameter, 70mm height). We investigated the properties of five 18650 cells, three of the first commercially available 21700, and three types of the similar 20700 cells in detail. In particular, the (i) specific energy/energy density and electrode thickness, (ii) electrode area and cell resistance, (iii) specific energy as a function of discharge C-rate, as well as (iv) heating behavior due to current flow are analyzed. Finally, the production effort for cells and packs are roughly estimated for 21700 cells compared to 18650 cells.

The nanoscale quantification of the electrochemical behavior in metals is critical to understanding the microstructure-corrosion relationship and subsequently controlling it. In this article, the application of advanced surface characterization techniques—atomic force microscopy (AFM), vertical scanning interferometry (VSI), digital holography microscopy (DHM), and other quantitative phase microscopy (QPM) techniques—for surface corrosion monitoring in metals at the micro- and nanoscale are systematically reviewed and discussed in detail. Interestingly in situ, real-time nanoscale topography evolution that enables measurement of time-dependent local dissolution rate as often tracked from numerical construction of QPM is also presented. This study demonstrates the considerable attributes of correlative advanced techniques for identifying nanoscale corrosion mechanisms, enabling the informed development of next-generation inhibition technologies, and improving corrosion predictive models.

In this paper, nickel oxide films were deposited on ITO-coated glass substrates by DC magnetron sputtering at different pressures(1.2 Pa ∼ 3.0 Pa). The effects of sputtering pressure on microstructure and electrochromic properties of nickel oxide films were investigated. The film thickness was measured by a surface profilometer. The crystal structure and surface morphology of the films were observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochromic properties of the films were studied by combining UV-visible spectrophotometer with electrochemical workstation. The results showed that the nickel oxide film obtained the best surface morphology (uniform grain size and the fewer surface cracks) and outstanding electrochromic performances, including large transmittance modulation (ΔT = 57.19%), high coloration efficiency (CE = 33.59 cm²·C⁻¹) and fast switching speed (t_c = 4.63 s, t_b = 4.87 s) at a wavelength of 550 nm when the sputtering pressure was 2.4 Pa. And after 500 electrochemical cycles, the transmittance modulation could continue to increase to 61.49% and the coloration efficiency can still be maintained at about 28.21 cm²·C⁻¹, which showed excellent cycling durability.

Optimizing platinum (Pt) utilization is a necessary step towards developing affordable electrocatalysts for fuel cells and related technologies. Electrodeposition is a scalable approach to preparing Pt nanoparticles (NPs). Herein, Cl⁻ and Br⁻ ions are used in excess as additives during the electrodeposition of Pt NPs to influence nucleation and growth processes as a means of tuning particle morphology and their electrocatalytic activity. Adding NaCl formed larger particles with urchin-like morphologies while adding NaBr produced smaller, more uniform NPs that were evenly dispersed across the substrate. Mixtures of these two halide ion species improved surface coverage and size distribution of the NPs. Particle size was further decreased, and their surface coverage increased by combining the addition of excess halide ions with using a higher applied potential to initiate "nucleation" followed by a lower applied potential to promote particle "growth." Mass activity towards the oxygen reduction reaction was the highest for Pt NPs electrodeposited in the presence of Br⁻. The addition of cetyltrimethylammonium chloride and cetyltrimethylammonium bromide during electrodeposition produced small NPs with an even higher mass activity, which was attributed to the formation of porous nanostructures. This study demonstrates techniques to improve Pt utilization and electrocatalytic activity of electrodeposited Pt NPs.

"Zero-excess" lithium-metal batteries represent a very promising next-generation battery concept, enabling extremely high energy densities. However, lithium metal deposition is often non-uniform and accompanied by severe side reactions with the electrolyte, limiting Coulombic efficiency and, thus, energy density and cycle life. To address this issue, we introduced a thin polymer-based artificial interphase at the negative electrode. The influence of this interphase on the lithium deposition, and generally the reactions occurring at the negative electrode, was evaluated by galvanostatic stripping/plating tests and a thorough ex situ analysis via scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDX), scanning photoemission microscopy (SPEM), and soft-X-ray absorption spectroscopy (soft-XAS). The results demonstrate that the introduction of such a polymer-based interlayer allows for more stable cycling and reduces dendritic lithium growth owing to the formation of a more homogeneous, thin, and fluorine-rich passivation layer.

The limitation of low-cost and high-safety aqueous manganese-based materials for electrochemical energy storage is largely hampered by their poor cyclic stability, which is usually caused by the manganese dissolution and interfacial kinetics. Here we synthesize a composite electrode which possesses unique structural properties for aqueous supercapacitor application and exhibits higher area specific capacitance. The remarkable long cycle stability of Mn₃P₂O₈/TiN on titanium (Mn₃P₂O₈/TiN@Ti) outperforms that most manganese-based pseudocapacitive electrode materials. The designed unique structure is attractive for quick charge migration, which confirms that the appropriate anodizing of substrate, electrodeposition of active substances and their in situ loading, is an efficient strategy to improve kinetics for high power density pseudocapacitive supercapacitor energy storage application.

The nanoscale quantification of the electrochemical behavior in metals is critical to understanding the microstructure-corrosion relationship and subsequently controlling it. In this article, the application of advanced surface characterization techniques—atomic force microscopy (AFM), vertical scanning interferometry (VSI), digital holography microscopy (DHM), and other quantitative phase microscopy (QPM) techniques—for surface corrosion monitoring in metals at the micro- and nanoscale are systematically reviewed and discussed in detail. Interestingly in situ, real-time nanoscale topography evolution that enables measurement of time-dependent local dissolution rate as often tracked from numerical construction of QPM is also presented. This study demonstrates the considerable attributes of correlative advanced techniques for identifying nanoscale corrosion mechanisms, enabling the informed development of next-generation inhibition technologies, and improving corrosion predictive models.

Twin boundaries are planar defects between two domains exhibiting mirror symmetry. Nano-twinned metallic materials contain numerous twin boundaries in parent grains exhibiting submicrometer twin spacing. Owing to their unique mechanical and electrical properties, nano-twinned metals have been studied extensively. Although the mechanical strength of the metal can be drastically increased by shrinking grains, nanocrystalline metals lose their ductility (i.e., the strength–ductility tradeoff), and their electrical conductivity is considerably lowered owing to electron scattering at dense grain boundaries. However, nano-twinned metallic materials can overcome these limitations and exhibit excellent strength, ductility, and electrical conductivity. In this paper, the structure and properties of nano-twinned Cu films are reviewed, and direct current and pulse electrodeposition for forming twin boundaries in Cu films and controlling the twin structure and thickness are summarized. Furthermore, the applications of nano-twinned Cu materials for fabricating electronics are presented.

The biosensor is a rapidly expanding field of science owing to its wide variety of applications in healthcare, pharmacology, environmental control, food quality assessment, security and defense, and, most notably, diagnostics. Among biosensors, electrochemical biosensors are immensely popular because of their high sensitivity, low detection limit, automation capabilities, low testing cost, and the emergence of electrochemical disposable devices capable of dealing with extremely small sample volumes. Biomolecule immobilization is a crucial step in biosensor development that necessitates the functionalization of the transducer surface. In 2007, polydopamine (PDA) is introduced as a substrate-independent coating material rich in catechol, imine, and amine groups, which provides a perfect environment for dense biomolecule immobilization on the transducer surface. PDA brings the world of possibilities for attaching biomolecules, changing their bio-catalytic capabilities, transferring electrons rapidly, and offering a rapid interface to provide a range of electrochemical signals to design unique diagnostic tools. This review attempts to assemble existing research progressed on PDA-based electrochemical biosensors in terms of enzymatic biosensors (based on H₂O₂, glucose, alcohol, and laccase), genosensors (DNA sensing), immunosensors, and aptasensors. Further, literature on the detection of thrombin, tumour markers, amino acids, and other therapeutically significant analytes has been collated to provide a comprehensive assessment of PDA-based biosensors. Furthermore, the future potential of PDA-based biosensors for the construction of smart sensor systems leveraging artificial intelligence and Internet of things technologies was discussed in this article.

The scarcity of fresh water resource has become one of the top concerns of modern society. Various water treatment technologies have been developed for the reuse of seawater and capacitive deionization (CDI) holds superior advantages as a promising electrosorption desalination technology. Since electrode material is the key factor in controlling the performance of CDI, recent years have witnessed considerable research progress in the rational design and fabrication of Zn-based MOF-derived carbon materials applied as electrode materials for CDI. In this review, Zn-based MOF-derived carbon materials, including MOF-5 derived carbons, ZIF-8 derived carbons and innovation Zn-based MOF derived carbons, are systematically overviewed based on their MOF template precursors. Among them, ZIF-8 derived carbon electrode materials are summarized in detail and different approaches for the improvement of their CDI performance are particularly discussed. We believe this review could function as a guidance of innovative development of Zn-based MOF-derived carbon materials and provide future directions for further improving their CDI performance.

Emphasis on clean energy has led to a widespread focus on lithium-ion batteries. However, a major obstacle is their degradation with several cycles or calendar aging. Battery Management System relies on an essential model-based algorithm to protect the battery from operating outside the safety limit. Thus, this work attempts to answer important research questions on battery models: (1) Are physics-based electrochemical models (EM) robust enough to identify internal cell degradation and abnormal battery behavior? (2) How are the structural simplifications and mathematical order reductions imposed on the EMs and what are their trade-offs? (3) How to apply simplified EM for safer and more efficient battery operation? (4) What are the prospects and obstacles of employing EM-based algorithms in the future? This paper presents a detailed analysis of EM from a modeling and application perspective. The paper introduces battery operating mechanisms, typical failures, and their effects. Followed by an analysis of full order EM (Pseudo 2-Dimensional), and further classification into simpler and advanced reduced-order models. The study demonstrates the gaps in theoretical understanding and their implementation for real-time battery operations such as in thermal management, energy utilization, and fault diagnosis and prognosis.

Emphasis on clean energy has led to a widespread focus on lithium-ion batteries. However, a major obstacle is their degradation with several cycles or calendar aging. Battery Management System relies on an essential model-based algorithm to protect the battery from operating outside the safety limit. Thus, this work attempts to answer important research questions on battery models: (1) Are physics-based electrochemical models (EM) robust enough to identify internal cell degradation and abnormal battery behavior? (2) How are the structural simplifications and mathematical order reductions imposed on the EMs and what are their trade-offs? (3) How to apply simplified EM for safer and more efficient battery operation? (4) What are the prospects and obstacles of employing EM-based algorithms in the future? This paper presents a detailed analysis of EM from a modeling and application perspective. The paper introduces battery operating mechanisms, typical failures, and their effects. Followed by an analysis of full order EM (Pseudo 2-Dimensional), and further classification into simpler and advanced reduced-order models. The study demonstrates the gaps in theoretical understanding and their implementation for real-time battery operations such as in thermal management, energy utilization, and fault diagnosis and prognosis.

Lithium (Li) metal anodes are essential for developing next-generation high-energy-density batteries. However, Li dendrite/whisker formation caused short-circuiting issue and short cycle life have prevented lithium metal from being viably used in rechargeable batteries. Numerous works have been done to study how to regulate the Li growth in electrochemical cycling by using external stacking forces. While it is widely agreed that stack pressure positively affects the lithium plating/stripping process, the optimized pressure range provided by different works varies greatly because of the difference in the pressure control setup. In this work, a pressure control apparatus is designed for Li metal batteries with liquid and solid-state electrolytes (SSE). With considerations of minimizing cell to cell variation, a reusable split cell and pressure load cell are made for testing electrochemical cells with high precision pressure control. The capability of the designed setup is demonstrated by studying the pressure effect on the Li plating/stripping process.

Ternary metal halides A₃MX₆, (A = Li⁺, Na⁺; M = trivalent metal; X = halide) are a promising family of solid electrolytes for potential applications in all-solid-state batteries. Recent research efforts have demonstrated that chemical substitution at all three sites is an effective strategy to controlling battery-relevant material properties. The A₃MX₆ family exhibits a wide breadth of structure and anion sublattice types, making it worthwhile to comprehend how chemical substitutions manifest desirable functional properties including ion transport, electrochemical stability, and environmental tolerance. Yet, a cohesive understanding of the materials design principles for these substitutions have not yet been developed. Here, we bring together prior literature focused on chemical substitutions in the A₃MX₆ ternary metal halide solid electrolytes. Using materials chemistry perspectives and principles, we aim to provide insights into the relationships between crystal structure, choice of substituting ions and the extent of substitutions, ionic conductivity, and electrochemical stability. We further present targeted approaches to future substitution studies to enable transformative advances in A₃MX₆ solid electrolytes and all-solid-state batteries.

Active cathode material and graphite anode material are routinely mixed with conductor and binder to improve the electric conductivity and mechanical stability of electrodes. Despite its benefits, this carbon binder domain (CBD) impedes ionic transport and reduces the active surface area, thus impacting the battery performance. We consider a composite spherical particle, whose active-material core is coated with CBD, and its homogeneous counterpart, for which we derived equivalent electrical conductivity, ionic diffusivity, and reaction parameters in the Butler-Volmer equation. These equivalent characteristics are defined to ensure that the same mass and charge enter the composite and homogenized spheres. They are expressed in terms of the volume fraction of the active material and transport properties of the active material and CBD. In general, the equivalent effective diffusion coefficient and reaction parameters are time-dependent and exhibit two-stage behavior characterized by the reaction delay time. At later times, these characteristics are time-independent and given explicitly by closed-form formulae. The simplicity of these expressions facilitates their use in single- and multi-particle representations of Li-ion and Li-metal batteries.

A model for impedance of a PEM fuel cell cathode taking into account oxygen transport in the cathode catalyst layer (CCL), gas–diffusion layer (GDL) and in channel is solved analytically. A formula for the cathode impedance is valid for the cell current densities below 100 mA cm⁻² and air flow stoichiometries exceeding 10. Least–squares fitting of experimental spectrum using the analytical result takes about 5 s on a standard PC. Fitting returns Tafel slope of the oxygen reduction reaction, double layer capacitance, CCL proton conductivity and oxygen diffusivities of the CCL and GDL. Analytical impedance can be coded as a user–defined function for a standard spectra fitting software supplied with EIS–meters.

Optimizing platinum (Pt) utilization is a necessary step towards developing affordable electrocatalysts for fuel cells and related technologies. Electrodeposition is a scalable approach to preparing Pt nanoparticles (NPs). Herein, Cl⁻ and Br⁻ ions are used in excess as additives during the electrodeposition of Pt NPs to influence nucleation and growth processes as a means of tuning particle morphology and their electrocatalytic activity. Adding NaCl formed larger particles with urchin-like morphologies while adding NaBr produced smaller, more uniform NPs that were evenly dispersed across the substrate. Mixtures of these two halide ion species improved surface coverage and size distribution of the NPs. Particle size was further decreased, and their surface coverage increased by combining the addition of excess halide ions with using a higher applied potential to initiate “nucleation” followed by a lower applied potential to promote particle “growth.” Mass activity towards the oxygen reduction reaction was the highest for Pt NPs electrodeposited in the presence of Br⁻. The addition of cetyltrimethylammonium chloride and cetyltrimethylammonium bromide during electrodeposition produced small NPs with an even higher mass activity, which was attributed to the formation of porous nanostructures. This study demonstrates techniques to improve Pt utilization and electrocatalytic activity of electrodeposited Pt NPs.

Capacity and coulombic efficiency are often used to assess the performance of Li-ion batteries, under the assumption that these quantities can provide direct insights about the rate of electron consumption due to growth of the solid electrolyte interphase (SEI). Here, we show that electrode properties can actually change the amount of information about aging that can be directly retrieved from capacity measurements. During cycling of full-cells, only portions of the voltage profiles of the positive and negative electrodes are accessible, leaving a reservoir of cyclable Li⁺ stored at both electrodes. The size and availability of this reservoir depends on the shape of the voltage profiles, and accessing this extra Li⁺ can offset some of the capacity that is consumed by the SEI. Consequently, capacity and efficiency measurements can, at times, severely underestimate the rate of side reactions experienced by the cell. We show, for example, that a same rate of SEI growth would cause faster capacity fade in LiFePO₄ than in NMC cells, and that the perceived effects of aging depend on testing variables such as depth of discharge. Simply measuring capacity may be insufficient to gauge the true extent of aging endured by Li-ion batteries.

Lithium difluoro(dioxalato)phosphate (LiDFDOP) has been systemically studied as an electrolyte additive singly and in combination with co-additives fluoroethylene carbonate (FEC) and vinylene carbonate (VC) in LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811)/artificial graphite (AG) pouch cells. Long-term cycling tests at room and elevated temperatures (20 °C, 40 °C, and 55 °C) with different upper cutoff voltages (4.06 V and 4.20 V) were performed. These results were combined with ultra-high precision coulometry (UHPC), ex-situ gas measurements, and automatic cell storage tests to reveal multiple aspects of cell performance. A density functional theory (DFT) calculation has also been performed and compared to formation data to reveal the mechanistic aspects of LiDFDOP reduction. Radar plots and a figure-of-merit (FOM) approach were further utilized to summarize results and rank additive and additive combination performance for the NMC811/AG cells. This work highlights an effective additive and suitable co-additives for use in NMC811/graphite cells and gives important insights for future electrolyte additive studies.

A PEM fuel cell with a hydrophobically treated cathode catalyst layer (CL) demonstrates ∼220% peak power increase with humidified air at 70 °C. To understand the reasons of the increase, a mathematical model was developed focusing on the oxygen-water two-phase transport phenomena in the CL. It suggests the treatment affects the CL in two ways. First, the interface of the ionomer layer exposed to the gas pores becomes more hydrophobic, facilitating less liquid water coverage and faster water drainage from the CL and resulting in better performance at high current densities. Second, it also affects the hydration level in the ionomer phase resulting in higher oxygen concentration in the ionomer phase on and in the catalyst agglomerates, leading to higher performance over the whole polarization curve. The properties having significant influence on the model fitting the experimental data are the capillary pressure property of the CL, the hydrophobic ionomer ratio in the catalyst agglomerate, and the oxygen solubility/diffusivity in the Nafion® phases. With this experimentally verified model, additional case studies combining the hydrophobic gas diffusion material with the hydrophobic CL demonstrate that the membrane’s self-humidification (zero-net-water flux) and peak power enhancement (∼15%) can be reached simultaneously, providing direction for the future materials development.

Most research on the hydrogen embrittlement of steel dealt with the interaction of hydrogen with the metal bulk microstructural features, whereas the first contact with hydrogen-containing environments occurs at the metal surface. Steel (when un-polarized) is always covered with an oxide layer, varying in composition and thickness. The impact of the oxide layer on the hydrogen transport is, however, not fully understood. This study focused on the effect of controlled pre-formed thermal oxide layers at the exit side on the hydrogen transport through the surface of SEA 1010 steel, considering two distinct thermally produced oxide types as test cases. Results demonstrated that thermal oxides can greatly limit hydrogen diffusion, with bilayers (hematite/magnetite) having a greater effect compared to magnetite layers. Increased oxide thickness resulted also in greater limiting diffusion. The main objective of this manuscript is to provide experimental evidence concerning the effect of oxide layers on the hydrogen transport through steel. Model thermal oxide layers were used to emphasize the importance of considering the surface characteristics when investigating hydrogen transport through metallic components.

β-MoSi2 is one of the expected silicide candidates for thermoelectric material because of its semi-conductive and metastable characteristics. However, it is not easy to fabricate β-MoSi2 phase under low temperature condition as easily anticipated from the equilibrium Mo-Si binary phase diagram. In this study, the formation of β-MoSi2 by electrochemical silicification of a Mo substrate with a thickness of 0.5 mm in CaCl2-based melts containing SiO2 has been confirmed. Throughout XRD analysis, the formation of metastable β-MoSi2 phase was identified on a Mo substrate by potentiostatic electrolysis below 973 K. The results of TEM combined with EDS analysis at the Mo/β-MoSi2 interface showed the inverse concentration gradients of Mo and Si in the width of ca. 25 nm. In addition, we examined the growth process of β-MoSi2 by using a partially Pt-coated Mo substrate since the reduction of Si ions does not proceed at the Pt-coated area. The cross-sectional SEM image of the substrate demonstrated that a homogeneous film of β-MoSi2 was grown with almost the same thickness on both sides of the Mo substrate and the melt region. The results indicated that the growth of β-MoSi2 was caused by the mutual diffusion of Mo and Si atoms.

In the second part of the paper series on a noninvasive method to determine the local high frequency resistance (HFR) distribution in polymer electrolyte fuel cells (PEFC), the method is applied to an operating PEFC stack. While in the first part of this paper series the approach of using multiple surface attached electrodes to locally inject 1 kHz AC currents into a cell and to measure the resulting voltage amplitudes at the flow field’s surface was introduced. Its sensitivity was assessed using a stack fed only by nitrogen at different humidification levels. Here, it is confirmed that the approach works also during electrochemical operation. First, the method’s spatial resolution is further explored and improved by using multiple stimulation patterns after examining the local sensitivity of the different electrode combinations to changes in membrane conductivity by finite element model simulations of the current injection. The method is then applied to a stack operated at different current densities, inlet humidities and gas flow configurations. The HFR distributions are in good agreement with literature data and compare well with the global cell HFR. Finally, the method’s transient capabilities are highlighted by measuring the HFR distribution during a current jump and cell drying.

For many years, composite electrolytes (CEs) consisting of a mixture of inorganic solid electrolytes (ISEs) and polymer electrolytes (PEs) have been investigated as promising materials for the scalable production of solid-state batteries. It is believed that CEs can overcome limitations of the single components, namely the low room-temperature conductivity and lithium ion transference number of PEs and the poor mechanical properties and high temperature processing necessary for ISE ceramics. To facilitate ion transport in the CE between the electrodes a low and stable charge transfer resistance between PEs and ISEs is required. In this study, we investigate by means of electrochemical impedance spectroscopy how polymer crystallinity influences the charge-transfer resistance of hetero-ionic interfaces between polyethylene oxide (PEO)-based electrolytes and Li1.5Al0.5Ti1.5(PO4)3 (LATP) as well as Li6.25Al0.25La3Zr2O12 (LLZO) as ISEs. Crystallization of PEO based electrolytes below their melting temperature leads to an increased charge-transfer resistance. On the other hand, electrolytes based on the amorphous poly[2-(2-(2-methoxyethoxy)ethoxy)ethyl glycidyl ether (PTG) do not show an increased charge transfer resistance. Finally, the conductivity of ISE-rich CEs is measured as a function of their temperature and composition for elucidating how the interface resistance influences charge transport in ISE-rich composite electrolytes.

Electrochemical dehalogenation of polyhalogenated compound is an inefficient process as the working electrode is passivated by the deposition of short-chain polymers that form during early stages of electrolysis. Herein, we report use of 1,1,1,3,3,3-hexaflouroisopropanol (HFIP) as an efficient reagent to control C–H formation over radical association. Debromination of 1,6-dibromohexane was examined in the presence of Ni(II) salen and HFIP as the electrocatalyst and hydrogen atom source, respectively. Electrolysis of 10 mM 1,6-dibromohexane and 2 mM Ni(II) salen in the absence of HFIP yields 50% unreacted 1,6-dibromohexane and ~40% unaccounted for starting material whereas electrolysis with 50 mM HFIP affords 65% n-hexane. The mechanism of hydrogen atom incorporation was examined via deuterium incorporation coupled with high-resolution mass spectrometry, and density functional theory (DFT) calculations. Deuterium incorporation analysis revealed that the hydrogen atom originated from the secondary carbon of HFIP. DFT calculations showed that the deprotonation of hydroxyl moiety of HFIP, prior to the hydrogen atom transfer, is a key step for C-H formation. The scope of electrochemical dehalogenation was examined by electrolysis of 10 halogenated compounds. Our results indicate that through the use of HFIP, formation of short-chain polymers is no longer observed and monomer formation is the dominant product.

The paper focuses on the analysis of initiation and propagation of CO₂ corrosion in several samples of low-alloy steel with different microstructures using scanning electrochemical microscopy (SECM) and other microscopy techniques. It is found that the corrosion rate and the mode of corrosion are highly sensitive to the microstructure. The overall current density is much higher and more uniformly distributed for the tempered martensite structure than for samples having either a ferritic-pearlitic microstructure or a microstructure combining ferritic, bainitic and martensitic-austenitic regions. As a result, the sample with the tempered martensite structure undergoes uniform corrosion, while the other two samples undergo selective corrosion. The SECM maps show that regions of polygonal ferrite generate larger anodic currents than the pearlitic structure in the early stages of corrosion. The residual cementite lamellae provide greater cathodic surface areas after the initial dissolution of ferritic lamellae within pearlite, promoting galvanic corrosion and subsequently enhanced dissolution of ferritic lamellae. According to SECM data, the dissolution of iron in polygonal ferritic grains is 2.4 times faster than that of ferritic lamellae in pearlitic regions.