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.

Capacity measurements and related quantities are the first layer of information acquired during testing of Li-ion cells. It is generally considered that elevated values of coulombic efficiency and capacity retention are absolute indicators of the existence of a stable solid electrolyte interphase (SEI). Here, we challenge this notion by analyzing how the effect of side reactions on cell capacity depends on the choice of electrodes. More specifically, we demonstrate that the extent of measurable capacity fade due to SEI growth is modulated by the shape of the voltage profile of the cathode and anode at the end of charge and discharge half-cycles. This shape-dependency creates a mismatch between SEI growth and cell capacity loss, which is relatively small for graphite anodes but sizable for silicon-containing electrodes. We illustrate this point by showing that, at the same coulombic efficiency and capacity retention, cells containing silicon-based materials could actually exhibit rates of SEI growth that are as much as ≥ 40% higher than graphite cells. The main implication of this behavior is that, for certain systems, capacity measurements may be an unreliable source of information about the extent of reactions at the SEI, allowing other consequences of these side reactions (such as electrolyte depletion) to proceed unchecked while the cell appears to be stable.

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.

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.

Reduced-order battery lifetime models, which consist of algebraic expressions for various aging modes, are widely utilized for extrapolating degradation trends from accelerated aging tests to real-world aging scenarios. Identifying models with high accuracy and low uncertainty is crucial for ensuring that model extrapolations are believable, however, it is difficult to compose expressions that accurately predict multivariate data trends; a review of cycling degradation models from literature reveals a wide variety of functional relationships. Here, a machine-learning assisted model identification method is utilized to fit degradation in a stand-out LFP-Gr aging data set, with uncertainty quantified by bootstrap resampling. The model identified in this work results in approximately half the mean absolute error of a human expert model. Models are validated by converting to a state-equation form and comparing predictions against cells aging under varying loads. Parameter uncertainty is carried forward into an energy storage system simulation to estimate the impact of aging model uncertainty on system lifetime. The new model identification method used here reduces life-prediction uncertainty by more than a factor of three (86% ± 5% relative capacity at 10 years for human-expert model, 88.5% ± 1.5% for machine-learning assisted model), empowering more confident estimates of energy storage system lifetime.

Single crystal Li[Ni_0.5Mn_0.3Co_0.2]O₂//graphite (NMC532) pouch cells with only sufficient graphite for operation to 3.80 V (rather than ≥4.2 V) were cycled with charging to either 3.65 V or 3.80 V to facilitate comparison with LiFePO₄//graphite (LFP) pouch cells on the grounds of similar maximum charging potential and similar negative electrode utilization. The NMC532 cells, when constructed with only sufficient graphite to be charged to 3.80 V, have an energy density that exceeds that of the LFP cells and a cycle-life that greatly exceeds that of the LFP cells at 40 °C, 55 °C and 70 °C. Excellent lifetime at high temperature is demonstrated with electrolytes that contain lithium bis(fluorosulfonyl)imide (LiFSI) salt, well beyond those provided by conventional LiPF₆ electrolytes. Ultra-high precision coulometry and electrochemical impedance spectroscopy are used to complement cycling results and investigate the reasons for the improved performance of the NMC cells. NMC cells, particularly those balanced and charged to 3.8 V, show better coulombic efficiency, less capacity fade and higher energy density compared to LFP cells and are projected to yield lifetimes approaching a century at 25 °C.

In this work, novel near-zero volume expanding Si-dominant electrodes are presented as promising anodes for next-generation Li-ion batteries. The electrodes contain micrometer-size nano-porous Silicon particles with a carefully tuned morphology and synthesized via a scalable and cost-effective route. Volume expansion during electrochemical Li-Si alloying/de-alloying is found to be almost completely suppressed. Bi-layer pouch cells manufactured with the abovementioned Si-anodes, having industrial relevant areal capacities (≥3 mAh cm⁻²), and LiNi_0.6Mn_0.2Co_0.2O₂ cathodes, show indeed negligible volume expansion as demonstrated by operando dilatometric measurements during galvanostatic cycling and post-mortem SEM cross-sectional analysis.

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.

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.

Mechanical degradation of electrode materials is an important failure mode in lithium-ion batteries. High-energy-density cathode materials like nickel-rich NMC (LiNi_xMn_yCo_zO₂) undergo significant anisotropic volume expansion during cycling that applies mechanical stress to the material. Computed tomography (CT) of cells can be used to image cell-level and electrode-level changes that result from long-term cycling, without the need for cell disassembly or destructive sampling. Previous work by our group has used synchrotron CT to show cathode thickness growth and depletion of liquid electrolyte after long-term (>2 years) cycling of polycrystalline NMC622/graphite cells. These phenomena were attributed to cathode microcracking, but direct evidence of this was not available at the time. In this study, we present in-situ, sub-micron CT of these unmodified pouch cells, providing new insights into the morphological changes occurring at the particle level. These results confirm that extensive microcracking and dramatic morphological changes are occurring in the cathode that were not previously observed. Combined with the cell-level and electrode-level scans presented previously, this study provides a complete, multi-scale picture of cathode microcracking and how its effects propagate throughout the cell.

In water electrolyzers, polymer electrolyte membranes (PEMs) such as Nafion can accumulate cations stemming from salt impurities in the water supply, which leads to severe cell voltage increases. This combined experimental and computational study discusses the influence of sodium ion poisoning on the ionic conductivity of Nafion membranes and the ion transport in a thereon based water electrolysis cell. Conductivities of Nafion and aqueous solutions with the same amount of dissolved cations are measured with impedance spectroscopy and compared with respect to Nafion's microstructure. The dynamic behavior of the voltage of a water electrolysis cell is characterized as a function of the sodium ion content and current density, showing the differences of the ion transport at alternating and direct currents. These experimental results are elucidated with a physical ion transport model for sodium ion poisoned Nafion membranes, which describes a proton depletion and sodium ion accumulation at the cathode. During proton depletion, the cathodic hydrogen evolution is maintained by the water reduction that forms hydroxide ions. Together with sodium ions from the membrane, the formed hydroxide ions can diffuse pairwise into the water supply, so that the membrane's sodium ions can be at least partly be replaced with anodically formed protons.

An ideal cathode for proton ceramic fuel cell (PCFC) should have superior oxygen reduction reaction activity, high proton conductivity, good chemical compatibility with electrolyte and sufficient stability, thus rational design of the electrode material is needed. Here, by taking advantage of the limited solubility of nickel in perovskite lattice, we propose a new dual phase cathode developed based on nickel doping manipulation strategy. We rationally design a perovskite precursor with the nominal composition of Ba(Co_0.4Fe_0.4Zr_0.1Y_0.1)_0.8Ni_0.2O_3−δ (BCFZYN0.2). During high temperature calcination, a nanocomposite, composed of a B-site cation deficient and nickel-doped BCFZY perovskite main phase and nanosized NiO minor phase, is formed. The NiO nanoparticles effectively improve the surface oxygen exchange kinetics and the B-site cation deficiency structure enhances proton conductivity, thus leading to superior ORR activity of BCFZYN0.2. Furthermore, a low thermal expansion coefficient (15.3 × 10^–6 K⁻¹) is achieved, ensuring good thermomechanical compatibility the electrolyte. A peak power density of 860 mW cm⁻² at 600 °C is obtained from the corresponding PCFC, and the cell operates stably for 200 h without any significant degradation. The proposing strategy, by providing a new opportunity for the development of highly active and durable PCFC cathodes, may accelerate the practical use of this technology.

Even though solid oxide fuel/electrolysis cells (SOFC/SOEC) are already commercially available, the effect of electrochemical polarization on the electrochemical properties and overpotentials of individual electrodes is largely unexplored. This is partly due to difficulties in separating anode and cathode impedance features and overpotentials of operating fuel cells. For this, we present a novel three-electrode geometry to measure single-electrode impedance spectra and overpotentials in solid oxide cells. With this new design, we characterise polarised porous La_0.6Sr_0.4FeO_3−δ (LSF) electrodes by simultaneous impedance spectroscopy and ambient pressure XPS measurements. With physically justified equivalent circuit models, we can show how the overpotential-dependent changes in the impedance and XPS spectra are related to oxygen vacancy and electronic point defect concentrations, which deterimine the electrochemical properties. The results are overall in very good agreement with the key findings of several previous studies on the bulk defect chemistry and surface chemistry of LSF. They show for example the exsolution of Fe⁰ particles during cathodic polarisation in H₂ + H₂O atmosphere that decrease the polarization resistance by roughly one order of magnitude.

Hydrogen crossover poses a critical issue in terms of the safe and efficient operation in polymer electrolyte membrane water electrolysis (PEMWE). The impact of key operating parameters such as temperature and pressure on crossover was investigated in the past. However, many recent studies suggest that the relation between the hydrogen crossover flux and the current density is not fully resolved. This study investigates the hydrogen crossover of PEMWE cells using a thin Nafion 212 membrane at current densities up to 10 A cm⁻² and cathode pressures up to 10 bar, by analysing the anode product gas with gas chromatography. The results show that the hydrogen crossover flux generally increases over the entire current density range. However, the fluxes pass through regions with varying slopes and flatten in the high current regime. Only considering hydrogen diffusion as the single transport mechanism is insufficient to explain these data. Under the prevailing conditions, it is concluded that the electro-osmotic drag of water containing dissolved hydrogen should be considered additionally as a hydrogen transport mechanism. The drag of water acts opposite to hydrogen diffusion and has an attenuating effect on the hydrogen crossover in PEMWE cells with increasing current densities.

The traditional electric furnace pyrolysis to produce heteroatom doped carbon faces the time-consuming issue due to the fixed size of furnace chamber and indirect heat transfer. Herein a fast Joule-heating pyrolysis method, viz., powering on the C, N, Fe-containing, conductive polyaniline precursor at fixed direct current (DC) voltage for a specific time, is put forward. The polyaniline precursor begins to decompose thermally when being powered with a DC voltage of 5.0 V upwards. In the pyrolysis products, Fe and N co-doping of carbon material leads to C–N bonding and C-Fe bonding in a certain way. The direct peroxide-peroxide fuel cell (DPPFC) with the optimal Fe, N codoped carbon material as anode and cathode can generate an open circuit voltage of 0.85 V and a peak power density of 29.7 mW cm⁻² in ambient temperature, which is highly competitive compared with other DPPFCs with anode and/or cathode made of noble metals.

A review of experimental author's works proving the existence of the phenomenon of the electrochemical phase formation in metals and alloys via a supercooled liquid state stage is presented. The research findings focused on the electrochemical formation of metastable structures and intermediate phases, as well as on the structural features accompanying them. Electrochemical amorphous phase formation in metals and alloys, electrochemical quasicrystalline phase formation in metals, and electrochemical polymorphic phase formation in metals are discussed. Electrochemical hydrogen-related structure formation in metals, electrochemical high-defect crystalline phase formation in metals, and electrochemical texture-inhomogeneous structure formation in metals are considered. Electrochemical formation of intermediate phases in metals and alloys, electrochemical formation of eutectics in metallic alloys, and electrochemical formation of chemical compounds at the metallic cathode/electrodepositing metal interface are analyzed. Electrochemical reduction of ions in metals and alloys at a liquid cathode versus a solid chemically identical one, electrochemical phase formation of metals at chemically identical solid or liquid cathode, and electrochemical phase formation of alloys at chemically identical solid or liquid cathode are discussed.

Lithium plating on the negative electrode of Li-ion batteries remains as a great concern for durability, reliability and safety in operation under low temperatures and fast charging conditions. High-accuracy detection of Li-plating is critically needed for field operations. To detect the lithium plating is to track its multiphysics footprint since lithium plating often is a localized event while the driving force from chemical, electrical, thermal and mechanical origins could vary with time and locality which makes the detection and characterization challenging. Here, we summarize the multiphysical footprints of lithium plating and the corresponding state-of-the-art detection methods. By assessing and comparing these methods, the combination of capacity/voltage differential, R–Q mapping and Arrhenius outlier tracking could be promising and effective for battery diagnosis, prognosis and management. We analyze the origins of quantitative error in sample preparation, overly simplified assumption and dynamic evolution of the plated Li, and recommend the in situ and quantitative chemical analysis method, such as in situ NMR, EPR, X-ray and neutron. In addition, we propose the four conjectures on the capacity plunge, lithium plating, pore clogging, electrolyte drainage and rapid SEI growth, can be aligned and unified to one scenario basically triggered by lithium plating.

Epitaxial electrodeposition of Co, Cu and Ru is compared and contrasted. The seed layer for electrodeposition of all three metals was an epitaxial Ru(0001) film that was deposited at an elevated temperature onto a sapphire(0001) substrate and annealed post deposition. The epitaxial orientation relationship of the electrodeposited film and the seed layer, the epitaxial misfit strain, the role of symmetry of the seed layer versus the electrodepositing layer is addressed. In addition, the impact of underpotential deposition on film nucleation, and the growth morphology of the films is discussed. It is shown that epitaxial electrodeposition of metallic films to thicknesses of tens of nanometers is readily achievable.

This paper 1189 was presented during the 241st Meeting of the Electrochemical Society, May 29–June 2, 2022.

Increasing energy demand throughout the world produces great environmental issues, therefore, renewable and clean energy sources, such as tidal energy, wind energy, solar energy and geothermal energy, are desirable request. Meanwhile, developing a new critical energy storage technology to balance the instantaneous energy supply and demand of arranged electric energy is urgent. Rechargeable flow batteries are solutions for storing electricity in form of chemical energy, containing positive and negative electrodes reserved in two separate containers, which have the advantages of low self—discharge and independent scaling of power, therefore considered as promising energy storage technologies. Ionic liquids (ILs) have been widely studied and used in energy storage devices, such as lithium ion battery, for their unique prospective properties. Herein, the key role of ILs and their applications in supporting electrolytes, separators and additives in flow batteries are highlighted in this review. The approaches and challenges in developing ILs supported flow batteries are discussed, and a significative overview of the opportunities of ILs promote flow batteries are finally provided, which is expected to help achieving further improvements in flow batteries.

Pathogenic bacteria are a major public cause of foodborne and waterborne infections and are currently among the most serious public health threats. Conventional diagnostic techniques for bacteria, including plate culturing, the polymerase chain reaction, and the enzyme-linked immunosorbent assay, have many limitations, such as time consumption, high rates of false results, and complex instrument requirements. Aptamer-based electrochemical biosensors for bacteria address several of these issues and are promising for bacterial detection. This review discusses the current advances in electrochemical aptasensors for pathogenic bacteria with regard to the sensing performance with various specific aptamers for different types of bacteria. The advantages and disadvantages of these electrochemical aptasensors were investigated with the aim of promoting the development and commercialization of electrochemical aptasensors for the point-of-care detection of bacteria.

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.

While Li−carbon monofluoride (CF_x) is the current energy leader among primary batteries, the technology is maturing, motivating further fundamental study of Li battery chemistry based on C−F redox. This study examines the possibility to conduct multi-electron carbon reduction using a candidate class of liquid CF_x analogues, perfluoroalkyl iodides (C_nF_2n+1I, with F/C ratios of x > 2), in supporting electrolyte as catholytes for Li cells. The large, polarizable iodine supports electrochemical reduction with concerted F⁻ ligand expulsion, forming lithium fluoride (LiF) as the main solid discharge product. Under initial conditions (1 M reactant and 0.3 mA cm⁻² in dimethylsulfoxide), only limited defluorination (1.5 e⁻/molecule) is accessed. Governing factors for C−F bond redox are further investigated, including reactant concentration, discharge rate, temperature, and solvent properties (e.g. catholyte viscosity). A maximum of 8 e⁻/C₆F₁₃I, or 8/₁₃ available F, is accessible in the voltage range 2.8−1.9 V vs Li/Li⁺ with low reactant concentrations (0.1 M) and rates (20 μA cm⁻²). The data indicate that multiple handles exist to tailor extended C−F bond activation in these reactants. However, premature reaction termination caused by deactivation of intermediates, which is particularly exacerbated at higher concentrations and/or rates, is likely to be a persistent challenge for practical applications.

In water electrolyzers, polymer electrolyte membranes (PEMs) such as Nafion can accumulate cations stemming from salt impurities in the water supply, which leads to severe cell voltage increases. This combined experimental and computational study discusses the influence of sodium ion poisoning on the ionic conductivity of Nafion membranes and the ion transport in a thereon based water electrolysis cell. Conductivities of Nafion and aqueous solutions with the same amount of dissolved cations are measured with impedance spectroscopy and compared with respect to Nafion’s microstructure. The dynamic behavior of the voltage of a water electrolysis cell is characterized as a function of the sodium ion content and current density, showing the differences of the ion transport at alternating and direct currents. These experimental results are elucidated with a physical ion transport model for sodium ion poisoned Nafion membranes, which describes a proton depletion and sodium ion accumulation at the cathode. During proton depletion, the cathodic hydrogen evolution is maintained by the water reduction that forms hydroxide ions. Together with sodium ions from the membrane, the formed hydroxide ions can diffuse pairwise into the water supply, so that the membrane’s sodium ions can be at least partly be replaced with anodically formed protons.

Even though solid oxide fuel/electrolysis cells (SOFC/SOEC) are already commercially available, the effect of electrochemical polarization on the electrochemical properties and overpotentials of individual electrodes is largely unexplored. This is partly due to difficulties in separating anode and cathode impedance features and overpotentials of operating fuel cells. For this, we present a novel three-electrode geometry to measure single-electrode impedance spectra and overpotentials in solid oxide cells. With this new design, we characterise polarised porous La_0.6Sr_0.4FeO_3−δ (LSF) electrodes by simultaneous impedance spectroscopy and ambient pressure XPS measurements. With physically justified equivalent circuit models, we can show how the overpotential-dependent changes in the impedance and XPS spectra are related to oxygen vacancy and electronic point defect concentrations, which deterimine the electrochemical properties. The results are overall in very good agreement with the key findings of several previous studies on the bulk defect chemistry and surface chemistry of LSF. They show for example the exsolution of Fe⁰ particles during cathodic polarisation in H₂ + H₂O atmosphere that decrease the polarization resistance by roughly one order of magnitude.

Hydrogen crossover poses a critical issue in terms of the safe and efficient operation in polymer electrolyte membrane water electrolysis (PEMWE). The impact of key operating parameters such as temperature and pressure on crossover was investigated in the past. However, many recent studies suggest that the relation between the hydrogen crossover flux and the current density is not fully resolved. This study investigates the hydrogen crossover of PEMWE cells using a thin Nafion 212 membrane at current densities up to 10 A cm⁻² and cathode pressures up to 10 bar, by analysing the anode product gas with gas chromatography. The results show that the hydrogen crossover flux generally increases over the entire current density range. However, the fluxes pass through regions with varying slopes and flatten in the high current regime. Only considering hydrogen diffusion as the single transport mechanism is insufficient to explain these data. Under the prevailing conditions, it is concluded that the electro-osmotic drag of water containing dissolved hydrogen should be considered additionally as a hydrogen transport mechanism. The drag of water acts opposite to hydrogen diffusion and has an attenuating effect on the hydrogen crossover in PEMWE cells with increasing current densities.

Glycerol Electrooxidation Reaction (GEOR) has been herein investigated on Rh/C and Rh/SnO₂-C prepared by polyol method. The particle mean sizes were found to be 2.0 and 1.8 nm in Rh/C and Rh/SnO₂-C, respectively. The alloying degree reached 63% in Rh/SnO₂-C, confirming a Sn-Rh alloy formation. The activity towards GEOR on Rh/SnO₂-C was almost 5-fold higher than on Rh/C, as demonstrated by electrochemical measurements in alkaline medium. This trend indicated the beneficial effect of the SnO₂-C carbon-oxide composite support in the catalyst composition. Analysis of the products generated after the bulk electrolysis using high-performance liquid chromatography (HPLC) and FTIRS demonstrated that at 0.55 V vs RHE the main reaction products were glycerate ion and carbonate (CO₃²⁻). Then, a C–C–C cleavage was demonstrated with the CO₃²⁻ formation at low potentials. During the testings conducted in a home-made acrylic direct glycerol fuel cell at room temperature in 0.5 mol l⁻¹ NaOH, the maximum power density (390 μW cm⁻²) obtained on a Rh/SnO₂ anode, was 5-fold higher than that on Pd/C. These testings demonstrated that the co-generation of sustainable energy and value-added products is a promising way to valorize glycerol.

All solid-state batteries (ASSBs) are considered among the most promising next-generation energy storage devices but are currently still limited in terms of performance. To advance the development process in an efficient way, appropriate characterization methods are needed. Herein, we demonstrate chronoamperometry to rapidly evaluate the performance of ASSBs. Examples are given using argyrodite solid electrolyte together with various cathode active materials. It is shown that chronoamperometry provides equivalent rate capability information to common galvanostatic testing procedures, while being much simpler and significantly faster (e.g. by a factor between 8 and 33 for the tested materials). The high data density allows accurate model-based analysis to identify the rate limiting mechanism, such as electrical or diffusion limitations, and to determine the active material utilization at very low rates. An effective C-rate is proposed, which describes the rate performance of the utilizable active material. The observed electrode- and active material-specific performance differences are explained by morphological effects, supported by scanning electron microscopy analyses of the cathode cross sections. The results demonstrate the ability of chronoamperometry to rapidly quantify electrochemical performance and provide a deeper understanding of the limitations of ASSBs.

The effects of temperature, Ti(III) ion concentration, and current density on the electrodeposition of Ti films were investigated in the eutectic LiF–LiCl melt at 823–973 K. The Ti(III) ions were prepared by adding Li₂TiF₆ and Ti metal to the melt. The diffusion coefficients of Ti(III) were 1.4, 1.8, 2.3, and 3.2 × 10⁻⁵ cm² s⁻¹, at 823, 873, 923, and 973 K, respectively. Galvanostatic electrolysis was conducted at 823–973 K. The surface roughness (S_a) of the Ti films decreases with decreasing temperature. Thus, the electrodeposition of Ti films was conducted at the lowest temperature of 823 K with various Li₃TiF₆ concentrations (0.55–7.1 mol%) and cathodic current densities (50–1200 mA cm⁻²). The Sa was lower at higher Ti(III) ion concentrations and lower current densities. The smoothest Ti films with a S_a of 1.23 µm and a thickness of 10 μm were obtained at a cathodic current density of 50 mA cm⁻² and Li₃TiF₆ concentration of 7.1 mol%.

Lithium sulfur (Li–S) batteries have received significant attention as one of the energy storage systems with excellent prospects for emerging applications due to their high energy density and low-cost. However, there are fundamental challenges impeding the commercialization of Li–S batteries. Notorious among those challenges is the “polysulfide shuttle” consisting of the dissolution into the electrolyte solvent and subsequent crossover to the anode of long-chain lithium polysulfides. Sparingly solvating electrolytes have been exploited as an approach to reduce the dissolution of polysulfides and thereby the shuttle effect. Using an optical in operando lithium-sulfur cell and ex situ UV–vis spectroscopy, we elucidate the speciation of polysulfides in fully and sparingly solvating electrolytes for Li–S batteries. Extensive literature meta-analysis reveals that the most unambiguous effect of sparingly solvating solvent is in improving the coulombic efficiency of sulfur-cells. Experimental optical imaging and UV–vis characterization elucidate a shift towards shorter-chain polysulfides in electrolytes with increasing lithium-salt concentration (more sparingly solvating). The shift to shorter-chain polysulfides corresponds to a reduction of polysulfide species participating in shuttling which corroborate the increased coulombic efficiency in sparingly-solvating electrolytes.

We provide a simple and inexpensive manual DC-offset method for extending the accepted voltage range of a battery cycler to negative voltages, without interfering with the actual operation of the electrochemical cell under the test or exceeding the voltage specs of the battery cycler instrument. We describe the working principles of the method and validate the proposed setup by operating short-term and long-term redox flow battery cycling using a compositionally symmetric cell, with open-circuit voltage of zero, and full cell configurations. The method can be used to extend the capability of battery cycler instrumentation to operate any electrochemical cell that requires the polarity to be reversed during operation. Applications include cycling of other symmetric cells (e.g., Li-ion cells), implementation of polarity reversal steps for rejuvenation of electroactive species or rebalancing electrochemical cells, and alternating polarity for electrochemical synthesis.

Electrochemical cells using rechargeable lithium metal anodes are sensitive to operating temperature and stack pressure. Current understanding generally assumes that temperature drives changes in lithium metal surface chemistry while stack pressure impacts the anode morphology. In this study, we provide quantifiable evidence for these assumptions and propose mechanisms to guide understanding of temperature and pressure effects on lithium metal cell dynamics. Beyond the direct coupling of pressure with mechanics and temperature with kinetics, we also explore possible effects of temperature on cell mechanics and stack pressure on cell chemistry. We investigate an electrolyte composition based on LiDFOB salt, using a range of operando and ex situ techniques. Mechanistic mapping of temperature- and pressure-dependent cell behavior will aid development of improved lithium metal batteries.

The lithium stripping process generates vacancies, which may accumulate as voids and lead to uneven current distribution and dendrite growth in following plating cycles. A stack pressure is typically required during stripping, but how to optimize the stack pressure is not clear. In this work, extremely lithiophilic Li/Li2O and lithiophobic Li/LiF interfaces were used to reveal the combining effect of interface interaction and stack pressure induced lithium creep on the stripping critical current density (CCD). A multi-scale simulation scheme with density functional theory, kinetic Monte Carlo (KMC) simulations, and an analytical model was developed. The analytical model predicted lithiophobic interfaces require a higher stack pressure than lithiophilic interfaces to reach the same CCD. The KMC simulations also showed higher stack pressure is needed at lithiophobic interfaces to accelerate Li vacancy diffusion into the bulk and maintain a flat surface. This stack pressure needs to be high enough to alter the Li forward-and-backward hopping barriers at the interface. This multiscale simulation scheme illustrates the importance to include the chemical-mechanical effects during Li stripping morphology evolution. It can be used to design ideal interlayer coating materials to maintain a flat Li surface during cycling.