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Water-soluble binders—locust bean gum (LBG) and carboxymethyl cellulose (CMC) were tested with the SnS anode modified by new conducting material polypyrrole—carbon black composite (PPyCB) and compared with the environmentally unfriendly widely used polyvinylidene fluoride (PVdF) as an organic binder. The electrochemical properties of tested electrodes were investigated by galvanostatic charging/discharging tests, cyclic voltammetry, and electrochemical impedance spectroscopy. Kinetic parameters of electrode processes were calculated from resistances. The first discharge capacities were 2150 mAh g−1, 1250 mAh g−1, and 960 mAh g−1 for SnS-PPyCB-LBG, SNS-PPyCB-CMC, and SnS-PPyCCB-PVdF, respectively. The exchange current density for the SnS-PPyCB electrode is in the range of 4.6 × 10−6 mA cm−2 for the system with carboxymethyl cellulose to 1.97 × 10−6 mA cm−2 in the cell with LBG. Compared to PVdF, locust bean gum is an equally effective binder and may even enhance electrode kinetics. [ABSTRACT FROM AUTHOR]

Most research on the electrochemical dynamics in materials for high-energy Li-ion batteries has focused on the global behavior of the electrode. This approach is susceptible to misleading analyses resulting from idiosyncratic kinetic conditions, such as surface impurities inducing an apparent two-phase transformation within LiNi0.8Co0.15Al0.05O2. Here, nano-focused X-ray probes are used to measure delithiation operando at the scale of secondary particle agglomerates in layered cathode materials during charge. After an initial latent phase, individual secondary particles undergo rapid, stochastic, and largely uniform delithiation, which is in contrast with the gradual increase in cell potential. This behavior reproduces across several layered oxides. Operando X-ray microdiffraction ((Formula presented.) -XRD) leverages the relationship between Li content and lattice parameter to further reveal that rate acceleration occurs between Li-site fraction (xLi) ≈0.9 and ≈0.5 for LiNi0.8Co0.15Al0.05O2. Physics-based modeling shows that, to reproduce the experimental results, the exchange current density (i0) must depend on xLi, and that i0 should increase rapidly over three orders of magnitude at the transition point. The specifics and implications of this jump in i0 are crucial to understanding the charge-storage reaction of Li-ion battery cathodes.

As part of a carbon-neutral national policy, there has been an increasing demand for the development of an eco-friendly transportation system. Particularly, polymer electrolyte membrane fuel cells (PEMFCs) are being evaluated as suitable fuel cell railway vehicles that meet the requirements of moderate operating temperatures and high-power conditions. However, the different degradations that occur during cyclic load operation damage their performance. In this study, a high-power PEMFC unit (225 cm2) was designed and fabricated to explore its long-term electrochemical characteristics before its application in railway vehicles. To solve the non-uniformity caused by the large area, the deterioration factors based on the progress of the cycle (change in the electrochemical properties and decrease in the electrochemical active surface area (ECSA)) were experimentally measured. A performance evaluation was conducted numerically based on the load cycle considering the operating conditions (temperature and flow rate) of the prototype railway vehicle. Further, an empirical large-area fuel cell numerical analysis model was constructed to improve the reliability of the current model by considering the parameters representing nonlinear deterioration characteristics. From the results, the maximum difference in power reduction rates after 2,000 cycles between the actual experimental results and numerical analysis results was approximately 11.6%. Finally, the performance was predicted under different conditions by predicting the Pt particle size through curve fitting and by applying the ECSA change based on the temperature, voltage, and humidity changes. When all the conditions were considered, the maximum power decreased by 79.4% when compared to numerical predictions after 2,000 cycles based on the experimental conditions of the prototype train. When a sensitivity analysis was conducted based on the simulation results, the temperature change in the fuel cell had the most significant influence on the reduction in the ECSA and the resulting decrease in the electrochemical power. • A high-power PEMFC (225 cm2) was used for railway vehicles. • The degree of degradation during cyclic operation was evaluated experimentally. • A performance evaluation tailored to railroad operating conditions was conducted. • An empirical model was developed by considering the nonlinear deterioration characteristics. • The numerical predictions corresponded with approximately 11.6% of the experimental data. [ABSTRACT FROM AUTHOR]

To meet the ever-growing worldwide electric vehicle demand, the development of advanced generations of lithium-ion batteries is required. To this end, modelling is one of the pillars for the innovation process. However, modelling batteries containing a large number of different mechanisms occurring at different scales remains a field of research that does not provide consensus for each particular model or approach. Parametrization as part of the modelling process appears to be one of the issues when it comes to building a high-fidelity model of a target cell. In this paper, a particular parameter identification is therefore discussed. Indeed, even if Butler–Volmer is a well-known equation in the electrochemistry field, identification of its reaction rate constant or exchange current density parameters is lacking in the literature. Thus, we discuss the process described in the literature and propose a new protocol that expects to overcome certain difficulties whereas the hypothesis of calculation and measurement maintains high sensitivity. [ABSTRACT FROM AUTHOR]

The limitations of current benchmark oxygen electrocatalysts, such as RuO2, IrO2, and Pt/C, due to their high cost, scarcity, and unifunctionality, have inspired a search for more effective oxygen catalysts to advance sustainable enegry solutions. Hence, development of cost-effective bifunctional catalysts to overcome the issues associated with benchmark catalysts is crucial. Metal–organic framework composites containing conductive carbon materials present promising solutions to these challenges. This study reports the synthesis, characterization, and application of a metal–organic framework of cobalt-(II) tetra-(3-hydroxy tyramine) phthalocyanine polymer, poly-[Co(II)THTPc], for bifunctional oxygen electrocatalysis. The synthesis methodology is simple, cost-effective, and sustainable. To improve the catalytic performance of poly-[Co(II)THTPc], an organic-hybrid composite was prepared by incorporating Ketjen black (KB) nanoparticles at an optimized ratio. The resulting poly-[Co(II)THTPc]:KB (4:1, respectively) hybrid exhibited outstanding catalytic activity for OER bearing an overpotential of 359 mV on a Ni foam substrate and 371 mV on a glassy carbon electrode (GCE) substrate at 10 mA cm–2 current density in 1.0 M KOH at 5 mV s–1 scan rate. Furthermore, the same composite catalyst demonstrated an onset potential of 0.876 V vs RHE for ORR with a half-wave potential of 0.767 V vs RHE, obeying four-electron-transfer pathway in the same electrolyte and scan rate on GCE. In addition, the designed hybrid catalyst demonstrated improved catalytic properties compared to standard catalysts, including a lower Tafel slope, reduced charge-transfer resistance, and higher exchange current density for OER and ORR. The remarkable catalytic performance of the developed hybrid can be attributed to various synergistic effects, favorable π–π interactions, and increased number of electroactive sites that downshifts the D-band center of Co adsorption sites, effectively reducing the activation barrier of reaction intermediates in both the OER and ORR. Importantly, the low-cost bifunctional oxygen catalyst exhibited excellent stability and efficiency, making it a potential bifunctional oxygen electrocatalyst for large-scale integrated green energy systems. [ABSTRACT FROM AUTHOR]

Over the past few years, lithium-ion batteries have gained widespread use owing to their remarkable characteristics of high-energy density, extended cycle life, and minimal self-discharge rate. Enhancing the exchange current density (ECD) remains a crucial challenge in achieving optimal performance of lithium-ion batteries, where it is significantly influenced the rate of electrochemical reactions at the electrodes of a battery. To enhance the ECD of lithium-ion batteries, the Taguchi method is employed in this study. The Taguchi method is a statistical approach that allows for the efficient and systematic evaluation of a large number of experimental factors. The proposed method involves varying six input factors such as positive and negative electrode thickness, separator thickness, current collector area, and the state of charge (SOC) of each electrode; five levels were assigned for each control factor to identify the optimal conditions and maximizing the ECD at the positive electrode. Also, main effect screener analysis and sensitivity analysis were conducted to confirm Taguchi analysis results. The results show that the Taguchi method is an effective approach for optimizing the exchange current density of lithium-ion batteries. This paper shows that the separator thickness followed by the positive electrode thickness play the major role in determining the lithium-ion batteries response. The main effect screener analysis and sensitivity analysis show the same effect of the chosen control factor which validate the Taguchi analysis results. By identifying the optimal conditions, it is possible to improve the performance of lithium-ion batteries and potentially extend their use in a variety of applications. As case study, lithium-ion batteries with ECD at positive electrode of 6 A/m2 is designed and simulated using COMSOL multiphasic within a frequency range of 10 mHz to 1 kHz. Electrochemical impedance spectroscopy (EIS) analysis using is carried out. As the frequency increased, the real part of the impedance of the simulated battery relative to the ground decreased because the charge transfer mechanism shifted from ionic to electronic conductivity. Additionally, the imaginary part of the impedance of the simulated battery relative to the ground decreased at higher frequencies due to a reduction in capacitive effects, with only minor inductive effects. This study opens the door widely in front of researchers and manufactures to design a lithium-ion batteries at specific exchange current density that suits specific applications in forward and direct way instead of trial and error approach. [ABSTRACT FROM AUTHOR]

To meet the ever-growing worldwide electric vehicle demand, the development of advanced generations of lithium-ion batteries is required. To this end, modelling is one of the pillars for the innovation process. However, modelling batteries containing a large number of different mechanisms occurring at different scales remains a field of research that does not provide consensus for each particular model or approach. Parametrization as part of the modelling process appears to be one of the issues when it comes to building a high-fidelity model of a target cell. In this paper, a particular parameter identification is therefore discussed. Indeed, even if Butler–Volmer is a well-known equation in the electrochemistry field, identification of its reaction rate constant or exchange current density parameters is lacking in the literature. Thus, we discuss the process described in the literature and propose a new protocol that expects to overcome certain difficulties whereas the hypothesis of calculation and measurement maintains high sensitivity.

Most research on the electrochemical dynamics in materials for high‐energy Li‐ion batteries has focused on the global behavior of the electrode. This approach is susceptible to misleading analyses resulting from idiosyncratic kinetic conditions, such as surface impurities inducing an apparent two‐phase transformation within LiNi0.8Co0.15Al0.05O2. Here, nano‐focused X‐ray probes are used to measure delithiation operando at the scale of secondary particle agglomerates in layered cathode materials during charge. After an initial latent phase, individual secondary particles undergo rapid, stochastic, and largely uniform delithiation, which is in contrast with the gradual increase in cell potential. This behavior reproduces across several layered oxides. Operando X‐ray microdiffraction (μ$\umu$‐XRD) leverages the relationship between Li content and lattice parameter to further reveal that rate acceleration occurs between Li‐site fraction (xLi) ≈0.9 and ≈0.5 for LiNi0.8Co0.15Al0.05O2. Physics‐based modeling shows that, to reproduce the experimental results, the exchange current density (i0) must depend on xLi, and that i0 should increase rapidly over three orders of magnitude at the transition point. The specifics and implications of this jump in i0 are crucial to understanding the charge‐storage reaction of Li‐ion battery cathodes. [ABSTRACT FROM AUTHOR]

The metal electrodeposition into the nanopores of template of porous anodic alumina type under the conditions of mixed kinetics of metal deposition is studied theoretically using analytical and numerical methods. Two main periods of the process are studied: the non-steady-state formation of diffusion layer in the template pores and much longer process of pore filling with the metal. The effect of nonlinearity of the concentration dependence of the exchange current density of metal electrodeposition on the variation of the current density with the time during the diffusion layer formation and pore filling with the metal is studied. [ABSTRACT FROM AUTHOR]

This research paper describes a simplified and quick method for determining the exchange current densities of the H 2 O/H 2 system on powder composite electrodes made of hydrogen storage intermetallics. The method is based on the hydrogen storage electrode potential jump upon its galvanostatic overswitching from the cathodic to the anodic direction for low- and high charge/discharge rates. Indeed, research findings indicate that the discharge rate/exchange current density quotient depends either linearly or exponentially on the potential jump for low- and high-charge/discharge rates. This study also defines the applicability ranges for both types of dependencies with the best accuracy for calculating exchange currents (relative experimental error ≤5%) corresponding to potential jumps of up to 0.037 V (discharge rates of up to 0.2C) and 0.08–0.20 V (discharge rates over 0.3C). Furthermore, this study presents other instances of determining exchange currents versus cycling determination for different intermetallics and discusses the effect of the hydride material surface modification and charge/discharge rate conditions on the exchange current density. [Display omitted] • The exchange current density of the H 2 O/H 2 system, i H 2 O / H 2 0 , will be determined from the overswitch potential jump, Δ E (j) . • At low charge/discharge rate (up to 0.2C), the i H 2 O / H 2 0 increase linearly with a decrease in the Δ E (j) . • At high charge/discharge rate (above 0.3C), the i H 2 O / H 2 0 increase exponentially with a decrease in the Δ E (j) . [ABSTRACT FROM AUTHOR]

As a potential alternative to liquid organic electrolytes, solid polymer electrolytes provide good processability and interfacial properties. However, insufficient ionic conductivity limits its further development. To overcome these challenges, we propose the solution of synthetic clay Laponite as a filler in this work. Specifically, the ionic conductivity increases to 1.71×10−4 S cm−1 (60 °C) after adding 5 wt.% of Laponite to the PEO−LiClO4 system. The Laponite surface's negative charge enhances lithium ions dissociation and transport in the electrolyte: the lithium‐ion transference number increases from 0.17 to 0.34, and the exchange current density increases from 46.84 μA cm−2 to 83.68 μA cm−2. The improved electrochemical properties of composite electrolytes improve the symmetric cell's stability to at least 600 h. Meanwhile, the Li||LiFePO4 cells′ rate and long‐cycle performance are also significantly enhanced. This work's concept of Laponite filler demonstrates a novel strategy to enhance ion transport in polymer‐based electrolytes for solid‐state batteries. [ABSTRACT FROM AUTHOR]

The mechanism governing the pseudocapacitive lithium storage behavior is one of the most critical unsolved issues in conversion-type anodes for lithium-ion batteries. In this work, we, for the first time, demonstrate that the pseudocapacitive capability of iron oxide-based anodes is closely associated with the electronic structures of iron ions. As proof of concept, the introduction of amorphization, nitrogen doping, and oxygen vacancies reduces the coordination of iron ions and contributes significantly to the pseudocapacitive lithium storage capability of iron oxide, reaching up to 96% of the specific capacity at 1 mV·s−1. Due to the significantly modulated coordination environment, the 3d electrons of Fe(II) are delocalized with increased spin state and the energy band gap is narrowed, accompanied by an upshift of Fermi energy. The redox activity and carrier mobility of iron oxides are substantially increased, which substantially enhance the exchange current density and thereby improve the pseudocapacitive capability of iron oxide. [ABSTRACT FROM AUTHOR]

A microelectrode is useful to determine electrochemical parameters such as diffusion coefficient, exchange current density, and Tafel slope without the limitations of ion diffusion. This study aims to develop a new microelectrode for use in high-temperature molten salts, which has been evaluated by determining the parameters of the Sm(III)/Sm(II) reaction in a LiCl–KCl eutectic molten salt. The electrochemical and kinetic properties of the samarium ion in the temperature range 723–823 K were calculated using the limiting current from cyclic voltammograms and the Allen–Hickling equation. The results imply that kinetic parameters (exchange current density and charge transfer coefficient) critical for designing pyroprocesses can be obtained using the developed microelectrode.

Summary: Increasing efficiency and durability of fuel cells can be achieved through advanced model‐based optimal control of its operating conditions, and the efficient online estimation of fuel cell parameters and internal states is fundamental for the implementation of such advanced controllers. The exchange current density is a driving parameter of performance for the catalyst layer of proton exchange membrane fuel cells (PEMFC). This study presents a control‐oriented, stochastic filtering approach for online, continuous estimation of the exchange current density in low‐temperature PEMFCs. The fuel cell is framed as a Markov model where the exchange current density is posed as the stochastic hidden state. The physics‐based static equation of the exchange current density is converted into a state transition equation. This transition equation and the equation for cell voltage are used in the stochastic state estimator to approximate the posterior probability distribution of the exchange current density. In order to highlight the usefulness of the approach, the estimated value of the exchange current density is used to approximate the trend of the electrochemical active surface area (ECSA) in the catalyst layer and train a nonlinear auto‐regressive model. This data‐driven model is used to forecast the evolution in the ECSA associated with long‐term degradation. The estimation algorithm is successfully implemented and tested in two different experimental datasets.This study presents a control oriented, stochastic filtering approach for online, continuous estimation of the exchange current density in low temperature proton exchange membrane fuel cells. The fuel cell is framed as a Markov model where the exchange current density is posed as the stochastic hidden state and a particle filter algorithm is developed to estimate this hidden state. The estimated value of the exchange current density is used to approximate the trend of the electrochemical active surface area (ECSA) in the catalyst layer and train a nonlinear auto‐regressive model (NARMAX). This data‐driven model is used to forecast the evolution in the ECSA associated with long term degradation. The estimation algorithm is successfully implemented and tested with two different experimental datasets. [ABSTRACT FROM AUTHOR]

The precise assessment of the kinetic properties of graphite is crucial for the design of the material and the development of electrochemical models for lithium-ion batteries. However, conventional evaluation methods using composite electrodes fall short in excluding the influence of its porous structure and evaluating the influence of particle shape on kinetic behavior. In this work, we elucidate the impact of non-spherical morphology on kinetic behavior of single artificial graphite particle, employing the single-particle microelectrode technique. Three single artificial graphite particles with different sizes are pre-cycled and exhibit outstanding rate capability, maintaining a maximum capacity retention of 78.1 % at 200 C. Further, exchange current density and diffusion coefficients are determined through Tafel plots and the potentiostatic intermittent titration technique (PITT), respectively. It is found that the particle with a higher exposure of edge planes present elevated exchange current density and diffusion coefficients. Considering that the graphite particles typically feature an ellipsoidal rather than spherical shape, we propose an approach based on an ellipsoidal diffusion model for extracting diffusion coefficients. This model takes into account the non-spherical morphology of graphite, addressing the limitations inherent in the geometric assumptions of previous methods. The average relative error between the diffusion coefficients derived from the ellipsoidal diffusion model and the previous method using spherical assumptions is 215 %, indicating that accurately depicting the shape of ellipsoidal graphite particles in the model is crucial for obtaining correct estimates of kinetic parameters. This study offers direct experimental evidence of superior kinetic behavior of edge planes over basal planes. To leverage this characteristic, it is recommended to employ an out-of-plane aligned architecture for composite electrodes using novel techniques, e.g., 3D printing or magnetic alignment techniques. [ABSTRACT FROM AUTHOR]

Fullerenes have emerged as functional catalytic nanomaterials in a plethora of applications, mainly due to their distinctive electronic structures. Therefore, we investigated the electronic structures of different fullerenes (C60, C70, C76, C84, and C100) using density functional theory (DFT) calculations to identify the most suitable candidate as a hydrogen evolution reaction (HER) catalyst. The calculations showed that C76 exhibits the most convenient electronic structure suitable for HER. Consequently, the synergy between C76 nanospheres and nickel foam substrate as a highly efficient HER catalyst has been demonstrated and discussed. The results showed that C76 nanospheres–Ni foam exhibits a superior catalytic activity with an overpotential of 20 mV vs RHE at −10 mA cm–2, which is almost the same as the benchmark Pt/C catalyst. The calculated free energy and band structure revealed a significant increase in the electron density at the C76/Ni foam interface, indicating the synergy between C76 nanospheres and Ni. Moreover, the exchange current density (J0), charge transfer coefficient (α), and mass activity (MA) were determined to elucidate the kinetics of the HER upon loading the Ni foam with different masses of C76. The electrodes containing 0.48 and 0.53 mg of C76 exhibited high α and J0, revealing very fast HER kinetics on their surfaces. This observed drastic increase in J0 is accompanied by a reduction in the activation barrier, which is in agreement with the DFT results. [ABSTRACT FROM AUTHOR]

Kinetic data reporting the rate of electron transfer across an electrified interface are of fundamental as well as practical importance. They report the electric current caused by coupling the flow of electrons inside the electronically conducting electrode and the flow of ions in the adjacent ionically conducting phase. At equilibrium or rest, potential currents in both directions at the established dynamic equilibrium have the same absolute value: the net current is zero. This current describes the electrocatalytic activity of an electrode and is called the exchange current; with respect to the surface area, it is called the exchange current density. This study inspected the actually used surface areas because the reported activities may depend critically on the selection of this area. Charge transfer resistances corresponding to exchange currents I0 were determined for a simple redox system using a platinum disc electrode with constant geometric surface area but variable roughness. At all studied degrees of roughness, changes in I0 were found. With an electrochemically active surface area, exchange current densities j0 could be calculated, but the obtained values showed a dependency on roughness that could not be accounted for by using this surface area instead of the geometric one. It is suggested that j0 may be reported with respect to geometric surface area, but at least roughness data of the studied electrode should be provided. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hierarchy configuration of CCM is proposed for internal voltage sensing. • In-situ voltage deconvolution in an operating PEMWE can be easily achieved. • Kinetic loss of catalyst layers can be directly measured without reference electrode. • Exchange current densities and their dependency on temperature are experimentally determined. • Real-time monitoring of stability helps further development of advanced catalysts and electrodes. The electrode kinetics and degradation originations are key factors for proton exchange membrane water electrolyzer (PEMWE). However, it is hard to directly characterize these factors in an operating PEMWE, which is because of the coupled components. In this study, we fabricate a hierarchy configured catalyst coated membrane by implementing voltage sensing wires, which enables the in-situ characterization on each part in a PEMWE. Specially, using the integrated configuration, the voltages on anode and cathode electrode can be measured, which provides a chance for determining the kinetics of the electrode. The exchange current density and charge transfer coefficient could be easily obtained. This integrated hierarchy configuration provides a reliable pathway for developing usable catalyst materials and optimizing catalyst layers. The impedance on an inner component can also be measured, and we find that the kinetics are the main losses for both anode and cathode electrode, which contribute to more than 96.6% to electrode voltage loss in low current density range. Additionally, the technique can monitor the internal voltages in an operating PEMWE, which provides valuable data for performance change diagnostic and analysis. The hierarchy configuration enriches the PEMWE characterization methods, and has great promise for industrial applications due to its easy setup and high feasibility. [ABSTRACT FROM AUTHOR]

• Rational construction of N-containing carbon sheets with atomically doped NiP-CoP nanohybrids (NiP-CoP/NCS) by precipitation/calcination. • The as-formed NiP-CoP/NCS exhibited improved physicochemical merits. • The HER/OER electrocatalysis and stability of NiP-CoP/NCS are impressive. • The H 2 and O 2 production rates of NiP-CoP/NCS are superior to mono-metallic analogues. The pursuit of sustainable energy production has directed rigorous research in the field of electrocatalysis, particularly for water electrolysis (i.e., hydrogen evolution (HER) and oxygen evolution reactions (OER)). This study discloses the rational synthesis of N-containing carbon sheets atomically doped NiP-CoP nanohybrid (NiP-CoP/NCS) via precipitation/calcination. The fabrication method tailored the physicochemical merits for collective contribution to improved green hydrogen and oxygen production, elucidated by surface/bulk characterization and theoretical calculations. Thus, the NiP-CoP/NCS had improved HER activity at lower overpotential (ƞ 10 = 197.7/274.6 mV), higher exchange current density (j o = 0.71/0.67 mA/cm2), turnover frequency (TOF = 2.63/1.47 s-1), H 2 production rate (3601.63/2519.12 µmol/g/h) and superior stability after 24 h in acid/alkaline media, than NiP/NCS and CoP/NCS. Moreover, NiP-CoP/NCS delivered impressive OER activity at reduced ƞ 10 (309.1 mV), and Tafel slope (b a = 58.9 ± 3.0 mV/dec), but higher TOF (3.67 s-1) and O 2 production rate (3643.96 µmol/g/h) relative to NiP/NCS and CoP/NCS, besides higher stability for 24 h. These were further proved by theoretical calculations. This work indicates a deeper understanding of the fabrication methods of making efficient electrocatalysts for green and sustainable energy conversion. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Ru/Ni 3 N@Mo 2 C composite was synthesized by; pyrolysis, hydrothermal, and wet-chemical route. • Synergistic effect between Ru and the support (Ni 3 N@Mo 2 C) optimized HOR kinetics. • Interfacial electronic interactions in Ru/Ni 3 N@Mo 2 C modulate Ru's electronic structure. • The catalyst achieves a kinetic current density of 4.76 mA cm disk −2 @50 mV. The use of hydrogen as an intermediator to convert and store electrochemical energy has been a subject of significant interest and focus. Unfortunately, the slow alkaline hydrogen oxidation reaction (HOR) is a barrier to further development of hydrogen–oxygen fuel cells. Ruthenium (Ru) has recently been investigated as a possible replacement for platinum (Pt) catalyst in the HOR because of the similar hydrogen binding energy (HBE) to Pt. Herein, Ru species was loaded on Ni 3 N@Mo 2 C support, which was used as an electrocatalyst for HOR. The catalyst presents an exchange current density and kinetic current densities of 3.05 and 4.76 mA cm disk −2 that are 2 and 1.4 times greater than that of commercial Pt/C, respectively. The findings indicate that the Ni 3 N@Mo 2 C support reduces the hydrogen binding energy on Ru sites. This improves the Volmer step for HOR and increases the catalytic activity. This study thus provides some guidance in the designing of HOR catalysts for efficient hydrogen energy conversion. [ABSTRACT FROM AUTHOR]

We developed a thermo-electrochemical model of a 50 Ah pouch-type lithium-ion cell and utilized a cell model to build an 18.5 V/50 Ah module to analyze the thermal behavior under various operating conditions and design cooling systems for optimal operating temperature ranges. Specifically, the heat generated by electrochemical reactions was simulated through an electrochemical cell model, and then the calculated heat was coupled with a heat transfer model reflecting the actual 3D structure of the cell. By fitting two temperature-dependent parameters, i.e., the chemical diffusion coefficient and exchange current density, the model accurately estimated the electrochemical and thermal properties with errors less than 3%, even under wide temperature (25°C, 35°C, and 45°C) and C-rate (0.5, 1, 2, and 5C) conditions. Based on this reliable cell model, we built an 18.5 V/50 Ah module model with five cells in series to simulate both the amount of heat generated and the required heat sink. Finally, both the cell and module models were used to predict the electrochemical and thermal behaviors under actual wireless tram operations in Turkey. The model results were compared with experimental results to confirm their reliability.

The purpose of this study is to examine the effects of exchange current density, as dependent on operating parameters, on the activation polarization in an HTPEM fuel cell. In line with this purpose, cell performance tests were performed for different relative humidity levels (from 0 to 20% in steps of 5%) and six different acid doping levels (4.26, 4.53, 4.95, 5.51, 7.24, 7.51 H3PO4/RPU PBI) at constant cell temperature (120 °C). The exchange current densities, as dependent on acid doping level and relative humidity, were determined by fitting a zero‐dimensional steady‐state mathematical model to the cell performance test results. Finally, to investigate the activation polarization in the cell, the exchange current densities obtained were incorporated within a numerical model. The results show that the effects of relative humidity on the exchange current density are relatively limited at all acid doping levels when the relative humidity is greater than 5%. The exchange current densities exhibit a decreasing trend with increasing acid doping level. Furthermore, it was found that the acid doping level and relative humidity have a strong influence on the anode overpotential, whereas no significant effect on the cathode overpotential was observed. [ABSTRACT FROM AUTHOR]

In this work, the effects of the coexistence of Ni−Nx sites and Ni metal nanoparticles of Ni−N−C (nickel‐nitrogen‐carbon) materials on the thermodynamic Li nucleation overpotential (η) and kinetic exchange current density (j0) are systematically studied. Ni‐Nx sites guarantee reduced nucleation resistance on the hollow carbon sphere (HCS) host, while the low amount residual of Ni nanoparticles plays an adverse role. The Li nucleation overpotential was down to 10.6 mV and the exchange current density increased from 1.139 to 2.325 mA cm−2 when the residual Ni nanoparticles in the prepared Ni−N−C composite were removed. As a result, pure Ni‐Nx sites displayed an average CE of 98.4 % over 300 cycles and a stable Li plating/stripping behavior for over 800 h. [ABSTRACT FROM AUTHOR]

Kinetic data reporting the rate of electron transfer across an electrified interface are of fundamental as well as practical importance. They report the electric current caused by coupling the flow of electrons inside the electronically conducting electrode and the flow of ions in the adjacent ionically conducting phase. At equilibrium or rest, potential currents in both directions at the established dynamic equilibrium have the same absolute value: the net current is zero. This current describes the electrocatalytic activity of an electrode and is called the exchange current; with respect to the surface area, it is called the exchange current density. This study inspected the actually used surface areas because the reported activities may depend critically on the selection of this area. Charge transfer resistances corresponding to exchange currents I0 were determined for a simple redox system using a platinum disc electrode with constant geometric surface area but variable roughness. At all studied degrees of roughness, changes in I0 were found. With an electrochemically active surface area, exchange current densities j0 could be calculated, but the obtained values showed a dependency on roughness that could not be accounted for by using this surface area instead of the geometric one. It is suggested that j0 may be reported with respect to geometric surface area, but at least roughness data of the studied electrode should be provided.

Catalytic performance of MoN, WN and WC on hydrogen evolution reaction (HER)were investigated by first-principles calculations, especially considering the effect of strain. From the calculation we can see the catalytic ability has an opposite trend with the adsorption capacity. H coverage was found to affect WN catalytic activity obviously, however has no effect on MoN and WC. Comparing with the experiments, we inferred that although the top site has the strongest potential catalytic ability, the actual catalytic site for HER is hollow1 site. Some specific transition metal doping (Ni > Fe > Mn > W for MoN, Fe > Co for WN, Ni > Co > Fe> Mn for WC) may indirectly improve the HER catalytic performance. It is worth noting that applying a certain strain (e.g. 2.5% tensile strain for MoN, 5% compressive strain for WN, WC) is helpful for improving the HER catalytic performance. Our work is instructive for HER catalyst development in terms of doping and strain. [Display omitted] • Certain strains (e.g. 2.5% for MoN, -5% for WN, WC) are helpful for HER catalysts. • HER catalytic ability has opposite trends with adsorption capacity in MoN, WN and WC. • H coverage affects WN catalytic activity obviously however has no effect on MoN, WC. • Comparing with experiments, actual catalytic sites do not have best catalytic ability. • Some transition metal doping can indirectly improve the HER catalytic performance. [ABSTRACT FROM AUTHOR]

In this work, electrochemical behaviors of Mn(II) in LiCl-KCl melts were investigated at 723 K using cyclic voltammetry (CV), chronopotentiometry (CP) chronoamperometry (CA), and square wave voltammetry (SWV) techniques. Results from CV and SWV measurements show that the redox reaction of Mn(II) on a tungsten working electrode is a diffusion controlled quasi-reversible reaction with two electrons transferred, and the diffusion coefficient is determined as 1.01 × 10−5 cm2/s by using semi-integral method. The standard reaction rate constant of the order ≈ 10−3 cm s−1, determined by Nicholson method, placed the redox reaction of Mn in the quasi-reversible range per Matsuda-Ayabe criteria. CA results exhibit that the deposition of metal manganese on the tungsten cathode is an instantaneous nucleation process. Besides, the apparent standard potential of Mn(II)/Mn(0) couple and activity coefficient of Mn(II) are determined by EMF measurements. Additionally, the diffusion coefficients calculated by semi-integral method revealed that the temperature dependence obeyed the Arrhenius law. Finally, the exchange current density of Mn(II)/Mn(0) on tungsten electrode at various temperatures was analyzed by Tafel polarization technique. [ABSTRACT FROM AUTHOR]

The performance of lithium‐ion batteries can be analyzed and improved by appropriate electrochemical models. A challenging yet crucial part is the parameterization of these models. Until now, the literature has incompletely investigated and cited the charge transfer process parameters describing the lithium transfer between the active material particles in the electrode and the liquid electrolyte. Herein, a novel approach is presented for obtaining these charge transfer parameters. The well‐established experimental methods of electrochemical impedance spectroscopy and focused ion beam tomography are applied. By introducing both experimental results into a transmission line model, a reliable determination of the charge transfer parameters j0, k, and rCT can be achieved. The new approach is validated by comparing the results of four cathodes, all containing the state‐of‐the‐art active material NixMnyCo1−x−y (NMC), but with different microstructures and/or stoichiometries. [ABSTRACT FROM AUTHOR]

Abstract Due to an ultrahigh theoretical specific capacity of 3860 mAh g−1, lithium (Li) is regarded as the ultimate anode for high‐energy‐density batteries. However, the practical application of Li metal anode is hindered by safety concerns and low Coulombic efficiency both of which are resulted fromunavoidable dendrite growth during electrodeposition. This study focuses on a critical parameter for electrodeposition, the exchange current density, which has attracted only little attention in research on Li metal batteries. A phase‐field model is presented to show the effect of exchange current density on electrodeposition behavior of Li. The results show that a uniform distribution of cathodic current density, hence uniform electrodeposition, on electrode is obtained with lower exchange current density. Furthermore, it is demonstrated that lower exchange current density contributes to form a larger critical radius of nucleation in the initial electrocrystallization that results in a dense deposition of Li, which is a foundation for improved Coulombic efficiency and dendrite‐free morphology. The findings not only pave the way to practical rechargeable Li metal batteries but can also be translated to the design of stable metal anodes, e.g., for sodium (Na), magnesium (Mg), and zinc (Zn) batteries.

The study reports a novel patented test and the electrochemical cell for its implementation to estimate the area-specific exchange current density for photoactive powder. The test was employed for the photo-electrode reaction in the PEC water splitting. Testing procedure included impedance measurements and was carried out in the original three-electrode cell with an alkaline electrolyte where working Ni electrode behaves as an ideal polarized electrode and is in immediate contact with the photoactive powder additive. The application of this test is presented for the UV- and visible light photoactive TiO 2-x C x :nC powder. The test of TiO 2-x C x :nC powder confirmed that the polarization resistance of the designed electrochemical cell is due only to photoactive powder. The area-specific exchange current density was determined for the photo-electrode reactions on TiO 2-x C x :nC powder under UV- and visible light, as well as their ratio. The obtained ratio correlates well with the previous data on the rate constants for the UV- and visible-driven photocatalytic oxidation of a model solution performed in the presence of the same powder TiO 2-x C x :nC. [Display omitted] • Novel test for the area-specific exchange current density (I 0) of photoactive powder. • The developed test cell is based on the properties of an ideal polarized electrode. • Polarization resistance of the cell was confirmed as due only to photoactive powder. • Active Ti(O,C) 2 /C powder with 130 m2/g surface area was tested in alkaline solution. • I 0 of Ti(O,C) 2 /C was 1.8⋅10−10 A/cm2 for UV and 0.78⋅10−10 A/cm2 for visible light. [ABSTRACT FROM AUTHOR]

Due to an ultrahigh theoretical specific capacity of 3860 mAh g−1, lithium (Li) is regarded as the ultimate anode for high‐energy‐density batteries. However, the practical application of Li metal anode is hindered by safety concerns and low Coulombic efficiency both of which are resulted fromunavoidable dendrite growth during electrodeposition. This study focuses on a critical parameter for electrodeposition, the exchange current density, which has attracted only little attention in research on Li metal batteries. A phase‐field model is presented to show the effect of exchange current density on electrodeposition behavior of Li. The results show that a uniform distribution of cathodic current density, hence uniform electrodeposition, on electrode is obtained with lower exchange current density. Furthermore, it is demonstrated that lower exchange current density contributes to form a larger critical radius of nucleation in the initial electrocrystallization that results in a dense deposition of Li, which is a foundation for improved Coulombic efficiency and dendrite‐free morphology. The findings not only pave the way to practical rechargeable Li metal batteries but can also be translated to the design of stable metal anodes, e.g., for sodium (Na), magnesium (Mg), and zinc (Zn) batteries. [ABSTRACT FROM AUTHOR]

Polyacrylonitrile (PAN)–based gel polymer electrolytes (GPEs) consisting of plasticizers ethylene carbonate (EC) and propylene carbonate (PC) and different compositions of tetrabutylammonium iodide (TBAI) salt have been investigated. The GPEs have been characterized by electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), and X-ray diffraction (XRD) techniques. EIS study shows that the GPE containing 30 wt% TBAI has the lowest bulk impedance, Rb (23 Ω), and highest room temperature ionic conductivity (3.46 × 10−3 S cm−1). Conductivity-temperature relationship in the temperature range studied obeys Arrhenius rule. The Ea value is decreased with TBAI percentage and is the lowest (12.59 kJ/mol) for GPE containing 30 wt% TBAI. From LSV experimental data, the limiting current density (Jlim), apparent diffusion coefficient of triiodide ion ( D I 3 − ∗ ), and exchange current density (J0) have been calculated. The highest value for each of these parameters is 5.00 mA cm−2, 6.59 × 10−7 cm2 s−1, and 0.63 mA cm−2, respectively, for the highest conducting GPE. All samples are amorphous. LSV at stainless steel showed that the electrochemical stability window is 2.2 V. The cyclic voltammetry (CV) was performed from 1 to 1000 cycle which showed good electrochemical stability. [ABSTRACT FROM AUTHOR]

Two representative parameters, exchange current density (j0) and charge transfer coefficient (α), in a standard fuel cell model of polymer electrolyte membrane fuel cells (PEMFCs) were experimentally investigated. The polarization characteristics and the corresponding electrochemical impedance spectra of the normal PEMFCs were measured and Tafel curves were calculated from them, where j0 and ? were finally calculated. As a result, the calculated j0 was 0.11- 0.70 A/cm2, while the α was 0.056-0.023, depending on the operating temperature. Here, the j0 is extremely overestimated while α is underestimated as compared with those in literature. Although the reason for such difference is not clear, it is expected that it could affect the predicted performance by the model significantly if the fuel cell performance is improved highly in the future so the activation overvoltage corresponding to identical current is lowered. [ABSTRACT FROM AUTHOR]

Normally, the Nernst voltage calculated from the concentration of the reaction gas in the flow channel is considered to be the ideal voltage (reversible voltage) of the hydrogen-oxygen fuel cell. The Nernst voltage loss in fuel cells in most of the current literature is thought to be due to the difference in concentration of reaction gas in the flow channel and concentration of reaction gas on the catalyst layer at the time as when the high net current density is generated. Based on the Butler-Volmer equation in the hydrogen-oxygen fuel cell, this paper demonstrates that Nernst voltage loss caused by concentration difference of reaction gas in the flow channel and reaction gas on the catalyst layer at equilibrium potential. According to the relationship between the current density and the concentration difference it can be proven that Nernst voltage loss does not exist in hydrogen-oxygen fuel cells because there is no concentration difference of reaction gas in the flow channel and on the catalytic layer at equilibrium potential when the net current density is zero. [ABSTRACT FROM AUTHOR]

The kinetics of zinc dissolution in concentrated potassium hydroxide solution were determined as a function of KOH concentration, amount of added ZnO, and temperature through linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The measurements were evaluated with a simplified reaction scheme in which an intermediate ZnI species is formed on the electrode surface that subsequently reacts to a soluble ZnII species. Analysis of the LSV data with a two-step Butler–Volmer kinetics showed that the transfer coefficients and the surface coverage of the intermediate are approximately constant in the entire range of operation conditions, whereas the exchange current density for the first reaction step is about five times larger than for the second step. Analysis of the dynamic EIS measurements resulted in very similar current densities than obtained from the quasi-stationary LSV method. For the first time, activation energies describing the temperature dependence of the exchange current density were also determined. [ABSTRACT FROM AUTHOR]

The electrochemical characteristics of electrolyte-supported solid oxide fuel cells containing pure perovskite anode of La0.3Y0.1Sr0.4TiO3−δ, (LYSTA-) and composite anodes with varying fractions (30 and 50 wt%) of yttria-stabilized zirconia (YSZ), LYSTA- (30)YSZ and LYSTA- (50)YSZ, were studied in humidified methane. The 8 wt% CeO2 and 4 wt% NiO, denoted as (84), were impregnated into the pure and composite anodes for efficient electrooxidation of methane. The studies were carried out to qualitatively estimate the kinetic parameter, exchange current density (io), for methane electrooxidation. Evaluation in a 3-electrode configuration with an asymmetric reference electrode yielded the following activity trend: (84)LYSTA- > (84)LYSTA- (30)YSZ > (84)LYSTA- (50)YSZ in the high-overpotential region, with io values of 133.2 ± 32.5, 40.8 ± 16.6, and 47.9 ± 16.3 mA cm−2 at 900 °C, respectively. The presence of YSZ in the composite anodes leads to decrease in io and degrading performance. Impedance studies clubbed with equivalent circuit modeling along with physical characterization were used to account for decreased io values in composite anodes. Metal support interactions arising between Ni and CeO2 are studied using a high-resolution transmission electron microscope. Solid oxide fuel cell (SOFC) studies with (84)LYSTA- anode yielded a maximum power density of 591 mW cm−2 in hydrogen and 429 mW cm−2 in methane. [ABSTRACT FROM AUTHOR]