Electrode Overpotential Research Articles

Enhanced Oxygen Evolution Reaction Performance of NiMoO4/Carbon Paper Electrocatalysts in Anion Exchange Membrane Water Electrolysis by Atmospheric-Pressure Plasma Jet Treatment.

NiMoO4 was grown on carbon paper (CP) by a hydrothermal method. A rapid and high-temperature atmospheric-pressure plasma jet (APPJ) process was used to generate more oxygen-deficient NiMoO4 on the CP surface to serve as an electrode material for the oxygen evolution reaction (OER). After 60 s of APPJ treatment, the overpotential of the electrode at 100 mA/cm2 decreased to 790 mV and that at 10 mA/cm2 decreased to 368 mV. Additionally, the charge transfer resistance decreased from 2.8 to 1.2 Ω, indicating that APPJ treatment effectively reduced the electrode overpotential and impedance. The effect of NiMoO4/CP/APPJ-60 s on the anion exchange membrane water electrolysis (AEMWE) system was also tested. At a system temperature of 70 °C and current density of 100 mA/cm2, the energy efficiency reached 95.1%, and the specific energy consumption decreased from 4.02 to 3.83 kWh/m3. These results demonstrate that the APPJ-treated NiMoO4/CP electrode can effectively enhance the OER performance in water electrolysis and improve the energy efficiency of the AEMWE system. This approach shows promise in replacing precious metal electrodes, thereby potentially reducing the cost and providing an environmentally friendly alternative.

Breaking the Pt Electron Symmetry and OH Spillover towards PtIr Active Center for Performance Modulation in Direct Ammonia Fuel Cell.

The growing interest in low-temperature direct ammonia fuel cells (DAFCs) arises from the utilization of a carbon-neutral ammonia source; however, DAFCs encounter significant electrode overpotentials due to the substantial energy barrier of the *NH2 to *NH dehydrogenation, compounded by the facile deactivation by *N on the Pt surface. In this work, a unique catalyst, Pt4Ir@AlOOH/NGr i.e., Pt4Ir/ANGr, is introduced composed of PtIr alloy nanoparticles controllably decorated on the pseudo-boehmite phase of AlOOH-supported nitrogen-doped reduced graphene (AlOOH/NGr) composite, synthesized via the polyol reduction method. The detailed studies on the structural and electronic properties of the catalyst by XAS and VB-XPS reveal the possible electronic modulations. The optimized Pt4Ir/ANGr composition exhibits a significantly improved onset potential and mass activity for AOR. The DFT study confirms the OHad species spillover by AlOOH and Pt4Ir (100) facilitates the conversion of the *NH2 to *NH with minimal energy barriers. Finally, testing of DAFC at the system level using a membrane electrode assembly (MEA) with Pt4Ir/ANGr as the anode catalyst, demonstrating the suitability of the catalyst for its practical applications. This study thus uncovers the potential of the Pt4Ir catalyst in synergy with ANGr, largely addressing the challenges in hydrogen transportation, storage, and safety within DAFCs.

Monitoring Electrochemical Dynamics through Single-Molecule Imaging of hBN Surface Emitters in Organic Solvents.

Electrochemical techniques conventionally lack spatial resolution and average local information over an entire electrode. While advancements in spatial resolution have been made through scanning probe methods, monitoring dynamics over large areas is still challenging, and it would be beneficial to be able to decouple the probe from the electrode itself. In this work, we leverage single molecule microscopy to spatiotemporally monitor analyte surface concentrations over a wide area using unmodified hexagonal boron nitride (hBN) in organic solvents. Through a sensing scheme based on redox-active species interactions with fluorescent emitters at the surface of hBN, we observe a region of a linear decrease in the number of emitters against increasingly positive potentials applied to a nearby electrode. We find consistent trends in electrode reaction kinetics vs overpotentials between potentiostat-reported currents and optically read emitter dynamics, showing Tafel slopes greater than 290 mV·decade-1. Finally, we draw on the capabilities of spectral single-molecule localization microscopy (SMLM) to monitor the fluorescent species' identity, enabling multiplexed readout. Overall, we show dynamic measurements of analyte concentration gradients on a micrometer-length scale with nanometer-scale depth and precision. Considering the many scalable options for engineering fluorescent emitters with two-dimensional (2D) materials, our method holds promise for optically detecting a range of interacting species with exceptional localization precision.

Mitigation of Negative-Electrode Degradation in Vanadium Redox Flow Batteries

Electrode overpotentials are among the major factors that impact the performance of redox flow batteries (RFBs). However, even though the all-vanadium redox flow battery (VRFB) is the most mature flow-battery chemistry, a recent review article has pointed out that “there is poor agreement between the reported values of kinetic parameters” [1]. Major contributors to this disagreement are the wide variety of carbon materials that are used as electrodes and because the kinetics of both the V(II)/V(III) and V(IV)/V(V) reactions on carbon depend on the electrode pretreatments. The role of surface functional groups and the mechanisms of electron transfer for these reactions is not well understood [1]. There is general agreement that the V(IV)/V(V) kinetics are more facile than the V(II)/V(III) kinetics [2, 3]. Multiple researcher groups have reported electrode overpotential increases with time, and “there is evidence that it occurs mainly on the negative electrode” [1]. Additionally, “reversing the polarity of the VRFB has been suggested as one strategy to recover lost performance but not all investigators have found this strategy effective” [1]. Exposing the V(II)/V(III) electrode to V(IV)/V(V) electrolyte may increase the roughness and oxidize the electrode, which can both improve the activity. It has also been suggested that reversing the polarity may remove impurities, such as copper metal from the negative electrode [4]. More recently, it has been proposed that surface activity may be improved by oxidizing adsorbed V(II) [5]. We hypothesize that V(II)/V(III) electrode degradation on graphitic carbon-fiber electrodes is primarily due to the adsorption of a contaminate that is oxidized when exposed to V(IV)/V(V) electrolyte. We will describe what we suspect is the relevant contaminate species, and we will show the stability of the V(II)/V(III) electrode can be substantially improved by simply removing certain electrolyte-wetted components from the VRFB test apparatus. References A. Bourke, D. N. Buckley, et.al., “JES, 170 (2020). 10.1149/1945-7111/acbc99 D. Aaron, T. A. Zawodzinski, et. al., ECS Electrochem. Letters, 2 (2013) 10.1149/2.001303eel N. Pour, Y. Shao-Horn, et.al., J. of Physical Chemistry C, 119 (2015).10.1021/jp5116806 D. Reynard, H. Girault, et.al., ChemSusChem, 12 (2019). 10.1002/cssc201802895T. Greese and G. Reichennauer, J. Power Sources, 500 (2021). 10.1016/j/jpowsour.2021.229958

Comparing Electrode Overpotential Contributions in Vrfbs Amongst Multiple Techniques

Redox flow batteries (RFBs) offer a potential remedy for the escalating need for energy storage amid the ongoing transition from carbon-intensive fossil energy to renewable energy sources. Yet, many RFB chemistries are shown to have low energy efficiencies which can be attributed, in part, to ineffective electrode materials. Identifying overpotential contributions from electrodes under operating conditions is a key step in understanding how to design better RFB electrodes Previously, three-electrode setups using rotating disk electrodes (RDE) were the effective technique at isolating overpotentials; however, this can only be accomplished by looking at one side of the RFB at a time. RDEs do not easily replicate the operational conditions of a power cell or the porous nature of carbon electrodes used in RFBs. Alongside the normal operation of an RFB, symmetry cells are another approach that can be utilized in quantifying the performance of electrodes. The advantage of a symmetrical cell setup allows us to monitor the overpotential contributions of two different electrodes in the same electrolyte concurrently. Membrane-based reference electrodes (MBRE), and other reference electrode integration concepts, allow us to use three-electrode techniques in operational RFB power cells. As a case study, we examined the effect of oxidative electrode treatments on the positive and negative side of the VRFB using multiple methods. While other studies have shown that an untreated negative electrode may be the key inhibitor in VRFB performance, we have quantified the overpotential at 50% state of charge to be 194 mV when 50 mA cm-2 is applied. After an oxidative treatment is applied to the negative electrode, the overpotential is reduced to 111 mV. Applying this to other techniques, we can compare the effectiveness of a non-symmetry cell setup vs. a symmetry cell setup, which displayed that oxidative treatment techniques appear to have an opposite effect on the positive electrode. A treated-positive electrode shows an overpotential of around 100 mV whereas an untreated-positive electrode only contributes 15 mV less of overpotential. These findings are further compared using common reference electrodes placed in the electrolyte tank, providing insights into the effectiveness of power cell techniques in improving RFB electrode performance.

Electrochemical H2O2 Production Modelling for an Electrochemical Bandage

Hydrogen peroxide (H2O2) is an environmentally friendly oxidizing agent used to treat wound infections. We have developed an electrochemical bandage (e-bandage), which generates H2O2 in situ and shown that it exhibites in vitro and in vivo efficacy. The electrochemical bandage comprises carbon fabric working and counter electrodes, as well as an Ag/AgCl quasi-reference electrode, separated by cotton fabric and the electrolyte is delivered by Xanthan gum with phosphate buffer saline. While the chemistry and electrochemistry of the e-bandage have been experimentally characterized, the system level description could aid in better designing these devices. Here, a model called electrochemical hydrogen peroxide production (EHPP) was used to evaluate factors influencing electrochemical generation of H2O2, including electrode potential, diffusion and reaction rates, temperature, and various geometries. EHPP model parameters estimated based on experimental results indicate that: (i) with diffusion limitations caused by changes in physical conditions (e.g., drying of hydrogel), the rate of H2O2 generation decreases, (ii) higher working electrode overpotentials increase H2O2 generation and higher counter electrode overpotentials do not affect H2O2 generation, (iii) increasing the distance between electrodes by adding more hydrogel reduces H2O2 generation, (iv) net H2O2 generation decreases ∼12% with temperature, and (v) H2O2 production is most effective in the initial 48 h of operation.

On the kinetics of electrodeposition in a magnesium metal anode

Magnesium (Mg) metal batteries are promising for next-generation energy storage due to Mg’s abundance and potential for improved energy densities through two-electron redox in cathodes and thin film anodes supporting high current densities. However, reversible and uniform electrodeposition of Mg necessary for high-energy-density Mg batteries continues to be plagued by challenges traceable to energy barriers to desolvation in liquid electrolytes, the stabilization of passivation layers that impede Mg diffusion at electrified interfaces, and deleterious high-asperity electrodeposition morphologies. Thus, the specific impact and coupling of factors such as (i) composition of the salt solution, (ii) electrode overpotential, and (iii) reversible stripping/plating on the interfacial kinetics of electrodes remains an area of intense interest. This study investigates the effects of overpotential time-transients and electrolyte concentration using experimentally-guided phase-field methods and compares them with an electrochemical spherical cap model. Complex dynamics at the electrode/electrolyte interface involve transient changes in overpotential, influencing nucleation, diffusion, and crystallization, ultimately altering surface evolution. We find that the Damkohler number converges to approximately one for a symmetric Mg-Mg cell using 0.1 M Mg[TFSI]2 in 1:1 v/v diglyme/dimethoxyethane suggesting a subtle balance between reactive and diffusive forces. The results indicate the formation of dendritic structures is primarily driven by limitations in electrolyte transport. In addition, we determine the limiting current density of this cell under various electrolyte concentrations, which is an essential step in successful battery design and operation. Our findings underscore the critical role of overpotentials in underpinning reaction kinetics and non-equilibrium growth dynamics during metal electrodepositon.

Numerical Simulation of Flow Field Structure of Vanadium Redox Flow Battery and its Optimization on Mass Transfer Performance

The structural design of the flow channel of a redox flow battery directly affects ion transport efficiency, electrode overpotential, and stack performance during charge-discharge cycles. A tapered hierarchical interdigitated flow field design that has independent flow channel structures for different levels of flow was developed in this work. Especially, the secondary branch channels are the tapered type and the corresponding cross-sections are gradually reduced along the flow direction, which is beneficial for improving the flow rate at the end of channels and enhancing mass transfer. The performances of a vanadium redox flow battery with interdigitated flow field, hierarchical interdigitated flow field, and tapered hierarchical interdigitated flow field were evaluated through 3D numerical model. The results showed that at 240 mA cm−2 and 6 ml s−1, the pump-based efficiency of the hierarchical interdigitated flow field increased by 4%-7% compared with the interdigitated flow field. Furthermore, the pump-based efficiency with tapered hierarchical interdigitated flow field increased by 1.6%-3% compared with the hierarchical interdigitated flow field. This indicates that the tapered hierarchical interdigitated flow field shows further advantages in redox flow battery applications.

Spontaneous Molecule Aggregation for Nearly Single‐Ion Conducting Sol Electrolyte to Advance Aqueous Zinc Metal Batteries: The Case of Tetraphenylporphyrin

AbstractZn metal as a promising anode of aqueous batteries faces severe challenges from dendrite growth and side reactions. Here, tetraphenylporphyrin tetrasulfonic acid (TPPS) is explored as an electrolyte additive for advanced Zn anodes. It is interesting to note that TPPS spontaneously assembles into unique aggregates. As they adsorb on the Zn anode, the aggregates enhance the resistance to electrolyte percolation and dendrite growth compared to single molecules. Meanwhile, TPPS facilitates anion association in the solvation sheath of Zn2+, and boosts the transference number of Zn2+ up to 0.95. Therefore, anion‐related side reactions and anion‐induced electrode overpotentials are reduced accordingly. In this context, the electrolyte containing TPPS exhibits excellent electrochemical performance. Even under a high loading of MnO2 (25 mg cm−2), a limited Zn supply (N/P ratio=1.7), and a lean electrolyte (15 μL mAh−1), the full cells still represent a higher cumulative capacity compared to the reported data. The advantages of this electrolyte are also adapted to other cathode materials. The pouch cells of Zn||NaV3O8 ⋅ 1.5H2O realize a capacity of ~0.35 Ah at 0.4 C under harsh conditions.

Spontaneous Molecule Aggregation for Nearly Single-Ion Conducting Sol Electrolyte to Advance Aqueous Zinc Metal Batteries: The Case of Tetraphenylporphyrin.

Zn metal as a promising anode of aqueous batteries faces severe challenges from dendrite growth and side reactions. Here, tetraphenylporphyrin tetrasulfonic acid (TPPS) is explored as an electrolyte additive for advanced Zn anodes. It is interesting to note that TPPS spontaneously assembles into unique aggregates. As they adsorb on the Zn anode, the aggregates enhance the resistance to electrolyte percolation and dendrite growth compared to single molecules. Meanwhile, TPPS facilitates anion association in the solvation sheath of Zn2+, and boosts the transference number of Zn2+ up to 0.95. Therefore, anion-related side reactions and anion-induced electrode overpotentials are reduced accordingly. In this context, the electrolyte containing TPPS exhibits excellent electrochemical performance. Even under a high loading of MnO2 (25 mg cm-2), a limited Zn supply (N/P ratio=1.7), and a lean electrolyte (15 μL mAh-1), the full cells still represent a higher cumulative capacity compared to the reported data. The advantages of this electrolyte are also adapted to other cathode materials. The pouch cells of Zn||NaV3O8 ⋅ 1.5H2O realize a capacity of ~0.35 Ah at 0.4 C under harsh conditions.

Experimental characterization and non-isothermal simulation of a zero-gap alkaline electrolyser with nickel-iron porous electrode

The availability of self-supported porous electrodes with excellent hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalytic activity has been an important cornerstone for the performance of alkaline water electrolysers (AWEs). In addition, the management of heat and two-phase flow during ion/electron transfer in porous electrodes poses significant challenges to the stable operation of AWE electrolysers. In this work, a two-dimensional non-isothermal multiphysical model considering two-phase flow, mass, heat and charge transfer processes is developed based on COMSOL Multiphysics and well validated with reliable experimental data. The model exhibits excellent agreement with actual electrolyser operating voltages between 323–343 K, and the relative error is within acceptable 2.2% even at high current densities up to 1.5 A cm−2. In addition, the electrode kinetic data obtained based on standard three-electrode experiments allow the model to predict the corresponding HER and OER overpotentials of the porous electrodes with great accuracy, as well as to obtain the distribution of temperature and ionic species inside the porous electrodes under various volumetric flow rates and current densities. This work provides a practical and reliable guide for the design of porous electrodes and the performance enhancement of electrolysers from both experimental and simulation perspectives.

Study of a novel microstructured air electrode/electrolyte interface for solid oxide cells

Solid Oxide Cells (SOCs) are promising high temperature electrochemical devices to obtain clean energies from renewable sources. Their high operating temperatures (800–1000 °C) contribute to the degradation of the cell components. Intermediate Temperature SOCs (IT-SOCs) appear as an alternative to decrease the operating temperatures (600–800 °C) and avoid cell degradation, nevertheless, the electrochemical performance is affected by energy dissipation, principally by the air electrode overpotentials. This work presents the surface modification of Ce0.80Sm0.20O2-δ (SDC) electrolyte by Femtosecond Laser Micromachining (FLM) to increase the surface/area ratio and therefore improve the electrochemical performance. A pattern with an equally spaced pillar shape microstructure was obtained and characterized. (La0.60Sr0.40)0.95Co0.20Fe0.80O3-δ (LSCF) powder was used as porous air electrode to determine the electrochemical benefits of the pattern. Polarization resistance (Rp) of air electrode in patterned sample was about five times lower than in flat one at 600 °C and after 45 h, which suggested an improvement in the electrical and chemical features over time. These enhancements could be explained by the synergistic effect among surface/area ratio, nano-microcrystalline domains and superficial Ce3+ concentration in the patterned electrolyte. Rp values are higher than those reported for best air electrodes, however, FLM has proven its benefits in electrochemical performance.

Beyond Constant Current: Origin of Pulse-Induced Activation in Phase-Transforming Battery Electrodes.

Mechanistic understanding of phase transformation dynamics during battery charging and discharging is crucial toward rationally improving intercalation electrodes. Most studies focus on constant-current conditions. However, in real battery operation, such as in electric vehicles during discharge, the current is rarely constant. In this work we study current pulsing in LiXFePO4 (LFP), a model and technologically important phase-transforming electrode. A current-pulse activation effect has been observed in LFP, which decreases the overpotential by up to ∼70% after a short, high-rate pulse. This effect persists for hours or even days. Using scanning transmission X-ray microscopy and operando X-ray diffraction, we link this long-lived activation effect to a pulse-induced electrode homogenization on both the intra- and interparticle length scales, i.e., within and between particles. Many-particle phase-field simulations explain how such pulse-induced homogeneity contributes to the decreased electrode overpotential. Specifically, we correlate the extent and duration of this activation to lithium surface diffusivity and the magnitude of the current pulse. This work directly links the transient electrode-level electrochemistry to the underlying phase transformation and explains the critical effect of current pulses on phase separation, with significant implication on both battery round-trip efficiency and cycle life. More broadly, the mechanisms revealed here likely extend to other phase-separating electrodes, such as graphite.

(Invited) Developing Electrodes for Solid Oxide Fuel Cells What I Learned from Anil Virkar about Designing High Performance Electrodes

The performance of state-of-the-art solid oxide fuel cells (SOFC) and electrolyzers (SOEC) are largely limited by the overpotentials at the electrodes, both anode and cathode. The electrode overpotentials can be categorized by i) concentration of gas species, ii) charge transfer, and, iii) ionic transport near the interface, with the magnitude and contribution of each dependent on the cell geometry and operating conditions. One of the strategies of reducing overpotentials and improving electrode performance is the use of functionally grade electrodes wherein individual layers are optimized for porosity, conductivity, and three phase boundaries. Outer current collecting layers are designed with substantial porous microstructures and from highly electronically conductive materials resulting in low sheet resistance. Whereas the electrode layer near the electrolyte interface can be comprised of a two phase electrolyte-electrocatalyst composite in order to extend the effective three phase boundary layer beyond the electrolyte surface.The effects of various microstructural and material properties on the various electrode overpotentials were investigated. The influence of porosity and pore structure on the effective N2-O2 binary gas diffusion in the air electrode and resulting concentration polarization was studied. Likewise, highly porous anode supports were developed and characterized with the intent to decrease gas transport concentration overpotentials. Given electrodes that are adequately thin or have sufficient porosity in order to facilitate gas diffusion and reduce concentration polarizing, a substantial portion of the electrode overpotential can be attributed to the charge transfer and transport of the oxide ion from the electrode into the electrolyte, especially at lower temperatures. The critical transition region between the electrode and the electrolyte may span only a few microns but is essentially the equivalent of the ‘last mile problem’ for a fuel cell.Composite electrode layers nearest to the electrolyte were studied with regard to microstructure and materials selection. The activation overpotential was measured and related to the electrode properties including, three phase boundary density, the ionic transport within this layer, and the charge transfer of the electrocatalyst. In particular, the influence of the ionic conductivity of the electrolyte phase in the composite electrode on the electrode polarization was investigated. In addition, the microstructure of this electrolyte phase within the composite phase was studied and the sensitivity of necks between sintered electrolyte particles on ionic transport was estimated. A unique fabrication method was developed that produced an electrolyte skeleton with improved particle-to-particle necking and yet extremely porous, that could subsequently be infiltrated with an electrocatalyst material. Applying and combining the various strategies outlined above, highly efficient electrodes were developed and demonstrated for solid oxide fuel cells.

Electrolyte Flow through Porous Carbon Electrodes Under Compression in the Hydrogen-Bromine Redox Flow Battery

The conditions of electrolyte flow affect the performance of redox flow batteries through the combined effect of pumping energy and electrode overpotential. In the hybrid hydrogen-bromine flow battery the conditions of electrolyte flow depend on the trans-membrane pressure exerted by hydrogen gas in the membrane electrode assembly, which has a compressive effect on the liquid side electrode.This study aims at characterizing the effect of hydrogen pressure on flow characteristics and investigate its effect on transport behavior. We selected two types of porous carbon electrodes, carbon paper and carbon cloth, with and without surface conditioning, and study liquid flow at the compression ratios expected in a hydrogen-bromine cell under increasing operation pressure.Combination of electrode characterization with electrolyte velocity measurements obtained by particle image velocimetry in flow-through configuration allow characterization of liquid flow through porous electrodes, and attempt to relate it to electrode morphology. Electrochemical testing is then is used to reveal the effect of electrode compression on electrochemical active surface area, estimated by the capacitance of the double layer, and cell polarization.The velocity field is revealed to be highly dependent on the fiber structure of the electrode and surface conditioning. The effect of compression manifests early and impacts the uniformity of flow through the porous structure. Additionally, the changes in active area and cell resistance result in a complex combination of factors that determine cell polarization. Figure 1

Effect of temperature on the electrode overpotential of molten carbonate electrolysis and fuel cells with inert-gas step addition method

This study explores molten carbonate electrolysis and fuel cell behaviour across temperatures from 823 to 973 K using steady-state polarization (SSP), electrochemical impedance spectroscopy (EIS), and inert-gas step addition (ISA) techniques. The findings reveal that total voltage loss decreases with rising temperature in fuel cell (FC) and electrolysis (EC) modes. The ohmic loss similarly declines as temperature increases. The ISA method determines the gas-phase mass transfer-induced overpotential, which increases as temperature increases in both modes at the hydrogen electrode (HE). This indicates that pore diffusion resistance strongly affects the HE in both modes. The liquid-phase mass transfer-induced overpotential at the oxygen electrode (OE) exhibits a much smaller value in EC mode than in FC mode at all temperatures. The increased O2 and CO2 partial pressures and decomposition of sufficient amounts of carbonate electrolytes to generate O2 in EC mode would reduce the liquid-phase resistance and its induced overpotential at the OE in the temperature range.

Decoupling of Reaction Overpotentials and Ionic Transport Losses within 3D Porous Electrodes in Zero-Gap Alkaline Electrolysis Cells

Designing more efficient and productive alkaline electrolysis (AE) cells requires the development of electrode microstructures that facilitate mass transport and reduce associated ionic transport losses within the electrodes. Here we propose a method, relying on a minimum of three reference electrodes, that allows to decouple the Galvani potential losses (GL) associated with ionic migration within each of the electrodes from the overall electrode overpotential. This provides additional insight along with the separation of the voltage losses within the anode, cathode, and separator that is also achieved during zero-gap operation at industrially relevant conditions. Different Nickel electrode structures have been investigated to assess the effect of thickness, surface area, and porosity on the GL within the electrodes. The GL in the anode are higher than in the cathode for the same electrode structure and decrease upon decreasing electrode thickness. Reducing the cathode thickness, while maintaining the same specific surface area, improves performance more compared to the anode. Moreover, electrodes with large pore diameter (0.43 mm) were observed to facilitate the oxygen evolution reaction (OER), whereas electrodes with small pore diameter (0.23 mm) and large surface area are beneficial for the hydrogen evolution reaction (HER). Overall, the proposed methodology provides vital information in guiding the microstructural optimization of electrodes for advanced alkaline electrolysis cells.

Cycling-Induced Capacity Increase of Bulk and Artificially Layered LiTaO3 Anodes in Lithium-Ion Batteries.

Tantalum-based oxide electrodes have recently drawn much attention as promising anode materials owing to their hybrid Li+ storage mechanism. However, the utilization of LiTaO3 electrode materials that can deliver a high theoretical capacity of 568 mAh g-1 has been neglected. Herein, we prepare a layered LiTaO3 electrode formed artificially by restacking LiTaO3 nanosheets using a facile synthesis method and investigate the Li+ storage performance of this electrode compared with its bulk counterpart. The designed artificially layered anode reaches specific capacities of 474, 290, and 201 mAh g-1, respectively, at 56 (>500 cycles), 280 (>1000 cycles), and 1120 mAg-1 (>2000 cycles) current densities. We also determine that the Li+ storage capacity of the layered LiTaO3 demonstrates a cycling-induced capacity increase after a certain number of cycles. Adopting various characterization techniques on LiTaO3 electrodes before and after electrochemical cycling, we attribute the origin of the cycling-induced improvement of the Li+ storage capacity in these electrodes to the amorphization of the electrode after cycling, formation of metallic tantalum during the partially irreversible conversion mechanism, lower activation overpotential of electrodes due to the formation of Li-rich species by the lithium insertion mechanism, and finally the intrinsic piezoelectric behavior of LiTaO3 that can regulate Li+ diffusion kinetics.

Nernst Equations and Concentration Chemical Reaction Overpotentials for VRFB Operation

The vanadium redox flow battery (VRFB) has been intensively examined since the 1970s, with researchers looking at its electrochemical time varying electrolyte concentration time variation equations (both tank and cells, for negative and positive half cells), its thermal time variation equations, and fluid flow equations. Chemistry behavior of the electrolyte ions have also been intensively examined too. Our focus in this treatment is a new approach to understanding the physics, chemistry, and electronics of the VRFB by looking at the equilibrium and non-equilibrium aspects of the battery. Detailed examination of the behavior inside the porous electrodes of the electrolyte concentration is done by distinguishing between the concentrations near the pore surface wall and volume elements away from the solid surface-electrolyte boundary. Relationship to the battery charging or discharging current and current density is performed allowing macroscopic overpotentials to be determined for each electrode. These are concentration overpotentials and their exact relationship to the battery potentials is developed carefully so that a rigorous basis is established. It is found that there are two overpotentials making up the negative electrode overpotential, due to the and ions. Similarly, there are two overpotentials making up the positive electrode overpotential, due to the and ions.

(Invited) Developing Electrodes for Solid Oxide Fuel Cells What I Learned from Anil Virkar about Designing High Performance Electrodes

The effects of various microstructural and material properties on the electrode overpotentials of solid oxide fuel cells (SOFC) were investigated. A review of the influence and sensitivity of porosity and pore structure on the effective gas diffusivity and resulting concentration polarization of electrodes is presented. The doping of Ni in the anode support as a means to improve redox cycling and stability was demonstrated. Composite electrode layers nearest to the electrolyte were studied with regard to microstructure and materials selection. In particular, the influence of the ionic conductivity of the electrolyte phase in the composite electrode on the electrode polarization was investigated. A fabrication method was developed that produced an electrolyte skeleton with improved particle-to-particle necking and yet extremely porous, that could subsequently be infiltrated with an electrocatalyst material. Applying and combining the various strategies outlined, highly efficient electrodes were developed and demonstrated for solid oxide fuel cells.