The Experts below are selected from a list of 1842 Experts worldwide ranked by ideXlab platform
Richard G Compton - One of the best experts on this subject based on the ideXlab platform.
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Single entity electrochemistry and the electron transfer Kinetics of hydrazine oxidation
Nano Research, 2021Co-Authors: Ruiyang Miao, Lidong Shao, Richard G ComptonAbstract:The mechanism and Kinetics of the electro-catalytic oxidation of hydrazine by graphene oxide platelets randomly decorated with palladium nanoparticles are deduced using single particle impact electrochemical measurements in buffered aqueous solutions across the pH range 2–11. Both hydrazine, N2H4, and protonated hydrazine N2H5+ are shown to be electroactive following Butler-Volmer Kinetics, of which the relative contribution is strongly pH-dependent. The negligible interconversion between N2H4 and N2H5+ due to the sufficiently short timescale of the impact voltammetry, allows the analysis of the two electron transfer rates from impact signals thus reflecting the composition of the bulk solution at the pH in question. In this way the rate determining step in the oxidation of each specie is deduced to be a one electron step in which no protons are released and so likely corresponds to the initial formation of a very short-lived radical cation either in solution or adsorbed on the platelet. Overall the work establishes a generic method for the elucidation of the rate determining electron transfer in a multistep process free from any complexity imposed by preceding or following chemical reactions which occur on the timescale of conventional voltammetry.
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an experimental comparison of the marcus hush and butler volmer descriptions of electrode Kinetics applied to cyclic voltammetry the one electron reductions of europium iii and 2 methyl 2 nitropropane studied at a mercury microhemisphere electrode
Chemical Physics Letters, 2011Co-Authors: Martin C Henstridge, Yijun Wang, Juan G Limonpetersen, Eduardo Laborda, Richard G ComptonAbstract:Abstract We present a comparative experimental evaluation of the Butler–Volmer and Marcus–Hush models using cyclic voltammetry at a microelectrode. Numerical simulations are used to fit experimental voltammetry of the one electron reductions of europium (III) and 2-methyl-2-nitropropane, in water and acetonitrile, respectively, at a mercury microhemisphere electrode. For Eu (III) very accurate fits to experiment were obtained over a wide range of scan rates using Butler–Volmer Kinetics, whereas the Marcus–Hush model was less accurate. The reduction of 2-methyl-2-nitropropane was well simulated by both models, however Marcus–Hush required a reorganisation energy lower than expected.
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An experimental comparison of the Marcus–Hush and Butler–Volmer descriptions of electrode Kinetics applied to cyclic voltammetry. The one electron reductions of europium (III) and 2-methyl-2-nitropropane studied at a mercury microhemisphere electrode
Chemical Physics Letters, 2011Co-Authors: Martin C Henstridge, Yijun Wang, Eduardo Laborda, Juan G. Limon-petersen, Richard G ComptonAbstract:Abstract We present a comparative experimental evaluation of the Butler–Volmer and Marcus–Hush models using cyclic voltammetry at a microelectrode. Numerical simulations are used to fit experimental voltammetry of the one electron reductions of europium (III) and 2-methyl-2-nitropropane, in water and acetonitrile, respectively, at a mercury microhemisphere electrode. For Eu (III) very accurate fits to experiment were obtained over a wide range of scan rates using Butler–Volmer Kinetics, whereas the Marcus–Hush model was less accurate. The reduction of 2-methyl-2-nitropropane was well simulated by both models, however Marcus–Hush required a reorganisation energy lower than expected.
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An experimental comparison of the Marcus–Hush and Butler–Volmer descriptions of electrode Kinetics applied to cyclic voltammetry. The one electron reductions of europium (III) and 2-methyl-2-nitropropane studied at a mercury microhemisphere electrode
Chemical Physics Letters, 2011Co-Authors: Martin C Henstridge, Yijun Wang, Eduardo Laborda, Juan G. Limon-petersen, Richard G ComptonAbstract:We present a comparative experimental evaluation of the Butler-Volmer and Marcus-Hush models using cyclic voltammetry at a microelectrode. Numerical simulations are used to fit experimental voltammetry of the one electron reductions of europium (III) and 2-methyl-2-nitropropane, in water and acetonitrile, respectively, at a mercury microhemisphere electrode. For Eu (III) very accurate fits to experiment were obtained over a wide range of scan rates using Butler-Volmer Kinetics, whereas the Marcus-Hush model was less accurate. The reduction of 2-methyl-2-nitropropane was well simulated by both models, however Marcus-Hush required a reorganisation energy lower than expected. © 2011 Elsevier B.V. All rights reserved
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A comparison of Marcus–Hush vs. Butler–Volmer electrode Kinetics using potential pulse voltammetric techniques
Journal of Electroanalytical Chemistry, 2011Co-Authors: Eduardo Laborda, Martin C Henstridge, Ángela Molina, Francisco Martínez-ortiz, Richard G ComptonAbstract:Abstract Simulated voltammograms obtained by employing Butler–Volmer (BV) and Marcus–Hush (MH) models to describe the electrode Kinetics are compared for commonly used potential pulse techniques: chronoamperometry, Normal Pulse Voltammetry, Differential Multi Pulse Voltammetry, Square Wave Voltammetry and Reverse Pulse Voltammetry. A comparison between both approaches is made as a function of the heterogeneous rate constant, the electrode size, the applied potential and the electrochemical method, establishing the conditions in which possible differences might be observed. The effect of these differences in the extraction of kinetic parameters, diffusion coefficients and electrode radii are examined, and criteria are given to detect possible deviations of the experimental system from Butler–Volmer Kinetics from the behaviour of the chronoamperometric limiting current. The Butler–Volmer model predicts the appearance of an anodic peak in Reverse Pulse Voltammetry for irreversible processes and a peak split of differential pulse voltammograms for quasireversible processes with a value of the transfer coefficient very different from 0.5 (smaller than 0.3 for a reduction process). These striking phenomena are studied by using the Marcus–Hush approach, which also predicts the anodic peak for slow electrode reactions in Reverse Pulse Voltammetry but not the split of the curve in differential pulse techniques.
Martin Z. Bazant - One of the best experts on this subject based on the ideXlab platform.
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Thermodynamic stability of driven open systems and control of phase separation by electro-autocatalysis
Faraday discussions, 2017Co-Authors: Martin Z. BazantAbstract:Motivated by the possibility of electrochemical control of phase separation, a variational theory of thermodynamic stability is developed for driven reactive mixtures, based on a nonlinear generalization of the Cahn–Hilliard and Allen–Cahn equations. The Glansdorff–Prigogine stability criterion is extended for driving chemical work, based on variations of nonequilibrium Gibbs free energy. Linear stability is generally determined by the competition of chemical diffusion and driven autocatalysis. Novel features arise for electrochemical systems, related to controlled total current (galvanostatic operation), concentration-dependent exchange current (Butler–Volmer Kinetics), and negative differential reaction resistance (Marcus Kinetics). The theory shows how spinodal decomposition can be controlled by solo-autocatalytic charge transfer, with only a single faradaic reaction. Experimental evidence is presented for intercalation and electrodeposition in rechargeable batteries, and further applications are discussed in solid state ionics, electrovariable optics, electrochemical precipitation, and biological pattern formation.
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Li Intercalation into Graphite: Direct Optical Imaging and Cahn–Hilliard Reaction Dynamics
The journal of physical chemistry letters, 2016Co-Authors: Yinsheng Guo, Martin Z. Bazant, Raymond B. Smith, Dmitri K. Efetov, Junpu Wang, Philip Kim, Louis E. BrusAbstract:Lithium intercalation into graphite is a critical process in energy storage technology. Studies of Li intercalation Kinetics have proved challenging due to structural and phase complexity, and sample heterogeneity. Here we report direct time- and space-resolved, all-optical measurement of Li intercalation. We use a single crystal graphite electrode with lithographically defined disc geometry. All-optical, Raman and reflectance measurements distinguish the intrinsic intercalation process from side reactions, and provide new insight into the microscopic intercalation process. The recently proposed Cahn–Hilliard reaction (CHR) theory quantitatively captures the observed phase front spatial patterns and dynamics, using a two-layer free-energy model with novel, generalized Butler–Volmer Kinetics. This approach unites Cahn–Hilliard and electrochemical Kinetics, using a thermodynamically consistent description of the Li injection reaction at the crystal edge that involves a cooperative opening of graphene planes...
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Charge transfer Kinetics at the solid–solid interface in porous electrodes
Nature Communications, 2014Co-Authors: Peng Bai, Martin Z. BazantAbstract:Interfacial charge transfer is widely assumed to obey the Butler–Volmer Kinetics. For certain liquid–solid interfaces, the Marcus–Hush–Chidsey theory is more accurate and predictive, but it has not been applied to porous electrodes. Here we report a simple method to extract the charge transfer rates in carbon-coated LiFePO_4 porous electrodes from chronoamperometry experiments, obtaining curved Tafel plots that contradict the Butler–Volmer equation but fit the Marcus–Hush–Chidsey prediction over a range of temperatures. The fitted reorganization energy matches the Born solvation energy for electron transfer from carbon to the iron redox site. The Kinetics are thus limited by electron transfer at the solid–solid (carbon-Li_ x FePO_4) interface rather than by ion transfer at the liquid–solid interface, as previously assumed. The proposed experimental method generalizes Chidsey’s method for phase-transforming particles and porous electrodes, and the results show the need to incorporate Marcus Kinetics in modelling batteries and other electrochemical systems. Electrochemical Kinetics are usually described by the Butler–Volmer equation. Bai and Bazant propose a method to extract reaction rates for porous electrodes from experiments and show the necessity of using Marcus charge transfer theory in place of the conventional Kinetics.
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Phase Separation Dynamics in Isotropic Ion-Intercalation Particles
SIAM Journal on Applied Mathematics, 2014Co-Authors: Yi Zeng, Martin Z. BazantAbstract:Lithium-ion batteries exhibit complex nonlinear dynamics, resulting from diffusion and phase transformations coupled to ion-intercalation reactions. Using the recently developed Cahn--Hilliard reaction (CHR) theory, we investigate a simple mathematical model of ion intercalation in a spherical solid nanoparticle, which predicts transitions from solid-solution radial diffusion to two-phase shrinking-core dynamics. This general approach extends previous lithium-ion battery models, which either neglect phase separation or postulate a spherical shrinking-core phase boundary, by predicting phase separation only under appropriate circumstances. The effect of the applied current is captured by generalized Butler--Volmer Kinetics, formulated in terms of diffusional chemical potentials, and the model consistently links the evolving concentration profile to the battery voltage. We examine sources of charge/discharge asymmetry, such as asymmetric charge transfer and surface “wetting" by ions within the solid, which ...
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Boundary Layer Analysis of Membraneless Electrochemical Cells
Journal of The Electrochemical Society, 2013Co-Authors: William A. Braff, Cullen R. Buie, Martin Z. BazantAbstract:A mathematical theory is presented for the charging and discharging behavior of membraneless electrochemical cells that rely on slow diffusion in laminar flow to separate the half reactions. Ion transport is described by the Nernst-Planck equations for a flowing quasi-neutral electrolyte with heterogeneous Butler-Volmer Kinetics. Analytical approximations for the current-voltage relation and the concentration and potential profiles are derived by boundary layer analysis (in the relevant limit of large Peclet numbers) and validated against finite-element numerical solutions. Both Poiseuille and plug flows are considered to describe channels of various geometries, with and without porous flow channels. The tradeoff between power density and reactant crossover and utilization is predicted analytically. The theory is applied to the membrane-less Hydrogen Bromine Laminar Flow Battery and found to accurately predict the experimental and simulated current-voltage data for different flow rates and reactant concentrations, during bothcharginganddischarging.Thisestablishestheutilityofthetheorytounderstandandoptimizetheperformanceofmembrane-less
Fritz H. Bark - One of the best experts on this subject based on the ideXlab platform.
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Diffusion-migration transport in a system with Butler-Volmer Kinetics, an exact solution
Electrochimica Acta, 1995Co-Authors: Artjom V. Sokirko, Fritz H. BarkAbstract:Abstract Steady one-dimensional electrolysis of a metal salt in a system with a supporting electrolyte is considered. The electrolyte in the system investigated is made up of three ionic species, one of which takes part in the electrode reactions. Attention is restricted to the quite common cases where the transfer coefficient in the Butler-Volmer law for the electrode Kinetics is 1 2 . For reasons of algebriac simplicity, the main part of the paper deals with the special case with two species of cations of charge numbers 2 and 1, respectively, and one species of anions of charge number 1. However, all results are easily generalized to any set of charge numbers. In the special case of a binary electrotype, an exact explicit simple expression is computed for the polarizarion curve. Also the drops in ohmic potential, concentration overpotential in the electrolyte and the surface overpotentials. are computed as functions of the electric current density. In the general case with three ionic species, an exact expression for the polarization curve is given in implicit form. In the limiting case of the polarization curve and the aforementioned parts of the difference in potential between the electrodes. For the diffusion layer configuration, and explicit expression for the polarization curve is computed for a system with arbitrary charge numbers and a more general form of the Butler-Volmer law.
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Properties of polarization curves for electrochemical cells described by Butler-Volmer Kinetics and arbitrary values of the transfer coefficient
Electrochimica Acta, 1995Co-Authors: Yurij I. Kharkats, Artjom V. Sokirko, Fritz H. BarkAbstract:Theoretical investigation of potentiostatic electrolysis of a metallic salt in three component electrolyte solution was carried out for a cell consisting of two identical parallel electrodes. Analytical and numerical results are given for polarization curves for electrochemical cells with arbitrary values of trans- fer coefficient LY and exchange current density. Theoretical analysis of the electrodiffusion problem, based on an exact solution of the Nernst-Planck equations with boundary conditions of Butler-Volmer type, led to a formula for the polarization curve that is similar to the Tafel equation but with an effective transfer coefficient αeff = a(l - α). It was shown that, under certain conditions, the polarization curve can have two inflection points.
Shinichi Sawada - One of the best experts on this subject based on the ideXlab platform.
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solid polymer electrolyte water electrolysis systems for hydrogen production based on our newly developed membranes part i analysis of voltage current characteristics
Progress in Nuclear Energy, 2008Co-Authors: Shinichi Sawada, Tetsuya Yamaki, T Maeno, Masaharu Asano, Akihiro Suzuki, Takayuki Terai, Yasunari MaekawaAbstract:Abstract A new solid polymer electrolyte water electrolysis system was constructed using an original proton exchange membrane (PEM). The highly proton-conductive PEM was prepared by the γ-ray-induced post-grafting of styrene into a crosslinked-polytetrafluoroethylene (PTFE) film and subsequent sulfonation. The water vapor to be electrolyzed was controlled at a constant relative humidity and introduced into the cell at different temperatures up to 80 °C. As the cell voltage was increased, the current became higher; the maximum current was 50 mA/cm 2 at 2.5 V at a temperature of 80 °C, corresponding to a hydrogen production rate of 0.38 mL/min cm 2 in the normal state (25 °C, 1 atm). The voltage–current characteristics were analyzed with a theoretical model based on Butler–Volmer Kinetics for electrodes and transport resistance through the PEM. This analysis revealed that the anode exchange current density and interfacial resistance determined the electrolysis performance.
Vikram Deshpande - One of the best experts on this subject based on the ideXlab platform.
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The initiation of void growth during stripping of Li electrodes in solid electrolyte cells
Journal of Power Sources, 2021Co-Authors: Ss Shishvan, Norman A. Fleck, Vikram DeshpandeAbstract:Abstract We analyse the initiation of void growth in the Li electrode during the stripping phase of an Li-ion cell with a solid (ceramic) electrolyte. We first show that standard Butler-Volmer Kinetics fails to predict the observed void formation. This motivated us to recognise that void initiation/growth involves power-law creep of the Li electrode that is linked to the motion of dislocations. We show, via thermodynamic considerations, that dislocations significantly affect the interface Kinetics and use variational principles to develop a modified form of Butler-Volmer Kinetics for the interface flux that is associated with a deforming Li electrode. Numerical solutions are presented for the coupled flux of Li + in a single-ion conductor solid electrolyte and the associated creep deformation of the Li electrode for an imposed stripping current. This involves solution of a Laplace equation for flux in the electrolyte and the nonlinear Stokes flow equations for a power-law creeping solid in the electrode. These two domains are coupled together via the modified Butler-Volmer relation. The calculations predict that an increasing stack pressure needs to be exerted with increasing cell current to avoid the initiation of void growth and are in excellent quantitative agreement with measurements for an Li/LLZO/Li cell.
