Electrode Kinetic Parameters Research Articles

Genuine differential voltammetry

A novel form of differential voltammetry is proposed, developed through the implicit anodic and cathodic current components of the experimentally accessible conventional net current measured in a voltammetric experiment. By employing basic mathematical modelling of an electrode reaction of a dissolved redox couple at a conventional, macroscopic electrode within the framework of the Butler-Volmer electrode kinetic model, the implicit anodic and cathodic current components of the net conventional current are clearly defined and can be estimated. Consequently, a novel form of differential current, calculated as the difference between anodic and cathodic implicit current components associated with a single potential of the voltammetric experiment, can be established. This differential current demonstrates remarkable characteristics in terms of electrode kinetics and analytical performance, particularly in cases involving fast, seemingly electrochemically reversible electrode processes. It holds promise to be analytically superior to the best-known differential voltammetric techniques so far (e.g., square-wave voltammetry), as well as provides a means for estimating the rate constants of very fast, apparently reversible electrode processes at macroscopic electrodes under mild experimental conditions (i.e., studied at slow potential scan rates). The practical implication of the novel methodology is significant: a simple linear sweep voltammogram of a quasi-reversible electrode reaction with unknown electrode kinetic parameters can be readily transformed into the novel type of differential voltammogram through a convolution procedure of the conventional net current, paving a new way for studying electrode processes by voltammetry.

Toward Stable Al Negative Electrodes of Aluminum-Ion Batteries: Kinetic Parameters and Electrode Structure.

Rechargeable aluminum-ion batteries have attracted significant attention as candidates for next-generation energy storage devices owing to their high theoretical capacity, safe performance, and abundance of raw materials. Al metal is the best option as the negative electrode, while its issues such as dendrite growth and corrosion accompanying hydrogen evolution in ionic liquid electrolyte have been seriously overlooked. Understanding the electrochemical mechanism of the surface evolution behavior of Al metal is a vital pathway for solving these issues. Kinetic parameters and electrode structure are the two key parameters that affect the surface evolution behavior of Al negative electrodes. Herein, the qualitative relationship between the kinetic parameters and surface evolution behavior of the Al negative electrode was established through a combination of in-situ optical technology and multi-physical field numerical simulation method. The key kinetic parameters, including ion concentration and transfer coefficient, exhibited different laws of influence on the surface evolution behavior, such as dendrite growth and corrosion. The electrochemical mechanism on the surface evolution was explored to guide the optimization design of Al-ion batteries. Based on the coupling design of the electrode structure and kinetic parameters, a highly stable porous aluminum structure composed of Al powder with a particle size of 100 μm was constructed to obtain highly stable and high-performance aluminum-ion batteries. This method provides new sight into the design of high-performance aluminum-ion batteries.

Dual Behavior of Dispersed Ni Nanoparticles for Hydrogen Evolution Reaction at the Interface of Ni/Alkaline Solution

The electrode kinetic parameters, that is, the interaction parameter (ɡ), fractional coverage (θ), and equilibrium constant (K), for the Frumkin adsorption isotherm in the Volmer step cannot be readily determined using conventional methods. These parameters for the Frumkin isotherm of H for the hydrogen evolution reaction (HER) in the Ni/0.1 M KOH (H2O and H2O + dispersed Ni nanoparticles) solutions were determined using the phase-shift method. The Frumkin isotherms of H are K = 9.8 × 10−4 exp(−5.7θ) mol−1 for the 0.1 M KOH (H2O) solution and K NPs = 1.2 × 10−4 exp(−3.5θ) mol−1 for the 0.1 M KOH (H2O + dispersed Ni NPs) solution. The dispersed Ni NPs behave as electrostatic shielding for the H adsorption in the Volmer step and as an electrocatalyst for the H2 evolution in the Tafel and/or Heyrovsky steps. The dual behavior of the dispersed Ni NPs in the HER was similar regardless of the weight of the dispersed Ni NPs. The electrostatic shielding behavior of the dispersed Ni NPs in the HER has been previously overlooked or missed. We hope that the dual behavior of dispersed NPs at the interfaces of electrocatalysts/solutions will be studied in more detail for their potential applications.

Effect of binary additives on performance of the undivided soluble-lead-redox-flow battery

Cycle-life of Soluble-Lead-Redox-Flow-Batteries (SLRFBs) is impacted due to formation of lead dendrites at anode and oxygen evolution at cathode. In this regard, addition of certain surfactants to the electrolyte helps preventing dendrite formation while adding fluoride salts reduces the rate of oxygen evolution reaction. Since SLRFB has a common electrolyte, understanding the combined effect of such additives on individual electrodes as well as on the overall SLRFB performance is desirable, which is lacking in the literature. Accordingly, in the present study, the combined effect of sodium lignosulfonate (SLS) and sodium fluoride (NaF) additives on the overall cell performance, individual electrodes, electrode kinetics, crystallographic phase formation, and surface morphology of electrodeposits is reported. The electrochemical data on SLRFB are analyzed in the light of electrode-kinetic parameters, namely limiting current-density, exchange current-density and Tafel-slope. The study reveals that adding NaF additive enhances the kinetics of Pb/Pb2+ and Pb2+/Pb4+ redox couples as compared to the pristine electrolyte or with SLS additive. The exchange current-density is higher with NaF additive as compared to NaF and SLS binary combined additive. It is also observed from cyclic voltammograms that the peak current decreases in the presence of binary additive indicating sluggish electrode kinetics. SEM images and galvanostatic charge–discharge studies suggest that binary additive results in uniform electrodeposit which improves the cycle-life of SLRFB.

Identification of Mechanistic Subtleties that Apply to Voltammetric Studies at Boron-Doped Diamond Electrodes

The α-[S2W18O62]4–/5– and α-[S2W18O62]5–/6– polyoxometalate (POM) reduction processes at boron-doped diamond (BDD) disk electrodes in acetonitrile (0.50 M [n-Bu4N][PF6]) have been investigated using large-amplitude Fourier transformed alternating current (FTAC) voltammetry. The origins of subtle differences in experimental data and simulated data modeled assuming the Butler–Volmer relationship with ion-paring implicitly included, planar diffusion and a uniform surface are considered. Parameters estimated are the apparent heterogeneous electron-transfer kinetics (kapp0′), apparent formal reversible potential (Eapp0′), and apparent charge transfer coefficient (αapp′). The electrode kinetic parameters, in contrast to theoretical predictions of the model employed, are dependent on frequency, POM concentration, and the data analysis method. Reasons for nonconformance to the model include the adsorption of POM on graphite-like sp2-bonded carbon impurities, limitations in the availability of charge carriers in BDD, and the method of incorporating ion pairing when slow electrode kinetics apply. Masking of the sp2 carbon-rich (edge) region of the BDD disk provided FTAC voltammetric data that complied much more closely with the simulated data. Nevertheless, data analysis still produces a concentration dependence in the estimated kapp0′ values, which is considered in terms of the assumption of an infinite number of charge carriers. Conclusions derived from this study are likely to be generally applicable to electrode kinetic investigations at BDD electrodes.

Stepwise Global Sensitivity Analysis of a Physics-Based Battery Model using the Morris Method and Monte Carlo Experiments

Physics-based battery models can be very complex and require careful experimental validation, but yield greater insights into the internal processes and their interactions than other cell modelling approaches. The complexity is associated with the large number of input parameters that (a) have varying degrees of identifiability, (b) can be constant or varying, and (c) appear in complex combinations with the model variables and each other. The current work studies this complexity by proposing a unique stepwise approach and purposefully addresses the computational cost associated with estimating these parameters. An initial set of 50 input parameters is reduced to only 8 highly influential parameters that can be subjected to parameter optimization. Elementary effects analysis using the Morris method is applied and demonstrates that the electrode kinetic parameters dominate the cell’s voltage response as simulated by the model. These influential parameters are subjected to variance-based sensitivity analysis using Monte Carlo experiments and Jansen’s formulae for variance decomposition. The first-order and total sensitivities during various modes of operation indicate that the charge transfer coefficients and effective exchange current densities have the most influence on the model error and should be subjected to further optimization. The model error’s sensitivity also reveals high parameter identifiability within subsets of the experimental data and indicates that some parameter values might be valid for longer timescales rather than shorter timescales. The proposed stepwise approach can be applied to any complex physics-based cell model regardless of the cell’s chemistry, format or form factor.

Unraveling Oxygen Electrocatalysis Mechanisms and Investigating the Role of Vulcan Carbon on a Thin Film Oxygen Deficient Perovskite La0.6Sr0.4CoO3- δ

Alkaline-based metal-air batteries require a low-resistance, bifunctional oxygen electrode to perform fast oxygen electrocatalysis during charging and discharging cycles. However, achieving good oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctionality has proven challenging. In this work, a perovskite-structured and oxygen-deficient oxide, La0.6Sr0.4CoO3- δ (LSCO), has been investigated as a model bifunctional thin-film oxygen electrode for alkaline metal-air cells. The rotating disk electrode (RDE) configuration in combination with common electrochemical techniques such as linear sweep voltammetry (LSV) and cyclic voltammetry (CV) were applied to characterize the behavior of the ORR and OER taking place on LSCO in 0.1 M KOH solution. The results show that the oxygen electrocatalysis process on LSCO in the alkaline media follows a multistep charge-transfer pathway. A physics-based, generalized electrochemical model, encompassing two sequential 2e- steps with HO2 - as an intermediate species and one parallel 4e- step, along with peroxide dissolution, has been established to account for the multi-step charge transfer behavior with very satisfactory results, yielding a series of important electrode kinetic parameters for the elementary reactions considered. After forming the base concept of oxygen electrocatalysis on the LSCO, the effect of the Vulcan carbon (XC-72R) mass ratios on the ORR/OER were also investigated and a synergistic effect between the perovskite-oxide and the XC-72 was observed to affect the reaction mechanism. Finally, the bifunctionality of the LSCO towards ORR was clearly elevated through the addition of a commercial, noble-metal 20% wt Pt/C, where even the slightest addition of the Pt/C dominated the ORR trending and the smallest amounts of LSCO trumped the OER characteristic profiles. Keywords: oxygen electrocatalysis; perovskite-oxide; rotating disk electrode, linear sweep voltammetry.

Does power ultrasound affect heterogeneous electron transfer kinetics?

Most of the observations seen in the application of power ultrasound in electrochemistry or also known as sonoelectrochemistry are due to enhanced mass-transport of electroactive species from the bulk solution to the electrode surface caused by efficient stirring, acoustic streaming and cavitation. However, fundamental studies on the effect of ultrasound on electrode kinetics i.e. on the electron-transfer are scarce. The main question still remains to be answered:Does power ultrasound affect heterogeneous electron transfer kinetics?This opinion paper discusses the effect of ultrasonic frequency and intensity upon the electrode kinetic parameters such as the half-wave potential (E1/2) and the apparent heterogeneous rate constant (ko). A few sonoelectrochemical studies have highlighted changes in half-wave potential and in apparent heterogeneous rate constant for both quasi-reversible and irreversible systems when the data were compared to silent conditions. These observations are thought to be due to the contribution of mass-transport and macroscopic temperature effects, as well as the continuous cleaning of the electrode surface caused by the collapse of high-energy cavitation bubbles and the production of high velocity jets of liquid. However, there still remains mechanistic controversy in assigning whether these findings could also be due to localised temperature increases, the contribution of sonolysis products or solely due to enhanced mass-transport at the electrode surface. Thus, the effect of stirring, macroscopic temperature and sonication time upon these electrode kinetic parameters is also shown to be important factors in comparing the validity of any sonoelectrochemical effects.

Integration of Heuristic and Automated Parametrization of Three Unresolved Two‐Electron Surface‐Confined Polyoxometalate Reduction Processes by AC Voltammetry

AbstractThe thermodynamic and electrode kinetic parameters that describe each of the three unresolved proton‐coupled two‐electron transfer processes of surface‐confined Keggin‐type phosphomolybdate, [PMo12O40]3− adsorbed onto glassy carbon electrode in 1.0 M H2SO4 have been elucidated by comparison of experimental and simulated AC voltammmetric data. Modelling of this problem requires the introduction of over 30 parameters, although this may be reduced to about half this number when intelligent forms of data analysis are introduced. Heuristic (i. e., an experimenter based trial and error method) and automated data optimization approaches are integrated in this very extensive parameter estimation exercise. However, obtaining a unique solution remains challenging for reasons that are outlined. In the final analysis and using the automated strategy, estimates of six reversible potentials, lower limits of the six electron transfer rate constants, the double layer capacitance, uncompensated resistance and surface coverage are reported, with others (such as the charge transfer co‐efficient) present in the model being unobtainable for reasons that are provided. The fit to experimental data using parameters obtained by automated data optimisation is excellent and slightly superior to that obtained by heuristic analysis. The parameters obtained by either method account for differences in shapes and current magnitudes of each of the overall two electron processes.

Modelling ac voltammetry with MECSim: facilitating simulation–experiment comparisons

Summary Here we introduce the Monash Electrochemistry Simulator (MECSim) software package that allows most aspects of ac voltammetry to be simulated when a single sine wave or a combination of sine waves are superimposed onto a dc ramp. The MECSim software and companion tool kits can be downloaded free of charge from http://www.garethkennedy.net/MECSim.html where there is also instructional documentation. Features accommodated in the simulation model include non-linear background capacitance, uncompensated resistance, Butler–Volmer and Marcus–Hush electron transfer, chemical reactions involving surface confined and solution phase species and stationary or rotating disc electrode mass transport with linear diffusion. Companion tool kits are also provided that allow Fourier transformed ac voltammograms with harmonic analysis to be generated along with other forms of data presentation. The MECSim format in combination with parameter optimisation tool kit also facilitates the implementation of sophisticated forms of experiment-theory comparisons needed to estimate the electrode kinetic and other parameters. MECSim software is computationally efficient and based on flexible code that can be used in cluster computing as well as on a single machine. Typical simulations take seconds to run on a laptop and parameter searches needed to tackle the inverse problem can be achieved efficiently. Capabilities of MECSim are illustrated in this article by comparing simulated results with those obtained experimentally.

Review on the Determination of Frumkin, Langmuir, and Temkin Adsorption Isotherms at Electrode/Solution Interfaces Using the Phase-Shift Method and Correlation Constants

This review article described the electrochemical Frumkin, Langmuir, and Temkin adsorption isotherms of over-potentially deposited hydrogen (OPD H) and deuterium (OPD D) for the cathodic H2 and D2 evolution reactions (HER, DER) at Pt, Ir, Pt-Ir alloy, Pd, Au, and Re/normal (H2O) and heavy water (D2O) solution interfaces. The Frum-kin, Langmuir, and Temkin adsorption isotherms of intermediates (OPD H, OPD D, etc.) for sequential reactions (HER, DER, etc.) at electrode/solution interfaces are determined using the phase-shift method and correlation constants, which have been suggested and developed by Chun et al. The basic procedure of the phase-shift method, the Frumkin, Lang-muir, and Temkin adsorption isotherms of OPD H and OPD D and related electrode kinetic and thermodynamic param-eters, i.e., the fractional surface coverage (0 ≤ θ ≤ 1) vs. potential (E) behavior (θ vs. E), equilibrium constant (K), interaction parameter (g), standard Gibbs energy (ΔGθ˚) of adsorption, and rate (r) of change of ΔGθ˚ with θ (0 ≤ θ ≤ 1), at the interfaces are briefly interpreted and summarized. The phase-shift method and correlation constants are useful and effective techniques to determine the Frumkin, Langmuir, and Temkin adsorption isotherms and related electrode kinetic and thermodynamic parameters (θ vs. E, K, g, ΔGθ˚, r) at electrode/solution interfaces.

Synthesis and electrochemical characterization of binary carbon supported Pd3Co nanocatalyst for oxygen reduction reaction in direct methanol fuel cells

Binary carbon supports are applied to make the membrane electrode assembly (MEA) of passive direct methanol fuel cells (PDMFCs) and their comprehensive electrochemical characterization is considered. Electrocatalytic properties for the oxygen reduction reaction (ORR) are evaluated using polarization curves and electrochemical impedance spectroscopy (EIS) in PDMFC. The best efficiency is obtained when the mass ratio of multi-walled carbon nanotubes (MWCNTs) and Vulcan XC-72R (VC) is 25:75. The results of the electrode kinetic parameters indicate that introduction of MWCNTs as a secondary support delivers high available surface area, good electronic conductivity, and fast ORR kinetics. In addition to the significant role of Pd3Co active surface area on kinetic of the system, the improvement of kinetic parameters is also associated with the decrease of activation energy for ORR on binary-support electrode resulting in a notable enhancement of kinetic parameters. An 8-h lifetime test is performed for the single cell to evaluate the durability in which the MEA is made using MWCNT/VC with the mass ratio of 25:75. The test results show that the mentioned ratio of MWCNT and VC support results in highest stability and durability.

New Low to Medium Temperature Electrolyte Separation Method and System for Alkaline Water Electrolysis

The a novel electrolysis technology was developed by Advanced Hydrogen Products is a patented method of maintaining separation of product gases (hydrogen and oxygen) by using fluid flow through porous electrodes rather than a gas impermeable membrane. This eliminates the need for any type of membrane. Eliminating the need for a membrane in alkaline electrolysis allows the device to operate at temperatures above 120 °C, where most ion conducting membranes would degrade and fail. Operating at higher temperatures reduces the anode and cathode overpotentials substantially. The reduction in overpotentials allows non-platinum group metals to be used, while increasing the electrical efficiency at comparable current densities. In addition, the device is operated at high pressure for electrochemical compression of the product gas. The method by which separation occurs is by flow of the alkaline electrolyte solution through the porous cathode and anode electrodes where hydrogen and oxygen gases are generated. The product gases are then separated from the electrolyte that is re-circulated back into the electrolyzer stack. The new method has advantages over traditional methods. By not having a membrane it is able to operate at a much higher temperature than current membrane separators allow. Not having a membrane is also beneficial since the membranes are costly and more prone to failure than other parts. Figure 1 A conceptual illustration of the electrode compared to standard electrode designs Immobilized electrolytes are able to operate at higher temperatures, but have a higher resistance than the new method. At higher temperatures with higher catalytic activity, Ohmic resistances become more important. In comparison, for low temperature cells, which typically use platinum group metals, the incredibly thin polymer type membranes offer a lower resistance. The newmethod takes advantage of both higher catalytic activity at high temperatures, and lower Ohmic resistance than immobilized electrolytes. The new electrolyzer method also reduces the Ohmic losses due to bubbles. Note that additionally, the electrolyte conductivity is also increased by not having a membrane. The pure electrolyte has a conductivity of at least 3 times greater than most immobilized electrolytes. The initial tests at low temperatures have been shown that gas crossover was low enough that the oxygen product side failed to ignite when given an ignition source and that hydrogen was produced due to ignition of the hydrogen product side. Based on the increase in exchange current density, resulting from the increased temperature, the hydrogen production method should achieve a current density of 1A/cm2 at 1.5V and 2A/cm2 at 1. 75 V[1]. A high temperature bipolar plate model is currently being built. The current state of the art in electrolysis is limited by the catalysts and operating temperature of the membrane. Alkaline electrolysis has a long history, and as such is generally the most cost effective of electrolysis methods. Although it has lower current density, it has much lower material costs, making it the most effective choice in water electrolysis. In the area of renewable energy integration and grid-stabilization, low capital cost is very important for cost effective hydrogen production. Most current separation membranes are unable to operate above 100 °C. Investigation into higher temperature membranes has been the subject of research since the 1970’s (Fig. 2). As of yet, no membrane has been developed that is cost effective above 100 °C. This results in choice between using a larger amount of lower cost materials such as nickel, or a smaller amount of higher cost materials such as platinum. By eliminating the membrane, the operating temperature can be increased and dramatically improve the efficiency of the system. An increase in the operating temperature from 80 °C to 240 °C results in the exchange current density of nickel that is comparable to platinum. Significant savings will result from efficiently producing high current-densities utilizing non-precious metals. [1] Miles et al. “Effect of Temperature on Electrode Kinetic Parameters for Hydrogen and Oxygen Evolution Reactions on Nickel Electrodes in Alkaline Solutions”, J. Electrochem. Soc.123, 332-336 (1976). Figure 1

Performance of MIEC Cathodes in SOFC Stacks Evaluated by Means of FEM Modeling

Solid oxide fuel cells (SOFC) are connected in series to stacks by metal interconnectors (MIC). Hereby, the potentially high performance of anode-supported cells (ASC) is significantly reduced. [1,2]. Conclusively, gas diffusion polarisation at the mixed conducting cathode contributes close to the sum of all ohmic losses to the overall polarization, both controlling stack performance.In order to investigate the matter further, a 2D FEM repeat unit model was developed, which accounts to ohmic and polarisation loss on a stack level [3]. In the model the physical processes i) gas diffusion in the porous electrodes, ii) electric /ionic conduction in the electrodes and electrolyte as well as iii) the electrochemical electrode reactions are incorporated. Electrode microstructure is implemented via 3D reconstruction of FIB-tomography images [5,6]. Electrode kinetic parameters are determined via EIS evaluations [4]. Performance predicted by the model was validated with the help of current/voltage-characteristics measured on high performance anode supported cells.The model calculations demonstrate the interdependence of cathode material parameters (thickness, porosity, conductivity, electrode kinetics) and MIC-design, and widen the understanding on their influence on stack performance. The results show i) that an optimal MIC-design depends on the cathode material parameters and ii) a well-chosen cathode thickness increases the overall power output.[1] L. Blum, W. A. Meulenberg, H. Nabielek, R. Steinberger-Wilckens, Worldwide SOFC Technology Overview and Benchmark, International Journal of Applied Ceramic Technology2 pp. 482-492 (2005).[2] M. Kornely, A. Leonide, A. Weber, E. Ivers-Tiffée, Journal of Power Sources 196 (17), pp. 7209-7216 (2011).[3] H. Geisler, M. Kornely, A. Weber, E. Ivers-Tiffée, ECS Trans. 57, pp. 2871-2881 (2013).[4] A. Leonide, Y. Apel, E. Ivers-Tiffée, ECS Trans. 19, pp. 81-109 (2009)[5] J. Joos, T. Carraro, A. Weber, E. Ivers-Tiffée, J. Power Sources 196, pp. 7302-7307 (2011).[6] J. Joos, M. Ender, I. Rotscholl, N. H. Menzler, E. Ivers-Tiffée, J. Power Sources 246, pp.819-830 (2014)

Copper–iron–molybdenum mixed oxides as efficient oxygen evolution electrocatalysts

Ternary Cu, Fe and Mo mixed oxides having a nominal compositional formula, CuxFe2-x(MoO4)3 (0 ≤ x ≤ 1.5), have been prepared by a co-precipitation method at pH ≈ 2 and characterized by FT-IR, XRD, XPS, TEM and anodic polarization techniques for use as electrocatalysts for the oxygen evolution reaction (OER) in alkaline solutions. The crystallites of oxides with x ≤ 1 have the monoclinic crystal structure. The OER study shows that replacement of Fe in the Fe2(MoO4)3 matrix by 0.25-1.0 mol Cu increases the apparent electrocatalytic activity. However, 1.5 mol Cu-addition is detrimental to the OER activity. At E = 1.51 V (vs. RHE) in 1 M KOH, the catalytic activity of the oxide with x = 1 was approximately 50 times the activity of the base oxide (i.e. Fe2(MoO4)3). The Tafel slope of oxides with 0.25 ≤ x ≤ 1.5 ranged between 31 and 37 mV. The reaction order of OH(-) concentration was nearly unity for oxides with x = 0.25 and 1.5 and it was ∼2 for oxides with x = 0.5, 0.75, and 1.0. Suitable reaction mechanisms consistent with the electrode kinetic parameters have also been proposed.

Nanocarbon Paste Electrodes

AbstractThe electrochemical behaviour of carbon paste electrodes prepared using nanocarbon and mineral oil was investigated and the results contrasted with different carbon and carbon pastes electrodes. The composition of carbon paste was studied by performing cyclic voltammetry performed in 0.1 M KCl solution in the presence of 4.0 mM Ru(NH3)6Cl3, a well‐characterized redox system commonly used to test the electrode behaviour. After optimisation of the paste composition, the sensors chosen were tested for the analysis and characterization of three different systems: Ru(NH3)63+/2+, FcCH2OH/FcCH2OH+ and acetaminophen. The ability to obtain high quality voltammetry from the nanocarbon electrode was demonstrated and simulation of the voltammetry allowed the extraction of electrode kinetic parameters with high precision.

New Approach to Electrode Kinetic Measurements in Square-Wave Voltammetry: Amplitude-Based Quasireversible Maximum

The influence of the potential pulse height of square-wave voltammetry (SWV) (i.e., the SW amplitude) is studied for a variety of quasireversible electrode mechanisms, including a simple solution-phase electrode reaction at a planar or spherical electrode, a solution phase electrode reaction coupled with a reversible follow-up chemical reaction, and a diffusionless surface confined electrode reaction. The electrode kinetics of all the electrode mechanisms depends critically on the SW amplitude, and the quasireversible kinetic region is a function of both frequency-related electrode kinetic parameters and the SW amplitude. Thus, a novel methodology for electrode kinetics measurements is proposed by altering the SW amplitude only, at a fixed frequency of the SW potential modulation, that is, at a constant scan rate of the voltammetric experiment. Electrode kinetic measurements at a constant SW frequency are of exceptional importance especially when complex electrode mechanisms are studied, which depend on several frequency-related kinetic parameters. The electrode kinetic measurements are based on a novel feature termed the "amplitude-based quasireversible maximum", manifested as a parabolic dependence of the amplitude-normalized net SW peak current versus the SW amplitude. The position of the amplitude-based quasireversible maximum depends on the standard rate constant of the electrode reaction, enabling estimation of this important kinetic parameter in a simple and fast procedure. The novel quasireversible maximum is attributed to all studied electrode mechanisms, implying that it is a general feature of most electrode mechanisms under conditions of SWV.

Cross-linked luminescent films via electropolymerization of multifunctional precursors for highly efficient electroluminescence

To fabricate stable organic light-emitting diodes, a cross-linked network that firmly fixes the position of the chromophore is an ideal structure, because quenching caused by aggregation and/or phase separation effects can be effectively restrained in such robust films. Herein, in situ electropolymerization (EP) of fluorene-based precursors containing multi-electroactive carbazole units (multi-functionality) is utilized to construct highly cross-linked, smooth and compact luminescent films for highly efficient and stable electroluminescent devices. Cyclic voltammetry (CV), UV and atomic force microscopy (AFM) studies of the series of precursors with varied functionality (2, 4 and 8) reveal that increasing the functionality of the EP precursor can significantly increase the deposition rate, cross-linking degree and packing density as well as the luminous efficiency and stability of the fabricated EP films. The electrode kinetic parameters, determined by CV and chronocoulometry (CC), indicate that such improvements in EP film properties could be attributed to the enhanced interfacial electron-transfer rate. These observations could potentially offer a new approach to adjust the microstructures of EP films and provide a simple way of enhancing the performance of organic luminescent devices.

Development and electrochemical studies of membrane electrode assemblies for polymer electrolyte alkaline fuel cells using FAA membrane and ionomer

This paper provides guidelines on the fabrication and operation of alkaline fuel cells using quaternary ammonium hydroxide anion exchange membrane (FAA-3 – fumatech), and includes a discussion of the electrode kinetic parameters based on the composition of the catalytic layer. The best peak power density performance, 223 mW cm−2 was obtained with an electrode formed from Pt/C, 0.8 mgPt cm−2 and 25% of FAA-3 ionomer in the catalyst layer for both the cathode and the anode. We demonstrate that the platinum loading can be lowered to values close to 0.5 mgPt cm−2, without appreciably affecting the fuel cell performance characteristics. The experimental fuel cell data were analyzed using theoretical models of the electrode structure and its kinetics studied over the assembling parameters. We show that most of the electrode systems present limiting currents, with some showing diffusion limitations in the gas channels and/or in the ionomer film covering the catalyst nanoparticles. We also provide some general strategies using Tafel slopes on evaluating the ionomer interaction with the electrode kinetics for the oxygen reduction reaction.

Estimation of electrode kinetic and uncompensated resistance parameters and insights into their significance using Fourier transformed ac voltammetry and e-science software tools

In transient forms of voltammetry, quantitative analysis of electrode kinetics and parameters such as uncompensated resistance (Ru) and double layer capacitance (Cdl) are usually undertaken by comparing experimental and simulated data. Commonly, the skill of the experimentalist is heavily relied upon to decide when a good fit of simulated to experimental data has been achieved. As an alternative approach, it is now shown how data analysis can be based on implementation of e-science software tools. Previously, a standard heuristic data analysis approach applied to the oxidation of ferrocene in acetonitrile (0.1M Bu4NPF6) at a glassy carbon electrode using higher order harmonics available in Fourier transformed ac voltammetry implied that the heterogeneous charge transfer rate constant k0 is ⩾0.25cms−1 with the charge transfer coefficient (α) lying in the range of 0.25–0.75. Application of e-science software tools to the same data set allows a more meaningful understanding of electrode kinetic data to be provided and also offers greater insights into the sensitivity of the IRu (Ohmic drop) on these parameters. For example, computation of contour maps based on a sweep of two sets of parameters such as k0 and Ru or α and k0 imply that α is 0.50±0.05 and that k0 lays in the range 0.2–0.4cms−1 with Ru around 130Ohm. Quantitative evaluation of k0, α and Ru for the quasi-reversible [Fe(CN)6]3-+e⇌[Fe(CN)6]4- process at a glassy carbon electrode in aqueous media is also facilitated by use of e-science software tools. In this case, when used in combination with large amplitude Fourier transformed ac voltammetry, it is found for each harmonic that k0 for the electrode process lies close to 0.010cms−1, α is 0.50±0.05 and Ru is ⩽10Ohm.