Heterogeneous Electron Transfer Kinetics Research Articles

Global kinetic analysis of cyclic voltammograms at a spherical electrode

The global method for analyzing electrochemical processes controlled by diffusion and by the kinetics of heterogeneous electron transfer is redeveloped or application to electrodes haveing a spherical geometry. Heretofore, the method has been restricted to experiments in which plannar diffusion is the sole mode of transport to the electrode surface. The global method is based on a three-dimensional concept and has the advantage of using all of the data available from a voltammogram to measure the heterogeneous charge-transfer rate constant, the reversible halfwave potential, the diffusion coefficient, and the charge-transfer coefficient. Cyclic voltammetry of 2-methyl-2-nitropropane reduction at a mercury sphere is reported. The parameters measured by spherical global analysis are concordant and in excellent agreement with literature values.

Correlation of heterogeneous electron transfer rate with structural change and environmental factors in the two-electron oxidation of W 2(CO) 8(μ-SBz) 22−

Oxidation of the thiolate-bridged tungsten(0) dimer, W 2(CO) 8(μ-SBz) 2 2−, occurs by transfer of two electrons at the same potential. The process appears paradoxical because the reaction exhibits facile heterogeneous kinetics despite large changes in structure and formation of a metal-metal bond within the W 2S 2 core. However, the electrode reaction actually consists of overlapping one-electron transfers of which the second is slightly more favorable than the first; e.g., W 2(CO) 8(μ-SBz) 2 2− ⇌ W 2(CO) 8(μ-SBz) 2− 2+e 2− (at E 1 o') and W 2(CO) 8(μ-SBz) 2 2− ⇌ W 2(CO) 8(μ-SBz) 2 + e 2− (at E o' 2) [ E 1 o' = −0.859 and E 2 o' = −0.881 V vs. Ag/Ag + (0.01 M)]. This conclusion is supported by a qualitative Marcus theory analysis of the heterogeneous electron transfer kinetics, which indicates that acceptable values of k s,h are obtained if the structural and solvational changes required for two-electron transfer are partitioned equally between the one-electron steps, and by digital simulations, which give a good fit to experimental curves if it is assumed that the one-electron transfer kinetics are facile and Δ E o' = −0.022 V. Electron transfer takes place to and from a metal-metal antibonding orbital whose energy varies significantly with the angle of the W-S-W bridge. Thus, the structural changes that accompany the first electron transfer reduce the thennodynamic requirements of the second and lead to transfer of two electrons at the same potential. The heterogeneous electron transfer kinetics are less sensitive to solvent properties than predicted by the dielectric continuum model of the Marcus theory, but k s,h decreases from 2 × 10 −2 to 6 × 10 −4 cm s −1 as electrode material is changed in the following order: Hg/Au ⪢ glassy C ⪢ Au ⪢ Pt. A similar sequence of electrode material dependence is exhibited by other electrochemical reactions accompanied by large structural change; possible reasons for this behavior are discussed.

Quantitative correlations of heterogeneous electron-transfer kinetics with surface properties of glassy carbon electrodes

Raman spectra, capacitance (C{degree}), phenanthrenequinone (PQ) adsorption, and heterogeneous electron-transfer rates for ferri/ferrocyanide, dopamine, and ascorbic acid were monitored after fracturing, polishing, and laser activating glassy carbon electrodes (GC-30). Alterations in the Raman spectrum indicate changes in carbon microstructure, while PQ adsorption and C{degree} provide measures of microscopic surface area. It was observed that polishing caused minor changes in carbon disorder and microscopic surface area, but the polished surface had poor electron-transfer kinetics. A k{degree} of above 0.5 cm s{sup {minus}1} was observed for Fe(CN){sub 6} for the first time. A clean, fractured GC surface exhibited a k{degree} of 0.5 cm s{sup {minus}1} and was very active toward ascorbic acid and dopamine oxidation. The results are consistent with a surface-cleaning mechanism for laser activation, accompanied by little or no observable surface restructuring or roughening.

On the form of the single coulostatic decay curve

A plot of ΔE/Δt 1/2 versusE as obtained from a single coulostatic decay curve resembles a classical voltammogram. Calculations by digital simulation show that for a reversible electrode reaction the coulostatic “voltammogram” is shifted to potentials slightly negative of the reversible half-wave potential. Analysis of published data for the reduction of aqueous Pb(II) at a mercury electrode shows that the results were affected by heterogeneous electron transfer kinetics.

Fast-scan cyclic voltammetry as a method to measure rapid heterogeneous electron-transfer kinetics

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFast-scan cyclic voltammetry as a method to measure rapid heterogeneous electron-transfer kineticsDavid O. Wipf, Eric W. Kristensen, Mark R. Deakin, and R. Mark. WightmanCite this: Anal. Chem. 1988, 60, 4, 306–310Publication Date (Print):February 15, 1988Publication History Published online1 May 2002Published inissue 15 February 1988https://doi.org/10.1021/ac00155a006RIGHTS & PERMISSIONSArticle Views3400Altmetric-Citations217LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (708 KB) Get e-Alerts Get e-Alerts

Solvent effects of the heterogeneous electron-transfer kinetics of bacteriochlorophyll a and bacteriopheophytin a at platinum and gold electrodes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSolvent effects of the heterogeneous electron-transfer kinetics of bacteriochlorophyll a and bacteriopheophytin a at platinum and gold electrodesTherese M. Cotton and Randall L. HealdCite this: J. Phys. Chem. 1987, 91, 14, 3891–3898Publication Date (Print):July 1, 1987Publication History Published online1 May 2002Published inissue 1 July 1987https://doi.org/10.1021/j100298a032RIGHTS & PERMISSIONSArticle Views58Altmetric-Citations7LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts

Heterogeneous electron transfer kinetics for a variety of organic electrode reactions at the mercury-acetonitrile interface using either tetraethylammonium perchlorate or tetraheptylammonium perchlorate electrolyte

The electrode reactions of 26 compounds have been studied by cyclic voltammetry at mercury electrodes using acetonitrile as solvent and either 0.10 M tetraethylammonium perchlorate (TEAP) or 0.10 M tetra-n-heptylammonium perchlorate (THpAP) as supporting electrolyte. The standard potentials of the compounds ranged from −0.07 to −2.90 V vs. the Ag/AgNO 3 reference electrode. In several of the redox couples studied, the charge on the ionic partner was localized on a few atoms which is expected to cause the outer reorganization energy to be high, giving small electron transfer rate constants. However, is some instances it does not appear that the degree of charge localization is great enough to account fully for the small rate constants. It is argued that the inner reorganization energy should not be ignored in such cases. The rate constants observed for THpAP were always smaller than those for TEAP when the values were small enough to measure in at least one electrolyte. This general result was explained by a suppression of the probability of electron transfer by an adsorbed film containing mainly tetra-n-heptylammonium ions. The interpretation was supported by measurement of the activation parameters for nitroethane in the two electrolytes. The activation enthalpies were almost identical but the preexponential factor for THpAP was only 1/44 that for TEAP.

Electrochemical investigations of platinum-methyluracil-blue and the related binuclear complex [(NH 3) 2Pt(MeU) 2Pt(NH 3) 2](NO 3) 2

The redox behavior of the head-to-head bis(μ- (1-methyluracilato- N 3, O 2)-bis( cis-diammine platinum(II)) dinitrate, PtMeU, and platinum 1-methyluracil blue, PtMeUB, was studied by cyclic voltammetry (CV), rotating disk voltammetry (RDV), and controlled-potential coulometry (CPC). Redox titrimetry, electrochemistry/electron paramagnetic resonance spectroscopy (EPR), and liquid chromatography (LC) served as complementary techniques. The former reactant exhibits two-step electro-oxidation, consistent with the formation of a mixed-valence Pt(II, III) state en route to Pt(III, III). The latter also appears to oxidize to a uniform Pt(III) state. Although the oxidative-reductive electrochemistry of both reactants exhibits chemical reversibility, the heterogeneous electron-transfer kinetics are notably sluggish. The latter appears to be associated with the formation of an inhibiting film on the electrode surface. A slow conversion of PtMeU to a PtMeUB-like state was revealed by CV and LC. The complex, oligomeric nature of PtMeUB was revealed by means of gradient LC examination. Comparing oxidative and reductive electrolysis curves for PtMeUB yielded an average platinum oxidation state of 2.08. All observed behavior for PtMeUB, as well as for PtMeU, is accounted for by invoking +2 and +3 oxidation states for platinum; redox titrimetry using Ce(IV) revealed inconsequential oxidation of both of these systems beyond the III state. An estimate of molecular weight for the platinum blue was made by employing RDV in conjunction with the Einstein-Stokes equation.

Heterogeneous electron-transfer kinetics for some multiply bonded dirhenium complexes

Standard electrochemical rate constants k ex ob have been measured for the two sequential one-electron oxidations of triply-bonded dirhenium(II) complexes Re 2X 4(PR 3) 4, where X = Cl or Br, and PR 3 = a monodentate tertiary phosphine, and also for allied complexes in methylene chloride, acetonitrile, and N, N-dimethylformamide at platinum electrodes. The objective is to explore the possible dependence of k ex ob upon the known differences in the structural changes accompanying electron transfer. Although significant and even substantial variations in k ex ob were observed for closely related redox couples, the reactivity trends appear to be chiefly a consequence of differences in electrostatic work terms at the metal/solution interface. Comparisons are made with recent results for mononuclear organometallic redox couples.

A study of electrode kinetics by global analysis of a single electrochemical experiment

An efficient method is presented for analyzing electrochemical processes controlled by diffusion and by the kinetics of heterogeneous electron-transfer. The method is based on a three-dimensional concept and has the advantage of utilizing all the data available from a voltammetric experiment. The three-dimensional method provides a useful diagnosis of whether Butler-Volmer kinetics is appropriate and, if so, for calculating the standard heterogeneous charge transfer rate constant, reversible halfwave potential, diffusion coefficient and charge transfer coefficient. Experiments on the [Cr(CN) 6 ] 3− + e − [Cr(CN) 6 ] 4− reaction using cyclic voltammetry are reported and the parameters so determined are shown to agree with literature values.

A study of electrode kinetics by global analysis of a single electrochemical experiment

An efficient method is presented for analyzing electrochemical processes controlled by diffusion and by the kinetics of heterogeneous electron-transfer. The method is based on a three-dimensional concept and has the advantage of utilizing all the data available from a voltammetric experiment. The three-dimensional method provides a useful diagnosis of whether Butler-Volmer kinetics is appropriate and, if so, for calculating the standard heterogeneous charge transfer rate constant, reversible halfwave potential, diffusion coefficient and charge transfer coefficient. Experiments on the [Cr(CN) 6] 3−+ e −[Cr(CN) 6] 4− reaction using cyclic voltammetry are reported and the parameters so determined are shown to agree with literature values.

Polymer films on electrodes: Part XVIII. Determination of heterogeneous electron transfer kinetics at poly(vinylferrocene) and nafion/Ru(bpy) 2+3 polymer-modified electrodes by convolution voltammetry

Convolution voltammetry was used to evaluate the rates of heterogeneous charge transfer to ferrocene groups in poly(vinylferrocene) and to Ru(bpy) 2+ 3 in Nafion-modified electrodes under semi-infinite conditions. This technique allows correction for uncompensated resistance and double layer capacitance, as well as detrmination of the diffusion coefficient, D, transfer coefficient, α, and half-wave potential, E 1/2, from a single cyclic voltammogram. Vinylferrocene in solution and a bound copolymer of vinylferrocene and styrene in a ratio of 58:42 were also examined. For the polymer films, the heterogeneous charge transfer rate constants, k°, are 10 −4 ≥ k° ≥ 10 −5 cm/s; these values are about two order of magnitude smaller than those for the similar species in homogeneous solution. The values of k°/ D 1/2, however, are comparable to those in soluton; 10 > ( k°/ D 1/2) > 0.1 s −1/2.

Interfacial electrochemistry of cytochrome c at tin oxide, indium oxide, gold, and platinum electrodes

Cyclic voltammetry has been used to study the heterogeneous electron transfer kinetics of horse heart cytochrome c in pH 7 tris/cacodylate media at several electrode surfaces. Reversible voltammetric responses (formal heterogeneous electron transfer rate constant>10−2 cm/s) were observed at bare gold electrodes and at tin-doped indium oxide semiconductor electrodes for certain experimental conditions. Quasireversible voltammetric responses were more typically observed at fluorine-doped tin oxide semiconductor electrodes, bare platinum electrodes, and at the indium oxide electrodes. Reaction rates at bare metal electrodes were strongly dependent on pretreatment procedures and experimental protocol. Reaction rates at metal oxide electrodes were strongly dependent on solution conditions, pretreatment procedures, and on the hydration state of the electrode surface. A general mechanistic scheme involving both interfacial electrostatic and chemical interactions is proposed for cytochrome c electrode reactions. The asymmetric distribution of surface charges on cytochrome c appears to play a dominant role in controlling electron transfer rates by its interaction with the electric field at the electrode surface. Electron transfer distances are also considered, and it is concluded that electron transfer between an electrode surface and the exposed heme edge of properly oriented cytochrome c molecules involves maximum distances of ca. 0.6–0.9 nm.

Interfacial electrochemistry of cytochrome c at tin oxide, indium oxide, gold, and platinum electrodes

Cyclic voltammetry has been used to study the heterogeneous electron transfer kinetics of horse heart cytochrome c in pH 7 tris/cacodylate media at several electrode surfaces. Reversible voltammetric responses (formal heterogeneous electron transfer rate constant>10 −2 cm/s) were observed at bare gold electrodes and at tin-doped indium oxide semiconductor electrodes for certain experimental conditions. Quasireversible voltammetric responses were more typically observed at fluorine-doped tin oxide semiconductor electrodes, bare platinum electrodes, and at the indium oxide electrodes. Reaction rates at bare metal electrodes were strongly dependent on pretreatment procedures and experimental protocol. Reaction rates at metal oxide electrodes were strongly dependent on solution conditions, pretreatment procedures, and on the hydration state of the electrode surface. A general mechanistic scheme involving both interfacial electrostatic and chemical interactions is proposed for cytochrome c electrode reactions. The asymmetric distribution of surface charges on cytochrome c appears to play a dominant role in controlling electron transfer rates by its interaction with the electric field at the electrode surface. Electron transfer distances are also considered, and it is concluded that electron transfer between an electrode surface and the exposed heme edge of properly oriented cytochrome c molecules involves maximum distances of ca. 0.6–0.9 nm.

Rotating disk electrode voltammetric determination of the heterogeneous electron transfer kinetics of soluble spinach ferredoxin

The heterogeneous electron transfer kinetics of soluble spinach ferredoxin reacting at modified gold electrodes have been characterized by both steady state and transient electrochemical methods. The steady state analysis was conducted at a methyl viologen modified gold disk electrode using rotating disk hydrodynamic voltammetry. The results presented are the first reported steady state kinetic parameters observed for the unmediated reduction of ferredoxin at this surface. Single potential step chronoabsorptometry was utilized to observe the transient kinetic behavior of ferredoxin at modified gold minigrid electrodes. The kinetic parameters reported herein were evaluated using a recetly advanced, generalized analysis that is applicable to heterogeneous electron transfer systems that exhibit any degree of reversibility. Both analyses yield a formal heterogeneous electron transfer rate constant, k s,h 0' , and electrochemical transfer coefficient, α, in the following ranges: 1×10 −4 cm/s< k s,h 0' <6×10 −4 cm/s and 0.4<α<0.5 for the experimental conditions employed. These results indicated that ferredoxin exhibits quasi-reversible heterogeneous electron transfer kinetics at this electrode surface. Moreover, agreement between the methods utilized to characterize this reaction points to a direct one-electron transfer process between the modified gold electrode surface and ferredoxin as the rate determining step.

Rotating disk electrode voltammetric determination of the heterogeneous electron transfer kinetics of soluble spinach ferredoxin

The heterogeneous electron transfer kinetics of soluble spinach ferredoxin reacting at modified gold electrodes have been characterized by both steady state and transient electrochemical methods. The steady state analysis was conducted at a methyl viologen modified gold disk electrode using rotating disk hydrodynamic voltammetry. The results presented are the first reported steady state kinetic parameters observed for the unmediated reduction of ferredoxin at this surface. Single potential step chronoabsorptometry was utilized to observe the transient kinetic behavior of ferredoxin at modified gold minigrid electrodes. The kinetic parameters reported herein were evaluated using a recetly advanced, generalized analysis that is applicable to heterogeneous electron transfer systems that exhibit any degree of reversibility. Both analyses yield a formal heterogeneous electron transfer rate constant, k s,h 0', and electrochemical transfer coefficient, α, in the following ranges: 1×10 −4 cm/s< k s,h 0'<6×10 −4 cm/s and 0.4<α<0.5 for the experimental conditions employed. These results indicated that ferredoxin exhibits quasi-reversible heterogeneous electron transfer kinetics at this electrode surface. Moreover, agreement between the methods utilized to characterize this reaction points to a direct one-electron transfer process between the modified gold electrode surface and ferredoxin as the rate determining step.

Heterogeneous electron-transfer kinetic parameters of metalloproteins as studied by channel-flow hydrodynamic voltammetry

Channel-flow hydrodynamic voltammetry was used to study the direct electron-transfer reactions of two metalloproteins, myoglobin and cytochrome c , under steady-state conditions at methyl viologen modified (MVM) gold foil electrodes. Utilization of a dual working electrode cell with this technique permitted determination of the heterogeneous electron-transfer kinetics for both the reduction and oxidation of myoglobin. The formal heterogeneous electron-transfer rate constants in pH 7.00 phosphate buffered solutions were found to be 8.9 (±1.5)×10 −5 cm s −1 for the reduction, and 7.7 (±1.2)×10 −5 cm s −1 for the reoxidation of myoglobin. The transfer coefficient values obtained were 0.21 (±0.01) for the reductive (α) and 0.82 (±0.01) for the oxidative (1−α) electrode reactions. Ionic strength and pH dependences were observed in these direct electron-transfer reactions. Collective current efficiency measurements in the myoglobin experiments indicated that an overall simple charge-transfer process occurred at the respective electrode interfaces. A formal rate constant of 3.4 (±0.2)×10 −5 cm s −1 with a transfer coefficient of 0.25 (±0.01) for the reduction (α) of cytochrome c was obtained by this hydrodynamic technique. The use of channel-flow hydrodynamic voltammetry in characterizing an electrode reaction as well as an interpretation of the data presented are discussed.

Heterogeneous electron-transfer kinetic parameters of metalloproteins as studied by channel-flow hydrodynamic voltammetry

Channel-flow hydrodynamic voltammetry was used to study the direct electron-transfer reactions of two metalloproteins, myoglobin and cytochrome c, under steady-state conditions at methyl viologen modified (MVM) gold foil electrodes. Utilization of a dual working electrode cell with this technique permitted determination of the heterogeneous electron-transfer kinetics for both the reduction and oxidation of myoglobin. The formal heterogeneous electron-transfer rate constants in pH 7.00 phosphate buffered solutions were found to be 8.9 (±1.5)×10 −5 cm s −1 for the reduction, and 7.7 (±1.2)×10 −5 cm s −1 for the reoxidation of myoglobin. The transfer coefficient values obtained were 0.21 (±0.01) for the reductive (α) and 0.82 (±0.01) for the oxidative (1−α) electrode reactions. Ionic strength and pH dependences were observed in these direct electron-transfer reactions. Collective current efficiency measurements in the myoglobin experiments indicated that an overall simple charge-transfer process occurred at the respective electrode interfaces. A formal rate constant of 3.4 (±0.2)×10 −5 cm s −1 with a transfer coefficient of 0.25 (±0.01) for the reduction (α) of cytochrome c was obtained by this hydrodynamic technique. The use of channel-flow hydrodynamic voltammetry in characterizing an electrode reaction as well as an interpretation of the data presented are discussed.

Spectroelectrochemical determination of the heterogeneous electron transfer kinetics of soluble spinach ferredoxin

Heterogeneous electron transfer rate parameters for soluble spinach ferredoxin are reported using a recently developed single potential step spectroelectrochemical technique. The reductive kinetics were measured by monitoring the decrease in absorbance as a function of time for several overpotential steps at methyl viologen modified optically transparent gold minigrid electrodes. These measurements yielded an average formal heterogeneous electron transfer rate constant (k f,h o′ = 6.5 (±1.3) × 10 −5 cm/s) and electrochemical transfer coefficient (α = 0.60 ± (0.16)) at pH 7.5. These results are the first heterogeneous electron transfer rate parameters reported for this species.

343 - Heterogeneous electron transfer kinetics of sperm whale myoglobin

Very little information has been reported describing the heterogeneous electron transfer kinetics of biological molecules at electrodes. We report here the first application of a recently developed spectroelectrochemical technique to the measurement of the heterogeneous electron transfer kinetics of a biological molecule, sperm whale myoglobin, at a methyl viologen modified gold minigrid electrode. The overpotential dependence of the heterogeneous electron transfer rate constant for the reduction of myoglobin at this surface gives rise to values of the formal heterogeneous electron transfer rate constant [ k o′ f,h = 3.88 (± 0.07) × 10 −11 cm/s] and the transfer coefficient [α = 0.88 (± 0.01)] for this electrocatalyzed process. The importance of studying the heterogeneous electron transfer kinetics of biological molecules lies in the fact that many physiological electron transfer reactions occur heterogeneously. Though myoglobin does not function in this manner physiologically, our initial study has been directed at this molecule owing to its stability and ready availability. It is expected that this technique will be applied to other optically transparent electrodes and other biological molecules thereby providing new insights into understanding biological redox reactions.