Browsing by Subject "Electrode kinetics"

Now showing 1 - 3 of 3
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    Electrochemical determination of kinetic parameters of surface confined redox probes in presence of intermolecular interactions by means of Cyclic Voltammetry. Application to TEMPO monolayers in gold and platinum electrodes
    (Elsevier, 2021-01-01) González Sánchez, Joaquín; Sequí Castellano, Alfonso; Química Física
    Application of Cyclic Voltammetry to the characterisation of redox kinetics of surface confined redox probes is usually based on the linear regression of the peak potentials versus the logarithm of the scan rate under fully irreversible redox conditions by following the well-known method due to E. Laviron. This method implicitly assumes the Butler-Volmer formalism under ideal conditions, a fact that, in spite of the broad use of this method, strongly restrict its applicability. Here, we propose a combination of the Marcus-Hush-Chidsey formalism and the presence of intermolecular interactions in order to extract kinetic information of the CV curves. Full-width at half-maximum (fwhm) and its correlation with the peak potentials reveals to be very useful to evaluate both kinetics and interactions influences with high sensitivity and accuracy. Experimental analysis of the CV curves of electroactive monolayers of the persistent radical TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) directly attached to gold and platinum electrodes in two aprotic solvents (Ethanol and Propylene Carbonate) have been carried out.
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    Influence of Intermolecular Interactions in the Redox Kinetics Performance of Surface Confined Probes by Square Wave Voltammetry
    (2019-10) Gonzalez, Joaquin; Sequí Castellano, Jose Alfonso; Química Física
    Analysis of the Square Wave Voltammetry (SWV) responses of surface confined electroactive probes under finite kinetics conditions, by considering the influence of intermolecular interactions on the current, is presented. This non-ideality gives rise to very significant deviations in the most relevant features of the current potential response as compared with predictions of ideal models. The theoretical model does not require that the dependence of the rate constant with the potential (i. e., Butler-Volmer or Marcus-Hush kinetic formalisms) is explicitly established a priori. Both location and height of the Quasi-Reversible Maximum and symmetry of the SWV current-potential curves are strongly affected by the interaction parameters G=aOO+aRR-2aOR and S=aRR-aOO (with aij being the interaction coefficient for species i and j). Quantitative methods for obtaining kinetic and interaction parameters of the redox probes are presented, based on the measurement of the peak currents and potential under quasi-reversible conditions where the current exhibits two asymmetric peaks. A discussion is done concerning the deviations found in the estimation of the rate constants with SWV when intermolecular interactions are not considered. The above methods have been applied to the characterisation of mixed ferrocenylundecanethiol / decanethiol monolayers on gold electrodes at an ethanolic medium for which the SWV is clearly non-ideal
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    Voltammetric kinetic studies of electrode reactions: guidelines for detailed understanding of their fundamentals
    (American Chemical Society, 2022-12-27) González Sánchez, Joaquín; Laborda Ochando, Eduardo; Molina Gómez, Ángela; Química Física; Facultad de Química
    Theoretical and practical foundations of basic electrochemical concepts of heterogeneous charge transfer reactions that underline electrochemical processes are presented for their detailed study by undergraduate and postgraduate students. Several simple methods for calculating key variables, such as the half-wave potential, limiting current, and those implied in the kinetics of the process, are explained, discussed, and put in practice through simulations making use of an Excel document. The current–potential response of electron transfer processes of any kinetics (i.e., any degree of reversibility) are deduced and compared for electrodes of different size, geometry, and dynamics, namely: static macroelectrodes in chronoamperometry and normal pulse voltammetry, and static ultramicroelectrodes and rotating disc electrodes in steady state voltammetry. In all cases, a universal, normalized current–potential response is obtained in the case of reversible (fast) electrode reactions, whereas this is not possible for nonreversible processes. For this last situation, different widely used protocols for the determination of the kinetic parameters (the mass-transport corrected Tafel analysis and the Koutecký–Levich plot) are deduced, proposing learning activities that highlight the foundations and limitations of such protocols, as well as the influence of the mass transport conditions. Discussions on the implementation of this framework and on the benefits and difficulties found are also presented.