Browsing by Subject "Electrode kinetics"

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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