Browsing by Subject "Rotating disc electrode"

Now showing 1 - 3 of 3
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    Nuances of the voltammetry of homogeneous multi-electron molecular catalysts: an analytical theory for two-electron catalysis
    (Elsevier, 2022-03) Laborda, Eduardo; González Sánchez, Joaquín; Molina, Angela; Química Física
    A wide range of cases of homogeneous two-electron molecular catalysts of electrochemical reactions, as a paradigm of multi-electron catalysis, are investigated in voltammetry through a novel and rigorous analytical theory. Simple expressions are deduced for the current-potential response at static and rotating macroelectrodes in all possible situations in terms of catalytically active pathway(s), rate constant(s) and formal potentials of the electron transfers. Criteria and procedures have been proposed to identify the true catalytic states and pathways. The results reveal fundamental differences in the voltammetry of multi-electron catalysts with respect to that of mono-electron ones (EC’ mechanism), specifically with regard to the impact of mass transport on the features of the signal and on the accessibility to pure kinetic conditions.
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    Square Wave Voltcoulommetry of two-electron molecular electrocatalytic processes with adsorbed species. Application to the surface O2 reduction in acetonitrile at anthraquinone-modified glassy carbon electrodes
    (Elsevier, 2023-03-10) Hernández Tovar, José Víctor; López Tenés, Manuela; Gonzalez, Joaquín; Química Física
    An adequate analysis of the performance and efficiency of a given multi-redox molecular electrocatalyst versus a particular substrate of interest requires the knowledge of the overall reaction pathway and the determination of the rate constants of the catalytic steps taking place. For this purpose, a theoretical model is presented for the Square Wave Voltcoulommetry response of surface-confined two-electron catalysts, that is, molecular species with two different redox states that can act in different electrocatalytic forms as a function of the applied potential. The rigorous theoretical model incorporates convective mass transport effects and non-idealities in the electrochemical behaviour of the immobilized redox probes. The results obtained have been applied to the study of the surface oxygen reduction in an aprotic medium (acetonitrile) at an anthraquinone-modified glassy carbon electrode. The charge-potential responses indicate that the reaction pathway involves two different catalytic routes due to the two reduction products of the anthraquinone moiety, that is, the semiquinone anion radical and the dianion. A Koutecky-Levich approach, combined with the fittings of the experimental responses to the theoretical expressions deduced here, has allowed us to obtain the values of the different thermodynamic (formal potential, interaction parameters, surface coverage) and kinetic (rate constant) parameters of the process.
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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.