Browsing by Subject "Cyclic voltammetry"

Now showing 1 - 5 of 5
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    Analytical theory for ion transfer-electron transfer coupled reactions at redox layer/thick film-modified electrodes
    (Elsevier, 2020-02) Laborda, Eduardo; González Sánchez, Joaquín; Molina, Angela; Química Física
    Electrodes modified by liquid films or plasticized polymeric membranes containing a redox species offer valuable alternatives for the study of ion transfers and bimolecular electron transfers at liquid|liquid interfaces with conventional electrode arrangements and stable interfaces. The ion-to-electron (or electron-to-electron) transducer affects the electrochemical signal, complicating the accurate analysis of experimental data. This can be reduced through the use of an electrode surface-attached redox species of well-defined electrochemical behaviour. As will be demonstrated, the voltammetry of these systems show significant deviations with respect to individual charge transfers, which must be considered for appropriate diagnosis and quantitative analysis. For this, a simple analytical theory is presented here, deducing mathematical expressions for the current-potential response, as well as for the potential difference at the two polarized interfaces, the surface excess of the redox species and the ion interfacial concentrations.
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    Application of voltammetric techniques at microelectrodes to the study of the chemical stability of highly reactive species
    (American Chemical Society (ACS), 2014-12-31) Laborda, Eduardo; Olmos, José Manuel; Torralba, Encarnación; Molina, Ángela; Química Analítica
    The application of voltammetric techniques to the study of chemical speciation and stability is addressed both theoretically and experimentally in this work. In such systems, electrode reactions are coupled to homogeneous chemical equilibria (complexations, protonations, ion associations,…) that can be studied in a simple, economical and accurate way by means of electrochemical methods. These are of particular interest when some of the participating species are unstable given that the generation and characterization of the species are performed in situ and in a short time scale. With the above aim, simple explicit solutions are presented in this paper for quantitative characterization with any voltammetric technique and with the most common electrode geometries. From the theoretical results obtained, it is pointed out that the use of square wave voltammetry in combination with microelectrodes is very suitable. Finally, the theory is applied to the investigation of the ion association between the anthraquinone radical monoanion and the tetrabutylammonium cation in acetonitrile medium.
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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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    Insights into the cyclic voltammetry of surface-confined molecules undergoing two-electron transfers of any reversibility and any ordering of the formal potentials: unravelling the apparent governing factors
    (Elsevier, 2023-09-10) López Tenés, Manuela; González Sánchez, Joaquín; Laborda, Eduardo; Molina, Angela; Química Física
    The cyclic voltammetry (CV) of surface-immobilized electroactive species undergoing two-electron transfers (so-called surface EE mechanism) is comprehensively studied in this work, considering any electron transfer kinetics (k0′ 1 , k0′ 2 ) and any values of their formal potentials (E0′ 1 , E0′ 2 ). Hence, a large number of possible situations arise, which are systematized through the definition of apparent electrochemical rate constants for both electron transfers (which account for the combined effect of k0′ i (i = 1, 2), ΔE0′ (= E0′ 2 - E0′ 1) and the scan rate), with their values and ratio determining the features of the voltammetric signal. Guidelines are established for the elucidation of the reversibility of the process as a function of the relative values of such apparent rate constants, which reflects on the symmetry of the CV signals in the forward and reverse scans. Thus, as the second transfer is more favorable than the first one, kinetically and/or thermodynamically, the process behaves as more irreversible. Also, simple protocols of quantification of the corresponding kinetic and thermodynamic parameters are given on the basis of the analysis of the height, width, number and position of the CV peaks.
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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.