Análisis de la respuesta electroquímica de procesos de transferencia de carga entre especies confinadas en superficies conductoras en presencia de interacciones intermoleculares

Abstract

Electroactive monolayers are electrochemical systems which present electroactive moieties confined at conducting interfaces that form bi-dimensional structures. These systems have a great interest due to their applications, like the development of new platforms and bio-platforms to create sensors, as well as their role in the development of electrical energy generation and storing devices. In order to optimize these applications, it is crucial to characterize and model the behavior of the electroactive monolayers, which it is usually done by using an “ideal” approach, that works by using a simplified vision of the experimental behavior of these systems. However, in the literature it can be found several experimental results that show a series of deviations from this “ideal” view, that are usually called “non-idealities”. In the present report, the study of one of the main causes of these “non-idealities” is addressed: the presence of intermolecular interactions among the electroactive moieties. In order to achieve this purpose, a theoretical model for the current-potential-time response has been proposed, and an electrochemical analysis of these systems has been done by using different electrochemical techniques (Chronoamperometry and Chronocoulometry, Square Wave Voltacoulommetry and Voltammetry, and Cyclic Voltammetry). Methods for obtaining the interaction parameters (G and S) that characterized the type and intensity of the intermolecular interactions, as well as the thermodynamic and kinetic parameters of the charge transfer process, have been proposed for all the electrochemical techniques. These methods have been applied to different electrochemical systems of interest (specifically to monolayers of ferrocenylalkylthiols and TEMPO radical). The error in the estimation of the kinetic parameters of the monolayer when intermolecular interactions are not considered, which can be of several orders of magnitude, has been calculated. The chapters of this report are devoted to the development of the theoretical model above mentioned as well as for each of the different electrochemical techniques under analysis. Moreover, a discussion of the possible interpretations of the obtained values of the interaction parameters and their relation with the charge of the monolayer, the electrolytic mediums and the conducting interface has been included. This analysis provides relevant results like the redefinition of the “ideal state”, usually identified as a low charge monolayer scenario, which is revealed to be inaccurate, as well as the influence of the ionic pairing in the intermolecular interactions. Finally, in the last chapter of this report, the study of a catalytic reaction scheme is held, due to the special relevance of these systems and their many applications. The electrochemical response of these processes has been modeled considering both “ideal” behavior and the presence of intermolecular interactions, focusing in the steady-state response of the system in the case of a reversible chemical step. In this sense, the influence of the intermolecular interactions in the current-potential response has been studied. The theoretical analysis presented has been checked by analyzing the experimental behaviour of a binary monolayer of decanothiol/ferrocenylundecanethiol in the presence of potassium ferro and ferricyanide. The charge transfer constants, the interaction parameters, and the constants of the catalytic step have been determined, revealing that the direct and reverse constants are different.