Kinetic instabilities in electrochemical systems: a theoretical contribution

Author(s)

Melke Augusto do Nascimento

• Document type: Doctoral Thesis
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Instituto de Química de São Carlos (IQSC/BT)
• Defense date: 2011-12-09

Examining board members

Hamilton Brandão Varela de Albuquerque; Carlos Ventura D'Alkaine; Luis Gustavo Dias; Gerd Bruno da Rocha

• Advisor: Hamilton Brandão Varela de Albuquerque

Abstract

More than just an exotic phenomenon, oscillations of potential and current are often found in several electrochemical systems. Although oscillatory processes at solid/liquid electrified interfaces have been reported a long time ago, just few theoretical studies have been done so far. This Thesis comprises two parts: the first one analyzes kinetic instabilities observed in electrochemical systems by using a model consisting of three non-linear coupled ordinary differential equations that represent a prototype of the complex behavior observed in electrocatalytic systems. Specifically, this prototype captures the general characteristics of electrochemical oscillators that display a negative differential resistance partially hidden for an N-shaped current/potential curve. The model was studied using conventional analyses and stability diagrams, Lyapunov exponents and the evaluation of the period of oscillations. From the stability diagrams it was possible to describe the behavior of the system taking into consideration the homoclinic Shilnikov condition. The Lyapunov and period analyses showed in a very detailed manner the chaotic and periodic behavior of the model, where it is observed the existence of self-organized structures in the domains of periodicity on a chaotic background. Those structures are known as shrimps. The observation of such structures that are also found in other systems reinforces the idea of structural universality for codimension two phenomena. The second part of the Thesis deals with the analysis of the oscillatory drift by using multivariate analysis techniques to an experimental time series obtained for the electroxidation of methanol on polycrystalline Pt. The results showed that it is possible to describe the influence of the drift during the oscillatory behavior by means of three variables that act on the surface of the electrode. (AU)

• FAPESP's process: 07/04522-0 - Oscillatory kinetics in electrocatalysis: modeling and numerical simulations
• Grantee: Melke Augusto do Nascimento
• Support Opportunities: Scholarships in Brazil - Doctorate