A theoretical study of the electrochemical reduction of oxygen

Multi-dimensional potential energy surfaces have been constructed for the experimentally found most probable rate-determining step in electroreduction of oxygen on Pt(lll) and Pt(100) using a combination of experimental data in Morse functions and ASED-MO (a semi-empirical quantum mechanical technique). The minimum energy path for the reaction has been extracted by Euler's single step method. In agreement with the position of Schmickler [W. Schmickler, Interfacial Electrochemistry, Oxford University Press, 1996] for atom transfer reactions, the Marcus continuum model (in which the Gibbs energy is related to rearrangements among the solvent molecules by means of quadratic expressions) has been avoided. Instead the interaction of the proton with the librating solvent molecules in its environments is described by model considerations (ion-dipole and ion-ion induced dipole interactions). A treatment of non-adiabacity has been made by means of Landau-Zener formalism and the quantum properties of the proton are taken into account using an Eckart barrier for the calculation of tunneling. On this basis, the kinetic parameters, e.g. the activation energies, entropies of activation, the symmetry factors and reaction rates of the model reaction, have been calculated. (C) 1998 Elsevier Science S.A. All rights reserved.