ABSTRACT
This chapter compares the oxide growth mechanism under gas-phase and electrochemical conditions. The differences between the surface oxide and the bulk-type one and their distinct physical and chemical properties are presented. Various oxidation reaction pathways involving OHChem or Ochem, as an intermediate of the process, are reviewed. Three experimental procedures applied to formation of surface oxides, namely potentiostatic polarization, galvanostatic polarization, and potential cycling, are discussed. A review of numerous in situ and ex situ techniques used to characterize the chemical nature of the surface oxides, their thickness, and the degree of hydration is presented. The surface-oxide growth can be limited by various processes such as the electron transfer, the interfacial escape of the metal cation from the metal, the surface place exchange, and the transport of the metal cation across the film. Because each of these rate-determining steps can give rise to a distinct kinetic formulation (kinetic law), mathematical equations are provided for each of them. Diagnostics criteria, which can assist one in examination of the mechanism and kinetics applicable to the system under study, are presented and discussed. Selected results for the surface oxidation of Rh, Pt, and Au under potentiostatic conditions are presented and discussed to illustrate the theoretical consideration.
