Study of the surface oxide growth on platinum and nickel electrodes at well-defined polarization potential, time and temperature conditions

Anodic polarization of Pt electrodes in 0.5 M aqueous H2SO 4 at various polarization potentials (Ep) from 0.90 to 1.50 V, for polarization times (tp) up to 104 s, and at 278 ≤ T ≤ 323 K leads to formation of sub-monolayer and monolayer oxide films. These oxide layers reveal only one feature in the oxide-reduction profiles, the OC1 peak, which corresponds to the reduction of PtO to Pt. The oxide growth behavior is influenced by the experimental conditions such as Ep, tp, and T, and in general the higher Ep and/or longer tp and/or higher T, the thicker the oxide layer. An increase of Ep and/or tp shifts the OC1 peak towards less-positive potentials. On the other hand, an increase of T does not lead to shift the OC 1 peak. Theoretical data treatment indicates that the growth of PtO follows two distinct kinetic laws, each arising from a different growth mechanism: (i) the logarithmic growth for oxide whose thickness is up to 1 ML of PtO, and (ii) the inverse-logarithmic growth for oxide whose thickness is more than 1 ML of PtO. The dipole moment of the Ptδ+- Od-chem , surface species that drives the place exchange is consistently 1.30 ± 0.10 D. The electric field, E, which drives the interfacial Pt2+ escape is determined to be consistently in the 109 V m-1 range. (Abstract shortened by UMI.).