INDEPENDENCE OF FORMATION AND REDUCTION OF MONOLAYER SURFACE OXIDE ON PT FROM PRESENCE OF THICKER PHASE-OXIDE LAYERS

On Pt surfaces at which thick, phase-oxide types of films have been generated by strong anodic oxidation, it is shown that, following incomplete reduction of the oxide layer over the quasi-2-D oxide reduction region, a regeneration of the quasi-2-D surface oxide can be achieved with the thick phase-oxide layer remaining intact. The nature of the behaviour observed indicates that first the 2-D oxide film must be formed with the 3-D film being subsequently generatable upon and above it under strong anodic polarization conditions. Upon reduction, the 2-D film is first reduced beneath the thick oxide film, independently of subsequent reduction of the latter. These results suggest an independence of the 2-D processes occurring at the Pt-metal interface from the quasi-3-D film growth processes that can also take place, leading to thick films having electrochemical stabilities substantially greater than that of the quasi-2-D underlying film.