Voltammetric investigation of platinum oxides. I. Effects of ageing on their formation/reduction behavior as well as catalytic activities for methanol oxidation

The formation and reduction behavior of platinum oxides on various titanium-platinized electrodes was investigated by means of cyclic voltammetry (cv) in H2SO4 With and without methanol. The cv results indicated that PtOHads with the coexistence of bare Pt atoms and the presence of hydroxyl Pt(IV) species are responsible for the electrocatalytic oxidation of methanol in the potential ranges of premonolayer and monolayer oxide formation, respectively. The electrocatalytic activity of PtOHads was found to be enhanced by ageing of the Pt deposits through means of either repeated cv or immersion in water for 15 days although the ageing processes would decrease their surface area. Scanning electron microscope (SEM) was used to examine any changes in surface morphology of the Pt deposit after ageing. X-ray photoelectron spectroscopic (XPS) spectra revealed a negative shift in binding energy of the surface Pt atoms after a repeated potential cycling. X-ray diffraction (XRD) patterns revealed a change in crystalline structure from polycrystalline to amorphous after this ageing treatment. (C) 1999 Elsevier Science Ltd. All rights reserved.