2013 Volume 54 Issue 4 Pages 582-587
The methanol oxidation activity of Pt oxide can be significantly improved by heat reduction in a H2 atmosphere or by electrochemical reduction using a cathodic current. Therefore, the Pt oxide is expected to be a novel anode catalyst for DMFC. In this study, measurement of the electrochemical active surface area by CO stripping voltammetry, analysis of the chemical bonding state by XPS and determination of the O/Pt atomic ratio by EPMA were carried out to investigate the cause of the improvement in the methanol oxidation activity of the Pt oxide by the reduction treatment. Although the methanol oxidation current remarkably increased by electrochemical reduction treatment of the Pt oxide thin film prepared by reactive sputtering in 100% O2, the effect of the reduction on the methanol oxidation activity was not recognized at all for the Pt thin film prepared in 100% Ar. For the Pt oxide thin films, it was shown that there was a close correlation between the methanol oxidation current and the electrochemically active surface area obtained by CO stripping voltammetry. Moreover, the quantitative analysis by EPMA clearly showed that the O/Pt atomic ratio of the Pt oxide thin film having a high activity for the methanol oxidation reaction decreased to about 0.1 by the electrochemical reduction. These results together with the XPS analysis suggested that the residual oxygen related to the Pt–O bond was activating the methanol oxidation for the electrochemically reduced Pt oxide thin films.