Methanol oxidation enhanced by the presence of O2 at novel Pt–C co-sputtered electrode

In this paper, we describe a novel electrode that exhibits sensitized methanol electrooxidation in an oxygen atmosphere. A binary Pt–C electrode has been developed for use as the anode catalyst of a direct methanol fuel cell using a co-sputtering technique. Characterizations of the electrodes revealed that the sputtered Pt–C forms nanosize and phase-separated Pt and C domains, in which the Pt particle size decreases and its crystallinity gradually becomes amorphous with increasing C content. The current density of methanol oxidation in deaerated conditions exhibited a maximum value at a C content of 23 at%. The result can be well explained from the viewpoints of the morphology and binding energy of Pt. The methanol oxidation current is sensitized by O2 when the Pt–C electrode contains >23 at% C, and the extent of sensitization increases monotonically with C content. This phenomenon is not observed at a Pt electrode. The sensitization mechanism was investigated by considering the reduction reaction of O2; it was clarified that the amount of adsorbed species created by O2 reduction increases with increasing C content. It was deduced that the Pt–OH produced by O2 reduction participates in oxidation of Pt–CO, which is believed to be the rate-determining step of the methanol electrooxidation.