The role of hydrous oxide species on platinum electrocatalysts in the methanol/air fuel cell

Abstract

The important role of incipient hydrous oxide species in electrocatalytic processes at noble metal electrodes was highlighted in recent work carried out in this laboratory. In the present case it was established that thick deposits of such material can be produced readily on platinum in 3.0 M H 2SO 4 at 60°C (typical methanol/air fuel cell conditions) by multicycling the electrode potential between suitable limits. Such deposits, which usually consisted of two hydrous oxide components, displayed a suprisingly high resistance to both dissolution and reduction in the rather severe, hot concentrated acid, environment. In a number of cases (in particular at 80°C) a small peak, attributed to adatom oxidation ( ie incipient hydrous oxide formation) was observed in the double layer region in cyclic voltammograms recorded for clean polycrystalline platinum in acid solution. The role of these incipient oxides in methanol/air fuel cell processes is outlined; while these species are a major factor in certain types of electrocatalytic processes their very low coverage, and consequently low response, makes their investigation extremely difficult. It was pointed out, for the first time, that there is a direct analogy between incipient hydrous oxide formation on platinum in aqueous media and earlier data for smaller platinum clusters: such clusters also undergo anomalous oxidation, ie they react readily with oxygen from the gas phase under conditions where bulk platinum is unreactive.