THE STABILITY OF HYDROUS OXIDE-FILMS ON PLATINUM

The stability of hydrous oxide films grown on platinum in both acid and base was investigated as a function of holding potential in solutions of different pH. In contrast to similar films grown on gold - whose behaviour was described earlier - the stability of the bulk of the hydrous oxide deposits on platinum was not very dependent on solution pH. This was attributed to a rather facile rearrangement, in the case of platinum, of the initially anionic oxide species to a virtually neutral state. However, there was invariably a minor component in these deposits that was difficult to reduce in base; this probably involves an outer layer of oxide material (the latter being in contact with the aqueous phase) which retained its hyperextended, anionic form. Reduction of the bulk hydrous oxide in base showed a marked degree of inhibition in the region of O V(RHE); the effect seemed to be related to the presence of weakly bound hydrogen on the platinum surface. The hydrous oxide growth process on platinum showed a marked dependence on electrode history - this is a topic for further investigation.