The electrocatalytic behaviour of palladium in acid and base

Abstract

Anomalous oxidation of noble metals such as platinum is now an established feature of metal cluster/ oxygen gas reactions. The same type of process at polycrystalline metal electrodes in aqueous media is assumed to give rise to incipient hydrous oxide formation. This approach was used here to rationalize the electrocatalytic behaviour of palladium, with regard to both oxidations and reductions, in aqueous acid and base. The activity of palladium was not dramatically different to that of platinum, and the presence of an unusual peak at about 0.23 V vs RHE in the case of palladium in acid is rather similar in character to the so-called anomalous hydrogen peak previously described for platinum under similar conditions. For both metals (and a similar claim was made recently for gold) an adatom/incipient hydrous oxide transition is assumed to be involved, and it is interesting that the onset/termination potential for hydrazine oxidation under potential sweep conditions virtually coincided with the potential for this minor peak or transition.