Mediation of oxidation reactions at noble metal anodes by low levels of in situ generated hydroxy species

Abstract

The study of organic oxidation reactions at noble metal electrodes in aqueous media is frequently complicated by surface deactivation effects. Hydrazine is a very useful model compound for this type of work as it is both highly reactive and free of complications due to poisoning. It was demonstrated that for several metals (Au, Pt, Pd and possibly Rh) the potential for the onset of oxidation of dissolved species at low pH coincided approximately with that for hydrous oxide reduction in the absence of oxidisable species. Compact monolayer oxides, and high levels of adsorbed hydrogen, have an inhibiting effect—the latter is particularly marked with Ir and Ru. With the other metals (and also, according to earlier data, with both Ag and Cu in base) the effective oxidising agents were apparently low levels of hydrous oxide species generated at low coverage, adatom sites at the electrode—solution interface. There may be also some activation of the dissolved species due to adsorption or coordination at active centres on the electrode surface.