Cyclic voltammetry responses of metastable gold electrodes in aqueous media

Gold is the noblest of metals and it is widely assumed that the surface of a gold electrode only begins to undergo oxidation in aqueous media at ca. 1.36 V (RHE) in acid or ca. 1.25 V in base. However, recent work in this laboratory has shown that, following thermal activation, gold atoms at the surface of a gold electrode may undergo oxidation in acid solution at potentials as low as 0.3 V. In the present work, in which the gold was allowed to cool rapidly from the molten state, oxidation responses were observed for gold in base at E<0.0 V. Such unusual behaviour is attributed to low gold-atom lattice stabilization energy plus the operation of a super-Nernstian E/pH effect. It appears, as outlined recently for silver, that a range of surface active states are available for metals; these give rise to a range of premonolayer oxidation and multilayer hydrous oxide reduction responses; such non-equilibrium surface states are often quite important with regard to electrocatalysis.