Importance of Metastable States in Electrocatalytic Processes at Metal Surfaces in Aqueous Media

Solid metals and their surfaces can trap or store energy; it appears, therefore, that, for any solid metal in aqueous media, there are two limiting types of surface electrochemistry, one relating to the equilibrated (low-energy) metal atoms, and the other, to the metastable (high-energy) metal atoms. With real metal surfaces, the low-energy state is usually dominant, but the metastable state behavior is often vital with regard to low coverage surface active site behavior. The most significant effects of surface metastability are that it lowers the oxidation potential of the atoms in this state to values within the double layer region and forms the basis of facile interfacial redox couples which often function as mediators in electrocatalytic processes. This rather novel approach was explored with regard to the electrocatalytic behavior of copper in base; the applicability of the approach to the three Group 11 metals (Cu, Ag, and Au) was illustrated, and its relevance to the use of platinum in fuel cell electrocatalysis was outlined.