In Situ Electrochemical AFM: Travelling Waves and Pit Growth during Au Dissolution

Abstract

Kinetics, mechanism and self-organization evolution during electrochemical dissolution of gold (gold leaching) in acidic thiourea or alkaline thiosulfate solutions can be clarified through in Situ electrochemical (EC) AFM at the mesoscopic level. Pit-induced layer dissolution and travelling waves as well as the transition from pit-induced layer dissolution to wave-type dissolution could be observed by using in situ EC-AFM at open-circuit potential (OCP) of Au(111) bead electrode in acidic thiourea solutions. A proposed scheme gives an interpretation for the pit-induced layer and wave dissolution of Au(111) through the bonding interaction of sulfur atoms with gold atoms located at different positions on Au(111). Pits and pit-induced layer dissolution of Au(111) plane could be observed through in situ EC-AFM as the potential applied potentiostat above OCP in cupric ammoniacal thiosulfate solutions, where the pits dissolution present autocatalytic growth in depths, radius and numbers. The role of copper(II) anions and ammonia during the electrochemical dissolution of Au(111) plane is to dissolve the passivated sulfur comes from the decomposition of thiosulfate or chemical dissociation of polythionates produced by thiosulfate on the surface of Au(111) bead electrode, rather than to oxidize Au0 to Au+ for copper(II) ammonia complex according to the our study with in Situ EC-AFM.