CYCLIC VOLTAMMETRIC STUDIES ON THE REDUCTION OF A GOLD OXIDE SURFACE LAYER

Cathodic reduction of a stationary surface layer of gold compounds formed anodically on a gold electrode in 0.5 M H 2 SO 4 solution at E =1.7 V, i.e. prior to oxygen evolution, has been investigated. With the initial amount of gold oxide on the electrode surface being constant, linear dependences of j p on v , log j c on E and log j p on E p were established. It has been found that the parameters d E /d log j c , d E p /d log j p and d E p /d log v at 1.2 V (SHE)> E > E p are close to the theoretical value of 2.3 R T / F . Such Tafel behaviour is expected for the cathodic process in the case of a reversible metal|metal oxide electrode. It has been proposed that the reversibility of the cathodic process may be determined by the equilibrium of the following surface reaction: Au · H 2 O+2H 2 O⇔(Au(OH) 3 ) s +3H + +3e − where Au · H 2 O represents the gold surface atoms with electrostatically adsorbed H 2 O, and (Au(OH) 3 ) s is Au(OH) 3 in the form of the surface layer. This equilibrium may exist at the interface only when the Au(OH) 3 layer is present on the electrode surface. The equilibrium potential of this reaction was evaluated as 1.28±0.01 V.