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 H2SO4 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 dE/d log j(c), dE(p)/d log j(p) and dE(p)/d log v at 1.2 V (SHE) > E > E-p are close to the theoretical value of 2.3RT/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 . H2O+ 2H2O double left right arrow (Au(OH)(3))(s) + 3H(+) + 3e(-) where Au . H2O represents the gold surface atoms with electrostatically adsorbed H2O, 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), layer is present on the electrode surface. The equilibrium potential of this reaction was evaluated as 1.28 +/- 0.01 V. (C) 1999 Elsevier Science S.A. All rights reserved.