Cyclic voltammetric studies on the reduction of a gold oxide surface layer

Cathodic reduction of a stationary surface layer of gold compounds formed a nodically on a gold electrode in 0.5 M H2SO4 solution at E = 1.7 V, i.e. pr ior 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 f ound 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. Suc h Tafel behaviour is expected for the cathodic process in the case of a rev ersible metal\metal oxide electrode. It has been proposed that the reversib ility of the cathodic process may be determined by the equilibrium of the f ollowing 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 ads orbed 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 i s present on the electrode surface. The equilibrium potential of this react ion was evaluated as 1.28 +/- 0.01 V. (C) 1999 Elsevier Science S.A. All ri ghts reserved.