Electrochemical properties of anodic gold oxide layers—I

Abstract

The potentiostatic growth of gold oxide layers was investigated at pH = 0, 2, and 6.2 in the potential range 1.4 V ⪕ ϵ ⪕ 2.3 V (vs hess) and for polarization times between 10−4 and 103 s. At ϵ < 2.0 V the growth of monomolecular oxide layers (oxide 1) with a thickness up to 10 A was observed. This process takes place according to a high field mechanism. In this range, the double layer capacity decreases with increasing thickness d. With increasing ϵ there is a continuous change of oxide growth. At ϵ > 2.0 V a potential dependent linear growth law is observed with the formation of thick layers (oxide 2) up to 600 A or more. In this range, further peaks arise in the cathodic charging curves, and the double layer capacity becomes independent of d. It follows that on the monomolecular boundary layer (oxide 1) the bulk oxide 2 is formed, which has a good ionic and electronic conductivity. Hence, the potential drop is small in oxide 2, but large in oxide 1. Even at high potentials the rate-determining step is the field dependent ionic migration in oxide 1.