Surface Oxidation of Gold Electrodes

Abstract

The surface oxides formed on electropolished gold by potentiostatic anodization in the range 1.2-1.85v vs. H+/H2 have been studied by galvano- static reduction at current densities between 10 and 1000 tm/cm2. Molar perchlorate solutions of pH 0.06 to 2.8 were employed. The extent of oxide formation is determined by the potential of anodization; the charge in- creasing linearly with the potential of formation in the range of 1.45-1.8v. Cathodic chronopotentiograms show that reduction of the oxide occurs at a definite potential which depends on the cathodic current density. Current- potential curves, constructed from the chronopotentiograms, follow a Tafel relation with a slope of 41 mv. The electrochemical order of the reduction reaction is --1.4 with respect to pH. Ease of reduction of the oxide, as measured by its rate of reduction at a fixed potential at any given pH, decreases with increase of potential of formation of the oxide. A mechanism for reduction is suggested in which it is assumed that the reduction of an intermediate (Au~I) is the slow step in the over-all process.