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 galvanostatic reduction at current densities between 10 and 1000 µa/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 increasing 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 (AuII) is the slow step in the over‐all process.