No 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 tm/cm 2. 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. Currentpotential 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.

No abstract

No abstract

Overpotential measurements for the Fe + + +/Fe + + couple on passive Ni, Fe, and Ti, were carried out in solutions of fixed ionic strength but of varying pH. Tafel lines were generally obtained with exchange currents between 10 -7 and 10 -5 amp/cm 2 and cathodic transfer coefficients of about 0.45. The anodic transfer coefficients were less, particularly with Ti and Fe electrodes. A limiting anodic current, which was unrelated to diffusion of Fe + + ion in solution, was observed under certain conditions on Fe and Ti. The contribution of ionic current to the total current through the film is negligible in most cases. In general, the passive film has rectifying properties, the easy direction of electron flow being from metal to solution. This rectification is additional to the usual Faradaic rectification observed with most electrochemical reactions. The apparent transfer coefficients, calculated from the anodic and cathodic polarization curves, yield sums significantly less than unity. The results demonstrate the existence of a potential drop across the passive film, the magnitude of which depends on the thickness and composition of the film.The electrochemical cell was described previously (9). Potentials were measured through a Luggin-Haber capillary probe 0.05 cm OD placed 0.10 cm