The electro reduction of nitric oxide on bulk platinum in acid solutions

Abstract

The electroreduction of nitric oxide on smooth platinum in aqueous perchloric and sulfuric acid solutions has been studied using linear potential sweep and rotating disc electrode techniques. Three peaks were observed with linear sweep voltammetry. The first is a well-resolved peak at E = 0.25 V vs sce. Analysis yields a Tafel slope of approximately 0.110 V which is independent of acid concentration and a pseudo-first order rate constant that varies linearly with hydrogen ion activity. The second order rate constant was found to be k° = 0.43 cm 4 mol −1 s −1. Discrepancies between these values and previously reported literature values are explained in terms of an electrode reduction pretreatment in situ and the state of the platinum surface. A second peak at 0.1 V vs sce is not well resolved, but evidence is presented suggesting that this peak is related to nitrogen formation at a zero oxidation state on a reduced electrode. A third peak at −0.1 V vs sce appears to be a mixed diffusion-adsorption peak associated mainly with ammonia synthesis. The rotating disc electrode experiments support these conclusions. Both techniques produce evidence of kinetic complications in the first step of the electrochemical reduction and these are discussed in terms of solution chemistry and the surface state (pretreatment history) of the electrode.