ANION SURFACE INTERACTIONS .2. NITROUS-OXIDE REDUCTION AS A PROBE OF ANION ADSORPTION ON TRANSITION-METAL SURFACES

The reduction of nitrous oxide on several transition metal surfaces in aqueous sulphuric and perchloric acids has been studied using cyclic voltammetry. It is proposed that the rate-limiting step is the decomposition of N2O(ads) to gaseous dinitrogen and adsorbed oxygen. Adsorbed hydrogen appears not to play an essential, catalytic role in this irreversible process. The electroreduction current itself is believed to arise solely from rapid reduction of the adsorbed oxygen intermediate, i.e. O(ads) + 2H+ + 2e- --> H2O, and the rate of the reaction is greatest when the number of free metal sites is maximised. A strong correlation between anion adsorption-desorption and hysteresis in the N2O reduction current as a function of the potential has been used to demonstrate that perchlorate may be reduced to chloride (as described recently by Wieckowski and coworkers) on a variety of metal electrode surfaces. These include polycrystalline palladium, rhodium, lr{111} and Pt{110}. As a result of our investigations, we re-''amine the assertion made by Parsons and coworkers that strongly adsorbed hydrogen must be invoked to explain the voltammetry of nitrous oxide reduction on Pt{111}.