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 decompo sition of N2O(ads) to gaseous dinitrogen and adsorbed oxygen. Adsorbed hydrogen appears not to play an essential, catalytic role in this irr eversible 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 grea test when the number of free metal sites is maximised. A strong correl ation between anion adsorption-desorption and hysteresis in the N2O re duction current as a function of the potential has been used to demons trate that perchlorate may be reduced to chloride (as described recent ly by Wieckowski and coworkers) on a variety of metal electrode surfac es. These include polycrystalline palladium, rhodium, lr{111} and Pt{1 10}. As a result of our investigations, we re-''amine the assertion ma de by Parsons and coworkers that strongly adsorbed hydrogen must be in voked to explain the voltammetry of nitrous oxide reduction on Pt{111} .