The effect of preadsorbed sulfur on nitric oxide reduction on porous platinum black electrodes

Abstract Sulfur can be deposited on porous platinum black gas diffusion cathodes to influence the course of the electrogenerative reduction of nitric oxide. Polarization (performance) curves and reactor selectivity data are compared for untreated cathodes and those treated with reduced SO 2 . Pure and dilute nitric oxide cathode feeds were used. With pure nitric oxide, the limiting current corresponding to nitrous oxide production was reduced 65% by preadsorbed sulfur. With dilute nitric oxide the two limiting currents observed were only slightly decreased by sulfur deposition. With both feeds adsorbed sulfur affects product distribution at low cell potentials so that hydroxylamine production is favored. The surface of the platinum black electrodes was characterized by hydrogen adsorption, and sulfur coverages on treated electrodes were determined by cyclic voltammetry in a separate three-electrode cell. The results from electrogenerative reduction are discussed in terms of steric and mechanistic consequences of sulfur coverages.