POISONING EFFECTS OF ARSENIC SPECIES ON H ADSORPTION AND KINETIC-BEHAVIOR OF THE H-2 EVOLUTION REACTION AT PT IN KOH SOLUTION

Effects of catalyst poisons on the kinetics of the cathodic hydrogen e volution reaction are of interest in relation to changes in coverage b y the H intermediate and coupled changes of reaction mechanism. Also, the effects of poisons are of practical significance in promoting sorp tion of H into transition metals and inhibiting corrosion. Experiments were carried out on the effects of As species on the kinetics of H-2 evolution at Pt electrodes in aqueous KOH as a model system where quan titative information can be derived on coverage by the overpotential-d eposited (OPD) H that is the intermediate in the H-2 evolution reactio n. Arsenic poison effects on the states of underpotential-deposited H by means of cyclic voltammetry were also discussed. For the OPD H, rec ording and analysis of open-circuit potential relaxation transients in the absence and presence of As poison species provides information on the H coverage and the effects of the co-adsorbed poison on it. Kinet ic simulation calculations provide quantitative estimates of the chang es in rate constants of reaction steps arising from the presence of th e poison.