ELECTROCHEMICAL PROMOTION OF A DISPERSED PLATINUM CATALYST

The effect of electrochemical promotion or nonfaradaic electrochemical modification of catalytic activity (NEMCA effect) was investigated fo r the first time on highly dispersed Pt catalyst (dispersion 0.2-1) su pported on polycrystalline Au films which had been deposited on Y2O3-s tabihzed ZrO2 (YSZ), an O2- conductor. The oxidation of ethylene to CO 2 was chosen as a model reaction. It was found that the catalytic rate of ethylene oxidation could be reversibly enhanced by up to a factor of 5 via electrical current or potential application between the suppo rted Pt/Au catalyst and a counter Au electrode also deposited on the Y SZ ionic conductor. The increase in catalytic rate is typically a fact or of 10(3) higher than the rate, I/2F, of electrochemical supply or r emoval of O2- to (from) the dispersed Pt/Au catalyst from (to) the sol id electrolyte. Analysis of the time constant of the catalytic rate up on current application or interruption suggests that, as in previous e lectrochemical promotion studies with continuous metal film catalysts, the observed promotional phenomena are due to electrochemically contr olled migration (spillover and backspillover) of anionic oxygen betwee n the solid electrolyte and the metal catalyst surface and to the effe ct of this anionic oxygen on the chemisorptive bond strength of coadso rbed oxygen and ethylene. (C) 1998 Academic Press.