Electrochemical Promotion of Ethylene Oxidation over Rh Catalyst Thin Films Sputtered on YSZ and TiO[sub 2]/YSZ Supports

The effect of electrochemical promotion of catalysis or nonfaradaic electrochemical modification of catalytic activity or electropromotion was investigated for the model reaction of ethylene oxidation on sputter-coated Rh films. The thin (40 nm) Rh films were deposited on -stabilized- (YSZ) and on YSZ coated with a thin porous layer. It was found that the catalytic activity of Rh for oxidation can be reversibly enhanced via anodic current or potential application by up to a factor of 80 and that the increase in the oxidation rate is up to 2000 times larger than the rate of supply of to the Rh catalyst-electrode. Smaller anodic currents cause periodic catalytic rate and potential oscillations. The layer was found to enhance the open-circuit catalytic activity and to stabilize the electrochemically promoted catalyst state. The observed pronounced electrochemical promotion behavior is due to the anodically controlled migration (back spillover) of species from YSZ to the Rh/gas interface and the concomitant destabilization, via repulsive lateral interactions, of the formation of surface The electropromotion of such thin metal catalyst films with metal dispersion near 10% is of significant importance for the practical utilization of the electrochemical promotion of catalysis.