Electrochemical enhancement of carbon monoxide oxidation over yttria-stabilized zirconia supported platinum catalysts I. Effect of catalyst morphology on kinetic behavior

Two Pt electrodes with different morphologies were prepared and studied usi ng an oxygen-ion conducting solid electrolyte electrochemical cell. Electro de 1 had a very porous catalyst/solid electrolyte interface and hence a hig h exchange current density while electrode 2 had a much less porous interfa ce and consequently a lower exchange current density. Open-circuit reaction rate measurements showed that the effective Pt surface areas of the two el ectrodes were similar. Carbon monoxide oxidation at temperatures from 623 t o 773 K was performed over the two electrodes. Under similar gas-phase cond itions and at the same overpotentials electrode 1 showed a nonfaradaic modi fication of activity while electrode 2 did not (the current densities passe d were very different due to a difference in the exchange current densities of the electrodes). This suggests that the work functions of the two elect rodes were not modified to the same extent by a similar imposed overpotenti al. A model is suggested whereby the kinetics of electrochemical oxygen sup ply to (or removal from) the electrode surface must be relatively fast comp ared to the rate of decomposition and reaction of an electrochemically indu ced spillover species to observe rate modifications. (C) 1999 The Electroch emical Society. All rights reserved.