Electrochemical promotion of CO oxidation on Pt/YSZ: The effect of catalyst potential on the induction of highly active stationary and oscillatory states

We have investigated the kinetics, rate oscillations and electrochemical promotion of CO oxidation on Pt deposited on YSZ using a standard oxygen reference electrode at temperatures 300-400 degrees C. We have found that electropromotion is small (rho < 3) when the catalyst potential U-WR, is below 0.4 V and very pronounced (rho similar to 9, Lambda similar to 1500) when U-WR exceeds 0.4 V. This sharp transition in the electropromotion behavior is accompanied by an abrupt change in reaction kinetics and in catalyst potential. For fixed temperature this transition, which leads to a highly active electroprornoted state, occurs at specific P-O2(1/2)/P-CO ratio and catalyst potential. It is shown via comparison with independent catalyst potential-catalyst work function measurements that the transition corresponds to the onset of extensive O2- spillover from YSZ onto the catalyst Surface, and concomitant establishment of an effective double layer at the catalyst-gas interface, which is the cause of the highly active electropromoted state. (C) 2009 Elsevier B.V. All rights reserved.