A solid electrolyte catalytic reactor was used to investigate the change in catalytic activity of the electrode upon conduction of O2- ions through the electrolyte, The reactor consisted of an yttria-stabilized zirconia electrolyte disk on which a thin him of the Ag electrode was deposited, As the catalyst potential was applied below the open circuit potential or, equivalently, as O2- ions were electrochemically removed from the Ag catalyst electrode to the counter electrode through the solid electrolyte, its influence on the O-2 exchange reaction in He-O-2 flow and CH3OH oxidation to HCHO and CO2 in He-O-2-CH3OH flow was investigated, It was found from the O-2 exchange reaction study that slow diffusion of adsorbed oxygen to the catalyst-electrolyte-gas three-phase boundary, where charge transfer took place, caused a limiting current, In CH3OH oxidation, a lowered open circuit potential was observed when CH3OH was added to the He-O-2 how Lowering the catalyst potential below this new open circuit potential was found to cause a reversible, somewhat nonfaradaic increase in the rate of CO2 formation, but had little effect on the rate of HCHO formation. Based on the rate equations, this behavior was interpreted in terms of an activated surface reaction between adsorbed species due to the change in the catalyst work function with changing catalyst potential.