The catalytic activity for the gas phase combustion of ethylene of an IrO2 film, used as electrode in a solid electrolyte cell, can be increased by polarizing the metal-solid electrolyte interface. The catalytic activity remains higher even after current interruption. To explain the increase in the open circuit rate after polarization the authors speculate that the IrO2 catalyst is oxidized at the catalyst-solid electrolyte interface, forming IrO2+d which is transported by surface and/or bulk diffusion to the gas exposed catalyst, thus modifying its catalytic activity. [on SciFinder (R)]