The catalytic activity of an IrO2 catalyst used as an electrode on a YSZ solid electrolyte cell for the gas-phase combustion of ethylene can be increased by electrochem. pretreatment. Thus, the polarization of the IrO2 electrode during 90 min at 300 mA, relative to a gold electrode, both deposited on YSZ, increases the activity of the IrO2 catalyst after current interruption by a factor of 3. In situ catalyst work function measurements showed that after the electrochem. pretreatment the IrO2 catalyst obtains higher work function. The activation of the catalyst is explained through the formation of a higher oxide, IrO2+d. [on SciFinder (R)]