The catalytic activity of IrO2 catalyst used as an electrode on a YSZ solid electrolyte cell for the gas phase combustion of ethylene can be increased by electrochem. pre-treatment. Thus, the polarization of the IrO2 electrode for 90 min at 300 mA, relative to a Au 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. pre-treatment 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)]