The electrochem. promoted induction of self-sustained catalytic rate and potential oscillations during C2H4 oxidn. was studied over sputtered Rh thin (40 nm catalyst films interfaced with ZrO2 (8 mol% Y2O3)). The reaction rate oscillates simultaneously with the catalyst potential, and always in the opposite direction. The electrochem. induced oscillatory rate is typically 60 times larger than the open-circuit catalytic rate and 1000 times larger than the electrochem. rate of O2- supply to the catalyst. The phenomenon is completely reversible and only obsd. under anodic polarization where the rate oscillates between the values corresponding to metallic Rh and surface Rh2O3. The oscillations are caused by the electrochem. controlled backspillover of O2- to the catalyst surface and the concomitant, via repulsive lateral interactions, decompn. of surface Rh oxide followed by surface reoxidn. to Rh2O3 by gaseous O2. [on SciFinder (R)]