A model for the electrochem. promotion induced by electrochem. generated promoting species is proposed. The formation rate of promoters is assumed to be proportional to the availability of free surface sites at the solid electrolyte/catalyst/gas three-phase boundary, and their spreading out over the gas exposed catalyst surface to be rapid compared to the rate of their consumption. The model predicts exponential catalytic rate transients with current dependent polarization and current independent relaxation behavior. It enables detn. of the max. limiting value of the Faradaic efficiency, being a current independent property of the catalytic system. The validity of the model was confirmed by anodic galvanostatic promotion expts. of ethylene combustion over IrO2/YSZ catalyst at highly oxidative feed conditions. [on SciFinder (R)]