Transient behavior of electrochemical promotion of gas-phase catalytic reactions

Electrochemical promotion (EP) of gas-phase catalysis with O2−-conducting solid electrolytes is addressed. The behavior of the reference electrode, prepared by deposition of a gold film, was found to be quasi-reversible, 12O2/O2− being the potential determining redox couple. A fairly symmetrical potential distribution in the electrochemical cell was calculated. The IR drop correction was shown to be negligible at low currents typical to EP experiments. The electrochemical activation of catalysis is due to the act of promoters at the catalyst | gas interface. A model is proposed to describe catalytic reaction rate transients assuming free surface site dependent formation, rapid spreading-out and first order rate consumption of O2− promoters. The model predicts exponential catalytic rate transients with current dependent polarization and current independent relaxation behavior. It enables determination of the maximum limiting value of the Faradaic efficiency, being a current independent property of the catalytic system. The validity of the model is confirmed for anodic galvanostatic EP of ethylene combustion over IrO2/YSZ catalyst.