Non-Faradaic electrochemical modification of catalytic activity: the work function of metal electrodes in solid electrolyte cells

Abstract

The catalytic activity and selectivity of metal films used as electrodes in solid electrolyte cells can be altered dramatically and reversibly by polarizing the metal-solid electrolyte interface. This effect, termed non-Faradaic electrochemical modification of catalytic activity (NEMCA) leads to steady state catalytic rate increases up to 3×10 5 times higher than the steady state rate of removal or supply of ions. Catalytic rates can be enhanced reversibly up to 7000%. The NEMCA effect has been already demonstrated with O 2− and Na + conducting solid electrolytes using Pt, Pd, Ag, Ni, Rh and Au electrodes. In the present work we summarize some of the common experimental findings of previous studies and discuss the origin of NEMCA which lies in the controlled variation of the catalyst surface work function upon polarization of the catalyst-solid electrolyte interface. We show both experimentally, using a Kelvin probe, and theoretically that in solid electrolyte cells there exists a one-to-one correlation between ohmic-drop-free electrode potential and gas-exposed electrode surface work function. Thus solid electrolyte cells with metal electrodes can be used both to measure and to control the gas-exposed electrode work function. This controlled variation in catalyst-electrode work function is due to ion spillover and results in significant variations in the binding strength of chemisorbed species, thus causing the NEMCA effect.