In Situ Controlled Promotion of Catalyst Surfaces Via Solid Electrolytes: The NEMCA Effect

摘要

The catalytic activity and selectivity of metal films interfaced with solid electrolytes can be varied in situ in a dramatic and reversible manner by applying currents or voltages (typically ±1-2 V) between the catalyst film and a counter electrode also deposited on the solid electrolyte. Catalytic rates can thus be varied by up to a factor of 200. The induced steady-state change in catalytic rate is up to five orders of magnitude larger than the steady-state rate of electrochemical supply of ionic species from the solid electrolyte onto the catalyst surface. This novel effect termed Non-Faradaic Electrochemical modification of catalytic activity (NEMCA) has been studied for over 40 catalytic reactions on Pt, Rh, Pd, Ag, Ni and IrO_2 catalysts using a variety of solid electrolytes (O~(2-), F~-, Na~+ , H~+ conductors) and also, more recently, in aqueous alkaline solutions. Besides potential technological applications, this new effect allows for a systematic study of the role of promoters in heterogeneous catalysis. In this paper the main features of in situ controlled promotion are reviewed and the origin of the effect is discussed on the basis of recent XPS, TPD and cyclic voltammetric investigations.