ELECTROCHEMICAL PROMOTION IN CATALYSIS - NON-FARADAIC ELECTROCHEMICALMODIFICATION OF CATALYTIC ACTIVITY

The catalytic activity and selectivity of the gas-exposed electrode su rface of metal electrodes in solid electrolyte cells is altered dramat ically and reversibly upon polarizing the metal-solid electrolyte inte rface. The induced steady-state change in catalytic rate can be up to 9000% higher than the normal (open-circuit) catalytic rate and up to 3 x 10(5) higher than the steady-state rate of ion supply. This new eff ect of non-faradaic electrochemical modification of catalytic activity (NEMCA) has been already demonstrated for more than 30 catalytic reac tions on Pt, Pd, Rh, Ag, Au and Ni surface by using O2-, F-, Na+ and H + conducting solid electrolytes. There is also a recent demonstration for an aqueous electrolyte system. In this paper the common features o f previous NEMCA studies are summarized and the origin of the effect i s discussed in light of recent in situ work function and XPS measureme nts which showed that: (1) solid electrolyte cells with metal electrod es are work function probes and work function controllers, via potenti al application, for their gas-exposed electrode surfaces; and (2) NEMC A is due to an electrochemically driven and controlled spillover of io ns from the solid electrolyte onto the gas-exposed electrode surface. These spillover ions establish an effective electrochemical double lay er and act as promoters for catalytic reactions. This interfacing of e lectrochemistry and catalysis offers several exciting theoretical and technological possibilities.