Cg. Vayenas et al., ELECTROCHEMICAL PROMOTION IN CATALYSIS - NON-FARADAIC ELECTROCHEMICALMODIFICATION OF CATALYTIC ACTIVITY, Electrochimica acta, 39(11-12), 1994, pp. 1849-1855
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.