Prof. Costas G. Vayenas, Department of Chemical Engineering, 
              University of Patras, Greece

    Electrochemical Activation of Catalysis using Solid Electrolytes

Abstract

Promoters can affect the chemisorptive and catalytic properties of 
solid catalysts in a very pronounced manner. In recent years it has 
been found that conductive solid catalysts can also be promoted 
electrochemically via the effect of Electrochemical Promotion or 
non-Faradaic Electrochemical Modification of Catalytic Activity 
(NEMCA).1-6
The metal catalyst is interfaced with a solid electrolyte (such as 
Y2O3-ZrO2, an O2- conductor1-3, _-Al2O3, a Na+ conductor4, or Nafion, 
a H+ conductor5) and an electrical current or potential (2V) is 
applied between the catalyst and an inert counter electrode in a 
fuel-cell-type or single-pellet-type catalytic reactor.
The induced increase in catalytic rate is up to 200 times larger than 
the open-circuit catalytic rate and up to 3x105 times larger than the 
rate of electrochemical supply of ions onto the catalyst surface.
The origin of electrochemical promotion will be discussed in light of 
several surface spectroscopic investigations including XPS, TPD, ACS 
and STM and the similarities with classical chemical promotion will 
be analyzed.
Rules dictating the four main types of classical and electrochemical 
promotion will be formulated (electrophobic, electrophilic, volcano 
and inverted volcano behavior) and a mathematical model, taking into 
account partial electron transfer upon chemisorption, will be 
presented which provides a good qualitative fit to all aspects of 
promotion-induced kinetics.

References
1. "The Dependence of Catalytic Activity on Catalyst Work Function", 
C.G. Vayenas, S. Bebelis and S. Ladas, Nature  343, 625-627 (1990).
2.  "Electrochemical Promotion", by J. Pritchard, Nature 343, 
pp.592-593 (1990).
3. "The Electrochemical Activation of Catalysis", C.G. Vayenas, M.M. 
Jaksic, S. Bebelis and S.G. Neophytides, in «Modern Aspects of 
Electrochemistry» (J.O'M. Bockris, B.E. Conway and R.E. White eds) 
Vol. 29, pp. 57-202 Plenum Press, NY, (1995).
4. "Electrochemical Modification of Catalytic Activity", C.G. Vayenas 
and I.V. Yentekakis, «Handbook of Catalysis», (G. Ertl, H. Knätzinger 
and J. Weitcamp eds) VCH Publishers, Weinheim, pp. 1310-1338 
(1997).C. Cavalca and G.L. Haller, J. Catal. 177, 389 (1998).
5. L. Ploense, M. Salazar, B. Gurau and E.S. Smotkin, J. Amer. Chem. 
Soc. 119, 11550 (1999).
6. "Electrocatalysis: Past, present and Future" in J.O'M. Bockris and 
Z.S. Minevski, Electrochimica Acta 39, 1471-79 (1994), last section, 
1478 "NEMCA 1990's"