Solid State Ionics 136–137 (2000) 687–692 www.elsevier.com / locate / ssi Electrochemical promotion of oxide catalyst for the gas phase combustion of ethylene * J. Nicole, Ch. Comninellis EPFL – Institute of Chemical Engineering, Swiss Federal Institute of Technology, CH-1015 Lausanne, Switzerland Abstract The reaction rate, the catalyst potential, the catalyst work function and the voltammetric charge have been in situ measured during a galvanostatic transient of ethylene combustion on an IrO catalyst at 3808C. It was found that the catalytic activity 2 of an IrO catalyst could be increased by electrochemical pretreatment. In situ catalyst work function measurements showed 2 that after the electrochemical pretreatment the IrO catalyst has a higher work function. Cyclic voltammetry measurements 2 have shown that there is a linear relation between the voltammetric charge and the rate of ethylene combustion. The activation of the catalyst was explained through the formation of a higher oxide in a two-stage mechanism.  2000 Elsevier Science B.V. All rights reserved. Keywords: IrO catalyst; Gas phase combustion; Solid electrolyte; Electrocatalysis; NEMCA 2 1. Introduction electrochemical promotion (EP) or non-Faradaic electrochemical modification of catalytic activity Recently it was found that the catalytic activity (NEMCA) [2–6]. and selectivity of a metal catalyst, supported on solid The in situ variation and monitoring of the amount electrolytes, for example Y O -stabilized ZrO of promoters under reaction conditions open new 2 3 2 (YSZ), can be altered dramatically upon polarising possibilities not only for a better understanding of the catalyst-solid electrolyte using a solid electrolyte the mechanism of spillover and promotion, but also cell of the type: in the development of a new generation of catalysts for practical applications. reactants(g), catalyst / solid electrolyte /Au, reac- In this paper we summarise previous EP studies [7–11] together with some new results on ethylene tants(g). (C H ) complete combustion on IrO and discuss 2 4 2 In this cell the catalyst was used as the working the origin of the EP in the light of recent work electrode and Au as the counter electrode. function and cyclic voltammetry investigations [12]. This phenomenon was discovered by Vayenas in 1988 [1] and has been reported in the literature as 2. Experimental The electrochemical cell used consists of a thin *Corresponding author. Fax: 141-21-693-3190. rectangular electrolyte plate (26 313 mm and 1 mm E-mail address: christos.comninellis@epfl.ch (Ch. Comninel- lis). thick) of 6 mol.% YSZ. Gold paste counter (50 0167-2738 / 00 / $ – see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S0167-2738(00)00511-7