Components for PEM fuel cell systems using hydrogen and CO containing fuels J. Divisek, a H.-F. Oetjen, a V. Peinecke, a V. M. Schmidt b * and U. Stimming c a Institut fuÈr Energieverfahrenstechnik, Forschungzentrum JuÈlich, 52425 JuÈlich, Germany b Institut fuÈr Umwelttechnik, Fachhochschule Mannheim, Windeckstrasse 110, 69163 Mannheim, Germany c Physik-Department E 19, Technische UniversitaÈt MuÈnchen, James-Frank-Strasse 1, 85748 Garching, Germany (Received 14 January 1998; in revised form 14 January 1998) AbstractÐProton exchange membrane fuel cells (PEMFC) show a signi®cant performance drop in CO con- taining hydrogen as fuel gas in comparison to pure hydrogen. The lower performance is due to CO adsorp- tion at the anode thus poisoning the hydrogen oxidation reaction. Two approaches to improve the cell performance are discussed. First, the use of improved electrocatalysts for the anode, such as PtRu alloys, can signi®cantly enhance the CO tolerance. On the other hand, CO poisoning of the anode could be avoided by the use of non-electrochemical methods. For example, the addition of liquid hydrogen peroxide to the humidi®cation water of the cell leads to the formation of active oxygen by decomposition of H 2 O 2 and the oxidation of CO. In such a way a complete recovery of the CO free cell performance is achieved for H 2 /100 ppm CO. # 1998 Elsevier Science Ltd. All rights reserved Key words: proton exchange membrane fuel cell (PEMFC), CO poisoning, CO removal, PtRu anodes, H 2 O 2 addition. INTRODUCTION The proton exchange membrane fuel cell (PEMFC) is regarded as highly attractive for mobile as well as stationary applications due to his high power den- sity at temperatures of 60±1008C and his compact cell design. The cell can be operated using dierent energy carriers as shown in Fig. 1. The utilization of methanol or natural gas require a reformer which produces a hydrogen rich synthesis gas. The required process heat is supplied by a catalytic hea- ter. In the case of methanol, a fuel with a compo- sition of 74% H 2 , 25% CO 2 and 1±2% CO of the dry gas can be obtained with a high methanol con- version rate [1, 2]. The CO concentration must be reduced in a separate gas treatment unit down to <10 ppm if conventional carbon supported Pt is used as anode catalyst. Otherwise, CO molecules adsorb strongly on active sites of catalyst and inhi- bit the hydrogen oxidation reaction at the anode. In addition to optimization of the gas treatment unit in the periphery of the fuel cell, several approaches are being discussed to solve the CO problem. One possibility is the search for an anode catalyst which oxidize adsorbed CO at lower electrode potentials than Pt showing at the same time a high activity for hydrogen oxidation. A signi®cant improvement of the cell performance has been described for CO levels up to 250 ppm using PtRu alloys as anode catalyst [3]. On the other hand, the internal CO removal by injection of oxygen into the fuel gas ¯ow has been demonstrated to reach the cell per- formance of CO free hydrogen [4]. The same per- formance as in pure hydrogen was observed with fuels containing 100±500 ppm CO [5]. Recently, it has been reported that the addition of H 2 O 2 show comparable results [6]. The decomposition of H 2 O 2 to active oxygen leads to CO oxidation and to an enhanced cell performance. The aim of the present paper is to report recent results on the evaluation of cell performance in CO containing hydrogen. The ®rst part is devoted to the use of Pt and PtRu as anode catalysts. The sec- ond approach is the CO removal by oxygen which Electrochimica Acta, Vol. 43, No. 24, pp. 3811±3815, 1998 # 1998 Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain 0013±4686/98 $19.00 + 0.00 PII: S0013-4686(98)00140-6 *Author to whom correspondence should be addressed. Tel.: +49 621 292 6307; Fax: +49 621 292 6470; E-mail: v.m.schmidt@t-online.de 3811