Calorimetric study of the reversibility of CO pollutant adsorption on high loaded Pt/carbon catalysts used in PEM fuel cells Georgeta Postole 1 , Simona Bennici, Aline Auroux * Institut de Recherches sur la Catalyse et l’Environnement de Lyon, UMR 5256, CNRS-UCBLyon1, 2 av. Albert Einstein, 69626 Villeurbanne Cedex, France 1. Introduction It is universally accepted that hydrogen is one of the most promising energy carriers, as it can be used as a clean fuel in a variety of energy end-use sectors, including conversion to electricity without CO 2 emission [1–3]. Therefore its demand will greatly increase in the near future. Proton exchange membrane fuel cells (PEMFCs) have great potential for mobile and stationary power supply applications [4,5]. The biggest advantage of PEMFCs over internal combustion engines in automotive vehicles is the absence of emissions when using hydrogen as the fuel and air as the oxidant [6]. In proton exchange membrane fuel cells, hydrogen is oxidized at the anode; free protons which appear as a result of this oxidation enter into the electrolyte and they are transported to the cathode. Such power devices operate at high efficiency when pure hydrogen is used. However, the production, storage, and refuelling infrastruc- ture are still significant obstacles to the widespread adoption of hydrogen as a fuel [7]. To avoid such difficulties, the use of hydrogen-rich synthetic gas obtained from steam-reforming or partial oxidation of alcohols or hydrocarbons can be a feasible choice, but in this case the efficiency of PEMFCs would fail due to the presence of impurities such as CO, H 2 S, NH 3 , organic sulphur- carbon and carbon-hydrogen compounds in hydrogen fuel [8–11]. Using special selective oxidation catalysts, the CO concentration in hydrogen can be further reduced to approximately 2–100 ppm. But even at this level, the CO-poisoning effect could significantly affect the long-term performance of the PEMFC stack [12]. Although a huge variety of materials have been investigated, so far the most common catalyst for hydrogen/oxygen fuel cells on the anode and cathode sides is nano-dispersed platinum supported on active carbon [2,3,5,11,13]. The most important disadvantage of Pt/C materials is that their catalytic activity is negatively affected, even at low temperatures, by traces of CO present in the feedstock at concentrations as low as 10 ppm [14–17]. The CO-poisoning effect for hydrogen adsorption arises from a blocking of the surface active sites by CO, as carbon monoxide molecules are much more strongly bonded to the surface than hydrogen and the oxidation potential of adsorbed CO is much higher than that of adsorbed hydrogen [18]. The adsorbed CO not only affects the reactivity of Applied Catalysis B: Environmental 92 (2009) 307–317 ARTICLE INFO Article history: Received 21 June 2009 Received in revised form 27 July 2009 Accepted 3 August 2009 Available online 7 August 2009 Keywords: Microcalorimetry Differential heat of adsorption Carbon monoxide Platinum Carbon support ABSTRACT A major obstacle to the broader use of fuel cells is the poisoning of supported Pt catalysts by the CO present in virtually all feeds. In this paper, the microcalorimetry technique was employed to study and compare the CO adsorption properties of different commercial carbon-supported platinum catalysts with high Pt loading, aimed to be used in proton exchange membrane fuel cells (PEMFCs) applications. Combined with other techniques of characterization, such as BET, XRD, TPD-MS and TPR, adsorption microcalorimetry has permitted a better understanding of the studied systems. The pore architecture of Pt/C catalysts was found to influence the kinetics of heat release during CO adsorption. The accessibility of CO molecules to the adsorption sites increased with the mesoporosity of the catalyst. The degree of catalyst poisoning by CO upon successive air/H 2 /CO cycles varied between 2 and 30% for the different studied samples. These results confirm that the surface chemistry of the catalyst, and in particular the Pt deposition method, affects the surface site energy distribution and consequently the adsorptive properties towards H 2 and CO. It was found that both H 2 and CO are chemisorbed on the investigated samples. Pt/C powders exhibit higher differential heats of carbon monoxide adsorption in comparison with hydrogen adsorption. A reaction between pre-adsorbed H 2 and CO from the gas phase takes place on Pt/C catalysts as a result of competitive adsorption. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +33 472 44 53 98; fax: +33 472 44 53 99. E-mail address: aline.auroux@ircelyon.univ-lyon1.fr (A. Auroux). 1 Permanent address: Institute of Physical Chemistry ‘‘Ilie Murgulescu’’ of the Romanian Academy, Spl. Independentei 202, 060021 Bucharest, Romania. Contents lists available at ScienceDirect Applied Catalysis B: Environmental journal homepage: www.elsevier.com/locate/apcatb 0926-3373/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2009.08.009