Analysis of the high-temperature methanol oxidation behaviour at carbon-supported Pt /Ru catalysts A.S. Arico ` a, *, V. Baglio a , A. Di Blasi a , E. Modica a , P.L. Antonucci b , V. Antonucci a a CNR-Institute for Transformation and Storage of Energy, 398 via Salita Santa Lucia Sopra Contesse, 98126 Messina, Italy b Department of Mechanics and Materials, University of Reggio Calabria, Reggio Calabria, Italy Received 18 November 2002; received in revised form 12 May 2003; accepted 28 May 2003 Abstract Methanol oxidation behaviour at three Pt  /Ru catalysts varying by the concentration of active phase on the carbon support has been investigated in a wide temperature range (80  /130 8C). An increase of the adsorbed methanolic residue stripping charge is observed with the increase of catalyst dispersion. As the temperature is increased, the stripping peak potential shifts more negatively accounting for a lower activation barrier for the reaction. An increase of temperature above 90 8C also produces a strong decrease in the coverage of adsorbed methanolic residues. The fuel cell performance is significantly enhanced by catalysts with intrinsically high catalytic activity, whereas the methanol reaction rate appears to be less influenced by an increase in coverage of active species. Catalysts characterized by a higher degree of alloying and metallic behaviour on the surface appear to be more active towards methanol oxidation. However, the physico-chemical properties of the catalysts have less influence on the anode electrochemical behaviour at high temperature since CO poisoning is alleviated under such conditions. The decrease of CO-like species coverage with temperature and the methanol tolerance characteristics of a Pt/C cathode are also discussed in relation to the crossover drawback of direct methanol fuel cells. # 2003 Elsevier B.V. All rights reserved. Keywords: Stripping of adsorbed methanol; Pt  /Ru catalysts; Direct methanol fuel cell; X-ray diffraction; X-ray photoelectron spectroscopy 1. Introduction Direct methanol fuel cells (DMFCs) operating at high temperatures are becoming an important area of re- search. Significant advantages of these systems are the enhanced methanol oxidation kinetics and the reduced size and complexity of the fuel cell device [1  /5]. A direct methanol fuel cell based on a high-temperature proton conducting membrane with suitable conductivity and stability up to 130  /150 8C and characterized by low thermal and water management constraints would become a viable system for mobile applications. How- ever, methanol electro-oxidation at 130 8C is an activa- tion controlled reaction with a Tafel slope of 130 mV dec 1 [6]; the optimal Pt/Ru relative composition in the bulk and on the surface is about 1:1 [7,8]. The bifunctional effect appears to govern the reaction mechanism at high temperatures, with the removal of adsorbed carbon monoxide species being the rate- determining step [6  /8]. At present, most of the efforts have been addressed towards the development of high- temperature membranes since this is a key aspect to achieve good performance and prolonged life-time [5,8,9]. Yet, although interesting results have been obtained by high-temperature operation, the significant amount of the required noble metal loading (1  /2 mg cm 2 ) [1] indicates that further development of the anodic catalyst is needed. This aspect may be addressed through a better comprehension of the high-temperature behaviour and as in depth analysis of the various factors influencing the performance. One of the main disadvantages of high-temperature operation is the high-pressure requirement to maintain a good hydration level inside the membrane. Besides these aspects, the pressure is expected to have a significant influence on the coverage of reacting molecules and * Corresponding author. Tel.:  /39-090-624234/7; fax:  /39-090- 624247. E-mail address: arico@itae.cnr.it (A.S. Arico `). Journal of Electroanalytical Chemistry 557 (2003) 167  /176 www.elsevier.com/locate/jelechem 0022-0728/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0022-0728(03)00369-3