Carbon supported Pt–Co alloys as methanol-resistant oxygen-reduction electrocatalysts for direct methanol fuel cells Jose ´ Ricardo Cezar Salgado a , Ermete Antolini a,b, * , Ernesto Rafael Gonzalez a a Instituto de Quı ´mica de Sa ˜o Carlos, USP, C.P. 780, Sa ˜o Carlos, SP 13560-970, Brazil b Scuola di Scienza dei Materiali, Via 25 Aprile 22, 16016 Cogoleto, Genova, Italy Received 28 June 2004; received in revised form 5 November 2004; accepted 11 November 2004 Available online 22 December 2004 Abstract The electrocatalysis of the oxygen reduction reaction on carbon supported Pt and Pt–Co (Pt/C and Pt–Co/C) alloy electrocatalysts was investigated in sulphuric acid (both in the absence and in the presence of methanol) and in direct methanol fuel cells (DMFCs). In pure sulphuric acid Pt–Co/C alloys showed improved specific activity towards the oxygen reduction compared to pure platinum. In the methanol containing electrolyte a higher methanol tolerance of the binary electrocatalysts than Pt/C was observed. The onset potential for methanol oxidation at Pt–Co/C was shifted to more positive potentials. Accordingly, Pt–Co/C electrocatalyts showed an improved performance as cathode materials in DMFCs. # 2004 Elsevier B.V. All rights reserved. Keywords: Pt–Co/C alloy; Oxygen reduction electrocatalyst; Direct methanol fuel cells 1. Introduction Direct methanol fuel cells (DMFCs) are promising electrochemical energy converters for a variety of applica- tions because of the system simplicity. The two basic electrode reactions of the DMFC are: CH 3 OH þ H 2 O ! CO 2 þ 6H þ þ 6e (1) 3 2 O 2 þ 6H þ þ 6e ! 3H 2 O (2) The liquid-feed system does not require any fuel processing equipment and can be operated even at room temperatures. Another advantages of the DMFC is the fact that it does not require complex humidification and heat management mod- ules as in the hydrogen fed proton exchange membrane (PEM) fuel cell system because the dilute methanol + water mixtures circulating around the DMFC provides the neces- sary humidification and heat regulation. These advantages allow the DMFC to be customized for use in portable electronic devices [1]. The major problems, which decrease the efficiency of conversion of the chemical energy of the methanol fuel to electrical energy in a DMFC, are the slow methanol electrooxidation reaction kinetics at conventional Pt anode electrocatalysts and the methanol crossover through the polymer electrolyte. The poor kinetics of metha- nol oxidation at the anode is mostly due to self-poisoning of the surface by reaction intermediates such as CO, which are formed during dehydrogenation of the methanol [2]. There- fore, in order to improve the efficiency of the DMFC, anode electrocatalysts are required which combine a high activity for methanol dehydrogenation and an improved tolerance towards CO poisoning [3–6]. Additionally, as it is well known, when two solutions of different concentrations are separated by a membrane, a diffusion of the solute takes place across the membrane from the more concentrated to the more dilute solution. This transport process gives rise to one of the major chemical problems in direct methanol fuel cells, where a difference of methanol concentration exists between the anodic and the cathodic compartments. The methanol transport through www.elsevier.com/locate/apcatb Applied Catalysis B: Environmental 57 (2005) 283–290 * Corresponding author. Tel.: +55 16 3373 9951/+39 010 916 2880; fax: +55 16 3373 9952/+39 010 918 2368. E-mail address: ermantol@libero.it (E. Antolini). 0926-3373/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2004.11.009