Oxygen Reduction Reaction Kinetics of SO2-Contaminated Pt3Co and Pt/Vulcan Carbon Electrocatalysts

Sulfur dioxide, SO2, is a common impurity in air that is known to deactivate electrocatalysts for the oxygen reduction reaction (ORR) at proton exchange membrane fuel cell cathodes. The SO2 poisoning of a Vulcan-carbon-supported platinum cobalt alloy (Pt3Co/VC) is compared to that of a standard platinum (Pt/VC) electrocatalyst using cyclic voltammetry (CV) and rotating ring-disk electrode (RRDE) methodology at controlled concentrations of S(IV) in an oxygen-free solution. The CV and RRDE measurements show that for electrodes with the same Pt loading, the Pt3Co/VC is two times more active than the Pt/VC. Upon exposure to S(IV) solutions, the Pt3Co/VC nanoparticle electrocatalysts are more poisoned than the Pt/VC ones, and their initial sulfur coverage is higher. The poisoning of both catalysts is accompanied by an increase in the amount of H2O2 production, as adsorbed sulfur species inhibit the four-electron ORR. The Pt3Co/VC electrocatalyst loses 80% activity in a 0.0001 M S(IV) compared to a 30% loss by the Pt/VC electrocatalysts. The adsorbed sulfur species are more easily removed from the Pt3Co/VC than the Pt/VC by potential cycling, implying a weaker bonding between S-x species and Pt3Co/VC. We conclude that Pt3Co is more susceptible to poisoning by SO2 than Pt at a given Pt loading, but its activity is more easily recovered. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3126383] All rights reserved.