Oxygen Reduction Reaction Kinetics of SO[sub 2]-Contaminated Pt[sub 3]Co and Pt/Vulcan Carbon Electrocatalysts

Sulfur dioxide, , 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 poisoning of a Vulcan-carbon-supported platinum cobalt alloy 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 is two times more active than the Pt/VC. Upon exposure to S(IV) solutions, the 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 production, as adsorbed sulfur species inhibit the four-electron ORR. The 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 than the Pt/VC by potential cycling, implying a weaker bonding between species and . We conclude that is more susceptible to poisoning by than Pt at a given Pt loading, but its activity is more easily recovered.