Structure-Activity Relationships for the Oxygen Reduction Reaction in Porous Hollow PtNi/C Nanoparticles

Enhancing the specific activity and the mass activity of catalysts for the oxygen reduction reaction (ORR) in proton-exchange membrane fuel cells is currently achieved by alloying Pt with an early or late transition metal. By using hollow PtNi/C nanoparticles with different physicochemical properties (Ni content, lattice parameter, specific surface area), we show that structural defects such as grain boundaries also contribute to the enhancement of the ORR kinetics. Their concentration was quantified by means of the structure sensitivity of the electrooxidation of a COads monolayer, that is, the presence of an oxidation prepeak in the COads stripping voltammogram. A straightforward relationship is established between the ratio of the charge under the prepeak Q(pp,CO) to the total COads electrooxidation charge and the specific activity for the ORR. The present study provides a knowledge base for designing more efficient ORR electrocatalysts.