(753f) Oxygen Reduction Reaction On Pt Nanoparticles Supported On Defective Graphene From First Principles

The oxygen reduction reaction (ORR) is of central focus amidst ongoing studies of electrode reactions in polymer electrolyte membrane (PEM) fuel cells due to the slow kinetics that take place at the cathode. To improve ORR kinetics, Pt and Pt alloy nanocatalysts supported on graphene, graphene nanoplatelets, and nanoscale graphite have been recently utilized, but few theoretical studies of the ORR mechanisms on graphene-supported Pt nanoparticles have been conducted. We have investigated the mechanisms of ORR on Pt₁₃ nanoparticles supported on defective graphene to understand the effect of the defective graphene support on ORR and with predicted details of ORR pathways. Density functional theory (DFT) predictions using the projector-augmented wave (PAW) method within the generalized gradient approximation (GGA) have been employed to construct free energy diagrams for the ORR over supported and unsupported Pt₁₃ nanoparticles, which provides the stability of possible intermediates in the electrochemical reaction pathways. The defective graphene support lowers not only the activation energy for O₂ dissociation from 0.37 to 0.16 eV, but also the energy barrier of the rate-limiting step by reducing the stability of HO* species. Also, it has been observed that charge is transferred from the Pt₁₃ nanoparticle to both defective graphene and the ORR intermediate species. We demonstrate that the defective graphene support may provide a balance in the binding of ORR intermediates on Pt₁₃ nanoparticles by tuning the relatively high reactivity of free Pt₁₃ nanoparticles that bind the ORR intermediates too strongly subsequently leading to slow kinetics. Details of physical and electronic properties of defective graphene-supported Pt nanoparticle systems are also provided.