Engineering Pt-Pt coordination environment to enhance the four-electron oxygen reduction reaction

The oxygen reduction reaction (ORR) in proton exchange membrane fuel cells plays an important role in the H2 economy. Pt-based alloy catalysts with tuned d-band centres are widely regarded as the most efficient catalysts. Here we report that the average size of Pt domains in a Pt-Pd alloy, described as the Pt-Pt coordination number (C.N.), may measure the coordination environment of Pt and its effect on the d-states, to serve as a key geometric descriptor for the ORR activity. The decrease of Pt-Pt C.N. from 10.8 in commercial Pt nanoparticles to 1.33 in Pt1Pd493 alloy leads to an exponential increase in the Pt mass activity from 0.18 to 4.86 A/mgPt. Density functional theory calculations show that low C.N. sites of Pt within the Pd host have low O-O dissociation barriers, favouring the four-electron dissociative pathway. The precise engineering of Pt-Pt C.N. in an alloy is critical for optimising metal use in the activation of chemically stable compounds, particularly in the context of catalysis for renewable energy.