Strategies to Improve the Oxygen Reduction Reaction Activity on Pt-Bi Bimetallic Catalysts: A Density Functional Theory Study.

Decreasing the level of use of Pt in proton exchange membrane fuel cells is of great research interest both academically and industrially. In this work, we systematically studied the oxygen reduction reaction (ORR) following the four-electron association mechanism at various Pt-Bi surfaces with density functional theory calculations. The results showed that the introduction of Bi changes the potential-determining step of ORR. Moreover, the hydroxy adsorption free energy (GOH*) can be used as a descriptor of ORR activity, and 0.74 eV is the ideal GOH* for it to reach its maximum. Notably, we also found that the tensile strain introduced by Bi and electron transfer between Pt and Bi synergize to modulate the d-band of Pt to contract, shift downward, and break the 5d96s1 valence electron configuration of Pt, and accordingly, PtBi(100), with the lowest d-band center, gives the best ORR activity, which is even slightly higher than that of Pt(111).