Maximum catalytic activity of Pt₃M in Li-O₂ batteries: M=group V transition metals

Li-O₂ batteries are considered as promising power sources for electric vehicles due to their remarkably high energy density. However, low rate capability and short cycle life caused by sluggish oxygen reduction/evolution reaction (ORR/OER) kinetics limit their practical applications. Here, we investigate the catalytic activities of Pt₃M bimetallic alloys (M=3d, 4d, and 5d transition metals) for improving the ORR and OER kinetics using first-principles calculations. We found that the group 5 elements (V, Nb, and Ta in 3d, 4d, and 5d periods, respectively) are the most effective alloy components for high catalytic activity. Pt₃V, Pt₃Nb, and Pt₃Ta alloys exhibit considerably lower ORR and OER overpotentials (by 71-77% and 57-59%, respectively) than those of Pt. The catalytic activities are successfully described by the adsorption strengths of reaction intermediate species (Li and LiO₂) on the alloy surface rather than the d-band center of the alloy surface and are fundamentally controlled by the amount of surface charge. The superior catalytic activities of Pt₃M alloys with the group 5 elements originate from their electron-rich surfaces and can also be interpreted in terms of the integration of mechanical interplay and chemical interplay of Pt and M, i.e., an appropriate trade-off between surface strain and ligand effects.