Abstract:Octahedral Pt-Ni nanoparticles surrounded by (111) facet are considered as promising oxygen reduction reaction (ORR) catalysts. It has been reported that the ORR activities of Pt-Ni octahedral nanoparticles are greatly influenced by the Pt:Ni atomic ratio. The relationship between the Pt:Ni atomic ratio of Pt-Ni octahedron and the corresponding ORR activity is presented as a volcano plot without explanation. Herein, by synthesizing Pt-Ni octahedral nanoparticles with composition of Pt<sub>3</sub>Ni, PtNi and PtNi<sub>2</sub>, we found an abnormal ORR specific activities in the order of Pt<sub>3</sub>Ni> PtNi<sub>2</sub>> PtNi. Meanwhile, with the same Pt loading, the sequence of ORR mass activity is Pt<sub>3</sub>Ni≈ PtNi<sub>2</sub>> PtNi. The surface lattice contraction and the utilization of Pt were considered to explain these phenomenon. The extent of surface lattice contraction is decreased as Pt<sub>3</sub>Ni> PtNi<sub>2</sub>> PtNi, consistent with the sequence of ORR specific activity, which challenges the previous experience that the more Ni was incorporated into the Pt lattice, the higher the surface lattice contraction yielded. While the mass activity is a balance between specific activity and surface Pt utilization. The results indicated that the ORR activity can be adjusted by tuning the surface tension and surface Pt utilization.