Thermal annealing synthesis of double-shell truncated octahedral Pt-Ni alloys for oxygen reduction reaction of polymer electrolyte membrane fuel cells

Abstract

Shape-controlled Pt-Ni alloys usually offer an exceptional electrocatalytic activity toward the oxygen reduction reaction (ORR) of polymer electrolyte membrane fuel cells (PEMFCs), whose tricks lie in well-designed structures and surface morphologies. In this paper, a novel synthesis of truncated octahedral PtNi_3.5 alloy catalysts that consist of homogeneous Pt-Ni alloy cores enclosed by NiO-Pt double shells through thermally annealing defective heterogeneous PtNi_3.5 alloys is reported. By tracking the evolution of both compositions and morphologies, the outward segregation of both PtO_x and NiO are first observed in Pt-Ni alloys. It is speculated that the diffusion of low-coordination atoms results in the formation of an energetically favorable truncated octahedron while the outward segregation of oxides leads to the formation of NiO-Pt double shells. It is very attractive that after gently removing the NiO outer shell, the dealloyed truncated octahedral core-shell structure demonstrates a greatly enhanced ORR activity. The as-obtained truncated octahedral Pt_2.1Ni core-shell alloy presents a 3.4-folds mass-specific activity of that for unannealed sample, and its activity preserves 45.4% after 30000 potential cycles of accelerated degradation test (ADT). The peak power density of the dealloyed truncated octahedral Pt_2.1Ni core-shell alloy catalyst based membrane electrolyte assembly (MEA) reaches 679.8 mW/cm², increased by 138.4 mW/cm² relative to that based on commercial Pt/C.

Key words： dealloyed Pt-Ni alloys; truncated octahedron; double-shell; thermal annealing; oxygen reduction reaction (ORR)

Acknowledgments

This work was financially supported by the National Key R&D Program of China (No. 2016YFB0101201) and the National Natural Science Foundation of China (Grant No. 21533005).

Electronic Supplementary Material

Supplementary material is available in the online version of this article at https://doi.org/10.1007/s11708-020-0667-2 and is accessible for authorized users.

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