1. Institute of Fuel Cells, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China 2. Shanghai Hydrogen Propulsion Technology Co., Ltd, Shanghai 201804, China 3. SJTU-Paris Tech Elite Institute of Technology, Shanghai Jiao Tong University, Shanghai 200240, China 4. Institute of Fuel Cells, School of Mechanical Engineering, MOE Key Laboratory for Power Machinery and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
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 PtNi3.5 alloy catalysts that consist of homogeneous Pt-Ni alloy cores enclosed by NiO-Pt double shells through thermally annealing defective heterogeneous PtNi3.5 alloys is reported. By tracking the evolution of both compositions and morphologies, the outward segregation of both PtOx 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 Pt2.1Ni 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 Pt2.1Ni 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.
The PtNi3.5 NPs were in situ deposited on carbon powders through solvothermal synthesis
Acid-treated Pt3Ni/C
An acid pickling was applied to as-prepared PtNi3.5/C
PtNi3.5/C
Thermally annealed as-prepared PtNi3.5/C under H2 (5 vol% in Ar)
Acid-treated Pt2.1Ni/C
An acid pickling was applied to PtNi3.5/C
acid-treated Pt3Ni/C
Thermally annealed the acid-treated Pt3Ni/C under H2 (5 vol% in Ar)
AnnealedAr PtNi3.5/C
Thermally annealed as-prepared PtNi3.5/C under pure Ar
Tab.1
Fig.1
Fig.2
Fig.3
Fig.4
Fig.5
Sample
FWHM of {111} facets/(° )
lattice spacing of {111} facets/nm
As-prepared PtNi3.5/C
2.063
0.216
Acid-treated Pt3Ni/C
2.436
0.221
PtNi3.5/C
1.738
0.215
Acid-treated Pt2.1Ni/C
1.601
0.217
AnnealedAr PtNi3.5/C
1.992
0.216
Tab.2
Fig.6
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