Composition-Graded PdxNi1–x Nanospheres with Pt Monolayer Shells as High-Performance Electrocatalysts for Oxygen Reduction Reaction

It is undoubtedly desirable, albeit very challenging, to appropriately balance the catalytic activity, electrochemical durability, and noble-metal (NM) utilization when developing Pt-based catalysts for oxygen reduction reaction (ORR). Accordingly, in this work, a versatile and effective strategy that promises the nanostructure of both composition-graded core and mono- or multilayer shell is proposed to synthesize highly uniform, sub-10 nm PdxNi1–x@Pt nanospheres (NSs) as high-performance ORR electrocatalysts. Highly uniform and composition-graded PdxNi1–x NSs are previously obtained via a facile one-pot Ni-substitution-based process, and then Pt mono- or multilayer shells are coated onto them through Cu underpotential deposition coupled with Pt2+ galvanic displacement. Results show that carbon-supported PdxNi1–x@Pt electrocatalysts possess both high catalytic activity and highly efficient NM utilization toward ORR. The optimized Pd0.42Ni0.58@Pt/C exhibits 0.61 mA cm–2, 0.42 A mg–1Pd+Pt, and 1.45 A mg–1Pt @ 0.9 V (vs RHE) in the area-specific, NM-mass-specific, and Pt-mass-specific activity, respectively, reaching 2.8, 3.3, and 11.2 times relative to those of the commercial Pt/C. Moreover, Pd0.42Ni0.58@Pt/C also has a satisfactory electrochemical durability, preserving its high ORR catalytic activity even after 12 000 potential cycles of the accelerated degradation test. The synthetic mechanism of PdxNi1–x NS core, Pt monolayer shell and their combined effects on the catalytic activity, electrochemical durability, and NM utilization of PdxNi1–x@Pt/C toward ORR are comprehensively investigated.