Core-Shell Nanostructured Au@Ni_mPt₂ Electrocatalysts with Enhanced Activity and Durability for Oxygen Reduction Reaction

Fabricating Pt-alloy and core-shell nanostructures with Au NPs in the cores are considered as two general approaches to improving the performance of Pt-based catalysts for the cathodic oxygen reduction reaction (ORR) in acidic electrolyte. These two approaches are combined herein to develop a heteroseed-mediated solvothermal method for synthesizing nearly monodisperse core-shell structured Au@Ni_mPt₂ nanoparticles (NPs) of 5.0-6.5 nm (with the atomic ratio of Ni/Pt/Au = m/2/1) as ORR catalysts. With respect to controlling the amount and relative concentrations of the metal precursors in the starting solution, this method enables not only facile manipulation of the shell composition and thickness but also fine-tuning of the core-shell interaction and surface electronic structures of the resultant Au@Ni_mPt₂ NPs, endowing the Au@Ni_mPt₂ NPs with improved Pt activity and durability for ORR. Subjecting the Au@Ni_mPt₂ NPs to an ex situ pretreatment in flowing 2%CO/Ar at 300 °C is shown to result in further improved Pt activity. Data are also presented to correlate the intrinsic Pt activity with experimentally determined CO adsorption property (CO-stripping peak potential) of Pt for the Au@Ni_mPt₂ samples, and to show the excellent electrochemical durability of the Au@Ni_mPt₂ NPs during 20 000 potential cycles between 0.6 and 1.1 V (vs RHE) in O₂-saturated 0.1 M HClO₄. Compared with the commercial E-TEK Pt/C catalyst, the most-active Au@Ni₂Pt₂ NPs exhibit 3-4- and 4-6-fold higher Pt activity at 0.9 V before and after the 20 000 potential cycles, respectively. Factors relevant to the activity and durability control of the Au@Ni_mPt₂ catalysts for ORR are discussed.