Development of Highly-Active Catalysts toward Oxygen Reduction by Controlling the Shape and Composition of Pt-Ni Nanocrystals

Electrocatalysts comprised of Pt-Ni alloy nanocrystals have garnered substantial attention due to their outstanding performance in catalyzing the oxygen reduction reaction (ORR). Herein, we present the synthesis of Pt-Ni nanocrystals with a variety of controlled shapes and compositions in an effort to investigate the impact of the Ni content on the formation of {111} facets and thereby the ORR activity. By completely excluding O-2 from the reaction system, we could prevent the generation of Ni(OH)(2) on the surface of the nanocrystals and thereby achieve a linear relationship between the atomic ratio of Pt to Ni in the nanocrystals and the feeding ratio of the precursors. The atomic ratio of Pt to Ni in the Pt-Ni nanocrystals was tunable within the range of 1.2-7.2, while their average sizes were kept around 9 nm in terms of edge length. In addition, a quantitative correlation between the area ratio of {111} to {100} facets and the feeding ratio of Pt(II) to Ni(II) was obtained by adjusting the mole fraction of the Ni(II) precursor in the reaction mixture. For the catalysts comprising octahedral nanocrystals, their specific ORR activities exhibited a positive correlation with the Pt/Ni atomic ratio. After the accelerated durability test, both specific and mass activity displayed a volcano-type trend with a peak value at a Pt/Ni atomic ratio of 1.6.

Automated summary

In this study, Pt-Ni nanocrystals with controlled shapes and compositions were synthesized to investigate the impact of Ni content on the formation of {111} facets and ORR activity. By excluding O-2 completely, a linear relationship was achieved between the atomic ratio of Pt to Ni in the nanocrystals and the feeding ratio of the precursors. The specific ORR activities of octahedral nanocrystals exhibited a positive correlation with the Pt/Ni atomic ratio, with a peak value at a Pt/Ni atomic ratio of 1.6 after the accelerated durability test.