A core-shell Pd1Ru1Ni2@Pt/C catalyst with a ternary alloy core and Pt monolayer: enhanced activity and stability towards the oxygen reduction reaction by the addition of Ni

A core-shell structured catalyst, Pd1Ru1Ni2@Pt/C, with a ternary alloy as its core and a Pt monolayer shell was prepared using a two-stage strategy, in which Pd1Ru1Ni2 alloy nanoparticles were prepared by a chemical reduction method, and then the Pt monolayer shell was generated via an underpotential deposition method. It was found that the addition of Ni to the core played an important role in enhancing the catalyst's oxygen reduction activity and stability. The optimal molar ratio of Pd : Ru : Ni was about 1 : 1 : 2; the catalyst with this optimal ratio had a half-wave potential approximately 65 mV higher than that of a PdRu@Pt/C catalyst, and its mass activity was up to 1.06 A mg(-1) Pt, which was more than five times that of a commercial Pt/C catalyst. The catalyst's structure and composition were characterized using X-ray powder diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and energy-dispersive X-ray spectrometry. The core-shell structure of the catalyst was demonstrated by the EDS mapping results and supported by the XPS results. We also performed a stability test that confirmed the catalyst's superior stability in comparison to that of commercial JM Pt/C (20 wt% Pt).