Effect of Atomic Ordering Transformation of PtNi Nanoparticles on Alkaline Hydrogen Evolution: Unexpected Superior Activity of the Disordered Phase

Abstract

Compared to the acidic hydrogen evolution reaction (HER), the sluggish reaction rate in an alkaline electrolyte makes it a priority to develop highly efficient and cost-effective catalysts. Incorporation of Pt with transition metals to form alloy nanocrystals with different structures and atomic distributions has been reported as a promising approach to enhance HER activity and improve Pt utilization. However, whether the structural ordering of the Pt-based bimetallic alloy affects the HER activity still remains unknown. Here, we synthesized PtNi/C nanoparticles through a modified coprecipitation method and obtained their ordered and disordered phases at different annealing temperatures in a reducing atmosphere. It is contrary to our expectation that the disordered PtNi/C exhibited a superior activity toward the HER in alkaline media compared with the ordered PtNi/C. To understand this interesting phenomenon, a systematic study combining X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) was conducted. In addition, we studied the mechanism of the HER in an alkaline electrolyte based on newly constructed models. The density functional theory (DFT) calculation demonstrated that the unexpected activity change may be attributed to the synergistic effect between the formation of Ni/Pt–OH bonds and the increased degree of disorder of Pt and Ni atoms on their surface.