Core–Shell Structure of NiSe₂ Nanoparticles@Nitrogen-Doped Graphene for Hydrogen Evolution Reaction in Both Acidic and Alkaline Media

It is extremely significant to develop nonprecious electrocatalysts with high efficiency and remarkable stability in both acidic and alkaline media for hydrogen evolution reaction (HER). Herein, for the first time, we synthesize a core–shell structure of NiSe₂@­nitrogen-doped graphene (NiSe₂@­NG), which is constructed by NiSe₂ nanoparticles encapsulated in ultrathin N-doped graphene shells derived from a Ni-based metal–organic framework. The optimized NiSe₂@­NG hybrid exhibits outstanding electrocatalytic performance. In acidic (or alkaline) media, the hybrid has a low onset potential of −163 (or −171) mV vs RHE, a small overpotential of 201 (or 248) mV vs RHE at −10 mA cm^–2, and particularly a low Tafel slope of 36.1 (or 74.2) mV dec^–1. Furthermore, the hybrid also delivers outstanding cycling and current–time stability in acidic and alkaline electrolytes. The outstanding catalytic performance of the hybrid is attributed to its unique core–shell architecture, which not only significantly improves the conductivity and creates numerous active sites to enhance the electrocatalytic activity but also guarantees the chemical and structural stability of the NiSe₂ core, thus improving the stability of the electrocatalyst. This work provides a novel perspective to design and synthesize highly efficient nonprecious electrocatalysts for HER in both acidic and alkaline solutions.