Multi-interface collaboration of graphene cross-linked NiS-NiS₂- Ni₃S₄ polymorph foam towards robust hydrogen evolution in alkaline electrolyte

Electrocatalytic hydrogen production in alkaline media is extensively adopted in industry. Unfortunately, further performance improvement is severely impeded by the retarded kinetics, which requires the fine regulation of water dissociation, hydrogen recombination, and hydroxyl desorption. Herein, we develop a multi-interface engineering strategy to make an elaborate balance for the alkaline hydrogen evolution reaction (HER) kinetics. The graphene cross-linked three-phase nickel sulfide (NiS-NiS₂-Ni₃S₄) polymorph foam (G-NNNF) was constructed through hydrothermal sulfidation of graphene wrapped nickel foam as a three-dimensional (3D) scaffold template. The G-NNNF exhibits superior catalytic activity toward HER in alkaline electrolyte, which only requires an overpotential of 68 mV to drive 10 mA·cm⁻² and is better than most of the recently reported metal sulfides catalysts. Density functional theory (DFT) calculations verify the interfaces between nickel sulfides (NiS/NiS₂/Ni₃S₄) and cross-linked graphene can endow the electrocatalyst with preferable hydrogen adsorption as well as metallic nature. In addition, the electron transfer from Ni₃S₄/NiS₂ to NiS results in the electron accumulation on NiS and the hole accumulation on Ni₃S₄/NiS₂, respectively. The electron accumulation on NiS favors the optimization of the H* adsorption, whereas the hole accumulation on Ni₃S₄ is beneficial for the adsorption of H₂O. The work about multi-interface collaboration pushes forward the frontier of excellent polymorph catalysts design.