▎ 摘　　要

Construction of tightly bonded interfaces is an indispensable and critical strategy for promoting the catalytic performances of composite structures. In this study, a novel two-dimensional (2D) composite was successfully fabricated through the simultaneous formation of cobalt sulfide (Co9S8) nanosheets and N-, S-doped graphene (NSG). Cobalt-thiourea with graphene oxide was used as the precursor for a low-temperature and one-step pyrolysis. The optimal Co9S8/NSG-220 achieved a small onset overpotential of 147 mV, a low Tafel slope of 97 mV.dec(-1), superior long-term durability after 16 h, and high faradic efficiency (nearly 100%) for the hydrogen evolution reaction (HER) in an acid electrolyte. The tightly bound sheet-on-sheet structure significantly enhanced the intrinsic catalytic activity due to the mutual activation effects between the components. Based on the experimental investigation and density functional theory calculations, the mutual activation effects induced by the electron transfer across the active interface constructed between NSG and Co9S8 was proposed as a key factor in the origin of superior catalytic activity. The HER catalytic activities were further improved by doping Mo into the composites. This design inspires new thoughts for exploring 2D composites prepared using molecular precursors with controlled compositions and morphologies as performance-enhanced electrocatalysts for future sustainable clean energy conversion.