▎ 摘　　要

Molybdenum sulfide is an intensely attractive noble-metal-free electrocatalyst for the hydrogen evolution reaction (HER). How to enhance electrical conductivity and maintain high intrinsic activity and active site density remains a challenge. Herein, we design a novel composite catalyst, which is composed of molybdenum sulfide clusters and defective graphene, holding excellent intrinsic activity, high-density active sites and high conductivity simultaneously. The strong S-C covalent bonds between clusters and graphene ensure the structural stability of the composite, avoiding the long-standing deactivation problem caused by cluster desorption. The clusters possess high-density active sites and the graphene acts as the conducting path to transport electrons from the electrode to active sites efficiently. Moreover, the simulations of diffusion of clusters on defective graphene demonstrate that the composite catalyst is easy to synthesize by a simple drop-casting procedure.