▎ 摘　　要

Direct decoration of transition metallic dichalcogenides such as molybdenum disulfide (MoS2) on pristine graphene is extremely difficult owing to its surface inertness. Under assistance of supercritical carbon dioxide, we develop a unique synthesis of a high-quality hybrid nanostructure with ultrafine MoS2 nanosheets supported on pristine graphene that exhibits excellent properties as an advanced catalyst for electrocatalytic hydrogen evolution reaction (HER). These include a Tafel slope of similar to 42 mV.decade(-1), onset potential as low as similar to 58 mV and small potential of 81 mV for 10 mA.cm(-2) current density, much superior than those obtained from other carbon-based counterparts such as carbon black, carbon nanotubes, and reduced graphene oxide. Both these potentials are the best available values ever achieved so far among all graphene or carbon nanotube-supported molybdenum sulfide. The exceptional HER activity is found to be closely associated with high density of exposed edge sites of ultrafine MoS2 nanosheets being firmly and uniformly anchored on inherently conductive graphene sheets as a result of high wettability between the supercritical fluid and inert carbon surfaces. The facile yet effective supercritical method can also be applicable to a wide range of electrochemically active nanospecies in the development of highly efficient graphene-based nano-catalysts for broad energy applications.