The electrocatalytic hydrogen evolution reaction (HER) is known to be an important technique for efficient hydrogen production, and the development of a highly active electrocatalyst with lower overpotential is a key issue. In this study, we demonstrated the rapid, one-pot synthesis of highly active molybdenum dichalcogenide/ reduced graphene oxide (Mo(S,Se)/rGO) electrocatalysts from cost-effective and environmentally friendly substances using reductive supercritical conditions. We found that edgerich MoS 2 is synthesized under a high-density ethanol condition and successfully controlled the composition of molybdenum dichalcogenide (MoS 2−x Se x ) nanoflowers at the atomic level by varying the ratio of chalcogen sources. The electrocatalytic HER activity increased with the formation of an edges-rich structure and a solid solution of MoS 2 and MoSe 2 , and by complexing with graphene. The synthesized MoS 0.9 Se 1.1 /graphene showed excellent HER properties that can be categorized into the highest-activity group of the previously reported molybdenum dichalcogenide and its composite. Such high electrocatalytic HER performance should be the result of optimizing the hydrogen adsorption free energy of MoS 2−x Se x and effectively forming conductive paths between MoS 0.9 Se 1.1 and graphene. This rapid one-pot process using supercritical ethanol will be suitable for the mass production of highly active molybdenum dichalcogenide electrocatalysts.

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