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Since the electrocatalytic activity of layered molybdenum disulfide (MoS2) for hydrogen evolution reaction (HER) closely depends on its exposed edges, the morphology and size of the material are critically important. Herein, we introduce a novel solvent-evaporation-assisted intercalation method to fabricate the hybrid of alternating MoS2 sheets and reduced graphene oxide layers, in which the nanosize of the MoS2 nanosheets can be effectively controlled by leveraging the confinement effect within the two-dimensional graphene layers. Significantly, the resulting MoS2/reduced graphene oxide (RGO) composite shows excellent catalytic activity for HER characterized by higher current densities and lower onset potentials than the conventional pre-exfoliated RGO supported MoS2 nanosheets. Further experiments on the effect of oxidation degree of graphene, the crystallinity of MoS2, and the exposed active site density on the HER performance of the MoS2/RGO composites show that there is an optimum condition for the catalytic activity of HER due to a balance between the numbers of exposed active sites of MoS2 and the internal conductive channels provided by graphene.

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