Enabling Colloidal Synthesis of Edge-Oriented MoS2 with Expanded Interlayer Spacing for Enhanced HER Catalysis.

By selectively promoting heterogeneous nucleation/growth of MoS2 on graphene monolayer sheets, edge-oriented (EO) MoS2 nanosheets with expanded interlayer spacing (∼9.4 Å) supported on reduced graphene oxide (rGO) sheets were successfully synthesized through colloidal chemistry, showing the promise in low-cost and large-scale production. The number and edge length of MoS2 nanosheets per area of graphene sheets were tuned by controlling the reaction time in the microwave-assisted solvothermal reduction of ammonium tetrathiomolybdate [(NH4)2MoS4] in dimethylformamide. The edge-oriented and interlayer-expanded (EO&IE) MoS2/rGO exhibited significantly improved catalytic activity toward hydrogen evolution reaction (HER) in terms of larger current density, lower Tafel slope, and lower charge transfer resistance compared to the corresponding interlayer-expanded MoS2 sheets without edge-oriented geometry, highlighting the importance of synergistic effect between edge-oriented geometry and interlayer expansion on determining HER activity of MoS2 nanosheets. Quantitative analysis clearly shows the linear dependence of current density on the edge length of MoS2 nanosheets.