Spatially confined synthesis of large-sized MoS2 nanosheets in molten KSCN toward efficient hydrogen evolution.

Low-temperature KSCN molten salt is a promising technique to synthesize defect-rich MoS2 catalysts for hydrogen evolution reaction (HER). However, owing to the fast ion diffusion rate for rapid crystal growth, the resultant catalysts show a morphology of microsphere, which aggregates from MoS2 nanosheets, to suppress the catalytic performance. In this work, large-sized few-layer MoS2 nanosheets are synthesized via a spatial confinement strategy by adding inert NaCl into the KSCN molten salt. With the NaCl spacer to physically block the long-distance ion diffusion and isolate the chemical reaction, the MoS2 nucleation and subsequent crystal growth could be controlled, guiding the nanosheets to grow along the narrow gap between the NaCl crystals to avoid aggregation. As a result, ultrathin MoS2 nanosheets with a large geometry size are constructed. Profiting from the architecture to expose active sites and boost charge transfer kinetics, the large-sized few-layer MoS2 nanosheets exhibit an impressive HER performance, showing a small η10 of 160 mV and a low Tafel slope of 53 mV dec-1 with excellent stability. This work provides not only an efficient HER catalyst but also a facile spatial confinement technique to design and synthesize a large spectrum of transition metal sulfides for broad uses.