High-metallic-phase-concentration Mo_1-xW_xS₂ nanosheets with expanded interlayers as efficient electrocatalysts

In most cases, layered transition metal dichalcogenides (LTMDs), containing metallic phases, show electrochemical behavior different from their semiconductor counterparts. Typically, two-dimensional layered metallic 1T-MoS₂ demonstrates better electrocatalytic performance for water splitting compared to its 2H counterpart. However, the characteristics of low metallic phase concentration and poor stability limit its applications in some cases. Herein, we demonstrate a simple and efficient bottom-up wet-chemistry strategy for the large-scale synthesis of nanoscopic ultrathin Mo_1-xW_xS₂ nanosheets with enlarged interlayer spacing and high metallic phase concentration. Our characterizations, including X-ray absorption fine structure spectroscopy (XAFS), high-angle annular dark-fieldscanning transmission electron microscopy (HAADF-STEM), and X-ray photoelectron spectroscopy (XPS) revealed that the metallic ultrathin ternary Mo_1-xW_xS₂ nanosheets exhibited distorted metal-metal bonds and a tunable metallic phase concentration. As a proof of concept, this optimized catalyst, with the highest metallic phase concentration (greater than 90%), achieved a low overpotential of about-155 mV at a current density of -10 mA/cm², a small Tafel slope of 67 mV/dec, and an increased turnover frequency (TOF) of 1.3 H₂ per second at an overpotential of -300 mV (vs. reversible hydrogen electrode (RHE)), highlighting the importance of the metallic phase. More importantly, this study can lead to a facile solvothermal route to prepare stable and high-metallicphase-concentration transition-metal-based two-dimensional materials for future applications.