Beyond 1T‐phase? Synergistic Electronic Structure and Defects Engineering in 2H‐MoS2xSe2(1‐x) Nanosheets for Enhanced Hydrogen Evolution Reaction and Sodium Storage

Abstract Two‐dimensional layered MoSe2 has been proved to be promising electrocatalyst toward hydrogen evolution reaction (HER), although the typical disadvantages of poor conductivity and limited density of active sites in 2H‐phase restrict further development. Here, a clear evidence is presented in partially‐crystallized 2H‐MoS2xSe2(1‐x) nanosheets (NS) to demonstrate that: i) in both 2H‐ and 1T‐phase, single factor such as phase, conductivity, or defects will not determine or restrict the catalytic activity in MoSe2, and ii) synergistic tuning at least two factors will greatly enhance the overall HER performance than single factor no matter in 2H‐ or 1T‐MoSe2 crystal structures. The enhanced catalytic activity with η10=136 mV vs RHE, and a Tafel slope of 50 mV dec−1 are achieved in the optimized 2H‐MoS0.2Se1.8‐160 NS, which is the best among pure MoSSe materials without heterogeneous atom doping to our knowledge. In addition, 2H‐MoS0.2Se1.8/rGO anodes exhibit a stable reversible capacity of 396 mA h g−1 after 100 cycles at 0.5 A g−1. These discoveries provide a unique opportunity to comprehensively understand the single factor or multi‐factors mechanism for HER, which serves as the general design and modulation principles for further synthesize and applications of MoSe2‐based materials toward HER and other catalytic applications.