Cost effective electrocatalysts for hydrogen evolution reactions are attractive for energy conversion and storage progress. A high performance hydrogen evolution reaction (HER) electrocatalyst of 3D MoS 2 nanostructure modified by tungsten incorporation is produced via hydrothermal method. By means of controllable tungsten incorporation, an optimized catalyst with rich defects was developed, exhibiting high hydrogen evolution activities. In general, the 3D MoS 2 -W3 exhibits an overpotential as low as 200 mV, accompanied with high exchange current density of 6.9 μA cm −2 and excellent stability after 3000 cycles. This work paves a new route in the design of efficient and durable non-precious-metal electrocatalysts for HER in acidic medium. Sustainable hydrogen production has attracted growing attention, and an advanced catalyst for the electrochemical hydrogen evolution reaction (HER) that results in increased efficiency of this important electrochemical process is urgently required.1-3 Although excellent HER performance has been reached for platinum and other precious metals, 4 replacing the expensive and rare catalysts with cost effective and high efficient alternatives still attract scientists' attention toward making the hydrogen production more economic and competitive. [5][6][7] During the past few years, transitional metal sulfides such as nanometer-scaled MoS 2 and WS 2 have attracted considerable attention in HER fields because of their low cost, high chemical stability, and excellent electrocatalytic properties. [8][9][10][11][12][13] Studies concluded that the unsaturated sulfur atoms on the edges of the 2D MoS 2 layers play a crucial role in HER catalysis 14 and the electric conductivity of catalysts is another crucial factor to affect the electrocatalytic activity. [15][16][17] Hence, increasing the number of active sites is an efficient pathway to enhance the HER activity. 18,19 The latest reported results show a new strategy to fabricate a new oxygen-incorporated MoS 2 ultrathin nanosheets catalyst that preferentially exposes active sites by incorporating oxygen atoms.20 Zhou et al. prepared ultrathin MoS 2(1−x) Se 2x alloy nanoflakes with monolayer or few-layer thickness, which possessed more active sites than single MoS 2 .21 Rao et al. studied rhenium-doped nanoparticles of MoS 2 with fullerene-like structures (IF-MoS 2 ), that not only changes the intrinsic nature of the MoS 2 but also increases its reactivity. 22Cationic doping with a small fraction of cobalt or nickel is also used to promote the electrocatalytic performance of MoS 2 . Besides, Ni, Co and Fe were adopted to improve the intrinsic activity, and more highly conductive materials were added to improve the electrical contact, including graphene, carbon nanotubes, carbon nanospheres, and so on. [23][24][25] With respect to the last issue, the structure design of MoS 2 has attracted great attentions to obtain more active sites. 26 Both of WS 2 and MoS 2 are transition-metal sulfides, which have the similar crystal structure. Moreover...

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