Tungsten Disulfide (WS2) is considered to be a promising Hydrogen Evolution Reaction (HER) catalyst to replace noble metals (such as Pt and Pd). However, progress in WS2 research has been impeded by the inertness of the in-plane atoms during HER. Although it is known that microstructure and defects strongly affect the electrocatalytic performance of catalysts, the understanding of such related catalytic origin still remains a challenge. Here, we combined a one-pot synthesis method with wet chemical etching to realize controlled cobalt doping and tunable morphology in WS2. The etched products, which composed of porous WS2, CoS2 and a spot of WOx, show a low overpotential and small Tafel slope in 0.5 M H2SO4 solution. The overpotential could be optimized to -134 mV (at 10 mA/cm2) with a Tafel slope of 76 mV/dec at high loadings (5.1 mg/cm2). Under N2 adsorption analysis, the treated WS2 sample shows an increase in macropore (>50 nm) distributions, which may explain the increase inefficiency of HER activity. We applied electron holography to analyze the catalytic origin and found a low surface electrostatic potential in Co-doped region. This work may provide further understanding of the HER mechanism at the nanometer scale, and open up new avenues for designing catalysts based on other transition metal dichalcogenides for highly efficient HER.
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