Abstract
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.
Highlights
Hydrogen has been considered as a promising clean energy source to remedy the shortage of fossil fuel supply and pollution problems
We studied the influence of different annealing conditions and passivation by 4-nitrobenzene-diazonium (4-NBD) on Hydrogen Evolution Reaction (HER) capability and stability, which can be seen in Supplementary Material (Fig. S1)
We studied the influence of microstructure on high-performance Co-doped WS2-based HER catalyst
Summary
Tungsten Disulfide (WS2) is considered to be a promising Hydrogen Evolution Reaction (HER) catalyst to replace noble metals (such as Pt and Pd). We applied electron holography to analyze the catalytic origin and found a low surface electrostatic potential in Co-doped region. Apart from the edges, the majority of the basal surfaces are catalytically inert, which is the main limitation of bare TMDCs compared with noble metal catalysts. WS2 or MoS2 in the metallic 1T phase contains a higher density of exposed active sites, better conductivity and catalytic performance[21,22], which can be obtained by chemical exfoliation from sample in the semiconducting 2H phase[23]. A specific catalyst composed of Cobalt-doped and surface-etched WS2 was synthesized, showing efficient HER activity. Potentials were referenced to a reversible hydrogen electrode (RHE) by adding a value of 0.262 V (0.244 + 0.0591 × pH)
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