An efficient WSe₂/Co_0.85Se/graphene hybrid catalyst for electrochemical hydrogen evolution reaction

Transition metal doped layered transition metal dichalcogenides (TMDs) are regarded as promising hydrogen evolution reaction (HER) candidates due to exposed active sites at both edges and basal planes. Hydrogen absorption free energy on active sites in doped materials are adjusted to thermoneutral state for ideal bond breaking to favour the HER process after the introduction of transition metal ions in their crystalline structures. Considering the importance of the active site, charge transfer, and hydrogen adsorption free energy to HER, cobalt-containing sandwich-type polyoxometalates are used as a precursor to fabricate cobalt doped WSe₂ nanosheets via CVD selenization method. Reduced graphene oxides (rGO) are further introduced into cobalt doped WSe₂ nanosheets for solving the non-ohmic contact with current collectors, leading to enhanced exchange current density. Co-WSe₂/rGO₂ composites exhibit Tafel slope of 64 mV dec^-1, overpotential of 217 mV at 10 mA cm^-2, exchange current density of 15.3 × 10^-3 mA cm^-2, charge transfer resistance of 68 Ω, and the activity is maintained after 3 h. The activated basal planes, good conductivity and adjusted hydrogen absorption free energy are attributed to enhance the HER performance. The present work opens a new avenue for the fabrication of transition metal doped TMDs using polyoxometalates with determined composition as precursors to fabricate superior HER electrocatalysts.