Low loaded MoS2/Carbon cloth as a highly efficient electrocatalyst for hydrogen evolution reaction

Active edge sites of MoS₂ nanosheets exhibit promising futures for hydrogen evolution reaction (HER), comparable with remarkable performances of highly cost platinum. However, 3D structures of MoS₂ suffer from a lack of high mobility and unexposed active sites which lower the electrocatalytic activity. In this study, we show that there is a balance between increasing the active sites on the one hand and managing the charge transfer to facilitate the reaction on the other hand, and achieving this balance increases the efficiency of the electrocatalyst tremendously. For this purpose, we directly attached exfoliated MoS₂ nanosheets onto carbon cloth (CC) substrate as a 3D network of conductive fibers via electrophoretic deposition at different applied voltages and deposition times, without adding any binder. This strategy gives rise to superior exposure of active sites while still maintaining good charge transferability over the whole 3D structure. Thus, a trace amount of loaded catalyst is enough to reach the benchmark current density of 10 mA/cm² towards H₂ production with a low overpotential of 137 mV vs. RHE. The Stability of the optimum structures under continuous operation was examined up to 50 min and further confirmed with 500 successive cyclic voltammetry (CV) sweeps. To understand the adsorption nature of hydrogen, density functional theory (DFT) was employed for the MoS₂/graphene in both cases of pristine and defected MoS₂. The results of hydrogen adsorption free energy calculations revealed that H adsorption on the S site is the most stable adsorption configuration and with increasing the MoS₂ thickness, the MoS₂/graphene activity towards hydrogen evolution decreases. A similar trend is also observed for the defected MoS₂/graphene composite up to two-layer MoS₂ and the activity remains the same for three-layer MoS₂. The experimentally observed charge transfer into the MoS₂ upon adsorption of the hydrogen atom and water molecule is also confirmed by our DFT calculations.