Defect and strain engineered MoS₂/graphene catalyst for an enhanced hydrogen evolution reaction

Molybdenum disulfide (MoS₂) has been demonstrated as a promising non-precious metal electrocatalyst for the hydrogen evolution reaction (HER). However the efficiency of the HER falls short of expectations due to the large inert basal plane and poor electrical conductivity. In order to activate the MoS₂ basal plane and enhance the hydrogen evolution reaction (HER) activity, two strategies on the hybrid MoS₂/graphene, including intrinsic defects and simultaneous strain engineering, have been systematically investigated based on density functional theory calculations. We firstly investigated the HER activity of a MoS₂/graphene hybrid material with seven types of point defect sites, V _S, V_S2, V _Mo, V _MoS3, V _MoS6, Mo_S2 and S2_Mo. Using the hydrogen adsorption free energy (ΔG _H) as the descriptor, results demonstrate that four of these seven defects (V _S, V _S2, Mo_S2, V _MoS3) act as a catalytic active site for the HER and exhibited superior electrocatalytic activity. More importantly, we found that ΔG _H can be further tuned to an ideal value (0 eV) with proper tensile strain, which effectively optimizes and boosts the HER activity, especially for the V _S, V _S2, V _MoS3 defects and Mo_S2 antisite defects. Our results demonstrated that a proper combination of tensile strain and defect structure is an effective approach to achieve more catalytic active sites and further tune and boost the intrinsic activity of the active sites for HER performance. Furthermore, the emendatory d-band center of metal proves to be an excellent descriptor for determining H adsorption strength on defective MoS₂/graphene hybrid material under different strain conditions. In addition, the low kinetic barrier of H₂ evolution indicated that the defective MoS₂/graphene system exhibited favorable kinetic activity in both the Volmer-Heyrovsky and the Volmer-Tafel mechanism. These results may pave a new way to design novel ultrahigh-performance MoS₂-based HER catalysts.