Optimization of the in-plane activity of MoS₂ monolayer by Pd-S bonds for hydrogen evolution reaction

Simulate to hydrogenase, 2D molybdenum disulfide (MoS2) as a typical member among transition metal dichalcogenides have received extensive attentions for hydrogen evolution reaction (HER). However, it is found that the exposure plane of 2D MoS2 is inert to HER whereas the edge sites are more active. Herein, Pd doping strategy is applied to significantly enhance the in-plane activity of MoS2 monolayer, and the structure-activity relationship is studied in detail. The centimeter-scale monolayer Pd-MoS2 films with Pd-S bonds were prepared. For the Pd-MoS2 with 7.4 at% Pd amount, the overpotential of HER decreases to 163 mV (vs. RHE) at 5 mA cm-2 and 205 mV (vs. RHE) at 10 mA cm-2. DFT calculations reveal that the Delta GH* is dramatically reduced to-0.12 eV at the S site adjacent to Pd atom in 2H Pd-MoS2. Moreover, the charge transfer efficiency significantly increases with increasing the Pd dopant amount for the Pd-MoS2 when compared to the MoS2. This work provides insights into the structure modification of 2D MoS2 for tuning the electrocatalytic HER performance.