Grain Boundaries Trigger Basal Plane Catalytic Activity for the Hydrogen Evolution Reaction in Monolayer MoS2

Monolayer molybdenum disulfide (MoS2) is considered to be a promising catalyst for replacing noble metals for the large-scale production of hydrogen through the hydrogen evolution reaction (HER). However, the catalytic activity sites are located at the limited edges and massive inert sites in the basal plane. Triggering the basal plane catalytic activity for the HER is desired to improve the catalytic behavior of monolayer MoS2. In this work, we studied the catalytic behavior of the grain boundaries (GBs) in monolayer MoS2 using first-principle calculations based on density functional theory (DFT). The results show that the Gibbs free energy for hydrogen adsorption on MoS2 can be greatly reduced from 1.93 eV on pristine MoS2 to 0.01 eV on MoS2 with GBs, which indicate that the presence of GBs in the MoS2 monolayer can trigger the basal plane catalytic activity for the HER. The S vacancy, the bridge site of the Mo-Mo dimer, and the top site of the S atom of the S-S dimer are the catalytically active sites. GBs could be a general way to generate new active sites in two-dimensional transition metal dichalcogenides, thus providing a new routine to improve the catalytic efficiency for the HER.