Investigating the stability and role of defects in vertically aligned WS2/MoS2 heterojunctions on OER activity using first principles study

Two-dimensional (2D) transition metal dichalcogenides (TMDs) based van der Waals (vdW) heterostructures are of technological importance in optical and electrical devices. In this report, using first principles calculation, we find that induced defects in vdW WS2/MoS2 heterostructures can be used to alter the electronic structure and photocatalytic properties. For instance, the band gap of WS2/MoS2 heterostructure significantly changes when S or Mo/W defects are incorporated in the form of vacancy or adatoms. Also, the existence of vacancy improves the interaction between the WS2 and MoS2 layers, which facilitates charge transfer and optical properties. Moreover, the oxygen evolution reaction (OER) study suggests that the existence of defects in WS2/MoS2 heterostructures improves the overall OER process. Although S defects are thermodynamically more stable, the OER activity is boosted by incorporating the Mo defect. For example, a significant decrease in the overpotential (ƞ = 1.48 V) is observed when one Mo vacancy is incorporated in WS2/MoS2 than that of clean WS2/MoS2 configuration (ƞ = 2.15 V). This study explores in detail the role of various defects in the 2D WS2/MoS2 vdW heterostructures, which can be used to achieve new properties for various optical and electrical applications.