2D Janus transition metal dichalcogenides: Contact nature engineered optical and catalytic properties

Deliberate manipulation of the atomic types and geometry of two-dimensional materials in contact, can profoundly alter their physical, chemical, and electronic properties. In this paper, we investigated the impact of interface coupling pattern and distance on the electronic, optical, and catalytic properties of 2D Janus Transition Metal Dichalcogenides (TMDs) bilayers MXY (M = Mo, W; X, Y = S, Se, Te). Our findings reveal that the bandgap of TMDs can be easily narrowed extensively by breaking their inversion symmetry, either by changing the nature of atoms to larger size or by adopting the coupling configurations with non-identical atoms facing each other. Additionally, interfacial coupling pattern and distance turn out to be more practical strategies to alter the optical response of Janus TMD compared to simply changing the atomic type on Janus end. By reducing the interlayer distance, there is a redshift and splitting of absorption peaks in TMD bilayers as a result of symmetry breaking and lifting of the degeneracy of electronic states. Strikingly, the energy cost needed to initiate water splitting in the oxygen evolution reaction lowers by reducing the interlayer distance compromised by increasing limiting potential. The interlayer distance for an optimum catalytic OER cycle on the 2H-MoSSe Janus bilayer was around 3.5 Å. The hydrogen evolution reaction is more likely to occur on the S surface of Janus 2H-MoSSe in an alkaline medium. Decreasing the interlayer distance lowers the energy barrier for H 2 O destabilization and facilitates easier H₂ desorption from the active site during HER. These findings underscore the importance of engineering interface coupling pattern and distance in advancing the application of Janus TMDs in photocatalysis and electrocatalysis. • Interface coupling pattern and distance are more practical way to alter the optical response of Janus TMD than atomic type. • Decreasing the interlayer distance lowers the energy barrier for H 2 O destabilization and facilitates easier H₂ desorption. • The interlayer distance for an optimum catalytic OER cycle on the 2H-MoSSe Janus bilayer was around 3.5 Å.