Photocatalytic activity of MoS2 with water monolayers: Global optimization

Atomically thin MoS2 has emerged to be promising for photocatalytic water splitting benefiting from its suitable geometrical and electronic structure for light harvesting. A better understanding of how water molecules affect the band edge levels of MoS2 is critical for promoting the interfacial reactivity. Here, we determine the structures of water monolayers on MoS2 using global optimizations achieved by molecular dynamics in combination with local minimization. It is shown that cyclic water clusters are formed on a surface through a hydrogen-bonding network. The absolute band edge positions are explored taking into account the derivative discontinuity of the exchange-correlation functional. Shifts in band edges are observed with the increase in H2O coverage, while bandgaps tend to be slightly decreased. In particular, the band alignment relative to water redox potentials has been investigated in detail. We find that the dimer configuration is likely to suppress the hydrogen evolution reaction (HER), while the polygon clusters lift the conduction band by 0.2-0.7 eV, and thus, they would enhance HER. This effect is explained in terms of the linear dependence of the band edge offset on an interface electric dipole arising from water assemblies. Published under an exclusive license by AIP Publishing.

Automated summary

This study investigates the structure of water monolayers on MoS2 and their effect on the band edge levels. The results show the formation of cyclic water clusters through a hydrogen-bonding network. With increasing H2O coverage, shifts in band edges and slight decreases in bandgaps are observed. The band alignment relative to water redox potentials is also examined, revealing that polygon clusters can enhance the hydrogen evolution reaction by lifting the conduction band. This effect is explained by the linear dependence of the band edge offset on an interface electric dipole arising from water assemblies.