Intrinsic defect engineered Janus MoSSe sheet as a promising photocatalyst for water splitting.

The Janus MoSSe sheet has aroused significant attention due to its band edge position and intrinsic dipole moment, making it a strong candidate for water splitting photocatalysis. However, weak water adsorption seriously prevents its further application. Here, first-principles calculations are used to explore the effect of intrinsic defects on water adsorption and conversion at the Janus MoSSe sheet. First-principles calculation results clearly show that intrinsic defects (S, Mo, and Mo) can effectively alter the interaction between water and the MoSSe sheet. Except for S defects, the adsorption energy of water at Mo or Mo defects can be significantly increased by -1.0 to -1.5 eV with respect to the weak water adsorption on a pristine MoSSe sheet of about -0.24 eV. More importantly, the energy barrier for water conversion can be dramatically lowered by 48% to 0.7 eV at Mo or Mo defects, together with a more stable final state. Such significant enhancement of the adsorption energy is attributed to the red shift of water energy levels, resulting from the strong interaction between O2p orbitals and Mo3d orbitals. It is shown that the intrinsic defects have the potential to change the photocatalytic reactivity of the surface, and thus this may serve as an important way to design photocatalysts for water splitting.