Enhanced photocatalytic performance of ZnO monolayer for water splitting via biaxial strain and external electric field

The photocatalytic capability of ZnO monolayer for water splitting is restricted by low absorption in the visible light region due to its wide band gap. Here, using density functional theory calculations, we present a theoretical study on tuning the band gap via biaxial strain and electric field to enhance photocatalytic performance of ZnO monolayer. Our theoretical calculations show that ZnO monolayer at 10% biaxial tensile strain has suitable band edge positions for photocatalytic water splitting, and its band gap reduces to 2.70 eV, which is smaller than that of the other widely studied photocatalysts. Meanwhile, the oxidation capacity of the ZnO monolayer at 10% biaxial tensile strain is increased, which is beneficial for improving the efficiency of the photocatalytic water splitting reaction. Thus, the ZnO monolayer at 10% biaxial tensile strain is a promising water splitting photocatalyst. Interestingly, the ZnO monolayers at 10% and 7.5% biaxial compressive strains are suitable for hydrogen production but not for oxygen evolution and can be considered to be a Z-type photocatalyst. Furthermore, we find that an external electric field has only a weak effect for enhancing photocatalytic performance. Our theoretical work shows that biaxial strain can effectively enhance the performance of the ZnO monolayer for photocatalytic water splitting.