The structural, electronic and optical properties of the two-dimensional (2D) heterostructure of ZnO/GeC are calculated using hybrid density functional theory. The results suggest that the ZnO monolayer has a stable contact with the GeC monolayer. Biaxial strains can significantly tune the bandgaps and band alignments of the ZnO/GeC heterostructures and all the strained heterostructures are beneficial for absorbing visible light. The induced built-in electric field across the ZnO/GeC heterostructure interface can reduce photoinduced carrier recombination rates, which is favorable for enhancing the photocatalytic performance. In particular, the band edge positions of the ZnO/GeC heterostructures of biaxial strains of , 0, 2%, 4%, and 6% are thermodynamically favorable for overall water redox processes in the pH range of 6.9–12.4, 9.4–13.1, 12.1–14.0, 12.9–14.0, 12.5–14.0, 10.9–14.0 and 5.5–8.6. Our investigation exhibits an effective method to design 2D material based water-splitting photocatalysts.

With adapted bandgap for absorbing visible light, suitable band edge positions, and induced electric field inhibiting photoexcited carrier recombination, 2% strained ZnO/AlN composite is a promising water-splitting photocatalyst.