Two-dimensional Hf2CO2/GaN van der Waals heterostructure for overall water splitting: a density functional theory study

Designing two-dimensional heterojunction with an appropriate band structure is a promising route to search new photocatalyst toward overall water splitting. In the present work, the Hf2CO2 monolayer was integrated with planar and buckled GaN monolayer to construct the Hf2CO2/GaN heterostructures. We then performed a systematic investigation on the stability, electronic structure and carrier mobility of the Hf2CO2/GaN heterostructures based on the density functional theory. Due to the negative formation energy and positive frequency modes in phonon dispersion spectra, the designed Hf2CO2/GaN–C′B′, Hf2CO2/GaNH2–C′A′ and Hf2CO2/GaNH2–A′C′ are energetically stable. The Hf2CO2/GaN–C′B′ and Hf2CO2/GaNH2–C′A′ heterostructures have the suitable band structures which satisfy the requirements of photocatalytic water splitting. The VBM and CBM of the stable heterostructures are completely dominated by GaN (GaNH2) layer and Hf2CO2 layer, respectively, which is beneficial to the spatial separation of photogenerated hole and electron. With comparison to GaN monolayer, the designed heterostructures exhibit enhanced response to both visible and ultraviolet light. The electron mobilities of Hf2CO2/GaNH2 heterostructures are as high as ~ 2 × 104 cm2 V− 1 s− 1. The Hf2CO2/GaN heterostructures can be considered as the potential candidates for the applications of both photocatalytic water splitting and optoelectronic devices.