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 Hf 2 CO 2 monolayer was integrated with planar and buckled GaN monolayer to construct the Hf 2 CO 2 /GaN heterostructures. We then performed a systematic investigation on the stability, electronic structure and carrier mobility of the Hf 2 CO 2 /GaN heterostructures based on the density functional theory. Due to the negative formation energy and positive frequency modes in phonon dispersion spectra, the designed Hf 2 CO 2 /GaN–C′B′, Hf 2 CO 2 /GaNH 2 –C′A′ and Hf 2 CO 2 /GaNH 2 –A′C′ are energetically stable. The Hf 2 CO 2 /GaN–C′B′ and Hf 2 CO 2 /GaNH 2 –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 (GaNH 2 ) layer and Hf 2 CO 2 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 Hf 2 CO 2 /GaNH 2 heterostructures are as high as ~ 2 × 10 4 cm 2 V − 1 s − 1 . The Hf 2 CO 2 /GaN heterostructures can be considered as the potential candidates for the applications of both photocatalytic water splitting and optoelectronic devices.