Halogen-driven bandgap opening in graphdiyne for overall photocatalytic water splitting

In this work, we studied the electronic band structure of the halogen (F, Cl, and Br) functionalized graphdiynes (GDYs) by using hybrid density functional theory. The results revealed that the bandgap energies of modified GDYs increase as the number of halogen atoms increases. It is also found that the position of the valence band maximum (VBM) is influenced by the electronegativity of halogen atoms. The higher the electronegativity, the deeper the VBM of the GDYs modified by the same number of halogen atoms. Importantly, our results revealed that the bandgap of GDY could be effectively tuned by mixing types of halogen atoms. The new generated conduction band and valence band edges are properly aligned with the oxidation and reduction potentials of water. Further thermodynamic analysis confirms that some models with mixing types of halogen atoms exhibit higher performance of overall photocatalytic water splitting than non-mixing models. This work provides useful insights for designing efficient photocatalysts that can be used for overall water splitting.