2D-HfS2 as an efficient photocatalyst for water splitting

Abstract

Two dimensional monolayer nanostructures for water splitting solar photocatalysts are drawing more attention due to their extraordinary properties. Using first principles calculations we have systematically investigated the structural, electronic and vibrational properties of corresponding HfS₂ monolayers in both hexagonal (1H) and trigonal (1T) phases. The most stable adsorption configurations and adsorption energies are calculated. The adsorption energy of H₂O on the substrate is 646.53 kJ mol⁻¹ for the 1H-phase and 621.65 kJ mol⁻¹ for the 1T-phase of HfS₂. This shows that H₂O molecules have a stronger interaction with the HfS₂ substrate. The calculated redox potentials of H₂O splitting lie properly astride the valence and conduction bands, suggesting that the monolayers of 1H- and 1T-HfS₂ show the same characteristics as a photocatalyst for water splitting. Furthermore, we also calculated that the optical band gaps for the 1H and 1T phases of HfS₂ are 2.60 eV and 3.10 eV, respectively. We have also calculated Raman spectrum signatures of the monolayer 1H and 1T-phase of the in-plane vibrational mode of the Hf and S atoms (E_1g) and the out-of-plane vibrational mode of S atoms (A_1g and A_2u). Our work suggests that a lot more research and attention in this field is needed for the practical application of the material as visible light active photocatalysts.