Understanding the electronic structure of Y2Ti2O5S2 for green hydrogen production: a hybrid-DFT and GW study

Utilising photocatalytic water splitting to produce green hydrogen is the key to reducing the carbon footprint of this crucial chemical feedstock. In this study, density functional theory (DFT) is employed to gain insights into the photocatalytic performance of an up-and-coming photocatalyst Y2Ti2O5S2 from first principles. Eleven non-polar clean surfaces are evaluated at the generalised gradient approximation level to obtain a plate-like Wulff shape that agrees well with the experimental data. The (001), (101) and (211) surfaces are considered further at hybrid-DFT level to determine their band alignments with respect to vacuum. The large band offset between the basal (001) and side (101) and (211) surfaces confirms experimentally observed spatial separation of hydrogen and oxygen evolution facets. Furthermore, relevant optoelectronic bulk properties were established using a combination of hybrid-DFT and many-body perturbation theory. The optical absorption of Y2Ti2O5S2 weakly onsets due to dipole-forbidden transitions, and hybrid Wannier-Mott/Frenkel excitonic behaviour is predicted to occur due to the two-dimensional electronic structure, with an exciton binding energy of 0.4 eV.

Automated summary

Utilising photocatalytic water splitting is crucial for producing green hydrogen and reducing the carbon footprint of this important chemical feedstock. This study employs density functional theory (DFT) to gain insights into the photocatalytic performance of a promising photocatalyst, Y2Ti2O5S2, from first principles. The study evaluates eleven non-polar clean surfaces at the generalised gradient approximation level and further considers the (001), (101), and (211) surfaces at the hybrid-DFT level to determine their band alignments. The study also establishes relevant optoelectronic bulk properties using a combination of hybrid-DFT and many-body perturbation theory.