A theoretical investigation of Ta3N5/BaTaO2N heterostructure for solar water splitting

Heterostructure engineering represents a powerful strategy for enhancing the photocatalytic performance of semiconductor materials. In this study, we employ first-principles calculations to systematically investigate the geometric structure, stability, electronic properties, optical absorption, band alignment, and surface reactions of Ta₃N₅/BaTaO₂N heterostructure − a promising photocatalytic system for water splitting. Two distinct Ta₃N₅(110)/BaTaO₂N(200) interface models were constructed based on experimental observations, considering different terminations of BaTaO₂N(200). Our calculations reveal that the interfacial bonding in Ta₃N₅(110)/BaTaO₂N(200)_Ba is weaker than in Ta₃N₅(110)/BaTaO₂N(200)_Ta, as evidenced by adhesion energy analysis. Ab initio molecular dynamics (AIMD) simulations confirm the thermodynamic stability of both heterostructures. Electronic structure analysis demonstrates that the preserved direct bandgap character in these heterostructures suggests favorable optical transition properties, while the combined bandgap energies extend light absorption across a broader spectral range compared to individual components. Local density of states (LDOS) further reveals that the valence and conduction band edges are spatially separated across different atomic layers, promoting efficient charge transfer. Both heterojunction models exhibit a type-II band alignment, with Ta₃N₅ displaying lower valence and conduction bands than BaTaO₂N, thereby driving photogenerated electrons toward Ta₃N₅ and holes toward BaTaO₂N for effective carrier separation. Mechanistic studies show that the Ta₃N₅(110)/BaTaO₂N(200) heterostructure maintains the intrinsic hydrogen evolution reaction (HER) activity of Ta₃N₅(110) while notably improving the oxygen evolution reaction (OER) performance compared to pristine BaTaO₂N(200). These findings provide fundamental insights into the interfacial effects governing photocatalytic efficiency in Ta₃N₅/BaTaO₂N heterojunctions and offer valuable guidance for the rational design of high-performance semiconductor photocatalysts for renewable energy applications.