Band Engineering of Aurivillius Perovskites through Halogen Incorporation for Enhanced Photocatalytic H ₂ Production

Photocatalytic hydrogen evolution (PHE) is a key pathway toward clean and sustainable hydrogen production. Although Bi2WO6 is one of the most widely explored Aurivillius photocatalysts, its ability to drive the reduction half-reaction remains limited, mainly due to its band positions and moderate charge-carrier dynamics. Therefore, fine-tuning of both the valence and conduction bands is essential to further enhance its PHE activity. In this work, we address this limitation by employing a mixed-cation and mixed-anion band-engineering approach. An oxyfluoride Aurivillius compound, Bi2W0.5Nb0.5O5.5F0.5, was rationally designed and synthesized by partially substituting W6+ with the lower-valence Nb5+ cation, thereby enabling charge balance for fluoride incorporation. Oxyfluoride exhibits a significantly higher cocatalyst-free PHE (31.5 μmol) in 5 h compared to that of the oxide compound Bi2WO6 (18.9 μmol). The incorporation of Nb5+ and F– ions introduces local lattice distortions by altering M–X (M = metal; X = O2–/F–) bond lengths and inducing octahedral tilting within the perovskite layers. These structural changes modify the orbital interactions between cations and anions, leading to a tuned electronic band structure with an elevated reduction potential and a slightly narrower band gap. As a result, light absorption and charge carrier separation are enhanced, promoting a more efficient electron transfer for hydrogen evolution. The compound also demonstrates excellent structural and photocatalytic stability over repeated cycles. This study highlights that compositional tuning through mixed-anion and mixed-cation design is an effective strategy for modulating the structure–property relationship and enhancing the photocatalytic activity of Aurivillius-type materials.