Continually band-tunable bismuth oxyhalides BiOBr1–xIx as O2-evolving photocatalysts for visible-light-driven Z-scheme water splitting

Abstract

Continuous and compositionally controllable band-structure tuning remains a central challenge in visible-light-driven photocatalytic water splitting. Here, we demonstrate that layered bismuth oxyhalide solid solutions (BiOBr_1-xI_x) can provide a continuously tunable platform for rational band engineering in visible-light-driven Z-scheme water splitting. By exploiting the intrinsic halide-dependent band tunability of BiOBr_1-xI_x solid solutions, we achieved a balance between extended visible-light absorption and a sufficient reaction thermodynamic driving force. The optimal composition (x = 0.1) exhibited sustained O₂ evolution in the presence of Fe³⁺ as a reversible electron acceptor, reflecting the interplay between enhanced visible-light absorption and competing thermodynamic and charge-transport limitations. Suppression of iodine depletion via arc plasma deposition of metallic Pt cocatalysts further enhanced the activity by preserving the composition. When integrated as the O₂-evolving photocatalyst in a Z-scheme system, stoichiometric and steady overall water splitting was achieved for over 50 h under visible light. These findings establish compositionally tunable bismuth oxyhalide solid solutions as versatile materials for rational valence-band engineering in visible-light-driven water splitting.