Layered Perovskite Oxychloride Bi₄NbO₈Cl: A Stable Visible Light Responsive Photocatalyst for Water Splitting

Mixed anion compounds are expected to be a photocatalyst for visible light-induced water splitting, but the available materials have been almost limited to oxynitrides. Here, we show that an oxychrolide Bi₄NbO₈Cl, a single layer Sillen-Aurivillius perovskite, is a stable and efficient O₂-evolving photocatalyst under visible light, enabling a Z-scheme overall water splitting by coupling with a H₂-evolving photocatalyst (Rh-doped SrTiO₃). It is found that the valence band maximum of Bi₄NbO₈Cl is unusually high owing to highly dispersive O-2p orbitals (not Cl-3p orbitals), affording the narrow band gap and possibly the stability against water oxidation. This study suggests that a family of Sillen-Aurivillius perovskite oxyhalides is a promising system to allow a versatile band level tuning for establishing efficient and stable water-splitting under visible light.