Lead Bismuth Oxyhalides PbBiO₂X (X = Cl, Br) as Visible-Light-Responsive Photocatalysts for Water Oxidation: Role of Lone-Pair Electrons in Valence Band Engineering

We show that layered oxyhalides PbBiO₂X (X = Cl, Br, I) with a Sillén-type structure possess band levels appropriate for visible-light-induced water splitting. Under visible light, PbBiO₂Cl and PbBiO₂Br with band gap (BG) of 2.51 and 2.48 eV, respectively, stably oxidized water to O₂ in the presence of an Fe³⁺ electron acceptor. A comparison with structurally related SrBiO₂Cl and BaBiO₂Cl (BG = 3.55 and 3.54 eV) combined with DFT calculations revealed a significant interaction between O 2p and Pb 6s orbitals leading to the upward shift of the valence band maximum in PbBiO₂X as compared with (Sr,Ba)­BiO₂Cl. Z-scheme water splitting into H₂ and O₂ has been demonstrated using PbBiO₂Cl as an O₂-evolving photocatalyst, coupled with an appropriate H₂-evolving photocatalyst in the presence of an Fe³⁺/Fe²⁺ redox mediator.