Bismuth-based layered-perovskite oxyiodides for visible-light water splitting Kanta Ogawa 1 , Aron Walsh 1 , and Ryu Abe 2 1 Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ, UK, 2 Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan Water splitting photocatalysis using semiconductor photoabsorbers is a promising way to produce clean H 2 by utilizing solar energy, where developing efficient visible-light responsive photocatalyst is desired. Materials containing iodine usually exhibit band gaps much narrower than those of their chloride and bromide counterparts owing to the low electronegativity, as seen in metal halide perovskite. However, they have rarely been used for photocatalytic water splitting (involving oxygen (O 2 ) evolution). Although the high-energy I 5p band contributes to the negative-shift of valence band maximum to reduce the band gap, the iodide ions are preferentially oxidized by photogenerated holes, which decomposes the photocatalyst itself and deactivates water oxidation. 1 In the present study, we demonstrate that Sillén–Aurivillius oxyiodides (Bi 4 NbO 8 X ( n = 1), Ba M Bi 3 Nb 2 O 11 I ( n = 2;), Bi 5 BaTi 3 O 14 X ( n = 3), and Bi 6 NbWO 14 X) with layered-perovskite structures serve as efficient photocatalysts for water splitting. 2 They have narrower band gaps and much higher activities than their chloride counterparts. An unusually high energy O 2p band surpasses I 5p, thus avoiding photo-instability and achieving efficient water oxidation. The energetic location of the O 2p band is rationalized from the underlying crystal structure and chemical bonding. The analysis extends to the conduction band shifts, where Bi 4 NbO 8 I, Bi 5 BaTi 3 O 14 I, and Bi 6 NbWO 14 I are negatively shifted as compared to their chloride counterparts. The inter-layer Bi-Bi interaction plays an important role in tuning conduction band. On the other hand, iodine introduction to Ba M Bi 3 Nb 2 O 11 I ( n = 2) exerts little influence on the position of the conduction band minimum, which is due to the contribution of the perovskite to its conduction band. This study not only paves the way for Bi-based oxyiodides as water splitting photocatalysts, but offers pathways to control their optoelectronic properties. References 1. H. Suzuki, H. Kunioku, M. Higashi, O. Tomita, D. Kato, H. Kageyama and R. Abe, Chem. Mater. , 2018, 30 , 5862–5869. 2. K. Ogawa, H. Suzuki, C. Zhong, R. Sakamoto, O. Tomita, A. Saeki, H. Kageyama and R. Abe, J. Am. Chem. Soc. , 2021, 143 , 8446–8453.
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