Band Engineering of Double-Layered Sillén–Aurivillius Perovskite Oxychlorides for Visible-Light-Driven Water Splitting

Recently, Bi 4 MO 8 X (M = Nb and Ta; X = Cl and Br), Sillén–Aurivillius-type single-layered perovskite oxyhalides, have been shown to be promising visible-light-responsive photocatalysts with unique valence band structures. Here, we report on the synthesis, structures, and photocatalytic properties of a series of double-layered analogues A 4 A′M 2 O 11 Cl (A, A′ = Bi, Pb, Ba, and Sr; M = Ta, Nb, and Ti). Fourteen compounds including ten unreported compounds were successfully synthesized via a two-step method with various combinations of preliminary-prepared multimetal oxide and oxyhalide precursors. In a marked contrast to Bi 4 MO 8 X with an almost unvaried valence band maximum (VBM) and conduction band minimum (CBM), both VBM and CBM of A 4 A′M 2 O 11 X are variable to some degree, with a change of compositions. In Sr 2 Bi 3 M 2 O 11 Cl, for example, Sr-site replacement by Pb and Ba resulted in a shift of the valence and conduction band edges toward narrowing the band gaps. Structural characterizations and density functional theory/Madelung calculations revealed that the observed band edges are mainly understood in terms of the interaction between the Bi/Pb 6s 2 lone pair and O 2p orbitals and Madelung site potentials of Bi 3+ cations. Furthermore, compounds with a higher occupancy of Bi 3+ in the fluorite layer showed improved conductivity of photoexcited electrons, leading to better photoelectrochemical performance for water oxidation under visible light.