Enhanced Photocatalytic O₂ Evolution over Layered Perovskite Oxyiodide Ba₂Bi₃Nb₂O₁₁I through Flux Synthesis and Surface Modifications

Sillén-Aurivillius oxyiodides, particularly Ba₂Bi₃Nb₂O₁₁I with double-perovskite layers, are promising photocatalysts for visible-light-driven water splitting due to their excellent light absorption and carrier transport properties. However, efforts to enhance their photocatalytic performance through advancements in synthesis methods or surface modifications remain limited. Here, we report the flux synthesis of Ba₂Bi₃Nb₂O₁₁I and the optimization of cocatalyst loading. Single-phase Ba₂Bi₃Nb₂O₁₁I was successfully synthesized using molten alkali iodide salts under appropriate reaction conditions. The heating rate during the synthesis significantly influenced crystallinity and carrier lifetime, as shown by time-resolved microwave conductivity measurements. By optimizing the reaction conditions to enhance crystallinity (prolong carrier lifetime), the flux-synthesized sample exhibited a higher sacrificial O₂ evolution rate than that prepared via the conventional solid-state reaction. Furthermore, precise control over the loading conditions of the iron-ruthenium oxide cocatalyst ((Fe,Ru)O<i>_<i>x</i></i>) significantly enhanced nonsacrificial O₂ evolution from an aqueous Fe³⁺ solution. Electrochemical analysis revealed that the tuned loading conditions enhanced the catalytic activity of the (Fe,Ru)O<i>_<i>x</i></i> cocatalyst for both water oxidation and Fe³⁺ reduction. Finally, Z-scheme water splitting using the optimized (Fe,Ru)O<i>_<i>x</i></i>-loaded Ba₂Bi₃Nb₂O₁₁I photocatalyst showed superior efficiency than that using the previously reported unoptimized sample. This study provides valuable insights into enhancing the O₂ evolution activity of oxyiodide photocatalysts for water-splitting applications.