Cs₃Bi₂Cl₃Br₆:g-C₃N₄ Nanostructure-Based Thin Film Photocatalysts for Hydrogen Production under Daylight and Simulated Light

The strategic design of nanocomposites and their rationally constructed heterojunctions offer an effective approach for enhancing light harvesting and optimizing energy conversions. Herein, we report the design and synthesis of an aqueous-stable, lead-free Cs3Bi2Cl3Br6 perovskite integrated with g-C3N4. An excellent band alignment of Cs–Bi-based perovskite with g-C3N4 was achieved by tuning the anion in the Cs–Bi-based perovskite, leading to remarkable photocatalytic performance. The construction of a hybrid nanocomposite in a thin film device achieved an impressive photocatalytic hydrogen generation rate of 341 μmol h–1 g–1, which is 16 times higher than that of the perovskite@g-C3N4 in powder form. The test results are albeit higher when a quartz reactor is used, where 20 mg of the optimized catalyst reaches up to 539 μmol g–1 h–1 with an apparent quantum efficiency (AQE) of 1.32%. Spectroscopic studies, including photoluminescence (PL) and time-correlated single photon counting (TCSPC), have established the presence of a long-lived charge-separated state and confirmed excited state electron injection into g-C3N4. Cs3Bi2Cl3Br6@g-C3N4 heterojunctions not only accelerate charge transfer but also significantly enhance the hydrogen evolution rate and stability of the photocatalysts.