Enhanced photocatalytic hydrogen evolution through suppressed electron–hole recombination in Cs2AgBiBr6-NC/g-C3N4 nanocomposites

Abstract

Cs₂AgBiBr₆ (CABB), a lead-free halide double perovskite, is a stable material with a suitable band gap for photocatalytic applications. Although its potential in photocatalytic H₂ evolution has been reported, the efficiency is relatively low for bulk CABB. As the surface protective ligands may act as a recombination center for electron and holes, there are very few reports of H₂ evolution using Cs₂AgBiBr₆ nanocrystals (CABB-NC) in the literature. Herein, we report the synthesis of a CABB-NC/g-C₃N₄ nanocomposite with an enhanced H₂ evolution rate through suppressing the electron–hole recombination by anchoring the CABB-NC on g-C₃N₄ sheets. The in situ synthesis process of the nanocomposite prevents agglomeration of CABB-NC and reduces the size to the range of 4–6 nm compared to CABB-NC alone, even after post-synthesis washing processes. The CABB-NC/g-C₃N₄ nanocomposite exhibits excellent photocatalytic performance with a hydrogen evolution rate of 268 μmol g⁻¹ h⁻¹ under visible light irradiation (λ ≥ 420 nm), which is much higher than that reported for bulk CABB. The highly dispersed particles anchored on the g-C₃N₄ matrix enhance the separation and transportation of the photogenerated electron–hole pair. Quenching of the photoluminescence is observed in the CABB-NC/g-C₃N₄ nanocomposite compared to the CABB-NC, and the higher photocurrent (4.4 mA) generated by the CABB-NC/g-C₃N₄ nanocomposite compared to that of CABB-NC (1.5 mA) indicates efficient charge transfer between CABB-NC and g-C₃N₄ and explains the higher photocatalytic activity shown by the nanocomposite. Furthermore, the low charge transfer resistance exhibited by the CABB-NC/g-C₃N₄ nanocomposite compared to CABB-NC and g-C₃N₄ indicate the suitability of the in situ synthesis of CABB-NC for efficient, durable and sustainable photocatalytic hydrogen evolution.