Lead-Free HalideDouble-Perovskite Nanocrystals onAg-Modified g‑C₃N₄ for Enhanced HydrogenEvolution via Synergistic Photoexcitation and Electron Injection

Lead-free halide double-perovskite Cs₂AgBiBr₆ nanocrystals (CABB-NC) have proven to be effective photocatalysts for the evolution of H₂ from HBr solutions. However, the photocatalytic hydrogen evolution efficacy of CABB nanocrystals is hampered by its detrimental charge recombination at the nanoscale domain. To address the challenge, Ag nanoparticles were anchored on the CABB-NC-g-C₃N₄ (AgCABBgCN) frameworks so that the plasmonic effect of silver nanoparticles (Ag NPs) could be effectively used, and synergistic photoexcitation and electron injection resulted in an enhanced hydrogen evolution performance. The AgCABBgCN system exhibited a significant photocatalytic hydrogen evolution rate (HER) of 479 μmol g^–1 h^–1, which is 10 times and 1.78 times higher than the HER of pure CABB-NC and CABB-NC/g-C₃N₄ systems, respectively. The diffuse reflectance spectra indicate an enhancement in the absorption coefficient over the entire visible range due to the surface plasmon resonance effect of the Ag NPs. The high-resolution transmission electron microscopy (HRTEM) and photoelectrochemical measurements suggest strong interfacial electron coupling between the Ag nanoparticles and CABB-NC on the g-C₃N₄ framework. The strong coupling between the CABB NCs and Ag NPs greatly promotes the generation and separation of photoinduced charge carriers while suppressing their recombination. Furthermore, the experimental results suggest a possible mechanism based on Schottky and n–n-type heterojunctions leading to synergistic photoexcitation and electron injection resulting in enhanced photocatalytic hydrogen evolution. The recyclability and reusability of the photocatalyst are demonstrated by its excellent photocatalytic cycling stability after 1 h of six repeated photocatalytic cycle experiments.