Bandgap funneling in bismuth-based hybrid Perovskite photocatalyst with efficient visible-light-driven hydrogen evolution

The photocatalytic system using hydrohalic acid (HX) for hydrogen production is a promising strategy to generate clean and renewable fuels as well as value-added chemicals (such as X₂/X₃⁻). However, it is still challenging to develop a visible-light active and strong-acid resistive photocatalyst. Hybrid perovskites have been recognized as a potential photocatalyst for photovoltaic HX splitting. Herein, a novel environmentally friendly mixed halide perovskite MA₃Bi₂Cl_9–xI_x with a bandgap funnel structure is developed, i.e., confirmed by energy dispersive X-ray analysis and density functional theory calculations. Due to gradient neutral formation energy within iodine-doped MA₃Bi₂Cl₉, the concentration of iodide element decreases from the surface to the interior across the MA₃Bi₂Cl_9–xI_x perovskite. Because of the aligned energy levels of iodide/chloride-mixed MA₃Bi₂Cl_9–xI_x, a graded bandgap funnel structure is therefore formed, leading to the promotion of photoinduced charge transfer from the interior to the surface for efficient photocatalytic redox reaction. As a result, the hydrogen generation rate of the optimized MA₃Bi₂Cl_9–xI_x is enhanced up to ≈341 ± 61.7 µmol h⁻¹ with a Pt co-catalyst under visible light irradiation.