Depressing charge recombination in hybrid perovskites by introducing dynamic electron/energy relay couple towards enhanced photocatalytic hydrogen production

Organic-inorganic hybrid perovskites (OIHPs) like methylammonium lead iodide perovskite (MAPbI₃) are attractive candidates for solar hydrogen production. However, the serious charge recombination occurring on OIHPs seriously impairs the photocatalytic performance, defining the imperative to develop efficient strategies that can address this issue. Herein, we show that by introducing dynamic Cu/(CuI₂)^- couple as the electron/energy relay station, drastically improved extraction of photogenerated electrons from MAPbI₃ can be achieved, thus leading to significantly depressed charge recombination and enhanced photocatalytic hydrogen production. We find that the electrons generated from MAPbI₃ can be efficiently captured by the (CuI₂)^- ions in the reaction solution to produce metallic Cu as the electron/energy storage medium, therefore retarding the recombination of photogenerated charges and realizing the simultaneous storage of photon energy. Subsequently, the in-situ generated metallic Cu reacts with HI to release the as-stored solar energy, realizing decoupled off-light hydrogen generation that resembles the dark reduction reaction in natural photosynthesis. Moreover, metallic Cu can also act as a hydrogen evolution reaction (HER) co-catalyst to promote the proton reduction reaction with photogenerated electrons from MAPbI₃. By further introducing Pt as the HER co-catalyst, additional drastic enhancement in both dark HER and light-driven proton reduction reaction can be realized. Consequently, the photocatalytic hydrogen evolution activity of MAPbI₃ is enhanced by ca. 2334 times through the cascade interplay of the Cu/(CuI₂)^- couple and Pt co-catalyst, achieving an outstanding solar-to-hydrogen (STH) energy conversion efficiency of ca. 5.25%.