Lead halide perovskite (LHP) nanocrystals have recently been actively investigated for photocatalysis, owing to their inexpensive fabrication and excellent optoelectronic properties. However, LHP nanocrystals have not been used for artificial photosynthesis in aqueous solution, owing to their high sensitivity to water. In this study, water‐tolerant cobalt‐doped CsPbBr3/Cs4PbBr6 nanocrystals have been prepared with the protection of hexafluorobutyl methacrylate. The resultant materials are employed as efficient photocatalysts for visible‐light‐driven CO2 reduction in pure water. The perovskite nanocrystals with 2 % cobalt doping afford an impressive overall yield of 247 μmol g−1 for photocatalytic CO2 conversion into CO and CH4, using water as an electron source. This study represents a significant step for practical artificial photosynthesis by using LHP nanocrystals as photocatalysts in aqueous solution.

The instability and low inferior catalytic activity of metal-halide perovskite nanocrystals are crucial issues for promoting their practical application in the photocatalytic field. Herein, we in situ coat a thin graphdiyne (GDY) layer on CsPbBr3 nanocrystals based on a facile microwave synthesis method, and employ it as a photocatalyst for CO2 reduction. Under the protection of GDY, the CsPbBr3-based photocatalyst delivers significantly improved stability in a photocatalytic system containing water concomitant with enhanced CO2 uptake capacity. The favorable energy offset and close contact between CsPbBr3 and GDY trigger swift photogenerated electron transfer from CsPbBr3 to doping metal sites in GDY, boosting a remarkable improvement in the photocatalytic performance for CO2 reduction. Without adding traditional sacrificial reductants, the cobalt-doped photocatalyst achieves a high yield of 27.7 μmol g–1 h–1 for photocatalytic CO2 conversion to CO based on water as a desirable electron source, which is about 8 times higher than that of pristine CsPbBr3 nanocrystals.

The judicious design of efficient electron mediators to accelerate the interfacial charge transfer in a Z‐scheme system is one of the viable strategies to improve the performance of photocatalysts for artificial photosynthesis. Herein, ultrathin and small‐size graphene oxide (USGO) nanosheets are constructed and employed as the electron mediator to elaborately exploit an efficient CsPbBr3‐based all‐solid‐state Z‐scheme system in combination with α‐Fe2O3 for visible‐light‐driven CO2 reduction with water as the electron source. CsPbBr3 and α‐Fe2O3 can be closely anchored on USGO nanosheets, owing to the existence of interfacial strong chemical bonding behaviors, which can significantly accelerate the photogenerated carrier transfer between CsPbBr3 and α‐Fe2O3. The resultant improved charge separation efficiency endows the Z‐scheme system exhibiting a record‐high electron consumption rate of 147.6 µmol g−1 h−1 for photocatalytic CO2‐to‐CO conversion concomitant with stoichiometric O2 from water oxidation, which is over 19 and 12 times higher than that of pristine CsPbBr3 nanocrystals and the mixture of CsPbBr3 and α‐Fe2O3, respectively. This work provides a novel and effective strategy for improving the catalytic activity of halide‐perovskite‐based photocatalysts, promoting their practical applications in the field of artificial photosynthesis.

The well‐known toxicity of lead‐halide‐perovskite (LHP) nanocrystals limits their commercial applications in photocatalysis. Herein, an in situ controlled growth strategy is reported for lead‐free perovskite nanocrystals (Cs3Bi2I9) on the surface of ultrathin Bi2WO6 nanosheets through co‐sharing Bi atoms, to generate a direct Z‐scheme heterojunction of Cs3Bi2I9/Bi2WO6. Co‐sharing of the Bi atom can enable intimate contact and strong electron coupling between Cs3Bi2I9 and Bi2WO6, which can effectively promote the interfacial charge transfer between Cs3Bi2I9 and Bi2WO6 complying with a Z‐scheme pathway. The resulting efficient charge transfer and well‐preserved redox ability of Cs3Bi2I9/Bi2WO6 heterojunction endow it with a significant improvement of photocatalytic activity for the conversion of CO2‐to‐CO integrated with water oxidation, exhibiting a fourfold increase compared with pure Cs3Bi2I9 nanocrystals. This study paves a new avenue for the construction of efficient Z‐scheme heterojunction based on lead‐free halide perovskite, which should stimulate further passion on the development of high performance of lead‐free halide perovskite materials for photocatalytic application.

We have firstly demonstrated the photocatalytic utilization of a halide perovskite for combining reduction of CO2 with selective oxidation of methanol.