Improving the stability of lead halide perovskite quantum dots (QDs) in a system containing water is the key for their practical application in artificial photosynthesis. Herein, we encapsulate low‐cost CH3NH3PbI3 (MAPbI3) perovskite QDs in the pores of earth‐abundant Fe‐porphyrin based metal organic framework (MOF) PCN‐221(Fex) by a sequential deposition route, to construct a series of composite photocatalysts of MAPbI3@PCN‐221(Fex) (x=0–1). Protected by the MOF the composite photocatalysts exhibit much improved stability in reaction systems containing water. The close contact of QDs to the Fe catalytic site in the MOF, allows the photogenerated electrons in the QDs to transfer rapidly the Fe catalytic sites to enhance the photocatalytic activity for CO2 reduction. Using water as an electron source, MAPbI3@PCN‐221(Fe0.2) exhibits a record‐high total yield of 1559 μmol g−1 for photocatalytic CO2 reduction to CO (34 %) and CH4 (66 %), 38 times higher than that of PCN‐221(Fe0.2) in the absence of perovskite QDs.

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.

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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.

Theauthors declare no conflict of interest.Keywords: CO 2 reduction ·i ron ·metalorganic frameworks (MOFs) ·perovskite quantum dots · photocatalysis Figure 3. a) Mott-Schottky plots of PCN-221(Fe 0.2 )and b) MAP-bI 3 @PCN-221(Fe 0.2 ). c) Steady-state photoluminescence spectrao f PCN-221, PCN-221(Fe 0.2 ), MAPbI 3 @PCN-221,a nd MAPbI 3 @PCN-221-(Fe 0.2 ). d) Time-resolved photoluminescence decays of PCN-221, PCN-221(Fe 0.2 ), MAPbI 3 @PCN-221, and MAPbI 3 @PCN-221(Fe 0.2 )with ET519LP as long-wavelength pass filter,after excitation at 375 nm.