Boosting CsPbBr 3 ‐Driven Superior and Long‐Term Photocatalytic CO 2 Reduction under Pure Water Medium: Synergy Effects of Multifunctional Melamine Foam and Graphitic Carbon Nitride (g‐C 3 N 4 )

Achieving high‐efficiency and long‐term CO 2 photoreduction under an aqueous environment is still a challenge for CsPbBr 3 ‐based catalysts due to the poor humidity resistance. Herein, multifunctional melamine foam (MF) and graphitic carbon nitride (g‐C 3 N 4 ) are selected to modify CsPbBr 3 , successfully realizing efficient and long‐term CO 2 reduction under pure H 2 O medium. The 3D framework of MF can support CsPbBr 3 , avoiding its degradation due to direct contact with the aqueous solution. In addition, the abundant porosity of MF can accelerate H 2 O evaporation, achieving sufficient blending of CO 2 with H 2 O vapor. These functions lead to the enormously enhanced conversion efficiencies of MF/CsPbBr 3 and MF/g‐C 3 N 4 compared to powdery catalysts. Photocatalytic activities of MF/CsPbBr 3 ‐g‐C 3 N 4 are further improved due to the accelerated charge migration, and accordant sites of electron accumulation and CO 2 adsorption in composites. The best product yield of the composite is 975.57 μmol g −1  h −1 , and the corresponding electron consumption rate reaches 2571.27 μmol g −1  h −1 , surpassing almost all the already reported CsPbBr 3 ‐based catalysts whether in H 2 O or organic solvent media. Moreover, the strong surface hydrophobicity and excellent photothermal effect of MF/CsPbBr 3 ‐g‐C 3 N 4 result in long‐term and stable photocatalytic activity, with no obvious CO and CH 4 decrease after continuous reaction for 76 h.