Atmospheric CO₂-to-acetaldehyde artificial photosynthesis in metallo hydrogen-bonded organic frameworks

Abstract Artificial photosynthesis of acetaldehyde from atmospheric CO 2 is highly promising, yet remains severely limited by low CO 2 concentration in air and sluggish proton transfer kinetics. Herein, we report metallo hydrogen-bonded organic frameworks (MHOFs) of HNNU-X (X = O, S, Se) which enable acetaldehyde synthesis directly from air, water, and natural sunlight. Among them, HNNU-Se exhibits a competitive acetaldehyde production rate of 557.1 μmol g⁻¹ h⁻¹ with high electron-based selectivity of 95% under outdoor conditions, without need of sacrificial agents. Mechanistic studies reveal that HNNU-X creates a proton-rich microenvironment in which [Zn(tpy)] 2+ cations function as CO 2 capture and activation sites for direct air capture, while [XCN] – anions serve as proton shuttles, facilitating rapid transfer of in-situ generated H⁺ from solar-driven water oxidation to adsorbed CO 2 . This work enables the synergistic coupling of CO 2 reduction and H 2 O oxidation, thereby achieving efficient artificial photosynthesis of acetaldehyde.