Nanostructurally Engineering Covalent Organic Frameworks for Boosting CO₂ Photoreduction

Herein, a series of imine-linked covalent organic frameworks (COFs) are developed with advanced ordered mesoporous hollow spherical nanomorphology and ultra-large mesopores (4.6 nm in size), named OMHS-COF-M (M = H, Co, and Ni). The ordered mesoporous hollow spherical nanomorphology is revealed to be formed via an Ostwald ripening mechanism based on a one-step self-templated strategy. Encouraged by its unique structural features and outstanding photoelectrical property, the OMHS-COF-Co material is applied as the photocatalyst for CO₂-to-CO reduction. Remarkably, it delivers an impressive CO production rate as high as 15 874 µmol g^-1 h^-1, a large selectivity of 92.4%, and a preeminent cycling stability. From in/ex situ experiments and density functional theory (DFT) calculations, the excellent CO₂ photoreduction performance is ascribed to the desirable cooperation of unique ordered mesoporous hollow spherical host and abundant isolated Co active sites, enhancing CO₂ activation, and improving electron transfer kinetics as well as reducing the energy barriers for intermediates *COOH generation and CO desorption.