Efficient Photocatalytic CO₂ Reduction in Ellagic Acid-Based Covalent Organic Frameworks

Employing covalent organic frameworks (COFs) for the photocatalytic CO₂ reduction reaction (CDRR) to generate high-value chemical fuels and mitigate greenhouse gas emissions represents a sustainable catalytic conversion approach. However, achieving superior photocatalytic CDRR performance is hindered by the challenges of low charge separation efficiency, poor stability, and high preparation costs associated with COFs. Herein, in this work, we utilized perfluorinated metallophthalocyanine (MPcF₁₆) and the organic biomolecule compound ellagic acid (EA) as building blocks to actualize functional covalent organic frameworks (COFs) named EPM-COF (M = Co, Ni, Cu). The designed EPCo-COF, featuring cobalt metal active sites, demonstrated an impressive CO production rate and selectivity in the photocatalytic CO₂ reduction reaction (CDRR). Moreover, following alkaline treatment (EPCo-COF-AT), the COF exposed carboxylic acid anion (COO^-) and hydroxyl group (OH), thereby enhancing the electron-donating capability of EA. This modification achieved a heightened CO production rate of 17.7 mmol g^-1 h^-1 with an outstanding CO selectivity of 97.8% in efficient photocatalytic CDRR. Theoretical calculations further illustrated that EPCo-COF-AT functionalized with COO^- and OH can effectively alleviate the energy barriers involved in the CDRR process, which facilitates the proton-coupled electron transfer processes and enhances the photocatalytic performance on the cobalt active sites within EPCo-COF-AT.