Pore-Space Design of Cobalt–Porphyrin Covalent Organic Frameworks Suppresses Inactive Bridged-CO Intermediates for Selective CO 2 Electroreduction

Metalated covalent organic frameworks (M-COFs) hold promise for CO₂ capture and electrocatalytic conversion with their tunable cavities, well-defined metal centers, and extended charge delocalization. However, the systematic impact of the framework architecture on the CO₂ electroreduction selectivity remains underexplored. Herein, we report a series of cobalt-porphyrin COFs, namely, Co-TBCOF, Co-TTCOF, and Co-TQCOF, with enlarged cavity apertures from 2.5 to 3.2 and 3.8 nm by extending linear dialdehyde linkers. Experiment and computation confirm increased interlayer spacing from 3.64 to 4.01 and 4.81 Å, enhancing the CO₂ adsorption capacity. The structural expansion also promotes charge delocalization, increasing the electropositivity of the Co sites and strengthening the CO₂ activation. During electrocatalytic CO₂ reduction, the CO Faradaic efficiency rises from 84.3% (Co-TBCOF) and 78.2% (Co-TTCOF) to 93.3% (Co-TQCOF) in H-cell. In situ ATR-SEIRAS and theoretical calculations reveal that the smaller-pore COFs (Co-TBCOF and Co-TTCOF) stabilize both active terminally bound *CO (τ-CO) and an inactive interlayer-bridged *CO (η²-CO) that hinders desorption. In contrast, the larger interlayer spacing in Co-TQCOF prevents stable η²-CO formation, enabling highly selective CO production solely via the τ-CO pathway. This work demonstrates that linker-mediated control over cavity size, stacking, and charge distribution in M-COFs enhances CO₂ capture and conversion, offering design insights for molecularly defined porous electrocatalysts.