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.
Zheng et al. (Tue,) studied this question.