Robust mesoporous two-dimensional covalent organic frameworks enabled by biphenyl-porphyrin for accelerated CO₂...

Covalent organic frameworks (COFs) incorporating metalloporphyrin units have gained significant attention as electrocatalysts for CO₂ reduction. However, conventional phenylporphyrin-based COFs are fundamentally limited by narrow pore sizes (<3 nm), which impose severe mass transfer resistance and impede catalytic turnover. Herein, we report a biphenyl porphyrin-based COF (DpPor-COF) with an expanded pore size of ∼3.8 nm, constructed from 5,10,15,20-tetra(4-formylbiphenyl)porphyrin and p-phenylenediamine. Subsequent metallation with Fe³⁺, Co²⁺, and Ni²⁺ furnishes atomically dispersed M-N₄ sites (M-DpPor-COF), effectively suppressing metal leaching while expanding the electrochemical active surface area. Among the series, Co-DpPor-COF delivers a CO Faradaic efficiency (FE_CO) of 94% at -0.65 V vs. RHE with a high turnover frequency (TOF) of 477 h^-1, and maintains stable operation over 120 h. In situ infrared spectroscopy and DFT calculations reveal that transition metal centers lower the energy barrier for key intermediate steps in CO₂-to-CO conversion, enhance charge density at the porphyrin core, and facilitate CO desorption. This work establishes a versatile strategy for concurrent pore engineering and active-site optimization, offering valuable insights for designing next-generation porous electrocatalysts.