Electrostatic Field Effects in Covalent Organic Frameworks for Photocatalytic CO₂-to-CO Conversion beyond 1000 mmol...

Covalent Organic Frameworks (COFs) with unique π-structures and exceptional stability are promising candidates for photocatalytic CO₂ conversion. However, most reported COFs exhibit significant recombination of photo-generated charges and holes, along with low CO₂ chemisorption, leading to suboptimal photocatalytic performance. Here, we designed covalently linked two-dimensional cobalt (II) porphyrin layers and introduced various tetra-alkylammonium cations (─CH₂N⁺(CH₃)₃, ─CH₂CH₂N⁺(CH₃)₃, or ─CH₂CH₂CH₂N⁺(CH₃)₃). The tetra-alkylammonium cations within the ionic covalent organic framework (iCOF) stabilize the intermediates of the photoreduction reaction and accelerate the reaction kinetics through electrostatic field interactions, thereby facilitating the conversion of *CO₂ to *CO. Molecular dynamics simulations further indicate that tetra-alkylammonium side chains increase CO₂ residence time in the pores, thereby enhancing interaction with catalytically active sites. Furthermore, the electrostatic field effects of the tetra-alkylammonium cations increase the charge density at the Co center, stabilize CO₂ reaction intermediates, and facilitate proton transfer. Remarkably, these advantageous effects synergistically contribute to the photocatalytic CO₂-to-CO conversion. The CoTph-3C-N⁺ COF achieves an impressive CO initial production rate of 1006 mmol g_Co ^-1 h^-1 and a quantum efficiency of 5.67% at 420 nm, which is 17 times that of the pristine COF. This strategy offers a novel approach to designing various photocatalytic systems aimed at efficient chemical transformations.