Asymmetric N-Ru-S dipole within covalent organic framework enhances internal electric field for efficient CO2 photoreduction

Abstract

Asymmetric electron distribution at single-atom centers offers a promising pathway to enhance photocatalytic CO₂-to-CO conversion; however, direct visualization of how such symmetry-breaking influences local electric fields and reaction coordinates remains elusive. Herein, an asymmetric N-Ru-S motif was constructed in a thiophene-based covalent organic framework (Ru/Py-bTDC) via post-synthetic metalation. Under visible light in a gas-solid system without sacrificial agents, Ru₁₀/Py-bTDC exhibited a CO production of 226.88 μmol·L^–1, representing a 13-fold increase over pristine Py-bTDC. In-situ Kelvin probe force microscopy revealed that the N-Ru-S unit acts as a directional nanoscale dipole, intensifying the internal electric field (IEF) by 6.15-fold and steering photogenerated electrons toward Ru sites to facilitate charge separation. In-situ Fourier transform infrared spectroscopy and theoretical calculations demonstrated that the enhanced IEF promotes CO₂ activation, lowering the energy barrier for *COOH formation from 2.63 to 0.40 eV and shifting the rate-determining step to *CO desorption. This work establishes a direct spatial correlation between atomic-scale asymmetry, IEF enhancement, and optimized reaction kinetics, offering a design strategy to overcome both charge separation and activation barriers in CO₂ photoreduction through symmetry-breaking coordination.