Engineering the Electronic Microenvironment with Bromine Functionalization for High‐Selectivity Photocatalytic CO 2 Reduction

Surface halogen atom modification represents a promising strategy for regulating the photocatalytic performance of covalent organic frameworks (COFs). In this study, a surface bromine atom modification strategy is proposed for TzPm-COF material, which finely tunes its donor-acceptor (D-A) structure and significantly enhances both the activity and selectivity of CO₂ photoreduction. By virtue of the in situ Kelvin probe force microscopy (KPFM), along with others spectral technology we confirm that bromine functionalization effectively facilitates the separation and migration of photogenerated charge carriers. Accordingly, the as-prepared TzPm-COF-2Br exhibits a remarkable CO production rate of 155 µmol g^{- 1} h^{- 1} under visible-light-driven CO₂ reduction, approximately 2.7 times higher than that of TzPm-COF (57 µmol g^{- 1} h^{- 1}), along with exceptional selectivity (99.4%), which surpasses the majority of analogous CO-producing photocatalysts in overall performance. Relying on the functional theory (DFT) calculations, we further confirm the introduction of bromine atoms promoted directional electron transfer from TAPTz donors to PMDCA-2Br acceptors through intrinsic polarization effects, thereby enhancing the adsorption and activation of CO₂ at oxygen sites on PMDCA units. This work provides a rational material design strategy for developing functionally modified COFs toward efficient and selective photocatalytic CO₂ reduction.