Tuning charge carrier transport in isostructural covalent organic frameworks for enhanced photocatalytic CO2 reduction

Abstract

Covalent organic frameworks (COFs) have demonstrated photocatalytic potential for CO2 reduction, yet their structure-property correlations, particularly concerning charge-carrier dynamics, remain poorly understood. Herein, we constructed a series of isostructural porphyrin-bicarbazole COFs (BCz-Por(M)-COF (M = H2, Co, and Ni)) through strategic integration of dual electron-donating moieties, achieving localized charge confinement within porphyrin units. Benefiting from the structural advantages, BCz-Por(Co)-COF showed an excellent CO production rate of 15411.8 μmol g-1 h-1, surpassing its BCz-Por(Ni)-COF and BCz-Por(H2)-COF counterparts by 4.2-fold and 68.2-fold, respectively, in photocatalytic CO₂-to-CO conversion. Both experimental and theoretical results reveal that the synergy of Co and porphyrin-bicarbazole COF establishes dual-channel charge-transport pathways, which simultaneously facilitates efficient in-plane charge separation and enables anisotropic out-of-plane charge migration. The efficient charge separation can activate and stabilize the key intermediates, thereby boosting its photocatalytic efficiency. This work highlights the potential of regulating charge-carrier dynamics in improving the photocatalytic performance of COFs-based photocatalysts.