Integration of Redox-Active Viologen Moiety into Bifunctional Covalent Organic Framework for Boosting Electrochemical...

The electrochemical overall CO₂ reduction involving concurrent CO₂ reduction reaction (CO₂RR) and oxygen evolution reaction (OER) could realize energy conversion but still remains a grand challenge. Herein, a bifunctional cationic covalent organic framework (Vg-Por(Co)-COF) is constructed by the redox-active viologen unit and cobalt porphyrin building block to enhance the electrochemical CO₂ overall reaction. The redox-active viologen moiety can switch from its original dicationic state to a neutral state, which could facilitate in transfer electron to the active center and enhance the cathodic CO₂RR. While the anodic OER process, the viologen group can maintain its electron-deficient oxidation state, and induces the cobalt active center to a trivalent state, which is conducive to the occurrence of the OER. When Vg-Por(Co)-COF is employed as both cathodic and anodic catalysts, high CO Faradic efficiencies over 90% are achieved at 2.6 to 3.3 V. The Vg-Por(Co)-COF || Vg-Por(Co)-COF system achieves a current density of 9.76 mA cm^-2 at 3.2 V, outperforming both the Vg-Por(Co)-COF || Pt and the neutral COF electrocatalyst COF-366-Co || COF-366-Co systems under the same conditions. This work opens up a new avenue for exploring bifunctional materials toward efficient electrochemical CO₂ overall reaction.