Viologen linker as a strong electron-transfer mediator in the covalent organic framework to enhance electrocatalytic CO2 reduction

Abstract

Covalent organic frameworks (COFs) are promising candidates for the CO₂ electroreduction reaction (CO₂RR) due to their advantages of tunable structures, abundant active sites, and strong CO₂ adsorption enrichment. However, the poor conductivities of the traditional COFs usually result in a low current density in the CO₂RR and limits their use in industrial applications. Herein, viologen units as strong electron-transfer mediators (ETMs) were inserted into the backbones of Co-porphyrin-based COF (Por(Co)-Vg-COF) nanosheets to enhance the electronic conductivity and improve the CO₂RR activity. The obtained Por(Co)-Vg-COF displayed a good conductivity of 3.7 × 10⁻⁷ S m⁻¹ and thus exhibited a very high selectivity towards CO production (>98%) in a wide range of applied potentials from −0.6 V to −0.9 V versus the reversible hydrogen electrode (RHE) in neutral aqueous solution, which surpassed all the conventional COF electrocatalysts. Moreover, Por(Co)-Vg-COF was employed as the first COF electrode in an acidic/alkaline system, and achieved a high FE_CO of up to 91% at −0.9 V versus RHE in acidic electrolyte and a current density of 251 mA cm⁻² at −1.3 V versus RHE in 1 M KOH aqueous electrolyte. This work provides a facile strategy to enhance the CO₂RR performance by improving the electronic conductivity of porous framework materials via the introduction of an ETM in their backbone.