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

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 x 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 FECO 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.