Boosting electrocatalytic CO2 reduction reaction over viologen-functionalized metal-organic frameworks by enhancement of electron-transfer capacity

Although the highly porous crystalline metal-organic frameworks (MOFs) are promising candidates as active electrocatalysts for CO2 reduction reaction (CO2RR), their poor electronic conductivities severely limit their applications. Viologens (Vg) and their derivatives are able to act as electron-transfer mediators (ETMs) to facilitate rapid electron transfer to active sites but have not yet been integrated into MOFs for the CO2RR. Herein, viologen groups are integrated into cobalt porphyrin (Por(Co))-based MOFs for the first time to act as ETMs to enhance the electron-transfer capacity and thus improve the activity of the CO2RR. The obtained optimal Vg-Por(Co)-MOF(9 : 1) (Por(Co) : Vg = 9 : 1) showed excellent catalytic performance with a high faradaic efficiency of CO (FECO = 93.8%, 2.3 V) and large CO partial current density of (j(CO)) 111.1 mA cm(-2) at 2.9 V in the CO2RR in a membrane electrode assembly (MEA) system. The FECO and j(CO) values for Vg-Por(Co)-MOF(9 : 1) are about 1.9 and 2 times larger than those of Por(Co)-MOF containing free Vg as the ETM (49.2% and 51.4 mA cm(-2), respectively). Such excellent performance of Vg-Por(Co)-MOF(9 : 1) also surpasses that of the majority of other cobalt-based electrocatalysts, which make it stand out as being among the benchmark electrocatalysts for CO2 to CO generation. This work offers an efficient method for designing extremely effective porous frameworks for enhanced electrocatalysis through increasing electrical conductivity.