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

Abstract

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 (FE_CO = 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 FE_CO 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.