Permselective MOF-Based Gas Diffusion Electrode for Direct Conversion of CO₂ from Quasi Flue Gas

Industrial activities lead to a substantial share of current anthropogenic CO₂ emissions and are some of the most challenging to abate. Direct utilization of industrial flue gases to produce fuels or value-added chemicals is challenging due to the presence of impurities and low concentrations of CO₂. Herein, we demonstrate a rational assembly of a permselective gas diffusion electrode (PGDE) for direct CO₂ conversion from quasi flue gas (i.e., 10-15% CO₂, 4% O₂, and N₂ balance at 100% relative humidity). The electrode design consists of a metal-organic framework (MOF) based mixed matrix membrane (MMM) that enables the selective permeation of CO₂ to a silver electrocatalyst. The MOF is CALF-20, notable for the ability to physisorb CO₂ in wet gas streams. Applying this approach, we convert N₂-diluted CO₂ streams to CO at a faradaic efficiency of 95% compared to 58% for the nonmodified counterpart electrode with MMM. The PGDE retained its electrochemical performance when introducing O₂ by preventing ∼84% loss of current toward parasitic oxygen reduction reaction (ORR) and reported 30 mA cm^-2 CO partial current density. Further, wetting the gas stream showed a negligible effect on the MOF and the electrochemical performance. Using our PDGE, we report nearly constant CO selectivity over 19 h in a membrane electrode assembly electrolyzer. This approach offers the potential for direct utilization of low-concentration CO₂ while avoiding the economic and environmental costs of obtaining purified CO₂ feedstocks.