Abstract
Efficient electrochemical reduction of CO(2) (eCO(2)RR) in air and flue gas to high-purity products is crucial for reducing atmospheric CO(2) levels. However, low CO(2) concentrations (400 ppm in air, 15% in flue gas) and reducible impurities present significant challenges. To address this, we developed an electrolyzer integrating a self-supporting metal-organic framework-based mixed-matrix molecular sieve membrane (MOF-MMM), a conductive diffusion layer and a Bi nanoparticle catalytic layer. This design enables simultaneous gas purification and eCO(2)RR while avoiding electroreduction of impurities (SO(2), NO, O(2)). The MOF-MMM enriches CO(2) from 15% to 82.5% in flue gas or from 0.04% to 2.05% in air. Under acidic conditions, enriched CO(2) is reduced to formic acid. Using flue gas as feedstock, the eCO(2)RR current reaches 9000 mA with 100% Faradaic efficiency, producing 23 mL of pure HCOOH after 4 h, representing state-of-the-art performance. Using air as feedstock, it achieves 98.2% FE(HCOOH) with a record partial current density of 5.3 mA cm(-2) at 2.5 V, yielding 177 200 μmol h(-1) g(-1), which is 5000 times higher than reported catalysts without molecular sieves. This integrated approach enables the direct transformation of dilute CO(2) emissions into transportable liquid fuels, offering dual environmental benefits through carbon utilization and sustainable chemical production.