Continuously Producing Highly Concentrated and Pure Acetic Acid Aqueous Solution via Direct Electroreduction of CO₂

It is crucial to achieve continuous production of highly concentrated and pure C₂ chemicals through the electrochemical CO₂ reduction reaction (eCO₂RR) for artificial carbon cycling, yet it has remained unattainable until now. Despite one-pot tandem catalysis (dividing the eCO₂RR to C₂ into two catalytical reactions of CO₂ to CO and CO to C₂) offering the potential for significantly enhancing reaction efficiency, its mechanism remains unclear and its performance is unsatisfactory. Herein, we selected different CO₂-to-CO catalysts and CO-to-acetate catalysts to construct several tandem catalytic systems for the eCO₂RR to acetic acid. Among them, a tandem catalytic system comprising a covalent organic framework (PcNi-DMTP) and a metal-organic framework (MAF-2) as CO₂-to-CO and CO-to-acetate catalysts, respectively, exhibited a faradaic efficiency of 51.2% with a current density of 410 mA cm^-2 and an ultrahigh acetate yield rate of 2.72 mmol m^-2 s^-1 under neutral conditions. After electrolysis for 200 h, 1 cm^-2 working electrode can continuously produce 20 mM acetic acid aqueous solution with a relative purity of 95+%. Comprehensive studies revealed that the performance of tandem catalysts is influenced not only by the CO supply-demand relationship and electron competition between the two catalytic processes in the one-pot tandem system but also by the performance of the CO-to-C₂ catalyst under diluted CO conditions.