Tandem Acidic CO₂ Electrolysis Coupled with Syngas Fermentation: A Two-Stage Process for Producing Medium-Chain Fatty Acids

Abstract

The tandem application of CO2 electrolysis with syngas fermentation holds promise for achieving heightened production rates and improved product quality. However, the significant impact of syngas composition on mixed culture-based microbial chain elongation remains unclear. Additionally, effective methods for generating syngas with an adjustable composition from acidic CO2 electrolysis are currently lacking. This study successfully demonstrated the production of medium-chain fatty acids from CO2 through tandem acidic electrolysis with syngas fermentation. CO could serve as the sole energy source or as the electron donor (when cofed with acetate) for caproate generation. Furthermore, the results of gas diffusion electrode structure engineering highlighted that the use of carbon black, either alone or in combination with graphite, enabled consistent syngas generation with an adjustable composition from acidic CO2 electrolysis (pH 1). The carbon black layer significantly improved the CO selectivity, increasing from 0% to 43.5% (0.05 M K+) and further to 92.4% (0.5 M K+). This enhancement in performance was attributed to the promotion of K+ accumulation, stabilizing catalytically active sites, rather than creating a localized alkaline environment for CO2-to-CO conversion. This research contributes to the advancement of hybrid technology for sustainable CO2 reduction and chemical production.

Solid Electrolytes for Low-Temperature Carbon Dioxide Valorization: A Review

“…On the other hand, microbes exhibit high specificity and selectivity, making them valuable for synthesizing pharmaceuticals, commodity chemicals, fuels, feedstocks, and fertilizers . This synergy between electrocatalysis and microbial metabolism has led to the development of hybrid electro-biosystems, − opening up promising avenues for efficient production of various high value-added compounds. In fact, the promise of tandem catalysts, tandem electrode structures, and cascade CO 2 RR catalytic systems for sustainable CO 2 conversion has been highlighted very recently, , whereas the potential of hybrid electro-biosystems has not been fully explored.…”