Enhancing microbial CO₂ electrocatalysis for multicarbon reduction in a wet amine-based catholyte

Microbial CO₂ electroreduction (mCO2ER) offers a promising approach for producing high-value multicarbon reductants from CO₂ by combining CO₂ fixing microorganisms with conducting materials (i. e., cathodes). However, the solubility and availability of CO₂ in an aqueous electrolyte pose significant limitations in this system. This study demonstrates the efficient production of long-chain multicarbon reductants, specifically carotenoids (~C₄₀), within a wet amine-based catholyte medium during mCO2ER. Optimizing the concentration of the biocompatible CO₂ absorbent, monoethanolamine (MEA), led to enhanced CO₂ fixation in the electroautotroph bacteria. Molecular biological analyses revealed that MEA in the catholyte medium redirected the carbon flux towards carotenoid biosynthesis during mCO2ER. The faradaic efficiency of mCO2ER with MEA for carotenoid production was 4.5-fold higher than that of the control condition. These results suggest the mass transport bottleneck in bioelectrochemical systems could be effectively addressed by MEA-assissted mCO2ER, enabling highly efficient production of valuable products from CO₂.