Microbial Electrosynthesis from CO₂reaches Productivity of Syngas and Chain Elongation Fermentations

Summary Microbial electrosynthesis allows the electrochemical upgrading of CO 2 . However, higher productivities and energy efficiencies are needed to reach a viability that can make the technology transformative. Here we show how a biofilm-based microbial porous cathode in a directed flow-through electrochemical system can continuously reduce CO 2 to even-chain C2-C6 carboxylic acids during 248 days. We demonstrate a 3-fold higher biofilm concentration, volumetric current density, and productivity than the state of the art, up to a new record of -35 kA m -3 cathode and 69 kg C m -3 cathode day -1 , at 60-97% and 30-35% faradaic and energy efficiencies, respectively. Most notably, the volumetric productivity resembles those achieved in lab-scale and industrial syngas (CO-H 2 -CO 2 ) fermentation and chain elongation fermentation. This work highlights key design parameters for efficient electricity-driven microbial CO 2 reduction. There is need and room to improve the rates of electrode colonization and microbe-specific kinetics to scale-up the technology.