Microbial electrosynthesis (MES) electrode microbiome encompassing microorganisms able to reduce carbon dioxide (CO2), in commodity and specialty chemicals from electrical energy obtained from renewable sources. Targeted loci

Microbial electrosynthesis allows the reduction and electrical upgrading of CO2. However, higher productivities and energy efficiencies are needed to reach industrial viability. Here we show that a biofilm-based microbial porous cathode in a directed flow-through electrochemical system is able to continuously reduce CO2 to even-chain C2-C6 carboxylic acids over 248 days. We demonstrate a 3 fold higher biofilm concentration, volumetric current density, and productivity than the state of the art, up to 35 kA m 3cathode and 69 kgC m-3cathode day-1, at 60-97% and 30-35% faradaic and energy efficiencies. Most notably, these volumetric productivities are now comparable to rates achieved in lab-scale and industrial syngas (CO-H2-CO2) and chain elongation fermentation. This work highlights key design parameters for efficient electricity-driven microbial CO2 reduction. Further improvements in rates of electrode colonization and microbe-specific kinetics should be aimed for, towards scaling-up the technology.16S rRNA-sequencing allowed to identify the dominant microbial species responsible for the elongation of CO2 to Medium Chain Carboxylic Acids. The findings underscore the remarkable capability of microbial electrosynthesis to attain reactor-scale performances comparable to established technologies, establishing the viability of the novel directed-flow-through reactor as a potentially scalable system