Boosting Microbial CO₂ Electroreduction by the Biocompatible and Electroactive Bimetallic Fe–Mn Oxide Cathode for Acetate Production

The electroreduction of carbon dioxide (CO2) to high-value organic chemicals by the microbial electrosynthesis (MES) system relies heavily on the electrochemical properties of the electrode materials. In this work, CO2 reduction for acetate production was greatly boosted by decorating the carbon felt cathode using the Fe–Mn bimetallic oxides, using an enriched anaerobic mixed culture dominated by the homoacetogen Acetobacterium wieringae. In comparison with the unmodified carbon felt as the cathode in the MES reactor, modification with MnFe2O4 increased the acetate production rate from 28 to 78 g/(m2·d), higher than those with MnO at 59 g/(m2·d) and Fe2O3 at 62 g/(m2·d), and the relative abundance of A. wieringae increased dramatically from 51 to 87% in the biofilm. This was probably due to the mediated electron uptake via the redox cycles of Mn(III)/(II) and Fe(III)/(II), improved specific surface area, and enhanced hydrophilicity of the cathode, benefiting from the synergistic effect of Fe and Mn ions. Overall, this study provides a facile and promising electrode modification strategy for MES with Fe–Mn bimetallic oxides for efficient CO2 conversion and acetate production, bringing the world closer to achieving carbon neutrality.