Effect of iron-based oxide-modified electrodes on the selectivity of carbon chain elongation metabolites in electro-fermentation system.

This study explored the electrode modification by iron-based materials (IBM) including Fe2O3, Fe3O4, and FeN in the aim of promoting the medium-chain fatty acids (MCFA) production by electro-fermentation (EF). Results showed that the modification of cathodes with IBM increased MCFA production by 15 %-169 %. FeN exhibited the best performance, achieved the maximum MCFA production of 4450.2 mg COD/L and triggered longer-chain MCFA (i.e., caprylate) production of 211.7 mg COD/L. Electrochemical analyses demonstrated that IBM modification promoted the electrochemical activity of electrodes by reducing the charge transfer resistance by 15-62 %. Microbial analysis illustrated that IBM modification promoted microbial cooperation in the system by enriching chain elongation (CE) functional microorganisms (Fermentimonas sp., Blautia sp. and Anaerosalibacter sp.) and electrochemically active bacteria (Bacillus sp.) to facilitate MCFA generation. Metabolic pathways analysis indicated that IBM modification significantly promoted the production of Acetyl-CoA for the CE process and enhanced the relative abundances of functional genes involved in reverse β-oxidation (RBO) pathway.