Impact of non-noble bimetallic oxides on bioelectrochemical reduction of carbon dioxide to volatile fatty acids

The conversion of CO₂ into value-added chemicals via microbial electrosynthesis (MES) offers a promising route for sustainable production of high-value chemicals. The study evaluates five bimetallic oxides (FeCuO, FeSnO, SnCuO, MnCuO, and CoMnO) for their impact on mixed microbial cultures capable of CO₂ utilization. FeSnO significantly enhanced acetogenic and chain-elongating activity while suppressing acetoclastic methanogenesis. When used to coat carbon felt cathodes in MES cells, FeSnO increased CO₂ conversion efficiency to over 90 %, and enabled the production of butyrate and caproate at rates up to 566 mg (L_c d)⁻¹ and 89 mg (L_c d)⁻¹, respectively. Maximum product selectivity reached 53 % for butyrate and 10 % for caproate, surpassing by 4-fold those achieved with unmodified cathodes. Electrochemical impedance spectroscopy revealed that FeSnO coatings decreased charge transfer resistance from 209.4 Ω to 0.9 Ω, while promoting biofilm formation. These findings suggest that FeSnO coating not only enhances electrochemical performance but also facilitates microbial chain elongation critical for successful CO₂ conversion to medium-chain fatty acids.