Conductive Magnetite Nanoparticles Enhance the Microbial Electrosynthesis of Acetate from CO2 while Diverting Electrons away from Methanogenesis

Microbial electrosynthesis (MES) is an emerging technology which exploits microbial cells to convert CO into fuels, and value-added chemicals using electrons supplied by a solid-state cathode. Methane and acetic acid are typically the main CO-reduction products attained in microbial electrosynthesis studies, although the production of other more valuable products has also been reported. So far, however, practical strategies to manipulate and steer the distribution of CO reduction products during microbial electrosynthesis, particularly when mixed microbial cultures are employed as catalysts, are lacking. To specifically address this issue, here we investigated the influence of magnetite nanoparticles (NPs) supplementation (to a final concentration of 300 mg Fe L) on the microbial electrosynthesis process. Results demonstrated, that cells supplemented with magnetite NPs, exhibited a substantially higher yield of acetate production relative to unamended controls (up to 8.5 times higher, during the run with the cathode set at a potential of -700 mV vs. SHE, with a corresponding cathode capture efficiency of 17%) and, correspondingly, a lower yield of methane production (52% in the magnetite-supplemented cell vs. 74% in the unamended control cell). Abiotic experiments indicated that the observed effects derived from magnetite catalyzing the biotic and abiotic hydrogen evolution reaction.