Boosting the Microbial Electrosynthesis of Formate by <i>Shewanella oneidensis</i> MR-1 with an Ionic Liquid Cosolvent

Microbial electrosynthesis (MES) is a rapidly growing technology at the forefront of sustainable chemistry, leveraging the ability of microorganisms to catalyze electrochemical reactions to synthesize valuable compounds from renewable energy sources. The reduction of CO₂ is a major target application for MES, but research in this area has been stifled, especially with the use of direct electron transfer (DET)-based microbial systems. The major fundamental hurdle that needs to be overcome is the low efficiency of CO₂ reduction largely attributed to minimal microbial access to CO₂ owing to its low solubility in the electrolyte. With their tunable physical properties, ionic liquids present a potential solution to this challenge and have previously shown promise in facilitating efficient CO₂ electroreduction by increasing the CO₂ solubility. However, the use of ionic liquids in MES remains unexplored. In this study, we investigated the role of 1-ethyl-3-methylimidazolium acetate ([EMIM][Ac]) using <i>Shewanella oneidensis</i> MR-1 as a model DET strain. Electrochemical investigations demonstrated the ability of <i>S. oneidensis</i> MR-1 biocathodes to directly convert CO₂ to formate with a faradaic efficiency of 34.5 ± 26.1%. The addition of [EMIM][Ac] to the system significantly increased cathodic current density and enhanced the faradaic efficiency to 94.5 ± 4.3% while concurrently amplifying the product yield from 34 ± 23 μM to 366 ± 34 μM. These findings demonstrate that ionic liquids can serve as efficient, biocompatible cosolvents for microbial electrochemical reduction of CO₂ to value-added products, holding promise for more robust applications of MES.