Liquids and Microbial Electrolysis Cells for Boosted CO₂ Methanogenesis: Role of Interfacial Electron Transfer

This study explores the improvement of CO2 methanogenesis using microbial electrolysis systems (MESS) and ionic liquids (ILs). The microbial community adapted to CO2 methanogenesis showed performance enhancement over time, achieving 0.46 mmol/cycle of specific methane production in the combined MESS and IL system, while it was around 0.28 mmol/cycle for MES only. Under non-electrified conditions, methane production was quite lower (0.1 mmol/cycle). The highest CO2 conversion efficiency was achieved in the MESS/IL (M-I-E) group, followed by microbiology (M), MESS/IL (M-I), and MESS(M-E). ILs enhanced the electrochemical activity of MESS, resulting in a higher current to 0.61 ± 0.05 mA and a higher Coulombic efficiency to 68.8 ± 3%, compared to 0.45 ± 0.05 mA and 55.6 ± 2% for MESS alone. Further evidence for the improvements was shown by the reduced charge transfer resistance (2.37 ± 0.08 Ω) and enhanced biomass accumulation at the cathode. The microbial community analysis pointed out a significant shift in dominant species, including a significant increase in methanogens such as Methanobacterium sp. and Methanoculleus bourgensis. Metabolic responses showed upregulation of key genes involved in the transporters, Wood–Ljungdahl pathway, and tricarboxylic acid (TCA) cycle, indicating that IL layers could provide channels directly or through outside cellular entities for electrons to efficiently shuttle for enhanced methanogenesis. These findings gain insights into the synergistic benefits of ILs and MESS in boosting CO2 methanogenesis and provide insights into the underlying mechanisms.