Redox mediator-modified biocathode enables highly efficient microbial electro-synthesis of methane from carbon dioxide

Regulating cathodic interface properties towards highly effective CH 4 production from CO 2 is of great importance for energy storage using microbial electro-synthesis (MES). Herein, the feasibility and mechanism of two typical redox mediators , neutral red (NR) and anthraquinone-2, 6-disulfonate (AQDS), were evaluated for the improvement of CH 4 formation from CO 2 reduction in mixed-culture biocathodes of MESs. Results showed that the CH 4 formation rates of biocathodes after modification with NR and AQDS were 5.8 and 3.5 times higher than that of unaltered cathodes. Moreover, the coulombic efficiency of CH 4 formation improved from 44.27 ± 4.01% of the control cathode to 64.30 ± 4.83% and 62.26 ± 2.87% after modification with NR and AQDS, respectively. Consequently, the energy efficiency of MESs after cathode modification with NR and AQDS increased to 58.33 ± 3.17% and 53.21 ± 4.11% compared to 38.20 ± 3.12% without modification. Such improvements were likely attributed to the enhanced extracellular electron transfer of microbes, the reduction in internal resistances and the enrichment of hydrogenotrophic methanogens in the mixed-culture biocathodes after modification with NR and AQDS. This study provides an alternative strategy to regulate cathodic interface in MESs for renewable energy storage and biomethane production from CO 2 .