Promoted electromethanosynthesis in a two-chamber microbial electrolysis cells (MECs) containing a hybrid biocathode covered with graphite felt (GF)

•Graphite felt (GF) is a suitable electrode modification material.•Hybrid GF-biocathode showed promise in promoting electromethanogenesis efficiencies.•Methane yield reached 80.9 mL/L reactor at −1.4 V after 24 h with ηCECH4ηCECH4 of 194.4%.•Electron transfer pathways involved cathode-to-cell and cell-to-cell processes.•Further work might be done in overpotential reduction and membrane fouling control.

Microbial electromethanogenesis, relying on electrochemically active biofilm on biocathode to convert carbon dioxide to methane, provides a novel approach for renewable energy storage. One key factor that governs electron exchange and methane formation efficiencies is the electrode material. To promote methane production, a biocathode via modifying plain carbon stick with a layer of graphite felt (GF) (hereafter referred as “hybrid GF-biocathode”) was developed and evaluated in a two-chamber microbial electrolysis cells (MECs). Methane production with hybrid GF-biocathode reached 80.9 mL/L at the potential of −1.4 V after 24 h of incubation with coulombic efficiency of 194.4%. The tests by flushing three substrates (CO2, N2 and H2–CO2 [80:20]) revealed that direct electron transfer rather than intermediate H2 contributed more to the electromethanogenesis. Cyclic voltammetry showed that GF enhanced the microbial electrocatalysis activity and reduced the cathode overpotential needed for methane production. Scanning electron microscope and fluorescence in situ hybridization analysis confirmed that the three-dimensional GF afforded the abundant space for the growth of electroactive microorganisms and promoted the electron exchange (e.g. cathode-to-cell etc.) via severing as “artificial pili”. This study reveals that GF with the open structure and high conductivity has the substantial potential to upgrade electromethanogenesis efficiency.

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