Microbial electrosynthesis for CO2 conversion and methane production: Influence of electrode geometry on biofilm development

Electromethanogenesis is a process of microbial electrosynthesis (MES) in which electroactive microorganisms reduce carbon dioxide (CO2) to produce methane (CH4), using a cathode as an electron donor. The efficiency of this reaction is greatly determined by the establishment of a robust microbial community on the biocathodes, which eventually affects the global performance of the bioreactor. Moreover, the development of the biofilm depends on several characteristics of the electrodes, more specifically their material and geometry. Since electrode geometry is a crucial parameter, this study aims at evaluating the sole influence of the electrode shape by installing carbon‐based electrodes with two different constructions (brush and carbon felt) of biocathodes in an electromethanogenic reactor for CO2 capture. The overall performance of the reactors showed coulombic efficiencies around 100%, with high‐quality biogas reaching methane concentrations above 90%. The results reveal that the electrode geometry affects the individual biocathode performance, and the carbon brush showed a bigger contribution to current generation and electrical capacitance, exhibiting higher peak hydrogen production compared to the carbon felt, which could be reflected in higher CO2 capture and methane generation. Both geometries showed a greater proliferation of archaea over bacteria (between 53 and 85%), which was more significant on the brush than on the carbon felt. Archaea community was dominated by Methanobacterium in carbon felt electrodes and codominated with Methanobrevibacter in brush electrodes, while bacteria analyses showed a very similar community for both geometries. © 2022 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd.