Bio-reduced graphene oxide on hollow fibers as gas-diffusible anodes for enhancing bioelectrochemical methane oxidation

Bioelectrochemical methane oxidation provides opportunities for conversion of methane into electricity, fuels with higher energy intensity and value-added chemicals. Previous studies indicate that methane bioavailability due to low solubility of methane and sluggish extracellular electron transfer (EET) of methane-oxidizing consortium are two of main kinetic limitations for the performance of methane-fuelled bioelectrochemical systems. In this study, tubular gas-diffusible electrodes were synthesized through in situ bio-reduction of graphene oxidation (GO) on hollow fibers (HFs). A special methanotrophic consortium dominated by ‘Candidatus ‘Methanoperedens nitroreducens’ was found to be capable of reducing GO to reduced graphene oxide (rGO) with c-type cytochrome playing an essential role in its EET. We used this new-found feature for self-assembly of highly conductive rGO on HFs, thereby yielding methanotrophic biofilm/rGO matrix wrapped HFs as gas diffusible electrodes. The rGO-deposited HFs boosted the current output associated with the bioelectrochemical methane oxidation by 6 times, compared to an unamended control. This improvement can be ascribed to the development of an rGO network on the HFs, which converted commercial HFs to conductive electrodes and increased the contact area between microbes and electrodes by incorporating biomass in the three-dimensional microporous rGO scaffold. The strategy developed in this study can be extended to other bioelectrochemical systems suffering from the issue of low aqueous solubility.