Enhanced electricity generation and effective water filtration using graphene-based membrane air-cathodes in microbial fuel cells

Air-cathodes in microbial fuel cells that can also filter wastewater provide the dual benefits of electricity production and reduction of the effluent chemical oxygen demand. Air-cathodes prepared using a novel activated carbon/graphene membrane (2, 5 or 10% graphene by weight) prepared by phase inversion have good conductivities (5.6 ± 0.5 to 7.3 ± 0.6 mS cm⁻¹) compared to control (3.0 ± 0.4 mS cm⁻¹, activated carbon, no graphene). The cathode with 5 wt% graphene produces the highest maximum power density of 1460 ± 10 mW m⁻², which is 58% higher than that the control (928 ± 8 mW m⁻²). The increased power is due to an 88% reduction in charge transfer resistance of 6.0 ± 0.3 Ω (cathode with 5 wt% graphene) compared to the control. Following a cycle of treatment and current generation, 60 ± 1% of the chemical oxygen demand is removed from the remaining chemical oxygen demand, producing an effluent chemical oxygen demand concentration of 20 ± 1 mg L⁻¹. Biomass (4.99 ± 0.02 mg-protein cm⁻²) is decreased by 33% compared to the control. These results demonstrate that cathodes made with graphene can produce electricity and a high quality effluent with low cathode biofouling.