Three-Dimensional Graphene Nanosheets as Cathode Catalysts in Standard and Supercapacitive Microbial Fuel Cell

Three-dimensional graphene nanosheets (3D-GNS) were used as cathode catalysts for microbial fuel cells (MFCs) operating in neutral operating conditions. 3D-GNS catalysts showed high performance towards oxygen electroreduction in neutral media with high current densities and low hydrogen peroxide generation compared to activated carbon (AC). 3D-GNS was incorporated into air-breathing cathodes based on AC with three different loadings (2, 6 and 10 mgcm-2). Performances in MFCs showed that 3D-GNS had the highest performances with power densities of 2.059±0.003 Wm-2, 1.855±0.007 Wm-2 and 1.503±0.005 Wm-2 for loading of 10, 6 and 2 mgcm-2 respectively. Plain AC had the lowest performances (1.017±0.009 Wm-2). The different cathodes electrodes were also investigated in supercapacitive MFCs (SC-MFCs). The addition of 3D-GNS decreased the ohmic losses by 14-25%. The decrease in ohmic losses allowed the SC-MFC with 3D-GNS (loading 10 mgcm-2) to have the maximum power (Pmax) of 5.746±0.186 Wm-2. At 5 mA, the SC-MFC featured a capacitive response that increased from 0.027±0.007 F with AC to 0.213±0.026 F with 3D-GNS (loading 2 mgcm-2) and further to 1.817±0.040 F with 3D-GNS (loading 10 mgcm-2). This is the first time that a capacitance of the order of magnitude of Farads is shown related to microbial fuel cell system.