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 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 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 (P(max)) of 5.746 ± 0.186 Wm(-2). At 5 mA, the SC-MFC featured an “apparent” 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)).