Scaling up self-stratifying supercapacitive microbial fuel cell

Self-stratifying microbial fuel cells with three different electrodes sizes and volumes were operated in supercapacitive mode. As the electrodes size increased, the equivalent series resistance decreased, and the overall power was enhanced (small: ESR 1⁄4 7.2 U and Pmax- 1⁄4 13 mW; large: ESR 1⁄4 4.2 U and Pmax 1⁄4 22 mW). Power density referred to cathode geometric surface area and displacement volume of the electrolyte in the reactors. With regards to the electrode wet surface area, the large size electrodes (L-MFC) displayed the lowest power density (460 mW cm2) whilst the small and medium size electrodes (S-MFC, M-MFC) showed higher densities (668 mW cm2 and 633 mW cm2, respectively). With regard to the volumetric power densities the S-MFC, the M-MFC and the L-MFC had similar values (264 mW mL1, 265 mW mL1 and 249 mW cm1, respectively). Power density normalised in terms of carbon weight utilised for fabricating MFC cathodes-electrodes showed high output for smaller electrode size MFC (5811 mW g1-C- and 3270 mW g1-C- for the S-MFC and L- MFC, respectively) due to the fact that electrodes were optimised for MFC operations and not supercapacitive discharges. Apparent capacitance was high at lower current pulses suggesting high faradaic contribution. The electrostatic contribution detected at high cur- rent pulses was quite low. The results obtained give rise to important possibilities of per- formance improvements by optimising the device design and the electrode fabrication.