Three-dimensional graphene nanosheets as cathode catalysts in standard and supercapacitive microbial fuel cell

Abstract

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 (Pmax) 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).

Design of Iron(II) Phthalocyanine‐Derived Oxygen Reduction Electrocatalysts for High‐Power‐Density Microbial Fuel Cells

“…Two different catalyst loadings (0.1 and 0.6 mg cm −2 ) were used for the experiments. It was shown previously that an increase in loading could hinder the catalyst kinetics 38, 68, 69…”

“…As the material loading on the disk increased, the peroxide detected decreased significantly 38, 68, 69. Therefore, two extreme loadings, one low (0.1 mg cm −2 ) and one high (0.6 mg cm −2 ), were selected to obtain reasonable data for the ORR with these catalysts.…”

“…A thick catalytic layer of porous carbonaceous material can trap the intermediate peroxide inside the pores, where the H 2 O 2 is consumed (either by chemical decomposition or by electrochemical reduction to water) without being detected on the ring 38, 68, 69. As the material loading on the disk increased, the peroxide detected decreased significantly 38, 68, 69.…”

“…A direct comparison can instead be made with previously presented work in which an identical (i) MFC configuration (single‐chamber MFC), (ii) operating temperature [(22±2) °C], (iii) altitude above sea level [experiments conducted in Albuquerque, New Mexico, at 1500 m above mean sea level (AMSL)], (iv) electrolyte (50 % activated sludge, 50 % 0.1  m K‐PB (potassium phosphate buffer), and 0.1  m KCl (potassium chloride)), (v) mixed‐culture bacteria, (vi) organic compound (sodium acetate), and (vii) membrane‐less configuration were utilized 22, 23, 38, 43, 46. The obtained maximum power density achieved [(243±7) μW cm −2 ] is one of the highest power densities recorded under the same operating conditions and is second only to that of (251±2) μW cm −2 for Fe‐AAPyr (AAPyr=aminoantipyrine) 43.…”

“…Since this pioneering study, activated carbon has been used frequently as a cathode catalyst in different types of MFCs 27, 28, 29, 30, 31. It should be noted that other carbonaceous materials such as carbon nanotubes,32 activated carbon fibers,33 modified carbon black,34 and graphene35, 36, 37, 38 were also studied as cathode catalysts in MFCs. On the other hand, systematic research into carbonderived cathodes revealed intrinsic low ORR activities, high overpotentials, and low power generation.…”