Simultaneously enhancing power density and coulombic efficiency with a hydrophobic Fe–N4/activated carbon air cathode for microbial fuel cells

Abstract

The application of microbial fuel cells (MFCs) for electricity generation is still hindered by relatively low power densities and coulombic efficiencies. Here a hydrophobic Fe–N4 macromolecule catalyst was directly immobilized on the activated carbon (AC) surface to fabricate a hydrophobic Fe–N4/AC air cathode. With a 10 wt% Fe–N4/AC cathode, a maximum power density of 2.5 ± 0.1 W m−2 was obtained, which was 25% higher than plain AC cathodes (2.0 ± 0.01 W m−2). The additional hydrophobicity due to the Fe–N4 macromolecule catalyst simultaneously reduced water electrolyte evaporation and oxygen intrusion for improved coulombic efficiency. The coulombic efficiency was increased to 20 ± 0.5% for the 10 wt% Fe–N4/AC cathode, which was ~54% higher than that of the AC cathodes (13 ± 0.2%) at an external resistance of 1000 Ω. The use of hydrophobic Fe–N4 macromolecule catalyst is the first attempt to simultaneously improve the power density and coulombic efficiency by tuning the catalyst hydrophobicity, which also explores a new direction of catalyst engineering for the advancement of MFCs.