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

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.