Atomically dispersed Fe–N4 moieties in porous carbon as efficient cathode catalyst for enhancing the performance in microbial fuel cells

Microbial fuel cells (MFCs) play significant role in solving energy crisis and water pollution, while their scale-up is restricted by the sluggish oxygen reduction reaction (ORR) on the cathode. Herein, the influence of different metal and nitrogen co-doped porous carbon (Fe-NpC, Mn-NpC and Ni-NpC) on the ORR reactivity are investigated, which is obtained in the following order: Fe-NpC > Mn-NpC > Ni-NpC. The X-ray absorption spectroscopy verifies the Fe-NpC catalyst having atomically dispersed Fe–N4 moieties. The Fe-NpC catalyst exhibits an ultrahigh specific surface area of 2099 m2 g−1 and splendid ORR performance with a rather positive half wave potential of 0.902 V in alkaline and 0.705 V (vs. Reversible Hydrogen Electrode) in neutral electrolytes. The excellent ORR characteristic provides sufficient feasibility for Fe-NpC as cathode catalyst to construct MFC. The Fe-NpC-MFC performs the highest power density of 1793 ± 77 mW m−2, open circuit voltage of 775 mV, favorable output stability of 6.0% decline in 430 h, and chemical oxygen demand removal of 90.3 ± 4.3%, all surpassing the benchmark Pt/C-MFC. This study demonstrates that the combination of the longevity of Fe-NpC catalyst with its atomically dispersed Fe–N4 structure can ensure a stable and long-term application in MFCs treating wastewater.