Metallic State FeS Anchored (Fe)/Fe₃O₄/N-Doped Graphitic Carbon with Porous Spongelike Structure as Durable Catalysts for Enhancing Bioelectricity Generation

The critical issues in practical application of microbial fuel cells (MFCs) for wastewater treatment are the high cost and poor activity and durability of precious metal catalysts. To alleviate the activity loss and kinetic barriers for oxygen reduction reaction (ORR) on cathode, (Fe)/Fe₃O₄/FeS/N-doped graphitic carbon ((Fe)/Fe₃O₄/FeS/NGC) is prepared as ORR catalyst through a one-step method using waste pomelo skins as carbon source. Various characterization techniques and electrochemical analyses are conducted to illustrate the correlation between structural characteristics and catalytic activity. MFCs with Fe/Fe₃O₄/FeS/NGC (900 °C) cathode produces the maximum power density of 930 ± 10 mW m^–2 (Pt/C of 489 mW m^–2) and maintains a good long-term durability, which only declines 18% after 90 day operation. Coulombic efficiency (22.2%) obtained by Fe/Fe₃O₄/FeS/NGC (900 °C) cathode is significantly higher than that of Pt/C (17.3%). Metallic state FeS anchored in porous NGC skeleton can boost electron transport through the interconnected channels in spongelike structure to improve catalytic activity. Charge delocalization of C atoms can be strengthened by N atoms incorporation into carbon skeleton, which correspondingly contributes to the O₂ chemisorptions and O–O bond weakening during ORR. Energetically existed active components (Fe and N species) are more efficient than Pt to trap and consume electrons in catalyzing ORR in wastewater containing Pt-poisoning substances (bacterial metabolites). (Fe)/Fe₃O₄/FeS/NGC catalysts with the advantages of durable power outputs and environmental-friendly raw material can cover the shortages of Pt/C and provide an outlook for further applications of these catalysts.