Bimetallic organic framework-derived, oxygen-defect-rich FexCo3-xS4/FeyCo9-yS8 heterostructure microsphere as a highly efficient and robust cathodic catalyst in the microbial fuel cell

The sluggish kinetics of cathodic oxygen reduction reaction (ORR) is one of the critical factors hindering the development of microbial fuel cells (MFCs). Herein, the metal organic framework (MOF)-derived Fe x Co 3-x S 4 /Fe y Co 9-y S 8 (FeCoS(MOF)) is in-situ grown on nickel foam as ORR catalyst with high doping of N and S. Results show that based on the role of FeCoMOF, the FeCoS(MOF) microspheres are made up of nanosheets piling-up without phase aggregation and structural collapse. Meanwhile, more defects are generated, resulting in low internal resistance, high quality activity and high turnover frequency . In the MFC with the FeCoS(MOF) cathode, the maximum power density is 2.55 times of that of Pt/C cathode. The excellent ORR activity is due to the unique morphology and rich oxygen defects, which shortens electronic transmission distance, facilitates the exposure of more active sites, and improves oxygen adsorption and conductivity. Moreover, the durability of FeCoS(MOF) cathode outperforms Pt/C cathode, with stable output voltage maintains for 2 months, while the Pt/C cathode decreases to 67% of the initial voltage. This work provides inspiration for developing efficient MOF-derived ORR catalyst.