Co8FeS8 wrapped in Auricularia-derived N-doped carbon with a micron-size spherical structure as an efficient cathode catalyst for strengthening charge transfer and bioelectricity generation

The main issues regarding the practical application of microbial fuel cells (MFCs) are the poor activity and tolerance of oxygen reduction reaction (ORR) catalysts in wastewater. In this study, Auricularia chelated with Co, Fe and S ions is used as a nitrogen (N)-enriched carbon source to prepare N-doped bimetallic sulfide (Co8FeS8)-embedded carbon spheres (Co8FeS8/NSC) using a hydrothermal method. The effects of various temperatures (800-950 degrees C) on the structure and catalytic activity of Co8FeS8/NSC catalysts are investigated. The MFC with a Co8FeS8 /NSC (900 degrees C) cathode obtained the maximum power density of 1.002 W m(-2), which is higher than that of Pt/C (0.88 W m(-2)). After 1440 h of operation, the power density of the Co8FeS8/NSC (900 degrees C) cathode only declined by 5.49%, indicating that the Co8FeS8 activity, charge transfer and O-2 transport were slightly influenced by the attached microbes and poisonous substances in the wastewater. The electrochemical results indicate that Co8FeS8/NSC (900 degrees C) mainly proceeds by a 4e(-) ORR pathway, indicating that Co8FeS8 (Co(2+)and Fe2+) wrapped in NSCs (carbon spheres) can trigger synergistic effects to provide more active sites and high electrical conductivity to achieve the rapid kinetics required for the ORR. Moreover, the porous structures of the NSCs (220.97 m(2) g(-1)) with incorporated pyridinic N, pyrrolic N and graphitic N can provide abundant available channels for O-2 and OH- transport to ensure the preferential accessibility of the reactant molecules to active sites. This indicates that Auricularia-derived Co8FeS8\NSC catalysts have great potential as alternatives for precious metal-based catalysts in neutral electrolyte MFCs. (C) 2020 Elsevier Inc. All rights reserved.