Nitrogen-doped Co/Co9S8/partly-graphitized carbon as durable catalysts for oxygen reduction in microbial fuel cells.

Durability of catalysts for oxygen reduction reaction (ORR) is the key factor for governing the performance of microbial fuel cells (MFCs). The cobalt (Co) chelated polyaniline (PANI) is used as the nitrogen and carbon sources to prepare the N-doped Co/Co 9 S 8 /partly-graphitized carbon (Co/Co 9 S 8 /NPGC) catalysts. Structure-activity correlations for Co/Co 9 S 8 /NPGC are explored by tuning the heating temperature (600–1000 °C) to investigate how the active components (Co/Co 9 S 8 ) and N-doped functionalities (N-species) influence the ORR activity. As temperature increases, the gradual crystallization of Co originating from the reduction of Co 9 S 8 is conducted to form the Co/Co 9 S 8 heterojunction. MFCs with Co/Co 9 S 8 /NPGC (800 °C) cathode obtain the highest power density (1156 mW m −2 ) and the lowest charge transfer resistance (11.1 Ω) after 75 d running, which are better than commercial Pt/C (10 wt.%). Although the sole Co 9 S 8 plays a limited role in ORR, the resulting Co/Co 9 S 8 is found to be indispensable to achieve high activity and durability in MFCs cathodes. The dominant ORR pathways of Co/Co 9 S 8 /NPGC (800 and 900 °C) are the four-electron O 2 reduction, which are attributed to the co-existence of pyridinic N, graphitic N and Co-N x species. These new N-doped metal sulfide/PGC composites show promise for applications in MFCs. [ABSTRACT FROM AUTHOR]