Low-temperature synthesized nitrogen-doped iron/iron carbide/partly-graphitized carbon as stable cathode catalysts for enhancing bioelectricity generation

Low efficiency of oxygen reduction reaction (ORR) across cathode interfaces constitutes an obstacle to the bioelectricity generation in microbial fuel cells (MFCs). Advances in the property of carbon-based catalysts for ORR will have far-reaching implications for MFCs. Melamine is used as both carbon and nitrogen sources for preparing nitrogen-doped Fe-species/partly-graphitized carbon (Fe-species/NPGC) catalysts at relatively low temperature (640–700 °C). Main crystalline phases in Fe-species/NPGC-x (x = 640, 650, 660 and 700) change from iron carbide (Fe3C) to α-Fe as temperature increases. The OCO groups and structurally-bonded nitrogen (Fe-bonded N, pyridinic N and pyrrolic N) in PGC skeleton are favorable for improving electrical conductivity and catalytic activity. Single chamber MFCs with Fe/Fe3C/NPGC-650 generate power density of 1323 mW m−2, which is higher than those of Fe-species/NPGC-x (x = 640, 660 and 700) and Pt/C (1191 mW m−2). Minimum power density decline (1.75%) is achieved by Fe/NPGC-660, which is far lower than that (17.11%) of Pt/C. The highest coulombic efficiency (30%) is obtained by Fe/Fe3C/NPGC-650 due to the sufficient active-sites (embedded Fe3C or FeN species) and easy charge transport across the triphase interfaces, which are conducive to “capture–consume” the electrons for catalyzing ORR.