Green and facile synthesis of iron oxide nanoparticle-embedded N-doped biocarbon as an efficient oxygen reduction electrocatalyst for microbial fuel cells

Developing a cost-effective, long durable and high performance cathode catalyst for oxygen reduction reaction (ORR) is crucial for the practical application of microbial fuel cells (MFCs). In this work, iron oxide nanoparticle-embedded N-doped hierarchically porous carbon (Fe/N-C), synthesized through a hydrothermal treatment and subsequent carbonization procedures using Chlorella pyrenoidosa as the N and C source and FeCl(2 )as the iron source, was developed as a promising alternative ORR catalyst in MFCs. Experiments showed that the Fe/N-C catalyst formed more active sites of embedded iron oxide nanoparticles and had rich hierarchical porous structure that could enhance the mass transport and the exposure of active sites. Due to the higher number of active sites and a shortened mass/electron transfer pathway resulting from the embedded iron oxide nanoparticles, the Fe/N-C catalyst exhibited an excellent ORR performance with a more positive half-wave potential than does Pt/C in a 50 mM phosphate buffer solution. Additionally, the chronoamperometry tests showed that the Fe/N-C catalyst maintained 87.6% of the current after 18,000 s operation, which was significantly higher than 76.2% for Pt/C. An MFC using the Fe/N-C catalyst delivered the maximum power density of 2740 +/- 160 mW m(-2), which was 48% higher than that obtained with the commercial 20 wt% Pt/C (1846 +/- 66 mW m(-2)) at the same catalyst loading. Therefore, the present work provides a green and facile method for developing a high-activity ORR electrocatalyst for MFC applications.