Co9S8 nanoparticles encapsulated in N,S co-doped hierarchical carbon as an efficient oxygen reduction electrocatalyst for microbial fuel cells

The Co9S8 nanoparticles encapsulated in a N/S co-doped hierarchical porous carbon (Co9S8@HN/S-C) is successfully synthesized to accelerate oxygen reduction reaction (ORR) of microbial fuel cell (MFC). Herein, we prepared the Co9S8@HN/S-C catalyst using a bimetallic (Zn, Co) zeolite imidazolium salt framework as the precursor, which is carbonized at high temperature and then treated with thiourea pyrolysis. The Co9S8@HN/S-C catalyst exhibits an abundant porous structure (pore volume & AP; 0.46 cm3 g-1) and high specific surface area (485 m(2) g(-1)). Benefiting from the active Co9S8 species and N/S co-doped hierarchical porous carbon (HN/ S-C), the Co9S8@HN/S-C exhibits excellent ORR properties in alkaline solution. The half-wave potential (E-1/2) and an onset potential are 0.91 V and 1.01 V (vs. RHE), respectively, which outperforms most previously reported non-precious metal catalysts. In addition, the assembled MFC with Co9S8 @HN/S-C as cathode catalyst also exhibits excellent electrical performance and stability, with the maximum output power density of 1436.5 mW m(-2) and a stable output voltage of 0.59 V, which is better than the most recently reported MFC cathode materials, such as Co9S8 /NHCS (704 mW m(-2), 0.5 V) and Co/Co9S8 /NPG (1156 mW m(-2), 0.562 V), etc. More notably, the outstanding chemical oxygen demand (COD) removal rate can reach 80%, and the coulomb effi-ciency of Co9S8 @HN/S-C based MFC is also better than that of commercial Pt/C. This universal method can be widely used to prepare high-performance electrocatalysts for MFC in wastewater treatment and recovery of electricity.