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

Abstract

• Co 9 S 8 @HN/S-C (Co 9 S 8 encapsulated in N/S co-doped porous carbon) is successfully synthesized. • Co 9 S 8 @HN/S-C exhibits high ORR electrocatalytic in alkaline and neutral media. • MFCs with Co 9 S 8 @HN/S-C show high power density of 1436.5mWm −2. • Outstanding chemical oxygen demand (COD) removal rate (80%) The Co 9 S 8 nanoparticles encapsulated in a N/S co-doped hierarchical porous carbon (Co 9 S 8 @HN/S-C) is successfully synthesized to accelerate oxygen reduction reaction (ORR) of microbial fuel cell (MFC). Herein, we prepared the Co 9 S 8 @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 Co 9 S 8 @HN/S-C catalyst exhibits an abundant porous structure (pore volume ≈ 0.46 cm 3 g −1 ) and high specific surface area (485 m 2 g −1 ). Benefiting from the active Co 9 S 8 species and N/S co-doped hierarchical porous carbon (HN/S-C), the Co 9 S 8 @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 Co 9 S 8 @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 Co 9 S 8 /NHCS (704 mW m −2 , 0.5 V) and Co/Co 9 S 8 /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 efficiency of Co 9 S 8 @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.