Nitrogen and Sulfur Codoped Graphene Macroassemblies as High-Performance Electrocatalysts for the Oxygen Reduction Reaction in Microbial Fuel Cells

Microbial fuel cells (MFCs) are receiving considerable attention for generating clean and sustainable electrical energy directly from wastewater. The development of highly efficient, durable, and inexpensive oxygen reduction electrocatalysts is vital to the fabrication of commercially viable MFCs. Herein, nitrogen (N) and sulfur (S) codoped graphene aerogels (NSGAs) were synthesized hydrothermally via an environmentally benign method, and their application potential as electrocatalysts for the oxygen reduction reaction (ORR) in double-chamber MFCs was systematically evaluated. The NSGAs displayed outstanding electrocatalytic activity for ORR in both cyclic voltammogram experiments and electrochemical impedance spectroscopy measurements. Further, when applied as cathodes in MFCs, the NSGAs could deliver a maximum volumetric power density of up to 13.78 +/- 0.43 W m(-3), which was nearly two times higher than that of the conventional platinum/carbon catalyst (7.01 +/- 0.36 W m(-3)). The impressive electrocatalytic performance of the NSGAs can be attributed to their interconnected porosity, and the presence of N and S elements with diverse bonding states in their two-dimensional nanoscale building blocks. The outcome of this investigation lays out an important research direction for the development of the next generation of robust metal-free ORR electrocatalysts for application in MFCs and related devices.