Easy-to-operate and low-temperature synthesis of gram-scale nitrogen-doped graphene and its application as cathode catalyst in microbial fuel cells.

Nitrogen-doped graphene (NG), with unique electronic properties, is showing great promise for a wide range of practical applications. However, the reported approaches for NG synthesis are usually complex, require high temperatures, produce lower atomic ratios of nitrogen to carbon (N/C), and do not deliver products in a reasonably large quantity. Here we report an easy-to-operate and low-temperature method to synthesize NG in gram-scale quantities with a denotation process. High-resolution transmission electron microscopy, Raman spectroscopy, and X-ray diffraction characterization suggested that the synthesized NG films were uniformly multilayered and had a high crystalline quality. In the graphene sheets the existence of nitrogen substitution with an atomic ratio of N/C 12.5%, which was greater than those reported in the literature, was confirmed by X-ray photoelectron spectroscopic analysis. In the neutral phosphate buffer solution, the synthesized NG was demonstrated to act as a metal-free electrode with excellent electrocatalytic activity and long-term operation stability for oxygen reduction via a combination of two-electron and four-electron pathways. When the NG was applied as the cathode catalyst of microbial fuel cells (MFCs), the obtained maximum power density was comparable to that of conventional platinum catalyst. More importantly, MFCs with NG produced power more stably and less expensively than those with Pt catalyst, indicating that the synthesized NG might be used as a good alternative to Pt catalyst in MFCs with a long run.