Three-dimensional nitrogen-doped carbon nanotubes/graphene structure used as a metal-free electrocatalyst for the oxygen reduction reaction

A three-dimensional (3D) nitrogen-doped carbon nanotubes/graphene (NCNTs/G) composite was prepared by pyrolysis of pyridine over a graphene-sheet-supported Ni catalyst. The morphology and structure of the NCNTs/G composite was investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. Tangled NCNTs with lengths of several hundred nanometers are sparsely, but tighly, distributed on graphene sheets, forming quasi-aligned NCNT arrays. The N content in the NCNTs/G measured by X-ray photoelectron spectroscopy is about 6.6 at. %. The NCNTs/G shows a higher activity and selectivity to the oxygen reduction reaction in alkaline electrolyte compared with undoped CNTs/G, as demonstrated by cyclic voltammetry, rotating disk electrode, and rotating ring-disk electrode measurements. The results indicate that the 3D NCNTs/G composite has potential application in fuel cells.