Synthesis of hybrid carbon spheres@nitrogen-doped graphene/carbon nanotubes and their oxygen reduction activity performance

The hybrid architecture of carbon spheres@nitrogen-doped graphene/carbon nanotubes (CS@N-G/CNT) was synthesized by a hydrothermal and ultrasonic-assisted method. It consisted of one-dimensional CNTs and two-dimensional N-doped graphene (N-G) supporting zero-dimensional carbon spheres (CSs). The electrocatalytic activity of the hybrid CS@N-G/CNT shows a better oxygen reduction reaction (ORR) than CS, CNT, N-G, and CS@N-G in alkaline media. More importantly, it displays both a higher mass activity and better stability than a commercial Pt/C. The high electrocatalytic activity and stable oxygen reduction electrocatalyst could be attributed to the higher surface areas and larger pore volume, as well as the synergistic effects of the different dimensional carbon materials, which was beneficial to the diffusion of the electrolyte and O₂ during the ORR.