N-doped hollow carbon spheres have attracted great attention in recent years beacause of their excellent properties.In this work,different nitrogen-doped carbon hollow sphere materials,with 250 nm average diameter,were prepared via a low-temperature hydrothermal method using glucose as carbon source,dicyandiamide or melamine as nitrogen source.Their electrochemical behaviors were investigated by cyclic voltammetry(CV)and oxygen reduction reaction(ORR)polarization curve test.The results show that the performance of N-doped carbon hollow spheres have been enhanced to different degrees with the addition of different nitrogen source.All of the as-prepared metal-free N-doped carbon hollow spheres present excellent electrochemical behaviors.