The oxygen reduction reactions (ORR) play a crucial role in the electrochemical energy storage devices, such as fuel cell, metal-air batteries [1], [2], [3]. However, their larger scale applications are hindered by the sluggish slow kinetics of the ORR. Up to now, platinum (Pt)-based catalysts are still known as the best ORR electrocatalysts owing to the relatively low overpotential, high catalytic activity and current density [4]. Nevertheless, the scarcity and high cost of Pt-based materials [5] limit their wider application. Therefore, the search and development of highly efficient and cost-effective catalysts for ORR is highly desirable. Recently, an enormous amount of research effort goes into the synthesis of carbon-based electrocatalysts doped by heteroatoms (e.g., N) to replace Pt-based catalysts. The introduction of N atoms break the sp2 hybridization of carbon, inducing a lone pair of electrons, thus altering the charge and spin density of adjacent carbon atoms. Therefore, the modified carbon materials generate active sites for ORR.