Gradually Anchoring N and Fe, Zn Atoms on Monodispersed Carbon Nanospheres: Their Contribution to the Oxygen Reduction Reaction under Analogous Structure

In dual metal-nitrogen doped carbon catalysts, the prestored metal atoms like Fe, Co, and Ni have strong thermal catalytic effect and reunion ability during carbonization process that can easily cause variable carbon structures and irremovable nanoparticles, while Zn atoms present good "fencing" effect and high volatile nature, enabling atomic dispersion of other metal atoms and porosity elevation of the carbons. The different effects on the carbon nanostructures will obscure the contribution of each doped atoms to active sites and ORR performance. In this paper, various Zn-N, Fe-Zn, and Fe-Zn-N decorated carbon nanospheres (CNS) with analogous structure were prepared to distinguish the contributions of N, Fe, and Zn atoms. We found that the nitrogen coordinated Fe single site other than Zn single site and Fe-Zn dual site should dominate the active sites with contribution trend of N > Fe >> Zn. Meanwhile, Zn plays an important role in making pores, boosting atomic utilization and specific surface area (SSA). The Fe-Zn-N doped carbon nanospheres (0.6 mg cm(-2)) can achieve a high limiting current density of 6.69 mA cm(-2) and positive onset/half-wave potentials of 0.95 and 0.84 V, respectively.