Hierarchical Porous Carbon Doped with Iron/Nitrogen/Sulfur for Efficient Oxygen Reduction Reaction

Hierarchical porous Fe/N/S-doped carbon with a high content of graphitic nitrogen (FeNS/HPC) has been successfully synthesized by a facile dual-template method. FeNS/HPC shows not only macropores resulting from the dissolution of the SiO2 template, but abundant mesopores were also obtained after removing the in situ generated Fe2O3 nanoparticles on the ultrathin (similar to 4 nun) carbon shell of the macropores. Moreover, micropores are produced during the thermal pyrolysis of the carbon precursors. With respect to the electrochemical performance in the oxygen reduction reaction (ORR), FeNS/HPC not only exceeds other prepared porous carbon materials completely but also shows higher onset potential (0.97 vs 0.93 V), half-wave potentials diffusion current density (5.5 vs 5.3 mA cm(-2)) than those of Pt/C. Furthermore, FeNS/HPC also exhibits outstanding stability and methanol tolerance, making it a competent candidate for ORR The following aspects contribute to its excellent ORR performance. (1) High content of graphitic N (5.1%) and codoping of pyridinic N species, thiophene-S, FeNx, and graphitic carbon-encapsulated iron nanoparticles, providing highly active sites. (2) The hierarchical porous mesh structure with micro-, meso-, and macroporosity, accelerating the mass transfer and facilitating full utilization of the active sites. (3) The high specific surface area (1148 m(2) g(-1)) of the graphitic carbon shell, assuring a large interface and, rapid electron conduction for ORR.