Nitrogen-Doped Hierarchical Porous Hollow Carbon Microspheres for Electrochemical Energy Conversion

Nitrogen-doped hierarchical porous hollow carbon microspheres (N-HPHCS) are synthesized using melamine-formaldehyde (MF) resin as carbon and nitrogen sources, sulfonated polystyrene microspheres (SPS) as the core template, and SiO2 nanoparticles as the mesopore forming agent. The obtained microspheres are composed of SPS core and MF/SiO2 composite shell (SPS@MF/SiO2). This SPS@MF/SiO2 is then calcined and acid-treated to obtain N-HPHCS. During the calcination, SPS core is removed, and the micropores are formed on the shell owing to the thermal decomposition of the MF resin. After chemical etching of the SiO2 nanoparticles, mesopores are generated on the carbon shell. The as-prepared sample of N-HPHCS has high surface area and large pore volume, and exhibits catalytic activity toward oxygen reduction reaction (ORR). The electrocatalytic performance of N-HPHCS can be ascribed not only to the doped nitrogen atoms, but also to the hierarchical porous structure.