Volatilizable template-assisted scalable preparation of honeycomb-like porous carbons for efficient oxygen electroreduction

The electrocatalytic activity of nitrogen-doped carbons towards the oxygen reduction reaction is largely determined by the concentration of active nitrogen dopants and the electrochemically accessible surface area. Herein we report a novel, facile route for the preparation of N-doped carbons based on direct pyrolysis of polypyrrole nanosheet precursors synthesized by confining the polymerization on the surface of NaCl crystals using FeCl3 as both the initiator and dopant. In the heating-up process of pyrolysis, a large amount of homogeneously distributed FeCl3 dopant and its derivatives gradually evolved into volatile nanoparticles which helped to generate abundant hierarchical macro- and mesopores, resulting in honeycomb-like porous carbons with a high content of nitrogen dopants ranging from 7 to 18 at%, a large surface area, and an ORR activity superior to that of commercial Pt/C in alkaline electrolytes. Significantly, by using the best sample that was prepared at 800 degrees C (HPC-800) as the air electrode, a Zn-air battery was found to display a specific capacity of 647 mA h g(-1) at 10 mA cm(-2) and a negligible loss of voltage even after continuous operation for 110 h, a performance markedly better than that with Pt/C as the air cathode. The results not only highlight the significance of precursor engineering in the synthesis of highly efficient nitrogen-doped carbon catalysts for oxygen electroreduction, but also suggest the high potential of the interfacially confined polymerization method in the scalable preparation of cost-effective, highly porous carbons for electrochemical energy storage and conversion devices.