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

Abstract

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 meso-pores, 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 °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.