Hierarchically open-porous carbon networks enriched with exclusive Fe–Nx active sites as efficient oxygen reduction catalysts towards acidic H2–O2 PEM fuel cell and alkaline Zn–air battery

Abstract The development of both H2–O2 proton exchange membrane fuel cells (PEMFCs) and Zn-air batteries are challenged by high-efficiency air cathodes with a high oxygen reduction reaction (ORR) electrocatalytic-activity. The increase of density and accessibility of active sites are widely accepted effective approach to boost the oxygen reduction reaction. In this work, we develop a template-free g-C3N4-assisted pyrolysis strategy to transform ZIF-8 polyhedrons to hierarchically open-porous carbon networks incorporated exclusive Fe–Nx active sites. Due to the integration of high specific surface area, highly open porous architecture with meso/micro-pores, and high-density Fe-Nx active species, the electro-catalysis performance of optimal catalysts exceed commercial Pt/C in alkaline solution, and is comparable to that of commercial Pt/C in acidic solution, which is one of the best recently reported carbon-based electrocatalysts. Impressively, when it is used as an air cathode catalyst, it achieves a high power density of 481 mW·cm−2 in acidic H2–O2 proton exchange membrane fuel cell (PEMFC) and an excellent performance in the alkaline Zn–air battery (a high power density of 121 mW·cm−2).