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

The development of both H-2-O-2 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-N-x active sites. Due to the integration of high specific surface area, highly open porous architecture with meso/micropores, and high-density Fe-N-x 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 H-2-O-2 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)).