Single-atomic iron-nitrogen 2D MOF-originated hierarchically porous carbon catalysts for enhanced oxygen reduction reaction

The requirement of sustainable energy is of great significance for easing the energy shortage crisis, in which the oxygen reduction reaction (ORR) in metal-air batteries and fuel cells plays a crucial role in efficient energy conversion. The development of noble-metal-free, efficient, and stable ORR electrocatalysts is highly desirable but remains a significant challenge. Herein, we report an atomically dispersed Fe and N co-doped hierarchically porous carbon (Fe-SA/HPC) catalyst derived from two-dimensional leaf-like ZIF-L with preeminent ORR activity. The Fe-SA/HPC catalyst, benefitting from hierarchically porous structure and rich highly-dispersed active sites of FeNx, put up ORR performance with a half-wave potential (E1/2) of 0.91 V vs. the reversible hydrogen electrode (RHE) in 0.1 M KOH electrolyte. The current density with a 0.382 mg cm−2 loading of catalyst in a rotating disk electrode (RDE) test can reach 24.65 mA cm−2 at 0.8 V, which is nearly twice that of commercial 20 wt% Pt/C. Density functional theory calculations demonstrate that the co-regulation of defects and graphitic nitrogen can optimize the local electronic redistribution for active sites and endow them with a lower free-energy barrier towards the ORR. This work provides certain inspiration for the development of highly reactive atomic metal catalysts through rational topology structure engineering and nitrogen moiety regulation.