Hierarchically Porous Fe-N-C Single-Atom Catalysts via Ionothermal Synthesis for Oxygen Reduction Reaction

Platinum group metal (PGM)-free electrocatalysts have emerged as promising alternatives to replace Pt for the oxygen reduction reaction (ORR) in anion exchange membrane fuel cells (AEMFCs). However, traditional synthesis methods limit the single-atom site density due to metal agglomeration at higher temperatures. This work explores the preparation of hierarchically porous atomically dispersed electrocatalysts for the ORR. The materials were prepared via ionothermal synthesis, where magnesium nitrate was used to prepare hierarchically porous carbon materials. The in-situ formed Mg-N_x sites were trans-metalated to yield ORR-active Fe-N_x sites. The resulting carbon-based catalysts displayed excellent electrocatalytic activity, attributed to the atomically dispersed Fe-N_x active sites and high meso- and macroporosity that enhanced the mass transport and exposed more accessible active sites.