A rational synthetic approach to a highly active Fe–N–C catalyst for efficient electrochemical oxygen reduction†

Single atoms of iron coordinated to nitrogen embedded in a carbon support (Fe–N–C) are the most active platinum group metal-free catalysts for the oxygen reduction reaction (ORR) in renewable energy devices. However, Fe–N–C catalysts, usually derived from Fe-doped zeolitic imidazole frameworks, suffer from limited activity due to restricted utilization of their active sites, which are buried deep inside the carbon matrix. Herein, we report a unique and facile design approach based on the interplay between the oxidation state of Fe in the precursor and modulation of synthetic parameters to regulate the particle size, surface area and Fe doping towards increased accessible ORR active sites. The synthesized Fe–N–C catalyst demonstrates remarkably high ORR activity in 0.1 M KOH with an onset and half-wave potential of 0.988 V and 0.903 V vs. RHE, respectively, excellent 4e⁻ selectivity and durability. Our work paves the way for a new discussion in understanding the role of fundamental parameters that affect the material's properties through a unique design strategy.