Highly active sites of low spin FeIIN4 species: The identification and the ORR performance

Over recent years, catalytic materials of Fe-N-C species have been recognized being active for oxygen reduction reaction (ORR). However, the identification of active site remains challenging as it generally involves a pyrolysis process and mixed components being obtained. Herein Fe3C/C and Fe2N/C samples were synthesized by temperature programmed reduction of Fe precursors in 15% CH4/H2 and pure NH3, respectively. By acid leaching of Fe2N/C sample, only single sites of FeN4 species were presented, providing an ideal model for identification of catalytic functions of the single sites of FeN4 in ORR. A correlation was conducted between the concentration of FeIIN4 in low spin state by Mossbauer spectra and the kinetic current density at 0.8 V in alkaline media, and such a structure-performance correlation assures the catalytic roles of low spin FeIIN4 species as highly active sites for the ORR.