Supramolecular confinement synthesis of ultrafine iron nitride nanocrystals for the oxygen reduction reaction in Zn-air batteries

Non-noble metal nitrides have emerged as highly efficient and robust substitutes for platinum-based catalysts toward the oxygen reduction reaction. Herein, we demonstrate a supramolecular confinement strategy to synthesize ultrafine iron nitride (Fe₃N, less than 1.5 nm) nanocrystals embedded in a nitrogen-doped carbon matrix, in which the pre-formed Fe-N coordination bonds can anchor the Fe₃N nanocrystals and prevent their agglomeration during the pyrolysis process. Reducing the size of Fe₃N nanocrystals is conducive to exposing more accessible Fe-N-C ORR active sites and consequently facilitating electrocatalytic ORR activity. The optimized Fe₃N/NC-800 exhibits a positive half-wave potential of 0.83 V versus RHE, along with favorable stability and superior tolerance toward methanol. The power density and specific capacity of the optimized Zn-air batteries associated with Fe₃N/NC-800 are as high as 90.91 mW cm⁻² and 691.59 mA h g⁻¹, respectively. Briefly, a feasible supramolecular confinement strategy is proposed for the construction of ultrafine nanocrystals.