Confined-Space-Assisted Preparation of Fe3O4-Nanoparticle-Modified Fe-N-C Catalysts Derived from a Covalent Organic Polymer for Oxygen Reduction

Iron-nitrogen-carbon (Fe-N-C) has been considered as one of the most promising nonprecious metal catalysts for the oxygen reduction reaction (ORR) in fuel cells and metal air batteries. Herein, we prepare a highly active Fe3O4/Fe-N-C catalyst (named COP@K1O-Fe-900), for the ORR from a layered tetraphenylporphyrin-based (TPP-based) covalent organic polymer (COP) grown in nanoconfined space as precursors, followed by iron ion incorporation and a pyrolysis process. The nanoconfined space, i.e., montmorillonite (K10) template, contributes to the unique layered structure of designed precursors and enables Fe3O4 nanoparticles to disperse uniformly in the resulting layered Fe-N-C catalyst. The nanoconfined space reduces the iron-based particle size from similar to 50-150 to similar to 10 nm. An enhancement of 50 mV was obtained after using layer space confinement for half-wave potential. Moreover, the half-wave potential of the newly developed COP@K10-900 exceeds 20 mV as compared to the benchmark Pt/C in alkaline media. Therefore, we believe that this work can provide an important guideline for designing highly active M-N-C catalysts that can be widely used in energy conversion and storage devices.