N-doped-carbon-coated Fe3O4 from metal-organic framework as efficient electrocatalyst for ORR

Nowadays, the hybrids of non-noble metal and heteroatom-doped carbon, especially, transition-metal-nitrogen-carbon materials, have been extensively studied as promising next-generation oxygen reduction reaction (ORR) catalysts in energy conversion. However, the pyrolysis of normal metal/nitrogen/carbon-containing precursors usually generates uncontrollable agglomeration or inhomogeneous microstructure, hence leading to insufficient exposure of the active sites and poor mass transport. In this work, a new strategy for fabricating N-doped-carbon-coated Fe3O4 (denoted as NC@Fe3O4) is proposed by the pyrolysis of polyaniline (PANI)-coated Fe-based metal organic frameworks (MIL-101-Fe). The optimal catalyst exhibits a very positive ORR onset potential close to that of Pt/C, quasi-four-electron-transfer pathway and high long-term cycle stability in alkaline media. This work demonstrates the crucial role of thin PANI film (a highly conductive skeleton and heteroatoms sources) together with MOFs to rationalize the superior ORR performance for the resulting NC@Fe3O4. The generality of the conductive-polymer-layer-assisted synthetic strategy is expected to further boost the electrocatalytic activity of universal non-noble-metal hybrid electrocatalyst for practical fuel-cell applications.