Ordered Hierarchically Micro- and Mesoporous Fe–Nx-Embedded Graphitic Architectures as Efficient Electrocatalysts for Oxygen Reduction Reaction

Abstract

A series of novel ordered hierarchically micro- and mesoporous Fe–N x -embedded graphitic architectures (Fe–N–GC) are directly prepared by the simple pyrolysis of the different nitrogen heterocyclic compounds and iron chlorides in the confined mesochannels of SBA-15. Among these porous Fe–N–GC materials, the sample prepared by heating 2,2-bipyridine and Fe chelates at 900 °C shows the more positive ORR onset potential and half-wave potential (E 1/2) values than commercial Pt–C catalysts in 0.1 M KOH, which illustrate that it is one of the most-promising nonprecious metal catalysts (NPMCs) among the reported NMPCs in alkaline medium. Moreover, unlike nitrogen-doped carbons and Co 3 O 4 /carbon composites, high ORR current density (5.2 mA cm –2, 0.6 V) over this Fe–N–GC electrode with catalyst loading of 0.6 mg cm –2 can be also obtained in 0.1 M HClO 4 acidic solution, which is about 0.6 mA cm –2 larger than that over the electrode of commercial Pt/C with 20 μg Pt cm –2 loading. In addition, the effective embedding of active moieties in the graphitic frameworks and a direct four-electron reduction pathway in ORR contributes to its high durability in both alkaline and acidic media. Its excellent ORR activity should be ascribed to the optimized balance between active site density and capability for mass and charge transport. Such hierarchically porous Fe–N x –graphitic materials hold great promise for the practical utilization in cathode catalyst layers of proton exchange membrane fuel cells.