Ordered mesoporous Fe (or Co)-N-graphitic carbons as excellent non-precious-metal electrocatalysts for oxygen reduction

Novel mesoporous Fe (or Co)-Nx-C non-precious-metal catalysts (NPMCs) have been fabricated by a simple nanocasting-pyrolysis method using 1,10-phenanthroline metal chelates as the precursors. Owing to the ordered hexagonal mesostructures, appropriate surface area, large-pore channels, and well-distributed metal-Nx moieties embedded within the graphitic carbon backbones, the prepared metal-Nx-C materials exhibit excellent catalytic activity for oxygen reduction reaction (ORR) in both alkaline and acidic media. The prepared Fe-Nx-C materials, when prepared with an optimized catalyst loading on the electrode, exhibit more positive ORR onset-potential and half-wave potential (E1/2) than commercial Pt/C catalysts and the previously reported NPMCs in 0.1 M KOH electrolyte. They also have the comparable ORR onset-potential and current densities to Pt/C electrode in 0.1 M HClO4 electrolyte. Moreover, ORR over mesoporous Fe-Nx-C was found to proceed by the direct four-electron mechanism with high selectivity in both electrolytes. The mesoporous Fe-Nx-C materials demonstrated higher ORR catalytic activity compared to the NPMCs made by alternative methods. Analysis of the catalytic behavior, structure and nature of surface species of Nx-C materials allows us to ascribe the origin of the excellent ORR catalytic activity of mesoporous Fe (or Co)-Nx-C in both electrolytes to Fe (or Co)-Nx moieties embedded within the graphitic carbon frameworks.