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

Abstract

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 0.1M KOH electrolyte. They also have the comparable ORR onset-potential and current densities to Pt/C electrode in 0.1M 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.