Metal organic framework derived iron-nitrogen doped porous carbon support decorated with cobalt and iron as efficient nanocatalyst toward oxygen reduction reaction

Abstract

Two porous carbon supports as N-doped carbon (NC) and Fe/N-co-doped carbon (Fe-NC), are obtained from ZIF-8 (zeolitic imidazolate framework) and Fe@ZIF-8, respectively, through the pyrolysis process. They are then decorated with transition metals using a modified polyol method to precipitate Fe, Co, and Fe–Co nanoparticles. The as-prepared catalysts are characterized by different physicochemical, morphological, and electrochemical characterization methods. Field emission scanning electron microscopy images show well-defined preserved polyhedron morphology for all prepared catalysts. Transmission electron microscopy images confirm a uniform distribution of metal nanoparticles through the surface of the supports. X-ray photoelectron spectroscopy results illustrate the existence of high content of graphitic and pyridinic nitrogen. Oxygen reduction reaction (ORR) results show the prepared support, which is in-situ doped with iron (Fe-NC), has better ORR performance than NC support. The results also display Co and Fe nanoparticles' coincident precipitation on the supports can improve ORR. This finding indicates both in-situ and ex-situ metal doping can be beneficial for good ORR performance. The optimum catalyst (Fe–Co/Fe-NC) illustrates enhanced ORR activity and stability with onset potential ~0.9VRHE in 0.1 M HClO4. Superior performance is associated with a synergistic effect between small and uniform dispersion of Co and Fe nanoparticles and appropriate nitrogen content.