Exploring the active sites of nitrogen-doped graphene as catalysts for the oxygen reduction reaction

Nitrogen-doped graphene is studied as a kind of non-noble metal catalyst for the oxygen reduction reaction in the cathode of fuel cells. Graphene is synthesized by pyrolyzing ion exchange resin and nitrogen doping is realized by a second pyrolysis step with nitrogen precursor. High resolution transmission electron microscopy proves the graphene is composed by 8-10 graphitic layers. The defect of graphene caused by nitrogen doping is detected by Raman spectra. The nitrogen group of the doped graphene is studied in detail with X-ray photoelectron spectroscopy spectra and a special type of nitrogen: valley-N is distinguished. The valley-N is proved to play an important role in the oxygen reduction reaction. Nitrogen content is found not directly related with the activity of the oxygen reduction reaction. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.