The key role of metal dopants in nitrogen-doped carbon xerogel for oxygen reduction reaction

Highly active non-precious metal catalysts based on nitrogen-doped carbon xerogel (NCX) for the oxygen reduction reaction (ORR) is prepared with resorcinol(R)-formaldehyde (F) resin as carbon precursor and NH3 as nitrogen source. NCX samples doped with various transition metal species are investigated to elucidate the effect of transition metals on the structure and ORR activity of the products. As-prepared NCX catalysts with different metals are characterized using nitrogen-adsorption analysis, X-ray diffractometry, X-ray photoelectron spectroscopy, and Raman spectroscopy. The structural properties and ORR activities of the catalysts are altered by addition of different metals, and NO( doped with iron exhibits the best ORR activity. Metal doping evidently promotes the formation of more micropores and mesopores. Raman and XPS studies reveal that iron, cobalt, and nickel can increase pyridinic-N contents and that iron can catalyse the formation of graphene structures and enhance quaternary-N contents. Whereas the total N-content does not determine ORR activity, Metal-N-4/C-like species generated from the interaction of the metals with nitrogen and carbon atoms play important roles in achieving high ORR activity. (C) 2014 Elsevier B.V. All rights reserved.