Role of two carbon phases in oxygen reduction reaction on the CoePPyeC catalyst Hoon T. Chung, Gang Wu, Qing Li, Piotr Zelenay * Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA article info Article history: Available online 21 June 2014 Keywords: Polymer electrolyte fuel cell (PEFC) Oxygen reduction reaction Non-precious metal catalyst Carbon Polypyrrole abstract In spite of a significant progress in their performance in recent years, the heat-treated metal-nitrogenecarbon (M-NeC) non-precious metal catalysts for oxygen reduction reac- tion (ORR) at the cathode of polymer electrolyte fuel cells (PEFCs) are in need of further improvement to match the activity and, especially, the stability of Pt-based nanoparticle catalysts of oxygen reduction. A better understanding of the role of individual components in M-NeC catalysts is vital for the development of more advanced formulations. In this work, using a cobalt-polypyrrole-carbon catalyst system as an example, we demonstrate that carbon originating from the organic nitrogen precursor (ONP) has different properties than the carbon support. Unlike the carbon originating from polypyrrole, the support carbon helps to enhance ORR performance but negatively impacts the stability. To the best of our knowledge, this may be the first time that the properties of the ONP-derived carbon are being differentiated from the properties of carbon in the carbon support, emphasizing the potential importance of carbon phases in ORR electrocatalysis on heat-treated M-NeC catalysts. Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Introduction Although the polymer electrolyte fuel cell (PEFC) has long been recognized as a potential power source for zero-emission ve- hicles, it still remains economically uncompetitive with the internal combustion engine. Among other major PEFC com- ponents, the platinum (Pt) catalyst in the cathode and anode are the most expensive single cell constituent, accounting for almost a half of the stack cost. The necessary cost reduction can be achieved by either lowering platinum content in fuel cell electrodes or eliminating altogether eliminating Pt. This is especially important for the cathode where the intrinsically sluggish oxygen reduction reaction (ORR) requires substantially higher Pt loading than the much faster hydrogen oxidation reaction (HOR) at the anode. The potential use of non-precious metal materials to Pt replacement in the PEFC cathode has attracted much atten- tion in recent years. The most promising catalysts are metal- nitrogenecarbon (M-NeC) formulations obtained by heat- treating precursors of transition metals (mainly Fe and Co), nitrogen, and carbon [1e6]. Though the exact nature of the active site(s) developed during heat treatment still remains the subject of intense research, all components of M-NeC catalysts (transition metal, nitrogen functionalities, and spe- cific carbons) have been reported to affect the ORR activity of such catalysts. The role of metal in M-NeC catalysts is controversial, with some groups viewing the transition metal * Corresponding author. Tel.: þ1 505 667 0197; fax: þ1 505 605 4292. E-mail address: zelenay@lanl.gov (P. Zelenay). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 39 (2014) 15887 e15893 http://dx.doi.org/10.1016/j.ijhydene.2014.05.137 0360-3199/Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.