Cite this: RSC Advances, 2013, 3, 9904 Polypyrrole-derived mesoporous nitrogen-doped carbons with intrinsic catalytic activity in the oxygen reduction reaction3 Received 7th February 2013, Accepted 15th April 2013 DOI: 10.1039/c3ra41719k www.rsc.org/advances Marta Sevilla,* a Linghui Yu, b Tim Patrick Fellinger, b Antonio B. Fuertes a and Maria- Magdalena Titirici c N-doped mesoporous carbons containing small amounts of graphitic carbon have been successfully prepared using the nanocasting technique. Polypyrrole was used as N-dopant carbon precursor and SBA- 15 or silica xerogel as templates. Graphitic carbon domains provide a good electronic conductivity of up to 0.33 S cm 21 , a necessary property for electrochemical applications, while a mesoporous structure reduces mass transport limitations. These characteristics are further combined with a high N content (3.55–5.45 wt%). As a result, the as-prepared materials exhibit an enhanced intrinsic electrocatalytic activity towards the oxygen reduction reaction (ORR). They exhibit an onset potential of y290 to 270 mV vs. Ag/AgCl and a current density in the lower potential regime that exceeds that of a commercial platinum catalyst in a basic medium. Their behavior is superior to that of Vulcan XC72R carbon. Furthermore, unlike commercial Pt catalysts, they are unaffected by the methanol cross-over effect. It was found that the graphitic content must be well-balanced as, on the one hand, it enhances conductivity but, on the other hand, it selectively catalyses an unfavorable 2e 2 process. Introduction Nitrogen-containing carbons have attracted increasing interest among the scientific community over the past few years as they improve the properties of bulk carbon for use in various applications. The incorporated nitrogen functional groups have a deep effect on the carbon properties. In particular, electrical conductivity, basicity, oxidation stability, and cataly- tic activity are directly affected and often enhanced when nitrogen is introduced into the carbon structure. 1,2 The performance of these materials is strongly dependent on the amount of nitrogen in the carbon host as well as on its local structure. Nitrogen-doping in carbon materials can be performed either directly during synthesis or by post-synthetic treatment. However, post-treatment methodologies often yield only surface functionalization. 3–5 The bulk material properties are not affected. In contrast, ‘‘in situ’’ doping during solid synthesis using nitrogen-containing precursors ensures the homogeneous incorporation of nitrogen throughout the entire carbon material. Several N-doped carbons have been prepared using this method. For example, high surface area porous carbons with a high nitrogen content have been synthesized by means of cyclotrimerization reactions between carbonitriles and cyano-containing ionic liquids under ionothermal condi- tions, 6–10 and by nanocasting or chemical activation using as carbon precursor N-containing organic compounds 11,12 or mixtures of nitrogen-containing compounds (i.e. melamine, urea, etc.) and N-free materials. 13 Furthermore, N-doped CNTs and CNFs have been synthesized by methods similar to that used to synthesize bulk CNTs, but using precursors such as melamine, 14 benzylamine, 15 acetonitrile, 16 N-heterocycles, 17,18 phthalocyanines, 18 and again specific ionic liquids. 19 Bulk nitrogen-doped carbons have been commonly inves- tigated as metal-free catalysis for the electrochemical oxygen reduction reaction (ORR). This reaction takes place in the cathodic compartment of polymer–electrolyte membrane fuel cells, membrane-reactors for the production of hydrogen peroxide and metal-air batteries. 2,8,20,21 There is a great interest in to replace the expensive fuel cell electrodes containing supported noble metals such as Pt and Ru. In this sense, it was found that metal phthalocyanine complexes exhibit a certain catalytic activity in ORR. 22 Such complexes are known to be the catalytically active centers of redox-active enzymes. Other metal macrocycles, such as metalloporphyrins, have also been selected as cathode catalysts for ORR. 23 To increase the stability and durability of these catalysts during the electrochemical operation, these complexes have been a Instituto Nacional del Carbo´n (CSIC), P. O. Box 73, Oviedo 33080, Spain. E-mail: martasev@incar.csic.es b Max-Planck Institute of Colloids and Interfaces, Am Muhlenberg 1, 14476, Potsdam, Germany c Queen Mary University of London, School of Engineering and Materials Science, Mile End Road, E1 4NS, London 3 Electronic supplementary information (ESI) available. See DOI: 10.1039/ c3ra41719k RSC Advances PAPER 9904 | RSC Adv., 2013, 3, 9904–9910 This journal is ß The Royal Society of Chemistry 2013 Published on 16 April 2013. Downloaded by Queen Mary, University of London on 12/06/2013 12:56:28. View Article Online View Journal | View Issue