Electrocatalysis of oxygen reduction by iron-containing nitrogen-doped carbon aerogels in alkaline solution Ave Sarapuu a, *, Kristiina Kreek b , Kaarel Kisand a , Mati Kook c , Mai Uibu d , Mihkel Koel b , Kaido Tammeveski a, 1 a Institute of Chemistry, University of Tartu, Ravila 14a, 50411 Tartu, Estonia b Institute of Chemistry, Tallinn University of Technology, Akadeemia tee 15, 12618 Tallinn, Estonia c Institute of Physics, University of Tartu, W. Ostwald Str. 1, 50411 Tartu, Estonia d Laboratory of Inorganic Materials, Tallinn University of Technology, Ehitajate tee 5, 12618 Tallinn, Estonia A R T I C L E I N F O Article history: Received 31 October 2016 Received in revised form 9 January 2017 Accepted 18 January 2017 Available online 25 January 2017 Keywords: Carbon aerogel Oxygen reduction Electrocatalysis Non-precious metal catalyst Nitrogen doping A B S T R A C T Iron-containing nitrogen-doped carbon aerogels (CAs) were prepared by pyrolysis of organic aerogels of variable composition synthesised from melamine, 5-methylresorcinol and 2,6-dihydroxy-4-methyl- benzoic acid. The structure and composition of the catalyst materials were characterised by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, atomic absorption spectros- copy and N 2 -adsorption analysis. The electrocatalytic activity of CAs for oxygen reduction reaction (ORR) was evaluated using the rotating disk electrode (RDE) method in alkaline solution and increase of the ORR activity with increasing the nitrogen and iron content was revealed. Low peroxide production on Fe-containing N-doped CA-based catalysts and their high methanol tolerance suggest that these could be suitable cathode catalysts for alkaline fuel cells. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction Nitrogen-doped carbon nanomaterials have attracted a great deal of attention in recent years as possible candidates to substitute platinum-based cathode catalysts in low-temperature fuel cells [1–6]. In acidic media the electrocatalytic activity of these non-precious metal catalysts towards the oxygen reduction reaction (ORR) still does not surpass that of Pt-based catalyst materials [1–6]; however, in alkaline solution, they may even outperform state-of-the-art benchmark Pt/C catalysts [1–14]. Although some metal-free N-doped nanocarbon materials have shown rather good ORR performance [15–19], higher activity has been observed for materials containing transition metals, such as iron or cobalt [9–12,20–30]. The synthesis of metal-containing N-doped carbon catalysts usually involves pyrolysis of high surface area carbon materials (carbon black, carbon nanotubes, graphene, etc.) in the presence of nitrogen and transition metal precursors [5]. Another option is the carbonisation of nitrogen- and metal-containing organic materials, in which case care must be taken to achieve a suitable porous structure of the catalyst [31]. One commonly used method to prepare the materials of precisely determined porosity is using sacrificial templates that are removed by leaching after pyrolysis [25,32,33]. Carbon aerogels (CAs) of high porosity are also obtained by pyrolysis of organic aerogels, which can be prepared by sol-gel polycondensation of various precursors, for example, resorcinol and formaldehyde [32–34]. The structure and properties of resulting CAs are determined by the composition and synthesis procedure of organic gels and conditions of the following pyrolysis [32,33]. Besides high specific surface area and tuneable pore size distribution, CAs feature high electrical conductivity and stability and are therefore advantageous electrocatalyst materials for various applications, including low-temperature fuel cells [34,35]. There is a number of studies of carbon aerogel- or xerogel-based materials as ORR catalysts [36–50]. The electrocatalytic activity of these catalysts towards the ORR greatly depends on the choice of precursors for the synthesis of organic aerogels and synthesis conditions. If nitrogen-containing precursors are used [38–43] or pyrolysis is carried out in the presence of NH 3 [44–46], N-doped carbon materials can be obtained that show remarkably higher ORR activity as compared to undoped CAs [42–44]. Similarly, N-doped CAs prepared from sustainable precursors by hydrother- mal carbonisation are more active ORR electrocatalysts than nitrogen-free CAs [47–49], yet considerably less active as * Corresponding author.: Tel.:+ +372 7375277; fax: +372 7375181. E-mail address: ave.sarapuu@ut.ee (A. Sarapuu). 1 ISE member. http://dx.doi.org/10.1016/j.electacta.2017.01.157 0013-4686/© 2017 Elsevier Ltd. All rights reserved. Electrochimica Acta 230 (2017) 81–88 Contents lists available at ScienceDirect Electrochimica Acta journa l home page : www.e lsevier.com/loca te/ele cta cta