Nitrogen-Doped Carbide-Derived Carbon/Carbon Nanotube Composites As Cathode Catalysts for Anion Exchange Membrane Fuel Cell Application

Due to the increasing energy consumption, there is a need for renewable energy production devices. Low temperature fuel cells are among the possible options, but their performance is limited by the sluggish kinetics of the electrochemical oxygen reduction reaction (ORR) at the cathode. The most efficient electrocatalysts for the ORR are based on expensive and scarce noble metals, mainly platinum. As more sustainable replacements, various non-precious metal or entirely metal-free catalysts could be used. The latter ones include heteroatom-doped nanocarbons.1,2 Herein, a composite of carbide-derived carbon and carbon nanotubes (CDC/CNT) is doped with nitrogen by pyrolyzing of a mixture containing CDC, CNT and a nitrogen precursor at 800 °C. A composite of carbons were chosen on the premise of obtaining a feasible structure with both micro- and mesopores, which should be beneficial in the anion exchange membrane fuel cell (AEMFC) application. Four different precursors of nitrogen (cyanamide, dicyandiamide, urea or melamine) were used and compared in order to find the most suitable one.3 For the physico-chemical characterization of the catalysts SEM, XPS, Raman spectroscopy and N2 adsorption studies were applied. These proved indeed that a novel carbon structure was formed and the doping with nitrogen was successful with all four precursors (≥3 at% of N). The electrocatalytic activity of the four N-doped catalyst materials was studied in 0.1 M KOH using RDE and RRDE methods. The four N-CDC/CNT catalyst materials exhibited virtually the same and good activity toward the ORR. In order to assess the possible application of the N-CDC/CNT material, it was employed as a cathode catalyst in AEMFC together with a HMT-PMBI4 membrane. The tests were conducted at different conditions and the best performance with peak power density of 310 mW cm–2 was obtained at 70 °C with 1 bar back pressure (Figure 1). This good performance shows that the metal-free N-CDC/CNT materials are promising cathode catalysts for the AEMFC application.3 References A. Sarapuu, E. Kibena-Põldsepp, M. Borghei, and K. Tammeveski, J. Mater. Chem. A, 6, 776-804 (2018). C.Z. Zhu, H. Li, S.F. Fu, D. Du, and Y.H. Lin, Chem. Soc. Rev., 45, 517-531 (2016) J. Lilloja, E. Kibena-Põldsepp, A. Sarapuu, A. Kikas, V. Kisand, M. Käärik, M. Merisalu, A. Treshchalov, M. Rähn, J. Leis, V. Sammelselg, Q. Wei, S. Holdcroft, and K. Tammeveski, Appl. Catal., B, 272, 119012 (2020). A.G. Wright, J.T. Fan, B. Britton, T. Weissbach, H.F. Lee, E.A. Kitching, T.J. Peckham, and S. Holdcroft, Energy Environ. Sci., 9, 2130-2142 (2016). Figure 1

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