Iron and Nitrogen-Doped Graphene As Cathode Catalyst for Anion Exchange Membrane Fuel Cell

Polymer electrolyte membrane fuel cells (FC) are devices in which electricity is produced via chemical reaction. Most often, hydrogen and oxygen are used as fuel and oxidizing agent in FC, respectively. Currently, proton-exchange membrane (PEM) fuel cells have already found applications for example in fuel cell electric vehicles, although the high Pt loading needed on the PEMFCs cathode for the oxygen reduction reaction (ORR) makes these devices expensive. Thus, anion-exchange membrane (AEM) FCs have been considered as an alternative technology to PEMFC especially in terms of the price, since Pt-free (e.g. metal-nitrogen/carbon) catalysts have shown promising ORR results in alkaline conditions. But not so many M-N/C materials have been tested in single-cell AEMFC test-systems because of the lack of commercially available AEM with high conductivity and stability as well as high performance anion exchange ionomers that has hold back the real era of AEMFCs.1 In recent years, great progress in the field of AEMs has been made.2 Thus, in this study, a simple synthesis procedure was used to prepare an active ORR catalyst based on Fe,N-graphene for AEMFC application.3 The synthesis of the catalyst involved the mixing of 1,10-phenanthroline, iron(II)acetate, polyvinylpyrrolidone and graphene (GRA) or graphene oxide (GO) followed by a high temperature pyrolysis. According to the different physico-chemical analyses including but not limited to X-ray photoelectron spectroscopy (XPS), 57Fe Mössbauer spectroscopy and inductively coupled plasma mass spectrometry (ICP-MS), the doping procedure was successful because both synthesized materials (Fe-N-GO and Fe-N-Gra) contained Fe and nitrogen moieties and showed better ORR performance than the undoped materials. Furthermore, the half-cell experiments conducted by using the rotating disc electrode (RDE) method revealed that Fe-N-Gra exhibited much higher ORR electrocatalytic activity in terms of onset potential and half-wave potential than Fe-N-GO in alkaline medium. This is attributed to the higher surface area, micro-/mesoporous nature and larger amount of Fe-Nx moieties present in Fe-N-Gra compared to Fe-N-GO, as shown by different physico-chemical methods. Almost half of the iron was confirmed to be in highly active Fe-Nx form by 57Fe Mössbauer spectroscopy (Fig. 1a). Based on these results, the Fe-N-Gra as ORR catalyst was further selected to apply this for AEMFC test using hexamethyl-p-terphenyl poly(benzimidazolium) (HMT-PMBI) anion-exchange membrane.4 The performance of the AEMFC single-test with Fe-N-Gra as cathode was very promising. Namely, the peak power density (P max) for Fe-N-Gra was 243 mW cm–2 (Fig. 1b),3 which is a quite good result compared to the ones published in the literature. References A. Sarapuu, E. Kibena-Põldsepp, M. Borghei, and K. Tammeveski, J. Mater. Chem. A, 6, 776 (2018). D. R. Dekel, J. Power Sources, 375, 158–169 (2018). R. Sibul, E. Kibena-Põldsepp, S. Ratso, M. Kook, M. T. Sougrati, M. Käärik, M. Merisalu, J. Aruväli, P. Paiste, A. Treshchalov, J. Leis, V. Kisand, V. Sammelselg, S. Holdcroft, F. Jaouen, and K. Tammeveski, ChemElectroChem, 7, 1739–1747 (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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