Polyacrylonitrile‐Derived Co or Fe Containing Nanofibre Catalysts Prepared Via Electrispinning for Alkaline Membrane Fuel Cell Cathode

Abstract

An increasing worldwide energy demand drives the need for the development of more efficient and greener energy production and storage technologies (1). In recent years, carbon nanofibres (CNFs) have drawn a lot of attention and been widely studied to address these topical problems. For example, the CNF-based materials can be employed as an oxygen reduction reaction (ORR) catalyst at the fuel cell cathode. The CNFs are appealing because of their attractive properties e.g. high specific surface area, high length/diameter ratio, specific porosities and multiple functionalities. For the preparation of CNFs, a simple and versatile technique called electrospinning can be applied (2).In our previous papers regarding CNFs, we have investigated the pyrolyzed electrospun composite materials without added transition metals as ORR catalysts in 0.1 M KOH (3, 4). For further optimization of the catalyst material ORR activity, we have now included the Co or Fe precursors to the electrospinning solution. For the first time, the Fe- or Co-containing polyacrylonitrile (PAN)-based CNFs were studied as a cathode catalyst in the anion exchange membrane fuel cell (AEMFC) (5).The composite catalyst materials were prepared via electrospinning of Iron(II) acetate or Cobalt(II) acetate containing PAN solution with and without ionic liquid (IL). The electrospun nanofibres were pyrolysed at different temperatures and acid treated. The materials consisted of CNFs with diameter from ca. 200 to 700 nm. The composition of the catalysts included C, O, N and corresponding transition metal (Fe or Co). In 0.1 M KOH solution, the best performing ORR catalyst material was Fe‐containing CNF without IL prepared at 800 °C (Fe‐PAN‐A800). The best AEMFC performance was observed for Fe‐containing CNF with IL prepared at 1000 °C. The maximum power density value of this catalyst (Fe/IL‐PAN‐A1000) was 289 mW cm−2, which was 82 % of the value obtained with the commercial Pt/C cathode catalyst (Figure 1). The reasons behind the good performance at the AEMFC cathode were considered to be high specific surface area, mesoporous CNF cross‐linked structure and the presence of ORR‐active N species and Me−Nx sites (5).References A. Sarapuu, E. Kibena-Põldsepp, M. Borghei and K. Tammeveski, Journal of Materials Chemistry A, 6, 776 (2018). A. Barhoum, K. Pal, H. Rahier, H. Uludag, I. S. Kim and M. Bechelany, Applied Materials Today, 17, 1 (2019). M. Mooste, E. Kibena-Põldsepp, L. Matisen, M. Merisalu, M. Kook, V. Kisand, V. Vassiljeva, A. Krumme, V. Sammelselg and K. Tammeveski, Catalysis Letters, 148, 1815 (2018). M. Mooste, E. Kibena-Põldsepp, V. Vassiljeva, M. Merisalu, M. Kook, A. Treshchalov, V. Kisand, M. Uibu, A. Krumme, V. Sammelselg and K. Tammeveski, Journal of Materials Science, 54, 11618 (2019). M. Mooste, E. Kibena-Põldsepp, V. Vassiljeva, A. Kikas, M. Käärik, J. Kozlova, V. Kisand, M. Külaviir, S. Cavaliere, J. Leis, A. Krumme, V. Sammelselg, S. Holdcroft and K. Tammeveski, ChemCatChem, 12, 4568 (2020). Figure 1