Simple Polypyrrole Based Preparation for Fe-N-C Catalysts for the Oxygen Reduction Reaction

Abstract

Hydrogen based fuel cells could play an imprtant role for future CO2-free energy supply, especially with respect to the transportation and automotive sector. However, efficient fuel cell catalyst mostly rely on the precious metal platinum. The contributions of platinum based catalysts and their application are estimated with up to 40% of the overall stack costs [1], [2]. Furthermore, taking into account the released CO2 equivalents, soil acidification and fresh water consumption the mining and production of precious metals leaves a great ecological foot-print [3].FeNC catalysts are a promising alternative to replace platinum for the oxygen reduction reaction. However, still several challenges need to be faced. A low voumetric activity, a poor long-term stability in the device and difficuilties during scale-up of the preparation procedure are the main issues. Especially for the high performing catalysts that are based on zeolitic imidazolate frameworks (ZIFs) [4], [5], the scale-up of the ZIF synthesis and subsequent FeNC preparation seems difficuilt while maintaining the same material properties [6], [7].Here, we present a simple prepration for FeNC catalysts that relys on nanostructured polypyrrole. Because the presented method is based on a simple polymer the scale-up seems easier in realizationWe will discuss the impact of different aspects as amount and kind of iron precursor, level and kind of doping agents, and pyrolysis temperature and their impact on fuel cell performance data and structural composition. The variation of these aspects leads to significant variation in structural composition, activity, selectivity and stability of these catalysts. For example, very low levels of hydrogen peroxide formation are found even for low catalyst loadings during RRDE [8]. Further, by an increase of the pyrolsis temperature from 800°C to 1000°C the retained current density after 50 hours of potentiastatic testing at 0.5 V could be increased by a factor of 1.6.[1] S.T. Thompson, D. Papageorgopoulos, Platinum group metal-free catalysts boost cost competitiveness of fuel cell vehicles, Nat Catal, 2 (2019) 558-561. [2] A.R. Wilson, J.P. Marcinkoski, D., Fuel Cell System Cost, DOE Hydrogen and Fuel Cells Program Record, in Departement of Energy, 2016. [3] P. Nuss and M.J. Eckelmann, PLOS one, Vol. 7 Life Cycle Assessment of Metals: A Scientific Synthesis, 2014. [4] E. Proietti, F. Jaouen, M. Lefevre, N. Larouche, J. Tian, J. Herranz, J.-P. Dodelet, Nature Commun., 2, 416, 2011. [5] D. Zhao, J.-L. Shui, L. R. Grabstanowicz, C. Chen, S. M. Comment, T. Xu, J. Lu, D.-J. Liu, Adv. Mater., 26, 7, 2013. [6] M. Hovestadt, J. Vargas Schmitz, T. Weissenberger, F. Reif, M. Kaspereit, W. Schwieger, M. Hartmann, Scale-up of the Synthesis of Zeolitic Imidazolate Framework ZIF-4, Chem-Ing-Tech, 89 (2017) 1374-1378. [7] T. Johnson, M.M. Lozinska, A.F. Orsi, P.A. Wright, S. Hindocha, S. Poulston, Improvements to the production of ZIF-94; a case study in MOF scale-up, Green Chem, 21 (2019) 5665-5670. [8] L. Ni, C. Gallenkamp, S. Paul, M. Kübler, P. Theis, S. Chabbra, K. Hofmann, E. Bill, A. Schnegg, B. Albert, V. Krewald, U. I. Kramm, Active Site Identification in FeNC Catalysts and Their Assignment to the Oxygen Reduction Reaction Pathway by In Situ 57Fe Mössbauer Spectroscopy, Adv. Energy Sustainability Res., 2, 2021