Influence of Ink Composition and Operation Parameters on the Performance of Fe-N-C

Abstract

The application of proton exchange fuel cells (PEFCs) in the automotive sector is rising to be an alternative to petroleum fuel based transportation. Nevertheless, the obstacle of cost reduction of the PEFC remains, which is due to highly expensive Pt catalysts on the cathode side for oxygen reduction reaction (ORR).[1] A possible way to substitute Pt for ORR is the use of Fe-N-C-catalysts which have been shown to be a promising option.[2] For Fe-N-C-catalysts the required catalyst loading needs to be significantly higher than for Pt-based catalysts in order to achieve sufficient current densities. This leads to a change in catalyst layer thickness of roughly one order of magnitude where transport phenomena of gases and liquids become more important.[3] Based on this, the gap between Pt/C and Fe-N-C at high current densities is significantly higher compared to the kinetic controlled region. Therefore, further optimization is needed in order to enhance activity also under high current flow. In addition to this, it need to be understood to what extent problems in the transport properties affect the durability behavior of Fe-N-C catalysts in fuel cells. The ionomer distribution and loading of the catalyst layer has found to be crucial for proton transport towards the active sites, but also influences the hydrophilicity of the catalysts pores which enhances gas transport resistance. [1] In addition, it has been shown that the preparation of the membrane electrode assembly (MEA) for the fuel cell plays a key role. [3] The widely used hot-pressing technique might influence the catalyst layer pore size which is also an important parameter for species transport. In this work, different catalyst to ionomer ratios are evaluated in fuel cell tests for Fe-N-C catalysts. Furthermore, the preparation by hot-pressing is investigated in respect to the application of different compression pressures. The results are brought in relation to structural investigations of the MEAs and serve for the validation of a theoretical model. [1] S. Komini Babu, et al. ACS Appl. Mater. Infertaces 2016, 8, 32764-32777 (2016) [2] U.I. Kramm, et al. J. Am. Chem. Soc., 138 (2), 635–640 (2016) [3] X. Yin, et al. ECS Transactions, 77 (11) 1273-1281 (2017) [4] S. Komini Babu, et al. Journal of The Electrochemical Society, 164 (9), F1037-F1049 (2017)