The Influence of Argon, Air and Hydrogen Gas on Thermal Conductivity of Gas Diffusion Layers and Temperature Gradients in PEMFCS

Abstract

Many renewable electricity sources (e.g., wind and solar) are intermittent, and in many cases peak production does not align with peak consumption. One way to store this excess renewable energy is by means of hydrogen gas through the process of water electrolysis. The stored energy in hydrogen gas can be recovered with a fuel cell when needed. [1] This way fuel cells can be an energy buffer and help to stabilize power systems based on renewable energy sources. A proton exchange membrane fuel cell (PEMFC) consists of several components. The membrane electrode assembly (MEA) is sandwiched between gas diffusion layers (GDLs) on each side. GDLs in fuel cells have to satisfy a range of conflicting demands. They must deliver good mass transport, but also good electrical and thermal transport. In this work the thermal conductivity of two commercial GDLs was measured with either hydrogen, air, or argon present inside their pores. The results show an increase of up to 19% with regard to the thermal conductivity for the Freudenberg H1410 GDL with hydrogen present in the pores as opposed to measurements with air present. The thermal conductivity in the Sigracet 10BA GDL was also enhanced, with an increase of 15% with hydrogen present in the pores. This correlates with the thermal conductivity of hydrogen gas, which is higher than that of air. Furthermore, the results suggest that the GDL materials have a lower thermal conductivity with argon gas present in the pores. The thermal conductivity for Freudenberg H1410 increased from 0.119 ± 0.011 WK-1m-1 for air to a thermal conductivity of 0.140 ± 0.015 WK-1m-1 for hydrogen gas at a compaction pressure of 10 bar. The thermal conductivity of Sigracet 10BA increased from 0.30 ± 0.05 WK-1m-1 for air to a thermal conductivity of 0.32 ± 0.03 WK-1m-1 for hydrogen gas at a compaction pressure of 10 bar. These results suggest that the gas present in the pores has a significant influence on the thermal conductivity of the GDL. Additionally, a 2D thermal model has been constructed to represent the impact of the results on the temperature distribution inside a fuel cell, see figure 1. The considerable temperature gradients inside the single cells need to be considered when assessing lifetime and degradation effects [1-4]. Judging by the scarcity of data on this in the literature this is not the case as of today. Figure 1: PEMFC land temperature profiles saturated with air, argon, or hydrogen on the anode side. The dashed vertical lines represent the border between different materials in the MEA References [1] O. S. Burheim, Engineering Energy Storage, 1st edition, Academic Press, 2017. [2] R. Bock, A.D. Shum, X. Xiao, H. Karoliussen, F. Seland, I.V. Zenyuk and O.S. Burheim, Thermal conductivity and compaction of GDL-MPL interfacial composite material, J. Electrochem. Soc. 2018 165(7): F514-F525 [3] R. Bock, H. Karoliussen, B. G. Pollet, M. Secanell, F. Seland, D. Stanier and O. S. Burheim, The influence of graphitization on the thermal conductivity of catalyst layers and temperature gradients in proton exchange membrane fuel cells, International Journal of Hydrogen Energy, In-press 2018 [4] R. Bock, A. Shum, T. Khoza, F. Seland, N. Hussain, I. V Zenyuk and O. S. Burheim Experimental Study of Thermal Conductivity and Compression Measurements of the GDL-MPL Interfacial Composite Region, ECS Trans. 2016 75(14): 189-199 Figure 1