Microstructure Simulation and Virtual Material Design of Electrospun Gas Diffusion Layers for Polymer Electrolyte Membrane Fuel Cells

Abstract

Polymer electrolyte membrane fuel cells (PEM-FC) are promising electrochemical devices for the production of electrical power without local emissions of CO2. In the PEM-FC, hydrogen and oxygen electrochemically react to produce water and heat. The generated liquid water is necessary for protonic conductivity in the electrolyte membrane, but excess liquid water hinders reactant gas diffusion from the gas flow channels to the reaction sites. Therefore, effective water management is vital for achieving high power density with PEM-FCs. In this context, a well-designed gas diffusion layer (GDL) must simultaneously facilitate the transport of reactants, excess liquid water, electrons, and heat. Here, we present a characterization of electrospun gas diffusion layers (eGDL) as a new material used in PEM-FCs [1]. Compared to conventional GDL materials such as carbon paper (e.g. Toray-H-60) with fiber diameters in the range of 7 to 10 micrometers [2], the fiber diameters of the eGDL materials are in the range of 150 to 600 nanometers only. While the improved performance of the PEM-FC with eGDLs has been shown in experiments [1], we describe the eGDL properties based on its micro-structure. The basis of this characterisation is the virtual material design as in [3,4]. Based on 2D microscopic images of the eGDL, its 3D structure is reconstructed as stochastically overlapping straight fibers with appropriate orientation. Given the bulk geometric properties of the fibers, we calculate single and multiphase properties by solving the appropriate partial differential equations. Examples of these parameters are the thermal and electrical conductivity, the diffusivity, and the capillary pressure-saturation curves. Finally, the determined parameters are used as inputs to a 1D PEM-FC model and the modeling results are compared to experimental data. REFERENCES [1] Chevalier, S.; Lavielle, N.; Hatton, B. D.; Bazylak, A. (2017). Novel electrospun gas diffusion layers for polymer electrolyte membrane fuel cells: Part I. Fabrication, morphological characterization, and in situ performance, Journal of Power Sources, Vol. 352, 272–280. doi:10.1016/j.jpowsour.2017.03.098 [2] Mathias, M.; Roth, J.; Fleming, J.; Lehnert, W.L. (2003). Handbook of Fuel Cells: Fundamentals, Technology, and Applications. John Wiley & Sons, Hoboken, NJ. [3] Schulz, V. P.; Becker, J.; Wiegmann, A.; Mukherjee, P. P.; Wang, C.-Y. (2007). Modeling of Two-Phase Behavior in the Gas Diffusion Medium of PEFCs via Full Morphology Approach, Journal of The Electrochemical Society, Vol. 154, No. 4, B419. doi:10.1149/1.2472547 [4] Wargo, E. A.; Schulz, V. P.; Çeçen, A.; Kalidindi, S. R.; Kumbur, E. C. (2013). Resolving macro- and micro-porous layer interaction in polymer electrolyte fuel cells using focused ion beam and X-ray computed tomography, Electrochimica Acta, Vol. 87, 201–212. doi:10.1016/j.electacta.2012.09.008 Figure 1