Comparison of Graphites as Micro Porous Layer Materials for Polymer Electrolyte Fuel Cells

To date, Micro Porous layer (MPL) fabrication has relied heavily on the use of carbon black. Macroporosity engineering is increasingly employed to enhance water drainage under high current density conditions; such engineering is typically realized through advanced MPL processing or the incorporation of exotic carbon structures. Graphite as an MPL precursor remains an underexplored base material and may be a highly tunable and affordable alternative. Here, MPLs made of three different graphites are prepared through coating on commercial Gas Diffusion Layers (GDLs) and characterized using ex-situ and in-situ experimental techniques. Two commercial materials are tested, acting as a comparison with state-of-the-art materials. Ex-situ characterization includes various imaging techniques for studying the MPLs morphology, conductivity measurements, air permeability measurements, porosity scanning, and mercury intrusion porosimetry. By combining ex-situ results with fuel cell testing, operated on a 5 cm 2 active area cell under differential conditions, it was possible to characterize the different MPLs under different wet conditions and estimate how the structural properties of the MPL affect performance. The results indicate that an increase in average porosity does not necessarily improve performance, and suggest that the presence of a preferential pore size may be more critical for enhancing gas transport and liquid water removal. Furthermore, the findings demonstrate that a graphite-based MPL can outperform state-of-the-art materials.