A Structure and Durability Comparison of Membrane Electrode Assembly Fabrication Methods: Self-Assembled Versus Hot-Pressed
Jennifer Hack, T. M. M. Heenan, F. Iacoviello, N. Mansor, Q. Meyer, P. Shearing, N. Brandon and D. J. L. Brett - Electrochemical Innovation Lab, Department of Chemical Engineering, University College London, London WC1E 7JE, United Kingdom ; Department of Earth Sciences and Engineering, Royal School of Mines, Imperial College London, London SWX WYZ, United Kingdom
The most common means of fabricating membrane electrode assemblies (MEAs) for polymer electrolyte fuel cells (PEFCs) involves a hot-press step. The conditions used to perform the hot-press impacts the performance and durability of the fuel cell.
However, the hot-press process is not essential for achieving operational MEAs and some practitioners dispense with the hot-press stage altogether by using a self-assembled approach. By performing the integration of the components in-situ during fuel cell assembly, there is the potential to lower the cost and time of manufacture. This study investigates the electrochemical performance and mechanical microstructure of MEAs that were either hot-pressed or self-assembled (non-hot-pressed) and compared at beginning-of-test (BOT) and end-of-test (EOT), following accelerated stress testing. Hot-pressed and self-assembled MEAs were found to show negligible difference in their performance and almost identical performance degradation. X-ray computed tomography (X-ray CT) showed distinct differences in the microstructure of the electrodes. In addition to a crack network in the catalyst layer, the self-assembled samples exhibit indentations that were not present in the hot-pressed sample. It was concluded that in-situ assembly of MEAs could be a suitable means of fabricating PEFC MEAs.
How Amira-Avizo Software is used
Post-processing was carried out using Avizo software (Avizo, Thermo Fisher Scientific, Waltham Massachusetts, USA), by cropping each dataset to a 400 μm × 400 μm × 345 μm interfacial subvolume. Each dataset was then manually segmented into five phases using the ‘magic wand’ tool according to the material grayscale values: pore, GDLs, cathode CL, Nafion and anode CL. The GDL phases consist of all fibers, PTFE additive and MPL, since the similarity of grayscale values of the MPL and fibers meant that segmentation of these two phases was not possible. Because the CLs are the main focus of this study, the GDLs were not separated into the constituent anode and cathode GDL phases. The 3D structures of the materials were visualized using volume renderings of the segmented phases, to give an appreciation of the layers of the MEA in each sample. These are accompanied by solid-pore percentage compositions quantified by the average volume of a slice-by-slice analysis of each material, in each sample, to ensure sufficient statistical representation.