Visualization, Understanding, and Mitigation of Membrane Irregularities in Gas Diffusion Electrode-Based Polymer Electrolyte Membrane Fuel Cells

Abstract

Polymer electrolyte membrane fuel cells (PEMFCs) show great promise for their applications in electric vehicles. Most studies on PEMFCs typically use catalyst-coated membranes (CCMs); however, gas-diffusion-electrodes (GDEs) offer advantages for large-scale manufacturing with roll-to-roll coating systems. Additional procedures including hot-pressing and coating a thin ionomer overlayer are necessary in the fabrication process of GDE-based membrane electrode assemblies (MEAs) to improve the otherwise poor catalyst layer/membrane interface.1,2 However, these procedures may also introduce potential irregularities and/or defects, especially when thin membranes are used. Limited understanding exists regarding if and to what extent such irregularities impact PEMFC performance and lifetime.In this study, NREL’s custom fuel cell hardware that enables quasi in-situ infrared (IR) thermography studies3 was utilized to visualize spatial hydrogen crossover in GDE-based MEAs to identify and locate Nafion membrane irregularities. The MEA cross-sectional structure of the membrane irregularity was investigated by scanning electron microscopy (SEM) imaging. The impact of membrane irregularities on open-circuit voltage (OCV), hydrogen crossover and PEMFC initial H2/air performance was systematically studied. The effect of micro-porous layer (MPL) surface roughness of gas diffusion media (GDM) on the membrane irregularity formation mechanism was investigated. By employing GDM with a smoother MPL surface and fine tuning the MEA fabrication process, including compression force and hot-pressing temperature, membrane irregularities were successfully mitigated. Furthermore, IR assisted accelerated stress testing (IR-AST) of MEAs containing different amounts of beginning-of-test membrane irregularities was investigated. These membrane irregularities were demonstrated to be seeds of failure points and dramatically shorten the MEA lifetime. Reference: (1) Wang, M.; Medina, S.; Pfeilsticker, J. R.; Pylypenko, S.; Ulsh, M.; Mauger, S. A. Impact of Microporous Layer Roughness on Gas-Diffusion-Electrode-Based Polymer Electrolyte Membrane Fuel Cell Performance. ACS Appl. Energy Mater. 2019, 2 (11), 7757–7761. https://doi.org/10.1021/acsaem.9b01871.(2) Mauger, S. A.; Pfeilsticker, J. R.; Wang, M.; Medina, S.; Yang-Neyerlin, A. C.; Neyerlin, K. C.; Stetson, C.; Pylypenko, S.; Ulsh, M. Fabrication of High-Performance Gas-Diffusion-Electrode Based Membrane-Electrode Assemblies. J. Power Sources 2020, 450, 227581. https://doi.org/https://doi.org/10.1016/j.jpowsour.2019.227581.(3) Phillips, A.; Ulsh, M.; Neyerlin, K. C.; Porter, J.; Bender, G. Impacts of Electrode Coating Irregularities on Polymer Electrolyte Membrane Fuel Cell Lifetime Using Quasi In-Situ Infrared Thermography and Accelerated Stress Testing. Int. J. Hydrogen Energy 2018, 43 (12), 6390–6399. https://doi.org/https://doi.org/10.1016/j.ijhydene.2018.02.050. Figure 1