Abstract
Differentiating between the various polytetrafluoroethylene based structures inside polymer electrolyte membrane fuel cells with a degree of certainty is necessary to optimize manufacturing processes and to investigate possible degradation mechanisms. We have developed a novel method using fluorescence microscopy for distinguishing the origin and location of PTFE and/or Nafion® in Membrane Electrode assemblies and the gas diffusion media from different sources and stages of processing. Fluorescent material was successfully diffused into the PTFE based structures in the GDM by addition to the ‘ink’ precursor for both the microporous layer and the catalyst layer; this made it possible to map separately both layers in a way that has not been reported before. It was found that hot pressing of membrane coated structures resulted in physical dispersion of those layers away from the membrane into the GDM itself. This fluorescence technique should be of interest to membrane electrode assembly manufacturers and fuel cell developers and could be used to track the degradation of different PTFE structures independently in the future.
Highlights
Polytetrafluoroethylene (PTFE) based polymers play several important roles in polymer electrolyte membrane fuel cells (PEMFCs)
PTFE based polymers are used as hydrophobic coatings on carbon fibers, binder agents for catalyst layer (CL) inks, to provide structural integrity for microporous layers (MPL) and as an adhesive binder for the various layers that form the final membrane electrode assembly (MEA)
Numeric assessment of the two separate PTFE layers (MPL and CL) in this sample was impossible when based on Fluorine internationaljournalofhydrogenenergy 4 1 ( 2 0 1 6 ) 1 7 6 3 1 e1 7 6 4 3 converted to ‘black’ or ‘white’ is set at 50% of the total brightness of all pixels in the equivalent grayscale image
Summary
Polytetrafluoroethylene (PTFE) based polymers play several important roles in polymer electrolyte membrane fuel cells (PEMFCs). This is reliant on the assumptions that the platinum doped carbon particles are uniformly spread through region of interest, and that the PTFE based polymers used in the MPL ‘ink’ are dispersed throughout the material in the same way This ‘functionalized’ MPL is equivalent to the dual layer catalyst systems suggested by some researchers [15e18], and according to their finding it must be acknowledged that fuel cell performance is changed by this approach. To date there has been no work done to assess the interaction of catalyst ink formulations and their impact on PTFE distributions in the GDM or CCS type fuel cell assemblies This is due to the inability of SEM/EDX techniques in generating clear separation of the elemental species in the carbon based fibers, the carbon based catalyst inks, the carbon (PTFE) based GDM binder agents and the Carbon (PTFE) based catalyst ink suspensions. Higher weight percentages generated a more complete coverage of the GDM surface as shown in figures (c & d)
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