Nafion Nanothin Films

In the conventional catalyst layer of polymer electrolyte fuel cells, the ionomer (e.g. Nafion) exists as an ultra-thin film (4-10 nm thick) coating the Pt/C catalyst aggregates. Recent studies [1-12], including those from our group, have begun to investigate the properties and structure of such thin ionomer films. Thickness-dependent properties including proton conduction (7, 11), wettability of free-surface(5), water uptake (2, 6) and water diffusivity (9) of such ultra-thin ionomer films have been observed. The influence of substrate and processing method has also been observed (12). A number of the properties of the thin ionomer films differ significantly from the much thicker counterpart, i.e. the free film or bulk ionomer membrane. The nanostructure of these films are less understood. And, although indirect methods such as x-ray reflectivity (1) and grazing incidence (2) small angle x-ray scattering (GISAXS) have been employed a clear picture of the nanostructure of these thin films has not emerged.

The presentation will summarize the current understanding of ionomer thin film structure and properties. Results of recent and ongoing work on direct imaging of thin Nafion films to probe the nano-features of the phase-segregated morphology will be presented. Results of thermal behavior of thin films investigated using in-situ thermal ellipsometry will also be presented.

 Reference:

1. A. Dura et al.,  Macromolecules 42 (2009), 4769-4774.
2. M.A. Modestino et al.,  Macromolecules 2013, 46 (3), pp 867–873, 2013
3. M. Bass et al., Macromolecules 44 (2011), 2893–2899.
4. Dishari, K. S.; Hickner, A. M. ACS Macro Lett., 1 (2012), 291-295.
5. D.K Paul et al., Macromolecules, 46 (2013), 3461–3475
6. A. Kongkanand J. Phys. Chem. C, 115 (2011) 11318–11325.
7. D.K. Paul, D. K Electrochem. Comm., 13 (2011), 774-777.
8. A. Modestino et al., Macromolecules, 45 (2012), 4681–4688.
9. S.A. Eastman, Macromolecules, 45 (2012), 7920−7930.
10. D.K. Paul and K. Karan J. Phys. Chem. C, 118 (2014), 1828–1835.
11. D.K. Paul et al., J. Electrochem. Soc., 161 (2014), F1395-F1402
12. A. Kusoglu et al Adv. Funct. Mater. 2014, 24 (30), 4763-4774