期刊
ADVANCED FUNCTIONAL MATERIALS
卷 29, 期 37, 页码 -出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adfm.201902699
关键词
confinement; functional coating; Nafion; orientation; thin films
类别
资金
- U. S. Department of Energy
- Office of Energy Efficiency and Renewable Energy
- Fuel Cells Technology Program from General Motors Corporation [DE-EE0000470]
- Office of Naval Research [N00014-10-1-0875]
- U. S. Army Research Office [W911NF-11-1-0411]
- Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy [DE-AC02-05CH11231]
- Fuel Cell Technologies Office, Energy Efficiency and Renewable Energy Office, of the U.S. Department of Energy (DOE) [DE-AC02-05CH11231]
- Corning Foundation
- Corning Faculty Fellowship in Materials Science and Engineering
The effects of film thickness and substrate composition on the ionomer structure in porous electrodes are critical in understanding pathways toward developing higher performance electrochemical devices, including fuel cells and batteries. Insights are gained into the molecular and nanostructural orientation dependence for thin Nafion films (12-300 nm thick) on gold, platinum, and SiO2 model substrates. Molecular orientation is determined from the birefringence measured using spectroscopic ellipsometry, while the nanostructural orientation of the ionic domains is measured using grazing-incidence small-angle X-ray scattering. Density functional theory calculations for the molecular polarizability of the Nafion backbone and side chain show complimentary contributions to the measured birefringence values for the material. Nafion films prepared on SiO2 substrates exhibit a nearly isotropic molecular and nanostructural orientation. Films on gold and platinum display parallel backbone orientations, relative to the substrate, with decreasing film thickness. However, a birefringence transition toward molecular isotropy is observed for 30 nm thick films on Au and Pt; while the ionic nanostructured domains continuously align parallel to the substrate. This apparent isotropic molecular orientation with increasing domain orientation highlights the difference between the backbone and side chain orientation, a key finding for elucidating transport in confined films at the interfaces.
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