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In-Situ Method for Measuring the Mechanical Properties of Nafion Thin Films during Hydration Cycles

Published

Author(s)

Kirt A. Page, Jae W. Shin, Scott Eastman, Brandon W. Rowe, Sangcheol Kim, Ahmet Kusoglu, Kevin G. Yager, Gery R. Stafford

Abstract

Perfluorinated ionomers, in particular Nafion, are an essential component in hydrogen fuel cells, as both the proton exchange membrane and the binder within the catalyst layer. During normal operation of a hydrogen fuel cell the ionomer will progressively swell and de-swell in response to the changes in hydration, resulting in a mechanical fatigue and ultimately failure with time. In this study we have developed and implemented a cantilever bending technique in order to investigate the swelling- induced stresses in biaxially constrained Nafion thin films. By monitoring the deflection of a cantilever beam coated with a polymer film as it is exposed to varying humidity environments, the swelling induced stress-thickness of the polymer film can be measured. By combining the stress-thickness results with a measurement of the swelling strain as a function of humidity, by quartz crystal microbalance (QCM) and x-ray reflectivity (XR), the swelling stress can be determined. Using this technique we can further estimate the Young's modulus of thin Nafion films as a function of relative humidity. The resulting modulus values indicate orientation of the ionic domains within the polymer films which was confirmed by grazing incidence small angle x-ray scattering (GISAXS). This study represents a measurement platform that can be expanded to incorporate novel ionomer systems and fuel cell components to mimic the stress state of a working hydrogen fuel cell.
Citation
ACS Applied Materials and Interfaces

Keywords

stress, thin films, Nafion, curvature, modulus, humidity

Citation

Page, K. , Shin, J. , Eastman, S. , Rowe, B. , Kim, S. , Kusoglu, A. , Yager, K. and Stafford, G. (2015), In-Situ Method for Measuring the Mechanical Properties of Nafion Thin Films during Hydration Cycles, ACS Applied Materials and Interfaces (Accessed April 19, 2024)
Created August 14, 2015, Updated October 12, 2021