Vibrational Spectroscopy and 2D Correlation Analysis as a Probe of Structure in Ionomer Membrane Materials

Abstract

Infrared and Raman spectroscopy are being applied to gain insights into ionomer membrane properties and the structure and content of water inside membrane pores and channels. In one area of focus, infrared bands associated with interfacial water molecules are being examined. The high internal surface area of materials, such as Nafion 112, enables water interacting with interfaces inside membrane pores and channels to be detected with the use of simple infrared sampling methods. Water structure is probed through measurements on H2O/D2O mixtures in combination with classical vibrational calculations and electronic structure simulations. Additionally, infrared spectroscopy is being investigated as a simple method for determining membrane water content. A combination band associated with vibrations of -CF groups is used as an internal standard. Efforts in applying the approach to compare differences in water uptake by fluorinated ionomer materials prepared with and without inorganic filler materials will be discussed. A second area is focused on Raman spectroscopy as a probe of ionomer framework structure. The potential for in situ Raman measurements in fuel cell systems and depth profiling within membrane via confocal methods is motivating basic studies of membrane structure through Raman measurements on ionomer materials. Early results that indicate the performance of UV Raman will be presented.