(437c) Multicomponent Transport of Water and Methanol in Nafion®

Authors: 
Elabd, Y. A. - Presenter, Department of Chemical Engineering, Drexel University
Hallinan, D. T. Jr. - Presenter, University of California, Berkeley


Fuel cells offer an innovative and environmentally benign alternative to current power sources; however, increasing current fuel cell efficiencies requires new polymer electrolyte membranes (PEMs) (i.e., Nafion® replacements) with higher proton conductivities at higher temperatures, adequate water management, and reduced fuel crossover. In all of these areas, a fundamental understanding of multicomponent transport of molecules and ions in PEMs is desired for advancing fuel cell research. Specifically, for the direct methanol fuel cell (DMFC), methanol crossover is a critical concern as it deters both fuel efficiency and power output by interfering with the cathode reduction reaction. In this study, the multicomponent transport of water and methanol in Nafion® was investigated using time-resolved Fourier-transform infrared, attenuated total reflectance (FTIR-ATR) spectroscopy. This technique not only provides molecular-level contrast between diffusants and polymers in real time, but also can measure chemical interactions between diffusants and polymers through shifts in the infrared spectra. Characteristic infrared frequencies associated with water, methanol, and the polymer membrane were identified and quantified at each time step. Water and methanol diffusion and polymer relaxation were measured simultaneously for a range of methanol concentrations. Furthermore, transient interactions between both diffusants and the polymer membrane were observed via changes in infrared band shape and location. These experiments were coupled with classic gravimetric sorption and permeation techniques to elucidate the methanol crossover phenomena in PEMs.