Water Dynamics in Nafion Fuel Cell Membranes: the Effects of Confinement and Structural Changes on the Hydrogen Bond Network
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- 作者：David E. Moilanen ; Ivan R. Piletic ; Michael D. Fayer
- 刊名：Journal of Physical Chemistry C
- 出版年：2007
- 出版时间：June 28, 2007
- 年：2007
- 卷：111
- 期：25
- 页码：8884 - 8891
- 全文大小：146K
- 年卷期：v.111,no.25(June 28, 2007)
- ISSN：1932-7455
文摘
The complex environments experienced by water molecules in the hydrophilic channels of Nafion membranesare studied by ultrafast infrared pump-probe spectroscopy. A wavelength-dependent study of the vibrationallifetime of the O-D stretch of dilute HOD in H2O confined in Nafion membranes provides evidence of twodistinct ensembles of water molecules. While only two ensembles are present at each level of membranehydration studied, the characteristics of the two ensembles change as the water content of the membranechanges. Time-dependent anisotropy measurements show that the orientational motions of water moleculesin Nafion membranes are significantly slower than in bulk water and that lower hydration levels result inslower orientational relaxation. Initial wavelength-dependent results for the anisotropy show no clear variationin the time scale for orientational motion across a broad range of frequencies. The anisotropy decay is analyzedusing a model based on restricted orientational diffusion within a hydrogen bond configuration followed bytotal reorientation through jump diffusion.