Dynamics of Fe Cations in Nafion Membranes Studied by Nuclear Resonant Quasielastic Scattering of Synchrotron Radiation : Condensed Matter: Electronic Properties, etc.

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Nuclear resonant quasielastic scattering from ferrous cations in ion-exchange Nafion membranes was measured at room temperature, and the intrinsic dynamics of the cations inside the spherical regions surrounded by the sulfonic groups of Nafion was studied. For the analysis, the formula of nuclear resonant absorption for a particle diffusing in a sphere with an impermeable surface was derived. The formula indicates that the effect of the surface upon the diffusive motion is small if the radius of the sphere is larger than a critical value; in the case of ^<57>Fe ions, the value is about 2 Å. As the radius of the spherical regions in our Nafion samples is estimated to be about 5 Å, the existence of the surface can be ignored and the intrinsic dynamics of Fe cations can be extracted. The diffusion coefficient estimated from the least squares fit was (1.12 ± 0.13) × 10^<-5> cm^2/s for 15 wt% water content. This value is in good agreement with that of Fe cations in an HCI solution. As a result, Fe cations in Nafion diffuse as freely as those in solutions.
社団法人日本物理学会の論文
2000-12-15