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Self-diffusion of ions in Nafion-117 membrane having mixed ionic composition
Sanhita Chaudhury1, Chhavi Agarwal, A K Pandey
1Radiochemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085, India.
The Journal of Physical Chemistry. B
|January 10, 2012
Summary
Self-diffusion coefficients (SDCs) for Na(+), Cs(+), and Ba(2+) in Nafion-117 membranes were studied. Ion transport behavior varied significantly, particularly for Ba(2+) in mixed Na(+)-Ba(2+) and Ag(+)-Ba(2+) systems.
Area of Science:
- Materials Science
- Electrochemistry
- Polymer Science
Background:
- Nafion-117 is a perfluorinated ionomer membrane widely used in electrochemical applications.
- Understanding cation transport in mixed-cationic Nafion membranes is crucial for optimizing performance in devices like fuel cells.
- Previous studies have focused on single-cation systems, leaving mixed-cation behavior less understood.
Purpose of the Study:
- To determine the self-diffusion coefficients (SDCs) of Na(+), Cs(+), and Ba(2+) in Nafion-117 membranes with various mixed cationic compositions.
- To investigate the influence of ionic composition on cation mobility and membrane conductivity.
- To elucidate the underlying mechanisms governing cation transport in different mixed-cation systems.
Main Methods:
- Preparation of Nafion-117 membranes with controlled mixed cationic compositions (Na(+)-Cs(+), Cs(+)-Ba(2+), Na(+)-Ba(2+), Ag(+)-Ba(2+)) via ion exchange.
- Determination of SDCs using a radiotracer technique.
- Measurement of membrane specific conductivity using AC impedance spectroscopy.
Main Results:
- SDCs of cations were independent of ionic composition in Na-Cs and Cs-Ba systems.
- In Na-Ba and Ag-Ba systems, Ba(2+) SDCs decreased significantly with increasing Na(+) or Ag(+) content, respectively.
- Membrane conductivity showed a parabolic increase with Na(+) content in Na-Ba systems, contrasting with a linear increase in Na-Cs systems.
Conclusions:
- Cation transport mechanisms in Nafion-117 are strongly dependent on the specific combination of cations present.
- The observed differences in SDCs and conductivity are attributed to variations in cation transport pathways influenced by ionic composition.
- This study provides fundamental insights into ion transport in complex Nafion membrane systems, relevant for advanced material design.
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