Diffusion and interfacial transport of water in Nafion

Qiao Zhao, Paul Majsztrik, Jay Benziger

Research output: Contribution to journalArticlepeer-review

164 Scopus citations

Abstract

Water absorption, membrane swelling, and self-diffusivity of water in 1100 equivalent weight Nafion were measured as functions of temperature and water activity. Free volume per water at 80 °C, determined from water uptake and volume expansion data, decreases with water content in the membrane from 12 cm3/mol at λ = 0.5 H2O/SO3 to 1.5 cm3/mol at λ = 4. The change in free volume with water content displays a transition at λ = 4. Limiting water self-diffusivity in Nafion was determined by pulsed gradient spin echo NMR at long delay times. The limiting self-diffusivity increases exponentially with water activity; the rate of increase of diffusivity with water content shows a transition at λ = 4. The tortuosity of the hydrophilic domains in Nafion decreased from 20 at low membrane water activity to 3 at λ = 4. It suggested a change in the connectivity of the hydrophilic domains absorbed water occurs at λ ∼ 4. The diffusivity results were employed to separate the contributions of diffusional and interfacial resistance for water transport across Nafion membranes, which enabled the determination of the interfacial mass transport coefficients. A diffusion model was developed which incorporated activity-dependent diffusivity, volume expansion, and the interfacial resistance, and was used to resolve the water activity profiles in the membrane.

Original languageEnglish (US)
Pages (from-to)2717-2727
Number of pages11
JournalJournal of Physical Chemistry B
Volume115
Issue number12
DOIs
StatePublished - Mar 31 2011

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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