Role of conditioning on water uptake and hydraulic permeability of Nafion® membranes
Journal of Membrane Science(2006)
摘要
The performance of ion-exchange membranes under pressure differential conditions is important for a number of separations and for fuel cell applications. Fluid transport properties under pressure are also key to understanding electrochemically-driven pumping and pressurization systems. The physicochemical properties and performance of perfluorosulfonic acid membranes varies considerably with conditioning treatment. In this study, hydraulic permeability and water uptake are measured as a function of membrane treatment for Nafion® membranes that are contacted with aqueous electrolyte solutions. Several conditioning/contacting solution treatments are evaluated including exchanged cation, manner of cation exchange, anion effect, and heat treatment. For Nafion® 117 membranes, these treatments resulted in water content ranging from 3.8 to 20.2 water molecules/fixed sulfonate site and hydraulic permeability ranging from 3.78×10−16 to 1.79×10−13m/sPa. Similar to water uptake, a systematic decrease in hydraulic permeability is observed with the alkali series Li+>Na+>K+. Interestingly, the as-received H+ form and the Li+ form have nearly identical water content but the permeability of the H+ form is a factor of 6–7 higher than the Li+ form, regardless of heat treatment. Evaluation based on an equivalent pore model and Poiseuille flow shows good agreement for pore radii ranging from 1.0 to 2.0nm.
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关键词
Water transport,Ion-exchange membranes,Ionomer membranes
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