Ion and Water Transport Characteristics of Perfluorosulfonated Ionomer Membranes with H⁺ and Alkali Metal Cations

Abstract

Ion and water transport characteristics of Nafion ionomer membranes were investigated systematically in the mixed cation form of H+ and various kinds of alkali metal cation systems, which were prepared by equilibrating the membranes in the mixtures of HCl and alkali chloride in aqueous solutions of various mixing ratios. The membrane cationic composition showed that cations of larger atomic number had a higher affinity to sulfonic acid groups but less water content in the membrane than those of smaller atomic numbers. The net ionic conductivity was decreased, in any case, by the presence of alkali metal cations in the membrane. Different kinds of the interaction mode among cations were observed between H/Li or H/Na systems and H/K, H/Rb, or H/Cs systems. The interaction between alkali metal cations appeared to increase as the atomic number of the alkali metal cation increased. The water transference coefficient (electro-osmosis drag coefficient) increased from 2.5 to more than 10 by the presence of alkali metal cations. In the mixed systems, these cations were found to cause less water molecule drag than in the case of individual ions, in the presence of H+ ion. Overall, the transport characteristics of H+ and alkali metal cations influenced each other by way of the water molecules when they coexist in the membrane.

Mathematical Modelling of Cation Contamination in a Proton‐exchange Membrane

“…Finally, the net water flux per proton flux (i.e., proportional to the current density) in the membrane, b, is plotted as a function of y KM h i for various current densities in Figure 4. A value of 2.92 is observed regardless of the current density value for a pure proton membrane, which is close to that observed in the literature for the electro-osmotic coefficient for a liquid-equilibrated membrane [10,15]. In this simulation, the water back-flux is not significant since both sides of the membrane are in contact with a unit water-activity reservoir and water is not being generated as it would in a PEFC.…”

“…b is a constant taken equal to -151 J mol -1 [10]. As there are three unknown flux densities, one needs three material balances, which are of the form…”

“…The hydrogen partial pressures on both electrodes are set to 1 bar. [10]. See reference [12] for a more indepth explanation of the regression.…”

Dynamic model of ion and water transport in ionic polymer-metal composites

“…For Na + type Nafion-117 membrane, the range of K is about 3.4 ∼ 32 × 10 −18 (m 2 /(s · Pa)). 48,50 Assuming the solution in IPMCs is ideal dilute, it can be obtained the improved NP equations from Eq. (22) …”

Miniature Biofuel Cells with Improved Stability Under Continuous Operation

“…Nafion membrane is a cation exchange membrane, which serves to transport protons from the anode to the cathode. However, it has long been known that other cations also have an affinity for the membrane [15,16]. For example, the Na þ from the Na-PBS buffer can compete with protons for anionic sulfonic sites within the membrane pores, impeding the passage of protons from the anode to the cathode and decreasing the cell performance.…”