The effect of additives on the ionic conductivity performances of perfluoroalkyl sulfonated ionomer membranes

Improvements of ionic conductivity of perfluoroalkyl sulfonated polymer mem branes by a film recasting method with several kinds of additives are repor ted. Nafion film was liquefied by dissolving in ethanol/water (50/50) at 23 0 degrees C in a high pressure vessel to make a 10% polymer solution. This solution was cast on a glass petri dish with a solvent dimethylformamide, t ogether with some additives, and the film was dried in an oven at 70 degree s C for 2 h, then at 130-150 degrees C in a vacuum. The resulting film was cut and mounted on an electrochemical cell for AC impedance measurements. T he conductivity of the films was compared with that of original Nafion in d ry and wet states. The effective increase in ionic conductivity was observe d for three kinds of additives: the moisture absorbing reagents such as mol ecular sieve, organic sulfonate compounds such as alkylbenzene sulfonates, and structure aligning copolymers with ion exchange sites. These results of fered supporting data to the criteria for designing high performance ion co nducting membranes, which were proposed in a previous study based on the io n and water transport model in Nafion membranes [1]. (C) 1999 Published by Elsevier Science B.V. All rights reserved.