Investigation of the effects of electric fields on the nanostructure of Nafion and its proton conductivity

Abstract

Nafion, the most popular cation exchange membrane, was cast while charged in an electric field to enhance the proton conductivity of the membrane. This electrically modified Nafion shows dramatically increased conductivity compared to the pristine membrane. The enhancement of proton conductivity is a result of changes in the membrane nanostructure, as shown by transmission electron microscopy, X-ray diffraction, and Fourier transform-IR spectroscopy. In particular, the membrane crystallinity was increased by 7% in the electrically modified membrane. As a result of the structural changes, the conductivities were enhanced from 0.137 to 0.231 S cm⁻¹ in the in-plane aligned membrane and from 0.111 to 0.276 S cm⁻¹ in the through-plane aligned membrane. Furthermore, the through-plane conductivity has been calibrated using a pressure control system for accurate comparison with reference values. Through the calibration process, the membrane resistance has been separated from the measured resistance, which is the sum of the membrane and interfacial resistances. Thus, the real proton conductivity of Nafion has been calculated in the through-plane direction. In this study, we have succeeded in improving the ionic conductivity of Nafion to its highest value to the best of our knowledge. Based on our results, not only can the improved Nafion be used itself, but this technique can be applied to other kinds of ion exchange membranes for use in energy systems.