Enhancement of protonic conductivity in the near surface regions of radiation induced polymer electrolyte membranes

New protonic conduction processes of the perfluorosulfonic acid polymer electrolyte membranes by gamma-ray irradiation at the dose up to 530 kGy and room temperature in air have been found by a direct current (DC) resistance measurement. The conductivities between the polymer electrolyte and the electrode, made of platinum, at 300 and 373 K in vacuum were enhanced to be about two and one, respectively, order of magnitude higher than that of the unirradiated one. The new and original activation energies of the conductivities in the temperature range below and above 343 K were distinguished to be 0.12 ± 0.05 and 0.84 ± 0.03 eV, respectively, which corresponded to potential energy of hydrogen diffusion due to the radiation induced defects and the existing sulfonate group. It was also revealed by means of ultraviolet, visible and infrared optical absorption and hydrogen ion-exchange capacity measurements that the radiation induced defects such as fluorocarbon and peroxy radicals, and C=O including in carbonyl groups were related to the new proton conduction processes. The modification of the hydrogen absorption characteristics due to the radiation induced defects in the near surface regions induces the enhancement of the proton conductivity.