Protonic conduction processes of gamma-ray-irradiated perfluorosulfonic acid membranes

New protonic conduction processes of perfluorosulfonic acid membranes by gamma-ray irradiation at a dose of up to 240 kGy at room temperature in air have been found by direct current resistance measurement. The conductivities of the membranes at 373 and 300 K in vacuum are enhanced to approximately one and two orders of magnitude higher, respectively, than the conductivities of an unirradiated membrane. The new and original activation energies required for the conductivities in the temperature range below and above 343 K are determined to be 0.12 ± 0.05 and 0.84 ± 0.03 eV, respectively, which correspond to the potential energy of the hydrogen diffusion due to radiation-induced defects and the existing sulfonate group. By means of ultraviolet, visible, and infrared optical absorption and by hydrogen-ion-exchange capacity measurements, it is revealed that radiation-induced defects such as fluorocarbon and peroxy radicals, and C = O bonds included in carbonyl groups are related to the new proton conduction processes. The modification of hydrogen absorption characteristics due to the radiation-induced defects in near-surface regions induces the enhancement of the proton conductivity.