Role of UV irradiation of Nafion membranes on ionic groups responsible for proton conduction and mechanical strength: A FTIR spectroscopic analysis

This work presents an evidence of why proton conductivity of Nafion increases with increase in UV-radiation dosage and drops beyond ultraviolet radiation dosage of 198 mJ cm(-2). FTIR spectroscopic analysis is used to analyse the shifting of the peaks of groups responsible for proton conduction (i.e. sulfonic acid (-SO3H) and hydronium (H3O+) ions) of Nafion irradiated by various dosages of UV-radiation. The analysis showed that crosslinking of -SO3H increases up-to UV-radiation dosage of 198 mJ cm(-2). Beyond this optimum UV-radiation dosage the chain-scission of these groups takes place. On the other hand, UV-radiation has significant degradation effect on H3O+. FTIR spectra of H3O+ show that even with slightest dosage of UV-radiation, chain-scission takes place. Further, the effect of UV-radiation of Nafion on the groups responsible for providing mechanical strength, i.e. -CF2 is also analysed using FTIR spectroscopy. The analysis showed that the intensity of transmission spectrum of -CF2 increases up-to UV-radiation dosage of 198 mJ cm(-2) and drops beyond this dosage indicating that there is a possibility of enhancing the mechanical stability up to this dosage. These analysis show that optimum dose of UV-radiation is an effective tool for enhancing the proton-hopping mechanism and thereby, proton conductivity, and also the mechanical stability of Nafion.