Effect of a Protonation Process on the Mechanical Properties of Proton Exchange Membranes

To enhance battery performance and eliminate impurities, the proton exchange membranes made of perfluorosulfonic acid are protonated prior to use or storage. In this investigation, changes in the tensile and stress relaxation properties of the perfluorinated sulfonic acid polymer Nafion®115 proton exchange membranes were studied before and after protonation treatment. The effect of material orientation and strain rate on the tensile properties was also determined. The causes of the mechanical behavior both before and after protonation were analyzed, with a focus on the molecular chain motion perspective. The results illustrate that pretreating with protonation can enhance the membrane's yield strength and elastic modulus, but decrease its viscosity and hardening modulus. The underlying causes of these changes are elucidated through a model grounded in molecular chain aggregates movement.