In this study, we focused on the chemical feature about sulfonic group of perfluorosulfonic acid (PFSA) by first principle calculation in low hydration levels. Our study could elucidate two facts about the chemical property of PFSA, the one is why deprotonation reaction of sulfonic group of PFSA is not occurred in hydration level one and two and the other is notable feature of deprotonation reaction in hydration level three by B3LYP/6-311+G(d,p) level calculation. In the hydration level three, activation energy of deprotonation reaction of sulfonic group was 0.70 kcal/mol. Although this activation energy includes computational error, it is considered that this deprotonation reaction would proceed in the operation temperature of polymer electrolyte fuel cell smoothly. And total energy of product was lower than the reactant by 3.72 kcal/mol. From these results, deprotonation reaction of sulfonic group in hydration level three would proceed to product efficiently. In addition, reverse reaction is hard to occur by the thermal energy of 350 K which is operation temperature of polymer electrolyte fuel cell.
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