Sakai Hironori, Tokumasu Takashi
Institute of Fluid Science, Tohoku University , 2-1-1, Katahira, Sendai, Miyagi, Japan.
J Phys Chem A. 2014 Jan 9;118(1):275-82. doi: 10.1021/jp409781s. Epub 2013 Dec 19.
A reaction analysis for deprotonation of the sulfonic group in a model molecule of perfluorosulfonic acid (PFSA) at low hydration levels was performed. PFSA is usually adopted as a polymer electrolyte membrane in polymer electrolyte fuel cells. In hydration level three, the deprotonation reaction certainly occurs. The deprotonated state produced is more stable than the predeprotonated state by 3.72 kcal/mol. In addition, its activation energy is very low. Although quantitative discussion of this activation energy is difficult considering the computational error, it can be said qualitatively that H(+) is abstracted smoothly from the sulfonic group because of a low activation energy. From the results of bond-order analysis, the produced H3O(+) is strongly bound by the SO3(-) group. Thus, diffusivity of H3O(+) would be low. In hydration level four or more, we found a possibility that the diffusivity of H3O(+) increases because the hydrogen-bond strength between H3O(+) and SO3(-) is lower or SO3(-) cannot bind H3O(+) directly by forming an Eigen cation.
对低水化水平下全氟磺酸（PFSA）模型分子中磺酸基团的去质子化反应进行了分析。PFSA通常用作聚合物电解质燃料电池中的聚合物电解质膜。在水化水平为3时，去质子化反应肯定会发生。产生的去质子化状态比质子化前的状态稳定3.72千卡/摩尔。此外，其活化能非常低。尽管考虑到计算误差，对该活化能进行定量讨论很困难，但定性地说，由于活化能低，H(+) 很容易从磺酸基团中被夺取。根据键级分析结果，生成的H3O(+) 与SO3(-) 基团强烈结合。因此，H3O(+) 的扩散率会很低。在水化水平为4或更高时，我们发现H3O(+) 的扩散率可能会增加，因为H3O(+) 与SO3(-) 之间的氢键强度较低，或者SO3(-) 不能通过形成特征阳离子直接结合H3O(+) 。
