Ureña Nieves, Pérez-Prior M Teresa, Levenfeld Belén, García-Salaberri Pablo A
Departamento de Ciencia e Ingeniería de Materiales e Ingeniería Química, IAAB, Universidad Carlos III de Madrid, 28911 Leganés, Spain.
Departamento de Ingeniería Térmica y de Fluidos, Universidad Carlos III de Madrid, 28911 Leganés, Spain.
Polymers (Basel). 2021 Jan 23;13(3):363. doi: 10.3390/polym13030363.
The effect of relative humidity (RH) and degree of sulfonation (DS) on the ionic conductivity and water uptake of proton-exchange membranes based on sulfonated multiblock copolymers composed of polysulfone (PSU) and polyphenylsulfone (PPSU) is examined experimentally and numerically. Three membranes with a different DS and ion-exchange capacity are analyzed. The heterogeneous structure of the membranes shows a random distribution of sulfonated (hydrophilic) and non-sulfonated (hydrophobic) domains, whose proton conductivity is modeled based on percolation theory. The mesoscopic model solves simplified Nernst-Planck and charge conservation equations on a random cubic network. Good agreement is found between the measured ionic conductivity and water uptake and the model predictions. The ionic conductivity increases with RH due to both the growth of the hydrated volume available for conduction and the decrease of the tortuosity of ionic transport pathways. Moreover, the results show that the ionic conductivity increases nonlinearly with DS, experiencing a strong rise when the DS is varied from 0.45 to 0.70, even though the water uptake of the membranes remains nearly the same. In contrast, the increase of the ionic conductivity between DS=0.70 and DS=0.79 is significantly lower, but the water uptake increases sharply. This is explained by the lack of microphase separation of both copolymer blocks when the DS is exceedingly high. Encouragingly, the copolymer membranes demonstrate a similar performance to Nafion under well hydrated conditions, which can be further optimized by a combination of numerical modeling and experimental characterization to develop new-generation membranes with better properties.
实验和数值研究了相对湿度（RH）和磺化度（DS）对基于聚砜（PSU）和聚苯砜（PPSU）的磺化多嵌段共聚物质子交换膜的离子电导率和吸水率的影响。分析了三种具有不同DS和离子交换容量的膜。膜的非均相结构显示出磺化（亲水）和非磺化（疏水）域的随机分布，其质子传导率基于渗流理论进行建模。介观模型在随机立方网络上求解简化的能斯特-普朗克方程和电荷守恒方程。在测量的离子电导率和吸水率与模型预测之间发现了良好的一致性。由于可用于传导的水合体积的增加和离子传输路径曲折度的降低，离子电导率随RH增加。此外，结果表明，离子电导率随DS非线性增加，当DS从0.45变化到0.70时，离子电导率会大幅上升，尽管膜的吸水率几乎保持不变。相比之下，DS = 0.70和DS = 0.79之间离子电导率的增加明显较低，但吸水率急剧增加。这是由于当DS极高时，两种共聚物嵌段缺乏微相分离。令人鼓舞的是，共聚物膜在充分水合条件下表现出与Nafion相似的性能，通过数值模拟和实验表征相结合可以进一步优化，以开发具有更好性能的新一代膜。
