Gomaa Mahmoud Mohammed, Sánchez-Ramos Arturo, Ureña Nieves, Pérez-Prior María Teresa, Levenfeld Belen, García-Salaberri Pablo A, Elsharkawy Mohamed Rabeh Mohamed
Physics Department, Faculty of Science, Minia University, Minia P.O. Box 61519, Egypt.
Department of Thermal and Fluids Engineering, Universidad Carlos III de Madrid, 28911 Leganes, Spain.
Polymers (Basel). 2022 Apr 21;14(9):1688. doi: 10.3390/polym14091688.
Free volume plays a key role on transport in proton exchange membranes (PEMs), including ionic conduction, species permeation, and diffusion. Positron annihilation lifetime spectroscopy and electrochemical impedance spectroscopy are used to characterize the pore size distribution and ionic conductivity of synthesized PEMs from polysulfone/polyphenylsulfone multiblock copolymers with different degrees of sulfonation (SPES). The experimental data are combined with a bundle-of-tubes model at the cluster-network scale to examine water uptake and proton conduction. The results show that the free pore size changes little with temperature in agreement with the good thermo-mechanical properties of SPES. However, the free volume is significantly lower than that of Nafion, leading to lower ionic conductivity. This is explained by the reduction of the bulk space available for proton transfer where the activation free energy is lower, as well as an increase in the tortuosity of the ionic network.
自由体积在质子交换膜（PEM）的传输过程中起着关键作用，包括离子传导、物质渗透和扩散。正电子湮没寿命谱和电化学阻抗谱被用于表征由具有不同磺化度（SPES）的聚砜/聚苯砜多嵌段共聚物合成的PEM的孔径分布和离子电导率。实验数据在簇-网络尺度上与管束模型相结合，以研究水的吸收和质子传导。结果表明，自由孔径随温度变化很小，这与SPES良好的热机械性能一致。然而，自由体积明显低于Nafion，导致离子电导率较低。这可以通过质子转移可用的本体空间减少（其中活化自由能较低）以及离子网络曲折度增加来解释。
