Free volume of poly(perfluorosulfonic acid)/SiO2 composite proton exchange membranes by Xe-129 NMRстатья
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Дата последнего поиска статьи во внешних источниках: 9 ноября 2017 г.
Аннотация:Poly(perfluorosulfonic acid)/silica (PFSA/SiO2) composites were investigated by Xe-129 NMR spectroscopy and relaxometry. Xe-129 chemical shift extrapolated to zero pressure was used for calculation of average free volume hole size. This quantity reaches a maximum at 2 wt.% SiO2 that could be correlated to the performance of composites proton exchange membrane. Xe-129 longitudinal magnetization relaxation revealed a bimodal distribution of the free volume that was explained by the presence of xenon atoms in the backbone and pendant-chain domains. Thus, the free volume is heterogeneous and depends on the content of SiO2. Implications of the free volume changes for the hydrogen crossover through PFSA/SiO2 membranes are also discussed.