Mixed membrane matrices (MMMs) made up with Nafion and nanocrystals of zirconium metal–organic framework (MOF) UiO-66 or the analogous sulfonated SO₃H-UiO-66 were prepared by varying the filler loading and the size of the crystals. The combined effects of size and loading, together with the presence of sulfonic groups covalently linked to the MOFs, were studied with regard to the conductivity and mechanical properties of the obtained composite matrices. A large screening of membranes was preliminarily made and, on the most promising samples, an accurate conductivity study at different relative humidities and temperatures was also carried out. The results showed that membranes containing large crystals (200 nm average size) in low amounts (around 2%) displayed the best results in terms of proton conductivity values, reaching values by 30% higher than those of pure Nafion, while leaving the mechanical properties substantially unchanged. On the contrary, MMMs containing MOFs of small size (20 nm average size) did not show any conductivity improvements if compared to pure Nafion membranes. The effect of MOF sulfonation was negligible at low filler loading whereas it became important at loading values around 10%. Finally, membranes with a high filler loading (up to 60 wt %) of sulfonated UiO-66 showed a slight reduction of conductivity in comparison with membranes loaded at 20% of nonsulfonated ones.

中文翻译：

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基于Nafion / UiO-66 / SO ₃ H-UiO-66纳米MOF的混合膜基质：揭示了晶体尺寸，磺化和填料负载对机械和导电性能的影响

由Nafion和锆金属-有机骨架（MOF）UiO-66或类似的磺化SO _3的纳米晶体组成的混合膜基质（MMM）H-UiO-66通过改变填料的填充量和晶体的尺寸来制备。关于获得的复合基体的电导率和机械性能，研究了尺寸和负载的综合效应以及共价连接到MOF的磺酸基团的存在。初步对膜进行了大筛分，并且在最有希望的样品上，还进行了在不同相对湿度和温度下的精确电导率研究。结果表明，含有少量（约2％左右）大晶体（平均2％）的膜表现出最好的质子传导率值，比纯Nafion膜高出30％，同时保留了机械性能基本不变。相反，与纯Nafion膜相比，含有小尺寸（平均尺寸20 nm）的MOF的MMM并未显示出任何导电性的提高。在低填充量下，MOF磺化的影响可忽略不计，而在约10％的填充量下，MOF磺化作用变得很重要。最后，与载有20％非磺化膜的膜相比，磺化UiO-66的填料填充量高（最高60 wt％）的膜的电导率略有降低。