Enhancing Proton Conductivity and Dimensional Stability of Nanofiber Proton Exchange Membranes through In Situ Growth of MOF-Modified PVDF Nanofibers

Proton exchange membranes often encounter challenges with proton conductivity and dimensional stability under conditions of high temperature and low humidity. Incorporating proton-conductive nanofibers into the membrane fortifies its dimensional stability and establishes extra proton transfer channels at the interface between the fibers and matrix, thereby improving proton conductivity. This study utilized polyvinylidene fluoride (PVDF) fibers as a base material, modified with ethylenediamine to yield amine-functionalized cross-linked structures. UiO-66-NH2 and UiO-66-NH2–SO3H were then grown in situ on these fibers, and the resultant structures were integrated with Nafion to fabricate metal–organic framework (MOF)-modified nanofiber proton exchange membranes (NFPEMs). We examined the growth of MOFs and their role in enhancing the nanofiber proton exchange membrane's properties. Both UiO-66-NH2 and UiO-66-NH2–SO3H were successfully incorporated, resulting in a maximum enhancement of proton conductivity by 149.69 and 80.38%, respectively, compared with PVDF@Nafion, and the proton conductivity of the MOF-loaded membrane reaches 152.11 ms/cm at 80 °C and 100% relative humidity. The swelling rates were also significantly reduced by up to 59.16 and 57.94%, relative to Nafion, effectively boosting dimensional stability and thermal stability. These improvements are attributed to the additional proton transfer channels formed by the MOFs, the contribution of acid–base pairs, limitations imposed by MOF porosity on water molecule mobility, and the supportive three-dimensional network conferred by PVDF. Findings from this research provide valuable guidance for the design of NFPEMs.