Constructing interconnected nanofibers@ZIF-67 superstructure in nafion membranes for accelerating proton transport and confining methanol permeation

A high-performance proton exchange membrane was successfully prepared by incorporating an interconnected PMIA nanofiber@ZIF-8 network (ZHNFs) into Nafion solution, in which the unique ZHNFs were fabricated via in-situ growth of ZIF-67 on the surface of hierarchical PMIA nanofibers (HNFs) with multiscale nanofibers and high hydrophilicity. The hybrid membrane presents an outstanding performance with a peak proton conductivity of 0.277 S cm−1 at 80 °C, 100RH% and a decreased methanol permeability of 1.415 × 10−7 cm2 s−1, implying a promising application in direct methanol fuel cells. The superior performance of the membranes could be due to the interconnected structure, high specific surface area of 122.637 m2 g−1 and active chemical bond of (−N–H) of ZHNFs. Specifically, the 3D interconnected structure of ZHNFs provides consecutive conduction path for protons, ensuring the improvement of proton conductivity. The effective interfacial acid-base pairs (−N–H … −SO3H) formed via the tight interactions between the –N–H bonds in ZHNFs and –SO3H groups in Nafion matrix could effectively ameliorate the compatibility of the nanofiber fillers and Nafion matrix, further promoting the methanol barrier of the hybrid membranes. Moreover, the generated acid-base pairs are beneficial for the efficient and rapid proton transfer via providing abundant proton conducting sites.