Constructing amino-functionalized flower-shaped ZnO@Al2O3 nanofibers composite membrane (ZANFs/SPSF) with hierarchical proton conductive pathways and excellent methanol resistance

Abstract

Traditional nanofiber-hybrid proton exchange membranes (PEMs) are limited in their further application due to differences in proton conductivity between vertical and horizontal orientations. In this study, we design and synthesize a novel type aminated flower-shaped ZnO@Al2O3 nanofibers and then filling its three-dimensional interstices with sulfonated polysulfone (SPSF) to obtain a nanofiber composite proton exchange membrane (ZANFs/SPSF). The Al2O3 nanofibers provide long-range and stable proton transport nanochannels in plane, while the flower-shaped ZnO on its surface provide additional vertical transport channels for protons. This combination of 1D and 2D conductive pathways forms a typical 3D hierarchical proton conductive configuration, optimizing the proton transfer pathway. Specifically, the amino groups (-N-H) on the nanofibers surface not only form acid-base pairs with sulfonic acid groups (-SO3H), providing a rich hydrogen bonding network for proton hopping, but also have a similar structure to the polyether sulfone groups (–SO2–NH-), which significantly improves the compatibility between the nanofibers and SPSF. Additionally, the flower-like pleated surface of the nanofibers has a high contact area with the SPSF, providing more proton hopping sites, improving the utilization efficiency of proton carriers, and also resulting in a more stable structure. Moreover, the crosslinked network of nanofibers serves as a barrier to further inhibit methanol permeation. The ZANFs/SPSF exhibits excellent parallel proton conductivity of 348 mS cm−1 at 80 °C and 100% RH, which is 2.7 times higher than that of SPSF under the same conditions, and achieves a peak power density of 405.7 mW cm−2. This approach presents a unique perspective for the preparation of high-performance PEMs for methanol fuel cells.