Surface Enriched Sulfonic Acid Ionic Clusters of Nafion Nanofibers as Long-Range Interconnected Ionic Nanochannels for Anisotropic Proton Transportation: Phenomenon and Molecular Mechanism

Construction of long-range interconnected ionic channels in proton exchange membranes (PEMs) is the key to realize anisotropic proton transportation. But, how to effectively modulate ionic channels at the molecular level still remains a great challenge for modern nanoenergy technology. Here, surface enriched sulfonic acid ionic clusters in Nafion (NF)/ZnO nanofibers are successfully designed and fabricated as long-range interconnected ionic channels, in which the ZnO nanofiller (nano-ZnO) act as an inducer to enable the spatial deformation and inversion of sulfonic acid groups in NF molecule from the inside to the surface of the NF/ZnO nanofibers, due to the strong intermolecular electrostatic interactions between nano-ZnO and the  CF 2 of NF backbones. The phenomenon and molecular mechanism are visually confirmed by physicochemical analysis. Ultimately, the NF/ZnO nanofibers demonstrate the relative higher of proton conductivity up to 253.2 mS cm -1 and power density of 115.72 mW cm -2 than that of reported NF-based PEMs. This study, for the first time, reveals that the surface enrichment of sulfonic acid ionic clusters is an efficient strategy to construct long-range interconnected ionic channels in the NF-based PEMs, proves that the formation of the ionic channels could be efficiently modulated by controlling the molecular activity and morphology of nanofiller.