Abstract:

Objective Proton-exchange membrane (PEM) as a key component of fuel cells represent an important area of research that drives the rapid development of new energy technologies. The exchange of protons depends on the proton carriers and pathways within the membrane, making the optimization of these two structures crucial for achieving efficient proton transport. Current research primarily focuses on simple functional structures of metal-organic frameworks (MOF) and nanofibers, with slow improvements in proton conductivity. To tackle the challenges associated with proton transport in PEMs, a strategy has been put forth that involves the creation of a multi-scale micro-phase interface structure and multifunctional acid-base ion domains. The multi-scale architecture of the MOF composite nanofibers (physical microenvironment) and the functional ion domains situated between the MOF, fiber matrix, and polymer matrix (chemical microenvironment) markedly influence the performance of the proton exchange membrane. The study also investigates the synergistic effects of these physicochemical structures on proton transport.

Method Polyvinylidene fluoride (PVDF) nanofibers were prepared using electrospinning technology. Following this, the nanofibers were subjected to a polydopamine (PDA) chemical treatment within a buffer solution, succeeded by the in situ growth of a metal-organic framework (MOF) under conditions of high temperature and pressure. This process yielded nanofibers featuring a multi-scale micro-phase interface structure and multifunctional acid-base ion domains. Finally, a dense composite proton exchange membrane was fabricated using a sulfonated polyphenylsulfone (SPSF) solution through a compatible immersion method.

Results The results of EDS mapping showed that PDA was chemically bonded onto the nanofibers. Scanning electron microscopy images clearly revealed the presence of MOF particles, indicating good results from the in-situ growth treatment. Performance tests of the composite membrane demonstrated that the multi-scale micro-nanofiber structure significantly increased the interfacial interaction area of the micro-phases and effectively modulated the proton transport sites within the membrane through acid-base ion interactions, thereby enhancing the overall performance of the composite proton exchange membrane. The prepared proton exchange membrane exhibited an improved water uptake of 55.56%, with swelling limit of 18.32%. The proton conductivity of the composite membrane reached 0.165 S/cm, representing an increase of 100.97% compared to the SPSF membrane. The methanol permeability coefficient was significantly reduced with as low as 2.139 × 10^-7 cm²/s of methanol permeability, achieving an 11-fold increase in selectivity compared to the SPSF membrane.

Conclusion The multi-scale microphase interface structure based on in-situ growth of MOF nanofibers and the synergistic construction strategy of multifunctional acid alkali ion domains is proven to effectively enhance the comprehensive performance of proton exchange membranes from both structural and functional perspectives, and promote the development of the next generation of novel nanofiber composite proton exchange membranes.

Key words: nanofiber, proton exchange membrane, proton conduction channel, direct methanol fuel cell, metal organic framework