Dong Xiaokun,Li Yongzhe,Wei Gang,Zhao Shuhui,Gao Shugang,Gao Jiangshan,He Yan
Carbon quantum dots (CQDs) are compatible with perfluorosulfonic acid (PFSA) polymers due to their rich hydrophilic functional groups and nanoscale particle size, making them suitable as inorganic fillers for proton exchange membranes. In this work, CQDs synthesized by a simple microwave-assisted pyrolysis method were used to improve the performance of PFSA proton exchange membranes. Research indicates that at 80 °C and 100% relative humidity (RH), the proton conductivity of the PFSA membrane increased to 254 mS/cm with the addition of 0.5 wt% CQDs filler, compared to 249 mS/cm for the original PFSA membrane. This enhancement in proton conductivity is likely attributed to the hydrophilic functional groups present on CQDs, such as carboxyl groups (–COOH) and amino groups (–NH 2 ). Furthermore, a notable decrease in hydrogen permeability was observed in the composite membranes due to the incorporation of CQDs. Specifically, the hydrogen permeability of the PFSA/CQDs-2 composite membrane was reduced by approximately 44% compared to the original PFSA membrane. This reduction in hydrogen permeability is likely a result of cross-linking between the sulfonic acid groups in PFSA and the amino groups in CQDs. In conclusion, CQDs contribute to better proton conductivity, lower hydrogen permeability, and enhanced thermal and mechanical stability for PFSA membranes, making them a potential membrane material for high-temperature operation in proton exchange membrane fuel cells.
The design and synthesis of proton exchange membranes (PEMs) with controllable microstructure and sulfonation degree play a crucial role in enhancing their performance and expanding their application. In this study, the disulfonic acid monomer is designed and prepared to synthesize the comb-like disulfonic PEMs with controllable ion exchange capacity. The results show that the side chain structure and more concentrated sulfonic acid groups facilitate the aggregation of sulfonic acid groups in the polymer, improve the microphase separation morphology of PEMs, and increase the ionic conductivity. The proton conductivity of the DS-PXIDI-60 membrane is approximately 300 mS cm −1 . The PEMs with controllable microstructure are prepared by introducing comonomers, including 9,9-dimethylxanthrene, biphenyl, and p-terphenyl, with different reactivity, spatial structure, and solubility. Biphenyl is copolymerized to form a copolymer with an alternating structure, and 9, 9-dimethylxanthrene is copolymerized to form a random copolymer. In addition, it is worth noting that p-terphenyl is copolymerized to form a microblock structure of the copolymer, with more excellent comprehensive properties. DS-PXITp-60 exhibits better performance than Nafion 212 in redoxflow batteries and fuel cells. Therefore, such molecular design and synthesis strategies provide a reference guide for the development of high-performance PEMs.
Magnetic field treated perfluorosulfonate ionomer (PFSI) membranes (M-PMs) with improved through-plane proton conductivity are facilely fabricated though solvent casting of PFSI/Fe 3 O 4 nanocomposite dispersion without any third additive under magnetic field followed by discarding the Fe 3 O 4 nanoparticles . In the PFSI/Fe 3 O 4 nanocomposite membrane, Fe 3 O 4 nanoparticles are clearly uniaxially aligned by magnetic field. Subsequently, M-PMs are obtained by removing Fe 3 O 4 from the nanocomposite membranes to eliminate the negative effect of Fe 3 O 4 on proton conducting. The effect of magnetic field treatment on M-PMs' performance is investigated by both in- and through-plane proton conductivity. The results demonstrate that the through-plane proton conductivity of the M-PMs prepared from PFSI/Fe 3 O 4 nanocomposite membrane with optimized Fe 3 O 4 content is enhanced, while the in-plane proton conductivity is reduced compared to the pristine PFSI membrane, which indicate through-plane anisotropic phenomenon of proton conducting in the membranes. Such magnetic field treated PFSI membranes exhibit good appropriateness for using in electrochemical applications, for example fuel cells.
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