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Anion-exchange membranes (AEM) are prepared from chloromethylated poly(ether ether ketone) (CMPEEK), which is quaternized by N,N,N′,N′-tetramethyl-1,4-phenylenediamine (TMPD) and 1-methylimidazole using a two-step method. TMPD can not only improve the mechanical properties but also provide more ion exchange groups and improve the availability of quaternary ammonium (QA) groups. By varying the amount of TMPD in the membrane casting solution, the comprehensive properties of the membranes are optimized and intensified. The anion conductivity is increased from 0.028 S cm−1 of the imidazolium functionalized poly (ether ether ketone) (ImPEEK) control membrane to 0.042 S cm−1 of the TMPD/ImPEEK membrane with a TMPD content of 5 wt%. Meanwhile, a 31.5% increase in ultimate tensile strength and a 27.8% increase in Young's modulus of the TMPD/ImPEEK membrane are achieved. This study exploited a facile approach to solving the trade-off relation between anion conductivity and mechanical properties.

The design of new types of proton-conductive materials with high proton conductivity has sparked tremendous interest. Covalent organic framework (COF), a new category of porous crystalline materials possessing well-defined porosity and tunable functionality, holds great potential as next-generation proton conductors. Here, triazole COF loaded with phosphotungstic acid (HPW@COF) has been incorporated into sulfonated poly(ether ether ketone) (SPEEK) matrix to fabricate SPEEK/HPW@COF composite membranes. The one-dimensional channels of COF lined with protonated triazole (triazolium cations) by hydroscopic HPW and neutral triazole as well as counter anions (PO40W123−) could act as proton-donors and -acceptors forming interconnected hydrogen-bonding networks, thus greatly facilitating proton conduction via Grotthuss-type mechanism particularly under low RH. Accordingly, SPEEK/HPW@COF displayed 35.5 times higher proton conductivity than the plain SPEEK at 65 °C, 40% RH. Moreover, the proton conductivity of SPEEK/HPW@COF remained constant during soaking in water for 15 days, indicating the excellent immobilization of HPW due to the electrostatic interaction between basic nitrogen sites and HPW as well as the confinement effect of microporous COF channels. These results demonstrated that N-heterocycles functionalized COFs gave great promise as effective hosts to encapsulate proton carriers.

Proton exchange membranes (PEMs) have triggered growing attention in energy-related applications due to their fundamental and technological significance. In this work, silica-based nanoscale ionic materials (NIMs-SiO2) were synthesized and incorporated into sulfonated poly (ether-ether-ketone) (SPEEK) to prepare nanocomposite membranes. NIMs-SiO2 could not only provide extra proton transfer sites, but also enhanced the hydrophilicity of the membranes, leading to decrease of the activation energy. The nano-scale size (7 nm) and the functional groups of the NIMs-SiO2 lead to good interfacial adhesion with SPEEK, improving the mechanical properties of the membranes. Consequently, SPEEK/NIMs-SiO2(5) exhibited the highest proton conductivity and peak power density, which were 1.92 and 1.51 folds higher than the pristine SPEEK membranes, respectively. The results showed the nanocomposite membranes had potential as alternative proton exchange membranes for corresponding devices.