Preparation and characterization of side-chain poly(aryl ether ketone) anion exchange membranes by superacid-catalyzed reaction

Recent Advances in Direct Synthesis of Functional Polymers of Intrinsic Microporosity Based on (Super)Acid Catalysis

Polymers of intrinsic microporosity (PIMs) are an emerging class of amorphous organic porous materials with solution processability, which are widely used in a multitude of fields such as gas separation, ion conduction, nanofiltration, etc. PIMs have adjustable pore structure and functional pore wall, so it can achieve selective sieving for specific substances. In order to meet the functional requirements of PIMs, two principal methods are used to synthesize functional PIMs, namely, post-modification of PIMs precursors and functionalization of monomers. A number of post-modification routes have been reported, however, the direct synthesis of functional PIMs with diverse groups still remains a challenge. The synthesis of PIMs through the acid-catalyzed polyhydroxyalkylation has been demonstrated to be an effective solution, exhibiting the advantages of wider substrates range, milder reaction conditions, and higher molecular weight. Recently, a series of functional substrates for direct synthesis of PIMs have been proposed. This article presents a review and summary of recent advances in synthesizing PIMs via acid-catalyzed polyhydroxyalkylation, and the synthesis route and structure-activity relationship are emphasized, which provides a versatile platform for the direct synthesis of functional PIMs.

Fluorinated poly(p-triphenyl piperidine) anion exchange membranes with robust dimensional stability for fuel cells

Anion exchange membrane fuel cells (AEMFCs), which are more economical than proton exchange membrane fuel cells (PEMFCs), stand out in the context of the rapid development of renewable energy. Superacid-catalyzed ether-free aromatic polymers have recently received a lot of attention due to their exceptional performance, but their development has been hampered by the trade-off between the dimensional stability and ionic conductivity of anion exchange membranes (AEMs). Here, we introduced fluoroketones containing different numbers of fluorinated groups (x = 0, 3 and 6) in the main chain of p-terphenyl piperidine because of the favorable hydrophobic properties of fluorinated groups. The results show that fluorinated AEMs can enhance OH- conductivity by building more aggregated hydrophilic channels while ensuring dimensional stability. The PTF6-QAPTP AEM with more fluorinated groups has the most excellent performance at 80 °C with an OH- conductivity of 142.7 mS cm-1 and a swelling ratio (SR) of only 4.55 %. Additionally, it exhibits good alkali durability, with the OH- conductivity and quaternary ammonium (QA) cation retaining at 93.45% and 92.6%, respectively, after immersion in a 2 M NaOH solution at 80 °C for 1200 h. In addition, the power density of the PTF6-QAPTP based single cell reaches 849 mW cm-2 when the current density is 1600 mA cm-2. The PTF6-QAPTP based cell has a voltage retention of 88% after 80 h of stability testing at a constant current density of 300 mA cm-2 at 80 °C.

Pyrrolidinium-Based Hyperbranched Anion Exchange Membranes with Controllable Microphase Separated Morphology for Alkaline Fuel Cells

It is well acknowledged that the microphase-separated morphology of anion exchange membranes (AEMs) is of vital importance for membrane properties utilized in alkaline fuel cells. Herein, a rigid macromolecule poly(methyldiallylamine) (PMDA) is incorporated to regulate the microphase morphology of hyperbranched AEMs. As expected, the hyperbranched poly(vinylbenzyl chloride) (HB-PVBC) is guided to distribute along PMDA chains, and longer PMDA cha leads to a more distinct microphase morphology with interconnected ionic channels. Consequently, high chloride conductivity of 10.49 mS cm^-1 at 30 °C and suppressed water swelling ratio lower than 30% at 80 °C are obtained. Furthermore, the β-H of pyrrolidinium cations in the non-antiperiplanar position increases the energy barrier of β-H elimination, leading to conformationally disfavored Hofmann elimination and increased alkaline stability. This strategy is anticipated to provide a feasible way for preparing hyperbranched AEMs with clear microphase morphology and good overall properties for alkaline fuel cells.

Strong and Flexible High-Performance Anion Exchange Membranes with Long-Distance Interconnected Ion Transport Channels for Alkaline Fuel Cells

Anion exchange membrane fuel cells (AEMFCs), which operate on a variety of green fuels, can achieve high power without emitting greenhouse gases. However, the lack of high ionic conductivity and long-term durability of anion-exchange membranes (AEMs) as their key components is a major obstacle hindering the commercial application of AEMFCs. Here, a series of homogeneous semi-interpenetrating network (semi-IPN) AEMs formed by cross-linking a copolymer of styrene (St) and 4-vinylbenzyl chloride (VBC) with branched polyethylenimine (BPEI) were designed. The pure carbon copolymer skeleton without sulfone/ether bonds accompanied by the semi-IPN endows the AEMs with excellent chemical stability. Moreover, the cross-linking effect of flexible BPEI chains is supposed to promote the "strong-flexible" mechanical properties, while the presence of multiquaternary ammonium groups can boost the formation of microphase separation, thereby enhancing the ionic conductivity of these AEMs. Consequently, the optimized (S₁V₁)₃Q AEM exhibits an excellent hydroxide conductivity of 106 mS cm^-1 at 80 °C, as well as more than 81% residual conductivity after soaking in 1 M NaOH at 60 °C for 720 h. Furthermore, the H₂/O₂ fuel cell assembled with (S₁V₁)₃Q AEM delivers a peak power density of 150.2 mW cm^-2 at 60 °C and 40% relative humidity. All results indicate that the approach of combining a pure carbon backbone polymer with a semi-IPN structure may be a viable strategy for fabricating AEMs that can be used in AEMFCs for long-term applications.