Polyfluorene/Poly(vinylbenzyl chloride) Cross-Linked Anion-Exchange Membranes with Multiple Cations for Fuel Cell Applications

Abstract

An ideal anion-exchange membrane (AEM) must possess good dimensional stability, excellent alkaline stability, and good ionic conductivity. In this study, polyfluorene/poly-(vinylbenzyl chloride) (PVBC) cross-linked AEMs with multiple cations are prepared. A cross-linked structure is introduced to enhance the mechanical strength (>30 MPa) and dimensional stability (swelling ratio < 15%) of these AEMs. All PHF x TP 100−x − PVBC-and PMF x TP 100−x −PVBC-based AEMs exhibit excellent alkaline stability after treating with 2 M KOH at 80 °C for 30 days, which is attributed to the ether-free backbone and cross-linked structure. The long hydrophobic alkyl side chains of PHF 10 TP 90 − PVBC favors the construction of microphase separation within the membrane, leading to higher conductivity and cell performance (64.56 mS cm −1 and 323 mW cm −2 , at 80 °C) than those of the PMF 10 TP 90 −PVBC (57.56 mS cm −1 and 100 mW cm −2 at 80 °C).The results indicate that polyfluorene/PVBC cross-linked AEMs with multiple cations are prospective membrane materials for fuel cells.

Separators and Membranes for Advanced Alkaline Water Electrolysis

“…There are several reports on cross-linking achieved in a blending approach using polymers functionalized with benzylhalide or alkyl halide groups that react via Menshutkin reactions during membrane casting. Examples of these polyfunctional cross-linking polymers include poly­(vinylbenzyl chloride), benzylbrominated poly­(phenylene oxide) and bromohexylated − and chloromethylated styrene-(ethylene- co -butylene)-styrene (SEBS) triblock copolymers. The latter is a type of thermoplastic elastomers that may introduce a separate rubber phase in the AEM to significantly enhance mechanical properties.…”

Modification of Hydrophobic Diacid Units for Enhanced Poly(crown ether) Anion-Exchange Membrane Performance

“…30 Moreover, the apparent activation energy (E a ) of ion transfer of those membranes can be calculated according to the following formula: E a = −b × R, where R is the gas constant (8.314 J K −1 mol −1 ) and b is the slope of the straight line obtained from the plot of lnσ against 1000/T. 20 As can be seen in Figure S6, the E a of QAPCE-1.4P is 14.44 kJ mol −1 , which suggests that less energy is required for the OH − transportation and a high ion conducting efficiency in QAPCE-1.4P. Furthermore, a comparison of the OH − conductivity of the as-prepared membranes with other AEMs reported in recent years is presented in Figure 5b.…”

“…Despite these efforts, there are very few commercialized AEMs owing to their poor alkali stability as well as inadequate ionic conductivity. Compared with PEMs, AEMs exhibit a lower ion transfer ability because OH – served as the carrier ion in AEMs has an ion mobility 57% lower than H + , resulting in a low ionic conductivity . Meanwhile, it has been proven that the cationic groups may be degraded in an alkaline environment at 80 °C via several mechanisms such as nucleophilic substitution, Hofmann elimination, or nitrogen ylide formation. , Therefore, enhancing the OH – transport ability and alkali resistance of AEMs has become one of the most important issues to be dealt with.…”

Current Challenges on the Alkaline Stability of Anion Exchange Membranes for Fuel Cells

“…Li et al [117] grafted hydrophilic and flexible polyethylene glycol chains onto imidazolium to prepare cross-linked PPO-based AEMs. These AEMs exhibited excellent film-formed abilities with reasonable mechanical strengths of 18.7-31.8 MPa and high elongations at break of 21.2 %-133.3 %, as well as good alkaline stability after immersion in 1 M NaOH at 80 °C for 1248 h. To further improve the alkaline stability of cross-linked membranes, Ding et al [118] cross-linked ether-free polyfluorene with flexible aliphatic chains. The rigid polyfluorene chains provides high tensile strength and dimensional stability in water, even at high temperatures, whereas the flexible polyolefin chains improved the flexibility of the polymer network.…”

“…grafted hydrophilic and flexible polyethylene glycol chains onto imidazolium to prepare cross‐linked PPO‐based AEMs. These AEMs exhibited excellent film‐formed abilities with reasonable mechanical strengths of 18.7–31.8 MPa and high elongations at break of 21.2 %–133.3 %, as well as good alkaline stability after immersion in 1 M NaOH at 80 °C for 1248 h. To further improve the alkaline stability of cross‐linked membranes, Ding et al [118] . cross‐linked ether‐free polyfluorene with flexible aliphatic chains.…”