Dual reinforced composite membranes from in-situ ionic crosslinked quaternized chitosan filled quaternized polyvinylidene fluoride nanofiber for alkaline direct methanol fuel cell

The main obstacle of high-performance cationic functionalization chitosan (CS) as anion exchange membranes (AEMs) is the trade-off between mechanical stability and ionic conductivity. Here, in-situ ionic crosslinking between the deprotonated hydroxyl group and quaternary ammonium group under alkaline conditions was ingeniously applied to improve the mechanical stability of highly quaternized CS (HQCS) with high IEC (>2 mmol g(-1)). Meanwhile, to further reduce the swelling and enhance the hydroxide conductivity, a mechanically robust hydroxide ion conduction network, quaternized electrospun poly(vinylidene fluoride) (QPVDF) nanofiber, was subsequently used as the filling substrate of in-situ crosslinked HQCS to prepare dual reinforced thin AEMs. The introduction of a robust QPVDF nanofiber mat can not only greatly improve the mechanical properties and limit swelling, but also create facile ion transport channels. Notably, the HQCS/QPVDF-74.0 composite mem-brane demonstrates perfect dimensional stability, high mechanical performance and excellent alkaline stability, as well as superior ionic conductivity of 66.2 mS cm(-1) at 80 degrees C. The thus assembled alkaline direct methanol fuel cell displays a maximum power density of 132.30 mW cm(-2) using 5 M KOH and 3 M methanol as fuels at 80 degrees C with satisfactory durability.

Automated summary

In this study, the mechanical stability and ionic conductivity of highly quaternized chitosan (HQCS) were improved by in-situ ionic crosslinking, and a mechanically robust hydroxide ion conduction network was introduced using quaternized electrospun poly(vinylidene fluoride) (QPVDF) nanofiber. The resulting composite membrane exhibited excellent dimensional stability, mechanical performance, alkaline stability, and ionic conductivity, making it suitable for alkaline direct methanol fuel cells with satisfactory durability.