Constructing the basal nanofibers suit of layer-by-layer self-assembly membranes as anion exchange membranes

Abstract

Anion exchange membranes (AEMs) with layered structures were constructed through the combination of layer-by-layer (LBL) self-assembly membranes and a couple of electrospun nanofibers membranes by the cold pressing method. The LBL self-assembly membranes were formed through alternate depositing positively charged polyurethane (PU), quaternized chitosan (QCS) and negatively charged phosphotungstic acid (HPW). The electrostatic interaction and intermolecular hydrogen bonds drove the LBL self-assembly process. The layered structure facilitated the hydroxide ions conduction owing to the reduced conduction resistance. As a result, (PU/HPW/QCS/HPW)200 membranes exhibited a hydroxide conductivity of 49.1 mS/cm at 80 °C. However, the sustained attack from hydroxyl groups could cause the degradation of polymer skeleton and even the breakdown of membranes. The electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofibers membranes were combined with the LBL self-assembly membrane, expecting to enhance the chemical stability of AEMs. The external PVDF-HFP nanofibers membranes regulated the hydroxide ions permeation and protected the internal LBL self-assembly membranes from hydroxide ions attracting reminiscent of a breathable and warm sweater. The prepared (PU/HPW/QCS/HPW)200 membranes exhibited the fine stability on the basis of the long-term hydroxide conductivity. Specifically, the hydroxide conductivity of the AEMs was 12.3 mS/cm at 80 °C and it reached 14.3 mS/cm while immersing into 1M KOH at 80 °C for 888 h. Furthermore, the prepared AEMs exhibited fine dimensional stability and mechanical property owing to the compact and well-ordered structure.