Mussel-inspired functionalized LDH as covalent crosslinkers for constructing micro-crosslinking fluorenyl-containing polysulfone-based composite anion exchange membranes with enhanced properties

The low ionic conductivity and poor dimensional stability severely influence the application of anion exchange membranes (AEMs). Therefore, how to balance the problem of excessive swelling of polymer matrix caused by increasing ion conductivity becomes an important challenge. Herein, 3-(dimethylamino)-1- propylamine (DMAPA) and polyethyleneimine (PEI) were grafted to the surface of layered double hydroxide (LDH) through mussel-inspired chemistry. The sheet-like functionalized LDH (DLDH and PLDH) as both filler and crosslinker was incorporated into the quaternized fluorenyl-containing polyethersulfone (QPFSU) matrix to get a series of new composite anion exchange membranes (AEMs). The as-prepared micro-crosslinked AEMs were found to form more hydrophilic conductive ion clusters owing to the generation of new quaternary ammonium groups during the crosslinking reaction. The micro-crosslinked AEMs have better dimensional stability while having higher OH− conductivity. Especially the ion conductivity of CQPFSU-1%-PLDH membrane can reach 86.8 mS cm−1 at 80 °C with excellent dimensional and chemical stability (SR is 9.6% at 80 °C, 21.8% decrease in OH− conductivity at 60 °C in 1.0 M NaOH for 200 h). Overall, the micro-crosslinking method for functionalized LDH modified AEMs achieves a balance between ion conductivity and dimensional stability of AEMs.