Flexibly crosslinked and post-morpholinium-functionalized poly(2,6-dimethyl-1,4-phenylene oxide) anion exchange membranes

Morpholinium-functionalized cross-linked poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) anion exchange membranes were prepared using a crosslinking/post-functionalization method. 4,4'-(oxybis(ethane-2,1-diyl)) dimorpholine (OEDM) having a flexible long chain and hydrophilic ether bond was for the first time used as the crosslinker. The brominated PPO reacted with OEDM, forming a crosslinked structure and accomplishing partial functionalization. Further functionalization was carried out by immersion in N-methyl- morpholine aqueous solution. The degree of crosslinking was controlled by varying the proportion of brominated PPO to OEDM because excessive bromomethyl groups ensured the occurrence of crosslinking reaction. The cross-linked structure promoted the formation of micro-phase separation and effectively limited swelling. The crosslinked membrane shows much higher conductivity and lower swelling ratio compared to non-crosslinked one at similar IEC. The highest hydroxide conductivity that the crosslinked membrane achieves is 35 mS cm(-1)- at 20 degrees C. The power density for the H-2/O-2 single cell assembled with this membrane is up to 193 mW cm(-2). In addition, the crosslinked PPO-MmOH-Cr membrane exhibits good alkaline stability with conductivity loss of less than 15% after soaking in 1 M KOH for 96 h. (C) 2019 Hydrogen Energy Publications LLC. (C) Published by Elsevier Ltd. All rights reserved.