Physically-crosslinked anion exchange membranes by blending ionic additive into alkyl-substituted quaternized PPO

Abstract

An additive-induced physically crosslinked system for use as anion exchange membranes was developed by blending an additive (DHBQA) containing both long alkyl (C12, dodecyl) and quaternary ammonium groups into a dodecyl-substituted and quaternary ammonium-functionalized PPO (poly(2,6-dimethyl-1,4-phenylene oxide)) (C12-PPO-QA). The additive, whose diammonium groups act as ion conductors, and whose long alkyl chains bind to the alkyl chains of the C12-PPO-QA polymer through van der Waals interactions, induced the formation of ion clusters as well as physical crosslinking of the C12-PPO-QA polymer. Controlling the amount of additive to maximize its intermolecular interactions with the polymer resulted in a PPO-10.8 membrane (10.8 wt% of additive relative to polymer) with very high ion conductivities of 49.2 mS cm−1 at 20 °C and 107.6 mS cm−1 at 80 °C and low swelling ratios of 18.2% at 20 °C and 33.3% at 80 °C, as well as excellent mechanical and alkaline stability. The H2/O2 single cell performance using PPO-10.8 reached a maximum power density about 60 mW cm−2, higher than that of the PPO-0 sample.