Hydrogen Bonding Dominated Anion-Exchange Membranes Based on Flexible and Rigid Backbones

This work presents a synthesis strategy to yield DQPVB-EVOH anion-exchange membranes (AEMs) by grafting hydroxyl-containing bis-cationic side chains onto a rigid poly(4-vinylbenzyl chloride) (PVB) backbone (DQPVB) and blending it with a flexible ethylene vinyl alcohol copolymer (EVOH). The intermolecular hydrogen bonding between the hydroxyl groups on DQPVB side chains and those on flexible EVOH delivers good tensile strength (TS = 8.3-22.9 MPa), high elongation at break (EB = 94.9-218.5%), restricted swelling degree (SD = 12.0-42.7%), and high water uptake (WU = 106.8-311.2%) of the AEMs. The bis-cationic properties promote a high ion-exchange capacity (IEC = 2.77-4.01 mmol g(-1)) for DQPVB-EVOH AEMs, contributing to their improved ionic conductivity (IC = 51.3-89.3 mS cm(-1) at 80 degrees C). Additionally, the absence of polar groups on the PVB backbone, coupled with high water uptake, diminishes the nucleophilic attack ability of hydroxyl groups, resulting in good alkali stability for DQPVB-EVOH AEMs. (After soaking in 1 M KOH at 80 degrees C for 360 h, IEC retentions = 86.2-93.5% and IC retentions = 85.5-95.6%.) A H-2/O-2 fuel cell based on the DQPVB-EVOH-0.5 AEM exhibits a maximum power density of 303.6 mW cm(-2). In comparison, QPVB-EVOH-0.5, which is formulated by blending singly cationic-grafted quaternized PVB (QPVB) with EVOH, exhibits excessive swelling at 30 degrees C due to the lack of hydrogen bond cross-linking. It has a SD of up to 95.8% with an IEC of 2.36 mmol g(-1), making it not feasible.