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

Abstract

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 °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 °C for 360 h, IEC retentions = 86.2–93.5% and IC retentions = 85.5–95.6%.) A H₂/O₂ 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 °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.