The design and synthesis of a long-side-chain-type anion exchange membrane with a hydrophilic spacer for alkaline fuel cells

Outstanding alkaline stability and high conductivity make side-chain-type anion exchange membranes (AEMs) become one of the ideal materials for AEM fuel cells (AEMFCs). However, the hydrophobic alkyl spacer between polymer backbones and cationic groups in AEMs limited their performance in AEMFCs. Herein, we demonstrated the design and synthesis of long-side-chain-type AEMs containing a hydrophilic ethylene oxide (EO) spacer using an appropriate EO-based monomer via click reaction. The obtained PPO-O-40 membrane with EO spacers showed higher hydroxide conductivity (52.1 mS cm-1 at 20 degrees C) than its counterpart with an alkyl spacer (PPO-C40). The improved chemical stability of the PPO-O-x membrane was validated by an alkaline stability test for soaking in 1 M NaOH at 60 degrees C for 864 h. More importantly, an AEMFC assembled with the PPO-O-40 membrane displayed an outstanding peak power of 690 mW cm-2 at 60 degrees C under the optimal relative humidity of the anode. The short-term durability test observed a voltage decay rate of 6.1 mV h-1 during the continuous operation for 8 h at 200 mA cm- 2. This work provides an alternative way to design highly conductive and durable side-chaintype AEMs containing a hydrophilic spacer for alkaline fuel cell application.