Improving Alkali Stability of Anion Exchange Membrane by a Super Water-Retention Strategy

Abstract

Designing highly stable anion exchange membranes (AEMs) is of vital importance for anion exchange membrane fuel cells (AEMFCs). Herein, the study presents that elevating current density and reducing relative humidity can dramatically lower local hydration number (λ) of the cathode in AEMFCs and therefore result in the rapid degradation of AEMs. To address this issue, a water-retention strategy has been proposed to alleviate the hydroxide attack. The crosslinked poly (aryl N-silanylmethyl-piperidinium) (Si-TP-100-x) AEMs are prepared to increase the amount of bound water on cations by introducing hydrophilic Si─O bonds, and thus improving the alkali stability under low λ conditions. The Si-TP-100-4 exhibits improved ex-situ stability than the benchmark AEM in 2 m KOH-MeOH solution (λ = 4) at 80 °C. The in situ cell tests demonstrate that the AEMFC with Si-TP-100-4 can achieve a high peak power density of 1.32 W cm⁻² and simultaneously offer lower voltage decay rate than the controlled experiment at 1000 mA cm⁻² at 95 °C. The post-mortem analysis of membrane-electrode assembly further reveals that membrane and ionomer in cathode concurrently suffer from a significant degradation. This work provides an avenue for developing highly stable anion exchange polymers from the perspective of cation hydration.