High‐Performance Anion Exchange Membrane Water Electrolyzers Enabled by Highly Gas Permeable and Dimensionally Stable Anion Exchange Ionomers

Abstract

Designing suitable anion exchange ionomers is critical to improving the performance and in situ durability of anion exchange membrane water electrolyzers (AEMWEs) as one of the promising devices for producing green hydrogen. Herein, highly gas-permeable and dimensionally stable anion exchange ionomers (QC6xBA and QC6xPA) are developed, in which bulky cyclohexyl (C6) groups are introduced into the polymer backbones. QC6₅₀BA-2.1 containing 50 mol% C6 composition shows 16.6 times higher H₂ permeability and 22.3 times higher O₂ permeability than that of QC6₀BA-2.1 without C6 groups. Through-plane swelling of QC6₅₀BA-2.1 decreases to 12.5% from 31.1% (QC6₀BA-2.1) while OH^- conductivity slightly decreases (64.9 and 56.2 mS cm^-1 for QC6₀BA-2.1 and QC6₅₀BA-2.1, respectively, at 30 °C). The water electrolysis cell using the highly gas permeable QC6₅₀BA-2.1 ionomer and Ni_0.8Co_0.2O in the anode catalyst layer achieves two times higher performance (2.0 A cm^-2 at 1.69 V, IR-included) than those of the previous cell using in-house ionomer (QPAF-4-2.0) (1.0 A cm^-2 at 1.69 V, IR-included). During 1000 h operation at 1.0 A cm^-2, the QC6₅₀BA-2.1 cell exhibits nearly constant cell voltage with a decay rate of 1.1 µV h^-1 after the initial increase of the cell voltage, proving the effectiveness of the highly gas permeable and dimensionally stable ionomer in AEMWEs.