Incorporating chrysene units to improve the performance of poly(arylene piperidinium) and poly(arylene quinuclidinium) anion exchange membranes for water electrolysis

Abstract

Chrysene-containing polymers functionalized with piperidinium- and quinuclidinium cations, respectively, are prepared by polyhydroxyalkylation and studied as anion exchange membranes (AEMs). Experimental results, supported by theoretical considerations, indicate that the chrysene units significantly enhance alkaline stability; a poly(chrysene piperidinium) AEM shows only 16% total ionic loss, compared to 37% for a corresponding poly(terphenyl piperidinium) benchmark after 20 days in 5 M NaOH at 90 °C. Quinuclidinium-functional AEMs show an even higher stability without any detectable degradation or ionic loss after the same conditions during 40 days. In addition, the chrysene units promote microphase separation, facilitating hydroxide conductivity, which reaches up to 182 mS cm⁻¹ at 80 °C. A selected AEM containing 25% chrysene units is evaluated in a water electrolyzer (AEMWE) single cell with plain Ni foams as electrodes, reaching a current density of 704 mA cm⁻² at 2.5 V and 90 °C, thereby outperforming a benchmark PiperION^® AEM under the same conditions. An in-situ durability test at 500 mA cm⁻² during 200 h at 90 °C further confirms the high performance of the AEM. This study demonstrates the significant improvements in AEM stability, hydroxide conductivity, and electrolyzer performance achievable by incorporating chrysene units in the polymer backbone.