Effect of Interstitial Alkyl Chain Engineering of Anion Exchange Membrane for Improved CO2 Electrolyzer

Anion exchange membranes (AEMs) are emerging as crucial components for application in electrochemical CO2 reduction reactions. However, there are very few reports on structural design strategies for AEMs that regulate water management while suppressing cation crossover—issues responsible for cathode flooding and salt precipitation. In this study, our rationally designed poly(bisfluorene)-based AEM with alkyl chains (PBFA-QA) demonstrates improved contact properties with the CL and a well-developed ion transport channel. Thus, PBFA-QA significantly mitigates cathode flooding and salt precipitation compared to commercial AEMs (X37-50 RT and PiperION). Consequently, PBFA-QA achieves a CO partial current density of 331.7 mA cm‒2, which is much higher than that of X37-50 RT (188.7 mA cm‒2), and PiperION (179.7 mA cm‒2), respectively. Furthermore, we achieved a Faradaic efficiency for CO exceeding 92.3%, maintaining stable operation at 200 mA cm‒2 with PBFA-QA, a performance not attainable with X37-50 RT and PiperION.