Crosslinked polyfluorene-based membranes with well-balanced properties for anion exchange membrane fuel cells

Abstract

Developing high-performance anion exchange membranes (AEMs) with balanced properties is crucial for the advancement of AEM fuel cells. However, the current performance and durability of AEMs are not promising due to the lack of balance in their properties, where one property, such as swelling ratio, is often sacrificed for another, such as hydroxide conductivity. Consequently, despite recent progress, achieving a trade-off among the various properties of AEMs remains a substantial challenge. Herein, we address this issue through the optimization of crosslinking degree in ether-free polyfluorene-based AEMs. The results demonstrate that an optimal crosslinking degree significantly improves the swelling ratio (<15.9 %), water uptake (<78.0 %), and mechanical properties (>35 MPa), while simultaneously enhancing hydroxide conductivity (>144.6 mS cm ^-1), owing to improved microphase separated morphology. Moreover, the alkaline and oxidative stability of the prepared membranes surpasses that of most state-of-the-art AEMs and represents one of the best-reported chemical stability results, with over 93 – 95 % remaining hydroxide conductivity, ion exchange capacity, and tensile strength after 1080 h in 3 M NaOH solution at 80 °C. Furthermore, the AEM fuel cell achieves a peak power density of 1.03 W cm⁻² and excellent durability with a voltage decay rate of 0.62 mV h⁻¹, surpassing the performance of commercial PiperION^TM AEM under identical testing conditions.