High Tg Norbornene-Based Aems with Excellent Hydroxide Conductivity and Mechanical Robustness

Abstract

Anion exchange membranes (AEMs) are a key component in many electrochemical energy devices such as fuel cells, electrolyzers, and flow batteries. Though much progress has been made in the development of AEMs, the chemical and mechanical stability of the membrane remains an issue for long-term operation. Studies have demonstrated that the absence of heteroatom linkages such as ether, sulfide, and sulfone in the backbone improve the long term alkaline and mechanical stability of AEMs. Here we report our study on the development of highly robust and chemically stable polyolefin membranes and ionomers. The norbornene-based membranes and ionomers were successfully synthesized by vinyl-addition polymerization of norbornene derivatives. They exhibit a high glass temperature (Tg>200°C) that provides mechanical stability at elevated temperatures. The length of the pendant quaternary ammonium group greatly influences ease of quaternarization, conductivity, and water uptake. Thin stable membranes can be fabricated at 20-30 µm, to assure low ASR values. The membranes exhibit excellent hydroxide conductivity (>120 mS/cm at 80°C, in water) and stability towards hydroxide ions. The fuel cell performance of the AEMs will also be discussed.