Highly conductive and chemically stable alkaline anion exchange membranes via ROMP of trans-cyclooctene derivatives

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 116; no. 20; pp. 9729 - 9734
• Main Authors: You, Wei, Padgett, Elliot, MacMillan, Samantha N., Muller, David A., Coates, Geoffrey W.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 14.05.2019
• Subjects: alkaline anion exchange membrane; Anion exchange; Anion exchanging; block and random copolymer; Block copolymers; Catalysts; Cations; Chemical degradation; Conduction; Conductivity; Copolymers; cross-linked polymer; Crosslinking; Fuel cells; Fuel technology; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Magnetic resonance spectroscopy; Membranes; Monomers; NMR; NMR spectroscopy; Nuclear magnetic resonance; Organic chemistry; Physical Sciences; Polymerization; Polymers; Stability; trans-cyclooctene; Transmission electron microscopy; block and random copolymer; trans-cyclooctene; alkaline anion exchange membrane; transmission electron microscopy; cross-linked polymer
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1900988116

Alkaline anion exchange membranes (AAEMs) are an important component of alkaline exchange membrane fuel cells (AEMFCs), which facilitate the efficient conversion of fuels to electricity using nonplatinum electrode catalysts. However, low hydroxide conductivity and poor long-term alkaline stability of AAEMs are the major limitations for the widespread application of AEMFCs. In this paper, we report the synthesis of highly conductive and chemically stable AAEMs from the living polymerization of trans-cyclooctenes. A trans-cyclooctene–fused imidazolium monomer was designed and synthesized on gram scale. Using these highly ring-strained monomers, we produced a range of block and random copolymers. Surprisingly, AAEMs made from the random copolymer exhibited much higher conductivities than their block copolymer analogs. Investigation by transmission electron microscopy showed that the block copolymers had a disordered microphase segregation which likely impeded ion conduction. A cross-linked random copolymer demonstrated a high level of hydroxide conductivity (134 mS/cm at 80 °C). More importantly, the membranes exhibited excellent chemical stability due to the incorporation of highly alkaline-stable multisubstituted imidazolium cations. No chemical degradation was detected by ¹H NMR spectroscopy when the polymers were treated with 2 M KOH in CD₃OH at 80 °C for 30 d.