(291e) Chemical Stability and Ion Transport in Polymerized Ionic Liquid Anion Exchange Membranes

Non-platinum (low-cost), long-lasting, solid-state alkaline fuel cells (AFCs) require anion exchange membranes (AEMs) that have high alkaline chemical stability, high hydroxide ion conductivity, and adequate mechanical properties. In this study, numerous polymerized ionic liquid (PILs) were synthesized with various covalently attached cations (butylimidazolium, butylmethylimidazolium, trimethylammonium, butylpyrrolidinium, trimethylphosphonium) and various backbone/cation pairings (backbones: ethyl methacrylate, undecyl methacrylate, undecyl acrylate, styrene; covalently attached cations: butylimidazolium, trimethylammonium, butylpyrrolidinium). Their alkaline chemical stability was quantified using ¹H NMR spectroscopy, and the styrene/butylpyrrolidinium pairing proved to be highly chemically stable, with no degradation in 20 equivalents (0.5 M) KOH at 60 °C for 168 h.

Considering the high alkaline chemical stability of the styrene/pyrrolidinium-based PIL, the conductivity and chemical stability of a PIL block copolymer (ABCBA pentablock terpolymer) with a styrene/pyrrolidinium-based PIL block was investigated. A high hydroxide conductivity of 43.4 mS cm^-1 at 60 °C in liquid water was achieved and no degradation or loss of conductivity was observed in the membrane after 168 h in 1 M KOH at 60 °C. PIL block copolymers utilizing a styrene/pyrrolidinium backbone/cation pairing in the PIL block represent a promising chemistry for producing highly conductive, chemically stable, robust AEMs for implementation in future solid-state AFCs.