(Invited) Polymerized Ionic Liquid Block Copolymers As Solid-State Electrolytes in Alkaline Fuel Cells
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Alkaline fuel cells (AFCs) that employ solid-state anion exchange membranes (AEMs) as the electrolyte separator are of great interest as they produce high power densities at low operating temperatures (< 200 C) and enable the use of non-platinum electrodes (e.g., nickel), significantly reducing cost relative to proton exchange membrane fuel cells. Several challenges limiting the wide scale use of membrane-based AFCs is the alkaline chemical stability and ion transport of polymers used as AEMs. Recently, polymerized ionic liquid (PIL) block copolymers with a range of chemically stable heterocyclic cations have become candidates to investigate for AFCs. PIL block copolymers constitute an emerging class of polymers and a distinct set of block copolymers that synergistically combine the advantageous properties of both PILs and block copolymers and are synthetically highly versatile with numerous cation and anion chemistries available. Specifically, the unique physiochemical properties of PILs, such as high solid-state ionic conductivity, high chemical, thermal and electrochemical stability, and widely tunable physical properties (e.g., via anion exchange), are incorporated in the block copolymer architecture, which allows for self-assembly into a range of nanostructures, where morphology type and domain size are tunable. In this talk, the synthesis, alkaline chemical stability, and ion transport of numerous PIL block copolymers developed in our research group will be discussed. More specifically, both the cation and backbone chemistry have a significant effect on alkaline chemical stability and various chemistries and chain architectures have a significant impact on ion conductivity. The AFC performance of PIL block copolymers as both the electrolyte and ionomer in the catalyst layer will also be discussed.
