Here we explore the versatility of metal-cation-based anion exchange membranes (AEMs) to determine if metals other than just ruthenium can be implemented in this platform. Previously, our group synthesized a ring-opening-metathesis polymerization (ROMP)-based AEM featuring cationic ruthenium complexes to replace less stable organic cations. While these membranes demonstrated excellent chemical stability, mechanically robust properties and good conductivity, the choice of ruthenium, a rare earth metal, was not ideal for this type of application. Therefore, we synthesized AEMs containing more abundant metals, nickel and cobalt, in an effort to replace ruthenium. This was accomplished by synthesizing new monomers containing homoleptic metal complexes with norbornene functionalized terpyridine ligands. These monomers were then polymerized and crosslinked using ROMP to form AEMs which were tested for their water uptake, chemical and mechanical stability, and anion conductivity to elucidate whether nickel, cobalt, or both could be viable substitutes for ruthenium. The choice of metal effected neither water uptake nor mechanical properties and, despite more labile coordination bonds introduced through nickel and cobalt, all AEMs maintained excellent alkaline stability. However, changing the metal-cation in the AEM appeared to have an effect on the ability of the membrane to conduct anions, suggesting that the nature of the cation plays an important role in AEM performance. Results indicate that the nickel-containing AEM had the best conductivity of all three metals studied, demonstrating that other metals can be used in these types of AEMs, and in fact, there may be better options than ruthenium for overall performance.

Going beyond ruthenium in metal-cation-based anion exchange membranes

253rd National Meeting (2017)

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