N-Heterocyclic Carbene Ligands' Electronic Effects on Metallopolymer Anion Exchange Membranes

Metallopolymers are intriguing prospective materials for use as anion exchange membranes (AEMs) in fuel cells and water electrolysis applications. Metallopolymers potentially offer high ion conductivity due to the multivalent nature of metal cations; however, similar to organic cations, the durability of the organic component can be compromised by the alkaline environment. To develop AEMs with long operational lifetimes, the fundamental relationship between the metal-ligand pair and alkaline stability needs to be understood. Here, we synthesize metallopolymers with different N-heterocyclic carbene ligand side chains that are connected to gold cations to study the ligand electronic effects on the AEM relevant properties. Interestingly, when tested under the same conditions, the different metallopolymers present markedly different alkaline stabilities, ion conductivities, and water uptake values. Explanation for such discrepancies is provided based on data from organometallic complexes. Designing optimized complexes with the correct electronic parameters can advance the development of practical AEMs for alkaline fuel cells and water electrolyzers.