Ultra-Stable Imidazolium-Based Anion Exchange Membranes for Alkaline Fuel Cell Applications

The development of cationic polymers for anion-exchange membranes (AEMs) with high alkaline stability and conductivity is a considerable challenge in materials chemistry. However, the commonly employed organic cations have limited alkaline stability, especially at high temperatures, which restricts the commercialization of AEM alkaline fuel cell technology. To address this problem, we have designed and synthesized a series of novel imidazolium-based AEMs for alkaline fuel cell applications. Degradation rates and mechanisms of small organic cations were analyzed by NMR spectroscopy and rationalized using density functional theory (DFT) calculations. The substituent selection at each position of the imidazolium ring has a dramatic effect on the overall cation stability, correlating to the stability profiles of corresponding AEMs. The most stable imidazoliums were chosen to polymerize robust AEMs, while their stability was examined by dynamic vapor sorption (DVS) technique, and conductivity was measured with the four-probe method. The results have shown the superior alkaline stability and conductivity of our imidazolium-based AEMs even at high temperature (80 °C), confirming they are promising AEM candidates for practical application in alkaline fuel cell.