Stability Descriptors for (Benz)imidazolium-Based Anion Exchange Membranes

(Benz)imidazolium-based polymers are a promising class of anion exchange membrane materials for alkaline fuel cells and electrolyzers. This study focuses on the alkaline stability of (benz)imidazolium-based compounds by exploring the relationship between molecular structure and degradation rate. A correlation analysis, using ab initio quantum chemical calculations, reveals suitable stability descriptors for three types of compounds, namely, benzimidazoliums, penta-substituted imidazoliums, and bis-arylimidazoliums. The strongest correlation is found between the Gibbs free energy change of the C-2 hydroxide attack step and the experimental stability. Notably, the activation energy and Gibbs free energy change of the hydroxide attack on C-2 display a high correlation. Identifying computationally efficient descriptors is a crucial prerequisite for the screening and inverse molecular design of imidazolium-based compounds with high alkaline stability.