Understanding the alkaline stability of imidazolium and benzimidazolium functionalized poly(phenylene oxide) based hydroxide exchange membranes

• Published in: Materials today : proceedings Vol. 51; pp. 2550 - 2555
• Main Authors: Rao, Anil H.N., Murthy Shekhar, S., Halashankar Swamy, M.H., Pranava, H.K., Kushal, P.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 2022
• Subjects: Alkaline stability; Benzimidazolium; Hydroxide exchange membranes; Methyl imidazolium; Hydroxide exchange membranes; Alkaline stability; Benzimidazolium; Methyl imidazolium
• ISSN: 2214-7853; 2214-7853
• DOI: 10.1016/j.matpr.2021.12.352

•Methyl imidazolium and benzimidazolium functionalized PPO membranes was prepared.•Hydroxide ionic conductivity and membrane physical properties were investigated.•Methyl imidazolium functionalized PPO mmebrane displayed excellent alkaline stability compared to benzimidazolium PPO membrane due to hyperconjugation effect.
The imidazolium and benzimidazolium groups containing poly(phenylene oxide) (PPO) hydroxide exchange membrane were synthesized and characterized. The membranes were cast by solution casting method yielding transparent, flexible, and rigid membranes. The physical properties of the membrane, such as ion exchange capacity (IEC), water absorption, and swelling behavior, were investigated. A comparative study of imidazolium and benzimidazolium functionalized PPO membrane focusing on hydroxide conductivity, and alkaline stability was comprehensively examined. The C2 substituted methyl imidazolium membrane displayed unique morphology and conductivity of 15 mSCm−1 at 25 °C. Due to the sterically protected methyl group at the C2 position, imidazolium functionalized PPO membrane showed higher alkaline stability for 700 h. Furthermore, benzimidazolium cations would be more easily attacked by a nucleophile (OH−) than imidazolium cations, resulting in ring-opening of the heterocyclic ring.