Alkaline Stability Study of Poly(Norbornene)‐Based Stereocyclic and Cross‐Linked Anion Exchange Membranes

ABSTRACT The anion exchange membrane (AEM) fuel cell has become a low‐cost next‐generation fuel cell technology due to continuous research. The overall properties of AEMs are significantly affected by the proper configuration of cationic groups in the polymer backbone. A method to address the relationship between equilibrium ion conductivity, mechanical strength, and stability has been presented by constructing unique hydrophilic and hydrophobic microphase separation structures. The AEMs have a hydrophilic and hydrophobic microphase separation structure. A type of AEMs has been designed and synthesized by using polynorbornene diblock copolymer as the main chain, 1,4‐diazabicyclo[2,2,2]octane (DABCO) as the cross‐linking agent, and trimethylamine (TMA) as the quaternary ammonium salt reagent. Anion exchange membranes with varying degrees of cross‐linking were synthesized by controlling the amount of cross‐linking agent. These membranes were named CL‐aPNB‐ x ‐DABCO‐TMA. The AFM phase diagrams and SAXS diagram indicated that CL‐aPNB‐ x ‐DABCO‐TMA has a distinct hydrophobic region, wider ion transport channel, and more reliable ion transport capability. The highest ionic conductivity was observed in CL‐aPNB‐5%‐DABCO‐TMA, which was 135.41 mS cm −1 at 80°C. After being soaked in hot alkali (80°C, 1 M NaOH) for 35 days, over 83.9% of the initial OH − conductivity was retained.