A strategy to construct alkali-stable anion exchange membranes bearing ammonium groups via flexible spacers

Abstract

A novel strategy is provided to construct alkali-stable poly(phenylene oxide) based anion exchange membranes to alleviate cation-induced degradation.

Configuring Anion‐Exchange Membranes for High Conductivity and Alkaline Stability by Using Cationic Polymers with Tailored Side Chains

“…Hydroxide ion conductivity of AEMs based on different polymers carrying QA or imidazolium groups via alkyl spacer units: PPO‐7Q, gQAPPO, PFBFF, and PAES containing fluorene units . The respective IEC values are given within parentheses, and the conductivity of a PPO with QA groups directly on the backbone (PPO‐1Q) is shown for comparison …”

“…Xu and co‐workers have prepared PPOs carrying QA groups placed on phenylpropyl spacer units (designated gQAPPO, Scheme h) . Phenyl propylbromide side chains were connected to PPO by reacting arylbrominated PPO with pre‐made borylated 1‐bromo‐3‐phenylpropane in a Pd catalyzed Suzuki coupling, before quaternization using trimethylamine.…”

“…This was found to greatly exceed the conductivity of a corresponding PPO with QA groups directly on the backbone. The alkaline stability of the gQAPPO membranes was probed by immersing a membrane in 1 m NaOH at 60 °C over 168 h, and ≈90% of the OH − conductivity was reported to be retained …”

Cationic Metallo‐Polyelectrolytes for Robust Alkaline Anion‐Exchange Membranes

“…[2a,b,m, 3] Them ost popular approach is the use of quaternary ammonium cation (QAC)-containing polymers.H owever, QACs are prone to degradation through Hofmann elimination (E2) or nucleophilic substitution (S N 2) under highly basic conditions.O ver the past few years,s everal strategies have been adopted to improve the alkaline stability of AEM backbones:1 )protect ammonium cations using steric hindrance,c onformational restrictions or inductive effects; [4] 2) explore alternative stable cations such as benzyl quaternary guanidinium, [5] imidazolium, [6] and phosphonium [7] to slow down degradation. [2a,b,m, 3] Them ost popular approach is the use of quaternary ammonium cation (QAC)-containing polymers.H owever, QACs are prone to degradation through Hofmann elimination (E2) or nucleophilic substitution (S N 2) under highly basic conditions.O ver the past few years,s everal strategies have been adopted to improve the alkaline stability of AEM backbones:1 )protect ammonium cations using steric hindrance,c onformational restrictions or inductive effects; [4] 2) explore alternative stable cations such as benzyl quaternary guanidinium, [5] imidazolium, [6] and phosphonium [7] to slow down degradation.…”

Comb‐Like Poly(Ether‐Sulfone) Membranes Derived from Planar 6,12‐Diaryl‐5,11‐Dihydroindolo[3,2‐b]Carbazole Monomer for Alkaline Fuel Cells

“…Bae's research team focused on designing AEMs with QA pendant side chains and a hydrophobic polymer backbone, which were more resistant to reaction in the presence of OH – . Another example was that of AEMs based on poly(phenylene oxide) with different flexible side chains that showed excellent OH – conductivity and high thermochemical stability . It is noteworthy that AEMs containing flexible side chains and strong π‐π stacking structures were successfully obtained by Yamaguchi's group.…”