In response to prepare high-stable and ion-conducting polyelectrolyte for hydroxide exchange membrane (HEM) applications, we present an ultrastable polyelectrolyte based on six-membered heterocyclic 6-azonia-spiro[5.5]undecane (ASU) and polyphenyl ether (PPO). A series of ASU-functionalized PPO polyelectrolytes (ASU-PPO), which can be easily dissolved in low-boiling pointing solvent, have been successfully synthesized by a remote-grafting method. The ASU precursor is stable in 1 M NaOH/DO at 80 °C for 2500 h as well as in 5 M NaOH/DO at 80 °C for 2000 h, and the predicted half-life of the ASU precursor would exceed 10 000 h, even higher in the future. Besides, these remote-grafting ASU-PPO polyelectrolytes are stable in 1 M NaOH at 80 °C for 1500 h. Robust and pellucid segmented ASU and triple-ammonium-functionalized PPO-based HEMs attach OH conductivity of 96 mS/cm at 80 °C and realize maximal power density of 178 mW/cm under current density of 401 mA/cm.

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In order to develop a high-performance and longterm stable anion exchange membrane (AEM), ether-bond-free poly(biphenyl bromohexyl indole) (PPHIN) was prepared and explored as a highly alkaline stable polymer backbone. Combining two alkyl chain modification strategies, a series of flexible doublecationic side chains with different lengths of extender chains were grafted onto the PPHIN backbone to improve the hydrophilic/ hydrophobic microphase separation, ionic conductivity, and alkaline stability of the AEM. The resulting PPHIN-N1C possessed a high hydroxide conductivity of 136 mS/cm at 80 °C due to the well-developed microphase separation. Furthermore, the PPHIN-N8C with a long extender chain exhibited high ionic conductivity (103 mS/cm), a low swelling ratio, and excellent alkaline stability. The ionic conductivity of PPHIN-N8C only decreased by 13% after soaking in 2 M NaOH at 80 °C for 1000 h, which was attributed to the steric hindrance of the extender hydrophobic alkyl chain. The single cell using the PPHIN-N8C membrane has a maximum peak power density of 216 mW/cm 2 at a current density of 472 mA/cm 2 at 80 °C. The results suggest that this type of PPHIN-based AEM is promising in anion exchange membrane fuel cell application.

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