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.

As a key component of anion exchange membrane fuel cells (AEMFCs), anion exchange membranes (AEMs) have been investigated in the last decades. Herein, a series of multication cross-linkers were introduced into side-chain-type poly(p-terphenyl isatin) to develop high-performance and long-term stable AEMs. Additionally, the effects of the hydrophilic cross-linker length on the membrane performance were systematically investigated. The resulting cross-linked membranes possess a low swelling ratio (<18% at 80 °C) and high tensile strength (51.1−58.3 MPa). Notably, the cross-linker length influences the AEM internal morphology. With hexyl as the spacer between backbones and cation groups in the cross-linker, 0.9q-PTI-6C exhibits the highest hydroxide ion conductivity of 118.5 mS/cm at 80 °C, which is ascribed to well-developed ion channels. Furthermore, alkyl spacer chains and cross-linked networks contribute to the excellent alkali stability of membranes. After immersion in 2 M NaOH for 1200 h at 80 °C, 0.9q-PTI-8C only shows 11 and 12.7% losses in ion conductivity and ion exchange capacity (IEC), respectively. The fuel cell fabricated using 0.9q-PTI-6C can achieve the maximum power density of 310 mW/cm 2 at 80 °C.