Multication Cross-Linked Poly(p-terphenyl isatin) Anion Exchange Membranes for Fuel Cells: Effect of Cross-Linker Length on Membrane Performance

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/cm2 at 80 °C.