Fluorinated Poly(aryl piperidinium) Anion Exchange Membranes with High OH ^– Conductivity: The Synergy of Microphase Separation and Free Volume

Anion exchange membranes (AEMs), as the core component of anion exchange membranes fuel cells (AEMFCs), exhibit high OH– conductivity and dimensional stability, which are critical for continuous and stable power generation. In this paper, the synthesis of 6,6′-dimethoxy-3,3,3′,3′-tetramethyl-1,1′-spirobiindane (SBI) was introduced, and it was synthesized to prepare a series of fluorinated poly(aryl piperidinium) microporous AEMs (QFPTP-SBI-m). The thermodynamic incompatibility in the polymer drives the formation of the microphase separation structure. The hydrophobic regions can restrict the swelling of the membrane, and the hydrophilic regions serve as ion transport channels. Additionally, the introduction of SBI monomers increases the free volume between the chains and reduces the transport resistance. The synergistic effect of microphase separation and free volume is utilized to regulate the properties of the AEMs. QFPTP-SBI-20% exhibited high OH– conductivity (197.53 mS cm–1), and the peak power density (PPD) reached 1.08 W cm–2 at a current density of 2.5 A cm–2. The WU of 41.36% and SR of 15.99% at 80 °C ensure good dimensional stability. Furthermore, the OH– conductivity was reduced by 8.71% after 1700 h (3 M NaOH). The prepared QFPTP-SBI-20% area exceeded 140 cm2, indicating its significant potential for large-scale applications.