Poly(spirofluorene)-Based Anion Exchange Membranes for Alkaline Electrochemical Energy Devices

Abstract

Anion exchange membranes (AEMs) with high conductivity and low hydrogen permeability guarantee efficient and reliable AEM fuel cells (AEMFCs) and water electrolyzers (AEMWEs). In this work, two monomeric spirofluorenes, spiro-[cyclopentane-1,9′-fluorene] (CPF) and spiro[cyclohexane-1,9′-fluorene] (CHF), were synthesized by a ring-closing reaction and further embedded into the poly(arylene alkylene) backbone to lower the ion transport resistance without compromising the gas barrier property of the AEM. The π−π stacking of the polymer backbone is weakened by the introduction of spirofluorene units, contributing to increased intermolecular spacing and improved microporous contents. On the other hand, despite the presence of spirocyclic units, an affordable low specific H 2 permeation of 28 pmol cm −1 s −1 was observed for the AEM. Moreover, an excellent hydroxide conductivity of 169 mS cm −1 at 80 °C was also recorded owing to the rapid ion transport caused by the microporosity. Benefiting from the good performance of the AEM, the engineered AEMFC based on PCHTPA exhibits a peak power density of 1.3 W cm −2 and an in situ durability of 330 h. Moreover, AEMWE shows a high current density of 3.2 A cm −2 at 2.0 V and excellent Faradaic efficiency of 98.4% with a hydrogen purity of 99.92%.