Advances in basic-group-containing polyaromatic membranes via superacid-catalyzed polyhydroxyalkylation for high...

High temperature proton exchange membrane fuel cells (HT-PEMFCs), operating at 120-200 °C, offer clear advantages over low temperature systems, including faster electrode kinetics, higher carbon monoxide tolerance, and simplified heat and water management. The core of HT-PEMFCs is the high temperature proton exchange membrane (HT-PEM), whose structure and stability largely determine cell performance and lifetime. In this Feature Article, we review recent advances in HT-PEMs based on basic heterocycle-containing polyaromatics synthesized via superacid-catalyzed polyhydroxyalkylation, with emphasis on our contributions over the past five years. Two main material platforms are discussed: polyaromatics incorporating basic groups into the polymer main chain and those bearing side-chain basic functionalities. We mainly analyze their structural characteristics, and highlight how molecular design controls properties such as phosphoric acid doping and retention, conductivity, mechanical strength, and chemical robustness. Key strategies to mitigate the performance trade-offs are also summarized, including post-functionalization, copolymerization, formation of polymers of intrinsic microporosity, branching, chemical crosslinking, and polymer blending. In addition, we compare the fuel cell performance and durability of HT-PEMs prepared via superacid-catalyzed polyhydroxyalkylation. Finally, we discuss the major challenges facing this field, such as long-term stability under harsh conditions, phosphoric acid loss, and the need for scalable and cost-effective synthesis. By clarifying structure-property relationships and design principles, this review provides guidance for the development of high-performance, economically viable HT-PEMs and supports progress toward next-generation HT-PEMFC technologies.