Well‐Miscible Polymer Blend Membranes from Branched Tröger's Base Polymer and Quaternized Polymer as Proton Exchange Membranes for High‐Temperature Fuel Cells

The development of high‐performance polymer electrolyte membrane is crucial for advancing high‐temperature proton exchange fuel cells (HT‐PEMFCs). For this purpose, a branched Tröger's base polymer (TPB‐BTB) is designed and synthesized from 1,3,5‐tri(4‐aminophenyl)benzene (TPB), o ‐tolidine, and dimethoxymethane in trifluoroacetic acid, enabling a superacid‐catalyzed polymerization reaction to proceed under mild conditions. The resulting TPB‐BTP is integrated with a chemically stable and mechanically robust quaternized polymer (QPAF‐4) to form QPAF‐4/TPB‐BTB blend membranes. Structural characterization via X‐ray diffractometer (XRD) and fourier transform infrared (FTIR) spectroscopy confirms strong interpolymer interactions, contributing to enhanced membrane integrity. The blend membranes exhibited higher phosphoric acid (PA) absorption and better thermal and mechanical stability than those of the parent QPAF‐4 membrane. Furthermore, a PA‐doped blend membrane with the optimized composition (QPAF‐4/TPB‐BTB10) demonstrates nearly twofold the proton conductivity (32.3 mS cm −1 ) compared to a PA‐doped QPAF‐4 membrane (15.1 mS cm −1 ) under harsh conditions (5% relative humidity and 120 °C). A PA‐doped QPAF‐4/TPB‐BTB10 membrane achieves a maximum peak power density of 721.6 mW cm −2 at 160 °C and a current density of 1.95 A cm −2 , outperforming PA‐doped QPAF‐4 (683.0 mW cm −2 at 1.81 A cm −2 ) without backpressure, highlighting its great promise for HT‐PEMFCs.