Piperidine Molecular Engineering in Polyaromatic Membranes for High-Performance High Temperature Proton Exchange Membrane Fuel Cells

High temperature proton exchange membrane fuel cells (HT-PEMFCs) require polymer electrolytes that simultaneously achieve efficient proton transport, excellent chemical durability, and mechanical stability under harsh operating conditions. Poly(terphenyl piperidine) (PTP) based membranes have emerged as promising candidates owing to their rigid aromatic backbones and strong acid-base interactions with phosphoric acid (PA); however, the influence of piperidine molecular structures on membrane properties remains largely unexplored and limited chemical stability need to be solved. Herein, we report a molecular engineering strategy that regulates the intrinsic piperidine configuration in PTP polymers to establish the relationship between piperidine structure, PA interaction, and membrane performance. Five structurally different piperidone monomers, including N-methyl-4-piperidone, 4-piperidone hydrochloride monohydrate, piperidine-3-one hydrochloride, N-propyl-4-piperidone, and N-benzyl-4-piperidone, are employed to polymerize with terphenyl through superacid-catalyzed Friedel–Crafts polymerization to obtain PTP, PTP-4-H, PTP-3-H, PTPP, and PTBP, respectively. The results reveal that N-substituents on the piperidine ring strongly affect polymer chain packing, PA affinity, oxidative stability, and mechanical properties. Among the investigated polymers, PTP-4-H with unsubstituted piperidine units exhibits the optimal balance between chemical stability, proton conductivity and mechanical robustness. Furthermore, biphenyl units are introduced into the PTP-4-H backbone to increase the density of piperidine functional groups and construct more efficient proton-conducting networks. The optimized P(TP70%-BP30%–4-H)/PA membrane achieves a high proton conductivity of 83 mS cm–1 at 180 °C and maintained a tensile strength of 8.0 MPa after PA doping. When assembled into an H2/O2 single cell without external humidification or back pressure, the membrane delivers a peak power density of 1039 mW cm–2 at 180 °C. This work provides insights into the molecular-level regulation of piperidine-containing aromatic polymers and demonstrates that rational control of piperidine configuration and density is an effective strategy for developing high-performance HT-PEMs.