Sulfonic Acid Side-Chain-Engineered Poly(terphenylacetylpyridine) Membranes for HT-PEMFC Applications

Abstract

High-temperature proton-exchange membranes (HT-PEMs) are key components for HT-PEM fuel cells (HT-PEMFCs), owing to their ability to enable efficient proton transport under anhydrous operating conditions. Although phosphoric acid (PA)-doped polybenzimidazole (PBI) membranes have been extensively investigated for HT-PEMFCs, their complicated synthetic procedures, poor processability, and reliance on potentially carcinogenic monomer restrict their application. In this work, a series of pyridine-containing poly(terphenylacetylpyridine) (PTAP)-based membranes functionalized with sulfonic acid side chains are successfully designed and synthesized through a facile superacid-catalyzed polyhydroxyalkylation strategy followed by Menshutkin-type grafting reactions. Benefiting from the ether-free rigid aromatic backbone and the synergistic interactions among pyridine groups, sulfonic acid moieties, and PA molecules, the optimized PTAP-20%SO3/179%PA membrane simultaneously exhibits enhanced PA retention of 96.7%, improved proton conductivity of 76.5 mS cm–1 at 180 °C, a satisfactory mechanical strength of 9.5 MPa, and excellent chemical stability. The single cell based on the above membrane delivers a peak power density of 676 mW cm–2 at 160 °C under nonhumidified H2/O2 conditions without backpressure, together with stable open-circuit voltages above 0.91 V. This study demonstrates an effective molecular engineering strategy for constructing high-performance HT-PEMs with balanced PA retention, chemical stability, proton conductivity, and fuel-cell performance.