Porous Aromatic Framework with Imidazole Group-Reinforced High-Temperature Proton Exchange Membrane with Promoted Proton Transport Efficiency and Power Density

Abstract

The plasticizing effect leading to a marked deterioration in mechanical properties and a substantial leakage of phosphoric acid (PA), which occurs at a high PA-doping level, is a critical challenge for polybenzimidazole (PBI) high-temperature proton exchange membranes (HT-PEMs) doped with PA (PA–PBI). The plasticizing effect leading to a marked deterioration in mechanical properties and a substantial leakage of PA, which occurs at a high PA-doping level, is a critical challenge for PA−PBI membranes. In this study, novel porous aromatic frameworks framed with imidazole groups were synthesized, which can afford extra proton transport sites and develop a perfect hydrogen bonding network with PA. The obtained HT-PEM-doped poly[4,4′-(diphenyl ether)-5,5′-bibenzimidazole] (OPBI) with 10% PAF-226-PA exhibited a tensile strength of 116.5 MPa, a proton conductivity of 0.17 S cm^–1 at 200 °C, and a peak power density of 641.57 mW cm^–2 with a catalyst Pt/C loading of merely 0.3 mg cm^–2, demonstrating good potential for application in HT-PEM fuel cells. The formed hydrogen bond network enhanced proton mobility and helped retain the PA, mitigating the PA loss, enhancing the interfacial interaction between PAF-226-PA and OPBI, and thus improving the electrochemical and mechanical performance of HT-PEMs for high-performance, high-temperature fuel cells.