Preparation And Characterization Of Cerium Phosphate Nanoparticle/Post Cross-Link Polybenzimidazole Composite Membrane For Htpemfcs

As an environmentally clean and efficient energy, proton exchange membrane fuel cell (PEMFC) is widely used in the fields of aerospace industry, transportation, distributed power plants and mobile power source. Nowadays, the development of PEMFC mainly focuses on the high temperature proton exchange membrane fuel cell (HTPEMFC). It is characterized by faster electrode reaction kinetics, simpler water and heat management, more fuel choice and co-generation. Phosphoric acid (PA) doped polybenzimidazole (PBI) was gained much attention for its excellent stabilities and high proton conductivity under high temperature.However, during the process of PBI membrane fabrication, commercial PBI resin suffers from low phosphate content, poor processability and deficient oxidation resistance. In this paper, a series of phosphoric acid doped PBI membranes were prepared by microwave post cross-link method and sol-gel method. In order to improve the oxidation resistance of the membranes, cerium phosphate nanoparticle was used as radical scavenger in PBI membranes. The dimensional stability and oxidation resistance of membranes have been greatly improved. Specific research contents are as follows.1. Cerium phosphate nanoparticle was prepared by hydrothermal method and modified with 3-aminopropyl-triethoxysilane to improve the dispersity in polymer matrix. The surface-modified cerium phosphate nanoparticle was characterized by FT-IR, SEM-EDX, XRD, TEM, and SEM. Quenching test of hydroxyl radical was designed to check the oxidation resistance of cerium phosphate nanoparticle. The result indicates that cerium phosphate nanoparticle can quench the hydroxyl radical in Fenton’s reagent, and the quenching efficiency reaches to 64%.2. Under microwave condition, five kinds of aliphatic chain PBI oligomers (Hex-1-5) and pyridine-based PBI oligomers (Py-1-5) were synthesized by tuning the molar ratio of 3,3’-diaminobenzidine (DAB) and adipic acid or 2,6-Pyridinedicarboxylic acid(1.06,1.09,1.14,1.2 and 1.25). Starting from these oligomers and N-substituted polyethylene polyamine methyl propionate cross-linking agents, sixteen kinds of cross-link PBI membranes were prepared by novel microwave post cross-link method and sol-gel method. The cross-link PBI membranes were characterized by Fenton test, proton conductivity, and mechanical performance. The results show that the cross-linked PBI membranes prepared from oligomers Hex-1 and Py-1 with cross-linking agent ETDA-4MA show the best comprehensive performance.The cerium phosphate/cross-link PBI composite membranes were prepared from Hex-1, Py-1, ETDA-4MA and cerium phosphate nanoparticle by microwave cross-linking. The performance of composite membranes was characterized by mechanical performance, chemical stability, thermal stability, and proton conductivity. The result indicates that the addition of cerium phosphate nanoparticle in 1 wt% can improved the comprehensive performance of cross-linked PBI membranes. After 168 h room temperature Fenton test, the residual mass of M-CePO4/Hex-1-ETDA-4MA and M-CePO4/Py-1-ETDA-4MA was 89% and 93%, respectively. The proton conductivity of M-CePO4/Hex-1-ETDA-4MA and M-CePO4/Py-1-ETDA-4MA reached up 79 mS·cm-1 and 101 mS·cm-1 at 160℃(anhydrous condition), respectively.