Nitrogen Heterocyclic Compounds Grafted Polyhedral Oligomeric Silsesquioxanes For High Temperature Polymer Electrolyte Membrane Applications

Proton exchange membrane fuel cells(PEMFCs) have been considered as attractive energy conversion devices for both automobiles and stationary applications because of their high energy density, high energy conversion efficiency, and environmental friendliness. High-temperature operation of PEMFCs in the range of 100-200℃is further beneficial because of the improved fuel efficiency and the reduced catalyst poisoning by CO. The proton conductivity of proton exchange membranes containing sulfonic acids(-SO3H), such as Nafion, dramatically decreaess at temperatures higher than 100℃because of the fast evaporation of water in the membrane. Hereby, the development of new proton conduction medium becomes an important issue for HT-PEMFCs. In this thesis, two compounds containing nitrogen heterocyclic moiety and polyhedral oligomeric silsesquioxane(POSS) were first synthesized, and according composite membranes containing designed nitrogen heterocyclic moiety grafted on POSS and Nafion were fabricated.The membranes were characterized with different phyical and electrochemical techniques and the following conclusion has been drawn as following:(1) Through the hydroilysis of chloropylsiloxanes the functionalized POSS were synthesized, which containing eight organic activity chains. With eletrophilic substitution reaction, imidazole and triazole moieties were grafted onto the surface of formed POSS particles. Different characterization techniques were applied to confirm the designed chemical struture of the synthesized caompounds.(2) The SEM,AFM,EFM and linear scanning spectrum distribution images of the two composite membranes showed that the POSS-imidazole and POSS-triazole can be uniformly distributed in the composite membrane, and the thermo-mechanical properties of the membranes were tested by TMA and TG.At the temperature close to the glass transition temperature, the POSS-imidazole and POSS-triazole remarkably reinforce the physical dimension of the membrane when the Nafion polymer structure is destroyed. The cell assembled with Nafion/POSS-imidazole and Nafion/POSS-triazole composite membranes has a relatively stable performance, and achieves a voltage of 0.501V(Nafion/POSS-imidazole) and 0.465 V (Nafion/POSS-triazole) at a current density of 200mAcm-2 at 120℃under 33% relative humidity, which are better than the other high-temperature proton exchange membran, giving this membrane a potential electrolyte for high-temperature fuel cell applications.