Study On Structure Design,Preparation And Properties Of Imidazolium-type Anion Exchange Membranes Based On PPO Polymer

As a kind of clean, efficient and green energy conversion device, fuel cells is promising to be one of the most outstanding technologies in new energy. Anion exchange membrane fuel cells (AEMFCs), due to the nonprecious metal catalyst, higher anode reaction kinetics and lower fuels permeability, have drawn wide attentions of many researchers in recent years.Anion exchange membrane (AEM), which is the core component of AEMFCs, largely determined the final performances of fuel cells. Therefore, the AEMs with excellent comprehensive performances have always been pursued by the scientists. Thus, it is meaningful to design and synthesize the novel AEMs with high conductivity and outstanding chemical stability, and we expect that our findings open a door for explored high performance AEMs, not only in novel cationic structure, but methodology. In this dissertation, the following works have been performed:1. A series of anion exchange membranes (AEMs) with different degrees of substitution were prepared by azide-alkyne cycloaddition between azidomethylated PPO and a novel alkyne-containing imidazolium, and their structures were confirmed by NMR, FT-IR and HRMS. The corresponding AEMs exhibited distinct hydrophobic/hydrophilic phase-separated morphology at higher imidazolium content, as evidenced by AFM and SAXS techniques, which favors for the construction of interconnected hydroxide transport channels. As a result, the as-prepared AEMs exhibited higher conductivity (95 mS/cm, 80 ℃,100%RH) than conventional imidazolium benzylic-type AEM (55 mS/cm,80 ℃, 100% RH) with even lower IEC.2. Constructing new AEMs with better alkaline stability imidazolium cation and a flexible spacer by "click chemistry", can not only improve the alkaline stability and ion conductivity of the AEMs, but also provide the suitable site on 1,2,3-thiazole rings for hydrogen bond, which is benefit for OH-migration due to the aggregation of ionic cluster and increase of hydration number. This strategy possess high efficiency and universality, and it also put forward a reasonable and convenient idea for the structure design of AEMs. Moreover, the results demonstrated that the introduction of a 1,2,3-triazole moiety into the polymer side chain does not compromise its thermal and alkaline stability.3. Electron donating groups were introduced into the C2 position of imidazole ring, which can effectively reduce the electropositivity of the related carbon atom by electron delocalization due to the conjugation effects. Hence, the nucleophilic attack of OH- at the C2 position was significantly restricted and the corresponding imidazolium cation showed excellent alkaline stability.1H NMR results demonstrated that the imidazolium salt with C2-substituted by methylthio group was quite stable in 4 M NaOH solution at 80 ℃ after 7 days. Furthermore, the charge distribution of C2 position was also confirmed by a theoretical calculation employing the DFT method. Therefore, we confirmed that the imidazolium salt with methylthio substituent showed excellent chemical stability and its application in anion-exchange membranes was also studied preliminary.