Preparation Of Imidazolum-Based Anion Exchange Membranes And Study The Trasmission Mechanisms Of OH~-

Anion exchange membrane (AEM) plays an important role in energy storage system, such as fuel cells and flow batteries. It could separate the positive and negative electrolytes or fuels to prevent energy loss. And hydroxyl ion could transfer through AEM to form current circuit. However, the hydroxyl ion conductivity of AEM is about 0.01 S·cm-1, which is relatively low comparing to the commercial Nafion membrane (conductivity of H+is 0.1 S·cm-1). And the chemical stability of AEM is not that good.The preparation technology of AEM is mature, and many kinds of tests are utilized to evaluate the membrane properties. Because of the low hydroxyl ion conductivity, AEM hardly can be put into commercial use, which is a waste of time and raw materials. The performance of AEM might not be consistent with the expectation. So predicting the hydroxyl ion conductivity in AEM and investigating the effect of functional groups by molecular dynamics simulation is of significance.To improve the properties of AEM, a kind of imidazole functionalized AEM was synthesized with 2,5-bis(2,3,4,5,6-pentafluorophenyl)-1,3,4-oxadiazole (FPOx) and 4,4’-isopropylidenebis (2,6-dimethylphenol). Moreover, hydroxyl ion conductivity in AEM with different structure were studied using Material Studios (MS).(1) A series of fluorinated poly (aryl ether oxadiazole) membranes based on imidazolium salts were prepared via copolymerization between FPOx and 4,4’-isopropylidenebis (2,6-dimethylphenol). Then N-vinyl imidazole was added to bring in functional groups. Thermal cross-linking method was used to improve the membrane property. The hydroxyl ion conductivity was at 10-2 S-cm1 level, which was 9.02×10-2 S·cm-1 at 80℃. And the methanol permeability is 10 times lower than that of Nafion 117 membrane.(2) AEM based on 25% DS.50% DS and 75% DS were studied by molecular dynamics simulation with Materials Studio (MS). RDF (Radial distribution function) of N+-N+, N-OH-O was analyzed. The results showed that the hydroxyl ion would appear around imidazole groups at the biggest probability, which could promote the transfer of hydroxyl ion. Hydroxyl ion conductivity simulated by MSD (Mean square displacement) was 2.75×10-2 S cm-1. The force between methanol and imidazole was weak, which could prevent the diffusion of methanol effectively.(3) Line-type, Meta-type, and Diagonal-type AEMs were studied. The simulation results showed that the Line-type and the Diagonal-type AEMs were respectively beneficial and unfavorable to hydroxyl ion transfer, and the conductivity were expected to be 7.74×10-2 S-cm-1 and 1.78×10-2 S·cm-1 respectively.