Enhanced Hydroxide Conductivity Of Polysulfone Anion Exchange Membrane By Doping Nanocomposite

Alkaline anion exchange membrane Fuel cells (AAEMFCs) have been recognized as one of the most promising clean power technologies applied in vehicles and mobile electronic devices. As one of the key components of AAEMFCs, alkaline anion exchange membranes (AAEMs) serve as fuel/oxidant separator and hydroxide conductor simultaneously. Unfortunately, low hydroxide conductivity is still a big challenge for commercialization. In order to enhance the hydroxide conductivity of AAEMs, an effective way is increasing ion exchange capacity (IEC). By increasing IEC, the concentrations of functional groups are effectively raised, and large amounts of functional groups dispersed in the membrane make the channels easy to be interconnected, leading to high conductivity. However, the large IEC also results in excessive water uptake, thus causing severe swelling and poor mechanical strength of the membrane. Recently, it was found that raising the regional aggregation of functional groups could facilitate the formation of the continuous channels at a low IEC.In this work, a new method was proposed to prepare the membrane with the regional aggregation of functional groups by incorporating nanocomposites surface-functionalized with a large number of functional groups.In the first work,1,4-Diazabicyclo[2.2.2]octane (DABCO) surface-functionalized SiO2 (SiO2-Da) nanocomposites were prepared by the reaction of DABCO, y-Chloropropyl triethoxysilane and SiO2 nanocomposites. To obtain the composite membrane, SiO2-Da and DABCO functionalized polysulfone (PSf-Da) were mixed. The properties of the composite membrane (PSf-Da/SiO2-Da) had been test. With the mass ratio increase from 0% to 12%, hydroxide conductivity of PSf-Da/SiO2-Da keeps increasing, and when the mass ratio reaches 12 wt.%, hydroxide conductivity of PSf-Da/SiO2-Da shows the highest conductivity, eg., the hydroxide conductivity of the composite membrane based on PSf-Da with functionalization degree of 102% reaches 38 mS cm-1 (at 20 ℃), and PSf-Da-102% membrane is 24 mS cm-1.To improve the hydroxide conductivity of the composite membrane, imidazolium surface-functionalized SiO2 (SiO2-Im) nanocomposites were synthesized by the reaction of 1, 2-Dimethylimidazole, y-Chloropropyl triethoxysilane and SiO2 nanocomposites. The obtained SiO2-Im nanocomposites were incorporated into imidazolium functionalized polysulfone (PSf-Im) to fabricate composite alkaline anion exchange membranes. The uniform dispersion of nanocomposites in the membrane was demonstrated by SEM. With increasing mass ratio of SiO2-Im from 0% to 20%, hydroxide conductivity of composite membrane dramatically increased at first and then decreases. The composite membrane with 12 wt.% of SiO2-Im shows the highest conductivity, e.g., the hydroxide conductivity of the composite membrane based on PSf-Im with functionalization degree of 76% reaches 32 mS cm-1 (at 20 ℃) that is 68% higher than the membrane’s without doping SiO2-Im (19 mS cm-1). In addition, adding SiO2-Im has a slight effect on water uptake and swelling ratio of composite membrane. It indicates that doping surface-functionalized nanocomposites is a simple and effective method to enhance the hydroxide conductivity without increasing swelling. But the SiO2-Im nanocomposites are non-stable in hot alkaline solution, shown in the data of alkaline stability test.By using Al2O3 nanocomposite to replaces SiO2, alkaline stability of the surface-functionalized nanocomposites would be improved. The imidazolium surface functionalized Al2O3 (Al2O3-Im) nanocomposites were prepared by the reaction of 1, 2-Dimethylimidazole, y-Chloropropyl Triethoxysilane and Al2O3 nanocomposites. The composite membrane PSf-Im/Al2O3-Im was prepared as the same method. The properties of water uptake, swelling ratio, hydroxide conductivity and morphology were investigated. The effect of the SiO2-Im nanocomposites dosage on the properties of the membrane was also studied. As expected, PSf-Im/Al2O3-Im showed stability in alkaline. By immersing a membrane sample in a 1 M KOH solution at 60 ℃. The degradation of the membrane sample was evaluated by testing the change of hydroxide conductivity. After 30 h, the hydroxide conductivity of PSf-Im/Al2O3-Im still keep at 35 mS cm-1 (40 mS cm-1 at beginning).