Preparation And Characterization Of Alkaline Quaternary Ammonium Anion-exchange Membranes For Fuel Cells

Anion exchange membrane fuel cells(AEMFC) have attracted great attention,due to its simple structure, low catalyst price, fast oxidation under the condition of alkaline and low fuel permeability. Anion exchange membrane(AEM), as a crucial component of AEMFC, serves as the hydroxide ion carrier and separator of the fuel and the oxidant. There are mainly two preparation methods for novel anion exchange membrane at present. One way is to modify the existing membrane materials, which can not only increase the membrane usage but also maintain high conductivity. The other way is to synthesize new membrane materials through designing novel monomers. Basing on the work mentioned above, In this paper, a series of novel anion exchange membrane were synthesized and modified. And we analyzed the ion exchange capacity, water uptake, swelling ratio, mechanical properties and chemical stability of the membranes.1. Firstly, we prepared BrPPO whose bromination degree is 55.2% by bromine methylation reaction with polyphenylene oxide as raw materials. Thestructure of polymer was characterized by 1H-NMR and FT-IR. Then 0.006 g palygorskite was added into BrPPO solution, 0.294 g Br PPO are dissolved in CHCl3. After using ultrasonic, a polystyrene ether film with the content of palygorskite was 2%. In the same way, we got polystyrene ether membranes in which the conent of palygorskite is 4% and 6%. Finally, a series of the quaternary ammonium-PPO/palygorskite composite membrane were prepared after quaternization and alkalization process. Ion-exchange capacity, water uptake, ion conductivity, mechanical property and thermal stabilities of polyphenylene oxide and composite membrane were tested. The experimental results show that the QPPO/6%palygorskite membrane has good mechanical,thermal stabilities and chemical stabilities which are better than other membrane.Hydroxide ion conductivity is 21.5mS.cm-1 at 80 ℃ under 100% relative humidity. The AEM still exhibited high hydroxide ion conductivities(over 18 mS.cm-1) in 5 mol.L-1 NaOH at 60℃ for 1 days. The conductivity of pure PPO is 9.2 mS.cm-1. The above suggest that palygorskite inorganic material modification is an effective method to prepare high-performance AEMs.2. DMBHF was synthesized from 9-fluorenone and 2,6-dimethylphenol.poly(arylene ether ketone)s were synthesized by polycondensation reaction with 9,9’-Bis(3,5-dimethyl-4-hydroxyphenyl) fluorene(DMHPE) and4,4’-difluorobenzophenone(DFBP). Then we obtained poly(arylene eher ketone)s membrane containing fluorine group by bromination, quaternization and alkalization reactions. The structures of poly(arylene ether ketone)s(PAEKs), brominated poly(arylene ether ketone)s(BPAEKs), and quaternizated poly(arylene ether ketone)s(QPAEKs) ionomers are confirmed by 1H-NMR spectroscopy and fourier transform infrared spectroscopy(FT-IR). The water uptakes, swelling ratio, hydroxide ion conductivities, ion exchange capacities(IEC), chemical stabilities and mechanical properties of the membranes are assessed. The experimental results show that the IEC of the ionomers varied from 1.50 to 2.32 mmol.g-1 owing to the increase of bromination degree. The QPAEK-c membrane with IEC value of 2.32 mmol.g-1 displays the best hydroxide ion conductivity of 33.6 mS.cm-1 at 80℃ and it still keeps a high hydroxide ion conductivity of 27.3 mS.cm-1 being conducted with 3 M Na OH solution at 60℃ for 24 h. The results above implys the ionomers membrane possesses a vast range of application prospect.