Preparation And Characterization Of PEEKK-based Alkaline Anion Exchange Membranes

As novel clean energy technologies, alkaline anion exchange membrane fuel cells (AAEMFCs) is arousing wide public concern due to its high power density and energy density. Compared with proton exchange membrane fuel cells (PEMFCs), they can offer fast electrode kinetics, ues no platinum catalyst and low fuel crossover. However its ionic conductivity, water uptake, swelling ratio, dimensional stability under high temperature need to be further advanced. As a new polymer material, poly(ether ether ketone ketone)(PEEKK) possess high heat-resistant property and mechanical strength because the exist of ketone functional group, and it has not been used to prepare AAEM. In this study, poly (ether ether ketone ketone)(PEEKK) is selected as the substrate material to synthesis high ionic conductivity AAEM.In this research, the concentrated sulphuric acid is used as solvent and catalyst, and chloromethyl octyl ether (CMOE) as chloromethylation reagent to synthesis CMPEEKK. Based on a series of tentative experiments, the reasonable proportion of reactants were determined as M(PEEKK):V(H2SO4):V(CMOE)=0.5g:25ml:10ml, the reasonable reaction temperature was0℃, the stirring speed is500rpm. CMPEEKK with different DC were successfully synthesized by altering reaction time, and the solubility test indicated that all these CMPEEKK with different DC have good dissolvability in high boiling point casting membrane solvents.The QAPEEKKOH membranes were prepared through three steps:first CMPEEKK membranes were prepared by solution casting method, next the CMPEEKK membranes were soaked in trimethylamine aqueous solution and KOH solution to complete quaternization and alkalization process. And also the ionic exchange capacity (IEC), ionic conductivity (IC), water uptake and swelling ratio of QAPEEKKOH membranes were tested. Along with the DC from66%increase to113%, the IEC from1.46mmol g-1increase to2.29mmol g-1correspondingly. Except the QAPEEKKOH-113%membranes were excessive swelled under60℃aqueous solution result in IC dropped. The IC, water uptake and swelling ratio of other membranes were all went up as the temperature and DC increased. Especially the IC of QAPEEKKOH-113%membrane can reach35.4mmol g-1in distilled water at20℃. Meanwhile the water uptake and swelling ratio were120.3%and42.9%respectively. To further enhance the1C, reduce water uptake and swelling ratio,1-methyl imidazole was used as quaternization reagent to prepare ImPEEKKOH membranes. Compared with the QAPEEKKOH membranes, the water uptake and swelling ratio decreased significantly under the same DC. So in order to acquire high IC, more ionic exchange groups were introduced into the polymer chain by increase DC. And the IC of ImPEEKKOH-143%membrane (IEC=2.59mmol g-1) as high as37.2mmol g-1in distilled water at20℃. Also TGA and tensile test manifested that the ImPEEKKOH membranes possess high thermal stability (TOD:206℃) and mechanical stability (tensile strength:22.49MPa, break elongation:48%).