Study On Intensification Of Proton Conduction Property Of Proton Exchange Membrane Using Multifunctional Hollow Microspheres

Aiming at improving the proton conductivity of proton exchange membranes,inspired by the structure and function of vacuole in plant cells, a series of vacuolesimilar multifunctional hollow microspheres were prepared and then incorporated intothe sulfonated polyether ether ketone (SPEEK) matrix to fabricate novel protonexchange membranes for application in direct methanol fuel cell. The effects of thesefillers on the performance of the resultant membranes were studied systematically.Inorganic hollow titania spheres (HTS) were synthesized by soft templatemethod, followed by phosphorylation using amino trimethylene phosphonic acid(ATMP) as chelating reagent and then incorporated into SPEEK to fabricatehigh-performance SPEEK/HTSP hybrid proton exchange membranes. The thermalstability, anti-swelling property and methanol resistance of the membranes wereenhanced by the incorporation of HTSP. It was found that the HTSP served as waterreservoirs and hence increased the water uptake of membranes. Meanwhile, thephosphorylate acid groups enriched onto the HTSP could constructed an uninterruptedpathway within the membrane for proton migration. SPEEK/HTSP-15hybridmembranes exhibited the highest proton conductivity about2.39×10-2S/cm and2.56×10-1S/cm at room temperature and70oC, respectively, which were about threetimes and twice of that of pure SPEEK membrane under the same conditions.Organic imidazole microcapsules (IMCs) were prepared via distillation-precipitation polymerization and then imidazole microcapsules loaded withphosphotungstic acid (IMCs-HPW) were prepared by directly immersing method.The resultant IMCs-HPW were incorporated into the SPEEK to fabricatehigh-performance SPEEK/IMCs-HPW composite proton exchange membranes. Theembedded IMCs-HPW significantly improved the water absorption and waterretention ability of the membrane. Meanwhile, anti-swelling ability and methanolbarrier property were improved which were originated from the strong electrostaticattraction between the alkaline imidazole groups of microcapsules and sulfonic acidgroups of SPEEK. Besides, IMCs-HPW, serving as acid reservoirs, constructed novellow energy barrier pathways for proton transfer with the aid of absorbed water withinthe microcapsules as well as at the interface region of the microcapsules and SPEEK,thus enhancing proton conduction capacity. At room temperature,SPEEK/IMCs-HPW-15composite membranes exhibited the highest proton conductivity of0.0316S/cm which was about three times of that of pure SPEEKmembrane.Poly(methacrylic acid) encapsulated imidazole microcapsules (IMCs-PMAA)were synthesized via distillation-precipitation polymerization and incorporated intoSPEEK to fabricate high-performance SPEEK/IMCs-PMAA composite protonexchange membranes. The introduction of microcapsules increased the water uptakeof membranes. The strong electrostatic attraction between the imidazole groups ofmicrocapsules and sulfonic acid groups of SPEEK restricted the mobility of polymerchains and decreased the hydrophilic nanochannel size, consequently improvedanti-swelling ability and methanol barrier property of composite membranes. sulfonicacid-imidazole pairs formed proton pathways at IMCs-SPEEK interface. Carboxylicacid groups with high hydration energy further optimized the water environmentwithin the membrane and constructed novel proton transfer paths inside themicrocapsules and enhanced the proton conductivity. SPEEK/IMCs-PMAA-20composite membranes exhibited the highest proton conductivity about0.0266S/cm atroom temperature and100%RH which was about three times of that of pure SPEEKmembrane. Moreover, the proton conductivity of SPEEK/IMCs-PMAA compositemembranes remained stable at40oC and20%RH after90min, when the filler contentof IMCs-PMAA in the membranes was higher than10wt.%.