Study On Functional Membrane Materials Of Side-chain Type Sulfonated Heterocyclic Poly(arylene Ether Ketone)s

Functional membrane is the key component in a variety of battery systems,such as proton exchange membrane fuel cells(PEMFCs),direct methanol fuel cells(DMFCs)and vanadium redox flow batteries(VRFBs).This material has become one of research focuses in fields of polymer science,electrochemistry and energy science.For PEMFC or VRFB,Nafion membrane is the most widely used functional membrane.Although,Nafion membrane exhibts good chemical stability and high proton conductivity,it remains some defects such as high methanol(or vanadium ions)crossover rate and high cost.Therefore,in this thesis,several series of novel side-chain type sulfonated heterocyclic poly(arylene ether ketone)s including SPAEK,SPPEK-dPs and SPPEK-Ps were synthesized.The performances of the corresponding functional membranes were investigated.The main results of these studies are as follows.Sulfonated poly(arylene ether ketone)s(SPAEKs)were synthesized via direct nucleophilic polycondensation from 4,5-sulfonic diphenyl-2,3,6,7-tetraazaanthracene-1,8-dione(STAIK)&4,8-sulfonic diphenyl-2,3,6,7-tetraazaanthracene-1,5-dione(STATK),4-(4-hydroxyphenyl)-2,3-phthalazin-l-ketone(DHPZ)and 4,4-difluorobenzophenone(DFB).The inherent viscosity of SPAEK-30 was 2.52 dL g-1.The TGA measurement showed that 5%weight loss of this new sulfonated polymer is at 367 ?,suggesting the good thermal stablity.Moreover,the proton conductivity of SPAEK-30 was 2.56×10-2 S cm-1 at 95 0C and 100%relative humidity.A series of sulfonated poly(phthalazinone ether ketone)s containing 3,5-diphenyl phthalazinone moieties(SPPEK-dPs)were prepared by the sulfonation of poly(aryl ether ketone)s containing 3,5-diphenyl phthalazinone moieties(PPEK-dPs),which were synthesized via direct nucleophilic polycondensation from 4-(3,5-diphenyl-4-hydroxyphenyl)-2,3-phthalazin-l-ketone(DHPZ-dP),DHPZ and DFB.The molecular structures were assessed by FTIR and 1H-NMR.The ion exchange capacities(IEC)of these sulfonated polymers was in the range of 0.99?1.81 mmol g-1.SPPEK-dP proton exchange membranes demonstrate good mechanical property as well as dimensional,thermal,and oxidative stability.The proton conductivities of SPPEK-dP membranes can be increased with enhancing the IEC and measurement temperature.The proton conductivity of SPPEK-dP-55 was 13.18×10-2 S cm-1 at 95 ?.Furthermore,the methanol diffusion coefficients of SPPEK-dP membranes were in the range of 1.2×10-8?1.09×10-7 cm2 s-1 depending on IEC value.Remarkably,the selectivity of SPPEK-dP membranes was 5?7 times higher than that of Nafion 117 membranes under the same conditions.The performances of VRFB cells with SPPEK-dP membranes were investigated.Results showed that the area resistances can be declined from 1.09 ? cm2 to 0.30 ? cm2 while the IEC value were measured from 0.99 mmol g-1 to 1.81 mmol g-1.SPPEK-dP membranes were impermeable to the bulky hydrated VO2+ ion and exhibited low V3+ ion permeability in the range of 1.01×10-5?3.88×10-5 cm min-1.The chemical stability test of the membranes showed that weigh loss of SPPEK-dPs was lower than 5.3%and the tentile strength remained 50 MPa,after immersed in V02+ solution for 60 days.The study of SPPEK-dP membranes in vanadium redox flow batteries show that the energy efficiencies(EE)of the cells were in the range of 83.2%?87.4%at 40 mA cm-2.The self-discharge time of VRFB employing SPPEK-dP-45 membrane was about 278 h at the state of charge(SOC)of 50%,which was far longer than that of Nafion 115(90 h).The charge-discharge cycles performance of SPPEK-dP-45 showed that the columbic efficiency(CE),voltage effciency(VE),and EE were 98.8%,84.5%and 83.5%at 60 mA cm-2,respectively.A series of novel sulfonated poly(phthalazinone ether ketone)s containing pendant phenyl moieties(SPPEK-Ps)were synthesized by sulfonation reactions of poly(aryl ether ketone)s containing 3-phenyl phthalazinone moieties(PPEK-Ps).The relevant performances of SPPEK-P membranes for VRFB were studied.The chemical structures of the polymers were confirmed by 1H-NMR and FTIR analysis.The physicochemical properties and single cell performance of SPPEK-P membranes were systematically evaluated,revealing that the membranes were thermally,chemically and mechanically stable.The area resistances of SPPEK-P-90 and SPPEK-P-100 membranes were 0.75 ? cm2 and 0.34 ? cm2,respectively.SPPEK-P membranes were also impermeable to the bulky hydrated VO2+ ion and exhibit low V3+ ion permeability,where SPPEK-P-90 was 2.53×10-5 cm min-1,whereas Nafion 115 membrane was 9.0×10-4 cm min-1.Compared with Nafion 115,SPPEK-P-90 membrane demonstrated comparable CE and EE,where the CE was 98.5%and the EE was 83%at 60 mA cm-2.Moreover,the SPPEK-P-90 membrane exhibited stable performance in cell over 100 charge-discharge cycles.The relationships between the structures and properties of three sulfonated poly(phthalazinone ether ketone)s with the similar IEC values were studied,including SPPEK,SPPEK-P-70 and SPPEK-dP-35.The measurements of solubility indicated that the three sulfonated polymer can be dissolved in common solvents,and the solubility can be improved with increasing the number of the side chains.The TGA measurements showed the thermal stabilities of the three sulfonated polymers were similar.The comparison of chemical stability showed that SPPEK-P-70 and SPPEK-dP-35 were more stable in vanadium acid solution,while SPPEK was relatively poor.The performances of the corresponding functional membranes showed that the sulfonated aromatic polymers with side chains exhibited lower area resistance and higher proton conductivity.The above results indicated that the introduction of phenyl sulfonic acid side chain to aromatic polymer was beneficial for improving the solubility,chemical stability and proton conductivity.