| The fuel cells are devices which convert the chemical energy into electronic energy.Traditionally,the polyelectrolyte membrane fuel cells contain proton exchange membrane fuel cells(PEMFCs)and anion exchange membranes fuel cells(AEMFCs).Among them,anion exchange membrane fuel cells are considered as the promising approach due to usage of non-precious metal catalyst and higher oxygen reduction kinetic.But the insufficient chemical stability and low hydroxide ion conductivity of anion exchange membranes(AEMs)are huge hinderance for widespread application of AEMFCs.To solve the problem,various methods are used to develop good performance AEMs in this study,such as crosslinked membranes,composite membranes and grafting the side chain to membranes.Furthermore,the aryl-ether free polymers are used as backbones of AEMs in the whole research.The chemical structure of the prepared AEMs was characterized by nuclear magnetic resonance(1H-NMR)and Fourier transform infrared spectroscopy(FT-IR).The performance of the prepared AEMs was evaluated by water uptake,swelling ratio,mechanical properties,thermal stability,alkaline stability,and oxidation stability.The details of this paper are described as follow:The poly(N-allylisatin biphenyl)-co-poly(alkylene biphenyl)s(PIB-co-PAB)were synthesized by super-acid catalyst Friedel-Crafts polymerization and the intrinsic viscosity of PIB-co-PAB was 2.58 dL·g-1 at 25℃ in DMAC..The anion exchange membranes(Spiro-PIB-co-PAB)were obtained from cyclo-quaternization by 1,5-dibromopentane.The crosslinker was used to improve the chemical stability and dimensional stability via thiol-ene "click chemistry".The results exhibited that the crosslinked membranes possessed higher ionic conduction and mechanical properties.Especially,the anion exchange membrane of ion exchange capacity of 2.16 mmol·g-1(pcs-PIB-co-PAB2.16)had the highest ion conductivity of 86.3 mS·cm-1 at 80℃.The swelling ratio of pcs-PIB-co-PAB2.16 membrane was 21.2%at 80℃.The distinct microphase separation of pcs-PIB-co-PAB2.16 was observed by transmission electron microscope(TEM).Finally,pcs-PIB-co-PAB2.16 possessed good alkaline stability,which remained 65.2%of hydroxide conductivity after storage in 1 M NaOH solution at 80℃ for 1000 h.However,the oxidation stability of pcs-PIB-co-PAB2.16 kept 83.3%of original mass after immersing in 80℃ Fenton’s reagent.The piperidinium cations functionalized aryl-ether free poly(biphenyl-alkylene)s(PB-g-PipVBC)were synthesized by super-acid catalyzed Friedel-Crafts polycondensation and atom transfer radical polymerization(ATRP).After optimizing the amount of PipVBC monomers,the PB-g-3PipVBC showed the best performance among three kinds of membranes.To further improve the dimension stability and hydroxide conductivity of PB-g-3PipVBC membranes,the pre-designed ionic porous polymeric nanospheres were used to fabricate the composite membranes with PB-g-3PipVBC.The results indicated that the ionic nanospheres in composite membranes were helpful to construct microphase separation morphology.And the distinct microphase structure was observed by TEM.The scanning electron microscope(SEM)images of PB-1 sphere and PB-3sphere revealed uniform morphology without obvious defect.The PB-1sphere showed the highest hydroxide conductivity of 65.6 mS·cm-1 at 80℃,while the PB-3sphere possessed the better alkaline stability and retained 66.3%of hydroxide conductivity after storage in 1 M NaOH at 80℃ for 1000 h.Furthermore,the PB-1 sphere and PB-3sphere exhibited lower swelling ratio than PB-g-PipVBC,indicating the composite membranes have advantage on constructing microphase separation.The poly(isatin biphenylene)s(PIBs)were synthesized by super-acid catalyzed Friedel-Crafts polycondensation and the intrinsic viscosity of PIB was 0.62 dL·g-1 at 25℃ in DMAC.The long flexible alkyl chains tethered with trimethylammonium(QA),1-methylprrolidinium(Pyr),and 1-methylpiperidinium(Pip)were grafted to PIB backbones by Menshutkin reaction.The Results of atomic force microscope(AFM)and TEM showed that the AEM tethered long alkyl side chain exhibited distinct microphase-separated morphology.In particular,the QAPIB membranes possessed the highest hydroxide conductivity of 93.9 mS·cm-1 at 80℃ among three kinds of AEMs.Additionality,the PIB tethered Pip showed the best alkaline stability and kept 71.7%of hydroxide conductivity after immersing in 1 M NaOH solution at 80℃ for 1050 h.The oxidation stability of AEMs tethered with Pyr and Pip reached 108 h,along with weight decrease of 37.4%after storage in Fenton’s reagent at 80℃.Furthermore,the platinum-catalyzed H2-O2 fuel cell using QAPIB membrane showed the peak power density of 1.24 W.cm-2.The present study indicated the aryl-ether free polymer backbone and long flexible hydrophobic side chain are helpful to fabricate good performance AEMs.To improve further the chemical stability of the prepared AEMs,the poly(N-allylisatin-co-piperidine aromatic)s(BP90 or TPP-x)(x represents the mole of 1-Methyl-4-piperidone)were synthesized by super-acid catalyzed Friedel-Crafts polycondensation.The polymers possessed high molecular weight and the intrinsic viscosity was 1.8 dL·g-1 at 25℃ in DMAC.Subsequently,the self-crosslinking membranes were fabricated by UV-light initiation.The results indicated that the crosslinked membranes(QCBP90 or QCTPP-x)had better dimensional stability and tensile strength than un-crosslinked membranes(QNBP90 or QNTPP-x).Furthermore,the QNTPP90 membranes possessed the highest hydroxide conductivity of 56.5-124.4 mS·cm-1 at 20 to 80℃.However,the hydroxide conductivity of QCTPP90 decreased to 30.1-108.8 mS·cm-1 at 20 to 80℃.Additionally,the tensile strength of membranes was over 10.5 MPa.Moreover,the QNTPP90 and QCTPP90 membranes showed good alkaline stability,which can retain 97.0%of hydroxide conductivity after storage in 1 M NaOH solution at 80℃ for 1500 h.Meanwhile,they also possessed good oxidation stability after immersed in Fenton’s reagent at 80℃ for 43 h.This investigation could provide important insights for development of AEMs with good performance. |
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