| Because of its high efficiency and low pollution,direct methanol fuel cells?DMFC?become one of clean energy in the 21st century.One of the problems of direct methanol fuel cells?DMFC?is methanol permeation.The high temperature operation can accelerate the speed of electrode reaction and decrease the crossover of methanol.As all of other components in the fuel cells could withstand high temperature,it is significant to develop high temperature and low relative humidity?RH?proton exchange membranes?PEMs?.In the paper,polybenzimidazole?PBI?high temperature PEMs was studied as followings:?1?The prepration of proton conductor.A new proton conductor Zr?phytate?Zr-PA?was prepared by zirconium oxychloride?ZrOCl2·8 H2O?and phytic acid.FT-IR showed that the desired product was obtained.SEM and TEM indicated Zr-PA was the shuttle shape and lamellar.XRD showed the new material had generated.TG-DTA revealed Zr-PA would not decompose below 140?.Conductivities of Zr-PA at different temperatures and RH were measured.At 100%RH and 140?,the conductivity of Zr-PA?3:4 molar ratio?was 0.099 S cm-1,Eact was 20.78 kJ mol-1.At 50%RH,the conductivity was 0.042 S cm-1,Eact was 20.7 kJ mol-1.In dry oven,the conductivity was 0.018 S cm-1,Eact was 20.32 kJ mol-1.?2?The prepation of oPBI/chloromethylated polysulfone?CMPSU?crosslinked membrane doped with Zr-PA.CMPSU of different chlorinity was prepared by polysulfone and chloromethylation reagent?trimethylchlorosilane and paraformaldehyde?with stannic chloride as catalyst.The chlorinity was measured.oPBI was prepared by3,3'-diaminobenzidine and 4,4'-oxybis-?benzoic acid?by melt polycondensation method.oPBI/CMPSU crosslinked membrane was prepared by oPBI and CMPSU.The obtained membrane had good oxidation stability,mechanical strength,dry and wet deformation and methanol resistance.Zr-PA doped crosslinked membrane was prepared in order to improve the conductivity of crosslinked membrane.FT-IR showed oPBI and CMPSU crosslinked with each other,and hydrogen bonds between Zr-PA and oPBI/CMPSU formed.SEM indicated the membrane was still smooth when doped moderate Zr-PA.EDX and XRD showed Zr-PA was homodisperse in the membrane.TG-DTA indicated the membrane would not decompose below 140?.oPBI/CMPSU/Zr-PA membrane still kept good mechanical strength,ethanol resistance.The oxidation stability improved with the doping of Zr-PA.Conductivities of oPBI/CMPSU/Zr-PA at different temperatures and RH were measured.At 100%RH and 50%RH,conductivities of oPBI/CMPSU?20%?/Zr-PA?20%?could reach 0.06 S cm-1 and 0.021 S cm-1 at 140?,respectively.In dry oven,the conductivity was 0.0097 S cm-1.?3?H3PO4 and binudear cobalt phthalocyaninesulfonate?SDPC?dopted oPBI/CMPSU crosslinked membrane were prepared.FT-IR showed crosslinked membrane and H3PO4and bi-CoPC had formed hydrogen bonds.SEM showed the surface of doped crosslinked membrane was compact,and the cross-section had no through-hole.EDX indicated proton conductor was homogeneously dispersed in the membrane.TG-DTA revealed after doping H3PO4 and bi-CoPC,the membrane could still work under 200?.Results showed the membrane owned good oxidation stability,mechanical strength and methanol resistance.Because of the doping of bi-CoPC,the crosslinked membrane owned certain oxygen reduction performance.The onset potentials was-0.15V?Hg/HgO?in aqueous alkaline medium.When in acidic medium,onset potentials was 0.06V vs.Hg/Hg2SO4.The Conductivities at different temperatures and RH were measured.At 100%RH and 180?,the conductivity H3PO4 doped oPBI/CMPSU?20%?/SDPC?30%?was 0.1044 S cm-1.At50%RH,the conductivity of H3PO4 doped oPBI/CMPSU?20%?/SDPC?30%?could reach0.0511 S cm.In dry oven,it was 0.031 S cm-1.?4?IronIII sulfophenyl phosphate intercalated phosphotungstic acid?FeSPP-PWA?was prepared.FeSPP-PWA was doped into oPBI/CMPSU crosslinked membrane to improve its conductivity.FT-IR showed hydrogen bonds formed between crosslinked membrane and FeSPP-PWA.SEM showed the surface of oPBI/CMPSU?20%?/FeSPP-PWA?23%?membrane was flat,and the cross-section had no through-hole.EDX and XRD indicated when certain FeSPP-PWA doped into crosslinked membrane no phase separation occurred.TG-DTA revealed oPBI/CMPSU/FeSPP-PWA had good thermostability.The oxidation stability also improved.ForoPBI/CMPSU?20%?/FeSPP-PWA?23%?crosslinked membrane,its mechanical strength and methanol resistance(10-8 cm2 s-1)still kept excellent.Conductivities at different temperatures and RH were measured.At 100%RH and 180?,the conductivity of oPBI/CMPSU?20%?/FeSPP-PWA?23%?could reach 0.13 S cm-1.At50%RH and 180?,the conductivity was 0.036 S cm-1.In dry oven,it still could be 0.003S cm-1. |
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