From polymers to fuel cells A look at new understandings ….ppt

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1、Progress Towards New Heterocycle-Containing Proton Exchange MembranesFebruary 7,2008Corinne LipscombMahanthappa Group2Hydrogen Fuel CellsHoffman,P.Tomorrows Energy.The MIT Press:Cambridge,Massachusetts,2001.The H-RacerCompletely Hydrogen-Powered CarAre being researched for:Automobiles Cell phones Po

2、rtable electronics NASAs continued useHave been used in:NASA missions since Gemini Concept vehicles Toys3The Hydrogen Fuel Cell External circuit for electrons Oxygen ions and protons form H2O Palladium CatalystCarrette,L.;Friedrich,K.A.;Stimming,U.Fuel Cells 2001,1,5-39.Proton Exchange(Polymer Elect

3、rolyte)Membranes4Ideal Material High proton conductivity Low electron conductivity Low permeability to fuel and oxidant Low water permeability Chemically,thermally,and mechanically stable Inexpensive Ability to be fashioned into Membrane Electrode Assemblies(MEAs)5The Industry Standard Nafion-1964 E

4、.I.du Pont de Nemours and Co.Connolly,D.J.;Gresham,W.F.(E.I.Du Pont de Nemours and Company).USA.U.S.Pat.3,282,875,1966.6Synthesis of NafionFree radical initiatedPressure to control gaseous monomerConnolly,D.J.;Gresham,W.F.(E.I.Du Pont de Nemours and Company).USA.U.S.Pat.3,282,875,1966.7Advantages of

5、 NafionStable material Selective ion permeabilityCompatible with current fuel cell technologyHigh proton conductivity under aqueous conditions 0.1 S/cmDeluca,N.W.;Elabd,Y.A.J.Polym.Sci.,Part B:Polym.Phys.2006,44,2201-2225.Schmidt-Rohr,K.;Chen,Q.Nat.Mater.2008,7,75-83.ConductivityTypically measured i

6、nSeimens/cm(S/cm)1 S=1 -18Disadvantages of Nafion Low conductivity at low water content Permeable to MeOH(Direct Methanol Fuel Cell)Poor mechanical strength at high temperatures Processability and fabrication issuesDOE goal-0.1 S/cm at 120C and 50%relative humidityNafion cannot meet this goal.Hickne

7、r,M.A.;Ghassemi,H.;Kim,Y.S.;Einsla,B.R.;McGrath,J.E.Chem.Rev.2004,104,4587-4611.Deluca,N.W.;Elabd,Y.A.J.Polym.Sci.,Part B:Polym.Phys.2006,44,2201-2225.9Proton Conduction Mechanisms Structural diffusion or proton“hopping”Grotthus mechanism in H2O Rearrangement of hydrogen bonds simultaneously Protons

8、 transferred quickly Vehicular diffusion Proton carried by one molecule Diffusion Protons transferred slowlyKreuer,K.D.Solid State Ionics 1997,94,55-62.10Water Mimics Mineral acids-H2SO4,H3PO4 Heterocycles High boiling Immobilization possible11Tg-Glass Transition Temperature Amorphous solids-glasses

9、,polymers,etc.Below Tg-solid-like behavior material becomes rigid upon cooling Above Tg-liquid-like behavior material softens upon heating Some variability-depends on the heating/cooling rate Above Tg segmental mobility increases significantly important in conductivity12Polymer Molecular WeightsMn-N

10、umber Average Molecular WeightPDI-Polydispersity Index the breadth of the distributionGPC-Gel Permeation Chromatography13NomenclatureHeterocycle-Spacer lengthTz6Heterocycle-Spacer length-PolymerIm5SiSmall MoleculesPolymer14Conducting Heterocycle SolventsEW=740 g/molKreuer,K.D.;Fuchs,A.;Ise,M.;Spaeth

11、,M.;Maier,J.Electrochim.Acta 1998,43,1281-1288.15Impedance Spectroscopy Experimental Apply sinusoidal potential Measure current response Usually done at high frequencies Impedance Real term-Resistance Change in amplitude Imaginary term-Capacitance Phase shift At high freq.goes to zero Conductivity16

12、Proton ConductivityImidazole dopedPyrazole dopedHeterocycles can conduct protons like water.Kreuer,K.D.;Fuchs,A.;Ise,M.;Spaeth,M.;Maier,J.Electrochim.Acta 1998,43,1281-1288.17Imidazole ImmobilizationHerz,H.G.;Kreuer,K.D.;Maier,J.;Scharfenberger,G.;et al.Electrochim.Acta 2003,48,2165-2171.ex.18Free R

13、adical Polymerization19Proton ConductivitiesHerz,H.G.;Kreuer,K.D.;Maier,J.;Scharfenberger,G.;et al.Electrochim.Acta 2003,48,2165-2171.Immobilized imidazoles can conduct protons.10b(Tg=32C)12 atom spacer10a(Tg=51C)6 atom spacerBoth polymers stable to 200C20Poly(siloxane)BackbonesPersson,J.C.;Jannasch

14、,P.Macromolecules 2005,38,3283-3289.V4D321Anionic ROP MechanismTHFV4D322Benzimidazole Poly(siloxanes)CopolymerV4/D3Feed ratioMol%XVinyl siloxaneMn(GPC)Final Comp.PDIFinal Comp.Bz5Si-5133002.2Bz5Si0.516158001.4Bz5Si1.12533106001.4Bz5Si357108001.3Persson,J.C.;Jannasch,P.Macromolecules 2005,38,3283-328

15、9.23Tg and Heterocycle ContentTg rises with heterocycle content for poly(siloxanes).Thermally stable to 200CPersson,J.C.;Jannasch,P.Macromolecules 2005,38,3283-3289.24H+Conductivity vs.BzIm Content At lower temperatures-conductivity depends on Tg At higher temperatures-conductivity depends on hetero

16、cycle contentFor conductivity to be unaffected by segmental mobility:T Tg+50CPersson,J.C.;Jannasch,P.Macromolecules 2005,38,3283-3289.25PEO BackbonesPersson,J.C.;Jannasch,P.Chem.Mater.2006,18,3096-3102.26Stability and Physical PropertiesCopolymer%BzImMn(g/mol)GPCPDISample 11837701.12Sample 24658801.

17、03Sample 35568501.03Sample 46584201.03Sample 586160781.07Persson,J.C.;Jannasch,P.Chem.Mater.2006,18,3096-3102.Tg rises with heterocycle content for multiple polymers.27Conductivity and Mass FractionAbsolute Proton ConductivityIntrinsic Proton ConductivityPersson,J.C.;Jannasch,P.Chem.Mater.2006,18,30

18、96-3102.IncreasingBenzimidazoleContentSample 1Sample 2Sample 3Sample 4Sample 5Bz8PEO28Triazole Tethered PolyacrylatesMartwiset,S.;Woudenberg,R.C.;Granados-Focil,S.;et.al.Solid State Ionics 2007,178,1398-1403.Tz6HMTz629Triazole Tethered Polyacrylatesn=6-8 X,Y,and Z controlled with feed ratiosTz6HMTz6

19、PEGMartwiset,S.;Woudenberg,R.C.;Granados-Focil,S.;et.al.Solid State Ionics 2007,178,1398-1403.30Conductivity with Acid DopingDoping with TFA increases conductivity significantlySampleMol%TFATg(C)1130-272100-21380-25450-25520-2660-25Samples had 28 mol%PEG and30 mol%HMTz6 compared to Tz6Sample 2Sample

20、 3Sample 1Sample 4Sample 5Sample 6Martwiset,S.;Woudenberg,R.C.;Granados-Focil,S.;et.al.Solid State Ionics 2007,178,1398-1403.31Proton Conductivity&TgSampleMol%PEGTg(C)A52-43B30-29C22-19D13-3E016As Tg goes down-goes upSamples had the same Mol%HMTz6 compared to Tz6Sample ASample BSample CSample DSampl

21、e EMartwiset,S.;Woudenberg,R.C.;Granados-Focil,S.;et.al.Solid State Ionics 2007,178,1398-1403.32Intrinsic Conductivity&Tg As more PEG added,mass fraction of heterocycle goes downDecreasing mass fraction ofthe heterocycle:decreases Tg decreases conductivitySample ASample BSample CSample DSample EMart

22、wiset,S.;Woudenberg,R.C.;Granados-Focil,S.;et.al.Solid State Ionics 2007,178,1398-1403.Decreasing Tg:increases conductivityMass fraction of heterocycle and Tg are interconnected.33Imidazole PolysiloxanesIm5Im8Scharfenberger,G.;et.al.J.Fuel Cell 2006,6,237-250.34Imidazole Polysiloxanes70%cyclictrimer

23、sScharfenberger,G.;et.al.J.Fuel Cell 2006,6,237-250.PartialHydrolysisIm5Same polymerization carried out with Im835Triazole Tethered PolysiloxanesGranados-Focil,S.;Woudenberg,R.C.;Yavuzcetin,O.;et.al.Macromolecules 2007,40,8708-8713.36Triazole Tethered PolysiloxanesTz2SiFBz2SiTz8SiGranados-Focil,S.;W

24、oudenberg,R.C.;Yavuzcetin,O.;et.al.Macromolecules 2007,40,8708-8713.37Conductivity&Tether LengthTz2SiTg=19C43%Het.Im5SiTg=41C36%Het.Im8SiTg=7C28%Het.Tz8SiTg=-5C28%Het.1000/KGranados-Focil,S.;Woudenberg,R.C.;Yavuzcetin,O.;et.al.Macromolecules 2007,40,8708-8713.Scharfenberger,G.;et.al.J.Fuel Cell 2006

25、,6,237-250.Different heterocycles needdifferent tether lengths.38Conductivity and pKapKa 14Tz2Si higher than FBz2SiDespite having:the same pKa the same tether length Tg factored outT-TgGranados-Focil,S.;Woudenberg,R.C.;Yavuzcetin,O.;et.al.Macromolecules 2007,40,8708-8713.Same pKas different conducti

26、vities39Conductivity and pKapKapKaDespite having:Tg factored out the same tether length the same mass fraction a higher pKaHigher pKa has a higher conductivityGranados-Focil,S.;Woudenberg,R.C.;Yavuzcetin,O.;et.al.Macromolecules 2007,40,8708-8713.Tz8SiIm8SiScharfenberger,G.;et.al.J.Fuel Cell 2006,6,2

27、37-250.40Conductivity and pKa Tg masks pKa effects Mass fraction more dominant than pKa Different heterocycles form the aggregates necessary for proton conduction under different conditions.Each polymer system shouldbe optimized separately.41Conclusions Tg is the most dominant effect Mass fraction o

28、f the heterocycle also dominant Tether length and pKa are concerns Immobilization decreases vehicular diffusion allowing for structural diffusion Polymers shown-10-6-10-3 S/cm Nafion-10-1 S/cm Heterocycle-containing polymers present a new routetowards non-aqueous proton conduction at high temperatur

29、es42Future Directions Optimization of tether length,mass fraction,Tg,and acid doping Block copolymers-systematic control over morphology and mechanical properties Living polymerization techniques-systematic control over PDI and molecular weight Protocols for evaluation of PEMs TGA for thermal stabil

30、ity,DSC for Tg,&GPC for polydispersity index and molecular weight EIS for proton conductivity Protocols for hydrogen fuel cells Rheology for mechanical stability Membrane Electrode Assemblies43AcknowledgementsProfessor Mahesh MahanthappaThe Mahanthappa Group Erin Henninger Joan Widin Chris Bates David BunckPractice Talk Antendees Mary Beth Anzovino Matt Bierman Maren Buck Matt Christianson Jeremy Higgins Beth Landis Katie Partridge Dr.Dino RessHelpful Conversations Beth Landis