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Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,Progress Towards New Heterocycle-Containing Proton Exchange Membranes,February 7, 2008,Corinne Lipscomb,Mahanthappa Group,2,Hydrogen Fuel Cells,Hoffman, P.,Tomorrows Energy.,The MIT Press: Cambridge, Massachusetts, 2001.,The H-Racer,Completely Hydrogen-Powered Car,Are being researched for:,Automobiles,Cell phones,Portable electronics,NASAs continued use,Have been used in:,NASA missions,since Gemini,Concept vehicles,Toys,3,The Hydrogen Fuel Cell,External circuit for electrons,Oxygen ions and protons form H,2,O,Palladium Catalyst,Carrette, L.; Friedrich, K. A.; Stimming, U.,Fuel Cells,2001,1, 5-39.,Proton Exchange (Polymer,Electrolyte) Membranes,4,Ideal 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),5,The I,ndustry Standard,Nafion - 1964,E. 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.,6,Synthesis of Nafion,Free radical initiated,Pressure to control,gaseous monomer,Connolly, D. J.; Gresham, W. F. (E.I. Du Pont de Nemours and Company). USA. U. S. Pat. 3,282,875, 1966.,7,Advantages of Nafion,Stable material,Selective ion permeability,Compatible with current fuel,cell technology,High proton conductivity under,aqueous conditions 0.1 S/cm,Deluca, 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.,Conductivity,Typically measured in,Seimens/cm (,S/cm),1 S = 1,-1,8,Disadvantages of Nafion,Low conductivity at low water content,Permeable to MeOH (Direct Methanol Fuel Cell),Poor mechanical strength at high temperatures,Processability and fabrication issues,DOE goal - 0.1 S/cm at 120,C and,50% relative humidity,Nafion cannot meet this goal.,Hickner, 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.,9,Proton Conduction Mechanisms,Structural diffusion or proton “hopping”,Grotthus mechanism in H,2,O,Rearrangement of hydrogen,bonds simultaneously,Protons transferred quickly,Vehicular diffusion,Proton carried by one molecule,Diffusion,Protons transferred slowly,Kreuer, K. D.,Solid State Ionics,1997,94, 55-62.,10,Water Mimics,Mineral acids - H,2,SO,4, H,3,PO,4,Heterocycles,High boiling,Immobilization possible,11,T,g,- Glass Transition Temperature,Amorphous solids - glasses, polymers, etc.,Below T,g,- solid-like behavior,material becomes rigid upon cooling,Above T,g,- liquid-like behavior,material softens upon heating,Some variability - depends on the heating/cooling rate,Above T,g,segmental mobility increases significantly,important in conductivity,12,Polymer Molecular Weights,M,n,- Number Average Molecular Weight,PDI - Polydispersity Index,the breadth of the distribution,GPC - Gel Permeation,Chromatography,13,Nomenclature,Heterocycle-Spacer length,Tz6,Heterocycle-Spacer length-Polymer,Im5Si,Small Molecules,Polymer,14,Conducting Heterocycle Solvents,EW = 740 g/mol,Kreuer, K. D.; Fuchs, A.; Ise, M.; Spaeth, M.; Maier, J.,Electrochim. Acta,1998,43, 1281-1288.,15,Impedance 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,Conductivity,16,Proton Conductivity,Imidazole doped,Pyrazole doped,Heterocycles can conduct protons like water.,Kreuer, K. D.; Fuchs, A.; Ise, M.; Spaeth, M.; Maier, J.,Electrochim. Acta,1998,43, 1281-1288.,17,Imidazole Immobilization,Herz, H. G.; Kreuer, K. D.; Maier, J.; Scharfenberger, G.; et al.,Electrochim. Acta,2003,48, 2165-2171.,ex.,18,Free Radical Polymerization,19,Proton Conductivities,Herz, H. G.; Kreuer, K. D.; Maier, J.; Scharfenberger, G.; et al.,Electrochim. Acta,2003,48, 2165-2171.,Immobilized imidazoles can conduct protons.,10b (T,g,= 32C),12 atom spacer,10a (T,g,= 51C),6 atom spacer,Both polymers stable to 200C,20,Poly(siloxane) Backbones,Persson, J. C.; Jannasch, P.,Macromolecules,2005,38, 3283-3289.,V4,D3,21,Anionic ROP Mechanism,THF,V4,D3,22,Benzimidazole Poly(siloxanes),Copolymer,V,4,/D,3,Feed ratio,Mol% X,Vinyl siloxane,M,n,(GPC),Final Comp.,PDI,Final Comp.,Bz5Si,-,5,13300,2.2,Bz5Si,0.5,16,15800,1.4,Bz5Si,1.125,33,10600,1.4,Bz5Si,3,57,10800,1.3,Persson, J. C.; Jannasch, P.,Macromolecules,2005,38, 3283-3289.,23,Tg and Heterocycle Content,T,g,rises with heterocycle content for poly(siloxanes).,Thermally stable to 200C,Persson, J. C.; Jannasch, P.,Macromolecules,2005,38, 3283-3289.,24,H,+,Conductivity vs. BzIm Content,At lower temperatures -,conductivity depends,on T,g,At higher temperatures -,conductivity depends on,heterocycle content,For conductivity to be unaffected by segmental mobility:,T T,g,+ 50C,Persson, J. C.; Jannasch, P.,Macromolecules,2005,38, 3283-3289.,25,PEO Backbones,Persson, J. C.; Jannasch, P.,Chem. Mater.,2006,18, 3096-3102.,26,Stability and Physical Properties,Copolymer,% BzIm,M,n,(g/mol),GPC,PDI,Sample 1,18,3770,1.12,Sample 2,46,5880,1.03,Sample 3,55,6850,1.03,Sample 4,65,8420,1.03,Sample 5,86,16078,1.07,Persson, J. C.; Jannasch, P.,Chem. Mater.,2006,18, 3096-3102.,T,g,rises with heterocycle content for multiple polymers.,27,Conductivity and Mass Fraction,Absolute Proton Conductivity,Intrinsic Proton Conductivity,Persson, J. C.; Jannasch, P.,Chem. Mater.,2006,18, 3096-3102.,Increasing,Benzimidazole,Content,Sample 1,Sample 2,Sample 3,Sample 4,Sample 5,Bz8PEO,28,Triazole Tethered Polyacrylates,Martwiset, S.; Woudenberg, R. C.; Granados-Focil, S.; et. al.,Solid State Ionics,2007,178, 1398-1403.,Tz6,HMTz6,29,Triazole Tethered Polyacrylates,n = 6-8,X, Y, and Z controlled with feed ratios,Tz6,HMTz6,PEG,Martwiset, S.; Woudenberg, R. C.; Granados-Focil, S.; et. al.,Solid State Ionics,2007,178, 1398-1403.,30,Conductivity with Acid Doping,Doping with TFA increases conductivity significantly,Sample,Mol % TFA,Tg (C),1,130,-27,2,100,-21,3,80,-25,4,50,-25,5,20,-26,6,0,-25,Samples had 28 mol% PEG and,30 mol% HMTz6 compared to Tz6,Sample 2,Sample 3,Sample 1,Sample 4,Sample 5,Sample 6,Martwiset, S.; Woudenberg, R. C.; Granados-Focil, S.; et. al.,Solid State Ionics,2007,178, 1398-1403.,31,Proton Conductivity & T,g,Sample,Mol % PEG,T,g,(C),A,52,-43,B,30,-29,C,22,-19,D,13,-3,E,0,16,As T,g,goes down -, goes up,Samples had the same Mol %,HMTz6 compared to Tz6,Sample A,Sample B,Sample C,Sample D,Sample E,Martwiset, S.; Woudenberg, R. C.; Granados-Focil, S.; et. al.,Solid State Ionics,2007,178, 1398-1403.,32,Intrinsic Conductivity & T,g,As more PEG added,mass fraction of,heterocycle goes down,Decreasing mass fraction of,the heterocycle:,decreases,T,g,decreases conductivity,Sample A,Sample B,Sample C,Sample D,Sample E,Martwiset, S.; Woudenberg, R. C.; Granados-Focil, S.; et. al.,Solid State Ionics,2007,178, 1398-1403.,Decreasing T,g,:,increases conductivity,Mass fraction of heterocycle and T,g,are interconnected.,33,Imidazole Polysiloxanes,Im5,Im8,Scharfenberger, G.; et. al. J.,Fuel Cell,2006,6, 237-250.,34,Imidazole Polysiloxanes,70% cyclic,trimers,Scharfenberger, G.; et. al. J.,Fuel Cell,2006,6, 237-250.,Partial,Hydrolysis,Im5,Same polymerization carried out with Im8,35,Triazole Tethered Polysiloxanes,Granados-Focil, S.; Woudenberg, R. C.; Yavuzcetin, O.; et. al.,Macromolecules,2007,40, 8708-8713.,36,Triazole Tethered Polysiloxanes,Tz2Si,FBz2Si,Tz8Si,Granados-Focil, S.; Woudenberg, R. C.; Yavuzcetin, O.; et. al.,Macromolecules,2007,40, 8708-8713.,37,Conductivity & Tether Length,Tz2Si,T,g,= 19C,43% Het.,Im5Si,T,g,= 41C,36% Het.,Im8Si,T,g,= 7C,28% Het.,Tz8Si,T,g,= -5C,28% Het.,1000/K,Granados-Focil, S.; Woudenberg, R. C.; Yavuzcetin, O.; et. al.,Macromolecules,2007,40, 8708-8713.,Scharfenberger, G.; et. al. J.,Fuel Cell,2006,6, 237-250.,Different heterocycles need,different tether lengths.,38,Conductivity and pK,a,pK,a, 14,Tz2Si higher, than FBz2Si,Despite having:,the same pK,a,the same tether length,T,g,factored out,T-T,g,Granados-Focil, S.; Woudenberg, R. C.; Yavuzcetin, O.; et. al.,Macromolecules,2007,40, 8708-8713.,Same pK,a,s,different,conductivities,39,Conductivity and pK,a,pK,a,pK,a,Despite having:,T,g,factored out,the same tether length,the same mass fraction,a higher pK,a,Higher pK,a,has,a higher conductivity,Granados-Focil, S.; Woudenberg, R. C.; Yavuzcetin, O.; et. al.,Macromolecules,2007,40, 8708-8713.,Tz8Si,Im8Si,Scharfenberger, G.; et. al. J.,Fuel Cell,2006,6, 237-250.,40,Conductivity and pK,a,T,g,masks pK,a,effects,Mass fraction more dominant than pK,a,Different heterocycles form the aggregates,necessary for proton conduction under,different conditions.,Each polymer system should,be optimized separately.,41,Conclusions,T,g,is the most dominant effect,Mass fraction of the heterocycle also dominant,Tether length and pK,a,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 route,towards non-aqueous proton conduction at high temperatures,42,Future Directions,Optimization of tether length, mass fraction,T,g, 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 stability, DSC for T,g, &,GPC for polydispersity index and molecular weight,EIS for proton conductivity,Protocols for hydrogen fuel cells,Rheology for mechanical stability,Membrane Electrode Assemblies,43,Acknowledgements,Professor Mahesh Mahanthappa,The Mahanthappa Group,Erin Henninger,Joan Widin,Chris Bates,David Bunck,Practice Talk Antendees,Mary Beth Anzovino,Matt Bierman,Maren Buck,Matt Christianson,Jeremy Higgins,Beth Landis,Katie Partridge,Dr. Dino Ress,Helpful Conversations,Beth Landis,
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