Develop the methodology for the fabrication of 3D cross-linked, hydrocarbon-based membranes using immobilized heteropolyacids (HPAs) as the proton conducting moiety

Dec, S. F.

Herring, A. M.

Pern, F. F. J.

Turner, J. A.

UNT Digital Library

Advanced Fuel Cell Membranes Based on HeteropolyacidsJohn A. Turner and F. J. John PernHydrogen and Electricity, Systems and Infrastructure GroupNational Renewable Energy LaboratoryGolden, CO 80401-3393Andrew M. Herring* and Steven F. Dec*** Department of Chemical Engineering and ** Department of Chemistry and GeochemistryColorado School of MinesGolden, CO 80401-1887May 18, 2006 Project ID #FC4This presentation does not contain any proprietary or confidential informationNREL/PR-560-39972Presented at the 2006 DOE Hydrogen, Fuel Cells & Infrastructure Technologies Program Review in Washington, D.C., May 16-19, 20062Disclaimer and Government LicenseThis work has been authored by Midwest Research Institute (MRI) under Contract No. DE-AC36-99GO10337 with the U.S. Department of Energy (the “DOE”).  The United States Government (the “Government”) retains and the publisher, by accepting the work for publication, acknowledges that the Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for Government purposes.Neither MRI, the DOE, the Government, nor any other agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe any privately owned rights.  Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not constitute or imply its endorsement, recommendation, or favoring by the Government or any agency thereof.  The views and opinions of the authors and/or presenters expressed herein do not necessarily state or reflect those of MRI, the DOE, the Government, or any agency thereof. 3OverviewTimeline• Project start date: FY 2005• Project end date: tbd• Percent complete: tbdBudget• Total project funding– DOE share: $300k• Funding received in FY05: – $150K (0.3 FTE)• Funding for FY06: – $150K (0.3 FTE)Targets• Low humidity operation (25% RH).• High conductivity ~0.1 S/cm• Cost $40/m2Barriers• Barriers addressedO. Stack materials and manufacturing costsP. DurabilityPartner/Subcontract• Colorado School of Mines– Prof. Andrew M. Herring– Dr. Steven F. Dec4Objectives• Develop the methodology for the fabrication of 3D cross-linked, hydrocarbon-based membranes using immobilized heteropolyacids (HPAs) as the proton conducting moiety.– Conductivity ~0.1 S/cm at 120ºC and <1.5 kPa H2O• Develop immobilization technology based on covalent attachment of HPAs to oxide nano-particles. • Acquire an improved understanding of HPAs and their salts made by custom synthesis. – HPAs make up a class of inorganic proton conductors that exhibithigh proton conductivity at low humidity (below 25% RH) and at elevated temperatures (well above 100°C). • Conduct relevant characterizations of the membranes to better understand their structural, chemical, and thermal properties/stability and proton conductivity.  5HPAs: High H+ Conductivity, High Thermal Stability; Vast Structural Diversity; Known Redox Catalysts Keggin[SiW12O40]4-H4SiW12O40-26H2O (W12-STA)Lacunary(allows easy attachment points)[SiW11O39]8-H8SiW11O39-26H2O (W11-STA)Dawson[P2W18O62]6-H6P2W18O62-xH2O6Strategies for Immobilizing HPAsA. Binding Approaches:1. Covalent bonding to oxide nano-particles insitu, which can bond covalently to, or embed physically in, a polymeric matrix2. Direct embedding in a polymeric matrix 3. Covalent bonding directly to a polymeric matrix (CSM/3M collaboration, poster #FCP-6)B. Modification of Lacunary HPAs:1. By bonding with functional silanes that can then be cross-linked or polymerizedC. Fabrication Approaches:1. Sol gel method2. Immobilized via silylation onto supporting particles3. Simple blendingD. Polymeric Matrix:1. Organic2. Inorganic 3. Organic-inorganic hybridRef. 14: “Heteropoly and Isopoly Oxometalates,”by M. T. Pope, Springer-Verlag, New York, 1983, Chap. 7, Fig. 7.8, p. 126.7Key Concept and Components in Composite Membrane Fabrication8Procedure for Fabricating 3D Cross-Linked HPA/SiO2/Functional Silane Sol Gel Composite & PEM Membrane with PMG TEOS + Functional Silane + pH = 1.35 H2O + HPASol Gel CompositeSol SolutionHost Polymer Dissolved in THF or EtOHdiluted with THF or EtOHLiquid Mixturesolution castAs-cast Filmthermal or UV X-linkingCured PEMaged (gelled) solutionBonded STA%, IEC, & Other Analyses/TestsCuring Agent, X-linkerSilanes: Methacrylate-type: Z-6030Epoxy-type: A-186, A-187HPAs: H4SiW12O40 (W12-STA)H8SiW11O39 (W11-STA)K8SiW10O36 (KW10-STA)Polymer: PMG or BSPPO(3D Network of SiO2/silane/HPA/PMG)9Formation of SiO2 Nano-Particles in Composite Matrix upon Thermal Treatments (TEM Analysis)As grown with 10x diluted PEM-#9D solutionAnnealed at 80°C for 20 minAnnealed at 140°C for 5 minAnnealed at 190°C for 2 min50 nm 50 nm 20 nm50 nm10Flexibility of PEM Membranes Fabricated with High HPA LoadingPEM-#9B,C,D Films: W12-STA/(PMG + Cross-Linker) = 174 Wt%11-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4Absorbance 1000   2000   3000   4000  Wavenumbers (cm-1)Immobilizing the HPABinding HPA with Z-6030 Silane in Sol Gel Composite Î W12-STA RetainedW12-STA/SiO2/Z-6030As-madeH2O-washedZ-603012-HSiWSiO2(W12-STA washed off easily without Z-6030)12Chemical Stability of Membrane and Composite PEM20304050607080901000 5 10 15 20 25Exposure Time (h)Normalized Weight %Chemical Stability Test of PEM Films in Fenton ReagentControl (no W12-STA)PEM-#5PEM-#6 in H2OPEM-#6Fenton’s Reagent:       4 ppm Fe2+ +  3% H2O2 at 68oCPEM-#5: W12-STA at 165 wt%, cured at 145oC/2-ton/5-min PEM-#6: W12-STA at 153 wt%, cured at 145oC/1-ton/5-min Weight loss due to W12-STA extraction13 0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018 0.020 0.022 0.024 0.026 0.028 0.030 0.032Absorbance 1000   1500   2000   2500   3000   3500   4000  Wavenumbers (cm-1)Control (no W12-STA &SiO2)Control (no W12-STA)PEM-#7 (W12-STA at 174 wt%)PEM Mechanical Strength and Flexibility Reduced by Increasing HPA Loading FTIR-ATR Spectra of Cured Control Blanks and PEM-#7(H2O)Film FlexibilityReducedLow STA wt%High STA wt%14H+ Conductivity as a Function of Cell Temperature at 100% RH0510152025301 11 21 31 41 51 61 71 81 91 101CV Scan SequenceH+ Conductivity (mS/cm)Forward Scan (-0.50V - 0.0V)Return Scan (0.0V - -0.50V)Proton Conductivity of PEM-#9D, Film #1, Strip#3Scan Range:    -0.50V - +0.50VScan Rate (mV/s):10  50  10010   50  10010   50  10010  50  10010   50  100 1027oC/100%RH80oC/100%RH70oC/100%RH60oC/100%RH40oC/100%RH15Improving H+ Conductivity with Higher HPA Loading and Better Membrane FabricationTable 1.  PEM Compositions vs Proton Condutivity Derived from I-V Curves of CV ScansWeight RatioPEM ID HPA Host Polymer X-LinkerHPA/(PMG + X-Linker) 80oC/100%RH 100oC/46%RH 120oC/23%RH11 HSiW12Ox BSPPO No 0.56 0.152 HSiW12Ox PMG Yes 0.81 6.93 HSiW11Ox PMG Yes 1.09 6.4, 10.46 2.41 0.854 KSiW10Ox PMG Yes 1.05 7.56, 13.3 1.61 0.255 HSiW12Ox PMG Yes 1.50 8.86 HSiW12Ox PMG Yes 1.54 15.577 HSiW12Ox PMG Yes 1.74 14.55 2.18 HSiW12Ox PMG Yes 1.74 19.17 3.819B HSiW12Ox PMG Yes 1.74 22.289C HSiW12Ox PMG Yes 1.74 21.159D HSiW12Ox PMG Yes 1.74 25.45 [28.25 at 70oC/100%RH]Nafion 112 SO3H 149.9 98.99 49.251 Values of the proton conductivity at 120oC/23%RH are with large uncertainty because of rapidly lost linearity on I-V curvesComponents Best Proton Conductivity (mS/cm)16High H+ Diffusion Coefficients for Composite Membrane0.0E+005.0E-061.0E-051.5E-052.0E-052.5E-053.0E-0520 40 60 80 100 120Temperature (oC)H+ Diffusion Coefficient (cm2/s)(8.8 mS/cm at 80oC/100%RH)NafionPEM-#5Proton Diffusion Data from PFG-NMR Measurements(W12-STA at 150 wt%)17-1.50-1.25-1.00-0.75-0.50-0.250.0025 50 75 100 125 150 175 200 225Temperature (oC)Heat Flow (W/g)DSC Thermograms of W12-STA, SiO2, and Two Sol Gel CompositesW12-STASiO2 Sol GelTEOS-0303A (Z-6030)TEOS-0304 (A-186)606570758085909510025 75 125 175 225Temperature (oC)Weight (%)-0.35-0.25-0.15-0.050.050.150.25Heat Flow (W/g)TGA and DSC Thermograms for PEM-20050823 MembraneTGADSC22oC80oC145oC145oC22oC80oCTGA and DSC of as-cast, 80oC-pressed, and 145oC-cured PEMW12-STA/SiO2/Z-6030W12-STA/SiO2/A-186PEM-#6: W12-STA loading level at 153 wt%/ (PMG+ X-linker)Moisture Retaining Capability of W12-STA and Sol Gel Composites (DSC Analysis)18Summary of AccomplishmentsPEM Fabrication and Performance• We have shown the ability to retain HPAs into a polymer-composite matrix of our design.• Properties of HPA-based composite PEMs:– high chemical stability (Fenton’s reagent test)– good thermal stability (with highly reactive W12-STA)– good mechanical flexibility– effective binding of silicotungstic acids (Wn-STA) with select functional silanes (n = 10, 11, 12)– high Wn-STA loading [HPA/(PMG + X-Linker) > 150 wt%] – moderate proton conductivity (25 mS/cm at 80oC/100%RH)• Clear progress towards meeting the DOE targets 19Achieving Fundamental GoalsFuture Work• To continue to improve/modify/optimize the current PEM composite formulation, fabrication, and processing conditions– to enhance PEM’s thermal stability in the 90-120oC range– to improve mechanical strength and flexibility– to reduce membrane thickness and improve film uniformity• To continue to develop immobilization strategies for various HPAs, custom-synthesized at CSM, that show high proton diffusion coefficients and thermal stability. • To understand the binding mechanism of HPA with functional silanes and SiO2 nano-particles in the polymer matrix.• To understand the proton conduction mechanism in the 3D cross-linked composite membranes in order to further improve proton conductivity at low humidity and elevated temperatures.202005 Reviewers’ Comments“One of the few new, alternative ideas for membranes in the whole DOE program”• Issues:– …needs to present conductivity values for membranes with “fixed” HPAs…• Done– HPA approach is sound as a demonstration but water solubility must be addressed…• Excellent progress has been made in this regard– Nafion doped in HPAs has been shown to be feasible…the PI is in need of new insight.• Not part of our project, those figures were for introduction to HPAs only• Our project is focused on developing a composite hydrocarbon membrane using HPAs as the proton conducting moiety that will meet the DOE targets for operation at low RH and higher temperatures• Future:– Need durability studies in actual operating fuel cell conditions and …thermal and RH cycling…gas crossover measurements• PEMs of 3D cross-linked PMG matrix were not available yet at the time• These subjects will be investigated for HPA-based PEMs this summer21Presentations and Publications1. A. M. Herring, J. A. Turner, S. F. Dec, M. A. Sweikart, J. L. Malers, F. Meng, F. J. Pern, J. Horan, and D. Vernon; "The Use of Heteropoly Acids in Composite Membranes for Elevated Temperature PEM Fuel Cell Operation; Lessons Learnt from Three Different Approaches," 2004 Joint International Meeting, W1 - Fourth International Symposium on Proton Conducting Membrane Fuel Cells, 206th ECS Meeting, October 3-8, 2004, Honolulu, HI.2. F. J. Pern, J. A. Turner, and A. M. Herring; "Hybrid Proton-Carrier Polymer Composites for High-Temperature FCPEM Applications," in Nanostructured Materials in Alternative Energy Devices, edited by Erik M. Kelder, Edson Roberto Leite, Jean-Marie Tarascon, and Yet-Ming Chiang (Mater. Res. Soc. Symp. Proc. 822, Warrendale, PA , 2004), pp. S.8.6.1 –S.8.6.6.3. A. M. Herring, J. A. Turner, S. F. Dec, M. A. Sweikart, J. Malers, F. Meng, J. Pern, J. Horan, and D. Vernon; “The Use Of Heteropoly Acids In Composite Membranes for Elevated Temperature PEM Fuel Cell Operation; Lessons Learnt from Three Different Approaches.” Fuel Cell Seminar, 2004.4. F. J. Pern, J. A. Turner, Fanqin Meng, and A. M. Herring; “Sol-Gel SiO2-Polymer Hybrid Heteropoly Acid-Based Proton Exchange Membranes,” MRS 2005 Fall Meeting, Energy and The Environment Symposium, Session A: The Hydrogen Cycle—Generation, Storage, and Fuel Cells. In press.5. F. J. Pern, J. A. Turner, and A. M. Herring; “Hybrid Proton Exchange Membranes Based on Heteropoly-Acid and Sulfonic-Acid Proton Conductors,” ECS 2006, Abstract (accepted for oral presentation)6. J. L. Horan , J. Turner , A. M. Herring, and S. Dec; “Structure and Dynamics of Non-Commercial Heteropoly Acids for Fuel Cell Applications,” ECS 2006, Abstract 7. N. V. Aieta, M. Kuo, F. Meng, J. Turner,  and A. M. Herring; “The Use of Heteropolyacids as Additives for Low Humidity Operation of Nafion Membranes for PEM Fuel Cell Applications,” ECS 2006, Abstract 8. A. M. Herring, R. J. Stanis, J. Ferrell III, M. Kuo, J. Turner, and M. Samaroo; “The Use of Heteropoly Acids as Electrocatalysts for the Oxygen Reduction Reaction in PEM Fuel Cells,” ECS 2006, Abstract 9. R. J. Stanis, A. M. Herring, M. Kuo, and J. Turner; “Increased CO Tolerance of Pt Electrodes by Addition of Adsorbed Heteropoly Acids and Salts in PEM Fuel Cell Anode Catalysts,” ECS 2006, Abstract 

Advanced Fuel Cell Membranes Based on Heteropolyacids

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Advanced Fuel Cell Membranes Based on Heteropolyacids

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