Bidrawn, Fred

Glass, Robert S

Gorte, Raymond J

Gross, Michael D

Martin, L. P

Vohs, John M

Wang, Wei

Woo, Leta Y

English

ScholarlyCommons@Penn

University of PennsylvaniaScholarlyCommonsEnergy Research Group Presentations Energy Research GroupMay 2007Electrodes for Solid Oxide Electrolysis (SOE) andNatural-Gas Assisted Steam Electrolysis (NGASE)Raymond J. GorteUniversity of Pennsylvania, gorte@seas.upenn.eduJohn M. VohsUniversity of Pennsylvania, vohs@seas.upenn.eduWei WangUniversity of PennsylvaniaMichael D. GrossUniversity of PennsylvaniaFred BidrawnUniversity of PennsylvaniaSee next page for additional authorsFollow this and additional works at: http://repository.upenn.edu/pennergy_presentationsPresentation for Department of Energy: Hydrogen Storage Merit Review on May 14-17, 2007.This paper is posted at ScholarlyCommons. http://repository.upenn.edu/pennergy_presentations/5For more information, please contact libraryrepository@pobox.upenn.edu.Gorte, Raymond J.; Vohs, John M.; Wang, Wei; Gross, Michael D.; Bidrawn, Fred; Glass, Robert S.; Woo, Leta Y.; and Martin, L. P.,"Electrodes for Solid Oxide Electrolysis (SOE) and Natural-Gas Assisted Steam Electrolysis (NGASE)" (2007). Energy ResearchGroup Presentations. 5.http://repository.upenn.edu/pennergy_presentations/5Electrodes for Solid Oxide Electrolysis (SOE) and Natural-Gas AssistedSteam Electrolysis (NGASE)Keywordssolid oxide steam electrolysis, solid oxide fuel cells, natural gas assisted electrolysis, catalysisCommentsPresentation for Department of Energy: Hydrogen Storage Merit Review on May 14-17, 2007.Author(s)Raymond J. Gorte, John M. Vohs, Wei Wang, Michael D. Gross, Fred Bidrawn, Robert S. Glass, Leta Y. Woo,and L. P. MartinThis presentation is available at ScholarlyCommons: http://repository.upenn.edu/pennergy_presentations/5Electrodes for Solid Oxide Electrolysis (SOE) and Natural-Gas Assisted Steam Electrolysis (NGASE)R. J. Gorte, J. M. Vohs, W. Wang, M. D. Gross, F. Bidrawn, & S. W. Jung Chemical & Biomolecular Eng., University of PennsylvaniaR. S. Glass, L. Woo, & L. P. Martin Lawrence Livermore National LaboratorySOEO2- →H2OH2O2e-NGASEO2- →H2OH2CH4e-CO2 + H2ONo external power required.Produces pure H2.High efficiency possible.Membrane can be mixed conductingCTP Hydrogen Corp: www.ctphydrogen.comElectrolysis requires V> VNernstSOE are more efficient- low cathode losses- lower Nernst Potential (TΔS)Cathode: H2/H2OAnode Nernst PotentialH2/H2O1.0V0.5V– 0.5VairCOCH40VEnergy-0.1-0.0500.050.10.150.20.250.3-0.1 0 0.1 0.2 0.3 0.4 0.5 0.6Current density (A/cm2)Potential (V)conversion 10% conversion 50% conversion 80% conversion <3%1023KNGASE Works!60% H2O, 4% H2, Co/ceria | YSZ(50 μm) | Pd/ceria, CH4SpontaneousReactionResearch Issues:1) We need electrodes capable of utilizing methane.2) We need to understand the effect of polarity on electrodes.The common air electrode, La0.8Sr0.2MnO3, changes with polarization.a) LSM is activated by cathodic (fuel cell) polarization.b) LSM is deactivated by anodic (SOE) polarization.Ni electrodes ubiquitous but form carbon fibers; we need alternatives.Ni(M. L. Toebes, et al., Catalysis Today, 2002)Electrode IElectrode IIElectrolyteImpregnate active components using1. Aqueous salt solutions2. Perovskite nanoparticles3. Molten salts4. ElectrodepositionTape casting/lamination with pore formersLSF-YSZYSZElectrode and Cell Fabrication:Advantages:1. Separate firing temperatures for YSZ and active phase.- Avoids solid-state reactions between LSF & YSZ.- Can use low-melting solids (CuO).2. Composite is non-random structure.Mixed powdersImpregnatedLSMPercolation threshold for random mediaLSCo Weight Fraction in YSZ 0% 35% 45% 55%CTE (10-6/K), 300 to 1073 K 10.3 11.7 12.6 12.6b) CTE of LSCo-YSZa) Electrical conductivity of LSM-YSZ700ºC in air, composites calcined at 1523 K.CTE of LSCo is 23x10-6/KCu-based anodes are stable in hydrocarbons but not suitable for CH4 utilization•Low catalytic activity (ceria is the catalyst)•Limited to use at lower temperatures; sintering causes loss of electrode conductivity.700ºC 900ºC B Cu    BCuSolution 1: Electroplate Cu onto Co cermetsIdea: “Coat” thermally stable Co with chemically stable Cu:CoCu and Co do not form alloysCu Anode Ni CermetCuSO4 + H2S04 SolutionDCCu2+eVO4 -e-Co cermetKey is to deposit evenly throughout the pores; Co plating is much easier than CuBut Cu segregates to Co surfaceXPS of 250-nm Co film on Cu with heatingCoheatingCo plated Cu stable in CH4 at 800ºC for 3 hCu-Co          Co only 01230 10 20 30 40 50time / hOhmic Resistance / Ω cm2CuCu-CoDramatic increase in thermal stability with Cu-CoRΩ as a function of time at 900ºCSolution 2: Ceramic anodesProblem: Oxides have either poor conductivity at low P(O2) or poor catalytic activityConcept: Separate the two required functionsYSZ electrolyteAnode current collector:Porous ceramic, optimized for conductivityAnode functional layer:Optimized for catalytic performanceThin to avoid need for high conductivityKey point:If δ = 10 μm and Rohmic must be < 0.1 Ω.cm2, σ need only be 0.01 S/cm!δ00.20.40.60.811.20 0.4 0.8 1.2 1.6Current Density / A cm-2Voltage / V00.10.20.30.40.50.60.7Power Density / W cm-2650ºC800ºC750ºCH2 (3% H2O)00.20.40.60.811.21.40 0.4 0.8 1.2 1.6Current Density / A cm -2Voltage / V00.10.20.30.40.50.6Power Density / W cm-2CH4 (3% H2O)800ºC750ºC700°C20 μmPorous YSZ-active regionLa0.3Sr0.7TiO3 current collectorYSZ electrolyteCurrent collector:La0.3Sr0.7TiO3Functional layer:1wt%Pd-40wt% ceria in YSZCatalysis is crucial!0.00.20.40.60.81.01.20.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4i / A cm-2V / V0100200300400500600Power Density / mW cm-2PdNiCuCeO2700°C H2 (3% H2O)-0.10.10.30.50.70.91.10.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6Z Re / Ω cm2-Z Im / Ω cm2PdNiCuCeO2Need combination of ceria and metal40 wt% CeO2Pd 1 wt%Ni 1 wt%Cu 5 wt%A remaining issue:Conductivity of ceria layer is not stable at low P(O2):log PO2 (atm)-30 -28 -26 -24 -22 -20 -18 -16O/Ce atomic ratio1.701.751.801.851.901.952.00Need to develop other ways to make functional layer conductive:1)   Use composites of YSZ with doped SrTiO32)   Dope the YSZ with Ce, Ti, or Nb.J. Power Sources 164 (2007) 42Ceria film in porous YSZWet H2 at 973 K (1.1 V)     Methanol (1.25 V)IECR 45(2006) 55611.1V1.25V973 K1073 K1173 KHow does polarity affect electrodes?Characterization:Impedance spectroscopy allows separation of electrode and electrolyte losses:00.20.40.60.811.21.41.6-1 -0.5 0 0.5 1Current density (A/cm2)Voltage (V)VNernstLosses(electr)Losses(fuel cell)00.10.20.30.3 0.4 0.5 0.6 0.7 0.8Z Re, ohm*cm2-Z Im, ohm*cm2450 mA/cm2OCV- 450 mA/cm2Slope of V-i curve Electrolyte losses-1-0.500.511.520 0.5 1 1.5 2 2.5 3 3.5Z Re, Ω.cm2-Z Im, Ω.cm22 kHz0.8 Hz1.6 Hz3 Hz4 HzPolarization activation with LSM-YSZLSM-YSZCeO2 – Pd- C - YSZ700°C, H2/3%H2O, OCV after applying current- 850 mA/cm2- 60 mA/cm2- 0 mA/cm2 - 150 mA/cm2Note: These changes are reversible. τ ~ 120 minutes.ESSL, 7 (2004) A111-A114.What we believe is happening:YSZ1) Dense LSM covers YSZ Gaps in LSM film caused by reduction2) Performance limited by Gas can get to YSZ interface.oxygen diffusion.Process driven by surface interactions between LSM & YSZYSZLSMElectrode before activation Activated ElectrodeLSM Particles on YSZ (100): Effect of calcination temperature850°C 1050°C 1150°CESSL, 9 (2006) A237-2402 μm x 2 μmCalcination at 1150°CReduced in H2 (10%H2O) at 700°CMovement of particles is reversible:1) LSM is stable in 10%H2O-90% H2 at 700ºC.2) Reducing LSM-YSZ electrode “activate” it.Consequences for electrolysis (anode environment is oxidizing):0 50 100 150 200 250 3000.00.20.40.60.81.01.21.4Cell potential (V)Time (min) 1.251.31.351.41.45-20 10 40 70 100 130 160 190Time (min)Cell potential (V)0.511.522.533.5Electrode impedance ( -cm2)285 mA/cm2; 700ºC; 85%H2-15%H2O| airLSM-YSZ anode                      LSF-YSZ anodeJECS, 153 (2006) A2066.Publications Citing DOE Support (2006 -)1. "Electrodeposition of Cu into a Highly Porous Ni/YSZ Cermet", S. Jung, M. D. Gross, R. J. Gorte, and J. M. Vohs, Journal of the Electrochemical Society, 153 (2006) A1539-43.2. "Enhanced Thermal Stability of Cu-Based, SOFC Anodes by Electrodeposition of Cr", M. D. Gross, J. M. Vohs, and R. J. Gorte, Journal of the Electrochemical Society, 153 (2006) A1386-90.3. "A Comparison of LSM, LSF, and LSCo for Solid Oxide Electrolyzer Anodes", Wensheng Wang,Yingyi Huang, Sukwon Jung, John M. Vohs, and Raymond J. Gorte, Journal of the Electrochemical Society, 153 (2006) A2066-70.4. "A Study of Thermal Stability and Methane Tolerance of Cu-Based SOFC Anodes with Electrodeposited Co", M. D. Gross, J. M. Vohs, and R. J. Gorte, Electrochimica Acta, 52 (2007) 1951.5. "A strategy for achieving high-performance with SOFC ceramic anodes", M. D. Gross, J. M.Vohs, and R. J. Gorte, Electrochemical and Solid State Letters, 10 (2007) B65-69.6. "The Stability of LSF-YSZ Electrodes Prepared by Infiltration", W. Wang, M. D. Gross, J. M.Vohs, and R. J. Gorte, Journal of the Electrochemical Society, 154 (2007) B439-457. "Impedance characterization of a model Au/YSZ/Au electrochemical cell in varying oxygen andNOx concentrations", L. Y. Woo, L. P. Martin, R. S. Glass, and R. J. Gorte, Journal of the Electrochemical Society, 154 (2007) J129.8. "Multilayer High Performance Ceramic Anodes", M. D. Gross, R. J. Gorte, and J. M. Vohs, ECS Transactions - Solid Oxide Fuel Cells, Volume 7, accepted.9. "Hydrogen Production via CH4 and CO Assisted Steam Electrolysis", W. Wang, J. M. Vohs, and R. J. Gorte, Topics in Catalysis, accepted.10. "An examination of SOFC anode functional layers based on ceria in YSZ", M. D. Gross, J. M.Vohs, and R. J. Gorte, Journal of the Electrochemical Society, accepted.11. "Recent Progress in SOFC Anodes for Direct Utilization of Hydrocarbons", M. D. Gross, J. M.Vohs, and R. J. Gorte, Journal of Materials Chemistry, accepted.Support Layers can be added for strength:Laminated cellDense YSZPorous YSZDense YSZPorous YSZFinal ProductFFC, Inc.

Electrodes for Solid Oxide Electrolysis (SOE) and Natural-Gas Assisted Steam Electrolysis (NGASE)

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Electrodes for Solid Oxide Electrolysis (SOE) and Natural-Gas Assisted Steam Electrolysis (NGASE)

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