Hara, S.

Shikazono, N.

Tada, T.

Umeno, Y.

English

Engineering Conferences International

Engineering Conferences InternationalECI Digital ArchivesHarnessing The Materials Genome: AcceleratedMaterials Development via Computational andExperimental ToolsProceedingsFall 10-4-2012Multiscale Modeling for Material Design of SolidOxide Fuel Cell ElectrodeY. UmenoThe University of TokyoS. HaraThe University of TokyoT. TadaThe University of TokyoN. ShikazonoThe University of TokyoFollow this and additional works at: http://dc.engconfintl.org/materials_genomePart of the Biomedical Engineering and Bioengineering CommonsThis Conference Proceeding is brought to you for free and open access by the Proceedings at ECI Digital Archives. It has been accepted for inclusion inHarnessing The Materials Genome: Accelerated Materials Development via Computational and Experimental Tools by an authorized administrator ofECI Digital Archives. For more information, please contact franco@bepress.com.Recommended CitationY. Umeno, S. Hara, T. Tada, and N. Shikazono, "Multiscale Modeling for Material Design of Solid Oxide Fuel Cell Electrode" in"Harnessing The Materials Genome: Accelerated Materials Development via Computational and Experimental Tools", J.-C. Zhao, TheOhio State Univ.; M. Asta, Univ. of California Berkeley; Peter Gumbsch Institutsleiter Fraunhofer-Institut fuer WerkstoffmechanikIWM; B. Huang, Central South University Eds, ECI Symposium Series, (2013). http://dc.engconfintl.org/materials_genome/16(A CREST project supported by JST)October 4, 20121Y. Umeno, T. Tada, S. Hara and N. ShikazonoThe University of Tokyo, JapanEngineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USAOther contributors:Dr. J.-M. Albina and Mr. A. Kubo (also at Univ. Tokyo)TPBOctober 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 2Why SOFC?- High power generation efficiency (~60%)- Variety of fuel typeENE-FARM type S: First residential SOFC by JX Nippon Oil&Energy(We focus on anode)トリプルサイクル発電SOFC SystemSOFCstackmIssues:- Evaluation of power generation efficiency- Mechanism of degradation / Change in microstructure- Understanding reaction processσSOFCCellElectrodes Boundaries cm~mm ~µm ~nmOctober 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 3Charge transfer reactions, chemical bonding~ÅFor better design of SOFC, issues that range over different length scales must be addressed.We are performing simulations  covering a wide length scale (ab initio DFT / atomistic model / meso-scale monte carlo / lattice Boltzmann method / etc.)FIB-SEMOctober 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 4MC for sinteringLB for diffusion/ tortuosity/overpotDFT for phase transDFT for reactionEfficiency of power generation (µ strct)Deformation(degradation)Reaction at TPB: Effect of atomic structureKMC for ec currentOctober 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 5Carl Zeiss NVision40 yxz CarbonsputteringEpoxy infiltrationIwai, H. et al., J. Power Sources, 195 (4) , pp. 955-961 (2010). Typical acceleration voltage 1–2 kV October 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 6» Lattice Boltzmann Eq.˃ fi ： Distribution functions of gas concentration, electron &  ion electrochemical potentials in direction i˃ fieq ： Equilibrium distribution function» Advantages of LBM˃ Simple to treat complex geometries fi t + ∆t, rr + rci( )= fi t, rr( )− 1t* fi t,rr( )− fieq t, rr( ){ }+ wi∆tAdvection Collision Production˃ Very powerful for simulating flows inside porous media» Typically, 1.5 ～ 20 million voxelsOctober 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 7Calculation models• Governing equations– H2 & H2O Diffusionin pores – Electron conductionin Ni– Oxide ion conductionFiCDDy211 reacH1K,HOH,HH22222=∇+−∇−αreacee ~ iF−=∇∇−− µσO2 ~ i=∇∇ − µσD : Diffusion coefficient [m2 / s]C : Molar concentration [mol / m3]σ : Conductivity [S / m]         : Electrochemical potential [J/mol]µ~21OHH221−=MMαShikazono, N. et al.,  J. Electrochem. Soc., 157 (5), pp. B665-B672 (2010).in YSZ• Reaction current at TPB– Exchange current per unit LTPBreacO22F − ×−×= −RTppi54.0OH03.0H01052.1exp4.3122−= actactTPB0reac exp2exp ηηRTFRTFLiiireac : Reaction current per vol. [A/m3][A/m3] B. de Boer, Ph. D. Thesis, University of Twente, (1998).A. Bieberle et. al., J. Electrochem. Soc., 148(6), A646-A656 (2001). ×−×=RTppi567.0OH11.0H010849.0exp0013.022October 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 8YSZ surface distribution−∆ 2O~µOxide ion electrochemical potential distribution in YSZ Electrolytecollectorz = 1.178 µmcross section1.2 % H2O － 98.8 % H2,  i = 0.7 A/cm2ElectrolyteCurrent collector31 µmOctober 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 9Kanno, D., Shikazono, N., et al., Electrochimica Acta, 56 (11), 4015 (2011).October 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 10Kanno, D., Shikazono, N., et al., Electrochimica Acta, 56 (11), 4015 (2011).October 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 11Jij(qi,qj): Surface (interface) energyqi,qj: Crystal grain numberδ(qi,qj): Kronecker deltaN: Total number of sitesn: The number of nearest sitesG. Hassold et. al, J. Am. Ceram. Soc. (1990),1 11 (1 ( ))2N nij i ji jE J q qδ= == −∑ ∑Total System Energy E:Pore GrainkBT: thermal fluctuationsSimple Monte Carlo AlgorithmOctober 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 12October 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 13Initial structure 5000MCS3000MCS1000MCSComputational time: 30-50 hours per 5000 MCSYSZ phase is fixed.1 Monte Carlo Step (MCS) step:  a number of attempted moves equal to the number of the N sites.real MCSt Ct=October 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 140.50.60.70.80 1000 2000 3000 4000 5000①②③④⑤⑥averageG. J. Nelson et.al, Acta Mater. 60 (2012)MCSThis workOctober 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 1533.544.555.560 1000 2000 3000 4000 5000①②③④⑤⑥averageG. J. Nelson et.al, Acta Mater. 60 (2012) This workMCSOctober 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA16Pure ZrO2: Tetragonal to monoclinic transformationThe transition barrier is defined as the energy difference between the monoclinic phase and the saddle point. From Luo et al. (VASP/LDA):∆EMEP  = 0.17 eV/ZrO2 molecule= 16.3 kJ/mole Solid-state NEB (VASP/GGA):∆EMEP  = 0.112 eV/ZrO2 molecule= 10.8 kJ/moleConsidering that the energy surface from Luo et al. is obtained by a simple internal coordinates and lattice mixing (no relaxation involved except for the initial tetragonal and final monoclinic phase), our value is in fairly good agreement with their results. October 4, 201217Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USAYSZ: Tetragonal to monoclinic transformation 2 starting configurations:Eichler et al.,PRB 64 174103 (2001)- Etot is lower by ca. 0.32 eV ( > 0.04%)- Used as benchmark to validate the calculations. Y2Zr30O63October 4, 201218Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA∆EMEP  = 0.077 eV/ (ZrO2 - 3.3mol% Y2O3 )  molecule= 7.4 kJ/mole∆EMEP  = 0.071 eV/ (ZrO2 - 3.2mol% Y2O3 )  molecule= 6.9 kJ/moleTM transition: Effect of hydrostatic pressure• +5 kB:∆EMEP = 0.071 eV/ (ZrO2 - 3.2mol% Y2O3 )  molecule• +10 kB:- Unstable - Barrier (if any?): ∆EMEP = 0.059 eV/ (ZrO2 - 3.2mol% Y2O3 )  moleculeAbove 10 kB, the energy barrier is sufficiently low or almost inexistent to allow the transformation tetragonal  monoclinic.The shear stress might be a more dominant factor for activating the t  m transformation.+October 4, 201219Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USATM transition: Effect of HEichler et al. Another conf.∆EMEP = 0.0706 eV/ (ZrO2 - 3.2mol% Y2O3 )  molecule(still ongoing)The transition barrier remains unchanged, however two saddle points are involved this time in the transformation. It is not clear whether this is an artifact of the simulation.This result needs to be confirmed by the configuration from Eichler et al. (Ongoing)October 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA20O2-+H2=H2O+2e-NiH-spilloverO-spilloverO-spillover: Oxygen in oxide moves to metal surface.T. Horita et al., Solid State Ionics 177, 1941 (2006).H-spillover:Hydrogen adsorbed on metal movesto oxide.Other mechanisms are also proposed, but we have not yet reached consensus on the reaction mechanism of the water generation reaction.YSZ(O-rich)October 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 21Reactant ProductTransition State (TS)0.59 eV0.72 eVMoved O is still charged negatively(i.e., no discharge)(Charge of O: -0.47） （-0.45） （-0.45）October 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 220.08 eV0.68 eVReactant ProductTS(Charge on H: -0.44） （-0.21） （+0.10）The charge on H changes in this reaction（H/Ni  H/Oxide + (-)0.5e-/Ni）October 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 23Reactant ProductTS0.01 eVEa = 0.16 eVEasy for water generationWater generationon fully hydroxylatedoxide surfaceYSZNiYSZNiYSZNiPossible reaction stepsfor water generationOctober 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 24FIB-SEMMC for sinteringWorking separately??October 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 25We are working on to establish a real framework of multiscale modeling by handing over data to different length scales. LB for diffusion/ tortuosity/overpotDFT for phase transDFT for reactionEfficiency of power generation: µ-strucDeformation & degradationReaction at TPB: Effect of atomic structureOctober 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA26(J. Appl. Phys. 98, 103513 (2005).)October 4, 201227Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA5x5x5 super cell (1500 atoms,Y2O3 8mol dope: 420Zr, 80Y, 960O, 40Vo )・12 configurations for Y,Vacancy・First 10,000 jump are withdrawn ・Total jump 3,000,000 for each configuration  ~0.02 ms simulation at 700K・Calculate MSD & Self diffusion Coeff. ( ) ( ) 2002 1)( ∑ −−= trttrNtr iittrD tV 6/)(lim 2∞→=Local Exchange current density at a reduced condition as PO2=10-22 atm. ~5 nmMETAL BlockGAS BlockYSZ BlockOctober 4, 201228Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA2468101214161820 Current density (A/cm3)Time (µs) +Z -Z0.00.5 1.01.5zCharged vacancyNeutral vacancyOxygenZirconiumYttriumNickelHydrogenOctober 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA29Charge shift (polarization), which is essential for oxides, can be expressed.ELSRtot VVV +=pppqqqEL VVVV ++=( )6Buck −=−rerV r βγα βVSR : Short Range Interaction・Buckingham Type VEL : Electrostatic ContributionVqq : Charge-ChargeVpq : Dipole-ChargeVqq : Dipole-DipoleAdditional DoF for diople moment is given to each atom.+-Dipole momentIon coreElectronDipole MomentPotential fittingOctober 4, 201230Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA( )ijijij ijijji rfrrqa∑≠= 3SRp( ) ( )∑=−=40 !kbrkijijijijekbrcrfObtained by repeated loop until self-consistency is achieved. 12 snapshots with random displacement of atoms Energy, stress and forces calculated by ab initio DFT methodPotfit package (potfit.itap.physik.uni-stuttgart.de) is employed for fitting.Path 1Path 2Path 3Remarkable improvement!October 4, 201231Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USAP. K. Shelling, et al., J. Am. Ceram. Soc. 84 1609 (2001)ReaxFF potential fitting tool has been developed (interface btw. potfit /LAMMPS).Fitting of potential for reaction process is now ongoing!October 4, 201232Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USAFIB-SEMDFT for reactionData-passing to bridge btw different models (now being partly done) will be expanded. Potential fitting and MD simulations will play a major role.Atomistic model (MD)October 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 33MC for sinteringLB for diffusion/ tortuosity/overpotDFT for phase transEfficiency of power generationDeformation: Effect of microstructureReaction at TPB: Effect of atomic structureCharge-representing interatomic modelKMC for ec currentOctober 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 34October 4, 201235Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USAOctober 4, 201236 Both energies and forces have been sufficiently fitted. Crystal stability is being checked by MD. Crystal structure seems stable, but deviation of oxygen positions is rather large. Including more configurations may be needed. Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USAExample of force vectorsAb initio Fitted potential・3D network of metal・3D network of oxide・Vacuum (gas molecules)・Contact between metal/oxideA TPB model must includeNo simulations holding these conditions But, adopted models are  (A) a single Ni on oxide, (B) single Ni layer on oxide October 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 37Remove Ni atomswithin shaded regionProjected Density of StatesP234 Point contact NiUp-spinDensity of StatesspｄLP234 Line contact NiUp-spinDensity of Statesspｄ-8 -6 -4 -2 0 2-4-3-2-101   Down-spinE-Ef(eV)Density of States○Sharp peaks ○Small DOS at Ef Atomic-like NiPolarizability to perturbationssmall BIGpc-Ni: chemically hard lc-Ni: chemically soft-8 -6 -4 -2 0 2-4-3-2-101   Down-spinE-Ef(eV)Density of States○Broad DOS Metallic NiOctober 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 38Zr (@ pc-Ni) Zr (@ lc-Ni)» Non-zero DOS at Ef chemical softness Zr (@ pc-Ni)Zr (@ lc-Ni)Projected DOS (Zr)0.00.51.01.52.0GapSpin UpMIGS on Zr (@ lc-Ni)= soft Zr & soft NiNo MIGS on Zr (@ pc-Ni)= hard Zr & hard NiProjected DOS (-8 -6 -4 -2 0 2-2.0-1.5-1.0-0.5  E – EF (eV)Spin DownZr (@ pc-Ni)Zr (@ lc-Ni)October 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 39remove-0.19-0.11-0.11Redistribution is quite local event. Pc-Ni get electrons (-0.19 e-), but Pc-Ni does not have metallic DOS.  capacitive redistribution.Oxygen is charged by -0.45 e.remove-0.08-0.06-0.03-0.10-0.11Redistribution is not local. Lc-Ni get electrons (sum: -0.20 e-), and Lc-Ni has metallic DOS.  discharge-like redistribution.-0.03 e- are distributed on 2nd layer NiOctober 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 40» TPB including point- and line-contact Ni atomsPC     LCPDOS of Ni Atomic-like MetallicChemical Hard       SoftStructure Disordered OrderedPDOS of ZrResponseNo MIGS (hard)capacitiveMIGS (soft)discharge-like• Chemical “hardness/softness” (in an extended meaning) is a good guideline in the modeling of TPB• Question: Is the TPB model (~300 atoms) practical for reaction analysis? We need a smaller (practical) TPB model including the chemical/physical properties  Atomic contact TPB model (< 100 atoms)October 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 41Single atom contact-8 -6 -4 -2 0 2-4-3-2-101234    Density of StatesE-Ef(eV)P’PDOS of Ni: Ni(P’)spｄCorresponds to Chemically HARD TPBZr has no MIGS (not shown)Atomic-like PDOSUp-spinDown-spinThree atoms contactL’PDOS of Ni: Ni(L’)spｄDensity of StatesE-Ef(eV)Metallic PDOS-8 -6 -4 -2 0 2-4-3-2-101234    Up-spinDown-spinCorresponds to Chemically SOFT TPBZr has MIGS (not shown)T. Tada and S. Watanabe, J. Phys. Chem. C 113, 17780 (2009). O ctober 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 42PDOS of Ni Atomic-like MetallicChemical Hardness SoftnessAtom contact Single atom Three atomsPDOS of Zr No MIGS MIGSResponse capacitive discharge-likePC     LCPDOS of Ni Atomic-like MetallicChemical Hardness SoftnessStructure Disordered OrderedPDOS of ZrResponseNo MIGS (hard)capacitiveMIGS (soft)discharge-likeOctober 4, 2012Engineering Conferences International: Material Genome Initiative,  Sep 30 - Oct 5 2012, Vail Colorado, USA 43

Multiscale Modeling for Material Design of Solid Oxide Fuel Cell Electrode

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Multiscale Modeling for Material Design of Solid Oxide Fuel Cell Electrode

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