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MASc Research work

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MASc Research work

  1. 1. SOFC CATHODES: EXPERIMENTS ON MATERIAL STABILITY AND NOVEL TEST SYSTEM DEVELOPMENT NAKKIRAN ARULMOZHI CHEMICAL ENGINEERING DEPARTMENT QUEEN’S UNIVERSITY Supervisor :Dr. KARAN MASc Thesis Defense 28th Feb 2012
  2. 2. SOLID OXIDE FUEL CELL(SOFC) Thomas L. Cable etal Int. J. Appl. Ceram. Technol., 8 [1] 1–12 (2011)Schematic Representation of SOFC Polarization curve showing performance of SOFC 1
  3. 3. MOTIVATIONHandbook of fuel cells : Fundamentals, technology, Singhal SC, Kendall K,. 2003. High-temperature solid oxideand applications, Chichester, England; Hoboken, N.J.: fuel cells fundamentals, design, and applications.Wiley 2
  4. 4. SOFC CATHODE: REQUIREMENTS AND CHALLENGESFunctional Requirement Perovskite type material (ABO3 structure)Electrocatalytic activity Mnn+,Con+,Fen+,Nin+,Electronic and oxygen ion conductivities Cun+,…etcMaterial stability(w.r.t temperature and chemicalenvironment ) La3+,Ce3+,Nd3+,Sm3+, Eu3+,Gd3+,Tb3+,Dy3+… Material Stability Need for Rapid Test System La0.5Ba0.5CoO3-δ • New material development is possible multiple substitution at A and B site But to find best performing material which is also stable requires testing of many different material composition Amin and Karan 2010, J. Electrochem. Soc. 157 2 B285. 3
  5. 5. THESIS- OBJECTIVEObjective -1: Stability of newly developed barium-based cathodematerial (La0.5Ba0.5CoO3-δ) in the presence of carbon dioxideatmosphereObjective -2: Development of a test system for rapid testing ofmultiple electrodes 4
  6. 6. PART-ICarbonate Formation in LBC-CO2 System- Reaction Pathway, Kinetics and Thermodynamics 5
  7. 7. ALKALI METAL CARBONATE FORMATION -GENERAL DISCUSSIONWell Studied Alkali earth Oxide/CO2 reaction AO CO2 ACO3Distinction between thermodynamic phase boundary andkinetic limitationLBC-CO2 system Air contain 330 ppm of CO2 La 0.5 Ba0.5CoO3 xCO2 BaCO3 decomposed phasesWhat are the decomposed phases ?What is the reaction pathway and kinetics ?What is the phase boundary of LBC - CO2 System ? 6
  8. 8. PART-AReaction Pathway and Kinetics of LBC- CO2 reaction 7
  9. 9. NON-ISOTHERMAL STUDIES IN PURE CO2 106 5.5 wt% 106 Sample collected Cooling 800 104 Temperature Weight % Weight % 104 4.2 wt% 600 102 102 400 Heating 100 100 Thermogram Temperature scan rate 200 98 200 400 600 800 1000 100 200 300 400 500 Temperature C Time in minPost TGA phases Barium carbonate-BaCO3 La2CoO4 Cobalt oxide -CoOProposed EndReactionValidating using 245.04 22 100.17 98.65 56.19 12Wt gain % Theoretical Wt gain = 4.1% 8
  10. 10. TRACKING INTERMEDIATE PHASE CHANGE USING HT-XRD UNDER SIMILAR CONDITION OF TGA EXPERIMENT LaCoO3 La2CoO4 Emergence of Barium carbonate – rhombohedra Emergence of Barium carbonate (ortho) and Cobalt oxide peak ●- LBC/LCO ♦- barium carbonate (ortho) ■ - barium carbonate (rhombo) ▲- cobalt oxide ▼-La2CoO4 9
  11. 11. PROPOSED REACTION PATHWAY La0.5Ba0.5CoO3-δ 30-500° C La0.5Ba0.5CoO3-Δδ + δ’O 2 ↑ ½ CO2 500-800°C ½ LaCoO3 + ½ BaCO3(ortho)+ ½ CoO+(1-2δ)/4 O 2↑ 800- 900°C ½ LaCoO3 + ½ BaCO3(rhombo) Theoretical mass + ½ CoO+ (1-2δ)/4 O 2↑ gain -5.7% 900°C ¼ La2CoO4 + ½ BaCO3(rhombo) Theoretical mass + ¾ CoO+(1.5- 2δ)/4 O 2↑ change-4.1 %Validation of reaction pathway through TGA mass gain“ For the first time reaction pathway was proposed for LBC-CO2,a complex hightemperature heterogeneous process using combination of HT-XRD and TGA” 10
  12. 12. REACTION KINETICS IN PURE CO2 ISOTHERMAL STUDIESHomogenous Model Ea = 128 KJ/mol. 11
  13. 13. Phase boundary of LBC-CO2 reaction 12
  14. 14. , EQUILIBRIUM THERMODYNAMICS OF LBC-CO2 REACTIONThe reaction Gibbs energyReaction quotient, Q has the formAssume activity of solid = 1Therefore reaction Gibbs energy “At a particular partial pressure, the temperature at reaction starts was considered as phase boundary point where reaction is at equilibrium ”At Equilibrium, r G 0 Need to determine the reaction onset temperature In-order to find phase boundary 13
  15. 15. REACTION ONSET TEMPERATURE DETERMINATIONScan Rate - 2°C/min Scan Rate - 0.3°C/min 14
  16. 16. PHASE BOUNDARY AND THERMODYNAMICS PARAMETER Prediction of under SOFC operating Condition PO2 in air-0.21 PCO2in air -380 ppm PO2 from supplier δ-assumptionΔrH° -183.8 KJ/mol. ΔrS° -212.44 J/mol.K 15
  17. 17. PART-II Development of test system for rapid testingof multiple electrodes of reproducible features 16
  18. 18. NOVEL TEST SYSTEM DEVELOPMENTNeedFabrication methods that yield reproducible electrodes and testing methods that can examineseveral electrodes in a short period of timeFramework ProposedFabricating electrodes of multiple electrode of reproducible geometry -Materials PrinterRapid testing of multiple electrodes - Micro contact Impedance spectroscopyWork DoneOptimization of material printer parameters for printing electrodesA micro-contact impedance system for measuring multiple electrode was setup and commissionedTesting methods and Protocol development for performance studies 17
  19. 19. INKJET PRINTING USING MATERIALS PRINTERElectrode Design for Printing Electrolyte Substrate – Yttria stabilized zirconia (YSZ) Cathode– commercial silver ink Sintering – 200° C for 2 hrsPrinted Silver (Ag) Electrode – 3d and surface profile 18
  20. 20. NOVEL TEST SYSTEM FOR MULTIPLE ELECTRODE MEASUREMENTConventional Electrochemical Cell Design My Electrochemical Cell DesignConventional Electrochemical Reactor design My Electrochemical Reactor design 19
  21. 21. DECONVOLUTION OF IMPEDANCE SPECTRA “Impedance study at Ag/YSZ interface is well established ”Jimenez R, Kloidt T, Kleitz M. 1997. Reaction‐Zone expansions and mechanism of the O, Ag/Yttria‐Stabilized zirconiaelectrode reaction. J. Electrochem. Soc. 144 : 582 700 physicochemical process Z ECM representation of diff Diffusion 600 Ag CPE Rct Charge Transfer 500 Electrolyte Ohmic Re 400 Total Electrode Polarization Impedance 300 Charge transfer -Im Z/ Ohmic Resistance Impedance Deconvolution of Impedance Diffusion Impedance 200 Spectra using ECM model HF LF semi-circle 100 semi-circle HF Intercept 0 Re Rct Z diff -100 CPE -200 0 200 400 600 800 1000 Re Z/ 20
  22. 22. VALIDATION OF TEST SYSTEM Do we have the effect of counter electrode ? How ideal are my identical electrodes ? 400 ME-1 Vs counter 350 ME-2 Vs counter M ME-1 Vs ME-2 E 9 300 EIS EIS EIS EIS EIS 250 M E 1 200 -ImZ/ 150 100 50 0 100 200 300 400 500 600 700 800 Re Z/Electrode to electrode variation of nine identical electrodes Temperature Ohmic Resistance Electrode Polarization (oC) (Ohm) (Ohm) Mean Standard Deviation Mean Standard Deviation 460 325 45 738 110 500 159 20 208 31 525 117 12 130 17 21
  23. 23. ESTIMATION OF KINETIC PARAMETERS OF SOFCEa of Ionic conductivity =0.93 eV Ea of charge transfer resistance 2.9 eV Ea of Diffusion resistance 1.19 eV -7.5 Electrolyte conductivity Linear Fit 6 -8.0 4 ln ln R/ -8.5 2 High Frequency Resistance Low Frequency Resistance Fit Curve 1 -9.0 0 14.5 15.0 15.5 16.0 1.25 1.30 1.35 1/kT -1 -1 1000T /K 22
  24. 24. SUMMARY OF CONTRIBUTIONSStability of LBC-CO2 System:•First in-depth study that examined the reactivity of a potentially promising SOFCcathode material, La0.5Ba0.5CoO3, with carbon dioxide.• Through a combination of different techniques – Pathway and kinetics of LBCreaction with CO2 was established•Thermodynamic phase boundary for carbonate formation in the LBC-CO2 system wasestablished and extended to actual SOFC operation condition.Rapid Test System Development:• Rapid testing of the multiple electrodes was successfully demonstrated•Test protocols developed for fabrication and testing of multiple miniature electrodes 23
  25. 25. Acknowledgment• Professors, Research associates & grad students of FCRC• Polymer Characterization Lab (PCL), Chemical Engineering Department Queen’s University• Dr Thangadurai University of Calgary• X-Ray Lab , Dept. of Geological Sciences and Geological Engineering, Queen’s University 24

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