Iowa State University Capstones, Theses and Graduate Theses and Dissertations Dissertations 2009 Modeling of Solid Oxide Fuel Cell functionally graded electrodes and a feasibility study of fabrication techniques for functionally graded electrodes Reuben Flesner Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/etd Part of the Mechanical Engineering Commons Recommended Citation Flesner, Reuben, "Modeling of Solid Oxide Fuel Cell functionally graded electrodes and a feasibility study of fabrication techniques for functionally graded electrodes" (2009). Graduate Theses and Dissertations. 11063. https://lib.dr.iastate.edu/etd/11063 This Thesis is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Graduate Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. i Modeling of Solid Oxide Fuel Cell functionally graded electrodes and a feasibility study of fabrication techniques for functionally graded electrodes by Reuben Richard Flesner A thesis submitted to the graduate faculty in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Major: Mechanical Engineering Program of Study Committee: Gap-Yong Kim, Major Professor Steve W. Martin Sriram Sundararajan Iowa State University Ames, Iowa 2009 Copyright © Reuben Richard Flesner, 2009. All rights reserved. ii TABLE OF CONTENTS LIST OF FIGURES .............................................................................................................v LIST OF TABLES ........................................................................................................... viii ACKNOWLEDGEMENTS ............................................................................................... ix ABSTRACT .........................................................................................................................x CHAPTER 1. INTRODUCTION ........................................................................................1 1.1 Motivation ..................................................................................................................1 1.2 Research Framework .................................................................................................3 1.2.1 Feasibility Study of Fabrication Techniques for Functionally Graded SOFC Electrodes .....................................................................................................................3 1.2.2 Modeling of Graded SOFC Electrodes ...............................................................4 1.3 Research Objectives ...................................................................................................4 1.4 Thesis Organization ...................................................................................................5 CHAPTER 2. OVERVIEW OF SOLID OXIDE FUELS CELLS ......................................6 2.1 Theory ........................................................................................................................6 2.2 Efficiencies and Polarizations ....................................................................................8 2.3 SOFC Configurations ..............................................................................................10 2.4 Graded Electrodes ....................................................................................................12 2.5 Practical Considerations ..........................................................................................12 2.5.1 Factors that Influence Conductivity ..................................................................13 2.5.2 Summary of SOFC Component Primary Properties .........................................13 CHAPTER 3. FEASABILITY STUDY OF SOFC FABRICATION TECHNIQUES .....14 3.1 Wet Ceramic Fabrication Techniques ......................................................................15 3.1.1 Tape Casting .....................................................................................................16 3.1.2 Screen Printing ..................................................................................................17 3.1.3 Spin Coating ......................................................................................................18 3.1.4 Dip Coating .......................................................................................................19 3.1.5 Extrusion Casting ..............................................................................................19 3.1.6 Tape Calendaring ..............................................................................................20 3.2 Spray Fabrication Techniques .................................................................................21 3.2.1 Plasma Spraying ................................................................................................21 3.2.2 Electrostatic Spray Deposition ..........................................................................22 3.2.3 Ultrasonic Mist Spray Pyrolysis .......................................................................24 iii 3.2.4 Vapor Deposition Techniques ...........................................................................25 3.3 Comparison of Techniques for Graded Electrode Structure Fabrication ................26 CHAPTER 4. MODELING OF SOFC ..............................................................................29 4.1 Model Review ..........................................................................................................30 4.1.1 Macro Model Review .......................................................................................30 4.1.2 Micro Model Review ........................................................................................31 4.1.3 Functionally Graded Electrode Model Review .................................................32 4.2 Developed Model .....................................................................................................33 4.2.1 Developed Macro Model ..................................................................................33 4.2.2 Developed Micro Model ...................................................................................37 4.3 Model Integration ....................................................................................................40 4.4 Complete SOFC Electrode Model with Functional Grading ...................................41 4.4.1 Model Assumptions and Limitations ................................................................41 4.4.2 Particle Size and Porosity Grading Profiles ......................................................42 4.5 Equation System Solver Flow ..................................................................................43 CHAPTER 5. MODELING RESULTS & DISCUSSION ................................................45 5.1 Model Validation with Literature ............................................................................45 5.2 Justification of Model Input Parameters ..................................................................47 5.3 Analysis of Homogeneous Electrodes .....................................................................48 5.4 Effect of Graded SOFC Electrodes on Power Output .............................................50 5.4.1 Effect of Linear Particle Size Grading ..............................................................51 5.4.2 Effect of Nonlinear Particle Size Grading ........................................................59 5.4.3 Particle Size Grading Design ............................................................................62 5.4.4 Effect of Porosity Grading ................................................................................66 5.5 Effect of Electronic/Ionic Conducting Particle Volume Fraction ...........................70 5.6 Effect of Super-Ionic Conducting Material .............................................................72 CHAPTER 6. CONCLUSIONS & SCIENTIFIC CONTRIBUTIONS ............................75 6.1 Conclusions ..............................................................................................................75 6.2 Scientific Contributions ...........................................................................................76 CHAPTER 7. RECOMMENDED FUTURE WORK .......................................................78 CHAPTER 8. REFERENCES ...........................................................................................79 APPENDIX A: HOMOGENEOUS ELECTRODE MODEL CODE ...............................83 APPENDIX B: PARTICLE SIZE GRADED ELECTRODE MODEL CODE ................90 iv APPENDIX C: POROSITY GRADED ELECTRODE MODEL CODE .........................96 v LIST OF FIGURES Figure 1. Electricity flow for 2007 from the Energy Information Administration [1]. ............ 1 Figure 2. Efficiency of power generation techniques verses scale [5]. .................................... 2 Figure 3. Electrolyte-supported SOFC. .................................................................................... 6 Figure 4. Anode triple phase boundary site model. .................................................................. 7 Figure 5. Nernst potential verses temperature using Nernst equation from table values [6]. ... 8 Figure 6. Typical Polarization V-I Curve of SOFC [22]. ........................................................