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Making anodes for solid oxide fuel cells Dimuthu Dharshana Kodippili Arachchige

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Semester project under the module ENE401 Fuel Cell Technology-Autumn 2013, University of Agder, Grimstad, Norway

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Making anodes for solid oxide fuel cells Dimuthu Dharshana Kodippili Arachchige

  1. 1. MAKING ANODES FOR SOLID OXIDE FUEL CELLS USING TAPE CASTING METHOD Bernard Sisara Gunawardana Dimuthu Dharshana Arachchige Semester Project on ENE401 Fuel Cell Technology-Autumn 2013
  2. 2. Overview  Introduction  Methodology  Tape casting  Sintering  Results and discussion  Future works  Conclusion 2
  3. 3. Introduction 3 What is a SOFC..?  Solid Oxide Fuel Cell (SOFC) is an electrochemical conversion device that produces electricity directly from oxidizing a fuel at a higher temperature(6500C-10000C)  In a SOFC, the electrolyte is a solid ceramic material. The anode and cathode are made from special inks that coat the electrolyte. Unlike other types of fuel cells, no precious metals, corrosive acids, or molten materials are required  Application in stationary power, marine power or Aircraft APUs  If a SOFC operates continuously a long period then it has a long operating life, unless parts of the fuel cell would break down so often due to the higher temperature
  4. 4. 4 Introduction Cont….. How SOFC Operates..? Anode Reactions  Steam reforming CH4+ H2O = 3H2 +CO  CO2 reforming CH4 + CO2 = 2H2 +2CO Cathode Reactions In a typical SOFC, Efficiency is about 60% Operating temperature is about 1,000°C. Output is up to 100 kW CH4
  5. 5. Methodology 5 Formulation of slurry for anode a) Solvent as distilled water b) Solvent as propanol Ingredient Powder Binder Solvent Plasticizer Dispersant Total Ingredient Powder Binder Solvent Plasticizer Dispersant Total Description NiO-YSZ PVA 30% Distilled Water Glycerol Tween 80 Weight/(g) 5 3.5 2.2 1 0.4 12.1 Formulation of slurry for electrolyte Ingredient Powder Binder Solvent Plasticizer Dispersant Total Description YSZ PVA 30% Distilled Water Glycerol Tween 80 Weight/(g) 10.15 10 5.85 3.15 0.7 29.85 Description NiO-YSZ PVA 30% Propanol Glycerol Tween 80 Weight/(g) 5 3.5 1.4 1 0.4 11.3
  6. 6. Methodology Contd.. 6 Experimental mixing  Zirconia grinding medium in the form of balls were used to mill the slurry and disperse agglomerations.  Ball milling machine was used for proper mixing of the slurry with Zirconia balls Removing bubbles using a vacuum chamber a) Air bubbles in slurry foam b) Removing air bubbles by vacuum chamber  Having bubbles may cause to form defected and non uniform casted layers
  7. 7. Tape casting Tape casting steps 1) Tape caster is placed above the film carrier 2) Gap between film carrier and the casting plate is set to desired value 3) An amount of slurry is poured to the glass plate 4) Pipet edge is kept as close as to the film carrier in order to minimize the formation of air bubbles 5) Tape caster is pushed slowly and steadily along the guided width of the glass plate 7
  8. 8. Tape casting contd.. 8 Tape casted layers a) Nio-Ysz layer without vacuuming b) Ysz layers with vacuuming
  9. 9. 9 Sintering To check high temperature properties of the tape casted samples Powder beds 3x3 cm2 samples on the ceramic plates Colored ceramic plates; NiO casting Samples with powder beds  First few test runs, sintering was unsuccessful  Ceramic plates showed sign of reactivity towards NiO-YSZ samples  A thin flat powder bed of YSZ was laid between the sample and the support plates
  10. 10. Sintering cont.. 10 Carbolite Muffle Furnace (CMF) Carbolite Muffle Furnance Sintering programme in the CMF Removing additives in non-violent way under low temperature conditions, prevents any formation of cracks, rapid gas expansions, etc.
  11. 11. Results and discussion 11 Results on tape casting a) Unsuccessfully sintered Nio-Ysz samples b) Sintered YSZ layer at 14000C
  12. 12. 12 Results contd…… Microstructural observation a) Microstructure of NiO-YSZ layer before sintering observed through optical microscope b) Microstructural observation of sintered NiO-YSZ through SEM
  13. 13. Future works 13 Microstructural analysis and validation  Microstructural analysis using Atomic Force Microscope (AFM) will help to study the degree of dispersity, particle size, porosity and the tendency of agglomeration.  Possible to control the mechanical strength and conductivity of anode. Substrate tests to obtain desired V-I characteristic, thermal and redox stability  The samples are hydrogen thermal reduced in the test furnace in a temperature about 800 °C and voltage is measured against variable current. Optimizing slurry composition  Performance of different slurry compositions for better thermal stability and conductivity properties.  Conductivity as a function of volume of Ni  Foreign additives; Cu, Zn
  14. 14. Conclusion 14  It is required to modify, test and repeat the slurry samples in an iterative manner to obtain an optimized composition  Optimum Sintering Temperature (OST) has to be decided based on grain size, and boundaries Eg: OST is changed with the volume of % Ni : 1400 0C for 40% Ni  Adjustable tape casting device is a well designed apparatus for low cost tape casting ,allowing to control the thickness of anode and electrolyte down to a desired value.
  15. 15. 15 Thank You..!!