SOLID OXIDE FUEL CELLS

3,208 views

Published on

Published in: Education, Technology, Business
0 Comments
2 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
3,208
On SlideShare
0
From Embeds
0
Number of Embeds
9
Actions
Shares
0
Downloads
307
Comments
0
Likes
2
Embeds 0
No embeds

No notes for slide

SOLID OXIDE FUEL CELLS

  1. 1. An upgraded version of Batteries
  2. 2.  A fuel cell is an electrochemical energy conversion device that converts hydrogen and oxygen into electricity, heat, and water as a result of a chemical reaction.
  3. 3. 1. CATHODE- the positive electrode 2. ANODE- the negative electrode 3. ELECTROLYTE- in which the reactions take place 4. AN INTERCONNECT(in case of a stack)- for electron transfer 5. SEALS- To act as barrier between components
  4. 4.  Highly efficient electric power generation system (can be as high as 70-80%)  Effective utilization high temperature waste heat  Environmental friendly power generation
  5. 5.  A single fuel cell generates a tiny amount of direct current (DC) electricity. In practice, many fuel cells are usually assembled into a stack. Cell or stack, the principles are the same.
  6. 6.  Ionically conductive -oxygen ion transport  Chemically stable (at high temperatures as well as in reducing and oxidizing environments)  Gas tight/free of porosity  Uniformly thin layer (to minimize ohmic losses)
  7. 7. Most widely used electrolyte is Yttrium doped zirconium oxide (YSZ)  Advantages of YSZ i. ionic conductivity ii. chemical stability iii. mechanical strength  Disadvantages of YSZ i. low ionic conductivity
  8. 8.  Solution I. Decrease the thickness of the YSZ electrolyte II. Find other materials to replace the yttrium like Scandium-doped zirconium oxide has higher conductivity than YSZ but high cost of scandium is a disadvantage
  9. 9.  High electronic conductivity  Chemically compatible with neighboring cell component (usually the electrolyte)  Should be porous  Stable in an oxidizing environment  Large triple phase boundary  Catalyze the dissociation of oxygen  Adhesion to electrolyte surface
  10. 10. Lanthanum strontium manganite(LSM) is the cathode Advantages of LSM I. Compatibility with doped zirconia electrolytes II. Similar coefficient of expansion to YSZ and thus limits stresses
  11. 11.  Disadvantages of LSM I. LSM is a poor ionic conductor, and so the electrochemically active reaction is limited to the triple phase boundary (TPB) where the electrolyte, air and electrode meet. II. LSM works well as a cathode at high temperatures, but its performance quickly falls as the operating temperature is lowered below 800 °C.
  12. 12.  Electrically conductive  High electro-catalytic activity  Large triple phase boundary  Stable in a reducing environment  Can be made thin enough to avoid mass transfer losses, but thick enough to provide area and distribute current  Thermal expansion coefficient similar neighboring cell component  Chemically compatible with neighboring cell component  Fine particle size
  13. 13.  Ceramic anode layer must be very porous to allow the fuel to flow towards the electrolyte  The most common material used is a cermet made up of nickel mixed with the ceramic material that is used for the electrolyte  The anode is commonly the thickest and strongest layer  The anode’s job is to use the oxygen ions that diffuse through the electrolyte to oxidize the hydrogen fuel
  14. 14. ADDITIONAL USES:  Function of the anode is to act as a catalyst for steam reforming the fuel into hydrogen.  This provides another operational benefit to the fuel cell stack because the reforming reaction is endothermic, which cools the stack internally.
  15. 15.  Stable under high temperature oxidizing and reducing environments  Very high electrical conductivity  High density with “no open porosity”  Strong and high creep resistances for planar configurations  Good thermal conductivity  Phase stability under temperature range  Resistant to sulfur poisoning, oxidation and carburization  Low materials and fabrication cost
  16. 16.  The interconnect can be either a metallic or ceramic layer that sits between each individual cell.  It connects each cell in series, so that the electricity each cell generates can be combined.  a metallic 95Cr-5 Fe alloy is the most commonly used interconnect  Ceramic materials are also under considerations DRAWBACKS: these ceramic interconnect materials are very expensive as compared to metals.
  17. 17.  Electrically insulating  Thermal expansion compatibility with other cell components  Chemically and physically stable at high temperatures  Gastight  Chemically compatible with other components  Provide high mechanical bonding strength  Low cost
  18. 18.  PURPOSE produce an electrical current that can be directed outside the cell to do work  GENERAL WORKING OF FUEL CELLS 1. Hydrogen atoms enter a fuel cell at the anode 2. Hydrogen atoms are now ionized, and carry a positive electrical charge. 3. Negatively charged electrons provide the current through wires to do work.
  19. 19.  In some cells, Oxygen enters the fuel cell at the cathode and combines with the electrons and hydrogen.  In other cell types the oxygen picks up electrons and then combines with hydrogen  Electrolyte must permit only the appropriate ions to pass between the anode and cathode  Fuel cells create electricity chemically. Therefore, fuel cells are more efficient in extracting energy from a fuel
  20. 20.  Alkali fuel cells  Molten Carbonate fuel cells (MCFC)  Phosphoric Acid fuel cells (PAFC)  Proton Exchange Membrane (PEM) fuel cells  Solid Oxide fuel cells (SOFC)
  21. 21.  Fuel cells can continuously make electricity if they have a constant fuel supply.  SOFCs that operate at higher temperatures -- between about 1100 and 1800 degrees Fahrenheit  Can run on a wide variety of fuels, including natural gas, biogas, hydrogen and liquid fuels such as diesel and gasoline
  22. 22.  Each SOFC is made of ceramic materials, which form three layers: the anode, the cathode and the electrolyte  The big advantage to fuel cells is that they're more efficient than traditional power generation
  23. 23.  SOFC essentially consists of two porous electrodes separated by a dense, oxide ion conducting electrolyte.  Oxygen supplied at the cathode (air electrode) reacts with incoming electrons from the external circuit to form oxide ions  These ions migrate to the anode (fuel electrode) through the oxide ion conducting electrolyte.
  24. 24.  At the anode, oxide ions combine with hydrogen (and/or carbon monoxide) in the fuel to form water (and/or carbon dioxide), liberating electrons.  Electrons (electricity) flow from the anode through the external circuit to the cathode.
  25. 25. ADVANTAGES  high efficiency,  long-term stability,  fuel flexibility,  low emissions, and  relatively low cost. DISADVANTAGES  high operating temperature which results in longer start-up times and mechanical and chemical compatibility issues.
  26. 26.  SOFC are being targeted for use in power and heat generation for homes and businesses as well as auxiliary power units for electrical systems in vehicles.  SOFC also can be linked with a gas turbine, in which the hot, high pressure exhaust of the fuel cell can be used to spin the turbine, generating a second source of electricity.  Using planar SOFCs, stationary power generation systems of from 1-kW to 25-kW size have been fabricated and tested by several organizations
  27. 27.  Rolls-Royce Fuel Cell Systems Ltd is developing a SOFC gas turbine hybrid system fueled by natural gas for power generation applications on the order of a megawatt (e.g. Futuregen).  Ceres Power Ltd. has developed a low cost and low temperature (500–600 degrees) SOFC stack using cerium gadolinium oxide (CGO) in place of current industry standard ceramic, yttria stabilized zirconia (YSZ), which allows the use of stainless steel to support the ceramic.
  28. 28.  Solid Cell Inc. has developed a unique, low cost cell architecture that combines properties of planar and tubular designs, along with a Cr-free cermet interconnect.  The high temperature electrochemistry center (HITEC) at the University of Florida, Gainesville is focused on studying ionic transport, electro catalytic phenomena and micro structural characterization of ion conducting materials.  SiEnergy Systems, a Harvard spin-off company, has demonstrated the first macro-scale thin-film solid-oxide fuel cell that can operate at 500 degrees.
  29. 29.  Delphi Automotive Systems are developing an SOFC that will power auxiliary units in automobiles and tractor-trailers  Research is also going on in reducing start-up time to be able to implement SOFCs in mobile applications

×