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Fuel Cell

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Fuel Cell

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  1. Fuel Cell • Introduction • Historical Notes • Types of Fuel Cells • Fuel Cell Electrochemistry • Advantages of Fuel Cells • Applications of Fuel Cells • Advanced Hydrogen Production Technologies • Advanced Hydrogen Transport and Storage Technologies

  2. 5-1 IntroductionWhat is a Fuel Cell • A fuel cell → an electrochemical device that combines hydrogen and oxygen to produce electricity, with water and heat as its by-product. 

  3. 5-2 Historical NotesFinally Coming of Age • In 1839, Sir William Grove reasoned that it should be possible to react hydrogen with oxygen to generate electricity. • In 1889, fuel cell was coined by Ludwig Mond and Charles Langer, who attempted to build the first practical device using air and coal gas.

  4. 5-2 Historical Notes Finally Coming of Age • In early 20th Century, fuel cells were forgot • A lack of understanding of materials and electrode kinetics. • Internal combustion engine was developed. • Petroleum was discovered and rapidly exploited.

  5. 5-2 Historical NotesFinally of Coming Age • In 1932, the first successful fuel cell device was built by engineer Francis Bacon. • He improved on the expensive platinum catalysts employed by Mond and Langer with a hydrogen-oxygen cell using a less corrosive alkaline electrolyte and inexpensive nickel electrodes.

  6. 5-2 Historical NotesFinally of Coming Age • Until 1959, Bacon and his coworkers were able to demonstrate a practical five-kilowatt system capable of powering a welding machine. • In October of that same year, Harry Karl Ihrig of Allis-Chalmers Manufacturing Company demonstrated his famous 20-horsepower fuel cell-powered tractor.

  7. 5-2 Historical NotesFinally of Coming Age • In the late of 1950s, fuel cells were noticed • NASA began to search some electricity generator for space mission. • Nuclear reactors as too risky, batteries as too heavy and short live, and solar power as cumbersome, NASA turned to fuel cells.

  8. 5-2 Historical NotesFinally of Coming Age • In 1960s, fuel cells would be the panacea to the world energy problem. The some qualities that make fuel cells idea for space exploration were considered. (ex. Small size, high efficiency, low emission.) • Nearly 30 years US$1 billion in research have been devote to address the barriers to the use of fuel cells for stationary application.

  9. 5-2 Historical NotesFinally of Coming Age • Fortunately • A number of manufacturers have supported numerous demonstration initiatives and ongoing research and development into stationary application. • Phosphoric acid fuel cells is being offered commercially, and more advanced designs, such as carbonate fuel cells and solid oxide fuel cells, are the focus of major electric technologies. • Full-sized (commercial) cells and full-height stacks have been successfully demonstrated for the carbonate fuel cell design.

  10. 5-2 Historical NotesFinally of Coming Age • It has taken more than 150 years to develop the basic science and to realize the necessary materials improvement for fuel cells to become a commercial reality. The fuel cell is finally coming of age!!

  11. 5-2 Historical NotesFinally of Coming Age

  12. 5-2 Historical NotesFinally of Coming Age

  13. 5-3 Types of Fuel CellsOverview of Fuel Cells • Fuel Cells generate electricity through an electrochemical process in which the energy stored in a fuel is converted directly into DC electricity. • Electrical energy is generated without combusting fuel, so fuel cells are extremely attractive from an environmental stand point.

  14. 5-3 Types of Fuel CellsOverview of Fuel Cells • Attractive fuel cell characteristic • High energy conversion efficiency • Modular design • Very low chemical and acoustical pollution • Fuel flexible • Cogeneration capability • Rapid load response

  15. 5-3 Types of Fuel CellsOverview of Fuel Cells • Basic operating principle of fuel cells • An input fuel is catalytically reacted in fuel cell to create an electric current. • The input fuel passed over the anode where it catalytically splits into ions and electrons. • The electrons go through an external circuit to serve an electric load while the ions move through the electrolyte toward the oppositely charge electrode. • At electrode, ions combine to create by-products, primarily water and CO2.

  16. 5-3 Types of Fuel CellsOverview of Fuel Cells • The figure of basic operating principle

  17. 5-3 Types of Fuel CellsOverview of Fuel Cells • Fuel Cell Characteristics

  18. 5-3 Types of Fuel CellsOverview of Fuel Cells

  19. 5-3 Types of Fuel CellsOverview of Fuel Cells • Four primary types of fuel cells which are based on electrolyte employed • Phosphoric Acid Fuel Cell • Molten Carbonate Fuel Cell • Solid Oxide Fuel Cell • Proton Exchange Membrane Fuel Cell

  20. 5-3 Types of Fuel CellsOverview of Fuel Cells • A comparison of the fuel cell types

  21. 5-3 Types of Fuel CellsOverview of Fuel Cells • Fuel cells are typical grouped three section

  22. 5-3 Types of Fuel CellsPhosphoric Acid Fuel Cells • The most mature fuel cell technology • Among low temperature fuel cell, it was showed relative tolerance for reformed hydrocarbon fuels. • It could have widespread applicability in the near term.

  23. 5-3 Types of Fuel CellsPAFC Design an Operation • The sketch of PAFC operation

  24. 5-3 Types of Fuel CellsPAFC Design an Operation • The components of PAFC • Electrolyte : liquid of acid • Electrolyte carriers : Teflon bonded silicone carbide matrix (pore structure→capillary action to keep liquid electrolyte in place) • Anode : platinum catalyzed, porous carbon • Cathode : platinum catalyzed, porous carbon • Bipolar plate : complex carbon plate

  25. 5-3 Types of Fuel CellsPAFC Design an Operation • The most designs of PAFC • The plates are “bi-polar” in that they have grooves on both side – one side supplies fuel to anode of one cell, and the other side supplies air or oxygen to the cathode of the adjacent cell.

  26. 5-3 Types of Fuel CellsPAFC Design an Operation • The PAFC reactions Anode : H2 → 2H+ + 2e- Cathode : ½ O2 + 2H+ +2e- → H2O

  27. 5-3 Types of Fuel CellsPAFC Design an Operation • The characteristics of PAFC operation • Some acid may be entrained in fuel or oxidant streams and addition of acid may be after many hours of operation. • The water removed as steam on the cathode by flowing excess oxidant past the back of electrodes.

  28. 5-3 Types of Fuel CellsPAFC Design an Operation • The temperature effect to PAFC The product water removal procedure required that the system operated at temperature around 375°F (~190°C). • At lower temperature : the water will dissolve in the electrolyte and not be removed as steam. • At high temperature (approximately 410°F~ (~210°C) : the phosphoric acid begins to decompose.

  29. 5-3 Types of Fuel CellsPAFC Design an Operation • How does excess heat be removed • Proved carbon plates containing cooling channels. • Air or liquid coolant, can be passed through these channels to remove heat.

  30. 5-3 Types of Fuel CellsPAFC Design an Operation • PAFC performance characteristics • Power density : 160 to 175 watts/ft2 • Thermal energy supplied at : ~ 150°F (only a portion at 250°F to 300°F) • Efficiency : • With pressurized reactants : 36% to 42% (HHV) • Supply usable thermal energy : 31% to 37% (HHV)

  31. 5-3 Types of Fuel CellsProton Exchange Membrane Fuel Cells (PEMFC) • The introduction of PEMFC • PEMFC has higher power density than any other fuel cell system. • PEMFC has comparable performance with the advanced aerospace AFC. • PEMFC can operate on reformed hydrocarbon fuels. • PEMFC uses a solid polymer electrolyte eliminates the corrosion.

  32. 5-3 Types of Fuel CellsProton Exchange Membrane Fuel Cells • The introduction of PEMFC 5. Its low operating temperature (70-85 oC): a. provides instant start up: 50 % maximum power immediately at room T & full operating power within 3 min. b. require no thermal shielding to protect personnel. 6.Advances in performance and designs offer the possibility of lower cost.

  33. 5-3 Types of Fuel CellsPEMFC Designs and Operation • The sketch of PEMFC operation

  34. 5-3 Types of Fuel CellsPEMFC Designs and Operation • The sketch of PEMFC operation

  35. 5-3 Types of Fuel CellsPEMFC Designs and Operation • The components of PEMFC • Electrolyte : polymer membrane. • Anode : thin sheet of porous, graphitized paper. (water-proofed with PTFE or Teflon, with one surface being applied with a small amount of Pt-black) • Cathode : (the same as above). • Bipolar plate : graphite.

  36. 5-3 Types of Fuel CellsPEMFC Designs and Operation • The features of the electrolyte • Electronic insulator, but an excellent conductor of hydrogen ions. • The acid molecules are fixed to the polymer, but the protons on these acid groups are free to migrate through the membrane. • Solid polymer electrolyte→electrolyte loss is not an issue with regard to stack life. • Be handled easily and safely.

  37. 5-3 Types of Fuel CellsPEMFC Designs and Operation • The heart of PEMFC The electrolyte is sandwiched between the anode and cathode, and the three components are sealed together under heat and pressure to product a single “membrane/electrode assembly” (MEA, < 1mm thick).

  38. 5-3 Types of Fuel CellsPEMFC Designs and Operation • The features of the bipolar plates • The bipolar plates are called “flow field plates”. • They make electrical contact with the back of the electrodes and conduct the current to the external circle. • They supply fuel to the anode and oxidant to the cathode.

  39. 5-3 Types of Fuel CellsPEMFC Designs and Operation • Useable fuel for PEMFC • Pure hydrogen • Reformed Hydrocarbon fuels: • Without removal or recirculation of by-product CO2. • The traces of CO produced during the reforming process must be converted to CO2(a simple catalytic process).

  40. 5-3 Types of Fuel Cells PEMFC Designs and Operation • The PEMFC reactions Anode : H2 → 2H+ + 2e- Cathode : O2 → 4H+ + 4e- → 2H2O

  41. 5-3 Types of Fuel CellsPEMFC Designs and Operation • The characteristics of PEMFC operation • The electrode reactions are analogous to those in PAFC. • The PEMFC operates at about 175°F (80℃). • The water is produced as liquid water and is carried out the fuel cell by excess oxidant flow. • Fully operating power is available within about 3 minute under normal condition.

  42. 5-3 Types of Fuel CellsPEMFC Designs and Operation

  43. 5-3 Types of Fuel CellsPEMFC Designs and Operation • The performance of PEMFC recently • At 0.7V/cell on hydrogen and oxygen, 65psia : 850A/ft2 (~0.91 A/cm2) • At 0.7V/cell on hydrogen and air, 65psia : 500A/ft2 (~0.54 A/cm2)

  44. 5-3 Types of Fuel CellsPEMFC Designs and Operation • The performance of Ballard/Dow PEMFC At 0.7V/cell: • At 65psia, hydrogen/oxygen : 2000A/ft2 • At 65psia, hydrogen/air : 1000A/ft2 At 0.5V/cell, : • At 65psia, hydrogen/oxygen : 4000A/ft2 ↓ 2000 W/ft2

  45. 5-3 Types of Fuel CellsPEMFC Designs and Operation • The power density of PEMFC • a factor of 10 greater than other FC systems → a significant reduction in stack size and cost. • In 5kW production fuel cell stacks, 0.7V at 650 A/ft2 on hydrogen/air at 45psi, stack dimensions 9.8 * 9.8 * 16.7 in: stack-only power density of over 5.4 kW/ft3 • 1.25 kW/ft3 on hydrogen/air at 45psi, if including fuel/oxidant controls, cooling, product water removal • Approaching 14.2 kW/ft3 are certainly feasible.

  46. 5-3 Types of Fuel CellsPEMFC Designs and Operation • When HC/air are to be used, higher T FC, the MCFC, SOFC, and to some extent, PAFC, have an efficiency advantage over PEMFC. ↑ waste heat can be used to drive air compressors, reforming of HC fuels, electric generation or other thermal load

  47. 5-3 Types of Fuel CellsPEMFC Designs and Operation • Using either air or liquid cooling ↓ a compact power generator and the excess heat of PEMFC is to be used for • space heating or residential hot water • utility cogeneration applications

  48. 5-3 Types of Fuel CellsPEMFC Designs and Operation • The pressure effects to all fuel cells • Performance is improve by pressuring the air. • Find an balance about the energy and financial cost associated with compressing air and the improved performance. • Rule of thumb: < 45 psia • ∵PEMFC uses a solid electrolyte ∴ a significant pressure differential can be maintained across the electrolyte→low P fuel & higher P air

  49. 5-3 Types of Fuel CellsPEMFC Designs and Operation • A very significant cost penalty of PEMFC as compared with PAFC • The PEMFC uses platinum at both the anode and cathode. • presently, 0.001 oz/in2 ~0.6 oz/kW for H2/air • Los Alamos National Lab & Texas A &M Univ., 0.00007 oz/in2 ~0.042 oz/kW for H2/air or ~0.021 oz/kW for H2/ O2 • Be expected to reduce platinum requirement to 0.035 oz/kW (1 g/kW) or about $2/kW.

  50. 5-3 Types of Fuel Cells Molten Carbonate Fuel Cells • The goals of developing MCFC • In 1960’s: operating directly on coal→ but that seems less likely today. • Operation on coal-derived fuel gases or natural gas is viable.