Chapter 5 Fuel Cell

1
Chapter 5 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 US1 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 375F (190C).
• At lower temperature the water will dissolve in
  the electrolyte and not be removed as steam.
• At high temperature (approximately 410F
  (210C) 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 150F (only a
  portion at 250F to 300F)
• 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, lt 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 175F (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 lt 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 1960s operating directly on coal? but that
  seems less likely today.
• Operation on coal-derived fuel gases or natural
  gas is viable.

51
5-3 Types of Fuel Cells Molten Carbonate Fuel
Cells
52
5-3 Types of Fuel Cells Molten Carbonate Fuel
Cells
53
5-3 Types of Fuel Cells Molten Carbonate Fuel
Cells
54
5-3 Types of Fuel Cells Molten Carbonate Fuel
Cells
55
5-3 Types of Fuel Cells Molten Carbonate Fuel
Cells
56
5-3 Types of Fuel Cells Molten Carbonate Fuel
Cells
57
5-3 Types of Fuel Cells Molten Carbonate Fuel
Cells
58
5-3 Types of Fuel Cells Molten Carbonate Fuel
Cells
59
5-3 Types of Fuel Cells Molten Carbonate Fuel
Cells
60
5-3 Types of Fuel Cells Molten Carbonate Fuel
Cells
61
5-3 Types of Fuel CellsMCFC Design and Operation

• The sketch of MCFC operation

62
5-3 Types of Fuel CellsMCFC Design and Operation

• The components of MCFC
• Electrolyte a molten carbonate salt mixture,
  usually consists of lithium carbonate and
  potassium carbonate.
• Electrolyte carriers a porous, insulating and
  chemically inert ceramic (LiAlO2) matrix.
• Anode a highly porous sintered nickel powder,
  alloyed with chromium to prevent agglomeration
  and creep at operating T.
• Cathode a porous nickel oxide material doped
  with lithium.

63
5-3 Types of Fuel CellsMCFC Design and Operation

• The MCFC reactions
• Anode H2 CO3-2 ? H2O CO2 2e-
• CO CO3-2 ? 2CO2 2e-
• Cathode O2 2CO2 4e- ? 2CO3-2
• ?
• require a system for collecting CO2 from the
  anode exhaust and mixing it with the cathode feed
  stream

64
5-3 Types of Fuel CellsMCFC Design and Operation

• The MCFC reactions
• before CO2 is collected, any residual H2 in the
  spent fuel stream must be burned.
• Future systems may incorporate membrane
  separators to remove H2 for recirculation back
  to the fuel stream.

65
5-3 Types of Fuel CellsMCFC Design and Operation

• MCFC v.s. PAFC
• operating T ?, the theoretical operating voltage
  and the maximum theoretical fuel efficiency for a
  MCFC ?.
• On the other hand, operating T ?, the rate of
  electro-chemical and thus current at a given
  voltage ?.
• ?(net
  effect)
• The operating voltage of the MCFC is higher than
  the PAFC at the same current density. (higher
  fuel efficiency)
• As size and cost scale roughly with electrode
  area, a MCFC should be smaller and less expansive
  than a comparable PAFC.

66
5-3 Types of Fuel CellsMCFC Design and Operation

• The high operating T characteristics of MCFC
• Operating at between 1110F(600?) and
  1200F(650?) ?necessary to achieve sufficient
  conductivity of the electrolyte
• To maintain this operating T, a higher volume of
  air is passed through the cathode for cooling
  purposes.
• In combined cycle operation, electrical
  efficiencies are in excess of 60(HHV). The T of
  excess heat is high enough to yield high P
  steam?turbine
• At the high operating T, MCFC could operate
  directly on the gaseous HC fuels such as natural
  gas ?would be reformed to produce H2 within the
  fuel cell itself.

67
5-3 Types of Fuel CellsMCFC Design and Operation

• The high operating T characteristics of MCFC
• 4. At high operating temperature(1200 F/650
  C), noble metal catalysts are not required.
• 5. At high operating temperature(1200F), the
  salt mixture is liquid and is a good ionic
  conductor.
• 6. The cell performance is sensitive to
  operating temperature.
• A change in cell T from 1200F to 1110F results
  in a drop in voltage 15. (?ionic and electric
  resistance? electrode kinetics?

68
5-3 Types of Fuel CellsMCFC Design and Operation

• The high operating T characteristics of MCFC
• The electrolyte boil-off has an insignificant
  impact on cell stack life.
• A more significant factor of life expectancy has
  to do with corrosion of the cathode.

69
5-3 Types of Fuel CellsSolid Oxide fuel cells

• The introductions of the SOFC
• uses a ceramic, solid-phase electrolyte which
  reduces corrosion considerations and eliminates
  the electrolyte management problems associated
  with the liquid electrolyte fuel cells.
• To achieve adequate ionic conductivity in such a
  ceramic?must operate at about 1830 F (1000 C).
• At that T, internal reforming of carbonaceous
  fuels should be possible, and the waste heat
  would be easily utilized by conventional thermal
  electricity generating plants to yield excellent
  fuel efficiency.

70
5-3 Types of Fuel CellsSOFC Design and Operation

• The sketch of SOFC operation

71
5-3 Types of Fuel CellsSOFC Design and Operation

• The SOFC reactions
• Anode H2 O-2 ? H2O 2e-
• CO O-2 ? CO2 2e-
• CH4 4O-2 ? 2H2O CO2 8e-
• Cathode O2 4e- ? 2O-2
• It is significant that the SOFC can use CO as its
  direct fuel.

72
5-3 Types of Fuel CellsSOFC Design and Operation

• The components of the SOFC
• Electrolyte solid ceramic.
• Materials dense yttria(???)-stabilized
  zirconia(???)an excellent conductor of
  negatively charged oxygen (oxide) at high T.
• Anode a porous nickel/zirconia cermet
• Cathode Sr-doped (?, strontium) lanthanum(?)
  manganite(???)

73
5-3 Types of Fuel CellsSOFC Design and Operation

• The components of the SOFC
• SOFC is a solid state device and shares certain
  properties and fabrication techniques with
  semi-conductor devices.
• The Westinghouse cell design the FC around a
  porous Zirconia support tube through which air is
  supplied to the cathode which is deposited on the
  outside of the tube. A layer of electrolyte is
  then deposited on the outside of the cathode and
  finally a layer of anode is deposited over the
  electrolyte.
• A number of cells are connected together by high
  T semiconductor contacts.

74
5-3 Types of Fuel CellsSOFC Design and Operation
75
5-3 Types of Fuel CellsSOFC Design and Operation
76
5-3 Types of Fuel CellsSOFC Design and Operation

• The components of the SOFC
• The anode consists of metallic Ni and
  Y2O3-stablized ZrO2 skeleton, which serves to
  inhibit sintering of the metal particles and to
  provide a thermal expansion coefficient
  comparable to those of the other fuel materials.
• The most common cathode material (a p-type
  conductor) Sr-doped (?, strontium) lanthanum
  manganite (Lal-xSrxMnO3, x0.10-0.15
• Both anode and cathode structures are fabricated
  with a porosity of 20-40 to facilitate mass
  transport of reactant and product gases.

77
5-3 Types of Fuel CellsSOFC Design and Operation

• SOFC performance characteristics
• 0.6V/cell at about 232 A/ft2
• Lifetimes are over 30000(hrs).
• The efficiencies of unpressurized SOFCs 45
  (HHV)
• The efficiencies of pressurized SOFCs 60
  (HHV)
• Bottoming cycle, using the high T waste heat,
  could add another few to the fuel efficiency.

78
5-3 Types of Fuel CellsSOFC Design and Operation

• temperature management
• maintain proper volume of the air stream
  into the cell.

79
5-3 Types of Fuel CellsSOFC Design and Operation

• high operating T characteristics of SOFCs
• The SOFC operates at approximately 1830F
  (1000C).
• The high operating temperature offers the
  possibility of internal reforming.
• As in MCFCs, CO does not act as a poison and can
  be used directly as a fuel.
• The SOFC can tolerant several orders of magnitude
  more sulfur than other fuel cells.
• The SOFC requires a significant start-up time.

80
5-3 Types of Fuel CellsSOFC Design and Operation

• high operating T characteristics of SOFCs
• 6. The cell performance is very sensitive to
  operating T.
• A 10 drop in T ? 12 drop in cell performance
  due to the increase in internal resistance to the
  flow of oxygen ions.
• 7. The high T also demands that the system
  include significant thermal shielding to protect
  personnel and to retain heat. ?not for
  transportation applications.

81
5-4 Fuel Cell ElectrochemistryInternal Reforming

• In a conventional fuel cell system, a
  carbonaceous fuel is fed to a fuel processor
  where it is steam reformed to produce H2 (as well
  as CO CO2).
• Ni reforming catalyst is extremely sensitive to
  sulfur in the feed gas.

82
5-4 Fuel Cell ElectrochemistryInternal Reforming

• Internal reforming in MCFC SOFC at high T?
  eliminate external fuel reformers ?highly
  efficient, simple, reliable and cost effective
• 2 alternative approaches to internal reforming
• Indirect Internal reforming (IIR)
• Direct Internal reforming (DIR)
• Methane and steam reforming reaction
• (750-900 oC)
• CH4 H2O ? CO 3H2 (endothermic, ?H53.87
  kcal/mol, favored by high T low P, Plt 5 atm)

83
5-4 Fuel Cell ElectrochemistryInternal Reforming

• IIR reformer section is separated, but adjacent
  to the anode.
• Advantage 1.the exthermic heat of the cell can
  be used for
• the endothermic
  reforming reaction
• 2. reformer cell
  environments dont
• have a direct physical
  effect on each
• other
• Disadvantage the conversion of methane to
  hydrogen is not promoted as well as in the DIR.
  

84
5-4 Fuel Cell ElectrochemistryInternal Reforming

• DIR hydrogen consumption reduces its partial
  pressure?driving the methane reforming reaction
  to the right.
• For MCFC, one developers approach where IIR
  DIR have been combined.

85
5-4 Fuel Cell ElectrochemistryInternal Reforming

• A supported Ni catalyst (e.g. Ni supported on MgO
  or LiAlO2) provides sufficient catalytic activity
  to sustain the steam reforming reaction at 650 oC
  to produce sufficient H2 .
• At open circuit, about 83 CH4 ?H2 (equilibrium
  concentration at 650 oC )
• When current is drawn from the cell, H2 is
  consumed and H2Ois produced ? CH4 conversion ?
  and approaches 100 at H2 utilization gt 50
• ?
• Thermal management and adjustment of H2
  utilization is important to the internal
  reforming of MCFC stacks

86
5-4 Fuel Cell ElectrochemistryInternal Reforming

• Currently, the concept of internal reforming has
  been successfully demonstrated for 10,000 hrs. in
  2-3 kW stacks and for 250 hrs in a 100 kW stack.

87
5-4 Fuel Cell ElectrochemistryMCFC

• The electrochemical reactions occurring in MCFCs
• Anode H2 CO3-2 ? H2O CO2 2e-
• Cathode ½ O2 CO2 2e- ? CO3-2
• Overall H2 ½ O2 CO2 (cathode) ? H2O CO2
  (anode)
• The reversible potential equation
• E E RT/2F ln(PH2P1/2O2/PH2O)
• RT/2F ln(PCO2,c/PCO2,a) F96500
  Columb/mol.

88
5-4 Fuel Cell ElectrochemistryMCFC

• The electrochemical reactions occurring in MCFCs
• Transfer CO2 from anode exit gas to the cathode
  inlet gas (CO2 transfer device)
• Produce CO2 by combustion of the anode exhaust
  gas which is mixed with the cathode inlet gas
• Supply CO2 from an alternate source.

89
5-4 Fuel Cell ElectrochemistrySOFC

• The electrochemical reactions occurring in SOFCs
  (1000 oC)
• Anode H2 O-2 ? H2O 2e-
• Cathode ½ O2 2e- ? O-2
• Overall H2 ½ O2 ? H2O
• The corresponding Nernst equation
• E E RT/2F ln(PH2PO21/2 /PH2O)

90
5-5Advantages of Fuel Cells Environmental
Acceptability

• Because fuel cells are so efficient, CO2
  emissions are reduced for a given power output.
• By 2000, FC power plants will decrease CO2
  emissions by 0.6 MMT of carbon equivalent.
• FC is quiet, emitting only 60 dBs at 100 ft.
• Emissions of SOx and NOx are 0.003 and 0.0004
  pounds/megawatt-hour.

91
5-5Advantages of Fuel Cells Efficiency

• Dependent on type and design, the fuel cells
  direct electric energy efficiency ranges form 40
  to 60 percent (LHV).
• Characteristics
• Operates at near constant efficiency, independent
  of size and load.
• Efficiency is not limited by the Carnot Cycle.
• For the fuel cells/gas turbine system, the
  efficiency achieves 70 percent (LHV).
• When by-product heat is utilized, the total
  efficiency of the fuel cell systems approach 85
  percent.

92
5-5Advantages of Fuel Cells Distributed Capacity

• Distributed generation reduces the capital
  investment and improves the overall conversion
  efficiency of fuel to end use electricity by
  reducing transmission losses.
• Losses presently 8-10 of the generated
  electrical power is lost between the generating
  station and the end user.
• Many smaller units are statistically reliable,
  avoid failing at one time as in the case of one
  large generator.

93
5-5Advantages of Fuel Cells Permitting

• Permitting and licensing schedules are short due
  to the ease in siting.

94
5-5Advantages of Fuel CellsModularity

• The fuel cell is inherently modular.
• Be configured in wide range of electrical
  outputs, ranging from a nominal 0.025 to greater
  than 50-megawatt (MW) for a natural gas fuel cell
  to greater than 100-MW for the coal gas fuel cell.

95
5-5Advantages of Fuel Cells Fuel Flexibility

• The primary fuel source for the fuel cell is
  hydrogen, which can be obtained from
• Natural gas
• Coal gas
• Methanol
• Landfill gas
• Other fuels containing hydrocarbons.
• Advantage of fuel flexibility
• The power generation can be assured even when a
  primary fuel source unavailable.

96
5-5Advantages of Fuel CellsCogeneration
Capability

• High-quality heat is available for cogeneration,
  heating, and cooling.
• Fuel cell exhaust heat is suitable for use in
  residential, commercial, and industrial
  cogeneration applications.

97
5-6Applications of Fuel CellsIntroduction

• In theory, a fuel cell can power anything that
  runs on electricity. The following applications
  can take particular advantage of a fuel cell's
  attributes.

98
5-6Applications of Fuel CellsCars, Trucks, and
Buses

• Most vehicles today rely on an internal
  combustion engine (ICE).
• Electric motors are much more suitable
• They deliver their maximum torque at low rpm,
  just when a vehicle needs it most.
• A driver heads downhill or puts on the brakes, an
  electric motor can double as a generator to
  recapture that energy and covert it back to
  electricity for subsequent use.

99
5-6Applications of Fuel CellsCars, Trucks, and
Buses

• The choke point of electric motor
• The short range and tedious recharging of the 1st
  generation
• A fuel cell powers the vehicle's electric motor
• These problems can be overcome. A hydrogen tank
  can be refueled in about five minutes.
• It has a similar range to a conventional
  automobile.

100
5-6Applications of Fuel CellsBusinesses and
Homes

• The reasons of fuel cells are attractive in
  stationary applications
• They deliver unparalleled fuel efficiencies,
  especially in Combined Heat Power (CHP)
  applications.
• Fuel cells offer a new level of reliability
• If a blackout occurs, they will keep essential
  mechanical components and external landmark
  signage online.
• Fuel cells offer highly reliable, high-quality
  electricity.

101
5-6Applications of Fuel CellsLaptops, Cell
Phones, and other Electronics

• Fuel cells will find their first widespread use
  in portable electronics
• These "micro fuel cells" offer far higher energy
  densities than those of comparably sized
  batteries. The typical laptop can operate
  unplugged for ten hours or more.
• Micro fuel cells also offer the added appeal of
  eliminating the need for battery chargers and AC
  adapters, as they require refueling instead of
  recharging.

102
5-7 Advanced Hydrogen Production Technologies

• Introduction
• Hydrogen is a clean, sustainable resource with
  many potential applications.
• Hydrogen is now produced primary by steam
  reforming of natural gas.
• For applications requiring extremely pure
  H2?electrolysis, a relatively expensive process
• Three process of producing hydrogen
  photobiological, photoelectrochemical,
  thermochemical.

103
5-7 Advanced Hydrogen Production Technologies

• Introduction
• Photobiological photoelectrochemical
  processes uses sunlight to split water into H2
  and O2
• Thermochemical processes, including gasification
  and pyrolysis systems, use heat to produce H2
  from sources such as biomass and solid waste.

104
5-7 Advanced Hydrogen Production Technologies

• PHOTOBIOLOGICAL PRODUCTION
• Most photobiological system use the natural
  activity of bacteria and green algae to produce
  hydrogen. (chlorophyll absorbs sunlight and
  enzymes use energy to dissociate H2 from H2O)
• Two significant limitations
• Low solar convertion efficiencies.(56 of suns
  energy to H2 energy)
• Nearly all enzymes are inhibited in their
  hydrogen production by presence of oxygen.

105
5-7 Advanced Hydrogen Production Technologies

• PHOTOBIOLOGICAL PRODUCTION
• 3. The way to overcome oxygen intolerance and
  increase conversion efficiencies
• A new green algae strains the Chlamydomonas
  (???) strain ? has H2-evolving enzymes more
  tolerant of O2 extracted from strains of bacteria
  ? produce H2 and O2 simultaneously. 10
  efficiency
• Cell-free processes theoretical efficiency
  approach 25

106
5-7 Advanced Hydrogen Production Technologies

• PHOTOBIOLOGICAL PRODUCTION
• Cell-free processes
• c. In a cell-free system both O2-evolving
  H2-evolving enzymes are immobilized onto opposite
  sides of a solid, conducting surface.
• d. Light is used by one enzyme to oxidize
  water, creating a flow of electrons to the other
  enzymes, where H2 is produced.

107
5-7 Advanced Hydrogen Production Technologies

• PHOTOBIOLOGICAL PRODUCTION
• Genetic forms of Chlamydomonas
• 20 efficiency

108
5-7 Advanced Hydrogen Production Technologies

• PRODUTION BY PHOTOELECTRO-CHEMICAL (PEC)
  TECHNOLOGY
• PEC production uses semiconductor technology in
  one-step process of splitting water directly upon
  sunlight illumination.
• A PEC system
• a photovoltaic cell ? produce electric current
  when exposed to light
• Electrolyzer

109
5-7 Advanced Hydrogen Production Technologies
110
5-7 Advanced Hydrogen Production Technologies

• PRODUTION BY PHOTOELECTRO-CHEMICAL (PEC)
  TECHNOLOGY
• Advantage producing low-cost renewable
  hydrogen.
• The two limited factor of an efficient and
  cost-effective PEC system
• The high voltage required to dissociate water.
• The corrosiveness of aqueous electrolytes.

111
5-7 Advanced Hydrogen Production Technologies

• PRODUTION BY PHOTOELECTRO-CHEMICAL (PEC)
  TECHNOLOGY
• The way to overcome limits
• The structure ? the multijunction device gt 1.6 eV
• Material
• Gallium based (GalnP2, GaAs) ? provide higher
  voltages requires for electrolysis and have
  relatively high solar efficiency efficiency is
  more than 25 , but is expensive.
• Amorphous silicon ? efficiency is more than 13
  , but cost is low.

112
5-7 Advanced Hydrogen Production Technologies

• PRODUTION BY PHOTOELECTRO-CHEMICAL (PEC)
  TECHNOLOGY
• 4. The sketch of a multijunction device

113
5-7 Advanced Hydrogen Production Technologies

• THERMOCHEMICAL PRODUCTION
• Gasification and pyrolysis using heat to
  produce a vapor from which hydrogen can be
  derived use a conventional steam reforming
  process.
• Pyrolysis
• Biomasswood, grasses, and agricultural and
  municipal waste, is broken down into highly
  reactive vapors and carbonaceous residue, or
  char.
• The vapors, when condensed into pyrolysis oil,
  can be steam reformed to produce hydrogen.

114
5-7 Advanced Hydrogen Production Technologies

• THERMOCHEMICAL PRODUCTION
• A typical biomass feedstock produces 65 oils
  and 8 char by wt. with the remainder consisting
  of water and gas.
• The char is burn to provide the required heat for
  the pyrolysis reaction.
• A fast-pyrolysis reactor is directly linked to a
  steam reformer.(1217 hydrogen by weight of dry
  biomass)
• Advantage the lowest-cost production method,
  but it needs to identifying optimum reformer
  catalysts.

115
5-7 Advanced Hydrogen Production Technologies

• THERMOCHEMICAL PRODUCTION
• Gasification of municipal solid waste (MSW)
• It is low-cost, sustainable source of hydrogen
  production.
• MSW, on average, consists of about 70 by weight
  of biomass material.
• Gasification results in an easily cleaned fuel
  gas from which hydrogen can be reformed.

116
5-7 Advanced Hydrogen Production Technologies

• THERMOCHEMICAL PRODUCTION
• The Texacos high-temperature gasification
• Result in a high yield of hydrogen and produces a
  non-hazardous, glass-like ash byproduct.

117
5-8Advantages Hydrogen Transport and Storage
Technologies

• INTRODUCTION
• The future use of hydrogen will require the
  creation of a distribution infrastructure of safe
  and cost-effective transport and storage.
• Different applications need different types of
  storage technology
  Stationary storage utility
  electricity generation energy efficient and cost
  are important
  Mobile storage
  fueling a vehicle size and weight are important

118
5-8Advantages Hydrogen Transport and Storage
Technologies

• INTRODUCTION
• 3. Physical and solid-state storage systems that
  will meet these diverse future application
  demands.

119
5-8Advantages Hydrogen Transport and Storage
Technologies

• PHYSICAL STORAGE SYSTEM
• Physical states are commercially available and
  currently in use.
• Hydrogen is generally in form of compressed gas
  or cryogenic liquid, referred to as physical
  storage.
• Focusing on increasing the energy content per
  unit of volume or weight of hydrogen storage
  system.

120
5-8Advantages Hydrogen Transport and Storage
Technologies

• PHYSICAL STORAGE SYSTEM
• Hydrogen gas is currently stored at high
  pressures of 1417 MPa.
• New graphite composite material has potential for
  storing hydrogen at pressure up to 41 Mpa.
• These materials may make it possible for hydrogen
  gas to be a cost-effective fuel.

121
5-8Advantages Hydrogen Transport and Storage
Technologies

• One Possible Future Hydrogen Infrastructure
• Distributing H2 fuel in the form of compressed
  gas is a potential growth market for zero
  emission vehicles.
• Fleet refueling stations would supplied by truck
  with liquid H2 from existing plants.
• As demand increased, small dedicated pipeline
  systems would be built to provide gaseous H2 from
  new centralized reforming plants.
• A pipeline serving 80,000 fuel-cell cars
• Deliver hydrogen gas at about 13 per gigajoule,
  the energy equivalent of about 0.45 per liter of
  gasoline.

122
5-8Advantages Hydrogen Transport and Storage
Technologies

• SOLID-STATE STORAGE METHOD
• Solid-state transport and storage technologies
  are safer and have the potential to be more
  efficient than gas or liquid storage.
• Refers to chemical or physical binding of H2 to a
  solid material.
• Research stage?needs to improve the volumetric
  density or the gravimetric density.
• The most promising solid-state technologies are
  metal hydrides, gas-on-solids adsorption system,
  and glass microspheres.

123
5-8Advantages Hydrogen Transport and Storage
Technologies

• METAL HYDRIDESrelease H2 by dehydride
• Advantages high volumetric density, safety, and
  the ability to deliver pure hydrogen at constant
  pressure.
• Disadvantages low gravimetric density,
  expressed as hydrogen as a percent of total
  hydride weight (wt)
• They are suitable for stationary storage, but
  limited for use in vehicles.

124
5-8Advantages Hydrogen Transport and Storage
Technologies

• METAL HYDRIDES
• The work of future develop hydrides with higher
  gravimetric densities that can operate under
  temperatures and pressures consistent with mobile
  storage.
• The more promising hydride technologies
  improved metal alloys, high-efficiency metal
  hydrides, non-classical metal hydride complexes.

125
5-8Advantages Hydrogen Transport and Storage
Technologies

• Improved Metal Alloys
• Capacities 2.5 wt 6.2 wt depending on the
  composition.
• Thin film alloys of magnesium-aluminum-nickel-tita
  nium have exhibited improved gravimetric and
  volumetric energy densities.
• Efforts are being made to scale up production of
  these alloys.

126
5-8Advantages Hydrogen Transport and Storage
Technologies

• High-Efficient Metal Hydrides
• Metal hydrides that dehydride hydrogen at very
  high temperatures offer greater storage
  efficiency at less cost than lower temperature
  hydrides under development.
• They are suitable to use on stationary storage,
  but not available in mobile system.
• A phase change material can be used to retain
  hydriding energy as heat of fusion and then
  return the heat for the dehydriding process.

127
5-8Advantages Hydrogen Transport and Storage
Technologies

• High-Efficient Metal Hydrides
• 4. A Ni-coated Magnesium hydride material and the
  salt mixture can be placed in a shell-and-tube
  heat exchanger to perform this process.

128
5-8Advantages Hydrogen Transport and Storage
Technologies

• Nonclassical Metal Hydride Complexes
• Nonclassical polyhydride metal complexes (PMCs)
  may overcome the weight density problem of
  hydride storage system.
• Classical PMCs they have high gravimetric
  density, but generally undergo irreversible
  dihydrogen elimination.
• Nonclassical PMCs they are allowing a complete
  release of hydrogen under mild condition and
  without high vacuum.

129
5-8Advantages Hydrogen Transport and Storage
Technologies

• GAS-ON-SOLID ADSORPTION
• The principle of storage the ability of
  high-surface-area carbons, when chemically
  activated, to retain hydrogen on their surfaces.
• The action of above is called adsorption, and it
  happens at relatively high pressures and
  extremely cold temperatures.
• Hydrogen is released at atmospheric pressure and
  ambient temperature.

130
5-8Advantages Hydrogen Transport and Storage
Technologies

• GAS-ON-SOLID ADSORPTION
• The storage capacity of microcrystalline
  currently 4.8 wt hydrogen at 87K and 6Mpa.
• The bar of storage capacity relatively low
  volumetric and gravimetric densities the
  cryogenic temperature required high cost of the
  process.
• Two technologies that may increase the potential
  for this storage medium carbon nanotubules and
  carbon aerogels.

131
5-8Advantages Hydrogen Transport and Storage
Technologies

• Carbon Nanotubules
• A new form of high-surface carbon material.
• It has the potential for substantially increase
  the volumetric and gravimetric densities.
• It contains microscopic pores of uniform size
  that encourage micro-capillary filling by
  hydrogen condensation.
• It lets hydrogen gas condense into a liquid state
  at relatively high temperature.

132
5-8Advantages Hydrogen Transport and Storage
Technologies

• Carbon Nanotubules
• Preliminary results on nanotubule-containing
  samples 8.4 wt hydrogen at 82K and 0.07Mpa.
• The direction of work in future improve the
  quantity of hydrogen stored at near-ambient
  temperature.

133
5-8Advantages Hydrogen Transport and Storage
Technologies

• Carbon Nanotubules

134
5-8Advantages Hydrogen Transport and Storage
Technologies

• Carbon Aerogels
• A special class of open-cell foams with an
  ultra-fine cell/pore size, high surface area, and
  a solid matrix.
• The process of creating carbon aerogels be
  usually synthesized from the aqueous
  polycondensation of resorcinol(????,???) with
  formaldehyde (??), followed by supercritical
  extraction and pyrolysis-at about 1050?-in an
  inert atmosphere.

135
5-8Advantages Hydrogen Transport and Storage
Technologies

• Carbon Aerogels
• Synthesized aerogels have a nanocrystalline
  structure with micro-pores less than 2 nanometer
  in diameter.
• Results on the aerogels-containing sample 3.7
  wt hydrogen at 8.3MPa.
• The direction of work in future improve maximum
  hydrogen adsorption over a wide range of
  temperatures and pressures.

136
5-8Advantages Hydrogen Transport and Storage
Technologies

• GLASS MICROSPHERES
• These glass spherical structures diameters of
  25 to 500 microns and wall thickness of
  approximately 1 micron.
• The process of storing hydrogen at 200? to
  400?, the increased permeability of the glass
  permits the spheres to be filled by hydrogen
  under pressure by immersion in high-pressure
  hydrogen gas, when cooled to ambient temperature,
  the hydrogen is locked.

137
5-8Advantages Hydrogen Transport and Storage
Technologies

• GLASS MICROSPHERES

138
5-8Advantages Hydrogen Transport and Storage
Technologies

• GLASS MICROSPHERES
• Subsequent raising of the temperature will
  release the hydrogen.
• Spheres synthesized are defect-free and have a
  membrane tensile stress at failure of about
  1000MPa, yielding a burst pressure three times as
  great as commercially-produced spheres.

139
5-8Advantages Hydrogen Transport and Storage
Technologies

• GLASS MICROSPHERES
• A small bed of such microspheres can contain
  hydrogen mass fraction 10 at about 62MPa.
• In test, 95 of a microsphere has been filled or
  release in about 15 minutes at 370?.