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, higer 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 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
• Operating directly on coal, but that seems less.
• Operation on coal-derived fuel gas or natural gas
  is viable.

51
5-3 Types of Fuel CellsMCFC Design and Operation

• The sketch of MCFC operation

52
5-3 Types of Fuel CellsMCFC Design and Operation

• The component of MCFC
• Electrolyte a molten carbonate salt mixture,
  consist of lithium carbonate and potassium
  carbonate.
• Anode a highly porous sintered nickel powder,
  alloyed with chromium.
• Cathode a porous nickel oxide material doped
  with lithium.
• Electrolyte carriers a porous, insulating and
  chemically ceramic matrix.

53
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

54
5-3 Types of Fuel CellsMCFC Design and Operation

• The MCFC compares with PAFC
• As the operating temperature increases, the
  theoretical operating voltage for a fuel cell
  decrease and with it the maximum theoretical fuel
  efficiency.
• The operating voltage of the MCFC is higher than
  the PAFC at the same current density.
• As size and cost scale roughly with electrode
  area, a MCFC should be smaller and less expansive
  than a comparable PAFC.

55
5-3 Types of Fuel CellsMCFC Design and Operation

• The relations of high operating temperature and
  MCFC
• Operating at between 1110F(600?) and
  1200F(650?).
• In combined cycle operation, electrical
  efficiencies are in excess of 60(HHV).
• At the high operating temperature, the gaseous
  hydrocarbon fuel such as natural gas would be
  reformed to produce hydrogen within the fuel cell
  itself.

56
5-3 Types of Fuel CellsMCFC Design and Operation

• The relations of high operating temperature and
  MCFC
• 4. At high operating temperature(1200F), noble
  metal catalysts are not required.
• 5. At high operating temperature(1200F), the
  salt mixture is liquid and is a good conductor.
• 6. The cell performance is sensitive to
  operating temperature.
• A change in cell temperature from 1200F to
  1110F results in drop in voltage 15.

57
5-3 Types of Fuel CellsMCFC Design and Operation

• How does excess heat reuse and remove
• The temperature of excess heat is high enough to
  yield high pressure steam, which may be fed to
  turbine to generate additional electricity.
• To achieve sufficient of conductivity of the
  electrolyte, a higher volume of air is passed
  through the cathode for cooling purpode.

58
5-3 Types of Fuel CellsSolid Oxide fuel cells

• The introductions of the SOFC
• 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, however, the system must operate at
  about 1830 F (1000 C).
• At that temperature, internal reforming of
  carbonaceous fuels should be possible, and the
  waste heat from such a device would be easily
  utilized by conventional thermal electricity
  generating plants to yield excellent fuel
  efficiency.

59
5-3 Types of Fuel CellsSOFC Design and Operation

• The sketch of SOFC operation

60
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- ? 2O2-2
• It is significant that the SOFC can use CO as its
  direct fuel.

61
5-3 Types of Fuel CellsSOFC Design and Operation

• The components of the SOFC
• Electrolyte solid ceramic.
• Materials dense yttria-stabilized zirconia
• It is an excellent conductor at high
  temperatures.
• Anode a porous nickel/zirconia cermet
• Cathode magnesium-dope lanthaum manganate

62
5-3 Types of Fuel CellsSOFC Design and Operation

• SOFC performance Characteristics
• It development cells and small stacks 0.6V/cell
  at about 232 A/ft2
• Lifetimes are over 30000(hr).
• The efficiencies of unpressurized SOFCs 45
  (HHV)
• The efficiencies of pressurized SOFCs 60
  (HHV)
• Using the waste heat, could add fuel efficiency
  of the SOFC system.

63
5-3 Types of Fuel CellsSOFC Design and Operation

• How does manage temperature
• Maintain proper volume of the air stream into the
  cell.

64
5-3 Types of Fuel CellsSOFC Design and Operation

• The relations of high operating temperature and
  SOFC
• The SOFC operates at approximately 1830F
  (1000C).
• The high operating temperature offers the
  possibility of internal reforming.
• The SOFC can tolerant several orders of magnitude
  more sulfur than order fuel cells.
• The SOFC requires a significant start-up time.

65
5-3 Types of Fuel CellsSOFC Design and Operation

• The relations of high operating temperature and
  SOFC
• The cell performance is very sensitive to
  operating temperature.
• A 10 drop in temperature ? 12 drop in cell
  performance
• 6. The high temperature also demands that the
  system include significant thermal shielding to
  protect personnel and to retain heat.

66
5-4 Fuel Cell Electrochemistryinternal reformer

• In a conventional fuel cell system, a
  carbonaceous fed to a fuel processor where it is
  steam reformed to produce H2.
• Methane and steam reforming reaction
• CH4 H2O ? CO 3H2

67
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(PH2/PH2O)
• RT/2F ln(PCO2,c/PCO2,a)

68
5-4 Fuel Cell ElectrochemistrySOFC

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

69
5-5Advantages of Fuel Cells Environmental
Acceptability

• Because fuel cells are so efficient, CO2
  emissions are reduced for a given power output.
• Example
• By 2000, decrease CO2 emissions by 0.6 MMT of
  carbon equivalent.
• Emissions of SOx and NOx are 0.003 and 0.0004
  pounds/megawatt-hour.

70
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.
• 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 efficiency
  of the fuel cell systems approach 85 percent.

71
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 percent
• Many smaller units are statistically reliable.

72
5-5Advantages of Fuel Cells Permitting

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

73
5-5Advantages of Fuel CellsModularity

• The fuel cell is inherently modular.
• Be configured in wide range of electrical output,
  form 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.

74
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.

75
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 application.

76
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.

77
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.

78
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.

79
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.

80
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.

81
5-7 Advanced Hydrogen Production Technologies

• Introduction
• Hydrogen is a clean, sustainable resource with
  many potential application.
• Hydrogen is now produced primary by steam
  reforming of natural gas.
• This is relatively expensive process that uses
  electric current to dissociate water.
• Three process of producing hydrogen
  photobiological, photoelectrochemical,
  thermochemical.

82
5-7 Advanced Hydrogen Production Technologies

• PHOTOBIOLOGICAL PRODUCTION
• Most photobiological system use the natural
  activity of bacteria and green algae to produce
  hydrogen.
• Two significant limitation
• Low solar converting efficiencies.(56 of suns
  energy to hydrogen energy)
• Nearly all enzymes are inhibited in their
  hydrogen production by presence of oxygen.

83
5-7 Advanced Hydrogen Production Technologies

• PHOTOBIOLOGICAL PRODUCTION
• 3. The way to overcome oxygen intolerance and
  increase conversion efficiencies
• A green algae the Chlamydomonas strain ?
  product hydrogen and oxygen simultaneously.
• Cell free process theoretical efficiency
  approach 25

84
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

85
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.

86
5-7 Advanced Hydrogen Production Technologies

• PRODUTION BY PHOTOELECTRO-CHEMICAL (PEC)
  TECHNOLOGY
• The way to overcome limits
• The structure ? the multijunction device
• Material
• Gallium based (GalnP2, GaAs) ? efficiency is more
  than 25 , but is expensive.
• Amorphous silicon ? efficiency is more than 13
  , but cost is low.

87
5-7 Advanced Hydrogen Production Technologies

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

88
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
• Biomass is break into highly reactive
  vapors and carbonaceous resident, or char.
• The vapors, when condensed into pyrolysis oil,
  can be steam reformed to produce hydrogen.

89
5-7 Advanced Hydrogen Production Technologies

• THERMOCHEMICAL PRODUCTION
• The char is burn to provide the required heat for
  the pyrolysis reaction.
• The fast way to produce hydrogen is directly
  linked to a steam reformer.(1217 hydrogen by
  weight of dry biomass)
• Advantage the lowest cost production methods,
  but it needs catalysts.

90
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, consist about 70 by weight of
  biomass material.
• Gasification result in an clean fuel gas from
  which hydrogen can be reformed.

91
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.