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

Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

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Page 1: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

Fuel Cell Fuel Cell IntroductionIntroduction Historical NotesHistorical Notes Types of Fuel CellsTypes of Fuel Cells Fuel Cell ElectrochemistryFuel Cell Electrochemistry Advantages of Fuel CellsAdvantages of Fuel Cells Applications of Fuel CellsApplications of Fuel Cells Advanced Hydrogen Production Advanced Hydrogen Production

TechnologiesTechnologies Advanced Hydrogen Transport and Storage Advanced Hydrogen Transport and Storage

TechnologiesTechnologies

Page 2: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-1 Introduction5-1 IntroductionWhat is a Fuel CellWhat is a Fuel Cell

A fuel cell → an electrochemical device that A fuel cell → an electrochemical device that combines hydrogen and oxygen to produce combines hydrogen and oxygen to produce electricity, with water and heat as its by-product. electricity, with water and heat as its by-product. 

Page 3: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-2 Historical Notes5-2 Historical NotesFinally Coming of AgeFinally Coming of Age

In 1839, Sir William Grove reasoned that it shouIn 1839, Sir William Grove reasoned that it should be possible to react hydrogen with oxygen to gld be possible to react hydrogen with oxygen to generate electricity.enerate electricity.

In 1889, fuel cell was coined by Ludwig Mond aIn 1889, fuel cell was coined by Ludwig Mond and Charles Langer, who attempted to build the find Charles Langer, who attempted to build the first practical device using air and coal gas.rst practical device using air and coal gas.

Page 4: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-2 Historical Notes5-2 Historical Notes Finally Coming of Age Finally Coming of Age

In early 20th Century, fuel cells were forgot In early 20th Century, fuel cells were forgot

1.1. A lack of understanding of materials and A lack of understanding of materials and electrode kinetics.electrode kinetics.

2.2. Internal combustion engine was developed.Internal combustion engine was developed.

3.3. Petroleum was discovered and rapidly exploited. Petroleum was discovered and rapidly exploited.

Page 5: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-2 Historical Notes5-2 Historical NotesFinally of Coming AgeFinally of Coming Age

In 1932, the first successful fuel cell device was In 1932, the first successful fuel cell device was built by engineer Francis Bacon. built by engineer Francis Bacon.

He improved on the expensive platinum catalysts He improved on the expensive platinum catalysts employed by Mond and Langer with a hydrogen-employed by Mond and Langer with a hydrogen-oxygen cell using a less corrosive alkaline electroxygen cell using a less corrosive alkaline electrolyte and inexpensive nickel electrodes. olyte and inexpensive nickel electrodes.

Page 6: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-2 Historical Notes5-2 Historical NotesFinally of Coming AgeFinally of Coming Age

Until 1959, Bacon and his coworkers were able tUntil 1959, Bacon and his coworkers were able to demonstrate a practical five-kilowatt system cao demonstrate a practical five-kilowatt system capable of powering a welding machine. pable of powering a welding machine.

In October of that same year, Harry Karl Ihrig of In October of that same year, Harry Karl Ihrig of Allis-Chalmers Manufacturing Company demonAllis-Chalmers Manufacturing Company demonstrated his famous 20-horsepower fuel cell-powestrated his famous 20-horsepower fuel cell-powered tractor.red tractor.

Page 7: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-2 Historical Notes5-2 Historical NotesFinally of Coming AgeFinally of Coming Age

In the late of 1950s, fuel cells were noticed In the late of 1950s, fuel cells were noticed

1.1. NASA began to search some electricity NASA began to search some electricity generator for space mission.generator for space mission.

2.2. Nuclear reactors as too risky, batteries as too Nuclear reactors as too risky, batteries as too heavy and short live, and solar power as heavy and short live, and solar power as cumbersome, NASA turned to fuel cells.cumbersome, NASA turned to fuel cells.

Page 8: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-2 Historical Notes5-2 Historical NotesFinally of Coming AgeFinally of Coming Age

In 1960s, fuel cells would be the panacea to the In 1960s, fuel cells would be the panacea to the world energy problem. The some qualities that world energy problem. The some qualities that make fuel cells idea for space exploration were make fuel cells idea for space exploration were considered. (ex. Small size, high efficiency, low considered. (ex. Small size, high efficiency, low emission.) emission.)

Nearly 30 years US$1 billion in research have Nearly 30 years US$1 billion in research have been devote to address the barriers to the use of been devote to address the barriers to the use of fuel cells for stationary application. fuel cells for stationary application.

Page 9: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-2 Historical Notes5-2 Historical NotesFinally of Coming AgeFinally of Coming Age

FortunatelyFortunately

1.1. A number of manufacturers have supported numerous A number of manufacturers have supported numerous demonstration initiatives and ongoing research and demonstration initiatives and ongoing research and development into stationary application.development into stationary application.

2.2. Phosphoric acid fuel cells is being offered Phosphoric acid fuel cells is being offered commercially, and more advanced designs, such as commercially, and more advanced designs, such as carbonate fuel cells and solid oxide fuel cells, are the carbonate fuel cells and solid oxide fuel cells, are the focus of major electric technologies.focus of major electric technologies.

3.3. Full-sized (commercial) cells and full-height stacks Full-sized (commercial) cells and full-height stacks have been successfully demonstrated for the have been successfully demonstrated for the carbonate fuel cell design. carbonate fuel cell design.

Page 10: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-2 Historical Notes5-2 Historical NotesFinally of Coming AgeFinally of Coming Age

It has taken more than 150 years to develop It has taken more than 150 years to develop the basic science and to realize the the basic science and to realize the necessary materials improvement for fuel necessary materials improvement for fuel cells to become a commercial reality. cells to become a commercial reality. The fuel cell is finally coming of age!!The fuel cell is finally coming of age!!

Page 11: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-2 Historical Notes5-2 Historical NotesFinally of Coming AgeFinally of Coming Age

Page 12: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-2 Historical Notes5-2 Historical NotesFinally of Coming AgeFinally of Coming Age

Page 13: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 5-3 Types of Fuel CellsTypes of Fuel CellsOverview ofOverview of Fuel Cells Fuel Cells

Fuel Cells generate electricity through an Fuel Cells generate electricity through an electrochemical process in which the energy electrochemical process in which the energy stored in a fuel is converted directly into DC stored in a fuel is converted directly into DC electricity.electricity.

Electrical energy is generated without Electrical energy is generated without combusting fuel, so fuel cells are extremely combusting fuel, so fuel cells are extremely attractive from an environmental stand point.attractive from an environmental stand point.

Page 14: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsOverview ofOverview of Fuel Cells Fuel Cells

Attractive fuel cell characteristic Attractive fuel cell characteristic

1.1. High energy conversion efficiencyHigh energy conversion efficiency

2.2. Modular designModular design

3.3. Very low chemical and acoustical pollutionVery low chemical and acoustical pollution

4.4. Fuel flexibleFuel flexible

5.5. Cogeneration capabilityCogeneration capability

6.6. Rapid load responseRapid load response

Page 15: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsOverview ofOverview of Fuel Cells Fuel Cells

Basic operating principle of fuel cellsBasic operating principle of fuel cells1.1. An input fuel is catalytically reacted in fuel An input fuel is catalytically reacted in fuel

cell to create an electric current.cell to create an electric current.2.2. The input fuel passed over the anode where it The input fuel passed over the anode where it

catalytically splits into ions and electrons.catalytically splits into ions and electrons.3.3. The electrons go through an external circuit to The electrons go through an external circuit to

serve an electric load while the ions move serve an electric load while the ions move through the electrolyte toward the oppositely through the electrolyte toward the oppositely charge electrode.charge electrode.

4.4. At electrode, ions combine to create by-At electrode, ions combine to create by-products, primarily water and COproducts, primarily water and CO22..

Page 16: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsOverview ofOverview of Fuel Cells Fuel Cells

The figure of basic operating principle The figure of basic operating principle

Page 17: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsOverview ofOverview of Fuel Cells Fuel Cells

Fuel Cell CharacteristicsFuel Cell Characteristics

Page 18: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsOverview ofOverview of Fuel Cells Fuel Cells

Page 19: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsOverview ofOverview of Fuel Cells Fuel Cells

Four primary types of fuel cells which are Four primary types of fuel cells which are based on electrolyte employed based on electrolyte employed

1.1. Phosphoric Acid Fuel CellPhosphoric Acid Fuel Cell

2.2. Molten Carbonate Fuel CellMolten Carbonate Fuel Cell

3.3. Solid Oxide Fuel CellSolid Oxide Fuel Cell

4.4. Proton Exchange Membrane Fuel CellProton Exchange Membrane Fuel Cell

Page 20: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsOverview ofOverview of Fuel Cells Fuel Cells

A comparison of the fuel cell types A comparison of the fuel cell types

Page 21: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsOverview ofOverview of Fuel Cells Fuel Cells

Fuel cells are typical grouped three section Fuel cells are typical grouped three section

Page 22: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

The most mature fuel cell technology The most mature fuel cell technology

1.1. Among low temperature fuel cell, Among low temperature fuel cell, it was showed relative tolerance for reformed hydrocarbon fuels.

2. It could have widespread applicability in the near term.

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPhosphoric Acid Fuel CellsPhosphoric Acid Fuel Cells

Page 23: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPAFC Design an OperationPAFC Design an Operation

The sketch of PAFC operationThe sketch of PAFC operation

Page 24: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPAFC Design an OperationPAFC Design an Operation

The components of PAFC The components of PAFC

1.1. Electrolyte : liquid of acidElectrolyte : liquid of acid

2.2. Electrolyte carriers : Teflon bonded silicone caElectrolyte carriers : Teflon bonded silicone carbide matrix (pore structure→capillary action trbide matrix (pore structure→capillary action to keep liquid electrolyte in place)o keep liquid electrolyte in place)

3.3. Anode : platinum catalyzed, porous carbonAnode : platinum catalyzed, porous carbon

4.4. Cathode : platinum catalyzed, porous carbonCathode : platinum catalyzed, porous carbon

5.5. Bipolar plate : complex carbon plate Bipolar plate : complex carbon plate

Page 25: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPAFC Design an OperationPAFC Design an Operation

The most designs of PAFCThe most designs of PAFC

1.1. The plates are “bi-polar” in that they have The plates are “bi-polar” in that they have grooves on both side – grooves on both side –

one side supplies fuel to anode of one cell, and one side supplies fuel to anode of one cell, and the other side supplies air or oxygen to the the other side supplies air or oxygen to the cathode of the adjacent cell. cathode of the adjacent cell.

Page 26: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPAFC Design an OperationPAFC Design an Operation

The PAFC reactions The PAFC reactions

Anode : HAnode : H2 2 → 2H→ 2H++ + 2e + 2e--

Cathode : ½ OCathode : ½ O2 2 + 2H+ 2H+ + +2e+2e- - → H→ H22OO

Page 27: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPAFC Design an OperationPAFC Design an Operation

The characteristics of PAFC operationThe characteristics of PAFC operation

1.1. Some acid may be entrained in fuel or oxidant Some acid may be entrained in fuel or oxidant streams and addition of acid may be after streams and addition of acid may be after many hours of operation.many hours of operation.

2.2. The water removed as steam on the cathode by The water removed as steam on the cathode by flowing excess oxidant past the back of flowing excess oxidant past the back of electrodes.electrodes.

Page 28: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPAFC Design an OperationPAFC Design an Operation

The temperature effect to PAFCThe temperature effect to PAFC

The product water removal procedure required The product water removal procedure required that the system operated at temperature around that the system operated at temperature around 375°F (~190°C).375°F (~190°C).

1.1. At lower temperature : the water will dissolve At lower temperature : the water will dissolve in the electrolyte and not be removed as in the electrolyte and not be removed as steam.steam.

2.2. At high temperature (approximately 410°F~ At high temperature (approximately 410°F~ (~210°C) : the phosphoric acid begins to (~210°C) : the phosphoric acid begins to decompose.decompose.

Page 29: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPAFC Design an OperationPAFC Design an Operation

How does excess heat be removedHow does excess heat be removed

1.1. Proved carbon plates containing cooling Proved carbon plates containing cooling channels.channels.

2.2. Air or liquid coolant, can be passed Air or liquid coolant, can be passed through these channels to remove heat.through these channels to remove heat.

Page 30: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPAFC Design an OperationPAFC Design an Operation

PAFC performance characteristics PAFC performance characteristics

1.1. Power density : 160 to 175 watts/ftPower density : 160 to 175 watts/ft22

2.2. Thermal energy supplied at : ~ 150°F (only a Thermal energy supplied at : ~ 150°F (only a portion at 250°F to 300°F)portion at 250°F to 300°F)

3.3. Efficiency :Efficiency :

a.a. With pressurized reactants : 36% to 42% With pressurized reactants : 36% to 42% (HHV)(HHV)

b.b. Supply usable thermal energy : 31% to 37% Supply usable thermal energy : 31% to 37% (HHV)(HHV)

Page 31: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsProton Exchange Membrane Fuel Cells Proton Exchange Membrane Fuel Cells

(PEMFC)(PEMFC) The introduction of PEMFCThe introduction of PEMFC

1.1. PEMFC has higher power density than any PEMFC has higher power density than any other fuel cell system.other fuel cell system.

2.2. PEMFC has comparable performance with the PEMFC has comparable performance with the advanced aerospace AFC.advanced aerospace AFC.

3.3. PEMFC can operate on reformed hydrocarbon PEMFC can operate on reformed hydrocarbon fuels.fuels.

4.4. PEMFC uses a solid polymer electrolyte PEMFC uses a solid polymer electrolyte eliminates the corrosion.eliminates the corrosion.

Page 32: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsProton Exchange Membrane Fuel CellsProton Exchange Membrane Fuel Cells

The introduction of PEMFCThe introduction of PEMFC

5.5. Its low operating temperature (70-85 Its low operating temperature (70-85 ooC): C):

a.a. provides instant start up: 50 % maximum pow provides instant start up: 50 % maximum power immediately at room T & full operating poer immediately at room T & full operating power within 3 min.wer within 3 min.

b.b. require no thermal shielding to protect pers require no thermal shielding to protect personnel.onnel.

6.6. Advances in performance and designs offer the Advances in performance and designs offer the possibility of lower cost.possibility of lower cost.

Page 33: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPEMFC Designs and OperationPEMFC Designs and Operation

The sketch of PEMFC operationThe sketch of PEMFC operation

Page 34: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPEMFC Designs and OperationPEMFC Designs and Operation

The sketch of PEMFC operationThe sketch of PEMFC operation

Page 35: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPEMFC Designs and OperationPEMFC Designs and Operation

The components of PEMFCThe components of PEMFC

1.1. Electrolyte : polymer membrane.Electrolyte : polymer membrane.

2.2. Anode : thin sheet of porous, graphitized Anode : thin sheet of porous, graphitized paper. (water-proofed with PTFE or Teflon, paper. (water-proofed with PTFE or Teflon, with one surface being applied with a small with one surface being applied with a small amount of Pt-black) amount of Pt-black)

3.3. Cathode : (the same as above).Cathode : (the same as above).

4.4. Bipolar plate : graphite.Bipolar plate : graphite.

Page 36: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPEMFC Designs and OperationPEMFC Designs and Operation

The features of the electrolyteThe features of the electrolyte

1.1. Electronic insulator, but an excellent conductoElectronic insulator, but an excellent conductor of hydrogen ions.r of hydrogen ions.

2.2. The acid molecules are fixed to the polymer, bThe acid molecules are fixed to the polymer, but the protons on these acid groups are free to ut the protons on these acid groups are free to migrate through the membrane.migrate through the membrane.

3.3. Solid polymer electrolyte→electrolyte loss is Solid polymer electrolyte→electrolyte loss is not an issue with regard to stack life.not an issue with regard to stack life.

4.4. Be handled easily and safely.Be handled easily and safely.

Page 37: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPEMFC Designs and OperationPEMFC Designs and Operation

The heart of PEMFCThe heart of PEMFC

The electrolyte is sandwiched between the The electrolyte is sandwiched between the anode and cathode, and the three components anode and cathode, and the three components are sealed together under heat and pressure to are sealed together under heat and pressure to product a single “membrane/electrode product a single “membrane/electrode assembly” (MEA, < 1mm thick).assembly” (MEA, < 1mm thick).

Page 38: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPEMFC Designs and OperationPEMFC Designs and Operation

The features of the bipolar plates The features of the bipolar plates

1.1. The bipolar plates are called “flow field The bipolar plates are called “flow field plates”.plates”.

2.2. They make electrical contact with the back of They make electrical contact with the back of the electrodes and conduct the current to the the electrodes and conduct the current to the external circle.external circle.

3.3. They supply fuel to the anode and oxidant to They supply fuel to the anode and oxidant to the cathode.the cathode.

Page 39: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPEMFC Designs and OperationPEMFC Designs and Operation

Useable fuel for PEMFCUseable fuel for PEMFC

1.1. Pure hydrogen Pure hydrogen

2.2. Reformed Hydrocarbon fuels: Reformed Hydrocarbon fuels:

a.a. Without removal or recirculation of by-Without removal or recirculation of by-product COproduct CO22..

b.b. The traces of CO produced during the The traces of CO produced during the reforming process must be converted to COreforming process must be converted to CO22

(a (a

simple catalytic process).simple catalytic process).

Page 40: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel Cells PEMFC Designs and Operation PEMFC Designs and Operation

The PEMFC reactions The PEMFC reactions

Anode : HAnode : H2 2 → 2H→ 2H++ + 2e + 2e--

Cathode : OCathode : O2 2 → 4H→ 4H+ + + 4e+ 4e- - → 2H→ 2H22OO

Page 41: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPEMFC Designs and OperationPEMFC Designs and Operation

The characteristics of PEMFC operationThe characteristics of PEMFC operation

1.1. The electrode reactions are analogous to those The electrode reactions are analogous to those in PAFC.in PAFC.

2.2. The PEMFC operates at about 175°F (80 ).℃The PEMFC operates at about 175°F (80 ).℃

3.3. The water is produced as liquid water and is The water is produced as liquid water and is carried out the fuel cell by excess oxidant carried out the fuel cell by excess oxidant flow.flow.

4.4. Fully operating power is available within Fully operating power is available within about 3 minute under normal condition.about 3 minute under normal condition.

Page 42: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPEMFC Designs and OperationPEMFC Designs and Operation

Page 43: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPEMFC Designs and OperationPEMFC Designs and Operation

The performance of PEMFC recentlyThe performance of PEMFC recently

1.1. At 0.7V/cell on hydrogen and oxygen, 65psia : At 0.7V/cell on hydrogen and oxygen, 65psia : 850A/ft850A/ft2 2 (~0.91 A/cm(~0.91 A/cm22))

2.2. At 0.7V/cell on hydrogen and air, 65psia : At 0.7V/cell on hydrogen and air, 65psia : 500A/ft500A/ft2 2 (~0.54 A/cm(~0.54 A/cm22))

Page 44: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPEMFC Designs and OperationPEMFC Designs and Operation

The performance of Ballard/Dow PEMFCThe performance of Ballard/Dow PEMFC At 0.7V/cell:At 0.7V/cell:1.1. At 65psia, hydrogen/oxygen : 2000A/ftAt 65psia, hydrogen/oxygen : 2000A/ft22

2.2. At 65psia, hydrogen/air : 1000A/ftAt 65psia, hydrogen/air : 1000A/ft22

At 0.5V/cell, :At 0.5V/cell, :1.1. At 65psia, hydrogen/oxygen : 4000A/ftAt 65psia, hydrogen/oxygen : 4000A/ft22

↓↓ 2000 W/ft2000 W/ft22

Page 45: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPEMFC Designs and OperationPEMFC Designs and Operation

The power density of PEMFC The power density of PEMFC

1.1. a factor of 10 greater than other FC systems → a a factor of 10 greater than other FC systems → a significant reduction in stack size and cost.significant reduction in stack size and cost.

2.2. In 5kW production fuel cell stacks, 0.7V at 650 A/ftIn 5kW production fuel cell stacks, 0.7V at 650 A/ft2 2

on hydrogen/air at 45psi, stack dimensions 9.8 * 9.8 on hydrogen/air at 45psi, stack dimensions 9.8 * 9.8 * 16.7 in: stack-only power density of over 5.4 * 16.7 in: stack-only power density of over 5.4 kW/ftkW/ft3 3

3.3. 1.25 kW/ft1.25 kW/ft3 3 on hydrogen/air at 45psi, if including on hydrogen/air at 45psi, if including fuel/oxidant controls, cooling, product water removalfuel/oxidant controls, cooling, product water removal

4.4. Approaching 14.2 kW/ftApproaching 14.2 kW/ft3 3 are certainly feasible.are certainly feasible.

Page 46: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPEMFC Designs and OperationPEMFC Designs and Operation

When HC/air are to be used, higher T FC, the When HC/air are to be used, higher T FC, the MCFC, SOFC, and to some extent, PAFC, MCFC, SOFC, and to some extent, PAFC, have an efficiency advantage over PEMFC.have an efficiency advantage over PEMFC.

↑ ↑

waste heat can be used to drive air waste heat can be used to drive air compressors, reforming of HC fuels, electric compressors, reforming of HC fuels, electric generation or other thermal loadgeneration or other thermal load

Page 47: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPEMFC Designs and OperationPEMFC Designs and Operation

Using either air or Using either air or liquid coolingliquid cooling

↓ ↓

a compact power generatora compact power generator

and the excess heat of PEMFC is to be used forand the excess heat of PEMFC is to be used for

1.1. space heating or residential hot waterspace heating or residential hot water

2.2. utility cogeneration applications utility cogeneration applications

Page 48: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPEMFC Designs and OperationPEMFC Designs and Operation

The pressure effects to all fuel cells The pressure effects to all fuel cells 1.1. Performance is improve by pressuring the air.Performance is improve by pressuring the air.2.2. Find an balance about the energy and financial Find an balance about the energy and financial

cost associated with compressing air and the icost associated with compressing air and the improved performance.mproved performance.

3.3. Rule of thumb: < 45 psiaRule of thumb: < 45 psia4.4. ∵∵PEMFC uses a solid electrolytePEMFC uses a solid electrolyte ∴ ∴ a significant pressure differential can be maa significant pressure differential can be ma

intained across the electrolyte→low P fuel & hintained across the electrolyte→low P fuel & higher P airigher P air

Page 49: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsPEMFC Designs and OperationPEMFC Designs and Operation

A very significant cost penalty of PEMFC as A very significant cost penalty of PEMFC as compared with PAFCcompared with PAFC

1.1. The PEMFC uses platinum at both the anode The PEMFC uses platinum at both the anode and cathode.and cathode.

2.2. presently, 0.001 oz/inpresently, 0.001 oz/in22 ~0.6 oz/kW for H ~0.6 oz/kW for H22/air /air

3.3. Los Alamos National Lab & Texas A &M Los Alamos National Lab & Texas A &M Univ., 0.00007 oz/inUniv., 0.00007 oz/in22 ~0.042 oz/kW for H ~0.042 oz/kW for H22/air /air or ~0.021 oz/kW for Hor ~0.021 oz/kW for H22/ O/ O22

4.4. Be expected to reduce platinum requirement to Be expected to reduce platinum requirement to 0.035 oz/kW (1 g/kW) or about $2/kW.0.035 oz/kW (1 g/kW) or about $2/kW.

Page 50: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel Cells Molten Carbonate Fuel Cells Molten Carbonate Fuel Cells

The goals of developing MCFCThe goals of developing MCFC

1.1. In 1960’s: operating directly on coal→ but In 1960’s: operating directly on coal→ but that seems less likely today.that seems less likely today.

2.2. Operation on coal-derived fuel gases or Operation on coal-derived fuel gases or natural gas is viable.natural gas is viable.

Page 51: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel Cells Molten Carbonate Fuel Cells Molten Carbonate Fuel Cells

Page 52: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel Cells Molten Carbonate Fuel Cells Molten Carbonate Fuel Cells

Page 53: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel Cells Molten Carbonate Fuel Cells Molten Carbonate Fuel Cells

Page 54: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel Cells Molten Carbonate Fuel Cells Molten Carbonate Fuel Cells

Page 55: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel Cells Molten Carbonate Fuel Cells Molten Carbonate Fuel Cells

Page 56: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel Cells Molten Carbonate Fuel Cells Molten Carbonate Fuel Cells

Page 57: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel Cells Molten Carbonate Fuel Cells Molten Carbonate Fuel Cells

Page 58: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel Cells Molten Carbonate Fuel Cells Molten Carbonate Fuel Cells

Page 59: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel Cells Molten Carbonate Fuel Cells Molten Carbonate Fuel Cells

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5-3 Types of Fuel Cells5-3 Types of Fuel Cells Molten Carbonate Fuel Cells Molten Carbonate Fuel Cells

Page 61: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsMCFC Design and OperationMCFC Design and Operation

The sketch of MCFC operationThe sketch of MCFC operation

Page 62: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsMCFC Design and OperationMCFC Design and Operation

The components of MCFCThe components of MCFC

1.1. Electrolyte : a molten carbonate salt mixture, usually Electrolyte : a molten carbonate salt mixture, usually consists of lithium carbonate and potassium consists of lithium carbonate and potassium carbonate. carbonate.

2.2. Electrolyte carriers : a porous, insulating and Electrolyte carriers : a porous, insulating and chemically inert ceramic (LiAlOchemically inert ceramic (LiAlO22) matrix. ) matrix.

3.3. Anode : a highly porous sintered nickel powder, Anode : a highly porous sintered nickel powder, alloyed with chromium to prevent agglomeration and alloyed with chromium to prevent agglomeration and creep at operating T.creep at operating T.

4.4. Cathode : a porous nickel oxide material doped with Cathode : a porous nickel oxide material doped with lithium.lithium.

Page 63: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsMCFC Design and OperationMCFC Design and Operation

The MCFC reactionsThe MCFC reactions

Anode : HAnode : H22 + CO + CO33-2 -2 → H→ H22O + COO + CO2 2 + 2e+ 2e--

CO + COCO + CO33-2-2 → 2CO → 2CO2 2 + 2e+ 2e--

Cathode : OCathode : O22 + + 2CO2CO2 2 + 4e+ 4e-- → 2CO → 2CO33-2-2

↓↓

* * requirerequire a system for collecting COa system for collecting CO2 2 from the from the

anode exhaust and mixing it with the cathode anode exhaust and mixing it with the cathode feed streamfeed stream

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5-3 Types of Fuel Cells5-3 Types of Fuel CellsMCFC Design and OperationMCFC Design and Operation

The MCFC reactionsThe MCFC reactions

* * before CObefore CO2 2 is collected, any residual His collected, any residual H22 in the in the

spent fuel stream must be burned.spent fuel stream must be burned.

* * Future systems may incorporate membrane Future systems may incorporate membrane separators to remove Hseparators to remove H2 2 for recirculation back for recirculation back

to the fuel stream.to the fuel stream.

Page 65: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsMCFC Design and OperationMCFC Design and Operation

MCFC v.s. PAFC MCFC v.s. PAFC 1.1. operating T ↑, the theoretical operating voltage and thoperating T ↑, the theoretical operating voltage and th

e maximum theoretical fuel efficiency for a MCFC ↓. e maximum theoretical fuel efficiency for a MCFC ↓. 2.2. On the other hand, operating T ↑, the rate of electro-cOn the other hand, operating T ↑, the rate of electro-c

hemical and thus current at a given voltage ↑.hemical and thus current at a given voltage ↑. ↓ ↓(net effect)(net effect)a.a. The operating voltage of the MCFC is higher than the The operating voltage of the MCFC is higher than the

PAFC at the same current density. (higher fuel efficiePAFC at the same current density. (higher fuel efficiency)ncy)

b.b. As size and cost scale roughly with electrode area, a As size and cost scale roughly with electrode area, a MCFC should be smaller and less expansive than a “cMCFC should be smaller and less expansive than a “comparable” PAFC.omparable” PAFC.

Page 66: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsMCFC Design and OperationMCFC Design and Operation

The high operating T characteristics of MCFCThe high operating T characteristics of MCFC1.1. Operating at between 1110°F(600 ) and 1200°F(65℃Operating at between 1110°F(600 ) and 1200°F(65℃

0 ) ←necessary to achieve sufficient conductivity o℃0 ) ←necessary to achieve sufficient conductivity o℃f the electrolytef the electrolyte

2.2. To maintain this operating T, a higher volume of air iTo maintain this operating T, a higher volume of air is passed through the cathode for cooling purposes. s passed through the cathode for cooling purposes.

3.3. In combined cycle operation, electrical efficiencies arIn combined cycle operation, electrical efficiencies are in excess of 60%(HHV). The T of excess heat is hige in excess of 60%(HHV). The T of excess heat is high enough to yield high P steam→turbineh enough to yield high P steam→turbine

4.4. At the high operating T, MCFC could operate directlAt the high operating T, MCFC could operate directly on the gaseous HC fuels such as natural gas ←wouly on the gaseous HC fuels such as natural gas ←would be reformed to produce Hd be reformed to produce H22 within the fuel cell itself. within the fuel cell itself.

Page 67: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsMCFC Design and OperationMCFC Design and Operation

The high operating T characteristics of MCFC The high operating T characteristics of MCFC 4.4. At high operating temperature(1200 °F/650 At high operating temperature(1200 °F/650

°C), noble metal catalysts are not required.°C), noble metal catalysts are not required.5. 5. At high operating temperature(1200°F), the At high operating temperature(1200°F), the

salt mixture is liquid and is a good ionic salt mixture is liquid and is a good ionic conductor.conductor.

6.6. The cell performance is sensitive to operating The cell performance is sensitive to operating temperature.temperature.

a.a. A change in cell T from 1200°F to 1110°F A change in cell T from 1200°F to 1110°F results in a drop in voltage ~15%. ( ionic and ∵results in a drop in voltage ~15%. ( ionic and ∵electric resistance↑& electrode kinetics↓electric resistance↑& electrode kinetics↓

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5-3 Types of Fuel Cells5-3 Types of Fuel CellsMCFC Design and OperationMCFC Design and Operation

The high operating T characteristics of MCFC The high operating T characteristics of MCFC

7.7. The electrolyte boil-off has an insignificant The electrolyte boil-off has an insignificant impact on cell stack life.impact on cell stack life.

8.8. A more significant factor of life expectancy A more significant factor of life expectancy has to do with corrosion of the cathode.has to do with corrosion of the cathode.

Page 69: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsSolid Oxide fuel cellsSolid Oxide fuel cells

The introductions of the SOFCThe introductions of the SOFC

1. uses a ceramic, solid-phase electrolyte which reduces corrosion considerations and eliminates the electrolyte management problems associated with the liquid electrolyte fuel cells.

2. To achieve adequate ionic conductivity in such a ceramic→must operate at about 1830 °F (1000 °C).

3. 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.

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5-3 Types of Fuel Cells5-3 Types of Fuel CellsSOFC Design and OperationSOFC Design and Operation

The sketch of SOFC operationThe sketch of SOFC operation

Page 71: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

The SOFC reactionsThe SOFC reactions

Anode : HAnode : H2 2 + O+ O-2 -2 → H→ H22O + 2eO + 2e--

CO + OCO + O-2 -2 → CO→ CO2 2 ++ 2e2e--

CHCH4 4 + 4O+ 4O-2 -2 → 2H→ 2H22O + COO + CO2 2 + 8e+ 8e--

Cathode : OCathode : O2 2 + 4e+ 4e- - → 2O→ 2O-2-2

It is significant that the SOFC can use CO as its It is significant that the SOFC can use CO as its direct fuel.direct fuel.

5-3 Types of Fuel Cells5-3 Types of Fuel CellsSOFC Design and OperationSOFC Design and Operation

Page 72: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsSOFC Design and OperationSOFC Design and Operation

The components of the SOFCThe components of the SOFC

1.1. Electrolyte : solid ceramic.Electrolyte : solid ceramic.

a.a. Materials : dense yttria(Materials : dense yttria( 氧化釔氧化釔 )-stabilized zir)-stabilized zirconia(conia( 氧化鋯氧化鋯 )—an excellent conductor of ne)—an excellent conductor of negatively charged oxygen (oxide) at high T.gatively charged oxygen (oxide) at high T.

2.2. Anode : a porous nickel/zirconia cermetAnode : a porous nickel/zirconia cermet

3.3. Cathode : Sr-doped (Cathode : Sr-doped ( 鍶鍶 , strontium) lanthanu, strontium) lanthanum(m( 鑭鑭 ) manganite() manganite( 錳化物錳化物 ))

Page 73: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsSOFC Design and OperationSOFC Design and Operation

The components of the SOFCThe components of the SOFC– SOFC is a solid state device and shares certain proSOFC is a solid state device and shares certain pro

perties and fabrication techniques with semi-conduperties and fabrication techniques with semi-conductor devices.ctor devices.

– The Westinghouse cell design: the FC around a poThe Westinghouse cell design: the FC around a porous Zirconia support tube through which air is surous Zirconia support tube through which air is supplied to the cathode which is deposited on the outpplied to the cathode which is deposited on the outside of the tube. A layer of electrolyte is then deposide of the tube. A layer of electrolyte is then deposited on the outside of the cathode and finally a laysited on the outside of the cathode and finally a layer of anode is deposited over the electrolyte.er of anode is deposited over the electrolyte.

– A number of cells are connected together by high A number of cells are connected together by high T semiconductor contacts.T semiconductor contacts.

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5-3 Types of Fuel Cells5-3 Types of Fuel CellsSOFC Design and OperationSOFC Design and Operation

Page 75: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsSOFC Design and OperationSOFC Design and Operation

Page 76: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsSOFC Design and OperationSOFC Design and Operation

The components of the SOFCThe components of the SOFC– The anode consists of metallic Ni and YThe anode consists of metallic Ni and Y22OO33-stabliz-stabliz

ed ZrOed ZrO22 skeleton, which serves to inhibit sintering skeleton, which serves to inhibit sintering of the metal particles and to provide a thermal expof the metal particles and to provide a thermal expansion coefficient comparable to those of the other ansion coefficient comparable to those of the other fuel materials.fuel materials.

– The most common cathode material (a p-type condThe most common cathode material (a p-type conductor): Sr-doped (uctor): Sr-doped ( 鍶鍶 , strontium) lanthanum mang, strontium) lanthanum manganite (Lal-xSrxMnOanite (Lal-xSrxMnO33, x=0.10-0.15, x=0.10-0.15

– Both anode and cathode structures are fabricated wBoth anode and cathode structures are fabricated with a porosity of 20-40 % to facilitate mass transpoith a porosity of 20-40 % to facilitate mass transport of reactant and product gases.rt of reactant and product gases.

Page 77: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsSOFC Design and OperationSOFC Design and Operation

SOFC performance characteristicsSOFC performance characteristics

1.1. 0.6V/cell at about 232 A/ft0.6V/cell at about 232 A/ft22

2.2. Lifetimes are over 30000(hrs).Lifetimes are over 30000(hrs).

3.3. The efficiencies of unpressurized SOFCs : 45The efficiencies of unpressurized SOFCs : 45% (HHV)% (HHV)

4.4. The efficiencies of pressurized SOFCs : 60The efficiencies of pressurized SOFCs : 60% (HHV)% (HHV)

5.5. Bottoming cycle, using the high T waste heat, Bottoming cycle, using the high T waste heat, could add another few % to the fuel efficiency.could add another few % to the fuel efficiency.

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5-3 Types of Fuel Cells5-3 Types of Fuel CellsSOFC Design and OperationSOFC Design and Operation

temperature management—temperature management—

maintain proper volume of the air stream into maintain proper volume of the air stream into the cell.the cell.

Page 79: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsSOFC Design and OperationSOFC Design and Operation

high operating T characteristics of SOFCs high operating T characteristics of SOFCs 1.1. The SOFC operates at approximately 1830°F The SOFC operates at approximately 1830°F

(1000°C).(1000°C).2.2. The high operating temperature offers the possThe high operating temperature offers the poss

ibility of internal reforming.ibility of internal reforming.3.3. As in MCFCs, CO does not act as a poison anAs in MCFCs, CO does not act as a poison an

d can be used directly as a fuel.d can be used directly as a fuel.4.4. The SOFC can tolerant several orders of magnThe SOFC can tolerant several orders of magn

itude more sulfur than other fuel cells.itude more sulfur than other fuel cells.5.5. The SOFC requires a significant start-up time.The SOFC requires a significant start-up time.

Page 80: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-3 Types of Fuel Cells5-3 Types of Fuel CellsSOFC Design and OperationSOFC Design and Operation

high operating T characteristics of SOFCshigh operating T characteristics of SOFCs6.6. The cell performance is very sensitive to operati The cell performance is very sensitive to operati

ng T.ng T.a.a. A 10% drop in T → 12% drop in cell performA 10% drop in T → 12% drop in cell perform

ance due to the increase in internal resistance tance due to the increase in internal resistance to the flow of oxygen ions.o 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 transportatio→not for transportation applications.n applications.

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5-4 Fuel Cell Electrochemistry5-4 Fuel Cell ElectrochemistryInternal ReformingInternal Reforming

In a conventional fuel cell system, a In a conventional fuel cell system, a carbonaceous fuel is fed to a fuel processor carbonaceous fuel is fed to a fuel processor where it is steam reformed to produce Hwhere it is steam reformed to produce H2 2 (as (as

well as CO &COwell as CO &CO22).).

Ni reforming catalyst is extremely sensitive to Ni reforming catalyst is extremely sensitive to sulfur in the feed gas.sulfur in the feed gas.

Page 82: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-4 Fuel Cell Electrochemistry5-4 Fuel Cell ElectrochemistryInternal ReformingInternal Reforming

Internal reforming in MCFC & SOFC at high T→ Internal reforming in MCFC & SOFC at high T→ eliminate external fuel reformers →highly efficieneliminate external fuel reformers →highly efficient, simple, reliable and cost effectivet, simple, reliable and cost effective

2 alternative approaches to internal reforming:2 alternative approaches to internal reforming:– Indirect Internal reforming (IIR)Indirect Internal reforming (IIR)– Direct Internal reforming (DIR)Direct Internal reforming (DIR)

Methane and steam reforming reaction: Methane and steam reforming reaction: (750-900 (750-900 ooC)C) CHCH4 4 + H+ H22O → CO + 3HO → CO + 3H2 2 (endothermic, ΔH=53.8 (endothermic, ΔH=53.8

7 kcal/mol, favored by high T & low P, P< 5 atm)7 kcal/mol, favored by high T & low P, P< 5 atm)

Page 83: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-4 Fuel Cell Electrochemistry5-4 Fuel Cell ElectrochemistryInternal ReformingInternal Reforming

IIR: reformer section is separated, but adjacent tIIR: reformer section is separated, but adjacent to the anode. o the anode. – Advantage: 1.the exthermic heat of the cell can be usAdvantage: 1.the exthermic heat of the cell can be us

ed for ed for

the endothermic reforming reactionthe endothermic reforming reaction

2. reformer & cell environments don’t2. reformer & cell environments don’t

have a direct physical effect on eachhave a direct physical effect on each

otherother– Disadvantage: the conversion of methane to hydrogeDisadvantage: the conversion of methane to hydroge

n is not promoted as well as in the DIR. n is not promoted as well as in the DIR.

Page 84: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-4 Fuel Cell Electrochemistry5-4 Fuel Cell ElectrochemistryInternal ReformingInternal Reforming

DIR: hydrogen consumption reduces its partial DIR: hydrogen consumption reduces its partial pressure→driving the methane reforming reactipressure→driving the methane reforming reaction to the right.on to the right.

For MCFC, one developer’s approach where IIFor MCFC, one developer’s approach where IIR & DIR have been combined.R & DIR have been combined.

Page 85: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-4 Fuel Cell Electrochemistry5-4 Fuel Cell ElectrochemistryInternal ReformingInternal Reforming

A supported Ni catalyst (e.g. Ni supported on MgO or A supported Ni catalyst (e.g. Ni supported on MgO or LiAlOLiAlO22) provides sufficient catalytic activity to sustain ) provides sufficient catalytic activity to sustain the steam reforming reaction at 650 the steam reforming reaction at 650 ooC to produce suffiC to produce sufficient Hcient H2 2 ..

At open circuit, about 83% CHAt open circuit, about 83% CH44 →H →H22 (~equilibrium co (~equilibrium concentration at 650 ncentration at 650 ooC )C )

When current is drawn from the cell, HWhen current is drawn from the cell, H22 is consumed a is consumed and Hnd H22Ois produced → CHOis produced → CH44 conversion ↑ and approache conversion ↑ and approaches 100% at Hs 100% at H22 utilization > ~50% utilization > ~50%

↓ ↓

Thermal management and adjustment of HThermal management and adjustment of H22 utilization is i utilization is important to the internal reforming of MCFC stacksmportant to the internal reforming of MCFC stacks

Page 86: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-4 Fuel Cell Electrochemistry5-4 Fuel Cell ElectrochemistryInternal ReformingInternal Reforming

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

Page 87: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-4 5-4 Fuel Cell ElectrochemistryFuel Cell ElectrochemistryMCFCMCFC

The electrochemical reactions occurring in MCFCsThe electrochemical reactions occurring in MCFCs

1.1. Anode : HAnode : H2 2 + CO+ CO33-2 -2 → H→ H22O + COO + CO2 2 + 2e+ 2e--

2.2. Cathode : ½ OCathode : ½ O22 + CO + CO22 + 2e + 2e- - → CO→ CO33-2-2

3.3. Overall : HOverall : H2 2 + ½ O+ ½ O22 + CO + CO22 (cathode) → H (cathode) → H22O + COO + CO2 2

(anode) (anode)

4.4. The reversible potential equation : The reversible potential equation :

E = E° + RT/2F ln(PE = E° + RT/2F ln(PHH22PP1/21/2

OO22/P/PHH22OO)) + +

RT/2F ln(PRT/2F ln(PCOCO2,c2,c/P/PCOCO2,2,aa) ; F=96500 Columb/mol.) ; F=96500 Columb/mol.

Page 88: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-4 5-4 Fuel Cell ElectrochemistryFuel Cell ElectrochemistryMCFCMCFC

The electrochemical reactions occurring in MCFThe electrochemical reactions occurring in MCFCsCs

Transfer COTransfer CO22 from anode exit gas to the cathode inlet from anode exit gas to the cathode inlet

gas (COgas (CO22 transfer device) transfer device)

Produce COProduce CO22 by combustion of the anode exhaust gas by combustion of the anode exhaust gas

which is mixed with the cathode inlet gaswhich is mixed with the cathode inlet gas Supply COSupply CO22 from an alternate source. from an alternate source.

Page 89: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-4 5-4 Fuel Cell ElectrochemistryFuel Cell ElectrochemistrySOFCSOFC

The electrochemical reactions occurring in SOThe electrochemical reactions occurring in SOFCs (~1000 FCs (~1000 ooC)C)

1.1. Anode : HAnode : H2 2 + O+ O-2 -2 → H→ H22O + 2eO + 2e--

2.2. Cathode : ½ OCathode : ½ O22 + 2e + 2e-- → O → O-2-2

3.3. Overall : HOverall : H2 2 + ½ O+ ½ O22 → H → H22O O

4.4. The corresponding Nernst equation The corresponding Nernst equation

E = E° + RT/2F ln(PE = E° + RT/2F ln(PHH22PPOO22

1/21/2 /P/PHH22OO))

Page 90: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-5Advantages of Fuel Cells5-5Advantages of Fuel Cells:: Environmental AcceptabilityEnvironmental Acceptability

Because fuel cells are so efficient, COBecause fuel cells are so efficient, CO22 emissi emissi

ons are reduced for a given power output.ons are reduced for a given power output. By 2000, FC power plants will decrease COBy 2000, FC power plants will decrease CO22 e e

missions by 0.6 MMT of carbon equivalent.missions by 0.6 MMT of carbon equivalent. FC is quiet, emitting only 60 dBs at 100 ft.FC is quiet, emitting only 60 dBs at 100 ft. Emissions of SOEmissions of SOxx and NO and NOx x are 0.003 and 0.000are 0.003 and 0.000

4 pounds/megawatt-hour.4 pounds/megawatt-hour.

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5-5Advantages of Fuel Cells5-5Advantages of Fuel Cells:: EfficiencyEfficiency

Dependent on type and design, the fuel cells direct Dependent on type and design, the fuel cells direct electric energy efficiency ranges form 40 to 60 electric energy efficiency ranges form 40 to 60 percent (LHV). percent (LHV).

Characteristics :Characteristics :1.1. Operates at near constant efficiency, independent of Operates at near constant efficiency, independent of

size and load.size and load.2.2. Efficiency is not limited by the Carnot Cycle.Efficiency is not limited by the Carnot Cycle.3.3. For the fuel cells/gas turbine system, the efficiency For the fuel cells/gas turbine system, the efficiency

achieves 70 percent (LHV).achieves 70 percent (LHV).4.4. When by-product heat is utilized, the total efficiency When by-product heat is utilized, the total efficiency

of the fuel cell systems approach 85 percent.of the fuel cell systems approach 85 percent.

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5-5Advantages of Fuel Cells5-5Advantages of Fuel Cells:: Distributed CapacityDistributed Capacity

Distributed generation reduces the capital Distributed generation reduces the capital investment and improves the overall investment and improves the overall conversion efficiency of fuel to end use conversion efficiency of fuel to end use electricity by reducing transmission losses.electricity by reducing transmission losses.

1.1. Losses : presently 8-10 % of the generated Losses : presently 8-10 % of the generated electrical power is lost between the generating electrical power is lost between the generating station and the end user. station and the end user.

Many smaller units are statistically reliable, Many smaller units are statistically reliable, avoid failing at one time as in the case of one avoid failing at one time as in the case of one large generator.large generator.

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5-5Advantages of Fuel Cells5-5Advantages of Fuel Cells:: PermittingPermitting

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

Page 94: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-5Advantages of Fuel Cells5-5Advantages of Fuel Cells::ModularityModularity

The fuel cell is inherently modular. The fuel cell is inherently modular.

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

Page 95: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-5Advantages of Fuel Cells5-5Advantages of Fuel Cells:: Fuel FlexibilityFuel Flexibility

The primary fuel source for the fuel cell is The primary fuel source for the fuel cell is hydrogen, which can be obtained from :hydrogen, which can be obtained from :

1.1. Natural gasNatural gas2.2. Coal gasCoal gas3.3. Methanol Methanol 4.4. Landfill gasLandfill gas5.5. Other fuels containing hydrocarbons.Other fuels containing hydrocarbons. Advantage of fuel flexibilityAdvantage of fuel flexibility1.1. The power generation can be assured even The power generation can be assured even

when a primary fuel source unavailable.when a primary fuel source unavailable.

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5-5Advantages of Fuel Cells5-5Advantages of Fuel Cells::Cogeneration CapabilityCogeneration Capability

High-quality heat is available for cogeneration, High-quality heat is available for cogeneration, heating, and cooling.heating, and cooling.

Fuel cell exhaust heat is suitable for use in Fuel cell exhaust heat is suitable for use in residential, commercial, and industrial residential, commercial, and industrial cogeneration applications.cogeneration applications.

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5-6Applications of Fuel Cells5-6Applications of Fuel CellsIntroduction Introduction

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

Page 98: Fuel Cell Introduction Introduction Historical Notes Historical Notes Types of Fuel Cells Types of Fuel Cells Fuel Cell Electrochemistry Fuel Cell Electrochemistry

5-6Applications of Fuel Cells5-6Applications of Fuel CellsCars, Trucks, and BusesCars, Trucks, and Buses

Most vehicles today rely on an internal Most vehicles today rely on an internal combustion engine (ICE). combustion engine (ICE).

Electric motors are much more suitableElectric motors are much more suitable

1.1. They deliver their maximum torque at low They deliver their maximum torque at low rpm, just when a vehicle needs it most. rpm, just when a vehicle needs it most.

2.2. A driver heads downhill or puts on the brakes, A driver heads downhill or puts on the brakes, an electric motor can double as a generator to an electric motor can double as a generator to recapture that energy and covert it back to recapture that energy and covert it back to electricity for subsequent use. electricity for subsequent use.

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5-6Applications of Fuel Cells5-6Applications of Fuel CellsCars, Trucks, and BusesCars, Trucks, and Buses

The choke point of electric motor The choke point of electric motor

1.1. The short range and tedious recharging of the The short range and tedious recharging of the 1st generation1st generation

A fuel cell powers the vehicle's electric motorA fuel cell powers the vehicle's electric motor

1.1. These problems can be overcome. A hydrogen These problems can be overcome. A hydrogen tank can be refueled in about five minutes.tank can be refueled in about five minutes.

2.2. It has a similar range to a conventional It has a similar range to a conventional automobile. automobile.

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5-6Applications of Fuel Cells5-6Applications of Fuel CellsBusinesses and HomesBusinesses and Homes

The reasons of fuel cells are attractive in stationary The reasons of fuel cells are attractive in stationary applications applications

1.1. They deliver unparalleled fuel efficiencies, especially They deliver unparalleled fuel efficiencies, especially in Combined Heat & Power (CHP) applications.in Combined Heat & Power (CHP) applications.

2.2. Fuel cells offer a new level of reliability : Fuel cells offer a new level of reliability :

a.a. If a blackout occurs, they will keep essential If a blackout occurs, they will keep essential mechanical components and external landmark mechanical components and external landmark signage online. signage online.

Fuel cells offer highly reliable, high-quality Fuel cells offer highly reliable, high-quality electricity. electricity.

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5-6Applications of Fuel Cells5-6Applications of Fuel CellsLaptops, Cell Phones, and other ElectronicsLaptops, Cell Phones, and other Electronics

Fuel cells will find their first widespread use in Fuel cells will find their first widespread use in portable electronicsportable electronics

1.1. These "micro fuel cells" offer far higher These "micro fuel cells" offer far higher energy densities than those of comparably energy densities than those of comparably sized batteries. The typical laptop can operate sized batteries. The typical laptop can operate unplugged for ten hours or more. unplugged for ten hours or more.

2.2. Micro fuel cells also offer the added appeal of Micro fuel cells also offer the added appeal of eliminating the need for battery chargers and eliminating the need for battery chargers and AC adapters, as they require refueling instead AC adapters, as they require refueling instead of recharging. of recharging.

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5-7 5-7 Advanced Hydrogen Production TecAdvanced Hydrogen Production Technologieshnologies Introduction Introduction

1.1. Hydrogen is a clean, sustainable resource with many Hydrogen is a clean, sustainable resource with many potential applications. potential applications.

2.2. Hydrogen is now produced primary by steam reformiHydrogen is now produced primary by steam reforming of natural gas.ng of natural gas.

3.3. For applications requiring extremely pure HFor applications requiring extremely pure H22→electr→electr

olysis, a relatively expensive processolysis, a relatively expensive process

4.4. Three process of producing hydrogen : photobiologicThree process of producing hydrogen : photobiological, photoelectrochemical, thermochemical. al, photoelectrochemical, thermochemical.

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5-7 5-7 Advanced Hydrogen Production TecAdvanced Hydrogen Production Technologieshnologies Introduction Introduction

Photobiological & photoelectrochemical procPhotobiological & photoelectrochemical processes uses sunlight to split water into Hesses uses sunlight to split water into H22 and O and O22

Thermochemical processes, including gasificatThermochemical processes, including gasification and pyrolysis systems, use heat to produce ion and pyrolysis systems, use heat to produce HH22 from sources such as biomass and solid wa from sources such as biomass and solid wa

ste.ste.

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PHOTOBIOLOGICAL PRODUCTIONPHOTOBIOLOGICAL PRODUCTION1.1. Most photobiological system use the natural aMost photobiological system use the natural a

ctivity of bacteria and green algae to produce ctivity of bacteria and green algae to produce hydrogen. (chlorophyll absorbs sunlight and ehydrogen. (chlorophyll absorbs sunlight and enzymes use energy to dissociate Hnzymes use energy to dissociate H22 from H from H22O)O)

2.2. Two significant limitations :Two significant limitations :a.a. Low solar convertion efficiencies.(5~6% of suLow solar convertion efficiencies.(5~6% of su

n’s energy to Hn’s energy to H22 energy) energy)

b.b. Nearly all enzymes are inhibited in their hydroNearly all enzymes are inhibited in their hydrogen production by presence of oxygen. gen production by presence of oxygen.

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PHOTOBIOLOGICAL PRODUCTIONPHOTOBIOLOGICAL PRODUCTION

3.3. The way to overcome oxygen intolerance and increase The way to overcome oxygen intolerance and increase conversion efficiencies :conversion efficiencies :

a.a. A new green algae strains: the Chlamydomonas (A new green algae strains: the Chlamydomonas ( 單單胞藻胞藻 ) strain → has H) strain → has H22-evolving enzymes more tolera-evolving enzymes more tolera

nt of Ont of O22 extracted from strains of bacteria → produce extracted from strains of bacteria → produce

HH22 and O and O22 simultaneously. 10% efficiency simultaneously. 10% efficiency

b.b. Cell-free processes : theoretical efficiency approach 2Cell-free processes : theoretical efficiency approach 25%5%

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PHOTOBIOLOGICAL PRODUCTIONPHOTOBIOLOGICAL PRODUCTION

Cell-free processes : Cell-free processes :

c. In a cell-free system : both Oc. In a cell-free system : both O22-evolving & H-evolving & H22--

evolving enzymes are immobilized onto evolving enzymes are immobilized onto opposite sides of a solid, conducting surface.opposite sides of a solid, conducting surface.

d. Light is used by one enzyme to oxidize water, d. Light is used by one enzyme to oxidize water, creating a flow of electrons to the other creating a flow of electrons to the other enzymes, where Henzymes, where H2 2 is produced. is produced.

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PHOTOBIOLOGICAL PRODUCTIONPHOTOBIOLOGICAL PRODUCTION

Genetic forms of Chlamydomonas : Genetic forms of Chlamydomonas :

20% efficiency20% efficiency

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PRODUTION BY PHOTOELECTRO-CHEMPRODUTION BY PHOTOELECTRO-CHEMICAL (PEC) TECHNOLOGY ICAL (PEC) TECHNOLOGY

1.1. PEC production uses semiconductor technologPEC production uses semiconductor technology in one-step process of splitting water directly y in one-step process of splitting water directly upon sunlight illumination.upon sunlight illumination.

2.2. A PEC system : A PEC system :

a.a. a photovoltaic cell → produce electric current a photovoltaic cell → produce electric current when exposed to lightwhen exposed to light

b.b. Electrolyzer Electrolyzer

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PRODUTION BY PHOTOELECTRO-PRODUTION BY PHOTOELECTRO-CHEMICAL (PEC) TECHNOLOGY CHEMICAL (PEC) TECHNOLOGY

3.3. Advantage : producing low-cost renewable Advantage : producing low-cost renewable hydrogen.hydrogen.

4.4. The two limited factor of an efficient and cost-The two limited factor of an efficient and cost-effective PEC system :effective PEC system :

a.a. The high voltage required to dissociate water.The high voltage required to dissociate water.

b.b. The corrosiveness of aqueous electrolytes.The corrosiveness of aqueous electrolytes.

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PRODUTION BY PHOTOELECTRO-CHEMICAL PRODUTION BY PHOTOELECTRO-CHEMICAL (PEC) TECHNOLOGY (PEC) TECHNOLOGY

5.5. The way to overcome limitsThe way to overcome limits : : a.a. The structure → the multijunction device > 1.6 eVThe structure → the multijunction device > 1.6 eVb.b. Material : Material :

1.1. Gallium based (GalnPGallium based (GalnP22, GaAs) → provide higher volt, GaAs) → provide higher voltages requires for electrolysis and have relatively high ages requires for electrolysis and have relatively high solar efficiency; efficiency is more than 25 % , but is solar efficiency; efficiency is more than 25 % , but is expensive.expensive.

2.2. Amorphous silicon → efficiency is more than 13 % , Amorphous silicon → efficiency is more than 13 % , but cost is low.but cost is low.

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PRODUTION BY PHOTOELECTRO-CHEMPRODUTION BY PHOTOELECTRO-CHEMICAL (PEC) TECHNOLOGY ICAL (PEC) TECHNOLOGY

4.4. The sketch of a multijunction device The sketch of a multijunction device

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THERMOCHEMICAL PRODUCTIONTHERMOCHEMICAL PRODUCTION

1.1. Gasification and pyrolysis : using heat to produce a vGasification and pyrolysis : using heat to produce a vapor from which hydrogen can be derived use a convapor from which hydrogen can be derived use a conventional steam reforming process.entional steam reforming process.

2.2. Pyrolysis : Pyrolysis :

Biomass—wood, grasses, and agricultural and municiBiomass—wood, grasses, and agricultural and municipal waste, is broken down into highly reactive vaporpal waste, is broken down into highly reactive vapors and carbonaceous residue, or char.s and carbonaceous residue, or char.

a.a. The vapors, when condensed into pyrolysis oil, can bThe vapors, when condensed into pyrolysis oil, can be steam reformed to produce hydrogen.e steam reformed to produce hydrogen.

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THERMOCHEMICAL PRODUCTIONTHERMOCHEMICAL PRODUCTION

b.b. A typical biomass feedstock produces ~ 65% oils and A typical biomass feedstock produces ~ 65% oils and 8% char by wt. with the remainder consisting of wate8% char by wt. with the remainder consisting of water and gas.r and gas.

c.c. The char is burn to provide the required heat for the pThe char is burn to provide the required heat for the pyrolysis reaction.yrolysis reaction.

d.d. A fast-pyrolysis reactor is directly linked to a steam rA fast-pyrolysis reactor is directly linked to a steam reformer.(12%~17% hydrogen by weight of dry biomeformer.(12%~17% hydrogen by weight of dry biomass)ass)

e.e. Advantage : the lowest-cost production method, but it Advantage : the lowest-cost production method, but it needs to identifying optimum reformer catalysts. needs to identifying optimum reformer catalysts.

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THERMOCHEMICAL PRODUCTIONTHERMOCHEMICAL PRODUCTION

3.3. Gasification of municipal solid waste (MSW) : Gasification of municipal solid waste (MSW) :

a.a. It is low-cost, sustainable source of hydrogen It is low-cost, sustainable source of hydrogen production.production.

b.b. MSW, on average, consists of about 70% by MSW, on average, consists of about 70% by weight of biomass material.weight of biomass material.

c.c. Gasification results in an easily cleaned fuel Gasification results in an easily cleaned fuel gas from which hydrogen can be reformed.gas from which hydrogen can be reformed.

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THERMOCHEMICAL PRODUCTIONTHERMOCHEMICAL PRODUCTION

4.4. The Texaco’s high-temperature gasification :The Texaco’s high-temperature gasification :

a.a. Result in a high yield of hydrogen and Result in a high yield of hydrogen and produces a non-hazardous, glass-like ash produces a non-hazardous, glass-like ash byproduct.byproduct.

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5-8Advantages Hydrogen Transport 5-8Advantages Hydrogen Transport and Storage Technologiesand Storage Technologies

INTRODUCTIONINTRODUCTION1.1. The future use of hydrogen will require the The future use of hydrogen will require the

creation of a distribution infrastructure of safe creation of a distribution infrastructure of safe and cost-effective transport and storage.and cost-effective transport and storage.

2.2. Different applications need different types of Different applications need different types of storage technology : storage technology : Stationary storage : utility electricity Stationary storage : utility electricity generation; energy efficient and cost are generation; energy efficient and cost are important important Mobile storage : fueling a vehicle; size and Mobile storage : fueling a vehicle; size and weight are importantweight are important

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INTRODUCTION INTRODUCTION

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

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PHYSICAL STORAGE SYSTEMPHYSICAL STORAGE SYSTEM

1.1. Physical states are commercially available and Physical states are commercially available and currently in use.currently in use.

2.2. Hydrogen is generally in form of compressed Hydrogen is generally in form of compressed gas or cryogenic liquid, referred to as physical gas or cryogenic liquid, referred to as physical storage.storage.

3.3. Focusing on increasing the energy content per Focusing on increasing the energy content per unit of volume or weight of hydrogen storage unit of volume or weight of hydrogen storage system.system.

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PHYSICAL STORAGE SYSTEMPHYSICAL STORAGE SYSTEM

4.4. Hydrogen gas is currently stored at high prHydrogen gas is currently stored at high pressures of 14~17 MPa.essures of 14~17 MPa.

5.5. New graphite composite material has potential New graphite composite material has potential for storing hydrogen at pressure up to 41 Mpa.for storing hydrogen at pressure up to 41 Mpa.

6.6. These materials may make it possible for hydrThese materials may make it possible for hydrogen gas to be a cost-effective fuel.ogen gas to be a cost-effective fuel.

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5-8Advantages Hydrogen Transport 5-8Advantages Hydrogen Transport and Storage Technologiesand Storage Technologies

One Possible Future Hydrogen Infrastructure One Possible Future Hydrogen Infrastructure

1.1. Distributing HDistributing H22 fuel in the form of compressed gas is fuel in the form of compressed gas is a potential growth market for zero emission vehicles. a potential growth market for zero emission vehicles.

2.2. Fleet refueling stations would supplied by truck with Fleet refueling stations would supplied by truck with liquid Hliquid H22 from existing plants. from existing plants.

3.3. As demand increased, small dedicated pipeline As demand increased, small dedicated pipeline systems would be built to provide gaseous Hsystems would be built to provide gaseous H22 from from new centralized reforming plants. new centralized reforming plants.

4.4. A pipeline serving 80,000 fuel-cell carsA pipeline serving 80,000 fuel-cell cars5.5. Deliver hydrogen gas at about $13 per gigajoule, the Deliver hydrogen gas at about $13 per gigajoule, the

energy equivalent of about $0.45 per liter of gasoline.energy equivalent of about $0.45 per liter of gasoline.

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5-8Advantages Hydrogen Transport 5-8Advantages Hydrogen Transport and Storage Technologiesand Storage Technologies

SOLID-STATE STORAGE METHODSOLID-STATE STORAGE METHOD

1.1. Solid-state transport and storage technologies are safeSolid-state transport and storage technologies are safer and have the potential to be more efficient than gas r and have the potential to be more efficient than gas or liquid storage. or liquid storage.

2.2. Refers to chemical or physical binding of HRefers to chemical or physical binding of H2 2 to a solito a soli

d material.d material.

3.3. Research stage→needs to improve the volumetric deResearch stage→needs to improve the volumetric density or the gravimetric density.nsity or the gravimetric density.

4.4. The most promising solid-state technologies are metaThe most promising solid-state technologies are metal hydrides, gas-on-solids adsorption system, and glass l hydrides, gas-on-solids adsorption system, and glass microspheres.microspheres.

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5-8Advantages Hydrogen Transport 5-8Advantages Hydrogen Transport and Storage Technologiesand Storage Technologies

METAL HYDRIDES—release HMETAL HYDRIDES—release H2 2 by dehydridby dehydridee

1.1. Advantages : high volumetric density, safety, Advantages : high volumetric density, safety, and the ability to deliver pure hydrogen at conand the ability to deliver pure hydrogen at constant pressure.stant pressure.

2.2. Disadvantages : low gravimetric density, exprDisadvantages : low gravimetric density, expressed as hydrogen as a percent of total hydride essed as hydrogen as a percent of total hydride weight (wt%)weight (wt%)

3.3. They are suitable for stationary storage, but liThey are suitable for stationary storage, but limited for use in vehicles.mited for use in vehicles.

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METAL HYDRIDESMETAL HYDRIDES

4.4. The work of future : develop hydrides with The work of future : develop hydrides with higher gravimetric densities that can operate higher gravimetric densities that can operate under temperatures and pressures consistent under temperatures and pressures consistent with mobile storage. with mobile storage.

5.5. The more promising hydride technologies : The more promising hydride technologies : improved metal alloys, high-efficiency metal improved metal alloys, high-efficiency metal hydrides, non-classical metal hydride hydrides, non-classical metal hydride complexes. complexes.

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Improved Metal AlloysImproved Metal Alloys

1.1. Capacities : 2.5 wt% ~ 6.2 wt% depending on Capacities : 2.5 wt% ~ 6.2 wt% depending on the composition.the composition.

2.2. Thin film alloys of magnesium-aluminum-Thin film alloys of magnesium-aluminum-nickel-titanium have exhibited improved nickel-titanium have exhibited improved gravimetric and volumetric energy densities.gravimetric and volumetric energy densities.

3.3. Efforts are being made to scale up production Efforts are being made to scale up production of these alloys.of these alloys.

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High-Efficient Metal HydridesHigh-Efficient Metal Hydrides1.1. Metal hydrides that dehydride hydrogen at verMetal hydrides that dehydride hydrogen at ver

y high temperatures offer greater storage efficiy high temperatures offer greater storage efficiency at less cost than lower temperature hydriency at less cost than lower temperature hydrides under development. des under development.

2.2. They are suitable to use on stationary storage, They are suitable to use on stationary storage, but not available in mobile system.but not available in mobile system.

3.3. A phase change material can be used to retain A phase change material can be used to retain hydriding energy as heat of fusion and then rethydriding energy as heat of fusion and then return the heat for the dehydriding process.urn the heat for the dehydriding process.

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High-Efficient Metal HydridesHigh-Efficient Metal Hydrides

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

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Nonclassical Metal Hydride Complexes Nonclassical Metal Hydride Complexes 1.1. Nonclassical polyhydride metal complexes (PNonclassical polyhydride metal complexes (P

MCs) may overcome the weight density problMCs) may overcome the weight density problem of hydride storage system.em of hydride storage system.

2.2. Classical PMCs : they have high gravimetric dClassical PMCs : they have high gravimetric density, but generally undergo irreversible dihyensity, but generally undergo irreversible dihydrogen elimination.drogen elimination.

3.3. Nonclassical PMCs : they are allowing a compNonclassical PMCs : they are allowing a complete release of hydrogen under mild condition lete release of hydrogen under mild condition and without high vacuum. and without high vacuum.

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GAS-ON-SOLID ADSORPTIONGAS-ON-SOLID ADSORPTION

1.1. The principle of storage : the ability of high-The principle of storage : the ability of high-surface-area carbons, when chemically surface-area carbons, when chemically activated, to retain hydrogen on their surfaces.activated, to retain hydrogen on their surfaces.

2.2. The action of above is called adsorption, and it The action of above is called adsorption, and it happens at relatively high pressures and happens at relatively high pressures and extremely cold temperatures. extremely cold temperatures.

3.3. Hydrogen is released at atmospheric pressure Hydrogen is released at atmospheric pressure and ambient temperature. and ambient temperature.

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GAS-ON-SOLID ADSORPTIONGAS-ON-SOLID ADSORPTION4.4. The storage capacity of microcrystalline curreThe storage capacity of microcrystalline curre

ntly : 4.8 wt% hydrogen at 87°K and 6Mpa.ntly : 4.8 wt% hydrogen at 87°K and 6Mpa.5.5. The bar of storage capacity : relatively low volThe bar of storage capacity : relatively low vol

umetric and gravimetric densities; the cryogenumetric and gravimetric densities; the cryogenic temperature required; high cost of the proceic temperature required; high cost of the process.ss.

6.6. Two technologies that may increase the potentTwo technologies that may increase the potential for this storage medium : carbon nanotubulial for this storage medium : carbon nanotubules and carbon aerogels.es and carbon aerogels.

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Carbon Nanotubules Carbon Nanotubules

1.1. A new form of high-surface carbon material.A new form of high-surface carbon material.

2.2. It has the potential for substantially increase thIt has the potential for substantially increase the volumetric and gravimetric densities.e volumetric and gravimetric densities.

3.3. It contains microscopic pores of uniform size tIt contains microscopic pores of uniform size that encourage micro-capillary filling by hydrohat encourage micro-capillary filling by hydrogen condensation.gen condensation.

4.4. It lets hydrogen gas condense into a liquid statIt lets hydrogen gas condense into a liquid state at relatively high temperature.e at relatively high temperature.

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Carbon NanotubulesCarbon Nanotubules

5.5. Preliminary results on nanotubule-containing sPreliminary results on nanotubule-containing samples : 8.4 wt% hydrogen at 82°K and 0.07amples : 8.4 wt% hydrogen at 82°K and 0.07Mpa.Mpa.

6.6. The direction of work in future : improve the qThe direction of work in future : improve the quantity of hydrogen stored at near-ambient teuantity of hydrogen stored at near-ambient temperature.mperature.

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Carbon NanotubulesCarbon Nanotubules

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Carbon AerogelsCarbon Aerogels

1.1. A special class of open-cell foams with an ultrA special class of open-cell foams with an ultra-fine cell/pore size, high surface area, and a sa-fine cell/pore size, high surface area, and a solid matrix.olid matrix.

2.2. The process of creating carbon aerogels : be usThe process of creating carbon aerogels : be usually synthesized from the aqueous polycondeually synthesized from the aqueous polycondensation of resorcinol(nsation of resorcinol( 間苯二酚間苯二酚 ,, 雷瑣辛雷瑣辛 ) wi) with formaldehyde (th formaldehyde ( 甲醛甲醛 ), followed by supercri), followed by supercritical extraction and pyrolysis-at about 1050 -℃tical extraction and pyrolysis-at about 1050 -℃in an inert atmosphere.in an inert atmosphere.

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Carbon AerogelsCarbon Aerogels

3.3. Synthesized aerogels have a nanocrystalline stSynthesized aerogels have a nanocrystalline structure with micro-pores less than 2 nanometeructure with micro-pores less than 2 nanometer in diameter.r in diameter.

4.4. Results on the aerogels-containing sample : 3.Results on the aerogels-containing sample : 3.7 wt% hydrogen at 8.3MPa.7 wt% hydrogen at 8.3MPa.

5.5. The direction of work in future : improve maxiThe direction of work in future : improve maximum hydrogen adsorption over a wide range omum hydrogen adsorption over a wide range of temperatures and pressures.f temperatures and pressures.

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GLASS MICROSPHERESGLASS MICROSPHERES

1.1. These glass spherical structures : diameters of These glass spherical structures : diameters of 25 to 500 microns and wall thickness of 25 to 500 microns and wall thickness of approximately 1 micron.approximately 1 micron.

2.2. The process of storing hydrogen : at 200 to ℃The process of storing hydrogen : at 200 to ℃400 , the increased permeability of the glass ℃400 , the increased permeability of the glass ℃permits the spheres to be filled by hydrogen permits the spheres to be filled by hydrogen under pressure by immersion in high-pressure under pressure by immersion in high-pressure hydrogen gas, when cooled to ambient hydrogen gas, when cooled to ambient temperature, the hydrogen is locked.temperature, the hydrogen is locked.

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GLASS MICROSPHERESGLASS MICROSPHERES

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GLASS MICROSPHERESGLASS MICROSPHERES

3.3. Subsequent raising of the temperature will Subsequent raising of the temperature will release the hydrogen.release the hydrogen.

4.4. Spheres synthesized are defect-free and have a Spheres synthesized are defect-free and have a membrane tensile stress at failure of about membrane tensile stress at failure of about 1000MPa, yielding a burst pressure three 1000MPa, yielding a burst pressure three times as great as commercially-produced times as great as commercially-produced spheres.spheres.

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5-8Advantages Hydrogen Transport 5-8Advantages Hydrogen Transport and Storage Technologiesand Storage Technologies

GLASS MICROSPHERESGLASS MICROSPHERES

5.5. A small bed of such microspheres can contain A small bed of such microspheres can contain hydrogen : mass fraction 10% at about hydrogen : mass fraction 10% at about 62MPa.62MPa.

6.6. In test, 95% of a microsphere has been filled In test, 95% of a microsphere has been filled or release in about 15 minutes at 370 .℃or release in about 15 minutes at 370 .℃