Benefits and Obstacles to the Success of FCs and the Development of a Hydrogen-Based Economy

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Benefits and Obstacles

to the Success of FCs and the Development of a Hydrogen-

Based Economy

Fuel Cell Fuel Cell

Chapter 5 Fuel Cell Chapter 5 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

5-1 Introduction5-1 IntroductionWhat 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.

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

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

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

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“I cannot but regard the experiment as an important one…”

William Grove writing to Michael Faraday, October 22, 1842

Sir William Grove (1811-1896)

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.

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 oxygen cell using a less corrosive alkaline electrolyte and inexpensive nickel electrodes. electrolyte and inexpensive nickel electrodes.

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In the 1950s Bacon successfully produced the In the 1950s Bacon successfully produced the first practical (alkaline) FC. first practical (alkaline) FC.

Francis T. Bacon

(1904-1992)


Until 1959, Bacon and his coworkers were able Until 1959, Bacon and his coworkers were able to demonstrate a practical five-kilowatt system to demonstrate a practical five-kilowatt system capable of powering a welding machine. capable 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 Allis-Chalmers Manufacturing Company demonstrated his famous 20-horsepower fuel demonstrated his famous 20-horsepower fuel cell-powered tractor.cell-powered tractor.


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.

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In the 1960s, NASA demonstrated some of In the 1960s, NASA demonstrated some of their potential applications in providing their potential applications in providing power during space flight.power during space flight.


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.


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.


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!!

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Then industry began to recognize the Then industry began to recognize the commercial potential of fuel cells.commercial potential of fuel cells.

But, due to But, due to technical barrierstechnical barriers and high and high investment costsinvestment costs, fuel cells were not , fuel cells were not economically competitive with existing economically competitive with existing energy technologies.energy technologies.

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Not anymore so!Not anymore so!

Polymer Electrolyte MembranePolymer Electrolyte Membrane Fuel Cells Fuel Cells (PEMFCs; or (PEMFCs; or Proton Exchange MembraneProton Exchange Membrane FCs) have become a ‘mature’ technology.FCs) have become a ‘mature’ technology.

Well, there still is much work that needs to be done to optimize the FC Well, there still is much work that needs to be done to optimize the FC system. system.

But hey, the gasoline IC engine is nearly 120 years old and still being But hey, the gasoline IC engine is nearly 120 years old and still being improved.improved.

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TransportationTransportation

The The California Low Emission Vehicle California Low Emission Vehicle ProgramProgram requires that beginning in 2003, requires that beginning in 2003, 10% of passenger cars delivered for sale in 10% of passenger cars delivered for sale in CA from medium or large sized CA from medium or large sized manufactures must be manufactures must be Zero Emission Zero Emission Vehicles Vehicles ((ZEVsZEVs))..


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Honda FCXHonda FCX

First fuel cell vehicle in the world to receive government certification (American Honda Motor Co., Inc., 7/24/2002).

Honda FCX specifications

Vehicle Length: 4165 mmWidth: 1760 mmHeight: 1645 mmMaximum Speed: 93 mph (150km/h)Driving Range: 220 miles (355km)Seating Capacity: 4 adults

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Motor Maximum Power Output: 80hp (60kW)Maximum Drive Torque: 201lb-ft (272Nm)Motor Type: AC synchronous Fuel Cell Stack Stack Type:PEFC (proton exchange membrane type - Ballard)Power Output:78kW

Power storage Honda Ultra Capacitor Fuel Type: Compressed gaseous hydrogenStorage Method: High-pressure hydrogen storage tank (5,000 psi)Fuel Capacity: 156.6 liter

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NECAR 5NECAR 5

2001 prototype FC automobile by 2001 prototype FC automobile by DaimlerChrysler.DaimlerChrysler.

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Drives and feels like a “normal” car.Drives and feels like a “normal” car. Top speed > 150 km/hr, with a power Top speed > 150 km/hr, with a power

output 0f 75 kW (100 hp).output 0f 75 kW (100 hp). Combines the Combines the low emission levelslow emission levels, the , the

quietnessquietness and the and the smoothnesssmoothness associated associated with EVs, while delivering a performance with EVs, while delivering a performance similar to that of an automobile with an IC similar to that of an automobile with an IC engine.engine.

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Fuel Cell BusFuel Cell Bus

In March 1998, Chicago became the first city in the world to put pollution-free, hydrogen fuel cell powered buses in their public transit system.

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• The PEM fuel cells were provided by The PEM fuel cells were provided by Ballard Power Systems. Ballard Power Systems.

• Air Products & Chemicals supplies the Air Products & Chemicals supplies the liquid hydrogenliquid hydrogen, which is converted to , which is converted to gas for bus use.gas for bus use.

• The The pilot programpilot program began in December began in December 1997 at the Chicago Transit Authority, 1997 at the Chicago Transit Authority, which will receive royalties for every bus which will receive royalties for every bus sold by Ballard, up to US$4 million. sold by Ballard, up to US$4 million.

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Fuel Cells, Prof. T.-S. Yang, NCKU/ME

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Back


Fuel Cells, Prof. T.-S. Yang, NCKU/ME

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Distributed Power GenerationDistributed Power Generation

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Other ApplicationsOther Applications

The world’s first prototype polymer electrolyte membrane fuel cell (on the right) used to provide all residential power needs for a home in Latham, New York. This 7 kW unit is attached to a power conditioner/storage unit that stores excess electricity. (Plug Power)

A laptop computer using a fuel cell power source can operate for up to 20 hours on a single charge of fuel. (Ballard Power Systems)

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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 5-3 Types 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.

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


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..


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


Fuel Cell CharacteristicsFuel Cell Characteristics



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


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


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

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

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


The components of PAFC The components of PAFC

1.1. Electrolyte : liquid of acidElectrolyte : liquid of acid

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


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.


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


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.


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.


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.


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)

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.

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

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

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

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


The sketch of PEMFC operationThe sketch of PEMFC operation

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

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The PEMFC StackThe PEMFC Stack

Energy Partners

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Effective commercial electric motors Effective commercial electric motors typically operate at 200-300 volts.typically operate at 200-300 volts.

Connect individual FCs in series to form a Connect individual FCs in series to form a FC stack that provides the required high FC stack that provides the required high voltage.voltage.

To decrease the overall volume and weight To decrease the overall volume and weight of the stack, use “bipolar plates.”of the stack, use “bipolar plates.”


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.


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.


The features of the electrolyteThe features of the electrolyte

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

2.2. The acid molecules are fixed to the polymer, The acid molecules are fixed to the polymer, but the protons on these acid groups are free to but 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.

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PEMPEM

Nafion resembles the plastic wrap used for sealing foods. (But thicker: 50 to 175 microns, i.e., 2 to 7 pieces of paper.)


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).


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.

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In an operating FC, the membrane is well In an operating FC, the membrane is well humidified, so that the electrolyte looks like humidified, so that the electrolyte looks like a moist piece of thick plastic wrap.a moist piece of thick plastic wrap.

PEMs are somewhat unusual electrolytes in PEMs are somewhat unusual electrolytes in that, in the presence of water, the negative that, in the presence of water, the negative ions are rigidly held within their structure. ions are rigidly held within their structure.

Only the positive ions (here the HOnly the positive ions (here the H++ ions, or ions, or protons) are free to carry positive charge protons) are free to carry positive charge through the membrane.through the membrane.

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PEMFCs are limited by the temperature PEMFCs are limited by the temperature range over which water is liquid. range over which water is liquid.

Operating PEMFCs at temperatures Operating PEMFCs at temperatures exceeding 100exceeding 100C is possible under C is possible under pressurized conditions, but that shortens the pressurized conditions, but that shortens the life of the cell.life of the cell.

Currently, PEMs cost about US$100 per Currently, PEMs cost about US$100 per square foot. square foot.

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Remaining ChallengesRemaining Challenges

producing membranes not limited by the producing membranes not limited by the temperature range of liquid water, possibly temperature range of liquid water, possibly based on another mechanism of protonic based on another mechanism of protonic conductionconduction

reducing membrane cost by developing reducing membrane cost by developing different membrane chemistriesdifferent membrane chemistries

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The Backing LayerThe Backing Layer

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Designed to maximize the current that can Designed to maximize the current that can be obtained from a MEA.be obtained from a MEA.

Usually made of a Usually made of a porousporous carbon paper or carbon paper or carbon cloth, typically 100 to 300 microns carbon cloth, typically 100 to 300 microns thick (4 to 12 sheets of paper).thick (4 to 12 sheets of paper).

The backing layers have to be made of a The backing layers have to be made of a material, such as carbon, that can conduct material, such as carbon, that can conduct the electrons exiting the anode and entering the electrons exiting the anode and entering the cathode.the cathode.

Also, they are often wet-proofed with Also, they are often wet-proofed with Teflon. Teflon.

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Being Porous Being Porous

ensures effective diffusion of each reactant ensures effective diffusion of each reactant gas to the catalyst on the MEAgas to the catalyst on the MEA

allows the gas to spread out as it diffuses, allows the gas to spread out as it diffuses, so that when it penetrates the backing, the so that when it penetrates the backing, the gas will be in contact with the entire surface gas will be in contact with the entire surface area of the catalyzed membrane. area of the catalyzed membrane.

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Also…..Also….. The backing layers assist in water The backing layers assist in water

management during FC operation.management during FC operation. The correct backing material allows the The correct backing material allows the

right amount of water vapor to reach the right amount of water vapor to reach the MEA to keep the membrane humidified.MEA to keep the membrane humidified.

The backing material also allows the liquid The backing material also allows the liquid water produced at the cathode to leave the water produced at the cathode to leave the cell so it doesn’t flood. cell so it doesn’t flood.

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The ElectrodesThe Electrodes

Expensive Pt based Expensive Pt based catalysts seem to be the catalysts seem to be the only catalysts capable of only catalysts capable of generating high rates of Ogenerating high rates of O2 2

reduction at the relatively reduction at the relatively low temperatures (~80°C) low temperatures (~80°C) at which PEMFCs operate.at which PEMFCs operate.

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The performance of the PEMFCs is limited by the The performance of the PEMFCs is limited by the slow rate of the Oslow rate of the O22 reduction half reaction, which reduction half reaction, which is more than 100 times slower than the His more than 100 times slower than the H2 2

oxidation half reaction.oxidation half reaction.

Cooling is required to maintain the temperature of Cooling is required to maintain the temperature of the FC stack at about 80°C.the FC stack at about 80°C.

At this temperature, the product water produced at At this temperature, the product water produced at the cathode is both liquid and vapor, and is carried the cathode is both liquid and vapor, and is carried out of the FC by the air flow.out of the FC by the air flow.

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Water and FC PerformanceWater and FC Performance ““Water management” is key to effective operation Water management” is key to effective operation

of a PEMFC.of a PEMFC.

Both the fuel and air entering the FC must be Both the fuel and air entering the FC must be humidifiedhumidified, to keep the PEM hydrated. , to keep the PEM hydrated.

Too little water prevents the membrane from Too little water prevents the membrane from conducting the protons well and the cell current conducting the protons well and the cell current drops.drops.

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If the air flow past the cathode is too slow to carry If the air flow past the cathode is too slow to carry all the product water out of the cell, the cathode all the product water out of the cell, the cathode “floods.” “floods.”

That hurts cell performance, too, because not That hurts cell performance, too, because not enough oxygen is able to penetrate the excess enough oxygen is able to penetrate the excess liquid water to reach the cathode catalyst sites. liquid water to reach the cathode catalyst sites.

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The Flow Fields/The Flow Fields/Current CollectorsCurrent Collectors

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The plates are made of a light-weight, The plates are made of a light-weight, strong, gas-impermeable, electron strong, gas-impermeable, electron conducting material.conducting material.

Graphite or metals are commonly used, Graphite or metals are commonly used, although composite plates are now being although composite plates are now being developed.developed.

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The side of the plate next to the backing layer The side of the plate next to the backing layer contains channels machined into the plate.contains channels machined into the plate.

The channels carry the reactant gas from the point The channels carry the reactant gas from the point at which it enters the FC to the point at which the at which it enters the FC to the point at which the gas exits.gas exits.

Flow field design (pattern, width, and depth) Flow field design (pattern, width, and depth) affects reactant gas distribution and water affects reactant gas distribution and water management.management.


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).

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Renewable Energy SystemsRenewable Energy Systems

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Future OpportunitiesFuture Opportunities

Impurities often present in the HImpurities often present in the H22 fuel feed fuel feed

stream bind to the Pt catalyst surface in the stream bind to the Pt catalyst surface in the anode, preventing Hanode, preventing H22 oxidation by blocking oxidation by blocking

Pt catalyst sites.Pt catalyst sites. Alternative catalysts which can oxidize HAlternative catalysts which can oxidize H2 2

while remaining unaffected by impurities while remaining unaffected by impurities are needed to improve cell performance.are needed to improve cell performance.


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Efficiency, Power and Energy of Efficiency, Power and Energy of PEMFCPEMFC

At 80°C, 1 atm, a single, At 80°C, 1 atm, a single, ideal Hideal H22/air FC provides /air FC provides

1.16 V at zero current.1.16 V at zero current. A good measure of A good measure of

energy conversion energy conversion efficiency for a FC is efficiency for a FC is IIactualactual/I/Iopen circuitopen circuit..

Back

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Thus a FC operating at 0.7 V has an efficiency of Thus a FC operating at 0.7 V has an efficiency of about 60%.about 60%.

P = I VP = I V Specific power = power/FC massSpecific power = power/FC mass Power density = power/FC volumePower density = power/FC volume

High specific power and power density are High specific power and power density are important for transportation applications, to important for transportation applications, to minimize the weight and volume of the FC as well minimize the weight and volume of the FC as well as to minimize cost.as to minimize cost.

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Rate of Heat GenerationRate of Heat Generation

V-I curve


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))


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


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.


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


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


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 cost associated with compressing air and the improved performance.improved 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 a significant pressure differential can be

maintained across the electrolyte→low P fuel maintained across the electrolyte→low P fuel & higher P air& higher P air


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.

99

Safety IssueSafety Issue

All fuels are inherently dangerousAll fuels are inherently dangerous; ; gasoline is no exception. gasoline is no exception.

Proper engineering, education, and common Proper engineering, education, and common sense reduce the risk.sense reduce the risk.

A hydrogen vehicle and supporting A hydrogen vehicle and supporting infrastructure can be engineered to be as infrastructure can be engineered to be as safe as existing gasoline systems.safe as existing gasoline systems.


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.

101

Summary

102

BenefitsBenefits

FCs are efficient, clean, and quiet.FCs are efficient, clean, and quiet. FCs are modular FCs are modular FCs may give us the opportunity to provide FCs may give us the opportunity to provide

the world with the world with sustainable electrical powersustainable electrical power. .

103

ObstaclesObstacles

FCs must obtain mass-market acceptance to FCs must obtain mass-market acceptance to succeed.succeed.

An infrastructure for the mass-market An infrastructure for the mass-market availability of Havailability of H22, or methanol fuel initially, , or methanol fuel initially,

must also develop.must also develop.

104

At present, a large portion of the investment At present, a large portion of the investment in FCs and hydrogen technology has come in FCs and hydrogen technology has come from auto manufacturers.from auto manufacturers.

Changes in government policy could also Changes in government policy could also derail FC and hydrogen technology derail FC and hydrogen technology development.development.

At present, Pt is a key component to FCs. At present, Pt is a key component to FCs.







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


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.


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


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.


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

the maximum theoretical fuel efficiency for a MCFC the maximum theoretical fuel efficiency for a MCFC ↓. ↓.

2.2. On the other hand, operating T ↑, the rate of electro-On the other hand, operating T ↑, the rate of electro-chemical and thus current at a given voltage ↑.chemical 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 PAFC at the same current density. (higher fuel efficiency)efficiency)

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 MCFC should be smaller and less expansive than a “comparable” PAFC.“comparable” PAFC.


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

1200°F(650 ) ←necessary to achieve sufficient ℃1200°F(650 ) ←necessary to achieve sufficient ℃conductivity of the electrolyteconductivity of the electrolyte

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

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

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


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↓


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.

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.

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

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.



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 )-stabilized zirconia(zirconia( 氧化鋯氧化鋯 )—an excellent conductor of )—an excellent conductor of negatively charged oxygen (oxide) at high T.negatively 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) , strontium) lanthanum(lanthanum( 鑭鑭 ) manganite() manganite( 錳化物錳化物 ))


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

properties and fabrication techniques with semi-properties and fabrication techniques with semi-conductor devices.conductor devices.

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




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

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

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

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


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

4.4. The efficiencies of pressurized SOFCs : 60% The 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.


temperature management—temperature management—

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


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 The high operating temperature offers the

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

and can be used directly as a fuel.and can be used directly as a fuel.4.4. The SOFC can tolerant several orders of The SOFC can tolerant several orders of

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


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

operating T.operating T.a.a. A 10% drop in T → 12% drop in cell A 10% drop in T → 12% drop in cell

performance due to the increase in internal performance due to the increase in internal resistance to the flow of oxygen ions.resistance to the flow of oxygen ions.

7. The high T also demands that the system include significant thermal shielding to protect personnel and to retain heat. →not for →not for transportation applications.transportation applications.

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.


Internal reforming in MCFC & SOFC at high T→ Internal reforming in MCFC & SOFC at high T→ eliminate external fuel reformers →highly eliminate external fuel reformers →highly efficient, simple, reliable and cost effectiveefficient, 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, (endothermic,

ΔH=53.87 kcal/mol, favored by high T & low P, ΔH=53.87 kcal/mol, favored by high T & low P, P< 5 atm)P< 5 atm)


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

used for used 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 hydrogen Disadvantage: the conversion of methane to hydrogen

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


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

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


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 C to produce sufficient Hsufficient H2 2 ..

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

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

↓ ↓

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


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.

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.

5-4 5-4 Fuel Cell ElectrochemistryFuel Cell ElectrochemistryMCFCMCFC

The electrochemical reactions occurring in The electrochemical reactions occurring in MCFCsMCFCs

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.

5-4 5-4 Fuel Cell ElectrochemistryFuel Cell ElectrochemistrySOFCSOFC

The electrochemical reactions occurring in The electrochemical reactions occurring in SOFCs (~1000 SOFCs (~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))

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

emissions are reduced for a given power emissions are reduced for a given power output.output.

By 2000, FC power plants will decrease COBy 2000, FC power plants will decrease CO22

emissions by 0.6 MMT of carbon equivalent.emissions 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 are 0.003 and

0.0004 pounds/megawatt-hour.0.0004 pounds/megawatt-hour.

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.

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.

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.

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.

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.

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.

5-6Applications 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.

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.

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.

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.

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.

5-7 5-7 Advanced Hydrogen Production Technologies 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 Hydrogen is now produced primary by steam reforming of natural gas.reforming of natural gas.

3.3. For applications requiring extremely pure For applications requiring extremely pure HH22→electrolysis, a relatively expensive process→electrolysis, a relatively expensive process

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

5-7 5-7 Advanced Hydrogen Production Technologies Introduction Introduction

Photobiological & photoelectrochemical Photobiological & photoelectrochemical processes uses sunlight to split water into Hprocesses uses sunlight to split water into H22

and Oand O22

Thermochemical processes, including Thermochemical processes, including gasification and pyrolysis systems, use heat to gasification and pyrolysis systems, use heat to produce Hproduce H22 from sources such as biomass and from sources such as biomass and

solid waste.solid waste.

5-7 5-7 Advanced Hydrogen Production Advanced Hydrogen Production TechnologiesTechnologies

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

activity of bacteria and green algae to produce activity of bacteria and green algae to produce hydrogen. (chlorophyll absorbs sunlight and hydrogen. (chlorophyll absorbs sunlight and enzymes use energy to dissociate Henzymes 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 Low solar convertion efficiencies.(5~6% of

sun’s energy to Hsun’s energy to H22 energy) energy)

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


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 -evolving enzymes more

tolerant of Otolerant of O22 extracted from strains of bacteria → extracted from strains of bacteria →

produce Hproduce H22 and O and O22 simultaneously. 10% efficiency simultaneously. 10% efficiency

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



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.



Genetic forms of Chlamydomonas : Genetic forms of Chlamydomonas :

20% efficiency20% efficiency


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

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




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.


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 , GaAs) → provide higher voltages requires for electrolysis and have relatively voltages requires for electrolysis and have relatively high solar efficiency; efficiency is more than 25 % , high solar efficiency; efficiency is more than 25 % , but is expensive.but is 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.



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


THERMOCHEMICAL PRODUCTIONTHERMOCHEMICAL PRODUCTION

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

2.2. Pyrolysis : Pyrolysis :

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

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



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 8% char by wt. with the remainder consisting of water and gas.water and gas.

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

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

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.



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.



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.

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


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.


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.


PHYSICAL STORAGE SYSTEMPHYSICAL STORAGE SYSTEM

4.4. Hydrogen gas is currently stored at high Hydrogen gas is currently stored at high pressures of 14~17 MPa.pressures 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 These materials may make it possible for hydrogen gas to be a cost-effective fuel.hydrogen gas to be a cost-effective fuel.


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.


SOLID-STATE STORAGE METHODSOLID-STATE STORAGE METHOD

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

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

solid material.solid material.

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

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


METAL HYDRIDES—release HMETAL HYDRIDES—release H2 2 by by dehydridedehydride

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

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

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


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.


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.


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

very high temperatures offer greater storage very high temperatures offer greater storage efficiency at less cost than lower temperature efficiency at less cost than lower temperature hydrides under development. hydrides 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 hydriding energy as heat of fusion and then return the heat for the dehydriding process.return the heat for the dehydriding process.


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.


Nonclassical Metal Hydride Complexes Nonclassical Metal Hydride Complexes 1.1. Nonclassical polyhydride metal complexes Nonclassical polyhydride metal complexes

(PMCs) may overcome the weight density (PMCs) may overcome the weight density problem of hydride storage system.problem of hydride storage system.

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

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


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.


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

currently : 4.8 wt% hydrogen at 87°K and currently : 4.8 wt% hydrogen at 87°K and 6Mpa.6Mpa.

5.5. The bar of storage capacity : relatively low The bar of storage capacity : relatively low volumetric and gravimetric densities; the volumetric and gravimetric densities; the cryogenic temperature required; high cost of cryogenic temperature required; high cost of the process.the process.

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


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

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

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


Carbon NanotubulesCarbon Nanotubules

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

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


Carbon NanotubulesCarbon Nanotubules


Carbon AerogelsCarbon Aerogels

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

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


Carbon AerogelsCarbon Aerogels

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

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

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


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.





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.



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 .℃

Documents

Benefits and Obstacles to the Success of FCs and the Development of a Hydrogen-Based Economy