Fuel Cell
Benefits and Obstacles
to the Success of FCs and
the Development of a HydrogenBased Economy
1
Chapter 5 Fuel Cell
Introduction
 Historical Notes
 Types of Fuel Cells
 Fuel Cell Electrochemistry
 Advantages of Fuel Cells
 Applications of Fuel Cells
 Advanced Hydrogen Production
Technologies
 Advanced Hydrogen Transport and Storage
Technologies

5-1 Introduction
What is a Fuel Cell

A fuel cell → an electrochemical device that
combines hydrogen and oxygen to produce
electricity, with water and heat as its by-product.
5-2 Historical Notes
Finally Coming of Age

In 1839, Sir William Grove reasoned that it
should be possible to react hydrogen with
oxygen to generate electricity.

In 1889, fuel cell was coined by Ludwig Mond
and Charles Langer, who attempted to build the
first practical device using air and coal gas.
Sir William Grove (18111896)
“I cannot but regard the experiment as an important
one…”
William Grove writing to Michael Faraday, October 22, 1842 5
5-2 Historical Notes
Finally Coming of Age

1.
2.
3.
In early 20th Century, fuel cells were forgot
A lack of understanding of materials and
electrode kinetics.
Internal combustion engine was developed.
Petroleum was discovered and rapidly exploited.
5-2 Historical Notes
Finally of Coming Age


In 1932, the first successful fuel cell device was
built by engineer Francis Bacon.
He improved on the expensive platinum catalysts
employed by Mond and Langer with a hydrogenoxygen cell using a less corrosive alkaline
electrolyte and inexpensive nickel electrodes.

In the 1950s Bacon successfully produced the
first practical (alkaline) FC.
Francis T. Bacon
(1904-1992)
8
5-2 Historical Notes
Finally of Coming Age


Until 1959, Bacon and his coworkers were able
to demonstrate a practical five-kilowatt system
capable of powering a welding machine.
In October of that same year, Harry Karl Ihrig of
Allis-Chalmers Manufacturing Company
demonstrated his famous 20-horsepower fuel
cell-powered tractor.
5-2 Historical Notes
Finally of Coming Age

1.
2.
In the late of 1950s, fuel cells were noticed
NASA began to search some electricity
generator for space mission.
Nuclear reactors as too risky, batteries as too
heavy and short live, and solar power as
cumbersome, NASA turned to fuel cells.

In the 1960s, NASA demonstrated some of
their potential applications in providing
power during space flight.
11
5-2 Historical Notes
Finally of Coming Age


In 1960s, fuel cells would be the panacea to the
world energy problem. The some qualities that
make fuel cells idea for space exploration were
considered. (ex. Small size, high efficiency, low
emission.)
Nearly 40 years US$1 billion in research have
been devote to address the barriers to the use of
fuel cells for stationary application.
5-2 Historical Notes
Finally of Coming Age

1.
2.
3.
Fortunately
A number of manufacturers have supported numerous
demonstration initiatives and ongoing research and
development into stationary application.
Phosphoric acid fuel cells is being offered
commercially, and more advanced designs, such as
carbonate fuel cells and solid oxide fuel cells, are the
focus of major electric technologies.
Full-sized (commercial) cells and full-height stacks
have been successfully demonstrated for the
carbonate fuel cell design.
5-2 Historical Notes
Finally of Coming Age

It has taken more than 150 years to develop
the basic science and to realize the
necessary materials improvement for fuel
cells to become a commercial reality.
The fuel cell is finally coming of age!!
Then industry began to recognize the
commercial potential of fuel cells.
 But, due to technical barriers and high
investment costs, fuel cells were not
economically competitive with existing
energy technologies.

15
Not anymore so!

Polymer Electrolyte Membrane Fuel Cells
(PEMFCs; or Proton Exchange Membrane
FCs) have become a ‘mature’ technology.

Well, there still is much work that needs to be done to optimize the FC
system.
But hey, the gasoline IC engine is nearly 130 years old and still being
improved.

16
Transportation

The California Low Emission Vehicle
Program requires that beginning in 2003,
10% of passenger cars delivered for sale in
CA from medium or large sized
manufactures must be Zero Emission
Vehicles (ZEVs).
17
5-2 Historical Notes
Finally of Coming Age
Honda FCX
Honda FCX specifications
Vehicle
Length:
4165 mm
Width:
1760 mm
Height:
1645 mm
Maximum Speed:
93 mph (150km/h)
Driving Range:
220 miles (355km)
Seating Capacity:
4 adults
First fuel cell vehicle in the world to receive government certification
(American Honda Motor Co., Inc., 7/24/2002).
19
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 hydrogen
Storage Method:
High-pressure hydrogen storage tank (5,000 psi)
Fuel Capacity:
156.6 liter
20
NECAR 5

2001 prototype FC automobile by
DaimlerChrysler.
21
Drives and feels like a “normal” car.
 Top speed > 150 km/hr, with a power
output 0f 75 kW (100 hp).
 Combines the low emission levels, the
quietness and the smoothness associated
with EVs, while delivering a performance
similar to that of an automobile with an IC
engine.

22
Fuel 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.
23
• The PEM fuel cells were provided by
Ballard Power Systems.
• Air Products & Chemicals supplies the
liquid hydrogen, which is converted to
gas for bus use.
• The pilot program began in December
1997 at the Chicago Transit Authority,
which will receive royalties for every bus
sold by Ballard, up to US$4 million.
24
25
26
Back
Fuel Cells, Prof. T.-S. Yang,
NCKU/ME
27
5-2 Historical Notes
Finally of Coming Age
Fuel Cells, Prof. T.-S. Yang,
NCKU/ME
29
Distributed Power Generation
32
Other 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)
33
34
5-3 Types of Fuel Cells
Molten Carbonate Fuel Cells
36
37
5-3 Types of Fuel Cells
Overview of Fuel Cells


Fuel Cells generate electricity through an
electrochemical process in which the energy
stored in a fuel is converted directly into DC
electricity.
Electrical energy is generated without
combusting fuel, so fuel cells are extremely
attractive from an environmental stand point.
5-3 Types of Fuel Cells
Overview of Fuel Cells

1.
2.
3.
4.
5.
6.
Attractive fuel cell characteristic
High energy conversion efficiency
Modular design
Very low chemical and acoustical pollution
Fuel flexible
Cogeneration capability
Rapid load response
5-3 Types of Fuel Cells
Overview of Fuel Cells

1.
2.
3.
4.
Basic operating principle of fuel cells
An input fuel is catalytically reacted in fuel
cell to create an electric current.
The input fuel passed over the anode where it
catalytically splits into ions and electrons.
The electrons go through an external circuit to
serve an electric load while the ions move
through the electrolyte toward the oppositely
charge electrode.
At electrode, ions combine to create byproducts, primarily water and CO2.
5-3 Types of Fuel Cells
Overview of Fuel Cells

The figure of basic operating principle
5-3 Types of Fuel Cells
Overview of Fuel Cells

Fuel Cell Characteristics
5-3 Types of Fuel Cells
Overview of Fuel Cells
5-3 Types of Fuel Cells
Overview of Fuel Cells

1.
2.
3.
4.
Four primary types of fuel cells which are
based on electrolyte employed
Phosphoric Acid Fuel Cell
Molten Carbonate Fuel Cell
Solid Oxide Fuel Cell
Proton Exchange Membrane Fuel Cell
5-3 Types of Fuel Cells
Overview of Fuel Cells

A comparison of the fuel cell types
5-3 Types of Fuel Cells
Overview of Fuel Cells

Fuel cells are typical grouped three section
5-3 Types of Fuel Cells
Phosphoric Acid Fuel Cells

1.
2.
The most mature fuel cell technology
Among low temperature fuel cell, it was
showed relative tolerance for reformed
hydrocarbon fuels.
It could have widespread applicability in the
near term.
5-3 Types of Fuel Cells
PAFC Design an Operation

The sketch of PAFC operation
5-3 Types of Fuel Cells
PAFC Design an Operation

1.
2.
3.
4.
5.
The components of PAFC
Electrolyte : liquid of acid
Electrolyte carriers : Teflon bonded silicone
carbide matrix (pore structure→capillary
action to keep liquid electrolyte in place)
Anode : platinum catalyzed, porous carbon
Cathode : platinum catalyzed, porous carbon
Bipolar plate : complex carbon plate
5-3 Types of Fuel Cells
PAFC Design an Operation

1.
The most designs of PAFC
The plates are “bi-polar” in that they have
grooves on both side –
one side supplies fuel to anode of one cell, and
the other side supplies air or oxygen to the
cathode of the adjacent cell.
5-3 Types of Fuel Cells
PAFC Design an Operation
The PAFC reactions
Anode : H2 → 2H+ + 2e
Cathode : ½ O2 + 2H+ +2e- → H2O
5-3 Types of Fuel Cells
PAFC Design an Operation

The characteristics of PAFC operation
1.
Some acid may be entrained in fuel or oxidant
streams and addition of acid may be after
many hours of operation.
The water removed as steam on the cathode by
flowing excess oxidant past the back of
electrodes.
2.
5-3 Types of Fuel Cells
PAFC Design an Operation

1.
2.
The temperature effect to PAFC
The product water removal procedure required
that the system operated at temperature around
375°F (~190°C).
At lower temperature : the water will dissolve
in the electrolyte and not be removed as steam.
At high temperature (approximately 410°F~
(~210°C) : the phosphoric acid begins to
decompose.
5-3 Types of Fuel Cells
PAFC Design an Operation

1.
2.
How does excess heat be removed
Proved carbon plates containing cooling
channels.
Air or liquid coolant, can be passed
through these channels to remove heat.
5-3 Types of Fuel Cells
PAFC Design an Operation

1.
2.
3.
a.
b.
PAFC performance characteristics
Power density : 160 to 175 watts/ft2
Thermal energy supplied at : ~ 150°F (only a
portion at 250°F to 300°F)
Efficiency :
With pressurized reactants : 36% to 42%
(HHV)
Supply usable thermal energy : 31% to 37%
(HHV)
5-3 Types of Fuel Cells
Proton Exchange Membrane Fuel Cells
(PEMFC)

1.
2.
3.
4.
The introduction of PEMFC
PEMFC has higher power density than any
other fuel cell system.
PEMFC has comparable performance with the
advanced aerospace AFC.
PEMFC can operate on reformed hydrocarbon
fuels.
PEMFC uses a solid polymer electrolyte
eliminates the corrosion.
5-3 Types of Fuel Cells
Proton Exchange Membrane Fuel Cells
The introduction of PEMFC
5. Its low operating temperature (70-85 oC):
a. provides instant start up: 50 % maximum
power immediately at room T & full operating
power within 3 min.
b. require no thermal shielding to protect
personnel.
6. Advances in performance and designs offer the
possibility of lower cost.

5-3 Types of Fuel Cells
PEMFC Designs and Operation

The sketch of PEMFC operation
5-3 Types of Fuel Cells
PEMFC Designs and Operation

The sketch of PEMFC operation
5-3 Types of Fuel Cells
PEMFC Designs and Operation
The PEMFC reactions
Anode : H2 → 2H+ + 2e
Cathode : O2 → 4H+ + 4e- → 2H2O
The PEMFC Stack
Energy Partners
61

Effective commercial electric motors
typically operate at 200-300 volts.

Connect individual FCs in series to form a
FC stack that provides the required high
voltage.

To decrease the overall volume and weight
of the stack, use “bipolar plates.”
62
5-3 Types of Fuel Cells
PEMFC Designs and Operation

1.
2.
3.
4.
The characteristics of PEMFC operation
The electrode reactions are analogous to those
in PAFC.
The PEMFC operates at about 175°F (80℃).
The water is produced as liquid water and is
carried out the fuel cell by excess oxidant flow.
Fully operating power is available within
about 3 minute under normal condition.
5-3 Types of Fuel Cells
PEMFC Designs and Operation

1.
2.
3.
4.
The components of PEMFC
Electrolyte : polymer membrane.
Anode : thin sheet of porous, graphitized paper.
(water-proofed with PTFE or Teflon, with one
surface being applied with a small amount of
Pt-black)
Cathode : (the same as above).
Bipolar plate : graphite.
5-3 Types of Fuel Cells
PEMFC Designs and Operation

1.
2.
3.
4.
The features of the electrolyte
Electronic insulator, but an excellent
conductor of hydrogen ions.
The acid molecules are fixed to the polymer,
but the protons on these acid groups are free to
migrate through the membrane.
Solid polymer electrolyte→electrolyte loss is
not an issue with regard to stack life.
Be handled easily and safely.
PEM
Nafion resembles the
plastic wrap used for
sealing foods. (But
thicker: 50 to 175
microns, i.e., 2 to 7
pieces of paper.)
66
5-3 Types of Fuel Cells
PEMFC Designs and Operation

The heart of PEMFC
The electrolyte is sandwiched between the
anode and cathode, and the three components
are sealed together under heat and pressure to
product a single “membrane/electrode assembly”
(MEA, < 1mm thick).
5-3 Types of Fuel Cells
PEMFC Designs and Operation

1.
2.
3.
The features of the bipolar plates
The bipolar plates are called “flow field
plates”.
They make electrical contact with the back of
the electrodes and conduct the current to the
external circle.
They supply fuel to the anode and oxidant to
the cathode.
In an operating FC, the membrane is well
humidified, so that the electrolyte looks like
a moist piece of thick plastic wrap.
 PEMs are somewhat unusual electrolytes in
that, in the presence of water, the negative
ions are rigidly held within their structure.
 Only the positive ions (here the H+ ions, or
protons) are free to carry positive charge
through the membrane.

69
PEMFCs are limited by the temperature
range over which water is liquid.
 Operating PEMFCs at temperatures
exceeding 100C is possible under
pressurized conditions, but that shortens the
life of the cell.
 Currently, PEMs cost about US$100 per
square foot.

70
Remaining Challenges

producing membranes not limited by the
temperature range of liquid water, possibly
based on another mechanism of protonic
conduction

reducing membrane cost by developing
different membrane chemistries
71
The Backing Layer
72
Designed to maximize the current that can
be obtained from a MEA.
 Usually made of a porous carbon paper or
carbon cloth, typically 100 to 300 microns
thick (4 to 12 sheets of paper).
 The backing layers have to be made of a
material, such as carbon, that can conduct
the electrons exiting the anode and entering
the cathode.
 Also, they are often wet-proofed with
Teflon.

73
Being Porous

ensures effective diffusion of each reactant
gas to the catalyst on the MEA

allows the gas to spread out as it diffuses, so
that when it penetrates the backing, the gas
will be in contact with the entire surface
area of the catalyzed membrane.
74
Also…..
The backing layers assist in water
management during FC operation.
 The correct backing material allows the
right amount of water vapor to reach the
MEA to keep the membrane humidified.
 The backing material also allows the liquid
water produced at the cathode to leave the
cell so it doesn’t flood.

75
The Electrodes

Expensive Pt based
catalysts seem to be the
only catalysts capable of
generating high rates of O2
reduction at the relatively
low temperatures (~80°C) at
which PEMFCs operate.
76

The performance of the PEMFCs is limited by the
slow rate of the O2 reduction half reaction, which
is more than 100 times slower than the H2
oxidation half reaction.

Cooling is required to maintain the temperature of
the FC stack at about 80°C.

At this temperature, the product water produced at
the cathode is both liquid and vapor, and is carried
out of the FC by the air flow.
77
Water and FC Performance

“Water management” is key to effective operation
of a PEMFC.

Both the fuel and air entering the FC must be
humidified, to keep the PEM hydrated.

Too little water prevents the membrane from
conducting the protons well and the cell current
drops.
78

If the air flow past the cathode is too slow to carry
all the product water out of the cell, the cathode
“floods.”

That hurts cell performance, too, because not
enough oxygen is able to penetrate the excess
liquid water to reach the cathode catalyst sites.
79
The Flow Fields/
Current Collectors
80

The plates are made of a light-weight,
strong, gas-impermeable, electron
conducting material.

Graphite or metals are commonly used,
although composite plates are now being
developed.
81

The side of the plate next to the backing layer
contains channels machined into the plate.

The channels carry the reactant gas from the point
at which it enters the FC to the point at which the
gas exits.

Flow field design (pattern, width, and depth)
affects reactant gas distribution and water
management.
82
5-3 Types of Fuel Cells
PEMFC Designs and Operation

1.
2.
a.
b.
Useable fuel for PEMFC
Pure hydrogen
Reformed Hydrocarbon fuels:
Without removal or recirculation of byproduct CO2.
The traces of CO produced during the
reforming process must be converted to CO2 (a
simple catalytic process).
84
85
Renewable Energy Systems
86
Future Opportunities
Impurities often present in the H2 fuel feed
stream bind to the Pt catalyst surface in the
anode, preventing H2 oxidation by blocking
Pt catalyst sites.
 Alternative catalysts which can oxidize H2
while remaining unaffected by impurities
are needed to improve cell performance.

87
5-3 Types of Fuel Cells
PEMFC Designs and Operation
Efficiency, Power and Energy of
PEMFC
At 80°C, 1 atm, a single,
ideal H2/air FC provides
1.16 V at zero current.
 A good measure of
energy conversion
efficiency for a FC is
Iactual/Iopen circuit.

Back
89

Thus a FC operating at 0.7 V has an efficiency of
about 60%.

P=IV
Specific power = power/FC mass
Power density = power/FC volume



High specific power and power density are
important for transportation applications, to
minimize the weight and volume of the FC as well
as to minimize cost.
90
Rate of Heat Generation
V-I curve
91
5-3 Types of Fuel Cells
PEMFC Designs and Operation

1.
2.
The performance of PEMFC recently
At 0.7V/cell on hydrogen and oxygen, 65psia :
850A/ft2 (~0.91 A/cm2)
At 0.7V/cell on hydrogen and air, 65psia :
500A/ft2 (~0.54 A/cm2)
5-3 Types of Fuel Cells
PEMFC Designs and Operation

1.
2.
1.
The performance of Ballard/Dow PEMFC
At 0.7V/cell:
At 65psia, hydrogen/oxygen : 2000A/ft2
At 65psia, hydrogen/air : 1000A/ft2
At 0.5V/cell, :
At 65psia, hydrogen/oxygen : 4000A/ft2
↓
2000 W/ft2
5-3 Types of Fuel Cells
PEMFC Designs and Operation

1.
2.
3.
4.
The power density of PEMFC
a factor of 10 greater than other FC systems → a
significant reduction in stack size and cost.
In 5kW production fuel cell stacks, 0.7V at 650 A/ft2
on hydrogen/air at 45psi, stack dimensions 9.8 * 9.8
* 16.7 in: stack-only power density of over 5.4
kW/ft3
1.25 kW/ft3 on hydrogen/air at 45psi, if including
fuel/oxidant controls, cooling, product water removal
Approaching 14.2 kW/ft3 are certainly feasible.
5-3 Types of Fuel Cells
PEMFC Designs and Operation

When HC/air are to be used, higher T FC, the
MCFC, SOFC, and to some extent, PAFC,
have an efficiency advantage over PEMFC.
↑
waste heat can be used to drive air
compressors, reforming of HC fuels, electric
generation or other thermal load
5-3 Types of Fuel Cells
PEMFC Designs and Operation
Using either air or liquid cooling
↓
a compact power generator
and the excess heat of PEMFC is to be used for
1. space heating or residential hot water
2. utility cogeneration applications

5-3 Types of Fuel Cells
PEMFC Designs and Operation

1.
2.
3.
4.
The pressure effects to all fuel cells
Performance is improve by pressuring the air.
Find an balance about the energy and financial
cost associated with compressing air and the
improved performance.
Rule of thumb: < 45 psia
∵PEMFC uses a solid electrolyte
∴ a significant pressure differential can be
maintained across the electrolyte→low P fuel
& higher P air
5-3 Types of Fuel Cells
PEMFC Designs and Operation

1.
2.
3.
4.
A very significant cost penalty of PEMFC as
compared with PAFC
The PEMFC uses platinum at both the anode
and cathode.
presently, 0.001 oz/in2 ~0.6 oz/kW for H2/air
Los Alamos National Lab & Texas A &M
Univ., 0.00007 oz/in2 ~0.042 oz/kW for H2/air
or ~0.021 oz/kW for H2/ O2
Be expected to reduce platinum requirement to
0.035 oz/kW (1 g/kW) or about $2/kW.
Safety Issue
All fuels are inherently dangerous;
gasoline is no exception.
 Proper engineering, education, and common
sense reduce the risk.
 A hydrogen vehicle and supporting
infrastructure can be engineered to be as
safe as existing gasoline systems.
 http://www.politicalhotwire.com/sciencetechnology/31548-will-hydrogen-car-blow-99
up-collision.html

5-3 Types of Fuel Cells
Molten Carbonate Fuel Cells

1.
2.
The goals of developing MCFC
In 1960’s: operating directly on coal→ but that
seems less likely today.
Operation on coal-derived fuel gases or natural
gas is viable.
Summary
101
Benefits
FCs are efficient, clean, and quiet.
 FCs are modular
 FCs may give us the opportunity to provide
the world with sustainable electrical power.

102
Obstacles
FCs must obtain mass-market acceptance to
succeed.
 An infrastructure for the mass-market
availability of H2, or methanol fuel initially,
must also develop.

103
At present, a large portion of the investment
in FCs and hydrogen technology has come
from auto manufacturers.
 Changes in government policy could also
derail FC and hydrogen technology
development.
 At present, Pt is a key component to FCs.

104
5-3 Types of Fuel Cells
Molten Carbonate Fuel Cells
5-3 Types of Fuel Cells
Molten Carbonate Fuel Cells
5-3 Types of Fuel Cells
Molten Carbonate Fuel Cells
5-3 Types of Fuel Cells
Molten Carbonate Fuel Cells
5-3 Types of Fuel Cells
Molten Carbonate Fuel Cells
5-3 Types of Fuel Cells
Molten Carbonate Fuel Cells
5-3 Types of Fuel Cells
MCFC Design and Operation

The sketch of MCFC operation
5-3 Types of Fuel Cells
MCFC Design and Operation

1.
2.
3.
4.
The components of MCFC
Electrolyte : a molten carbonate salt mixture, usually
consists of lithium carbonate and potassium
carbonate.
Electrolyte carriers : a porous, insulating and
chemically inert ceramic (LiAlO2) matrix.
Anode : a highly porous sintered nickel powder,
alloyed with chromium to prevent agglomeration and
creep at operating T.
Cathode : a porous nickel oxide material doped with
lithium.
5-3 Types of Fuel Cells
MCFC Design and Operation
The MCFC reactions
Anode : H2 + CO3-2 → H2O + CO2 + 2eCO + CO3-2 → 2CO2 + 2e
Cathode : O2 + 2CO2 + 4e- → 2CO3-2
↓
* require a system for collecting CO2 from the
anode exhaust and mixing it with the cathode
feed stream
5-3 Types of Fuel Cells
MCFC Design and Operation

The MCFC reactions
* before CO2 is collected, any residual H2 in the
spent fuel stream must be burned.
* Future systems may incorporate membrane
separators to remove H2 for recirculation back
to the fuel stream.
5-3 Types of Fuel Cells
MCFC Design and Operation

1.
2.
a.
b.
MCFC v.s. PAFC
operating T ↑, the theoretical operating voltage and
the maximum theoretical fuel efficiency for a MCFC
↓.
On the other hand, operating T ↑, the rate of electrochemical and thus current at a given voltage ↑.
↓(net effect)
The operating voltage of the MCFC is higher than the
PAFC at the same current density. (higher fuel
efficiency)
As size and cost scale roughly with electrode area, a
MCFC should be smaller and less expansive than a
“comparable” PAFC.
5-3 Types of Fuel Cells
MCFC Design and Operation

1.
2.
3.
4.
The high operating T characteristics of MCFC
Operating at between 1110°F(600℃) and
1200°F(650℃) ←necessary to achieve sufficient
conductivity of the electrolyte
To maintain this operating T, a higher volume of air
is passed through the cathode for cooling purposes.
In combined cycle operation, electrical efficiencies
are in excess of 60%(HHV). The T of excess heat is
high enough to yield high P steam→turbine
At the high operating T, MCFC could operate
directly on the gaseous HC fuels such as natural gas
←would be reformed to produce H2 within the fuel
cell itself.
5-3 Types of Fuel Cells
MCFC Design and Operation
The high operating T characteristics of MCFC
4. At high operating temperature(1200 °F/650 °C),
noble metal catalysts are not required.
5. At high operating temperature(1200°F), the salt
mixture is liquid and is a good ionic conductor.
6. The cell performance is sensitive to operating
temperature.
a. A change in cell T from 1200°F to 1110°F
results in a drop in voltage ~15%. (∵ionic and
electric resistance↑& electrode kinetics↓

5-3 Types of Fuel Cells
MCFC Design and Operation

7.
8.
The high operating T characteristics of MCFC
The electrolyte boil-off has an insignificant
impact on cell stack life.
A more significant factor of life expectancy
has to do with corrosion of the cathode.
5-3 Types of Fuel Cells
Solid Oxide fuel cells

1.
2.
3.
The introductions of the SOFC
uses a ceramic, solid-phase electrolyte which reduces
corrosion considerations and eliminates the
electrolyte management problems associated with the
liquid electrolyte fuel cells.
To achieve adequate ionic conductivity in such a
ceramic→must operate at about 1830 °F (1000 °C).
At that T, internal reforming of carbonaceous fuels
should be possible, and the waste heat would be
easily utilized by conventional thermal electricity
generating plants to yield excellent fuel efficiency.
5-3 Types of Fuel Cells
SOFC Design and Operation

The sketch of SOFC operation
5-3 Types of Fuel Cells
SOFC Design and Operation
The SOFC reactions
Anode : H2 + O-2 → H2O + 2eCO + O-2 → CO2 + 2eCH4 + 4O-2 → 2H2O + CO2 + 8e
Cathode : O2 + 4e- → 2O-2
 It is significant that the SOFC can use CO as its
direct fuel.
5-3 Types of Fuel Cells
SOFC Design and Operation

1.
a.
2.
3.
The components of the SOFC
Electrolyte : solid ceramic.
Materials : dense yttria(氧化釔)-stabilized
zirconia(氧化鋯)—an excellent conductor of
negatively charged oxygen (oxide) at high T.
Anode : a porous nickel/zirconia cermet
Cathode : Sr-doped (鍶, strontium)
lanthanum(鑭) manganite(錳化物)
5-3 Types of Fuel Cells
SOFC Design and Operation

The components of the SOFC
–
–
–
SOFC is a solid state device and shares certain
properties and fabrication techniques with semiconductor devices.
The Westinghouse cell design: the FC around a
porous Zirconia support tube through which air is
supplied to the cathode which is deposited on the
outside of the tube. A layer of electrolyte is then
deposited on the outside of the cathode and finally
a layer of anode is deposited over the electrolyte.
A number of cells are connected together by high
T semiconductor contacts.
5-3 Types of Fuel Cells
SOFC Design and Operation
5-3 Types of Fuel Cells
SOFC Design and Operation
5-3 Types of Fuel Cells
SOFC Design and Operation

The components of the SOFC
–
–
–
The anode consists of metallic Ni and Y2O3stablized ZrO2 skeleton, which serves to inhibit
sintering of the metal particles and to provide a
thermal expansion coefficient comparable to those
of the other fuel materials.
The most common cathode material (a p-type
conductor): Sr-doped (鍶, strontium) lanthanum
manganite (Lal-xSrxMnO3, x=0.10-0.15
Both anode and cathode structures are fabricated
with a porosity of 20-40 % to facilitate mass
transport of reactant and product gases.
5-3 Types of Fuel Cells
SOFC Design and Operation

1.
2.
3.
4.
5.
SOFC performance characteristics
0.6V/cell at about 232 A/ft2
Lifetimes are over 30000(hrs).
The efficiencies of unpressurized SOFCs :
45% (HHV)
The efficiencies of pressurized SOFCs :
60% (HHV)
Bottoming cycle, using the high T waste heat,
could add another few % to the fuel efficiency.
5-3 Types of Fuel Cells
SOFC Design and Operation

temperature management—
maintain proper volume of the air stream into
the cell.
5-3 Types of Fuel Cells
SOFC Design and Operation

1.
2.
3.
4.
5.
high operating T characteristics of SOFCs
The SOFC operates at approximately 1830°F
(1000°C).
The high operating temperature offers the
possibility of internal reforming.
As in MCFCs, CO does not act as a poison
and can be used directly as a fuel.
The SOFC can tolerant several orders of
magnitude more sulfur than other fuel cells.
The SOFC requires a significant start-up time.
5-3 Types of Fuel Cells
SOFC Design and Operation
high operating T characteristics of SOFCs
6. The cell performance is very sensitive to
operating T.
a. A 10% drop in T → 12% drop in cell
performance due to the increase in internal
resistance to the flow of oxygen ions.
7. The high T also demands that the system
include significant thermal shielding to protect
personnel and to retain heat. →not for
transportation applications.

5-4 Fuel Cell Electrochemistry
Internal Reforming
In a conventional fuel cell system, a
carbonaceous fuel is fed to a fuel processor
where it is steam reformed to produce H2 (as
well as CO &CO2).
 Ni reforming catalyst is extremely sensitive to
sulfur in the feed gas.

5-4 Fuel Cell Electrochemistry
Internal Reforming
Internal reforming in MCFC & SOFC at high T→
eliminate external fuel reformers →highly
efficient, simple, reliable and cost effective
 2 alternative approaches to internal reforming:
– Indirect Internal reforming (IIR)
– Direct Internal reforming (DIR)
 Methane and steam reforming reaction:
(750-900 oC)
CH4 + H2O → CO + 3H2 (endothermic,
ΔH=53.87 kcal/mol, favored by high T & low P,
P< 5 atm)

5-4 Fuel Cell Electrochemistry
Internal Reforming

IIR: reformer section is separated, but adjacent
to the anode.
– Advantage: 1.the exthermic heat of the cell can be
used for
the endothermic reforming reaction
2. reformer & cell environments don’t
have a direct physical effect on each
other
– Disadvantage: the conversion of methane to
hydrogen is not promoted as well as in the DIR.
5-4 Fuel Cell Electrochemistry
Internal Reforming
DIR: hydrogen consumption reduces its partial
pressure→driving the methane reforming
reaction to the right.
 For MCFC, one developer’s approach where IIR
& DIR have been combined.

5-4 Fuel Cell Electrochemistry
Internal Reforming
A supported Ni catalyst (e.g. Ni supported on MgO or
LiAlO2) provides sufficient catalytic activity to sustain
the steam reforming reaction at 650 oC to produce
sufficient H2 .
 At open circuit, about 83% CH4 →H2 (~equilibrium
concentration at 650 oC )
 When current is drawn from the cell, H2 is consumed
and H2Ois produced → CH4 conversion ↑ and
approaches 100% at H2 utilization > ~50%
↓
Thermal management and adjustment of H2 utilization is
important to the internal reforming of MCFC stacks

5-4 Fuel Cell Electrochemistry
Internal Reforming

Currently, the concept of internal reforming has
been successfully demonstrated for 10,000 hrs.
in 2-3 kW stacks and for 250 hrs in a 100 kW
stack.
5-4 Fuel Cell Electrochemistry
MCFC

1.
2.
3.
4.
The electrochemical reactions occurring in
MCFCs
Anode : H2 + CO3-2 → H2O + CO2 + 2eCathode : ½ O2 + CO2 + 2e- → CO3-2
Overall : H2 + ½ O2 + CO2 (cathode) → H2O +
CO2 (anode)
The reversible potential equation :
E = E° + RT/2F ln(PH2P1/2O2/PH2O) +
RT/2F ln(PCO2,c/PCO2,a) ; F=96500 Columb/mol.
5-4 Fuel Cell Electrochemistry
MCFC

The electrochemical reactions occurring in
MCFCs
 Transfer CO2 from anode exit gas to the cathode inlet
gas (CO2 transfer device)
 Produce CO2 by combustion of the anode exhaust gas
which is mixed with the cathode inlet gas
 Supply CO2 from an alternate source.
5-4 Fuel Cell Electrochemistry
SOFC

1.
2.
3.
4.
The electrochemical reactions occurring in
SOFCs (~1000 oC)
Anode : H2 + O-2 → H2O + 2eCathode : ½ O2 + 2e- → O-2
Overall : H2 + ½ O2 → H2O
The corresponding Nernst equation
E = E° + RT/2F ln(PH2PO21/2 /PH2O)
5-5Advantages of Fuel Cells
: Environmental Acceptability




Because fuel cells are so efficient, CO2
emissions are reduced for a given power
output.
By 2000, FC power plants will decrease CO2
emissions by 0.6 MMT of carbon equivalent.
FC is quiet, emitting only 60 dBs at 100 ft.
Emissions of SOx and NOx are 0.003 and
0.0004 pounds/megawatt-hour.
5-5Advantages of Fuel Cells:
Efficiency


1.
2.
3.
4.
Dependent on type and design, the fuel cells direct
electric energy efficiency ranges form 40 to 60
percent (LHV).
Characteristics :
Operates at near constant efficiency, independent of
size and load.
Efficiency is not limited by the Carnot Cycle.
For the fuel cells/gas turbine system, the efficiency
achieves 70 percent (LHV).
When by-product heat is utilized, the total efficiency
of the fuel cell systems approach 85 percent.
5-5Advantages of Fuel Cells:
Distributed Capacity

1.

Distributed generation reduces the capital
investment and improves the overall
conversion efficiency of fuel to end use
electricity by reducing transmission losses.
Losses : presently 8-10 % of the generated
electrical power is lost between the generating
station and the end user.
Many smaller units are statistically reliable,
avoid failing at one time as in the case of one
large generator.
5-5Advantages of Fuel Cells:
Permitting

Permitting and licensing schedules are short due
to the ease in siting.
5-5Advantages of Fuel Cells:
Modularity

1.
The fuel cell is inherently modular.
Be configured in wide range of electrical
outputs, ranging from a nominal 0.025 to
greater than 50-megawatt (MW) for a natural
gas fuel cell to greater than 100-MW for the
coal gas fuel cell.
5-5Advantages of Fuel Cells:
Fuel Flexibility

1.
2.
3.
4.
5.

1.
The primary fuel source for the fuel cell is
hydrogen, which can be obtained from :
Natural gas
Coal gas
Methanol
Landfill gas
Other fuels containing hydrocarbons.
Advantage of fuel flexibility
The power generation can be assured even
when a primary fuel source unavailable.
5-5Advantages of Fuel Cells:
Cogeneration Capability
High-quality heat is available for cogeneration,
heating, and cooling.
 Fuel cell exhaust heat is suitable for use in
residential, commercial, and industrial
cogeneration applications.

5-6Applications of Fuel Cells
Introduction

In theory, a fuel cell can power anything that
runs on electricity. The following applications
can take particular advantage of a fuel cell's
attributes.
5-6Applications of Fuel Cells
Cars, Trucks, and Buses


1.
2.
Most vehicles today rely on an internal
combustion engine (ICE).
Electric motors are much more suitable
They deliver their maximum torque at low rpm,
just when a vehicle needs it most.
A driver heads downhill or puts on the brakes,
an electric motor can double as a generator to
recapture that energy and covert it back to
electricity for subsequent use.
5-6Applications of Fuel Cells
Cars, Trucks, and Buses

1.

1.
2.
The choke point of electric motor
The short range and tedious recharging of the
1st generation
A fuel cell powers the vehicle's electric motor
These problems can be overcome. A hydrogen
tank can be refueled in about five minutes.
It has a similar range to a conventional
automobile.
5-6Applications of Fuel Cells
Businesses and Homes

1.
2.
a.

The reasons of fuel cells are attractive in stationary
applications
They deliver unparalleled fuel efficiencies, especially
in Combined Heat & Power (CHP) applications.
Fuel cells offer a new level of reliability :
If a blackout occurs, they will keep essential
mechanical components and external landmark
signage online.
Fuel cells offer highly reliable, high-quality
electricity.
5-6Applications of Fuel Cells
Laptops, Cell Phones, and other Electronics

1.
2.
Fuel cells will find their first widespread use in
portable electronics
These "micro fuel cells" offer far higher energy
densities than those of comparably sized
batteries. The typical laptop can operate
unplugged for ten hours or more.
Micro fuel cells also offer the added appeal of
eliminating the need for battery chargers and
AC adapters, as they require refueling instead
of recharging.
5-7 Advanced Hydrogen Production
Technologies

1.
2.
3.
4.
Introduction
Hydrogen is a clean, sustainable resource with many
potential applications.
Hydrogen is now produced primary by steam
reforming of natural gas.
For applications requiring extremely pure
H2→electrolysis, a relatively expensive process
Three process of producing hydrogen :
photobiological, photoelectrochemical,
thermochemical.
5-7 Advanced Hydrogen Production
Technologies


Introduction
Photobiological & photoelectrochemical
processes uses sunlight to split water into H2
and O2
Thermochemical processes, including
gasification and pyrolysis systems, use heat to
produce H2 from sources such as biomass and
solid waste.
5-7 Advanced Hydrogen Production
Technologies

1.
2.
a.
b.
PHOTOBIOLOGICAL PRODUCTION
Most photobiological system use the natural
activity of bacteria and green algae to produce
hydrogen. (chlorophyll absorbs sunlight and
enzymes use energy to dissociate H2 from H2O)
Two significant limitations :
Low solar convertion efficiencies.(5~6% of
sun’s energy to H2 energy)
Nearly all enzymes are inhibited in their
hydrogen production by presence of oxygen.
5-7 Advanced Hydrogen Production
Technologies

3.
a.
b.
PHOTOBIOLOGICAL PRODUCTION
The way to overcome oxygen intolerance and increase
conversion efficiencies :
A new green algae strains: the Chlamydomonas (單
胞藻) strain → has H2-evolving enzymes more
tolerant of O2 extracted from strains of bacteria →
produce H2 and O2 simultaneously. 10% efficiency
Cell-free processes : theoretical efficiency approach
25%
5-7 Advanced Hydrogen Production
Technologies
PHOTOBIOLOGICAL PRODUCTION
Cell-free processes :
c. In a cell-free system : both O2-evolving & H2evolving enzymes are immobilized onto
opposite sides of a solid, conducting surface.
d. Light is used by one enzyme to oxidize water,
creating a flow of electrons to the other
enzymes, where H2 is produced.

5-7 Advanced Hydrogen Production
Technologies

PHOTOBIOLOGICAL PRODUCTION
Genetic forms of Chlamydomonas :
20% efficiency
5-7 Advanced Hydrogen Production
Technologies

1.
2.
a.
b.
PRODUTION BY PHOTOELECTROCHEMICAL (PEC) TECHNOLOGY
PEC production uses semiconductor
technology in one-step process of splitting
water directly upon sunlight illumination.
A PEC system :
a photovoltaic cell → produce electric current
when exposed to light
Electrolyzer
5-7 Advanced Hydrogen Production
Technologies
5-7 Advanced Hydrogen Production
Technologies

3.
4.
a.
b.
PRODUTION BY PHOTOELECTROCHEMICAL (PEC) TECHNOLOGY
Advantage : producing low-cost renewable
hydrogen.
The two limited factor of an efficient and costeffective PEC system :
The high voltage required to dissociate water.
The corrosiveness of aqueous electrolytes.
5-7 Advanced Hydrogen Production
Technologies

5.
a.
b.
1.
2.
PRODUTION BY PHOTOELECTRO-CHEMICAL
(PEC) TECHNOLOGY
The way to overcome limits :
The structure → the multijunction device > 1.6 eV
Material :
Gallium based (GalnP2, GaAs) → provide higher
voltages requires for electrolysis and have relatively
high solar efficiency; efficiency is more than 25 % ,
but is expensive.
Amorphous silicon → efficiency is more than 13 % ,
but cost is low.
5-7 Advanced Hydrogen Production
Technologies
PRODUTION BY PHOTOELECTROCHEMICAL (PEC) TECHNOLOGY
4. The sketch of a multijunction device

5-7 Advanced Hydrogen Production
Technologies

1.
2.
a.
THERMOCHEMICAL PRODUCTION
Gasification and pyrolysis : using heat to produce a
vapor from which hydrogen can be derived use a
conventional steam reforming process.
Pyrolysis :
Biomass—wood, grasses, and agricultural and
municipal waste, is broken down into highly reactive
vapors and carbonaceous residue, or char.
The vapors, when condensed into pyrolysis oil, can
be steam reformed to produce hydrogen.
5-7 Advanced Hydrogen Production
Technologies

b.
c.
d.
e.
THERMOCHEMICAL PRODUCTION
A typical biomass feedstock produces ~ 65% oils and
8% char by wt. with the remainder consisting of
water and gas.
The char is burn to provide the required heat for the
pyrolysis reaction.
A fast-pyrolysis reactor is directly linked to a steam
reformer.(12%~17% hydrogen by weight of dry
biomass)
Advantage : the lowest-cost production method, but it
needs to identifying optimum reformer catalysts.
5-7 Advanced Hydrogen Production
Technologies

3.
a.
b.
c.
THERMOCHEMICAL PRODUCTION
Gasification of municipal solid waste (MSW) :
It is low-cost, sustainable source of hydrogen
production.
MSW, on average, consists of about 70% by
weight of biomass material.
Gasification results in an easily cleaned fuel
gas from which hydrogen can be reformed.
5-7 Advanced Hydrogen Production
Technologies

4.
a.
THERMOCHEMICAL PRODUCTION
The Texaco’s high-temperature gasification :
Result in a high yield of hydrogen and
produces a non-hazardous, glass-like ash
byproduct.
5-8Advantages Hydrogen Transport
and Storage Technologies

1.
2.
INTRODUCTION
The future use of hydrogen will require the
creation of a distribution infrastructure of safe
and cost-effective transport and storage.
Different applications need different types of
storage technology :
Stationary storage : utility electricity
generation; energy efficient and cost are
important
Mobile storage : fueling a vehicle; size and
weight are important
5-8Advantages Hydrogen Transport
and Storage Technologies
INTRODUCTION
3. Physical and solid-state storage systems that
will meet these diverse future application
demands.

5-8Advantages Hydrogen Transport
and Storage Technologies

1.
2.
3.
PHYSICAL STORAGE SYSTEM
Physical states are commercially available and
currently in use.
Hydrogen is generally in form of compressed
gas or cryogenic liquid, referred to as physical
storage.
Focusing on increasing the energy content per
unit of volume or weight of hydrogen storage
system.
5-8Advantages Hydrogen Transport
and Storage Technologies

4.
5.
6.
PHYSICAL STORAGE SYSTEM
Hydrogen gas is currently stored at high
pressures of 14~17 MPa.
New graphite composite material has potential
for storing hydrogen at pressure up to 41 Mpa.
These materials may make it possible for
hydrogen gas to be a cost-effective fuel.
5-8Advantages Hydrogen Transport
and Storage Technologies

1.
2.
3.
4.
5.
One Possible Future Hydrogen Infrastructure
Distributing H2 fuel in the form of compressed gas is
a potential growth market for zero emission vehicles.
Fleet refueling stations would supplied by truck with
liquid H2 from existing plants.
As demand increased, small dedicated pipeline
systems would be built to provide gaseous H2 from
new centralized reforming plants.
A pipeline serving 80,000 fuel-cell cars
Deliver hydrogen gas at about $13 per gigajoule, the
energy equivalent of about $0.45 per liter of gasoline.
5-8Advantages Hydrogen Transport
and Storage Technologies

1.
2.
3.
4.
SOLID-STATE STORAGE METHOD
Solid-state transport and storage technologies are
safer and have the potential to be more efficient than
gas or liquid storage.
Refers to chemical or physical binding of H2 to a
solid material.
Research stage→needs to improve the volumetric
density or the gravimetric density.
The most promising solid-state technologies are
metal hydrides, gas-on-solids adsorption system, and
glass microspheres.
5-8Advantages Hydrogen Transport
and Storage Technologies

1.
2.
3.
METAL HYDRIDES—release H2 by
dehydride
Advantages : high volumetric density, safety,
and the ability to deliver pure hydrogen at
constant pressure.
Disadvantages : low gravimetric density,
expressed as hydrogen as a percent of total
hydride weight (wt%)
They are suitable for stationary storage, but
limited for use in vehicles.
5-8Advantages Hydrogen Transport
and Storage Technologies

4.
5.
METAL HYDRIDES
The work of future : develop hydrides with
higher gravimetric densities that can operate
under temperatures and pressures consistent
with mobile storage.
The more promising hydride technologies :
improved metal alloys, high-efficiency metal
hydrides, non-classical metal hydride
complexes.
5-8Advantages Hydrogen Transport
and Storage Technologies

1.
2.
3.
Improved Metal Alloys
Capacities : 2.5 wt% ~ 6.2 wt% depending on
the composition.
Thin film alloys of magnesium-aluminumnickel-titanium have exhibited improved
gravimetric and volumetric energy densities.
Efforts are being made to scale up production
of these alloys.
5-8Advantages Hydrogen Transport
and Storage Technologies

1.
2.
3.
High-Efficient Metal Hydrides
Metal hydrides that dehydride hydrogen at
very high temperatures offer greater storage
efficiency at less cost than lower temperature
hydrides under development.
They are suitable to use on stationary storage,
but not available in mobile system.
A phase change material can be used to retain
hydriding energy as heat of fusion and then
return the heat for the dehydriding process.
5-8Advantages Hydrogen Transport
and Storage Technologies
High-Efficient Metal Hydrides
4. A Ni-coated Magnesium hydride material and
the salt mixture can be placed in a shell-andtube heat exchanger to perform this process.

5-8Advantages Hydrogen Transport
and Storage Technologies

1.
2.
3.
Nonclassical Metal Hydride Complexes
Nonclassical polyhydride metal complexes
(PMCs) may overcome the weight density
problem of hydride storage system.
Classical PMCs : they have high gravimetric
density, but generally undergo irreversible
dihydrogen elimination.
Nonclassical PMCs : they are allowing a
complete release of hydrogen under mild
condition and without high vacuum.
5-8Advantages Hydrogen Transport
and Storage Technologies

1.
2.
3.
GAS-ON-SOLID ADSORPTION
The principle of storage : the ability of highsurface-area carbons, when chemically
activated, to retain hydrogen on their surfaces.
The action of above is called adsorption, and it
happens at relatively high pressures and
extremely cold temperatures.
Hydrogen is released at atmospheric pressure
and ambient temperature.
5-8Advantages Hydrogen Transport
and Storage Technologies

4.
5.
6.
GAS-ON-SOLID ADSORPTION
The storage capacity of microcrystalline
currently : 4.8 wt% hydrogen at 87°K and
6Mpa.
The bar of storage capacity : relatively low
volumetric and gravimetric densities; the
cryogenic temperature required; high cost of
the process.
Two technologies that may increase the
potential for this storage medium : carbon
nanotubules and carbon aerogels.
5-8Advantages Hydrogen Transport
and Storage Technologies

1.
2.
3.
4.
Carbon Nanotubules
A new form of high-surface carbon material.
It has the potential for substantially increase
the volumetric and gravimetric densities.
It contains microscopic pores of uniform size
that encourage micro-capillary filling by
hydrogen condensation.
It lets hydrogen gas condense into a liquid
state at relatively high temperature.
5-8Advantages Hydrogen Transport
and Storage Technologies

5.
6.
Carbon Nanotubules
Preliminary results on nanotubule-containing
samples : 8.4 wt% hydrogen at 82°K and
0.07Mpa.
The direction of work in future : improve the
quantity of hydrogen stored at near-ambient
temperature.
5-8Advantages Hydrogen Transport
and Storage Technologies

Carbon Nanotubules
5-8Advantages Hydrogen Transport
and Storage Technologies

1.
2.
Carbon Aerogels
A special class of open-cell foams with an
ultra-fine cell/pore size, high surface area, and
a solid matrix.
The process of creating carbon aerogels : be
usually synthesized from the aqueous
polycondensation of resorcinol(間苯二酚,雷
瑣辛) with formaldehyde (甲醛), followed by
supercritical extraction and pyrolysis-at about
1050℃-in an inert atmosphere.
5-8Advantages Hydrogen Transport
and Storage Technologies

3.
4.
5.
Carbon Aerogels
Synthesized aerogels have a nanocrystalline
structure with micro-pores less than 2
nanometer in diameter.
Results on the aerogels-containing sample :
3.7 wt% hydrogen at 8.3MPa.
The direction of work in future : improve
maximum hydrogen adsorption over a wide
range of temperatures and pressures.
5-8Advantages Hydrogen Transport
and Storage Technologies

1.
2.
GLASS MICROSPHERES
These glass spherical structures : diameters of
25 to 500 microns and wall thickness of
approximately 1 micron.
The process of storing hydrogen : at 200℃ to
400℃, the increased permeability of the glass
permits the spheres to be filled by hydrogen
under pressure by immersion in high-pressure
hydrogen gas, when cooled to ambient
temperature, the hydrogen is locked.
5-8Advantages Hydrogen Transport
and Storage Technologies

GLASS MICROSPHERES
5-8Advantages Hydrogen Transport
and Storage Technologies

3.
4.
GLASS MICROSPHERES
Subsequent raising of the temperature will
release the hydrogen.
Spheres synthesized are defect-free and have a
membrane tensile stress at failure of about
1000MPa, yielding a burst pressure three
times as great as commercially-produced
spheres.
5-8Advantages Hydrogen Transport
and Storage Technologies

5.
6.
GLASS MICROSPHERES
A small bed of such microspheres can contain
hydrogen : mass fraction 10% at about 62MPa.
In test, 95% of a microsphere has been filled
or release in about 15 minutes at 370℃.