Fuel Cell Technology
SJSU E-10
October 25, 2007
Professor W. Richard Chung
Department of Chemical and Materials
Engineering
San Jose State University
Pictures of Battery
Cathode
Anode
What is A Fuel Cell?
• A fuel cell is an electrochemical energy
conversion device. It produces electricity from
external supplies of fuel (anode side) and
oxidant (cathode side).
• A fuel cell is similar to a battery in that an
electrochemical reaction is used to create
electric current. The charges can be released
through an external circuit via wire connections
to anode and cathode plates of the battery or
the fuel cell.
Fuel cells are different from batteries in
that they consume reactant, which must
be replenished, while batteries store
electrical energy chemically in a closed
system.
• The major difference between fuel cells and
batteries is that batteries carry a limited supply of
fuel internally as an electrolytic solution and solid
materials (such as the lead acid battery that
contains sulfuric acid and lead plates) or as solid
dry reactants such as zinc /carbon powders found
in a flashlight battery.
• Fuel cells have similar reactions; however, the
reactants are gases (hydrogen and oxygen) that
are combined in a catalytic process. Since the gas
reactants can be fed into the fuel cell and
constantly replenished, the unit will never run
down like a battery.
• Fuel cells are named based on the type of
electrolyte and materials used. The fuel cell
electrolyte is sandwiched between a positive and
a negative electrode.
• Because individual fuel cells produce low
voltages, fuel cells are stacked together to
generate the desired output for specific
applications. The fuel cell stack is integrated into
a fuel cell system with other components,
including a fuel reformer, power electronics, and
controls. Fuel cell systems convert chemical
energy from fossil fuels directly into electricity.
How does a fuel cell work?
A fuel cell consists of an anode,
cathode, and electrolyte
A fuel cell is consisted of two
electrodes (an anode and a cathode)
that sandwich an electrolyte (a
specialized material that allows ions to
pass but blocks electrons).
Fuel cells could power cleaner buses
and cars and could provide electricity,
heat and hot water to a home, but key
engineering and economic obstacles
remain which delay widespread
adoption of the technology.
http://www.greenjobs.com/Public/images/fuel-cell.jpg
The fuel (hydrogen) enters the fuel
cell, and this fuel is mixed with air,
which causes the fuel to be oxidized.
As the hydrogen enters the fuel cell, it
is broken down into protons and
electrons. In the case of PEMFC and
PAFC, positively charged ions move
through the electrolyte across a voltage
to produce electric power. (charging
mode)
The protons and electrons are then
recombined with oxygen to make water,
and as this water is removed, more
protons are pulled through the
electrolyte to continue driving the
reaction and resulting in further power
production.
In the case of SOFC, it is not protons
that move through the electrolyte, but
oxygen radicals. In MCFC, carbon
dioxide is required to combine with the
oxygen and electrons to form carbonate
ions, which are transmitted through the
electrolyte.
Common Types of Fuel Cell
• Metal hydride fuel cell Aqueous alkaline solution (e.g.
potassium hydroxide)
• Electro-galvanic fuel cell Aqueous alkaline solution
(e.g., potassium hydroxide)
• Direct formic acid fuel cell (DFAFC) Polymer
membrane (ionomer)
• Direct borohydride fuel cell Aqueous alkaline solution
(e.g., sodium hydroxide)
• Direct methanol fuel cell Polymer membrane
(ionomer)
• Protonic ceramic fuel cell H+-conducting ceramic oxide
• Solid oxide fuel cell (SOFC) O2--conducting ceramic
oxide (e.g., zirconium dioxide, ZrO2)
Fuel Cells
• There are four primary fuel cell technologies. These
include phosphoric acid fuel cells (PAFC), molten
carbonate fuel cells (MCFC), solid oxide fuel cells (SOFC),
and proton exchange membrane fuel cells (PEMFC). The
technologies are at varying states of development or
commercialization. Fuel cell stacks utilize hydrogen and
oxygen as the primary reactants.
• However, depending on the type of fuel processor and
reformer used, fuel cells can use a number of fuel
sources including gasoline, bio-diesel, methane
(hydrocarbons), methanol (alcohol), natural gas, “waste
material” and solid carbon.
• Air, chlorine and chlorine dioxide are reactants.
PEMFC
• Proton exchange membrane (PEM) fuel cells
work with a polymer electrolyte in the form of
a thin, permeable sheet. This membrane is
small and light, and it works at low
temperatures (about 80 degrees C, or about
175 degrees F). Other electrolytes require
temperatures as high as 1,000 degrees C.
PEM Fuel Cell (Proton Exchange Membrane
Fuel Cells)
Solid Oxide Fuel Cells ( SOFCs )
• A solid oxide fuel cell
(SOFC) is a device that
converts gaseous fuels
(hydrogen, natural
gas, gasified coal) via
an electrochemical
process directly into
electricity.
Air is supplied to the
cathode (air electrode)
At the cathode, the O2
molecules are ionized
Several advantages make SOFC more
attractive than Hydrogen fuel cells for some
applications
•
•
•
•
•
SOFCs are over 60% efficient
(conversion of fuel to
electricity) making them the
most efficient fuel cell currently
being developed.
The efficiency makes them a
good candidate for a
distributed power source
(generator or power plant).
Because they are solid, SOFCs
are quieter than other types,
making them good for indoor
applications.
The reactions in SOFC require a
high temperature. The
advantage is that this creates a
by-product of heat.
There are no liquids that cause
safety and environmental
http://www.ztekcorporation.com/sofc_200kw.htm
problems.
In SOFCs oxygen ions react with H2
from the fuel
The ionized oxygen
diffuses across the
electrolyte
At the anode, the O2- ions
react with H (in the fuel).
H2 + O2-  H2O + 2eThe reaction produces
electrons to do work and
water.
The anode and cathode are porous
while the electrode is dense
The anode and cathode must be porous to allow the air and fuel in
The electrolyte must be dense to prevent
the air and fuel from mixing.
F. Tietz, H.-P. Buchkremer, and D. Stöver, “Components manufacturing for solid
oxide fuel cells,” Solid State Ionics, 152-153 (2002) 373-381.
Nanomaterials play a key role in the
SOFCs
Large surface areas (nanopores) are
needed for oxygen transport within
the air electrode, as well as hydrogen
and water transport within the fuel
electrode.
Nanoporosity (i.e. pores less than 100
nm in size) can be attained by careful
processing of nanosized ceramic
particles.
Desired Cathode Structure
The anode would have the same
structure, but the gas that would flow
through is hydrogen.
Ceramics are needed to allow for the ionic
conduction
• The most common electrolyte material
is ZrO2 (zirconia), which is doped with
small amounts of Y2O3 (yttria). This
material is known as yttria-stabilized
zirconia (YSZ). This is a ceramic
material - a compound of a metal with
a non-metal.
• Ni/YSZ cermet (ceramic-metal
composite) is used as the anode
material because of its low cost. It is
also chemically stable at high
temperatures and its thermal
expansion coefficient is close to that of
the YSZ electrolyte.
• The cathode is based on a (La1-ySry)
MnO3-d (LSM) perovskite material.
J. Will, A. Mitterdorfer, C. Kleinlogel,
D. Perednis, and L.J. Gauckler,
“Fabrication of thin electrolytes for
second-generation solid oxide fuel
cells,” Solid State Ionics, 131 (2000)
79-96.
There are a number of materials related
research items to improve SOFCs
Thinner layers are being
designed to minimize ohmic
resistance.
Manufacturing processes are
being optimized for lower
temperatures to avoid
undesirable mixing.
New materials of higher
performance are being
investigated
S.C. Singhal, “Advances in solid oxide fuel cell
technology,” Solid State Ionics, 135 (2000) 305-313.
A.J. McEvoy, “Thin SOFC electrolytes and their
interfaces - a near-term research strategy,” Solid
State Ionics, 132 (2000) 159-165.
SOFC -- passing oxygen ions
across a solid electrolyte.
SOFC has a ceramic cathode that ionizes oxygen.
The cathode needs to be porous to allow air in.
The oxygen ions diffuse across a solid, dense,
ceramic electrolyte.
At the anode, the oxygen ions react with
hydrogen to form water and electrons.
The electrons can not flow through the
electrolyte so they leave through the load.
SOFC are being investigated for power plants and
generators. They have high efficiency, are quiet,
and have no liquids that can be unsafe or
dangerous to the environment.
Fuel Cell Applications
• Fuel cells are very useful as power sources in
remote locations, such as spacecraft, remote
weather stations, large parks, rural locations,
and in certain military applications.
• A fuel cell system running on hydrogen can be
compact, lightweight and has no major
moving parts. Because fuel cells have no
moving parts, and do not involve combustion,
in ideal conditions they can achieve up to
99.9999% reliability.
Toyota FCHV PEM FC fuel cell vehicle
Micro-fuel cell developed by Fraunise ISE for
use in applications such as cellular phones
The world's first certified Fuel Cell Boat (HYDRA),
Karl-Heine Kanal in Leipzig, Germany
A hydrogen fuel cell public bus accelerating at
traffic lights in Perth, Western Australia
“Warsitz Enterprises' portable fuel cell
power unit”
A fuel cell powers a laptop computer
Tomorrow, hydrogen's use as a fuel for fuel
cells will grow dramatically-for transportation,
stationary and portable applications.
(PlugPower 5-kW fuel cell (large cell),
H2ECOnomy 25-W fuel cell (small silver cell),
and Avista Labs 30-W fuel cell).
Fuel cells provide heat and power at the
Anchorage mail processing center
Hydrogen fueling station at California Fuel Cell
Partnership
General Motor’s EcoFlex car is showing its
HydroGen4 at the Frankfurt auto show in fall
2007
• The reactants flow in and reaction products
flow out while the electrolyte remains in the
cell. Fuel cells can operate virtually
continuously as long as the necessary flows
are maintained.
History
• The principle of the fuel cell was discovered by German
scientist Christian Friedrich Schönbein in 1838 and published
in the January 1839 edition of the "Philosophical Magazine".
Based on this work, the first fuel cell was developed by Welsh
scientist Sir William Robert Grove in 1843. The fuel cell he
made used similar materials to today's phosphoric-acid fuel
cell. In 1955, W. Thomas Grubb, a chemist working for the
General Electric Company (GE), further modified the original
fuel cell design by using a sulphonated polystyrene ionexchange membrane as the electrolyte. Three years later
another GE chemist, Leonard Niedrach, devised a way of
depositing platinum onto the membrane, which served as
catalyst for the necessary hydrogen oxidation and oxygen
reduction reactions. This became known as the 'GrubbNiedrach fuel cell'.
http://en.wikipedia.org/wiki/Fuel_cell
History (cont’d)
• GE went on to develop this technology with NASA,
leading to it being used on the Gemini space project.
This was the first commercial use of a fuel cell. It wasn't
until 1959 that British engineer Francis Thomas Bacon
successfully developed a 5 kW stationary fuel cell. In
1959, a team led by Harry Ihrig built a 15 kW fuel cell
tractor for Allis-Chalmers which was demonstrated
across the US at state fairs. This system used potassium
hydroxide as the electrolyte and compressed hydrogen
and oxygen as the reactants. Later in 1959, Bacon and his
colleagues demonstrated a practical five-kilowatt unit
capable of powering a welding machine. In the 1960s,
Pratt and Whitney licensed Bacon's U.S. patents for use
in the U.S. space program to supply electricity and
drinking water (hydrogen and oxygen being readily
available from the spacecraft tanks).
Fuel Cell Efficiency
The efficiency of a fuel is dependent on the
amount of power drawn from it. Drawing more
power means drawing more current, which
increases the losses in the fuel cell. As a general
rule, the more power (current) drawn, the lower
the efficiency. Most losses manifest themselves
as a voltage drop in the cell, so the efficiency of a
cell is almost proportional to its voltage. For this
reason, it is common to show graphs of voltage
versus current (so-called polarization curves) for
fuel cells.
A typical cell running at 0.7 V has an
efficiency of about 50%, meaning that 50%
of the energy content of the hydrogen is
converted into electrical energy; the
remaining 50% will be converted into heat.
(Depending on the fuel cell system design,
some fuel might leave the system unreacted, constituting an additional loss.)
Voltage Vs Current
2000
1800
1600
1400
Voltage (mV)
1200
1000
Series1
800
600
400
200
0
0
500
1000
1500
Current (mA)
2000
2500
Power Vs Voltage
1200
1000
Power (mW)
800
600
Series1
400
200
0
0
200
400
600
800
1000
Voltage (mV)
1200
1400
1600
1800
2000
Major Fuel Cells
PAFC
SOFC
MCFC
PEMC
No
Yes
Yes
Commercially
Available
Yes
Size Range
100-200kW
1kW-10MW
250kW-10MW
3-250kW
Fuel
Natural gas,
digester gas,
propane
Natural gas,
hydrogen, fuel
oil
Natural gas,
hydrogen
Natural gas,
hydrogen,
propane, diesel
Efficiency
36-42%
45-60%
45-55%
25-40%
Environmental
Nearly zero
emissions
Nearly zero
emissions
Nearly zero
emissions
Nearly zero
emissions
Other Features
Cogen (hot
water)
Cogen (hot
water, LP or HP
steam)
Cogen (hot
water)
Cogen (80oCwater)
Commercial
Status
Some
commercially
Available
Some
commercially
Available
Some
commercially
Available
Some commercially
Available
California Energy Commission:
http://www.energy.ca.gov/distgen/equipment/fuel_cells/fuel_cells.html
Process
• GE's Russell Hodgdon shows a polymer electrolyte in 1965. To
speed the reaction a platinum catalyst is used on both sides of
the membrane. Hydrogen atoms are stripped of their
electrons, or "ionized," at the anode, and the positively
charged protons diffuse through one side of the porous
membrane and migrate toward the cathode. The electrons
pass from the anode to the cathode through an exterior
circuit and provide electric power along the way. At the
cathode, the electrons, hydrogen protons and oxygen from
the air combine to form water. For this fuel cell to work, the
proton exchange membrane electrolyte must allow hydrogen
protons to pass through but prohibit the passage of electrons
and heavier gases. Efficiency for a PEM cell reaches about 40
to 50 percent. An external reformer is required to convert
fuels such as methanol or gasoline to hydrogen. Currently,
demonstration units of 50 kilowatt (kw) capacity are operating
and units producing up to 250 kw are under development.
Dr. Russell Hodgdon of GE demonstrated a
polymer electrolyte in 1965
Fuel Cell Lab Exercise
plug
Charging
H2 tank
Fuel
cell
O2 tank
plug
hose
Distilled Water
motor
Power meter
H2 tank
Fuel
cell
O2 tank
plug
Prop up the front wheels
water
reservoir
Future Developments
• Low temperature fuel cell stacks proton exchange membrane
fuel cell (PEMFC), direct methanol fuel cell (DMFC) and
phosphoric acid fuel cell (PAFC) make extensive use of catalysts.
Impurities poison or foul the catalysts (reducing activity and
efficiency), thus higher catalyst densities are required.
• Not all geographic markets are ready for SOFC powered m-CHP
appliances. Currently, the regions that the lead the race in
distributed generation and deployment of fuel cell m-CHP units
are the EU and Japan
• Although platinum is seen by some as one of the major
"showstoppers" to mass market fuel cell commercialization
companies, most predictions of platinum running out and/or
platinum prices soaring do not take into account effects of
thrifting (reduction in catalyst loading) and recycling.
Thank You!
Q&A
Q1. The major difference between
fuel cells and batteries is:
A. Fuel cells generate hydrogen gas, whereas
batteries consume stored solid or liquid
B. Fuel cells generate oxygen gas, whereas
batteries consume electricity
C. Fuel cells consume hydrogen gas, whereas
batteries consume stored solid or liquid
D. Fuel cells consume oxygen gas, whereas
batteries consume stored solid or liquid
E. Fuel cells consume water, whereas batteries
consume stored solid or liquid
Q2. Which of the following is the
by-product of a fuel cell reaction?
A. Water
B. Hydrogen
C. Oxygen
D. Electrolyte
E. All of the above
Q3. Which of the following is not a
reactant of a fuel cell?
A. Bio-diesel
B. Methane
C. Methanol
D. Air
E. Gasoline
Q4. Which of the following describes the
function of a fuel cell in a discharge mode?
A.
B.
C.
D.
E.
Air is supplied to the cathode side
Air is supplied to the anode side
Water is supplied to the cathode side
Water is supplied to the anode side
Hydrogen gas is supplied to the
cathode side
Q5. The efficiency of a fuel cell is
often determined by the:
A. Current drawn
B. Amount of reactants consumed
C. Voltage supplied
D. Operating temperature
E. Amount of oxidants used