Fuel Cell Technology - PowerPoint by 1hAsMAwq

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									   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 + 2e-

The 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   J. Will, A. Mitterdorfer, C. Kleinlogel,
  the YSZ electrolyte.                        D. Perednis, and L.J. Gauckler,
                                              “Fabrication of thin electrolytes for
                                              second-generation solid oxide fuel
• The cathode is based on a (La1-ySry)
                                              cells,” Solid State Ionics, 131 (2000)
  MnO3-d (LSM) perovskite material.
                                              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         S.C. Singhal, “Advances in solid oxide fuel cell
                                 technology,” Solid State Ionics, 135 (2000) 305-313.
investigated
                              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.
                                                The world's first certified Fuel Cell Boat (HYDRA),
                                                Karl-Heine Kanal in Leipzig, Germany
Toyota FCHV PEM FC fuel cell vehicle




Micro-fuel cell developed by Fraunise ISE for     A hydrogen fuel cell public bus accelerating at
use in applications such as cellular phones       traffic lights in Perth, Western Australia
“Warsitz Enterprises' portable fuel cell            A fuel cell powers a laptop computer
power unit”


                                           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
                                           Hydrogen fueling station at California Fuel Cell
Anchorage mail processing center
                                           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 ion-
  exchange 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 'Grubb-
  Niedrach 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 un-
reacted, constituting an additional loss.)
                                   Voltage Vs Current


               2000


               1800


               1600


               1400


               1200
Voltage (mV)




               1000                                                        Series1


                800


                600


                400


                200


                  0
                      0   500   1000                  1500   2000   2500
                                       Current (mA)
                                                Power Vs Voltage


             1200




             1000




              800
Power (mW)




              600                                                                                   Series1




              400




              200




                0
                    0   200   400   600   800        1000        1200   1400   1600   1800   2000
                                                  Voltage (mV)
                            Major Fuel Cells
                     PAFC            SOFC             MCFC              PEMC
Commercially                           No              Yes               Yes
                     Yes
  Available
  Size Range     100-200kW        1kW-10MW         250kW-10MW          3-250kW
     Fuel        Natural gas,     Natural gas,     Natural gas,       Natural gas,
                 digester gas,   hydrogen, fuel     hydrogen           hydrogen,
                   propane            oil                           propane, diesel
  Efficiency       36-42%           45-60%           45-55%            25-40%
Environmental     Nearly zero     Nearly zero       Nearly zero       Nearly zero
                  emissions       emissions         emissions         emissions
Other Features    Cogen (hot      Cogen (hot        Cogen (hot    Cogen (80oCwater)
                    water)       water, LP or HP      water)
                                    steam)
 Commercial         Some            Some              Some        Some commercially
   Status        commercially    commercially      commercially       Available
                   Available       Available         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


                                                                                 H2 tank
                                  Charging
                                                   Fuel
                                                   cell
                                                                                   O2 tank
                                                             plug


                                                                    hose   water
                                                                           reservoir



        Distilled Water




motor                                        Power meter


                              H2 tank
          Fuel
          cell
                               O2 tank
                      plug


  Prop up the front wheels
             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.   Air is supplied to the cathode side
  B.   Air is supplied to the anode side
  C.   Water is supplied to the cathode side
  D.   Water is supplied to the anode side
  E.   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

								
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