Fuel Cells An Alternate Energy Source

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Fuel CellsAn Alternate Energy Source

• Damion Dunlap
• Anthony Gleaton
• 19 October 2001

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Overview

• Why we need alternate energy sources
• Various alternatives to the IC engine
• Fuel Cells
• Components
• Connection
• Types of Fuel Cells
• Technical Notes Compressor Effects
• Wrap-Up

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Why do we need alternative energy sources?

• Reduce or alleviate dependence on fossil fuels
• Petroleum bound to run out eventually
• Pollution we only have one Earth

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What are the viable alternatives currently in use?

• Electric Vehicles
• Electric IC Hybrids
• Fuel Cell Vehicles

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Electric Vehicles

• Benefits
• No direct dependence on fossil fuels
• No pollution
• Drawbacks
• Electricity has to come from powerplant
• Coal primary source high pollution
• Relatively short range between charging

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How Electric Vehicles Work
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GM EV1 Electric Vehicle

• Acceleration 0-60 in lt9 sec.
• Top Speed 80mph
• Range 75-130 mi
• Torque 110 ft-lb
• Power 137 Hp

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Electric IC Hybrids

• Benefits
• Less pollution than traditional IC engine cars
• More range than Electric vehicles
• Easily refuelable
• Drawbacks
• Still has pollution
• Maintains dependence on fossil fuels
• Simply a intermediate step a compromise

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How Hybrid Vehicles Work

• Series Hybrid
• IC Engine turns a Generator
• Generator charges batteries or powers the motor

• Parallel Hybrid
• IC Engine Motor both connected to transmission
• Both can drive the vehicle independently

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Toyota Prius Hybrid Vehicle

• Price Only 20,480
• Range 48 Mi/Gas

• IC Engine
• 1.5 L70 Hp
• Electric Motor
• 44 Hp

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Fuel Cell Vehicles

• Benefits
• Dependence on fossil fuels can be eliminated
• Zero pollution only heat and water
• More efficient than all other alternatives
• Simplicity
• Drawbacks
• Infrastructure no Hydrogen stations
• Storage Hydrogen must be pressurized

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New Fuel Cell Innovation

• Solar-Powered Hydrogen Production and Fueling
  Station
• Uses photovoltaic array to extract hydrogen from
  water via electrolysis
• Installed at Honda RD Headquarters - July, 01

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GM Hydrogen1Fuel Cell S-10

• Gasoline reformer needs sulfur free gas
• Efficiency 40 overall
• 50 improvement vs. IC Engine
• Power 33 Hp
• Warm-Up Time
• 15 min.

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Comparing efficiencies

• Gasoline-powered car
• 20 overall
• Battery-powered electric car
• 90 for battery 80 for motor/inverter 40
  for power plant 90 for charging 26 overall
• Fuel cell powered electric car
• 80 for fuel cell 30-40 reformer 80 for
  motor/inverter 24-32 overall

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Social Changes NecessaryEnvironment before
Convenience

• Be willing to pay for environment
• Bigger isnt necessarily better
• Efficiency over Power
• More Power Less Efficient
• Select components for average not max power
• Average IC car only needs 20 Hp to cruise at 60
  Mph
• Must stop procrastinating
• Cant wait until petroleum runs out to do
  something
• Ex Energy Crisis of the late 70s

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Fuel Cells Overview

• What is a fuel cell?
• Fuel cell operation
• Types of fuel cells

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What is a fuel cell?

• Electrochemical energy conversion device
• Converts hydrogen and oxygen into electricity,
  heat, and water
• First built in 1839 by Sir William Grove
• NASA began first practical use in 1960s
• Typically provides DC voltage

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Proton Exchange Membrane

• Anodenegative post of fuel cell
• Conducts the electrons freed from hydrogen
  molecules so they can be used in an external
  circuit
• Disperses the hydrogen gas equally over the
  surface of the catalyst through etched channels

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Proton Exchange Membrane

• Cathodepositive post of fuel cell
• Conducts the electrons back from the external
  circuit to the catalyst
• Electrons are then recombined with hydrogen ions
  and oxygen atoms to form water
• Disperses oxygen equally over the surface of
  catalyst through etched channels

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Proton Exchange Membrane

• Electrolyteproton exchange membrane
• Specially treated material which only conducts
  positively charged ions
• Resembles ordinary kitchen plastic wrap
• Membrane blocks electrons, forcing them around
  the external circuit

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Proton Exchange Membrane

• Catalystspecial material that facilitates the
  reaction of oxygen and hydrogen
• Typically made of platinum powder very thinly
  coated onto carbon paper or cloth
• Rough and porous so that the maximum surface area
  of the platinum can be exposed to the hydrogen or
  oxygen
• Platinum-coated side of the catalyst faces the PEM

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PEM operation

• Animation courtesy of Ballard Power Systems
• Ballard Power Systems PEM
• Voltage output 0.6-0.7 volts per cell
• Fuel cells must be connected together

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Fuel cell stacks (edge connection)

• 1st method connect edges of each anode to the
  cathode of the next cell

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Fuel cell stacks (edge conn.)

• Problem electrons must flow across the face of
  the electrode to the current collection point at
  the top edge
• Produces a voltage drop

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Fuel cell stack (bipolar plate)

• 2nd method bipolar plate
• Makes connections all over one cathode and the
  anode of the next cell

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Bipolar plate design

• Bipolar plate feeds oxygen to cathode and fuel
  gas to anode
• Two gas supplies must be strictly separated
• Good electrical connection must be made between
  the two electrodes

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Bipolar plate design

• Conflicts
• Contact points should be large
• Gas flow over electrodes should be high
• Minimize electrical resistancethin plate
• Graphite is common material for plate
• Machining is expensive
• Plate is significant cost factor for fuel cell

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Bipolar plate design
Anode, electrolyte, and cathode in one piece
Bipolar plate
Bipolar plate
Hydrogen fed in here, and flows in channels over
the face of the anode
Oxygen or air fed in here over the face of the
cathode
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Types of fuel cells

• Some types of fuel cells can be used in power
  generation plants
• Others can be used in small portable applications
  or for powering cars
• Usually classified by type of electrolyte used

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Proton Exchange Membrane (PEM)

• Operating temperature 50-100C
• Mobile ion H
• Suitable for vehicles and mobile applications
• Uses one of the simplest reactions

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Alkaline (AFC)

• Operating temp 50-200C
• Mobile ion OH-
• One of the oldest designs
• Used by NASA
• Requires pure hydrogen and oxygen

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Phosphoric acid (PAFC)

• Operating temp 220C
• Mobile ion H
• Longer warm-up time than PEM
• Large numbers of 200kW (small stationary power)
  systems currently in use

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Molten carbonate (MCFC)

• Operating temp 650C
• Mobile ion CO32-
• Suitable for large stationary power generators
• Excess heat more power through steam

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Solid Oxide (SOFC)

• Operating temp 500-1000C
• Mobile ion O2-
• Suitable for large-scale stationary power
  generators (for factories or towns)
• Temp is high reliability a problem
• steam production increases overall efficiency of
  system

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Comparison of fuel cells
1 10 100 1k 10k
100K 1M 10M
AFC
MCFC
SOFC
PEMFC
PAFC
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Technical Notes Compressor Effects
Motor driven Compressor and PEM fuel cell system
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Effect of Compressoron Cell Voltage

• Power (electrical)
• Vc Cell Voltage
• I Current
• N number of cells in the stack
• Air Usage
• l Stoichiometric constant
• P Power
• Voltage Gain due to increase of Pressure Ratio
• , where C is an
  empirical constant

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Compressor Effect Cont.

• Compressor Power
• Temperature change can be determined using
  isentropic relationship and compressor efficiency
  equations.
• Power loss due to Compressor
• hm Mechanical efficiency of the motor driving
  the compressor
• Note
• Net Voltage Gain

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Wrap-Up

• Is the car quick and easy to refuel?
• Can it travel a good distance before refueling?
• How much pollution does it produce?
• Can it keep up with other cars on the road?
• Does it have muscle car potential?

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References

• Larminie, J. Dicks, A. Fuel Cell Systems
  Explained 2001
• www.howstuffworks.com/fuel-cell.html
• www.ballard.com
• www.fuelcells.org
• www.hfcletter.com