Fuel cells

1
Fuel cells
2
Fuel cell history

• First demonstrated in principle by British
  Scientist Sir Willliam Robert Grove in 1839.
• Groves invention was based on idea of reverse
  electrolysis.

3
What is a fuel cell

• Creates electricity through electrochemical
  process
• Operates like a battery
• Emits heat and water only

4
Parts of fuel cells

• There are 4 main parts
• Anode
• Cathode
• Catalyst
• Proton exchange membrane

5
Fuel cell theory

• A fuel cell consists of two electrodes - Anode
  and Cathode.
• Hydrogen and Oxygen are fed into the cell.
• Catalyst at Anode causes hydrogen atoms to give
  up electrons leaving positively charged protons.
• Oxygen ions at Cathode side attract the hydrogen
  protons.

6
Cont..

• Protons pass through electrolyte membrane.
• Electrons are redirected to Cathode through
  external circuit.
• Thus producing the current - power

7
Fuel cell working
8
Types of fuel cells

• Temp.C Application
• Alkaline (AFC) 70-90 Space
• Phosphoric Acid 150-210 Commercially
  available
• (PAFC)
• Solid Polymer 70-90 Automotive application
• (PEMFC)
• Moltan Carbonate 550-650 Power generation
• (MCFC)
• Solid Oxide 1000-1100 Power generation
• (SOFC)
• Direct Methanol 70-90 Under development
• (DMFC)

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Alkaline Fuel Cell

• Used in spacecraft to provide drinking water and
  electricity
• Electrolyte Aqueous solution of alkaline
  potassium Hydroxide
• Output of 300w -5KW
• Power generation efficiency of about 70
• Too expensive for commercial applications

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Phosphoric Acid Fuel cell

• Used in hospitals, nursing homes and for all
  commercial purposes
• Electrolyte Liquid Phosphoric acid
• Catalyst platinum
• Electrical efficiency of 40
• Advantages using impure hydrogen as fuel and 85
  of the steam can be used for cogeneration

11
Contd

• Disadvantages uses expensive platinum as
  catalyst
• Large size and weight
• Low power and current
• Existing PAFCs have outputs of 200kw and 1Mw are
  being tested

12
Proton Exchange Membrane Cells

• Also called as Solid Polymers and used for quick
  startup in automobiles, light duty vehicles and
  potentially to replace rechargeable batteries
• Electrolyte Solid organic polymer
  poly-perflourosulfonic acid.
• Catalyst Metals (usually platinum) coated on
  both sides of membrane act as catalyst
• Advantages Use of solid electrolyte reduces
  corrosion and management problems

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Contd..

• Disadvantages Sensitive to fuel impurities
• Cell outputs generally range from 50 to 250 kW.

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Molten Carbonate Fuel cell

• Majorly used for electric utility applications
• Electrolyte Liquid solution of lithium, sodium
  and/or potassium carbonates.
• Catalyst Inexpensive metals can be used as
  catalyst other than Platinum
• Advantages High operating temperature allow for
  inexpensive catalysts

15
Contd..

• Higher efficiency and flexibility to use more
  type of fuels like carbon monoxide, propane,
  marine gas due to high temperatures
• Disadvantage Higher temperature enhances
  corrosion and breakage of cell components
• High fuel to electricity generation of about 60
  or 85 with cogeneration.
• 10 kws -1 mws MCFCS have been tested

16
Solid Oxide Fuel Cell

• Highly promising fuel cell
• Used in big, high-power applications including
  industrial and large-scale central electricity
  generating stations
• Some developers also see SOFC use in motor
  vehicles
• Power generating efficiencies could reach 60 and
  85

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Cont..

• Two Variations
• One type of SOFC uses an array of meter-long
  tubes, and other variations include a compressed
  disc that resembles the top of a soup can
• Closer to commercialization
• Demonstrations of tubular SOFC technology have
  produced as much as 220 kW

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Direct Methanol Fuel Cells

• Similar to the PEM cells in that they both use a
  polymer membrane as the electrolyte
• The anode catalyst itself draws the hydrogen from
  the liquid methanol, eliminating the need for a
  fuel reformer.
• Efficiency of about 40
• typically operate at a temperature between
  120-190 degrees F

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Cont..

• Relatively low range
• Attractive for tiny to mid-sized applications, to
  power cellular phones and laptops
• Higher efficiencies are achieved at higher
  temperatures
• Major problem Fuel crossing over from the anode
  to the cathode without producing electricity.