Hydrogen as an energy source

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Hydrogen as an energy source
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Science fiction or not?

• In Jules Vern novel (1874) Mysterious Island, a
  shipwrecked engineer speculates about what will
  be used as a fuel when the worlds coal supply
  has been used up.
• Water, the engineer declares, I believe that
  water will one day be employed as fuel, that
  hydrogen and oxygen which constitute it, used
  singly or together, will furnish an inexhaustible
  source of heat and light

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Questions

• Is this simply science fiction, or is it
  energetically and economically feasible to break
  water into its component elements?
• Can hydrogen really serve as a useful fuel?
• What does it have to do with Solar energy and/or
  Nuclear fusion?

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To answer the question lets begin with the
basics

• How much energy is produced or released when H2
  is burned?
• H2(g) ½ O2 (g) -gt H2O(g)
• Can we calculate it?
• (Updated see ppt notes)

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Hydrogen

• Clearly, hydrogen has the potential of being a
  powerful energy source!!!
• IN FACT, Hydrogen has the highest heat of
  combustion of ANY known SUBSTANCE.
• Used in rockets, space shuttle, small batteries,
  etc
• High energy, low emission TANTILIZING for fuel
  in cars and other

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Sources of hydrogen

• Where can we get hydrogen?
• Reaction of metal with Acid
• On that Day I demoed Sodium Metal and Water
• Na(s) H2O(l) -gt NaOH H2
• More commonly (a metal w/ Sulfuric acid)
• Zn(s) H2SO4 -gt H2(g) ZnSO4
• Electrolysis
• Demoed the bubbling that occurs at an electrode
  surface. Remember the light bulb.
• H2O(l) -gt H2 ½ O2 (reverse reaction of
  combustion)
• Same amount of energy NEEDS TO BE INPUTED
• Discussed feasibility

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Sources of hydrogen (Contd)

• Hot steam over pure carbon (coke)
• Input 131 kJ/mol
• H2O C(s) -gt H2(g) CO(g)
• CO is carbon MONOXIDE!!
• Hot steam over methane (natural gas)
• Input 165 kJ/mol
• H2O CH4 -gt 4 H2 (g) CO2(g)
• CO2 Greenhouse gas

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How can we store it?

• If we succeed in producing H2 cheaply, we are
  still faced with the questions
• How do we store it?
• How do we transport it
• 1 gram occupies about 12 liters
• If stored as gaseous state, large heavy walled
  containers will be necessary! This eliminates
  the benefits of H2 as a fuel (high energy/low
  mass ratio)
• Liquefied at -250oC
• A lot of energy would be required!!

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2 methods that I am aware of

• Adsorption of H2 onto activated carbon
• Use of Li metal.
• Li is highly reactive metal
• Reaction of H2 gas can reduce the volume of 12
  liter to about 4-5 ml.
• Here is the chemistry
• Li(s) ½ H2(g) -gt LiH(s)
• Q Ok how do we get it back when we need it
• A Drop Lithium hydride (LiH) into water
• LiH H2O -gt H2 LiOH Produces Hydrogen gas

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Fuel Cells

• Same reaction without a flame!!

Conductive Wire
½ O2 oxygen gas
H2 gas
Proton Exchange Membrane (PEM)
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Hydrogen

• Consider Hydrogen for a minute

Hydrogen subatomic make-up 1 proton and 1
electron
e-
1 proton
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e-
The proton moves through the PEM and leaves an
electron behind
Proton can be designated H
e-
As the hydrogen travels It is light and will
travel upwards
e-
1 proton
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Fuel cell contd
2e-
Electrons moving through a wire ELECTRICITY
Proton or H
Proton or H
½ O2 oxygen gas
H2
Proton Exchange Membrane (PEM)
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Reactions occuring
2e-
Electrons moving through a wire ELECTRICITY
Proton or H
Proton or H
½ O2 oxygen gas
H2
H2 -gt 2H 2e-
2H 2e- ½ O2 (g) -gtH2O
Proton Exchange Membrane (PEM)
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Reactions of Fuel cells
Sum the reactions
H2 -gt 2H 2e-
2H 2e- ½ O2 (g) -gtH2O

H2 ½ O2 (g) -gtH2O
Conclusion Same bonds broken and formed as in
combustion reaction!!! Reactions are
equivalent Thus Energies are equivalent E
-239 kJ/mol FUEL CELLS ENERGY WITHOUT A FLAME
Consequences?
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Consequences

• No flame no generation of NOxs
• Less NOx Less pollutants
• more efficient than combustion (70 vs. 30)