Hydrogen Fuel Cells

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Hydrogen Fuel Cells

• David Lorse
• ESS 315

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What is a hydrogen fuel cell?

• Hydrogen fuel cells (HFCs) are a type of
  electrochemical cell.
• HFCs generate electricity by reduction and
  oxidation reactions within the cell.
• They use three main components, a fuel, an
  oxidant and an electrolyte.
• HFCs operate like batteries, although they
  require external fuel.
• HFCs are a thermodynamically open system.
• HFCs use hydrogen as a fuel, oxygen as an
  oxidant, a proton exchange membrane as an
  electrolyte, and emit only water as waste.

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How do they work?

• Fuel (H2) is first transported to the anode of
  the cell
• Fuel undergoes the anode reaction
• Anode reaction splits the fuel into H (a proton)
  and e-
• Protons pass through the electrolyte to the
  cathode
• Electrons can not pass through the electrolyte,
  and must travel through an external circuit which
  creates a usable electric current
• Protons and electrons reach the cathode, and
  undergo the cathode reaction

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Chemistry behind the technology
Oxidation At the anode of the cell, a catalyst
(platinum powder) is used to separate the proton
from the electron in the hydrogen fuel. Anode
half-reaction 2H2 ? 4H 4e- Eo 0.00V
Reduction At the cathode of the cell, a second
catalyst (nickel) is used to recombine the
protons, electrons, and oxygen atoms to form
water. Cathode half- reaction 4H O2 4e- ?
2H2O Eo 0.68V
In electrochemistry, the Eocell value (energy) of
a fuel cell is equal to the Eo of the cathode
half-reaction minus the Eo of the anode
half-reaction. For a hydrogen fuel cell, the two
half reactions are shown above. So to calculate
the energy of one fuel cell, we need to subtract
the anode energy from the cathode energy. For a
HFC, the Eocell 0.68V 0.00V which equals 0.68V
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Uses of hydrogen fuel cells
There are many different uses of fuel cells being
utilized right now. Some of these uses are

• Power sources for vehicles such as cars, trucks,
  buses and even boats and submarines
• Power sources for spacecraft, remote weather
  stations and military technology
• Batteries for electronics such as laptops and
  smart phones
• Sources for uninterruptable power supplies.

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Problems regarding hydrogen fuel cells

• Lack of hydrogen infrastructure
• Need for refueling stations
• Lack of consumer distribution system
• Cost of hydrogen fuel cells
• 2009 Department of Energy estimated 61/kw
• Honda FCX Clarity costs about half a million
  dollars to make
• Carbon cost of producing hydrogen
• Problems with HFC cars
• Short range (260 miles)
• Warm up time (5 minutes)

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References

• http//www.fueleconomy.gov/feg/fuelcell.shtml
• http//www.howstuffworks.com/fuel-efficiency/alter
  native-fuels/fuel-cell.htm
• http//www.energy.gov
• Chemical Principles, Sixth Edition, Zumdahl