Hydrogen Fuel Cells
Hydrogen fuel cells will power the vehicles, businesses and
home of the future. All hydrogen fuel cells are not alike, however.
There are several different kinds of hydrogen fuel cells, each
with different properties.
 U.
S. DOE |
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Types of H2 Fuel Cells:
- Proton Exchange Membranes (PEM)
- Alkaline Fuel Cell (AFC)
- Phosphoric Acid Fuel Cell (PAFC)
- Molten Carbonate Fuel Cell (MCFC)
- Solid Oxide Fuel Cell (SOFC)
- Direct Methanol Fuel Cell (DMFC)
Proton Exchange Membranes (PEM)
Proton exchange membranes (PEMs) have been the hydrogen fuel
cells of choice for hydrogen cars and vehicles. PEMs are also
known as Polymer Electolyte Membrane Fuel Cell (PEMFC) and are
exceptionally responsive to varying loads while driving and are
becoming much less expensive to manufacture. The low operating
temperature for the solid electrolyte PEM allows for a quick startup.
A thin platinum catalyst chemically activates the electrodes and
because of recent manufacturing technology that has thinned the
platinum layer, the cost for this portion of the PEM cell has
dramatically decreased.
Alkaline Fuel Cell (AFC)
The Alkaline Fuel Cell (AFC) was first developed and used by
NASA in the Gemini missions and subsequent Space Shuttle operations.
The advantage of AFCs is that they are very efficient and discharge
only pure water. This was water has been used as drinking water
for the astronauts and to cool electronic components. The disadvantage
of using an AFC is that the electrolyte, alkaline potassium hydroxide,
is exceptionally expensive.
Phosphoric Acid Fuel Cell (PAFC)
The Phosphoric Acid Fuel Cell (PAFC) has available since 1992
and offers the advantages of high reliability, quite operation,
and high efficiency. The PAFC has over 80-percent conversion energy
and can run on impure hydrogen.
Molten Carbonate Fuel Cell (MCFC)
The Molten Carbonate Fuel Cell (MCFC) uses a carbonate-salt-impregnated
ceramic matrix as an electrolyte. Because the MCFC operates at
800°F, it is best suited for large-scale, stationary applications
such as providing electricity for hospitals, hotels or industrial
facilitate that require electricity, heating and cooling around
the clock.
Solid Oxide Fuel Cell (SOFC)
The Solid Oxide Fuel Cell (SOFC) applications will be primarily
for large-scale stationary power generators such as generating
electricity for towns, factories or large scale compounds or campuses.
The SOFC operate at temperatures of 1000°F and use prefabricated
ceramic sandwiched between electrodes to generate electricity.
Direct Methanol Fuel Cell (DMFC)
The Direct Methanol Fuel Cell (DMFC) uses methanol reformed into
hydrogen to provide electricity. Most other fuel cells use hydrogen
directly in compressed or liquid form. The DMFC, however, incorporates
a method to use steam and methanol, reformed into usable hydrogen,
which can then be used by the fuel cell. The advantage of using
Methanol fuel cells is that methanol can be transported using
the current infrastructure.
Regenerative Fuel Cells
Besides the six different kinds of hydrogen fuel cells, there
is another kind of add-on system that can be part of any one of
these H2 fuel cells to regenerate hydrogen. Regenerative fuel
cell systems can use electricity from solar or wind power upon
the excess water made by the fuel cells with a process called
electrolysis to split the water back into hydrogen and oxygen,
which can then be run through the fuel cell to generate more electricity.
This cyclical, regenerative system is now under development by
NASA.
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