Perhaps the simplest way to describe the process a fuel cell uses to produce
electricity is to compare it to reverse electrolysis. Everyone is familiar with
the classic experiment of electrolysis, where direct current is conducted to an
anode and a cathode submerged in a liquid high in electrolytes (free ions as from
salts for example). The effect is that the electrical energy separates the
hydrogen and oxygen with the atoms of oxygen collecting at the anode and the atoms
of hydrogen collecting at the cathode.
In a fuel cell, the process is somewhat reversed. Gaseous hydrogen and oxygen flow
separately around either side of two electrolytic plates serving as anodes and
cathodes. These are separated by a thin polymer membrane which serves as a filter.
As free hydrogen and oxygen atoms collect on the plates, they are chemically
attracted to each other, but the polymer membrane prevents all but the small
hydrogen protons from passing through. The potential created by shearing off the
hydrogen proton from its electron is usable electricity and is carried around the
membrane in an external circuit. The byproducts of the fuel cell are heat (from
the proton electron separation), and water.
It sounds like the greatest thing since sliced bread except there are present
limitations: A single fuel cell produces just a fraction of a volt, so many fuel
cells must be stacked together to produce the desired amount of electricity; The
output of the fuel cell is directly proportional to the purity of the hydrogen.
Since it requires more energy to extract pure hydrogen than is produced by the fuel
cell, they are impractical as an energy source for most applications; Alternative
hydrogen fuel sources for fuel cells, such as methanol, natural gas, or petroleum
as more efficient when burned in traditional electrical production methods;
Finally, the membrane filter is very expensive because it is platinum covered. The
platinum coating acts as a catalyst to induce the disassociation of the hydrogen
protons from their electrons to facilitate the electrical potential.
Answered by: Stephen Portz, M.A., Technology Teacher, Space Coast Middle School
A fuel-cell generates electricity by combining hydrogen with oxygen. It is
exactly the opposite of electrolysis. Hydrogen is fed to one electrode and oxygen
to the other. The proton from the hydrogen migrates through the electrolyte to the
oxygen. The electron from the hydrogen goes through the electrical circuit to the
cathode, or oxygen side with the proton, to make water.
There are several different fuel-cell constructions. A proton-exchange-membrane
(PEM), Phosphoric Acid , molten-carbonate to name a few. It isn't necessary to
have pure hydrogen or oxygen. Fuels that have hydrogen can be used. Such as
gasoline, natural gas, methanol, etc... The fuel can either have the hydrogen
removed to feed into the cell (reformed) or fed directly, depending on the type of
Fuel cells have been around for a long time. The first fuel cell was built in
1839 by Sir William Grove. Only recently have they gained attention, because they
have very low emission of pollutants, and don't necessary need a hydrocarbon fuel
(gasoline) to operate. In fact, you could run a fuel cell by converting the
hydrogen back and forth from water to gas. Run the cell when you need it, and plug
it into electricity to split the hydrogen back to a gas from water.
Applications include the space shuttle, stationary power plants, car and bus
power supplies, and even power for hand held devices like cell phone.
Answered by: Scott Grasmick, B.A., health physicist
'As long as men are free to ask what they must; free to say what they think; free to think what they will; freedom can never be lost and science can never regress. '