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Hydrogen Fuel Cell
Name: Lina
Status: Student
Grade: 9-12
Location: NY
Country: United States
Date: November 2008
Question:
My partner and I are currently sophomores in high school working on a
research project where we are trying to use hydrogen particles to power a
prototype car. However we do have some questions and it would be great if you
were able to answer these questions:
1. How would you be able to cool the hydrogen fuel cell efficiently and
environmentally friendly?
2. Is there any way that we could separate hydrogen ions from oxygen ions
after electrolysis so that they do not recombine immediately?
Replies:
Hydrogen fuel is often compressed, usually into a liquid. Since boiling off the
liquid hydrogen back into a gas will cool it dramatically, you could use that
process to cool your fuel cell.
Your question about the electrolysis, I assume you are referring to the
separation of the original water, into your fuel? The usual method I know
of here is to separate the electrodes underwater, then simply capture each
stream of bubbles separately.
Ryan Belscamper
Hi Lina,
I am puzzled by your reference to something called "hydrogen
particles". I suspect you are referring to the hydrogen gas that
(together with oxygen from the air) is "fuel" for a fuel cell. In your
second question, by "electrolysis" I am assuming you are referring to
one method (electrolysis) used to create the hydrogen used to power a
fuel cell.
As I believe you know, hydrogen is not a fuel, but instead can be
thought of as an "energy transporter". A lot of energy must be used to
create hydrogen (for example by electrolysis of water). The hydrogen
is then stored on-board a car (either under very high pressure, or as
ultra-cold liquid hydrogen, or as a metal-hydride). The hydrogen is
then fed (together with air) to a fuel cell "Stack" on-board the car
which then produces electricity to drive the car's electric motor.
So, with that background, I will try to answer your two questions.
You asked how the fuel cell could be cooled in an environmentally
friendly way. The answer is quite simple. Fuel cells look like thin
plates, and are usually produced in stacks of many layers in order to
create the high voltage needed to drive a motor. As you imply, they
are nowhere near 100% efficient, and so generate a lot of waste heat.
Normal practice is to build cooling channels into the stack, through
which water is pumped. The water is circulated through these channels
to absorb the waste heat, then it flows into an ordinary radiator,
which passes the excess heat to the ambient air. The water exiting the
radiator is now cool, and is returned to the fuel cell stack again, to
repeat the process. Basically, this is exactly the same process by
which an ordinary car engine is cooled.
Looking at your second question, it appears you misunderstand the
basic process of electrolysis, which works this way:
Two electrodes are inserted some distance apart into a container of
water that has had some acid (such as sulfuric acid) added to increase
the water's electrical conductivity. One electrode (called the Anode)
is connected to the positive terminal of a source of DC power (such as
a (+) terminal of a battery or power supply). The other electrode
(called the Cathode) is connected to the negative terminal of the same
power source.
When electrical power is applied to the electrodes, the hydrogen ions
that are always present in water, are attracted to the cathode. This
is because a hydrogen ion is missing its electron and has a positive
charge, and is attracted to the negative cathode. The cathode supplies
the missing electron to the hydrogen ion, and this results in a
hydrogen atom. Two such hydrogen atoms then combine to make hydrogen
gas (H2). This is repeated over and over, and the hydrogen gas that
collects at the cathode bubbles to the surface and is collected for
storage.
By a more complex (but basically similar) process, oxygen ions (which
have a negative charge) are neutralized at the positively-charged
anode, then bubble off as oxygen gas.
As you can see, the hydrogen and oxygen are generated at opposite
electrodes, because the electrical charge of their ions is opposite.
For example, hydrogen ions (with their positive charge) are attracted
to the negatively-charged cathode, but oxygen ions (or more correctly,
hydroxyl ions) with their negative charge are repelled from the
cathode (opposite charges attract, but "like" charges repel).
So, separation of hydrogen and oxygen in an electrolysis cell is
automatically driven because the hydrogen and oxygen ions are charged
oppositely.
Regards,
Bob Wilson
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Update: June 2012
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