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Re: Fuel Cells



Fuel cells seem to be a big thing in the news these days. There's the fuel
cells powered by plutonium carried by Cassini, and there's this new scheme
for gas powered electric cars in which gasoline is decomposed to get at the
hydrogen which is then used to power the fuel cells.

Because of the publicity, I would like to bring these up in my general
physics classes. The problem is I don't know how they work. How do you
use the heat or the chemistry to produce electricity? Help.

The RTGs (Radioisotpe Thermoelectric Generators) aboard Cassini are like
those which are used on Voyagers 1 and 2 and Galileo. They are not fuel
cells; they work by generating heat with a consequent themocouple electrical
output (or rather the output of many thermocouples). The source of the
energy is radioactive decay of a nonfissionable isotope of plutonium; it is
not a nuclear reactor, either.

Fuel cells derive their electrical output by combining hydrogen and oxygen
more or less reversibly, thus bypassing the restrictions of thermodynamics
which diminish the efficiency of combustion engines which also combine
hydrogen and oxygen, but which must discharge waste energy to the
environment. See http://www.engr.uvic.ca/~dbryan/fuelcell.html for some fuel
cell information. The leading producer of fuel cells is located right here
in Burnaby, BC. You might take a look at their web pages* which contain some
explanation of the proton exchange membrane fuel cell that is now powering
buses in Vancouver and Chicago as well as a Mercedes minivan which is the
forerunner of their low emission vehicle effort. Chrysler and Honda will
also be using Ballard's technology.

Leigh

* http://www.ballard.com/