First some equivalences—1 Kwh=2,655,223 ft-lbs=3.6 megaJ. Particularly the 1 Kwh=3.6 megaJ will show up often in the following.
For our purposes we are defining a "fuel cell",FC, as a catalytic device that allows the oxidation of carbon and hydrogen but the output is in electrical energy form.
A legitimate question is how is this different from ordinary combustion?The objective of all this is a car that processes ordinary fuels with efficiency better than an ICE. Its exhaust will be CO2 and H2O but its mpg should be on the order of 70mpg.
In the recent past a lot of interest has been expressed on a hydrogen, H2, fueled car. At the moment interest has waned because of the lack of an infrastructure to deliver H2 gas to the filling stations on a national or even a state-wide basis. However Toyota, Honda, Nissan, Chrysler and some others have built demonstrators to test public interest.
Now H2 was pushed because the exhaust from the FC converter was water vapor and contributed no CO2 to the atmosphere. Also the theory was that the H2, if derived by electrolysis, was nearly infinite in supply. Tries at piping H2 aka CH4 weren't successful; the H2 molecule is so small in diameter that leakage through the pipe walls that contained CH4 was excessive. Hence H2 had to be locally generated. So the perfect fuel, H2 has been side-tracked for the moment. As a fuel H2 was very efficient and claimed 80% conversion to electrical energy form. The FC cars were quiet and drove well except for
the cost/availability of H2.