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Politics : Formerly About Advanced Micro Devices -- Ignore unavailable to you. Want to Upgrade?

To: Joe NYC who wrote (145534)	4/19/2002 3:27:41 PM
From: combjelly	Respond to of 1575396

"but are you saying that the fuel cell uses only hydrogen for creation of electricity?" Yep. There are other reactions that can be used, but the hydrogen cells are the most efficient. They also have had the most development because of the space program. "Leaving the carbon behind unused seems like not a very efficient way to go." But still more efficient than outright burning it. "What's wrong with hydrogen tanks?" If the tanks are steel, you will get hydrogen embrittlement. In addition, the molecule is so small it has the habit of leaking through the crystal structure of most metals. So pressurized isn't a good solution. I guess I don't have to go into the difficulties of liquid hydrogen... There are metals that readily take up hydrogen and form metal hydrides. Then when the hydride is heated, it gives off the gas a a reasonably low pressure. These work ok, but are costly and, probably more importantly, heavy. "What is actually the fuel for these fuel cells" Methane has the highest density of hydrogen, but other hydrocarbons can be used. It is run through what is called a reformer, to get the hydrogen. I never really looked into how they work, my main interest is in micro-fuel cells for portable work and they are usually direct conversion fuel cells. They usually take an alcohol-water solution, use the hydrogen from the alcohol leaving water and CO2. "And how does it beat electric power (batteries) for powering the cars?" Energy density. The highest energy density for batteries are LiIons. The polymer versions have a slightly lower density, but are lighter for a given power rating. The chemical energy is high enough that if they are mis-handled they will melt or even catch on fire. They have special fire extinguishers that are needed to put them out. Even so, a micro-fuel cell with an alcohol tank that is about the same size as a cellphone battery will give you a talk time of more than 10 hours. And they are not nearly as efficient as a PEM or molten carbonate fuel cell.