by David Shane

Created on: April 19, 2009   Last Updated: May 10, 2009

Switching to vehicles that use hydrogen instead of gasoline as fuel would have several benefits. Chief among these benefits: a significantly reduced dependence on an ever decreasing, and sometimes volatile, oil supply and reduced pollutant emissions.

There are several obstacles that must be overcome before we can get there. Some of them are on the society side; what manufacturer will build a hydrogen car when no hydrogen refueling infrastructure exists? But who would build a hydrogen infrastructure if there are no cars to use it? And how should we produce all this hydrogen?

But this is an article about the cars themselves, so let's talk about their needs. Basically, each car will need some way to store the hydrogen, and some way to use it to gain locomotive power.

1. STORING HYDROGEN

Hydrogen gas has an energy density of 143 MJ/kg, versus 46 MJ/kg for gasoline. This means that even if a vehicle could only use the hydrogen with the same efficiency that we can use gasoline, (and we can in fact do better), you would still need to carry a much smaller mass of hydrogen than gasoline to move your car the same distance. That's great news!

The bad news is that hydrogen is a gas (that is, a gas like oxygen, not a gas like gasoline!) at room temperature and the amount we would need occupies a much greater volume at normal pressures than liquid gasoline. Specifically, to get the energy in one gallon of gasoline we would need 380 standard cubic feet of hydrogen gas. For comparison, your car might have around 100 cubic feet of passenger volume total. So we need to get a little creative to store all the hydrogen we need. Here are three possibilities.

1a. Compressed gas storage

We've said that hydrogen gas takes up 380 "standard" cubic feet meaning this is the volume occupied at normal temperatures at atmospheric pressure. One thing we could do to reduce this is compress the gas, raising its pressure and decreasing the volume it must occupy. In fact, this is usually how hydrogen gas is stored in research labs today.

On the bright side this is a very simple storage solution, and refueling would be easy. This is the solution prototype vehicles available now have tended to use. However, we would end up sacrificing part or all of the hydrogen weight advantage as a result of the heavy tanks that must be used to store the very high pressure hydrogen.

Hydrogen is also the smallest molecule around, and thus especially prone to leaking out of seals. Any leaks that do occur

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