Question: What properties of the hydrogen gas make it so difficult to safely compress inside our cars?

Jemma Rowlandson answered on 15 Jun 2014:

Ooh, nice one. Well the main property is that hydrogen gas is a gas! In a gas the molecules are far apart and so they take up a lot of space. To put hydrogen gas in a car we have to squash the molecules close together inside a gas cylinder.

It takes a lot of energy to push the molecules close together which causes the gas to heat up. Heating up flammable hydrogen gas is never a good idea, so the cylinders we use have metal on the inside to take away the heat.

Another problem is that your gas tank is at a very high pressure. If you get a bottle of coke and shake it up this causes the pressure in the bottle to increase. What happens if you open the bottle too quickly? Well, as we’ve all done accidentally, the coke bursts out and you get soaked right?

Well the pressure in a hydrogen cylinder is 700 times more than in a bottle of coke. So imagine what would happen if the cylinder broke. Your heavy, metal cylinder would shoot off like a rocket, which would be very dangerous. The tanks we use are very strong (and expensive!) so this does not happen. Scientists like me are also looking at materials which soak up hydrogen gas like a sponge, so you would not need a gas cylinder at all!