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Is hydrogen good to be used in cars? How much of traveling can a car do with medium sized balloon filled with hydrogen? Is it worth it?

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Hydrogen escapes from vessels more readily than just about any other gas. All of the schemes to store hydrogen seem unwieldy. High pressure, low temperature, or hydrides. I've seen NH3-BH3 proposed as a way to store hydrogen. A good way to store hydrogen might be methanol.

Generating the hydrogen takes energy in the first place which factors in to the question of whether or not it is worth it.

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TBH one of the best ways to store hydrogen is just CH4. That's 4 hydrogen atoms per molecule with just one extra non-toxic atom. –  MSalters Aug 3 at 22:23
    
But methane is pretty powerful greenhouse gas, and you can't pretend it would never escape. Methanol is at least liquid and liquids are generally easier to handle and contain than gases. Not sure about Methanol's greenhouse gas properties. It is toxic, but we've put worse into the environment and it probably has a short half-life in the wild. If there were some way to electrolytically combine CO2 and H2 to make methanol, that would be cool. Could make fuel in a central location with clean energy and then ship it for use as fuel while stying carbon neutral. –  user137 Aug 4 at 5:26

The energy density of hydrogen at atmospheric pressure (which it roughly is inside a balloon) per unit volume is a mere 0.01005 MJ/L, which is roughly a factor 3600 less then that of gasoline (at 36 MJ/L).

A typical car does 15 km/L so where a gasoline filled balloon (say 3 L) does 45 km for you, a hydrogen filled balloon will get you only 12.5 meters, i.e. just out of the parking lot.

Therefore, any realistic application of hydrogen is to store it either at high pressure (e.g. 70 bar, where the energy density is about 6 MJ/L) or in so called metal hydrides which allow much higher energy densities. Another option which to me seems to most viable, is to use the Fischer-Tropsch process to make methane or even higher alkanes out of hydrogen and $\ce{CO}$. The big advantage of this route is that our current infrastructure of gas stations can still be used

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Storing it under higher pressure would mean more energy and I guess that does not really make it a good alternative or could it? –  user7063 Aug 3 at 18:05
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@user7063: That becomes more of a physics question, but in short hydrogen is a small molecule (second only to Helium, and the smallest diatomic molecule). That unfortunately means it leaks, badly. At 70 bar the problem is much worse. And because it leaks so easily through many materials, it also has the annoying property of embrittling them. –  MSalters Aug 3 at 22:21
    
@MSalters Do you have any reference about the leaking? I know that hydrogen molecules are tiny and will leak through many materials that other gas will not penetrate, but I also know that many chemical labs have steel containers with hydrogen at 200 bar and I have never heard of any leakage issues of those. Curious to know how safe those 200 bar steel containers are! –  Michiel Aug 4 at 5:23
    
@Michiel: For lab use, the weight of the container is not a major concern, but for cars it is. Even so, leakage is still taken seriously in stationary situations. I know the physics building at my alma mater had a "shed" for the hydrogen storage, which was designed to direct any explosions away from the main building. –  MSalters Aug 4 at 14:33

Hydrogen is very easy to leak. Any amount of hydrogen leak is dangerous. It's highly flammable, so if there's fire, naked light or electric spark nearby, it'll cause explosion and of course be dangerous for traffic. By the way, hydrogen leak will eventually float up and deplete ozone layer. Based on these facts, hydrogen isn't a promising fuel to be used in daily life.

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This is assuming that you are going to use hydrogen in the gaseous form. A lot of research is focused on metal hydrides which don't have the leakage problem. Granted, they have other issues, but using leakage as the sole reason to say hydrogen is not a promising fuel is a little bit jumping to conclusions –  Michiel Aug 5 at 5:19

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