At what temperature will water split into hydrogen and oxygen?

28 March 2010

Question

Hi,
 
I would like to know at what temperature does water (H2-0) separate into hydrogen and oxygen by thermal means?  
Thanks,
 
Bo Davis

Answer

Dave - You can do it electrically with about 1.3 volts of electricity. However, to do it thermally, you've got to heat it up to over 2,000 degrees centigrade. It's one of these things whereby the hotter you get, the more complete the dissociation - you split the molecules up. It is actually a suggested way of making hydrogen - you heat up water at very high temperatures. You then have to somehow separate out the hydrogen and oxygen because otherwise, it's easily hot enough to burn and condense back to water again, so you need some kind of membrane to separate the two. This does exist - it's a special kind of ceramic membrane, and you can separate the two gases and you get hydrogen out.

So, yes, it can happen somewhere about 2,000 degrees C.

Ben - And would it help if you were to add a catalyst? I know that they've been looking at using platinum to help do this. You find catalysts that help reactions happen at different temperatures. Could we find the right catalyst that therefore meant it didn't need to be quite so hot as 2,000 degrees?

Dave - Catalysts certainly help with electrolysis, doing it electrically. My knowledge of high temperature chemistry is very limited, but I think the fundamental thing that you're working against is the actual energy you need to split apart water molecules and thermally, that's an awful lot of energy. So, I would be surprised if you could gain that much.

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