Hydrogen/oxygen split from water

[BigB]

I know that sodium metal when added to water causes hydrogen gas to be released. Are there any other substances that have this property and why cant these be used in fuel cells to provide Hydrogen from normal water?

[jake-the-peg]

Yep Lithium, Potassium, Calcium and a number of others.

But they're very reactive so they don't occur as pure metals. You have to refine them from ores which takes more energy than you get from adding water and burning the hydrogen

[Space]

all the alkali metals have this property.

They are not used to provide hydrogen because the sodium gets transformed into something else during that reaction, and I suspect sodium metal isn't cheap.

[shammydodger]

Such reactions are uncontrolled and thus unsuitable for fuel cells. Further, they are too vigorous.

[OBonio]

Try and find footage of the Caesium + Water experiment. This is what science is all about :o)

http://www.seilnacht.com/film/english.html

http://video.google.com/videoplay?docid=-21342 66654801392897

[Zevon]

Anything that is more reactive than hydrogen will displace it and form an oxide or hytdroxide, sodium follows this reaction

Na + H20 goes to H + NaOH

Leaving sodium hydroxide as an unwanted product, the raection isn't that dangerous and nop worse than burning hydrogen but it results in sodium hydroxide which is caustic and doesn't release as much hydrogen as simplky electrolysing water which is what the cars wil do:

2H2O has a current passed through it and gives 2H2 and O2, This is a cheaper reaction in terms of materials and waste products.

[shammydodger]

Zevon

Agreed. And the sheer impracticalities of storing the alkali metals (and alkaline earth metals such as calcium) also mediate against their use in fuel cells. Such metals have to be stored in oil to prevent atmospheric oxidation. The electrolysis of water to produce hydrogen is ideal for the reasons you give, plus it is perfectly controllable in that the reaction can be instantly halted or started by the flick of a switch.

[Hamish]

I beg to differ Zeveron. Addition of Na to water can be exceptionally dangerous. The explosion limit for hydrogen in air is very low. Add enough sodium - not much, and the reaction will detonate. Usually the experiment is demonstrated with small amounts of Na - a large chunck will detonate. Scale is very important in this type of reaction. The reaction of CaH2 added to water in small amounts just generates a bit of fizz. Add water to a small pile of CaH2 and BANG. as a friend of mine found out.

[lord molly]

if you want to see the best ever explosion suing only two elements, try mixing the highly reactive metal, francium, with the highly reactive non metal, flourine. i have only seen this once, at the royal military collage of balistics at shrivenham. it was as if sgt thomas had thrown a 100lb ww2 bomb in the test area. only a total mass of 12g produced the same force as 40kg of TNT. awsome!!!