StevenRS - 23-2-2008 at 17:52
I have seen these advertised as the carrier for the hydrogen economy, and was wondering, could these be made in a home lab? I have a feeling NO, but
they are still interesting.
It would be cool to just pass hydrogen over a solid at a little pressure, and it just absorbs it, and they store H2 at a higher density than liquid
H2.
Nicodem - 24-2-2008 at 01:57
Alkali metal and alkaline earth metal hydrides form quite readily from the elements (for example, NaH forms already at 250°C while
CaH<sub>2</sub> at 400-500°C). I guess they can be made under lab conditions if you have the equipment, however I would not consider that
particularly safe. Working with hydrogen is a bit risky even under normal conditions. Add heating, pressure and highly flammable alkali metals,
possible traces of air in the tube furnace and you have your life on stake. Given the relatively very low price of NaH and CaH<sub>2</sub>
I see no reason for such risks.
Most transition metal hydrides are generally made by methods other than combining the elements (with several notable exceptions).
not_important - 24-2-2008 at 02:17
overviews
http://www1.eere.energy.gov/hydrogenandfuelcells/storage/met...
http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/iiib3_...
Mg-Ni alloys
http://www.scielo.org.ar/scielo.php?pid=S0327-07932002000400...
http://www.polymtl.ca/newmaterials/eng/journal/ejournal/july...
doped LiAlH4
http://www.osti.gov/energycitations/servlets/purl/795180-cWr...
JohnWW - 24-2-2008 at 20:11
The only problem with those hydrides of highly reactive Group I,II, and III metals, and even SiH4, as means for storing hydrogen without high
pressures, is that they are SPONTANEOUSLY FLAMMABLE on contact with air. Aluminohydrides and SiH4 are much more reactive than borohydrides because
attack by oxidants can occur through empty 3d orbitals.
The best metallic absorber of gaseous hydrogen is palladium; in fact, it readily forms an interstitial compound under moderate pressure of H2,
believed to be PdH2. This is why it is the most favored hydrogenation catalyst for laboratory and industrial use. However, it, and platinum (which is
also used for catalytic hydrogenation), and the other platinum-group metals, are far too rare and expensive for them to be used for large-scale
hydrogen storage. The best substitute for them is nickel, also used for catalytic hydrogenation (although not as good as palladium), being a
relatively common metal which makes its use for hydrogen storage a possibility.
[Edited on 25-2-08 by JohnWW]
StevenRS - 24-2-2008 at 21:19
Hmmm... So if I had a few kilos of Ni powder, how would I go about reacting it with hydrogen? Pressure? Heat?
microcosmicus - 24-2-2008 at 21:47
Another possibility is metallic organic frameworks. These are basically crystals of metal
ions held together by bidentate ligands which have plenty of holes in which to store the
gas. Also, this exotic new substance looks like something that could be made at home.
One procedure I encountered is to heat a solution of zinc nitrate, terephthalic acid, and
dimethyl formamide in a sealed tube. Ziinc nitrate is readily available. As Xenoid
recently found out the hard way, terephthalic acid can readily be produced by de-estrifying
soft-drink bottles. As for the dimethylfomamide, there is a thread here on how to
prepare it, One of these days, when I can make the third ingredient, I will have a
go at this.