Hydrogen Tablets

Lord Flasheart · Member

Hydrogen Tablets

10kBq Jaro · Senior Member

Lord Flasheart wrote:

Within the tablet, hydrogen is stored as long as desired, and when hydrogen is needed, ammonia is released through a catalyst that decomposes it back to free hydrogen.

Interesting article. Its unfortunate that it doesn't provide a more detailed description. The quoted sentence certainly could use one. The catalyst seems to perform two simultaneous functions - releasing the ammonia from the "sea-salt," and decomposing the ammonia into hydrogen and nitrogen. Aside from that being a pretty amazing feat, one is left wondering how the catalyst is introduced into the salt (or vice-versa), because it must obviously be absent at the time the ammonia is introduced into the salt, and for the duration of the storage period. Next is the question of how the salt and catalyst are separated again, after hydrogen extraction, so that at least the catalyst (if not the salt) can be re-used. If this separation process takes as much energy as what the hydrogen supplies, then its not a viable scheme. From the poor description, its impossible to tell either way....

iprimap · Veteran Member

I agree with 10kBq Jaro. However, I did a little more research and came up with the following web links that may interest those desiring more information about the catalytic decomposition of ammonia into hydrogen and nitrogen. Sadly, I am some two decades removed from US Naval Nuclear Power School in Orlando, Florida where I learned about topics such as these, so I cannot judge as to their technical merit.

Catalytic Ammonia Decomposition: COx-free Hydrogen Production for Fuel Cell Applications: http://www.chem.tamu.edu/rgroup/goodman/pdf%20files/cat-ltr-72-197-01.pdf

Nanostructured Catalyst Produces Hydrogen from Ammonia: http://www.greencarcongress.com/2005/03/nanocatalyst_pr.html

Hydrogen from Ammonia and Ammonia-Borane Complex for Fuel Cell Applications: http://www.eere.energy.gov/hydrogenandfuelcells/pdfs/32405b15.pdf

Some of the chemistry behind ammonia-borane complexes may be found at web page:

Borane-Ammonia Complexes Stabilized by Hydrogen Bonding: http://www.cchem.berkeley.edu/trngrp/traunerweb/Publications/Borane.pdf

To simply fuel a car with ammonia and exhaust only nitrogen and water vapor seems like a dream come true. I usually go by the motto, "If it's too good to be true, then it probably isn't."

But Lord Flasheart may be onto something - who knows?

Regards,

'Nuclear' Paul P.

10kBq Jaro · Senior Member

Thanks 'Nuclear' Paul - these are good references.... I downloaded them and had a quick look through them. Interesting reading for sure !

As for the original ammonia story (the "Hydrogen Tablets"), its interesting that one of the references states that "Due to extreme toxicity of ammonia, it is difficult to envision its widespread use as the future transportation fuel." (that paper even talks about hydrogen sulphide, which is probably an even worse poison ! ).

But one thing I noticed in all of them, is that while they say that ammonia is a good source of un-contaminated hydrogen that will NOT quickly poison the very sensitive fuel cells (as do CO or CO2 from reformed methanol & similar), they fail to mention that the oxygen for these fuel cells must likewise be quite pure, to avoid poisoning the fuel cells. So, where does that leave us ? ....with having to cary liquid oxygen on board, as well as the hydrogen source ?? That may be OK for NASA's Space Shuttle, but not for your average family sedan.

GoogleNaut · Guru

I scanned the pdf which details some of the chemistry of the ammonia process, and it leads me to think that the 'tablets' are infact platinum-rhodium impregnated zeolites. This is a little different take on the hydrogen storage by hydride method--storing the hydrogen as a hydride of nitrogen!

Jaro has a good point about poisons for the fuel cells--however, I would point out that it is possible to create a porous membrane 'filter' which can literally enrich the airflow of oxygen by allowing nitrogen to pass through but not oxygen. Presumably other trace gasses will be diverted by adjusting the pore sizes accordingly. But this is added expense and also sucks more energy from the system which is providing power to the wheels. In essence, it becomes a diminishing returns problem.

Obviously carrying the oxygen around with you in liquid form defeats the purpose of the whole system as the added weight will make any gains in efficiency from the fuel cell null and void.

I think that if fuel cell technology will take off it will be using a higher temperature wet-oxidation method using phosphate/phosphoric acid with platinum. Common poisons are sulfur, so neoprene and other sulfur based rubbers cannot be used for gaskets. I'm not sure if sulfur dioxide could be bad for it --probably-- (SO2 is definately bad for us too!) but there probably isn't enough in the air to be a problem.

I think a bigger problem facing fuel cells (other than sourcing the PGM's which are very expensive!), which rely upon the air for oxygen, will be particulate contamination from dust. Simply installing an airfilter on the intake of a compressor should alleviate this--for the same reasons that air filters are used on IC engines.

Still, using ammonia as an energy carrier might be more efficient than pure hydrogen as a cryogenic fluid. Ammonia can be carried as a liquid in compressed form without the need for cryogenics. Still, it cannot compete on the basis of raw energy density that hydrocarbons can. This is one reason why it is so difficult to replace hydrocarbons--they're so doggone convenient!

-- Edited by GoogleNaut at 23:30, 2005-09-13