[macfan74318]

Hello,

I'm new to the fourms so if I posted this is the wrong section I am very sorry. I have a question about a metal alloy that could bond to Hydrogen. I will give you a bit of background info first, I have entered the Intel Science and Engineering Fair and my project is to try and make Hydrogen a viable fuel alterative. My idea was to have Hydrogen bond to a metal alloy so that it could be stored more efficiently and have the bond broken with an electric charge. Also I would like it if the Metal Alloy could rebond to the Hydrogen in the cars tank. Also the Hydrogen in be in a gaseous form. Please help me out because I have a limited knolwedge of chemistry (I am currently in AP Chemistry) and any assistance will be appreciated. Also here is a example of what I was looking for but I dont understand how it works: http://www.horizonfuelcell.com/store/hydrostik.htm

Thanks,
Macfan

[Arkcon]

Here's a description of how this particular fuel cell works.  http://www.popsci.com/gadgets/article/2011-05/testing-goods-horizon-minipak-portable-fuel-cell-charger  Some other references I found online say that the sponge contained within is a titanium-manganese alloy.  http://www.udomi.de/downloads/UserManualHydrostikv8.pdf  Used to be, metal sponges for adsorbing hydrogen were made of platinum metals, glad we have some newer, cheaper, materials.  But, I don't know if a layman can get samples to work with, especially if they don't really understand the mechanism by which it works.

[Enthalpy]

You have to distinguish between a chemical compound and an adsorption.

Metal hydrides are, to my limited knowledge, dangerously unstable compounds (explosive, pyrophoric...) hard to imagine in public use. Unless someone succeeds or has succeeded in finding a harmless one. More opinions welcome!

Adsorption is rather ineffective in that it still takes a huge pressure to store a limited amount of hydrogen, where the best alloys achieve nearly one H atom per metal atom, if I didn't botch the estimate last time I saw data. Smaller than a hydrogen tank at room temperature, not smaller than a tank of cold hydrogen, and much heavier.

Ti-Mn is available at Sigma-Aldrich "for hydrogen storage". At their usual prices.

Some time ago I suggested on an other forum to try adsorption by abnormally light alloys, that is, whose volume exceeds the sum of the constituents. One example is Invar or Permalloy, an other is bell bronze, still others are shape memory alloys and some damping alloys like Mn-Cu, maybe Pb-Sn and Pb-In. Besides their abnormal properties (low Young modulus...) I just imagine, without an excellent reason, that they leave more room for hydrogen. That could be a funny, original and easy trial - nice simple project: get samples, put hydrogen pressure, measure. Same amount with less pressure? Or release hydrogen through a phase transition of a shape memory alloy?

To me, storing hydrogen adsorbed in a metal is just the wrong way. Instead of heavy metal to store a bit of hydrogen, just use an energy-carrying metal to produce the energy as needed. Magnesium, zinc, aluminium... are harmless as opposed to hydrogen, and weigh less than the hydrogen tank of any present technology.

This is already being investigated, including for cars. The serious mistake is that researchers still want to make hydrogen from the metal, which is a meaningless and ineffective complication. The proper way is to use the metal in a battery and replace this battery at the gas station. It takes an electrode more, and a depolarizer if air can't serve, but at least you get the full potential of the metal, and have good electricity without the still imperfect fuel cells. A recycled primary battery doesn't suffer the limits of a recharged secondary battery.

Marc Schaefer, aka Enthalpy

[cth]

There are several ways studied to store H₂, mostly:
- liquid H₂ -> needs to be cooled at very low temperature which is not energetically convenient;
- pressurised H₂ -> progresses have been made with lighter and stronger carbon-fiber containers. For safety reasons, storage can't go too high on pressure and it still needs a pump to pressurise the gas;
- H₂ chemically stored within metal hydrides -> can store a large amount of H₂ at low pressure, but it works at too high temperature, with a slow kinetic and the material structure is altered after too many filling cycles;
- H₂ physically stored (Van der Waals interactions) within nanoporous carbon structures (including metal-organic frameworks) -> rapid kinetic and little structure alteration after thousand of filling cycles (because H₂ is weakly held inside the structure), but amount of H₂ stored too low and at too low temperature (liquid N₂, 70K);
- thermal decomposition of NH₄BH₄ -> good proportion of H₂ released but the materials is damaged after use.

So far, no storing way has been able to meet all the requirements for automotive use: they all have advantages but also serious drawbacks, not to mention if they are economically viable.

To me, storing hydrogen adsorbed in a metal is just the wrong way. Instead of heavy metal to store a bit of hydrogen, just use an energy-carrying metal to produce the energy as needed. Magnesium, zinc, aluminium... are harmless as opposed to hydrogen, and weigh less than the hydrogen tank of any present technology.

I don't agree with that, it takes too much energy to make aluminium metal from aluminium oxide. This industry consumes enormous amount of electricity. You can't get all this energy back when you transform Al⁰ back into Al³⁺.


As batteries for car applications, at the moment they don't last long enough on their own before needing recharge.

Anyway we don't know where a technological breakthrough will happen.

[Enthalpy]

The usual differing opinion, just in case someone was on risk of having understood:

- Liquefaction needs negligible energy, as compared to a combustion in a flame or fuel cell.
- Pumps have no serious drawbacks. Each gas station has many ones. Little tank volume at high pressure makes the same boom as much volume at low pressure. The common 350b look good.
- Cold pressured gas looks best, like 200b and 90K (as liquid nitrogen). Nearly the liquid's density, for hydrogen.

Reducing a metal takes in essence the same energy as is gained back by oxidation (which doesn't produce the oxide). This is a lot, as is desired from a fuel. Losses appear at reduction and oxidation processes, just as they do when hydrogen is produced and used, or a battery is charged.

For the cycle efficiency, magnesium and zinc must be better than aluminium.

My proposal is a primary battery, to be replaced at the gas station and recycled. No worry with the number of cycles nor the slow charge hence. Self-discharge as well is widely solved at primary batteries.

"Recycling" can mean then: replace the electrolyte and the consumed electrode (and the depolarizer if it's not air) by reprocessed ones, keep the rest.

By the way, cars are an important application near to us, but not the only market. Autobus, delivery vans, Post cars are easier to address.

Airliners may switch to liquid hydrogen as soon as fuel cells are powerful enough. Drones do it already. Remember 2/3 of the passengers survived the Hindenburg accident, more than at a typical aeroplane fire. Fast-running electric motors are smaller and lighter than gas turbines. Hydrogen is more bulky than kerosene for the same mechanical work but lighter (including the tank), a decisive advantage.