Another promising development in hydrogen storage

[chemisttree]

Last month at the International Symposium on Materials Issues in a Hydrogen Economy, held in Richmond, Virginia a new development in room temperature adsorption of large amounts of hydrogen (14% by weight!) was announced. The work was presented by Bellave Shivaram and Adam Phillips, of the University of Virginia.

Absorbing hydrogen at room temperature at these levels is a significant development. What remains to be worked out is if the substrate can be induced to easily give it back and if the catalyst (sorbent) can be recycled.

Titanium molecules complexed with ethylene, and bound to an inert support, created a thin film which strongly absorbed up to 14 per cent hydrogen by weight at room temperature. Most materials today absorb 7 to 8 per cent of hydrogen by weight, and that only at very low temperatures.

http://www.rsc.org/chemistryworld/News/2007/November/16110701.asp

The attached graphic shows how the complex is believed to function. The (green) hydrogen molecules are shown as ligands to (red) titanium atoms coupled to an (yellow) ethylene molecule.

 

[Q_Goest]

cool news. thanks.

I didn't see too many details on how the hydrogen is stored. Is it under any kind of pressure? Most carbon based systems I've seen are under some minor amount of pressure, and then heated and/or pressure reduced to remove the hydrogen.

 

[chemisttree]

I guess it is too early to tell. They haven't yet done any experiments to desorb the hydrogen.
That's troubling since it is such a trivial experiment. We'll have to wait and see I suppose. I'll keep an eye on it.

 

[David Harland]

I understand the fact that hydrogen has a large physical volume and that it boils at a certain pressure meaning that it needs to be stored cryogenically but what pressure can it be stored at before you get into problems and what would the storage size of the vessel that stored the hydrogen be to power a vehicle say 20 miles.

 

[Q_Goest]

Hi David,
Welcome to the board.

The primary means of storing hydrogen for fuel cell vehicles today is by high pressure. Cryogenic storage has been tried, but it really is too impractical. Cryogenic tanks will boil off due to heat influx, so you either use that hydrogen to power the vehicle (ie: run the car once a day) or vent the gas. You can imagine the problems with venting flammable hydrogen inside an enclosed space such as a garage, so for the most part, cryogenic storage has been ruled out with the possible exception of bus fleets or other highly controlled fleets of vehicles. Even there however, the cost of a cryogenic storage tank prohibits their application. I’m not aware of any bus fleets that use cryogenic storage, but there are plenty that use high pressure. Cryogenic storage also presents a number of complexities to the vehicle, such as vaporization, so it’s not very popular.

High pressure storage has been the primary means for almost all demonstration projects thus far. Vehicle tanks are generally carbon fiber composites for storage at either 350 or 700 bar (5000/10,000 psi). With that much pressure, a range of 300 miles is the most popular target for vehicle manufacturers. So most vehicles can go about 300 miles before needing to be refueled, regardless of storage pressure. Most projects today use the lower 350 bar storage due to a lack of equipment that goes to the higher pressure and also because to get 700 bar, one has to store the hydrogen at even higher pressure (~14,000 psi) prior to delivery to the vehicle.

Hydrogen is most commonly still delivered as a cryogenic liquid in tractor trailers capable of hauling over 10,000 gallons, but storage of hydrogen in vehicles is almost exclusively done as a gas. I’m not sure what the weight percent is for storing high pressure hydrogen, but I’d guess it’s about half the 14% mentioned in the OP. So the main focus in research today has been in hydrogen storage – albeit there are many other areas of active research as well.

 

[David Harland]

Thankyou for your reply, I think what i as trying to ask is if you had an ordinary gas cylinder what pressure could hydrogen be stored, at without anything else being done to it eg without using special alloys to absorb large amounts of the gas, just a plain old steel cylinder.

 

[Q_Goest]

The only problem with storing hydrogen in steel cylinders is "hydrogen embrittlement", a phenomena in which the hydrogen gets into the steel, weakening it. Low strength steels are much less susceptible, so making a very thick wall cylinder that can handle 20,000 psi is possible. There's no reason I know of that says you can't make an exceedingly thick wall cylinder of low strength steel that could handle even more pressure however, steel cylinders in general are impractical for automotive use.

 

[David Harland]

Thanks for that, i was aware that the gas might react with the steel but for example if you where to take a cylinder that did not react with the gas and had no issues with strength at what pressure could you safely store hydrogen gas without doing anything to it other than pressurising it.

 

[mheslep]

... I’m not aware of any bus fleets that use cryogenic storage, but there are plenty that use high pressure...

Do you mean for CNG? I just checked again, and I don't believe that as of this date there are any H2 bus 'fleets' operating anywhere in the world using compressed H2 or anything else. There are plenty of demonstration projects - three in Iceland, London has bought 10 (out a fleet of hundreds), etc, but no municipality wide fleets.

 

[Q_Goest]

Hi mheslep

Do you mean for CNG?

no, I meant hydrogen

I don't believe that as of this date there are any H2 bus 'fleets' operating anywhere in the world using compressed H2 or anything else. There are plenty of demonstration projects - three in Iceland, London has bought 10 (out a fleet of hundreds), etc, but no municipality wide fleets.

I mean there are bus fleets (ie: companies that operate large numbers of conventionally powered diesel busses) that are trying out hydrogen fuel cell busses. Perhaps it would have been better stated that there are many companies that operate bus fleets that are testing hydrogen fuel cell busses.

Then again, the term "many" should be clarified too. I suspect the total number of companies operating fuel cell busses are on the order of a few dozen.

 

[Constructe]

I believe many people are working on ways to bond hydrogen to chemicals to crystalize it. In the material maybe hyrdogen would be like 10-30% of the material. Bonding the hydrogen at room temperature is a good development if this works. After bonding I have heard that they can handle higher temperatures before releasing hydrogen gas. Perhaps that is how this will work.

 

[mgb_phys]

A 50Mph / 100 mile range H2 = fueld cell powered motorbike. No technical details of the storage technology, but the rider could lift the H2 tank out with one hand.

http://news.bbc.co.uk/2/hi/uk_news/england/7655831.stm

 

[mheslep]

A 50Mph / 100 mile range H2 = fueld cell powered motorbike. No technical details of the storage technology, but the rider could lift the H2 tank out with one hand.

http://news.bbc.co.uk/2/hi/uk_news/england/7655831.stm

Well pivot it up at least.
http://www.hydrogencarsnow.com/intelligent-energy-env.htm
1kw = 1.3HP motorcycle

The Intelligent Energy ENV will most likely be the first H2 vehicle to be mass-marketed to the public. It is expected to sell for $6,000 to $8,500 when it rolls out. The Intelligent Energy ENV has missed the first rollout date in the latter part of 2006 and now, since they've partner with Suzuki they are supposed to rollout in the later part of 2007. The British company has also decided to move their headquarters to California,...

2007. Is it out then?

 

[momar]

The primary means of storing hydrogen for fuel cell vehicles today is by high pressure. Cryogenic storage has been tried, but it really is too impractical. Cryogenic tanks will boil off due to heat influx, so you either use that hydrogen to power the vehicle (ie: run the car once a day) or vent the gas.

LLNL has demonstrated a cryogenic hydrogen storage system with no venting for at least https://publicaffairs.llnl.gov/news/news_releases/2008/NR-08-06-02.html" .

 

[Q_Goest]

Hi momar,

LLNL has demonstrated a cryogenic hydrogen storage system with no venting for at least https://publicaffairs.llnl.gov/news/news_releases/2008/NR-08-06-02.html" .

Thanks for the update. The LLNL tank is apparently a conventional vacuum jacketed storage tank with a thicker inner vessel:

Today’s automotive LH2 tanks operate at low pressure (2-10 atmospheres). The LLNL cryogenic capable pressure vessel is much stronger, and can operate at hydrogen pressures of up to 350 atmospheres (similar to scuba tanks), holding the hydrogen even as the pressure increases due to heat transfer from the environment. This high-pressure capability also means that a vehicle’s thermal endurance improves as the tank is emptied, and is able to hold hydrogen fuel indefinitely when it is about one-third full.

This isn't actually a new idea. Similar tanks have been built, just not for this kind of purpose. This concept has been considered however, but it's quickly dismissed for a few reasons. First is weight - the thicker inner vessel means a huge weight (and cost) increase. Second, in practice, you can't refill a cryogenic storage tank that's above the critical pressure. Sure you can force stuff in, but it's not a liquid, it's supercritical, and therefore there's no surface tension to separate the liquid from the gas. The end result is you can't get the liquid/gas interface and you can't get pressure down without venting off the hydrogen. Note the critical pressure for hydrogen is around 175 psig.

Just a side note as well... the concept of making a vessel capable of not venting for 6 days isn't unusual at all. Liquid helium vessels that are shipped overseas for example, spend 60 days enroute on a ship without venting, and LHe has a MUCH lower latent heat of boiling than LH2. The way it's done is to provide thermal shielding (ie: copper sheets interspaced with the MLI which then is thermally connected to a low temperature heat sink). The low temperature heat sink is generally liquid nitrogen, though even a very small venting of helium can be used as this heat sink. Both designs eliminate a tremendous amount of heat leak to the inner vessel. Problem with this techonolgy is the expense. Had LLNL come up with an economical way of reducing heat leak instead of using a brute force approach, there would be a whole lot more interest in the industry.

 

[mheslep]

As demonstrated here again liquid H2 is not practical for widescale transportation use. It keeps popping up because it shows well for demonstrations, as expected since it does so well on volumetric/gravimetric density charts: http://www.rsc.org/chemistryworld/Issues/2007/October/HydrogenStorageTargetsOutOfReach.asp
But, in terms of energy cost alone it places far behind compressed gas, and probably hydrides too.