High Density of Hydrogen Storage in MOFs Could Enable Practical Mobile Hydrogen Storage
02 April 2008
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| MOF-74 resembles a series of tightly packed straws comprising mostly carbon atoms (white balls) with columns of zinc ions (blue balls) running down the walls. Heavy hydrogen molecules (green balls) adsorbed in MOF-74 pack into the tubes more densely than they would in solid form. Click to enlarge. Source: NIST |
A research team from the National Institute of Standards and Technology (NIST), the University of Maryland and the California Institute of Technology has demonstrated that the metal-organic framework material MOF-74 can absorb more hydrogen than any unpressurized framework structure studied to date, and packs the molecules in more densely than they would be if frozen in a block.
By achieving technologically relevant levels of gravimetric density for stored hydrogen without either the extremely high pressures for gaseous hydrogen or extremely low temperatures for liquid hydrogen, MOF-74 could enable practical mobile hydrogen storage. The researchers describe their work in a paper published online in the ACS journal Langmuir.
One of several classes of materials that can bind and release hydrogen under the right conditions, MOFs have some distinct advantages over competitors, such as not requiring the high temperatures (110° to 500° C) some other materials need to release hydrogen.
MOF-74 is a porous crystalline powder developed at the University of California at Los Angeles. MOF-74 resembles a series of tightly packed straws comprising mostly carbon atoms with columns of zinc ions running down the inside walls. A gram of the material has about the same surface area as two basketball courts.
The researchers used neutron scattering and gas adsorption techniques to determine that at 77 K (-196° C), MOF-74 can adsorb more hydrogen than any unpressurized framework structure studied to date. NIST Center for Neutron Research scientist Craig Brown says that, though his team doesn’t understand exactly what allows the hydrogen to bond in this fashion, they think the zinc center has some interesting properties.
When we started doing experiments, we realized the metal interaction doesn’t just increase the temperature at which hydrogen can be stored, but it also increases the density above that in solid hydrogen. This is absolutely the first time this has been encountered without having to use pressure.
—Craig Brown
Although the liquid-nitrogen temperature of MOF-74 is not exactly temperate, it’s easier to reach than the temperature of solid hydrogen (-269° C). One of the goals of this research is to achieve energy densities great enough to be as economical as gasoline at ambient, and thus less costly, temperatures.
MOF-74 is a step forward in terms of understanding energy density, but there are other factors left to be dealt with that, once addressed, could further increase the temperature at which the fuel can be stored. Fully understanding the physics of the interaction might allow scientists to develop means for removing refrigeration or insulation, both of which are costly in terms of fuel economy, fuel production, or both.
The work was funded in part through the Department of Energy’s Hydrogen Sorption Center of Excellence.
Resources
Y. Liu, H. Kabbour, C.M. Brown, D.A. Neumann and C.C. Ahn. Increasing the density of adsorbed hydrogen with coordinatively unsaturated metal centers in metal-organic frameworks. Langmuir, ASAP Article 10.1021/la703864a. Published March 27, 2008.
IIRC liquid N is about -200 (Celsius) .. that's a tad too cold for a car. Can this be used in an industrial process?
Posted by: Neil | 02 April 2008 at 01:47 PM
We don't need hydrogen storage. We do need methane storage, because that's a readily available fuel from both fossil and biological sources.
Posted by: Rafael Seidl | 02 April 2008 at 03:02 PM
Theoretically, how good can any of these molecular matrix schemes be for storing gases at low pressure?
Won't they all have to overcome;
1. infusing the gas in the matrix in a timely fashion
2. offsetting the extra weight required by the matrix material
3. offsetting the interior volume required by the matrix material
4. releasing the gas predictably on demand to deliver as much energy as is required?
5. energy losses from injecting or extracting gases.
6. temperature variations from -20 C, to +40 C?
I suppose turning the gases into a virtual liquid at low pressure tremendously increases storage density, so even if only 20% of the tank volume is available to the gas, that still might be the equivalent of 200 atmospheres (SWAG) in a pressurized tank. I guess it would be more efficient than pressurization, but what do others think?
Posted by: Healthy Breaze | 02 April 2008 at 03:53 PM
Lets put it this way... liquid n is vastly easier to handle then liquid h and it costs vastly less to get it there in the first place as cheap industrial systems manage it all the time.
Soo this may well make it 100x cheaper to transport h2 in tube trucks made for liquid n.
Posted by: wintermane | 02 April 2008 at 05:54 PM
I don't think I will live to see a significant number of hydrogen powered LDVs and I'm pretty healthy. Battery electric makes too much sense.
Might this not come in handy for aviation applications where battery powered long distance flight is and will probably remain impractical?
Posted by: Bill Young | 02 April 2008 at 07:31 PM
Hydrogen is the long-term and bulk storage medium (fuel) of choice for renewable energy and even nuclear energy. Battery electricity can only store small amount and for shorter period of time, due to the excessive cost and the low energy density.
Methane is great as a transitional step to wean us off petroleum, due to already-existing infrastructure and the relative easy of handling and synthesizing NG. Long into the future, hydrogen will be the way to go, since it's the easiest and most efficient synthetic fuel to synthesize, directly from solar, wind and nuclear energy in a single step.
Posted by: Roger Pham | 03 April 2008 at 01:21 AM
You can already see that all the name brand Japanese firms are gearing up for major production of Lithium battery materials. Prices will drop rapidly once these batteries flood into the market.
On energy density, I would not be surprised to see 4x better energy density within 8 years. The advantages of rapid adoption cycles will make batteries a winner.
Posted by: Lulu | 03 April 2008 at 11:56 AM
Lithium battery is great for HEV's. Equipping hundreds of millions of cars at 1.5-2kwh-size packs will seriously strain lithium world-wide production, if production level can be met at all!
The energy density of lithium-based batteries cannot be much improved. This is a physical limitation based on the weight of lithium itself. Lithium-based batteries are lighter than nickel-based battery due to the much lighter weight of the lithium. The main hope is on the lowering of the price and increase durability of Lithium batteries.
Posted by: Roger Pham | 03 April 2008 at 05:44 PM
Roger
Are you sure, using Si nano wire Stanford university showed recently that it could potentially increase energy density 10 fold. Anyway if you consider a PHEV that can store enough electricty to run 50 miles you corver 80% of cars trips, if you can get 80miles then you cover 90%. So we don't need necessarilty more than foreseeable Li thechinology can offer. Honnestly the poor well to wheel effiency of H2 doesn't make it that promising even on the long term, especially in a world where energy will be expensive (as it is likely to be in the decades to come), well to wheel efficiency will really mater.
Posted by: Treehugger | 03 April 2008 at 07:09 PM
Treehugger,
Actually, well-to-wheel wise, H2 in a hybrid FCV (Honda FCX Clarity) or a future H2-ICE-HEV will be comparable to battery electricity in a future BEV.
Moreover, due to the fact that peak renewable energy collection (wind and solar) does not coincide with peak electricity consumption, both diurnally and seasonally. So, only about half of the time (or even less) that you can actually charge your BEV directly from solar or wind electricity. The rest of the time, you must burn the H2 (produced from excess solar or wind energy) in power plants or in the SOFC to generate electricity, then going thru all the transmission losses and internal losses within the BEV in order to get the power to the wheel, ending up at ~35% H2-to-wheel efficiency.
Whereas, if H2 fuel is used on board to generate power to be transmitted to the wheel, more efficiency will be the result, like in the Honda FCX Clarity at 60% well-to-wheel efficiency, or in the future H2-ICE-HEV at 50% well-to-wheel efficiency (my prediction).
H2 will simply be our future source of fuel for all types of consumption, much like today's NG, coal, petroleum, etc. Individual's preference will determine whether he/she will drive a BEV, FCV, H2-ICE-HEV...bicycle, public transit, walk, etc... :)
Posted by: Roger Pham | 03 April 2008 at 11:40 PM
I do not know that long into the future H2 will be the way. NG, SNG, CNG , ANG and variants are here now and very useful. Look at 100 years of oil and gasoline. Once they system finds something the works, it sticks with it. CO2 neutral SNG contained in ANG containers sounds good to me for quite some time.
Posted by: sjc | 04 April 2008 at 07:04 AM
Liquid fuels will continue to dominate given their energy density and ease of handling - I suppose you can pull H2 from them as needed for a fuel cell stack.
Posted by: Bill | 07 April 2008 at 07:35 PM
Hello Roger,
Peak Lithum is poor fallacy spead by the hydrogen lobby. See the link below:
http://www.evworld.com/article.cfm?storyid=1434
Theoretically Lithium battery EV’s have the potential to be much more efficient and practical than a hydrogen powered vehicle.
Battery energy is stored in the Anodes and the Cathodes of the battery, which Nanotechnology developments will soon improve dramatically.
As for off-peak storage of solar energy, I like Biodiesel or Ethanol from algae. They are a better energy carrier and have fewer problems to deal with.
For off-peak wind energy storage, I like compressed air.
Try reading the "Hype About Hydrogen" or this link: http://www.physorg.com/news85074285.html
Posted by: Dave | 16 April 2008 at 11:47 AM
Cell to wheel energy losses are released mostly as heat. Much of the year, we need this extra heat in our vehicles for comfort. Other times, this heat could be conveted to cooling for AC. This is a strong practical factor in favor of H2.
Posted by: Randell | 23 April 2008 at 03:02 PM