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Researchers Demonstrate 7.5 wt% Hydrogen Storage in MOFs

6 March 2006

Yaghi
The top-performing MOFs for hydrogen storage: MOF-177 and IRMOF-20

Chemists at UCLA and the University of Michigan have achieved hydrogen storage concentrations of up to 7.5 wt% in Metal Organic Framework (MOF) material—exceeding the the DOE target of 6.5% by 2010 for application in hydrogen fuel-cell cars. (Earlier post.)

The storage was achieved at a low temperature of 77 Kelvin (-196º C or -321º F).

The researchers worked with a series of microporous MOFs under saturation pressures varying between 25 and 80 bar across the series. MOF-177 showed the highest uptake on a gravimetric basis (7.5 wt %) and IRMOF-20 showed the highest uptake on a volumetric basis at 34 g/L.

We have a class of materials in which we can change the components nearly at will. There is no other class of materials where one can do that. The exciting discovery we are reporting is that, using a new material, we have identified a clear path for how to get above seven percent of the material’s weight in hydrogen.

We have achieved 7.5 percent hydrogen; we want to achieve this percent at ambient temperatures.

—Omar Yaghi, UCLA professor of chemistry

MOFs can be made from low-cost ingredients, such as zinc oxide and terephthalate, which is found in plastic soda bottles.

In previous research, Yaghi and colleagues reported that MOFs also can store large amounts of methane. Additionally, Yaghi has shown that MOFs store prodigious amounts of carbon dioxide at ambient conditions, a development relevant to preventing carbon dioxide emissions from power plants and automobile tailpipes from reaching the atmosphere.

We have materials that exceed the DOE requirements for methane, and we think we can apply the same sort of strategy for hydrogen storage.

—Omar Yaghi

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March 6, 2006 in Hydrogen, Vehicle Systems | Permalink | Comments (10) | TrackBack (0)

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Comments

This is excellent news. It would be great to see them working with a hydrogen tank manufacturer or automotive company to get this technology out of the lab and into the real world.

That would be nice if it didn't require a temp of 77K. Lets see, superconductor materials research has been working for decades to get materials to perform at ambient temps. I don't think this will be any different simply for the basic gas law equations...raise the temperature and watch the pressure get out of hand in a fixed volume.

There are lots of markets where liquid hydrogen is already used today. Anyone that doesn't realize that is in complete denial.

GM and BMW among others have been big proponents of liquid hydrogen storage for fuel cells. Take NASA with the space shuttle even. Liquid hydrogen is stored around 33K, so 77K is quite a bit warmer.

Liquid hydrogen only holds about 1.4 wt%, while this technology is about 5 fold better at 7.5 wt%.

In short, anywhere liquid hydrogen is used today, this could offer a better solution.

"The storage was achieved at a low temperature of 77 Kelvin (-196º C or -321º F)."

Liquid nitrogen temperature. You could probably run an engine off the liquid nitrogen that would be more efficent, safer and cheaper than storing hydrogen like that.


how exactly do you "run an engine off the liquid nitrogen"? do you mean burn it to NOx? N2 is pretty inert to combustion and not applicable to fuel cells, these being the long term reason for needing hydrogen storage capacity.

I think Mr. Schwartz means that you can run a sort of "reverse steam engine" using liquid nitrogen: The atmosphere serves as a heat source, and the liquid nitrogen serves as a heat sink, rather than a steam boiler serving as a heat source and the atmosphere servings as a heat sink.

Under the Carnot cycle, the maximum possible efficiency of such an engine could be 73.8% on a sunny day (70 F ambient temperature). I have no idea how thermally efficient an actual production model would be, nor what size and shape it would take, nor what its performance characteristics would be like, nor what the energy costs are for creating, storing and distributing the "fuel." I'm guessing that they would be about as much fun to drive as a reverse locomotive, but that's just me talking. I'm also guessing that if such a scheme were efficient, someone would have tried it already, but that's just me talking again. A Stirling cycle engine would work with the temperatures involved and at close to the maximum theoretical efficiency, but Stirling engines tend to be very bulky per unit of power output, and not very suitable for mobile applications.

I can imagine using cold hydrogen in a "co-generation" sense, to displace a conventional air conditioner. Considering that automotive air conditioners really do suck up a good deal of energy (see the "Ventilated Seats" posting from a few days ago), a co-cooling application would be a nifty trick.

Water is 10% hydrogen by weight but is unavailable as a fuel in this form. I think anhydrous ammonia (NH3) is 15% hydrogen by weight and could be used as a fuel in that form. We have decades of experience in safely manufacturing, shipping, and storing ammonia for agricultral use. So this "breakthrough" is only half as efficient at hydrogen storage as a century old technology.

Haven't done much homework on this, but I get the off-the-cuff impression that liberating free hydrogen from ammonia results in high temperatures and some significant degree of thermodynamic loss. How would that effect the overall efficiency and economics of the system? How much extra hydrogen would you have to produce, transport, carry and burn to make up for that?

Ammonia can be used as fuel without reforming. Its main drawback would be higher NOx production.

The reference to liquid nitrogen is, I imagine, clarified by looking up "nitrogen Economy" in Wikipedia. Liquifying nitrogen reguires energy. It can then be used in a heat engine either as a "cold source". It would work in a stirling engine with the heat source being the air at ambiant temperature. Or you could use it in a Rankin Cycle engine where you pump it through a heat exchanger (a boiler) and use the expanding nitrogen to do work. In otherwords another energy storage device. So what we REALLY need is a better battery...Anyway the problems with Liquid Nitrogen appears to be its low energy density-about 15 times less than fossil fuel, and getting a heat exchanger of practicable size which does not ice up. Tho' there is an interesting solution to this last problem described here http://www.eureka.findlay.co.uk/eureka_editorial/news_reference/FI-Nitrogen.htm

Although the development described is four years old and the car is yet to appear on the market.

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