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Ammonia Borane Appears Stable for Hydrogen Storage in Vehicles

11 September 2006

Researchers from the Pacific Northwest National Laboratory (PNNL) and Rohm and HAAS have determined that ammonia borane (AB) is a promising hydrogen storage material for fuel-cell vehicle applications due to its high hydrogen density and stability under typical ambient conditions.

Ammonia borane is a stable solid at room temperature that requires heating to near 100° C to release the hydrogen. PNNL had earlier found that ammonia borane (NH3BH3) and polyammonia borane (-NH2BH2-) within a scaffold of mesoporous silica templates demonstrated hydrogen storage capacities of > 12 wt.%. (Earlier post.)

There have been concerns over the materials stability in warm temperatures—for example, in a car parked in the hot sun.

PNNL and Rohm and HAAS Company researchers measured the thermal stability of the solid material from 40° C to 60° C, and assessed hydrogen release from 70° C to 90° C.

The experiments and calculations both indicate that the stability of ammonia borane relates to its purity and that it can remain stable for many days or longer in high temperatures. The research is also helping to determine if auxiliary cooling is required to minimize the inadvertent release of hydrogen in the tank and keep the vehicle safe.

Scott Rassat from PNNL presented the results at the 232nd National Meeting of the American Chemical Society in San Francisco.

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September 11, 2006 in Hydrogen, Vehicle Systems | Permalink | Comments (6) | TrackBack (0)

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Comments

So how does 12% compare with compressed H2 in a tank?

The material is a solid, so it can be built into the chassis of the car. It needn't compare to storage tanks, it merely replaces them.

Compressed H2 at 350 bar currently has a gravimetric capacity of about 6 wt.%, according to DOE. (Depending upon tank, rest of system, etc.)

Compressed H2 at 700 bar currently has a gravimetric capacity of about 4.5 to 5 wt.%, although it has a higher volumetric capacity than CH2 at 350 bar.

Neither meets volumetric or gravimetric DOE targets for 2007, much less targets for 2010 and 2015.

LH2 meets volumetric target for 2007 and slightly exceeds gravimetric target for 2007.

DOE chart on capacity and cost here:
http://www.eere.energy.gov/hydrogenandfuelcells/storage/tech_status.html

Everything has changed in the last few years.

1 The amount of h2 they need on the car has dropped by a factor of 3-4.

2 The capcity of a tank has gone up by a factor of 2.5.

3 Regneratuive breaking and plug in hybridization has eleimated the need for a quick start fuel cell AND dropped the power req of the fuel cell by a massive factor as it no longer needs to carry the entire peak load.

4 The cost of making h2 has dropped. ALOT.

Right now they are working on a few very important bits. Replacing the most costly parts of a fuel cell with cheaper materials.. already done but 2 more gens need to be built before they are satisfied. The tanks need to be cost reduced and standardized. Partly done already work is progressing. Cost of fuel.. still dropping. Cost of the battery pack and hybrid system now wanted with it... going down soon.

A few more generatios of fuel cell tank and h2 station and they will be there.

I have one of those touchless thermometers; you know, the one that looks like a snub-nose revolver and has a laser pointer to know what you're aiming at? This summer in Phoenix I got bored on one of our record-hot days. Air temp was 118F and I decided to see how hot the pavement was in the street in front of my house. The pavement was 160F. That's 71C. I've heard of cars parked in the hot sun reaching over 160F and Phoenix isn't even the hottest part of the USA!! This material will not work obviously since it begins outgassing hydrogen at temperatures that are easy to reach on a hot summer day.

Sid,
Why don't you put a thermometer into the fuel tank and measure the temperature there. You have to make a fair comparison before saying it will "obviously" not work. If this material requires heating to release the hydrogen, I'd expect it to be in an insulated box, which would reduce the rate of heating from external sources (the sun).

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