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Storing hydrogen in carbon nanotubes

Physicists from California have found a promising way to store hydrogen inside carbon nanotubes. By bombarding a film of carbon nanotubes with a hydrogen beam, they found that about 5% of the weight of the hydrogenated nanotubes came from the hydrogen atoms, which is not far from the goal of 6% fixed by the U.S. Department of Energy for 2010.

Everybody knows that we have to face two crisis related to energy: the exhaustion of fossil fuels and the global warming effect. One possible solution to these problems is to use hydrogen but we're not there yet. However, physicists from California have found a promising way to store hydrogen inside carbon nanotubes, according to this SLAC short news release. By bombarding a film of carbon nanotubes with a hydrogen beam, they found that about 65 percent of the carbon atoms had bonded to hydrogen atoms. In other words, 5% of the weight of the hydrogenated nanotubes came from the hydrogen atoms, which is not far from the goal of 6% fixed by the U.S. Department of Energy for 2010.

The Stanford Linear Accelerator Center (SLAC) news release starts with a somewhat futuristic tone.

Imagine this: your fuel gauge is hovering near empty. You stop by the nearest store, turn in your empty hydrogen cartridge, buy a full one and pop it into your car. Presto, you’re on your hydrogen-powered way again, emitting just the faintest traces of water out the tailpipe.

We're far from this, but researchers at Stanford, including Anders Nilsson's Surface Science and X-Ray Spectroscopy group, have recently shown that carbon nanotubes could be a promising material for storing hydrogen safely. Here is a short description of their experiments.

The basic idea is this: use electricity to split water into hydrogen (and oxygen) atoms, put the hydrogen into a fuel cell, which strips the electron from the hydrogen atom and forces it across a membrane, generating an electrical current which can power your car. The hydrogen ions are reunited with oxygen, making a watery exhaust.
In their attempt to store hydrogen, the researchers bombarded a film of carbon nanotubes with a hydrogen beam. Then they studied the film with different x-ray spectroscopy techniques to see if any hydrogen atoms had formed chemical bonds with the carbon. To their delight, they found that about 65 percent of the carbon atoms had bonded to hydrogen atoms.

And Anders Nilsson explains: "It was a surprise that we could get so many carbon-hydrogen bonds. It gives us hope it can be used as a material for storing hydrogen."

Below is a fancy illustration of the single-walled carbon nanotubes (SWCN) used for these experiments ("SWCN are essentially a one-atom-thick layer of carbon rolled into a tube") (Credit: SLAC). And here is a link to a larger version.

Single-walled carbon nanotubes at SLAC

This research work has been published by Physical Review Letters under the title "Hydrogenation of Single-walled Carbon Nanotubes" (Volume 95, Issue 22, Article 225507, November 23, 2005). Here are two links to the abstract and to the full paper (PDF format, 4 pages).

But you might prefer to read shorter versions of this technical paper, like this summary, from which the above image was extracted, or this longer version, both published by SSRL Science Highlights in January 2006 -- SSRL stands for "Stanford Synchrotron Radiation Laboratory." This last document gives lots of details about the recent experiments at SLAC.

Besides these scientific results, what's next for all of us?

The researchers estimated that five percent of the total weight of the hydrogenated nanotubes came from the hydrogen atoms, and they are already working to boost that number. For its FreedomCAR program, the Department of Energy has set the goal of developing a material that can hold six percent of the total weight in hydrogen by the year 2010.

But will we fill our cars with hydrogen cartridges in 2010? I don't think so. We'll have to wait longer than that.

Sources: Heather Rock Woods, Stanford Linear Accelerator Center news release, February 16, 2006; and various web sites

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