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The Race for Hydrogen

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Hydrogen Progress Challenged By Storage Issues

December 8th 2008

Energy / Environment - Honda Clarity Fueling

Many have heard the phrase “the hydrogen economy,” conjuring up images of blue skies, green fields, and a tidy white sedan noiselessly scooting along a pastoral back road. The reality of handling hydrogen as a fuel is not quite so rosy.

Today, we have pipelines that handle gasoline, diesel, natural gas, and ammonia. The metallurgy of the pipelines themselves is well understood, compressors and pumps are available to move the products, safety precautions are straightforward, and accidents are fairly rare. However, there is an important molecular implication for hydrogen, and its storage and distribution question.

Currently, the smallest molecule we commonly move by pipeline is natural gas or methane. The methane molecule contains five atoms with a total molecular weight of sixteen. But hydrogen is one eighth of that size, composed of just two skittish protons and their attendant electrons. Pressurize hydrogen in a metal pipeline and it will move not only through the pipeline but into the pipeline's metal structure, causing a destabilizing phenomenon known as “hydrogen embrittlement.” Hydrogen's behavior, in terms of the metals used to contain it, is only a little better than that of the loose neutrons produced in a nuclear reactor.

Once delivered to a filling station, making hydrogen mobile is the next problem. It doesn't become a liquid until very close to absolute zero. Many believe the only place to realistically see it in use for transportation is in the large tank on the belly of the space shuttle. Even though BMW promises its Hydrogen 8 vehicle will be fueled by liquid hydrogen, not the gaseous form, returning to the gaseous state compression is the only means to achieve high density aboard an auto, and that can make collisions dangerous. Of course, gasoline is dangerous on collision, but in the case of hydrogen, it will spontaneously combust at concentrations between 4 percent and 75 percent—and rapid release from a storage tank is one of the scenarios that can trigger a fire.

Honda has built but refuses to release to the market, a device the size of a small refrigerator called the Home Energy Center, that creates hydrogen by reforming it from natural gas, allowing home refueling. Water can be zapped with an electric charge—that is, electrolyzed—to safely create hydrogen gas. A Shell Station on Santa Monica Blvd. in Los Angeles is doing this today. A network of neighborhood refueling stations might be created to use either natural gas, ammonia, or simple water as the feedstock. Once created, the hydrogen would be available to fill the car, but again there is no rule stating that fuel must go in a tank, only our perceptions based on how cars have been built for the last century. Perhaps the barriers to vehicle use are not so much hydrogen's problem, but rather our own viewpoint. Consider this alternative scenario.

Rather than treating hydrogen's willingness to be intimate with the metals around it as a problem, many researchers have taken the opposite direction and are trying various metal hydrides as hydrogen carriers. A hydride is a combination of a metal atom and one or more hydrogen atoms that form a stable configuration. Those most often mentioned in research are the light metals such as lithium, sodium, and aluminum. But as researchers go further in their quest for a material that will stand up to the range of temperatures and the number of charge/discharge cycles an automobile must withstand, catalyst metals such as tantalum and structural metals such as titanium have begun to creep into research reports.

This search for the right material recently received a clever boost. Researchers in Holland invented a process they call hydrogenography. Materials testing formerly involved synthesizing a promising alloy then trying it under various conditions to measure its uptake and release of hydrogen. Now in the place of ponderous single compound examinations, a batch of thousands of different alloys is created in a thin film. The film is exposed to hydrogen, and an optical examination easily identifies promising candidates.

“Light” is a relative term in regard to weight. A hydride-based storage system will weigh four times the hundred and fifty pounds of a full gasoline tank, not an inconsiderable mass for a vehicle meant to be small and fuel efficient. But this will be a safe storage method. Hydrides store a great deal of hydrogen but unlike a pressure tank, they have to be coaxed to release their payload—-hence they'll remain stable in the event of a crash. Vehicle stability would be enhanced as well—unlike a top heavy SUV, the mass of the hydride storage system will be low to the ground where it won't increase the possibility of a rollover.

Nanotube-based storage is another promising area for hydrogen storage. Natural Nano, Inc. has received patents for both hydrogen storage and an ultracapacitor, but instead of the synthetic nanotubes based on carbon, theirs are halloysite clay. This type of clay, composed of aluminum, silicon, and hydrogen, has long been used for porcelain, china, and filtration applications. No weight savings is anticipated but being able to mine nanoscale hydrogen storage material rather than laboriously fabricating it from carbon is very attractive. Single-walled carbon nanotubes are over five hundred dollars per gram, while a ton of halloysite clay costs just four hundred dollars.

The research is promising, but hydrogen fueled vehicles have miles to go as they dramatically improve the dynamics of the science, economics, and storage challenges.

Cutting Edge Science Writer Neal Rauhauser is an analyst and consultant on energy and telecommunications. He is a member of the Stranded Wind Initiative and can be found at www.strandedwind.org.


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