Tuesday, August 28, 2007

Hydrogen Production

Interesting article here at PhysOrg, entitled "Engineers perfecting hydrogen-generating technology". Judging from the article, an alloy of aluminium and gallium (which is conveniently produced as a byproduct of aluminium production) could potentially be used to convert water into hydrogen, whilst oxygen bonds with the aluminium to form alumina, which can be recycled back into aluminium.

When water is added to the alloy, the aluminum splits water by attracting oxygen, liberating hydrogen in the process. The Purdue researchers are developing a method to create particles of the alloy that could be placed in a tank to react with water and produce hydrogen on demand.

From the article:

"The gallium is a critical component because it hinders the formation of an aluminum oxide skin normally created on aluminum's surface after bonding with oxygen, a process called oxidation. This skin usually acts as a barrier and prevents oxygen from reacting with aluminum. Reducing the skin's protective properties allows the reaction to continue until all of the aluminum is used to generate hydrogen, said Jerry Woodall, a distinguished professor of electrical and computer engineering at Purdue who invented the process.

I wish they made an effort to give more context to these articles: it would help if someone who knew more about this sort of thing were to draw up a "score sheet" showing the relative energy-densities, cost, benefits and problems with each of the various auto-powering technologies.

Lots more quotations:

"The U.S. Department of Energy has set a goal of developing alternative fuels that possess a "hydrogen mass density" of 6 percent by the year 2010 and 9 percent by 2015. The percent mass density of hydrogen is the mass of hydrogen contained in the fuel divided by the total mass of the fuel multiplied by 100. Assuming 50 percent of the water produced as waste is recovered and cycled back into the reaction, the new 80-20 alloy has a hydrogen mass density greater than 6 percent, which meets the DOE's 2010 goal.

Aluminum is refined from the raw mineral bauxite, which also contains gallium. Producing aluminum from bauxite results in waste gallium.

"This technology is feasible for commercial use," Woodall said. "The waste alumina can be
recycled back into aluminum, and low-cost gallium is available as a waste product from
companies that produce aluminum from the raw mineral bauxite. Enough aluminum exists in the United States to produce 100 trillion kilowatt hours of energy. That's enough energy to meet all the U.S. electric needs for 35 years. If impure gallium can be made for less than $10 a pound and used in an onboard system, there are enough known gallium reserves to run 1 billion cars.""

One of the problems with the predicted hydrogen economy is the difficulty of transporting and storing hydrogen safely and efficiently. Because this aluminium/gallium alloy can be transported as easily as oil: ""Particles made with this 80-20 alloy have good stability in dry air and react rapidly with water to form hydrogen.""

Another interesting idea is the possibility of converting conventional internal-combustion engines into hydrogen burning engines.

It also has obvious applications for boats: you wouldn't have to haul the raw water around with you.

The Purdue researchers had thought that making the process competitive with conventional energy sources would require that the alumina be recycled back into aluminum using a dedicated infrastructure, such as a nuclear power plant or wind generators. However, the researchers now know that recycling the alumina would cost far less than they originally estimated, using standard processing already available.

"Since standard industrial technology could be used to recycle our nearly pure alumina back to aluminum at 20 cents per pound, this technology would be competitive with gasoline," Woodall said. "Using aluminum, it would cost $70 at wholesale prices to take a 350-mile trip with a mid-size car equipped with a standard internal combustion engine. That compares with $66 for gasoline at $3.30 per gallon. If we used a 50 percent efficient fuel cell, taking the same trip using aluminum would cost $28.""

So the energy is generated somewhere, and "stored" in the aluminium/gallium alloy, which would produce hydrogen when needed, which could be used to power an engine.

This solves the problem of safely and efficiently storing and transporting hydrogen. For automobiles it does mean you'd have to lug around water and metal. 6 % hydrogen mass density doesn't seem like much to me, but it'll be interesting to see how this does genuinely compare with petrol.

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