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Aluminum Alloy Releases Hydrogen From Water
mdsolar writes "PhysOrg is reporting on a method of releasing hydrogen from water by oxidizing aluminum in an alloy with gallium. In the presence of water the aluminum oxidizes, leaving aluminum oxide, gallium, and hydrogen gas. The Purdue scientists who discovered the effect think this could help to overcome difficulties with hydrogen storage. Quoting: 'On its own, aluminum will not react with water because it forms a protective skin [of aluminum oxide] when exposed to oxygen. Adding gallium keeps the film from forming, allowing the aluminum to react with oxygen in the water.'"
Check the price on gallium. It's about $500 per kilogram, although there was a price spike a few years back and it passed $1000. It's a trace component in bauxite and coal. Way too expensive to be used as a fuel component.
Gallium is so expensive that it's not even cost effective in solar cells, where it works very well.
The hydrogen is burned and released into the atmosphere as water. Since you get water from the environment for this in the first place, that's not the problem. The problem is getting the aluminum back, which, if you RTFA, you would have seen can be done with "fused salt electrolysis".
The aluminum smelting process requires vast amounts of electricity.
quoting a random googled page : "On average, around the world, it takes some 15.7 kWh of electricity to produce one kilogram of aluminium from alumina. Design and process improvements have progressively reduced this figure from about 21kWh in the 1950's."
so it doesnt matter that it produces hydrogen. It's almost assured coal equivalent to or greater than the tank of gas it replaces was burned somewhere to get the aluminum.
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It's not a closed system because it requires energy to recycle the aluminum and gallium. Also, it's still not terribly efficient, since it requires 1 lb of aluminum per mile you drive.
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The article talks of local power plants that could be used to provide electricity without it having to be distributed on the grid, effectively closing the system and making it substantially more efficient. Efficiency with the aluminum should come as the technology matures.
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It is? I keep hearing that our uranium sources will only last for 50 years unless we seriously modernize our plants (so that they can process nuclear waste products as well).
I used to work in a uranium mine is south-western Colorado. There are still many, many mines there that have lots of uranium in them. It just isn't economical to mine them as we don't really use that much uranium. If we built more power plants and the price came up, those mines would open.
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No, it won't. The aluminum oxide is *hard* to convert into aluminum. That's the *reason* aluminum is expensive -- not because the oxide is expensive (it's dirt cheap), but because it takes *massive* amounts of energy to turn it back into aluminum. And, said energy has to come in the form of electricity. This is just an expensive way of storing and moving electrical energy -- and an inefficient one, too, when you remember that only some of the energy in the aluminum goes into cracking the water, and about half of it goes into heat.
The basic reaction is:
2Al + 3 H20 -> Al2O3 + 3 H2
Aluminium has an atomic mass of about 27, so 54g of Al will produce 6g of H2, i.e. it takes 9kg of Al to produce 1kg of H2. (We haven't been told how much gallium is required in the mix, so I'm ignoring this component.)
According to Wikipaedea, the goal for hydrogen storage in 2015 is 0.09 kg H2/kg. This process rates at 0.11 kg H2/kg before accounting for the gallium - so it is looking pretty good so far.
I've neglected the weight of water used in the reaction. If we include this, it doubles the required mass: 54g Al + 54g H2O to produce 6g H2. We may be able to recycle the engine exhaust to provide the required water. However, this scheme means that you gain weight as you run your car: everytime you use 6g of hydrogen, you turn 54g of Al into 102g of Al2O3, which you are still carrying.
I'm also worried about the efficiency of the fuel cycle, which will require returning large amounts of Al2O3 from fuel stations to a recycling plant, which then uses electricity to convert the Al2O3 back to Al.
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Not even close to true. Uranium is very plentiful. In fact, if necessary, it can be extracted from sea water. The cost of the fuel is negligable compared to the cost of handling/disposing/etc.
Alcan Aluminium works out of British Columbia, and is one of Canada's major Aluminium manufacturers. BC's electricity is provided via hydroelectric dams - very common amongst the west coast of Canada. I don't see why this cannot be a cheap, reliable and reusable source of energy for it.
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Wikipedia has an article on the Hall-Héroult process, the major method used to refine aluminum oxide into aluminum. Ill save you the time.
"In the Hall-Héroult process alumina, Al2O3 is dissolved in a carbon-lined bath of molten cryolite, Na3AlF6. Aluminium fluoride, AlF3 is also present to reduce the melting point of the cryolite. The mixture is electrolyzed, which reduces the liquid aluminium. This causes the liquid aluminium to be deposited at the cathode as a precipitate. The carbon anode is oxidized and bubbles away as carbon dioxide. The electrical current used by many smelters, has a very low voltage, but massive amperage. This is typically 3-5 volts, but 150,000 amperes."
So now were back to greenhouse gasses and massive amounts of electricity.
It takes electricity to recycle the aluminum oxide, but you can supply that electricity with clean sources (solar, wind, etc). Even if you only use power from the grid, you'd do it at night when the power is cheapest which would bring the base-load power generation closer to the peak always a good thing since peak power is typically generated using the least efficient means we've got (oil and natural gas power plants).
An increase in the base-load would allow more efficient plants to be constructed. This reduces the cost of peak power for everyone.
Not a bad side effect.
*sigh* back to work...
Aluminum oxide is an incredibly energy-intensive process... and not altogether clean, either. You have a molten cryolyte bath that you dissolve the alumina into you have fluorinated waste gasses, you slowly dissolve your carbon anodes, etc. Water electrolysis is so much simpler, and quite efficient to boot. The only real downside is the thermal losses if your electricity comes from a heat-driven power plant, but that applies to most any process that uses electricity.
Anyways, without knowing the energy efficiency of this aluminum+water->hydrogen+alumina, I wouldn't be ready to judge this tech yet.
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While it is true that Aluminium smelting uses up a lot of energy, the rest of the process is remarkably pollution-free (most of the catalysts are recycled and reused in smelters). As for the energy, there are places in the world that produce vast amounts of clean energy that is used for aluminium smelter. One example of this is Iceland (where I live).
Interesting link, but the aluminum-air battery appears to be only about twice as power-dense as zinc-air, which is an established technology used primarily in hearing-aid batteries. Neither seems likely candidates as secondary cells, which is what we really want.
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Aluminum isn't that light, 200 lb would end up being a cube about 20 cm x 20 cm... quite small and compact.
Three things make this a nonissue. Breeder reactors can extend this significantly; it's referring to only current mining methods; there is far more that can be extracted with increased effort; thorium can be bred into fuel and there's way more thorium than uranium. By the time all these options are used up, the ITER project's fusion offspring would have long been in operation.
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ITER will not get break even fusion on a commercial scale. just like it's predecessors. It may get controllable fusion, but it will not make break even and the costs of the energy out will be huge. Commercial failure.
But everybody involved has to paint the smiley face and if you don't well then you obviously are not a serious researcher and you do not get funding. Double if your research threatens the research dollars tied up in ITER.
ITER is trying to perform bench experiments on a huge scale with little or no proof the ideas behind it are workable. All the previous experiments using this design have failed, nice data, no results. They need to scale back and experiment on equipment that doesn't cost a fortune per shot.
They have all these experiments just to gain containment, then _if_ they get that a lot more to gain control, then they might try to light the fuse, _if_ they have containment and control. They're not sure they are going to get either and yet they want me to believe they know they are going to get commercial power.
What stands out to me is how much money and publicity is given to the supporting systems, it's like they've gone ahead and done the engineering before they've done the science. In successful projects very little is spent on engineering as it's all funneled into the science. Engineering is what you do when you know what you are doing. First you get the science working then you work on the engineering challenge.
It's a bunch of egghead egos playing with super sized Lego and trying not to let on they don't have a clue.
Aluminium is extracted via electrolysis and takes masses of electricity to produce. Hope you're adding this energy into your "zero sum".
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Breeder reactors can extend this significantly; it's referring to only current mining methods; there is far more that can be extracted with increased effort; thorium can be bred into fuel and there's way more thorium than uranium.
There's also decommisioned nuclear weapons which could potentially be used as fuel.