Jerry Woodall, Purdue University
Biodiesel is one option for powering cars of the future, but another fuel we could use is hydrogen. This has the benefit of producing only water when it burns, but can be expensive to extract and store. Weíve got Jerry Woodall on the line now to tell us about a simple way heís found to extract hydrogen from waterÖ
Jerry - We use aluminium as our high energy content material. Aluminium-like oil has a very high energy content, the only difference is aluminium will form an oxide skin so you canít use it for that purpose, whereas oil has all these stable hydrogen-carbon bonds and just sits there in the earth until youíre ready to burn it.
Chris - Now when you say you canít use aluminium in that way, youíre talking about using it exactly how?
Jerry - Well, if I want to take the aluminium and use it to split water into hydrogen and oxygen, and have the aluminium grab the oxygen, a piece of aluminium sitting on a shelf wonít do it because it has a passive layer of oxide already on it. So we thought that if we have a piece of aluminium with no oxide on it, it will readily split water.
Chris - And so how do you propose to do that? You would have to go through quite a lot of chemical steps normally to strip that protective oxide off.
Jerry - Thatís correct. This idea of using aluminium has been around for a long time, there are no less than 26 patents in the literature since about 2001; mechanical scrapings, aluminium powder and all these sorts of things. Theyíre ok, but theyíre not very practical. What I discovered is if I added the element gallium, which is a group 3 element on the periodic table, that gallium in the aluminium prevents the aluminium oxide from passivating it. So if you do that, and make an alloy, in chunks or particles or pellets, this material, when it comes into contact with water, will split the water. Liberating the hydrogen and forming aluminium oxide powder.
Chris - But you donít end up with the skin on the aluminium, the gallium seems to stop it somehow?
Jerry - Thatís how it does it.
Chris - Do you know how?
Jerry - The gallium prevents the passivating oxide from forming on solid aluminium.
Chris - Do you know how? And how did you discover it?
Jerry - Oh, yes. So the first experiment I did back in 1967 when I was still at IBM. It turns out I discovered this by having a liquid of gallium and aluminium, gallium melts just above room temperature. So I was working on a semiconductor material called, actually, gallium-aluminium-arsenide. What I discovered was that when I had these melts, which I used to grow the crystals from and was mostly gallium and aluminium, if I added water to that I was getting hydrogen coming off, in a big way Ė Boom Boom! So then, I sat down and figured it out; It turns out, if youíre aluminium in a pool of gallium, there is no solid oxide protecting you from further reaction. A water molecule comes along, the aluminium sees it, and splits it into hydrogen and oxygen.
Chris - So how would you see this being used practically, in a car for example, and why would it be better than just having a cylinder of hydrogen sitting in the back of the car?
Jerry - Oh because its hydrogen on demand. Aluminium is safe by itself, the aluminium gallium allow is safe by itself. So I can drive around and if I had a collision, god forbid, nothing would happen.
Chris - So how would the engine get the hydrogen in the right amounts?
Jerry - Very simple, I would have a bunch of aluminium in my Ďaluminium tankí if you will, and then I would feed water into it. I would feed it into a pool of gallium, and then add water, the hydrogen comes off and goes into your intake manifold, just like BMW uses.
Chris - How many, I donít suppose you could say miles to the gallon, but how far could you travel on how much aluminium? Is this viable?
Jerry - Okay, to drive a car the size of a US torus 350 miles you would need about 18 gallons of gasoline. I would need 320lb of aluminium to drive the same distance using an internal combustion engine.
Chris - So itís actually quite practical, this could be done.
Jerry - Yes, and itís economically practical right now also.
Chris - What about getting the aluminium back at the end? What are the waste products? How could you complete the loop and make sure itís clean?
Jerry - Right, this is very important that your readers and listeners understand this; you donít get this for free. We had all those dinosaurs, a long time ago, and we take them out of the ground for free as oil, and we canít grow them back again. Aluminium doesnít exist as pure aluminium, it exists as aluminium oxide, so once Iíve finished using the aluminium up to create my hydrogen, I have to get it back to aluminium again. Now, the major aluminium companies, the factories, take the aluminium oxide that they dig out of the ground, pass electricity through it to get it back to aluminium. You have to do that to get the fuel back again.
Chris - What about the gallium, can that be recycled?
Jerry - Yes, the gallium is totally inert, itís completely reusable. You can use it over and over again, it does not react, itís like a catalyst.
Chris - Brilliant, so to summarise you could envisage making these gallium-aluminium pellets, you put water onto them, react it to get the hydrogen. You get aluminium oxide and gallium back, you then clean that up and pass electricity through it in a power station, say a nuclear power station, or wind or tidal power station to make sure itís carbon neutral, so youíve got clean energy, and this is a way in which you could power the planet.
Jerry - Thatís correct, itís very green. You need to point out to your listeners however, if youíre not interested in making hydrogen, what Iím doing should not be of interest. People have asked me, Ďif it takes energy to get aluminium back out of aluminium oxide, why not just use the electricity itself?í Well, youíve got to get the electricity from someplace, maybe a coal-fired plant or something, that leaves a carbon footprint. So if you are willing to use hydrogen, which is very clean and green as you said earlier in the programme, if you are using a fuel cell or an internal combustion engine the reaction product is just plain old water. You can sniff it, it wont hurt you, you could use this in your house. So the point is this could be a very viable solution, thereís enough aluminium and gallium on the planets surface to run a billion cars continuously.