Why Would You Make Hydrogen From Aluminum?

Everyone loves "green" hydrogen these days. It's the miracle fuel. The trouble is, it takes a lot of renewable or clean energy to make it through electrolysis, and the process is only about 80% efficient. Then you have to store the stuff, which isn't so easy; it is a tiny molecule that finds ways to leak out. We use a lot of hydrogen that currently is steam reformed out of coal or methane (natural gas). Almost 2% of global CO2 emissions come from just making the hydrogen for ammonia. Before you even start thinking about cars or home heating, there is the existing industrial hydrogen that has to be cleaned up.

That's why this new system from a Pennsylvania startup, GenHydro, is interesting. Instead of using electricity to split water into hydrogen and oxygen, it uses scrap aluminum. Raw aluminum is highly reactive and grabs oxygen molecules wherever it can to make a skin of aluminum oxide or alumina. GenHydro has figured out a way to grind up the aluminum into a fine powder, remove the alumina in a reactor, and expose the raw aluminum to water. The oxygen in the water would rather dance with the aluminum, so the rejected hydrogen bubbles away for collection. The reaction gives off a great deal of heat as well, which is used to run a steam turbine and generate electricity. It sounds like a triple win: you get hydrogen, alumina, and electricity.

GenHydro CEO Eric Schraud tells Leigh Collins of Hydrogen Insight that "in the GenHydro process, every metric tonne of aluminum produces 111kg of hydrogen and 3.12MWh of electrical energy from the steam turbine." You don't need tanks or pipes for storage either; you can build it all into a unit the size of a Coke machine which you put where the hydrogen is needed, and just feed it aluminum.

Schraud says there is lots of it lying around: "It's everywhere—I'm sure the chair you're sitting on right now has an aluminum frame. [It's in] fences, windows, aluminum siding on homes, aluminum cans…" Nine million metric tons of aluminum gets landfilled in the U.S. each year, which Schraud says could produce about one million tons of clean hydrogen annually, and lots of electricity. Hydrogen Insight says, "The size of the potential market for GenHydro is vast, limited only by the supply of scrap aluminum."

This is where it gets confusing. We have devoted a lot of posts to aluminum production, noting how much energy it takes to get oxygen out of alumina—about 13 to 16 kWh per kilogram of aluminum, much of that made with dirty coal-fired electricity. The Hall-Héroult electrolytic process consumes 400 kilograms of carbon anodes per metric ton of aluminum because carbon is even a grabbier atom than aluminum, so after the electricity separates the oxygen from the aluminum, it bonds to make CO2.

And the alumina is made from bauxite, an ugly process on its own. So GenHydro is feeding a very dirty fuel into its hydrogen generator.

But it's scrap, you might say; they are not doing this with virgin aluminum. They are keeping it out of landfills. The problem here is that aluminum is easily recycled, with a carbon footprint that's one-twentieth that of virgin aluminum. It's valuable stuff. GenHydro says it is paying $700-800 per metric ton. To paraphrase futurist Alex Steffen, there is really no such thing as aluminum scrap; it is just useful stuff in the wrong place and should never be in landfills. It only exists because there are weird things happening in the aluminum market now, where the aluminum from beer cans is being imported from Saudi Arabia.

But the biggest problem is that every pound of aluminum that is turned back into alumina and hydrogen is likely a pound of aluminum that has to be replaced with virgin aluminum made from bauxite and alumina and then zapped with kilowatts of electricity. As Carl A. Zimring noted in his book on aluminum, recycling, "absent a cap on primary material extraction, does not close industrial loops so much as it fuels environmental exploitation." We have to recycle it all and use less of the stuff.

I was going to reach out to hydrogen expert Paul Martin for a comment about this, but he beat me to it with a post on LinkedIn where he pulled no punches:

"What's the cycle efficiency? What's the CO2 and toxic emissions intensity of the feed aluminum waste? Why not recycle it? Why is 9 million tonnes of aluminum landfilled every year and how do we stop that? And given that aluminum is MADE from alumina, how is it that they get more value for the alumina product than a recycler would pay for aluminum scrap? Let's be quite clear: aluminum is high in embodied energy and emissions. CO2 emissions are high because carbon anodes are consumed in the melt electrolysis. An aluminum soda can has an embodied energy equal to that can 1/3 full of gasoline. The metal is easily recycled with high yield, but is thrown away because many places lack deposit return for packaging and proper landfill sorting to remove metals."

Scrap aluminum shouldn't be turned back into alumina; it is useful stuff. This whole thing is silly.