If I get this right the "energy source" is the oxidization of aluminum so this is basically a scheme to store energy in aluminum (which made with electricity) and turn it into hydrogen by adding water.
That's my understanding too. The "We don’t need any energy input, and it bubbles hydrogen like crazy." is pretty confusing to me, knowing how much of an energy sink producing aluminium from bauxite is…
(I guess the question is if it's viable to replace e.g. Li-Ion batteries with an Aluminium + Water "tank")
I don't see any mention of how hot the Aluminium + Water ⇒ Al₂O₃ + H₂ reaction gets — any heat released from that would be pure waste of energy…
This method consumes both the aluminum and the gallium.
OK but first consider how much energy is required to create aluminum. And to create gallium.
Hint: it's FAR more than electrolysis which is far more than hydrogen from natural gas.
Aluminum is electrolytically refined at high heated temperature. It's so energy intensive that most aluminum refineries are co-located next to hydroelectric plants. Gallium primarily comes from NEW aluminum extraction from ore and none comes from recycling aluminum - the former takes 2x more energy than the latter.
Just an order-of-magnitude, back-of-the-envelope estimate easily shows you can NOT generate energy for a hydrogen economy this way under any circumstances.
Any details on efficiency vs other common forms of hydrogen production?
"We don’t need any energy input"
That's not really true. There's tons of engery used to mine, refine, and mill those metals. It's interesting that the gallium can simply be reused. I wonder what would be done with the oxidized aluminum.
Making aluminum from aluminum oxide by electrolysis, than reacting it with water to make hydrogen must have a lower efficiency than making directly hydrogen from water by electrolysis.
Gallium is inert in this application, its role is to prevent the passivation of aluminum that happens normally when aluminum is exposed to air and water.
An amalgam of aluminum (i.e. an alloy of aluminum with mercury) would produce hydrogen in the same way. The advantage of gallium in this application, and also in other applications where gallium is used to replace mercury, is that gallium is not toxic (because being trivalent, it forms insoluble compounds, unlike mercury, which forms soluble ions).
This method of making hydrogen is useful only for portable hydrogen generators, intended to be used in places where you could not carry a hydrolysis generator or compressed hydrogen.
Interesting. Are there any situations where carrying water would be better than carrying compressed (or hydride) tanks? I would think there wouldn't be much, if any weight benefit, especially with the recent advances in lightweight design for aircraft tanks.
There might be some situations where it isn't economical to recycle aluminum scrap where this could potentially be an alternative. In such cases the energy would already be a sunk cost.
It also might be more practical to transport aluminum over long distances than hydrogen, given hydrogen's low density and propensity to pass through container walls, especially with existing infrastructure. A standard freight train or bulk freighter could easily haul aluminum one way and aluminum oxide back. Perhaps it's a good way of integrating islands like iceland or hawaii into a hydrogen economy.
The Army Research Lab in Aberdeen,MD,also experimented and patented some applications for using Aluminium for H2 production. On closer review it is not feasible for large scale. Besides: producing Aluminium is extremely energy and CO2 intensive
Lots of things that are CO2 intensive now will not be in the future. We already shut down the majority of the coal power plants and replaced them with natural gas, and we'll then replace natural gas with solar and wind.
