Aluminum-gallium powder generates hydrogen from dirty water
news.ucsc.edu
news.ucsc.edu
(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.
"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.
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.
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.