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Iron-to-rust cycle tapped by scientists for safe renewable energy transport
(interestingengineering.com)
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this post was submitted on 10 Jul 2026
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The whole mass of iron powder does not need to be re-ground after every use. From what I've read so far, about half a percent experiences sintering and needs to be re-ground, and another half a percent breaks down into too fine of dust and needs to be filtered out of the exhaust, sintered, and then reground. The efficiency penalty of reprocessing the fuel is about 0.1% - 1 kWh of reprocessing for every 1 MWh of generation.
Ok so aluminum is still a better candidate than iron powder since it doesn't use hydrogen. I know I'm in the hydrogen sublemmy arguing against the use of hydrogen here, but green hydrogen uses a ton of electricity and it's an extra step that costs some energy efficiency, so why not cut out the need for green hydrogen and use electricity directly to smelt aluminum oxide into aluminum metal?
Aluminum carries 31MJ/kg of energy vs irons 7MJ/kg.
They also don't address how the iron oxide is reduced back it iron metal. I'm assuming they use DRI for that (Direct Reduced Iron) where you pelletized the oxide and pass hot hydrogen over it in an oven. You still need to sinter the pellets to allow for optimal gas contact around each pellet along with internal gas passage, which means you do need to grind it down after you reduce it back to metal. I don't know where your numbers are coming from.
Where did you find info on reducing a iron oxide powder without sintering directly? Is that a fluidized bed process? AFAIK there's either DRI pellets, or you do a vortex lance method the Chinese pioneered but that produces liquid iron and liquid slag.
Source for claim of 1% mass loss per cycle:
https://research.tue.nl/en/publications/combustion-of-micron-sized-iron-particles-in-a-drop-tube-reactor/
I think the deciding factor between iron and aluminum comes down to exhaust filtration.
Iron oxide in the exhaust can be collected cheaply with a combination of centrifugal and electrostatic forces and it tends to retain is grain size. Aluminum oxide is lighter, more electrically resistive, and tends to break down into too-small nanoparticles.
Yeah, you'd only need to sinter pellets to pump hydrogen through them in a static pile. A fluidized bed reactor can reduce the iron oxide powder as is, and keeping the temperature lower prevents sticky sintering at the cost of taking longer to complete.