[kilotaras]

27 tons of iron oxide have a volume of 5m^3 and can be stored in pretty much a hole in the ground.

2.7 tons of hydrogen have a volume of almost exactly 30000 m^3, requiring storing it under high pressure in specialized containers. Hydrogen is famous for being hard to store without losses.

For long-term storage storage and losses are a problem.

> But the round-trip efficiency of the tank is virtually 100%. The efficiency of the iron-based storage is only 50%

Maybe I'm missing something, but why? As you mentioned it takes 29kj to restore 3 moles of H2 out of (3 moles of H20 + 1 mole of Fe2O3). Where does 50% comes from?

[kilotaras]

i.e. the paper[0] states that first "discharging" produced 7.09kg of H2 out of 8.71 theoretically possible

the efficiency is super low, but again, according to the paper, "most of the energy input was due to thermal losses at the reactor surface (83.9%)", which also benefits from square/cube law.

[0] https://pubs.rsc.org/en/content/articlelanding/2024/se/d3se0...