[jillesvangurp]

1) generate hydrogen 2) store hydrogen in iron oxide 3) discharge hydrogen again 4) convert it into something useful (electricity, heat, movement, etc.).

All those steps lose energy. And there's stuff that happens in between involving pipes, leaky valves, tanks, compression, etc.

[DoctorOetker]

this is not compressed hydrogen storage, anyway your 2,3,4 are the same as my round trip storage efficiency 2