> “You can think of iron fuel as a clean, recyclable coal,” says Bergthorson.

I was under the impression that basically all naturally found iron is in the form of iron oxide. Which means you first have to put in energy to reduce it to pure iron, to then burn it and turn it back to iron oxide. That's much closer to what a battery does, or hydrogen, than it is to coal.

I imagine it's still useful in many applications since hydrogen is a pain to store and transport.