Interesting concept, but it’s basically trying to store hydrogen for winter, with up to 60% losses. It’s main advantages are that it’s kinda simple and shouldn’t have a charge/discharge limit, but it’s really just meant for cold climates where you would have a surplus of solar in the summer and you could use it much later, like in the winter. Not gonna be great for grid level storage, to lossy.

Not solved but it is a step in the right direction. Just powder rust and hydrogen in tanks

They’re using hydrogen to de-rust iron, and later let the iron rust again. I don’t have a degree in chemistry, but that sounds like a scam.

There are basically two sources of hydrogen that matter at an industrial scale: fossil fuel cracking (not clean energy) and electrolysing water. In the first case, if you want power it’s more green to burn the fossil fuel directly.

And if you’re electrolysing water and then using the hydrogen to chemically derust iron, it would (as far as i understand with high school chemistry) be strictly more efficient to electrolyse rust directly. The oxygen can dissipate into the environment or be reintroduced as necessary, like with a sacrificial metal for ship’s hulls.

It’s undoubtedly innovative that they have a relatively efficient way to store the latent chemical energy of hydrogen given an excess of hydrogen, but in terms of energy storage that is putting the cart before the horse.