Liquid hydrogen tanks are definitely a different problem, but I don't know if "orders of magnitude safer" is necessarily true. Many spacecraft have run into problems involving liquid hydrogen storage for a variety of reasons:

- Liquid hydrogen is so cold that many metals weaken

- Exposure to hydrogen itself weakens many metals (hydrogen embrittlement)

- Liquid hydrogen expands rapidly if exposed to heat, so venting is needed

- Hydrogen leaks through the smallest of seams

Now imagine trying to build a tank that prevents all that from happening, and it has to be lightweight for usage on spacecraft / aircraft.

I know nothing about it, but what about hydrogen cells ? It doesn't solve this issue ?

Hydrogen cells nothing to do with storage, it's for converting hydrogen to electricity

Oh, to me the name in french implied it stored energy. We say "Pile a Hydrogen".

In french we differenciate "batterie" and "pile", "pile" are one use, but I thought due to the name that the hydrogen cell would store energy.