didn't make it to fuel cells at this point, though it has been "nearly here"
for a couple decades.

If it works so extremely well for heavy, small volume welding bottle tanks why
hasn't it caught in the much more profitable market of fuel cells?

Excactly, as for 'honeycomb', I believe you're thinking of metal hydride
storage,
as is used for acetylene bottles, I think it's a well proven technology.

Cheers
Marty