Hydrogen sucks to work with, from everything I've heard. In addition to the combustion risk when oxygen is introduced, there's the fact that hydrogen molecules are tiny and like to slip through otherwise solid materials, which is annoying if you're trying to fuel a rocket, but it's eventually catastrophic for containment vessels, due to hydrogen embrittlement[1]. As tempting as it is for its benefits, I don't see it…
I've worked with hydrogen (H2) quite a bit recently. Embrittlement and leakage are easy to work around, but here are the pain points I've seen: 1. H2 is still expensive. Most fuel cells require very pure H2 (five nines; 99.999%), or else it can damage the internal membrane. This pure H2 is not very affordable outside of a limited number of fuelling stations. 2. The rules around H2 use and transportation are still fuz…
My understanding is that H2 is seeming to standardize upon 300-bar (aka: 4500ish PSI).
There's liquid and a few other more difficult storage (700-bar / 10,000 PSI for example). But 300-bar is where a lot H2 stuff is standardizing today.
Its not quite as dense as in liquid form, but it starts to be usable at 300-bar. Of course, the thicker and heavier steel needed to hold H2 at this pressure makes it unsuitable for say... drones. But its more than usable for H2 Forklifts and other smaller vehicles.