Location, location, location - there are many sites globally suitable for geological bulk hydrogen storage; the UK has had the Tesside site operational until recently since the early 1970s.

They were built 50 years ago. (Slightly before today).

Pumped hydrogen at Walpole is a great functional little project that eases the grid edge brown out problem. ( https://news.ycombinator.com/item?id=45332157 )

Scaling that up to the energy storage potential of the right geological structures of the sizes needed to power cities and run heavy industrial isn't as economically clearcut as you may assume.