Commercially viable hydrogen production starts with methane, goes through a combination of "steam reforming" followed by "shift reaction." So far as I know, liquefaction involves essentially mainstream cryogenic refrigeration.
It’s miraculous how the gas industry succeeded where clean coal failed.
There will be no green hydrogen. It’s a veneer. That the same folks building LNG terminals are pushing hydrogen isn’t a coïncidence. Even if we get a green hydrogen economy, there will constantly be an incentive to adulterate the supply.
Unless we can tap into some sort of "too cheap to meter but too hard to transport" energy source in the future.