As the subject says -- "fuel cell" -- that means no IC engine hydrogen and oxygen (from air) produce water and electricity directly. No Carnot cycle, no moving parts. After that the drive train is electric, just like a battery car.
You can make hydrogen by electrolysis, which is not so efficient, but you can do it whereever and whenever you have cheap electricity. Alternatively if you have methane that you are allowed to burn (whether it's natural gas or from rotting sewage) you can make hydrogen pretty cheaply from it.
See also the remarks above about Audi stress-testing their tank -- the only thing that touched it was an armour-piercing round, which made a hole and no fire. A hydrogen leak is generally much LESS dangerous than a gasoline leak because it doesn't hang around at ground level and soak into things. Given half a chance it'll just diffuse away.