Proton Exchange Membrane Fuel Cells

[Foxbat]

Ever wondered why diesel submarines are still around today when nuclear appears to be the better option for stealth purposes? Ever pondered how a diesel sub they can stay submerged for up to three weeks? I know I have...but then again, I am a very sad fellow

Anyhow, it's because modern diesel subs also utilise an air independent system called Proton Exchange Menbrane Fuel Cells alongside diesel power.
Proton-exchange membrane fuel cell - Wikipedia

Perhaps they don't have the endurance of nuclear subs but the diesel/proton fuel cell hybrid can give a smaller country a good edge in naval defence at a fraction of the cost of a nuclear hunter/killer. Class 212 diesel with PEMFC 260-580 million Euros (dependent on number ordered). Astute Class hunter/killer over 1.35 Billion pounds per boat - 2015 estimate(whatever that is in Euros).

 

[BigBadBob141]

Surely you mean that they use the fuel cell under water.
To run a diesel under water you need a snorkel, which means you have to stay just under the surface!
To run this fuel cell for any length of time you would need very large amounts of hydrogen and oxygen.
Perhaps these could be extracted from the surrounding water as you go?
Interesting!

 

[Vertigo]

...To run this fuel cell for any length of time you would need very large amounts of hydrogen and oxygen.
Perhaps these could be extracted from the surrounding water as you go?
Interesting!

That would require at least as much energy as you would get from using the hydrogen in the fuel cell.
Possibly you could use the energy from the diesel engine whilst running on the surface to get the hydrogen...

 

[Foxbat]

Surely you mean that they use the fuel cell under water.

Yes. That's what I meant.