>as much as 2-5 kilowatt-hours of electrical power
>could power submarines
Not really. I don't know about non-nuclear subs, but this is several orders of magnitude too low to be space effective for use on subs. I cant find any official public info, but suffice it to say subs run closer to 2MWs than 2KWs
> and even (running the process in reverse) a silent propulsion system for boats or submarines.
So the submarine would have on-board power generation that powers this, not that this would provide the power to the submarine.
10x10m for 2kW is 2kW per 100sqm.
That's pretty much nothing, propulsion-wise. A seawolf-sized sub (108m long and 12m wide) covered in this material would produce about 85kW. That's around the powertrain of a modern compact / city car: the nissan leaf's motor is 80kW.
It's not meant to produce energy in this case. That's what I'm saying.
An 85kW engine.
Which is — as I noted — about what you'd find on a compact EV (that's about 115hp).
Depends on the sub class. Midget subs are in the (tens of) kW range.
Attack subs are going to be in the MW to tens of MW at the shaft (though it can be lower for special cases e.g. Gotland's AIP is 2x75kW, the sub crawls at 5kn on AIP though).