[ursablanco]

At a guess, it doesn't need to create a full-on plasma, just needs a lot Hydrogen ions hitting the membrane. A small amount of ionization will suffice - sort of like 'micropayments' or a long tail phenomenon.

Because that's what the membrane filters do. See: http://en.wikipedia.org/wiki/Proton_exchange_membrane http://en.wikipedia.org/wiki/Proton_conductor Mainly they work on size - small versus really small.

Again, at a guess, it doesn't need to cool the other side - it's not a temperature gradient, it's a concentration gradient. And since the ions are being reacted back to H2 at a brisk rate, it's not a big problem. The more thermal energy you could maintain in the ions the better, because they wouldn't need as much heating once they'd been recycled.

It has a whiff of perpetual motion machine to it. Maxwell's Demon, I think.