[baybal2]

One very interesting refrigeration cycle I heard about recently is using a proton exchange fuel cell in reverse as a compressor for hydrocarbons or ammonia in a closed loop.

Protons jump across the membrane, creating a small pressure differential that is allegedly big enough to do heat pumping.

[crankylinuxuser]

Ammonia refrigerators were ones of the first types. And they get very cold, quick.

Of course, when ammonia leaks, it does some nasty damage.