Mofabio posted:

At temperatures and pressures unavailable to plants, the separations and reactions have the potential for higher efficiencies. For instance, plants spend a lot of energy stripping hydrogen from water. But at 3000K, water spontaneously splits into hydrogen and oxygen -- 100% efficiency (minus the subsequent separation), because it's just heat energy. Obviously there is a lot of engineering to do, but fortunately such a machine isn't a physics problem (there is enough water vapor and carbon dioxide in your room to feed you for days) or even a material science problem, it just needs (a lot of) brainpower and time.