How do proton exchange membrane electrolysers work? I've seen lots of videos, animations, and a few Wikipedia pages, but I'm still trying to figure out a few things.


Is an electrolyte needed to make the water conductive like an alkaline electrolyser?
Does the cathode remain dry? If so, how do the protons get across the gap from the membrane to the cathode?
Are platinum cathode and iridium anode catalysts required for the reaction, or just needed to speed it up a small amount? Why are these specific materials used?
PEM process allows to increase the density of current. the distance between the cathode and anode is relatively small. The polymer has acidic residues that can transfer protons. You can use pure liquid water or even water vapor (Energy Environ. Sci., 2011, 4, 2993).

Cathode and anode remain wet. They touch the PEM.

Pt and Ir are not required, but they worth the money. PEM itself is relatively expensive, so there is not much point to save on Pt or Ir. However they can be replaced with a cheaper material. But then efficiency drop to alkaline electrolysis method.