How do proton exchange membrane electrolysers work?
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.