The International Open Source Hydrogen On Demand Builders Network.
See the Xogens Patent on an Apparatus for producing Orthohydrogen and/or Parahydrogen, in the Attachment
Increasing the pressure will reduce bubble over-potential and improve "wet" surface of the electrodes.
For most cells I know the current draw is higher at higher pressure for same voltage, temperature and electrolyte.
There is balance between the electrical efficiency gain conferred by bubble over-potential and electrical efficiency lost by pressure itself ( since electrolysis is most efficient in vacuum).
Most important drawback is the leakage ....
Large plates, large surface exposed to increased pressure...considering the gaskets elasticity is reduced in time...etc.
This is one of reasons that I choose tube type electrodes.