Patent ID: 8721867

Claim:
A method of shutting down a water electrolysis apparatus which applies an electrolysis voltage between current collectors disposed on the respective sides of an electrolyte membrane thereby to electrolyze water to generate oxygen in an anode electrolysis chamber and hydrogen in a cathode electrolysis chamber under a pressure higher than atmospheric pressure, comprising the steps of: applying a voltage, which is lower than the electrolysis voltage, between the current collectors after the cathode electrolysis chamber stops supplying the hydrogen; reducing a pressure in at least the cathode electrolysis chamber while the voltage is being applied between the current rent collectors to return hydrogen that has leaked into the anode electrolysis chamber, to the cathode electrolysis chamber; and lowering the voltage applied as the pressure in at least the cathode electrolysis chamber is lowered, wherein the voltage applied is lowered depending on an amount of hydrogen cross leak from the cathode electrolysis chamber into the anode electrolysis chamber.