Fuel cell shut-down procedure including vaporization phase

1. A shut-down procedure for an electricity delivery system comprising a fuel cell, the fuel cell being fed with pure oxygen as oxidant from a pure oxygen circuit on the cathode side and hydrogen from a fuel gas circuit on the anode side and delivering an electrical voltage to an electrical power line, the shut-down procedure comprising:

an initial step during which the oxygen gas feed is interrupted;

an electrical consumption phase during which a hold current is drawn from the fuel cell until the pressure in the oxygen circuit is reduced to the vapor pressure of water at the temperature of the fuel cell; and

a vaporization phase during which water present in channels of the fuel cell is vaporized by pressure reduction produced in the electrical consumption phase.

2. The shut-down procedure according to claim 1 , wherein an interruption of the fuel gas feed is delayed relative to the interrupting of the oxygen feed so as to guarantee that all of the oxygen is consumed before the fuel gas.

3. The shut-down procedure according to claim 1 , the fuel cell comprises an electrolyte including a polymer membrane.

4. The shut-down procedure according to claim 1 , performed for a system installed in a vehicle.

5. The shut-down procedure according to claim 1 , wherein the pure oxygen and fuel gas feeds are interrupted simultaneously.

6. The shut-down procedure according to claim 5 ,

wherein the pure oxygen circuit on the cathode side is vented to atmosphere, and

wherein the procedure, at the start of the electrical consumption phase, brings the oxygen circuit into communication with the atmosphere or with an inert gas, until the pressure in the oxygen circuit drops to a predetermined pressure S above atmospheric pressure, guaranteeing that all the oxygen is consumed before the hydrogen.