NOVELTY - Shutting down fuel cell power plant (10) comprising fuel cell (12) having anode catalyst (14) and cathode catalyst (16) on opposed sides of electrolyte (18), comprises: (a) disconnecting primary load from fuel cell; (b) terminating flow of oxidant into cathode flow path; (c) connecting auxiliary load to fuel cell; (d) permitting transfer of hydrogen fuel from anode flow path to cathode flow path; (e) sensing amount of hydrogen within anode or cathode flow path; (f) terminating flow of hydrogen fuel into anode flow path; and (g) permitting release of hydrogen into anode and cathode flow paths.    USE - The method is useful for shutting down the fuel cell power plant (claimed), where the fuel cell power plants are useful in transportation vehicles, and as portable power plants or stationary power plants.    ADVANTAGE - The method: significantly eliminates the performance degradation of the plant; minimizes oxidation and corrosion within plant fuel cells at or during shut down of the plant, or upon restarting the fuel cell power plant; and provides for efficient passivation of the fuel cell catalysts or electrodes that reduces oxidative corrosion of the catalysts and its support materials by replacing oxygen in the fuel cell with hydrogen while shutting down the fuel cell.    DETAILED DESCRIPTION - Shutting down a fuel cell power plant (10) comprising at least one fuel cell (12) (having an anode catalyst (14) and a cathode catalyst (16) on opposed sides of an electrolyte (18), an anode flow path in fluid communication with the anode catalyst for directing hydrogen fuel to flow through the fuel cell and adjacent the anode catalyst, and a cathode flow path in fluid connection with the cathode catalyst for directing the oxidant stream to flow through the fuel cell and adjacent the cathode catalyst) for generating electrical current from hydrogen containing reducing fluid fuel and oxygen containing oxidant reactant streams, comprises: (a) disconnecting a primary load from the fuel cell; (b) terminating flow of the oxidant into the cathode flow path from an oxidant source; (c) connecting an auxiliary load to the fuel cell; (d) permitting transfer of the hydrogen fuel from the anode flow path into the cathode flow path; (e) sensing, while the fuel cell power plant is shut down, an amount of hydrogen within the anode or cathode flow path with a hydrogen sensor for detecting a concentration of hydrogen within the anode or cathode flow path; (f) terminating flow of hydrogen fuel into the anode flow path from a hydrogen fuel source whenever the anode and cathode flow paths are filled above an acceptable limit of hydrogen to maintain the fuel cell in a passive state; and (g) permitting release into the anode and cathode flow paths of hydrogen stored within a hydrogen reservoir for storing hydrogen secured in fluid communication with the anode flow path.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic representation of a hydrogen passivation shut down system for a fuel cell power plant.    Fuel cell power plant (10)    Fuel cell (12)    Anode catalyst (14)    Cathode catalyst (16)    Electrolyte (18)