NOVELTY - A fuel cell system for cooling oxygen sensitive components, comprises an air purification device for preparing a nitrogen gas stream, and having an inlet for receiving a flow of air and an outlet in fluid communication with a fuel cell stack anode for discharging the nitrogen gas stream.    USE - The system is used for cooling oxygen sensitive components, where fuel cells comprise solid oxide fuel cells, proton exchange membrane fuel cells, phosphoric acid fuel cells, or molten carbonate fuel cells (claimed). It is used as power generators in vehicle applications.    ADVANTAGE - Anode stack material or other heated components of combined fuel processor and stack assembly, are protected during cool down.    DETAILED DESCRIPTION - A fuel cell system for cooling oxygen sensitive components, comprises a fuel cell stack comprising a fuel cell(s) including an anode, a cathode, and an electrolyte disposed between the anode and cathode; a fuel reformer disposed in fluid communication with the fuel cell stack for supplying a flow of fuel to the anode; an air supply disposed in fluid communication with the fuel cell stack for supplying a flow of air to the cathode; an air purification device for preparing a nitrogen gas stream, and having an inlet for receiving a flow of air and an outlet in fluid communication with the fuel cell stack anode for discharging the nitrogen gas stream; a supply mechanism for supplying a flow of the nitrogen gas stream to the anode during fuel cell cool down and optionally, during fuel cell shut down; and an outlet for discharging a flow of oxygen enriched air, where flow of nitrogen gas stream balances pressure within the fuel cell cathode and anode during cool down.    An INDEPENDENT CLAIM is also included for a method for cooling oxygen sensitive components in a fuel cell system, comprising supplying air to an air purification device during cool down of a fuel cell system; treating the supplied air within the air purification device to produce a nitrogen gas stream and a waste stream comprising oxygen enriched air; and directing the produced nitrogen gas stream through the anode, the anode being in fluid communication with the air purification device.    DESCRIPTION OF DRAWING(S) - The figure is a block diagram depicting a fuel cell system and gas flow, during shut down.