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In operating a fuel cell comprising an oxidizing agent chamber subject to supply of an oxidizing agent gas and a fuel chamber subjected to supply of a fuel gas, sintering of noble metal particles such as platinum black as an electrode catalyst can be prevented from sintering by connecting the fuel c

In operating a fuel cell comprising an oxidizing agent chamber subject to supply of an oxidizing agent gas and a fuel chamber subjected to supply of a fuel gas, sintering of noble metal particles such as platinum black as an electrode catalyst can be prevented from sintering by connecting the fuel cell to an outside auxiliary load circuit and controlling the unit cell voltage to not more than 0.80 V at start or discontinuation to operate the fuel cell or during the operation of the fuel cell when an outside load becomes too low due to fluctuation of the outside load. The fuel cell performance can be improved thereby.

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1. A method for operating a fuel cell comprising an oxidizing agent chamber subject to supply of an oxidizing agent gas and a fuel chamber subject to supply of a fuel gas, which comprises, at start to operate the fuel cell, purging the oxidizing agent chamber and the fuel chamber with an inert gas,

1. A method for operating a fuel cell comprising an oxidizing agent chamber subject to supply of an oxidizing agent gas and a fuel chamber subject to supply of a fuel gas, which comprises, at start to operate the fuel cell, purging the oxidizing agent chamber and the fuel chamber with an inert gas, while connecting the fuel cell to an outside auxiliary load circuit, then heating the fuel cell, then replacing the inert gas in the oxidizing agent chamber and the fuel chamber with an oxidizing agent gas and a fuel gas, respectively, and feeding the gases thereto, thereby controlling a unit cell voltage to not more than 0.85 V, and then connecting the fuel cell to an outside load circuit, thereby starting the operation of the fuel cell. 2. A method according to claim 1, where the oxidizing agent gas is air, and the fuel gas is hydrogen or a hydrogenrich gas. 3. A method according to claim 1, wherein the unit cell voltage is controlled to not more than 0.80 V before connecting the fuel cell to the outside load circuit, thereby starting the operation of the fuel cell. 4. A method for operating a fuel cell comprising oxidizing agent chamber subject to supply of an oxidizing agent gas and a fuel chamber subject to supply of a fuel gas, which comprises, at start to operate the fuel cell, purging the oxidizing agent chamber and the fuel chamber with an inert gas, while connecting the fuel cell to an outside auxiliary load circuit, then heating the fuel cell, then replacing the inert gas in the oxidizing agent chamber and the fuel chamber with an oxidizing agent gas and a fuel gas, respectively, and feeding the gases thereto, thereby controlling a unit cell voltage to not more than 0.85 V, and then connecting the fuel cell to an outside load circuit, and cutting off the outside auxiliary load circuit, thereby starting the operation of the fuel cell; at discontinuation to operate the fuel cell, connecting the fuel cell to the outside auxiliary load circuit before cutting off the outside load circuit, cooling the fuel cell, while cutting off the outside load circuit, replacing the oxidizing agent gas in the oxidizing agent chamber and the fuel gas in the fuel chamber with an inert gas, controlling the unit cell voltage of the fuel cell to not more than 0.85 V, and then cutting off the outside auxiliary load circuit, thereby discontinuing the operation of the fuel cell. 5. A method according to claim 4, where the oxidizing agent gas is air, and the fuel gas is hydrogen or a hydrogen-rich gas. 6. A method according to claim 4, wherein the unit cell voltage is controlled to not more than 0.80 V at the start and discontinuation to operate the fuel cell. 7. A method for operating a fuel cell comprising an oxidizing agent chamber subject to supply of an oxidizing agent gas and a fuel chamber subject to supply of a fuel gas, which comprises, at start to operate the fuel cell, purging the oxidizing agent chamber and the fuel chamber with an inert gas, while connecting the fuel cell to an outside auxiliary load circuit, then heating the fuel cell, then replacing the inert gas in the oxidizing agent chamber and the fuel chamber with an oxidizing agent gas and a fuel gas, respectively, and feeding the gases thereto, thereby controlling a unit cell voltage to not more than 0.85 V, and then connecting the fuel cell to an outside load circuit, and cutting off the outside auxiliary load circuit, thereby starting the operation of the fuel cell; during the operation when an outside load becomes too low in the outside load circuit due to fluctuation of the outside load, connecting the fuel cell to the outside auxiliary load circuit, and controlling the unit cell voltage to not more than 0.85 V; and at discontinuation to operate the fuel cell, connecting the fuel cell to the outside auxiliary load circuit before cutting off the outside load circuit, cooling the fuel cell, while cutting off the outside load circuuit, replacing the oxidizing agent gas in the oxidizing agent chamber and the fuel gas in the fuel chamber with an inert gas, controlling the unit cell voltage of the fuel cell to not more than 0.85 V, and then cutting off the outside auxiliary load circuit, thereby discontinuing the operation of the fuel cell. 8. A method according to claim 7, where the oxidizing agent gas is air, and the fuel gas is hydrogen or a hydrogenrich gas. 9. A method according to claim 7, wherein the unit cell voltage is controlled to not more than 0.80 V at the start and discontinuation to operate the fuel cell, and during the operation, when the outside load becomes too low.