Patent ID: 7470481

Claim:
A fuel cell system comprising: at least one fuel cell having a fuel chamber including a fuel electrode, an oxygen chamber including an oxygen electrode and an electrolyte layer interposed between the fuel electrode and the oxygen electrode; a fuel gas discharge line for discharging residual air from the fuel chamber; a hydrogen concentration sensor for detecting hydrogen concentration in gas exiting the fuel chamber, the hydrogen concentration sensor being provided on the fuel gas discharge line apart from the fuel cell; a discharge valve provided on the fuel gas discharge line; and pressure regulating means for regulating a supply pressure of a flow of the fuel gas supplied to the fuel chamber at a first pressure, higher than a second pressure used in normal power generation, during a start-up power generating state when the fuel cell starts up power generation with opening of the discharge valve, until the detected hydrogen concentration of the fuel gas in the fuel chamber which is detected by the hydrogen concentration sensor exceeds a predetermined hydrogen concentration, and for reducing the supply pressure of the flow of the fuel gas to the fuel chamber to the second pressure, lower than the first pressure, and closing the discharge valve when the detected hydrogen concentration of the fuel gas in the fuel chamber exceeds the predetermined hydrogen concentration, to thereby establish a normal power generating state in which a flow of fuel gas into the fuel chamber is maintained at the second pressure for generating electric power.