Patent ID: 7348083

Claim:
A fuel cell system comprising a fuel cell having an anode and a cathode, wherein a hydrogen-containing gas is supplied to said anode and an oxygen-containing gas is supplied to said cathode for generating a load current, said fuel cell system further comprising: a humidifier for humidifying said oxygen-containing gas supplied to said cathode of said fuel cell; and an oxygen-containing gas flow rate controller for controlling a flow rate of said oxygen-containing gas supplied to said cathode such that humidity of said hydrogen-containing gas is maintained within a predetermined range less than 100%; a humidity sensor for detecting humidity of said hydrogen-containing gas; and a circulation passage for circulating said hydrogen-containing gas to supply said hydrogen-containing gas to said anode; wherein said humidity sensor is disposed in said circulation passage; and said fuel cell system is free of a humidifier for humidifying said hydrogen-containing gas supplied on an anode side of said fuel cell.