Fuel cell system having oxygen sensor, and control method thereof

A fuel cell system, comprising:

• a fuel cell stack;
• a hydrogen supply device configured to supply hydrogen to the fuel cell stack;
• an air supply device configured to supply air to the fuel cell stack;
• a controller configured to operate a fuel cell operation device;
• and
• an oxygen sensor installed in the fuel cell stack to detect an oxygen concentration in gases on an anode side,
• wherein during operation of the fuel cell system, the controller is configured to
• determine whether a current oxygen concentration on the anode side satisfies a predetermined condition that will generate a reverse voltage, based on a real time oxygen concentration value detected by the oxygen sensor and a first oxygen concentration reference value that corresponds to the current fuel cell operating current, and
• operate the fuel cell operation device to reduce the oxygen concentration on the anode side when the current oxygen concentration on the anode side is determined to satisfy the predetermined condition to prevent deterioration on the anode side due to generation of the reverse voltage in the cell of the stack.