Fuel cell system and operating method thereof

A fuel cell system, comprising:

• a fuel cell power generator configured to generate electric energy through an electrochemical reaction between hydrogen and oxygen;
• a fuel supplier configured to selectively supply fuel including the hydrogen to the fuel cell power generator;
• an oxidizing agent supplier configured to supply an oxidizing agent including the oxygen to the fuel cell power generator;
• a power source configured to supply a reverse current to the fuel cell power generator when the fuel cell power generator is restarted;
• and
• a controller configured to store temperature information detected from the fuel cell power generator when the fuel cell power generator stops generating power and configured to control the power source to selectively supply the reverse current to the fuel cell power generator according to the stored temperature information, such that, when the stored temperature information indicates a temperature greater than a temperature range, the power source supplies the reverse current to the fuel cell power generator while the fuel cell power generator is restarted and stops supplying the reverse current to the fuel cell power generator while the fuel cell power generator is generating power.