According to embodiments of the invention, an operational method of a fuel cell is provided. The method includes providing a fuel cell used to provide output power to a load, measuring an initial average voltage of the output power provided by the fuel cell, measuring a first average voltage of the output power after the output power has been provided to the load by the fuel cell for a first time interval, and stopping the fuel cell from providing output power to the load when a voltage difference between the initial average voltage and the first average voltage is more than a first allowable voltage difference.