NOVELTY - The method for operating an air-breathing-type polymer electrolyte membrane fuel cell comprising a fuel cell stack, comprises detecting an output current and a temperature of the fuel cell stack, comparing the detected output current and temperature with a maximum reference current value and a minimum reference current, maintaining the output current and temperature below the maximum reference current value and above the minimum reference current value, and electrically coupling a secondary power source to an external load electrically coupled to the fuel cell stack.    USE - The method is useful for operating an air-breathing-type polymer electrolyte membrane fuel cell, which is useful as a portable power supply for vehicles, a distributed power supply for houses and/or public buildings and a small power supply for electronic equipment.    ADVANTAGE - The method is capable of stably operating the air-breathing-type polymer electrolyte membrane fuel cell for a long time without the risk of corrosion or evaporation from the electrolyte and degrading stack performance due to dehydration of the membrane electrode assembly (MEA) and/or cathode flooding under high output and/or high temperature operation, where the fuel cell provides a high current density per unit area, has very high output characteristics and is highly reliable.    DETAILED DESCRIPTION - The method for operating an air-breathing-type polymer electrolyte membrane fuel cell comprising a fuel cell stack, comprises detecting an output current and a temperature of the fuel cell stack, comparing the detected output current and temperature with a maximum reference current value and a minimum reference current, maintaining the output current and temperature below the maximum reference current value and above the minimum reference current value, electrically coupling a secondary power source to an external load electrically coupled to the fuel cell stack when the output current exceeds the maximum reference current value, electrically isolating the fuel cell stack from the load for a predetermined time, electrically coupling a separate internal load with predetermined resistance to the fuel cell stack in addition to an external load when the output current is below the minimum reference current, cooling the fuel cell stack using a device coupled to the stack when the stack temperature exceeds the maximum reference temperature, and electrically coupling an internal variable resistor to the fuel cell stack for operating the stack for a predetermined time at an output current density exceeding a maximum output current density when the stack temperature is below the minimum reference temperature. The fuel cell stack comprises an anode electrode, a cathode electrode, and a polymer electrolyte membrane disposed between the electrodes. The maximum and minimum reference currents are 600 mA/cm2 and 200 mA/cm2 respectively, and the maximum and minimum reference temperatures are 50 degrees C and 36 degrees C respectively. One of the anode electrode and the cathode electrode comprises a catalyst layer, a diffusion layer, and a microporous layer. An INDEPENDENT CLAIM is included for an air-breathing-type polymer electrolyte membrane.    DESCRIPTION OF DRAWING(S) - The diagram shows a flow chart of a method for operating an air-breathing-type polymer electrolyte membrane fuel cell.    Sense stack output current (S10)    Supply electricity of secondary power supply to load (S12a)    Isolate load from stack for predetermined time (S12b)    Compare sensed output current with a minimum reference value (S13)    Further couple internal load to stack. (S14)