Fuel cell stack

A fuel cell stack comprising:

• a plurality of unit fuel cells stacked with each other, each of the unit fuel cells being formed by disposing separators so as to make close contacts with anodes and cathodes of membrane electrode assemblies, and each of the membrane electrode assemblies being formed by disposing the anode and the cathode on both sides of an electrolyte membrane;
• a reactant gas passage formed by a space between the separators and the anode and the cathode;
• a coolant passage formed between the separators by disposing at least one of the separators so as to make a close contact with another of the separators;
• a reactant-gas-supplying penetration hole and a reactant-gas-discharging penetration hole each communicating with the reactant gas passage and each penetrates the unit fuel cells in a stacking direction thereof;
• and
• a coolant-supplying penetration hole formed along a first side of the unit fuel cell and a coolant-discharging penetration hole formed along a second side of the unit fuel cell opposite the first side, each of said holes communicating with the coolant passage and each of said holes penetrating the unit fuel cells in a stacking direction thereof, wherein
• the coolant-supplying penetration hole and the coolant-discharging penetration hole are arranged in a horizontal direction opposing with each other so as to sandwich a power generating region therebetween;
• and
• the fuel cell stack further comprising:
• an air draining penetration hole formed along a third side of the unit fuel cell communicating with the coolant passage and arranged such that at least one part thereof is located at a higher position than an uppermost position of the coolant supplying penetration hole and the coolant-discharging penetration hole, and penetrates the unit fuel cells in the stacking direction;
• and
• a coolant draining penetration hole formed along a fourth side of the unit fuel cell opposite the third side and different from the first and second sides, the coolant draining penetration hole communicating with the coolant passage and arranged such that at least one part thereof is located at a lower position than a lowermost position of the coolant-supplying penetration hole and the coolant-discharging penetration hole, and penetrates the unit fuel cells in the stacking direction.