Patent ID: 7820315

Claim:
A fuel cell stack comprising a plurality of stacked unit fuel cells, wherein: each unit fuel cell has: a membrane electrode assembly in which an anode and a cathode interpose an electrolyte membrane; and a pair of separators, each made of a metal plate, which respectively closely contact the anode and the cathode, wherein each separator has a plurality of protruding lines which are arranged vertically in a zigzag manner so as to draw a waveform, and which protrude in a direction going away from the membrane electrode assembly; a space between the anode and the protruding lines of the separator which closely contacts this anode is used as a fuel gas passage through which a fuel gas flows; a space between the cathode and the protruding lines of the separator which closely contacts this cathode is used as an oxidant gas passage through which an oxidant gas flows; at least part of the separators are each arranged in close contact with another separator so that a coolant passage through which a coolant flows horizontally is formed between both separators in a manner such that the coolant passage crosses the fuel gas passage and the oxidant gas passage, the coolant passage having a lower coolant passage area formed on a back side of a lower portion of the gas passages and a upper coolant passage area on a back side of an upper portion of the gas passages, wherein the fuel gas passage, the oxidant gas passage, and the membrane electrode assembly has a lower portion corresponding to the lower coolant passage area and an upper portion corresponding to the upper coolant passage are, and in the coolant passage, a distance between corresponding points of adjacent waves of the waveform of the protruding lines forms a pitch, and the pitch is smaller in the lower coolant passage area than in the upper coolant passage area, such that the lower coolant passage area has a larger flow resistance than that of the upper coolant passage area in order to cool the lower portion of the fuel gas passage, the oxidant gas passage and the membrane electrode assembly less than the upper portion of the fuel gas passage, the oxidant gas passage, and the membrane electrode assembly.