Field of the Invention:
The present invention relates to a fuel cell stack including a plurality of fuel cells for generating electrical energy by electrochemical reactions of a fuel gas and an oxygen-containing gas. The fuel cells are stacked together in a stacking direction, and end plates are provided at both ends of the fuel cell stack in the stacking direction.
Description of the Related Art:
For example, a solid polymer electrolyte fuel cell employs a polymer ion exchange membrane as an electrolyte membrane, and the polymer electrolyte membrane is interposed between an anode and a cathode to form a membrane electrode assembly (MEA). The membrane electrode assembly and a pair of separators sandwiching the membrane electrode assembly make up a power generation cell for generating electricity. In use, typically, a predetermined number of the power generation cells are stacked together to form a fuel cell stack, e.g., mounted in a fuel cell vehicle (fuel cell electric automobile, etc.).
In the fuel cell, a fuel gas flow field for supplying a fuel gas to the anode and an oxygen-containing gas flow field for supplying an oxygen-containing gas to the cathode are provided in the surfaces of the separators. Further, a coolant flow field for supplying a coolant is provided between the adjacent separators along surfaces of the adjacent separators.
In the fuel cell, internal manifold structure has been adopted. In the internal manifold structure, fuel gas passages for allowing the fuel gas to flow through the fuel cell, oxygen-containing gas passages for allowing the oxygen-containing gas to flow therethrough, and coolant passages for allowing the coolant to flow therethrough extend through the fuel cells in the stacking direction. The fuel gas passages are a fuel gas supply passage and a fuel gas discharge passage. The oxygen-containing gas passages are an oxygen-containing gas supply passage and an oxygen-containing gas discharge passage. The coolant passages are a coolant supply passage and a coolant discharge passage.
In the fuel cell, at least one of the end plates is equipped with a fluid manifold connected to each passage for supplying or discharging fluid (fuel gas, oxygen-containing gas, or coolant). Further, a fluid supply pipe and a fluid discharge pipe are connected to the fluid manifold.
In this regard, a reactant gas as one of the oxygen-containing gas and the fuel gas is humidified beforehand, and the humidified reactant gas is then supplied to the fuel cell. Further, in the fuel cell, water tends to be produced at the cathode by electrochemical reaction, and back diffusion of the produced water toward the anode tends to occur. Consequently, water vapor may be retained in the fluid manifold, and the water vapor may be condensed to produce liquid water (condensed water). Under the circumstances, the fuel cell may be undesirably connected electrically to external equipment, etc. due to connection through the liquid water (i.e., liquid junction may occur).
As a fuel cell aimed to prevent production of water droplets in the reactant gas, for example, a solid polymer electrolyte fuel cell disclosed in Japanese Laid-Open Patent Publication No. 10-012262 is known. The fuel cell has a pressing plate for pressing a stack body of the fuel cell in a stacking direction. The pressing plate has a heating section at a position where a pipe connector is provided, for heating at least one of the oxygen-containing gas and the fuel gas.
The heating section has a cylindrical outer shape having substantially the same thickness as a body portion of the pressing plate. A cylindrical hollow area is provided in the heating section. The heating section has a gas conduction section for sealing the hollow area in an air-tight manner from the inside. At the center of the gas conduction section, a through hole as a passage of the oxygen-containing gas is formed. Further, according to the disclosure, since a heating medium heated by cooling the stack body is supplied to the hollow area, the oxygen-containing gas flowing through the gas conduction section is heated by the heating medium, and it is possible to suppress production of liquid water.
Moreover, in the fuel cell, a pair of coolant supply passages and a pair of coolant discharge passages may be arranged separately at both sides (in one of two pairs of opposite sides) of the separator. The coolant supply passages and the coolant discharge passages extend through the fuel cell in the stacking direction for allowing the coolant to flow through the fuel cell. In this regard, the fuel cell adopts a structure where the pair of coolant supply passages are connected together by a single coolant manifold, and the pair of coolant discharge passages are connected together by a single coolant manifold.
For example, in a fuel cell stack disclosed in Japanese Patent No. 5054080, electrolyte electrode assemblies and separators are stacked together, and rectangular end plates are provided at both ends of the fuel cell stack in the stacking direction. On two long opposite sides of the fuel cell stack, a pair of coolant supply passages are arranged oppositely at one end side of the long sides, and a pair of coolant discharge passages are arranged oppositely at the other end side thereof.
Further, a pair of manifold sections are provided at one of the end plates. The manifold sections are connected to at least the pair of coolant supply passages or the pair of coolant discharge passages. Moreover, a coupling section is provided for coupling the pair of manifold sections together. The width of the coupling section along the long side is smaller than the dimension of the pair of manifold sections.
As described above, since the pair of manifold sections are coupled by the coupling section having a narrow width, the manifold does not have a rectangular shape as a whole. According to the disclosure, increase in the pressure loss of the coolant flowing into the manifold is suppressed effectively, and the coolant can be supplied smoothly and uniformly to the fuel cell.