1. Field of the Invention
The present invention relates to a fuel cell stack formed by stacking a plurality of power generation cells in a stacking direction. A reactant gas discharge passage extends through the fuel cell stack for allowing a reactant gas after partially consumed in power generation reaction to flow through the reactant gas discharge passage in the stacking direction. An end plate is provided at one end of the fuel cell stack in the stacking direction, and a humidifier connected to the reactant gas discharge passage is attached to the end plate.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs an electrolyte membrane comprising a polymer ion exchange membrane. The electrolyte membrane is interposed between an anode and a cathode to form a membrane electrode assembly (MEA). The membrane electrode assembly is sandwiched between separators to form a power generation cell. In use, normally, a predetermined number of power generation cells are stacked together to form a fuel cell stack for use in a vehicle.
The fuel cell stack mostly adopts internal manifold structure for supplying a fuel gas and an oxygen-containing gas as reactant gases to anodes and cathodes of the stacked power generation cells, respectively. The internal manifolds include reactant gas supply passages and reactant gas discharge passages extending through the power generation cells in the stacking direction.
An external device such as a humidifier is connected to the reactant gas discharge passage of the fuel cell stack through a discharge pipe. In the structure, minute electrical current may flow from the portion connecting the fuel cell stack and the discharge pipe through condensed water (short-circuiting through liquid).
In an attempt to suppress short-circuiting through liquid of this type, for example, a fuel cell system as disclosed in Japanese Laid-Open Patent Publication No. 2005-332674 is proposed. As shown in FIG. 13, the fuel cell system includes a fuel cell stack 1. The fuel cell stack 1 has a stack body formed by stacking a plurality of cell modules 2. At opposite ends of the stack body in the stacking direction, end plates 3a, 3b are provided.
Supply pipes 4a, 5a, 6a and discharge pipes 4b, 5b, 6b are connected to one end plate 3a for the humidified hydrogen, the humidified air, and the coolant, respectively. The supply pipes 4a to 6a and the discharge pipes 4b to 6b are made of electrically insulating material.
However, in Japanese Laid-Open Patent Publication No. 2005-332674, in particular, the water produced in power generation reaction tends to be condensed, and retained in an air discharge passage (not shown) connected to the discharge pipe 5b. Further, water component of the water diffused back through the electrolyte membrane tends to be condensed, and retained in a hydrogen gas discharge passage (not shown) connected to the discharge pipe 4b. 
In the structure, the condensed water is discharged into the discharge pipes 4b, 5b by the reactant gas discharging pressure. As a result, short-circuiting may occur between the metal members through the liquid, i.e., the condensed water. In an attempt to address the problem, the discharge pipes 4b, 5b may be designed to be considerably elongated to increase the insulation resistance. However, since the discharge pipes 4b, 5b are made of electrically insulating material, if the discharge pipes 4b, 5b are elongated, the strength of the discharge pipes 4b, 5b may become insufficient. Further, the piping operation may become laborious, and the pipe structure may have a large scale.