1. Field of the Invention
The present invention relates to a monitor device for monitoring operating condition of a fuel cell including an electrolyte electrode assembly and separators sandwiching the electrolyte electrode assembly. The electrolyte electrode assembly includes a pair of electrodes and an electrolyte interposed between the electrodes.
2. Description of the Related Art
For example, a solid polymer fuel cell employs a polymer ion exchange membrane as a solid polymer electrolyte membrane. The solid polymer electrolyte membrane is interposed between an anode and a cathode to form a membrane electrode assembly. Each of the anode and the cathode is made of electrode catalyst and porous carbon. The membrane electrode assembly is sandwiched between separators (bipolar plates) to form the fuel cell.
In the fuel cell, a fuel gas such as a gas chiefly containing hydrogen (hereinafter also referred to as the hydrogen-containing gas) is supplied to the anode. The air or the like (hereinafter also referred to as the oxygen-containing gas) is supplied to the cathode. The catalyst of the anode induces a chemical reaction of the fuel gas to split the hydrogen molecule into hydrogen ions and electrons. The hydrogen ions move toward the cathode through the electrolyte membrane, and the electrons flow through an external circuit to the cathode, creating a DC electrical energy.
In this type of the fuel cell, generally, the cell voltage of the fuel cell is detected using a voltage detection device for detecting the operating condition of the fuel cell, e.g., in an attempt to determine whether the desired power generation performance is achieved or not. For example, Japanese Laid-Open Patent Publication No. 11-339828 discloses a fuel cell stack having a cell voltage measurement terminal.
According to the disclosure of Japanese Laid-Open Patent Publication No. 11-339828, as shown in FIG. 5, electrode units 1 and separators 2 are stacked together to form a fuel cell stack 3. Each of the electrode units 1 includes a hydrogen electrode 4a, an air electrode 4b, and a polymer ion exchange membrane 5 interposed between the hydrogen electrode 4a and the air electrode 4b. A hydrogen flow field 6a is formed between one of the separators 2 and the hydrogen electrode 4a, and an air flow field 6b is formed between the other of the separators 2 and the air electrode 4b. Further, a cooling water flow field 6c is formed between the adjacent separators 2.
A voltage measurement terminal 7 protrudes outwardly from an end of the separator 2. A socket (not shown) is connected to the voltage measurement terminal 7. Thus, the cell voltage in each electrode unit 1 is measured during operation of the fuel cell stack 3.
However, in Japanese Laid-Open Patent Publication No. 11-339828, since the voltage measurement terminal 7 protrudes outwardly from the end of the separator 2, it is difficult to maintain the desired sealing performance in the exposed metal portion. Therefore, foreign material may enter the fuel cell stack 3 from a position near the voltage measurement terminal 7 undesirably.
Further, since the voltage measurement terminal 7 is connected to the socket, the contact resistance is generated to cause the voltage drop. Thus, it is not possible to accurately measure the cell voltage.
Further, in the fuel cell stack 3, typically, it is necessary to detect various operating conditions such as the internal humidity, the internal pressure, or the internal temperature in addition to the cell voltage. In any cases, the same problem as with the voltage detection device occurs.