JP2004095301A - Measuring device for electrode potential of fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a measuring device for measuring a local potential of an electrode in a fuel cell, having a simple structure and enabling installation of two or more of them. <P>SOLUTION: A part of a fuel cell oxygen electrode 21 is used as a detecting piece 41 insulated from the surrounding oxygen electrode 21, the potential of a collecting member 32 brought into contact with the oxygen electrode is set as a reference potential, and a voltmeter 5 to measure a potential difference between the reference potential and the detecting piece 41 is provided. A measuring circuit is formed for every detecting piece 41, by providing a plurality of the detecting pieces 41 on the surface of the oxygen electrode 21, and by providing the voltmeter 5 to measure the potential difference when the potential of the collecting member 32 is set as the reference potential. Occurrence of an abnormal potential can be accurately detected by detecting the potential of each part. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrode potential measuring device in a fuel cell, and more particularly to an electrode potential measuring device for measuring a potential at a specific position (local part) in an electrode.
[0002]
[Prior art]
Conventionally, in a fuel cell using a polymer electrolyte membrane, a fuel gas or an oxidizing gas is ionized on both sides of the electrolyte membrane, and the ions permeate the electrolyte membrane to cause an electrochemical reaction. If a fuel gas and an oxidizing gas are present across the electrolyte membrane, the electrochemical reaction between the two continues. Conventionally, in order to stop the operation of the fuel cell, the supply of the fuel gas and the oxidizing gas to the fuel cell is stopped. In this case, since the fuel gas and the oxidizing gas remain in the fuel cell, the electrochemical reaction between the two continues until one of the remaining gases disappears.
[0003]
After the supply of the fuel gas or the oxidizing gas is stopped, when the residual gas reacts inside the fuel cell, the volume decreases, and the pressure in the fuel chamber (fuel gas flow path) side gradually decreases. When the internal pressure in the fuel chamber decreases, the oxidizing gas permeates through the electrolyte membrane from the oxidizing gas flow path and enters the fuel gas flow path. As a result, in the fuel chamber, a region in which the concentration of the fuel gas is particularly higher than the other region and a region in which the concentration of the oxidizing gas is particularly higher than the other region coexist, that is, in the same fuel chamber, the fuel gas and the oxidizing gas coexist. A state in which the gas is unevenly distributed occurs. When the uneven distribution of this gas increases, the part where the fuel gas is unevenly formed forms a local cell, and the part where the oxidizing gas is unevenly distributed acts to flow a current opposite to that during normal power generation. Corrosion causes faster deterioration.
In order to avoid such an abnormal reaction, it is necessary to monitor where and when the local battery is formed on the electrode surface on the fuel chamber side.
[0004]
[Problems to be solved by the invention]
Therefore, conventionally, as a method of measuring the potential distribution of the fuel electrode, instead of measuring the hydrogen concentration in the fuel chamber, a method of measuring the fuel electrode potential based on RHE (Reversible Hydrogen Electrode) using a salt bridge is known. . However, when this method is used, there is a problem that a salt bridge must be provided at each of the measurement sites with respect to the electrode surface, and the configuration becomes large.
[0005]
Also, in order to confirm the uneven distribution of hydrogen and other gases in the fuel chamber, it is necessary to install a plurality of detectors on the fuel electrode surface and compare their potentials. There is a problem in that the construction of each of the salt bridges is further increased in size. In particular, in a fuel cell in which fuel cell unit cells are stacked with a separator interposed therebetween to form a stack, a large number of fuel electrodes to be detected are arranged at small intervals, so that a detection unit using a salt bridge is provided. This further complicates the construction and is virtually impossible to mount.
Furthermore, in an atmosphere in which hydrogen and a gas other than hydrogen are mixed, the potential of RHE itself is not accurate, and it can be detected whether or not the phenomenon of abnormal potential has occurred. There was also a problem that it was difficult to detect.
[0006]
An object of the present invention is to provide an electrode potential measuring device in a fuel cell, which has a simple configuration and can be installed in plurals.
[0007]
[Means for Solving the Problems]
The present invention that achieves the above object has the following configuration.
(1) A detection piece provided at an oxygen electrode of a fuel cell unit cell in which a solid polymer electrolyte is sandwiched between an oxygen electrode and a fuel electrode, and configured so that a part of the oxygen electrode at a measurement position is insulated from surrounding oxygen electrodes. And a detection unit including a detection terminal electrically connected to the detection piece,
An electrode potential measuring device for a fuel cell, comprising: a potential measuring unit connected between an oxygen electrode and the detecting unit, the potential measuring unit detecting a potential difference between the potential of the oxygen electrode and the potential of the detecting unit using the oxygen electrode as a reference potential.
[0008]
(2) A fuel cell unit cell in which a solid polymer electrolyte is sandwiched between an oxygen electrode and a fuel electrode, and a separator having conductivity are provided alternately on an oxygen electrode of a fuel cell stack configured to have a measurement position. A detection piece configured such that a part of the oxygen electrode is insulated from the surrounding oxygen electrode, and a detection unit including a detection terminal connected to the detection piece so as to be able to conduct electricity and insulated from the separator.
An electrode potential measuring device for a fuel cell, comprising: a potential measuring unit connected between an oxygen electrode and the detecting unit, the potential measuring unit detecting a potential difference between the potential of the oxygen electrode and the potential of the detecting unit using the oxygen electrode as a reference potential.
[0009]
(3) The electrode potential measuring device for a fuel cell according to the above (1) or (2), which is arranged at a plurality of positions of the oxygen electrode.
[0010]
(4) The electrode potential measuring device according to claim 2 or 3, wherein the detection terminal is fixed to the separator via a holding member made of an insulating material.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a fuel cell electrode potential measuring device 1 of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing a configuration of a fuel cell stack 10 provided with a fuel cell electrode potential measuring device 1 of the present invention.
The fuel cell stack 10 includes a unit cell 2 and a separator 3. The unit cell 2 has a configuration in which a solid polymer electrolyte 23 is sandwiched between an oxygen electrode 21 and a fuel electrode 22. The oxygen electrode 21 and the fuel electrode 22 include reaction layers 211 and 221 that come into contact with the solid polymer electrolyte 23 and gas diffusion layers 212 and 222 that come into contact with the separator 3.
[0012]
The separator 3 has current collecting members 31 and 32 for contacting the oxygen electrode 21 and the fuel electrode 22, respectively, and for extracting current to the outside.
The current collecting members 31 and 32 are made of a material having conductivity and corrosion resistance. The current collecting members 31 and 32 are made of, for example, a material such as dense carbon and metal. In the case of using a metal, for example, a material obtained by subjecting a material such as stainless steel, a nickel alloy, a titanium alloy or the like to a corrosion-resistant conductive treatment can be used. Here, the corrosion-resistant conductive treatment includes, for example, gold plating.
[0013]
FIG. 2 is an exploded perspective view showing a positional relationship between the separator 3 and the unit cell 2. On the surface of the current collecting member 31 that contacts the fuel electrode 22, a plurality of convex portions 311 are formed at regular intervals in the orthogonal direction, and grooves 312 are formed in a lattice shape between the convex portions 311. I have. The flat part at the tip of each convex part 311 is a contact part 313 that comes into contact with the fuel electrode 22, and the fuel electrode 22 can be electrically connected via the contact part 313. The fuel chamber 30 through which the hydrogen gas flows is formed by the groove 312 and the surface of the fuel electrode 22. In the fuel chamber 30, hydrogen gas is supplied to the fuel electrode 22.
[0014]
A fuel gas supply hole 318 and a fuel gas discharge hole 317 are formed in the fuel chamber 30, and hydrogen gas flows into the fuel chamber 30 from the fuel gas supply hole 318 to supply hydrogen to the fuel electrode 22 while supplying hydrogen to the fuel electrode 22. It flows out of the gas discharge hole 317. In this embodiment, the current collecting member 31 is rectangular, and the fuel gas supply hole 318 and the fuel gas exhaust hole 317 are located at point-symmetrical positions with respect to the centroid of the current collecting member 31 in plan view (diagonal direction). , Respectively. As described above, the fuel chambers 30 are formed between the respective separators 3 and the unit cells 2.
[0015]
The fuel gas supply holes 318 of the respective fuel chambers 30 communicate with the fuel gas supply passages 319a formed in the stacking direction of the current collecting members 31 in the fuel cell stack 10, and the fuel gas discharge holes 317 In the fuel cell stack 10, the fuel cell stack 10 communicates with fuel gas discharge passages 319b formed in the direction in which the current collecting members 31 are stacked. The fuel gas supply passage 319a and each fuel gas supply hole 318 constitute a fuel gas manifold that distributes fuel gas to each fuel chamber 30.
[0016]
FIG. 3 is an overall perspective view of the current collecting member 32. A plurality of linearly and continuously raised convex portions 321 are formed at regular intervals on a surface of the current collecting member 32 that contacts the oxygen electrode 21, and a groove 322 is formed between the convex portions 321. You. That is, the convex portions 321 and the grooves 322 have a shape arranged alternately. The protruding portion 321 has a contact portion 323 in which a flat portion of the most protruding peak comes into contact with the oxygen electrode 21, and it is possible to conduct electricity with the oxygen electrode 21 via the contact portion 323. The groove 322 and the surface of the oxygen electrode 21 form an air flow passage 325 through which air flows.
[0017]
The groove 322 reaches both ends of the current collecting member 31, and the upper and lower ends of the air flow passage 325 are openings communicating with the outside of the fuel cell stack 10. One of the openings at both ends forms an air inflow portion 326 through which air flows in, and the other opening forms an air outflow portion 327 through which air flows out. The air that has flowed in from the air inflow portion 326 is brought into contact with the oxygen electrode 22 in the air flow passage 325 and is guided to the air outflow portion 327 while supplying oxygen to the oxygen electrode. In addition, at both ends of the current collecting member 32, holes 328 and 327 forming a fuel gas supply passage 319a and a fuel gas discharge passage 319b, respectively, at the time of lamination, are provided.
[0018]
The electrode potential measuring device 1 provided for the unit cell 2 and the current collecting member 32 having the above-described configuration will be described. As shown in FIG. 1, the electrode potential measuring device 1 includes a detecting unit 4, a voltmeter 5 serving as a potential measuring unit, a detecting unit 4 and a voltmeter 5, and a voltmeter 5 and a current collecting member 32. Are connected to each other.
[0019]
The detection unit 4 includes a detection piece 41 provided in the oxygen electrode 21, a detection terminal 42 connected to a surface of the detection piece 41, and a holding member 43 that holds the detection terminal 42. The detection piece 41 is obtained by cutting out a part of the oxygen electrode 21 and making it insulated from the surrounding oxygen electrode 21. An insulating portion 411 is provided between the detection piece 41 and the surrounding oxygen electrode 21. ing. The insulating portion 411 can be configured by filling an insulating material, or simply by providing a gap. The detection piece 41 is configured to be in contact with the solid polymer electrolyte 23 and to be able to conduct ions with the polymer electrolyte 23. With such a configuration, it is possible to detect an abnormal potential at a location where air (oxygen) is unevenly distributed on the fuel electrode 22 side.
[0020]
The detection terminal 42 can be made of a corrosion-resistant metal such as Pt, Au, Ti, and Ta. The holding member 43 holding the detection terminal 42 is fixed to the current collecting member 32 side, and is made of an insulating material. The holding member 43 has a function of holding the detection terminal 42 on the current collecting member 32 side and electrically insulating the detection terminal 42 from the current collecting member 32 and the surrounding oxygen electrode 21. The detection terminal 42 is configured to come into contact with the detection piece 41 of the oxygen electrode 21 when the fuel cell stack 10 is assembled by stacking the unit cell 2 and the current collecting member 32.
[0021]
One end of a conductor 61 is connected to the detection terminal 42, and the other end of the conductor 61 is connected to the voltmeter 5. The conducting wire 61 is covered with an insulating material, penetrates through the air flow passage 325 of the current collecting member 32, and extends from the end (the air flow passage 325) of the current collecting member 32 as shown in FIG. It is led out. The conducting wire 61 is coated with an insulating material, so that the current collecting member 32 and the conducting wire 61 are not energized by contact with the current collecting member 32 in the air flow passage 325.
[0022]
By leading the conducting wire 61 outward from the end of the current collecting member 32, the current collecting member 32 can be laminated, and the use of the electrode potential measuring device 1 of the present invention in the fuel cell stack 10 becomes easy.
One end of a conducting wire 62 is connected to the other terminal of the voltmeter 5, and the other end of the conducting wire 62 is connected to the current collecting member 32 on the oxygen electrode side. The conducting wire 62 is covered with an insulating material.
[0023]
A plurality of the electrode potential measuring devices configured as described above are provided on the oxygen electrode 21. For example, as shown in FIG. 2, three stages are provided in the vertical direction and five columns are provided in the horizontal direction, and each detection unit 41 is configured as an independent circuit to which the voltmeter 5 is connected.
[0024]
By detecting the electric potentials at such a plurality of positions, for example, as shown in FIG. 4, it is possible to monitor a change in the electric potential at each position of the electrode. When the curve of the position of the detection piece 41a is represented by a, the curve of the position of the detection piece 41b is represented by b, the curve of the position of the detection piece 41c is represented by c, and the curve of the position of the detection piece 41d is represented by d, the potential that changes over time is known. Can be. After the fuel supply is stopped and the load of the fuel cell is turned off, the portions (a, b, c) where the potential changes with time with the passage of time are in a state where hydrogen and oxygen are unevenly distributed in the fuel chamber 30. A place where a lot of air exists, and a place (d) where the potential is zero or negative is a place relatively filled with hydrogen.
[0025]
In the curve shown in FIG. 4, a potential difference occurs between the position of the detection piece 41d and the positions of the other detection pieces 41a to 41c. When this potential difference becomes a predetermined value or more, the abnormal potential Has occurred. When one potential is detected, an abnormal potential can be determined based on the amount of change from the position where the potential value is zero.
[0026]
【The invention's effect】
According to the first aspect of the present invention, it is not necessary to use a salt bridge, and the configuration of the measuring device can be simplified. Further, by using the oxygen electrode as the reference potential, the degree of the potential can be measured more accurately.
According to the second aspect of the present invention, since a salt bridge is not used, it can be used for a fuel cell stack in which many unit cells are stacked using a separator.
[0027]
According to the third aspect of the present invention, by measuring the potentials at a plurality of locations and comparing the measured potentials, it is possible to accurately and quickly detect the occurrence of the abnormal potential and the location of the occurrence.
According to the invention as set forth in claim 4, the detection terminal is held by using the holding member, and the detection terminal and the detection piece are connected by stacking the separator on the fuel cell unit cell. The electrode potential measuring device can be easily assembled.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a configuration of a fuel cell stack provided with a fuel cell electrode potential measuring device of the present invention.
FIG. 2 is an exploded perspective view showing a positional relationship between a separator and a unit cell.
FIG. 3 is an overall perspective view of a current collecting member.
FIG. 4 is a graph showing the change over time of the potential of each part of the electrode.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Electrode potential measuring device 10 Fuel cell stack 2 Unit cell 3 Separator 30 Fuel chamber 4 Detector 41 Detector piece 42 Detector terminal

Claims (4)

A detection piece provided at the oxygen electrode of the fuel cell unit cell in which the solid polymer electrolyte is sandwiched between the oxygen electrode and the fuel electrode, and configured so that a part of the oxygen electrode at the measurement position is insulated from the surrounding oxygen electrode; A detection unit having a detection terminal connected to the detection piece so as to be able to conduct electricity;
An electrode potential measuring device for a fuel cell, comprising: a potential measuring unit connected between an oxygen electrode and the detecting unit, the potential measuring unit detecting a potential difference between the potential of the oxygen electrode and the potential of the detecting unit using the oxygen electrode as a reference potential. A fuel cell unit cell in which a solid polymer electrolyte is sandwiched between an oxygen electrode and a fuel electrode, and a separator having conductivity are provided alternately on the oxygen electrode of a fuel cell stack configured by stacking, and the oxygen electrode at a measurement position is provided. A detection piece configured to be partially insulated from the surrounding oxygen electrode, and a detection unit including a detection terminal that is electrically connected to the detection piece and is insulated from the separator.
An electrode potential measuring device for a fuel cell, comprising: a potential measuring unit connected between an oxygen electrode and the detecting unit, the potential measuring unit detecting a potential difference between the potential of the oxygen electrode and the potential of the detecting unit using the oxygen electrode as a reference potential. The electrode potential measuring device for a fuel cell according to claim 1, wherein the electrode potential measuring device is disposed at a plurality of positions of the oxygen electrode. 4. The electrode potential measuring device for a fuel cell according to claim 2, wherein the detection terminal is fixed to the separator via a holding member made of an insulating material.

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