JPH0129027B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in phosphoric acid electrolyte fuel cells using, for example, phosphoric acid as an electrolyte, and particularly in matrix fuel cells equipped with a reservoir serving as an electrolyte storage section within the cell.

As is well known, the above-mentioned fuel cell consists of a fuel cell, a matrix pre-impregnated with an electrolytic solution, and an air electrode to form a single cell, and a bipolar plate combined with this or a gas passage partitioned off. It is configured to supply fuel and air to each electrode through a porous electrode substrate with ribs.

In such a fuel cell, it is necessary to always maintain an appropriate amount of electrolyte in the matrix in order to carry out the electrode reaction efficiently. On the other hand,
The volume of an electrolytic solution such as phosphoric acid impregnated into the matrix increases or decreases due to moisture absorption or the like as the operating state of the battery changes, such as when the battery is on or off. If this is left as it is, there is a risk that the electrolyte will excessively permeate into the electrode catalyst layer and inhibit the electrode reaction, so as a countermeasure to prevent this, the above-mentioned bipolar plate or porous electrode substrate that constitutes the fuel cell is used. A recess called a reservoir is defined in a part of the cell, and when the volume of the electrolyte increases, excess electrolyte that can no longer be held in the matrix is temporarily stored in the reservoir. When the volume of electrolyte decreases, the electrolyte is replenished from the reservoir to the matrix, thereby ensuring that the amount of electrolyte retained in the matrix is always maintained at an appropriate level. It is known what has been done.

Next, a conventional fuel cell equipped with the above-mentioned reservoir is shown in FIGS. 1 and 2. In the figure 1
7 is a cell composed of a fuel electrode base material 2, a catalyst layer 3 formed on the surface of the base material 2, a matrix 4, and an air electrode base material 6 on which a catalyst layer 5 is formed; The bipolar plates 8 and 9 stacked above and below are air passage grooves and fuel passage grooves formed on the upper and lower surfaces of the bipolar plate 7 so as to be perpendicular to each other. In such a fuel cell, an independent concave reservoir 10 is formed on the lower surface of the bipolar plate 7 at both left and right end portions in parallel with the fuel passage groove 9, and on the surface facing the reservoir 10, a reservoir 10 is formed. , a part of the fuel electrode base material 2 and the catalyst layer 3 are cut out, and the reservoir 10 and the matrix 4 are configured to communicate with each other.

With this configuration, when the volume of the electrolytic solution that has been impregnated in the matrix 4 increases, it permeates through the layers of the matrix 4 along the surface direction and is stored in the reservoir 10, and conversely, the electrolytic solution When the volume of matrix 1 decreases,
The electrolytic solution stored in the reservoir 10 is replenished to the matrix 4 so that the amount of electrolytic solution held at zero is not insufficient. This provides the function of keeping the amount of electrolyte held in the matrix 4 constant.

On the other hand, the matrix 10 is made of a material that has a high electrolyte retention ability in order to airtightly isolate the fuel gas and air even under differential pressure. For this reason, in order for the electrolyte to permeate and move within the layers of the matrix 10 over a long distance along the planar direction, a considerable liquid pressure is required depending on the moving distance, but the liquid pressure of the electrolyte is If it becomes too large, the catalyst layer 3 of both electrodes,
The water repellency of No. 5 cannot be maintained, and an excessive amount of electrolyte permeates into the reaction part of the catalyst layer, resulting in a problem of deteriorating the power generation performance of the battery. For this purpose, as described above, reservoirs 10 are defined at both end regions of the bipolar plate 7, and the electrolyte is absorbed into the reservoirs 10 by penetrating and moving within the matrix 10 in response to increase and decrease of the electrolyte. In the structure,
Particularly in the case of large-area electrodes, excessive electrolyte penetrates into the electrode catalyst over time due to changes in fluid pressure due to increases and decreases in the electrolyte due to repeated battery operation and suspension, resulting in the battery generating power. Since the performance deteriorates, it has been difficult to generate electricity efficiently over a long period of time. As a countermeasure to this problem, a structure may be considered in which an electrolyte movement path is provided within the matrix layer so that the electrolyte can move easily, but in order to reduce the electrolyte resistance during power generation of the battery and obtain a highly efficient battery. The thickness of the matrix is desirably thin, and the thickness of the matrix layer is usually about 0.1 mm, making it difficult to actually implement the method described above.

The present invention eliminates the above-mentioned drawbacks, and creates a reservoir that smoothly absorbs changes in the volume of the electrolyte while preventing excessive penetration of the electrolyte into the electrode catalyst layer, and that makes it possible to always maintain an appropriate amount of electrolyte in the matrix. An object of the present invention is to provide an improved structure of a fuel cell.

The present invention will be described in detail below based on illustrated embodiments.

FIG. 3, FIG. 4, and FIG. 5 show one embodiment of the present invention, and are a plan view, a side sectional view, and an enlarged detailed view of a main part of the side sectional view, respectively.

The basic structure of the fuel cell in the figure is shown in Figures 1 and 2.
It is similar to the conventional one shown in the figure. On the other hand, according to the present invention, a new code 1 is added inside the cell 1.
An electrolyte movement path indicated by 1 is additionally defined. This moving passage 11 is defined as a groove locally cut out in the catalyst layer 3 of the upper fuel electrode constituting the unit cell 1, and is located at both left and right end areas of the bipolar plate 7 as shown in the figure. It is formed in a mesh-like manner so as to straddle and communicate with the defined reservoir 10. To describe the structure of the moving passage 11 in more detail, the passage is formed in a groove surrounded by an electrode base material 2 on the upper surface, a catalyst layer 3 on the side surfaces, and a matrix 4 on the lower surface, and the left and right ends of the passage are surrounded by the reservoir 10. The electrode base material 2 is in communication with the reservoir 10 through a communication window hole 12 formed in the electrode base material 2 opposite to the electrode base material 2 . Note that the passage 11 is the catalyst layer 3
After coating and firing, the catalyst layer 3 is formed by mechanically notching it, or the catalyst layer 3 is formed in the area where the passage 11 is defined in advance.
A method is adopted in which a hole-forming agent is applied at the time of coating, and the passages 11 are formed at the same time in the firing process of the catalyst layer.

With this configuration, when the volume of the electrolyte that has been permeated and held in the matrix 4 increases, the excess electrolyte that can no longer be held in the matrix 4 moves through the electrolyte transfer passage 11. and stored in the reservoir 10. Conversely, when the volume of the electrolytic solution decreases, the electrolytic solution stored in the reservoir 10 is replenished into the matrix 4 through the passage 11. In this case, the flow path resistance of the passage 11 is
The flow path resistance within the porous matrix 4 is much lower than that in the case where the electrolyte moves in the planar direction within the layer of the porous matrix 4 as in the past. Since the electrolyte is provided in a shape, the electrolyte can be moved smoothly without requiring large hydraulic pressure. This eliminates the risk of excessive electrolyte penetrating over time into the repellent area of the catalyst layer 3 or electrode base material 2 that define the grooves that become the passages 11, and the electrode reaction can be maintained for a long period of time without any inhibition. Efficient power generation can be achieved across the board. This also applies to large-sized fuel cells with large electrode areas.

On the other hand, in the above structure, as shown in FIG.
By providing an electrolyte replenishment port 13 leading to the electrolyte replenishment port 13, if the absolute amount of electrolyte becomes insufficient over time due to long-term operation, the electrolyte replenishment port 13
As before, it is possible to replenish the matrix with electrolyte through the reservoir 10 by injecting the electrolyte from the outside into the reservoir 10 through the reservoir 10. Note that during operation, the replenishment port 13 is hermetically sealed with a blind plug or the like. In the illustrated example, the left and right reservoirs 10 are each provided with a replenishment hole 13, but this is to facilitate degassing when injecting electrolyte from the outside, and in practice only one of them may be used. Further, the reservoir 10 may be provided only on either the left or the right side.

Next, FIG. 6 shows another embodiment. First, this embodiment is slightly different from the previous embodiment in the structure of the cell. That is, as shown in the figure, ribbed porous electrode substrates 16 and 17 that partition the fuel gas passage 14 and the air passage 15 are used instead of the bipolar plate, and the fuel electrode catalyst layer 3 is formed on the plate surface of the electrode substrates 16 and 17, respectively. An air electrode catalyst layer 5 is formed by direct coating and firing, and a matrix 4 is sandwiched therebetween to form a single cell. Note 1
Reference numeral 8 denotes a separate plate for gas separation, and unit cells are stacked via this separate plate 18 to form a cell stack.

Now, in the above battery, the porous electrode substrate 16
Reservoirs (not shown) are defined at both left and right end areas, as in the previous embodiment. Note that the reservoir may be formed as a notch as a groove, or a hydrophilic layer portion may be formed in a part of the substrate of the electrode substrate 16 separated from a water-repellent gas diffusion region, and this hydrophilic portion may be used as a reservoir. be. In either case, as in the previous embodiment, a part of the catalyst layer 3 is cut out and an electrolyte transfer passage 19 is provided which communicates with the reservoir.
is formed in a mesh shape in the surface direction. Furthermore, in this embodiment, the moving passage 19 is not restricted by the thickness range of the catalyst layer 3, but is formed including a groove 19' that enters the area of the electrode substrate 16. Therefore, the depth of the grooves can be freely set without limiting the electrolyte transfer path only by the thickness of the catalyst layer 3, which is advantageous. In this example, similarly to the previous example,
When the volume of the electrolyte impregnated in the matrix 4 increases or decreases, the moving passages 19, 19'
The electrolyte can be smoothly moved between the matrix 4 and the reservoir through the cap. In addition, an electrode board 16 similar to the supply port 13 shown in FIG.
It can also be provided in

In addition, in each embodiment, the electrolyte movement passages 11, 1
It goes without saying that the dimensions and arrangement pattern of 9 and 19' are not limited to those shown in the illustration and can be freely designed. Furthermore, although the illustrated example shows an example in which the fuel electrode is located on the upper side and the air electrode is located on the lower side, it is also possible to turn this electrode arrangement upside down and provide the reservoir and electrolyte transfer passage on the upper air electrode side. good. Additionally, in the embodiments shown in FIGS. 3 and 4, instead of cutting out the already formed catalyst layer 3 to define the electrolyte transfer passages 11, cutouts are formed on the matrix 4 in the form of strips. It is also possible to arrange the electrodes in such a manner that the gaps remaining between the rectangular electrodes are used as electrolyte movement passages.

As described above, according to the present invention, the movement path of the electrolyte between the matrix and the reservoir is formed not in the matrix but in the groove defined in the electrode adjacent to the upper surface of the matrix. Even if the volume of the electrolyte increases or decreases, the electrolyte can be easily moved between the matrix and the reservoir without requiring much liquid pressure of the electrolyte. Therefore, while preventing the conventional drawback of excessive electrolyte permeating into the electrode reaction area due to increase in liquid pressure and deteriorating the power generation performance of the battery, it is possible to maintain an appropriate amount of electrolyte in the matrix at all times. This allows excellent effects to be achieved. Furthermore, by providing an electrolyte replenishment port that leads to the outside in the reservoir, even if the electrolyte becomes insufficient over time due to long-term operation, it is possible to replenish the electrolyte from the outside through this replenishment port. It also has the effect of allowing efficient power generation to continue for a long period of time.

[Brief explanation of drawings]

Figures 1 and 2 are a plan view and a vertical sectional view showing the structure of a conventional fuel cell, respectively, and Figure 3
4 are a plan view and a vertical sectional view showing the structure of one embodiment of the present invention, FIG. 5 is an enlarged view of the main part in FIG. 4, and FIG. 6 is a main part structure of another embodiment. FIG. DESCRIPTION OF SYMBOLS 1... Single cell, 3... Catalyst layer of electrode, 4... Matrix, 7... Bipolar plate, 10... Reservoir, 11, 19, 19'... Electrolyte movement path, 13
... Electrolyte supply port, 16, 17... Porous electrode substrate.

Claims (1)

[Scope of Claims] 1. A single cell is constructed by sandwiching a matrix impregnated with an electrolytic solution between two electrodes including a catalyst layer, and a bipolar plate is stacked over the electrodes of this single cell. Alternatively, in a matrix fuel cell in which a reservoir for storing surplus electrolyte in the cell is defined in a part of the porous electrode substrate, a part of the electrode catalyst layer is cut out and communicated with the reservoir. A matrix fuel cell is defined by defining an electrolyte movement path inside the unit cell that expands in the direction of the mating surfaces. 2. The fuel cell according to claim 1, wherein the electrolyte transfer path is defined across an electrode catalyst layer and a region of a porous electrode substrate adjacent to the catalyst layer. type fuel cell. 3. A matrix fuel cell according to claim 1, characterized in that the bipolar plate or the porous electrode substrate is provided with an electrolyte replenishment port that communicates with the reservoir and opens on the outer peripheral side surface. .