JPH02267868A - Fuel cell furnishing separator with gas permeable rib - Google Patents

Abstract

PURPOSE:To prevent the deterioration of electrode performance by using separators to which gas permeable ribs are connected so as to partition a unit cell. CONSTITUTION:Each separator of a pair of the upper and the lower separators 1 with gas permeable ribs consists of a square separator base member and numerous ribs 4 lined up almost parallel at a specific interval 3 and connected on both sides of the base member. The lining-up directions of the ribs 4 are almost vertical each other between those on the upper side and on the lower side of the base member. Between the separators 1, a positive electrode 6 and a negative electrode 7 are positioned placing an electrolyte matrix 5 between them, and they are laminated from the upper side in the order the separator - the negative electrode-the electrolyte matrix-the positive electrode - the separator, to form a unit cell. When a specific gas is fed to clearances 3 of the upper and the lower separators of the unit cell, and the electrolyte solution is fed between the electrodes 6 and 7, the gas is contacted to the lower side of the positive electrode 6 which is positioned over the clearances 3, and reacted with the electrolyte solution. A part of the gas permeates through the ribs 4 and reaches the contact surface of the ribs 4 and the positive electrode 6, and it is reacted with the electrolyte solution.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a gas permeable separator for partitioning unit cells of a fuel cell.

(Prior Art and its Problems) Conventionally, electrodes and separators constituting fuel cells have been proposed having various materials and structures. For example, a bipolar type fuel cell shown in FIG. 2(a) is used as a phosphoric acid fuel cell. The separator A of the fuel cell includes ribs B formed at predetermined intervals by milling on a graphite plate that has been subjected to gas impermeability treatment.
A fuel cell is formed by laminating a positive electrode C, a negative electrode, and an electrolyte matrix E between upper and lower separators A. In this fuel cell, gas is supplied to the electrodes C and D by flowing gas into the gap F between the ribs B, as shown in FIG. The smaller the width of the ribs B and the gap F, the better the gas diffusion and the better the performance of the fuel cell. However, according to the prior art, milling the graphite plate, especially forming narrow ribs B, This requires extremely precise technology, which is a bottleneck in reducing costs.

Further, electrodes C and D made of carbon paper or the like that are in direct contact with the ribs B are not directly supplied with gas due to the presence of the ribs B, which causes a decrease in electrode performance. Said rib B
If the pitch of the gap F is made as small as possible, the performance deterioration can be avoided, but as described above, this is extremely difficult from a cost standpoint.

In addition to the bipolar type, a ribbed electrode type shown in FIGS. 3(a) and 3(b) is also used. The separator G of this fuel cell is a thin film flat plate separator and does not require milling, but instead it is necessary to process thick carbon paper to form ribs J and gaps K as the negative electrode H and positive electrode (2).

In this method, as shown in Figure 3, etc., the gas is
The deterioration in electrode performance is slightly reduced because it is also supplied to the electrode part (2) through the part. However, it is still unavoidable that the processing cost for making the pitch between the ribs J and the gap finer will increase, and furthermore, the problem of processing and discarding expensive carbon paper is a major bottleneck in cost reduction, which remains unresolved. It remains as it is.

(Objective of the Invention) An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a fuel cell without deterioration in electrode performance.

(Means for Solving the Problems) The present invention provides a fuel cell consisting of a plurality of unit cells each containing a pair of gas diffusion electrodes, in which a large number of gases are arranged at predetermined intervals on an airtight separator base material. The fuel cell is characterized in that the unit cells are partitioned using separators formed by joining permeable ribs.

The present invention will be explained in detail below.

The feature of the present invention is that, unlike the prior art, when forming a ribbed separator, the thick separator base material itself is not processed, but a large number of ribs are joined at predetermined intervals on the thin separator base material. This is because we adopted a method that allows

By this method, the manufacturing cost of the ribbed separator can be significantly reduced, and furthermore, by forming the ribs from a gas-permeable material, deterioration in electrode performance can be suppressed to a minimum.

As the material of the separator base material used in the fuel cell of the present invention, those having airtight properties used as conventional separator base materials for fuel cells, such as metal plates and airtight carbon plates, can be used. For phosphoric acid fuel cells, it is best to use carbonaceous plates made of carbon paper or the like that have been treated to be airtight.

The material of the ribs to be joined to the separator base material is not particularly limited as long as the formed ribs have electrical conductivity and gas permeability, and metals, carbonaceous materials, etc. can be used. In phosphoric acid fuel cells, easily moldable carbon black, acetylene black, graphite powder, etc. are aggregated with a binder such as phenolic pitch to form a paste.
The paste is formed into a predetermined shape, arranged on the separator base material, and fired as appropriate, or the pitch is thermally decomposed and carbonized to be bonded, or the carbon black or the like is mixed with an appropriate binder. Bonding can be achieved by heating and curing the binder. Note that the ribs may be subjected to water-repellent treatment to the extent that gas permeability is not impaired.

In conventional ribbed separators, the rib width and the gap between the ribs were limited to about 1.2 mm due to cost or processability, but according to the present invention, both can be made even narrower. 0.5-1mm from the viewpoint of fabrication and performance
It is preferable that

Furthermore, the electrodes used for both the positive and negative electrodes are gas diffusion electrodes in which a water-repellent gas diffusion layer and a hydrophilic reaction layer are laminated, or gas diffusion electrodes in which a base material such as carbon paper is coated with a catalyst layer containing a catalyst metal. .

The laminated state of the unit cell is separator negative electrode - electrolyte - positive electrode - separator, and when the former gas diffusion electrode is used, the reaction layer of the gas diffusion electrode is on the electrolyte side of both electrodes, and the gas diffusion layer is on the separator side. be located.

When gas is supplied to the separator of a fuel cell configured in this way, for example, the former unit cell, it passes through the gap between the gas beams 1 and comes into direct contact with the positive or negative electrode, and permeates through the gas diffusion layer of the electrode, or the gas It contacts the electrode through the permeable ribs and passes through the gas diffusion layer to reach the reaction layer of the gas diffusion electrode. Here, the gas comes into contact with the electrolyte passing through from the opposite side of the electrode, and a reaction occurs. Energy is extracted by the reaction, and the resulting waste gas is disposed of to the outside through a path opposite to the feed gas.

Next, an example of a unit cell of a fuel cell according to the present invention will be explained based on FIG. 1(a) et al.

A pair of upper and lower gas-permeable ribbed separators 1 shown in FIG. It consists of 4. The arrangement directions of the ribs 4 of each separator 1 are substantially perpendicular to each other on the upper and lower surfaces of the separator base material 2. Note that in the separator used at the positive and negative ends of the stacked battery configuration, the ribs 4 are arranged only on one side.

A positive electrode 6 and a negative electrode 7 are located between the pair of separators 1 with the electrolyte matrix 5 interposed therebetween, and are laminated in order from the top: separator negative electrode - electrolyte matrix - positive electrode - separator to form a unit cell. ing. When a predetermined gas is supplied to each gap 3 between the upper and lower separators 1 of the unit cell and an electrolytic solution is supplied between the picture electrodes 6 and 7, the gas flows into the gap 3 as shown in FIG. It comes into contact with the lower surface of the positive electrode 6 located above and reacts with the electrolyte in the positive electrode. Also, a part of the gas passes through the gas-permeable rib 4 and reaches the contact surface between the rib 4 and the positive electrode 6, as shown in FIG. 1, and reacts with the electrolyte in the same manner.

Energy is extracted by the reaction, and the resulting waste gas is disposed of outside through a path opposite to the supply gas.

(Examples) Examples of the present invention will be described below, but these examples do not limit the present invention.

Example A commercially available 0.4 mm thick Gradi-carbon was used as a separator base material, and the base material was subjected to surface treatment. A paste containing acetylene black as the main material and phenolic pitch as the main binder was added to the base material to a width of 0.7 mm and a height of 0.7 mm.
7 mm and an interval of 0.7 mm, and finally baked at 900° C. in a nitrogen atmosphere to form a large number of ribs on the separator base material. After the firing, the rib surface was flattened to obtain a ribbed separator.

On the other hand, on the surface of commercially available 0.4 mm thick carbon paper,
Monoplatinum supported on carbon black with a platinum content of 0.5g/c
The catalyst layer supported by m' was hot pressed (J, εle
ctrochemical Soc, vol. 160, 351
to 357 pages) to form a positive electrode and a negative electrode.

The separator and both electrodes were assembled as shown in Fig. 1, and the cathode (positive electrode) characteristics were measured under a constant current density at 190°C in 100% phosphoric acid. , the rib width, height and gap were each 1 mm). The table shows the voltage values at a constant current density after removing the voltage drop due to resistance at an air utilization rate of 60%.

From the table of voltage values at a given current density, it can be seen that the fuel cell of this example has a remarkable effect of improving gas supply.

In the above embodiments, the ribs have a rectangular cross section, but the present invention is not limited to this, and may have any shape such as a trapezoid, a triangle, or a rectangle.

(Effects of the Invention) The fuel cell according to the present invention uses a separator formed by joining a large number of gas permeable ribs at predetermined intervals on an airtight separator base material.

Therefore, firstly, when manufacturing a ribbed separator as in the past, there is no need to machine the expensive carbon paper itself, which simplifies the manufacturing process and significantly reduces manufacturing costs.

Second, since the rib width and the gap between the ribs can be made narrower than before, gas diffusivity is improved and electrode performance can be dramatically improved.

Third, since the ribs are formed of a gas-permeable material, the supply gas contacts the entire surface of the electrode, and the deterioration of electrode performance in conventional fuel cells can be almost completely avoided.

Fourth, compared to conventional ribbed electrodes, in conventional ribbed electrodes, the ribs themselves form part of the electrode, so the ribs must be made of expensive materials with corrosion resistance, such as carbon paper. However, since the ribs of the present invention do not constitute electrodes and do not come into direct contact with the electrolyte, they can be constructed from inexpensive materials, and this also contributes to cost reduction.

[Brief explanation of drawings]

FIG. 1(a) is an exploded perspective view showing an example of a unit cell of a fuel cell according to the present invention, FIG. 1(b) is a vertical cross-sectional view taken along line A-A in FIG. a) is an exploded perspective view showing a unit cell of a conventional fuel cell, FIG. An exploded perspective view showing the unit cell, FIG. 3(b) is shown in FIG.
It is a longitudinal cross-sectional view taken along the line CC of a). 1...Separator, 2...Separator base material, 3...
- Gap, 4... Gas permeable rib, 5... Electrolyte matrix, 6... Positive electrode, 7... Negative electrode. Figure 1 (a) Figure 1 (b)

Claims (2)

[Claims] (1) In a fuel cell consisting of a plurality of unit cells each containing a pair of gas diffusion electrodes, a separator consisting of a large number of gas-permeable ribs joined at predetermined intervals on an airtight separator base material is used. A fuel cell characterized in that the unit cells are partitioned into sections. (2) The fuel cell according to claim 1, wherein the rib width and the gap between the ribs are 0.5 to 2 mm.