JPS6286666A - Fuel cell - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a fuel cell structure, and particularly to a gas passage and electrode structure suitable for improving cell performance.

[Background of the invention]

A cross-sectional view of the interior of a battery half cell having a conventional molten carbonate fuel cell structure is shown in FIG. The separator 4 for distinguishing the flow paths of the oxidizing gas and the fuel gas has an uneven rib structure,
The recess 5 serves as a gas passage, and the gas flows perpendicularly to the drawing. Further, the convex portion 6 is in contact with the current collector plate 3, and the current flowing through the current collector plate flows through this contact portion 10 to the separator. Note that the current collector plate 3 is in contact with the electrode 2 where an electrochemical reaction is performed, and the electrode 2 is further in contact with the electrolyte plate 1.
is in contact with.

In a fuel cell, wet sealing is performed using an electrolyte plate 1 to prevent gas leakage. In addition, electrolyte plate 1
, electrode 2. It is necessary to make good contact with the current collector plate 3 and separator 4 and to reduce contact resistance as much as possible. Therefore,
A load of 100 was applied to the battery to seal the gas and reduce contact resistance.

Generally, the larger this load is, the better the sealing characteristics and contact resistance will be. However, applying this load causes the following problems.

In the structure of this separator, the load is concentrated only on the surface lO in contact with the current collector plate, and the current collector surface 1 in the separator recess is
No large load is applied to 1.

As a result, the metal electrode of the porous body in the part where the load is applied is compressed, and as a result, as shown in Figure 10, the pores in the electrode are reduced, and the effective area for electrode reaction is reduced. It turns out. The width A of the rib and the width B of the gas flow path are approximately B/A = 1.0 to 1.5, and the electrode area subject to compression accounts for 40 to 50% of the total area, which has a large effect on battery performance. .

Next, since both ends of the concave portion of the separator 4 are fixed by the ribs 6, the separator 4 will protrude into the concave portion of the separator together with the current collector plate 3 due to thermal expansion. At this time, due to the difference in thermal expansion coefficient between the electrolyte plate and the electrolyte plate, contact between the electrolyte plate and the electrode deteriorates, and in extreme cases, a space 12 may be formed as shown in FIG. If such a situation occurs, the wettability of the electrode and the ionic conductivity will decrease, which will greatly affect the performance.

In order to deal with these problems, attempts have been made to make the current collector plate thicker in order to give it strength, but the corrosion of the current collector plate is severe on the anode side, and it cannot be said that it is fulfilling its role satisfactorily. On the contrary, corrosion increases electrical resistance, which is one of the causes of a decrease in battery output.

In addition, the current collector plate has a large number of holes with a diameter of about 2 to 3 m so that the gas in the gas flow path 5 can escape to the electrode 2. In order to maintain the strength, the hole diameter must be made large, or There is a limit to how many holes can be added. As a result, providing the current collector plate between the electrode and the gas flow path narrows the gas flow path to the electrode, which is disadvantageous in terms of gas mass transfer.

As a publicly known example related to these problems, JP-A-58-1
There are No. 31664 and Japanese Unexamined Patent Publication No. 129786/1986.

In the former, the conventional gas flow path is made of a metal porous body, and as mentioned above, it is effective against sagging and depression of the electrode, but unlike the conventional hollow gas flow path, the diffusion distance of the gas to the electrode surface is This becomes a disadvantageous condition for the electrochemical reaction process.

Further, no special measures are taken against creep deformation due to battery tightening.

The latter is because the ribbed electrodes used in phosphoric acid fuel cells can also be applied to molten salt fuel cells.

The manufacturing method is shown, and the wettability between the electrolyte plate and the electrode is improved, and the contact resistance between the electrode and the separator can be reduced. However, it is expected that the gas diffusion will be at the conventional level or that the thickness of the electrode will increase, so that the pore diffusion of the gas within the electrode will determine the rate of the electrochemical reaction. Also, similar to the previous known example,
They are not aware of the problem with creep deformation.

A major feature of known examples of the latter is that the gas flow path is devised so that the electrode and electrolyte plate are in contact with each other with uniform contact pressure over the entire surface. However, it has not yet been possible to provide an electrode structure that can promote this and increase the effective area of the electrode.

[Purpose of the invention]

The purpose of the present invention is to suppress creep deformation due to battery clamping force,
Prevents the reduction of the effective reaction area of the porous electrode and improves the wettability of the electrode.
The following two points are important factors for improving the diffusion of gas into the electrode and increasing the output of the fuel cell. First, one point is the effective area of the electrode, and the other circle is the diffusion of the reaction gas to the electrode surface. This effective electrode area refers to the area of the region where the surface of the porous body constituting the electrode is wetted with the electrolyte. The larger the area, the larger the reaction area, and the greater the battery output.

The effective area of the electrode can be increased by increasing the thickness of the electrode, but in conventional battery structures, the electrode existed between the electrolyte plate and the gas flow path. The spread to the whole area becomes worse. This is disadvantageous from the viewpoint of electrochemical reactions in which diffusion is dominant.

Therefore, the present inventors succeeded in significantly increasing the diffusion area and making the electrode thicker by passing the gas directly through the electrode so that the gas diffusion performance would not deteriorate even if the electrode became thicker. We believe that the increase in the diffusion distance caused by this can be minimized.

In addition, by creating a wide range of pore distribution in the electrode, which is a porous material, from small pore diameters to large pore diameters, we have created As a result, it becomes impossible to clearly distinguish between
In the past, when the electrode became too wet, the reaction surface area became saturated, which only worsened the gas diffusivity. It is used not only as a gas flow path but also as a reaction area, thereby increasing the effective area. In addition, since the electrode and gas flow path are integrated into a metal porous body with a high porosity, a separator reinforcing material is provided to prevent creep deformation due to the battery clamping force for gas sealing. By integrating the materials into a single flat plate, only the force required to make good contact with the electrolyte plate is applied to the electrode, and the greater force necessary for gas sealing between the electrolyte plate and the separator is applied. [Embodiment of the invention] Avoid contact with the electrode.

An embodiment of the present invention will be described below with reference to FIG. 1st
The figure is an enlarged cross-sectional view of a battery according to the present invention,
Only the simple side of the battery is shown. The electrode 2 is sandwiched between the electrolyte plate 1 and a separator 4 that separates the oxidizer and fuel flow paths. The electrode 2 is a porous structure made by sintering fine powder of metal (Ni) or metal oxide (N i O).

The electrode part 13 on the side closer to the electrolyte plate 1 is composed of particles with a small particle size and has a large specific surface, so that the surface of the electrode is well wetted with the electrolyte from the electrolyte plate, and the electrochemical reaction is most active. This is the area in which it is carried out.

The diameter of the particles increases from the electrolyte plate 1 toward the separator 4, and the pore diameter also increases in proportion to this. The holes 14 near the separator 4 have a stronger function as a gas flow path than the electrode section 13.

However, the middle part 15 of the electrode 2 also acts as a flow path for the gas 30, and the electrolytic solution from the electrolyte plate I can also permeate, and the surface of the middle part 15 of the electrode part 13 does not have good wettability. However, it can be said that this is a region that effectively functions as a @polar reaction region, and that the diffusion of gas 30 is also the best.

That is, FIG. 2 shows the relationship between the pore diameter and the wettability of the electrode 2 in the thickness direction. Since the gas 30 flows through the cross section of the electrode 2, it is unlikely that the flow path of the gas 30 is completely closed off by the electrolyte except for the electrode portion closest to the electrolyte plate 1; serves as a gas passage, and as shown in FIG. 3, the electrolytic solution 17 covers the metal particles 16, and the gas 30 flows through the flow path shown in 18.19. The diffusion area to 16 becomes considerably large. That is, the gas channels 18 and 19 not only function as channels but also have the effect of promoting diffusion because they are in direct contact with the reaction section.

From this, in this example, the entire wetted part of the electrode becomes the effective electrode area, and all parts other than the part completely immersed in the electrolyte become gas passages, which promotes diffusion and improves battery output. This will lead to

Furthermore, even if more electrolyte penetrates than necessary for some reason, the blocked area of the gas passage will expand near the electrolyte plate, as shown by the broken line in Figure 2, but the wettability of the electrode will increase up to the area near the separator. Since the number of areas where the condition is good increases,
The increase in the overall effective electrode area has the effect of preventing deterioration in battery performance due to deterioration in gas diffusivity in areas close to the electrolyte plate.

Additionally, by providing a gas flow path within the electrode, the area of contact between the electrolytic plate and the electrode is wider than before.

Furthermore, since the structure is uniform, sagging and depression of the electrode can be prevented, and the wettability of the electrode is improved, resulting in good ion conductivity and an increase in the effective area for electrode reaction.

FIG. 4 shows a single cell structure using an electrode structure, which is an external manifold type. The flow pattern is cross-flow type. Therefore, on the lower electrode side of the electrolyte plate, gas flows through the electrode 2 from the inlet lower to the outlet 8. Gas also flows on the upper side at right angles to this. The separator 4, the electrode 2, and the reinforcing member 9 bonded to the separator 4 are closely bonded to each other and have the shape of a single flat plate.

Two or more reinforcing members 9 are provided parallel to the gas flow, and the contact portion 32 with the electrolyte plate prevents further creep deformation of the electrode even if a tightening load is applied. . That is, when tightening, the surfaces of the separator 4, reinforcing member 9, and electrode 2 that are in contact with the electrolyte plate are aligned as shown in FIG. 4 when a load is applied, and the amount of deformation of the electrode 2 is The thickness of the electrode 2 is adjusted considering that it is larger than other members, so when the tightening force is applied, a large force is applied only to the separator 4 and the reinforcing material 9, and the electrode 2 is wetted. Only enough contact pressure is applied to provide good properties. Since the creep deformation of the electrode due to the tightening force is eliminated in this way, the effective area of the electrode can be maintained at the same level as at the beginning.

Note that in this embodiment, there is no need to use a current collector plate between the electrode and the grooved separator as in the conventional case, and the separator 4. Since the electrode 2 and the reinforcing member 9 have an integrated structure, the contact resistance between the electrode and the separator can be reduced, and the separator 4 can therefore serve as a current collector plate. Eliminating the need for a current collector plate eliminates the problem of contact resistance between the electrode and the current collector plate.

Also, regarding gas seals, an integrated structure of electrodes and separators is possible, so by adjusting the surfaces between the electrodes, separators, and reinforcing members before stacking the batteries, the reliability of the gas seal in the stacked structure will be increased.

Figure 5 shows the cell structure in the case of an internal manifold type, in which a vertical hole 31 is provided for supplying gas to each cell, the gas flows through the electrode 2 from the horizontal hole 33, and from the horizontal hole 34. , enters the vertical hole 32 and is discharged. The electrode 2, separator 4, and reinforcing member 9 are integrated in exactly the same way as in the external manifold type, and the same effects can be obtained.

FIGS. 6 and 7 show an example of a modification of the electrode structure of the present invention. The electrodes 20.2], 22 whose pore diameters continuously change from small to large can be made smaller in the region 40 with larger pore diameters in the direction perpendicular to the gas flow direction, so that the separator 4 It is arranged between the solute plate 1 and the separator 4.

The structure of a cell using this electrode structure is exactly the same as that shown in FIGS. 4 and 5. Further, the effect of this electrode structure is the same as that of the electrode structure shown in FIG. However, this embodiment has the advantage that the thickness of the electrode can be varied while keeping the pore distribution characteristics the same as the electrode structure shown in FIG.

Even if the electrode becomes too wet and the electrolyte penetrates into the electrode 24, it is possible to retain the electrolyte in the pores 45 in the electrode 24, thereby preventing the electrolyte from adhering to the separator 4 and accelerating corrosion. can be prevented. Furthermore, the electrode 24 can also contribute as an effective electrode area. Furthermore, it is also possible to impregnate the electrode 24 side with an electrolytic solution,
The effective area of the electrode can be increased.

Another embodiment of the present invention is shown in FIG. 8, which not only improves battery performance but also prevents loss of electrolyte in the battery.

The electrodes 25 and 26 shown in FIG. 1 are stacked so that the pore diameters increase from small to large and from small to large from the electrolyte plate 1 toward the separator 4. Grooves 50 are previously provided in the surfaces 52 where the two electrodes 25 and 26 touch, and an electrolyte replenisher 51 holding electrolyte is filled in the grooves. The electrolyte is retained in the pore region 48 of the electrode 26 and is transferred to the electrode 25 via the electrolyte replenisher 51.
It connects with the electrolyte inside and reaches the electrolyte plate 1. By introducing this electrolyte replenisher 51, it becomes possible to compensate for the loss of electrolyte in the electrolyte plate 1, and the battery performance can be maintained at the same level as the initial state. In this embodiment, the electrode surface must be sufficiently wetted with the electrolytic solution over the entire area inside the electrode 25.

〔Effect of the invention〕

According to the present invention, the effective reaction area of the porous electrode can be expanded, and the diffusion of gas into the electrode can be promoted, so that the output of the battery can be significantly improved.

[Brief explanation of drawings]

Figure 1 is a sectional view of an electrode structure according to an embodiment of the present invention, Figure 2 is a pore size distribution and wetting characteristic diagram, Figure 3 is an enlarged schematic diagram of an electrode, and Figures 4 to 8 are a diagram of an electrode structure according to an embodiment of the present invention. FIG. 9 is an axial sectional view of the electrode structure, and FIGS. 9 and 10 are sectional views of the conventional example. ■... Electrolyte plate, 2... Electrode, 3... Current collector plate, 4
Separator, 9 Reinforcing member, 52 Electrolyte replenisher.

Claims (1)

[Claims] 1. A fuel cell comprising a pair of electrodes, an electrolyte plate sandwiched between them, and a separation plate for separating and flowing fuel and oxidizing agent, wherein the inside of the electrodes is connected to the battery. A fuel cell characterized by an electrode structure having a porosity and cross-sectional area that allows the amount of gas required for operation to pass between the gas inlet and outlet without causing a large pressure loss. 2. The fuel cell according to claim 1, wherein the electrode, the separation plate, and the reinforcing member of the electrode are closely integrated into a flat plate shape. 3. The fuel cell according to claim 1, wherein the pores in the electrode have various pore diameters ranging from the average pore diameter of conventional electrodes to a larger pore diameter. structure. 4. The fuel cell according to claim 2, wherein the reinforcing member is arranged on the separation plate in parallel to the gas flow direction. 5. A fuel cell according to claim 3, characterized in that pores of different sizes are arranged randomly within the electrode. 6. The fuel cell according to claim 3, wherein the pore diameter is made smallest in a portion close to the electrolyte, and gradually increases toward the separation plate side. 7. In claim 3, the pore diameter is uniform in the thickness direction in the direction perpendicular to the gas flow direction, and the combination is such that a portion with a small pore diameter and a portion with a large pore diameter are adjacent to each other. A fuel cell is characterized by having a number of them lined up. 8. In claim 6, the structure is such that two layers are stacked, and the electrolyte plate and the separation plate have portions with small pore diameters, and a region with large pores is formed in the center of the electrode. Characteristic fuel cells. 9.Claim 5, 6, 7 or 8
A fuel cell characterized in that the region of the electrode with a small pore diameter is impregnated with an electrolyte in advance. 10. Claim 6, wherein the electrodes have a structure in which two layers are stacked, and the pore diameters are arranged from small to large to small to large from the electrolyte plate to the separation plate, and the electrodes are in contact with each other. A fuel cell characterized by having its surface impregnated with an electrolyte. 11. A fuel cell according to claim 3, characterized in that the electrode is made by laminating multiple layers of porous bodies made of various electrode materials having different peak values of pore distribution. 12. A fuel cell according to claim 10, characterized in that a member in which an electrolyte holding material is impregnated with an electrolyte is provided on the contact surface as a means for impregnating the electrolyte with an electrolyte.