JPH04315770A - Molten carbonate fuel cell - Google Patents

Abstract

PURPOSE:To uniform the gas concentration and temperature distribution of an electrode surface so as to make it easy to process a molten carbonate fuel cell during manufacture by providing openings each of which connects a separator side passageway to an electrode side passageway, and blocking that portion of the separator side gas passageway which is located behind the openings. CONSTITUTION:Openings 11,12 of diameter 2mmphi are provided in a position 50cm away from gas-passageway inlets provided at both side faces of the corrugated projecting portion of a passageway plate 10, and the outlet of a gas passageway 14b provided on the side of a separator 13 is blocked. When fed in the direction indicated by the arrow, fuel gas is first allowed to flow through a fuel-electrode side gas passageway 14a partitioned by the plate 10, a fuel electrode and the separator 13 and through a separator side passageway 14b, and hydrogen is consumed inside the passageway 14a. Therefore, water and carbon dioxide are generated from the electrode surface and hydrogen concentration is gradually decreased, but since the gas allowed to flow through the passageway 14b is allowed out of the openings 11,12 at a portion 50cm away from the fuel gas inlets and flows through the passageway 4a, the concentration of the hydrogen gas is raised again. Gas concentration and current density on the electrode surface are thereby uniformed so as to achieve high performance of a molten carbonate fuel cell and to facilitate the manufacture of the fuel cell.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molten carbonate fuel cell having an improved gas flow path structure and improved cell performance.

0002

2. Description of the Related Art FIG. 10 shows the basic structure of a molten carbonate fuel cell. In FIG. 10, 1 is a fuel electrode (cathode), and 2 is an oxidizer electrode (anode). Furthermore, an electrolyte plate 3 is arranged between the fuel electrode 1 and the oxidizer electrode 2. Electrolyte plate 3
holds electrolytes. These fuel electrodes 1, oxidizer electrodes 2, and electrolyte plates 3 are used as unit cells, and a plurality of unit cells are stacked with separators 4 in between.

[0003] The fuel electrode 1 disposed on the upper surface of the electrolyte plate 3 is spaced a desired distance from the edge of the electrolyte plate 3. An edge seal plate 5a is arranged between the electrolyte plate 3 and the separator 4 in a portion where the cathode 1 is not present. Fuel electrode 1
A perforated plate 6a, which is a current collector plate, and a channel plate 7a are laminated in order from the fuel electrode 1 side between the fuel electrode 1 and the separator 4.

[0004] Oxidizer electrode 2 placed on the bottom surface of electrolyte plate 3
is located a desired distance from the edge of the electrolyte plate 3. An edge seal plate 5b is arranged between the electrolyte plate 3 and the separator 4 in a portion where the oxidizer electrode 2 is not present. Between the oxidizing agent electrode 2 and the separator 4, a perforated plate 6b serving as a current collecting plate and a channel plate 7b are laminated in order from the oxidizing agent electrode 2 side.

[0005] The channel plates 7a and 7b are corrugated plates,
A gas flow path is formed between the separator 4 and the fuel electrode 1 or the oxidizer electrode 2, and the gas flow path on the separator side is separated from the gas flow path on the electrode side. A stack power generation element in which a plurality of unit cells as described above are stacked is housed in a housing.

[0006] Fuel gas (H2, CO2) is
The fuel gas is supplied in the direction shown in and flows along the gas flow path formed by the flow path plate 7a, and the fuel gas flowing through the flow path on the electrode side undergoes an electrode reaction at the fuel electrode 1. Similarly, the oxidant gas (AIR, CO2) is supplied in the direction shown by the arrow 9 and flows along the gas flow path formed by the flow path plate 7b.
Among them, the oxidizing gas flowing through the gas flow path on the electrode side undergoes an electrode reaction at the oxidizing agent electrode 2. Further, the oxidant gas also plays a role as a cooling gas for cooling the battery. (Hereinafter, fuel gas and oxidizing gas will be collectively referred to as "gas.")

[
However, when gas is supplied to the above-mentioned molten carbonate fuel cell, only the gas passing through the gas flow path on the electrode side constituted by the flow path plate is used for the electrode reaction, and the gas on the separator side is used for the electrode reaction. The gas flowing through the channel was passing through without being used in the electrode reaction.

[0008] Furthermore, in each electrode, before the gas circulates around the entire electrode, an electrode reaction between the gas and the electrode occurs near the gas flow path entrance of the electrode, and most of the gas is consumed. In comparison, the gas concentration decreases toward the gas flow path, making electrode reactions less likely to occur. In other words, it was difficult for the gas to contribute to the electrode reaction over the entire area of the electrode.

[0009] Furthermore, when looking at the temperature distribution on the cell, the fuel gas concentration is high near the entrance of the fuel gas flow path, and electrode reactions are likely to occur, resulting in a high cell temperature. However, since the oxidizing gas acts as a cooling gas, the temperature near the entrance of the oxidizing gas flow path is low. Therefore, for the entire cell, the temperature is highest in the part that is close to the inlet of the fuel gas flow path and far from the inlet of the oxidant gas flow path; This results in an uneven temperature distribution with the temperature being lowest in the area closest to the inlet. In a fuel cell, a portion of the fuel cell that has a high temperature is subject to large thermal stress, which causes a decrease in the reliability of the cell. In addition, electrolyte diffusion occurs partially, causing a reduction in battery life.

In order to solve the above problem, conventionally, in the gas flow path structure of a molten carbonate fuel cell, the corrugated flow path plate is separated into at least two pieces, and the corrugated flow path plate is divided into at least two parts, and the corrugated flow path plate is divided into at least two pieces, and the corrugated flow path plate is divided into at least two pieces, and the corrugated flow passage plate is divided into at least two parts, and the corrugated flow passage plate is divided into at least two parts, and the corrugated flow passage plate is divided into at least two parts, and the corrugated flow passage plate is separated into at least two pieces, and the corrugated flow passage plate is divided into at least two pieces in the gas flow passage structure of a molten carbonate fuel cell. Japanese Patent Laid-Open No. 1-140560 discloses a method in which the electrodes are installed in a staggered manner, and the gas flow path on the electrode side is connected to the flow path on the separator side, and the gas flow path on the separator side is connected to the flow path on the electrode side. .

[0011]

[Problems to be Solved by the Invention] However, the above-mentioned gas flow path structure requires a fixing process such as welding or brazing at least two separated corrugated flow path plates to the separator. increases, leading to higher costs.

In view of the above problems, the present invention provides a molten carbonate fuel cell that has a gas flow path structure that makes the gas concentration on the electrode surface as uniform as possible, makes the temperature distribution more uniform, and is easy to process during manufacturing. The purpose is to provide. [Structure of the invention]

[0013]

[Means for solving the problem] The above problem is solved by providing an opening portion connecting the flow path on the separator side and the flow path on the electrode side at a position a desired distance from the gas flow path inlet of the flow path plate, and This is achieved by closing the gas flow path on the separator side behind the opening in the flow direction of the gas.

That is, the present invention provides a plurality of unit cells comprising a fuel electrode, an oxidizer electrode facing the fuel electrode, and an electrolyte plate interposed between the fuel electrode and the oxidizer electrode; A separator interposed between each unit cell when stacking cells; A gas flow path is formed between an electrode facing the separator and the separator, and a gas flow path on the separator side and a gas flow path on the electrode side are formed. In a molten carbonate fuel cell comprising a separating flow path plate, the flow path plate has an opening that connects a gas flow path on the separator side and a gas flow path on the electrode side, and This is a molten carbonate fuel cell characterized in that the gas flow path on the separator side is closed at the rear of the opening.

[0015] The gas flow path structure in the fuel cell of the present invention can be effectively applied to either the gas flow path on the oxidant electrode side or the gas flow path on the fuel electrode side. However, it is practically preferable to apply it to the fuel electrode side. This is because even if the hydrogen concentration in the fuel gas is lower than the electrode reaction component of the oxidant gas, the hydrogen in the fuel gas can be used effectively. More preferably, both the oxidant electrode side gas flow path and the fuel electrode side gas flow path are applied. As a result, gas can be used effectively, and the temperature distribution on the electrodes becomes uniform, which is suitable for improving battery performance.

On the other hand, when closing the channel plate in the fuel cell of the present invention, any method of closing may be used. The channel plate may be closed by being filled with a substance having heat resistance at the operating temperature of the fuel cell, such as metal or ceramics, or by folding a part of the channel plate. It is easier to form a blockage by folding a part of the channel plate.
It requires fewer manufacturing steps and is advantageous in terms of manufacturing method.

[0017] The passage plate may be closed at any position in the passage plate as long as it is behind the opening of the gas passage on the separator side in the gas flow direction, but it may be placed immediately after the opening. It is preferable to close the channel because gas can more easily move from the separator side channel to the electrode side channel.

[0018]

[Operation] In the molten carbonate fuel cell of the present invention, half of the fuel gas or oxidant gas supplied at the gas flow path inlet flows through the gas flow path on the electrode side, and the remaining half flows through the gas flow on the separator side. flowing down the road. The gas flowing through the gas flow path on the electrode side causes an electrochemical reaction on the electrode surface, and most of the gas components are consumed along the way. On the other hand, the gas flowing through the gas flow path on the separator side does not participate in electrochemical reactions and flows without any change in composition. However, the unreacted gas that was flowing on the separator side from the opening in the channel plate that connects the gas channel on the separator side and the gas channel on the electrode side, which was provided at a certain distance from the gas channel inlet. begins to flow into the gas flow path on the electrode side. This increases the concentration of reactive components in the gas in the gas flow path on the electrode side, making it easier for electrode reactions to occur. In addition, since the rear part of the flow path on the separator side is closed off, the only outlet for the gas on the separator side is the opening, and as a result, gas flows from the separator side flow path to the electrode side flow path. It becomes easier to leak. Here, the effects of the present invention can be obtained even if the closed portion is not necessarily completely sealed.

[0019] By providing the gas flow path structure as described above, the decrease in gas concentration on the electrode surface due to non-uniform concentration in the longitudinal direction of the gas flow path is improved, the electrode and gas can be used effectively, and battery performance is improved. be able to.

[0020] Furthermore, in the present invention, when providing the apertures and the closed portions in the channel plate, there is no need for a fixing process such as gluing two or more channel plates to the separator, which is advantageous in manufacturing. It is.

Further, in the present invention, the distance from the gas flow path inlet to the opening of the flow path plate may be arbitrarily changed. In areas where openings are provided and gas is newly introduced, the gas concentration is high, electrode reactions are more likely to occur, and the temperature is also high. Therefore, by providing an opening at an arbitrary position, the temperature distribution on the cell can be averaged, and the performance of the battery can be improved. The invention will be explained in detail by the following examples.

[0022]

【Example】

(Example 1)

A unit cell of a molten carbonate fuel cell having a gas flow path structure as shown below in the fuel side gas flow path and the oxidant electrode side gas flow path was prepared. The area of the unit cell is 1×1
It was a square of 0.4 cm2.

FIG. 1 is a perspective view showing a gas passage structure on the fuel electrode side of a molten carbonate fuel cell according to an embodiment of the present invention. FIG. 2 shows the same gas flow path structure as FIG. 1, and the line A in FIG.
It is a sectional view when the channel structure is cut at -A'. 1 and 2, channel plate 10 is a corrugated metal plate similar to those used in conventional channel plates. Channel plate 10
A hole 11 and a hole 12 each having a diameter of 2 mmφ were provided at a position 50 cm from the gas flow path inlet on both sides of the wavy convex portion. Furthermore, the outlet of the gas flow path 14b on the separator 13 side was closed. Fuel gas was supplied in the direction shown by arrow 15.

Initially, the fuel gas flows through the channel plate 10 and the fuel electrode 16.
(The fuel electrode 16 is shown only in FIG. 2.) and the gas flow path 1 on the fuel electrode 16 side separated by the separator 13.
4a and the gas flow path 14b on the separator side. Approximately half of the fuel gas flows through the gas flow path 14a, causes an electrochemical reaction at the fuel electrode 16, and flows through the gas flow path 1.
Hydrogen is consumed within 4a, and produced gases, water and carbon dioxide, are produced from the electrode surface, and the hydrogen concentration gradually decreases. However, since the remaining half of the fuel gas flows through the gas flow path 14b, no reaction occurs and it has the same composition as the inlet.

[0026] At 50 cm from the fuel gas inlet,
The gas that previously flowed through the gas flow path 14b exits the openings 11 and 12 and now flows through the gas flow path 14a, which is the fuel electrode side gas flow path. Therefore, the hydrogen gas concentration in the gas flow path 14a, which once became low in the flow path 14a, increases again.
An electrochemical reaction is performed at the fuel electrode 16. In the above embodiment, an example was described in which the present invention was applied to the gas flow path on the fuel electrode side, but the present invention was similarly applied to the gas flow path on the oxidizer electrode side.

The channel plate used in this example was manufactured as follows. FIG. 3 shows a partially exploded view of the channel plate used in this example. When making the channel plate, first, a metal plate was cut to have apertures 11 and 12 that would serve as gas flow channels, and a convex portion 17 that would serve as a closing part, as shown in FIG. The convex portion 17 serving as the closing portion has a cross-sectional shape of the gas flow path. Thereafter, the cut metal plate was pressed into a wave shape as shown above. Then, the convex portion 17 was bent to close the gas flow path, thereby forming a closed portion. By providing the closed portions and the open holes in the channel plate as described above, the concentration distribution of gas on each electrode is improved, and battery performance is improved. A power generation test was conducted at 650° C. using the above molten carbonate fuel cell. FIG. 4 shows the relationship between the distance from the gas flow path entrance of the cell and the current density.

As shown in FIG. 4, the current density decreases due to the decrease in gas concentration in the gas flow direction, but the unreacted gas flows from the opening provided in the middle of the flow path to the separator side. As the gas flows out, the gas concentration increases, making it easier for electrode reactions to occur. This increases current density and improves performance. (Example 2)

[0029] A unit cell of a molten carbonate fuel cell in which the flow passage plates constituting the fuel side gas passage and the oxidant side gas passage have the structure shown below, and other conditions are the same as in Example 1. A power generation test was conducted at 650°C. The channel plate has an opening 5 cm long and 2 mm wide on the side surface of the wavy convex portion of the corrugated plate, and furthermore, a part of the convex portion on the gas outlet side is closed. As in Example 1, the closing portion is made by bending the convex portion at the end of the corrugated plate serving as the channel plate. FIG. 5 shows the relationship between the distance from the gas flow path entrance and the current density in the cell when a power generation test was conducted using the above molten carbonate fuel cell.

[0030] As in Example 1, by providing the openings, the current density increases midway through, and the performance is improved. Furthermore, since the openings are larger than in Example 1, more unreacted gas flows out from the separator side to the electrode side, so the decrease in current density is smaller than in Example 1. (Comparative example 1)

[0031] The flow passage plate constituting the gas flow passage on the fuel electrode side and the gas flow passage on the oxidizer electrode side was a corrugated plate having neither openings nor blockages, and other conditions were the same as in Example 1. In the unit cell of a molten carbonate fuel cell, the temperature is 650°C.
A power generation test was conducted. FIG. 6 shows the relationship between the distance from the gas flow path entrance and the current density in the cell at this time. As shown in FIG. 6, the current density decreases due to a decrease in gas concentration in the gas flow direction, and does not recover. Example 1
Both Example 2 and Example 2 have higher average current densities than Comparative Example 1, and the battery performance is improved. Further, the channel plate used in this example does not require a fixing process such as welding or adhesion to the separator, which is advantageous in manufacturing.

[0032] Another method of processing a channel plate is shown below. Figure 7 shows a developed view of the channel plate. First, a cut was made in the metal plate, leaving a portion as shown in FIG. 7, and the cut was pressed into a wave shape so that the line BB' in FIG. 7 was the top of the convex portion. and,
The part 18 surrounded by the cut was inserted. FIG. 8 is a perspective view showing a part of the channel plate processed by the above method. According to the above method, the opening and the closing part can be made at the same time as shown in FIG.

On the other hand, FIG. 9 shows a plan view from above of a channel plate to which the channel plates shown in Examples 1 and 2 are applied. In FIG. 9, 19 indicates the gas flow path on the separator side, and 20
indicates the gas flow path on the electrode side. Gas flow path 1 on separator side
9 and the gas flow path on the electrode side are formed by the unevenness of the plate. As the gas inlet approaches the outlet, the separator side flow path 20 becomes narrower, and the electrode side flow path 20 widens. The opening 21 is provided on the side surface of the convex portion of the flow path plate forming the electrode side gas flow path. Further, the outlet of the gas flow path 19 on the separator side is closed.

When gas is supplied in the direction of the arrow, the gas flowing through the separator side flow path 19 moves from the opening to the electrode side flow path 20. Gas flows into the electrode side flow path 20 from the separator side flow path 19, thereby increasing the gas flow rate. However, by adopting the above structure, the gas pressure in the electrode side flow path does not increase, and the gas flow from the separator side flow path increases. Gas moves more easily.

[0035]

As described above, according to the present invention, in a molten carbonate fuel cell, the gas concentration on the electrode surface decreases due to the concentration non-uniformity in the longitudinal direction within the gas flow path, and the current density decreases due to the current density non-uniformity. Non-uniform density distribution and non-uniform temperature distribution can be improved, which is extremely advantageous for improving the performance and extending the life of molten carbonate fuel cells. Furthermore, the flow path plate can be easily manufactured, and is suitable for mass production and cost reduction.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a gas flow path structure of a molten carbonate fuel cell according to Example 1.

FIG. 2 is a cross-sectional view showing the gas flow path structure of the molten carbonate fuel cell according to Example 1.

FIG. 3 is a developed view of the channel plate used in Example 1 and Example 2.

FIG. 4 shows the relationship between the distance from the gas flow path entrance of the cell and the current density in Example 1.

FIG. 5 shows the relationship between the distance from the gas flow path entrance of the cell and the current density in Example 2.

FIG. 6 shows the relationship between the distance from the gas flow path entrance of the cell and the current density in Comparative Example 1.

[Figure 7] Developed view of the channel plate.

FIG. 8 is a perspective view showing a part of the channel plate. Developed view of the channel plate.

FIG. 9 is a plan view of a channel plate to which the channel plate is applied.

[Figure 10] Basic configuration of a molten carbonate fuel cell.

[Explanation of symbols]

1...Fuel electrode (cathode) 2... Oxidizer electrode (anode) 3...Electrolyte plate 4...Separator 5a, 5b...edge seal plate 6a, 6b...perforated plate 7a, 7b...channel plate 8…Fuel gas supply direction 9... Oxidizing gas supply direction 10...Flow path plate 11...Opening part 12...Opening part 13...Separator 14...Gas flow path 15...Fuel gas supply direction 16...Fuel electrode 17...Convex part 18...Part surrounded by cuts 19...Gas flow path on the separator side 20...Gas flow path on the electrode side 21...Opening part

Claims (1)

[Claims] 1. A plurality of unit cells comprising a fuel electrode, an oxidizer electrode facing the fuel electrode, and an electrolyte plate interposed between the fuel electrode and the oxidizer electrode; the unit cells are stacked. a separator interposed between each unit cell; a gas flow path is formed between the separator and the electrode facing the separator, and a flow path is formed to separate the gas flow path on the separator side and the gas flow path on the electrode side; In a molten carbonate fuel cell comprising a passage plate, the passage plate has an opening that connects the gas passage on the separator side and the gas passage on the electrode side, and the passage plate has an opening on the separator side with respect to the gas flow direction. A molten carbonate fuel cell characterized in that the gas flow path is closed at the rear of the opening.