JPH0773059B2 - Molten carbonate fuel cell - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a molten carbonate fuel cell, and more particularly, to melting gas supply passages for a separator and an electrolyte plate with an insulating corrosion resistant material that is not easily corroded by molten carbonate. The present invention relates to a carbonate fuel cell.

[Conventional technology]

In a fuel cell which uses a gas such as natural gas as an energy source to generate a predetermined electric power by utilizing an electrochemical reaction, in order to reduce internal loss of the cell, JP-A-58-216365 and JP-A-59-27467 are used. And Japanese Patent Laid-Open No. 59-27468, it is known to use a metal collector frame (separator) that comes into contact with the outer peripheral surface of the electrode. In such a unit battery structure, there is a limit in power generation capacity. Therefore, in order to obtain a battery with a large capacity output, it is necessary to increase the size of the electrode, the electrolyte plate, and the separator, respectively, and further to stack these, so that technological development is important.

In order to increase the size and stack reliably, it is necessary to enlarge the gas inlet and increase the gas inlet so that the gas is evenly distributed over the entire surface of the electrode.

For example, in a small-sized molten carbonate fuel cell having an electrode area of about 100 cm ² , one cylindrical type anode and cathode gas supply passage was sufficient. In order to construct a KW class or MW class battery, it is necessary to increase the size of the separator, the electrode, the electrolyte plate, etc., and further stack a large number of unit cells in parallel, series, or series-parallel. In addition, the expansion of gas supply channels and their multipleization will be complicated, and the structure of gas supply channels will become complicated. In general, the wet seal portion where the separator and the electrolyte plate are in contact is insulated, but the cathode gas supply passage and the anode gas supply passage are not insulated.

When such a fuel cell is operated for a long time, the electrolyte flows out to the cell reaction gas supply path and moves to generate a local cell due to the Palace Reaction reaction by oxygen, carbonate and electrons by the gas supply which is a conductive material. Therefore, there is a problem of current loss. [Reference: Journal Electrochemical Society Electrochemical Science and Technology 2-1986 286 (J.Ele
ctrochem.Soc., Electro-Chemical Science and Techno
logy Feb.1986 pp286)] [Problems to be solved by the invention] In the above-mentioned conventional technology, the separator of the molten carbonate fuel cell is a conductive material, and the carbonate flows out from the electrolyte plate into the cathode gas supply passage. When moving, the carbonate adheres to the wall of the supply path (wet), and the power generation state of the battery, that is, oxygen and carbonate of the cathode gas, and electrons (1),
There is a problem that a current loss occurs due to the formation of the local cell as in the formula (2).

1 / 2O ₂ ＋ CO ₂ ＋ 2e ⁻ → CO ₃ ^2-- … (1) 2Li ⁺ ＋ CO ₃ ^2- → LiCO ₃ … (2) When the batteries are stacked, the total voltage becomes higher, so the current will flow more easily and the effect of current loss will occur. Also grows. Further, when the molten carbonate fuel cell is operated for a long time, the carbonate disappears, the internal resistance of the cell increases, and the cell performance deteriorates. Further, when the carbonate flows out and moves to the gas supply passage of the separator, the iron and lithium carbonate of the separator cause corrosion as shown in the formula (3).

The object of the present invention is to provide a stable long-term fuel cell by insulating the cell reaction gas supply path of the separator to prevent the generation of local cells due to the outflow of carbonate and to prevent corrosion due to other iron and lithium carbonate. To provide.

[Means for Solving the Problems]

The present invention relates to a molten carbonate fuel cell main body, in which a pair of positive and negative electrodes have a larger area than the positive and negative electrodes and are opposed to each other with an electrolyte plate containing a carbonate as an electrolyte, and the molten carbonate fuel cell main body comprises: Through a separator having a larger area than the Yin-Yo electrode, a plurality of the Yin-Yo electrodes are laminated with the polarities aligned, and a reaction gas supply passage unit for supplying each reaction gas to each Yin-Yo electrode surface provided on the separator, And a reaction gas supply path portion that is connected to the reaction gas supply path portion of the separator, is located around the positive and negative electrodes, and includes a reaction gas supply path portion that penetrates the stacked separator and the electrolyte plate. The molten carbonate fuel cell is characterized in that the inner surface of the reaction gas supply passage is coated with a dielectric and corrosion resistant material.

Further, it is characterized in that the insulating and corrosion resistant coating is performed by coating and sintering at least one powder of alumina, zirconia, titania, silicon carbide, lithium aluminate and silicon nitride.

[Action]

The inner surface of the gas supply passage of the separator that supplies the cell reaction gas corresponding to the pair of positive and negative electrodes of the molten carbonate fuel cell is coated with an insulating and corrosion-resistant material to generate a local cell when the carbonate flows out to the gas supply passage. Take precautions.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. As shown in FIG. 3, the molten carbonate fuel cell includes an electrolyte plate 3 and a pair of electrodes facing each other with the electrolyte plate sandwiched therebetween, that is, a cathode 4, an anode 5 and a separator 1 (metal Made) and has a separator
Air and CO ₂ are circulated from the cathode gas supply passage 2 that penetrates 1 and the electrolyte plate 3, and H ₂ and a reaction gas of CO ₂ are circulated from the anode gas supply 11 to the cathode chamber 6 and the anode chamber 7, respectively. Supplied. The carbon dioxide supplied to the cathode 4 reacts with oxygen and electrons to become carbonate ions and move to the anode.

At the anode 5, hydrogen as a fuel reacts with carbonate ions to generate carbon dioxide and water, and emits electrons through an external circuit separator. That is, the reaction of the following formula proceeds.

as a whole Further, since the carbonate is used in a molten state with the carbonate ion as a medium, the operating temperature of the battery is higher than the melting temperature of the carbonate.
It is 650 ° C.

Therefore, carbonate flows out into the cathode gas supply path 11 and the outside of the separator 1 to form a carbonate film connecting the anode-side separator 1 and the cathode-side separator 1. Then, as described above, oxygen reacts with carbon dioxide and electrons in that portion to form carbonate ions, and the reaction of development or palletic reaction of moving to the anode 5 occurs, forming a local cell and causing current loss. Therefore, 100 electrons generated by the original reaction of the battery
% It cannot be taken out as a current to the outside.

FIG. 4 is a cross-sectional view of a unit cell of a conventional molten carbonate fuel cell, and FIG. 5 is a cross-sectional view of the upper portion at the position of the cathode 4 in FIG.

H ₂ supplied from the anode gas supply path 11 of the separator 1
The fuel gas of CO ₂ and CO ₂ enters the anode chamber 7 and contacts the entire surface of the anode 5 uniformly, and the carbonate (C) generated at the cathode 4 by the O ₂ and CO ₂ supplied from the cathode gas supply passage 2
O ₃ ²⁻ ) is reacted through the electrolyte 3 to extract electric energy from the cathode 4 and the anode 5.

FIG. 6 shows that the cathode gas supply passage 2, the anode gas supply passage 11, the cathode gas outlet 8 and the anode gas outlet 12 are enlarged in order to increase the size of the entire battery and obtain a large output, and both reaction gases come to the electrode surface. It is designed to diffuse uniformly.

Moreover, the influence of the local cell at the time of electrolyte outflow is reduced by enlarging each supply path and the outlet and increasing the surface area.

FIG. 1 shows a first embodiment of the present invention for preventing the occurrence of local cells, in which the battery reaction gas supply passage of the separator 1 is an insulating coating gas supply passage 13.

FIG. 2 shows the second embodiment of the present invention in which the insulating pipe gas supply passage 14 is inserted into the gas supply passage of the separator 1 to prevent the occurrence of the above-mentioned local cell. As described above, by coating the gas supply passage that penetrates the separator 1 and the electrolyte plate 3 with the corrosion-resistant insulating material, the generation of local cells due to the outflow and movement of carbonate does not occur. Therefore, there is no transfer of electrons, no current loss, and the current obtained by the power generation of the battery is 100
% It can be collected outside.

Further, since the corrosion caused by the reaction between the outflowing carbonate and the iron in the separator 1 is also eliminated, the carbonate can be kept in a stable state without being consumed. Next, the experimental results of insulating treatment of the insulating coating gas supply passage 13 of the separator 1 of FIG. 1 with alumina will be described.

The electrolyte plate 3 is made of lithium aluminate as a substrate 400 × 4
A substrate of 00 mm and thickness of 2 mm was impregnated with a carbonate electrolyte (lithium carbonate: potassium carbonate = 62: 38 molar ratio) and used. The separator 1 was made of SUS310 and had the same size as the electrolyte plate, and two places were provided respectively for the cathode gas supply passage 2 and the anode gas supply passage 11.

A nickel electrode plate 300 × 300 mm was used as the anode 5, and a nickel oxide electrode plate 300 × 300 mm was used as the cathode 4. A power generation test was performed by supplying a mixed gas of 15% O ₂ -30% CO ₂ -55% N ₂ as an anode gas. As a result of examining the battery performance at a temperature of 650 ° C., the current density was 15
The unit cell battery voltage at 0 mA / cm ² was 0.90 V as shown in FIG. 7. Further, in the continuous power generation test at 150 mA / cm ² , almost no decrease was seen as shown in Fig. 8, and 0.87 V after 2500 hours and 0. 0 after 5000 hours.
It was 85V.

In the case of no insulating coating, it was about 0.85V after 2500 hours and about 0.80V after 5000 hours. As a result, it can be seen that the effect of insulation is that a stable output can be obtained for a long time.

The output of the laminated cell at this time was 486 W at the initial stage and 470 W after 2500 hours had elapsed.

Further, as shown in FIG. 2, the same characteristics as above can be obtained even in the result of using the insulating pipe gas supply passage 14.

In this way, by coating the metal separators constituting the molten carbonate fuel cell and the walls inside the cathode gas supply passage 2 and the anode gas supply passage 11 penetrating the electrolyte plate 3 with a corrosion-resistant insulating material, It is possible to prevent the carbonate from flowing out and moving into the cathode gas supply passage 2. Even if the carbonate flows out into the cathode gas supply passage 2 through another passage, there is no place for electron transfer by the local cell by insulating the cathode gas supply passage 2 of the metal separator, so no current flows. There is no current loss. Experiments have shown that the cell performance is stabilized by preventing corrosion.

In addition, what can be used as the corrosion resistant electrical insulating material is oxides such as alumina, zirconia, titania, silicon carbide, lithium aluminate, silicon nitride, and nitrides, and these powders are used as the cathode gas supply passage 2 and the anode. A method of applying or spraying to the surface of the gas supply path 11 for sintering treatment, and a method of burying a pipe of alumina or the like in the gas supply path are effective.

In the present embodiment, the gas supply passage is described as being coated with an insulating and corrosion resistant material. However, if there is a portion where the above-mentioned local cells are generated or corrosion occurs also in the other portion of the separator 1, that portion is partially coated with an insulating and corrosion resistant material. Of course you can.

〔The invention's effect〕

According to the present invention, by coating the inner surface of the gas supply passage of the molten carbonate fuel cell with an insulating and corrosion-resistant material, it is possible to prevent the generation and corrosion of local cells in the gas supply passage caused by the outflow of carbonate. It is possible to obtain a stable battery with good performance in the long term.

[Brief description of drawings]

FIG. 1 is a sectional perspective view showing an insulating coating of a gas supply passage of a separator showing an embodiment of the present invention, FIG. 2 is a sectional perspective view of a separator when an insulating pipe is used for the insulating coating, and FIG. FIG. 4 is a sectional perspective view showing the entire structure of a molten carbonate fuel cell in which cells are stacked, FIG. 4 is a sectional view of a single cell, FIG.
FIG. 7 is a cross-sectional view of the upper part of the cathode part, and FIGS. 7 and 8 are diagrams showing the relationship between the current density and the voltage and the degree of the voltage drop with time in the single cell experiment in which the gas supply path was insulated with alumina. It is a figure. 1 ... Separator, 2 ... Cathode gas supply path, 3 ...
Electrolyte plate, 4 ... Cathode, 5 ... Anode, 11 ... Anode gas supply path, 13 ... Insulation coating gas supply path, 14 ...
Insulation pipe gas supply path.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideo Okada 4026 Kuji Town, Hitachi City, Hitachi City, Ibaraki Prefecture, Hitachi Research Laboratory, Ltd. (72) Inventor Yoshio Iwase 4026 Kuji Town, Hitachi City, Ibaraki Prefecture, Hitachi City Corporation Hitachi Research Laboratory (72) Inventor Satoshi Kuroe 4026 Kuji Town, Hitachi City, Ibaraki Prefecture, Hitate Works, Ltd. Hitachi Research Laboratory (72) Inventor Yuichi Kamo 4026 Kuji Town, Hitachi City, Ibaraki Prefecture, Hitachi Research Institute, Ltd. (56) References JP-A-61-267268 (JP, A)

Claims (2)

[Claims] 1. A molten carbonate fuel cell main body comprising a pair of positive and negative electrodes having a larger area than the negative and positive electrodes and facing each other with an electrolyte plate containing a carbonate as an electrolyte, and the molten carbonate fuel cell main body. Is a plurality of layers with the polarities of the Yin-Yo electrodes aligned with each other through a separator having a larger area than the Yin-Yo electrodes.
Reactive gas supply passages for supplying respective reaction gases to the respective positive and negative electrode surfaces provided on the separator, and communicating with the reaction gas supply passages of the separator, located around the positive and negative electrodes, and laminated. In a molten carbonate fuel cell having a reaction gas supply passage consisting of the separator and the reaction gas supply passage portion penetrating the electrolyte plate, an inner surface of the reaction gas supply passage is coated with an insulating corrosion-resistant coating. Characterized molten carbonate fuel cell. 2. The insulating and corrosion-resistant coating is performed by coating and sintering one or more powders of alumina, zirconia, titania, silicon carbide, lithium aluminate, and silicon nitride. 2. A molten carbonate fuel cell according to item 1.