JPS6326960A - Sealing method for molten salt fuel cell - Google Patents

Abstract

PURPOSE:To prevent a decrease in cell performance, to increase safety and sealing capability, and to retain steady performance for a long time by using a sealant containing a material, which melts at less than cell operation temperature then change to a solid, in a part in which airtightness is required. CONSTITUTION:A sealant 9 is arranged in the periphery of an electrolyte body 1. As a material which melts at less than cell operation temperature then changes to a solid, hydroxide of alkali metal and/or alkali earth metal is used. The preferable material is the hydroxide of lithium, sodium, potassium, rubidium, strontium, or barium, and the sealant containing either one or a mixture of these compounds is used. For example, lithium hydroxide has a melting point of 467 deg.C and it melts at temperature exceeding the melting point and forms a liquid film in a part in which airtightness is required to increase airtightness. When a gas containing carbon dioxide is passed in this state, the lithium hydroxide is converted into the carbonate which is a solid, and a dry seal state or the similar state is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a sealing method for a fuel cell, and particularly to a sealing method suitable for a molten salt layered fuel cell.

[Conventional technology]

Fuel cells can directly convert the chemical energy of fuel into electrical energy, so they have high power generation efficiency, generate little harmful gas or liquid, and have low noise, making them environmentally friendly and a promising new fuel cell. *The development of this technology is active. Among these, molten salt fuel cells have particularly high power generation efficiency and can be used in a variety of fuels, from LNG to coal, and their early commercialization is desired.

A molten salt fuel cell includes a pair of gas-diffusing porous electrodes, a cathode and an anode, an electrolyte body holding a molten alkali metal carbonate electrolyte disposed between the electrodes, and the pair of gas-diffusing porous electrodes. A unit cell has a chamber through which an oxidizing agent can flow to supply an oxidizing agent to one of the porous electrodes, and a chamber through which a fuel can flow to supply fuel to the other of the pair of gas-diffusing porous electrodes. .

In addition, in practical scale molten salt fuel cell power generation plan 1-, the battery voltage is increased by arranging 18 layers of the unit cells in series, and the battery is enlarged to widen the effective area of the electrodes. It is intended to extract a large current and increase the capacity of the battery output, and is generally constructed as shown in FIG.

A separator 6 is provided with a cathode 2 and an anode 3 on both sides of the electrolyte body 1, and further includes chambers 4, 4' through which an oxidizing agent can flow and chambers 5, 5' through which fuel can flow outside.
．． 6' is arranged. 1 to 6 constitute a unit battery,
These are stacked one after another to form an 11M battery. The upper end plate is provided with a chamber through which the oxidizer can flow, and the lower end plate is provided with a chamber through which the fuel can flow. In addition, collectors (current collectors) are often provided between each cathode and each chamber through which each oxidizing agent can flow, and between each anode and each chamber through which fuel can flow.

However, in a molten salt fuel cell having such a structure, there is a high possibility that the reactant gas may leak to the outside of the cell. This possibility is particularly high at the peripheral edges of the battery where the electrolyte body 1 and the separators 6 and 6' are in contact with each other. As a gas sealing method in a molten salt fuel cell having such a structure, a method called a urethane sealing method is usually employed. That is, the purpose is to form a molten electrolyte liquid film on the contact surfaces of the electrolyte body 1 and the separators 6 and 6' to prevent leakage of reaction gas to the outside of the battery.

Another method is a method called a dry seal method. There is a method of disposing an insulating gasket, for example, a dense ceramic plate, at the peripheral edge of the electrolyte body 1 between the separators 6 and 6' to prevent leakage and outflow of the reaction gas and electrolyte to the outside of the battery (for example, , patent application 1984-1
01708).

In other types of fuel cells, such as phosphoric acid fuel cells, where the humidity transfer temperature is low, the following methods are used as sealing measures to prevent reactant gas and electrolyte from leaking or flowing out of the cell. Disclosed.

In JP-A No. 58-157063, a sealing material that can withstand phosphoric acid at high temperatures and can be melted is placed, heat treated, and the sealing material is attached to the cell and gas separation plate. A-R, and the sealing material is a tetrafluoroethylene-hexafluoropropylene copolymer and a perfluoroalkyl vinyl ether copolymer.

Furthermore, JP-A No. +1flSa-119172 discloses a prolo silicone rubber adhesive, and JP-A No.
No. 158-164155 discloses polytetrafluoroethylene and fluororubber, and these materials can be used.

[Problem that the invention seeks to solve]

The molten salt fuel cell, which is the main object of the present invention, operates at a high temperature of around 650°C, and the electrolyte used is a highly corrosive alkali metal carbonate. Therefore, it is currently difficult to find suitable materials that can withstand such environments.

Therefore, a wet seal method as described above or a dense ceramic plate is used. If Ft roars, we are in a situation where we have no choice but to apply the dry seal method.

However, the reliability of the wet seal method is not very high.
In addition, in the molten salt fuel cell manufactured by +1 Machizo, electrolysis 1! ! There is also a possibility that the liquid may leak out of the battery.

That is, by continuing to operate the battery for a long period of time under a high humidity condition of about 650° C., it is expected that the electrolyte solution held in the electrolyte body will gradually ooze out to the outside of the battery.

If this situation progresses, the reliability of the gas sealing properties achieved by the wet sealing method will decrease, and there will also be a lack of free space in the electrolyte, pinholes and cracks will occur in the electrolyte, and oxidation will occur. A crossover phenomenon of the agent, fuel, or generated gas may occur, which may cause deterioration in battery performance and may also cause safety problems.

On the other hand, the dry sealing method, which is another method, also has the following problems.

This method uses something close to a rigid body, such as a dense ceramic plate, which causes little deformation under load, so it is necessary to strictly control the dimensional accuracy of the battery components and insulating gasket based on the physical properties of the electrolyte body and electrodes. There is also the disadvantage that unless the sealing surface of the separator or insulating gasket is devised, the sealing characteristics cannot be improved unless the sealing surface is tightened at a fairly high pressure. Furthermore, even if the tightening pressure is increased to improve its sealing properties,
If the contact between the ffi electrode and the electrolyte body or collector is not optimized, battery performance may be affected due to, for example, compressive creep deformation of the electrode, excessive movement of electrolyte from the electrolyte body to the electrode, or dripping into the collector opening of the electrode. There is also a risk that secondary problems may occur, such as not being able to maintain it in the best condition.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for sealing a molten salt fuel cell that can maintain stable cell characteristics over a long period of time by applying a new sealing material and solving the problems of the prior art described above. .

[Means for solving problems]

The above object is achieved by improving the sealing method of a molten salt fuel cell.

The present invention features a pair of spaced apart gas diffusive porous electrodes and a ft! A plurality of unit cells are constructed by sandwiching an electrolyte body holding an electrolyte disposed between 14 and 144 with separators each having a chamber through which 2Aδ of an oxidizing agent can pass and/or a chamber through which fuel can flow. In stacked fuel cells, a sealing material containing a material that forms a molten state at a temperature below the cell operating temperature and then becomes a solid state is used in parts that require airtightness. There is a particular thing.

Specifically, the operating temperature of the battery, generally 550 to 70
By applying a sealing material composed of a material that melts at temperatures above 0°C and a material that holds it, a wet seal-like 1
pu is formed. As it is, it is nothing but the wet I-seal method that has been applied conventionally, but it can be changed to a solid state by utilizing the physical properties of this molten state substance or by using a forced chemical change from the outside. If it is possible to change the state to a dry seal state by changing the state to a dry seal state, the characteristics of both the wet seal method and the dry seal method can be utilized, and the present invention has been devised with this point in mind.

That is, in a wet seal state, the molten substance liquid film in the sealing material improves airtightness and prevents leakage of reactant gas or generated gas to the outside of the battery. In order to ensure the long-term stability and reliability of the seal area formed in this way, it is preferable that the melted substance liquid and electrolyte liquid be prevented from flowing out to the end of the battery or to the outside. By changing to a dry seal state, it is not necessary to strictly control the dimensional accuracy of the sealing material during battery assembly, the battery component electrodes, and the electrolyte body, and the purpose is to prevent the electrolyte from leaking outside. can be easily achieved, and its airtightness can also be maintained several times.

More specifically, the present invention is characterized by alkali metal and/or alkaline earth metal hydroxides as materials that change to a solid state after forming a molten state below the battery operating temperature. Can be done. Among these hydroxides, particularly preferred hydroxides are hydroxides of lithium, sodium, potassium, rubidium As, strontium, and barium, as listed in Table 1, and seals containing any of these or a mixture thereof. Materials can be used to achieve the objectives of the present invention.

For example, the melting point of lithium hydroxide is 467°C, and when it exceeds that temperature, it becomes a molten state and becomes a liquid substance in a sealing material containing it, forming a liquid film in areas that require airtightness. This improves airtightness. When such a state is reached, by passing a carbon dioxide-containing gas through the material, the hydroxide is converted into carbonate and becomes a solid pull, resulting in dry seal rot or a state close to it.

A state close to that means that the part of the sealing part that requires airtightness that has come into contact with carbon dioxide gas is in a solid state, and the inside of the sealing part that does not come into contact is in a wet sealing state.

In the above example, lithium hydroxide changes to lithium carbonate, whose melting point is 720°C, so i! Since it is higher than the pond operating temperature range of 550 to 700°C, it becomes a solid state. Moreover, as shown in Table 1, the volume per unit mole of hydroxide is larger than that of carbonate, so the change of hydroxide into carbonate creates voids in the sealing material. This does not occur and the sealing performance is not impaired. The same applies to lithium salts. As mentioned above, in order to convert hydroxide into carbonate, it is necessary to aerate gas containing carbon dioxide, but since carbon dioxide is contained in the oxidizing agent and fuel supplied during battery power generation, At that point, the hydroxide at the sealing site may change to carbonate and become a solid state.

Up to now, it has been stated that the first objective can be achieved as a new sealing material by utilizing the conversion of hydroxide into carbonate, but the special feature of the present invention is the airtightness The method is to use a sealing material containing a material that changes to a solid state after forming a molten state at a temperature below the battery operating temperature in the part that requires such a state.
Materials that undergo one change are included in the invention. Examples include precursors of lithium phosphate and polyacid salts. Phosphoric acid is also covered. It has been confirmed that if you add water to lithium phosphate and the material that holds it, mix well, form this into a sealing material, place it on the sealing area and heat it to 650℃, it will solidify into a glass-like shape. . Furthermore, if, for example, an alkali metal dihydrogen phosphate salt is used as a precursor of a polyacid, it undergoes dehydration condensation to become a white glassy alkali metal metaphosphate salt. It has been found that when such a reaction is carried out in admixture with a holding material, this polyacid acts as a strong binder and exhibits good sealing properties to the kif. Phosphoric acid also solidifies into glass through a similar reaction.

These materials are suitable for battery operating temperatures of 550-700℃.
It is preferable that the material is heat resistant and electronically insulating, and the material that holds it must also be heat resistant, electronically insulating, and stable against molten carbonate, which is the electrolyte. For example, lithium aluminate, lithium silicate, strontium titanate, α
- Alumina, zirconia, etc. are preferred.

A fuel cell is a highly efficient direct current generator that can directly convert the chemical energy contained in fuel into electrical energy through an electrochemical reaction at the three-phase interface of gas, liquid, and solid. While being supplied to the battery, the reaction product gas is discharged from the fuel cell. Therefore, it is not desirable for these gases to leak outside from abnormal parts other than the flow channels inside the fuel cell, and the above sealing material is used in areas that require airtightness to prevent leakage of reactant gases or generated gases. To prevent.

As mentioned above, the most important part that requires airtightness is the contact surface between the electric MW body and the separator, and specifically, as shown in FIG. Material 5] is arranged. in this case.

In the internal manifold method, as shown in Figure 2.

This sealing material 9 may be provided with a passage hole 10 for gas supply or discharge. When this sealing material 5 contains, for example, the above-mentioned hydroxide, this passage hole 10 may be provided with a passage hole 10 for gas supply or discharge. By flowing the contained gas, the object of the invention is achieved. In addition, the outer circumferential portion 11 of the sealing material exposed to the outside of the battery is
may be brought into contact with a carbon dioxide-containing gas. On the other hand, in the case of the external manifold method, the sealing material 9 is arranged in a state as shown in FIG. In the external manifold method, a gas supply or discharge manifold is attached to the outside of the manifold, but by supplying carbon dioxide-containing gas from this manifold, the exposed portion 12 of the sealing material comes into contact with the carbon dioxide gas and turns into carbonate. The objectives of the invention are achieved. Further, as shown in FIG. 1, an electrolyte body 1 and separators 6 and 6'
The contact surface has a wet seal structure, further improving sealing properties.

Another important part that requires airtightness is the gas seal part that requires insulation, where the oxidizer manifold and fuel manifold are attached to the end of the fuel cell in an external manifold type stacked fuel cell. be. The sealing properties of this portion can also be improved by using the sealing material of the present invention.

The shape of the sealing material can be any shape depending on the structure of the stacked fuel cell.

〔Example〕

Hereinafter, the contents of the present invention will be explained in more detail based on examples of the present invention.

Example 1 A schematic cross-sectional view of the structure of the molten salt fuel cell of the present invention is shown in the first example.
As shown in the figure.

A fuel cell having a structure in which a cathode 2 and an anode 3 are arranged on separators 6 and 6', respectively, an electrolyte body 1 is sandwiched between the two electrodes, and a sealing material 9 is provided at the peripheral edge of the electrolyte body 1. be.

Seal material 9 was manufactured as follows. After mixing barium hydroxide and γ-lithium aluminate powder at a ratio of 6:4 (heavy ratio), dry grinding was carried out in a vibrating mill for about 3 hours.
and mixed thoroughly. This operation was performed in a nitrogen gas atmosphere inside the hot mill.

After sizing this mixture, add water (approximately 5% by weight).
After controlling the humidity, it was press-molded using a cold press at a pressure of about 50 kg/i. Humidity control operations were also performed in a nitrogen atmosphere.

This molded body has an outer dimension L30n++ (/l).

A seal material 9 was prepared by cutting out a shape with a seal width of 20 fields and a thickness of 2.0 nn. In addition, around each side of the sealing material 9, six gas passage holes 10 of φ6 were provided on each side.

The electrolyte plate 1 has a porosity of about 60% and uses γ-lithium aluminate powder and fibers (powder/fiber = 80/20. heavy-duty ratio) as an electrolyte holding material. A certain mixed carbonate (lithium carbonate/potassium carbonate = 62
．． /38 molar ratio) was used. Its shape is 90 nn square and thickness 2. Onwu.

In addition, the cathode 2 and anode 3 are made of nickel oxide containing silver (5atoa+%) and nickel, respectively, and are gas-diffusive porous sintered bodies attached to S tJ S 310 and nickel wire mesh, respectively. ,
The shape is 80nm square, and the thickness is Q and 58 r.
rn and 0.60 mn were used. Separator 6
and 6' were made of 5USaLO and had an outer dimension of 130 m square, an electrode arrangement part of 80 m square, and a thickness of about 6 m.

This was assembled into a 5-cell stacked fuel cell, and the following experiments were conducted.

This laminated battery was tightened with pressure using battery cotton of approximately 0.5 kg/al, and heated to 65°C at a heating rate of 50°C/h from room temperature.
The temperature was raised to 0'C. In this case, the gas atmosphere inside the bell jar is a nitrogen gas atmosphere, and the inside of the battery is supplied with nitrogen from the anode gas and cathode gas lines at a rate of 0.5 Q/Q.
It was distributed for min. After the temperature reached 650° C., the TTI pond clamping pressure was increased to 2−/d, and then carbon dioxide gas was passed through the anode gas line and the cathode gas line at a flow rate of 5α/n. After maintaining this state for about 2 hours, the sealing properties were examined. The carbon dioxide gas was flowed as it was, and the flow rate at the inlet and outlet was measured. As a result, the sealing rate of the anode example is! 49.2%, and that of the cathode example was 99.8%.

Next, we conducted a single power generation experiment. The experimental conditions were a reaction temperature of 650°C.
, the anode gas composition is 80%l1z-20%COz,
The cathode gas composition was 30% CO2-70% air, and the anode gas was humidified by bubbling water at 45°C. The anode gas flow rate was 125Q/h.

The cathode gas flow rate was 350 Q/h. The battery performance at the beginning of the power generation experiment (after 30 hours) was 0.78 at 150 mA/d.
It showed a battery voltage of V, and almost no deterioration in performance was observed even after 500 hours.

Furthermore, the sealing properties at that point were also good for both the anode-1 side and the cathode example, with a rate of 99.5% for each.

It was 99.7%.

On the other hand, without using a sealant, the shape of WIM body 1 was changed to 13
In an example of a battery that was assembled and raised in the same manner as 0m5 square and generated 1 power, the initial sealing rate was 95.5% on the anode side.
, 93.5% for the cathode example, but 88.5% after 500 hours.

90.0%, indicating a decrease in its sealing properties. Also,
A gas crossover phenomenon was also observed after about 100 hours.

In addition, the battery performance is 150 m at the initial stage (after 30 hours).
A/ffl was 0.77V, but it decreased to 0.53V after 500 hours.

Example 2 In the same manner as in Example 1, a sealing material was molded using lithium hydroxide, sodium hydroxide, potassium hydroxide, and strontium hydroxide instead of barium hydroxide.
I conducted the same experiment. - As a result, the initial sealing rate was 99% or more on both the anode and cathode sides, indicating good sealing properties. Moreover, even after 500 hours, all of them exhibited sealing properties of about 99% or more.

Example 3 In the same manner as in Example 1, a sealing material was molded using lithium phosphate instead of barium hydroxide, and an experiment was conducted in the same manner as in Example 1.

Even after 500 hours, the sealing rate on the anode side was 99.
2%, and the sealing rate on the cathode side was 19.5%.

Example 4 A 5-cell stacked fuel cell of external manifold type was prototyped. Electrode area: 64 d, external dimensions: 70 m (vertical), 120 m (width)
, depth 120 on, and a sealing material having an outer dimension L 20 +Iln X 701 and a seal width 20 nrn was attached to the external manifold mounting surface of this battery, sandwiching it between the battery end and the manifold. The same sealing material as in Example 1 was used. In this way, an external manifold type battery was assembled.

The battery clamping pressure and the clamping pressure of the manifold mounting surface are each 2kg/r+(, 5'p/cd, and the temperature ranges from room temperature to 650℃.
The temperature rose to . In this case, nitrogen was flowed at 0.52/ffl1n from the oxidizer manifold and the fuel manifold. After the temperature reached 650°C, nitrogen, gas, and carbon dioxide gas were passed through at a flow rate of 5 u/mjn. below.

When the sealing properties were determined at 2111+ in the same manner as in Example 1, the sealing rate was 99.2% on the anode side and 98.9% on the cathode side, and no deterioration in the sealing properties was observed even after 500 hours.

〔Effect of the invention〕

According to the present invention, the respective advantages of the wet sealing method and the dry sealing method can be effectively exhibited, resulting in remarkable effects.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a battery structure according to an embodiment of the present invention, FIG. 2 is a top view of the middle part of the battery showing an internal manifold type battery structure, and FIG. 3 is a top view of the middle part of the battery showing an external manifold type structure. FIG.

Claims (1)

[Scope of Claims] 1. A pair of gas-diffusion porous electrodes spaced apart from each other and an electrolyte body holding an electrolyte disposed between the electrodes are connected to a chamber through which an oxidizing agent can flow and/or where a fuel can flow. In a stacked fuel cell formed by stacking a plurality of unit cells sandwiched by separators each having a chamber for circulation, a molten state is formed at a temperature below the cell operating temperature in the part that requires airtightness. A method for sealing a molten salt fuel cell, characterized by using a sealing material containing a material that later changes to a solid state. 2. A sealing method for a molten salt fuel cell according to claim 1, wherein the portion requiring airtightness is a peripheral end portion of the unit cell. 3. The method according to claim 1, wherein the part requiring an airtight body is a gas sealing part between the stacked fuel cell and the oxidizer and fuel manifold. How to seal batteries. 4. In the method according to claims 1 to 3, the material that changes to a solid state after forming a molten state below the battery operating temperature is a hydroxide of an alkali metal and/or an alkaline earth metal. 1. A method for sealing a molten salt fuel cell, characterized in that it is a molten salt fuel cell. 5. The method according to claim 4, wherein the hydroxide is any one or a mixture of hydroxides of lithium, sodium, potassium, rubidium, strontium, and barium. How to seal batteries. 6. In the method according to claims 1 to 3, the material that changes to a solid state after forming a molten state below the battery operating temperature is a precursor of lithium phosphate and polyphosphate. A method for sealing a molten salt fuel cell, characterized by: