JPS6161373A - Manufacture of separator for molten carbonate fuel cell - Google Patents

Abstract

PURPOSE:To obtain a compact, light cell having good corrosion resistant property by forming a protection film having good oxidizing corrosion resistant and reducing corrosion resistant properties on the surfaces of rib and outer frame. CONSTITUTION:Carbon steel, low alloy steel, stainless steel, chromium steel, or nickel base alloy steel is used as separator material. To make diffusion bonding, an intermediate material 8 is placed between an intermediate plate 6 and a rib 7, and they are heated at a temperature below the melting point of the intermediate plate 6, then pressed. A foil of the intermediate material is inserted between the intermediate plate 6 and rib 7, then they are processed for diffusion bonding. Thereby, a protection film having good oxidizing corrosion resistant and reducing corrosion resistant properties is formed on the surfaces of the rib and an outer frame. Therefore, a compact thin fuel cell having good corrosion resistant property can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a separator for a molten carbonate fuel cell, and particularly to a method for producing a separator for a molten carbonate fuel cell that is lightweight, has excellent corrosion resistance, and has a long life.

[Background of the invention]

In recent years, the development and research of energy-saving equipment has become important in response to the depletion of oil resources and soaring prices. One of these is a molten salt fuel cell that uses LNG and coal gas, which aims to save energy and replace oil, and is a thermal power generation technology that is part of new energy development.

FIG. 4 shows the basic structure of a molten carbonate fuel cell, which includes an electrolyte 1, an anode 2 and a cathode 3 as electrodes, a separator 4, an outer frame 9, and a gas supply pipe 10. A molten fuel cell is a fuel cell that uses an alkali metal carbonate such as lithium carbonate (Liz (03) or potassium carbonate (KzCOs) as an electrolyte and operates in a temperature range of 600 to 750C, which is above its melting point. By supplying hydrogen or a hydrogen-containing gas and supplying air as an oxidizing agent and carbon dioxide gas to the cathode, the electrochemical reaction shown in the following equation proceeds to generate electricity.

Anode (hydrogen electrode): 2 H2+ 2 C0va-→2C○2+2H20+4
e-・・・・・・・・・(1) Cathode (air electrode): 02+2C02+4e-→2CO32-・・・・・・
...(2)(1)+(2): 2Hz+Oz -2H
20... (8) The separator 4 serves to separate hydrogen combustion gas and oxidant gas, collect current, and also serve to hold the battery.

Although FIG. 4 shows the configuration of a single cell battery, in an actual device, a large number of batteries are stacked to increase the voltage and increase the capacity. FIG. 5 shows the basic structure of the separator 4 used in lamination. The separator 4 is a single plate with structures 5 for gas circulation provided on the front and back surfaces. The electrochemical reactions and gas atmospheres on the front and back surfaces are different, as shown in equations (1), (2), and (3) above. Therefore, the separator material is required to have excellent corrosive properties at 600 to 750 C and to both the atmosphere on the anode side (hydrogen-containing gas) and the atmosphere on the cathode side (oxidizing gas). Under such conditions, pure Ni and pure Cr can be considered as metal materials with excellent corrosion resistance, but these are expensive and rare metals, and are not suitable as materials for the separator 4 of batteries, which are used in large quantities. On the other hand, copper is promising in terms of corrosion resistance, but
Practical use is difficult because the high temperature strength at a temperature of 750C is low.

From the above points, stainless steel with high high temperature strength is conventionally used as a battery separator material.

However, general stainless steel has poor corrosion resistance such as pure Ni or pure C.
It was inferior in terms of quality, and it was unlikely that it would last until four years of periodic inspections.

On the other hand, in order to reduce the size and weight of the battery, the separator 4 preferably has the minimum necessary thickness, and preferably has a thickness of about 4 to 5 mm. However, it is difficult to machine the gas flow structure 5 with a depth of about 1+ nm on the front and back surfaces of stainless steel with a thickness of about 4 to 5 nm, and even if it is possible, it is difficult to machine. Later, the separator becomes warped due to processing, making it difficult to apply.

Therefore, conventionally, the thickness of the separator 4 is 10 mm.
At the same time, it was difficult to make the battery body smaller and lighter.

[Purpose of the invention]

The present invention has excellent corrosion resistance and a compact battery.

The present invention provides a method for manufacturing a separator for molten carbonate fuel cells that enables weight reduction.

[Summary of the Invention] The present invention provides ribs and outer parts made of the same material as above for forming gas flow passages and holding parts on one or both sides of an intermediate plate made of carbon (II), low alloy steel, Cr steel, or stainless steel. The molten carbonate fuel is characterized in that a separator for other uses is manufactured by joining the frames by diffusion bonding and then forming a protective film resistant to oxidative corrosion and reductive corrosion on these surfaces. It is.

[Embodiments of the invention]

FIG. 1 is a diagram illustrating the basic structure of a separator produced according to the present invention. The separator 4 consists of an intermediate plate 6 and ribs 7 arranged and fixed at appropriate intervals on the front and back surfaces of the intermediate plate 60, thereby forming grooves for gas circulation on the front and back sides. The intermediate plate 6 and the rib 7 are joined by diffusion bonding. Carbon steel, low alloy steel, stainless steel as separator materials.

Cr tf4+N' base alloy steel or the like is used.

To perform the above diffusion bonding, as shown in FIG. 2, an intermediate material 8 is applied between the intermediate plate 6 and the rib 7, and these
The materials are heated to a temperature below their melting point, and compressive stress is applied to the bonding surfaces so that the load is evenly applied to the joint surface. The intermediate material 8 is, for example, Ni-P (Ni: 90-99%, P: 1-10%) or Ni-B (Ni: 90-99%, B2 1-10%).
is desirable. Ni-P and Ni-B have a melting temperature of 980
C and 1400C, which is lower than the temperature of general structural steel. As shown in FIG. 2, when the intermediate material 8 is sandwiched and heated to a high temperature and compressive stress is applied, the intermediate material diffuses and migrates toward the base material (intermediate plate 6 and ribs 7). Furthermore, as time passes, the diffusion progresses,
Finally, the intermediate plate 6 and the rib 7 are completely joined. The time required for joining becomes shorter as the temperature approaches the melting temperature of the intermediate material. The heating temperature is approximately 300° below the melting point.
A range below C is desirable.

In order to heat the material to a high temperature, the atmosphere in the diffusion treatment step is preferably a non-oxidizing atmosphere from the viewpoint of preventing oxidation of the material.

As the intermediate material 8, it is preferable to use a material in which Ni--P or Ni--B, which is the component described above, is formed into a foil shape. Or Cr with Ni as the main component.

A crystalline or amorphous foil material containing elements such as Fe, Si, P+B, Mo, and Co, singly or in combination, is preferable. Bonding is achieved by inserting the foil-shaped intermediate material 8 between the intermediate plate 6 and the ribs 7, and then performing the diffusion bonding process described above. The thickness of the foil is preferably 1 mm or less, particularly preferably 20 μm or less.

In addition, before inserting the foil-shaped material as the intermediate material 8, the surfaces of the intermediate plate 6 and ribs 7 are plated with Ni-P and Ni-B, which are the components mentioned above. Good too. That is, a Ni-P or Ni-B plating film is formed on both or one of the surfaces of the intermediate plate 6 and the ribs 7 in advance, and then the intermediate plate 6 and the ribs 7 are bonded through the plating film in the same manner as described above. Diffusion bonding is performed. The thickness of the plating film is preferably 1 run or less, particularly preferably 20 μm or less. If the thickness of the plating film is too thick, it is not preferable because not only will the diffusion treatment be delayed for a long time, but also the high temperature strength of the joint will be reduced.

Separators are solution-treated after diffusion bonding.

When quenching treatment or standard treatment is performed, the elements of the intermediate material 8 of the diffusion bonding portion further migrate to the base material side because the temperature is maintained at a high temperature. Therefore, the joint is close to the base metal composition.
Joint performance will further improve.

FIG. 3 shows details of the structure of the separator of the present invention in which the intermediate plate and ribs integrated as described above are assembled together with the outer frame. An outer frame 9 with a gas feed pipe 10 surrounds the integrated intermediate plate 6 and ribs 7 shown in FIGS. 1 and 2.

The outer frame 9 has the role of holding the separator and preventing gas from leaking out of the battery. The thickness of the outer frame 9 is thicker than the thickness of the ribs 7 by the thickness of the electrodes mounted on the ribs 7. The intermediate plate 6 and the outer frame 9 are joined by a method similar to the diffusion bonding method for the intermediate plate 6 and the ribs 7 described above.

The gas feed pipe 10 is joined to the outer frame 9 using a joining method such as welding.

In addition, according to the present invention, the separator can be manufactured not only in a square shape as shown in FIG. 3 but also in a circular shape.

FIG. 6 shows a modification of the shape of the rib 7. That is, in the present invention, the ribs 7 of the separator are not only rectangular as shown in FIGS. It may be a rectangular parallelepiped (C). Furthermore, in addition to this, a circular stand or a cylindrical shape may be used.

After the intermediate plate 6 and the ribs 7 and the intermediate plate 6 and the outer frame 9 are diffusion bonded, as shown in FIG. 7, in order to improve the oxidation resistance and reduction corrosion resistance of the separator. Preferably, a protective film 11 is formed on the entire surface or inner surface of the separator. The protective film 11 is made of Ni, Cu+ Crr Co,
It is applied by Ag, Pa, etc., electroplating, chemical plating, etc. Note that the components of the protective film 11 may be Ni or Cr as long as they have excellent oxidation resistance and reduction corrosion resistance.

There is no problem even if other components are contained in addition to pure metals such as Cu, Pa, and Go. Further, the protective film 11 is not limited to a single layer, and may be formed by laminating a plurality of layers. Moreover, the components of the plurality of layers may be the same component or each layer may be a different component. If the protective film 11 is provided, the intermediate plate 6, ribs 7, and outer frame 11 of the separator can be made of inexpensive carbon steel or low alloy material because the protective film 11 has excellent oxidation resistance and reduction corrosion resistance. Application of steel, Cr steel, etc. becomes possible.

Specific examples based on the above description will be described below.

Example 1 Table 1 shows the chemical composition of the test materials used in the experiment.

12Cr heat-resistant steel was used as the test material.

1 υ test pieces were taken from the test materials shown in Table 1. The shape of the test piece is a cylinder with a diameter of 20 pieces and a length of 50 pieces. The entire surface of the test piece was finished with paper cutter No. 800. Using a commercially available electroless plating solution on the entire surface of such a test piece, Ni-P and Ni
-B plating was applied.

The plating thickness was 20 μm in both cases.

Next, using the above-mentioned plated test pieces, test pieces coated with the same type of plating material were longitudinally butted against each other to perform diffusion bonding. The heating conditions for diffusion bonding were as follows: Ni-P plated test piece was held at 800C for 4 hours, and Ni-B Metsugi test piece was heated at 1150C and held for 4 hours. The compression pressure during heating was set to 9:1000 in both cases. The atmosphere during diffusion bonding was an atmospheric environment.

After the above diffusion bonding, the test piece was heat treated.

The heat treatment was performed under the conditions of quenching: 1100C, held for 2 hours, then air cooled, and tempering: 650C, held for 2 hours, then air cooled.

Next, a tensile test piece was taken from the above test piece after heat treatment. The shape of the test piece was such that the joint was placed in the center of the parallel part, the diameter of the parallel part was 6φ, and the length of the parallel part was 24 mm.

Table 2 shows the tensile strength of the base material and the N i-P and Ni-B bonding materials. Both Nt-P and Ni-B joint materials have tensile strength comparable to that of the base metal.
It is clear that it exhibits excellent bonding performance.

Table 2 In particular, the tensile stress generated in the separator of an actual fuel cell is I
Since it is considered that the OK ratio is 7 to 2 or less, the above-mentioned diffusion bonding portion sufficiently satisfies this value.

Example 2 Next, the results of oxidative and reductive corrosion tests in the case where a surface protective film as described above was formed will be described.

The 12Cr steel shown in Table 1 was used as the base material of this example material. The shape of the corrosion test piece was 4 mm thick, 15 mm wide, and 25 mm long. Commercially available N was used for surface treatment (protective film 11).
Cr and Cu plating was performed by electroless Nl plating and electroplating using i-P and N5-B plating solutions.

On the other hand, commercially available SUS without surface treatment was used as a comparison material.
304°5US316. Inconel 625 and 12Cr steel shown in Table 1 were used.

The corrosion test was conducted by simulating the corrosive environment of the separator of an actual molten carbonate fuel cell. The test was conducted using test piece KL in advance.
1zco3: was coated with molten carbonate at a ratio of 2CO3 = 62:38 (7), and 6
It was carried out at 50C and held for 100 hours. Corrosion was evaluated based on the weight increase of the test piece after the corrosion test.

(Oxidizing atmosphere) Air: C02 = 70: 30 (Reducing atmosphere) H2: C02 = 80: 20 (Water vapor was mixed and fed at 1QQce for 1 hour) Figure 8 shows the results of a corrosion test under a reducing atmosphere. .

Comparative materials SUS 304, 5US316 and 1
Is the corrosion weight increase of 2Cr steel 1.5 to 2.2 Tn? /c
It is rIK. Corrosion increase of Inconel 625 is o, 2s
+rq/cni, and the reduction corrosion resistance was the best among the comparative materials. On the other hand, the material of this example with various protective films 11 formed on the surface has a corrosion resistance of approximately 0.1"i/crtl, which is significantly lower than that of the comparative material. In particular, when comparing the corrosion weight increase in the case of 12Cr steel, The example material of the present invention was 22
It is clear that it is twice as low.

FIG. 9 shows the results of a corrosion test in an oxidizing atmosphere. The corrosion weight increase is 0.7 to λ4 my/ctd in the comparative example, whereas it is 0.1 to 0.2 rrq in the example of the present invention.
/c! In d and a), it is clear that the example materials of the present invention have excellent corrosion resistance even in an oxidizing atmosphere.

Note that the method for forming the protective film 11 may also be applied to separators that are a single unit, in which the intermediate plate 6, ribs 7, and outer frame 9 are not configured separately, as shown in FIGS. 3 to 6. do not have.

〔Effect of the invention〕

As described above, according to the present invention, a separator for a molten carbonate fuel cell that does not require machining, is thin, inexpensive, and has excellent corrosion resistance can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of a separator according to an embodiment of the present invention, Fig. 2 is a partial side view showing its joining mode, Fig. 3 is a perspective view of the separator assembled with an outer frame, and Fig. 4 is a simple An exploded configuration diagram of a conventional molten carbonate fuel cell, Figure 5 is a diagram showing the main parts of a conventional stacked type molten carbonate fuel cell, and Figures 6 (a), (b), and (C) are from this book. A perspective view showing another example of ribs of a separator according to the invention, FIG. 7 is a partial cross-sectional view of a separator provided with a protective film according to the invention, FIG. 8 is a corrosion test result under a reducing atmosphere, and FIG. 9 FIG. 2 is a diagram showing the results of a corrosion test under an oxidizing atmosphere. 6... Intermediate plate, 7... Rib, 8... Intermediate material, 9...
... Outer frame, 10... Gas supply pipe. Patent applicant: Director of the Agency of Industrial Science and Technology Hirobe Yoda 1 Figure S Figure 6 (ko) Part rll Part G Solid material

Claims (1)

[Claims] 1. An intermediate plate made of carbon steel, low alloy steel, Cr steel, or stainless steel has ribs and an outer frame made of the same material as above for forming gas flow passages and holding parts on one or both sides of the intermediate plate. A method for producing a separator for a molten carbonate fuel cell, which comprises bonding by diffusion bonding, and then forming a protective film resistant to oxidative corrosion and reductive corrosion on these surfaces. 2. Diffusion bonding involves applying Ni-P or Ni-B plating to the joint surfaces of the intermediate plate, ribs, and outer frame in advance, and applying compressive stress to the joint while heating and maintaining the plated material below the melting temperature. A method for producing a separator for a molten carbonate fuel cell according to claim 1, comprising: 3. Diffusion bonding is performed in advance by applying Ni as the main component to the bonding surfaces of the intermediate plate, ribs, and outer frame, as well as other materials such as Cr, Fe, Si, P,
A patent that involves inserting a crystalline or amorphous foil material containing elements such as B, Mo, Co, etc. singly or in combination, and applying compressive stress to the joint while heating and maintaining the foil material below its melting temperature. A method for producing a separator for a molten carbonate fuel cell according to claim 1. 4. After diffusion bonding of the intermediate plate, ribs, and outer frame, solution treatment, quenching, or tempering treatment is performed in claim 1.
A method for producing a separator for a molten carbonate fuel cell according to item 1, 2 or 3. 5. The melt according to any one of claims 1 to 4, wherein the shape of the rib is a rectangular parallelepiped, a cube, a rectangular pedestal, a cylinder, a circular pedestal, or a rectangular parallelepiped with a corrugated upper part. Method for manufacturing separators for carbonate fuel cells. 6. The main components of the protective film are Ni-P, Ni-B, Cr, and Ni.
, Cu, Ag, or Pa, the method for producing a separator for a molten carbonate fuel cell according to any one of claims 1 to 5.