JPH0790440A - Metallic material for fused carbonate type fuel cell - Google Patents

Abstract

PURPOSE:To obtain a material suitable to separator used for fused carbonate type fuel cell by obtaining optimum materials as a cathode side metal and an anode side metal having specified chemical components, respectively, and cladding both materials. CONSTITUTION:The cathode side material for fused carbonate type fuel cell is composed, by wt., <=0.05% C, <=2% Si, <=2% Mn, 15-35% Cr, 1-7% Al, <=3% Ti, and the balance substantially Ni. The anode side material is composed of, by wt., <=0.05% C, <=2% Si, <=2% Mn, <=0.1% Cr, 1-7% Al, <=3% Ti and the balance substantially Ni. Both materials are clad in direct or through the other metal. By this constitution, the material for separator simultaneously satisfying plural conditions opposite with each other, such as acid resistance, reducing resistance and corrosion resistance, is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal material which can be used as a separator, a mask material and an electrode material of a molten carbonate fuel cell developed as a second generation type.
In addition to 1, Ni, Ti, Si, Mn, etc. are contained in the specific composition of the high Cr content Ni-base alloy for the cathode and C
clad with the Ni-based alloy for the anode side excluding r,
The present invention relates to a molten carbonate fuel cell metal material satisfying both reduction resistance and corrosion resistance.

[0002]

2. Description of the Related Art In recent years, as the demand for energy has increased, the amount of electric power consumption has also increased, and the current power generation system is no longer able to cover the demand. Development of new power generation systems is expected. . Fuel cells, which are new power generation systems, include phosphoric acid type (PAFC) that uses an aqueous phosphoric acid solution as an electrolyte, solid electrolyte type (SOFC) that uses zirconia-based ceramics as an electrolyte, and lithium carbonate, potassium carbonate as an electrolyte. Molten carbonate type (MC
FC).

Here, a molten carbonate fuel cell (hereinafter referred to as MC
The principle and basic structure will be briefly described by taking FC as an example. As shown in FIG. 3, the MCFC has a structure in which both sides of an electrolyte plate 1 in which a molten carbonate of an alkali metal and / or an alkaline earth metal is impregnated with a porous material such as lithium aluminate as an electrolyte is used as a fuel electrode ( A single cell 4 is sandwiched between an anode 2 and an air electrode (cathode) 3, and further, the single cell 4 is laminated in multiple layers via a separator 5 in order to obtain practical power, and the separator 5 and the fuel are combined. The passage space 6 formed between the electrodes (anode) 2 is supplied with H ₂ and CO serving as fuel, and the passage space 7 formed between the separator 5 and the air electrode (cathode) 3.
Basically, it is configured to be supplied with air.

The principle of power generation is as follows: (1) When H ₂ and CO are supplied to the fuel chamber, H _{2 that} has entered the fuel chamber is the anode and the CO ₃ in the electrolyte is caused by the reaction of formula 1.
Reacts with ^2- to produce H ₂ O and CO ₂ and releases e ⁻ . ^{_{H 2+ CO 3 2- → H 2}} O + CO 2 + 2e - 1 Equation (2) e ^- back to the cathode through an external load, power generation is performed. (3) CO in the fuel reacts with H ₂ O according to the equation 2 to generate H ₂
And CO ₂ are produced. The generated H ₂ and CO ₂ are effectively used. CO + H ₂ O → H ₂₊ CO ₂ 2 formula (4) O _{2 in the} air chamber and the recycled CO ₂ of formula 1 and formula ₂ are CO ₃ ^2- by the reaction of formula 3 at the cathode.
To produce CO ₃ ²⁻ in the electrolyte. _{1 / 2O 2 + CO 2 +} 2e - → CO 3 2- 3 Formula Incidentally, two equations and effective use of H ₂ O generated in one set, C
It is used to supplement the utilization rate of the three formulas of O ₂ . The above reaction is
When a pair of electrodes is inserted into water with electrolyte dissolved and an electric current is applied, hydrogen is generated on the surface of one electrode and oxygen is generated on the surface of the other electrode. It can be said that it is an application.

Now, in the above-mentioned MCFC configuration,
The presence of a separator is particularly important. Since the separator is required to have corrosion resistance against carbonates,
As the material, for example, stainless steel such as SUS310 series, or stainless steel with Ni clad to improve corrosion resistance on the anode side is generally used. The specific role of the separator is to partition the single cells when stacking the single cells, to form a supply path of O ₂ or CO ₂ for replenishing H ₂ and CO ₃ ^{2− serving} as fuel, and a fuel. It has a function of blocking H ₂ and O ₂ and CO ₂ which become the other, and also plays a role of holding the electrolyte plate.

In order to hold the electrolyte plate, by making the area of the electrolyte plate larger than the areas of the fuel electrode and the air electrode in advance, it becomes possible to easily stack with the separator.
The electrolyte plate can be held. At that time, the electrolyte plate also serves to insulate the separators from each other, but significant corrosion may occur at a portion where the separator comes into direct contact with the molten carbonate (hereinafter referred to as a mask portion, see reference numerals 8 and 9 in FIG. 3). It's a problem. The cause of this corrosion is that H ₂ of the fuel and H ₂ O, which is a reaction product, on the fuel electrode side, and O ₂ and recycled CO ₂ on the air electrode side, respectively, in the plane direction in the electrolyte. This is due to the generation of local batteries at the edges of the electrolyte plate.

With respect to the problem of the local battery generation, there is no means for solving it at this stage. Therefore, conventionally, a separator is directly contacted with molten carbonate, that is, the mask portions 8 and 9 of the separator 5 shown in FIG. 3 are aluminized. It was treated to prevent corrosion of the mask. As the aluminizing treatment, the aluminum intermetallic compound and aluminum oxide (alumina), which are hardly corroded by molten carbonate at high temperature, are sprayed,
A coating method such as a dipping method or a hot dipping method is adopted.

[0008]

In the environment encountered by MCFCs, metallic materials are exposed to more severe conditions due to thermal fatigue in addition to oxidation, hydrogen embrittlement or mixed salt corrosion. A Ni—Al alloy film containing a Ni ₃ Al phase is expected to be applied to a fuel cell due to its excellent high temperature characteristics, and is currently prepared by a thermal spraying or plating method.
However, the current method has problems such as poor adhesion to the base and many pores, and insufficient corrosion resistance. Further, if it is attempted to satisfy the contradictory conditions of acid resistance and reduction resistance and corrosion resistance at the same time, there is a risk that the alloy will become highly alloyed and become a difficult-to-process material, resulting in an expensive material.

In view of the fact that there is no metallic material excellent in corrosion resistance against molten carbonate in the known art, the present invention is
An object of the present invention is to provide a metal material for a molten carbonate fuel cell, which is configured to have the characteristics of the above-mentioned separator, mask material, and metal material for the cathode side as the electrode material or the optimum material as the metal material for the anode side.

[0010]

In order to solve the problem that there is no metallic material excellent in corrosion resistance against molten carbonate, the present invention adds Al or Al and Ti to a Ni-based alloy,
It has been found that the corrosion resistance to molten carbonate is improved by having an intermetallic compound, and therefore, Ni-based alloy further contains Al, Ti, Si, Mn, etc., and has high temperature characteristics suitable for use environment. A member for separating the intermetallic compound uniformly and further separating the oxidizing and reducing atmospheres, that is, by clad Ni-based alloys having different high temperature characteristics for the separator material,
The present inventors have completed the present invention by finding that a material satisfying the contradictory conditions of acid resistance and reduction resistance and corrosion resistance can be obtained at the same time.

That is, the present invention provides C 0.05 wt.
% Or less, Si 2 wt% or less, Mn 2 wt% or less, C
r 15-35 wt%, Al 1-7 wt%, Ti 3
It is a metal material for the cathode side for a molten carbonate fuel cell, which contains less than wt% and the balance is Ni and inevitable impurities. In addition, this invention is C 0.05 wt% or less, Si 2 wt% or less, Mn 2 wt% or less, Cr
0.1wt% or less, Al 1-7wt%, Ti 3wt
% Or less, and the balance being Ni and unavoidable impurities, which is a metal material for the anode side for a molten carbonate fuel cell.

Furthermore, the present invention provides C 0.05 wt%
Below, Si 2 wt% or less, Mn 2 wt% or less, Cr
15-35 wt%, Al 1-7 wt%, Ti 3w
a metal material for the cathode side containing t% or less and the balance being Ni and unavoidable impurities, C 0.05 wt% or less, Si 2 wt% or less, Mn 2 wt% or less, Cr
0.1wt% or less, Al 1-7wt%, Ti 3wt
% Or less, with the balance being Ni and unavoidable impurities, the metal material for the anode side is a direct or other metal,
We also propose a metal material for molten carbonate fuel cells that is clad with an alloy material interposed.

The reasons for limiting the composition of the metal material for the cathode side of the present invention will be described. When C is contained in excess of 0.05%, it forms chromium carbide and reduces the oxidation resistance, so the content is made 0.05% or less. It also binds to Ti and reduces the amount of effective Ti. Si has the effect of improving corrosion resistance and oxidation resistance, but if present in excess, it destabilizes the austenite structure and impairs hot workability, so it is 2%.
Below. Mn is an austenite-forming element and also has an effect of improving hot workability, but it is preferable that it is small because it slightly deteriorates the oxidation resistance. It may be contained in ordinary stainless steel and may be 2% or less. And Cr is a basic component of oxidation resistance and requires a minimum content of 15%. However, even if added in excess of 35%, the effect is saturated and the corrosion resistance to molten carbonate deteriorates. 35 wt%. Al is a basic component for forming an intermetallic compound, and it is necessary to contain Al in a minimum amount of 1%. However, if it is added in excess of 7%, the workability deteriorates, so it is set to 1 to 7%. Further, the alloy of the present invention is not based on iron because the workability is deteriorated when the iron-Cr alloy contains a few% of Al and the cost is increased. Ti is a basic component for forming an intermetallic compound together with Al. This alloy has a high Al concentration, and
Generation of N is suppressed. However, the effect is saturated even if added in excess of 3%, so the content is made 3% or less. Ni is a component that forms the basis of the metal material of the present invention, and occupies the remaining content of the above various components.

The reasons for limiting the composition of the metal material for the anode side of the present invention will be described. When C exceeds 0.05%, it binds to Ti and reduces the amount of effective Ti. S
i, Mn, Al and Ti are for the same reason as the metal material on the cathode side. Further, if Cr is contained, the reduction resistance deteriorates, so the content is made 0.1% or less.

[0015]

The present invention improves the corrosion resistance to molten carbonate by adding Al or Al and Ti to a Ni-based alloy as a metal material having excellent corrosion resistance to molten carbonate and improving the corrosion resistance to molten carbonate by having an intermetallic compound. Strength is also improved, and further, a predetermined amount of Cr is added to improve the corrosion resistance against the oxidizing atmosphere by the molten carbonate, and Ti, Si,
By containing Mn and the like and imparting high temperature characteristics suitable for the use environment, optimum characteristics as a cathode side metal material are obtained. Further, in order to satisfy the reduction resistance as the metal material on the anode side, the above-mentioned Al containing no Cr or the Ni-based alloy to which Al and Ti are added is optimal. The above-mentioned cathode-side or anode-side metal material is most suitable not only as a mask material, but also as a cathode-side or anode-side electrode material by powder metallurgical production of the alloy. Furthermore, as a conventional separator material, N
Although the i / austenitic stainless clad material and the Ni-plated austenitic stainless are used, satisfactory results have not been obtained in terms of corrosion resistance and high temperature strength.
By clad with a base alloy, the contradictory conditions of acid resistance and reduction resistance and corrosion resistance against molten carbonate are satisfied at the same time, the manufacturability of each metal material is good, and the cladding and workability of both materials are good. Most suitable as a separator material.

[0016]

【Example】

Example 1 Table 1 shows the chemical compositions of samples of the material of the present invention and a comparative material prepared for demonstrating the effect of the present invention. In the corrosion test, Li ₂ CO ₃ : K ₂ CO ₃ = 62: 38 (molar ratio) was used as a carbonate, and the carbonate was melted at a temperature of 680 ° C.
It is applied to the sample alloy, and as the atmosphere gas, air (Sample N
o. 1, 4, 5) or H ₂ gas (Samples 2, 3) were used and tested for 200 hours. The results are shown in FIG. 1, and the relationship between the test time on the horizontal axis and the thickness reduction due to corrosion on the vertical axis is shown. The reduced thickness of the material of the present invention is reduced to about 5 μm or less, showing that the corrosion resistance is significantly improved. Figure 2
Inventive material No. 1 shows the age hardening characteristic of 1. 650
The hardness is maximum at 700 ° C., and it is understood that it is suitable as a metal material for molten carbonate fuel cells from the viewpoint of mechanical properties.

[0017]

[Table 1]

[0018]

As a separator material, if it is attempted to simultaneously satisfy the contradictory conditions of acid resistance and reduction resistance and the corrosion resistance to molten carbonate, it becomes a highly alloyed material which becomes a difficult-to-process material and an expensive material. Ni / austenitic stainless clad materials and Ni-plated austenitic stainless steels have not provided satisfactory results in terms of corrosion resistance and high temperature strength. However, including Al according to the present invention, T
Cladding a Ni-based alloy having a high temperature characteristic of a high-Cr-containing Ni-based alloy containing i, Si, Mn, etc. for the cathode side and a Ni-based alloy for the anode side with Cr removed therefrom. In addition, the contradictory conditions of acid resistance and reduction resistance and corrosion resistance are satisfied at the same time, the manufacturability of each metal material is good, and the cladability and workability of both materials are good, which makes it an optimal separator material. In addition, the improved corrosion resistance of the material can be expected to extend the life of the fuel cell, eliminating the need for conventional aluminizing treatment on the mask,
Batteries can be provided at low cost.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between test time and thickness reduction.

FIG. 2 is a graph showing the relationship between aging temperature and hardness.

FIG. 3 is an explanatory view showing a laminated structure of a molten carbonate fuel cell.

[Explanation of symbols]

 1 Electrolyte plate 2 Fuel electrode 3 Air electrode 4 Single cell 5 Separator 6,7 Passage space 8,9 Mask part

Claims (3)

[Claims] 1. C 0.05 wt% or less, Si 2 wt
% Or less, Mn 2 wt% or less, Cr 15 to 35 wt
%, Al 1 to 7 wt%, Ti 3 wt% or less, and the balance being Ni and inevitable impurities, the cathode side metal material for a molten carbonate fuel cell. 2. C: 0.05 wt% or less, Si: 2 wt
%, Mn 2 wt% or less, Cr 0.1 wt% or less, Al 1 to 7 wt%, Ti 3 wt% or less, and the balance consisting of Ni and unavoidable impurities, the anode side metal for a molten carbonate fuel cell. material. 3. C 0.05 wt% or less, Si 2 wt
% Or less, Mn 2 wt% or less, Cr 15 to 35 wt
%, Al 1 to 7 wt%, Ti 3 wt% or less, and the balance of Ni and inevitable impurities for the cathode side metal material, C 0.05 wt% or less, Si 2w
t% or less, Mn 2 wt% or less, Cr 0.1 wt% or less, Al 1 to 7 wt%, Ti 3 wt% or less, the balance being Ni and unavoidable impurities, and the anode side metal material, directly or other A metal material for a molten carbonate fuel cell, which is clad with a metal or alloy material interposed.