JPH0413825B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an electrode material for molten carbonate fuel cells that has excellent electrode performance and corrosion resistance. [Prior Art] Molten carbonate fuel cells, which are second-generation fuel cells, have the advantages of high energy conversion efficiency, no pollution, and no need for expensive catalysts. Therefore, it is seen as a promising next-generation centralized power source or distributed power source, and a 1kW scale battery stack is currently being developed. Among these efforts, progress is being made in particular in the development of stacking technology, studies on increasing the size of batteries, and development of battery constituent materials including electrodes. These technologies are interrelated, and when one problem is solved, the next problem will be brought to the fore. However, one major problem at present is the molten carbonate type. Development of electrode materials, especially cathode materials, for fuel cells. [Problems to be Solved by the Invention] Currently, NiO is used as a cathode material because of its excellent corrosion resistance and electrode performance. However, this NiO cathode dissolves during battery use and precipitates as Ni in the electrolyte, which grows and short-circuits between the electrodes, shortening the battery life. Moreover, Ni is expensive, which, together with the problem of battery life mentioned above, causes an increase in power generation costs. There is also active research into using various oxides other than NiO as cathode materials, and there are reports that composite oxides such as perovskites are promising. However, such oxide electrodes still have insufficient strength, so
There is a question of whether it can withstand scale-up. The present invention was developed as a result of further studies on a wide variety of materials in view of the above-mentioned problems, and its purpose is to provide an electrode material for molten carbonate fuel cells that has excellent electrode performance and corrosion resistance. It is something to do. [Means for solving the problems] The electrode material of the present invention that can solve the above problems is Cr: 2 to 18% (meaning of weight %, the same applies hereinafter), Al: 1 to 10%, balance , Fe, and unavoidable impurities, and Si, Ni, and Si and Ni may be added as desired. [Function] The characteristics required for electrode materials are (1) excellent corrosion resistance (less dissolution from the cathode, less precipitation of dissolved components), (2) good electrical conductivity of the electrode. , (3) high mechanical strength, and (4) good moldability. As a result of examining various materials with a focus on satisfying these characteristics in general, and particularly satisfying characteristics (1) and (2), we have discovered an iron-based alloy consisting of the chemical components described below. They discovered that using these materials as electrode materials results in electrode materials with excellent electrode performance and corrosion resistance, and completed the present invention. Next, we will discuss the effects of the addition of each component on improving the corrosion resistance of iron-based alloys in a molten carbonate environment (see Sections 1 to 4 below).
The reasons for limiting the alloy composition of the iron-based alloy according to the present invention will be described with reference to Table 1. Cr: 2-18% The corrosion resistance of Fe-Cr alloys improves as the Cr content increases (see Table 1). Japanese Patent Publication No. 58-155662
It is also disclosed that ferrochrome (Cr content: 55-70%) is excellent as an electrode. However, there is a problem that the amount of Cr in the publication is extremely large, and the present inventors believe that if an appropriate amount of Al is added to this, sufficient corrosion resistance can be achieved even with the addition of Cr of 18% or less, or even 10% or less. They found that (see Table 4). It was found that when the Cr content exceeded 18%, corrosion resistance in a molten carbonate bath tended to deteriorate slightly, so it was set to 18% or less. Also, Cr
When added alone, corrosion resistance is insufficient even at 5%, but
Since corrosion resistance is exhibited even with a small amount of Cr due to the coexistence of Al and Si, the lower limit was set at 2% (see Table 4). Al: 1-10% Al is a main element for forming an alumina film, but corrosion resistance is better when added in a relatively small amount. 14
%, the corrosion resistance at the molten salt bath interface deteriorates, so the upper limit was set at 10% (see Table 2). however,
Since it cannot be said that the corrosion resistance of the interface could be sufficiently improved by adding Cr alone, we decided to add it in combination with Cr. Furthermore, since the effect is not obvious when less than 1% is added, the lower limit was set at 1%. Si: 2-20% Si has the effect of improving corrosion resistance in the gas phase of a molten carbonate environment (see Table 3). However, if it exceeds 20%, the effect disappears, so it was set below 20%. However, like Al, adding it alone does not provide sufficient corrosion resistance in the molten carbonate bath and at the interface, so it was added in combination with Cr and Al. In addition, since the effect is not clear when adding less than 2%, the lower limit is set at 2%.
%. Ni: 7 to 20% Ni is basically an undesirable element because it precipitates near the anode as corrosion progresses and shortens battery life. In order to improve the activity, it was decided to add 7 to 20% in combination with Cr and Al or in combination with Cr, Al, and Si (see Table 4). If less than 7% is added, the mechanical properties cannot be improved, and the contribution effect to the improvement of mechanical properties is
Since saturation occurs at 20%, the upper limit was set at 20%.

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[Table] [Example] An electrode was prepared from an electrode material having an alloy composition shown in Table 5, a molten carbonate fuel cell was prepared using the electrode, and the electrode performance was tested. The electrode itself is
The electrode material (iron alloy) is a powder of 50 μm or less,
When sintered at 1100° C. in a hydrogen gas atmosphere, a porous body with a bulk density of 3.5 g/cm ³ was formed, and this porous body was used as a skeleton to form an oxide film on its surface. The oxide film is mainly composed of alumina, which has excellent corrosion resistance, and is doped with Li and K, so it has good electrical conductivity.
The results are shown in Table 5. A comparison example using conventional NiO is also shown.

[Table] As is clear from Table 5, the electrode performance [OCV ^*1 (V)] of the electrode using the electrode material according to the present invention is almost inferior to that of the comparative example using NiO. I can see that there isn't. Moreover, the corrosion resistance (see Table 4) and moldability were good, the mechanical strength after molding was high, and the material cost was low. [Effects of the Invention] As described above, according to the present invention, an electrode material for a carbonate fuel cell that has excellent electrode performance and corrosion resistance and is low in cost can be obtained.

Claims (1)

[Claims] 1 Cr: 2 to 18% (meaning by weight, the same applies hereinafter) Al: 1 to 10% The balance is a molten carbonate type with excellent corrosion resistance, consisting of Fe and inevitable impurities. Electrode material for fuel cells. 2 Cr: 2-18% Al: 1-10% Si: 2-20% The balance is Fe and unavoidable impurities. An electrode material for a molten carbonate fuel cell having excellent corrosion resistance. 3 Cr: 2-18% Al: 1-10% Ni: 7-20% The balance is Fe and inevitable impurities. An electrode material for a molten carbonate fuel cell having excellent corrosion resistance. 4 Cr: 2-18% Al: 1-10% Si: 2-20% Ni: 7-20% The balance is Fe and unavoidable impurities for use in molten carbonate fuel cells with excellent corrosion resistance. electrode material.