JPH02291666A - Molten carbonate type fuel cell - Google Patents

Abstract

PURPOSE:To enhance the maintenability of electrolyte within an electrode by letting a reforming material be carried by the particle surface of a base material, letting a cathode porous electrode be furnished with a specified specific surface area, letting each primary pore be a specified fine pore in size, letting each secondary pore size be furnished with a specified pore distribution, and thereby increasing the surface area of the electrode. CONSTITUTION:The second component excellent in resistance to molten carbonate is added so that the surface roughness of particles is increased to a great extent. It is so constituted that a cathode porous electrode is furnished with the specific surface area of 1 to 100m<2>/g, each primary pore shall be the fine pore of 0.01 to 2mum in size, and each secondary pore size shall be furnished with the pore size distribution of 2 to 20mum. Since electrolyte is mainly held by primary pores, electrolyte is well held within the electrode. In addition, the porosity of a porous cathode shall be 50 to 60%, and furthermore, the electrolyte included in the porous cathode shall be 20 to 40% of the whole of holes by volume.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to molten carbonate fuel cells.

(Prior Art) JP-A-55-74065 states that stable performance can be obtained by adding a stabilizer in the form of an oxide or an alkali metal salt to an anode made of nickel, cobalt or a mixture thereof. Also, JP-A-62-826
No. 50 specifies that a cathode formed from nickel powder coated with silver as a raw material has a porosity of 60 to 80% and an average pore diameter of 2 to 20 μm, and that stable battery characteristics can be obtained.

[Problem to be solved by the invention]

Conventional cathodes have a specific surface area of about 0.7 rrf/g, but this does not provide a sufficient surface area for active electrode reactions to proceed. Therefore, the first object of the present invention is to significantly increase the electrode surface area.

Further, in the conventional cathode, the amount of electrolyte held in the electrode pores tends to decrease, and as the amount decreases, the electrode characteristics deteriorate. There is a known example (Japanese Unexamined Patent Publication No. 62-82650) in which the structure is regulated to obtain high performance.
There are no examples in which clear consideration has been given to controlling the state of electrolyte retention. Therefore, the second objective is to improve the pore structure in order to improve electrolyte retention.

In general, attempts have been made to use minute particles as a raw material base material in order to achieve a high specific surface area, but since the process of forming electrodes through reduction sintering is used,
There was a problem in that the raw material particles caused sintering among themselves, resulting in a significant decrease in the specific surface area. Therefore, the third aspect of the present invention
The purpose of this is to suppress the decrease in specific surface area during reduction sintering.

To summarize the above points, the objects of the present invention are: (1) to significantly increase the electrode surface area; (2) to improve electrolyte retention in the electrode; and (2) to suppress a decrease in the specific surface area during reduction sintering.

(Means for solving the problem) The purpose of the above item (2) is to add (carry) a second component that improves the surface area and has excellent molten carbonate resistance to the base material particles to improve the surface roughness and smoothness of the particles. By supporting a surface modifier, the specific surface area can be increased from about 0.7 rrr/g to about 100 times the conventional base material particle specific surface area.

The objective (2) can also be solved by carrying a modifying material on the surface of the base material particles to increase the surface roughness and smoothness in the same manner as above. Due to the supporting effect, fine pores of 0.01 to 2 μm are formed on the particle surface. The smaller the pore diameter, the greater the ability to hold the electrolyte, so the electrolyte can be fixed in the fine pores, reducing fluctuations in the amount of electrolyte.

The purpose of (2) is to carry the above-mentioned surface modifier to strengthen the parts of the base material particles that are prone to sintering and/or creep, or to diffuse them into the grains to reduce particle deformation and specific surface area. can be suppressed.

Therefore, the characteristics of the molten carbonate fuel cell of the present invention from the first viewpoint are: a pair of porous cathodes made of nickel oxide and/or cobalt oxide as a base material; and a porous anode made of nickel as a base material. In a molten carbonate fuel cell composed of a matrix plate containing an electrolyte sandwiched inside these electrodes, the cathode porous electrode is
Micropores with a specific surface area of ~100 rrr/g and a primary pore diameter of 0.01 to 2 μm and a secondary pore diameter of 2 to 20 μm
It has a pore distribution of μm.

In addition, the specific surface area of the cathode porous electrode is 1 to 100rd.
/g is limited to the conventional base material particle specific surface area of approximately 0.7
This is because even lrrf/g larger than mz/g already has some desired effect, and even if the value exceeds 100 rrf/g, no further improvement in performance can be expected.

In a preferred embodiment of the present invention, the electrolyte is mainly retained in the primary pores, so that the electrolyte is well retained in the electrode, and the porosity ratio in the porous cathode is 50 to 50. 60%, and the amount of electrolyte contained in the pores of the porous cathode is 20 to 40% of the pore volume.
(% by volume), the polarization value is minimized, resulting in favorable performance.

Further, the characteristics of the molten carbonate fuel cell of the present invention from the second or third point of view are a pair of porous cathodes whose base material is nickel oxide and/or cobalt oxide, and a porous cathode whose base material is nickel oxide and/or cobalt oxide. In a molten carbonate fuel cell composed of a porous anode as a material and a matrix plate containing an electrolyte sandwiched inside these electrodes, the porous electrode has a surface modifier supported on the surface of the base material particles. Alternatively, the porous electrode may have a surface modifier supported on the surface of the base material particles to form particles with a primary pore diameter of 0.01 to 2 μm. The material is molded using raw material particles in which the primary pore diameter of the micropores and secondary pores is increased in the pore distribution of 2 to 20 μm.

In addition, as mentioned above, in the pore distribution of micropores with a primary pore diameter of 0.01 to 2 μm and secondary pore diameters of 2 to 20 μm, ? The reason for using the raw material particles having an increased primary pore diameter is in correspondence with the objective (2).

The raw material particles include particles containing a surface modifier on the surface of the base material particle in the form of an oxide and/or alkali metal salt selected from the group consisting of chromium, aluminum, and zirconium, or in the form of a mixture thereof. More specifically, the surface modifier is CrzOi+Z on the surface of the base material particle.
Mention may be made of particles present in the form rO*, A1203 and/or LiAlO*.

The amount of the surface modifier applied to the base material particles is 0. Preferably, it is present in an amount of 5 to 20 (atomic %).

Next, in the method for producing raw material particles for forming a molten carbonate fuel cell of the present invention, the surface modifier is supported on the base material particles by applying a nitrate solution into the pores of a porous body formed into an electrode shape. It is characterized by producing raw material particles in which the specific surface area of the base material particles is significantly improved by impregnating the particles in the form of an oxalate solution, followed by drying and firing.

However, it goes without saying that the method for manufacturing a molten carbonate fuel cell of the present invention is not limited to this.

[For production]

By adding a surface modifier to the base material particles, the specific surface area of the particles can be increased from about 0.7rrf/g in the case of only the base material to 1~1rrf/g.
00trf/g. Therefore, the ratio of electrode reaction fields, that is, reaction active sites per unit electrode area increases, and a cathode with high initial activity can be obtained.

Further, the surface modifier forms fine pores of 0.01 to 2 μm. Pores of these diameters have high electrolyte retention, so
Fluctuations in the amount of electrolyte in the electrode are suppressed and the life of the electrode is improved.

Furthermore, it is highly effective in preventing growth and deformation of particles during reduction sintering and/or firing in an oxidizing atmosphere at high temperatures necessary in the manufacturing process, so that the surface area of the particles does not decrease.

Due to the above-described effects, the electrode characteristics are improved and the electrode life is also improved.

[Experiment example]

Experimental example 1? A compound containing Li-AI is deposited on nickel base particles with a diameter of 2 μm and a specific surface area of about 0.75 rW/g, and then a surface modifier mainly composed of LiAlO■ is added to the base particles by firing. obtain. The detailed manufacturing method is as shown in FIG. 1 kg of base material particles and 1 mol/l LiN
O30.3l and 1 mol#2 AI(NO+)+
0. 0.61 lmol/l (NHi) 2CO3 aqueous solution 2 is added to the slurry of mixed aqueous solution 1 of 3 42! ．． The hydroxides of Li and AI are deposited on the base material particles by dropping them. Next, by drying and firing at 350°C, LiA10 is formed on the surface and the first
As shown in the table, particles with a specific surface area about 120 times higher can be obtained. The amount added is 20 atomic % of the base material nickel.

(Margins below this page) Table 1: By reducing these particles at 700°C in an H2 atmosphere for 2 hours, the specific surface area decreases compared to before reduction, but the same
As shown in the table, a specific surface area approximately 20 times that of the base material can be maintained. It has been confirmed that the specific surface area of these particles hardly changes even if the reduction time is further increased. This is an effect of the surface modifier LiA]Oz. next,
Even after oxidation treatment at 700°C for 2 hours, the specific surface area remained approximately 18 times that of the base material.

Experimental example 2 LiNO3. The mixed aqueous solution 1 of AI(N(h)z is added in an amount of 0.5 to 20 (atomic)% of the base material, but by changing this amount, the surface area of the product can be changed. The relationship is shown in Table 2.

Table 2 Experimental Example 3 Even if a salt of La, Cr, Zr, an alkali metal salt, or a mixture thereof is used in place of Solution 1, the effect of improving the specific surface area as shown in Table 3 can be obtained. Is recognized.

Table 3 [Amounts added are all 2 (atomic)%] [Example] Example 1 The pore characteristics of the cathode made into an electrode using the base material particles prepared based on Experimental Example 1 were measured by water pressure injection method. Then, it looked like 3 in Figure 2. The figure also shows a conventional cathode (4 in Figure 2).

Fine primary pores of 0.01 to 2 μm, and approximately 2 to 10
The presence of pores with a diameter of μm can be confirmed. The pore characteristics after the electrode was impregnated with 40% of the pore volume of electrolyte and the battery was operated for 2000 hours, and the pore characteristics after the electrolyte contained in the electrode was washed with glacial acetic acid were measured in the third experiment. 5 and 6 in the diagram
Shown below. From the difference in the pore volume distribution of samples 5 and 6, it was confirmed that the electrolyte was retained in pores of approximately 0.3 μm or less, and the electrolyte retention capacity was increased due to the primary pores formed by the modifier. It is thought that there are.

For comparison, the pore characteristics measured after battery operation under the same conditions for the conventional cathode (4 in Figure 2) are shown in Figure 4.
As shown in the figure. There was almost no difference in distribution between electrode 8 after the final treatment after the test and the electrode after cleaning, and almost no electrolyte was retained. From the above results, it can be seen that the modifier has a remarkable effect of improving electrolyte retention.

Example 2 Figure 5 shows the unipolar characteristic measurement results of two conventional cathodes 4', 4'' and the modified cathode 3' produced in Experimental Example 1. The horizontal axis represents the electrode surface area, and the axis represents the unit polarization value. The modified cathode 3' has a larger specific surface area than the conventional cathodes 4' and 4', and therefore can be extracted under unit polarization. It can be seen that the current value is large and highly active.

Example 3 FIG. 6 shows the results of measuring electrolyte transfer rates in cathodes with different primary pore diameters using a weight change method.

The horizontal axis represents the pore diameter to the η power, and the vertical axis represents the moving speed.

The smaller the primary pore diameter, the lower the migration speed.

Therefore, it can be seen that the smaller the pore diameter, the greater the ability to hold the electrolyte. If the cathode 3' made of the base material made by the method of Experimental Example 1 is used, the primary pore diameter will be approximately 0.3μ.
Since the electrolyte retention force is less than
(average pore diameter of approximately 10 μm), the electrolyte movement rate is slower than that of the average pore diameter of approximately 10 μm. In other words, the improved cathode 3' has a higher electrolyte retention ability than the conventional cathode.

Example 4 The unipolar characteristics of the cathode produced in Experimental Example 1 are shown in 10 and 11 of FIG. 7 in comparison with a conventional cathode. The measurement conditions are:
The values are at 650°C, 70% air + 30% carbon dioxide, and oxygen utilization rate of 40%. As can be seen from the figure, the cathode of the present invention has reduced polarization compared to the conventional cathode. In other words, electrode activity is improved.

Example 5 In Experimental Example 1, by changing the amount of modifier added, the porosity can also be changed. Table 4 shows the relationship between the amount added and the porosity.

(Margins below this page) Table 4 Example 6 As shown in Figure 8, the cathode 11 produced in Example 1
And in the conventional cathode 10, the electrolyte occupancy rate in the electrode pores (the ratio of the volume occupied by the electrolyte in the electrode pores) is 0 to 8.
When changing to 0%, the occupancy rate of both cathodes is 20 ~
It can be seen that the polarization value shows the minimum at 40%. Also, in this case, at any occupancy rate, cathode 1 of Experimental Example 1
1 has small polarization.

〔Effect of the invention〕

According to the present invention, sintering of the raw nickel particles can be suppressed even under an oxidizing atmosphere at a temperature of around 700°C and a reducing atmosphere essential for the manufacturing process, so the surface area of the particles can be maintained high. I can do it. Therefore, when it is made into an electrode, it has the effect of becoming a cathode with high initial electrode activity. Furthermore, since fine pores are formed on the base material particles by the surface modifier, a cathode with high electrolyte holding power can be obtained, which has the effect of improving the electrode life.

[Brief explanation of drawings]

Figure 1 shows the manufacturing flow of a cathode with a high specific surface area. Table 1 shows changes in the specific surface area of base material particles (Ni powder), after a stabilizing material was deposited on the particles and fired, and after reduction firing. Table 2 shows the relationship between the amount of stabilizer (LiNO3, 81(NO3)3) mixed solution added and the specific surface area after reduction. ? Table 3 shows the specific surface area when using various stabilizer components. FIG. 2 Conventional cathode and NiOLiA according to Example 1
10 ■ Comparison of pore characteristics of added cathodes. Figure 3: 200 using NiO-LiA10■ cathode
FIG. 3 is a diagram showing the amount of electrolyte retained after 0 hours of battery operation. Figure 4 (comparison with Figure 3) Using a conventional cathode
FIG. 3 is a diagram showing the amount of electrolyte retained after 0 hours of battery operation. Figure 5 Relationship between electrode surface area and reaction rate. Figure 6 Relationship between pore diameter and electrolyte transfer rate. FIG. 7 is a diagram comparing the electrode characteristics of a conventional cathode and a cathode with a high specific surface area according to Example 1. FIG. 8 is a diagram comparing the relationship between electrolyte occupancy and polarization value in a conventional cathode and in Example 1. [Explanation of symbols] 1: 1 mol/f LiNO+aqueous solution 0.3
Mixed aqueous solution 2: 1 mol/l (NH3
) zcO + aqueous solution 0.6f3: NiO-Li
Pore distribution curve 3' of A10z cathode:
Polarization characteristic 4: Pore distribution curve of conventional NiO cathode 4'+4': // Polarization characteristic 5: Pore distribution curve of NiO-LiAtOz cathode after battery operation (including electrolyte) 6: With the same cathode as in 5 Pore distribution curve 7 after removing electrolyte: Electrolytic 'Efffi' retained in cathode 5
8: Pore distribution curve of conventional cathode after battery operation (including electrolyte) 9: Pore distribution curve after electrolyte is removed in step 8 10: Unipolar characteristics of conventional cathode

Claims (1)

[Claims] 1. A pair of porous cathodes made of nickel oxide and/or cobalt oxide as a base material, a porous anode made of nickel as a base material, and a matrix plate containing an electrolyte sandwiched between these electrodes. In a molten carbonate fuel cell composed of
It has a specific surface area of , and a primary pore diameter of 0.01 to 2 μm.
A molten carbonate fuel cell characterized by having a pore distribution in which the micropores and secondary pore diameters are 2 to 20 μm. 2. Claim 1, characterized in that the electrolyte is mainly held in the primary pores and the interface involved in the electrode reaction is wide.
The molten carbonate fuel cell described. 3. The molten carbonate fuel cell according to claim 1 or 2, characterized in that the proportion of pores in the porous cathode is 50 to 60%. 4. The molten carbonate according to any one of claims 1 to 3, wherein the amount of electrolyte contained in the pores of the porous cathode is 20 to 40 (vol%) of the pore volume. type fuel cell. 5. Molten carbonic acid consisting of a pair of porous cathodes made of nickel oxide and/or cobalt oxide as a base material, a porous anode made of nickel as a base material, and a matrix plate containing an electrolyte sandwiched between these electrodes. A molten carbonate fuel cell, wherein the porous electrode is formed of raw material particles that support a surface modifier and have an increased specific surface area. 6. Molten carbonic acid consisting of a pair of porous cathodes made of nickel oxide and/or cobalt oxide as a base material, a porous anode made of nickel as a base material, and a matrix plate containing an electrolyte sandwiched between these electrodes. In the salt-type fuel cell, the porous electrode supports a surface modifier on the surface of the base material particles, and has micropores with a primary pore diameter of 0.01 to 2 μm and 2 μm.
A molten carbonate fuel cell characterized in that it is molded using raw material particles having an increased primary pore size in a pore distribution with a secondary pore size of 2 to 20 μm. 7. The raw material particles are particles containing a surface modifier on the surface of the base material particle in the form of an oxide and/or alkali metal salt selected from the group consisting of chromium, aluminum, and zirconium, or in the form of a mixture thereof. The molten carbonate fuel cell according to claim 6, characterized in that: 8. The raw material particles have a surface modifier of Cr_ on the surface of the base material particles.
2O_3, ZrO_2, Al_2O_3 and/or Li
Molten carbonate fuel cell according to claim 6, characterized in that the particles are present in the form of AlO_2. 9. The surface modifier is 0.5 to 20 (atomic %) to the base material particles.
9. The molten carbonate fuel cell according to claim 5, wherein the molten carbonate fuel cell is present in an amount of .). 10. In the method for producing raw material particles for forming a molten carbonate fuel cell, a surface modifier is supported on the base material particles by adding a nitrate solution and/or oxalic acid into the pores of a porous body formed into an electrode shape. Production of raw material particles for forming molten carbonate fuel cells characterized by producing raw material particles with significantly improved specific surface area of base material particles by impregnating them in the form of a salt solution, followed by drying and firing. Law.