JP3724762B2 - Method for producing fuel electrode of solid oxide fuel cell - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for manufacturing a fuel electrode, in particular, it relates to a method for producing a fuel electrode of a solid oxide fuel cell (Solid Oxide Fuel Cell, hereinafter abbreviated as SOFC).
[0002]
[Prior art]
SOFC is a general term for a fuel cell that generates power by supplying two kinds of gases, an oxidant and a fuel, to the oxidant electrode and the fuel electrode, and uses a solid substance as a constituent material. In the SOFC, the following ceramics are widely used and are usually operated at a temperature around 1000 ° C.
[0003]
Electrolyte: Yttria stabilized zirconia (YSZ)
Fuel electrode: Nickel / zirconia cermet (Ni-YSZ)
Oxidant electrode: Strontium-doped lanthanum manganite (LSM)
[0004]
Here, Ni is frequently used as the metal of the fuel electrode because it is highly active against fuel gases such as hydrogen and carbon monoxide, is stable against YSZ, and is sulfur resistant when coal gas is used as the fuel. This is because of its excellent properties. As a method for producing a fuel electrode at a low cost, a slurry coating method is generally used in which YSZ powder or nickel oxide powder as raw materials are mixed with a ball mill or the like, applied as a paste to an electrolyte, and fired.
[0005]
The fuel electrode serves as a catalyst for reacting the fuel gas with the oxidant, and this electrode reaction field is a three-phase interface where Ni, YSZ, and the fuel gas are in contact. Therefore, increasing the three-phase interface length leads to an improvement in SOFC output characteristics. Furthermore, increasing the conductivity of the electrode itself also improves the output characteristics of the SOFC. Therefore, by adjusting the particle size and particle size ratio of nickel oxide powder and YSZ powder, high dispersion of Ni particles and YSZ particles to increase the three-phase interface, or the mixing ratio of nickel oxide powder and YSZ powder Studies have been made to increase conductivity by adjustment.
[0006]
[Problems to be solved by the invention]
However, since the SOFC has a structure in which the fuel electrode is in direct contact with the electrolyte, even if the fuel electrode itself has high performance, if the consistency with the thermal expansion and contraction with the electrolyte is not achieved, the interface stress The electrode peels off and cracks, and the performance cannot be fully exhibited. For this reason, the optimization of the fuel electrode by adjusting the particle size, particle size ratio, or mixing ratio of the nickel oxide powder and the YSZ powder is comprehensive considering the compatibility with the electrolyte, and the performance of the electrode itself is improved to some extent. I had to sacrifice.
[0007]
For example, when a fuel electrode is fabricated on an electrolyte membrane or an electrolyte substrate that has already been sintered, the electrolyte hardly sinters when firing the fuel electrode. Shrinkage during firing must be suppressed. As a method for suppressing shrinkage during firing, for example, a calcination treatment is performed in which the material powder is sintered in advance at a temperature lower than the firing temperature. However, in such a calcination treatment, the particle size and particle size distribution of the powder often change, and the optimum design as an electrode is impaired.
[0008]
The present invention solves the above problems by using nickel oxide powder with low crystallinity, that is, powder having a large variation in crystallinity, or a mixed powder of the nickel oxide powder and YSZ powder. It is intended to be illustrated.
[0009]
[Means for Solving the Problems]
[0010]
(First means)
The present invention, nickel oxide powder, or in the manufacturing method of the fuel electrode of the solid body electrolyte fuel cell you calcining a mixed powder of oxide powder with a nickel oxide powder and oxygen ion conductivity, compact of nickel oxide powder There together using an acid nickel powder as shrink at 850 ° C. from 400 ° C., the nickel oxide powder nickel nitrate, nickel sulfate, nickel chloride, nickel carbonate, thermal decomposition of one or more nickel compounds of nickel acetate, or These nickel compounds are produced by thermal decomposition of a precipitate obtained by neutralizing with one or more alkaline solutions of sodium hydroxide, potassium hydroxide and lithium hydroxide .
[0011]
(Second means)
According to the present invention, in the method for producing a fuel electrode of a solid oxide fuel cell described in the first means, the crystallinity of the nickel oxide powder is controlled by changing the thermal decomposition temperature of the nickel salt or precipitate. Or heat treating the nickel oxide powder obtained by thermal decomposition so that the nickel oxide powder compact shrinks at 400 ° C. to 850 ° C. at a temperature higher than the thermal decomposition temperature and lower than the sintering temperature of the fuel electrode. It is characterized by performing by doing .
[0012]
(Third means)
The present invention provides the method for producing a fuel electrode of a solid oxide fuel cell according to the first or second means , wherein the oxide having oxygen ion conductivity is yttria stabilized zirconia, partially stabilized zirconia, samaria dope. It is characterized by being ceria.
[0014]
[Action]
Nickel oxide used as a fuel electrode material for SOFC was obtained by thermal decomposition of nickel compounds such as nickel chloride and nickel nitrate, or neutralizing these nickel compounds with an alkaline solution such as sodium hydroxide and potassium hydroxide. It can be produced by thermal decomposition of the precipitate. At this time, if the thermal decomposition temperature is different, the crystallinity of the produced nickel oxide is different. Further, the crystallinity of nickel oxide changes even if heat treatment is performed at a temperature higher than the pyrolysis temperature after the thermal decomposition.
[0015]
When a sintered body is made of nickel oxide powders having different crystallinity, the shrinkage rate during sintering varies depending on the crystallinity. Therefore, if the thermal decomposition temperature or heat treatment temperature is adjusted, the shrinkage rate during sintering of nickel oxide can be adjusted, and if this is used, the heat during sintering when the fuel electrode is formed on the electrolyte can be adjusted. Consistency in contraction can be achieved.
[0016]
[Example 1]
The nickel oxide powder having low crystallinity was produced as follows. First, the aqueous nickel nitrate solution was neutralized with an aqueous potassium hydroxide solution, and the precipitate formed at this time was filtered out. Next, this was thermally decomposed at 400 ° C. to obtain nickel oxide, which was further pulverized and classified to obtain a nickel oxide powder having a black particle size of about 10 μm. The X-ray diffraction pattern of the nickel oxide powder thus obtained is shown in FIG. For comparison, an X-ray diffraction pattern of a commercially available green nickel oxide powder having the same particle size is also shown in FIG.
[0017]
Here, as shown in FIG. 3, a value α / C (hereinafter referred to as half width / peak value) obtained by grading the half width by the peak value of the count number is obtained and used as an index for evaluating crystallinity. It can be judged that the larger the half width / peak value, the lower the crystallinity. Comparing FIG. 1 with FIG. 2, the half width / peak value for the same diffraction angle is larger in FIG. 1 at any angle. Therefore, it can be said that the nickel oxide of the present invention has low crystallinity.
[0018]
The black nickel oxide powder of the present invention and a commercially available green nickel oxide powder were molded at a press pressure of 1 t / cm ² , and the relationship between the temperature of the molded body and the shrinkage ratio of the length was examined. The results are shown in FIG. 4, and in the nickel oxide powder of the present invention, large shrinkage is observed in the range of about 400 ° C. to 850 ° C. Furthermore, the nickel oxide powder of the present invention was heat-treated at a temperature of 500 to 1100 ° C. for 2 hours, and an X-ray diffraction test was performed after the heat treatment. FIG. 5 shows the relationship between the heat treatment temperature and the full width at half maximum / peak value on the (200) plane. As the heat treatment temperature increases, the full width at half maximum / peak value decreases, indicating that crystallization is progressing. Here, the temperature range in which the full width at half maximum / the peak value decreases coincides with the range of 400 to 850 ° C. in which a large shrinkage behavior is seen in FIG. Moreover, as a result of measuring the particle size and particle size distribution of the nickel oxide powder heat-treated in a temperature range from 400 to 800 ° C. by the circular center sedimentation method, there was no significant difference in the physical properties depending on the heat treatment temperature. As for the relationship between the progress of crystallization and the weight, thermogravimetric analysis (TG analysis) was performed in the range of room temperature to 1000 ° C., and as a result, almost no weight change was observed here. Therefore, this crystallization is due to a change in internal structure that does not involve the absorption or release of substances.
[0019]
Next, a press-molded body was produced from the nickel oxide powder of the present invention that was heat-treated at each temperature for 2 hours, and the relationship between the shrinkage in the length direction and the heat treatment temperature when fired at 1200 ° C. for 2 hours was also obtained. . The results are shown in FIG. 6, and it can be seen that shrinkage can be reduced by increasing the heat treatment temperature. Similarly, in the case where only the thermal decomposition temperature is changed in the range of 500 to 1100 ° C. without performing the heat treatment, the relationship between the thermal decomposition temperature and the shrinkage ratio is the same as the above result obtained with respect to the heat treatment temperature. The same tendency was shown.
[0020]
From these results, it is understood that the shrinkage ratio during firing can be adjusted by adjusting the crystallinity of nickel oxide by changing the thermal decomposition temperature when producing nickel oxide or the heat treatment temperature of nickel oxide having low crystallinity. In addition, the shrinkage rate is adjusted here by performing heat treatment or thermal decomposition at a temperature lower than the sintering temperature of nickel oxide, unlike the conventional method of calcining nickel oxide powder with high crystallinity. There is an advantage that the particle size of the nickel oxide powder hardly changes due to the pretreatment.
[0021]
In the above, an example was described about the production method of nickel oxide powder having low crystallinity and the adjustment of the shrinkage rate by controlling the crystallinity. Next, the Example at the time of using the nickel oxide powder of this invention as an electrode material of a fuel cell is shown.
[0022]
[Example 2]
A nickel oxide powder having a particle size of 10 μm produced by performing thermal decomposition at 400 ° C. with the material and production method shown in Example 1 above, and this at a temperature of every 100 ° C. in the range of 500 to 1000 ° C. The heat-treated material was used as a material for preparing a fuel electrode. These material powders are mixed as they are, or YSZ powder (8 mol% yttria stabilized) is mixed at a weight ratio of 50:50, and polyvinyl butyral as a material binder and terpineol as a solvent are mixed to form a slurry. It was. This was applied onto a YSZ disk (8 mol% yttria stabilized) having a diameter of 3 cm and a thickness of 0.5 mm so as to have a thickness of 0.1 mm, and baked at 1200 ° C. for 2 hours. For comparison, a fired body was produced in the same manner for a commercially available green nickel oxide powder having the same particle size.
[0023]
Evaluation of consistency between the produced fuel electrode and the YSZ disk as the electrolyte was performed by a mechanical method using a scratch tester. That is, the stylus (diameter 0.2 mm at the tip) and the membrane surface of the fuel electrode are brought into contact with each other vertically, and the underlying YSZ disk is moved at a constant speed while applying a linearly increasing load to the stylus. Move with. At this time, the load when the fuel electrode started to peel or crack was determined, and this value was defined as the adhesion between the fuel electrode and the electrolyte. And it was determined that the greater the value, the better the consistency.
[0024]
FIG. 7 shows the measurement results of the heat treatment temperature and adhesion for each sample. Both the nickel oxide powder of the present invention and the mixture of the nickel oxide powder of the present invention and the YSZ powder both have a large adhesion compared to the case of using a commercially available nickel oxide with good crystallinity, It can be seen that the consistency is good. Further, it can be seen that the adhesive strength tends to increase as the heat treatment temperature increases up to 800 ° C., and it is understood that the consistency between the fuel electrode and the electrolyte can be improved by controlling the crystallinity of nickel oxide. The reason why the adhesive force decreased at 900 ° C. or higher is considered to be that the sintering of nickel oxide occurred during the heat treatment and the sinterability decreased due to the increase in the particle size of nickel oxide.
[0025]
【The invention's effect】
As described above, according to the present invention, consistency with the electrolyte can be achieved by adjusting the crystallinity of the nickel oxide powder used as the raw material of the fuel electrode.
[Brief description of the drawings]
FIG. 1 is an X-ray diffraction pattern of black nickel oxide powder of the present invention.
FIG. 2 is an X-ray diffraction pattern of a commercially available green nickel oxide powder.
FIG. 3 is a diagram showing a method for calculating a value for evaluating the crystallinity of a sample from the full width at half maximum of the X-ray diffraction diagram and the peak value of the count number.
FIG. 4 is a graph showing the relationship between temperature and length shrinkage in press-molded bodies of black nickel oxide powder of the present invention and commercially available green nickel oxide powder.
FIG. 5 shows the relationship between the heat treatment temperature when the nickel oxide powder of the present invention is heat-treated for 2 hours and the value obtained by grading the half-value width on the (200) plane by the peak value of the count number, which was obtained from the X-ray diffraction test Figure.
FIG. 6 shows the relationship between the shrinkage ratio in the length direction of the molded body and the heat treatment temperature when a press-molded body made of the black nickel oxide powder of the present invention that has been heat-treated for 2 hours is fired at 1200 ° C. for 2 hours. Figure.
FIG. 7 is a graph illustrating a fuel electrode invented with the nickel oxide of the present invention and a fuel electrode prepared by mixing nickel oxide and YSZ of the present invention in a weight ratio of 50:50 by a heat treatment temperature of nickel oxide and a squelatch test. FIG.

Claims (3)

Nickel oxide powder, or in the manufacturing method of the fuel electrode of the solid body electrolyte fuel cell you calcining a mixed powder of oxide powder with a nickel oxide powder and oxygen ion conductivity, a molded body of nickel oxide powder is 400 ° C. with using a nickel oxide powder as shrink at 850 ° C., nickel nitrate to nickel oxide powder, nickel sulfate, nickel chloride, nickel carbonate, thermal decomposition of one or more nickel compounds of nickel acetate, or these nickel compounds, A method for producing a fuel electrode for a solid oxide fuel cell, comprising producing a precipitate obtained by neutralization with one or more alkaline solutions of sodium hydroxide, potassium hydroxide and lithium hydroxide . The method for producing a fuel electrode for a solid oxide fuel cell according to claim 1 , wherein the crystallinity of the nickel oxide powder is controlled by changing the thermal decomposition temperature of the nickel salt or precipitate, or by thermal decomposition. obtained, that done by molding of nickel oxide powder of nickel oxide powders, such as shrinkage at 850 ° C. from 400 ° C., a heat treatment at a temperature lower than the sintering temperature of the higher fuel electrode than the thermal decomposition temperature A method for producing a fuel electrode of a solid oxide fuel cell, characterized in that The method for producing a fuel electrode of a solid oxide fuel cell according to claim 1 or 2 , wherein the oxide having oxygen ion conductivity is yttria-stabilized zirconia, partially-stabilized zirconia, or samaria-doped ceria. A method for manufacturing a fuel electrode of a solid oxide fuel cell.

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