JP7058866B2 - Anode for solid oxide fuel cell and solid oxide fuel cell using this anode - Google Patents

Description

The present invention relates to an anode for a solid oxide fuel cell and a solid oxide fuel cell capable of exhibiting high power generation performance even at low temperatures and capable of stable operation.

A solid oxide fuel cell (SOFC) is a fuel cell that normally operates at a high temperature of over 900 ° C. It is very expensive as a material used for interconnectors (cylindrical type is called this) and separators (flat plate type is called this), which are one of the main parts, in order to withstand the high temperature during such operation. It is necessary to use a ceramic material (eg, a lantern chromite-based or titanium oxide-based ceramic material is exemplified). This was one of the major factors that hindered the cost reduction of SOFC equipment price and, by extension, the cost per unit power generation amount. If this temperature can be suppressed to around 700 ° C to 800 ° C, inexpensive stainless steel can be used for the interconnector (or separator), and the interconnector (or separator) that is considered to be inevitably generated due to high temperature operation exceeding 900 ° C. It is also possible to suppress performance deterioration (deterioration) due to the reaction between the fuel cell and the fuel cell, and it is expected to give a breakthrough in both the above problems, that is, the problem of reducing the equipment manufacturing price and the problem of improving the performance life. To. Therefore, various studies have been conducted to bring out sufficiently high power generation performance in such a so-called medium temperature range. Specifically, oxygen in the air is reduced at the cathode through an oxygen reduction reaction to produce oxide ions (O ^2- ), but the reaction of sending it to the inside of the solid electrolyte is considered to be slow, so this cathode material Many studies have been made on the reduction of resistance at the cathode / solid electrolyte interface.

Furthermore, in order to bring out the high power generation performance of maintaining high power generation efficiency even if the operating temperature of SOFC is reduced, a thin film solid electrolyte whose thickness is reduced from the usual 300 μm to 20 μm is used. It is desirable to do so.

However, since a solid electrolyte membrane, which is an oxide ceramic, cannot be produced as a self-standing film, a film is usually formed on a porous anode (cermet consisting of Ni and a solid electrolyte (YSZ)) support. Then, a single cell for a fuel cell is produced through a process of sintering (called co-sintering) together with a support having a cermet composition.

At this time, the thickness of the anode support needs to be about 1 to 2 mm. When the thickness of the solid electrolyte is about 300 μm, the thickness of the anode itself may be only about 40 μm or less because a solid electrolyte-supported cell can be produced by applying an anode or a cathode to the solid electrolyte and baking it. It turns out that. However, since the anode layer is very thick in the anode-supported thin film cell, minimizing the resistance component at the interface between Ni and 8YSZ (8 mol% yttria-stabilized zirconia) existing in the anode layer becomes an important issue. ..

In addition, another major problem with electrodes having a cermet composition of Ni and 8YSZ is the problem of grain growth of metallic Ni. First, the conduction mechanism of electrons and oxide ions in this type of electrode will be described. If Ni particles and 8YSZ particles are connected to each other in the anode layer, electrons move at the connecting portion between Ni particles, and oxide ions are diffused at the connecting portion between 8YSZ particles, then Ni At the contact point of 8YSZ, three electrons, oxide ions, and hydrogen can be formed (called a three-phase interface). This makes it possible to create a large number of active sites in the porous Ni-8YSZ cermet.

However, in that case, the optimum composition of Ni and 8YSZ is said to be Ni: 8YSZ = 3: 2 in weight ratio, but in this case, the weight ratio of 8YSZ may be large, and the resistance component at the interface becomes large. As a result, the internal resistance of the fuel cell is increased, resulting in a decrease in power generation performance.

Therefore, by increasing the Ni component, the electron conductivity can be increased and the resistance at the interface can be reduced. Furthermore, the porosity is also increased due to the effect of volume shrinkage accompanying the change from NiO to Ni, which is a plus for improving power generation performance. However, the increase in the Ni component facilitates the growth of Ni grains. It is said that there is a problem that the stability of power generation performance is lowered due to the growth of Ni grains even at an operating temperature of 700 ° C.

Several studies have been published to improve the anode performance by adding other substances to the anode material. In Non-Patent Documents 1 to 4, a perovskite compound (brown mirror light-related compound) having a composition of Sr ₍ Y _, Ce) O3 or Ba (Y, Ce) O3 known as a proton conductor is used as an anode in an amount of 4 to 5 wt%. It is added and the effect of addition is confirmed at a temperature of 800 ° C. or higher. However, since the temperature at which the addition effect is exhibited in these documents is 800 ° C., which exceeds the usable temperature of stainless steel, the problem that the material that can be used for the interconnector or the like is very expensive cannot be solved. .. Further, Non-Patent Document 5 discloses that platinum or a platinum group metal is supported on Sm-doped ceria particles to have electron conductivity and oxide ion conductivity, and these metals are placed in the anode layer at 0. It is reported that the addition of 2 to 0.3 wt% has found an effect of improving the anode performance at an operating temperature of 800 ° C. or higher. However, since the operating temperature of the anode based on this document is also high, stainless steel cannot be used for the interconnector or the like.

Therefore, from 700 ° C to 800 ° C, high power generation efficiency (54% or more of the theoretical power generation efficiency) and high performance of obtaining a large current density can be expected. There is a strong demand for SOFC anode materials that simultaneously satisfy the two requirements of ensuring high performance stability.

The subject of the present invention is an anode for achieving high power generation performance and suppression of Ni grain growth during operation in a region of operating temperature lower than that of a conventional ordinary SOFC such as 700 ° C., and an SOFC using such an anode. Is to provide.

According to one aspect of the present invention, a solid electrolyte, metallic nickel particles, and Ba ₂ In _1.7 (Zn _0.5 , Zr _0.5 ) _0.3 O ₅ , Ca ₂ Fe having a brown mirror light structure. Select from the group consisting of ₂ O ₅ , Sr ₂ Fe ₂ O ₅ , Ca ₂ In ₂ O ₅ , Sr ₂ In ₂ O ₅ , and Ba ₂ In ₂ O ₅ , and oxides TIO ₂ , CeO ₂ , and SnO ₂ . An anode for a solid oxide fuel cell comprising an anode reaction co-catalyst consisting of at least one of the above is provided.
Here, the solid electrolyte may be at least one selected from the group consisting of yttria-stable zirconia, ceria and ceria in which at least one element of Sm, Y and Gd is dissolved in a solid solution of 10 to 20 mol%.
Further, the anode reaction co-catalyst may be contained in an amount of 0.1 to 1 wt%.
Further, the anode reaction co-catalyst does not have to be amorphized.
Further, the anode reaction assisting catalyst is present on the surface of the solid electrolyte side in the grain boundary region of the solid electrolyte and the metal Ni particles, and on the surface of the anode reaction assisting catalyst on the surface of the solid electrolyte side. Diffusion of active oxygen may be promoted.
Further, the anode for the solid oxide fuel cell may be a fired body.
According to another aspect of the present invention, a solid oxide fuel cell using any of the above anodes is provided.

According to the present invention, it is possible to realize an SOFC capable of exhibiting high power generation performance and suppressing grain growth even in a low temperature region. In the past, it has been said that high performance and improved stability of anodes are in a trade-off relationship with each other. According to the present invention, the addition of a promoter has a great effect of being able to solve these two problems at the same time.

The figure which shows the XRD pattern of Ba ₂ In ₂ O ₅ and Ba ₂ In _1.7 (Zn _0.5 , Zr _0.5 ) _0.3 O ₅ . The figure which shows the measurement result of the oxygen partial pressure dependence of Ba ₂ In _1.7 (Zn _0.5 , Zr _0.5 ) _0.3 O ₅ by the Hebb-Wagner method. The figure which shows the electrode performance test result of the Example and the comparative example of this invention by the current cutoff method. The figure which shows the measurement result of the cathode overpotential (overvoltage) of the Example and the comparative example of this invention. The figure which compares the Tafel line of the Example and the comparative example of this invention. The figure which shows the change of the current density by the baking temperature and the addition amount of BM in the Example and the comparative example of this invention. The figure which graphically explains the mechanism which the power generation performance is improved by the addition of a promoter in this invention. The figure which shows the cross-sectional SEM image of the Example of this invention. The figure which shows the cross-sectional SEM image of the Example and the comparative example of this invention, and the particle size distribution of the cross section of these Examples and a comparative example.

The anode of the present invention is a conventional anode containing yttria-stabilized zirconia (YSZ) such as 8YSZ and metallic Ni particles, to which a promoter (anode reaction co-catalyst) that enables both suppression of grain growth and reduction of anode overvoltage is added. be. As this promoter, Ba ₂ In _1.7 (Zn _0.5 , Zr _0.5 ) _0.3 O ₅ (hereinafter referred to as BM) composed of a single phase of a brown mirror light type compound is used in the following examples. .. For the anode of the present invention, for example, a solid electrolyte powder such as YSZ, a Ni oxide powder, and a solid solution fine powder serving as a promoter are mixed and applied onto the solid electrolyte sintered body, and then about 1200 ° C to 1300 ° C. It can be produced by performing a baking process at the temperature of. As a result, the anode is formed as a fired body on the solid electrolyte sintered body. However, since the Ni component exists as a Ni oxide as it is, it is necessary to change it into metallic Ni particles. This can be achieved, for example, by heating to about 800 ° C. in a hydrogen atmosphere. In this hydrogen reduction treatment process, NiO is changed to metallic Ni, and at this time, pores are formed in the anode layer. At the same time, it is considered that the promoter diffuses to the surface of a solid electrolyte such as YSZ in a reducing atmosphere to form an active site.

In this way, the promoter spreads near the grain boundaries of YSZ and Ni, and forms a region on the surface of YSZ where oxide ions and the like can easily move, that is, a new active site region, so that FIG. 7 can be referred to. As will be described later, the reaction in which active hydrogen generated on the Ni surface and moved to the YSZ side reacts with oxide ions on this region to generate water is promoted. This is thought to cause a drop in anode overvoltage. Explaining the suppression of Ni grain growth, which is another action of the promoter, here, the grain growth pinning effect by the coexistence of the second phase, which has been known for a long time in the metal field, is used. Non-Patent Document 6 describes metal, but p. Equation 24 of 614 is the basis. Simply put, when the second phase coexists in the parent phase, the driving force for grain growth is determined by the balance between the grain growth inhibitory force due to the pores and the grain growth inhibitory force due to the second phase, and the particles in the second phase are determined. The finer the particles, the stronger the ability of the second phase to suppress grain growth, and the more dense the particles are. Please refer to Non-Patent Document 6 for a strict explanation.

As a result, in the anode of the present invention, active oxygen easily causes surface diffusion on a new active site region formed so as to spread near the grain boundary between a solid electrolyte such as YSZ and Ni particles, and moves lightly. Turn around. Therefore, in the anode of the present invention, the formation of water molecules becomes more active than in the conventional anode, and high activity is exhibited from the start of use. High power generation performance due to this high activity is stably maintained for a long period of time by suppressing the growth of Ni grains of the promoter. As described above, by adding the promoter, it is possible to simultaneously achieve both the improvement of the initial performance of the SOFC, which has been conventionally recognized as having a trade-off relationship, and the suppression of the performance deterioration due to the suppression of grain growth.

Here, instead of YSZ, ceria or ceria in which 10 to 20 mol% of Sm, Y or Gd is dissolved can be used. As for the promoter, in terms of suppressing grain growth, as described above, an effect can be expected if the promoter is a second phase fine particle different from the parent phase (in this case, Ni, YSZ, etc.). Therefore, like BM particles, if the second phase has ions and electrons flowing in the particles in the same manner and is different from Ni or YSZ, the overvoltage reduction as the promoter and the suppression of grain growth described above are both reasonable. The effect can be expected. Therefore, to give an example of a material that can be used as a promoter other than BM, Ca ₂ Fe ₂ O ₅ , Sr ₂ Fe ₂ O ₅ , Ca ₂ In ₂ O ₅ , and Sr ₂ In, which have a brown mirror light structure like BM, are shown. Examples thereof include oxides such as ₂ O ₅ , Ba ₂ In ₂ O ₅ , and TIO ₂ , CeO ₂ , and SnO ₂ .

Hereinafter, the present invention will be described in more detail based on examples, but of course, the present invention is not limited to the examples. Further, in the following description, 8YSZ is used as a solid electrolyte, and Ba ₂ In _1.7 (Zn _0.5 , Zr _0.5 ) _0.3 O ₅ composed of a single phase of a brown mirror light type compound is used as a promoter. However, this does not lose its generality.

In this example, a brown mirror light type compound was first prepared. Specifically, first, as starting materials, Ba (NO ₃ ) ₂ (99% or more, manufactured by Wako Pure Chemical Industries, Ltd.), In ₂ (NO ₃ ) _{3.4.7H 2} O (99.99%, manufactured by high-purity chemicals) ) And (NH ₄ ) ₂ CO ₃ (manufactured by Wako Pure Chemical Industries, Ltd.) were prepared.

In addition, Ba (NO ₃ ) ₂ powder and In ₂ (NO ₃ ) _{3.4.7H 2} O powder are contained in these two substances in a molar ratio of Ba and _In in BaInO3. Weighed to a molar ratio of 1: 1 and mixed in distilled water (more specifically, 5.8804 g of Ba (NO ₃ ) ₂ powder and 5.7539 g of In ₂ (NO ₃ ). ) _{3.4.7H 2O} powder was dissolved in 300 ml of distilled water, and these aqueous solutions were mixed). 43.2 g of (NH ₄ ) ₂ CO ₃ was dissolved in 300 ml of distilled water and heated to 45 ° C., and the above mixed aqueous solution was added dropwise to the (NH ₄ ) ₂ CO ₃ aqueous solution to prepare a uniform precipitate. The obtained precipitate was aged by continuing mixing at the same 45 ° C. for 24 hours, then the precipitate and the liquid were separated, washed with water, and sufficiently dried at room temperature under a nitrogen stream. By performing this heat aging treatment, that is, a treatment in which the precipitate is maintained at the same temperature after being prepared, the Ruchatry's law holds true between the solution and the precipitate, so that the precipitate is dissolved between the two. And reprecipitation are repeated. By continuing this process for an appropriate period of time, the particles of the precipitate are refined.

The dried powder was calcined under an oxygen stream at 450 ° C. for 2 hours under oxygen gas flow to synthesize a BaInO ₃ solid solution. The XRD pattern is shown in FIG. 1 (a). To this solid solution powder, ZnO powder (purity: 99.999%, manufactured by high-purity chemicals) and ZrO ₂ powder (TOSOH Company, 0Y grade) are weighed and added in a predetermined amount, and a ball mill is used with respect to this. By performing wet mixing, a mixture powder having the above BM composition was prepared.

Ba ₂ In _1.7 (Zn _0.5 , Zr _0.5 ) _0.3 O ₅ compound which becomes a single phase of brown mirror light phase by calcining this mixed powder in air at 1000 ° C. for 1 hour. Was synthesized. As a result of observing the Ba ₂ In _1.7 (Zn _0.5 , Zr _0.5 ) _0.3 O ₅ compound solid solution powder finally obtained by this synthetic process with SEM, the average particle size is about 0. It was about 1 μm. The XRD pattern of this compound solid solution powder is shown in FIG. 1 (b).

The promoter required in the present invention, that is, the anodic reaction activation co-catalyst, needs to have a function of promoting electron transfer and diffusion of oxide ions at the three-phase interface in the anodic layer.

Therefore, for the purpose of confirming whether or not the Ba ₂ In _1.7 (Zn _0.5 , Zr _0.5 ) _0.3 O ₅ compound has such properties, Ba ₂ In _1.7 (Zn _{0. 5} , Zr _0.5 ) _0.3 O ₅ compound was molded into pellets and then sintered in air at 1350 ° C. for 6 hours to prepare a sintered body. Platinum electrodes were baked on both sides of the obtained pellet-like sintered body, and DC conductivity measurement by the 4-terminal method was performed by changing the oxygen partial pressure from 1 atm to ^10-22 atm. The oxygen partial pressure was controlled using pure oxygen gas, air, nitrogen gas and wet hydrogen gas, and the oxygen partial pressure was checked using an oxygen sensor directly connected to the gas outlet side of the electric conductivity measuring device.

FIG. 2 shows the oxygen partial pressure dependence of the DC conductivity recorded from the Ba ₂ In _1.7 (Zn _0.5 , Zr _0.5 ) _0.3 O ₅ sintered body at 700 ° C. As can be seen from FIG. 2, in the low oxygen partial pressure region corresponding to the anode environment of the fuel cell, the measured DC conductivity changes (increases) in proportion to the -1 / 6th power of the change in the oxygen partial pressure. It was found that the DC conductivity measured in the high oxygen partial pressure region corresponding to the cathode environment changes (increases) in proportion to the + 1/6 power of the change in oxygen partial pressure.

This means that in the low oxygen partial pressure region (corresponding to the anode environment), this material exhibits semiconductor characteristics derived from Frenkel defects in which lattice defects occur at quasi-lattice positions, and electrons and oxide ions become the main carriers of conduction. Show that it is. On the other hand, in the high oxygen partial pressure region (corresponding to the cathode environment), the semiconductor characteristics derived from Frenkel defects are exhibited, and it is considered that holes and oxide ions are the main carriers of conduction. ..

While it is preferable for electrons and oxide ions to be the main conduction carriers in the anode environment of the fuel cell, it is also possible to know the proportion of each of the electrons and oxide ions contributing to conduction. is necessary. Therefore, the DC conductivity when a platinum plate is laid on the pellet-shaped sintered sample coated with a platinum cathode to minimize the ingress and egress of oxygen on the sample surface on the cathode side (blocking electrode method) is also included. It was measured.

As a result, the oxygen partial pressure dependence of the DC conductivity proportional to the oxygen partial pressure to the -1 / 6th power was observed, which is shown in the black-painted plot in FIG. Therefore, the DC conductivity measured using a blocking electrode at an oxygen partial pressure of 3 × ^10-22 atm and the DC conductivity obtained by conducting a conductivity measurement using a porous ordinary platinum electrode (non-blocking electrode method). When the ratio with and was calculated, the value of the ratio (corresponding to the ratio of the oxide ion carrier and the electron carrier, which corresponds to the so-called ion transport number) was about 0.5, and the oxide ion and the electron were almost half. It was found to be a mixed conductor that diffuses or moves in the sample at a rate of each.

In the present invention, Ba ₂ In _1.7 (Zn) is based on the idea that a material that helps both electrons and oxide ions to and from each other sufficiently at the interface between Ni and 8YSZ in the anode layer is a good promoter. _0.5 , Zr _0.5 ) _0.3 O ₅ powder was added to the electrode powder of Ni-8YSZ cermet composition so as to be in the range of 0.1 wt% to 1 wt% of the entire anode composition, and the temperature was 1300 ° C. The cell voltage (IR-free) is measured by the current cutoff method (a method of removing the IR overvoltage of the solid electrolyte and measuring only the overvoltage of the electrode reaction) for the power generation performance of the fuel cell single cell that has been baked at the temperature. bottom. As a comparative example, the same measurement was performed on a Ni-8YSZ sample containing no Ba ₂ In _1.7 (Zn _0.5 , Zr _0.5 ) _0.3 O ₅ powder. In FIG. 3, measurements of two samples in which the amount of Ba ₂ In _1.7 (Zn _0.5 , Zr _0.5 ) _0.3 O ₅ powder added is 0.1 wt% and 0.2 wt% of the entire anode composition are measured. The results and the measurement results of the additive-free Ni-8YSZ sample of the comparative example are shown. Explaining the measurement conditions here, the cathode of this fuel cell single cell was La _0.85 Sr _0.15 MnO ₃ , and the electrolyte was an 8YZA sintered body (thickness 0.5 mm). Further, an O ₂ gas flow of 80 SCCM was supplied to the cathode side, and a wet H ₂ gas (+ 3% H ₂ O) was supplied to the anode side. The operating temperature was 700 ° C. In the figure, the horizontal broken line indicates the level of power generation efficiency of 54%.

In the comparison shown in FIG. 3, in the fuel cell using oxygen and hydrogen, the effect of improving the battery performance is compared from the change in the value of the cell current at the cell voltage of 0.8 V, which is the cell voltage corresponding to the power generation efficiency of 54%. ing. From FIG. 3, it can be seen that at a cell voltage of 0.8 V, which shows high power generation efficiency, the performance is greatly improved by adding a small amount of promoter as compared with the case where no promoter is added.

However, the measured value of the cell voltage (IR-free) by this current cutoff method includes both the cathode overvoltage and the anode overvoltage. Therefore, by winding the platinum wire around the side surface of the pellet-shaped sintered body sample as the reference electrode and using the three-electrode method including the reference electrode, the cathode overvoltage is separated for the same sample as the one shown in FIG. The results of the measurement are shown in FIG.

The cathode overvoltage is the anode from the gas seals provided on both sides of the solid electrolyte sintered body that separates the anode (environment filled with wet hydrogen) and the cathode (environment filled with oxygen) in the fuel cell measuring device. It is said that the generated water molecules may change as they flow into the cathode side. Therefore, even if the cathode electrodes applied in the experiment are of the same type and the same amount is applied, it is necessary to confirm how much the cathode overvoltage fluctuates when measuring the fuel cell performance. It is considered that it will be possible to accurately evaluate the effect of the trace addition of the promoter appearing in FIG.

From FIG. 4, in the performance measurement experiment in this example, from the change in the cell voltage (IR-free) within 0.06 V at the cell current of 60 mAcm ^-2 , is it the performance improvement effect by adding the promoter? I can't argue.

Therefore, for the purpose of clarifying this point, a Tafel line is drawn using the data on the relationship between the cell voltage (IR-free) and the cell current obtained in FIG. 3, and the effect of adding a trace promoter into the anode layer is shown. We decided to make a more accurate estimate.

FIG. 5 shows a comparison result of Tafel wires obtained from the fuel performance evaluation results of the sample to which a small amount of promoter was added and the sample to which no promoter was added. From this figure, it was clarified that when the BM promoter is added in the anode layer by 0.1 wt% or more, the anode overvoltage performance lowering effect that contributes to the fuel cell performance appears.

Next, we investigated how this promoter addition effect is affected by the difference in electrode baking temperature. The results are shown in FIG. From FIG. 6, although the promoter addition effect appears only slightly when the electrode baking temperature is 1200 ° C., a large promoter addition effect appears when the baking temperature is increased by 100 ° C. to 1300 ° C. I understand. This figure also shows that the effect of adding the BM promoter becomes remarkable when the amount of BM added is from about 0.1 wt% to about 0.5 wt%.

When the addition amount exceeds 0.5 wt%, a by-product (for example, _BaZrO3 compound) is generated between BM and 8YSZ, and it is considered that the promoter addition effect is suppressed / inhibited. However, if the addition amount exceeds 0.5 wt% but is in the range of 1 wt% or less, the effect of the addition is gradually reduced, but the promoter addition effect is still exhibited as compared with the case of no addition. Therefore, the amount of the promoter added is preferably 0.1 wt% to 1 wt%, more preferably 0.1 wt% to 0.5 wt%. It is considered that the promoter addition effect appears according to the magnitude of the conductivity (that is, electron conductivity and oxide ion conductivity). From this point as well, x = 0.3 means that this effect is most remarkable and good. On the other hand, when the value of x deviates from 0.3, the effect is reduced with the case of x = 0.3 as the apex, but a certain effect is exhibited in a wide range compared to the case where no additive is added. It seems to be done.

Further, it is considered that the reason why the effect of adding the BM promoter differs depending on the firing temperature is that the diffusion of the cations constituting the BM increases at a temperature of about 1200 ° C. or higher and 1300 ° C. That is, since the BM particles become a nearly dense sintered body when sintered at 1350 ° C., it is considered reasonable to consider that the diffusion of the crystals constituting the BM increases at about 1300 ° C. When the baking temperature is raised to 1400 ° C, amorphization occurs and many physical properties change. Therefore, it is necessary to perform electrode baking of the promoter-added material at a temperature lower than 1400 ° C.

Next, the promoter addition and non-addition mechanism that the power generation performance is improved by diffusing the crystals constituting the BM compound in the anode layer and spreading near the grain boundaries of Ni and 8YSZ. Was compared. FIG. 7 shows a schematic diagram of the reaction near the grain boundaries in the two cases of no promoter (BM) addition (left side of FIG. 7) and addition (right side of FIG. 7).

As shown in FIG. 7, the oxide ion diffused inside YSZ is considered to become active oxygen on the YSZ surface, and the active hydrogen diverged on Ni while this active oxygen diffuses on the YSZ surface. It is thought that the formation of water molecules, which are the fuel cell anode reaction product, occurs in response to.

In the process of anodic reaction, the formation of water molecules is believed to be driven by the slow surface diffusion of active oxygen on the YSZ surface. Therefore, by adding a small amount of the BM promoter and baking the electrodes at a baking temperature near the sintering temperature of 1300 ° C., the BM crystals constituting the BM diffuse to the YSZ surface and partially cover this surface. .. FIG. 7 is an irregular gray region drawn on the horizontal plane of the left half in the right schematic diagram (with BM addition), showing a region on the YSZ surface partially covered by this BM crystal. Since electrons and oxide ions easily move on the surface and inside of the BM lattice covering this surface (mixed conductivity), it is considered that the surface diffusion of active oxygen on the BM layer is significantly faster than that on the YSZ surface alone. Be done.

As a result, it is considered that the generation of water molecules on the surface of YSZ is also activated, and as a result, the fuel cell power generation performance can be improved.

Next, a BM promoter was added to the entire anode layer so as to be 0.2 wt%, and the sample was baked at 1300 ° C. and the fuel cell performance was evaluated. (SEM) The observed image and the observation regions 1 to 4 for elemental analysis by EDX are shown in FIG. 8, and the elemental analysis results in each of these regions in the observation image are shown in the following table. According to FIGS. 8 and 2 below, the presence of Ba element and In element supporting the presence of BM particles in the observation regions 1 and 3 is below or near the detection limit, while in the observation regions 2 and 4, the main BM promoter particles are present. The clear observation of the constituents Ba and In elements confirmed the presence of BM promoter particles there.

Further, as shown in the subject of the present invention, the existence of BM promoter particles is supported in order to clarify that not only the anode activity is improved (and thus the power generation performance is improved) but also the long-term stability of the performance is achieved. It is necessary to show that the grain growth of the particles constituting the anode layer is also suppressed in the region.

Therefore, using a sample obtained by reducing NiO in the anode layer to Ni by baking at a temperature of 1300 ° C. and further reducing hydrogen, the range centered on the region where the presence of BM promoter particles was shown by elemental analysis. FIG. 9 shows the results of measuring the particle size distribution of the particles constituting the anode layer in the sample and comparing this with the sample to which the BM promoter particles were not added. The particle size distribution was measured for 400 particles by the intercept method, which measures the three-dimensional particle size distribution from the intercept length distribution.

As can be seen from FIG. 9, the particle size distribution observed from the region supported by the presence of the BM promoter particles has a peak average particle size on the smaller particle size side as compared with the sample without the addition of the BM promoter particles. It can be seen that there is. Here, all the samples whose particle size distribution was measured were subjected to electrode baking treatment at 1300 ° C. It should be noted that this temperature is higher than the so-called medium temperature range of 700 ° C to 800 ° C, which is the main operating temperature assumed by the anode of the present invention. That is, the grain growth in the BM-added sample to which the present invention is applied is clearer than that in the sample to which BM is not added, even though the sample is exposed to a temperature much higher than the actual assumed operating temperature. It is shown that the grain growth rate is much slower than that shown in FIG. 9 at the assumed operating temperature of the SOFC of the present invention, which is much lower than that. Therefore, the effect of suppressing the growth of grains in the anode layer of the present invention has been clarified.

It is considered that the effect of suppressing the growth of grains in the anode layer of the BM promoter particles and the effect of promoting the surface diffusion of active oxygen on the surface of the YSZ particles make it possible to improve the power generation performance by adding a small amount of BM. In addition, the power generation performance generally deteriorates due to the growth of Ni grains during the operation of the SOFC, but as explained above, when the anode of the present invention is operated at about 700 ° C. for a long time, it is included in the power generation performance. Due to the grain growth inhibitory effect of the BM promoter, such deterioration of power generation performance during operation is also suppressed, and therefore one of the major factors impairing the long-term stability of SOFC is greatly reduced.

As described in detail above, according to the present invention, as described with reference to FIG. 7, on a new active site region formed by a promoter at the interface between a solid electrolyte such as YSZ and Ni particles. By promoting the surface diffusion of active oxygen in Yttria, the formation of water molecules becomes active, exhibiting high power generation performance from the beginning even at low temperatures, and by suppressing grain growth, such high power generation from the start of use. Since it is possible to provide an anode for SOFC that maintains stable performance for a long period of time and SOFC using this anode, it is expected to be widely used in industry.

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Claims (7)

With solid electrolyte,
With metallic nickel particles,
Ba ₂ In _1.7 (Zn _0.5 , Zr _0.5 ) _0.3 O ₅ , Ca ₂ Fe ₂ O ₅ , Sr ₂ Fe ₂ O ₅ , Ca ₂ In ₂ O ₅ , having a brown mirror light structure. Anode for solid oxide fuel cells comprising an anode reaction co-catalyst consisting of at least one selected from the group consisting of Sr ₂ In ₂ O ₅ and Ba ₂ In ₂ O ₅ . The solid oxide according to claim 1, wherein the solid electrolyte is at least one selected from the group consisting of yttria-stable zirconia, ceria and ceria in which at least one element of Sm, Y and Gd is dissolved in 10 to 20 mol%. Axide for physical fuel cells. The anode for a solid oxide fuel cell according to claim 1 or 2, which contains 0.1 to 1 wt% of the anode reaction co-catalyst. The anode for a solid oxide fuel cell according to any one of claims 1 to 3, wherein the anode reaction co-catalyst is not amorphized. The anode reaction co -catalyst is present on the surface on the solid electrolyte side in the grain boundary region of the solid electrolyte and the metallic nickel particles.
The anode for a solid oxide fuel cell according to any one of claims 1 to 4, wherein the diffusion of active oxygen is promoted on the surface of the anode reaction assisting catalyst on the surface on the solid electrolyte side. The anode for a solid oxide fuel cell according to any one of claims 1 to 5, which is a fired body. A solid oxide fuel cell using the anode according to any one of claims 1 to 6.

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