JP2010174333A - Ammonia-decomposing element and power generator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive ammonia-decomposing element which can be miniaturized and has high-temperature resistance and oxidation resistance, and to provide a power generator. <P>SOLUTION: The ammonia-decomposing element 10 includes a porous anode 2 into which ammonia is introduced, and a porous cathode 3 into which an oxidizing gas is introduced. An ion-conductive material 1 having ion conductivity exists between the anode and the cathode. The cathode 3 is a sintered compact of metal particles 31 and ion-conductive ceramics 32. The metal particle 31 includes Ni and/or Fe as main constituents, and at least the surface region is converted into a high heat-resistant alloy. The high heat-resistant alloying treatment includes chromizing and aluminizing. The outermost surface layer of the metal particle 31 is oxidized to form an oxide with a thickness of 0.5-100 nm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an ammonia decomposing element and a power generation apparatus for decomposing ammonia, and more particularly to measures for improving oxidation resistance.

Ammonia is an essential compound for agriculture and industry, but is harmful to humans. Thus, many methods for decomposing ammonia in water or air have been disclosed.
Patent Document 1 discloses an example of a contact method using a chemical solution such as a neutralizing agent. In this method, atomized aqueous ammonia is brought into contact with an air stream to separate ammonia in the air and brought into contact with a hypobromite solution or sulfuric acid.
Patent Document 2 discloses an example of a combustion method. In this method, ammonia is separated into air by the same process as described above, and then ammonia is burned by a catalyst.
Patent Document 3 discloses an example of a thermal decomposition method. In this method, ammonia-containing wastewater is decomposed using a catalyst to be decomposed into nitrogen and water.

On the other hand, the following are publicly displayed as catalysts for ammonia decomposition reaction.
Patent Document 3 discloses porous carbon particles containing a transition metal component, a manganese composition, and an iron-manganese composition.
Patent Document 4 discloses a chromium compound, a copper compound, and a cobalt compound.
Patent Document 5 discloses platinum supported on an alumina three-dimensional network structure.
In the method of decomposing ammonia by a chemical reaction using the above catalyst, generation of nitrogen oxides NOx can be suppressed.
Patent Documents 6 and 7 propose a method of more efficiently promoting the thermal decomposition of ammonia at 100 ° C. or lower by using manganese dioxide as a catalyst.

Japanese Patent Application Laid-Open No. 07-031966 JP 07-116650 A Japanese Patent Laid-Open No. 11-347535 JP-A-53-011185 Japanese Patent Laid-Open No. 54-010269 JP 2006-231223 A JP 2006-175376 A

According to the contact method, combustion method, thermal decomposition method, etc., ammonia can be decomposed. However, the above method has a problem in that it requires chemicals and external energy (fuel), and requires periodic replacement of the catalyst, resulting in high running costs. In addition, the apparatus becomes large and, for example, when it is additionally provided in existing equipment, the arrangement may be difficult. In particular, when platinum is used, there are major problems such as resource depletion and high cost. In addition, there is a problem of discharging carbon dioxide.
In particular, in the combustion method, since air is required, a problem of exhausting NOx also occurs in a flame of 1000 ° C. or higher.

  An object of the present invention is to provide a low-cost ammonia decomposition element that can be miniaturized and has high oxidation resistance, and a power generator using the same.

The ammonia decomposition element of the present invention includes a porous anode into which ammonia is introduced, and a porous cathode that is paired with the anode and into which an oxidizing gas is introduced. Further, an ionic conductive material having ionic conductivity is interposed between the anode and the cathode. Here, the cathode is composed of nickel (Ni) and / or iron (Fe) as a main component, and includes metal particulates whose outermost layer is oxidized.
Some metal particles include only metal particles, only metal particle chains, and a mixture of both. The metal particle chain refers to a bead-like long and narrow metal body made of metal particles.

With the above configuration, when an oxidizing gas having a high temperature (for example, about 800 ° C.) is introduced to the cathode side and ammonia and a reducing gas (for example, hydrogen) are introduced to the anode side, the following effects can be obtained.
At the anode, oxygen ions sent from the cathode through the ion conductive material react with ammonia and the reducing gas (anode reaction), whereby ammonia is decomposed into water and nitrogen, and electrons are generated. Electrons generated by the anodic reaction are sent from the outside to the cathode. At the cathode, oxygen in the oxidizing gas (for example, air) is anionized by an electrochemical reaction (cathode reaction) between electrons sent from the anode and the oxidizing gas. The anion is sent to the anode through the ionic conductive material, and promotes decomposition of ammonia by an electrochemical reaction.
At this time, in the cathode, the metal particulate oxide film serves as a catalyst, and the electrochemical reaction between electrons and oxygen is promoted. In particular, it is known that when ammonia and hydrogen at a high temperature (for example, about 800 ° C.) are introduced into the anode, the electrochemical reaction at the anode and the cathode is promoted. Therefore, if the ammonia decomposing element is used at a high temperature, a large processing capacity can be secured with a small element. In addition, since it is not necessary to use an expensive noble metal such as platinum (Rt), the cost can be reduced.

Here, the surface region of the metal granular body is composed mainly of Ni or Fe, which is a ferromagnetic material. Thereby, in the precipitation process from the solution containing a ferromagnetic metal ion and a reducing ion, the aggregation action of a metal granular material is accelerated | stimulated. In other words, the ratio of the metal granular body becomes a chain that is continuous in the form of a bead or string. As a result, the conductivity of the metal particles is increased, the cathode reaction, which is an electrochemical reaction, is promoted, and the movement of anions to the ionic roadway material is also promoted.
In particular, since at least the surface region of the metal granular material is made of a high heat-resistant alloy, it exhibits high oxidation resistance even in a high-temperature oxidizing atmosphere. Therefore, deterioration of the cathode is suppressed, generation of deposits due to oxidation is also suppressed, and as a result, maintenance is almost unnecessary. Therefore, the running cost can be reduced.

  In particular, the surface region of the metal granular body can exhibit high oxidation resistance even at high temperatures by being enriched with chromium (Cr) and / or aluminum (Al). Examples of the processing for this purpose include chromizing and aluminizing.

  When the thickness of the oxidized outermost layer of the metal granular body is 0.5 to 100 nm, oxidation resistance can be reliably obtained even in a high-temperature oxidizing atmosphere of about 600 ° C. to 950 ° C., for example.

  The cathode is preferably a sintered body containing a metal granular body and an ion conductive ceramic. As a result, the flow of the oxidizing gas can be ensured at all positions of the cathode, and the reaction between oxygen and anions in the oxidizing gas can proceed while ensuring the catalytic action and the electronic conductivity. it can.

  A current collector of a porous metal body can be disposed on the side of the anode and / or cathode opposite to the ion conductive material. Thereby, the flowability of ammonia can be ensured at the current collector / electrode (anode, cathode) portion. In addition, high electrical conductivity can be ensured in the current collector / electrode (anode, cathode) part, so power transmission (fuel cell) or power consumption (electrolysis device) is lost. Can be done reliably.

  It can be set as the structure which can take out electric power from a cathode and an anode. As a result, power can be generated by using ammonia as a fuel and configuring the fuel cell with the ammonia decomposing element.

  Further, a heater for heating the ion conductive material, the anode, and the cathode can be further arranged to supply the power to the heater. Thereby, ammonia decomposition with excellent energy efficiency can be performed.

  A power generation device of the present invention includes the above ammonia decomposing element capable of taking out electric power, and includes an electric power supply component for supplying electric power to another electric device. Thereby, the ammonia decomposing element can be used as a power generator. Here, the power supply component may be a distribution wiring, a terminal, or the like.

  According to the ammonia decomposing element of the present invention, it is possible to reduce the size and realize a low-cost ammonia decomposing element. It is also easy to have a high oxidation resistance function. Furthermore, this ammonia decomposition apparatus can be used as a power generation apparatus.

It is a block diagram which shows roughly the structure of the ammonia decomposition element which concerns on Embodiment 1 of this invention. 3 is a cross-sectional view showing the internal structure of the ammonia decomposing element according to Embodiment 1. FIG. It is explanatory drawing of the flow of the molecule | numerator, ion, and an electron in a cathode collector and a cathode. It is explanatory drawing of the flow of the molecule | numerator, ion, and electron in an anode. (A), (b) is a figure which shows the procedure of an aluminizing and a chromizing process by a chemical reaction formula in order. It is a block diagram which shows roughly the structure of the ammonia decomposition element based on Embodiment 2 of this invention.

(Embodiment 1)
FIG. 1 is a block diagram schematically showing a configuration of an ammonia decomposition element 10 according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view showing the internal structure of the ammonia decomposing element 10 according to the first embodiment.
As shown in FIG. 1, the ammonia decomposing element 10 includes an anode 2 and a cathode 3 facing each other with the solid electrolyte 1 interposed therebetween. An anode current collector 8 is disposed outside the anode 2, and a cathode current collector 7 is disposed outside the cathode 3.

上記表１は、アンモニアが分解素子１０の使用態様を示すものである。

In Table 1 above, the usage of the decomposition element 10 by ammonia is shown.

  As shown in Table 1, the ammonia decomposing element 10 can generate power as a fuel cell, or can be operated by supplying power as an electrolyzer. In the first embodiment, as shown in FIG. 1, a case where the ammonia decomposing element 10 is used as a fuel cell will be described. This corresponds to the electrochemical reaction of R1 to R3 in Table 1. In particular, a case where ammonia and hydrogen are introduced into the anode 2 and air containing oxygen is introduced into the cathode 3, that is, a case where an electrochemical reaction of R1 in Table 1 is performed will be described. In the fuel cell, the anode 2 is often called a fuel electrode, and the cathode is often called an air electrode. In this description, the terms anode 2 and cathode 3 are used.

  The anode 2 is a sintered body mainly composed of a metal granular body 21 having a configuration to be described later and an oxygen ion conductive ceramic 22. The metal granular material 21 includes a metal particle and a metal particle chain formed by connecting metals. In the present embodiment, the case where the metal particle 21 is a metal particle chain will be described.

  As the oxygen ion conductive ceramic 22, SSZ (scandium stabilized zirconia), YSZ (yttrium stabilized zirconia), SDC (samarium stabilized ceria), LSGM (lanthanum gallate), GDC (gadria stabilized ceria) and the like are used. be able to.

  The cathode 3 is a porous body having voids 3h, and is a sintered body mainly composed of metal particulates 31 whose outermost surface is oxidized, oxygen ion conductive ceramics 32, and preferably silver particles 33. It is. The metal granular body 31 contains nickel (Ni) or iron (Fe) as a main component, and more preferably contains a trace amount of Ti of about 2 to 10000 ppm. At least the surface region of the metal granular body 31 is made into a high heat resistant alloy. Examples of the high heat-resistant alloying treatment include chromizing and aluminizing. The metal granular material 21 includes a metal particle and a metal particle chain formed by connecting metals. In the present embodiment, the case where the metal particle 21 is a metal particle chain will be described.

As the oxygen ion conductive ceramic 32, SSC (samarium strontium cobaltite), LSC (lanthanum strontium cobaltite), LSM (lanthanum strontium manganite), or the like can be used.
As the electrolyte 1, a solid oxide, molten carbonate, phosphoric acid, solid polymer, or the like having oxygen ion conductivity can be used. In particular, a solid oxide is preferable because it can be miniaturized and easily handled. As the solid oxide, SSZ, YSZ, SDC, LSGM, GDC, or the like can be used.

  The cathode current collector 7 and the anode current collector 8 are porous metal bodies having continuous pores, and are composed mainly of nickel (Ni) and / or iron (Fe). Further, at least the surface region of the metal porous body is made into a high heat-resistant alloy. Examples of the high heat-resistant alloying treatment include chromizing and aluminizing.

FIG. 3 is an explanatory diagram of the flow of molecules, ions, and electrons in the cathode current collector 7 and the cathode 3. FIG. 4 is an explanatory diagram of the flow of molecules, ions and electrons in the anode 2. Hereinafter, the operation of the ammonia decomposing element 10 of the present embodiment will be described with reference to FIGS. 2, 3 and 4.
The gas to be decomposed is ammonia (NH 3), and the gas that supplies oxygen ions is air, that is, oxygen (O 2). The ammonia passed through the anode current collector 8 diffuses to the anode 2 through the gap of the anode current collector. In the anode 2, the following reaction formula (1)
2NH3 + 3O2- → N2 + 3H2O + 6e- (1)
Electrochemical reaction (anodic reaction) occurs, and ammonia is decomposed. This reaction occurs at the three-layer interface where the outermost layer (oxide film) of the metal granular body 21, the solid electrolyte 1, and the air layer are in contact. N2 + 3H2O, which is the fluid after the reaction, is released from the anode 2.
The important functions of the metal particles 21 in the anode reaction are a function as a catalyst for an electrochemical reaction and a conductive function for transmitting electrons e ⁻ generated by the electrochemical reaction.

When an oxidizing gas (for example, air) is passed through the cathode current collector 7, oxygen in the air introduced into the cathode 3 is converted into the following reaction formula (2).
O2 + 2e− → 2O2− (2)
Electrochemical reaction (cathode reaction) according to This reaction occurs at the three-layer interface where the outermost layer (oxide film) of the metal granular body 31, the solid electrolyte 1, and the air layer are in contact. Oxygen ions O ²⁻ produced by the reaction reach the anode 2 from the ceramic 32 in the cathode 3 through the solid electrolyte 1. The oxygen ions O ²⁻ that have reached the anode 2 undergo a cathode reaction shown in the reaction formula (2) with ammonia, and the ammonia is decomposed.
The important functions of the metal particles 31 in the cathode reaction are a function as a catalyst for an electrochemical reaction and a conductive function for sending electrons e ⁻ for the electrochemical reaction.

  Further, the electrons e− generated at the anode 2 flow toward the cathode 3 through the load 5. As a result of the reactions shown in the reaction formulas (1) and (2), a potential difference is generated between the anode 2 and the cathode 3, and the cathode 3 has a higher potential than the anode 2. Therefore, the current I flows from the cathode 3 to the anode 2 through the load 5. In the above reaction, if the potential of the cathode 3 is not higher than that of the anode 2, the electrochemical reaction does not proceed. It generates electricity as a fuel cell.

  In the case of the ammonia decomposing element 10, it is preferable to shorten the passage time of oxygen ions in the electrolyte 1 and to secure the electrochemical reaction rate at each electrode. Therefore, in order to promote the entire electrochemical reaction, the heater is heated to, for example, 600 ° C. to 950 ° C. That is, if a part of the load 5 is a heater, ammonia decomposition efficiency can be improved. However, the ammonia decomposing element 10 is not necessarily maintained in the range of 600 ° C to 950 ° C.

-Points on the cathode side configuration-
In a fuel cell, ammonia is decomposed at 600 ° C. to 950 ° C. in an atmosphere in which an oxidizing gas for supplying oxygen ions flows, that is, a high-temperature oxidizing atmosphere. However, with respect to the metal granular body 31 made of Ni or the like, catalytic action deterioration and conductivity deterioration due to high-temperature oxidation occur.
Therefore, the metal granular body 31 in the cathode 3 of the present embodiment has high oxidation resistance in addition to the catalytic function and the conductive function. Specifically, at least the surface region of the metal granule 31 is made of a heat-resistant alloy, and the thickness of the outermost oxide film is suitable for a high-temperature oxidizing atmosphere in the range of 600 ° C to 950 ° C. , Is the point.
In the present embodiment, the metal particles 31 of the cathode 3 are mainly composed of nickel (Ni) and / or iron (Fe), and at least the surface region is made of a high heat-resistant alloy. The inside of the metal granular body 31 does not need to be made of a high heat resistant alloy. Rather, since the inside of the metal granular body 31 is not made of a high heat-resistant alloy, the electrical resistance value can be lowered and the conductivity can be increased. More preferably, the catalyst function is further enhanced by containing a trace amount of Ti of about 2 to 10000 ppm.
In particular, nickel (Ni) is a very suitable metal for producing a metal porous body having continuous pores because it is easy to produce a plated body and fine particles, and has a certain oxidation resistance performance. Has the advantage of

Examples of the high heat-resistant alloying treatment include chromizing and aluminizing. Thereby, the surface area | region of the metal granular material 31 becomes the enriched layer of Cr and / or Al. Ni and Fe itself have a catalytic action to promote the decomposition of oxygen, but the oxide of the Cr and / or Al-enriched layer formed by chromizing or aluminizing further enhances the promoting action of these metals. Can do.
The thickness of the outermost oxide layer 31b of the metal granular body 31 is in the range of 0.5 to 100 nm. By forming in this thickness range, it is possible to ensure the amount of ion transmission necessary for the electrochemical reaction and high oxidation resistance against a high-temperature oxidizing atmosphere. Moreover, when the thickness of the acid lower layer 31b is less than 0.5 nm, the catalytic effect is not exhibited, and when it exceeds 100 nm, the electrical resistance value increases and the electron conductivity decreases. That is, when the thickness of the acid lower layer 31b is in the range of 0.5 to 100 nm, both the catalytic effect and the electronic conductivity can be achieved.

  Moreover, a conductive function can be further improved by making the metal granule 31 into a metal grain chain. The metal particle chain (metal particle 31) is elongated in a string shape, and the content 31a covered with the oxide layer 31b is a good conductor metal (Ni). The electron e− flows smoothly through the contents 31a in the longitudinal direction of the string-like metal particle chain. For this reason, the conductivity of the electron e− to the cathode 3 can be kept high.

-Anode configuration-
The action of the metal particles 31 mainly composed of Ni in the cathode 3 is the same as that of the metal particles 21 in the anode 2 by replacing the gas from oxygen to ammonia.
Therefore, the metal granular material 21 of the anode 2 is also preferably a metal particle chain made of nickel (Ni). Ni may contain a little iron (Fe). More preferably, the catalyst function is further enhanced by containing a trace amount of Ti of about 2 to 10000 ppm.

-Effect of Embodiment 1-
As described above, a gas having a high oxidizing power including oxygen atoms is introduced into the cathode 3 and the cathode current collector 7. Metals exposed to a gas having high oxidizing power at a high temperature of 600 ° C. to 950 ° C. are oxidized by the gas except for special metals, and become unusable after a predetermined period. The form in which the cathode 3 becomes unusable is clogging due to increased oxidation (decreased air permeability, increased pressure loss), reduced current collecting performance, and the like. Note that the cathode current collector 7 also has the same deterioration in air permeability and conductivity due to high-temperature oxidation.
On the other hand, since the reducing gas flows on the anode side such as the anode 2 and the anode current collector 8, the problem of high-temperature oxidation hardly occurs.

Here, in the present embodiment, at least the surface region of the metal granular body 31 is subjected to high heat-resistant alloying treatment such as chromizing and aluminizing. Therefore, it exhibits high oxidation resistance even in a high-temperature oxidizing atmosphere. Therefore, deterioration of the metal part of the cathode 3 in a high-temperature oxidizing atmosphere and deposition of reaction products can be suppressed.
Therefore, almost no maintenance is required, and the running cost can be greatly reduced.

Moreover, the anode reaction and cathode reaction proceed at a very high reaction rate due to the configuration of the anode 2 and the cathode 3 described above. For this reason, a large amount of ammonia can be efficiently decomposed by a small element having a simple structure.
Moreover, since an expensive noble metal such as platinum (Pt) is not used, the initial cost can be reduced.
Furthermore, since power generation is possible as described above, for example, it is not necessary to supply the power of the heater built in the ammonia decomposition element 10 of the present embodiment from the outside, or the amount of supply from the outside can be reduced. . For this reason, it is excellent in energy efficiency.

Note that the decomposition of the decomposition target gas proceeds only by raising the temperature and bringing the decomposition target gas into contact with the catalyst. It is disclosed in prior literature and is well known as described above.
However, as described above, in the element constituting the fuel cell, oxygen ions are involved in the reaction at high temperature from the cathode 3 through the ion conductive solid electrolyte 1, and as a result, the generated electrons are conducted outside. The decomposition reaction rate is dramatically improved. One of the major features of the present invention is that it has the function of the cathode 3 and a configuration that provides the function.

表２は、クロム処理による耐食性の向上効果を示すデータである。この試験は、ＳＵＳ３０４（８〜１０％Ｎｉ，１８〜２０％Ｃｒ），ＳＵＳ３１０Ｓ（１９〜２２％Ｎｉ，２４〜２６Ｃｒ），４５Ｃｒ３０Ｎｉ合金の板材について、行なっている。試験温度は８００℃，９００℃で、０．１％ＳＯ_２，１５％ＣＯ_２，２％Ｏ_２，残Ｎ_２の成分のガスを、１００ｈｒの間流している。
表２に示されるように、クロマイジング処理を施したＳＵＳ等は、無処理材よりも、約５〜２０倍の耐食性，耐腐食量があることがわかる。つまり、カソード３の金属粒状体３１に、高耐熱合金化を行うことにより、高温の酸化雰囲気における耐酸化性が向上することがわかる。

Table 2 is data showing the effect of improving the corrosion resistance by the chromium treatment. This test is conducted on plate materials of SUS304 (8-10% Ni, 18-20% Cr), SUS310S (19-22% Ni, 24-26Cr), 45Cr30Ni alloy. The test temperatures were 800 ° C. and 900 ° C., and 0.1% SO ₂ , 15% CO ₂ , 2% O ₂ and the remaining N ₂ component gas were allowed to flow for 100 hr.
As shown in Table 2, it can be seen that SUS or the like subjected to chromizing treatment has about 5 to 20 times the corrosion resistance and corrosion resistance than the untreated material. That is, it can be seen that the oxidation resistance in a high-temperature oxidizing atmosphere is improved by forming the metal granular body 31 of the cathode 3 into a high heat-resistant alloy.

-Manufacturing method of metal granules-
Next, the manufacturing method of the metal granular materials 21 and 31 of said ammonia decomposition element 10 is demonstrated.
1. Formation of metal particles The cathode and anode metal particles 21 and 31 are preferably produced by a reduction deposition method. The reduction precipitation method of the metal particulates 21 and 31 is described in detail in Japanese Patent Application Laid-Open No. 2004-332047. The reduction precipitation method introduced here is a method using trivalent titanium (Ti) ions as a reducing agent, and the precipitated metal particles (Ni particles and the like) contain a small amount of Ti. For this reason, it can identify with what was manufactured by the reduction | restoration precipitation method by trivalent titanium ion by quantitatively analyzing Ti content. By changing the metal ions present together with the trivalent titanium ions, desired metal grains can be obtained. Further, in order to form a metal particle chain, Ni ions are allowed to coexist in the case of Ni. When a small amount of Fe ions is added, a Ni grain chain containing a small amount of Fe is formed. In order to form a chain, the metal is preferably a ferromagnetic metal and has a predetermined size or more. Since both Ni and Fe are ferromagnetic metals, a metal particle chain can be easily formed. The size requirement is that the ferromagnetic metal forms a magnetic domain and bonds with each other by magnetic force, and in the combined state, the metal is deposited → the growth of the metal layer occurs, and the entire metal body is integrated. ,is necessary. Even after metal grains of a predetermined size or more are bonded by magnetic force, metal deposition continues, for example, the neck at the boundary of the bonded metal grains grows thicker together with other portions of the metal grains.
Therefore, the average diameter D of the metal particles contained in the metal particles 21 and 31 of the anode 2 or the cathode 3 is preferably in the range of 5 nm or more and 500 nm or less. The average length L of the metal particle chain is preferably in the range of 0.5 μm or more and 1000 μm or less.
The ratio between the average length L and the average diameter D is preferably 3 or more. However, it may have dimensions outside these ranges.

Next, the metal particle chain 31 of the cathode 3 is subjected to a heat-resistant alloying treatment such as aluminizing and chromizing shown in FIGS. 5 (a) and 5 (b). Both aluminizing and chromizing may be performed.
FIG. 5A shows a specific example of aluminizing. In this method, a non-processed material is embedded in a steel case together with a preparation made of Fe—Al alloy powder and NH 4 Cl powder. Next, the case is sealed, and the sealed case is charged into a furnace and heated to 900 ° C. to 1050 ° C. Thereby, an Al diffusion / permeation layer can be obtained, and high-temperature oxidation resistance, wear resistance, and the like can be improved.
FIG. 5B shows a specific example of chromizing. In this method, a Ni-plated porous body (Me) is embedded in a case together with a preparation composed of Cr powder, Al2O3 powder and NH4Cl powder. Subsequently, it heats at 900 to 1100 degreeC in a furnace, passing H2 gas or Ar gas in a case. As a result, a Cr diffusion / permeation layer can be obtained, and the high-temperature oxidation resistance can be enhanced.
In FIGS. 5A and 5B, only the powder method is shown for both aluminizing and chromizing, but Al or Cr is diffused by using an existing arbitrary method such as a gas method or a molten salt method. Can penetrate.

The high heat-resistant alloying treatment may be performed after sintering described later. Before the process shown in FIGS. 5A and 5B, sintering described later is performed. Then, the fine powder containing Cr, or the fine powder containing Cr and the fine powder containing Al are rubbed into the porous portion of the sintered body and kept at a high temperature. Alternatively, chromizing and aluminizing are performed by maintaining a high temperature while flowing a gas containing Cr and Al through the sintered body.
Thereby, Cr, Al, etc. are infiltrated into the surface area of the metal granular bodies 31, 21, and chromizing, aluminizing, etc. are performed. Further, chromium oxide (CrO ₂ ) can be used in place of Cr for cost reduction. Thereafter, the next surface oxidation treatment is performed.
By this method, it is not necessary to raise the temperature region of the highly heat-resistant alloy to the sintering temperature, so that the catalytic function and the high-temperature oxidation resistance function can be kept high.
Moreover, only the surface area | region of the metal granule 21 and 31 exposed after sintering can be heat-resistant alloy-ized. In other words, when heat-resistant alloying treatment was performed before sintering, it was separated before sintering, but the boundaries of the metal particles or metal particle chain bonded after sintering were also made into a heat-resistant alloy, and the conductive function Gets worse. On the other hand, in this method, the boundary portion remains a metal mainly composed of Ni or Fe, so that the conductive function is maintained high.

2. Sintering The average diameter of the raw material powder of the ceramics 22 or 32 contained in the anode 2 or the cathode 3 is about 0.5 μm to 50 μm. The compounding ratio between the surface-oxidized metal particles 21 and 31 and SSZ22 and LSZ32 is in the range of 0.1 to 10 in terms of mol ratio.
A sintering method is performed by hold | maintaining for 30 minutes-180 minutes, for example in air | atmosphere atmosphere at the temperature of 1000 to 1600 degreeC.
The cathode 3 is composed of a sintered body such as a metal particle chain 31 with an oxide layer, LSM, and Ag particles 33. The average diameter of the Ag particles is preferably 10 nm to 100 nm. The compounding ratio of silver and LSM is preferably about 0.01 to 10.

3. Surface oxidation The metal particles 21 and 31 in the anode 2 and the cathode 3 are subjected to surface oxidation in order to enhance the catalytic action for promoting the electrochemical reaction.
Three types of surface oxidation treatments are suitable: (i) heat treatment oxidation by a vapor phase method, (ii) electrolytic oxidation, and (iii) chemical oxidation. In (i), it is good to process at 500-700 degreeC for 1 to 30 minutes in air | atmosphere. This is the simplest method. In (ii), surface oxidation is performed by applying a potential to about 3 V with reference to a standard hydrogen electrode and performing anodization. However, the oxide film thickness can be controlled by the amount of electricity according to the surface area. However, when the area is increased, it is difficult to uniformly form an oxide film. In (iii), the surface is oxidized by being immersed in a solution in which an oxidizing agent such as nitric acid is dissolved for about 1 to 5 minutes. Although the oxide film thickness can be controlled by time, temperature, and type of oxidizer, cleaning of chemicals is troublesome. Either method is suitable, but (i) or (iii) is more preferred.
A desirable thickness of the oxide layer is 0.5 to 100 nm. However, it may be outside this range. If the oxide film is too thin, the catalyst function will be insufficient. In addition, even a slight reducing atmosphere may cause metallization. Furthermore, since the ions are carried through the oxide film, a certain thickness is required. On the other hand, if the oxide film is too thick, the catalytic property is sufficiently maintained, but on the other hand, the electronic conductivity at the interface is impaired and the power generation performance is lowered.
The time of surface oxidation of the chain metal powder may be before the above-mentioned sintered body formation, but is preferably after the sintered body formation.

Next, a manufacturing process of the cathode current collector 7, in particular, a continuous pore porous body (hereinafter referred to as a plated porous body) will be schematically described.
First, a foamed resin is prepared by foaming a resin such as urethane. Subsequently, the pore continuation process which continues the foamed pore is performed. The pore continuation treatment includes a method of removing a film by dissolving a thin film remaining in the pores with a chemical solution having urethane solubility, or removing the film by an explosion treatment. However, it is not restricted to these methods. Further, urethane obtained by continuous pore processing with Bridgestone or the like can be obtained, and this method is preferably used. Thereafter, a conductive carbon film is attached to the pore inner walls, or a conductive thin film is formed by electroless plating or the like. Next, a metal plating layer is formed on the conductive carbon film or the conductive thin film by electroplating. This metal plating layer becomes the skeleton of the pore body. For metal plating, a plating solution containing nickel ions is preferably used to form a Ni plating layer. Ni has high-temperature oxidation resistance in the above-mentioned low temperature range, and the formation of a plating layer is easy. Next, the resin is dissipated by heat treatment to leave only the metal plating layer, thereby forming a Ni-plated porous body.
In order to obtain oxidation resistance at higher temperatures, an alloying treatment is applied to the Ni-plated porous body as described above. This alloying treatment is performed by introducing Cr, Al, and other metals from the outside into the surface layer. Usually, alloying is stopped only on the surface layer to form a plated porous body with an alloyed surface layer.
Further, nickel ions and other metal ions can be dissolved in the plating solution to make the plated body a nickel alloy. As such, a nickel alloy skeleton may be formed by directly forming an alloy plating layer.

(Embodiment 2)
FIG. 6 is a block diagram schematically showing the configuration of the ammonia decomposing element according to Embodiment 2 of the present invention. The reaction in the present embodiment is generally an electrolysis reaction as shown by reaction R4 in Table 1. That is, the ammonia decomposing element 10 is an electrolysis element, and decomposes ammonia by supplying electric power. Ammonia is introduced into the anode 2 and carbon dioxide is introduced into the cathode 3.
The anodic reaction is the same as in Embodiment 1, but the cathodic reaction is CO2 + 2e− → CO + O2−.
In this case, a power source 9 is arranged between the anode current collector 8 and the cathode current collector 7, and a potential difference (voltage) is applied from the outside so that the anode side becomes higher. The external power source 9 consumes power for the ammonia decomposition element 10.

As described above, although there is a difference in generation and consumption of electric power from the first embodiment, the configurations of the anode 2 / electrolyte 1 / cathode 3 and current collectors 7 and 8 are the same as those in the first embodiment. It is.
That is, the anode 2 and the cathode 3 are also composed of sintered bodies of the surface-oxidized metal particulates 21 and 31 and the ceramics 22 and 32 as in the first embodiment. As in the first embodiment, at least the surface region of the metal granular body 31 of the cathode 3 is made of a high heat resistant alloy. Therefore, a high oxidation resistance function can be exhibited in a high-temperature oxidizing atmosphere.
As a result, even with the ammonia decomposing element 10 of the present embodiment, a large amount of ammonia gas can be quickly processed with a small and simple element, and the initial cost and running cost are low.

  As described in the first embodiment, it is well known to decompose a gas to be decomposed under a catalyst. However, in this embodiment, carbon dioxide is used as an oxygen ion supply source in the electrochemical reaction, and it is easy to maintain and maintain while heating at 600 ° C. to 950 ° C. in order to obtain a practical decomposition rate. Can be. Regarding the improvement of the ammonia decomposition rate, as in the first embodiment, the oxygen ion generation promotion of the catalyst (silver particles, metal particle chain with oxide layer) at the cathode, and the same configuration excluding silver particles at the anode By providing the effect, the reaction speed can be greatly improved.

  Next, an example of actual verification using a specimen will be described. The used test bodies are Examples 1 to 8 and Comparative Examples 1 and 2 of the present invention. The materials and sizes of the respective parts in Examples 1 to 8 and Comparative Examples 1 and 2 are as shown in Table 3.

The time course of the ability to decompose air containing 20% ammonia at a predetermined temperature was measured by the test. The results are shown in Table 4. However, the processing capacity under the basic conditions in Table 4 is the one at the time when 5 h (5 hours) elapsed at the temperature of 800 ° C. using the specimen of Example 2. The processing capacity at this time is 1.1 mmol / cm ² · min, and Table 4 shows the processing capacity of each specimen as a relative value with this value being 100.

Table 4 shows the following.
Looking only at Example 1 (test numbers t1 to t3) in which the metal particles of the cathode were composed of Fe20% Ni, as the decomposition temperature increased to 700 ° C, 800 ° C, and 9000 ° C, the initial (5h) Although the processing capacity is high, if it is used for a long time (5000 hours (5000 hours)), the processing capacity decreases. This is thought to be due to the deterioration of the surface of the metal particulates.
Looking at Examples 2, 3, and 4 (test numbers t4 to t6) in which the metal particles are made of Ni and the thickness of the oxide layer is changed to 10 nm, 0.5 nm, and 100 nm, the thinner the oxide layer, Although the initial processing capacity (5h) is high, the processing capacity tends to decrease when used for a long time (5000h). This is presumably because the thinner the oxide layer, the more easily the surface of the metal particulates deteriorates.
As shown in Table 3, in Examples 5, 6 and 7, the metal particles were made of Ni, and the surface layer was made into a high heat-resistant alloy by Cr enrichment, Al enrichment and CrAl enrichment, respectively. It is. The processing capacities of Examples 5, 6, and 7 (test numbers t7 to t8) after 5000 hours have kept 50% or more of the basic conditions (when 5 hours have passed). In particular, the processing capacity of Example 7 in which the surface layer of the metal granular body was enriched with CrAl maintains 70% of the basic conditions even after 5000 hours. Therefore, high heat resistance is obtained even under high-temperature and high-oxidation conditions by alloying the surface layer of the metal granular body with Cr, Al, CrAl or the like. In particular, a remarkable effect can be exhibited by chromizing and aluminizing the surface of the metal granule.
In the case of Example 8 in which the metal granular body is made of Ni and Ag 10% is added (test number t10), the initial processing capacity (at the time of 5 hours) is high, but after 5000 hours, the processing capacity is 30 of the basic condition. It has fallen to about%. Therefore, it can be seen that sufficient oxidation resistance is not obtained only by addition of Ag.
In Comparative Examples 1 and 2 (test numbers t11 and t12) in which the metal granular body is made of Ni, the surface layer is not alloyed, and the thickness of the oxide layer is 0.3 nm and 1000 nm, both of them elapse for a long time Later processing capacity has declined. In particular, it can be seen that when the thickness of the oxide layer is reduced to 0.3 nm, the processing capability is remarkably lowered by such long use at a high temperature. That is, the catalyst function is not sufficiently developed due to the deterioration of the metal particulates. Therefore, the thickness of the oxide layer is preferably 0.5 nm or more.
When Comparative Example 2 in which the thickness of the oxide layer is 1000 nm is compared with Example 3 in which the thickness of the oxide layer is 0.5 nm, the processing capability is higher at 1000 nm after 5000 hours. However, in the case of Comparative Example 2, the processing capacity at 5 h and 500 h is considerably low. In addition, when such a thick oxide layer is present, the electron conductivity is lowered. Therefore, the thickness of the oxide layer is preferably 100 nm or less.

  The structure of the embodiment of the present invention disclosed above is merely an example, and the scope of the present invention is not limited to the scope of these descriptions. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

  The ammonia decomposing element of the present invention can be used as an ammonia decomposing apparatus for environmental protection or a power generation apparatus.

1 Ion conductive electrolyte (solid oxide electrolyte)
2 Anode 3 Cathode 3h Air gap 5 Load 7 Cathode current collector 7a Skeletal part 7h Air gap 8 Anode current collector 9 Power supply 21 Metal granular material 22 Ceramics 31 Metal granular material 32 Ceramics 33 Silver particles

Claims (9)

An element used to decompose ammonia,
A porous anode into which ammonia is introduced;
A porous cathode that is paired with the anode and into which an oxidizing gas is introduced;
An ionic conductive material interposed between the anode and the cathode and having ionic conductivity;
The cathode is an ammonia decomposing element comprising nickel (Ni) and / or iron (Fe) as a main component and containing metal particles whose outermost layer is oxidized. The ammonia decomposing element according to claim 1,
An ammonia decomposing element in which at least a surface region of the metal particles of the cathode is made of a high heat-resistant alloy and an outermost layer thereof is oxidized. The ammonia decomposing element according to claim 2,
The ammonia decomposition element, wherein the surface region of the metal particulate is enriched with chromium (Cr) and / or aluminum (Al). In the ammonia decomposition element according to any one of claims 1 to 3,
The ammonia decomposition element, wherein the oxidized outermost layer of the metal granular body has a thickness of 0.5 to 100 nm. In the ammonia decomposition element according to any one of claims 1 to 4,
The said cathode is an ammonia decomposition element which is a sintered compact of the said metal granular material and an ion conductive ceramic. In the ammonia decomposition element according to any one of claims 1 to 5,
An ammonia decomposing element, wherein a current collector of a porous metal body is arranged on the opposite side of the anode and / or cathode to the ion conductive material. In the ammonia decomposition element according to any one of claims 1 to 6,
An ammonia decomposition element capable of taking out electric power from the cathode and the anode. The ammonia decomposition element according to claim 7,
A heater for heating the ion conductive material, the anode and the cathode;
An ammonia decomposing element, wherein electric power extracted from the cathode and the anode is supplied to the heater. The ammonia decomposing element according to claim 8,
A power supply component for supplying the power to another electrical device;
A power generator equipped with.

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