JP2010159472A - Ammonia decomposing element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ammonia decomposing element which has high durability, is free from maintenance over a long period, and also, can work at a low running cost (1), and which has high treatment capacity and a high decomposing speed as a small-sized apparatus (2). <P>SOLUTION: The ammonia decomposing element 10 is provided with a cathode collector 7 in contact with a cathode 3, the cathode collector 7 is made of a metal porous body having continuous pores, the metal porous body is made of nickel or a nickel alloy, or the surface layer of the metal porous body of nickel or a nickel alloy is enriched with at least one kind selected from chromium (Cr), aluminum (Al), silver (Ag), gold (Au) and platinum (Pt). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an ammonia decomposing element, and more specifically, to an ammonia decomposing element that can decompose gas efficiently and is small in size and does not require maintenance.

  Ammonia is an indispensable compound for agriculture and industry, but it is harmful to humans. Therefore, many methods for decomposing ammonia in water and air have been disclosed. For example, in order to decompose and remove ammonia from water containing high-concentration ammonia, a method in which 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 Has been proposed (Patent Document 1). In addition, a method of separating ammonia in the air by the same process as described above and combusting with a catalyst is also disclosed (Patent Document 2). Moreover, a method for decomposing ammonia-containing wastewater into a nitrogen and water by using a catalyst has been proposed (Patent Document 3). As for the catalyst for promoting ammonia decomposition reaction, porous carbon particles containing a transition metal component, manganese composition, iron-manganese composition (Patent Document 3), chromium compound, copper compound, cobalt compound (Patent Document 4), alumina Platinum (Patent Document 5) and the like carried on a three-dimensional network structure made is disclosed. In the method of decomposing ammonia by a chemical reaction using the above catalyst, generation of nitrogen oxides NOx can be suppressed. Furthermore, a method for more efficiently promoting the thermal decomposition of ammonia at 100 ° C. or lower by using manganese dioxide as a catalyst has been proposed (Patent Documents 6 and 7).

JP-A-7-31966 Japanese Patent Laid-Open No. 7-116650 Japanese Patent Laid-Open No. 11-347535 JP-A-53-11185 JP 54-10269 A JP 2006-231223 A JP 2006-175376 A

  According to the above-described method using a chemical such as a neutralizing agent (Patent Document 1), a method of burning (Patent Document 2), a method using a thermal decomposition reaction using a catalyst (Patent Documents 3 to 7), etc. Is possible. However, the above method has a problem in that it requires chemicals and external energy (fuel), and requires periodic replacement and maintenance of the catalyst, resulting in high running costs. In particular, maintenance-free components are not allowed for a long period of time. In addition, the apparatus becomes large and, for example, when it is additionally provided in existing equipment, the arrangement may be difficult. In Japan, the downsizing of the device often has great practical benefits unless it impairs efficiency, and is usually highly evaluated. Moreover, in the method of burning ammonia, a problem of discharging carbon dioxide and NOx also occurs.

  The present invention (1) has high durability, is maintenance-free for a long period of time and can be operated at a low running cost, and (2) has a large processing capacity and a high decomposition rate in a small apparatus. An object of the present invention is to provide an ammonia decomposing element.

  The ammonia decomposing element of the present invention is an element for decomposing ammonia. This ammonia decomposing element is sandwiched between a porous anode into which ammonia or a gas containing ammonia is introduced, a porous cathode into which a gas containing oxygen atoms is introduced, and the anode and the cathode. An ion conductive material having oxygen ion conductivity and a cathode current collector in contact with the cathode. The cathode current collector is made of a porous metal body having continuous pores, and the porous metal body is made of nickel or a nickel alloy, or the surface layer of nickel or a nickel alloy is made of (chromium (Cr), aluminum (Al ), Silver (Ag), gold (Au), and platinum (Pt)).

In the above element, a gas containing oxygen atoms is introduced into the cathode, oxygen ions are generated at the cathode, and the oxygen ions are sent to the ion conductive material. In order to increase the diffusion rate of oxygen ions in the ion conductive material and to promote the electrochemical reaction at each electrode, the material is heated to a high temperature. For this reason, the vicinity of the cathode surface including the cathode current collector becomes a high-temperature oxidizing atmosphere. According to said structure, when decomposing | disassembling ammonia in gas by an electrochemical reaction, the following effect | action can be acquired.
(E1) By forming the cathode current collector with a metal porous body, a turbulent state of the gas is promoted while passing a gas containing ammonia. By making the gas turbulent, rather than letting it pass as a laminar flow, the opportunity for the gas to contact the cathode, the time, etc. can be lengthened to promote the decomposition reaction (electrochemical reaction). Thereby, the electrochemical reaction efficiency per cathode unit area can be increased.
(E2) Since the cathode current collector is a metal porous body, it is possible to ensure the inflow of electrons from the outside to the cathode and to facilitate charge transfer accompanying ammonia decomposition. This can prevent the exchange of electrons from becoming a bottleneck for electrochemical reactions.
(E3) By forming the metal porous body with nickel or the like, or with an enriched layer of chromium or the like, high-temperature corrosion (oxidation) performance that is literally the same as or superior to nickel can be provided. The vicinity of the cathode of the ammonia decomposing element is heated to a high temperature of, for example, 600 ° C. to 950 ° C., and a gas containing oxygen atoms such as air flows in to generate oxygen ions at the cathode. For this reason, the high temperature oxidation reaction of the metal proceeds in the cathode and the cathode current collector, and the durability (high temperature oxidation resistance) may be insufficient in practice. Nickel is easy to produce a plated body and fine particles, and therefore is a very suitable metal for producing a continuous porous metal porous body and has a certain high-temperature oxidation resistance. However, depending on the application, the high-temperature oxidation resistance is insufficient, and in such a case, a material having a better high-temperature oxidation resistance is used. The durability of the cathode current collector can be improved by forming the metal porous body with a material excellent in high-temperature oxidation resistance. As a result, the ammonia decomposition element can be used stably over a long period of time without maintenance such as replacement or repair of the cathode current collector.
Here, the nickel alloy may be a nickel base alloy containing other metals based on nickel, or an alloy of other metal bases based on other metals, in which nickel is contained. Also good. Further, the gas containing oxygen atoms introduced into the cathode refers to a gas containing molecules containing oxygen atoms, and refers to air, oxygen gas, NOx, water vapor, carbon dioxide, or a mixed gas of two or more of these.
The metal porous body is most broadly (1) a sintered body of metal particles or metal fibers, (2) a metal plated body formed using a foamed resin that has been subjected to pore continuation treatment, and (3) punching metal. Or a machined porous body such as expanded metal is preferably used. Also, any other thing may be used.

  Said metal porous body can be formed with a metal plating body. By forming a metal porous body with a metal plating body, it is not necessary to apply pressure to narrow the gap during molding. As a result, while ensuring the effect of (E1), the porosity can be increased, the air permeability is good, and the cathode current collector has a small pressure loss compared to the sintered body of metal particles or metal fibers. it can. The porous metal body often has a skeleton in which columnar metal plating bodies are continuous.

The porosity of said metal porous body can be 0.6 or more and 0.98 or less. Thereby, very good air permeability can be obtained. If the porosity is less than 0.6, the pressure loss becomes large, and if forced circulation by a pump or the like is performed, the energy efficiency is lowered, and bending deformation or the like occurs in the ion conductive material or the like. In order to reduce the pressure loss and prevent the ion conductive material from being damaged, the porosity is preferably 0.8 or more, and more preferably 0.9 or more. On the other hand, when the porosity exceeds 0.98, the electrical conductivity is lowered and the current collecting function is lowered.
(1) The pore size is SEM (Scanning Electric Microscopy:
By observation with a scanning electron microscope, (2) specific surface area was determined by the BET surface area method, and (3) porosity was determined from the surface area, volume and weight.

When a metal porous body is prepared using urethane, when the pore diameter of the metal porous body is x (mm) and the specific surface area is y (m ² / m ³ ), 400 ≦ (x−0.3) The structure which satisfy | fills y can be taken. As a result, an increase in pressure loss can be prevented while obtaining the effect (E1). In order to more strictly prevent an increase in pressure loss, 600 ≦ (x−0.3) y is preferable. The upper limit of (x−0.3) y is not particularly required, but in order to ensure the effect of (E2), for example, 3000 can be set as the upper limit. The asymptote in the hyperbola of the product of the hole diameter and the specific surface area represents the minimum limit value of 0.3 mm for the hole diameter. The minimum limit value of 0.3 mm is the minimum limit value when a porous metal body is manufactured using urethane. When melamine resin is used instead of urethane, the minimum limit value is 50 μm, that is, about 0.05 mm. The range of the metal porous body manufactured using the melamine resin is not particularly limited, but it goes without saying that the metal porous body manufactured using the melamine resin is also included in the scope of the present invention as long as the configuration requirements are met. . That is, if the above-mentioned constituent requirements such as porosity of the metal porous body manufactured using melamine resin are applicable, it is included in the scope of the present invention.

  The anode, the ion conductive material, and the cathode are in the form of an integrated MEA (anode / ion conductive material / cathode), and the cathode current collector is in sheet form, laminated in contact with the cathode, and oxygen atoms A gas flow path containing As a result, the effect of (E1) can be ensured, and the proportion of ammonia that passes through without being decomposed can be significantly reduced. Moreover, a thin ammonia decomposition element sheet | seat can be obtained by setting it as a sheet form, and a compact ammonia decomposition element can be obtained by laminating | stacking this. The final product ammonia decomposing element may have any shape, and can take a possible shape such as a plate shape or a cylindrical shape wound with a plate shape.

  The cathode may be a sintered body of ion conductive ceramics or a sintered body of ion conductive ceramics and silver. Thereby, high efficiency can be secured in the cathode reaction during the electrochemical reaction.

The above-described electrochemical reaction at the cathode is promoted by silver catalysis, but is often limited by the speed or time of movement of the ion conductive material of oxygen ions. In order to increase the moving speed of oxygen ions, the above ammonia decomposing element is usually provided with a heating device such as a heater, and is usually set at a high temperature, for example, 600 ° C. to 950 ° C. By raising the temperature, not only the ion transfer speed but also chemical reactions involving charge transfer at the electrodes are promoted.
Oxygen ions moving from the ion conductive material to the anode are generated and supplied by an electrochemical reaction at the cathode. A gas containing oxygen atoms is introduced into the cathode, and molecules containing oxygen atoms at the cathode react with electrons generated at the anode and passed through the circuit to generate oxygen ions. The generated oxygen ions move to the anode in the ionic conductive material. Electrons participating in the reaction at the cathode come from an external circuit (including a capacitor, a power source, and a power consuming device) that connects the anode and the cathode. The electrochemical reaction in the element may be a power generation reaction of a fuel cell or an electrolysis reaction.

  When the cathode contains silver particles, the silver particles have a catalytic action for the cathode reaction and conductivity for the current generated as a result of the cathode reaction. Thus, a large processing capacity can be secured. In addition, although ammonia to be decomposed is introduced into the anode, a neutralizing agent or the like is unnecessary, and it is not necessary to take out the reaction product, so that it can be operated at a low running cost.

  A heater for heating the ion conductive material, the anode and the cathode, and a temperature control system for controlling the temperatures of the ion conductive material, the anode and the cathode can be provided. In order to obtain a practical ammonia decomposition rate, it is necessary to set the oxygen ion diffusion rate in the ionic conductive material to a certain level or more, and the reaction rate in the electrode is also accelerated. Usually, a heater for heating to 600 ° C. to 950 ° C. and a temperature control system for controlling the temperature of the ion conductive material or the like are provided.

  In an electrochemical reaction in which ammonia is decomposed with oxygen ions, the cathode potential becomes higher than the anode potential, and power can be taken out from the cathode and the anode. In this case, power supply components (distribution wiring, terminals, etc.) for supplying power to other electrical devices can be provided.

  The extracted power can be supplied to the heater and / or the temperature control system, thereby increasing energy efficiency.

  According to the ammonia decomposition element of the present invention, even if it is heated to a high temperature in order to increase the decomposition rate, it is maintenance-free for a long period of time, is highly durable, and can be operated at a low running cost. Moreover, since it is heated to a high temperature to promote the electrochemical reaction of ammonia decomposition, it has a large processing capacity and a high decomposition rate with a small apparatus.

It is sectional drawing which shows the ammonia decomposition element in Embodiment 1 of this invention. It is a figure for demonstrating the state which decomposes | disassembles ammonia by making the ammonia decomposition element of FIG. 1 into a fuel cell (power generation element). FIG. 4 is a diagram for explaining the characteristics of a cathode current collector and a cathode in the ammonia decomposition element according to the first embodiment. FIG. 3 is a diagram for explaining a method of manufacturing a plated porous body of a cathode current collector of the ammonia decomposition element according to the first embodiment. It is a figure which shows the specific example of the method of performing an alloying process to a plating porous body, (a) is aluminizing, (b) is a figure which shows chromizing. It is a figure which shows the relationship between the specific surface area and the hole diameter of Ni plating porous body manufactured with the method of FIG. FIG. 3 is a diagram for explaining the characteristics of the anode in the ammonia decomposition element according to the first embodiment. It is sectional drawing which shows the ammonia decomposition element (electrolysis element) in Embodiment 2 of this invention.

(Embodiment 1)
FIG. 1 is a diagram showing an ammonia decomposing element 10 according to Embodiment 1 of the present invention. In the ammonia decomposing element 10, an anode 2 and a cathode 3 are arranged with an ionic conductive 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. The anode 2 is a sintered body mainly composed of a metal particle chain 21 having a surface oxide layer and an ion conductive ceramic (metal oxide) 22 and is a porous body through which a fluid can flow. The cathode 3 is also a porous body through which a fluid can flow. For example, the cathode 3 can be a sintered body mainly composed of an ion conductive ceramic 32 and silver (Ag) 33. Both the anode current collector 8 and the cathode current collector 7 are metal porous bodies having continuous pores. The material constituting the cathode current collector 7 will be described in detail later.
The electrolyte 1 may be anything as long as it has ionic conductivity, such as a solid oxide, molten carbonate, phosphoric acid, a solid polymer, and an electrolytic solution. The material of the electrolyte 1 will be specifically described later. As shown in Table 1, the ammonia decomposing element 10 can generate electric power as a fuel cell, or can be operated by supplying power as an electrolysis apparatus. In the first embodiment, as shown in FIG. 2, 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 is introduced into the anode 2 and air or 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, but in this description, the terms anode 2 and cathode 3 are used.

In FIG. 2, the gas to be decomposed is introduced into the anode 2 using the anode current collector 8 as a flow path. A fluid for supplying oxygen ions is introduced into the cathode through the cathode current collector 7 as a flow path. The introduced fluid undergoes a predetermined reaction at the cathode 3 or the anode 2 and is then discharged to the outside through the cathode current collector 7 or the anode current collector 8 as a flow path. The reaction R1 is an electrochemical reaction that involves power generation, and can extract power from the anode current collector 8 and the cathode current collector 7 and supply power to the load. As the load, a heating device (not shown), for example, a heater, incorporated in the ammonia decomposing element 10 can be used.
In the case of the ammonia decomposing element 10, in order to shorten the passage time of oxygen ions in the electrolyte 1 and to secure the electrochemical reaction speed at each electrode, in order to promote the entire electrochemical reaction, it is important to use a heater or the like. For example, it is heated to 600 ° C. to 950 ° C. (it may be used at other temperatures). 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. Forms in which the cathode current collector becomes unusable include clogging due to increased oxidation (decreased air permeability, increased pressure loss), decreased current collecting performance, and the like. Also in the cathode, the same deterioration in air permeability and conductivity due to high-temperature oxidation occurs. Since a reducing gas flows on the anode side such as the anode current collector, the problem of high-temperature oxidation hardly occurs.

(Point 1 in the embodiment of the present invention 1-high temperature oxidation resistance)
FIG. 3 is a diagram for explaining the role of the materials constituting the cathode 3 and the cathode current collector 7. The point of the embodiment of the present invention is that an electrochemical reaction is used for decomposing ammonia, and the electrochemical reaction is promoted. It is characterized in that it has durability against high-temperature oxidation of the body 7 and is a material that does not require or is easy to maintain. In order to obtain the action (E3), the cathode current collector 7 is formed of a porous body having continuous pores made of nickel or a nickel alloy, or the surface layer of the nickel or nickel alloy is made of (chromium (Cr) , Aluminum (Al), silver (Ag), gold (Au) and platinum (Pt)). This enhances the high temperature oxidation resistance (E3).
The cathode 3 in the present embodiment is a porous body having a void 3h, and is composed of Ag particles 33 and ceramics 32 through which oxygen ions pass. Among them, the Ag particles 33 have a catalytic function for greatly promoting the cathode reaction O ₂ + 2e ⁻ → 2O ²⁻ . The cathode current collector 7 is composed of the following materials by dividing 600 ° C. to 950 ° C. into, for example, a low temperature region and a high temperature region, or an atmosphere having a strong oxidizing power and a weak atmosphere. The distinction between the low temperature region and the high temperature region, or the strength of the oxidizing power does not need to be divided so clearly.
(Low temperature range or relatively weak oxidizing atmosphere):
The cathode current collector 7 is a porous metal body such as Ni having continuous pores 7h and having a skeleton 7a as a conductive portion. The porous metal body such as Ni may be any material as long as air permeability and conductivity are ensured. However, among them, a metal porous body having continuous pores in which triangular prism-like skeletons formed by Ni plating are three-dimensionally connected is preferable. Can be used. The manufacturing method will be described in detail later, but after making the pores of the foamed resin continuous, by forming a skeleton by metal plating, compared to a sintered body of metal particles and metal fibers, Air permeability is good and conductivity is secured.
The cathode 3 is a sintered body mainly composed of oxygen ion conductive ceramics 32 and silver (Ag) 33. As the oxygen ion conductive ceramic 32, it is preferable to use LSM (lanthanum strontium manganite), LSC (lanthanum strontium cobaltite), SSC (samarium strontium cobaltite) or the like. The silver of the catalyst may not be included depending on the conditions.
(High temperature range or highly oxidizing atmosphere):
The cathode current collector 7 for a high temperature region or an atmosphere having a strong oxidizing property can have durability even when the temperature is somewhat high when Ni is used for the metal porous body. However, it is preferable to reliably improve the high-temperature oxidation resistance by forming an enriched layer such as Cr on the surface layer of the porous body made of Ni. As described above, since nickel is easy to produce a plated body and fine particles, nickel is a very suitable metal for producing a continuous porous metal porous body and has a certain high-temperature oxidation resistance. However, using an alloy element that improves high-temperature oxidation resistance, such as Cr, based on the porous body made of Ni, in terms of ensuring good air permeability, long-term durability, and economic efficiency, It is a good idea.
Regarding the cathode 3 for the high temperature region or the atmosphere having a strong oxidizing property, the oxygen ion conductive ceramics 32 and the silver 33 in the cathode 3 are the same as those for the low temperature region.

(Point 2-ammonia decomposition reaction in the embodiment of the present invention)
Ammonia introduced into the anode 2 undergoes a reaction (anode reaction) of 2NH ₃ + 3O ²⁻ → N ₂ + 3H ₂ O + 6e ⁻ . N ₂ + 3H ₂ O as a fluid after the reaction is released from the anode 2 and the anode current collector 8. Further, O ₂ introduced into the cathode 3 undergoes a reaction of O ₂ + 2e ⁻ → 2O ²⁻ (cathode reaction). Oxygen ions generated at the cathode 3 reach the anode 2 from the oxygen ion conductive ceramics 32 in the cathode 3 through the solid electrolyte 1. Oxygen ions that have reached the anode 2 react with the ammonia and the ammonia is decomposed. Electrons e ⁻ generated at the anode 2 flow to the cathode current collector 7 and the cathode 3 through the load. In the above reaction, the electrochemical reaction does not proceed unless the potential of the cathode 3 is higher than that of the anode 2, but this potential condition is satisfied even if the potential is not applied from the outside. It generates electricity as a fuel cell.

  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, an electrochemical reaction is used to decompose gas molecules, the gas molecules to be decomposed are introduced into one electrode, and a gas that contributes to the electrochemical reaction of the decomposition is introduced into the other electrode. There have been few examples of using the electrons and oxygen ions to achieve significant acceleration of decomposition.

Next, an example of a method for producing a continuous pore porous body (hereinafter referred to as a plated porous body) having a skeleton formed of a metal plating body used for the cathode current collector 7 will be described. FIG. 4 is a diagram showing an example of a method for producing a plated porous body. In FIG. 4, 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 mainly includes film removal treatment. The thin film formed on the pores is continuously pored by removing the membrane by pressure treatment such as explosion treatment or chemical treatment. 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.
Although not shown in FIG. 4, 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.

FIG. 5 is a diagram showing a specific example of the Al or Cr addition treatment. FIG. 5A is a specific example of aluminizing. In this method, a Ni-plated porous body (indicated by “Me” in FIG. 5A) is embedded in a steel case together with a preparation composed 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 is 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, Al ₂ O ₃ powder and NH ₄ Cl powder. A Cr diffusion / permeation layer can be obtained by heating to 900 ° C. to 1100 ° C. in a furnace while passing H ₂ gas or Ar gas through the case. This Cr diffusion layer can also improve the high temperature oxidation resistance. In FIG. 5, only the powder method is shown for both aluminizing and chromizing, but Al or Cr can be diffused and permeated using any existing method such as a gas method or a molten salt method.

FIG. 6 shows the relationship between the specific surface area (y: m ² / m ³ ) and the pore diameter (x: mm) of the Ni-plated porous body produced by the method shown in FIG. The small black circles in FIG. 6 are actually measured values. It can manufacture by said method over hole diameter 0.05mm-3.2mm. When the urethane is used, the actual measurement value has a large specific surface area at the same pore diameter as compared to the hyperbola of (x−0.3) y = 400 or 600. Here, the minimum limit value (asymptotic line) of 0.3 mm of the hyperboloid hole diameter is obtained when urethane is used. When the value of (x−0.3) y is large, the pressure loss is reduced while maintaining the function of contacting the gas introduced into the cathode current collector 7 and sending the gas into the cathode 3 in a turbulent state. Produces a possible effect. For this reason, it is preferable to satisfy 400 ≦ (x−0.3) y. More preferably, 600 ≦ (x−0.3) y. Since there is a risk that a bad effect (such as a decrease in conductivity) may occur, the upper limit is preferably about 3000, more preferably about 2000.
When melamine is used instead of urethane, the minimum limit value of the pore diameter is 0.05 mm. The metal porous body manufactured using melamine does not show the expression of the product of the pore diameter and the specific surface area, but if the porosity falls within the range of 0.6 or more and 0.98 or less, it was manufactured using melamine. Metal porous bodies are also within the scope of the present invention.
In the case of a metal powder sintered body, the hole diameter is in the range of 0.05 mm to 0.3 mm, more preferably in the range of 0.10 to 0.2 mm. Further, the specific surface area is in a considerably smaller range than the relationship (x−0.3) y = 400 shown in FIG. 4 manufactured using a urethane porous mold. The porosity is also affected by the shape of the skeleton, but generally the higher the porosity, the greater the specific surface area. Therefore, the Ni plating porous body produced by the method shown in FIG. 4 can reduce pressure loss more than the metal powder sintered body while obtaining the same conductivity and the same turbulent flow generation action.

Next, the anode sides 2 and 8 and the electrolyte 1 will be described. The anode 2 and the anode current collector 8 are not particularly required to take measures against high-temperature oxidation, but it is inevitable that they are heated. The anode 2 is a sintered body mainly composed of a Ni particle chain 21 having a surface oxidized oxide layer and an oxygen ion conductive ceramic 22. 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), etc. are used. be able to.
The anode current collector 8 is preferably made of the same material as the cathode current collector for a low temperature region in order to ensure air permeability and conductivity.
The electrolyte 1 may be a solid oxide, molten carbonate, phosphoric acid, solid polymer, or the like having oxygen ion conductivity, but the solid oxide is preferable because it can be downsized and easily handled. As the solid oxide 1, SSZ, YSZ, SDC, LSGM, GDC or the like is preferably used.

FIG. 7 is a view for explaining the role of the material constituting the anode 2. The anode 2 is composed of a sintered body of a metal particle chain 21 whose surface is oxidized and SSZ22. The metal of the metal particle chain 21 is preferably Ni. Ni may contain a little iron (Fe). More preferably, Ti contains a trace amount of about 2 to 10000 ppm.
As described above, the Ni particle chain 21 with the surface oxide layer in the anode 2 may contain a little iron (Fe) in Ni. More preferably, Ti contains a trace amount of about 2 to 10000 ppm. (1) Ni itself has a catalytic action to promote the decomposition of ammonia. Further, the catalytic action can be further enhanced by containing a small amount of Fe or Ti. Furthermore, the nickel oxide formed by oxidizing this Ni can further greatly enhance the promoting action of these metals. (2) In addition to the above catalytic action, electrons are allowed to participate in the oxygen decomposition reaction at the anode. That is, the decomposition is performed in an electrochemical reaction. In the above anode reaction, there is contribution (generation) of electrons, and oxygen ions also participate to greatly improve the decomposition rate of ammonia. (3) In the anode reaction, electrons e ⁻ participate in the reaction. If the electron e ⁻ is not conducted out of the anode, the progress of the anode reaction is hindered. The metal particle chain 21 is elongated in a string shape, and the content 21a covered with the oxide layer 21b is a good conductor metal (Ni). The electrons e ⁻ flow smoothly in the longitudinal direction of the string-like metal particle chain. For this reason, the electron e ⁻ does not conduct outside from the anode 2 and flows out through the contents 21 a of the metal particle chain 21. The metal particle chain 21 makes the passage of electrons e ⁻ very good.

  Due to the configuration of the anode 2 and the cathode 3 described above, the anode reaction and the cathode reaction proceed at a very high reaction rate. For this reason, a large amount of ammonia can be efficiently decomposed by a small element having a simple structure. In addition, there is no risk of deterioration of the metal part on the cathode side due to high temperature oxidation, and maintenance is not required. Further, no reaction product is deposited, no maintenance is required, and the running cost can be greatly 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.

Next, each part of the ammonia decomposing element 10 other than the cathode current collector will be described.
1. Anode metal chain chain 21
The metal particle chain 21 is preferably manufactured by a reduction precipitation method. The reduction precipitation method of the metal particle chain 21 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. In the case of Ni, Ni ions are allowed to coexist. 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 must be a ferromagnetic metal and have 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. The average diameter D of the metal particle chain 21 contained in the anode 2 is preferably in the range of 5 nm to 500 nm. The average length L 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.

2. Surface Oxidation The Ni particle chain 21 in the anode 2 is preferably surface oxidized in order to enhance the catalytic action that promotes 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. Although it is the simplest method, it is difficult to control the oxide film thickness. 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 1 nm to 100 nm, and more preferably 10 nm to 50 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. 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.

3. Sintering The average diameter of the raw material powder of SSZ22 or LSM32 contained in the anode 2 or the cathode 3 is about 0.5 μm to 50 μm. The compounding ratio of the surface-oxidized metal particle chain 21 and SSZ22 is in the range of 0.1 to 10 in terms of a molar ratio.
The sintering method is, for example, in the atmosphere at a temperature of 1000 ° C. to 1600 ° C.
It is carried out by holding for 30 minutes to 180 minutes. The time of surface oxidation of the chain metal powder may be before or after the formation of the sintered body.
The cathode 3 is composed of a sintered body such as LSM 32 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.

(Embodiment 2)
FIG. 8 is a diagram showing an 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 anode reaction is the same as in Embodiment 1, but the cathode reaction is CO ₂ + 2e ⁻ → CO + O ²⁻ .
In this case, a potential difference (voltage) is externally applied between the anode current collector 8 and the cathode current collector 7 so that the anode side becomes higher. The external power source 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. Accordingly, the cathode current collector 7 is, for example, made of a continuous pore porous body having Ni as a skeleton for the low temperature region, and used for the high temperature region with diffusion permeation of Cr or Al. In particular, a Ni-plated skeleton is preferable for reducing pressure loss.
Further, in the anode 2, (1) promotion of reaction by nickel oxide (high catalytic function) by the surface-oxidized metal particle chain, and (2) securing of electric conductivity by the string-like good conductor of the metal particle chain. (High electron conductivity) can be obtained. As a result, a large amount of ammonia gas can be quickly processed by a small and simple element, and the maintenance cost (running cost) is 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. As for the improvement of the ammonia decomposition rate, as in the first embodiment, the catalyst (silver particles) at the cathode promotes the generation of oxygen ions, and the structure including the Ni particle chain at the anode and the effect are provided. The reaction rate can be greatly improved.

Next, an example of actual verification using a specimen will be described. The test specimens used were 8 types of gas decomposing apparatuses with a common anode and different cathode configurations. The anode has the following configuration and is common to eight types of test bodies.
(1) Anode current collector: Ni metal porous body (Celmet manufactured by Sumitomo Electric Industries, Ltd.), pore diameter 1900 μm, specific surface area 500 m ² / m ³
(2) Anode: catalyst Ni particle chain (thickness 100 nm, chain length 30 μm) / electrolyte SSZ
Table 2 shows the cathode current collectors and cathodes of the eight types of test specimens. For the cathode current collector, the conditions for pore diameter (specific surface area) and alloying were varied based on the Ni metal porous body. The effect of the presence or absence of silver on the cathode catalyst was also examined. About these test bodies, the temperature over 700 to 900 degreeC measured the change over 5 hours-5000 hours of the processing capacity of an abatement with respect to nitrogen gas (carrier gas) containing ammonia. The results are shown in Table 3.

From the results in Table 3, the following items could be confirmed. Course of processing power, and normalized performance during 5 hours after the test numbers t ₂ as 100. Capacity at 5 hours after the test numbers _{t 2} is 1.1mmol ^/ cm 2 · min. That is, this processing capacity was set to 100.
-Effect of processing temperature-
From the results of test numbers t ₁ , t ₂ , and t ₃ , in a short time up to about 5 hours, the processing temperature is higher as the temperature is higher in the range of 700 ° C. to 900 ° C. At 900 ° C., it is 2.6 times the processing capacity at 700 ° C. However, as the temperature rises, the processing capability decreases greatly with time. The processing capacity at 700 ° C. is the highest at 5000 hours. In 500 hours, there is no difference between 800 ° C. and 900 ° C., and it is maintained at about 80, which is larger than the processing capability 40 of 700 ° C. Such a reversal phenomenon is considered to be due to the effect of high temperature oxidation.
-Influence of catalyst-
In Test No. _{t 10} using silver in the cathode catalyst, as compared to _{t 5} using no silver was improved by about 1.4 times, 110 degree and high. This advantage is maintained at about 90 in 500 hours. However, at 5000 hours, the absolute value of the processing capacity is greatly reduced. This is considered to be caused by metal Ni in the metal porous body.
-Cathode current collector Pore diameter of metal porous body-
From the test numbers t ₂ , t ₄ , t ₅ , and t ₆ , it is possible to know the influence of the pore diameter of the metal porous body forming the cathode current collector. Within about 500 hours, the treatment capacity is higher when the pore diameter is smaller and the specific surface area is larger. However, at about 5000 hours, the larger the hole diameter, the higher the treatment capacity.
-Effect of alloying-
By the test numbers t ₃ , t ₅ , t ₆ and t ₇ , it is possible to know the influence of alloying (alloy diffusion to the surface layer) of the metal porous body forming the cathode current collector. By alloying, a great effect can be obtained after 5000 hours. With Ni alone, it is 15 in 5000 hours, but a remarkable effect of about 70 can be obtained by introducing Cr diffusion. Further, the same remarkable effect can be obtained by diffusion introduction of Al (test number t8) and Al—Cr (test number t9).
From the above, it is understood that alloying is effective in order to obtain a good abatement ability for a long period of time while suppressing running costs.

  Although the embodiments of the present invention have been described above, the embodiments of the present invention disclosed above are merely examples, and the scope of the present invention is not limited to these embodiments. 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.

  According to the ammonia decomposing element of the present invention, a large amount of gas can be efficiently decomposed by a small and simple element without using a large-scale apparatus, and maintenance is easy. In particular, alloying of the Ni porous body of the cathode current collector is effective. Furthermore, since it may be used also as a power generation device, it is possible to supply electric power to a heating device for keeping the ammonia decomposition element at a high temperature.

  DESCRIPTION OF SYMBOLS 1 Ion conductive electrolyte (solid oxide electrolyte), 2 Anode, 3 Cathode, 3h Air gap, 7 Cathode current collector, 7a Conductive part, 7h Continuous pore (gap), 8 Anode current collector, 10 Ammonia decomposition element, 21 Metal particle chain, 21a Core part of metal particle chain (metal part), 21b Oxidized layer, 22 Ion conductive ceramics (SSZ, etc.) of anode, 32 Ion conductive ceramics (LSM, etc.) of cathode, 33 Silver.

Claims (9)

An element for decomposing ammonia,
A porous anode into which ammonia or a gas containing ammonia is introduced;
A porous cathode that is paired with the anode and into which a gas containing oxygen atoms is introduced;
An ionic conductive material having oxygen ion conductivity sandwiched between the anode and the cathode;
A cathode current collector in contact with the cathode,
The cathode current collector is a porous metal body having continuous pores, and the porous metal body is made of nickel or a nickel alloy, or the surface layer of nickel or a nickel alloy is (chrome (Cr), aluminum (Al)) An ammonia decomposing element enriched with at least one of silver (Ag), gold (Au) and platinum (Pt).   The ammonia decomposition element according to claim 1, wherein the metal porous body is a metal plating body.   The ammonia decomposition element according to claim 1 or 2, wherein the porosity of the metal porous body is 0.6 or more and 0.98 or less. When urethane is used in the production of the metal porous body, when the pore diameter of the metal porous body is x (mm) and the specific surface area is y (m ² / m ³ ), 400 ≦ (x−0.3 The ammonia decomposing element according to any one of claims 1 to 3, wherein y) is satisfied.   The anode, the ion conductive material, and the cathode are in the form of an integrated MEA (Membrane Electrode Assembly) (anode / ion conductive material / cathode), the cathode current collector is in the form of a sheet, and the cathode The ammonia decomposing element according to claim 1, wherein the ammonia decomposing element is stacked in contact with a gas to form a gas flow path containing the oxygen atom.   The ammonia decomposing element according to any one of claims 1 to 5, wherein the cathode is a sintered body of an ion conductive ceramic or a sintered body of an ion conductive ceramic and silver.   The heater of heating the said ion conductive material, an anode, and a cathode, The temperature control system which controls the temperature of the said ion conductive material, an anode, and a cathode is provided, The any one of Claims 1-6 characterized by the above-mentioned. The ammonia decomposing element according to 1.   The ammonia decomposing element according to claim 1, wherein electric power can be taken out from the cathode and the anode.   The ammonia decomposition element according to claim 8, wherein the extracted electric power is supplied to the heater and / or the temperature control system.

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