JP5568865B2 - Gas decomposition element - Google Patents

Description

  The present invention relates to a gas decomposing element, and more specifically to a gas decomposing element that can efficiently decompose gas, is small, and is easy to maintain.

Due to the growing interest in the living environment, especially air, technological development to efficiently remove (decompose) trace amounts of harmful gas components in the atmosphere is being promoted. For example, as a catalyst for promoting an ammonia decomposition reaction, a chromium compound, a copper compound, a cobalt compound (Patent Document 1), platinum supported on an alumina three-dimensional network structure (Patent Document 2), and the like are 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 3 and 4).
Although automobiles equipped with diesel engines tend to increase, it is necessary to satisfy waste gas regulations, and various catalyst devices for reducing exhaust gas from diesel engines have been developed. Among these catalytic devices, the urea selective reduction system is recommended as one that efficiently reduces and purifies NOx into nitrogen and water in a temperature range where the engine speed is low (Non-patent Document 1). These exhaust gas purification devices are attached to the exhaust path of an automobile engine and purify the exhaust gas. For this purpose, the temperature of the exhaust passage and the NOx concentration are measured to control the injection amount of urea into the exhaust passage. For example, a device has been proposed in which a NOx sensor is provided at the subsequent stage of urea injection, and NO and NO ₂ are separately determined stoichiometrically to control the optimum urea injection amount (Patent Document 5). In addition, an oxidation catalyst and a urea selective reduction device are arranged in the exhaust path in the exhaust path, and NOx decomposition is performed using two NOx sensors arranged before and after the oxidation catalyst in the front stage of the urea selective reduction device. There is also a proposal of a method (patent document 6).
On the other hand, as known by summer photochemical smog and the like, not only a diesel engine but also a gaseous environment containing NOx is not preferable for a living organism. In order to decompose and remove NOx and the like in the atmosphere, a photocatalyst has been proposed in which calcium phosphate is dispersed and arranged in islands on a titanium oxide thin film covering the surface of a porous carrier (Patent Document 7).

JP-A-53-11185 JP 54-10269 A JP 2006-231223 A JP 2006-175376 A JP 2004-1000069 A Japanese Patent Laid-Open No. 2007-100508 Japanese Patent Laid-Open No. 2001-232206

Hirata, K., et al., “Urea Selective Reduction System for Large Car Diesel”, Automotive Technology, Vol.60, No.9, 2006, pp28-33

As for ammonia, ammonia can be decomposed by a method (patent documents 1 to 4) based on a thermal decomposition reaction using a catalyst. However, the above method has a problem in that the catalyst needs to be periodically replaced and maintained, and the running cost is high. In particular, maintenance-free components are not allowed for a long period of time. Furthermore, the apparatus becomes large, and for example, it may be difficult to arrange the apparatus when it is additionally provided in existing facilities.
On the other hand, the urea selective reduction device for decomposing NOx is one in which a urea selective reduction device that is large for an automobile is arranged in the exhaust system, resulting in an increase in weight. In addition, urea replenishment is required. For this reason, in the automobile field, there has been a demand for a NOx decomposing element that does not require replenishment of a reducing agent such as urea and that is easy to maintain and, if possible, maintenance-free. For automobiles, of course, small size and light weight create great value.
In addition, the photocatalyst that removes harmful substances such as NOx in the atmosphere is not limited to automobiles, and there is a tendency that the decomposition rate or decomposition efficiency is insufficient. Airports, railway stations, and other places where people are crowded require rapid decomposition of harmful substances, and photocatalytic decomposition may not be possible.
The above problems are not limited to ammonia and NOx, and the same can be said for the decomposition of VOC (Volatile Organic Compounds) such as methane and ethane, which are listed as malodorous gas components.

  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 is to provide a gas decomposition element.

The gas decomposition element of the present invention decomposes gas components. The gas decomposition element includes a porous cathode into which a first gas containing oxygen atoms is introduced, a porous anode that is paired with the cathode and into which a second gas different from the first gas is introduced; An ion conductive material having oxygen ion conductivity sandwiched between an anode and a cathode and a cathode current collector in contact with the cathode, wherein the gas component is the first gas or the second gas, or the first included as part of the gas or the second gas, the cathode current collector is a metal plating which is a metal porous body having continuous pores having a pore diameter of 0.05Mm～3.2Mm, nickel was formed by plating or the nickel-based alloy surface layer of the scaffold according to the plating as a scaffold, chromium (Cr), aluminum (Al), silver (Ag), gold (Au) and platinum (Pt), is enriched in at least one Cage, ion conductive material is made of a solid oxide, anode, solid oxide, and a cathode, formed as an integrated MEA of (Membrane Electrode Assembly) (anode / solid oxide / cathode), cathode current collector The body is in the form of a sheet, is laminated in contact with the cathode , occupies the flow path of the first gas containing oxygen atoms , and the cathode and the cathode current collector are heated to 250 ° C. to 950 ° C. characterized in der Rukoto those used.

In the gas decomposition element, a first 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 the gas component in 1st gas or 2nd gas by an electrochemical reaction, the following effect | action can be acquired. In addition, although the gas component to be decomposed may be the first gas or the second gas itself, it is usually contained only in a very small amount, so it is assumed that it is contained in the first gas or the second gas. ,explain.
(E1) By forming the cathode current collector from a porous metal body, the turbulent state of the gas is promoted while allowing the first gas to pass. By making the turbulent flow rather than letting the gas pass as a laminar flow, it is possible to promote the decomposition reaction (electrochemical reaction) by lengthening the opportunity, time, and the like of the first gas contacting the cathode. Thereby, the electrochemical reaction efficiency per cathode unit area can be increased.
(E2) Since the cathode current collector is a porous metal body, it is possible to ensure the inflow of electrons from the outside to the cathode and to facilitate the charge transfer accompanying the decomposition of the gas component. This can prevent the exchange of electrons from becoming a bottleneck for electrochemical reactions.
(E3) By forming the porous metal body with a layer enriched with chromium or the like, high-temperature corrosion (oxidation) performance exceeding that of nickel can be provided. The periphery of the cathode of the gas decomposition element is heated to a high temperature of, for example, 250 ° C. to 950 ° C., and the first gas containing oxygen atoms 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, a high-temperature oxidation resistance is insufficient, and a material with 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.
The metal porous body is not (1) a sintered body of metal particles or metal fibers mentioned as a reference example, but (2) a metal plating body formed by using a foamed resin subjected to pore continuation treatment. The nickel alloy may be a nickel-based alloy containing other metals based on nickel, or may be an alloy of other metals based on other metals containing nickel.
The first gas containing oxygen atoms introduced into the cathode refers to a gas containing molecules containing oxygen atoms, such as air, oxygen gas, NOx, water vapor, carbon dioxide, or a mixture of two or more of these. Point. The gas component to be decomposed may be contained in the first gas or in the second gas.

  The metal porous body is formed of a metal plated 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.
For metal porous bodies, (1) pore diameter is determined by SEM (Scanning Electric Microscopy) observation, (2) specific surface area is determined by BET surface area method, and (3) porosity is determined from surface area, volume and weight. be able to.

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 ionic conductive material, and the cathode are in the form of an integrated MEA (anode / ionic conductive material / cathode), and the cathode current collector is in the form of a sheet, laminated in contact with the cathode, and oxygen atoms The flow path of the 1st gas containing is formed. As a result, the effect of (E1) can be ensured, and the ratio of those that pass through without being decomposed at the cathode can be significantly reduced. Moreover, a thin gas decomposition element sheet | seat can be obtained by setting it as a sheet form, and a compact gas decomposition element can be obtained by laminating | stacking this. In addition, the gas decomposition element of the final product 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 is formed by sintering (a1) a sintered body of metal powder or metal particle chain and ion conductive ceramics, or (a2) firing of a metal powder or metal particle chain having an oxide layer and ion conductive ceramics. A ligature. Thereby, high efficiency can be secured in the cathode reaction during the electrochemical reaction. Further, since the range of efficiency is widened, an appropriate balance between the manufacturing cost and the performance can be achieved according to the performance required for the gas decomposition element.

  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 decomposition rate of the gas component, it is necessary to make the oxygen ion diffusion rate in the ion conductive material constant or higher, and the reaction rate in the electrode is also accelerated, so that the heating is performed at a high temperature. Usually, a heater for heating to 250 ° 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 a specific gas component is decomposed by oxygen ions, the cathode potential becomes higher than the anode potential, and power can be taken out from the cathode and the anode, which can be used. 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 a heater and / or temperature control system, which can increase energy efficiency.

  In the case of decomposition of NOx or decomposition of a malodorous component in the room, it is mounted on an automobile having an internal combustion engine, and the exhaust heat of the internal combustion engine can be used as a heat source for heating. A predetermined gas component can be decomposed with high energy efficiency.

  According to the gas 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 and highly durable over a long period of time, and can be operated at a low running cost. In addition, since it is heated to a high temperature to promote the electrochemical reaction of decomposition of a predetermined gas component, it has a large processing capacity and a high decomposition rate with a small apparatus.

It is a figure which shows the NOx decomposition element 10 which is a gas decomposition element in Embodiment 1 of this invention. It is a figure for demonstrating the electrochemical reaction by the gas decomposition element of FIG. It is a figure for demonstrating the role of the material which comprises the cathode of the gas decomposition | disassembly element of FIG. 1, and a cathode electrical power collector. It is a figure which shows an example of the manufacturing method of a plating porous body. 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 of Ni plating porous body manufactured by the method of FIG. 4 using urethane for foaming resin, and a hole diameter. It is a figure for demonstrating the role of the material which comprises the anode in the gas decomposition element of FIG. It is a figure which shows the NOx decomposition element of the gas decomposition element in Embodiment 2 of this invention. It is a figure which shows the ammonia decomposition element which is a gas decomposition element in Embodiment 3 of this invention. It is a figure for demonstrating the electrochemical reaction by the gas decomposition | disassembly element of FIG. It is a figure for demonstrating the role of the material which comprises the cathode 3 and the cathode collector 7 of the gas decomposition element of FIG. It is a figure for demonstrating the role of the material which comprises the anode in the gas decomposition element of FIG. It is a figure which shows the ammonia decomposition element 10 of the gas decomposition element in Embodiment 4 of this invention.

Before illustrating the specific structure of the gas decomposition element, Table 1 shows an example of an approximate electrochemical reaction to which the gas decomposition element in the embodiment of the present invention is applied. As shown in Table 1, the gas decomposition element 10 can generate electric power as a fuel cell, or can be operated by supplying power as an electrolysis apparatus. For example, in the case of NOx decomposition, a first gas containing NOx is introduced into the cathode, and ammonia (reaction R3 in Table 1), VOC (reaction R7), or water vapor (reaction R8) is introduced into the anode. In the case of reaction R3, a fuel cell can be configured and electric power can be used. In the case of reactions R7 and R8, electric power is input to cause an electrochemical reaction of electrolysis. In any reaction example, the first gas NOx containing oxygen atoms is introduced into the cathode.
In the decomposition of ammonia, reactions R1 to R3 and R5 are caused. In the case of this ammonia decomposition, there are those constituting the fuel cell (reactions R1 to R3) and those constituting the electrolysis (R5). In any ammonia decomposition reaction, a gas containing oxygen atoms is introduced into the cathode. Although the reactions R1 to R8 exemplified in Table 1 can be caused by using the gas decomposition element of the present invention, reactions other than those exemplified in Table 1 may be caused.

(Embodiment 1)
FIG. 1 is a diagram showing a NOx decomposition element 10 which is a gas decomposition element according to Embodiment 1 of the present invention. In this NOx decomposition 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 ionic conductive ceramic (metal oxide) 22 and is a porous body through which a second gas can flow. . The cathode 3 is a porous body through which the first gas can flow. For example, a metal particle chain 31 having a surface oxide layer, an ion conductive ceramic 32, and silver (Ag) 33 are used as main constituent materials. It can be set as the sintered compact. 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 is a solid oxide . The material of the electrolyte 1 will be specifically described later.

In FIG. 2, NOx to be decomposed is introduced into the cathode 3 through a flow path occupied by the cathode current collector 7. This NOx supplies oxygen ions. In this embodiment, the gas that undergoes an electrochemical reaction with oxygen ions that reach the anode 2 through the solid electrolyte 1 is water vapor (reaction R8 in Table 1). NOx undergoes a predetermined reaction at the cathode 3 to generate nitrogen, and this nitrogen is released to the outside through a channel occupied by the cathode current collector 7. Further, the water vapor undergoes a predetermined reaction at the anode 2 to generate hydrogen and oxygen, and these hydrogen and oxygen are released to the outside through a flow path occupied by the anode current collector 8.
In the case of the NOx decomposition 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, a heater is used. For example, it is heated to 250 ° C. to 600 ° C. As described above, NOx which is a gas (first gas) containing oxygen atoms and having a high oxidizing power passes through the cathode 3 and the cathode current collector 7. A metal exposed to a gas having high oxidizing power at a high temperature of 250 ° C. to 600 ° C. is oxidized by the gas except for a predetermined metal, and becomes 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 NOx decomposition, 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 effect of (E3), the cathode current collector 7 has a porous body having continuous pores, a surface layer of a metal porous body of nickel or a nickel alloy (chromium (Cr), aluminum (Al) and others. Enriched with at least one metal). 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 a metal particle chain 31 such as Ni having an oxide layer, Ag particles 33, and ceramics 32 through which oxygen ions pass. Among them, the Ag particles 33 and the oxide layer-attached metal particle chain 31 have a catalytic function for greatly promoting the cathode reaction 2NO ₂ + 4e ⁻ → N ₂ + 2O ²⁻ or NO + 2e ⁻ → N ₂ + O ²⁻ . As for the above-described metal particle chain 31 such as Ni, similarly to the cathode current collector, the catalytic action and conductivity are deteriorated due to high-temperature oxidation. For this reason, it is preferable to improve the high-temperature oxidation resistance of Ni grain chains by alloying metal parts or forming alloy layers. The cathode 3 and the cathode current collector 7 are made of the following materials by dividing 250 ° C. to 600 ° C. into, for example, a low temperature region and a high temperature region. The distinction between the low temperature region and the high temperature region, or the strength of the oxidizing power varies depending on the ratio of NO and NO _{2 in} NOx, the concentration in the atmosphere, and the like, so it is not necessary to separate them so clearly.

(Usage example given as a reference example = low temperature range or relatively weak oxidizing atmosphere):
As a reference example, a case where the present invention is used in a low temperature region or an atmosphere having a relatively low oxidizing property is shown. The cathode current collector 7 is a porous metal body having continuous pores 7h and having continuous pores of a skeleton such as Ni whose skeleton 7a serves 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-shaped skeletons formed by Ni plating are three-dimensionally connected is preferable. As a typical example, for example, Celmet (registered trademark) manufactured by Sumitomo Electric Industries, Ltd. Can be used. The manufacturing method will be described in detail later, but after making the pores of the foamed resin continuous, a manufacturing method in which a skeleton is formed by metal plating, compared with a sintered body of metal particles and metal fibers. The air permeability is remarkably good and the conductivity is ensured.
The cathode 3 is a sintered body mainly composed of a Ni particle chain 31 having an oxidized layer that is surface oxidized, an oxygen ion conductive ceramic 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 Ni grain chain is made of Ni as the metal of the metal grain chain and is relatively easy to manufacture and is known. In addition, the conductive part (metal part covered with the oxide layer) of the Ni grain chain may be Ni alone, or Ni containing Fe, Ti, or the like.

(High temperature range or highly oxidizing atmosphere):
The cathode current collector 7 for an atmosphere having a high temperature range or a strong oxidizing atmosphere can have sufficient durability depending on the composition of NOx and the like even when the temperature of the cathode current collector 7 is elevated to a certain level when Ni is used. . However, the high-temperature oxidation resistance is reliably improved 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, it is essential to use an alloy element that improves high-temperature oxidation resistance such as Cr, based on this Ni porous body, in terms of ensuring good air permeability, long-term durability, and economic efficiency. It is.
For the cathode 3 for high temperature region or highly oxidizing atmosphere, the oxygen ion conductive ceramics 32 and the silver 33 in the cathode 3 are the same as those for the low temperature region. In order to improve the high-temperature oxidation resistance, the surface layer of the Ni grain chain is a Cr-enriched layer, an Al-enriched layer, or another metal-enriched layer. Or it is good to form with nickel alloys, such as a Ni-Cr alloy, instead of forming said enriched layer.

(Point 2-NOx decomposition reaction in the embodiment of the present invention)
In the present embodiment, the gas to be decomposed is NOx, and this NOx supplies oxygen ions. The gas that reacts with oxygen ions at the anode 2 may be any of ammonia, VOC (such as CH ₄ ), and water vapor. Thereby, NOx decomposition by the electrochemical reaction of numbers R1 to R3 shown in Table 1 is possible. Among these reactions, since water vapor (H ₂ O) is easy to handle and economical, it will be described below by limiting to the electrochemical reaction of R3. The water vapor introduced into the anode 2 eventually undergoes a reaction of 2O ²⁻ → O ₂ + 2e ⁻ (anode reaction). O ₂ + H ₂ which is a fluid after the reaction is released from the anode. Further, NOx introduced into the cathode 3 reacts (cathode reaction) of 2NO + 4e ⁻ → N ₂ + 2O ²⁻ and 2NO ₂ + 8e ⁻ → N ₂ + 4O ²⁻ . Oxygen ions reach the anode 2 from the oxygen ion conductive ceramics 32 in the cathode 3 through the solid electrolyte 1. The oxygen ions that have reached the anode 2 react with the water vapor to decompose the water vapor. Further, the NOx decomposed at the cathode becomes nitrogen gas and is released from the cathode 3 and the cathode current collector 7. 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, if the potential of the cathode 3 is not higher than that of the anode 2, the electrochemical reaction does not proceed. However, if the potential is not applied from the outside, the potential relationship is reversed. It is necessary to apply.

In FIG. 3, the cathode 3 is composed of a sintered body of a surface-oxidized metal particle chain 31, LSM 32, and silver particles 33. The metal of the metal particle chain 21 is preferably nickel (Ni). Ni may contain a little iron (Fe). More preferably, Ti contains a trace amount of about 2 to 10000 ppm. (1) Ni itself has a catalytic action for promoting the decomposition of NOx. 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 decomposition reaction at the cathode. That is, the decomposition is performed in an electrochemical reaction. In the cathode reaction 2NO + 4e ⁻ → N ₂ + 2O ²⁻ and 2NO ₂ + 8e ⁻ → N ₂ + 4O ²⁻ , there is an contribution of electrons, and the decomposition rate of NOx is greatly improved. (3) In the cathode reaction, the electron e ⁻ participates in the reaction. If the electrons e ⁻ are not conducted to the cathode, the progress of the cathode reaction is hindered. The metal particle chain 31 is elongated in a string shape, and the content 31a covered with the oxide layer 31b 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 electrons e ⁻ do not conduct to the cathode 3 and flow through the contents 31 a of the metal particle chain 21. Due to the metal particle chain 31, the passage of electrons e ⁻ becomes very good.
The actions (1) to (3) of the Ni grain chain 31 in the cathode 3 are the same as those for the Ni grain chain 21 in the anode 2 by replacing the gas from oxygen to ammonia.

  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 process mainly includes a film removal process. 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. Metal plating uses a plating solution containing nickel ions 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.
Since the cathode current collector 7 is exposed to a stronger oxidizing atmosphere or is used at a higher temperature, in order to further improve the oxidation resistance, it is alloyed with the Ni-plated porous body as described above. Apply processing. 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 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. As a result, 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 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 an existing arbitrary 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 manufactured by the method shown in FIG. 4 using urethane as the foamed resin. 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) and the like 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 is a solid oxide having oxygen ion conductivity . Solid body oxide can be downsized, so it is easy to handle preferable. As the solid oxide 1, SSZ, YSZ, SDC, LSGM, 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 is the same as the Ni particle chain 31 with the surface oxide layer in the cathode 3 in promoting the electrochemical reaction (1), (2) and (3) Since the contents are almost the same, a detailed explanation is omitted.

  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 NOx 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.

Next, each part of the NOx decomposition element 10 other than the cathode current collector will be described.
1. Cathode and anode metal particle chain 21, 31
The metal particle chain bodies 21 and 31 are preferably manufactured by a reduction precipitation method. The reduction precipitation method of the metal particle chain bodies 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. 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 bodies 21 and 31 contained in 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 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.
The metal particle chain 31 of the cathode 3 is preferably used for a low temperature region. Similar to the cathode current collector 7, the metal particle chain 31 for the high temperature region is preferably subjected to an alloying treatment such as aluminizing or chromizing as shown in FIG. 5. That is, the Ni grain chain 31 contained in the cathode 3 of the NOx decomposition element 10 used in a high temperature range of 250 ° C. to 600 ° C. is provided with an enriched layer such as Cr or Al for high temperature oxidation resistance. preferable.

2. Surface oxidation Both the Ni grain chain 21 in the anode 2 and the Ni grain chain 31 in the high temperature region cathode and the low temperature region cathode 3 are surface oxidized in order to enhance the catalytic action for promoting the electrochemical reaction. It is better.
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 SSZ or LSM 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, 31 and SSZ22, LSM32 is in the range of 0.1 to 10 in terms of 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 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.
The time of surface oxidation of the chain metal powder may be before or after the formation of the sintered body.

(Embodiment 2)
FIG. 8 is a diagram showing the NOx decomposition element 10 of the gas decomposition element according to Embodiment 2 of the present invention. The reaction in the present embodiment corresponds to the reaction R3 in Table 1 and is also a power generation element (fuel cell). NOx is introduced into the cathode 3 through a flow path occupied by the cathode current collector 7, and ammonia is introduced into the anode 2. The cathode reaction is the same as in Embodiment 1, but the anode reaction is 2NH ₃ + 3O ²⁻ → N ₂ + 3H ₂ O + 6e ⁻ . In this case, the potential of the anode current collector 8 naturally becomes higher than the potential of the cathode current collector 7, and power can be extracted. For example, electric power can be supplied to this heater as a heater (not shown) of FIG. Further, this electric power may be supplied to the temperature control unit of the heater.

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. Therefore, the cathode current collector 7 is made of a porous body having continuous pores having Ni as a skeleton, and diffused and penetrated by Cr or Al. In particular, a Ni-plated skeleton is preferable for reducing pressure loss.
In the anode 2 and the cathode 3, (1) promotion of reaction by the nickel oxide 31 and the silver particles 33 (high catalytic function) by the surface-oxidized metal particle chain, and (2) string of the metal particle chain It is possible to ensure the electrical conductivity (high electronic conductivity) of the good conductor. As a result, a large amount of NOx 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 the present embodiment, in the electrochemical reaction, NOx itself is used as a gas for supplying oxygen ions, and ammonia is used as a gas for reacting with the oxygen ions in order to obtain a practical decomposition rate. While being heated, maintenance management can be facilitated by the high-temperature oxidation resistance performance on the cathode sides 3 and 7. As for the improvement of the NOx decomposition rate, as in the first embodiment, oxygen ion generation promotion (NOx decomposition promotion) of the catalyst (silver particles, metal particle chain with oxide layer) at the cathode and silver particles at the anode are performed. The reaction rate can be greatly improved by providing the same configuration and operational effects except the above.

(Embodiment 3)
FIG. 9 is a diagram showing an ammonia decomposition element 10 that is a gas decomposition element according to Embodiment 3 of the present invention. The structure of the ammonia decomposing element 10 is the same as that of the gas decomposing element of the first embodiment, in which the anode 2 and the cathode 3 are arranged with the ionic conductive electrolyte 1 interposed therebetween. The difference is that the cathode 3 does not include a metal particle chain having a surface oxide layer, and is a sintered body mainly composed of an ion conductive ceramic 32 and silver (Ag) 33. . The structures of the anode 2 and the electrolyte 1 are the same.
The electrolyte 1 is a solid oxide . For electrodeposition Kaishitsu 1 material, later specifically described. 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 third embodiment, as shown in FIG. 10, 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 FIG. 10, the gas to be decomposed is introduced into the anode 2 through the flow path occupied by the anode current collector 8. A fluid for supplying oxygen ions is introduced into the cathode through a flow path occupied by the cathode current collector 7. The introduced fluid undergoes a predetermined reaction at the cathode 3 or the anode 2, and then is discharged to the outside through a channel occupied by the cathode current collector 7 or the anode current collector 8. 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 Embodiment 3 -High-temperature oxidation resistance-)
The high-temperature oxidation resistance is particularly important because it is heated to 600 ° C. to 950 ° C. in the case of ammonia decomposition. That is, it is a more serious problem than the case of NOx decomposition heated to 250 ° C to 600 ° C.
FIG. 11 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 effect of (E3), the cathode current collector 7 is formed of a porous body having continuous pores made of nickel or a nickel alloy, and the surface layer of the nickel or nickel alloy is (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.

(Usage example given as a reference example = low temperature range or relatively weak oxidizing atmosphere):
As a reference example, a case where the present invention is used in a low temperature region or an atmosphere having a relatively low oxidizing property is shown. 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 these, a metal porous body having continuous pores in which triangular prism-like skeletons formed by Ni plating are three-dimensionally connected is preferable, and the above-mentioned Celmet (registered trademark) can be used as a typical example. 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):
For the cathode current collector 7 for high temperature region or highly oxidizing atmosphere, the high temperature oxidation resistance is reliably improved 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, it is essential to use an alloy element that improves high-temperature oxidation resistance such as Cr, based on this Ni porous body, in terms of ensuring good air permeability, long-term durability, and economic efficiency. It is.
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 Embodiment 3)
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.

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 is as described in the first embodiment. (See FIGS. 4 and 5). Further, the range of the relationship between the specific surface area (y: m ² / m ³ ) and the pore diameter (x: mm) in the metal porous body manufactured by the above method is the same as that of the first embodiment (FIG. 6). reference).
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) and the like 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 is a solid oxide having oxygen ion conductivity . Solid body oxide can be downsized, so it is easy to handle preferable. As the solid oxide 1, SSZ, YSZ, SDC, LSGM, GDC or the like is preferably used.

  FIG. 12 is a diagram for explaining the role of the material constituting the anode 2. The anode 2 is the same as that shown in FIG. 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.

(Embodiment 4)
FIG. 13 is a diagram showing an ammonia decomposition element 10 of the gas decomposition element according to Embodiment 4 of the present invention. The reaction in the present embodiment is generally an electrolysis reaction as shown in reaction R5 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. Therefore, the cathode current collector 7 is made of a continuous pore porous body having Ni as a skeleton and Cr or Al diffused and permeated. 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.

  In the present embodiment, carbon dioxide is used as an oxygen ion supply source in an electrochemical reaction, and maintenance is facilitated while heating at 600 ° C. to 950 ° C. in order to obtain a practical decomposition rate. be able to. As for the improvement of the ammonia decomposition rate, as in the third embodiment, the catalyst (silver particles) at the cathode promotes the production 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.

Example 1 NOx Decomposing Element
Next, an example of actual verification using a NOx decomposition specimen will be described. The test specimens used were eight types of gas decomposing elements with a common anode and a different configuration of the cathode. 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: Ni particle chain of catalyst (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. Test body numbers 5 to 7 are test bodies of the present invention. In addition, regarding the cathode catalyst, the influence of silver particles was examined by using Ni as a base of Ni particle chain. About these test bodies, the temperature over 300 hours-600 degreeC measured the change over 5 hours-10000 hours of the treatment capacity of detoxification 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 the abatement efficiency of 90% when a current of NOx1000ppm at 50ml ^/ cm 2 · min.
-Effect of processing temperature-
From the results of test numbers t ₁ , t ₂ , and t ₃ , the processing capability increases as the temperature increases in a short time up to about 500 hours in the temperature range of 300 ° C. to 500 ° C. At 10,000 hours, the treatment capacity at 300 ° C. is the highest. 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, in a short time, as compared with 80 of the test t ₅ with Ni particle chains bodies catalyst, high and 110. This advantage is maintained for up to about 500 hours. However, at 10,000 hours, it will be almost the same.
-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, after about 10,000 hours, there is no effect and the processing capacity is almost the same.
-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 in 10,000 hours after a long time. With Ni alone, it is 45 in 10,000 hours, but a remarkable effect of about 75 can be obtained by introducing Cr diffusion. Further, the same remarkable effect can be obtained by introducing diffusion of Al (test number t ₈ ) and Al—Cr (test number t ₉ ). However, there is almost no effect until about 500 hours.
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.

Example 2 Ammonia Decomposing Element
A verified example of the ammonia decomposing element 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: Ni particle chain of catalyst (thickness 100 nm, chain length 30 μm) / electrolyte SSZ
Table 4 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 5.

From the results in Table 5, 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 temperature 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 introducing diffusion of Al (test number t ₈ ) and Al—Cr (test number t ₉ ).
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 gas decomposition 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 an electric power generating apparatus, it is also possible to supply electric power to the heating apparatus for maintaining a gas decomposition element at 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 Gas decomposition element, 21 Metal grain chain, 21a Core part of metal grain chain (metal part), 21b Oxidation layer, 22 Ion conductive ceramics (SSZ etc.) of anode, 31 Metal grain chain, 31a Core part of metal grain chain (metal) Part), 31b oxide layer, 32 ion conductive ceramics of cathode (such as LSM), 33 silver.

Claims (8)

An element for decomposing a gas component,
A porous cathode into which a first gas containing oxygen atoms is introduced;
A porous anode that is paired with the cathode and into which a second gas different from the first gas 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 gas component is the first gas or the second gas, or is included in a part of the first gas or the second gas,
The cathode current collector is a metal plated body which is a metal porous body having continuous pores having a pore diameter of 0.05 mm to 3.2 mm, and the surface layer of the skeleton formed by plating using nickel or a nickel-based alloy formed by plating as a skeleton Is enriched in at least one of chromium (Cr), aluminum (Al), silver (Ag), gold (Au) and platinum (Pt),
The ion conductive material is made of a solid oxide, and the anode, the solid oxide, and the cathode are in the form of an integrated MEA (Membrane Electrode Assembly) (anode / solid oxide / cathode). The electric body has a sheet shape, is laminated in contact with the cathode, and occupies a flow path of the first gas containing the oxygen atoms,
The gas decomposing element, wherein the cathode and the cathode current collector are used while being heated to 250 ° C to 950 ° C.   The gas decomposition element according to claim 1, wherein the porosity of the metal porous body is 0.6 or more and 0.98 or less. When urethane is used for 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). ) Y is satisfied, The gas decomposition element according to claim 1 or 2.   The cathode comprises (a1) a sintered body of metal powder or metal particle chain and ion conductive ceramics, or (a2) a powder of metal powder or metal particle chain having an oxide layer and ion conductive ceramics. The gas decomposition element according to any one of claims 1 to 3, wherein the gas decomposition element is a ligated body.   5. The apparatus according to claim 1, further comprising: a heater that heats the ion conductive material, the anode, and the cathode; and a temperature control system that controls temperatures of the ion conductive material, the anode, and the cathode. The gas decomposition element as described in 2.   The gas decomposition element according to claim 1, wherein electric power can be taken out from the cathode and the anode. The gas decomposition element according to claim 6 , wherein the extracted electric power is supplied to the heater and / or the temperature control system.   The gas decomposition element according to claim 1, wherein the gas decomposition element is mounted on an automobile having an internal combustion engine, and the exhaust heat of the internal combustion engine is used as a heat source for heating.

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