JP2012028088A - Membrane electrode assembly, fuel cell, gas abatement device, and method of manufacturing membrane electrode assembly - Google Patents

Abstract

MEA, fuel cell, gas abatement apparatus, and MEA manufacturing method capable of allowing electrochemical reaction to proceed with high efficiency in general in electrochemical reactions involving gas decomposition, etc. I will provide a.
The MEA 7 is an MEA in which a porous substrate 3, a porous anode 2, an ion conductive solid electrolyte 1, and a porous cathode 5 are laminated. The anode 2 or the cathode 5 is brought into contact with one surface, and the porous anode 2 has a metal deposit 21 having a catalytic action for gas decomposition.
[Selection] Figure 1

Description

  The present invention relates to a membrane electrode assembly (MEA), a fuel cell, a gas abatement apparatus, and a method for manufacturing a membrane electrode assembly. More specifically, the present invention is easy to manufacture and highly efficient gas decomposition. The present invention relates to a membrane electrode assembly, a fuel cell, a gas abatement device, and a method for producing the membrane electrode assembly.

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).
Moreover, ammonia, hydrogen, and the like are usually contained in the waste gas of the semiconductor manufacturing apparatus. In order to completely remove the odor of ammonia, it is necessary to detoxify it to the ppm order. For this purpose, many methods have been used in which harmful gas is absorbed in water containing chemicals through a scrubber when discharging waste gas from a semiconductor manufacturing apparatus. On the other hand, in order to obtain an inexpensive running cost without input of energy, chemicals, or the like, there has been proposed an exhaust gas treatment of a semiconductor manufacturing apparatus in which ammonia is decomposed by a phosphoric acid fuel cell (Patent Document 4).

JP-A-7-31966 Japanese Patent Laid-Open No. 7-116650 Japanese Patent Laid-Open No. 11-347535 JP 2003-45472 A

Ammonia can be decomposed by a method using a chemical solution such as the above neutralizing agent (Patent Document 1), a combustion method (Patent Document 2), a method using a thermal decomposition reaction using a catalyst (Patent Document 3), etc. It is. However, the above-described method has a problem in that it requires chemicals and external energy (fuel), requires periodic replacement of the catalyst, and has a high running cost. In addition, the apparatus becomes large and, for example, when it is additionally provided in existing equipment, the arrangement may be difficult.
The device that uses phosphoric acid fuel cells for the removal of ammonia in the exhaust of compound semiconductor manufacturing (Patent Document 4) also improves the material such as pressure loss and electrical resistance that hinder the improvement of the removal capability There is no ingenuity to solve the problem. Economically, when gas decomposition is performed using MEA, there is a problem that it is difficult to obtain MEA that enables high-efficiency gas decomposition at low cost. The MEA is composed of an anode of a fuel electrode, a cathode of an air electrode, and a solid electrolyte sandwiched therebetween, and constitutes the heart of an electrochemical reaction device. Gas molecules containing hydrogen such as ammonia are introduced into the fuel electrode and the decomposition of the gas molecules proceeds. Both the anode is porous in order to make good contact with the gas molecules to be decomposed and the cathode is in good contact with oxygen molecules. The solid electrolyte sandwiched between the two is not porous, is formed of a dense wall that does not allow gas to pass through, and is formed of an ion conductive material that does not pass electrons but allows ions to pass.

  The present invention generally relates to electrochemical reactions involving gas decomposition and the like, and is capable of allowing the electrochemical reactions to proceed with high efficiency. The membrane electrode composite, fuel cell, gas abatement device, and It aims at providing the manufacturing method of a membrane electrode composite_body | complex.

The membrane electrode assembly (MEA) of the present invention is used for an electrochemical reaction involving gas decomposition. This MEA includes a porous substrate and an MEA in which a porous anode, an ion conductive solid electrolyte, and a porous cathode are laminated. An anode or a cathode is laminated to the porous substrate in contact with one surface of the porous substrate, and the porous anode is a porous layer of a metal having a catalytic action for gas decomposition or It has the precipitation layer.
According to the above-described configuration, since the laminated body composed of the anode / solid electrolyte / cathode is formed on one surface of the porous substrate, the production is simple and the production cost can be easily reduced. . Moreover, since the gas decomposition performed in the anode, also called a fuel electrode, is promoted by a metal having a catalytic action with respect to this gas decomposition, an electrochemical reaction involving the gas decomposition can be efficiently performed. The porous substrate does not need ionic conductivity and the like and can be obtained in any shape relatively easily.

The porous substrate may be a cylindrical body, and the anode may be stacked in a cylindrical shape in contact with the outer peripheral surface of the cylindrical body, and the solid electrolyte and the cathode may be stacked in a cylindrical shape on the anode.
Further, the porous substrate is a cylindrical body, the cathode is laminated in a cylindrical shape in contact with the inner peripheral surface of the cylindrical body, and the solid electrolyte and the anode are laminated in a cylindrical shape on the inner surface side of the cathode. Also good.
Thus, a gas requiring strict airtightness, for example, ammonia can be passed through the inside of the cylindrical MEA, and the cathode located outside the MEA can be easily brought into contact with oxygen. A method of manufacturing the above-mentioned cylindrical porous substrate with a material such as calcia-stabilized zirconia (CSZ) or silica (SiO ₂ ) is known.
Whether the MEA is laminated on the outer surface side or the inner surface side of the porous substrate of the cylindrical body depends on the size of gas molecules introduced into the anode (ease of movement in the porous substrate), The limit value of the gas outlet concentration, the structure of the current collector, the allowable pressure loss, the diameter of the cylindrical body, the porosity of the porous material forming the anode, and the like may be adopted.

The metal having a catalytic action can be composed of one or more of (Ni, Ni—Fe, Ni—Co, Ni—Cu, Ni—Cr, and Ni—W).
All of the above metals are relatively easily available, and the anode is easy to manufacture. For this reason, the electrochemical reaction accompanied by gas decomposition can be advanced with high efficiency, ensuring economic efficiency. Ni-Fe system or the like refers to Ni-Fe alloy or Fe-Ni alloy.

  The thickness of the anode can be 1 μm or more and 1 mm or less. In such an anode having a small thickness, the contact between the gas to be decomposed (fuel gas) and the whole anode can be improved, and the time required for movement of ions (oxygen ions or protons) can be shortened. As a result, the efficiency of the electrochemical reaction can be increased. When the anode thickness is less than 1 μm, an anodic reaction cannot be caused in a sufficient amount per area. On the other hand, if the thickness exceeds 1 mm, the portion that does not contribute to the reaction increases, and it takes time to move ions.

The anode can be made to have a thickness of 50 μm or less so that the anode does not contain ionic conductive ceramics.
The anode is porous and the solid electrolyte is dense, but the surface has irregularities, and the vicinity of the interface between them is in and out, partially overlapping. By setting the thickness of the anode to 50 μm or less, the specific gravity in the vicinity of the interface with the solid electrolyte is increased, and the anode can function even if the anode itself does not contain ionic conductive ceramics. In addition, since there is no movement time of ions in the anode, the progress rate of gas decomposition can be improved. In addition, since ion conductive ceramics are relatively expensive, it is also useful for reducing manufacturing costs.

  The anode may include an ion conductive ceramic. This allows gas decomposition to proceed using the entire thickness of the anode.

The thickness of the solid electrolyte can be 0.7 μm or more and 20 μm or less. As a result, the time for the ion to pass through the solid electrolyte can be shortened, and the rate of progress of the electrochemical reaction can be increased. Moreover, although heating was performed at a high temperature in order to shorten the passage time of the ionic solid electrolyte, the heating temperature can be further reduced. As a result, not only energy efficiency can be improved, but also the cost of heat resistance can be relaxed and inexpensive device materials can be used.
When the thickness of the solid electrolyte is less than 0.7 μm, it is difficult to form a dense layer essential for preventing gas passage (leakage). On the other hand, if it exceeds 20 μm, it takes time to pass ions.

The solid electrolyte can be oxygen ion conductive or proton conductive.
An oxygen ion conductive solid electrolyte is easily available and relatively excellent in economic efficiency, but the transfer rate of oxygen ions is relatively low. On the other hand, the proton conductive solid electrolyte has a high proton transfer rate and can increase the electrochemical reaction rate. However, it is limited to some materials such as barium zirconate and is expensive.

The anode, solid electrolyte, and cathode can be formed by electrophoresis or plating.
As a result, the anode, the solid electrolyte, and the cathode can be formed with a thin and accurate thickness. In particular, regarding the anode, a metal having a large catalytic action for gas decomposition can be easily deposited regardless of a single metal or an alloy to form a deposited layer or a porous layer. Also, the presence or absence of dispersion of the ion conductive ceramic powder can be easily controlled by using a dispersion plating method or the like. The plating method may be electroplating or electroless plating.

The porous substrate has a form that does not impair the porous property on at least one of the one surface and the other surface of the porous substrate, and the surface opposite to the solid electrolyte in the anode and the surface opposite to the solid electrolyte in the cathode. Conductors can be placed.
This facilitates the formation of a conductive connection between the electrode having a low electrical resistance and the current collector. The conductor in a form that does not impair the porosity may be anything as long as it has porosity and conductivity. For example, (1) metal mesh sheet (woven fabric, non-woven fabric, micro-hole punched sheet, etc.), lattice (circumference-bus) conductor, bus wiring, etc. (2) metal paste that becomes porous after sintering, silver This refers to paste.

The fuel cell of the present invention is characterized by using any one of the membrane electrode assemblies described above. Moreover, the gas abatement apparatus of the present invention is characterized by using any of the membrane electrode assemblies described above.
Thereby, in the fuel cell or the gas abatement apparatus, it is possible to realize a highly efficient electrochemical reaction while ensuring economic efficiency.
In order to supply electric power with the above fuel cell or the like, a predetermined level of voltage is required. For this reason, it is possible to adopt a configuration in which a single membrane electrode assembly arranged in a macro form is electrically insulated and separated into a plurality of portions, and the plurality of portions are connected in series by a conductor. As a result, for example, in a fuel cell or the like, the output voltage can be increased to provide a power source that is practically easy to use. The term “organized in a macro form” refers to an aspect in which it is reasonable to handle the unit as a unit without forming an anode or the like. For example, it refers to a cylindrical MEA. In the above-described invention, an insulating separation band is inserted into the cylindrical MEA, and the area is electrically separated into several areas, and these are connected in series, whereby the output voltage and the like can be increased.

The method for producing MEA of the present invention is a method for producing MEA used in an electrochemical reaction involving gas decomposition. In this MEA manufacturing method, a MEA of a laminate in which a porous anode, a solid electrolyte layer, and a porous cathode are laminated is formed by a step of preparing a porous substrate and electrophoresis or plating. And a step of sintering the porous substrate on which the MEA is formed. In the step of forming the MEA of the laminate, the MEA of the laminate is formed by bringing a porous anode or a porous cathode into contact with one surface of the porous substrate, and The formation of the anode is characterized in that an anode including a porous layer or a deposited layer of a metal having a catalytic action for gas decomposition is formed.
By the above method, MEA having a good gas resolution rate can be easily formed on the porous base material forming the MEA skeleton by electrophoresis or plating. As described above, the plating method may be an electroplating method or an electroless plating method. The plating method naturally includes a dispersion plating method.

In the electrophoresis method or the plating method, the anode can be formed in a form in which ion-conductive ceramic particles are dispersed in a porous layer or deposited layer of Ni or Ni alloy.
By the above method, an MEA that causes the anode reaction can be easily produced with the entire thickness from the vicinity of the interface with the solid electrolyte to the anode surface.

In addition, in the electrophoresis method or the plating method, the anode may be formed in a form in which the porous layer or precipitation layer of Ni or Ni alloy does not contain ion conductive ceramic particles.
By the above method, an anode reaction can be caused in the vicinity of the interface between the solid electrolyte and the anode. Since there is almost no movement of ions in the anode due to the anode reaction, the rate of progress of the electrochemical reaction can be increased.

A porous base material is used as a cylindrical body, and the anode is formed into a cylindrical shape by contacting the outer peripheral surface of the cylindrical body. Next, a solid electrolyte and a cathode are sequentially formed in a cylindrical shape on the outer surface side of the anode. be able to.
Further, the porous base material is formed into a cylindrical body, the cathode is formed into a cylindrical shape by contacting the inner peripheral surface of the cylindrical body, and then the solid electrolyte and the anode are sequentially formed in the cylindrical shape on the inner surface side of the cathode. Can be formed.
Thereby, cylindrical MEA can be manufactured easily. The cylindrical MEA can be arranged on the inner surface side or the outer surface side of the porous substrate of the cylindrical body, in any case, with the inner surface side of the cylindrical MEA as the anode and the outer surface side as the cathode. Whether the cylindrical MEA is the inner side or the outer side of the porous base material of the cylindrical body, as described above, the structure of the current collector, the allowable pressure loss, the diameter of the cylindrical body, and the anode are formed It can be employed in consideration of the porous porosity.

  According to the MEA and the like of the present invention, in general electrochemical reactions involving gas decomposition and the like, the electrochemical reactions can be advanced with high efficiency, and the economic efficiency can be improved.

It is a figure which shows the gas abatement apparatus using MEA in Embodiment 1 of this invention. It is the A section enlarged view of FIG. (A) is a figure of the dispersion | distribution plating method (electroplating method) which manufactures MEA of this Embodiment, (b) is a figure of the mechanism in which ceramic particles disperse | distribute in a plating solution with surfactant. It is a figure which shows MEA in Embodiment 2 of this invention. It is the A section enlarged view of FIG. It is a modification of Embodiment 2, and is a figure of the interface of the anode / solid electrolyte of MEA which is also one embodiment in this invention. It is a figure which shows MEA in Embodiment 3 of this invention. It is the A section enlarged view of FIG. It is a figure which shows the gas abatement (decomposition | disassembly) apparatus using MEA in Embodiment 4 of this invention. It is sectional drawing which follows the XX line of FIG. A metal mesh sheet | seat is shown, (a) is the sheet | seat which punched the hole, and (b) is a metal woven fabric. It is a figure which shows the fuel cell system of this invention.

(Embodiment 1)
FIG. 1 is a diagram showing a gas abatement apparatus 10 using an MEA 7 according to Embodiment 1 of the present invention. This gas abatement apparatus is a type of apparatus that repeatedly laminates flat MEAs. The laminated structure of one unit is as follows.
(Air space S / porous substrate 3 / cathode 5 / solid electrolyte 1 / anode 2 / passage P / partition wall W)
A gas or fuel gas to be decomposed such as ammonia flows through a passage P between the partition wall W and the anode 2. Since the plated porous body 11s for preventing passage is disposed, the above gas does not pass through and decomposes in contact with the anode 2 (anode reaction). The anode 2 is also called a fuel electrode. The plated porous body 11s constitutes an anode current collector together with prevention of gas passage. The anode current collector is usually composed of a plurality of parts, and the plated porous body 11s is one member thereof.
The cathode 5, also called an air electrode, faces the air space S and contacts the air to decompose oxygen molecules in the air (cathode reaction).
As a result of the electrochemical reaction at the two electrodes (anode and cathode), ions are generated on the one hand and electrons on the other hand. Ions pass through the solid electrolyte 1, electrons pass through an external circuit (not shown) with a load interposed therebetween, reach the counterpart electrode, and participate in the anode reaction or the cathode reaction, respectively.
For the porous substrate 3, porous ceramics such as calcia-stabilized zirconia (CSZ) and silica (SiO ₂ ) can be used.

FIG. 2 is an enlarged view of part A in FIG. Taking the decomposition of ammonia as an example, the case where the solid electrolyte 1 is oxygen ion conductive will be described. In FIG. 2, the solid electrolyte 1 is dense (non-porous) so as not to allow gas to pass through, but allows oxygen ions to pass but does not pass electrons. Ammonia NH ₃ flowing through the passage P undergoes the following electrochemical reaction with oxygen ions generated at the cathode 5 and passing through the solid electrolyte 1.
(Anode reaction): 2NH ₃ + 3O ²⁻ → N ₂ + 3H ₂ O + 6e ⁻
More specifically, a part of ammonia causes a reaction of 2NH ₃ → N ₂ + 3H ₂ , and this 3H ₂ reacts with oxygen ions 3O ²⁻ to generate 3H ₂ O. In this ammonia decomposition, the metal precipitate (layer) 21 or porous body (layer) 21 having catalytic action promotes decomposition. In addition to the metal precipitate 21 having catalytic action, the anode 2 contains oxygen ion conductive ceramic particles 22 and guides oxygen ions to the anode reaction site. Ammonia moves through the pores 2h to the decomposition site in the anode 2.
As a result of this anodic reaction, it is possible to prevent the ammonia decomposition process from becoming a bottleneck (rate-limiting process) of the entire electrochemical reaction, while reducing the outlet concentration described below to a predetermined level or less. The thickness of the anode 2 is 1 μm or more and 1 mm or less, but is particularly preferably 1 μm or more and 50 μm or less when thinned, and 25 μm or less when further thinned.
Air, particularly oxygen gas, is introduced into the cathode 5 so as to pass through the space S, and oxygen ions decomposed from oxygen molecules at the cathode 5 are sent toward the anode 2 toward the solid electrolyte 1. The cathode reaction is as follows.
(Cathode reaction): O ₂ + 4e ⁻ → 2O ²⁻
As a result of the above electrochemical reaction, electric power is generated, a potential difference is generated between the anode 2 and the cathode 5, and current flows from the cathode current collector to the anode current collector. If a load, for example, a heater for heating the gas abatement apparatus 10 is connected between the cathode current collector and the anode current collector, electric power for that purpose can be supplied. The supply of electric power to the heater may be partial, but in most cases, the supply amount of private power generation is often less than half of the electric power required for the entire heater.

<Anode>
A gas containing ammonia is introduced into the anode 2 and flows through the pores 2h. The anode 2 is a sintered body mainly composed of a catalyst, that is, a metal deposit 21 and an oxygen ion conductive ceramic 22. Here, the metal precipitate 21 is made of one or more of (Ni, Ni—Fe, Ni—Co, Ni—Cu, Ni—Cr, and Ni—W). Good.
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.

In addition to the above catalytic action, oxygen ions are allowed to participate in the decomposition reaction at the anode. That is, the decomposition is performed in an electrochemical reaction. In the above-mentioned anode reaction 2NH ₃ + 3O ²⁻ → N ₂ + 3H ₂ O + 6e ⁻ , oxygen ions contribute and greatly improve the decomposition rate of ammonia.
In the anode reaction, free electrons e ⁻ are generated. When the electrons e ⁻ stay on the anode 2, the progress of the anode reaction is hindered. The metal deposit 21 is a good conductor. The electrons e ⁻ flow smoothly through the metal precipitate 21. For this reason, the electrons e ⁻ do not stay in the anode 2 and are circulated to the external circuit through the metal precipitate 21. Due to the metal deposition 21, the electron e ⁻ path is very good. In summary, the characteristics of the embodiment of the present invention are the following (e1), (e2) and (e3) in the following anode.
(E1) Promotion of decomposition reaction by the metal deposit 21 (high catalytic function)
(E2) Decomposition promotion by oxygen ions (decomposition promotion in electrochemical reaction)
(E3) Ensuring continuity of electrons by the metal precipitate 21 (high electron conductivity)
By the above (e1), (e2) and (e3), the anode reaction is greatly promoted.
The decomposition of the decomposition target gas proceeds only by raising the temperature and bringing the decomposition target gas into contact with the catalyst. However, as described above, in the element constituting the fuel cell, oxygen ions are involved in the reaction from the cathode 5 through the ion conductive solid electrolyte 1, and as a result, the generated electrons are circulated through an external circuit, The decomposition reaction rate is dramatically improved. It is a major feature of the present invention to have the functions (e1), (e2), and (e3) described above, and a configuration that provides the functions.
Although the above description is for the case where the solid electrolyte 1 is oxygen ion conductive, the solid electrolyte 1 may be proton (H ⁺ ) conductive. In this case, the ion conductive ceramics 22 in the anode 2 is proton conductive. Ceramics such as barium zirconate may be used.

(When using metal precipitates and ion conductive ceramics): When the oxygen ion conductive metal oxide (ceramics) of the anode 2 is SSZ, the average diameter of the raw material powder of SSZ is 0.5 μm to 50 μm. It is good to be about. The metal precipitate 21 and SSZ22 are in the range of 0.1 to 10 in terms of molar ratio. A method for manufacturing the MEA 7 by the dispersion plating method will be described later.
The conditions for co-sintering the MEA 7 including the porous substrate 3 and the MEA main body 7a of the laminate are maintained, for example, in the atmosphere at a temperature of 1000 ° C. to 1600 ° C. for 30 minutes to 180 minutes. Do that.
(When using only a metal precipitate): The metal precipitate 21 is formed by a dispersion plating method or the like to be described later. In the case of a Ni—Fe alloy, the composition is preferably about Ni 60 at%, for example.
In co-sintering, the same thermal pattern as above is applied.

<Cathode>
Air, particularly oxygen molecules, is introduced into the cathode 5. The cathode 5 is a sintered body mainly composed of oxygen ion conductive ceramics. In this case, it is preferable to use LSM (lanthanum strontium manganite), LSC (lanthanum strontium cobaltite), SSC (samarium strontium cobaltite) or the like as the oxygen ion conductive ceramic.
In the cathode 5, it is preferable to contain silver particles having a strong oxygen catalytic action. Ag particles have a catalytic function that greatly promotes the cathode reaction O ₂ + 4e ⁻ → 2O ²⁻ . As a result, the cathodic reaction can proceed at a very high rate. The average diameter of the Ag particles is preferably 10 nm to 100 nm.
The above description is for the case where the solid electrolyte 1 is oxygen ion conductive. However, the solid electrolyte 1 may be proton (H ⁺ ) conductive. In this case, the ion conductive ceramic in the cathode 5 is proton conductive ceramic. For example, barium zirconate may be used.
The average diameter of SSZ in the cathode 5 is preferably about 0.5 μm to 50 μm. The sintering conditions are maintained at 1000 ° C. to 1600 ° C. for about 30 minutes to 180 minutes in an air atmosphere.

<Solid electrolyte>
As the electrolyte 1, a solid oxide, molten carbonate, phosphoric acid, solid polymer, or the like can be used, but the solid oxide is preferable because it can be downsized and easily handled. As the solid oxide 1, it is preferable to use oxygen ion conductive SSZ, YSZ, SDC, LSGM, GDC, or the like.
In addition, a reaction in which protons are generated at the anode 2 using, for example, barium zirconate (BaZrO ₃ ) as the solid electrolyte 1 and moved through the solid electrolyte 1 to the cathode 5 is also a desirable form of the present invention. When proton conductive solid electrolyte 1 is used, for example, when ammonia is decomposed, ammonia is decomposed at anode 2 to generate protons, nitrogen molecules and electrons, and protons are transferred to cathode 5 through solid electrolyte 1. Then, it reacts with oxygen at the cathode 5 to produce water (H ₂ O). Since protons are smaller than oxygen ions, the moving speed in the solid electrolyte is large. Therefore, a practical decomposition capacity can be obtained while lowering the heating temperature. The thickness of the solid electrolyte 1 is also easily set to a thickness that can ensure strength.

FIG. 3A is a diagram showing a dispersion plating method (electroplating method) for manufacturing the anode 2 of the MEA 7 of the present embodiment. In the plating solution, ions of the material to be deposited on the negative electrode and ceramic grains are dispersed. In the case of dispersing the ceramic particles, by using a surfactant, the molecules of the surfactant can be adhered to the surface of the ceramic particles and dispersed in the solution (see FIG. 3B). The plating bath is preferably agitated to maintain homogeneity.
When laminating the MEA main body portion 7 a in FIG. 1, the workpiece is plated in the plating bath of the cathode 5. The above electrolyte, for example, LSM is dispersed to form a plating layer on the workpiece. In order to obtain a porous cathode, it is preferable to form a plating layer under conditions of high voltage and low current, which are charring plating.
After forming the plating layer of the cathode 5, the plating layer of the solid electrolyte 1 is formed. The formation of the solid electrolyte 1 is also performed by the same dispersion plating except that the ceramic material is different. However, the solid electrolyte 1 is not porous, and the voltage and current are selected so as to form a dense layer after sintering.
After the plating layer of the solid electrolyte 1 is formed, the plating layer of the anode 2 is formed thereon. In the present embodiment, the anode 2 disperses particles of a solid electrolyte such as YSZ and dissolves metal ions such as Ni ions and Fe ions (see FIG. 3A). On the positive electrode, a Ni—Fe alloy plate, bar or wire serving as a supply source of these metal ions is arranged. Further, a porous substrate 3 / cathode 5 / solid electrolyte 1 which is a material to be plated (work) is disposed on the negative electrode, and a metal Ni—Fe precipitate 21 and ceramics are disposed on the solid electrolyte 1. A plating layer composed of the grains 22 is formed. As described above, for example, a Ni—Fe alloy of Ni: 60 at% may be used for the metal plate of the supply source.
Thereafter, porous substrate 3 / cathode plating layer / solid electrolyte plating layer / anode plating layer are co-sintered. As described above, the co-sintering condition is maintained at 1000 ° C. to 1600 ° C. for about 30 minutes to 180 minutes, for example, in an air atmosphere.

Instead of the electroplating method shown in FIG. 3, the plating layer of the MEA main body 7a may be formed by an electroless plating method. In particular, the solid electrolyte 1 is preferably formed by forming a plating layer by electroplating, and the anode 2 and the cathode 5 by electroless plating. In the electroless plating method, the growth rate of the plating layer is slow, so that the porous layer can be formed relatively easily.
When forming the plating layer of the anode 2 by electroless plating, it is preferable to place a catalyst such as palladium on the base. The catalyst for the surface treatment is commercially available under the name of CRP catalyst (Okuno Pharmaceutical Co., Ltd.). After the ground treatment, the work is immersed and held in an electroless solution in which YSZ is dispersed and Ni ions and Fe ions are dissolved. Depending on the holding time, the electroless plating layer of the anode 2 grows. In the electroless plating method, the electroless plating layer is porous unless the holding time is extended. This is the same for the cathode plating layer of the ceramic particle single plating layer and the anode plating layer made of metal and ceramic particles. In particular, when the thickness is reduced, it is easy to ensure porosity.
Although it may be tightened even by sintering, if a plating layer that secures porosity is taken into account, the porosity is maintained after sintering.

(Embodiment 2)
FIG. 4 is a diagram showing the MEA 7 according to Embodiment 2 of the present invention. This MEA 7 is a cylindrical body. For reference, the flow of ammonia and the flow of oxygen molecules, which are examples of gases to be decomposed, are shown. Ammonia or the like is in contact with the anode 2 on the inner surface side of the cylindrical MEA 7, and oxygen or air is in contact with the cathode 5 on the outer surface side of the cylindrical MEA. The laminated structure of the cylindrical body is as follows.
(Tubular porous substrate 3 / tubular porous anode 2 / tubular solid electrolyte 1 / tubular porous cathode 5)
The anode 2 is disposed inside the MEA main body 7a. Gases to be removed such as ammonia should be passed through the inside of the cylinder, which is convenient for airtightness, since leakage must be avoided extremely. On the other hand, the cathode 5 is located on the outside where it is easy to come into contact with air.
FIG. 5 is an enlarged view of a portion A in FIG. A hydrogen supply gas such as ammonia reaches the anode 2 through the porous substrate 3 from the passage P (see FIG. 4). In the anode 2, a metal precipitate 21 and an ion conductive ceramic 22 are positioned so as to surround the pores 2 h.
The anode reaction at the anode 2 and the cathode reaction at the cathode 5 are the same as those in the first embodiment.

FIG. 6 is a modification of the present embodiment, and is also an embodiment of the present invention. This modification is characterized in that the anode 2 is formed only of the metal deposit 21 and has no ion conductive ceramics.
In general, the interface between the solid electrolyte 1 and the anode 2 is not flat, and is intricate with respect to each other. For this reason, after the co-sintering, the ion conductive ceramic 15 of the solid electrolyte 1 enters the anode 2 made of only the metal precipitate 21. In other words, when the thickness of the anode 2 is small, the ion conductive ceramic 15 of the solid electrolyte 1 and the metal deposit 21 overlap at a relatively high rate in the thickness of the anode 2. For this reason, when the anode 2 is thin, the function of the anode can be fulfilled without mixing ion conductive ceramics such as YSZ in the anode 2.
By reducing the thickness of the anode 2, it is possible to increase the efficiency of the electrochemical reaction and increase the efficiency.
Furthermore, the amount of ion conductive ceramics such as YSZ, which is relatively expensive, can be suppressed to improve the economic efficiency.
By overlapping with the solid electrolyte 15 uneven on the surface of the solid electrolyte 1, the thickness at which the anode 2 can be formed by only the metal deposition layer 21 and can function as the anode is 5 μm or more and 50 μm or less, more preferably 5 μm or more and 25 μm. The following is recommended.
In order to form the anode 2 shown in FIG. 6, it is only necessary to disperse the ion conductive ceramic particles in the plating solution.

(Embodiment 3)
FIG. 7 is a diagram showing the MEA 7 according to Embodiment 3 of the present invention. This MEA 7 is also a cylindrical body. However, unlike the second embodiment, the MEA main body portion 7a is formed on the inner surface side of the cylindrical porous substrate 1. In the second embodiment, the MEA main body portion 7 a is formed on the outer surface side of the cylindrical porous substrate 1. MEA 7 in FIG. 7 has the following laminated structure in order from the inner surface side.
(Tubular porous anode 2 / tubular solid electrolyte 1 / tubular porous cathode 5 / tubular porous substrate 3)
The anodic reaction and the cathodic reaction are the same as the electrochemical reaction described in the first embodiment. However, in the present embodiment, the detoxification target gas such as ammonia or the fuel gas directly contacts the anode 2 without passing through the porous substrate 3. For this reason, it is desirable to use the MEA 7 of the present embodiment when the outlet concentration regulation on the order of ppm is targeted as in the gas abatement apparatus. The reason is that in the MEA 7 in the form of the second embodiment, the gas to be removed may remain in the porous substrate 3 and it may take a long time for removal to a very low concentration. is there. On the contrary, in the present embodiment, (T1) the gas to be detoxified does not stay in the porous base material 3, so that it can be detoxified to a very low concentration in a short time.

  FIG. 8 is an enlarged view of a portion A in FIG. The gas to be removed, such as ammonia, can contact the anode directly from the passage P. If the anode 2 is reached via the porous substrate 1, there is a risk that the gas movement will be congested in the porous substrate 1, which may hinder the gas processing capacity. In the present embodiment, (T2) gas directly contacts the anode 2 without any traffic jams, so that the gas processing capacity does not deteriorate due to the gas migration jams.

The manufacturing process of the MEA 7 is based on starting from the porous substrate 3. When performing dispersion electroplating or dispersion electroless plating using a cylindrical porous substrate 3 as a workpiece, plating is performed in the cylindrical porous substrate 3 so that a plating layer is uniformly formed inside. Ensure that the fluid flows smoothly and circulates. For this purpose, it is preferable to devise such that, for example, the stirrer is turned sideways (horizontally) like a ship screw and the plating solution is fed into the inner surface of the cylindrical porous substrate 3 in a horizontal posture.
Also, the anode 2 shown in FIG. 8 may be formed of only the metal deposit 21 without including the ion conductive ceramics, as in the modified example (see FIG. 6) in the second embodiment.

(Embodiment 4)
FIG. 9 is a diagram showing a gas abatement apparatus 10 using the MEA 7 according to Embodiment 4 of the present invention. FIG. 10 is a sectional view taken along line XX of FIG. In the present embodiment, in the MEA 7, a relatively large opening 3h is provided in the porous substrate 3, and a metal mesh sheet 12a that does not impair the porosity of the cathode 5 is disposed in the opening 3h. . The metal mesh sheet 12a is fixed to the cathode 5 together with the silver paste 12g sintered under the conditions matched with the silver paste. In FIG. 9, the upper and lower openings 2h are in the same position and appear to be connected, but instead the openings 3h have an opening diameter of a fraction of the circumference or are arranged intermittently. . The metal mesh sheet 12 a disposed so as to be in contact with the surface of the cathode 5 (surface opposite to the solid electrolyte 1) in the opening 3 h of the porous substrate 3 forms the main body of the cathode current collector 12. The metal mesh sheet 12a limited to each opening 3h is made continuous by an appropriate conductor or wiring (not shown) and functions as the cathode current collector 12.
Further, a metal mesh sheet 11 a that does not impair the porosity of the anode 2 is disposed on the surface of the anode 2. The metal mesh sheet 11 a disposed on the anode surface forms part of the anode current collector 11.
The metal mesh sheets 11a and 12a are preferably formed of, for example, Ni, Ni—Fe, Ni—Co, Ni—Cu, Ni—Cr, or Ni—W. For example, these metal nonwoven fabrics or metal nonwoven fabrics on which a plating layer of these metals is formed can be used.

The anode current collector 11 includes anode 2 / metal mesh sheet 11a / plated porous body 11s for preventing gas passage / center conductive rod 11k. A reducing gas such as ammonia containing hydrogen is introduced into the anode 2.
FIGS. 11A and 11B are views showing the metal mesh sheet 11a. FIG. 11 (a) shows a mesh formed by punching from a single-phase metal sheet, and FIG. 11 (b) shows a metal woven fabric, with the eyes enlarged and exaggerated. Either (a) or (b) may be used for the metal mesh sheet 11a. The metal mesh sheet 11a is formed of Ni, Ni—Fe, Ni—Co, Ni—Cu, Ni—Cr, or Ni—W, thereby adding to the metal precipitate 21 in the anode 2. These metal mesh sheets 11a can also exert catalytic action and promote decomposition of ammonia or the like.
In addition, in the case of Ni, Ni—Fe, Ni—Co, and Ni—Cu, it is easy to reduce and bond the metal mesh sheet 11 a to the anode 2. That is, reduction bonding can be performed without reducing the oxygen partial pressure so much.

The metal mesh sheet 12a constituting the cathode current collector 12 may be a woven fabric formed of Ni-Cr or Ni-W, or a metal woven fabric formed with a plating layer of these metals. The reason is that oxygen is introduced into the cathode 5 and oxidation is likely to proceed in a high temperature environment, but Ni—Cr or Ni—W metals are excellent in oxidation resistance. The durability of the cathode current collector 12 can be enhanced by using these metal mesh sheets 12a. The metal mesh sheet 12a constituting the cathode current collector 12 was partially cut out from the metal mesh sheet 11a of the anode current collector 11 shown in FIGS. 11A and 11B in accordance with the shape of the opening 3h. Is.
The silver paste remains as 12 g of silver particles. The silver particles 12g are a powerful catalyst that promotes the decomposition of oxygen molecules. For this reason, the progress of the oxidation reaction of the surrounding material can be made substantially very slow. As a result, although the metal mesh sheet 12a is formed of the above-mentioned oxidation resistant metal and has oxidation resistance, the durability can be further improved through the action of reducing the concentration of substantial oxygen molecules.
In addition, since silver is an excellent good conductor, the electrical resistance of the cathode current collector 12 can be lowered.

The manufacturing method of MEA 7 shown in FIG. 9 is basically the same as the manufacturing method of MEA in the first embodiment and the like. The difference is that there is an opening 3h, and the cathode current collector 12 and the anode current collector 11 are arranged. The manufacturing points are as follows.
(1) Opening 3h is made in porous substrate 3 before the dispersion plating treatment.
(2) At the time of the dispersion plating process, a detachable contact material is disposed in the opening 3h so that the cathode 5 is aligned with the cylindrical surface of the porous substrate 3 having the non-opening at the opening 3h. Keep it.
(3) A porous substrate 3 with an opening 3h / cathode 3 / solid electrolyte 1 / anode 2 was formed by dispersion plating (see FIGS. 3 (a) and 3 (b)), and the pad was removed. Then, co-sintering is performed before the metal mesh sheets 11a and 12a are arranged. The conditions for co-sintering are as described above.
(4) Anode current collector 11:
The metal mesh sheet 11a is reduction bonded to the co-sintered intermediate product in contact with the anode 2. As the conditions for the reduction bonding, when both an inert gas and a reducing gas are used, it is preferable that a small amount of gas such as ammonia is contained based on nitrogen gas. For example, (3% NH ₃ + N ₂ ) can be used. By using these non-oxidizing gases and performing a leak check, an oxygen partial pressure as low as about 1E-15 atm is achieved. The temperature is heated to a temperature at which diffusion occurs sufficiently, for example, about 950 ° C. If a sufficiently low oxygen partial pressure is realized, the reduction bonding proceeds automatically at the above 950 ° C. The holding time at 950 ° C. is preferably 20 minutes, for example. As a result, it is possible to obtain an electrode connection structure that allows good contact between the anode 2 and the gas to be decomposed and that has low electrical resistance.
It is preferable to use Celmet (registered trademark: Sumitomo Electric Industries, Ltd.) capable of selecting the porosity to a high range as the plated porous body 11s wound around the central conductive rod 11k. The sheet-like selmet 11s is wound around the central conductive rod 11k and charged into the metal mesh sheet 11a. At this time, it is preferable to sufficiently apply a metal paste such as Ni to the outer peripheral surface of the cermet 11s or the inner peripheral surface of the metal mesh sheet 11a. With the cermet 11s inserted, reduction bonding is performed again.
The reduction bonding between the anode 2 and the metal mesh sheet 11a and the reduction bonding between the metal mesh sheet 11a and the plated porous body 11s or the celmet 11s may be performed on the same occasion.
(5) Cathode current collector 11:
A metal mesh sheet 12a that matches the shape of the opening 3h is prepared, and the metal mesh sheet 12a is stopped in contact with the cathode 5 with a silver paste 12g and other stoppers. It is preferable to sinter in a nitrogen atmosphere at 900 ° C., for example, in accordance with the sintering conditions of the silver paste 12 g.
The metal mesh sheets 12a in the openings 3h arranged in isolation can be connected by a conductor or wiring (not shown) to form a single cathode current collector.

(Embodiment 5)
FIG. 12 is a diagram showing a gas decomposition system functioning as a fuel cell in Embodiment 5 of the present invention. In this fuel cell system 50, a hydrogen source that is a molecule containing hydrogen, such as ammonia, toluene, xylene, or the like is supplied from a hydrogen source and decomposed in the power generation cell 10 or the gas decomposition element 10. For the MEA (not shown) of the gas decomposition element 10, the MEA described in any of Embodiments 1 to 4 is used. Electricity is generated by the electrochemical reaction of gas decomposition described above. Part of this electric power is used for a heating device (heater) 41 for improving gas decomposition ability or power generation ability. The surplus power is AC / DC converted or boosted by the inverter 71 to be converted into a power form suitable for the external device. As a result, the fuel cell system of the present embodiment is used as a power source for electronic devices such as PCs and portable terminals, and a power source for electric devices with higher power consumption, using various hydrogen sources including organic substances such as sugars. Can be.
The gas that is decomposed and exhausted from the power generation cell 10 or the gas decomposition element 10 is treated safely by detecting the residual component concentration by the post-processing device (built-in sensor) 75. In this case, depending on the residual component concentration, it can be returned to the original and circulated.
In the fuel cell system 50, it is not necessary to extremely reduce the concentration of the gas component as in the case of gas abatement, and a high power generation capacity is achieved by performing an electrochemical reaction of decomposition at a high gas component concentration. Obtainable.

(Other electrochemical reactions)
Table 1 is a table illustrating other gas decomposition reactions to which the MEA of the present invention can be applied. The gas decomposition reaction R1 is the ammonia / oxygen decomposition reaction described in the first embodiment and the like. In addition, the catalyst and electrode of the present invention can be used for any of the gas decomposition reactions R2 to R20. That is, it can be used for ammonia / water, ammonia / NOx, hydrogen / oxygen /, ammonia / carbon dioxide gas, VOC (volatile organic compounds) / oxygen, VOC / NOx, water / NOx, and the like.

Table 1 only illustrates some of the many electrochemical reactions. The MEA of the present invention is applicable to many other reactions. For example, Table 1 is limited to reaction examples of the solid electrolyte having oxygen ion conductivity, but the reaction example in which the solid electrolyte is proton (H ⁺ ) conductivity as described above is also a powerful embodiment of the present invention. is there. Even if the solid electrolyte is made proton conductive, the ionic species that permeate the solid electrolyte become protons. However, in the gas combinations shown in Table 1, it is possible to achieve decomposition of gas molecules as a result. For example, in the reaction of (R1), in the case of a proton conductive solid electrolyte, ammonia (NH ₃ ) decomposes into nitrogen molecules, protons, and electrons at the anode, and the protons move through the solid electrolyte to the cathode. The electrons move through the external circuit to the cathode. At the cathode, oxygen molecules, electrons, and protons generate water molecules. As a result, ammonia is decomposed in combination with oxygen molecules, which is the same as when the solid electrolyte is oxygen ions.
The above electrochemical reaction is a gas decomposition reaction for the purpose of removing gas. However, there are gas decomposition elements that are not mainly intended for gas removal, and the gas decomposition elements of the present invention can also be used in such electrochemical reaction devices such as fuel cells.

  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 MEA and the like of the present invention, in general electrochemical reactions involving gas decomposition and the like, the electrochemical reactions can be advanced with high efficiency, and the economic efficiency can be improved. In particular, by making the porous base material into a cylindrical body, a gas processing apparatus that requires strict airtightness can be miniaturized, and can be easily installed near a gas generating apparatus. For this reason, it is no longer necessary to route high-concentration gas through piping to a large gas processing facility as in the prior art, and it is possible to prevent a major accident even in an earthquake or the like.

DESCRIPTION OF SYMBOLS 1 Solid electrolyte, 2 Anode, 2h Pore in anode, 3 Porous base material, 3h Opening part of porous base material, 5 Cathode, 7 MEA (membrane electrode complex), 7a MEA main body part, 10 Gas decomposition apparatus ( Element), 11 anode current collector, 11a metal mesh sheet, 11k center conductive rod, 11s porous metal body (plated porous body), 12 cathode current collector, 12a metal mesh sheet, 12g silver paste coating part (silver particles) , 15 ion conductive ceramics, 21 anode metal deposit or porous body, 22 anode ion conductive ceramics, 41 heater, 71 inverter, 75 aftertreatment device, P gas passage, S air space.

Claims (18)

A membrane electrode assembly (MEA) used for an electrochemical reaction involving gas decomposition,
A porous substrate;
A MEA in which a porous anode, an ion conductive solid electrolyte, and a porous cathode are laminated,
The anode or the cathode is brought into contact with one surface of the porous substrate and laminated on the porous substrate;
The membrane electrode assembly, wherein the porous anode has a porous layer or a deposited layer of metal having a catalytic action for the gas decomposition.   The porous substrate is a cylindrical body, the anode is in contact with the outer peripheral surface of the cylindrical body and laminated in a cylindrical shape, and the solid electrolyte and the cathode are laminated in a cylindrical shape on the anode. The membrane electrode assembly according to claim 1.   The porous substrate is a cylindrical body, the cathode is laminated in a cylindrical shape in contact with the inner peripheral surface of the cylindrical body, and the solid electrolyte and the anode are laminated in a cylindrical shape on the inner surface side of the cathode. The membrane electrode assembly according to claim 1, wherein:   The metal having a catalytic action is composed of one or more of (Ni, Ni-Fe series, Ni-Co series, Ni-Cu series, Ni-Cr series, and Ni-W series), Item 4. The membrane electrode assembly according to any one of Items 1 to 3.   The membrane electrode assembly according to any one of claims 1 to 4, wherein the anode has a thickness of 1 µm or more and 1 mm or less.   The membrane electrode assembly according to any one of claims 1 to 5, wherein the anode has a thickness of 50 µm or less, and the anode does not include an ion conductive ceramic.   The membrane electrode assembly according to claim 1, wherein the anode contains an ion conductive ceramic.   The thickness of the said solid electrolyte is 0.7 micrometer or more and 20 micrometers or less, The membrane electrode assembly of any one of Claims 1-7 characterized by the above-mentioned.   The membrane electrode assembly according to any one of claims 1 to 8, wherein the solid electrolyte is oxygen ion conductive or proton conductive.   The membrane electrode assembly according to any one of claims 1 to 9, wherein the anode, the solid electrolyte, and the cathode are formed by electrophoresis or plating.   At least one of the one surface and the other surface of the porous substrate, and the surface of the anode opposite to the solid electrolyte and the surface of the cathode opposite to the solid electrolyte are porous. The membrane electrode assembly according to any one of claims 1 to 10, wherein a conductor in a form that does not damage the surface is disposed.   A fuel cell using the membrane electrode assembly according to any one of claims 1 to 11.   A gas abatement apparatus using the membrane electrode assembly according to any one of claims 1 to 11. A method for producing a membrane electrode assembly (MEA) used in an electrochemical reaction involving gas decomposition,
Preparing a porous substrate; and
Forming an MEA of a laminate in which a porous anode, a solid electrolyte layer, and a porous cathode are laminated by electrophoresis or plating;
A step of sintering the porous substrate on which the MEA is formed,
In the step of forming the MEA of the laminate, the MEA of the laminate is formed by bringing the porous anode or the porous cathode into contact with one surface of the porous substrate. And the formation of the said anode forms the anode containing the porous layer or precipitation layer of the metal which has a catalytic action with respect to the said gas decomposition | disassembly, The manufacturing method of a membrane electrode assembly characterized by the above-mentioned.   15. The anode is formed in a form in which ion-conductive ceramic particles are dispersed in a porous layer or a deposition layer made of Ni or a Ni alloy in the electrophoresis method or the plating method. The manufacturing method of the membrane electrode assembly as described in any one of.   15. The anode according to claim 14, wherein, in the electrophoresis method or the plating method, the anode is formed in a form not containing ion conductive ceramic particles in a porous layer or a deposited layer of Ni or Ni alloy. A method for producing a membrane electrode assembly.   The porous base material is used as a cylindrical body, and the anode is formed into a cylindrical shape by contacting the outer peripheral surface of the cylindrical body. Next, a solid electrolyte and a cathode are sequentially formed in a cylindrical shape on the outer surface side of the anode. The method for producing a membrane electrode assembly according to any one of claims 14 to 16, wherein the membrane electrode assembly is formed as follows.   The porous base material is used as a cylindrical body, and the cathode is formed into a cylindrical shape by contacting the inner peripheral surface of the cylindrical body, and then a solid electrolyte and an anode are sequentially formed on the inner surface side of the cathode. It forms in a shape, The manufacturing method of the membrane electrode assembly of any one of Claims 14-16 characterized by the above-mentioned.

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