JP7281726B2 - Gas diffusion layer used for gas diffusion electrode of metal-air battery or fuel cell, gas diffusion electrode using the same, and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a gas diffusion layer used for a gas diffusion electrode of a metal-air battery or a fuel cell, a gas diffusion electrode using the same, and a method for producing the same.

A metal-air battery is an energy device that extracts the energy of a chemical reaction using a metal or metal compound as a negative electrode active material and oxygen as a positive electrode active material as electrical energy. Since the metal-air battery uses oxygen in the air as a positive electrode active material, the air electrode can be made very thin, and the weight and volume of the air electrode occupying the battery are extremely small. Therefore, since the battery does not contain a material containing a positive electrode active material, which is necessary for a normal battery, its theoretical energy density is extremely high compared to lithium ion batteries, which have a high energy density among current batteries. A metal-air battery can be used as a power source for vehicles, a stationary distributed power source for homes and factories, or a power source for portable electronic devices.

A gas diffusion electrode is usually used for the air electrode of a metal-air battery. A gas diffusion electrode is an electrode that can directly initiate an electrochemical redox reaction of a gaseous reactant. At the air electrode, oxygen in the air is used as an active material, and its reduction reaction proceeds. In the low current density region, the charge transfer of the oxygen reduction reaction becomes rate-limiting, while in the high current density region, oxygen supply becomes rate-limiting, and the voltage drops rapidly as the critical diffusion current density is approached (Non-Patent Document 1). . Therefore, in order to obtain a high-power metal-air battery, a highly active catalyst is used to facilitate charge transfer in the oxygen reduction reaction, and oxygen is smoothly diffused to obtain a large current. is necessary.

A gas diffusion electrode used for the positive electrode of a metal-air battery is generally composed of a catalyst layer, a gas diffusion layer, and a current collector in this order from the electrolyte side. The catalyst layer contains, for example, a catalyst, a conductive catalyst carrier such as hydrophilic carbon, and a binder such as PTFE. The gas diffusion layer contains, for example, hydrophobic carbon and a binder such as PTFE. The gas diffusion layer forms a smooth gas diffusion path and prevents leakage of the electrolytic solution and contamination of moisture from the air side (Non-Patent Document 2). Carbon black produced from acetylene gas (acetylene black) has a high structure, so inter-particle voids develop to effectively form gas diffusion paths. is suitable for As the current collector, Ni mesh (Non-Patent Document 3) or carbon fiber woven fabric (Patent Document 1) is usually used so as not to hinder the diffusion of oxygen. However, since these are woven metal wires or carbon fibers, the wires or fibers are not fixed to each other, so the electrical contact is unstable. The shape of the layer cannot be maintained, and there is a risk of peeling off.

In Patent Document 2, a Ni porous body is used as the gas diffusion electrode, and the porous body preferably has a porosity of 55 to 85% and a pore diameter of 200 μm or more and 550 μm or less. . This gas diffusion electrode is for a polymer electrolyte fuel cell using a proton-conducting solid polymer (Nafion, etc.) as an electrolyte. It is not suitable for use because it does not have the function of preventing leakage of the electrolyte solution and contamination of moisture from the air side, which are necessary for the gas diffusion layer for batteries.

In Patent Document 3, a second conductive layer (conductive Even when conductive carbon fibers are used as the conductive carbon material constituting the porous substrate), the conductive carbon fibers constituting the second conductive layer are prevented from protruding into the first conductive layer. found that it is possible to provide a conductive porous layer that can be used in batteries such as fuel cells and metal-air batteries in which the conductive layer is a film with few cracks. Therefore, the gas diffusion distance becomes long, the gas diffusibility decreases, and the output decreases.

JP-A-58-165254 JP 2017-33917 A JP 2014-197477 A

Electrochemistry, 2010, 78, pp 629-632. Electrochemistry, 2010, 78, pp. 529-539. Chemistry of Materials, 2013, 25, pp. 3072-3079.

As described above, conventional gas diffusion electrodes using a metal mesh or carbon fiber woven fabric as a current collector have unstable contact between the gas diffusion layer and the current collector, resulting in problems such as easy peeling and gas diffusion. There is a problem that the diffusion distance becomes long and the gas diffusibility decreases.

The present invention has been made in view of the above circumstances, and is used for gas diffusion electrodes of metal-air batteries or fuel cells that have excellent gas diffusibility, high rigidity, and stable electrical contact. It is an object of the present invention to provide a gas diffusion layer, a gas diffusion electrode using the same, and a method for manufacturing the same.

As a result of intensive studies to solve the above problems, the inventors of the present invention applied a suspension containing a carbon material and a resin binder to a metal foam and pressurized it to obtain The binding material forms a single layer without gaps, and in the composite layer thus formed, the foam metal and the carbon material are intricately entwined, so that the electrical contact is stable, and the present invention has been completed. .

That is, the gas diffusion layer of the present invention is a gas diffusion layer used for a gas diffusion electrode of a metal-air battery or a fuel cell, comprising a foam metal, a carbon material, and a resin binder, and containing at least one It is characterized by having a composite layer in which a foam metal is filled with a carbon material and a resin binder in the part.

The gas diffusion electrode of the present invention has the gas diffusion layer.

The metal-air battery of the present invention has the gas diffusion layer as a positive electrode.

The fuel cell of the present invention has the gas diffusion layer as a positive electrode.

The method for producing a gas diffusion electrode of the present invention is a method for producing a gas diffusion electrode used in metal-air batteries or fuel cells, comprising the following steps (A1) and (A2):
(A1) A first step of applying a suspension (a) in which a carbon material and a resin binder are dispersed to a foam metal and applying pressure in the thickness direction; and (A2) After step (A1), resin binding A process of heating and pressing in the thickness direction at a temperature at which the material softens or flows.

A preferred embodiment of the method further comprises the following step (B):
(B) After step (A1), a suspension (b) containing a carbon material, a resin binder, and a catalyst is further applied to the surface to which the suspension (a) has been applied, and pressure is applied in the thickness direction. process.

In a preferred embodiment of the above method, in step (A2), after steps (A1) and (B), each resin binder of suspensions (a) and (b) softens or flows in the thickness direction at a temperature at which it softens or flows. Apply heat and pressure.

INDUSTRIAL APPLICABILITY According to the present invention, there is provided a gas diffusion layer having excellent gas diffusibility, high rigidity, and stable electrical contact, which is used for a gas diffusion electrode of a metal-air battery or a fuel cell, and a gas using the same. Diffusion electrodes and methods of making same are provided. Such an excellent gas diffusion layer is expected to contribute to the manufacture of metal-air batteries and fuel cells that are inexpensive and have stable output, since the support and reinforcing materials can be made simpler than before.

(a) is a secondary electron image of the cross section of the gas diffusion electrode of Example 1, (b) is an elemental map of carbon, and (c) is an elemental map of nickel. (a) is a secondary electron image of the cross section of the gas diffusion electrode of Example 2, (b) is an elemental map of carbon, and (c) is an elemental map of nickel. (a) is a secondary electron image of the cross section of the gas diffusion electrode of Example 3, (b) is an elemental map of carbon, and (c) is an elemental map of nickel. (a) is a secondary electron image of the cross section of the gas diffusion electrode of Comparative Example 1, (b) is an elemental map of carbon, and (c) is an elemental map of nickel. It is an optical photograph of foamed nickel. 1 is a diagram showing current density-voltage characteristics of magnesium air batteries of Examples 1 to 3 and Comparative Example 1. FIG. FIG. 5 is a graph showing constant current characteristics of magnesium-air batteries of Example 3 and Comparative Example 1; 4 is a secondary electron image of a cross section of the gas diffusion electrode of Comparative Example 1 after constant current measurement.

The present invention will be described in detail below.
(Gas diffusion layer)
The foam metal used in the gas diffusion layer of the present invention functions as a current collector for the gas diffusion electrode. The gas diffusion layer of the present invention has a structure in which the pores of the foamed metal, which serves as a current collector, are filled with a carbon material without gaps, and the carbon material is entangled, so that electrical contact is stable and battery output is stable. is obtained.

Metal foams are metallic cellular structures with a large amount of small gas spaces and are characterized by a large amount of porosity, eg, 75-95% void.

Examples of foam metal materials include nickel, titanium, aluminum and alloys thereof. Among these, foamed nickel made of nickel is preferable from the viewpoint of functionality as a current collector and cost.

Considering the diameter of carbon materials such as hydrophobic carbon such as agglomerate of acetylene black, the average pore diameter of the foam metal to be filled with this must be sufficiently larger than this. The number of adhesion points between the carbon material and the foamed metal is reduced, the number of conductive paths is reduced, and the rigidity of the electrode is also reduced. From this point of view, the average pore size of the foam metal is preferably 200 μm or more and 5 mm or less. Here, the average pore diameter is the average value of 100 pores arbitrarily selected from the microscopic image, and the diameter of each pore is determined as the longest diameter. For example, among foamed metals, foamed nickel is a metal porous body having continuous pores in which a triangular prism-shaped skeleton is connected three-dimensionally.

Among foamed metals, commercial products of foamed nickel include, for example, "Celmet" manufactured by Sumitomo Electric Industries, "Metal Porous Body" manufactured by Nagamine Seisakusho, and the like. The specific surface area of foamed nickel is preferably 250 to 5800 m ² /m ³ .

The carbon material used for the gas diffusion layer of the present invention forms a conductive path by forming pores, and imparts hydrophobicity to suppress permeation of water into the electrode.

Hydrophobic carbon is preferable as the carbon material. Hydrophobic carbon is different from hydrophilic carbon having a large number of oxygen functional groups on its surface, and is hydrophobic. Examples thereof include carbon black, carbon nanotubes, and graphene. Among them, carbon black is preferable because it is porous, has low electrical resistance, and is inexpensive. Examples of carbon black, which is hydrophobic carbon, include acetylene black and furnace black.

The average particle size of the carbon material is preferably 20 nm or more and 50 nm or less. A carbon material having such an average particle diameter forms a dense conductive path when filled in the pores of the foam metal as described above, and has a structure in which the foam metal and the carbon material, which serve as a current collector, are entwined. Therefore, the electrical contact is stable, and a stable battery output can be obtained. Here, the average particle diameter is obtained by selecting 100 arbitrary particles in an image observed by a scanning transmission electron microscope, measuring the outer diameter of each particle, and calculating the number average value thereof. In carbon black, aggregates (primary aggregates) having a structure generally form agglomerates (secondary aggregates) due to physical forces such as van der Waals force, but when the carbon material is carbon black, The average particle size is the average particle size of the primary particles of the aggregate.

The resin binder used in the gas diffusion layer of the present invention has a binder function to bind the carbon material and a function to impart water repellency to the gas diffusion layer.

Resin binders include water-repellent resins such as fluororesins. Among these, fluororesins are preferred. Examples of fluororesins include polytetrafluoroethylene (PTFE), perfluorosulfonic acid polymer, polyvinylidene fluoride (PVdF), tetrafluoroethylene copolymers (FEP) and (PFE). Among them, polytetrafluoroethylene and perfluorosulfonic acid polymer are preferred.

The mass ratio of the carbon material and the resin binder used in the gas diffusion layer is preferably 30:70 to 95:5, and 60:5, considering that the resin binder exerts a binder function and a water repellent function. 40 to 90:10 is more preferred.

The form of the resin binder added in the production of the gas diffusion layer is not particularly limited, but it is preferably in the form of fine particles that are mixed with the carbon material and dispersed. It can be used for the production of gas diffusion layers. In this case, after dispersing the carbon material and the resin binder in an aqueous solvent in advance, a carbon material supporting the resin binder is prepared by drying to remove the solvent, and the resin binder is prepared. A suspension may be prepared by dispersing the carbon material supporting the in an organic solvent.

The gas diffusion layer of the present invention contains a foam metal, a carbon material, and a resin binder, and at least a part of the gas diffusion layer has a composite layer in which the carbon material and the resin binder are filled in the foam metal.

Depending on the manufacturing process, in one aspect, the gas diffusion layer of the present invention has a layer made of foamed metal and a composite layer continuous from the layer in the thickness direction. In this case, the pores of the metal foam are partially filled with the carbon material and the resin binder by pressurization in the manufacturing process, and part of the metal foam in the thickness direction becomes the composite layer. In another aspect, the entire thickness direction is a composite layer. In this case, almost all of the pores of the foam metal are filled with the carbon material and the resin binder by pressurization in the manufacturing process, the remaining pores of the foam metal are crushed, and the portion consisting only of the foam metal is Almost unrecognizable, the entire thickness direction of the foam metal becomes a composite layer. Therefore, when the entire thickness direction is a composite layer, observation with a scanning electron microscope shows that the carbon material and the resin binder are distributed throughout the thickness direction in the pores of the foam metal, and in particular, in the elemental map of carbon, , including that carbon derived from the carbon material is confirmed throughout the thickness direction. For example, carbon is present in the carbon element map in the range of 80% or more, 90% or more, or 95% or more of the thickness in which the metal is distributed in the element map of the foam metal such as nickel, and the carbon material All including being filled in foam metal. Among the above embodiments, the latter embodiment, in which the metal foam is entirely formed as a composite layer in the thickness direction, is preferable in view of obtaining a stable battery output.

The thickness of the gas diffusion layer of the present invention is preferably 0.5 mm or more and 1.5 mm or less, more preferably 0.7 mm or more and 1.3 mm or less. When there is a layer made of foam metal, the total thickness of the layer and the composite layer is the shortest distance for gas diffusion. The thinner the diffusion layer, the more advantageous it is for the diffusion of oxygen in the air. However, if the thickness of the gas diffusion layer is within the above range, the leakage of the electrolyte and the contamination of moisture from the air side can be suppressed while the gas diffuses. , and is suitable as a positive electrode for metal-air batteries and fuel cells. Even if the thickness of the gas diffusion layer is reduced in this way, the gas diffusion layer of the present invention has a structure in which the pores of the foamed metal serving as the current collector are filled with the carbon material without gaps. Electrical contact is stable, and stable battery output can be obtained.

(Gas diffusion electrode and manufacturing method thereof)
The gas diffusion electrode of the present invention has the gas diffusion layer of the present invention described above. Further, a catalyst layer is provided adjacent to this gas diffusion layer. The gas diffusion electrode of the present invention can omit the electrode support used in conventional gas diffusion electrodes due to the high rigidity of the gas diffusion layer of the present invention.

The composition of the catalyst layer in the gas diffusion electrode of the present invention is not particularly limited, but includes, for example, a catalyst, a carrier, and a resin binder.

The catalyst is not particularly limited as long as it promotes the oxygen reduction reaction during discharge and the oxygen oxidation reaction during charge. Examples thereof include noble metal catalysts such as platinum, metal oxide catalysts, and carbon catalysts. When the carrier is hydrophilic carbon or the like, the carrier itself may have a catalytic function.

As the carrier, for example, a conductive carbon material can be used. Hydrophilic carbon is preferable as the conductive carbon material. Hydrophilic carbon has many hydrophilic functional groups such as oxygen functional groups on its surface, and examples thereof include hydrophilic carbon black, carbon black whose surface is modified with functional groups, carbon nanotubes, graphene, and the like. Among them, hydrophilic carbon black is preferable because it is porous, has low electrical resistance, and is inexpensive. Examples of hydrophilic carbon black include Ketjenblack, Vulcan, and the like.

Examples of the resin binder include fluororesin and the like. Examples of the fluororesin include those exemplified above as the resin binder used for the gas diffusion layer.

In a preferred embodiment of the method for producing the gas diffusion electrode of the present invention, the suspension (a) in which the carbon material and the resin binder constituting the gas diffusion layer of the present invention are dispersed is applied to the foam metal, and the thickness It includes the step of applying pressure in a direction.

The suspension (a) is not particularly limited as long as it contains a carbon material and a resin binder. is preferably prepared by dispersing in a solvent. In this case, the particle size of the resin binder is preferably 0.1 to 0.5 μm. As the solvent, water and organic solvents are preferable, and examples thereof include alcoholic solvents such as isopropyl alcohol, ethanol, acetone, and n-butanol, benzene, and hexane.

The method of applying the suspension (a) to the foam metal is not particularly limited, but examples thereof include spray coating, screen printing, bar coater, spin coater, and blade method.

The step of applying the suspension (a) to the foam metal and applying pressure in the thickness direction is a step of applying heat and pressure in the thickness direction at a temperature at which the resin binder softens or flows, that is, promotes binding by the resin binder. However, in order to increase the thickness of the composite layer by filling more of the pores of the foamed metal with the carbon material and the resin binder, and to reduce the thickness of the gas diffusion layer, After the suspension (a) is applied to the foam metal and pressurized in the thickness direction (hereinafter also referred to as a suspension filling press step), it is preferable to perform a hot press step.

The apparatus used in the hot pressing step and suspension filling pressing step is not particularly limited as long as it is capable of pressure molding, and for example, a hydraulic press can be used. The rigidity of the electrode is increased by the uniaxial pressure molding of the hydraulic press machine, so it is suitable for the production of large electrodes, and since it can be produced with a manual hydraulic press, it does not require special production equipment, and the manufacturing process is simple. Suitable for mass production.

In order to form the gas diffusion layer and the catalyst layer, a suspension (b) containing components of the catalyst layer is prepared, and the suspension (b) is further applied to the surface to which the suspension (a) has been applied. , may be pressurized in the thickness direction.

Suspension (b) contains, for example, a carbon material, a resin binder, and a catalyst.

In the application of the suspension (a) to the foam metal, the application of the suspension (b) to the surface to which the suspension (a) is applied, the hot press step, and the suspension filling press step, these The steps before and after the procedure are arbitrary, and the pressurization may be performed only in the hot press step, or may be performed including the suspension filling press step. For example, after applying the suspension (a) to the foam metal, applying the suspension (b) to the surface coated with the suspension (a), pressurizing in a hot press process, or After applying the suspension (a) to the foam metal, a suspension filling press step is performed, and then the suspension (b) is applied to the surface to which the suspension (a) has been applied, and the suspension is It may be an embodiment in which the filling press step is performed and then the hot press step is performed, but in a preferred embodiment, the following steps (A1) and (A2) are included:
(A1) A step of applying a suspension (a) in which a carbon material and a resin binder are dispersed to a foamed metal and applying pressure in the thickness direction (suspension filling press step); and (A2) step (A1). After that, a step of heating and pressing in the thickness direction at a temperature at which the resin binder softens or flows (hot pressing step).

A further preferred embodiment further comprises the following step (B):
(B) After step (A), a suspension (b) containing a carbon material, a resin binder, and a catalyst is further applied to the surface to which the suspension (a) has been applied, and pressure is applied in the thickness direction. process.

In a particularly preferred embodiment, in step (A2), after steps (A1) and (B), the resin binders of suspensions (a) and (b) are heated in the thickness direction at a temperature at which they soften or flow. pressure.

The load in the suspension filling press step is not particularly limited, but in step (A1) it is preferably 100 to 500 kgfcm ⁻² , more preferably 300 to 450 kgfcm ⁻² . In step (B), 10 to 50 kgfcm ^-2 is preferable, and 30 to 45 kgfcm ^-2 is more preferable. In the suspension filling press step, the pores of the foamed metal are filled with more carbon material and resin binder in a state where the carbon materials are not bound together by the resin binder, thereby increasing the thickness of the composite layer and increasing the thickness of the composite layer. The thickness of the diffusion layer can be made smaller. As a result, the gas is diffused while suppressing the leakage of the electrolyte and the contamination of moisture from the air side. Due to the structure in which the pores of the foamed metal used as the current collector are filled with the carbon material without any gaps, the rigidity is high, the electrical contact is stable, and the stable battery output can be obtained.

In the above, regardless of whether pressurization is performed only in the hot press process or when the suspension filling press process is included, the load during the hot press process is not particularly limited, but is 50 to 300 kgfcm ⁻² . is preferred, and 100 to 200 kgfcm ⁻² is more preferred. The temperature in the hot pressing process is not particularly limited, but in the case of fluororesin such as PTFE, it is preferably in a range where decomposition does not occur above its melting temperature, for example 330 to 380°C.

After pressurization by the hot press step or the suspension filling press step, it is preferable to perform a drying treatment with a heating device such as a dryer in order to remove the solvent of the suspensions (a) and (b). .

(metal-air battery and fuel cell)
The gas diffusion electrodes of the present invention can be used in metal-air batteries and fuel cells. Metal-air batteries and fuel cells have a gas diffusion electrode at the positive electrode.

A metal-air battery uses a metal as a negative electrode active material, and a fuel cell uses a substance other than a metal such as hydrogen as a negative electrode active material.

In the metal-air battery and the fuel cell, an air electrode is installed as a positive electrode, and a metal electrode is installed as a negative electrode in the metal-air battery and a fuel electrode in the fuel cell through an electrolyte.

As the electrolyte, in the case of water-based metal-air batteries and fuel cells, water-based electrolytes that are commonly used as these electrolytes can be used.

Metals such as zinc, aluminum, and magnesium can be used as the metal electrode in the metal-air battery. A specific structure of the metal electrode may be the same as that of a known metal-air battery. The structure of the fuel electrode in the fuel cell is also not particularly limited, and may be the same as the structure of the fuel electrode of known fuel cells. As the catalyst for the fuel electrode, conventionally known metals, metal alloys, metal complexes, and catalysts in which fine catalyst particles are supported on a carrier such as a carbon material or a metal oxide can be used.

Oxygen or air may be supplied or naturally diffused to the air electrode, which is the positive electrode. In addition, it is necessary to supply a fuel substance to the fuel electrode side of the fuel cell. As the fuel substance, in addition to hydrogen gas, alcohols such as methanol can be used.

EXAMPLES The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.
[Example 1]
<1> Preparation of PTFE-supported hydrophobic carbon and PTFE-supported hydrophilic carbon Commercially available acetylene black (HS-100, manufactured by Denki Kagaku Kogyo) was dispersed in distilled water as a hydrophobic carbon for the gas diffusion layer, and 60% by mass of PTFE was added. Dispersion (particle size: 0.22 μm, D-210c, manufactured by Daikin Industries) was added so as to be 30% by mass with respect to acetylene black. This was ultrasonically dispersed to uniformly disperse and support the PTFE dispersion on the acetylene black, and the mixed liquid was filtered and dried at 120° C. to produce PTFE-supported hydrophobic carbon. Commercially available carbon black (Ketjenblack, manufactured by Lion) was used as the hydrophilic carbon used in the catalyst layer, and PTFE was supported in the same manner. In addition, this hydrophilic carbon having a large number of oxygen functional groups on its surface promotes the oxygen reduction reaction as a catalyst.

<2> Preparation of gas diffusion electrode Carbon ink was prepared by dispersing PTFE-supported hydrophobic carbon in ² -propanol. #7, manufactured by Sumitomo Electric Industries, Ltd.), and dried so as to be 14 mg per 1 cm ² . Similarly, the PTFE-supporting hydrophilic carbon ink dispersed in 2-propanol was coated on the hydrophobic carbon of the foamed nickel-hydrophobic carbon so that it was 6 mg per 1 cm ² and dried. The material was rapidly heated in an electric furnace to a temperature of 360° C. to melt the PTFE, pressed with a load of 38 kgfcm ⁻² using a hydraulic press, and then rapidly cooled. Finally, it was transferred to a dryer maintained at 120° C. to completely remove the solvent 2-propanol to obtain a gas diffusion electrode.

<3> Evaluation of battery performance Magnesium alloy (Mg: 90%, Al: 9%, Zn: 1%, thickness: 0.2%, thickness: 0.3%, magnesium alloy (Mg: 90%, Al: 9%, Zn: 1%, thickness: 0.3%) was used as the positive electrode for the gas diffusion electrode (electrode area: 13.3 cm ² ) produced as described above. 5 cm, electrode area: 3.8 × 5.8 cm ² ) was attached to the cell as a negative electrode, the distance between the electrodes was fixed to 1 cm, and the electron addition device was placed on the positive electrode and the negative electrode while being immersed in a 23 mass% NaCl aqueous solution. After connecting, an arbitrary constant resistance was connected using an electronic load device, and the voltage value and current value between the electrodes were measured. PLZ664WA manufactured by Kikusui Denshi Kogyo Co., Ltd. was used as an electronic addition device.

[Example 2]
A PTFE-supporting hydrophobic carbon and a PTFE-supporting hydrophilic carbon were produced in the same manner as in Example 1. Foamed nickel cut into the same size as in Example 1 was polished with a metal file until the thickness became 0.7 mm. PTFE-supported hydrophobic carbon was dispersed in 2-propanol to prepare a carbon ink, which was applied to polished foamed nickel in an amount of 14 mg/cm ² and dried. Similarly, the PTFE-supporting hydrophilic carbon ink dispersed in 2-propanol was coated on the hydrophobic carbon of the foamed nickel-hydrophobic carbon so that it was 6 mg per 1 cm ² and dried. The material was rapidly heated in an electric furnace to a temperature of 360° C. to melt the PTFE, pressed with a load of 38 kgfcm ⁻² using a hydraulic press, and then rapidly cooled. Finally, it was transferred to a dryer maintained at 120° C. to completely remove the solvent 2-propanol to obtain a gas diffusion electrode. Battery performance evaluation was performed in the same manner as in Example 1.

[Example 3]
A PTFE-supporting hydrophobic carbon and a PTFE-supporting hydrophilic carbon were produced in the same manner as in Example 1. A carbon ink was prepared by dispersing PTFE-supported hydrophobic carbon in 2-propanol, and this was applied to nickel foam cut into the same size as in Example 1 so as to be 14 mg per 1 cm ² and dried. A pressing machine was used to press with a load of 376 kgfcm ⁻² to obtain a foamed nickel/hydrophobic carbon composite. Similarly, the PTFE-supporting hydrophilic carbon ink dispersed in 2-propanol was applied to the prepared foamed nickel/hydrophobic carbon composite so as to be 6 mg per 1 cm ² , dried, and dried to 150 kgfcm using a hydraulic press. It was pressed with a load of ⁻² , rapidly heated in an electric furnace to a temperature of 360° C. to melt the PTFE, pressed with a load of 38 kgfcm ⁻² using a hydraulic press, and then rapidly cooled. Finally, it was transferred to a dryer maintained at 120° C. to completely remove the solvent 2-propanol to obtain a gas diffusion electrode. Battery performance evaluation was performed in the same manner as in Example 1. In the constant current measurement, the current density was fixed at 23 mAcm ^-2 and the cell voltage was measured.

[Comparative Example 1]
A PTFE-supporting hydrophobic carbon and a PTFE-supporting hydrophilic carbon were produced in the same manner as in Example 1. Carbon ink was prepared by dispersing PTFE-supported hydrophobic carbon in 2-propanol, and this was applied to a nickel mesh (100 mesh, manufactured by Nilaco) cut to 3.5 × 3.8 cm ² so that 14 mg per 1 cm ² Then, the PTFE-supporting hydrophilic carbon ink dispersed in 2-propanol was applied to the hydrophobic carbon in an amount of 6 mg per 1 cm ² , and this was rapidly heated in an electric furnace to a temperature of 360°C. The temperature was raised to melt the PTFE, pressed with a load of 38 kgfcm ⁻² using a hydraulic press, and then quenched. Finally, it was transferred to a dryer maintained at 120° C. to completely remove the solvent 2-propanol to obtain a gas diffusion electrode. Battery performance evaluation was performed in the same manner as in Example 1. Constant current measurement was performed in the same manner as in Example 3.

1 to 4 are secondary electron beam images of cross sections of gas diffusion electrodes of Examples 1 to 3 and Comparative Example 1, respectively, observed using a scanning electron microscope (JSM-6490LA, manufactured by JEOL Ltd.), carbon and nickel Element map. FIG. 5 is an optical photograph of foamed nickel. In Examples 1 and 2, a foamed nickel/hydrophobic carbon composite layer is partially formed, but a part of the foamed nickel is not combined with the hydrophobic carbon, and the characteristic nickel foam pores (100 to 500 μm) can be confirmed. On the other hand, in the gas diffusion electrode produced in Example 3, the characteristic pores of the original nickel foam cannot be confirmed by pressing at 376 kgfcm ⁻² , and the hydrophobic carbon is filled without gaps, and the nickel foam that has been compressed and crushed and one layer of the composite layer consisting of hydrophobic carbon.

6 shows the current density-voltage characteristics of the magnesium-air batteries of Examples 1 to 3 and Comparative Example 1. FIG. In metal-air batteries and fuel cells, in which oxygen in the air is the positive electrode active material, the oxygen reduction reaction proceeds at the air electrode. Therefore, the thinner the gas diffusion layer, the more advantageous the diffusion of oxygen in the air, as long as the leakage of the electrolyte and the contamination of moisture from the air side are prevented. In the gas diffusion electrodes of Examples 1 and 2, the combined thicknesses of the foamed nickel and foamed nickel/hydrophobic carbon composite layers were 1250 μm and 964 μm, respectively. are 1250 μm and 964 μm, respectively. Since the foamed nickel/hydrophobic carbon composite layer of the gas diffusion electrode of Example 3 has a thickness of 724 μm, the shortest distance of the gas diffusion path for oxygen in the air to reach the catalyst layer is 724 μm. In the electrodes of Examples 1 to 3, the shorter the shortest distance of the gas diffusion path, the higher the battery voltage obtained in the high current density region of about 10 mAcm ⁻² or more, and the maximum output was 41.6, 68.1, 80, respectively. 0.8 mWcm ⁻² , and Examples 2 and 3 showed performance higher than the maximum output of 46.5 mWcm ⁻² of the conventional magnesium-air battery using a gas diffusion electrode using nickel mesh.

7 shows the constant current characteristics of the magnesium-air batteries of Example 3 and Comparative Example 1. FIG. The battery voltage of the magnesium-air battery of Example 3 was relatively stable, but the battery voltage of the magnesium-air battery of Comparative Example 1 decreased from about 30 minutes and became unstable after about 50 minutes. FIG. 8 is a secondary electron beam image of the cross section of the gas diffusion electrode of Comparative Example 1 after constant current measurement. It was confirmed that the Ni mesh, which is a current collector, was partially separated from the hydrophobic carbon, which is the gas diffusion layer, so the mesh could not maintain the shape of contact with the gas diffusion layer, and the battery voltage became unstable. It was suggested.

Claims (13)

A gas diffusion layer used in a gas diffusion electrode of a metal-air battery or fuel cell using an aqueous electrolyte,
including foam metals, carbon materials, and resin binders,
At least part of the gas diffusion layer in the thickness direction is filled with the carbon material and the resin binder without gaps in the pores of the metal foam. Having a crushed composite layer for the portion not filled with the adhesive material ,
The average pore size of the foam metal is 200 μm or more and 5 mm or less,
A gas diffusion layer , wherein the carbon material is hydrophobic carbon . 2. The gas diffusion layer according to claim 1, comprising a layer made of said foamed metal and said composite layer continuous from said layer in the thickness direction. 2. The gas diffusion layer according to claim 1, wherein the entire thickness direction is the composite layer. The gas diffusion layer according to any one of claims 1 to 3, having a thickness of 0.5 to 1.5 mm. The gas diffusion layer according to any one of claims 1 to 4, wherein said foam metal is foam nickel. The gas diffusion layer according to any one of claims 1 to 5, wherein the carbon material has an average particle size of 20 nm or more and 50 nm or less. The gas diffusion layer according to any one of claims 1 to 6 , wherein the resin binder is a fluororesin. A gas diffusion electrode comprising the gas diffusion layer according to any one of claims 1-7 . A metal-air battery having the gas diffusion electrode according to claim 8 as a positive electrode. A fuel cell having the gas diffusion electrode according to claim 8 as a positive electrode. A method for producing a gas diffusion electrode for use in a metal-air battery or fuel cell, the method comprising the following steps (A1) and (A2):
(A1) a step of applying a suspension (a) in which a carbon material and a resin binder are dispersed to a foamed metal and applying pressure in the thickness direction; and (A2) after the step (A1), the resin binding. A process of heating and pressing in the thickness direction at a temperature at which the material softens or flows. 12. The method for producing a gas diffusion electrode according to claim 11 , further comprising step (B) of:
(B) After the step (A1), a suspension (b) containing a carbon material, a resin binder, and a catalyst is further applied to the surface to which the suspension (a) has been applied. The process of pressurizing. In the step (A2), after the steps (A1) and (B), the resin binders of the suspensions (a) and (b) are heated and pressed in the thickness direction at a temperature at which they soften or flow. 13. A method for manufacturing a gas diffusion electrode according to claim 12 .

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