WO2017043365A1 - Metal porous body, fuel cell, and method for manufacturing metal porous body - Google Patents

Abstract

A metal porous body having a three-dimensional mesh structure comprising a skeleton, and having a flat-plate-shaped external form having a pair of main surfaces and end surfaces linking the pair of main surfaces, wherein the skeleton has a main metal layer comprising nickel or a nickel alloy and an oxide layer formed on the surface of the main metal layer, and the oxide layer is not formed on the portion of the surface of the main metal layer that constitutes a part of the pair of main surfaces of the metal porous body.

Description

Porous metal body, fuel cell, and method for producing porous metal body

The present invention relates to a metal porous body, a fuel cell, and a method for producing a metal porous body.
This application claims priority based on Japanese application No. 2015-178157 filed on Sep. 10, 2015, and Japanese application No. 2016-014148 filed on Jan. 28, 2016, and is described in the aforementioned Japanese application. All the descriptions are incorporated.

A polymer polymer fuel cell (PEFC) using an ion exchange membrane as an electrolyte has been put into practical use for cogeneration, and a vehicle using this as a power source has begun to be put into practical use.
The basic structure of a polymer electrolyte fuel cell includes an anode, a membrane, and a cathode. The membrane is an ion exchange membrane, and a fluorine-based exchange membrane having a sulfone group is mainly employed. Due to the improvement of the characteristics of the membrane, the practical use of the polymer electrolyte fuel cell is promoted.

A solid polymer fuel cell is a unit cell in which a gas diffusion layer and a separator are arranged on the back of each electrode of an anode and a cathode, and this is used as a laminated structure (for example, Patent Document 1). The operating temperature is in the range of about 70 ° C. to 110 ° C. in consideration of performance, removal from the system due to evaporation of generated water, lifespan, and the like. Increasing the operating temperature improves the discharge characteristics. For cogeneration, there is an advantage that high-temperature exhaust heat can be obtained, but the lifetime is shorter than that at low temperatures.

As the gas diffusion layer, carbon paper obtained by processing carbon fibers into a nonwoven fabric is generally used, and the gas diffusion layer also functions as a current collector. Also, as a gas diffusion layer, a groove is provided in a carbon plate used as a separator to facilitate gas supply and discharge. Thus, it is common to use carbon paper and a groove together as a gas diffusion layer.
Note that the carbon paper also functions to suppress the membrane electrode assembly (MEA) from biting into the grooves of the separator.

JP 2011-129265 A

The porous metal body according to one aspect of the present invention is a porous metal body having a three-dimensional network structure composed of a skeleton and having an outer shape that is a flat plate shape having a pair of main surfaces and end faces connecting the pair of main surfaces. The skeleton includes a main metal layer made of nickel or a nickel alloy, and an oxide layer formed on the surface of the main metal layer. Of the surface of the main metal layer, the porous metal body A porous metal body in which the oxide layer is not formed in a portion forming a pair of main surfaces.

FIG. 1 is a diagram illustrating an outline of an example of a configuration of a cell of a fuel cell according to an embodiment of the present invention. FIG. 2 is a graph showing the evaluation results of the corrosion resistance of the porous metal bodies 1 to 3 produced in the examples. FIG. 3 is a graph showing the evaluation results of the power generation characteristics of the batteries A to D produced in the examples.

[Problems to be solved by the present disclosure]

溝 The porosity of the groove formed in the carbon plate used as the separator for the solid polymer fuel depends on how much the carbon plate is provided, but is practically about 50%. That is, the groove is provided in about ½ of the area of one surface of the carbon plate. Further, the shape of the groove is a rectangle, and the width thereof is about 500 μm.

In order to supply gas uniformly to the MEA at a low pressure, the width of the groove is preferably increased and deepened, and the ratio of the groove per unit area is preferably increased. However, the greater the number of grooves provided in the separator, the lower the conductivity of the separator, thereby reducing the battery characteristics. Since the influence of the conductivity of the separator on the battery characteristics is large, from the viewpoint of battery characteristics, the ratio of the grooves is small, and it is preferable that the groove is shallow.

Moreover, the smaller the groove width and the greater the number of grooves, the more uniformly the gas is supplied to the MEA. However, as the groove width decreases, the MEA is less likely to be grooved by the pressure applied when the cells are integrated, and the MEA is deformed and the function as the groove is reduced. This adverse effect becomes more prominent as the size of the battery increases and the number of batteries increases. In other words, the larger the electrode, the greater the number of cells, and the greater the required load, the greater.

As mentioned above, it is preferable to increase the ratio of the grooves formed in the separator in terms of gas supply, but it is better to reduce the ratio of the grooves in terms of electrical characteristics. Moreover, the precision of a groove | channel is requested | required and a separator will become expensive with the complexity of the process of forming a groove | channel. Further, since the groove is formed in one direction, for example, when water is clogged, the movement of gas is hindered.

Therefore, the present inventors examined using a metal porous body having a three-dimensional network structure as a gas diffusion layer. As a result, the porous metal body having a three-dimensional network structure has a very high porosity and can reduce pressure loss.
However, the conventional metal porous body made of nickel is inferior in corrosion resistance as compared with the carbon material, so there is room for improvement in this respect. As a metal porous body made of nickel having improved corrosion resistance, a metal porous body in which nickel is alloyed with tin or chromium has already been proposed. Although these nickel-tin alloy porous bodies and nickel-chromium alloy porous bodies are excellent in corrosion resistance as compared with metal porous bodies made of nickel, they do not achieve the same corrosion resistance as that of carbon materials.

The corrosion resistance of the metal porous body used as the gas diffusion layer does not always discharge, but is particularly problematic when used for a fuel cell that performs intermittent discharge such that discharge is stopped for a certain period and then discharged again. The reason is as follows.
In a solid polymer fuel cell, in a normal discharge, hydrogen containing water vapor is supplied to an anode to become hydrogen ions. This hydrogen ion moves to the cathode side through the ion exchange membrane, generates water by an electrochemical reaction, and goes out of the system. However, when the supply of hydrogen and air is stopped and the discharge is stopped, the generated water remaining in the gas diffusion layer flows backward and touches the ion exchange membrane. At this time, if the gas diffusion layer is a metal material and even a very small amount of metal is eluted in the generated water, it will adversely affect the ion exchange membrane, reducing the water retention of the membrane and reducing the discharge characteristics. End up. Therefore, the more severe the corrosion resistance is required for the gas diffusion layer of such a fuel cell with many pauses.

In view of the above problems, an object of the present invention is to provide a porous metal body that is excellent in corrosion resistance and can be used as a gas diffusion layer of a fuel cell.

Effects of this disclosure

に よ According to the above invention, it is possible to provide a porous metal body that is excellent in corrosion resistance and can be used as a gas diffusion layer of a fuel cell.

[Description of Embodiment of the Invention]
First, embodiments of the present invention will be listed and described.
(1) The metal porous body according to one aspect of the present invention is:
A porous metal body having a three-dimensional network structure composed of a skeleton, and having an outer shape of a flat plate having a pair of main surfaces and an end surface connecting the pair of main surfaces,
The skeleton is
A main metal layer made of nickel or a nickel alloy;
An oxide layer formed on the surface of the main metal layer;
With
Of the surface of the main metal layer, the oxide layer is not formed on the portion forming the pair of main surfaces of the metal porous body, the metal porous body,
It is.
According to the invention described in (1) above, it is possible to provide a porous metal body that has excellent corrosion resistance and can be used as a gas diffusion layer of a fuel cell.
In the metal porous body according to the embodiment of the present invention, “a pair of main surfaces of the metal porous body” refers to a pair of main surfaces in the outer shape of the metal porous body, and the main surface includes a cross-sectional portion of the skeleton. Is located.

(2) The porous metal body according to the embodiment of the present invention is the porous metal body according to (1), wherein the skeleton includes a conductive layer formed on a surface of the oxide layer.
According to the invention described in (2) above, a porous metal body having a conductive skeleton surface can be provided.

(3) The porous metal body according to the embodiment of the present invention is the porous metal body according to (2), wherein the conductive layer includes carbon powder and a binder.
According to the invention described in (3) above, it is possible to provide a porous metal body having a conductive layer having excellent corrosion resistance and adhesion on the surface of the skeleton.

(4) The porous metal body according to the embodiment of the present invention is the porous metal body according to (2) or (3), wherein the conductive layer contains silver.
According to the invention as described in said (4), the porous metal body which has the electroconductive layer excellent in electroconductivity on the surface of frame | skeleton can be provided.

(5) In the metal porous body according to the embodiment of the present invention, any one of (1) to (4) above, wherein the nickel alloy includes at least one of chromium, tin, and tungsten and nickel. The metal porous body according to one item.
(6) The porous metal body according to the embodiment of the present invention is the porous metal body according to any one of (1) to (5) above, wherein the oxide layer is nickel oxide.
According to the invention as described in said (5) or said (6), the metal porous body which has the frame | skeleton which was more excellent in corrosion resistance can be provided.

(7) A fuel cell according to an embodiment of the present invention is a fuel cell using the porous metal body according to any one of (1) to (6) above as a gas diffusion layer.
According to the invention described in (7) above, it is possible to provide a fuel cell having high output and excellent power generation per volume.

(8) A method for producing a porous metal body according to an embodiment of the present invention includes:
A method for producing a porous metal body according to (1) above,
A porous structure having a three-dimensional network structure composed of a skeleton, the outer shape being a flat plate shape having a pair of main surfaces and end faces connecting the pair of main surfaces, and the skeleton including a main metal layer made of nickel or a nickel alloy A preparation process for preparing the body;
A heat treatment step of forming an oxide layer on the surface of the main metal layer by heating the porous body in an oxidizing atmosphere;
A removing step of removing an oxide layer formed on a portion of the surface of the main metal layer that forms the pair of main surfaces;
It is a manufacturing method of the metal porous body which has this.
According to the invention as described in said (8), the manufacturing method of the porous metal body which is excellent in corrosion resistance and can be utilized as a gas diffusion layer of a fuel cell can be provided.

(9) A method for producing a porous metal body according to an embodiment of the present invention includes:
After the preparation step and before the heat treatment step,
It is a manufacturing method of the metal porous body as described in said (8) which has the acid treatment process which immerses the said porous body in an acidic solution, and dries.
(10) A method for producing a porous metal body according to an embodiment of the present invention includes:
The method for producing a porous metal body according to (9), wherein the acidic solution is nitric acid, sulfuric acid, hydrochloric acid, or acetic acid.
According to the invention as described in said (9) or said (10), the manufacturing method of the metal porous body which has a thick oxide layer on the surface of frame | skeleton can be provided.

(11) A method for producing a porous metal body according to an embodiment of the present invention includes:
After the heat treatment step,
The method for producing a porous metal body according to any one of (8) to (10), further including a conductive layer forming step of forming a conductive layer on a surface of the oxide layer.
According to the invention described in (11) above, it is possible to provide a method for producing the porous metal body described in (2) above. In the invention described in (11) above, the conductive layer formation step may be performed any time after the heat treatment step, may be performed before the removal step, or may be performed after the removal step.

[Details of the embodiment of the present invention]
Specific examples of the porous metal body according to the embodiment of the present invention will be described below. In addition, this invention is not limited to these illustrations, is shown by the claim, and it is intended that all the changes within the meaning and range equivalent to the claim are included.

<Metal porous body>
The porous metal body according to the embodiment of the present invention is a flat plate having an outer shape having a pair of main surfaces and end surfaces connecting the pair of main surfaces, and the skeleton has a three-dimensional network structure. The skeleton includes a main metal layer made of nickel or a nickel alloy and an oxide layer formed on the surface of the main metal layer. However, the said oxide layer is not formed in the part which comprises a pair of main surface of a metal porous body among the surfaces of a main metal layer.
As described above, the main metal layer is a portion made of nickel or a nickel alloy in the skeleton of the metal porous body. Moreover, the cross section of the skeleton is exposed on the main surface of the metal porous body.

In the porous metal body according to the embodiment of the present invention, an oxide layer of an element constituting the main metal layer is formed on the surface of the main metal layer constituting the skeleton of the metal porous body. In other words, nickel, a nickel alloy, or a metal oxide layer forming a nickel alloy is formed on the surface of the main metal layer.
Since the oxide layer is formed on the surface of the main metal layer, the metal porous body according to the embodiment of the present invention is superior in corrosion resistance to sulfuric acid or the like than nickel. For example, when nickel oxide is formed as an oxide layer on the surface of the main metal layer of the metal porous body, the nickel oxide has better corrosion resistance than nickel, so the corrosion resistance of the metal porous body is also improved.
On the other hand, the said oxide layer is not formed in a pair of main surface of the metal porous body which concerns on embodiment of this invention, ie, the cross-sectional part of frame | skeleton. Thereby, it can be made conductive by making a pair of main surface of a metal porous body contact other conductive materials.

Since the porous metal body according to the embodiment of the present invention has better corrosion resistance against sulfuric acid or the like than a conventional porous metal body made of nickel or a nickel alloy, it is preferably used as a gas diffusion layer for a fuel cell. Can do. In addition, porous metal has a high porosity and a three-dimensional network structure, so when used as a gas diffusion layer, gas pressure loss is reduced and gas diffusibility is improved. Can be made. Thereby, the power generation performance in MEA of a fuel cell can be improved.

In the metal porous body according to the embodiment of the present invention, a conductive layer is preferably formed on the oxide layer. Thereby, the surface of the skeleton of the metal porous body can be made conductive.
The material constituting the conductive layer is not particularly limited as long as it has conductivity and is formed into a film shape on the surface of the oxide layer of the porous metal body. It is preferable that it contains an agent. Thereby, a film-like conductive layer that adheres to the surface of the oxide layer of the metal porous body is formed.

As the conductive powder, for example, carbon powder can be preferably used. Carbon powder is preferable because it is lightweight and easily available. As the carbon powder, for example, carbon black, activated carbon, graphite or the like can be used alone or in combination. In addition to carbon powder, conductive powder such as gold, silver, palladium, copper, and aluminum can be used. Among these, silver powder can be preferably used in terms of corrosion resistance and conductivity.

As the binder, a resin can be preferably used. In particular, a resin having excellent film forming ability (film forming ability) and heat resistance can be preferably used. It is preferable to withstand heat of about 70 ° C. to 110 ° C., which is the operating temperature of the polymer electrolyte fuel cell.
Specifically, polyolefins such as polyethylene and polypropylene, polyacrylic acid ester, polyvinyl acetate, vinyl alcohol-polystyrene copolymer, ethylene-acrylic acid methyl ester copolymer, polymethacrylic acid ester, formalized polyvinyl Alcohol or the like can be used. These may be used alone or in combination. Furthermore, polyurethane, silicone resin, polyimide, and fluorine resin can also be preferably used as the resin.

The nickel alloy constituting the metal porous body is not particularly limited, and examples thereof include tin, chromium, aluminum, titanium, copper, cobalt, tungsten, iron, manganese, silver, gold, phosphorus, and boron. An alloy of at least one and nickel can be mentioned. It is preferably an alloy with a metal that forms an alloy with nickel and is superior in corrosion resistance to sulfuric acid or the like than nickel.
From the viewpoint of corrosion resistance and manufacturing cost, the nickel alloy is preferably an alloy containing nickel and at least one of chromium, tin, and tungsten. In the nickel alloy, the metal component contained other than nickel may be only one kind or plural kinds.
When there is only one kind of metal component other than nickel, the nickel alloy is preferably nickel chromium, nickel tin, or nickel tungsten.
In addition, the metal porous body which concerns on embodiment of this invention may contain the component which does not form an alloy with nickel intentionally or unavoidable besides nickel and a nickel alloy.

In addition, the thickness of the outer shape of the porous metal body, that is, the height of the end face connecting one main surface and the other main surface is preferably 0.10 mm or more and 1.20 mm or less. When the thickness of the outer shape of the metal porous body is 0.10 mm or more and 1.20 mm or less, it can contribute to miniaturization of the fuel cell when used as a gas diffusion layer of the fuel cell. In addition, since the porous metal body has little gas pressure loss and excellent gas diffusibility, the output of the fuel cell can be increased. When the thickness of the outer shape of the metal porous body is 0.10 mm or more, the mechanical strength of the metal porous body is maintained and the gas has a sufficient gas diffusion capacity. Therefore, it is preferably used as a gas diffusion layer of a fuel cell. it can. Moreover, when the thickness of the outer shape of the metal porous body is 1.20 mm or less, it is possible to contribute to miniaturization of the fuel cell. From these viewpoints, the thickness of the outer shape of the metal porous body is preferably 0.20 mm or more and 1.0 mm or less, and more preferably 0.30 mm or more and 0.80 mm or less.

金属 The porous metal body according to the embodiment of the present invention preferably has a porosity of 51% or more and 90% or less. When the porosity is 51% or more, gas pressure loss can be further reduced when the metal porous body is used as a gas diffusion layer of a fuel cell. Further, when the porosity is 90% or less, gas diffusibility can be further enhanced when the metal porous body is used as a gas diffusion layer of a fuel cell. This is because, since the metal porous body has a three-dimensional network structure, when the porosity decreases, the rate at which the gas hits the skeleton of the metal porous body increases. Furthermore, when the porosity of the metal porous body is 85% or less, the conductivity becomes excellent. From these viewpoints, the porosity of the metal porous body according to the embodiment of the present invention is more preferably 55% or more and 88% or less, and further preferably 60% or more and 85% or less.

In the porous metal body according to the embodiment of the present invention, the basis weight of nickel is preferably about 200 g / m ² or more and 1200 g / m ² or less. When the metal porous body contains other metal components, the basis weight of the total amount of the metal components is preferably about 200 g / m ² or more and 1200 g / m ² or less.
When the total amount of metal is 200 g / m ² or more, the strength and conductivity of the metal porous body can be sufficiently increased. Moreover, the raise of a manufacturing cost and the increase in a weight can be suppressed because the sum total of the metal amount of metal shall be 1200 g / m < ² > or less. From these viewpoints, the metal porous body according to the embodiment of the present invention preferably has a basis weight of 300 g / m ² or more and 1100 g / m ² or less, more preferably 400 g / m ² or more and 1000 g / m ² or less. More preferably it is.

The pore diameter viewed from above the metal porous body is preferably 100 μm or more and 700 μm or less. When the hole diameter is 100 μm or more, a high-power fuel cell can be obtained while suppressing the pressure loss of the fuel gas. Further, when the hole diameter is 700 μm or less, the fuel gas can be diffused smoothly, and the fuel use efficiency can be improved. From these viewpoints, the pore diameter of the metal porous body is more preferably 150 μm or more and 650 μm or less, and further preferably 200 μm or more and 600 μm or less. Here, “viewed from above” refers to the case of viewing from the thickness direction of the planar metal porous body.
The average pore diameter is a value obtained from the reciprocal of the number of cells of the metal porous body. The number of cells is a numerical value obtained by counting the number of cells on the outermost surface intersecting the line when a line having a length of 1 inch is drawn on the main surface of the metal porous body, and the unit is cell / inch. However, 1 inch shall be 2.54 cm.

<Fuel cell>
The fuel cell according to the embodiment of the present invention is a fuel cell using the porous metal body according to the embodiment of the present invention as a gas diffusion layer. The type of the fuel cell is not particularly limited, and may be a solid polymer fuel cell or a solid oxide fuel cell.
Hereinafter, a solid polymer fuel cell will be described as an example.

Conventional ion exchange membranes and the like in the polymer electrolyte fuel cell can be used.
For example, as a membrane / electrode assembly obtained by bonding an ion exchange membrane and a catalyst layer, a commercially available one can be used as it is. Both the anode and cathode platinum catalysts are integrated using a gas diffusion electrode carrying about 0.5 mg / cm ^{2 and} Nafion (registered trademark) 112 as an ion exchange membrane.

FIG. 1 is a schematic cross-sectional view of a single cell of a polymer electrolyte fuel cell.
In FIG. 1, a membrane-electrode assembly (MEA) M has activated carbon layers (2-1, 2-2) containing gas diffusion electrodes, that is, platinum catalysts, on both surfaces of an ion exchange membrane 1-1. A hydrogen electrode as an anode and an air electrode as a cathode, respectively. The current collector (3-1, 3-2) also serves as a bipolar current collector and a gas diffusion layer. For example, commercially available carbon paper treated with water repellency can be used. As the carbon paper, for example, a paper having water repellency to which a porosity of about 50% and a fluororesin of about 15% are added can be used.

As the separator (4-1, 4-2), for example, a commercially available graphite plate can be used. The gas diffusion layer (4-1-1, 4-2-1) is a porous metal body according to the embodiment of the present invention, and also serves as a gas supply / discharge path. Since the porous metal body according to the embodiment of the present invention is very thin compared to the conventional porous metal body, the fuel cell can be downsized.
Although FIG. 1 shows a single cell, a fuel cell that has been put to practical use is configured by stacking cells so that a desired voltage can be handled via a separator. Normally, since each cell is connected in series, if one side of the separator is a cathode, it is assembled so that the anode of the next cell comes to the other side, and the periphery is pressurized and integrated with bolts, nuts and the like.

<Method for producing porous metal body>
The metal porous body according to the embodiment of the present invention can be produced by various methods. Examples of the production method include the methods described in the above (8) to (11).
Below, each process of the manufacturing method of a metal porous body is demonstrated in detail.

-Preparation process-
This step is a step of preparing a porous body including a main metal layer made of nickel or a nickel alloy as a starting material. The porous body is a flat plate having an outer shape having a pair of main surfaces and end surfaces connecting the main surfaces, the skeleton has a three-dimensional network structure, and includes a main metal layer made of nickel or a nickel alloy. I just need it.
A method for producing a porous body having a main metal layer made of nickel or a nickel alloy is not particularly limited, but is preferably produced by the following plating method. That is, the surface of the skeleton of a resin molded body having a three-dimensional network structure is subjected to a conductive treatment, and subsequently plated with nickel or a nickel alloy, and then the resin molded body as a base material is removed, A porous body having a main metal layer made of a nickel alloy can be produced.

(Resin molding having a three-dimensional network structure)
As the flat resin molded body having a three-dimensional network structure used as the substrate, any known or commercially available one may be used as long as it is porous. For example, a resin foam, nonwoven fabric, felt, woven fabric, or the like can be used. Moreover, these can also be used in combination as needed. Although it does not specifically limit as a raw material, The thing which can be removed by incineration after plating a metal is preferable. In addition, in handling the resin molded body, a sheet-like material is preferably a flexible material because it breaks when the rigidity is high.

樹脂 It is preferable to use a resin foam as the resin molding. Examples of the resin foam include foamed urethane, foamed styrene, and foamed melamine resin. Among these, foamed urethane is preferable from the viewpoint of particularly high porosity.

The porosity of the resin molded body is not limited, and is usually about 60% to 97%, preferably about 80% to 96%. The thickness of the resin molded body is not limited, and is appropriately determined according to the use of the obtained porous metal body. Usually, it is about 600 μm or more and 5000 μm or less, preferably about 800 μm or more and 2000 μm or less. In addition, since the resin molded body has a very high porosity, a flat plate shape cannot be maintained when the thickness is 500 μm or less.
Below, the case where a foamed resin is used as a resin molded body having a three-dimensional network structure will be described as an example.

(Conductive treatment on the surface of the resin molded body)
The conductive treatment of the skeleton surface of the resin molded body is not particularly limited as long as it is a method capable of providing a conductive layer on the surface of the skeleton of the resin molded body. Examples of the material constituting the conductive layer (conductive coating layer) include metals such as nickel, tin, chromium, copper, iron, tungsten, titanium, and stainless steel, and carbon powder such as carbon powder. .
Specific examples of the conductive treatment include metal powders such as nickel, tin, and chromium, and conductive paints obtained by adding a binder to graphite powder, electroless plating treatment, sputtering, vapor deposition, ion plating, and the like. Preferred examples include phase treatment.

The electroless plating treatment using nickel can be performed by immersing the foamed resin in a known electroless nickel plating bath such as a nickel sulfate aqueous solution containing sodium hypophosphite as a reducing agent. If necessary, the resin molded body may be immersed in an activation liquid containing a trace amount of palladium ions (cleaning liquid manufactured by Kanigen Co., Ltd.) or the like before immersion in the plating bath.

As a sputtering process using nickel or chromium, for example, first, a resin molded body is attached to a substrate holder, and then a DC voltage is applied between the holder and a target (nickel or chromium) while introducing an inert gas. . The ionized inert gas thus collides with nickel or chromium, and the blown-off nickel particles or chromium particles may be deposited on the surface of the resin molded body.

When a conductive paint such as carbon powder or metal powder is applied, powder having conductivity on the surface of the skeleton of the resin molded body (for example, powder of metal material such as stainless steel, crystalline graphite, amorphous For example, a method of applying a mixture of carbon powder such as carbon black) and a binder. At this time, chromium powder, tin powder, or tungsten powder may be used in combination with the carbon powder. Thereby, the porous body which consists of nickel chromium, nickel tin, and nickel tungsten can be manufactured.

As the carbon powder, carbon black, activated carbon, graphite or the like can be used, and the material is not particularly limited. Carbon black may be used for the purpose of making the conductivity uniform, and fine graphite powder may be used for considering the strength of the conductive coating layer. Moreover, it is preferable to mix including activated carbon. You may add the thickener generally used, for example, carboxymethylcellulose (CMC) etc., when producing a slurry. The surface of the skeleton of the resin molded body can be made conductive by applying this slurry to the skeleton of the resin molded body that has been cut into a plate shape or a strip shape by adjusting the thickness.

(Formation of nickel plating layer)
The nickel plating layer may be formed using either electroless nickel plating or electrolytic nickel plating, but electrolytic nickel plating is preferable because of its higher efficiency. What is necessary is just to perform an electrolytic nickel plating process in accordance with a conventional method. As the plating bath used for the electrolytic nickel plating treatment, a known or commercially available bath can be used, and examples thereof include a watt bath, a chloride bath, a sulfamic acid bath, and the like.
The resin molded body having a conductive coating layer formed on the surface thereof by electroless plating or sputtering is immersed in a plating bath, and the resin molded body is connected to the cathode and the nickel counter electrode is connected to the anode to allow direct current or pulse intermittent current to flow. Thus, a nickel plating layer can be formed on the conductive coating layer.

What is necessary is just to adjust the basis weight of an electrolytic nickel plating layer so that the content rate of nickel may be 50 mass% or more as a final metal composition of a porous body.
In addition, in a porous body provided with the main metal layer which consists of nickel, it is preferable that the amount of nickel is about 200 g / m < ² > or more and about 1200 g / m < ² > or less. Further, in the case of a porous body including a main metal layer made of a nickel alloy containing other metal components, the basis weight of the total metal amount is preferably about 200 g / m ² or more and 1200 g / m ² or less. The basis weight of nickel or nickel alloy is more preferably 300 g / m ² or more and 1100 g / m ² or less, and further preferably 400 g / m ² or more and 1000 g / m ² or less.

In the case of manufacturing a porous body having a main metal layer made of nickel chromium or nickel tin, a chromium plating layer or a tin plating layer is further formed on the nickel plating layer, followed by heat treatment. It may be alloyed.
((Chrome plating layer formation))
When forming a chromium plating layer on a nickel plating layer, it can carry out as follows, for example. That is, it may be carried out according to a known chrome plating method, and a known or commercially available plating bath can be used. For example, a hexavalent chromium bath or a trivalent chromium bath can be used. A chrome plating layer can be formed by immersing a porous body to be plated in the chrome plating bath and connecting it to the cathode, connecting a chrome plate to the anode as a counter electrode, and applying a direct current or pulse intermittent current.

((Formation of tin plating layer))
The process of forming a tin plating layer on a nickel plating layer can be performed as follows, for example. That is, as a sulfuric acid bath, a plating bath having a composition of stannous sulfate 55 g / L, sulfuric acid 100 g / L, cresol sulfonic acid 100 g / L, gelatin 2 g / L, and β-naphthol 1 g / L is prepared. In the plating bath, tin plating is performed by setting the cathode current density to 2 A / dm ² , the anode current density to 1 A / dm ² or less, the temperature to 20 ° C., and the stirring (cathode oscillation) to 2 m / min. A layer can be formed.
In order to improve the adhesion of tin plating, it is desirable to perform strike nickel plating immediately before to remove the surface oxide film of the porous body and put it into the tin plating bath without being dried. Thereby, the adhesiveness of a tin plating layer can be improved.
The conditions for strike nickel plating can be as follows, for example. That is, by preparing a wood strike nickel bath having a composition of nickel chloride 240 g / L, hydrochloric acid (having a specific gravity of about 1.18) 125 ml / L, setting the temperature to room temperature, and using nickel or carbon for the anode It can be carried out.
The above plating procedure is summarized as follows: degreasing with an A-screen (cathodic electrolytic degreasing 5 A / dm ² × 1 minute), hot water washing, water washing, acid activity (hydrochloric acid immersion 1 minute), wood strike nickel plating treatment (5 to 10 A / dm) ² × 1 min), processed to tin plating, washed and dried without washing and drying.

(Plating solution circulation during plating)
In general, it is difficult to uniformly plate a substrate such as a resin molded body having a three-dimensional network structure. It is preferable to circulate the plating solution in order to prevent non-attachment to the inside or to reduce the difference in the amount of plating adhesion between the inside and the outside. As a circulation method, there are methods such as using a pump and installing a fan inside the plating tank. Also, if a plating solution is sprayed onto the resin molded body using these methods, or if the resin molded body is placed adjacent to the suction port, the plating solution can easily flow inside the resin molded body, which is effective.

(Removal of molded resin)
A porous body having a main metal layer made of nickel or a nickel alloy can be obtained by removing a resin molded body used as a substrate from a resin structure having a nickel plating layer or a nickel alloy plating layer formed on the surface. . By removing the resin molding, the nickel plating layer or the nickel alloy plating layer becomes the main metal layer of the skeleton of the porous body.
The method for removing the resin molding is not limited, and examples thereof include chemical treatment and combustion removal by incineration. In the case of incineration, for example, the heating may be performed in an oxidizing atmosphere such as air of about 600 ° C. or higher.
The obtained porous body is heat-treated in a reducing atmosphere as necessary to reduce the metal, thereby obtaining a porous body having a main metal layer made of nickel or a nickel alloy.

-Heat treatment process-
This step is a step of heat-treating the porous body including the main metal layer made of nickel or nickel alloy prepared above in an oxidizing atmosphere. By this step, an oxide layer of an element constituting the main metal layer is formed on the surface of the main metal layer.
The oxidizing atmosphere is not particularly limited as long as it is an atmosphere in which nickel or nickel alloy constituting the skeleton is oxidized. For example, it may be performed in an air atmosphere or an atmosphere containing 10% or more of oxygen.

Moreover, it is preferable to perform the heat processing temperature at about 300 degreeC or more and 1000 degrees C or less. By being 300 degreeC or more, the oxidation of nickel or a nickel alloy can be accelerated | stimulated. Moreover, excessive oxidation and deformation | transformation of frame | skeleton can be suppressed because it is 1000 degrees C or less.
From these viewpoints, the heat treatment temperature is more preferably 300 ° C. or more and 900 ° C. or less, and further preferably 350 ° C. or more and 850 ° C. or less.

In the heat treatment step, the heat treatment time may be a time during which nickel or a nickel alloy can be oxidized. For example, the soaking time may be about 15 minutes or more and about 2 hours or less.
By being 15 minutes or more, nickel or a nickel alloy can be sufficiently oxidized. Moreover, by being 2 hours or less, it can suppress that nickel or nickel alloy is oxidized too much and becomes embrittled. From these viewpoints, the heat treatment time is more preferably 20 minutes or longer and 1.5 hours or shorter, and further preferably 30 minutes or longer and 1 hour or shorter.

-Removal process-
This step is a step of removing the oxide layer formed on the portion forming the pair of main surfaces of the porous body from the oxide layer formed on the surface of the main metal layer by the heat treatment. Since the oxide layer is not formed on the portion constituting the main surface of the metal porous body, it is possible to conduct by bringing the main surface of the metal porous body into contact with another conductive material.
The method for removing the oxide layer formed on the main surface of the porous body including the main metal layer made of nickel or nickel alloy is not particularly limited, and the nickel or nickel alloy constituting the main metal layer is exposed. Any method can be used.
For example, a method of polishing using sandpaper or an abrasive, a method of etching with a chemical solution, a method of using a reducing agent, and the like can be preferably used.

The metal porous body which concerns on embodiment of this invention can be manufactured with the above manufacturing method.
In addition, it is possible to further increase the corrosion resistance by increasing the thickness of the oxide layer. In this case, it is preferable to produce a porous metal body by the following method.

-Acid treatment process-
It is preferable that a porous body including a main metal layer made of nickel or a nickel alloy is dipped in an acidic solution and dried, and then the heat treatment step is performed. As a result, the surface of the porous body is oxidized and roughened, whereby the oxidation easily proceeds, and the thickness of the oxide layer formed on the surface of the main metal layer can be increased.
As the acidic solution, for example, nitric acid, sulfuric acid, hydrochloric acid, acetic acid and the like can be used. It is preferable to use an aqueous solution of these acidic solutions. For example, when dilute nitric acid is used, the surface of the porous body becomes nickel nitrate, which is heated at 250 ° C. or higher to form nickel oxide. For this reason, more oxide layers can be formed than simply heating nickel.
By forming a thick oxide layer on the surface of the main metal layer of the skeleton of the porous metal body, the corrosion resistance of the porous metal body is enhanced. The metal porous body in which the oxide layer is formed exhibits excellent corrosion resistance in the generated water as compared with the metal porous body not having the oxide layer. Therefore, the metal porous body on which the oxide layer is formed can be used for a member that requires corrosion resistance in the generated water. For example, it is preferable as a gas diffusion layer for a fuel cell in which the number of stops increases due to long-term use. Can be used.

-Conductive layer formation process-
It is preferable to further form a conductive layer on the surface of the oxide layer of the porous metal body on which the oxide layer is formed. Thereby, the surface of the skeleton of the metal porous body can be made conductive. The conductive layer is not particularly limited as long as it is a conductive layer. However, considering that the metal porous body is used as a gas diffusion layer of a fuel cell, the conductive layer is preferably excellent in corrosion resistance.
Note that the conductive layer formation step may be performed any time after the heat treatment step, may be performed before the removal step, or may be performed after the removal step.

The conductive layer can be formed by applying a slurry containing conductive powder and a binder to the surface of the oxide layer of the metal porous body and drying it. For example, carbon powder can be used as the conductive powder. Carbon powder is preferable because it is lightweight and easily available. As the carbon powder, for example, carbon black, activated carbon, graphite or the like can be used alone or in combination. Further, as the conductive powder, powders such as gold, silver, palladium, copper, and aluminum can be used in addition to the carbon powder. Among these, silver powder can be preferably used in terms of corrosion resistance and conductivity.

As the binder, a resin can be preferably used. In particular, a resin having excellent film forming ability (film forming ability) and heat resistance can be preferably used. It is preferable to withstand heat of about 70 ° C. to 110 ° C., which is the operating temperature of the polymer electrolyte fuel cell.
Specifically, polyolefins such as polyethylene and polypropylene, polyacrylic acid ester, polyvinyl acetate, vinyl alcohol-polystyrene copolymer, ethylene-acrylic acid methyl ester copolymer, polymethacrylic acid ester, formalized polyvinyl Alcohol or the like can be used. These may be used alone or in combination. Furthermore, polyurethane, silicone resin, polyimide, and fluorine resin can also be preferably used as the resin.

The porous metal body obtained as described above preferably further includes a step of rolling to adjust the thickness of the outer shape to 0.10 mm or more and 1.20 mm or less.
-Thickening process-
This step is a step of rolling the metal porous body and adjusting the thickness so that the thickness of the outer shape becomes 0.10 mm or more and 1.20 mm or less. Rolling can be performed by, for example, a roller press or a flat plate press. By adjusting the thickness of the metal porous body, it is possible to make the thickness of the outer shape of the metal porous body uniform and eliminate the unevenness of the surface unevenness. Moreover, the porosity can be reduced by rolling the metal porous body. It is more preferable to roll so that the thickness of the outer shape of the metal porous body is 0.20 mm or more and 1.0 mm or less, and it is more preferable to roll so that the thickness is 0.30 mm or more and 0.80 mm or less. .
When the metal porous body is used as the gas diffusion layer of the fuel cell, a metal porous body having a thickness slightly thicker than the thickness of the gas diffusion layer when incorporated in the fuel cell is manufactured, The metal porous body may be deformed by the pressure at the time of incorporation so that the thickness becomes 0.10 mm or more and 1.20 mm or less. At this time, the porous metal body may be slightly rolled in advance to form a porous metal body having a thickness slightly thicker than the thickness of the gas diffusion layer when incorporated in the fuel cell. Thereby, the adhesion between the MEA of the fuel cell and the gas diffusion layer (metal porous body) can be further enhanced.

<Hydrogen production method and hydrogen production apparatus>
The metal porous body which concerns on embodiment of this invention can be used conveniently also for the hydrogen production use by water electrolysis besides a fuel cell use. Hydrogen production methods are broadly classified into [1] alkaline water electrolysis method, [2] PEM method, and [3] SOEC method, and any of these methods can use a porous metal body.

The alkaline water electrolysis method [1] is a method in which water is electrolyzed by immersing an anode and a cathode in a strong alkaline aqueous solution and applying a voltage. By using a metal porous body as an electrode, the contact area between water and the electrode is increased, and the efficiency of water electrolysis can be increased.
In the method for producing hydrogen by the alkaline water electrolysis method, the metal porous body preferably has a pore diameter of 100 μm or more and 5000 μm or less when viewed from above. When the pore size when the metal porous body is viewed from above is 100 μm or more, the generated hydrogen / oxygen bubbles are prevented from clogging the pores of the metal porous body and reducing the contact area between water and the electrode. be able to.
In addition, when the porous metal body is viewed from above, the pore diameter is 5000 μm or less, the surface area of the electrode is sufficiently increased, and the efficiency of water electrolysis can be increased. From the same viewpoint, the pore size when the metal porous body is viewed from above is more preferably 400 μm or more and 4000 μm or less.
The thickness and the amount of metal of the metal porous body may be appropriately selected depending on the scale of the equipment because it causes a deflection or the like when the electrode area increases. A plurality of porous metal bodies having different pore diameters can be used in combination in order to achieve both the elimination of bubbles and the securing of the surface area.
In addition, when using the metal porous body which concerns on embodiment of this invention as an electrode in an alkaline water electrolysis system, what is necessary is just to use the metal porous body which has a conductive layer on the surface of an oxide layer.

(2) The PEM method of [2] is a method of electrolyzing water using a solid polymer electrolyte membrane. By placing an anode and a cathode on both sides of the solid polymer electrolyte membrane and applying a voltage while flowing water to the anode side, hydrogen ions generated by water electrolysis move to the cathode side through the solid polymer electrolyte membrane And is taken out as hydrogen on the cathode side. The operating temperature is about 100 ° C. The polymer electrolyte fuel cell that generates electricity with hydrogen and oxygen and discharges water is operated in exactly the reverse manner with the same configuration. Since the anode side and the cathode side are completely separated, there is an advantage that high purity hydrogen can be taken out. Since both the anode and the cathode must pass through the electrode and allow water and hydrogen gas to pass through, the electrode needs a conductive porous body.

Since the porous metal body according to the embodiment of the present invention has high porosity and good electrical conductivity, it can be used for PEM water electrolysis as well as it can be suitably used for polymer electrolyte fuel cells. It can be used suitably. In the method for producing hydrogen by the PEM method, the metal porous body preferably has a pore diameter of 100 μm or more and 700 μm or less when viewed from above. When the porous metal body is viewed from above, the pore diameter is 100 μm or more, and the generated hydrogen / oxygen bubbles are clogged in the pores of the porous metal body, reducing the contact area between water and the solid polymer electrolyte membrane. Can be suppressed. Further, when the porous metal body is viewed from above, the pore diameter is 700 μm or less, so that sufficient water retention can be ensured, and water is prevented from passing through before reacting. Electrolysis can be performed. From the same viewpoint, the pore diameter when the metal porous body is viewed from above is more preferably 150 μm or more and 650 μm or less, and further preferably 200 μm or more and 600 μm or less.

The thickness and the amount of metal of the porous metal body may be appropriately selected depending on the scale of the equipment. However, if the porosity is too small, the pressure loss for allowing water to pass increases, so the porosity is 30% or more. It is preferable to adjust the thickness and the amount of metal. Also, in the PEM method, the electrical connection between the solid polymer electrolyte membrane and the electrode is a pressure bonding, so it is necessary to adjust the amount of metal so that the increase in electrical resistance due to deformation and creep during pressurization is within a practically acceptable range. . The amount of metal is preferably about 200 g / m ² or more and 1200 g / m ² or less, more preferably about 300 g / m ² or more and about 1100 g / m ² or less, 400 g / m ² or more and 1000 g / m ² or less. More preferably, it is about ² or less. In addition, a plurality of porous metal bodies having different pore diameters can be used in combination for ensuring porosity and electrical connection.

The SOEC method [3] is a method of electrolyzing water using a solid oxide electrolyte membrane, and the configuration differs depending on whether the electrolyte membrane is a proton conducting membrane or an oxygen ion conducting membrane. In the oxygen ion conductive membrane, hydrogen is generated on the cathode side for supplying water vapor, so that the hydrogen purity is lowered. Therefore, it is preferable to use a proton conductive membrane from the viewpoint of hydrogen production.
By placing an anode and a cathode on both sides of the proton conducting membrane and applying a voltage while introducing water vapor to the anode side, hydrogen ions generated by water electrolysis are moved to the cathode side through the solid oxide electrolyte membrane. In this method, only hydrogen is extracted on the cathode side. The operating temperature is about 600 ° C to 800 ° C. A solid oxide fuel cell that generates electricity with hydrogen and oxygen and discharges water is operated in exactly the reverse manner with the same configuration.

た め Since both the anode and the cathode need to permeate the electrode and allow water vapor and hydrogen gas to pass therethrough, the electrode must be conductive and have a porous body that can withstand a high-temperature oxidizing atmosphere, particularly on the anode side. Since the porous metal body according to the embodiment of the present invention has high porosity, good electrical conductivity, and high oxidation resistance and heat resistance, it can be suitably used for a solid oxide fuel cell. It can also be suitably used for SOEC water electrolysis. It is preferable to use a Ni alloy to which a metal having high oxidation resistance such as Cr is added for the electrode on the side that becomes an oxidizing atmosphere.

In the method for producing hydrogen by the SOEC method, the porous metal body preferably has a pore diameter of 100 μm or more and 700 μm or less when viewed from above. Since the pore diameter when the metal porous body is viewed from above is 100 μm or more, water vapor or generated hydrogen is clogged in the pores of the metal porous body, and the contact area between the water vapor and the solid oxide electrolyte membrane is reduced. This can be suppressed. Moreover, when the metal porous body is viewed from above, the pore diameter is 700 μm or less, so that it is possible to prevent the pressure loss from becoming too low and water vapor to pass through before sufficiently reacting. From the same viewpoint, the pore diameter when the metal porous body is viewed from above is more preferably 150 μm or more and 650 μm or less, and further preferably 200 μm or more and 600 μm or less.

The thickness of the metal porous body and the amount of metal may be appropriately selected depending on the scale of the equipment. However, if the porosity is too small, the pressure loss for introducing water vapor increases, so that the porosity is 30% or more. It is preferable to adjust the thickness and the amount of metal. In addition, in the SOEC method, since the electrical connection between the solid oxide electrolyte membrane and the electrode is a pressure bonding, it is necessary to adjust the amount of metal so that the increase in electric resistance due to deformation and creep during pressurization is within a practically acceptable range. . The amount of metal is preferably about 200 g / m ² or more and 1200 g / m ² or less, more preferably about 300 g / m ² or more and about 1100 g / m ² or less, 400 g / m ² or more and 1000 g / m ² or less. More preferably, it is about ² or less. In addition, a plurality of porous metal bodies having different pore diameters can be used in combination for ensuring porosity and electrical connection.

<Appendix>
The above description includes the following features.
(Appendix 1)
By electrolyzing water using a metal porous body having a three-dimensional network structure composed of a skeleton and having an outer shape as a plate having a pair of main surfaces and an end surface connecting the pair of main surfaces as an electrode A method for producing hydrogen that generates hydrogen, comprising:
The skeleton of the porous metal body includes a main metal layer made of nickel or a nickel alloy, and an oxide layer formed on the surface of the main metal layer,
The method for producing hydrogen, wherein the oxide layer is not formed on portions of the surface of the main metal layer that form a pair of main surfaces of the metal porous body.
(Appendix 2)
The skeleton is
The method for producing hydrogen according to appendix 1, comprising a conductive layer formed on a surface of the oxide layer.
(Appendix 3)
The method for producing hydrogen according to appendix 2, wherein the conductive layer includes carbon powder and a binder.
(Appendix 4)
The method for producing hydrogen according to supplementary note 2 or supplementary note 3, wherein the conductive layer contains silver.
(Appendix 5)
The method for producing hydrogen according to any one of appendix 1 to appendix 4, wherein the nickel alloy includes at least one of chromium, tin, and tungsten and nickel.
(Appendix 6)
The method for producing hydrogen according to any one of appendices 1 to 5, wherein the oxide layer is nickel oxide.
(Appendix 7)
The method for producing hydrogen according to any one of appendix 2 to appendix 6, wherein the water is a strong alkaline aqueous solution.
(Appendix 8)
The metal porous body is disposed on both sides of the solid polymer electrolyte membrane, the solid polymer electrolyte membrane and the metal porous body are brought into contact with each other, and each metal porous body acts as an anode and a cathode. The method for producing hydrogen according to any one of appendix 1 to appendix 6, wherein hydrogen is generated on the cathode side by supplying and electrolyzing.
(Appendix 9)
The metal porous body is disposed on both sides of the solid oxide electrolyte membrane, the solid polymer electrolyte membrane and the metal porous body are brought into contact with each other, and each metal porous body acts as an anode and a cathode. The method for producing hydrogen according to any one of appendix 1 to appendix 6, wherein hydrogen is generated by electrolyzing water to generate hydrogen on the cathode side.
(Appendix 10)
An apparatus for producing hydrogen capable of generating hydrogen by electrolyzing water,
A porous metal body having a three-dimensional network structure composed of a skeleton and having an outer shape having a pair of main surfaces and an end surface connecting the pair of main surfaces as an electrode;
The skeleton of the porous metal body includes a main metal layer made of nickel or a nickel alloy, and an oxide layer formed on the surface of the main metal layer,
An apparatus for producing hydrogen, wherein the oxide layer is not formed on portions of the surface of the main metal layer that form a pair of main surfaces of the porous metal body.
(Appendix 11)
The skeleton is
The hydrogen production apparatus according to appendix 10, comprising a conductive layer formed on a surface of the oxide layer.
(Appendix 12)
The hydrogen production apparatus according to appendix 11, wherein the conductive layer includes carbon powder and a binder.
(Appendix 13)
The hydrogen production apparatus according to appendix 11 or appendix 12, wherein the conductive layer contains silver.
(Appendix 14)
The hydrogen production apparatus according to any one of appendix 10 to appendix 13, wherein the nickel alloy includes at least one of chromium, tin, and tungsten and nickel.
(Appendix 15)
The hydrogen production apparatus according to any one of appendix 10 to appendix 14, wherein the oxide layer is nickel oxide.
(Appendix 16)
The hydrogen production apparatus according to any one of appendix 11 to appendix 15, wherein the water is a strong alkaline aqueous solution.
(Appendix 17)
Having an anode and a cathode on both sides of the solid polymer electrolyte membrane;
The anode and the cathode are in contact with the solid polymer electrolyte membrane;
A hydrogen production apparatus capable of generating hydrogen on the cathode side by electrolyzing water supplied to the anode side,
The hydrogen production apparatus according to any one of appendix 10 to appendix 15, wherein the metal porous body is used for at least one of the anode and the cathode.
(Appendix 18)
Having an anode and a cathode on both sides of the solid oxide electrolyte membrane;
The anode and the cathode are in contact with the solid polymer electrolyte membrane;
A hydrogen production apparatus capable of generating hydrogen on the cathode side by electrolyzing water vapor supplied to the anode side,
The hydrogen production apparatus according to any one of appendix 10 to appendix 15, wherein the metal porous body is used for at least one of the anode and the cathode.

Hereinafter, the present invention will be described in more detail based on examples. However, these examples are illustrative, and the metal porous body of the present invention is not limited thereto. The scope of the present invention is defined by the scope of the claims, and includes meanings equivalent to the scope of the claims and all modifications within the scope.

[Example 1]
-Fabrication of porous metal-
<Preparation process>
(Conductive layer formation process)
As a resin molded body having a three-dimensional network structure, a urethane resin foam sheet having a porosity of 90%, an average pore diameter of 450 μm, and a thickness of 1.3 mm was used. A slurry was prepared by dispersing 1000 g of graphite powder having an average particle size of 0.5 μm and 130 g of chromium powder having an average particle size of 5 μm in 5 L of an acrylic-styrene copolymer emulsion of 10% by mass. The urethane resin foam was immersed in this slurry. Then, the urethane resin foam was pulled up, excess slurry was removed between the rolls, and dried to make the surface of the skeleton conductive. The amount of chromium applied after drying was set to 70 g / m ² .

(Plating layer forming process)
The electroconductive urethane resin foam was subjected to electrolytic nickel plating by a known sulfamic acid bath method. Electrolytic nickel plating was performed with a known composition, that is, a bath mainly composed of nickel sulfamate 430 g / L, nickel chloride 7 g / L, and boric acid 32 g / L at a current density of 250 mA / cm ² . Thereby, the resin structure in which the main metal layer which consists of a nickel plating layer was formed in the surface of the frame of a resin fabrication object was obtained. The basis weight of nickel was set to 600 g / m ² .

(Removal of molded resin)
The resin structure was heated in the atmosphere at 800 ° C. for 15 minutes to incinerate and remove the resin and graphite powder added to the resin molded body and the slurry. After that, heat treatment is performed at 1000 ° C. for 25 minutes in a hydrogen atmosphere to reduce the metal that has been partially oxidized by heating in the air, and alloying and annealing to form a main metal layer whose skeleton is made of a nickel chromium alloy. A porous body was obtained. The uniformity of the alloy was confirmed by X-ray analysis and electron microscope.
Thereafter, the porous body including the main metal layer made of a nickel chromium alloy was adjusted to a thickness of 0.50 mm with a roller press. The porous body including the main metal layer made of a nickel-chromium alloy had a porosity of 84.6%, a basis weight of 670 g / m ² , a ratio of nickel to chromium of 90% by weight of nickel, and 10% by weight of chromium.

<Heat treatment process>
The porous body provided with the main metal layer made of the nickel-chromium alloy obtained above was heated in an air atmosphere at 500 ° C. for 1 hour to oxidize the skeleton. This confirmed that a uniform oxide layer was formed on the surface of the main metal layer by elemental mapping of the cross section of the skeleton by SEM-EDX.

<Removal process>
A pair of main surfaces of a porous body having an oxide layer formed on the surface of the main metal layer is polished by sandpaper to form an oxide formed on a portion of the main metal layer that forms the pair of main surfaces. The layer was removed.

<Conductive layer formation process>
A slurry was prepared by dispersing 450 g of graphite powder having an average particle diameter of 1.0 μm in 2.5 L of an 8% by mass aqueous polypropylene emulsion. The porous body obtained above was immersed in this slurry, and the slurry was applied to the surface of the skeleton. And the binding property of resin was improved by heat-processing for 30 minutes at 135 degreeC. As a result, a porous metal body 1 in which a conductive layer having corrosion resistance and conductivity was formed on the surface of the oxide layer was obtained.

-Fabrication of fuel cell-
The porous metal body 1 was used as a gas diffusion layer / gas supply / discharge path of a polymer electrolyte fuel cell (single cell).
In order to assemble a single cell using the metal porous body 1, a commercially available MEA was used, and the metal porous body 1 was cut into 5 × 5 cm to form the single cell shown in FIG. The MEA was sandwiched between two carbon papers, and the outside was sandwiched between two metal porous bodies 1 to form a single cell. In order not to leak the air electrode and the hydrogen electrode, a gasket and a concave graphite plate were used, and the four corners were fastened and fixed with bolts and nuts. This prevented the leakage of hydrogen and air from the cell as well as improving the contact of each constituent material. Since the separator graphite plate is practically a laminated battery, its thickness is about 1 to 2 mm. However, the example is a single cell and has a thickness of 10 mm to make it strong enough to withstand tightening. . This cell was designated as battery A.

[Example 2]
-Fabrication of porous metal-
<Preparation process>
(Conductive layer formation process)
As a resin molded body having a three-dimensional network structure, a urethane resin foam sheet having a porosity of 90%, an average pore diameter of 450 μm, and a thickness of 1.3 mm was used. A slurry was prepared by dispersing 900 g of graphite powder having an average particle diameter of 0.5 μm in 1 L of a 10% by mass acrylic ester aqueous emulsion. The urethane resin foam was immersed in this slurry. Then, the urethane resin foam was pulled up, excess slurry was removed between the rolls, and dried to make the surface of the skeleton conductive. The amount of graphite applied after drying was set to 20 g / m ² .

(Plating layer forming process)
The urethane resin foam imparted with conductivity was subjected to electrolytic nickel plating by a known sulfamic acid bath method. Electrolytic nickel plating was performed with a known composition, that is, a bath mainly composed of nickel sulfamate 430 g / L, nickel chloride 7 g / L, and boric acid 32 g / L at a current density of 250 mA / cm ² . Thereby, the resin structure in which the nickel plating layer was formed on the surface of the skeleton of the resin molding was obtained. The basis weight of nickel was set to 600 g / m ² .
Subsequently, tin plating was performed using a known sulfuric acid bath. The sulfuric acid bath was composed of stannous sulfate 55 g / L, sulfuric acid 100 g / L, cresol sulfonic acid 100 g / L, gelatin 2 g / L, and β-naphthol 1 g / L. In the sulfuric acid bath, the cathode current density is 2 A / dm ² , the anode current density is 1 A / dm ² or less, the temperature is 20 ° C., and the stirring (cathode oscillation) is 2 m / min. Formation was performed. The basis weight of tin was set to 150 g / m ² .
Thereby, the resin structure in which the main metal layer which consists of a nickel plating layer and a tin plating layer was formed on the conductive coating layer containing graphite powder was obtained.

(Removal of molded resin)
The resin structure was heated in the atmosphere at 800 ° C. for 15 minutes to incinerate and remove the resin (binder) and graphite powder added to the resin molded body and the slurry. After that, heat treatment is performed at 1000 ° C. for 50 minutes in a hydrogen atmosphere to reduce the metal that has been partially oxidized by heating in the atmosphere, and by alloying and annealing by thermal diffusion, the skeleton is made of a nickel-tin alloy. A porous body provided with a metal layer was obtained. The uniformity of the alloy was confirmed by X-ray analysis and electron microscope.
Thereafter, the thickness of the porous body including the main metal layer made of a nickel-tin alloy was adjusted to 0.50 mm with a roller press. The porous body including the main metal layer made of a nickel-tin alloy had a porosity of 82.4%, a basis weight of 750 g / m ² , and a nickel-tin ratio of 80 mass% nickel and 20 mass% tin.

<Acid treatment process>
The porous body provided with the main metal layer made of the nickel tin alloy obtained above was immersed in a 0.5N nitric acid aqueous solution at room temperature, immediately pulled up, and left at room temperature for 1 hour.
<Heat treatment process>
A porous body having a main metal layer made of a nickel-tin alloy after being immersed in the above nitric acid aqueous solution is heated in an air atmosphere at 500 ° C. for 1 hour to decompose and oxidize nickel nitrate forming the surface of the main metal layer I let you. Thus, it was confirmed by oxygen mapping by SEM-EDX of the cross section that more oxide layers were formed than the porous metal body of Example 1.

After that, in the same manner as in Example 1, the oxide layer in the portion constituting the pair of main surfaces of the porous body was removed, and a conductive layer having corrosion resistance and conductivity was formed on the surface of the oxide layer. This is designated as metal porous body 2.

-Fabrication of fuel cell-
A single cell of a fuel cell was produced in the same manner as in Example 1 except that the metal porous body 2 was used. This single cell was designated as battery B.

[Comparative Example 1]
The nickel plating in the same manner as in Example 2 and 700 g / m ^2, tin plating or acid treatment to obtain a porous body consisting only of nickel without application of oxide layers.
Thereafter, the porous body made of nickel was adjusted to a thickness of 0.50 mm with a roller press to obtain a porous metal body 3. The porous metal body 3 made of nickel had a porosity of 84.3%.

[Comparative Example 2]
A single cell was constructed using a general-purpose separator (graphite plate) with grooves formed as a gas diffusion layer. That is, the same MEA and carbon paper as the battery A were used for both the anode and the cathode. The grooves were 1 mm in both depth and width, and the width between the grooves was 1 mm. The apparent porosity of the gas diffusion layer is approximately 50%. This cell was designated as battery C.

[Comparative Example 3]
After forming the oxide layer by the method of Example 1, a metal porous body 4 was produced in the same manner as in Example 1 except that polishing and conductive layer application were not performed. Using this metal porous body 4, a single cell of a fuel cell similar to that of Example 1 was produced. This cell was designated as battery D.

[Evaluation of corrosion resistance]
Corrosion resistance of each metal porous body is determined by immersing the metal porous bodies 1 to 3 in a 10% aqueous solution of sodium sulfate adjusted to pH = 3 with sulfuric acid and examining the amount of Ni eluted when a potential of 0.8 V is applied for 1 hour. Evaluated. The elution amount of Ni was determined by ICP analysis of the liquid used in the test. The results are shown in FIG.

The amount of Ni elution of the metal porous bodies 1 and 2 produced in Examples 1 and 2 was 5 ppm or less, and excellent corrosion resistance was exhibited with respect to 34 ppm of the metal porous body 3 produced in Comparative Example 1.

[Evaluation of power generation characteristics]
For batteries A to D, hydrogen was supplied to the anode of each battery and air was supplied to the cathode, and the power generation characteristics were examined.
In addition, the apparatus which adjusts supply of each gas according to load was used. The ambient temperature of the electrode was 25 ° C., and the operating temperature was 80 ° C. The results are shown in FIG. In FIG. 3, the vertical axis represents voltage (V) and the horizontal axis represents current density (mA / cm ² ).

Batteries A and B using the porous metal bodies 1 and 2 produced in Examples 1 and 2 are higher in voltage even in a high current region than the battery C using the general-purpose separator of Comparative Example 2, and have excellent power generation characteristics. showed that. On the other hand, the battery D using the metal porous body 4 of Comparative Example 3 that was not polished had remarkably poor power generation characteristics. This is presumably because polishing was not performed and thus the electric resistance was high and sufficient current collecting performance could not be exhibited.

M Membrane / electrode assembly (MEA)
1-1 Ion exchange membrane 2-1 Gas diffusion electrode (activated carbon layer containing platinum catalyst)
2-2 Gas diffusion electrode (activated carbon layer containing platinum catalyst)
3-1 Current collector 3-2 Current collector 4-1 Separator 4-1-1 Gas diffusion layer 4-2 Separator 4-2-1 Gas diffusion layer

Claims (11)

1. A porous metal body having a three-dimensional network structure composed of a skeleton, and having an outer shape of a flat plate having a pair of main surfaces and an end surface connecting the pair of main surfaces,
   The skeleton is
   A main metal layer made of nickel or a nickel alloy;
   An oxide layer formed on the surface of the main metal layer;
   With
   A porous metal body in which the oxide layer is not formed on a portion of the surface of the main metal layer that forms a pair of main surfaces of the porous metal body.
2. The skeleton is
   The porous metal body according to claim 1, comprising a conductive layer formed on a surface of the oxide layer.
3. The metal porous body according to claim 2, wherein the conductive layer contains carbon powder and a binder.
4. The metal porous body according to claim 2 or 3, wherein the conductive layer contains silver.
5. The metal porous body according to any one of claims 1 to 4, wherein the nickel alloy includes at least one of chromium, tin, and tungsten and nickel.
6. The metal porous body according to any one of claims 1 to 5, wherein the oxide layer is nickel oxide.
7. A fuel cell using the porous metal body according to any one of claims 1 to 6 as a gas diffusion layer.
8. It is a manufacturing method of the metal porous body according to claim 1,
   A porous structure having a three-dimensional network structure composed of a skeleton, the outer shape being a flat plate shape having a pair of main surfaces and end faces connecting the pair of main surfaces, and the skeleton including a main metal layer made of nickel or a nickel alloy A preparation process for preparing the body;
   A heat treatment step of forming an oxide layer on the surface of the main metal layer by heating the porous body in an oxidizing atmosphere;
   A removing step of removing an oxide layer formed on a portion of the surface of the main metal layer that forms the pair of main surfaces;
   The manufacturing method of the metal porous body which has this.
9. After the preparation step and before the heat treatment step,
   The method for producing a porous metal body according to claim 8, further comprising an acid treatment step of immersing the porous body in an acidic solution and drying the porous body.
10. The method for producing a porous metal body according to claim 9, wherein the acidic solution is nitric acid, sulfuric acid, hydrochloric acid or acetic acid.
11. After the heat treatment step,
    The manufacturing method of the metal porous body as described in any one of Claims 8-10 which has a conductive layer formation process which forms a conductive layer in the surface of the said oxide layer.

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