Metal porous member and method for producing metal porous member

Abstract

Provided are: a metal porous member that can ensure a large contact area with a catalyst layer on the outermost surface thereof while suppressing attacks on the catalyst layer and an electrolyte membrane, can facilitate smooth exchange between water and generated oxygen, and can increase the reaction speed on the anode side; and a method for producing the metal porous member. A metal porous member according to the present invention is obtained by laminating at least a first layer 11 and a second layer 12 that are each formed of a metal porous body. The first layer 11 is composed of a sintered body obtained by using a spherical metal powder having an average particle diameter of 45 [μm] or less, and, in the outermost surface 10a on the side opposite from the second layer 12, the arithmetic average curvature (Spc) of peak points is 3.5 [1 / μm] or less and the density (Spd) of the peak points is 0.01 [1 / μm2] or more.

Description

Metallic porous member and method for manufacturing the same

[0001] The present invention relates to a metal porous member and a method for manufacturing a metal porous member.

[0002] Conventionally, various problems have been pointed out regarding the continued use of fossil fuels as energy sources, such as the depletion of fossil fuels and the progression of global warming due to the emission of greenhouse gases generated when fossil fuels are burned. In recent years, with the aim of solving the above-mentioned problems, active proposals have been made to generate electricity using alternative energy sources to replace fossil fuels, such as generating electricity using renewable energy sources such as solar, hydroelectric, and wind power, or using fuel cells that generate electricity using hydrogen fuel.

[0003] Among the alternative energy sources mentioned above, renewable energy is likely to generate surplus electricity because its power generation efficiency is affected by factors such as weather. For example, in the case of solar power, the amount of electricity generated during the day is large but the amount generated at night is small, so the surplus electricity generated during the day needs to be stored in a storage battery or the like. For this reason, the surplus electricity has been used, for example, to perform water electrolysis to convert it into hydrogen, which is then stored, in order to make effective use of the surplus electricity. The hydrogen stored in this way can be reconverted into electricity using, for example, a fuel cell, or can be used directly as hydrogen. Furthermore, by combining this with the storage of surplus electricity using a storage battery, it becomes possible to further promote the effective use of renewable energy and its introduction.

[0004] Several water electrolysis systems have been proposed for water electrolysis devices, depending on the type of electrolyte. Known water electrolysis systems include, for example, alkaline systems that use alkaline electrolytes, anion exchange membrane (AEM) systems that do not use precious metals as catalysts, and proton exchange membrane (PEM) systems that use solid polymer electrolyte membranes. Among these, PEM-type water electrolysis devices have various advantages, such as high safety and easy maintenance because they use only water as a raw material, high efficiency, high responsiveness to output fluctuations, and high purity of the hydrogen produced.

[0005] In a PEM-type water electrolysis device, protons produced in a reaction on the anode side pass through the PEM and then become hydrogen on the cathode side, so the reaction rate between the catalyst and water on the anode side is important for increasing the efficiency and rate of hydrogen production. The reaction rate on the anode side is largely dependent on the type, performance, and loading amount of the anode catalyst layer, but is also influenced by the performance of a porous transport layer (PTL) provided between the anode plate (electrode plate) and the anode catalyst layer.

[0006] The porous transport layer is made of a metal sintered body, for example, titanium, nickel, stainless steel, or alloys thereof, and is composed of a porous body having a predetermined porosity. The porous transport layer is a porous layer capable of exchanging liquid and gas, and is capable of discharging oxygen generated by the reaction in the adjacent catalyst layer and unreacted water to the outside, and collecting and / or transporting electrons generated by the electrochemical reaction.

[0007] From the viewpoint of increasing the efficiency and rate of production of oxygen and protons on the anode side, the porous transport layer used on the anode side is required to have a smooth outermost surface that is not aggressive to the catalyst layer or electrolyte membrane, and has surface properties that ensure a large contact area with the outermost surface catalyst layer, and also has a porosity of at least a certain level that allows for smooth exchange of water with the generated oxygen.

[0008] As the porous transport layer to be provided in the water electrolysis apparatus as described above, a single layer having a thickness of 0.3 mm and a bending strain at break of 0.005 or more has been proposed, which is made of a porous titanium body having three-dimensional surface texture of at least one surface with an arithmetic mean height Sa of 2.5 μm or less, a maximum height Sz of 30 μm or less, an aspect ratio Str of the surface texture of 0.93 or more, and an arithmetic mean curvature Spc of the ridge line of 4.8 (1 / μm) or less (see, for example, Patent Document 1).

[0009] Furthermore, a porous transport layer to be provided in a water electrolysis apparatus has been proposed, which is a single layer having a thickness of 0.3 mm and made of a porous titanium body having a titanium content of 97% by mass or more, an oxygen content of 0.9% by mass or more and 2.0% by mass or less, a carbon content of 0.01% by mass or more and 0.06% by mass or less, a porosity of 35% to 45% or less, an irreversible deformation amount of 5.0% or less after applying a pressure of 65 MPa, and a fracture bending strain of 0.005 or more (see, for example, Patent Document 2).

[0010] Furthermore, a porous transport layer disposed between a bipolar plate and a catalyst layer in an electrochemical cell has been proposed, which comprises at least a first porous layer (8, 10) and a second porous layer (4) containing irregularly shaped particles formed by sintering a conductive material, the average particle size decreasing from layer to layer, the irregularly shaped particles having an irregularity parameter equal to or less than a predetermined value and a circularity equal to or greater than a predetermined value, and the first porous layer (8, 10) that can come into contact with the catalyst layer has an average particle size smaller than that of the second porous layer (4) that can come into contact with the bipolar plate (see, for example, Patent Document 3).

[0011] International Publication No. WO 2023 / 145375 International Publication No. WO 2023 / 145374 European Patent No. 3914754

[0012] According to the porous bodies described in Patent Documents 1 and 2, when applied to a porous transport layer, the smooth outermost surface reduces aggressiveness to adjacent layers such as catalyst layers, and the certain degree of porosity allows for smooth exchange of liquid and gas.

[0013] However, when the porous bodies described in Patent Documents 1 and 2 are used in the porous transport layer, it is difficult to ensure a large contact area with the catalyst layer at the outermost surface, making it difficult to increase the reaction rate on the anode side. This may result in a decrease in the reaction rate on the cathode side, which increases the resistance value of the entire water electrolysis device and makes it difficult to increase the electrolysis efficiency.

[0014] On the other hand, as in the porous transport layer described in Patent Document 3, it is also possible to ensure a contact area with the catalyst layer by using a sintered body of particles having an average particle size smaller than that of the second porous layer (4) on the bipolar plate side for the first porous layer (8, 10) that can contact the catalyst layer. However, in Patent Document 3, irregularly shaped particles are used for the first porous layer (8, 10), and therefore the peak density (Spd) at the outermost surface is not appropriate, making it difficult to ensure a large contact area with the catalyst layer, etc. For this reason, as in Patent Documents 1 and 2, it is difficult to increase the reaction rate on the anode side, and the resistance value of the entire water electrolysis apparatus increases, making it difficult to increase the electrolysis efficiency.

[0015] The present invention has been made in view of the above problems, and aims to provide a metal porous member and a method for manufacturing a metal porous member that has a smooth outermost surface that is less aggressive to the catalyst layer and electrolyte membrane, ensures a large contact area with the outermost surface catalyst layer, and allows smooth exchange of water with generated oxygen, thereby increasing the reaction rate on the anode side.

[0016] In order to solve the above problems, the present inventors conducted extensive research. As a result, they found that by configuring a metal porous member constituting a porous transport layer used in a water electrolysis device with a laminated structure of at least a first layer and a second layer, and further optimizing the surface properties of the outermost surface of the first layer that contacts the catalyst layer, it is possible to ensure a large contact area with the catalyst layer while suppressing aggressiveness to the catalyst layer and electrolyte membrane. They also found that this makes it possible to improve the reaction rate on the anode side while smoothly exchanging water with generated oxygen, and further makes it possible to improve the water electrolysis efficiency by reducing the resistance value of the entire device, and thus completed the present invention.

[0017] That is, the present invention provides a laminated structure comprising at least a first layer and a second layer each made of a metal porous body, the first layer being made of a sintered body using spherical metal powder having an average particle size of 45 μm or less, and the outermost surface opposite to the second layer having an arithmetic mean curvature of peaks (Spc) of 3.5 μm or less and a peak density (Spd) of 0.01 μm or less. ２ The present invention provides a metal porous member characterized in that:

[0018] In the above-mentioned aspect of the metal porous member of the present invention, the second layer can be configured to be a sintered body made of spherical metal powder or irregularly shaped metal powder having an average particle size of 30 (μm) or more and 100 (μm) or less.

[0019] In the above-described aspect of the metal porous member of the present invention, the porosity of the first layer is more preferably 5% or more and 30% or less.

[0020] In the above-described aspect of the metal porous member of the present invention, the porosity of the second layer is more preferably more than 30% and not more than 70%.

[0021] In the above aspect of the metal porous member of the present invention, a configuration can be adopted in which the thickness of the first layer is 10 μm or more and 100 μm or less.

[0022] In the above aspect of the metal porous member of the present invention, a configuration can be adopted in which the total thickness of the first layer and the second layer combined is 100 μm or more and 500 μm or less.

[0023] In the above-described aspect of the metal porous member of the present invention, the first layer and the second layer can be configured to be sintered bodies of metal powders using any one or more selected from the group consisting of titanium, nickel, stainless steel, and alloys thereof.

[0024] The present invention provides a method for manufacturing a metal porous member, which obtains a sintered body in which at least a first layer and a second layer each made of a metal porous body are laminated, and which comprises: a first layer formation step in which spherical metal powder having an average particle size of 45 μm or less is spread in the form of a film on the smooth surface of a first jig, and then the film-like spherical metal powder is sintered at a temperature of 700°C or higher and 1200°C or lower in a vacuum atmosphere or an inert gas atmosphere to form a first layer; and a second layer lamination step in which spherical metal powder or irregularly shaped metal powder is sintered at a temperature of 700°C or higher and 1200°C or lower in a vacuum atmosphere or an inert gas atmosphere to form a second layer so as to overlap the first layer, thereby obtaining a laminate in which the first layer and the second layer are bonded together.

[0025] In the above-mentioned aspect of the manufacturing method for a metal porous member of the present invention, the second layer stacking step can employ a method in which the spherical metal powder or the irregularly shaped metal powder is spread in the form of a film on the smooth surface of a second jig, and then the first layer sintered in the first layer formation step is superimposed on the film, and the spherical metal powder or the irregularly shaped metal powder in the form of a film is sintered to form the second layer, thereby obtaining a laminate in which the first layer and the second layer are bonded together.

[0026] In the above-mentioned aspect of the manufacturing method for a metal porous member of the present invention, the second layer lamination step can employ a method in which the spherical metal powder or the irregularly shaped metal powder is scattered in the form of a film on the first layer sintered in the first layer formation step, and then the film-like spherical metal powder or the irregularly shaped metal powder is sintered to form the second layer, thereby obtaining a laminate in which the first layer and the second layer are bonded together.

[0027] In the above aspect, the method for manufacturing a metal porous member of the present invention preferably further includes, after the second layer lamination step, a rolling step in which the laminate in which the first layer and the second layer are bonded is sandwiched from both sides of the first layer and the second layer by a pair of rolling rolls and rolled.

[0028] According to the metal porous member of the present invention, as described above, the first layer is a sintered body made of spherical metal powder having an average particle size equal to or smaller than a predetermined value, and the arithmetic mean curvature (Spc) and peak density (Spd) of the peaks at the outermost surface are set within optimal ranges. This configuration ensures a large contact area while suppressing aggressiveness toward adjacent components. For example, by applying the metal porous member to the anode-side porous transport layer of a water electrolysis device, the reaction rate on the anode side can be improved while smoothly exchanging water with generated oxygen. Furthermore, the resistance of the entire device can be reduced, thereby improving water electrolysis efficiency. Therefore, when surplus electricity generated from renewable energy is converted into hydrogen using a water electrolysis device in which the metal porous member of the present invention is applied to the anode-side porous transport layer, hydrogen can be efficiently stored.

[0029] Furthermore, the method for manufacturing a metal porous member of the present invention includes a first layer forming step in which a spherical metal powder having an average particle size not greater than a predetermined value is sprayed onto the smooth surface of a first jig in the form of a film, and then sintered under predetermined conditions to form a first layer. Furthermore, a second layer lamination step in which a second layer is formed on top of the first layer is also employed. As described above, the use of spherical metal powder for the first layer provides excellent sprayability, making it possible to form a thin first layer simply by spraying and sintering, without the need for additional processes such as spray coating, binder mixing, or burn-off treatment. Furthermore, by employing the above method, the arithmetic mean curvature (Spc) and peak density (Spd) of the outermost surface of the first layer can be controlled within optimal ranges, resulting in a metal porous member that can ensure a large contact area while suppressing aggressiveness toward adjacent members. That is, when the obtained metal porous member is applied to, for example, the anode-side porous transport layer of a water electrolysis apparatus, the reaction rate on the anode side can be improved while smoothly exchanging water with generated oxygen, as described above, and further, a water electrolysis apparatus with improved water electrolysis efficiency due to a reduced resistance value of the entire apparatus can be realized. Therefore, a metal porous member suitable for a water electrolysis apparatus can be produced with good productivity using a simple process.

[0030] Other objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments of the present invention, which proceeds with reference to the accompanying drawings.

[0031] Fig. 1 is a cross-sectional view schematically illustrating one embodiment of a metal porous member according to the present invention. Fig. 2 is a view schematically illustrating one embodiment of a metal porous member according to the present invention, and is a partial cross-sectional view showing an enlarged view of a main part in Fig. 1. Fig. 3 is a view schematically illustrating one embodiment of a metal porous member according to the present invention, and is a schematic view showing an example of a water electrolysis device in which the metal porous member according to the present invention can be used as a porous transport layer.

[0032] Hereinafter, embodiments of the metal porous member and the method for manufacturing the metal porous member according to the present invention will be described in detail with reference to the drawings as appropriate. Note that, in order to make the features of the metal porous member of the present invention easier to understand, the drawings used in the following description may show characteristic parts slightly enlarged for convenience, and the dimensional ratios of each component may differ from the actual ones. Furthermore, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. Appropriate modifications can be made within the scope of the present invention.

[0033] <Water electrolysis device including a metal porous member (porous transport layer)> First, the configuration of a water electrolysis device to which the metal porous member according to the present invention can be applied will be described. Fig. 3 is a schematic diagram showing the configuration of a water electrolysis device 1, which is a type of electrochemical cell, to which the metal porous member described in this embodiment can be applied as a porous transport layer 10.

[0034] The metallic porous member described in this embodiment is applicable as a porous transport layer 10 included in the anode 2 of a water electrolysis device 1 and disposed between an anode plate 20 and an anode catalyst layer 22, as illustrated in Fig. 3. Therefore, in this specification, including the detailed description of the metallic porous member described later, both the metallic porous member and the porous transport layer will be described with the same reference numeral "10."

[0035] As shown in Fig. 3 , the water electrolysis device 1 is generally configured to include an anode plate 20, an anode 2 provided on the anode plate 20, a cathode 3, a cathode plate 30 provided on the cathode 3, a solid polymer electrolyte membrane 4 disposed between the anode 2 and the cathode 3, and a power source 5. Although not shown in detail in Fig. 3 , the water electrolysis device 1 is also provided with a water supply means that supplies water for electrolysis to a porous transport layer 10 that constitutes the anode 2.

[0036] The water electrolysis device 1 in the illustrated example is configured as a PEM-type water electrolysis device, using the above-described solid polymer electrolyte membrane (PEM: Proton Exchange Membrane) 4 .

[0037] The anode plate 20 is an electrode plate for applying a current to the anode 2, and may be a conductive metal plate such as stainless steel. The anode plate 20 may be configured as a monopolar plate by, for example, providing a gas flow path (not shown) for leading oxygen generated by a reaction in the anode 2 (anode catalyst layer 22) to the outside. Furthermore, when a cell stack is configured by stacking a plurality of water electrolysis devices 1, the anode plate 20 may be configured as a bipolar plate between the water electrolysis devices 1 by providing gas flow paths (not shown) on both sides for leading oxygen generated by a reaction to the outside.

[0038] The anode 2 is a membrane electrode (anode electrode) provided on an anode plate 20, and is configured as a membrane electrode having a porous transport layer 10 disposed on the anode plate 20, and an anode catalyst layer 22 laminated on the porous transport layer 10 or laminated on the solid polymer electrolyte membrane 4. The anode 2 provided in the illustrated water electrolysis apparatus 1 has a coating layer 21 provided between the porous transport layer 10 and the anode catalyst layer 22.

[0039] The porous transport layer 10 is also called a PTL (Porous Transport Layer), and uses the metal porous member of the present embodiment, which will be described in detail later. The porous transport layer 10, as will be described later, transports water (H ２O) is supplied to the anode catalyst layer 22, and oxygen (O ２ ) and unreacted water (H ２ O) to the outside, and a gas-liquid transport function, and a function of collecting and / or transporting electrons generated by an electrochemical reaction.

[0040] Since the porous transport layer 10 is required to smoothly exchange liquid and gas, it is made of a sintered body of metal powder, for example, titanium, nickel, stainless steel, alloys thereof, or a combination of these. The thickness of the porous transport layer 10 is not particularly limited, and although details will be described later, it can be determined appropriately while taking into consideration the smooth passage of liquid and gas.

[0041] Because of its function of causing the above-described reaction, the porous transport layer 10 is sometimes called a gas diffusion layer. The metal porous member that constitutes the porous transport layer 10 will be described in more detail later.

[0042] The anode catalyst layer 22 is disposed between the porous transport layer 10 and the solid polymer electrolyte membrane 4 and is made of, for example, iridium oxide (IrO ２ The anode catalyst layer 22 is made of a catalyst made of metal particles such as HCl, ... ２ O) is converted to a proton (H ＋ ) and electrons (e － ), and oxygen (O ２ ) generated in the anode catalyst layer 22. ＋ ) passes through the solid polymer electrolyte membrane 4 and heads toward the cathode 3. In addition, unreacted water and protons (H ＋ ) and oxygen (O ２ ) passes from the porous transport layer 10 through the flow channels of the monopolar plate or the bipolar plate and is discharged to the outside (see the chemical formula in Figure 3). ２ O → 2H ＋ +1 / 2O ２ +2e －....(1)

[0043] The anode catalyst layer 22 is made of iridium oxide (IrO ２ The anode catalyst layer 22 is not limited to those made of metal particles such as ruthenium (Ru) or manganese (Mn) oxides, and may also be made of various metal particles such as Ru (ruthenium) or Mn (manganese) oxides. In addition to the metal particles, the anode catalyst layer 22 may further contain carrier particles and a binder component such as an ionomer.

[0044] The thickness of the anode catalyst layer 22 is not particularly limited, but may be as thick as the above-mentioned water (H ２ O) to oxygen and protons (H ＋ The reaction efficiency for producing the hydroxybenzoate can be taken into consideration when determining the reaction temperature.

[0045] As described above, the coating layer 21 is disposed between the porous transport layer 10 and the anode catalyst layer 22 and is composed of, for example, a platinum thin film. The coating layer 21 has the effect of improving the corrosion resistance and electronic conductivity of the outermost surface 10a of the porous transport layer 10, and in the PEM-type water electrolysis apparatus described in this embodiment, the coating layer 21 is generally provided by applying a coating treatment to the outermost surface 10a of the porous transport layer 10. However, since the coating layer 21 is very thin compared to the height of the irregularities on the outermost surface 10a of the porous transport layer 10, it does not affect the various surface properties of the present invention. The coating layer 21 as described above can be formed, for example, by sputtering or other film formation methods.

[0046] The solid polymer electrolyte membrane 4 absorbs the protons (H ＋ ) toward the cathode 3. The solid polymer electrolyte membrane 4 is also called a PEM (Proton Exchange Membrane), and constitutes a PEM-type water electrolysis device.

[0047] The solid polymer electrolyte membrane 4 is a membrane that contains protons (H ＋An example of such a proton exchange membrane is a perfluorocarbon material such as commercially available Nafion (registered trademark), which has a hydrophobic Teflon (registered trademark) skeleton made of carbon and fluorine, and a perfluoro side chain having a sulfonic acid group.

[0048] The thickness of the solid polymer electrolyte membrane 4 is not particularly limited, and may be any of the above-mentioned proton (H ＋ ) can be appropriately determined while taking into consideration the function of selectively passing the

[0049] The cathode plate 30 is an electrode plate for applying a current to the cathode 3, and like the anode plate 20, can be a conductive metal plate such as stainless steel. Similarly to the anode plate 20, the cathode plate 30 can also be configured as a monopolar plate by providing a gas flow path (not shown) for leading hydrogen generated at the cathode 3 to the outside and guiding it to a storage tank or the like. Furthermore, like the anode plate 20, the cathode plate 30 can also be configured as a bipolar plate between the water electrolysis devices 1 by providing gas flow paths (not shown) on both sides for leading hydrogen generated by the reaction to the outside when a cell stack is configured by stacking a plurality of water electrolysis devices 1.

[0050] The cathode 3 is a membrane electrode (cathode electrode) provided on the cathode plate 30, and is configured as a membrane electrode having a cathode gas diffusion layer 31 arranged on the cathode plate 30, and a cathode catalyst layer 32 laminated on this cathode gas diffusion layer 31 or laminated on the solid polymer electrolyte membrane 4.

[0051] The cathode catalyst layer 32 is a catalyst layer disposed between the cathode gas diffusion layer 31 and the solid polymer electrolyte membrane 4. As expressed by the following formula (2), the cathode catalyst layer 32 converts protons (H ＋ ) and electrons (e － ) to produce hydrogen (H ２ ) is produced. ＋ +2e － →H２ ....(2)

[0052] The catalyst used in the cathode catalyst layer 32 is not particularly limited, and any known metal catalyst that has been conventionally used in this field can be appropriately adopted. Examples of such catalysts include platinum (Pt) and iridium oxide (IrO ２ Examples of suitable catalysts include catalysts made of various metal particles, such as cations, ...

[0053] The thickness of the cathode catalyst layer 32 is not particularly limited. ２ ) may be appropriately determined taking into consideration the reaction efficiency and reaction rate of the reaction.

[0054] The cathode gas diffusion layer 31 is a layer that converts hydrogen (H ２ ) is led to the outside via a monopolar plate or a bipolar plate, and unreacted water (H ２ The gas-liquid transport function is to discharge hydrogen (H O) from the monopolar or bipolar plate to the outside (see also the chemical formula in Figure 3). ２ ) is stored in, for example, a tank or the like (not shown).

[0055] The cathode gas diffusion layer 31 is not particularly limited, and may be any of various layer structures including a porous film of titanium, carbon, etc. Alternatively, the cathode gas diffusion layer 31 may be the same as the porous transport layer (metallic porous member) 10 provided in the anode 2.

[0056] The thickness of the cathode gas diffusion layer 31 is not particularly limited, but it is ２ O) and hydrogen (H ２ ) can be determined appropriately while taking into consideration the smooth passage of the

[0057] The power supply 5 has a positive electrode connected to the anode plate 20 and the anode 2 and a negative electrode connected to the cathode plate 30 and the cathode 3, thereby supplying a current for water electrolysis. The power supply 5 is not particularly limited, and any DC power supply obtained by known means, such as a power supply obtained by rectifying a commercial power supply or a battery power supply, or a power supply generated by renewable energy, can be used without any restrictions. Among these power supplies, it is preferable to use surplus power generated by renewable energy as the power supply 5, from the viewpoint that efficient generation and storage of hydrogen leads to effective utilization of surplus power.

[0058] The water used in the water electrolysis device 1 is not particularly limited, and in consideration of reaction efficiency and reaction rate, general pure water can be used in the PEM-type water electrolysis device 1 such as the example described in this embodiment.

[0059] According to the water electrolysis device 1, by being provided with the above configuration, hydrogen (H ２ In addition, according to the water electrolysis device 1, by employing the metal porous member of this embodiment, which will be described in detail later, as the porous transport layer 10 constituting the anode 2, oxygen and protons (H ＋ As the production efficiency of the hydrogen peroxide is increased, the resistance value of the entire device is reduced, thereby making it possible to improve the efficiency of water electrolysis.

[0060] <Metal Porous Member> The metal porous member and its manufacturing method of this embodiment will be described in detail below, mainly with reference to Figures 1 and 2 (also see the water electrolysis apparatus 1 shown in Figure 3 as appropriate). Figure 1 is a cross-sectional view that schematically illustrates the metal porous member 10 of this embodiment, and Figure 2 is a partial cross-sectional view that shows an enlarged view of a main part in Figure 1. The following description will also include an explanation of the effects of applying the metal porous member of this embodiment to the porous transport layer 10 of the water electrolysis apparatus 1 illustrated in Figure 3.

[0061] [Configuration of Metal Porous Member] The metal porous member 10 of this embodiment is generally configured as a multi-layer sintered body in which at least a first layer 11 and a second layer 12, each made of a metal porous body, are stacked.

[0062] The first layer 11 is a layer provided on the second layer 12, which will be described in detail later, and has an outermost surface 10a opposite to the second layer 12, which has specific surface properties. Therefore, the outermost surface 10a of the metal porous member 10 has the specific surface properties, which will be described in detail below. In the example shown in Figures 1 and 2, the metal porous member 10 is configured such that the first layer 11 and the second layer 12 have different porosities. That is, in the illustrated example, the proportion of pores 12b in the second layer 12 is greater than the proportion of pores 11b in the first layer 11.

[0063] Furthermore, when the metallic porous member of this embodiment is applied to the porous transport layer 10 in the water electrolysis apparatus 1 illustrated in FIG. 3 , the outermost surface 10 a is disposed on the anode catalyst layer 22 side with the coating layer 21 interposed therebetween, and the back surface 10 b, which is the exposed surface of the second layer 12, is disposed on the anode plate 20 side.

[0064] The first layer 11 is also called a microporous layer (MPL), and is a porous layer having a relatively small porosity and a thin and dense structure. As shown in Fig. 2, the first layer 11 is composed of metal particle portions 11a and pore portions 11b. Although not shown in detail, the pore portions 11b form a three-dimensionally connected network-like space.

[0065] The second layer 12 is also called MPS (Macro Porous Substrate), and is a porous layer having a relatively large porosity and a coarse structure that is thicker than the first layer 11. As shown in Fig. 2, the second layer 12 is composed of metal particle portions 12a and pore portions 12b, and although detailed illustration is omitted, the pore portions 12b form a three-dimensionally connected network-like space, similar to the pore portions 11b of the first layer 11.

[0066] The first layer 11 provided in the metal porous member 10 of this embodiment is composed of a sintered body of spherical metal powder having an average particle size of 45 μm or less. The first layer 11 has an arithmetic mean curvature (Spc) of peaks on the outermost surface 10a of 3.5 μm or less and a peak density (Spd) of 0.01 μm or less.２ ] or more.

[0067] The arithmetic mean curvature (Spc) [1 / μm] of the peaks described herein represents the average curvature, i.e., the average sharpness, of the main tip of the peaks on the outermost surface 10a of the first layer 11. The arithmetic mean curvature (Spc) of the peaks can be determined, for example, by observing the outermost surface 10a at 20x magnification using a laser microscope, measuring the surface roughness within a 500 μm × 500 μm field of view, selecting and measuring the curvature of peaks larger than a predetermined size, and then averaging the results obtained from several measurements. The smaller the arithmetic mean curvature (Spc) of the peaks, the more rounded the points of contact with adjacent members (e.g., the anode catalyst layer 22). On the other hand, the larger the arithmetic mean curvature (Spc) of the peaks, the more pointed the points of contact with adjacent members.

[0068] According to the metal porous member 10 of this embodiment, as described above, the arithmetic mean curvature (Spc) of the peaks on the outermost surface 10a of the first layer 11 is 3.5 [1 / μm] or less, so that the points of contact with adjacent members are rounded. As a result, by applying the metal porous member of this embodiment to the porous transport layer 10 provided on the anode 2 side of the water electrolysis device 1 illustrated in FIG. 3, aggressiveness to the anode catalyst layer 22 and the solid polymer electrolyte membrane 4 is suppressed, and oxygen and protons (H ＋ ) production efficiency is improved.

[0069] From the above viewpoint, the arithmetic mean curvature (Spc) of the peaks on the outermost surface 10a is more preferably 3.0 [1 / μm] or less. On the other hand, it is difficult from the viewpoint of industrial production to set the arithmetic mean curvature (Spc) of the peaks on the outermost surface 10a to 0.1 [1 / μm] or less, so this value is set as the lower limit.

[0070] Also, the peak density (Spd) [1 / μm ２

[0049] The peak density (Spd) is the number of peaks per unit area on the outermost surface 10a of the first layer 11. The peak density (Spd) can be determined, for example, by observing the outermost surface 10a at 20x magnification using a laser microscope, measuring the surface roughness within a 500 μm × 500 μm field of view, counting the peaks larger than a predetermined size, and dividing this count by the projected area of ​​the contour curved surface. A higher peak density (Spd) indicates a higher number of contact points with adjacent members (e.g., the anode catalyst layer 22).

[0071] According to the metal porous member 10 of this embodiment, as described above, the peak density (Spd) on the outermost surface 10a of the first layer 11 is 0.01 [1 / μm ２ ] or more, there are many contact points with adjacent members. As a result, by applying the metallic porous member of this embodiment to the porous transport layer 10 of the water electrolysis device 1, a large contact area with the anode catalyst layer 22 can be ensured, and as described above, oxygen and protons (H ＋ ) production efficiency is improved.

[0072] From the above viewpoint, the density of the peaks (Spd) on the outermost surface 10a is 0.02 [1 / μm ２ On the other hand, it is more preferable that the density of the peaks (Spd) on the outermost surface 10a is 0.3 [1 / μm ２ ] or more, the mesh of the outermost surface 10a becomes too fine, and the oxygen (O ２ ) and unreacted water (H ２ Therefore, it is preferable to set this value as the upper limit.

[0073] The first layer 11 in the metal porous member 10 of this embodiment is composed of a sintered body using spherical metal powder with an average particle size of 45 μm or less. In this way, by forming the metal porous member 10 into a multi-layer structure including at least the first layer 11 and the second layer 12 and using a spherical metal powder with a small average particle size sintered into the first layer 11, which is the outermost surface 10a side, the arithmetic mean curvature of the peaks (Spc) and the peak density (Spd), which are parameters of the outermost surface 10a, can be adjusted to the above-mentioned optimal ranges. That is, by applying the metal porous member of this embodiment to the porous transport layer 10 of the water electrolysis apparatus 1, the contact area between the porous transport layer 10 and the anode catalyst layer 22 can be secured while suppressing aggressiveness toward the anode catalyst layer 22, as described above. This allows for smooth exchange of water with generated oxygen while facilitating the transport of oxygen and protons (H ＋ ) production efficiency is improved.

[0074] From the above viewpoint, it is more preferable that the average particle size of the spherical metal powder used in the first layer 11 is 30 μm or less. On the other hand, if the average particle size of the spherical metal powder used in the first layer 11 is too small, the mesh of the outermost surface 10 a becomes too fine, as described above, and the oxygen (O ２ ) and unreacted water (H ２ Therefore, it is preferable to set the lower limit to 5 μm.

[0075] According to the metal porous member 10 of this embodiment, as described above, by adjusting each of the parameters of the surface properties of the outermost surface 10a of the first layer 11 to an optimum range, oxygen and protons (H ＋ As the production efficiency of the hydrogen peroxide is increased, the resistance value of the entire device is reduced, thereby making it possible to improve the efficiency of water electrolysis.

[0076] There are no particular limitations on the porosity of each of the first layer 11 and the second layer 12 constituting the metallic porous member 10 of this embodiment. On the other hand, when a metallic porous member is applied to the porous transport layer 10 of the water electrolysis apparatus 1 as shown in Fig. 3 , the porous transport layer 10 is required to ensure a sufficient contact area between the outermost surface 10a and the anode catalyst layer 22, and is also required to smoothly exchange water with generated oxygen.

[0077] In order to satisfy both of the above-mentioned conflicting characteristics, in the metal porous member 10 of this embodiment, it is preferable to adjust the manufacturing conditions described below so that the porosity of the first layer 11 is 5% or more and 30% or less, from the viewpoint of ensuring a contact area with the anode catalyst layer 22. If the porosity of the first layer 11 is 30% or less, it is possible to ensure a certain level of contact area with the anode catalyst layer 22 on the outermost surface 10a. Furthermore, by setting the porosity of the first layer 11 to 5% or more, oxygen (O ２ ) and unreacted water (H ２ From the above viewpoints, the porosity of the first layer 11 is more preferably 10% or more and 25% or less.

[0078] Furthermore, with regard to the second layer 12, from the viewpoint of ensuring permeability that allows smooth exchange between water and generated oxygen, it is preferable to adjust the manufacturing conditions described below so that the porosity is more than 30% and not more than 70%. If the porosity of the second layer 12 is more than 30%, the above-mentioned permeability can be sufficiently ensured. Furthermore, if the porosity of the second layer 12 is not more than 70%, the mechanical strength of the second layer 12 and the metal porous member 10 as a whole can be sufficiently ensured. Furthermore, from the above viewpoints, it is more preferable that the porosity of the second layer 12 is not less than 45% and not more than 60%.

[0079] The materials for the first layer 11 and the second layer 12 constituting the metal porous member 10 are not particularly limited, and may be sintered bodies using various metal powders. On the other hand, from the viewpoint of mechanical strength, corrosion resistance, etc., it is preferable that the material for each layer of the metal porous member 10 is a metal powder using one or more metals selected from the group consisting of titanium (Ti), nickel (Ni), stainless steel (SUS), and alloys thereof, and that the material be a sintered body of these metal powders.

[0080] When titanium powder is used as the metal powder for the first layer 11 and the second layer 12, it is preferable to use a metal powder having a titanium content of 97.0 mass % or more, more preferably 99.0 mass % or more, from the viewpoint of the mechanical strength, corrosion resistance, etc. In this case, the metal powder may contain small amounts of common impurities such as oxygen (O), nitrogen (N), carbon (C), silicon (Si), and iron (Fe) as inevitable impurities other than titanium.

[0081] Furthermore, when nickel powder is used as the metal powder used in the first layer 11 and the second layer 12, it is preferable to use a metal powder having a nickel content of 97.0 mass % or more, more preferably 99.0 mass % or more, from the viewpoints of mechanical strength, corrosion resistance, etc. In this case, the metal powder may contain small amounts of common impurities such as oxygen (O), aluminum (Al), iron (Fe), and silicon (Si) as inevitable impurities other than nickel.

[0082] The first layer 11 and the second layer 12 may be made of sintered bodies of metal powders of different materials, or may be made of metal powders of the same material.The first layer 11 and the second layer 12 may also be made of sintered bodies of the same spherical metal powder.

[0083] When the metallic porous member of this embodiment is applied to the porous transport layer 10 on the anode 2 side of a PEM-type water electrolysis device 1 as exemplified in Fig. 3, it is preferable to use a metallic sintered body made of titanium or titanium alloy powder. On the other hand, when the metallic porous member of this embodiment is applied to the porous transport layer on the anode side of an AEM-type water electrolysis device (not shown), it is preferable to use a metallic sintered body made of nickel or nickel alloy powder.

[0084] The porosity of the first layer 11 and the second layer 12 can be measured, for example, by the method described below. First, the cross sections of the first layer 11 and the second layer 12 are visually observed using a scanning electron microscope (SEM) or the like, and the areas of the pores 11b and 12b shown in Figure 1 or 2 are measured. Next, the measured areas of the pores 11b and 12b are each binarized to calculate the area ratio of the pores 11b in the first layer 11 and the area ratio of the pores 12b in the second layer 12. The measurement of the areas of the pores 11b and 12b and the calculation of the area ratios are then performed at several points in each of the first layer 11 and the second layer 12, and the average value can be used as the porosity.

[0085] The thickness of the first layer 11 constituting the metal porous member 10 is not particularly limited either, and can be determined taking into consideration, as described above, ensuring the contact area between the porous transport layer 10 and the anode catalyst layer 22 while suppressing the anode catalyst layer 22. From this perspective, the thickness of the first layer 11 of the metal porous member 10 is preferably 10 μm or more and 100 μm or less, and more preferably 30 μm or more and 80 μm or less.

[0086] The thickness of the second layer 12 is not particularly limited and can be determined as appropriate so as to enable smooth exchange of water with the generated oxygen, as described above. From the above-mentioned viewpoint, the thickness of the metal porous member 10 as a whole, which is the sum of the first layer 11 and the second layer 12, is preferably 100 μm or more and 500 μm or less, and more preferably 200 μm or more and 400 μm or less.

[0087] The second layer 12 is preferably made of a sintered body using a spherical metal powder or an irregularly shaped metal powder having an average particle size of 30 μm or more and 100 μm or less. In the metal porous member 10 of this embodiment, the second layer 12 is required to promote the exchange of water with the generated oxygen, and therefore, a relatively large porosity must be ensured. Thus, from the viewpoint of adjusting the porosity to a certain level or higher, the second layer 12 is preferably a sintered body using a spherical metal powder or an irregularly shaped metal powder having an average particle size equal to or greater than the lower limit of the above range. Furthermore, from the viewpoint of facilitating adjustment to increase the porosity, it is more preferable that the second layer 12 be made of a sintered body of an irregularly shaped metal powder.

[0088] If the average particle size of the spherical metal powder or irregular shaped metal powder used in the second layer 12 is too large, the porosity becomes too large, which raises concerns about ensuring mechanical strength, so the upper limit of the average particle size is preferably 100 (μm). If the average particle size of the spherical metal powder or irregular shaped metal powder used in the second layer 12 is too small, there is a concern that the exchange of water with the generated oxygen may become difficult, so the lower limit of the average particle size is preferably 30 (μm).

[0089] Furthermore, when the metal powder used in the second layer 12 is spherical, the above average particle size is the diameter of the spherical metal powder. On the other hand, when the metal powder used in the second layer 12 is irregularly shaped, the average particle size can be, for example, the diameter converted into the diameter of a spherical metal powder that exhibits physical properties equivalent to those of the irregularly shaped metal powder.

[0090] The average particle size of the spherical metal powder described in this specification can be determined from the results of measuring particle size and calculating particle size distribution using, for example, a commercially available laser diffraction / scattering particle size distribution measuring device using Mie scattering theory. Furthermore, the average particle size of the irregularly shaped metal powder described in this specification can also be determined by first measuring particle size and calculating particle size distribution using the same device as for the spherical metal powder, and then converting the determined average particle size into the diameter of a spherical metal powder exhibiting physical properties equivalent to those of the spherical metal powder described above, and applying this to the average particle size of the irregularly shaped metal powder.

[0091] When a multilayer structure using metal powders with different shapes and dimensions is employed in the first layer 11 and the second layer 12 of the metal porous member 10, each of the parameters of the surface properties of the outermost surface 10a can be controlled while maintaining a high overall porosity. That is, by forming the first layer 11 into a sintered body using spherical metal powder, the outermost surface 10a can have a smooth and dense structure, while the second layer 12 can have a structure that maintains an appropriate porosity.

[0092] As described above, in the metal porous member 10 of this embodiment, the first layer 11 has a thin, dense structure in which cornerless spherical metal powder is sintered, thereby increasing the arithmetic mean curvature (Spc) of the peaks on the outermost surface 10 a while increasing the peak density (Spd). This makes it possible to ensure a sufficient contact area while suppressing the aggressiveness of the outermost surface 10 a to the adjacent member (anode catalyst layer).

[0093] For example, if a spherical metal powder consisting of very fine particles is used for the metal porous member, aggressiveness toward the adjacent outermost surface member (anode catalyst layer) can be suppressed. However, small-sized spherical metal powders tend to form a dense structure after sintering, which may result in a sluggish exchange of liquid and gas. For this reason, this embodiment employs a multilayer structure including at least a first layer 11 and a second layer 12. The first layer 11 is configured to optimize each of the surface property parameters of the outermost surface 10a, and the second layer 12 is configured as a layer with a predetermined porosity. This makes it possible to suppress aggressiveness toward the adjacent surface member (anode catalyst layer 22), ensure contact area, and allow liquid and gas to pass through.

[0094] The water electrolysis device 1 can be operated with a single cell as shown in FIG. 3, but it may be necessary to increase the size for commercialization. ２Taking into consideration the production efficiency of the electrolyte membrane, a cell stack structure in which a plurality of unit cells are stacked can be adopted. On the other hand, whether the water electrolysis device 1 is a unit cell as illustrated in FIG. 3 or a cell stack, high pressure due to sandwiching between layers and an increase in internal pressure due to generated gas may occur. For this reason, for example, if the outermost surface of the porous transport layer is uneven or if the pores on the outermost surface are large, part of the porous transport layer may bite into the anode catalyst layer or the electrolyte membrane, causing damage to the anode catalyst layer.

[0095] In contrast, in the metal porous member of the present embodiment, the parameters of the surface properties of the outermost surface 10 a are optimized to form a relatively smooth surface, and therefore, even when the cell stack described above is constructed, it is possible to prevent the first layer 11 from biting into the anode catalyst layer 22 or the solid polymer electrolyte membrane 4. Furthermore, because the first layer 11 is a dense layer made of spherical metal powder, deformation due to the sandwiching pressure between the layers constituting the water electrolysis device 1 is also suppressed.

[0096] [Method for manufacturing a metal porous member] Hereinafter, a method for manufacturing a metal porous member of this embodiment will be described using as an example a method for manufacturing the metal porous member 10 of this embodiment shown in Figs. 1 and 2 .

[0097] The manufacturing method of the metal porous member 10 of this embodiment is a method for obtaining a sintered body in which at least a first layer 11 and a second layer 12, each made of a metal porous body, are laminated. The method includes the following "first layer forming step" and "second layer laminating step" in this order. (1) First Layer Forming Step: After scattering spherical metal powder in the form of a film on the smooth surface of a first jig (not shown), the film-like spherical metal powder is sintered in a vacuum or inert gas atmosphere at a temperature of 700°C to 1200°C to form the first layer 11. (2) Second Layer Laminating Step: In a vacuum or inert gas atmosphere, spherical metal powder or irregularly shaped metal powder is sintered in a temperature of 700°C to 1200°C to form the second layer 12 so as to overlap the first layer 11. This results in a laminate in which the first layer 11 and the second layer 12 are bonded together, thereby obtaining the metal porous member 10.

[0098] In this embodiment, a method further including the following "rolling step" after the above-mentioned "second layer lamination step" will be described as an example. (3) Rolling step The laminate in which the first layer and the second layer are bonded is rolled by sandwiching the first layer and the second layer from both sides between a pair of rolling rolls.

[0099] (First Layer Formation Step) In the first layer formation step, spherical metal powder is first spread in the form of a film on the smooth surface of a first jig (not shown). In the first layer formation step, a flat film-forming jig with a smooth surface can be used as the first jig. In addition, in the first layer formation step, metal powder containing any one or more of the above-mentioned metals selected from the group consisting of titanium, nickel, stainless steel, and alloys thereof can be used as the spherical metal powder for forming the first layer 11.

[0100] In the first layer forming step, the spherical metal powder is scattered on the smooth surface of the first jig so as to form a layer with a generally uniform thickness.

[0101] Next, the first jig with the spherical metal powder dispersed in a film form on its smooth surface is introduced into a sintering furnace (not shown), and the furnace is conditioned to a vacuum or inert gas atmosphere. When the sintering furnace is conditioned to an inert gas atmosphere, argon can be used as the inert gas, taking into account availability, cost, and other factors. The spherical metal powder film formed on the first jig is then sintered at a temperature of 700°C or higher and 1200°C or lower. The sintering time (heating time) is not particularly limited, but can be, for example, approximately 15 to 180 minutes. Thereafter, the first layer 11 is peeled off from the smooth surface of the first jig as needed. The first layer 11 can be formed by the first layer formation process described above.

[0102] (Second Layer Lamination Step) In the second layer lamination step, as described above, spherical metal powder or irregular shaped metal powder is sintered at a temperature of 700° C. or higher and 1200° C. or lower in a vacuum atmosphere or an inert gas atmosphere to form the second layer 12 so as to be superimposed on the first layer 11. The second layer lamination step in this embodiment can be performed by two methods, a "first method" and a "second method" as shown below, and each method will be described in turn.

[0103] First, a first method that can be employed as the second layer lamination step will be described below. In the first method, a spherical metal powder or irregularly shaped metal powder to be used for the second layer 12 is first spread on the smooth surface of a second jig (not shown) in the same manner as in the first layer formation step so as to achieve a generally uniform film thickness. In this case, the same second jig as the first jig can be used. Furthermore, the spherical metal powder or irregularly shaped metal powder for forming the second layer 12 can be a metal powder containing one or more of the above-mentioned metals selected from the group consisting of titanium, nickel, stainless steel, and alloys thereof.

[0104] Next, the first layer 11 sintered and formed in the first layer forming step is superimposed on the film-like spherical metal powder or irregularly shaped metal powder scattered on the smooth surface of the second jig, and in this state, the second jig is introduced into a sintering furnace (not shown). At this time, a weight jig (not shown) made of the same material as the first jig may be superimposed on the first layer 11 side to press the first layer 11 and the film-like spherical metal powder or irregularly shaped metal powder.

[0105] The spherical metal powder or irregular shaped metal powder formed into a film on the second jig is then sintered at a temperature of 700°C or higher and 1200°C or lower to form the second layer 12, thereby obtaining a laminate of the first layer 11 and the second layer 12. The sintering time (heating time) is not particularly limited, but can be, for example, about 15 to 180 minutes. The atmosphere in the sintering furnace can also be the same as that in the first layer formation step.

[0106] Next, a second method that can be employed as the second layer lamination step will be described below. In the second method, a spherical metal powder or irregularly shaped metal powder to be used for the second layer 12 is first scattered in the form of a film on the first layer 11 that has been sintered and formed in the first layer formation step. At this time, the spherical metal powder or irregularly shaped metal powder is scattered in the same manner as in the first method so that the film thickness of the spherical metal powder or irregularly shaped metal powder is roughly uniform.

[0107] Next, with the spherical metal powder or irregular-shaped metal powder dispersed in a film on the first layer 11, the first jig is introduced into a sintering furnace (not shown). At this time, a weight jig (not shown) made of the same material as the first and second jigs may be placed on top of the film of spherical metal powder or irregular-shaped metal powder to pressurize the film of spherical metal powder or irregular-shaped metal powder and the first layer 11. The film of spherical metal powder or irregular-shaped metal powder on the first layer 11 is then sintered at a temperature of 700°C to 1200°C to form the second layer 12, thereby obtaining a laminate of the first layer 11 and the second layer 12. The sintering time (heating time) is not particularly limited, but may be, for example, approximately 15 to 180 minutes. The atmosphere in the sintering furnace may be the same as that in the first method.

[0108] In the second layer lamination step, the metal porous member 10 consisting of a laminate in which the first layer 11 and the second layer 12 are bonded together is obtained by the first method or the second method described above.

[0109] (Rolling step) Next, in the rolling step, the laminate in which the first layer 11 and the second layer 12 are bonded together is peeled off from the first jig or the second jig, and then the first layer 11 and the second layer 12 are sandwiched from both sides and rolled by a pair of rolling rolls (not shown).

[0110] When a rolling step is provided in the manufacturing method of this embodiment, the roll pressure and the rolling allowance in the thickness direction have a significant effect not only on the thickness of the metal porous member 10 but also on the porosity. Therefore, by adjusting the above-mentioned conditions in the rolling step, it is possible to adjust the porosity of the first layer 11 and the second layer 12 to desired values, in addition to the thickness of the metal porous member 10. Furthermore, by performing the rolling step, the effect of further reducing the unevenness of the outermost surface 10a can be obtained.

[0111] According to the manufacturing method of the metal porous member 10 of this embodiment, as described above, excellent dispersibility is achieved by using spherical metal powder for the first layer 11. This makes it possible to form the first layer 11 consisting of a thin layer only by dispersing and sintering, without requiring special processes such as binder sintering or spray coating.

[0112] In addition, the spherical metal powder and irregularly shaped metal powder used in the manufacturing method of the metal porous member 10 of this embodiment can be obtained relatively easily and inexpensively in the desired particle size, which also contributes to reducing manufacturing costs.

[0113] Furthermore, by manufacturing the metal porous member 10 by sintering metal powder, complex flow paths are formed within the layer, and a metal porous member 10 is obtained that has sufficient permeability to allow smooth exchange between liquid and gas while also having sufficient mechanical strength.

[0114] <Effects> As described above, according to the metal porous member of this embodiment, the first layer 11 is made of a sintered body using spherical metal powder having an average particle size equal to or less than a predetermined value, and the arithmetic mean curvature (Spc) of the peaks and the peak density (Spd) of the outermost surface 10a are set within optimal ranges. This makes it possible to ensure a large contact area while suppressing aggressiveness toward adjacent members. For example, by applying this to the porous transport layer 10 on the anode 2 side of the water electrolysis device 1, it is possible to smoothly exchange water with generated oxygen while promoting the transport of oxygen and protons (H ＋ As the production efficiency of the hydrogen peroxide is increased, the resistance value of the entire device is reduced, thereby making it possible to improve the efficiency of water electrolysis.

[0115] Furthermore, the manufacturing method of the metal porous member of this embodiment employs a first layer forming step in which a spherical metal powder having an average particle size not greater than a predetermined value is sprayed onto the smooth surface of a first jig in the form of a film, and then sintered under predetermined conditions to form the first layer 11, and a second layer laminating step in which the second layer 12 is formed so as to overlap the first layer 11. As described above, the use of spherical metal powder for the first layer 11 provides excellent sprayability, making it possible to form the first layer 11 consisting of a thin layer by spraying and sintering alone, without additional processes such as spray coating, binder mixing, or burn-off treatment. Furthermore, by employing the above method, the arithmetic mean curvature (Spc) and peak density (Spd) of the outermost surface 10a of the first layer 11 can be controlled within optimal ranges, thereby obtaining a metal porous member that can ensure a large contact area while suppressing aggressiveness toward adjacent members. That is, when the obtained metal porous member is applied to, for example, the porous transport layer 10 on the anode 2 side of the water electrolysis device 1, the oxygen and protons (H ＋ As the production efficiency of the water electrolysis catalyst 1 is improved, the resistance value of the entire apparatus is reduced, thereby realizing a water electrolysis apparatus 1 with improved water electrolysis efficiency. Therefore, a metal porous member suitable for the water electrolysis apparatus 1 can be produced with good productivity through a simple process.

[0116] <Modifications of the present invention> Although the embodiments of the present invention have been described in detail above, the metal porous member and the method for manufacturing a metal porous member of the present invention are not limited to the above embodiments, and various changes and modifications can be made without departing from the principles of the present invention and the scope of the appended claims.

[0117] For example, in the above embodiment, an example is given in which the metal porous member (porous transport layer) is composed of two layers, the first layer 11 and the second layer 12, but this is not limiting and a laminated structure consisting of three or more layers can also be adopted. In such a case, after the first layer 11 is disposed on the outermost surface 10a, further layers such as functional layers having other additional functions or adhesive layers can be provided on the back surface 10b or between the first layer 11 and the second layer 12.

[0118] Furthermore, in the metal porous member 10 according to the present invention, even when the first layer 11 is formed by sintering only spherical metal powder using the above-described manufacturing method, irregularly shaped metal powder other than the spherical metal powder may inevitably be mixed in during industrial production. This may be due to, for example, irregularly shaped metal powder adhering to production equipment or the like being mixed in, or the spherical metal powder being deformed during the process to become irregularly shaped metal powder that is mixed in with the spherical metal powder.

[0119] Furthermore, for example, when a first layer 11 is formed by sintering spherical metal powder, and then a second layer 12 is formed so as to be superimposed on the first layer 11, some of the small irregular-shaped metal powder particles used to form the second layer 12 may enter the voids 12b in the first layer 11. In such a case, the first layer 11 will contain a small amount of irregular-shaped metal powder.

[0120] In the metal porous member 10 of the present invention, even if the first layer 11 is mainly composed of spherical metal powder but also contains a small amount of irregularly shaped metal powder, the arithmetic mean curvature (Spc) of the peaks and the density (Spd) of the peaks on the outermost surface 10a are within the above-mentioned ranges, so that the effect of ensuring a large contact area while suppressing aggressiveness toward adjacent members can be sufficiently obtained.

[0121] Similarly, even when the second layer 12 is formed by sintering only irregular metal powder, there is a possibility that spherical metal powder will inevitably be mixed in due to the contamination with spherical metal powder adhering to production equipment, etc. Conversely, there is also a possibility that irregular metal powder will be mixed in when spherical metal powder is used for the second layer 12.

[0122] In the metal porous member 10 according to the present invention, even if the second layer 12 contains a mixture of irregularly shaped metal powder and spherical metal powder, the above-mentioned predetermined porosity ensures permeability for liquids and gases. This, combined with the optimization of the arithmetic mean peak curvature (Spc) and peak density (Spd) in the first layer 11, makes it possible to simultaneously suppress attack on the anode catalyst layer 22 and the solid polymer electrolyte membrane 4, ensure a sufficient contact area, and ensure permeability for liquids and gases.

[0123] Therefore, the metal porous member 10 of the present invention includes all of the above-mentioned modified configurations, such as a configuration in which the first layer 11 is mainly composed of spherical metal powder but also contains a small amount of irregularly shaped metal powder, and a configuration in which the second layer 12 is a mixture of irregularly shaped metal powder and spherical metal powder.

[0124] Below, examples of the metal porous member of the present invention will be shown to explain the present invention more specifically, but the configuration of the metal porous member of the present invention is not limited by the specifications and conditions described in the following examples.

[0125] In this example, a sample of a metal porous member having a two-layer structure as shown in FIGS. 1 and 2 was prepared, and evaluated by measuring the arithmetic mean curvature (Spc) and density (Spd) of the peaks on the outermost surface, the porosity of the first layer and the second layer, and the electrical conductivity.

[0126] [1] Sample preparation method and conditions In this example, a first layer (see reference numeral 11 in Figures 1 and 2) was formed using a metal powder having the external shape shown in Table 1 below, and a second layer (reference numeral 12) was formed on the surface opposite to the outermost surface (reference numeral 10a) of the first layer, thereby preparing samples of the metal porous members of Examples 1 to 5 and Comparative Examples 1 to 4.

[0127] Of these, the spherical metal powder (spherical / spherical) used in the first layer had an average particle size of 45 μm or less and contained 99.0% by mass or more of titanium (Examples 1 to 5). The irregularly shaped metal powder used in the first layer had a diameter of 45 μm or less, converted to the diameter of a spherical metal powder exhibiting physical properties equivalent to those of the irregularly shaped metal powder, and contained 99.0% by mass or more of titanium (Comparative Examples 2 and 3). The irregularly shaped metal powder used in the second layer had a diameter of 100 μm or less, converted to the diameter of a spherical metal powder exhibiting similar physical properties, and contained 99.0% by mass or more of titanium. The average particle size of the spherical metal powder in this example was determined from the results of particle size measurements and particle size distribution calculations using a commercially available laser diffraction / scattering particle size distribution analyzer (manufactured by Horiba, Ltd., model number: Partica LA-960S2). In addition, for the average particle size of the irregularly shaped metal powder in this example, the particle size was first measured and the particle size distribution calculated using the same equipment as for the spherical metal powder, and the average particle size determined in this way was then converted into the diameter of a spherical metal powder exhibiting physical properties equivalent to those of the spherical metal powder and applied to the average particle size of the irregularly shaped metal powder.

[0128] In this example, the metal powders were first dispersed on the smooth surface of a first jig and sintered to form a first layer, which was then peeled off from the first jig (first layer formation process). Next, the irregularly shaped metal powder was uniformly dispersed on the smooth surface of a second jig in a film form, and the first layer was then superimposed on the film and sintered to produce a laminate (second layer lamination process). In both the first layer formation process and the second layer lamination process, sintering was performed using a commercially available sintering furnace and the manufacturing method described herein.

[0129] Then, using a commercially available rolling mill equipped with a pair of rolling rolls, the laminate obtained by the sintering process in the above step was sandwiched between the rolling rolls from above and below and rolled to smooth out any irregularities on both sides and adjust the overall thickness to about 200 to 300 μm (rolling step). At this time, the roll pressure and the rolling allowance in the thickness direction were adjusted so that the thickness of the metal porous member after the rolling process would be within the above range.

[0130]

[0131] According to the above procedures and conditions, the metal porous members of Examples 1 to 5 and Comparative Examples 1 to 4 were produced.

[0132] [2] Evaluation method and evaluation conditions In this example, the metal porous members of Examples 1 to 5 and Comparative Examples 1 to 4 obtained by the above procedure were evaluated as described below, and the results are shown in Table 1.

[0133] (1) Evaluation of arithmetic mean curvature (Spc) of peaks For each of the metal porous members of the Examples and Comparative Examples, the outermost surface of the first layer was observed at 20x magnification using a laser microscope, and the surface roughness was measured within a field of view of 500 μm × 500 μm. In this case, the curvature of peaks larger than a predetermined size was selected and measured, and this was repeated for several points to calculate the average value, which was evaluated as the arithmetic mean curvature (Spc) of peaks [1 / μm].

[0134] (2) Evaluation of Peak Density (Spd) For the metal porous members of each Example and Comparative Example, the outermost surface of the first layer was observed at 20x magnification using a laser microscope, and the surface roughness was measured within a field of view of 500 μm × 500 μm. In this case, peaks larger than a predetermined size were counted, and this count was divided by the projected area of ​​the contour curved surface to obtain the peak density (Spd) [1 / μm ２ ] was evaluated.

[0135] (3) Evaluation of the porosity of the first layer and the second layer For the metal porous members of each example and comparative example, the cross section was observed using a scanning electron microscope (SEM), and the area of ​​the pores in both the first layer and the second layer was measured. The measured areas of the pores in the first layer and the second layer were then binarized, and the area ratio of the pores in the first layer and the area ratio of the pores in the second layer were calculated. The measurement of the area of ​​the pores and the calculation of the area ratio were carried out at several points in each of the first layer and the second layer, and the average value was evaluated as the porosity.

[0136] (4) Evaluation of Electrical Conductivity (Conductivity) Each of the metal porous members of the Examples and Comparative Examples was used as a porous transport layer to fabricate a water electrolysis device, which is an electrochemical cell as shown in FIG. 3 . The electrical conductivity (conductivity) of each sample was evaluated by measuring the current density when a voltage was applied using this water electrolysis device.

[0137] In the present examples and comparative examples, a water electrolysis device 1 was fabricated in which both ends of a layer structure were sandwiched between an anode plate 20 and a cathode plate 30 configured as monopolar plates, and these layers were fixed together with bolts (not shown). In this case, the metal porous member of each example and comparative example was used as the porous transport layer 10 on the anode 2 side, and iridium oxide (IrO ２ The cathode gas diffusion layer 31 on the cathode 3 side was made of carbon fiber, and the cathode catalyst layer 32 was made of platinum (Pt) or iridium oxide (IrO ２ ) was used. In this example, as shown in FIG. 3 , a thin film made of Pt was formed by sputtering on the outermost surface 10 a of the porous transport layer 10. Furthermore, Nafion (registered trademark), which is readily available commercially, was used as the solid polymer electrolyte membrane 4 disposed between the anode catalyst layer 22 and the cathode catalyst layer 32 to fabricate the PEM-type water electrolysis device 1. Note that, although the PEM-type water electrolysis device 1 was fabricated and the evaluation test was performed in this example, it is also possible to configure the above-mentioned alkaline or AEM-type water electrolysis device and perform the evaluation test using the metal porous member of each sample as the porous transport layer.

[0138] In the present example and comparative example, the water electrolysis device 1 was used as a single cell, and the power source 5 was connected to the anode plate 20 and the cathode plate 30 to apply a voltage of 2.0 V, and the current density was measured to evaluate the conductivity. In Table 1, the current density in the sample of Example 1 was used as the reference, and each conductivity is shown as a ratio when Example 1 was set to "1". This conductivity is an index of the electrical characteristics of the cell, and is used to measure the amount of oxygen and protons (H ＋ This is an index that can be used to evaluate the production efficiency of CO₂, and ultimately the water electrolysis efficiency of the entire device.

[0139] [3] Test Results As shown in Table 1, in Examples 1 to 5, all of the samples in which the shape and average particle size of the metal powder constituting the first layer, the arithmetic mean curvature of the peaks (Spc) and the peak density (Spd) on the outermost surface were within the ranges specified in the present invention had electrical conductivities of 1 or more, and were confirmed to have excellent electrical properties. This confirmed that the water electrolysis devices 1 of Examples 1 to 5 had excellent electrochemical properties for oxygen and protons (H ＋ It was confirmed that the samples of Examples 1 to 5 had excellent water electrolysis efficiency, resulting in excellent water electrolysis efficiency. This is thought to be because the surface properties of the outermost surface 10a of the porous transport layer 10 were optimized in the samples of Examples 1 to 5, which reduced the anode catalyst layer 22 and the solid polymer electrolyte membrane 4 from being aggressive, and also ensured a contact area with the anode catalyst layer 22.

[0140] In contrast, in Comparative Example 1, the arithmetic mean curvature (Spc) of the peaks was large and did not satisfy the range specified in the present invention, and therefore, in a water electrolysis device in which each layer was stacked under high pressure, damage occurred to the anode catalyst layer, and the electrical conductivity was 0.92, which was inferior to those of Examples 1 to 5. Furthermore, in Comparative Example 2, an example in which an irregularly shaped metal powder was used in the first layer, the arithmetic mean curvature (Spc) of the peaks was extremely large, which led to damage to the anode catalyst layer, making it impossible to measure the current density and evaluate the electrical conductivity.

[0141] Comparative Example 3 is also an example in which an irregularly shaped metal powder is used in the first layer, but the peak density (Spd) is low and does not satisfy the range specified by the present invention, resulting in an insufficient contact area between the porous transport layer and the anode catalyst layer 22, and a conductivity of 0.82, which is inferior to Examples 1 to 5. Also, in Comparative Example 4, like Comparative Example 3, the peak density (Spd) is high and does not satisfy the range specified by the present invention, resulting in an insufficient contact area between the porous transport layer and the anode catalyst layer 22, and a conductivity of 0.88, which is inferior to Examples 1 to 5.

[0142] From the results of the present example and the comparative example as described above, it can be seen that by applying the metal porous member according to the present invention to the porous transport layer used on the anode side of the water electrolysis device, oxygen and protons (H ＋ It has become clear that this can increase the production efficiency of HCl, and consequently significantly increase the water electrolysis efficiency of the entire device.

[0143] The metal porous member of the present invention has a smooth outermost surface that is less aggressive to the catalyst layer, while ensuring a large contact area with the outermost surface of the catalyst layer and allowing smooth exchange of water with the generated oxygen, thereby increasing the efficiency of oxygen and proton production. Therefore, the metal porous member of the present invention is very suitable for applications such as converting surplus electricity generated from renewable energy into hydrogen and efficiently storing the hydrogen.

[0144] DESCRIPTION OF SYMBOLS 10...Metal porous member (porous transport layer) 10a...Outermost surface 10b...Back surface 11...First layer 11a...Metal particle portion 11b...Porous portion 12...Second layer 12a...Metal particle portion 12b...Porous portion 1...Water electrolysis device 20...Anode plate 2...Anode 10...Porous transport layer (metal porous member) 21...Coating layer 22...Anode catalyst layer 30...Cathode plate 3...Cathode 31...Cathode gas diffusion layer 32...Cathode catalyst layer 4...Solid polymer electrolyte membrane 5...Power source

Claims

1. A laminate comprising at least a first layer and a second layer each made of a metal porous body, wherein the first layer is made of a sintered body using spherical metal powder having an average particle size of 45 μm or less, and the outermost surface opposite to the second layer has an arithmetic mean curvature of peaks (Spc) of 3.5 μm or less and a peak density (Spd) of 0.01 μm or less. ２ ] or more.

2. The metal porous member according to claim 1, characterized in that the second layer is made of a sintered body using spherical metal powder or irregularly shaped metal powder having an average particle size of 30 μm or more and 100 μm or less.

3. A metal porous member according to claim 1 or 2, characterized in that the porosity of the first layer is 5% or more and 30% or less.

4. A metal porous member according to claim 1 or 2, characterized in that the porosity of the second layer is more than 30% and not more than 70%.

5. A metal porous member according to claim 1 or 2, characterized in that the thickness of the first layer is 10 μm or more and 100 μm or less.

6. A metal porous member according to claim 1 or 2, characterized in that the total thickness of the first layer and the second layer is 100 μm or more and 500 μm or less.

7. A metal porous member as described in claim 1 or claim 2, characterized in that the first layer and the second layer are made of a sintered body of metal powder using any one or more selected from the group consisting of titanium, nickel, stainless steel, and alloys thereof.

8. A method for manufacturing a metal porous member, which produces a sintered body comprising at least a first layer and a second layer, each of which is made of a metal porous body, comprising: a first layer forming step of scattering spherical metal powder having an average particle size of 45 μm or less in the form of a film on the smooth surface of a first jig, and then sintering the film of the spherical metal powder at a temperature of 700°C or higher and 1200°C or lower in a vacuum or inert gas atmosphere to form the first layer; and a second layer laminating step of sintering spherical metal powder or irregular shaped metal powder at a temperature of 700°C or higher and 1200°C or lower in a vacuum or inert gas atmosphere to form the second layer so as to overlap the first layer, thereby producing a laminate in which the first layer and the second layer are bonded together.

9. The method for manufacturing a metal porous member described in claim 8, characterized in that the second layer lamination process involves scattering the spherical metal powder or the irregularly shaped metal powder in the form of a film on the smooth surface of a second jig, and then superimposing the first layer sintered in the first layer formation process on top of it, and sintering the film-like spherical metal powder or the irregularly shaped metal powder to form the second layer, thereby obtaining a laminate in which the first layer and the second layer are bonded together.

10. A method for manufacturing a metal porous member as described in claim 8, characterized in that the second layer lamination process involves scattering the spherical metal powder or the irregularly shaped metal powder in the form of a film on the first layer sintered in the first layer formation process, and then sintering the film-like spherical metal powder or the irregularly shaped metal powder to form the second layer, thereby obtaining a laminate in which the first layer and the second layer are bonded together.

11. A method for manufacturing a metal porous member as described in claim 8, further comprising a rolling step, after the second layer lamination step, of rolling the laminate in which the first layer and the second layer are bonded together by sandwiching the first layer and the second layer from both sides using a pair of rolling rolls.

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