JP7230640B2 - POROUS ELECTRODE AND WATER ELECTROLYSIS CELL INCLUDING THE SAME - Google Patents

Description

TECHNICAL FIELD The present invention relates to a porous electrode suitable for an electrode for an electrolytic device and a water electrolysis cell having the same.

Currently, with the keyword of achieving a CO2 _- free society, there is an accelerating movement toward realizing a society that uses hydrogen as a major energy source. In this trend, hydrogen is expected to run short in the near future, and the development of technologies and materials for efficiently producing hydrogen is underway.
At present, a method of electrolyzing water with a water electrolyzer using renewable energy (RE) is considered promising as a method for producing hydrogen.
There are several types of water electrolyzers, such as solid oxide water electrolyzers (SOEC) and alkaline water electrolyzers (PAWEM), but they have particularly good electrolysis efficiency and are capable of producing high-purity hydrogen. A solid polymer type (PEM type) water electrolysis device is attracting attention.

A problem with the PEM type water electrolyzer lies in the anode electrode, and the anode electrode of the PEM type water electrolyzer is usually made of a porous material. Inside the anode electrode, the raw material water and oxygen gas generated after electrolysis are in a mixed state. There is a problem that the raw material water is not supplied to the reaction surface of , resulting in a decrease in electrolysis efficiency.
Therefore, it is necessary to optimize the structure of the anode electrode for water electrolysis in the PEM type water electrolyzer to improve the electrolysis efficiency.

At present, many anode electrodes are substituted with electrodes of a polymer electrolyte fuel cell (PEFC), which corresponds to the reverse reaction of water electrolysis.
On the oxygen electrode side of the PEFC, a reverse reaction to water electrolysis, that is, a reaction in which oxygen and hydrogen react to produce water is taking place.
The roles required of PEFC electrodes are to smoothly transport oxygen gas, the raw material, to the reaction surface, and to quickly discharge the water produced so as not to interfere with the movement of the oxygen gas, the raw material.

Conventionally, a flat plate-shaped porous metal body with a three-dimensional network structure has been used as an electrode so that water can be discharged efficiently, and the electrode performance is evaluated using low pressure loss as a physical quantity as an index. (See Patent Document 1).
Patent Document 1 discloses a plate-shaped porous metal body having a three-dimensional network structure containing Ni, a Ni content of 50% by mass or more, a thickness of 0.10 mm or more and 0.5 mm or less, and pores Electrodes for fuel cells are disclosed which consist of thin metallic porous bodies with a modulus of 55-85%.

Furthermore, techniques have been disclosed in which the electrode structure is improved in order to improve the dischargeability of liquid from the electrodes (see Patent Documents 2 and 3).
Patent Document 2 discloses a metal porous plate in which a plurality of polyhedral voids having sides formed by a skeleton of a sintered metal body are continuously formed to form a continuous polyhedral void, and has a porosity of 50% or more. , 98% or less metal porous plates are described.
In Patent Document 3, a porous metal laminate is formed by continuously forming a plurality of polyhedral voids whose sides are composed of a skeleton of a metal sintered body, and a porous layer and an adjacent layer are laminated and laser-processed. A technique of melting and solidifying to form a fused bonding layer is described.

In addition, as an electrode for the anode of a water electrolysis device, a structure is provided in which the pressure loss of water up to the water reaction part is reduced by developing the technical concept of the electrode structure of PEFC, and water is easily supplied to the water electrolysis reaction part. (See Patent Documents 4 and 5).
In Patent Document 4, a channel layer forming a first channel, an intermediate layer having pores from the channel layer, and an anode-side power feeder having a membrane support layer having pores from the intermediate layer are arranged on the anode side. A configuration integrated into the separator is described.
Patent Document 5 discloses a power feeder that constitutes an electrolysis cell in a water electrolysis device and is used in pressure contact with a solid electrolyte, wherein expanded metal is laminated to have a porosity of 50 to 95%, and a compressive elastic modulus of 5 to 50 MPa. is disclosed.

JP 2017-33917 A JP 2010-77490 A JP 2011-106023 A JP-A-2010-53401 JP-A-2001-279479

What is required of the anode electrode in the PEM-type water electrolysis apparatus described above is the function of retaining liquid water on the reaction surface for a longer period of time and the ability to quickly discharge the gas generated by the reaction. That is, in the anode electrode, a structure is required in which pressure loss of oxygen gas is low and pressure loss of liquid water is high.

However, the configuration described in Patent Document 1 is a technology for electrodes for fuel cells, and is a technology that can provide a porous body with a small pressure loss that allows both liquid and gas to escape well. There is a problem that the technical idea of keeping it for a long time is not seen.
The technique described in Patent Document 2 is a structure in which a plurality of metal porous bodies are laminated, and regions with different porosities can coexist in the plane of the electrode, and the porosity in the plane direction can be varied. Since the pore size cannot be varied, there is a problem that a structure that retains liquid for a long time and discharges gas quickly cannot be applied.

The technique described in Patent Document 3 makes it possible to manufacture an electrode having a plurality of layers with different pore sizes and porosities by laminating a plurality of porous bodies with different porosities and pore sizes and cutting them by laser fusion. However, although this technique can vary the pore diameter and porosity in the direction perpendicular to the plane, it cannot vary the pore diameter in the in-plane direction. For this reason, there is a problem that it cannot be applied to an electrode structure that retains liquid for a long time and discharges gas quickly.
The technology described in Patent Document 4 applies a power supply structure that reduces the pressure loss of both water and air in the electrode, so it cannot deal with an electrode structure that retains liquid for a long time and discharges gas quickly. There is
In the technique described in Patent Document 5, a power feeder is provided on the outside of the electrolytic reaction surface to facilitate water flow to the reaction surface. .

The present invention has been invented in view of the above-mentioned problems, and its object is suitable for use as an anode electrode of a PEM type water electrolysis device, etc., and an electrode that utilizes a reaction in which liquid is flowed into the electrode and gas is generated. It is an object of the present invention to provide a metal porous electrode and a water electrolysis cell equipped with the same, which is suitable for application to a liquid and can increase the pressure loss of a liquid and reduce the pressure loss of a gas.

(1) In order to achieve the above object, a porous electrode according to one aspect of the present invention is a porous electrode in which at least an odd number of conductive porous layers having a three-dimensional network structure are continuously arranged in the direction of liquid flow. In a specific odd-numbered reference porous layer, an even-numbered porous layer adjacent thereto, and a specific other odd-numbered downstream porous layer adjacent thereto along the direction of liquid flow, the reference porous layer The average pore diameter of the porous layer is in the range of 50 μm or more and 500 μm or less, and the average pore diameter of the odd-numbered downstream porous layer is in the range of 100 μm or more and 600 μm or less, and is larger than the average pore diameter of the reference porous layer. Also, the average pore diameter of the odd-numbered downstream porous layer is increased, and the pores present in the even-numbered porous layer are distributed in a range of 800 μm or less, and the even-numbered porous layer has It is characterized in that 3% or more of the existing pores have a pore diameter of more than 600 μm and 800 μm or less .

As a result of research conducted by the present inventor, an electrode structure on the anode side suitable for a water electrolysis device was investigated. .
For this reason, at least odd-numbered porous layers are provided, and for the odd-numbered reference porous layer, the even-numbered porous layer, and the next odd-numbered downstream porous layer, the average pore diameter of the reference porous layer is By increasing the average pore size of odd-numbered pores on the downstream side, gas can be easily discharged from the porous electrode.
In addition, since the even-numbered porous layers have pores whose lower limit is the average pore diameter of the reference porous layer, the presence of the even-numbered porous layers reduces the pressure loss of the liquid flowing through the porous electrode. can be made higher than the pressure loss of

The average pore diameter of each odd-numbered porous layer should be in the range of 50 μm to 600 μm in order to allow the liquid to flow inside the porous electrode and to smoothly discharge the gas generated inside the porous electrode. Therefore, the average pore diameter of the downstream porous layer must be larger than the average pore diameter of the reference porous layer. In addition, since pores having a pore diameter of more than 600 μm and not more than 800 μm are distributed in the even-numbered porous layers, the pressure loss of liquid flowing through the porous electrode can be made higher than the pressure loss of gas.

(3) In the porous electrode according to one aspect of the present invention, it is preferable that the average pore diameter of the reference porous layer is 50 μm or more smaller than the average pore diameter of the downstream porous layer.

The average pore diameter of the reference porous layer being 50 μm or more smaller than the average pore diameter of the downstream porous layer means that the average pore diameter of the downstream porous layer is 50 μm or more larger than the average pore diameter of the reference porous layer. do. As a result, when the liquid flows from the reference porous layer toward the downstream porous layer inside the porous electrode, a moderate pressure loss is generated, and the liquid stays on the reaction surface inside the porous electrode for a moderate amount of time. Holds and flows smoothly.

(4) In the porous electrode according to one aspect of the present invention, the even-numbered porous layer has a width of 50 μm or more along the direction of liquid flow, and 1/2 or less of the total length of the electrode along the direction of liquid flow. And it is preferably 5 mm or less.
If the width of the even-numbered porous layer is less than 50 μm, it becomes impossible to distinguish it from the odd-numbered porous layer, and it is difficult to exhibit the performance of the even-numbered porous layer provided as an interface between the odd-numbered porous layers. Become. Further, when the width of the even-numbered porous layers exceeds 1/2 of the total length of the electrode, the ratio of the odd-numbered porous layers that define the average pore diameter becomes low, and the reaction efficiency decreases. On the other hand, if the width of the even-numbered porous layer exceeds 5 mm, the strength of the porous layer 7 becomes weak and the porous electrode 1 tends to break at the porous layer 7 portion.

(5) In the porous electrode according to one aspect of the present invention, the porous layer preferably has a porosity of 70% or more and 98% or less.
If the porosity is in this range, it is possible to provide a porous electrode that is excellent in gas release, has a three-dimensional network structure and has the strength necessary for the porous electrode, and has an appropriate pressure drop against liquids. .

(6) In the porous electrode according to one aspect of the present invention, it is preferable that the porous layer is made of a metal porous sintered body.
In the case of a porous layer adopting the structure of a porous sintered body, a porous layer having a three-dimensional network structure can be obtained by, for example, mixing a foaming agent with a metal powder to form a foam, and then fusing the metal powders together.

(7) A water electrolysis cell according to one aspect of the present invention is a water electrolysis cell comprising the porous electrode according to (1) to (6), wherein the porous electrode and the porous electrode It comprises a first catalyst layer, an ion permeable membrane, a second catalyst layer, and a counter electrode, which are sequentially laminated on a side surface perpendicular to the direction of water flow.

With the water electrolysis cell according to the present embodiment, when water is electrolyzed using a porous electrode, oxygen gas generated on the reaction surface in the electrode can be quickly discharged to sufficiently supply water to the reaction surface, and water can be supplied to the reaction surface. It is possible to provide a water electrolysis cell that can perform electrolysis with high reaction efficiency by appropriately controlling the pressure loss of the reaction surface and appropriately retaining water on the reaction surface.

According to one aspect of the present invention, by making the average pore diameter of the downstream porous layer larger than the average pore diameter of the reference porous layer, the discharge of gas from the porous electrode can be improved. In addition, since the even-numbered porous layers are provided with a plurality of pores exhibiting a pore size distribution in a predetermined range equal to or larger than the average pore size of the reference porous layer, the existence of the even-numbered porous layers and the odd-numbered By combining the presence of the third porous layer, the pressure loss of the liquid flowing through the porous electrode can be adjusted to be high within a moderate range.
Therefore, the porous electrode has excellent gas discharge properties, can smoothly supply the liquid to the reaction part inside the electrode, and can hold the liquid flowing inside the electrode for the time necessary for the reaction, and has good reaction efficiency. It is possible to provide a water electrolysis cell equipped with

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows an example of the water electrolysis cell provided with the porous body electrode of 1st embodiment which concerns on this invention. FIG. 3 is a perspective view showing an example of a specific structure of the same porous electrode; FIG. 4 is a perspective view of the same porous electrode viewed from another angle; FIG. 4 is a perspective view showing a porous electrode according to a second embodiment of the invention; 1 is a photograph showing an example of X-ray fluoroscopic measurement of a porous electrode obtained in an example. 4 is a photograph showing an example of X-ray fluoroscopic measurement of a porous electrode obtained in Comparative Example.

Although the present invention will be described in detail below, the present invention is not limited to the embodiments described below.
FIG. 1 shows an example of a water electrolysis cell A having a porous electrode 1 according to a first embodiment of the present invention. 1 is drawn in an upright position. A first catalyst layer 2, an ion permeable membrane (solid polymer membrane) 3, a second catalyst layer 4, and a counter electrode 5 are sequentially laminated on one side (the left side in FIG. 1) of the porous electrode 1. there is In the water electrolysis cell A, the porous body electrode 1 is connected to the positive electrode side of a power source (not shown), and the counter electrode 5 is connected to the negative electrode side of the power source (not shown).
This water electrolysis cell A is an example of a so-called PEM type water electrolysis cell provided with an ion permeable membrane 3 .

In the example shown in FIGS. 1 and 2, the porous electrode 1 is composed of a first (odd-numbered) reference porous layer 6, a second (even-numbered) porous layer 7, and a third porous layer 7 in order from the bottom. It has a three-layer structure in which (odd-numbered) downstream porous layers 8 are laminated in the vertical direction.
In the water electrolysis cell A shown in FIG. 1, the electrodes 1 and 5 are energized from a power supply (not shown), and water is introduced into the reference porous layer 6 from the bottom side of the reference porous layer 6, and the introduced water is This is a water electrolysis cell that electrolyzes water by causing the reference porous layer 1, the porous layer 7, and the downstream porous layer 8 to flow in that order.
Electricity is applied to the electrodes 1 and 5 from a power source (not shown), and in the water electrolysis cell A, water is electrolyzed while the water flows in the order of the reference porous layer 6, the porous layer 7, and the downstream porous layer 8. The generated hydrogen ions are moved to the counter electrode 5 side through the ion permeable membrane 3, and hydrogen can be recovered at the counter electrode 5 made of a porous material electrode.

The porous electrode 1 is used as an anode, and the reaction shown by H ₂ O→2H ⁺ +2e ⁻ +1/2O ₂ is performed, and the counter electrode 5 is used as a cathode, and the reaction 2H ⁺ +2e ⁻ →H ₂ ↑ is performed, The overall reaction is H ₂ O→H ₂ +1/2O ₂ . The porous body electrode 1 is used as an anode electrode, and the counter electrode 5 is used as a cathode electrode.
Therefore, in the porous electrode 1 , when water is supplied from the reference porous layer 6 side, O ₂ gas is discharged from the upper portion of the downstream porous layer 8 and H ₂ gas is discharged from the upper portion of the counter electrode 5 .

In the water electrolysis cell A that performs water electrolysis as described above, water flows through the interior of the porous body electrode 1 serving as the anode electrode, and oxygen gas is generated therein. On the reaction surface for electrolyzing water inside the anode electrode, the presence of oxygen gas prevents contact between the water and the reaction surface. It is necessary to supply sufficient water to the surface.

For this reason, the porous electrode 1 of the present embodiment employs a three-layer structure in which a reference porous layer 6, a porous layer 7, and a downstream porous layer 8 are sequentially provided along the direction of water flow. The pore size, pore size distribution, porosity, width, etc. of each porous layer are set to specific values or ranges.
The reference porous layer 6, the porous layer 7, and the downstream porous layer 8 are porous layers made of Ti, Ti alloys, Ni, Ni alloys, noble metals such as Au and Pt, or alloys thereof. The reference porous layer 6, the porous layer 7, and the downstream porous layer 8 may be made of a conductive carbonaceous material in addition to these materials.
The reference porous layer 6, the porous layer 7, and the downstream porous layer 8 are made of, for example, a flat porous sintered body made of these materials, and have a three-dimensional network structure inside. .
The reference porous layer (odd-numbered porous layer) 6 is, for example, a porous layer having a predetermined average pore size within the range of 50 to 600 μm. For example, it is made of a porous sintered body having a three-dimensional network structure with an average pore diameter of 50 μm or 100 μm.

Let the average pore diameter here be the value calculated|required by the following method.
First, the porous layer to be measured is subjected to X-ray fluoroscopic measurement (device name: SMX1000, manufactured by SIMAZU Co., Ltd.), and using analysis software (VG studio max 3.2), the porous layer is photographed at intervals of 0.1 mm. A plurality of three-dimensional image data are obtained. For example, in the case of a strip-shaped porous layer, it is possible to assume a plurality of tomographic planes in the plate thickness direction and analyze the porous layer from one end to the other in the length direction by X-rays.
Using another analysis software (WinROOF Ver 7.0, manufactured by Mitani Shoji Co., Ltd.), the required number of 3D image data obtained in this way is binarized for the metal part and the void part for the cross-sectional image. The average pore diameter can be obtained by estimating the pore diameter from the binarized image and calculating the average value of the pore diameters.

The downstream porous layer (odd-numbered porous layer) 8 is, for example, a porous layer having a predetermined average pore size within the range of 50 to 600 μm. For example, it is made of a porous sintered body having a three-dimensional network structure with an average pore diameter of 500 μm or 600 μm. However, the average pore diameter of the downstream porous layer 8 is preferably larger than that of the reference porous layer 6 by 50 μm or more. In other words, the average pore diameter of the reference porous layer 6 is preferably smaller than the average pore diameter of the downstream porous layer 8 by 50 μm or more.
The material forming the downstream porous layer 8 is the same material as the material forming the reference porous layer 6 . For example, the reference porous layer 6 and the downstream porous layer 8 are made of porous sintered bodies of Ti or Ti alloys.

The average pore diameter of the reference porous layer 6 and the downstream porous layer 8 is preferably in the range of 50 to 600 μm. sexuality worsens. If the average pore diameter exceeds 600 μm, the number of conductive paths as electrodes is too small, and the first catalyst layer 2 cannot be effectively used. Therefore, when the water electrolysis cell A is configured, there is a problem that the electrolysis efficiency is lowered.
However, as described above, the average pore diameter of the downstream porous layer 8 is preferably larger than the average pore diameter of the reference porous layer 6 by 50 μm or more.
As a result, when the liquid is caused to flow from the reference porous layer 6 toward the downstream porous layer 8 inside the porous electrode 1 , a moderate pressure loss is generated, and the liquid is moderately applied to the reaction surface of the porous electrode 1 . It can flow smoothly while staying for a long time.

The even-numbered porous layers 7 are made of the same material as the reference porous layer 6 and the downstream porous layer 8, and have a three-dimensional network structure. Furthermore, the porous layer 7 is formed from a porous sintered body having a pore size larger than the average pore size of the reference porous layer 6 and having a pore size distribution within a predetermined range. ing.
In the even-numbered porous layers 7, the range of pore size distribution is preferably 2000 μm or less, more preferably 1000 μm or less.
If the upper limit of the pore size distribution of the porous layer 7 exceeds 2000 μm, the strength of the porous layer 7 becomes weak and the porous electrode 1 tends to break at the portion of the porous layer 7 .
The porous layer 7 contains pores with an average pore diameter of 50 μm or more and 500 μm or less, pores with an average pore diameter of 100 μm or more and 600 μm or less, and pores with an average pore diameter of 600 μm or more and 2000 μm or less. good too.

The pore size distribution of the porous layer 7 is, for example, 800 μm or less. In this case, the pores in the range of 200 μm or less are about 40% to 60%, the pores in the range of more than 200 μm to 600 μm are about 35% to 55%, and the pores in the range of more than 600 μm to 800 μm are 3% to 10%. Although the state included to some extent can be exemplified, it is not limited to this range. In the pore size distribution described above, % indicates the ratio of the number of pores.
When the pores in the range of more than 600 μm and 800 μm or less are less than 3%, the porous layer 7 becomes indistinguishable from the reference porous layer 6 and the downstream porous layer 8, and the porous layer 7 has the function of adjusting the pressure loss of the liquid. becomes less likely to occur.

The width of the porous layer 7 (the width along the flow direction of the liquid flowing inside the porous electrode 1: the thickness along the height direction of the porous electrode 1 in FIG. 1) is 50 μm or more. It is preferably 1/2 or less of the total length of 1 (total length along the liquid flow direction) and 5 mm or less. The total length of the porous electrode 1 must be 10 mm or more along the direction of liquid flow. We judged as follows.
If the width of the porous layer 7 is less than 50 μm, it becomes indistinguishable from the other porous layers 6 and 8, making it difficult for the porous layer 7 to function to adjust the pressure loss of the liquid. Moreover, if the width of the porous layer 7 exceeds 1/2, the ratio of the odd-numbered porous layers that define the average pore diameter decreases, and the reaction efficiency decreases. On the other hand, if the thickness exceeds 5 mm, the strength of the porous layer 7 becomes weak, and there is a problem that the porous electrode 1 is likely to break at the portion of the porous layer 7 .

The porosity of the reference porous layer 6, the even-numbered porous layer 7, and the downstream porous layer 8 is preferably 70% or more and 98% or less. If the porosity is less than 70%, the gas release property of the porous electrode 1 becomes poor, and if the porosity exceeds 98%, the strength of the porous layer itself is insufficient, and the strength required for the porous electrode 1 is insufficient. is not obtained.

"Manufacturing method of porous electrode 1"
An example of a manufacturing method for forming the porous electrode 1 from a porous titanium sintered body will be described below.
(Slurry preparation process)
In the slurry preparation step, titanium powder, titanium hydride powder, or a mixed powder thereof is mixed with an organic binder, a foaming agent, a plasticizer, water and, if necessary, a surfactant to prepare foamable slurry. As the raw material powder, for example, a mixed powder of pure titanium powder having an average particle size of 0.5 to 30 μm can be used.
Water-soluble methyl cellulose or polyvinyl alcohol can be used as an organic binder for binding the mixed powder. Neopentane, hexane and heptane can be used as blowing agents. Glycerin can be used as the plasticizer, and alkylbenzenesulfonate can be used as the surfactant.
For example, a mixed powder, an organic binder, a foaming agent, a plasticizer, a surfactant, and water are mixed to prepare a slurry. In this case, the foaming agent can be added in an amount of about 0.1 to 5% by mass.

As the binder (water-soluble resin binder), methylcellulose, hydroxypropylmethylcellulose, hydroxyethylcellulose, hydroxyethylmethylcellulose, carboxymethylcellulose ammonium, ethylcellulose, polyvinyl alcohol and the like can be used.
The foaming agent may be any one that can generate gas to form bubbles in the slurry, and is a volatile organic solvent such as pentane, neopentane, hexane, isohexane, isopeptane, benzene, octane, toluene, etc., having 5 to 8 carbon atoms. of water-insoluble hydrocarbon organic solvents can be used.
Examples of surfactants include anionic surfactants such as alkylbenzenesulfonates, α-olefinsulfonates, alkyl sulfates, alkyl ether sulfates, and alkanesulfonates, polyethylene glycol derivatives, polyhydric alcohol derivatives, and the like. of nonionic surfactants and amphoteric surfactants can be used.

Plasticizers are added to impart plasticity to molded bodies obtained by molding slurries. and esters such as diethyl phthalate, di-N-butyl phthalate, diethylhexyl phthalate, dioctyl phthalate, sorbitan monooleate, sorbitan trioleate, sorbitan palmitate and sorbitan stearate.

(Sheet forming process)
Next, these slurries are molded into a foamable sheet-like molding. Here, the molding process and the foaming process can be performed using a sheet molding machine using a known doctor blade device.
The sheet forming machine includes, for example, a carrier sheet that is driven by a conveying roller and that forms an endless track, a slurry storage section that is installed on the carrier sheet to store slurry, and a carrier sheet on the downstream side of the storage section. a doctor blade, a foaming bath, and a drying chamber.

In the forming step, a sheet forming machine is used to supply slurry from a slurry reservoir onto a carrier sheet, and a doctor blade adjusts the thickness of the slurry on the carrier sheet to a predetermined value to produce a sheet-like slurry.
When this sheet-shaped slurry is produced, two slurry reservoirs are provided adjacent to each other in the width direction of the carrier sheet, and slurry for forming the reference porous layer 6 is stored in one of the slurry reservoirs, Slurry for forming the downstream porous layer 8 is stored in the other slurry reservoir.

When two types of slurry are simultaneously supplied onto a carrier sheet from two slurry reservoirs so as to be adjacent to each other, and each of the two types of slurry is processed into a sheet by a doctor blade, the two adjacent slurries are mixed at the boundary. , can form a mixed layer at the boundary. In subsequent steps, the reference porous layer 6 is formed from one sheet-shaped slurry, the downstream porous layer 8 is formed from the other sheet-shaped slurry, and the porous layer 7 is formed from the mixed layer portion.

In the foaming process, the entire sheet-like slurry is inserted into a foaming tank together with the carrier sheet, and is maintained at, for example, a temperature of 70° C. and a humidity of about 90% for a required period of time, and hot air is blown into the drying chamber to dry it. By this foaming step, the foaming agent in the sheet-like slurry is foamed to produce a foamed molded product having a three-dimensional network structure and titanium powder located in the skeleton portion of this network structure.

After removing the foamed molded body from the carrier sheet and drying it in a degreasing furnace or the like, it is heated and held at 700 to 1300° C. in a vacuum atmosphere or the like. , a conductive sheet-like molded article having a three-dimensional network structure can be obtained.
In this sheet-like formed body, the reference porous layer 6 can be formed based on the slurry discharged from one slurry storage part, and the downstream porous layer 8 can be formed based on the slurry discharged from the other slurry storage part, An even-numbered porous layer 7 can be formed at the boundary where both slurries are mixed.
In this sheet-like molding, a plate-like porous layer having a three-layer structure shown in FIG. A solid electrode 1 can be obtained.

In the water electrolysis cell A equipped with the porous electrode 1 described above, the electrodes 1 and 5 are energized from a power supply (not shown), and water is supplied from the bottom side of the reference porous layer 6 to the inside of the reference porous layer 6. Water can be electrolyzed by introducing and causing the introduced water to flow through the reference porous layer 1, the porous layer 7, and the downstream porous layer 8 in that order. Then, hydrogen can be recovered from the counter electrode 5 side.
When water flows inside the porous electrode 1, the water first flows through the reference porous layer 6. Since the average pore diameter of the reference porous layer 6 is in the range of 50 μm to 500 μm, Water can flow smoothly, and there is no problem with the discharge of oxygen gas.
In addition, since the average pore diameter of the downstream porous layer 8 is larger than the average pore diameter of the reference porous layer 6 by 50 μm or more, the oxygen gas generated in these layers can be discharged well.
Furthermore, since the even-numbered porous layers 7 are provided with pores having a pore size distribution in the range of 2000 μm or less, when water moves from the reference porous layer 6 to the downstream porous layer 8, there is a moderate pressure loss against water. can be generated, and the pressure loss against the gas can be kept small.
Regarding this effect, the even-numbered porous layer 7 has pores with an average pore diameter of 50 μm or more and 500 μm or less derived from the reference porous layer 6 and pores with an average pore diameter of 100 μm or more and 600 μm or less derived from the downstream porous layer 8. In addition to the pores within the range, the inclusion of large pores having an average pore diameter of more than 600 μm and not more than 2000 μm generated by mixing the slurries of both layers provides better performance.

The even-numbered porous layers have a width of 50 µm or more, 1/2 or less of the total length of the electrode in the liquid flow direction, and 5 mm or less. can be set within a suitable range, and the presence of the even-numbered porous layers can produce a moderate pressure drop against water and a low pressure drop against oxygen gas.
In addition, since the width of the even-numbered porous layers 7 is set to 1/2 or less of the total length of the electrode and 5 mm or less, the ratio of the odd-numbered porous layers 6 and 8, which define the average pore diameter, to the entire electrode is sufficient. Electrolysis can be performed with good reaction efficiency as an electrode. Also, the strength required for the electrodes can be ensured.

"Second Embodiment"
FIG. 4 shows a second embodiment of the porous electrode according to the present invention.
The porous electrode 11 of this second embodiment includes the first porous layer 6, the second porous layer 7, the third porous layer 8, the fourth porous layer 9, and the fifth porous layer 9. The electrode has a five-layer structure in which the second porous layer 10 is continuously formed.
As in the second embodiment, a five-layer structure in which three odd-numbered porous layers and two even-numbered porous layers are provided may be employed.

Even when three odd-numbered porous layers are provided, the average pore diameters of the porous layers 6, 8, and 10 are preferably in the range of 50 μm to 600 μm, and are formed sequentially larger. . For example, the first (odd-numbered) porous layer 6 has an average pore diameter of 100 μm, the third (odd-numbered) porous layer 8 has an average pore diameter of 300 μm, and the fifth (odd-numbered) porous layer 8 has an average pore diameter of 300 μm. The average pore size of layer 10 can be set such as 600 μm.
Further, in this structure, the average pore diameter of the first porous layer 6 is smaller than the average pore diameter of the third porous layer 8 by 50 μm or more, and the third porous layer 8 is the fifth porous layer. It is preferably smaller than the average pore diameter of the porous layer 10 by 50 μm or more.
Since both the second porous layer 7 and the fourth porous layer 9 are even-numbered porous layers, the pore size distribution is preferably in the range of 2000 μm or less.
Further, both the second porous layer 7 and the fourth porous layer 9 have a width of 50 μm or more, preferably 5 mm or less.

In the porous electrode 11 of the second embodiment, the average pore diameters of the odd-numbered porous layers 6, 8, and 10 are the same as in the structure of the first embodiment, and the even-numbered porous layers The pore size distribution of the layers 7 and 9 is the same as in the structure of the first embodiment. The relationship between the odd-numbered porous layers 6, 8, 10 and the even-numbered porous layers 7, 9 is also the same as in the structure of the first embodiment.

Therefore, even in the porous electrode 11 of the second embodiment, similar to the porous electrode A of the first embodiment, due to the rapid discharge of oxygen gas and the occurrence of moderate pressure loss when water flows, , a water electrolysis cell with good water electrolysis efficiency can be constructed.

As shown in the first and second embodiments, four or more odd-numbered porous layers may be provided instead of two or three, and one or more even-numbered porous layers may be provided. Instead of two layers, three or more layers may be provided, and the number of layers to be provided is not limited.
However, since even-numbered porous layers are provided between odd-numbered porous layers, the number of porous layers constituting the entire porous electrode is preferably an odd number.

A total of 2% by mass of a foaming agent, an organic binder, a polyhydric alcohol plasticizer, and a surfactant were mixed with titanium powder (60% by mass) having an average particle size of 20 μm to prepare a first slurry having a composition of the balance being water. .
A total of 2% by mass of a foaming agent, an organic binder, a polyhydric alcohol plasticizer, and a surfactant were mixed with titanium powder (50% by mass) having an average particle size of 20 μm to prepare a second slurry having a composition of the balance being water. .

A first slurry and a second slurry are supplied onto a carrier sheet of a sheet forming machine so as to be adjacent to each other in the running direction of the carrier sheet, and a first slurry comprising the first slurry is supplied to one side in the width direction of the carrier sheet. A second slurry sheet was formed on the other side of the carrier sheet in the width direction. On the carrier sheet, the first sheet-like slurry and the second sheet-like slurry were mixed at the boundary portion to form a mixed layer.
A sheet in which the first sheet-like slurry, the mixed layer, and the second sheet-like slurry are integrated is placed in a foaming tank under the conditions of humidity: 75 to 95%, temperature: 30 to 40°C, and residence time of 10 to 20 minutes. It was foamed and subsequently dried in a drying cabinet. In this foaming step, the foaming agent was foamed to obtain a green sheet (foam molding) having a three-dimensional network structure and titanium powder located in the skeleton portion of the network structure.

This green sheet was heated and held at 1150° C. to sinter the titanium powder present in the skeleton portion of the three-dimensional network structure, thereby obtaining an electrically conductive sheet-like compact having a three-dimensional network structure made of titanium. .
In this sheet-shaped formed body, the portion formed from the first slurry is the first porous layer (reference porous layer), the portion formed from the mixed layer is the second (even-numbered) porous layer, and the portion formed from the mixed layer is the second porous layer. The portion formed from the slurry of No. 2 was used as the third (downstream odd-numbered) porous layer.
This sheet-like compact was cut into strips having a length of 55 mm and a width of 38 mm so as to include three porous layers, thereby obtaining a porous electrode. The thickness of this porous electrode was 0.1 mm.

For the first porous layer, the second porous layer, and the third porous layer of this porous electrode, X-ray fluoroscopic measurement (apparatus Name: SMX1000, manufactured by SIMAZU Corporation) was performed, and three-dimensional image data of the porous electrode was obtained using analysis software (VG studio max 3.2).
Using separate analysis software (WinROOF Ver 7.0, manufactured by Mitani Shoji Co., Ltd.) for each 3D image data, binarize the metal part and the void part for each cross-sectional image obtained by collecting multiple virtual cross-sections in the thickness direction. The average pore diameters of the first porous layer and the third porous layer were obtained by performing the treatment, estimating the pore diameter from this value, and calculating the average value.

The second porous layer is formed from a mixed layer of the first slurry and the second slurry, and the expansion agent contained in each slurry is mixed to cause abnormal expansion, etc., and is formed. The pore diameters were distributed over a wide range. For the second porous layer, the pore size distribution was obtained instead of the average pore size.
As a result of measurement, the average pore diameter of the first porous layer was 50 μm, the average pore diameter of the third porous layer was 600 μm, and the pore diameter of the second porous layer was 800 μm or less.
Using this porous electrode as a sample of Example 1, a test was conducted in which water was allowed to permeate and the water flow rate was measured. The sample of Example 1 was subjected to a test to transmit air and measure the air flow velocity.
The pressure loss was measured by placing a strip-shaped porous electrode in a cuboid-shaped cylinder that allows fluid (air/water) at 25°C to flow from one direction and controlling the flow rate with a mass flow meter. was obtained by measuring

Next, for comparison, strip-shaped porous electrodes (length 55 mm, width 38 mm, thickness 0.1 mm) having an average pore diameter of 50 μm were prepared using only the slurry used when forming the first porous layer. This porous electrode was used as a sample of Comparative Example 1.
Next, for comparison, strip-shaped porous electrodes (length 55 mm, width 38 mm, thickness 0.1 mm) having an average pore diameter of 600 μm were prepared using only the slurry used when forming the third porous layer. This porous electrode was used as a sample of Comparative Example 2.
Using these Comparative Examples 1 and 2, the pressure loss ratio in the water permeation test and the pressure loss ratio in the air permeation test performed on the sample of Example 1 were measured.
Test condition 1 employed a water flow rate of 0.6 m/s and an air flow rate of 30 m/s, and test condition 2 employed a water flow rate of 0.8 m/s and an air flow rate of 40 m/s.

The values of (pressure loss of water/pressure loss of air) for each sample of Example 1, Comparative Example 1, and Comparative Example 2 are shown in Table 1 below.

As is clear from the results shown in Table 1, the average pore diameter of the first porous layer was 50 µm, the pore diameter distribution of the second porous layer was 800 µm or less, and the average pore diameter of the third porous layer was 600 µm. In Example 1, the value of (pressure loss of water/pressure loss of air) was larger than those of Comparative Examples 1 and 2. A large ratio shown in Table 1 means that the pressure loss of water is large or the pressure loss of air is small.
Therefore, in the porous electrode of Example 1, it can be estimated that the pressure loss of water is large and the pressure loss of air is small compared to the porous electrodes of Comparative Examples 1 and 2. 1, and can provide a water electrolysis device with good reaction efficiency.

Regarding the porous electrode of Example 1, the pore distribution of the even-numbered porous layer was 800 μm or less, but the ratio of pores of 200 μm or less, the ratio of pores of more than 200 μm to 600 μm, and the ratio of pores of more than 600 μm to 800 μm The following pore ratios were measured.
As a result, the ratio of pores of 200 μm or less was 50%, the ratio of pores of more than 200 μm to 600 μm or less was 45%, and the ratio of pores of more than 600 μm to 800 μm or less was 5%.

FIG. 5 is a photograph showing an example of data analysis of the porous electrode of Example 1 after binarization processing by X-ray analysis.
A porous layer with an average pore diameter of 50 μm is formed on the lower half side of the strip-shaped porous electrode shown in FIG. 5, and a porous layer with an average pore diameter of 600 μm is formed on the upper half side of FIG. A state in which an even-numbered porous layer is formed in a portion is depicted.
The strip-shaped porous electrode body shown in FIG. 6 is drawn as an electrode body having pores with an average pore diameter of 50 μm as a whole.

A... Water electrolysis cell, 1... Porous body electrode, 2... First catalyst layer, 3... Ion permeable membrane (solid polymer membrane), 4... Second catalyst layer, 5... Counter electrode, 6... Reference porosity Porous layer (odd-numbered porous layer) 7 Porous layer 8 Downstream porous layer (odd-numbered porous layer) 9 Second even-numbered porous layer 10 Porous body Electrode, 11... second downstream porous layer.

Claims (6)

A porous electrode in which at least an odd number of conductive porous layers with a three-dimensional network structure are continuously arranged in the direction of liquid flow,
In a specific odd-numbered reference porous layer, an even-numbered porous layer adjacent thereto, and a specific other odd-numbered downstream porous layer adjacent thereto along the direction of liquid flow,
The average pore diameter of the reference porous layer is in the range of 50 μm or more and 500 μm or less, the average pore diameter of the odd-numbered downstream porous layer is in the range of 100 μm or more and 600 μm or less, and the average of the reference porous layer The average pore diameter of the odd-numbered downstream porous layer is made larger than the pore diameter, and
The pores present in the even-numbered porous layers are distributed in a range of 800 μm or less, and among the pores present in the even-numbered porous layers, the pores having a pore diameter of more than 600 μm and 800 μm or less account for 3%. A porous electrode characterized by comprising the above . 2. The porous electrode according to claim 1 , wherein the average pore diameter of the reference porous layer is 50 μm or more smaller than the average pore diameter of the downstream porous layer. 2. The method according to claim 1, wherein the even-numbered porous layer has a width of 50 μm or more along the direction of liquid flow, and is 1/2 or less and 5 mm or less of the total length of the electrode along the direction of liquid flow. Porous electrode. 4. The porous electrode according to claim 1, wherein the porous layer has a porosity of 70% or more and 98% or less. 5. The porous electrode according to any one of claims 1 to 4, wherein the porous layer is made of a metal porous sintered body. A water electrolysis cell comprising the porous electrode according to any one of claims 1 to 5 ,
The porous electrode, a first catalyst layer sequentially laminated on the side surface perpendicular to the direction in which water flows through the porous electrode, an ion permeable membrane, a second catalyst layer, and a counter electrode. A water electrolysis cell comprising:

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