JP6971944B2 - Catalyst laminates, membrane electrode composites, electrochemical cells, stacks, water electrolyzers and water utilization systems - Google Patents

Description

Embodiments of the present invention relate to catalyst laminates, membrane electrode composites, electrochemical cells, stacks, water electrolyzers and water utilization systems.

In recent years, electrochemical cells have been actively studied. Among the electrochemical cells, for example, the Polymer Electrolyte Water Electrolysis Cell (PEEC) is a large-scale energy storage system because it has excellent responsiveness to renewable energy such as photovoltaic power generation. It is expected to be used for hydrogen generation.

One major issue for the spread of PEEC is cost reduction by reducing the amount of precious metal catalyst used. Generally, a Pt nanoparticle catalyst is used as the cathode of PEEC and a particulate Ir-based catalyst is used as the anode in order to ensure sufficient durability and water electrolysis performance. In particular, Ir black and Ir oxide powders were used as the anodes, and the powders were slurryed with a solvent and applied onto the substrate, and then the solvent was removed in a drying step or the like and supported on the substrate. In this case, the adhesion between the catalyst layer and the base material is insufficient. Therefore, in a high load environment where the base material is corroded or operates at a high current density for a long time, the catalyst particles are gradually desorbed and the catalytic activity is active. There was a serious problem in durability, such as a decrease in durability. Further, there is a problem that Ir fine particles are aggregated, the specific surface area is lowered, and the transport of substances indispensable for the electrode reaction is hindered, so that sufficient water electrolysis efficiency cannot be obtained.

On the other hand, in the catalyst technology of the present inventors, the catalyst is sputtered on the substrate by the vacuum film forming method to secure the adhesion strength with the substrate and obtain relatively high durability with a small amount of catalyst. Can be done. In addition, the specific surface area and material transport efficiency that contribute to the electrolytic reaction are increased due to the introduction of pores into the catalyst layer using the pore-forming material and the laminated structure in which void layers that do not contain the catalyst are alternately stacked, resulting in a small amount of noble metal. However, sufficient electrolysis efficiency is obtained.

Japanese Unexamined Patent Publication No. 2012-204221 Japanese Unexamined Patent Publication No. 2010-333759 Japanese Unexamined Patent Publication No. 2016-62857

The catalyst laminate of the embodiment is a catalyst laminate including a plurality of catalyst layers containing at least one of a noble metal and a noble metal oxide and at least one of a non-noble metal and a non-noble metal oxide, and is a catalyst laminate having two or more first catalysts. The first catalyst in the atomic composition fraction of the noble metal, which comprises a layer and two or more second catalyst layers and is obtained by using line analysis by energy dispersive X-ray spectroscopy in the thickness direction of the catalyst laminate. The layer is less than the average of the highest and lowest atomic composition fractions of the noble metal. In the second catalyst layer, the atomic composition fraction of the noble metal is equal to or higher than the average of the highest value and the lowest value. A second catalyst layer exists between the first catalyst layers. The value obtained by dividing the atomic composition of the noble metal of the first catalyst layer by the atomic composition of the noble metal of the first catalyst layer is defined as Rm (A1), and the atomic composition of the noble metal of the second catalyst layer is the second. Assuming that the value obtained by dividing the atomic composition fraction of the non-precious metal in the catalyst layer is Rm (A2), Rm (A1)> Rm (A2).

The catalyst laminate of the embodiment is a catalyst laminate including a plurality of catalyst layers containing at least one of a noble metal and a noble metal oxide and at least one of a non-noble metal and a non-noble metal oxide, and is a catalyst laminate having two or more first catalysts. The first catalyst in the atomic composition fraction of the noble metal, which comprises a layer and two or more second catalyst layers and is obtained by using line analysis by energy dispersive X-ray spectroscopy in the thickness direction of the catalyst laminate. The layer is less than the average of the highest and lowest atomic composition fractions of the noble metal. In the second catalyst layer, the atomic composition fraction of the noble metal is equal to or higher than the average of the highest value and the lowest value. A second catalyst layer exists between the first catalyst layers.

SEM image of a conventional catalyst laminate. The figure of an example of the EDS line analysis which concerns on Example 1. FIG. HAADF image according to Example 1. A partially enlarged view of FIG. The binarized image of FIG. Schematic diagram of catalyst amount measurement in a catalyst layer. Sectional drawing of the membrane electrode complex (MEA) which concerns on 2nd Embodiment. The explanatory view which shows the manufacturing method of the catalyst laminate and the electrode which concerns on 2nd Embodiment. Sectional drawing of the electrochemical cell which concerns on 3rd Embodiment. Sectional drawing of the stack which concerns on 4th Embodiment. The figure which shows the water electrolysis apparatus which concerns on 5th Embodiment. The figure which shows the hydrogen utilization system of 6th Embodiment. The figure which shows the hydrogen utilization system of 7th Embodiment.

Hereinafter, embodiments will be described with reference to the drawings. It should be noted that the same reference numerals are given to the common configurations throughout the embodiments, and duplicate description will be omitted. In addition, each figure is a schematic diagram for explaining the embodiment and promoting its understanding, and the shape, dimensions, ratio, etc. are different from those of the actual device, but these are described below and known techniques. The design can be changed as appropriate by taking into consideration.

(First Embodiment)
FIG. 1 is an SEM image of a conventional catalyst laminate. The catalyst laminated structure in which two or more layers of the void layer 122 and the catalyst layer 121 are alternately laminated as shown in FIG. 1 has been developed as an electrode having relatively high durability and a high specific surface area. However, with respect to the anode for water electrolysis, the ends of the catalyst layers 121 having a thickness of several nanometers to several tens of nanometers are partially bonded to each other, and substantially all the catalyst layers 121 are constrained to the base material. This makes it possible to obtain a stable structure in which deformation is suppressed with respect to pressure in the stacking direction, and relatively high durability can be obtained. However, when continuously exposed to high current, high temperature, and high voltage, the load on the structure is large, and there is room for improvement in improving the durability while maintaining the material transport efficiency.

As a result of diligent research to solve this problem, the inventors have invented the catalyst laminate according to the first embodiment.

According to this embodiment, the catalyst laminate 10 is provided. The catalyst laminate 10 is a catalyst laminate 10 including a plurality of catalyst layers containing at least one of a noble metal and an oxide of a noble metal and at least one of an oxide of a non-precious metal and a non-noble metal.

This catalyst layer has the highest and lowest composition fractions of noble metal atoms measured in the energy dispersive X-ray spectroscopy (EDS) line analysis of the 10 cross sections of the catalyst laminate. A layer having a composition fraction below the average (first catalyst layer: A1 layer 11) and a layer having a composition fraction above the average of the maximum and minimum composition fractions of noble metal atoms (second catalyst). Layer: A layer containing the A2 layer 12).

The catalyst laminate 10 includes two or more first catalyst layers 11 and one or more second catalyst layers 12. The first catalyst layer 11 and the second catalyst layer 12 are arranged alternately. The second catalyst layer 12 is arranged between the first catalyst layers 11. It is preferable that the first catalyst layer 11 and the second catalyst layer 12 are in direct contact with each other.

FIG. 2 is an example of a chart (figure) obtained by EDS line analysis. The horizontal axis is the distance in the depth direction (nm), the vertical axis is the atomic composition fraction (atom%), and the Ir amount and Ni. The atomic composition fractions of Ir and Ni are shown when the total amount is 100%. In FIG. 2, since the laminated body structure is alternately stacked so that the A2 layer 12 exists between the A1 layer 11, the catalyst laminated body 10 can be prevented from being deformed, and high strength can be ensured. Even with a small amount of precious metal, it can exist stably under a high load environment of high current, high temperature, and high voltage. In addition, in FIG. 2, a part of the measurement depth up to about 70 nm is shown in the chart. Even in the region deeper than 70 nm, the A1 layer 11 and the A2 layer 12 are alternately present.

Further, since both the A1 layer 11 and the A2 layer 12 have a structure having a gap on the order of nm and the specific surface area can be increased, the substance can be smoothly transported and the catalytic activity can be improved.

The catalyst layer will be described in detail.
As the catalyst material used for the catalyst layer of the present embodiment, other additives can be appropriately selected depending on the electrode reaction. From the viewpoint of catalytic activity and durability, a noble metal or a noble metal oxide catalyst is contained, and the noble metal element contained in the catalyst layer is at least one selected from the group consisting of Ir, Pt, Ru, Rh, Os, Pd and Au. That is all. Further, from the viewpoint of forming a stable and strong laminated structure, non-precious metals or oxides thereof are contained, and the non-precious metal elements contained in the catalyst layer are Fe, Co, Ni, Mn, Al, Zn, Ta, W and Hf. , Si, Mo, Ti, Zr, Nb, V, Cr, Sn and at least one selected from the group consisting of Sr.

Regarding the shape, atomic ratio, and element distribution of the catalyst layer, in addition to scanning electron microscope (SEM) images and fluorescent X-ray analysis (XRF), transmission electron microscopes (Transmission Electron) It can be confirmed by element mapping of Microscope (TEM), High-Angle Annular Dark Field image (HAADF), and Energy Dispersive X-ray Spectroscopy (EDS) line analysis. ..

In this embodiment, the HAADF image and the EDS line analysis method are used because the thickness of the catalyst layer is particularly thin. The measurement method will be described.

FIG. 3 is an HAADF image of the catalyst laminate 10 of Example 1. The HAADF image is an image obtained by acquiring electrons scattered at a wide angle by an annular detector and outputting the image based on the signal intensity. The scattering angle θ depends on the atomic number Z, and the output image also has a contrast depending on Z. , Effective for identifying heavy elements.

The sample is embedded in resin and processed to a thickness of 0.1 μm for observation using a HAADF image. From FIG. 3, it can be seen that the catalyst laminate 10 according to the present embodiment has a configuration in which substantially uniform layered catalyst layers are laminated. FIG. 4 is an image obtained by observing a part of the HAADF image of FIG. 3, which will be described later, at a high magnification. In FIG. 4, a plurality of pillars 13 can be observed in the A2 layer 12. The pillar 13 will be described in detail later.

Element composition analysis is performed by EDS line analysis in order to obtain the non-precious metal atomic composition fraction (atom%) and the noble metal atomic composition fraction (atom%) of the catalyst layer. This measuring method will be described. In the EDS line analysis, the acceleration voltage is preferably about 15 kV.

In this measurement, the atomic composition of precious and non-precious metals is measured. First, HAADF images for 20 samples are prepared. For each of the samples thus obtained, EDS line analysis is performed from the HAADF image in the depth direction (base material direction) at intervals of 10 nm in the horizontal direction along the base material of the membrane electrode assembly. Based on the result of each line, the maximum and minimum values of the composition fraction of the noble metal atom are obtained, and the layer having the composition fraction less than the average thereof is designated as A1 layer 11, and the maximum value and the minimum value of the composition fraction are set. The layer having a composition fraction above the average is designated as A2 layer 12, and the boundary line between A1 layer 11 and A2 layer 12 is clarified by connecting the boundaries thereof. Even when a catalyst laminate is prepared using two or more types of precious metal and non-precious metal, the maximum value of the atomic composition fraction of the noble metal in the EDS line analysis is the total value of each noble metal (for example, the maximum value of the noble metal A). Calculated using the value + maximum value of precious metal B). This is also calculated for the lowest atomic composition fraction of the noble metal.

From the EDS line analysis, the non-precious metal ratio Rm in each layer, that is, the ratio of (non-precious metal composition fraction) / (precious metal composition fraction) of each of the A1 layer 11 and the A2 layer 12 Rm (A1), Rm (A2). Ask for. Rm (A1) is preferably between 0.1 and more and 1.0 or less. This is because the residual non-precious metal causes co-catalysis and increases the activity. However, if the proportion of the non-precious metal is too small (Rm (A1) is less than 0.1), the effect of the co-catalyst is small, and it becomes difficult to maintain a structure having appropriate voids (portion where the catalyst does not exist). Therefore, it is not preferable, and if the ratio of the non-precious metal is too large (Rm (A1) is larger than 1.0), the noble metal dissolves in the electrolyte membrane 23 in the membrane electrode composite 20, and the proton conduction of the electrolyte membrane 23 is performed. It is not preferable because it inhibits it. When Rm (A1) is in the range of 0.2 or more and 0.8 or less, the catalytic activity can be further improved and the decrease in proton conduction can be suppressed, which is more preferable. Further, Rm (A2) is preferably in the range of 0.01 or more and 0.45 or less. If the proportion of non-precious metals is too small (Rm (A2) is less than 0.01), the amount of voids is small and the diffusion of substances such as water and oxygen is slowed down, and the proportion of non-precious metals is large (Rm (A2)). This is because the non-precious metal is melted during the operation of the electrochemical cell (greater than 0.45), the A2 layer 12 is crushed, and the substance transport performance is deteriorated. Further, the range of Rm (A2) is more preferably 0.05 or more and 0.4 or less. If it is 0.05 or more, the catalytic activity is increased by the co-catalytic action of the non-precious metal and the overall characteristics are improved, and if it is 0.4 or less, the crushing of the A2 layer 12 can be further suppressed. Durability can be improved.

From the viewpoint of stability, it is preferable that the average thickness of the A1 layer 11 is thicker than the average thickness of the A2 layer 12. From the same viewpoint, it is more preferable that the average thickness of the A1 layer 11 is 1.5 times or more and 2.0 times or less the average thickness of the A2 layer 12. Further, the thicker the A1 layer 11, the worse the diffusivity of the substance moving inside the A1 layer 11, while if the A1 layer 11 is too thin, it is easily deformed and long-term stability cannot be ensured. Therefore, the average thickness of the A1 layer 11 The value is preferably 4 nm or more and 35 nm or less.

The thicker the A2 layer 12, the better the diffusivity of the substance moving inside the A2 layer 12, while if the A2 layer 12 is too thick, the A2 layer 12 will be crushed during the electrochemical cell operation or hot pressing, and the stability will be poor. Therefore, the average thickness of the A2 layer 12 is preferably 2 nm or more and 34 nm or less. When the average thickness of the A1 layer 11 is in the range of 10 nm or more and 25 nm or less and the average thickness of the A2 layer 12 is in the range of 5 nm or more and 20 nm or less, the stability and diffusivity of the catalyst laminate 10 can be further improved. More preferred.

The average thickness of each of the A1 layer 11 and the A2 layer 12 can be obtained by EDS line analysis. The average thickness of the A1 layer 11 is an average value of the thickness of the A1 layer 11 per layer calculated from the boundary line obtained from the line analysis. The average thickness of the A2 layer 12 is an average value of the thickness of the A2 layer 12 per layer calculated from the boundary line obtained from the line analysis.

In order to promote the transport of substances to the base material side of the catalyst laminate 10, it is effective to reduce the thickness of the entire catalyst laminate 10. By promoting this substance transport, the catalyst on the substrate side can be used, and the activity of the catalyst laminate 10 as a whole can be improved. Therefore, for example, when the thickness of the A2 layer 12 is constant and the amount of noble metal in the entire catalyst laminate 10 is constant, it is better to increase the thickness of each layer of the A1 layer 11 having a large amount of noble metal as a catalyst. The moving distance of the substance that passes through the laminate 10 and diffuses to the substrate can be shortened, and the activity of the catalyst laminate 10 as a whole can be improved. However, as described above, if the thickness of the A1 layer 11 per layer is increased, the material diffusibility is suppressed, which is not preferable.

Therefore, in the present embodiment, the A1 layer 11 can be made thick enough to improve the activity and material diffusivity of the catalyst laminated body 10, and the A2 layer 12 can be made the minimum thickness that does not hinder the material transport. The overall thickness of the catalyst laminate 10 can be reduced while improving the overall activity of the body 10.

The details of the method for producing the catalyst laminate 10 will be described later, but these laminated structures can be produced by laminating a mixed layer of a noble metal and a non-precious metal by multiple sputtering and then washing away a certain amount of the non-precious metal by etching. The structure before etching is proportional to the output ratio at the time of sputtering and the sputtering time, but the etching tends to elute non-precious metals, crush the A1 layer 11 and the A2 layer 12, and shrink each. When the ratio of the non-precious metal is large, the non-precious metal ratio (Rm) of the non-precious metal A1 layer 11 and the A2 layer 12 is high in both the A1 layer 11 and the A2 layer 12. However, since non-precious metals are easily melted by etching, even if there are too many non-precious metals in each layer, the non-precious metal ratio does not continue to increase and does not exceed a certain level.
However, when a large amount of non-precious metal is present in the A1 layer 11 and the A2 layer 12, if the concentration of the solution used for etching is low or the etching time is short, the etching cannot be sufficiently performed and the A1 layer 11 and the A2 layer 12 Non-precious metal ratio (Rm) tends to be high. Further, when the concentration of the solution used for etching is increased or the etching time is lengthened, the non-precious metal ratio (Rm) of the A1 layer 11 and the A2 layer 12 tends to decrease. In order to realize a structure that increases the amount of catalyst contained in the catalyst laminate 10 while suppressing the thickness of the entire catalyst laminate 10, the thickness of the A1 layer 11 and the A2 layer 12 described above must be within the range. It is more preferable that Rm (A1)> Rm (A2). By setting Rm (A1)> Rm (A2), sudden deformation can be suppressed, which can contribute to the improvement of durability.

Next, a method of measuring the presence of the catalyst present in the A1 layer 11 and the A2 layer 12 will be described.
First, an image is taken with a TEM. In imaging, 20 points within 10% from the intersection of the long side and the short side of the base material of the film electrode complex are observed. The observation unit appropriately sets the magnification so that the field of view is 200 nm × 200 nm in TEM imaging.

In order to confirm the presence of the catalyst present in the A1 layer 11 and the A2 layer 12 in the TEM image thus obtained, it is effective to obtain the black-and-white contrast ratio. By determining the black-and-white contrast ratio in the TEM image, as shown in FIG. 5, it is shown that the catalyst is present in the region close to white, and the portion where the catalyst is not present is shown in black. Analysis using the TEM image described below will be performed to clarify its structural features. The equipment and analysis conditions used for TEM observation, and the software used for image analysis are as follows.
[TEM measurement conditions]
InstructName = TalosF200X (manufactured by FEI)
Accelerating Voltage = 200,000V
Magnification = 320,000
[Software for TEM image analysis]
PhotoImpact (COREL product)
Image-Pro plus (manufactured by Media Cybernetics)

Hereinafter, the image analysis method will be described. First, a TEM image of a cross section of the catalyst laminate 10 was obtained by TEM observation. Using the image editing software PhotoImpact, the part where the catalyst does not exist is displayed in black and the catalyst part is displayed in white by monochrome binary (resolution: current image, shape: none). The image thus obtained was subjected to an automatic measurement function (measurement of the ratio of the black part and the white part) using the image analysis software Image-Pro Plus in each range of the A1 layer 11 and the A2 layer 12 of the TEM image. As a result, the ratio of the portion where the catalyst does not exist (region A) and the portion where the catalyst exists (region B) (region A ÷ (region A + region B) × 100) is obtained.

At this time, as shown in FIG. 6, the range of each of the A1 layer 11 and the A2 layer 12 is a straight line orthogonal to the thickness of each layer obtained by the EDS line analysis and is "enclosed" by the width of the TEM image. It is the range shown by.

The area ratio of the portion of each A1 layer 11 in the TEM image in which the catalyst does not exist is preferably 30% or more and less than 90%. This is because if it is 30% or more, the diffusion resistance of the substance moving in the A1 layer 11 can be suppressed, and if it is less than 90%, the structural durability of the A1 layer 11 can be maintained. A more preferable range is 50% or more and less than 80%. Within this range, it is possible to more efficiently achieve both structural durability and suppression of diffusion resistance of substances moving in the A1 layer 11.

In the A2 layer 12, the portion where the catalyst does not exist is preferably 30% or more and 95% or less in area ratio. This is because if it is less than 30%, the part where the catalyst does not exist is small, and the substance transport of water and oxygen generated for the reaction is delayed, causing an overvoltage rise. Further, if the portion where the catalyst does not exist is larger than 95%, the structure is fragile, the structure is crushed in long-term operation, the material diffusion is slowed down, and an overvoltage rise is caused. It is more preferable that the portion of the A2 layer 12 in which the catalyst does not exist is 35% or more and 70% or less. Within this range, the overvoltage increase caused by the slowing of material transport can be suppressed more efficiently.

As shown in FIG. 5, a catalyst may be present in the A2 layer 12 so as to connect the A1 layers 11 to each other. This catalyst portion is called a pillar 13. The presence of the pillars 13 allows the pillars 13 to act like columns in the A2 layer 12 in long-term operation, thereby maintaining the thickness of the A2 layer 12 and connecting the A1 layers 11 to each other. Therefore, it is possible to prevent the A1 layer 11 from peeling off.

In the catalyst laminate 10 provided by the present embodiment, the A1 layer 11 controls the composition of the noble metal atom and maintains the optimum thickness, while the A2 layer 12 is thin to the minimum thickness at which the reaction and the product can be diffused. Further, by having a structure in which the composition ratio of noble metal atoms and non-noble metal atoms is controlled, it is possible to realize a laminated structure in which strength and substance transport efficiency are ensured even with a small amount of noble metal.

(Second embodiment)
In the second embodiment, as shown in FIG. 7, a membrane electrode assembly (MEA) 20 including the catalyst laminate 10 according to the first embodiment is provided. The MEA 20 is composed of a first electrode 21 and a second electrode 22, and an electrolyte membrane 23 arranged between them.

A first gas diffusion layer (base material) 21B and a first catalyst laminate 21A are arranged in order from the drawing on the first electrode 21 adjacent to the electrolyte membrane 23. A second gas diffusion layer (base material) 22B and a second catalyst laminate 22A are arranged in the second electrode 22 in order from the bottom of the drawing. The catalyst laminate 10 is arranged on the base material.

First, the base material and the electrolyte membrane constituting the MEA20 will be described in order.

<Base material>
The base material of the electrode is generally required to be porous and conductive. When used as an anode of a water electrolysis cell, a titanium material is generally used to ensure durability. The form of the base material is not particularly limited, and examples thereof include a titanium mesh, a cloth made of titanium fibers, a titanium non-woven fabric, and a titanium sintered body. The water electrolysis performance may be improved by adjusting the aperture ratio of the porous base material, particularly the structure of the portion in contact with the catalyst laminate 10, or surface treatment of the base material such as blast treatment. It is considered that this is because the water supply to the catalyst laminate 10 and the discharge of the electrode reaction product became smooth, and the electrode reaction in the catalyst laminate 10 was promoted. Another coating layer may be attached on the substrate. A dense, conductive coating layer may greatly improve the durability of the electrode. The coating layer is not particularly limited, but a metal material, a ceramic material such as an oxide or a nitride, carbon or the like can be used.

<Electrolyte membrane>
The electrolyte membrane is often required to have ionic conductivity. Examples of the electrolyte membrane having proton conductivity include fluororesins having a tungstic acid group (for example, Nafion (manufactured by DuPont), Flemion (manufactured by Asahi Kasei Co., Ltd.), and Ashibreck (manufactured by Asahi Glass Co., Ltd.)), and hydrocarbon films. Inorganic substances such as tungstic acid and phosphotungstic acid can be used.

The thickness of the electrolyte membrane can be appropriately determined in consideration of the characteristics of MEA. From the viewpoint of strength, solubility resistance and output characteristics of MEA, the thickness of the electrolyte membrane at the time of drying is preferably 10 μm or more and 200 μm or less.

Hereinafter, a method for manufacturing an electrode having the catalyst laminate 10 and a structure and a manufacturing method for the MEA according to the present embodiment will be described with reference to FIG.

As for the anode, a material including a catalyst material and a pore-forming material are formed on the Ti base material 21B using a vacuum device to prepare a precursor of the catalyst laminate 10. For the production of the Ir oxide-based catalyst laminate 10, a reaction sputtering method such as adding oxygen gas to the chamber using a sputtering apparatus is particularly suitable. In this case, it is possible to greatly improve the durability of the electrode and the characteristics of the electrochemical cell by optimizing parameters such as power supply power and substrate temperature during sputtering (step 1).

Next, a part of the non-precious metal is removed from the precursor of the catalyst laminate 10 by selective etching with a chemical such as an acid or an alkali to obtain an electrode (step 2).

Basically, in the precursor of the catalyst laminate 10, a catalyst material containing a noble metal as a main component and a pore-forming material made of a non-precious metal are sequentially formed on a substrate by sputtering or vapor deposition at the same time. In film formation, the composition ratio of precious metal and non-precious metal in each layer before etching of the catalyst laminate 10, the number of layers, the layer thickness, etc. are determined by the power supply power and gas pressure at the time of film formation of the precursor, and the catalyst material and the pore-forming material. It can be adjusted by the film formation ratio. More specifically, the smaller the precious metal output, the thinner the thickness of the A1 layer 11 and the A2 layer 12, and the larger the precious metal output, the thicker the thickness of the A1 layer 11 and the A2 layer 12. Further, even in the etching process of the pore-forming material using a chemical solution such as acid or alkali, the thickness and shape of the catalyst layer, the composition ratio in the catalyst layer, and the structure of the catalyst laminate 10 can be adjusted.

Further, the structure of the catalyst laminate 10 can be adjusted by performing post-treatment such as heat treatment after removing the pore-forming material, and the catalytic activity can be adjusted arbitrarily by adjusting these laminate structures. It is possible to improve the durability (step 3).

For example, Rm (A1) and Rm (A2) can be controlled by washing with an acid aqueous solution such as nitric acid, hydrochloric acid, or sulfuric acid or an alkaline aqueous solution such as sodium hydroxide, potassium hydroxide, or ammonia with time, concentration, and temperature as parameters. Is possible.

Further, although the crystal structure of the catalyst layer after sputtering may be amorphous, the crystal structure can be oriented by heat treatment to further improve the catalytic activity and durability.
Although the method for producing the oxide-based catalyst laminate 10 has been described so far, when the oxide-free catalyst laminate 10 is produced, it is produced by the same method except that oxygen is not used for the environment at the time of sputtering. be able to.

Further, one layer of the catalyst laminate 10 contains a noble metal, a noble metal oxide, and a non-precious metal, but the other layers include only a noble metal and a non-precious metal. , It can be similarly produced by changing the spatter environment.

Depending on the base material, the catalyst laminate 10 is often formed directly, but by the process of direct formation, a dense interface layer can be formed between the catalyst laminate 10 and the base material, and the base material protective layer can be formed. It is possible to significantly suppress the deterioration of the base material.

The MEA 20 according to the present embodiment is produced by using the above-mentioned catalyst laminate 10 as at least one of the first and second catalyst laminates 21A and 22A in FIG. 7 and binding the MEA 20 to the electrolyte membrane 23.

Generally, the catalyst laminate 10 and the electrolyte membrane 23 are bonded to each other by heating and pressurizing to prepare the MEA 20. When the base material for forming the catalyst laminate 10 is a gas diffusion layer, both electrodes of the ME 20 are laminated and bonded as shown in FIG. 7 with the electrolyte membrane 23 sandwiched between the catalyst laminate 21A and the electrode containing the catalyst laminate 22A. This gives MEA 20. When the base material for forming the catalyst laminate 10 is a transfer base material, the catalyst laminate 10 is transferred from the transfer base material to the electrolyte membrane 23 by heating and pressurizing, and then gas diffusion is performed on the catalyst laminate 10. The layer can be arranged and bonded to the counter electrode to make the MEA 20.

Joining of each member as described above is generally performed using a hot press machine. The press temperature is higher than the glass transition temperature of the polymer electrolyte used as a binder in the first electrode 21, the second electrode 22, and the electrolyte membrane 23, and is generally 100 ° C. or higher and 300 ° C. It is as follows. The press pressure and the press time depend on the hardness of the first electrode 21 and the second electrode 22, but in general, the pressure is 5 kg / cm ² or more and 200 kg / cm ² or less, and the time is 5 seconds. 20 minutes from.

The following process may be adopted for joining the catalyst laminate 10 and the electrolyte membrane 23. The electrolyte membrane 23 is formed on the base material with the catalyst laminate 10, and the counter electrode catalyst laminate 10 is attached on the electrolyte membrane 23. If the base material is a gas diffusion layer, it can be used as it is as MEA20. When the base material is a transfer base material, the gas diffusion layer is replaced before use as MEA20.
The MEA provided by the present embodiment can secure strength and substance transport efficiency by providing the catalyst laminate according to the first embodiment, and can provide sufficient durability and water electrolysis performance even with a small amount of precious metal. can.

(Third embodiment)
According to the third embodiment, an electrochemical cell comprising the MEA according to the second embodiment is provided.

FIG. 9 shows the configuration of the electrochemical cell 300 according to the present embodiment. The MEA has a structure in which a catalyst laminate 31A is formed on a base material 31B as a first electrode 31, a catalyst laminate 32A is formed on a base material 32B as a second electrode 32, and an electrolyte membrane 33 is sandwiched therein. It has become. A current collector plate 36, 37 and a tightening plate 38, 39 are attached to both sides of the MEA via gaskets 34, 35, and the electrochemical cell 300 is manufactured by tightening with an appropriate pressure.

By providing the electrochemical cell according to the second embodiment with the MEA according to the second embodiment, it is possible to provide sufficient durability and water electrolysis performance even with a small amount of precious metal.

(Fourth Embodiment)
According to this embodiment, a stack is provided. The stack 400 according to the present embodiment includes the electrochemical cell according to the third embodiment.

FIG. 10 shows the configuration of the stack according to the present embodiment. The stack 400 has a configuration in which a plurality of electrochemical cells 41 are connected in series. A stack is made by attaching tightening plates 42 to both ends of the electrochemical cell and tightening with an appropriate pressure.

By including the electrochemical cell according to the third embodiment, the stack according to the present embodiment can provide sufficient durability and water electrolysis performance even with a small amount of precious metal. Since the amount of hydrogen produced in the water electrolysis cell 300 made of one MEA 200 is small, a large amount of hydrogen can be obtained by forming a stack 400 in which a plurality of water electrolysis cells 300 (41) are connected in series.

(Fifth Embodiment)
FIG. 11 is a diagram showing a water electrolyzer according to a fifth embodiment.
In the fifth embodiment, the stack 400 is used for the water electrolyzer 500. As shown in FIG. 9, a stack of water electrolysis cells stacked in series is used as a water electrolysis stack 400. A power supply 51 is attached to the water electrolysis stack 400, and a voltage is applied between the anode and cathode. A gas-liquid separation device 52 for separating generated gas and unreacted water and a mixing tank 53 are connected to the anode side of the water electrolysis stack 400, and the mixing tank 53 is manufactured with ion-exchanged water for supplying water. Liquid is sent from the device 54 by the pump 55, mixed from the gas-liquid separation device 52 through the check valve 56, mixed in the mixing tank 53, and circulated to the anode. Oxygen generated at the anode passes through the gas-liquid separation device 52, and oxygen gas is obtained. On the other hand, on the cathode side, a hydrogen purification device 58 is continuously connected to the gas-liquid separation device 57 to obtain high-purity hydrogen. Impurities are discharged via a path having a valve 59 connected to the hydrogen purification apparatus 58. In order to stably control the operating temperature, it is possible to control the heating of the stack and the mixing tank, the current density at the time of thermal decomposition, and the like. In the water electrolyzer 500, the MEA 200 or the electrochemical cell 300 can be used in addition to the stack 400.

By providing the stack according to the fourth embodiment, the water electrolyzer according to the present embodiment can provide sufficient durability and water electrolysis performance even with a small amount of precious metal.

(Sixth Embodiment)
FIG. 12 is a diagram showing a hydrogen utilization system 600 according to a sixth embodiment.
In the sixth embodiment, the water electrolyzer 500 is used. As shown in FIG. 12, the electric power from the electric power source 61 such as solar power generation and wind power generation is converted into hydrogen gas by the water electrolyzer 500. Further, the hydrogen gas is directly supplied to the hydrogen power generation device 62 via the hydrogen power generation device 62 or the hydrogen gas tank 63. In the hydrogen power generation device 62, it is converted into electricity by reacting with air and can be used as electric power for the drive device 64. The hydrogen power generation device may be 62, a hydrogen gas turbine, a fuel cell, or the like, and the drive device 64 may be a car, a household appliance, an industrial device, or the like. By using the electrode of the present invention, it becomes possible to construct the hydrogen utilization system of the sixth embodiment with low power consumption and high durability.

(7th Embodiment)
FIG. 13 is a diagram showing a hydrogen utilization system 700 according to a seventh embodiment.
In the seventh embodiment, a unitized regenerative fuel cell (URFC) that switches between hydrogen production and power generation by water electrolysis is mounted. A water electrolysis stack 400 is used for a reversible fuel cell. As shown in FIG. 13, a stack of water electrolysis cells 300 stacked in series is used as a water electrolysis stack 400. A power source 71 for solar power generation, wind power generation, or the like is attached to the water electrolysis stack 400, and a voltage is applied between the anode and cathode in the hydrogen production mode. A gas-liquid separation device 72 for separating generated gas and unreacted water and a mixing tank 73a are connected to the anode side of the water electrolysis stack 400, and the mixing tank 73a is manufactured with ion-exchanged water for supplying water. Liquid is sent from the device 74 by the pump 75a, mixed in the mixing tank 73a through the check valve 75b from the gas-liquid separation device 72, and circulated to the anode. Oxygen generated at the anode passes through the gas-liquid separation device 72, and oxygen gas is obtained. On the other hand, on the cathode side, a hydrogen purification device 77 is continuously connected to the gas-liquid separation device 76 to obtain high-purity hydrogen. The high-purity hydrogen gas is stored in the hydrogen gas tank 73b. Impurities are discharged via a path having a valve 78 connected to the gas-liquid separator 76.

On the other hand, in the power generation mode, the high-purity hydrogen stored in the hydrogen tank 73b is supplied to the water electrolysis stack 400 and reacts with the outside air to be converted into electricity by the fuel cell reaction and used as the electric power of the drive device 79. be able to. Examples of the drive device 79 include cars, home appliances, industrial devices, and the like. By using the electrode of the present invention, it is possible to construct the hydrogen utilization system of the seventh embodiment, which is compact and compact, consumes less power, and has high durability.

(Example)
Hereinafter, examples and comparative examples will be described.

(Example 1)
<Manufacturing of electrodes>
(PEEC standard cathode)
As a base material, carbon paper Toray 060 (manufactured by Toray Industries, Inc.) having a carbon layer having a thickness of 25 μm was prepared. A catalyst layer having a laminated structure including a void layer was formed on this substrate by a sputtering method so that the loading density of the Pt catalyst was 0.1 mg / cm ^{2, and an electrode having a porous catalyst layer was obtained.} This electrode was used as the standard cathode for Examples and Comparative Examples.

(Making PEEC anode)
A titanium mesh base material was prepared as a base material.
On this substrate, a laminated body of a catalyst precursor composed of a noble metal and a non-noble metal or a mixture of oxides thereof was obtained by a reactive sputtering method. In the film formation, the precious metal and the non-precious metal are simultaneously sputtered so that desired values can be obtained in the composition ratio of the noble metal and the non-precious metal, the composition ratio of the oxygen atom and the metal atom, the number of layers, and the layer thickness of each layer of the precursor. The output (W) and spatter time (s) were adjusted as shown in Table 1.

More specifically, sputtering is performed for 180 seconds in oxygen-argon with the RF output of the noble metal Ir being 100 W and the DC output of the non-precious metal Ni being 750 W. Subsequently, the RF output of Ir is 25 W and the DC output of Ni is 50 W, and sputtering is performed for 180 seconds. Further, the RF output of the noble metal Ir is 100 W, and the DC output of the non-precious metal Ni is 750 W, and sputtering is performed for 180 seconds. Subsequently, the RF output of Ir is 25 W and the DC output of Ni is 50 W, and sputtering is performed for 180 seconds. These are repeated until the desired amount of Ir is obtained.

After sputtering, a part of Ni is removed by etching, and the etching time is adjusted so as to obtain a desired value. A laminate of A1 layer and A2 layer of the catalyst aggregate, which is a mixture of Ir and Ni, is prepared, and then heat treatment is performed to obtain an electrode composed of the catalyst laminate. The amount of precious metal catalyst is 0.1 mg / cm ² .

The required size was appropriately cut out from each electrode, and each film thickness and atomic composition fraction in the catalyst laminate were determined by EDS line analysis. The measuring method is as described in the first embodiment.
The analysis results of the prepared electrodes are shown in Table 2. In addition, pillars were confirmed from the cross-sectional HAADF image of Example 1.

<Making MEA for PEEC>
A 5 cm × 5 cm square section was cut from the PEEC standard cathode and each anode. Various PEEC MEAs were obtained by combining a standard cathode, an electrolyte membrane (Nafion 115 (manufactured by DuPont)) and an anode by thermocompression bonding.

<Making PEEC single cell>
The obtained MEA was set between two separators provided with a flow path to prepare a PEEC single cell (electrochemical cell).

<Catalyst evaluation>
For the evaluation of the catalyst, it was converted to MEA and incorporated into the electrochemical cell for evaluation, the cell temperature was set to 80 ° C. ^{, continuous operation was performed at 2 A} / cm 2 while supplying water to the anode, and the initial cell voltage was measured after 50 hours had passed. The voltage was used as an index of performance.

The evaluation criteria at this time are less than 1.9 V ... A, 1.9 to 2.0 V ... B, and when larger than 2.0 V ... C.
Further, the cell voltage was measured while performing continuous operation at 5 A / cm ² , and the operation time at the time when the voltage rose to 110% of the initial voltage was defined as the endurance time. The evaluation criteria at this time are that the durability time is less than 200 hours ... C, 200-2000 hours ... B, and greater than 2000 hours ... A. The results are shown in Table 2.

(Examples 2 to 11)
A catalyst laminate was produced by the reaction sputtering method in the same manner as in Example 1. The conditions at that time are as shown in Table 1. The results are shown in Table 2.

(Comparative Examples 1 to 11)
A catalyst laminate was produced by the reaction sputtering method in the same manner as in Example 1. The conditions at that time are as shown in Table 1. The results are shown in Table 2.

From Table 2, the single cell incorporating the MEA of Examples 1 to 11 has a lower electrolytic voltage (V) and higher durability than the single cell incorporating the MEA of Comparative Examples 1 to 11.

Further, the average thickness of the A1 layer is thicker than the average thickness of the A2 layer, the A1 layer is in the range of 4 nm or more and 35 nm or less, the A2 layer is in the range of 2 nm or more and 34 nm or less, and the Rm (A1) is in the range of 0.10 or more and 1.0 or less. , When Rm (A2) is in the range of 0.01 or more and 0.45 or less, and Rm (A1)> Rm (A2), it can be seen that both voltage and durability are good.

Further, under the condition of producing a precursor by the reactive sputtering of Ir and Ni of Example 1, the sputter output is adjusted by using a target having a noble metal amount of Ir30% and Ru70%, and IrRu and Ni are simultaneously sputtered. rice field. The spattering conditions are shown in Table 3 (Examples 12 to 22, Comparative Examples 12 to 23). The sample subjected to the simultaneous sputtering in this way was subjected to the same acid treatment and heat treatment as in Example 1, converted into MEA, and the electrolytic performance was evaluated in the evaluation cell. The results obtained are shown in Table 4.
Since the catalytic activity is improved by about 50 mV by adding Ru, the evaluation criteria at this time are less than 1.85 V ... A, 1.85 to 1.95 V ... B, and more than 1.95 V ... C. , And said. The durability time was evaluated as described above. As a result, the same performance as in Example 1 was obtained.

As described above, according to some of the present embodiments described above, it is possible to provide a catalyst laminate and a film electrode complex that are structurally stable and have high durability even in a long-term operation with a small amount of noble metal. .. At the same time, the electrochemical cell, the stack and the water electrolyzer using this catalyst layer laminate and the film electrode composite can exhibit high stability and high durability.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

10: Catalyst laminate, 11: A1 layer, 12: A2 layer, 13: pillar, 200: film electrode composite, 21: first electrode, 21A: first catalyst laminate, 21B: first substrate, 22 : 2nd electrode, 22A: 2nd catalyst laminate, 22B: 2nd base material, 23: electrolyte membrane, 300: electrochemical cell, 31: 1st electrode, 31A: 1st catalyst layer, 31B: 1st Base material, 32: 2nd electrode, 32A: 2nd catalyst layer, 32B: 2nd base material, 33: electrolyte membrane, 234, 35: gasket, 36, 37: current collector plate, 38, 39: tightening plate, 38A, 39A: Flow path, 400: Stack, 41: Electrochemical cell, 42, 43: Tightening plate, 51: Power supply, 52: Mixing tank, 53, 57: Gas-liquid separator, 54: Ion-exchanged water production device, 55: Pump, 56: Check valve, 58: Hydrogen purification device, 59: Valve; 120: Electrode, 121: Catalyst layer, 122: Void layer, 600: Hydrogen utilization system, 61: Power source, 62: Hydrogen power generation device , 63: Hydrogen gas tank, 64: Drive device, 700: Hydrogen utilization system, 71: Power source, 72: Gas-liquid separator, 73a: Mixing tank, 73b: Hydrogen gas tank, 74: Ion exchange water production device, 75a: Pump , 75b: Check valve, 76: Gas-liquid separator, 77: Hydrogen purification device, 78: Valve, 79: Drive device

Claims (14)

A catalyst laminate comprising a plurality of catalyst layers containing at least one of a noble metal and a noble metal oxide and at least one of a non-noble metal and a non-noble metal oxide.
With two or more first catalyst layers and two or more second catalyst layers,
In the atomic composition fraction of the precious metal obtained by using line analysis by energy dispersive X-ray spectroscopy with respect to the thickness direction of the catalyst laminate.
The first catalyst layer is less than the average of the highest and lowest atomic composition fractions of the noble metal.
In the second catalyst layer, the atomic composition fraction of the noble metal is equal to or higher than the average of the highest value and the lowest value.
The second catalyst layer exists between the first catalyst layers ,
The value obtained by dividing the atomic composition fraction of the non-precious metal of the first catalyst layer by the atomic fraction of the noble metal of the first catalyst layer is defined as Rm (A1), and the value of the noble metal of the second catalyst layer is defined as Rm (A1). Assuming that the value obtained by dividing the atomic composition fraction of the non-precious metal in the second catalyst layer by the atomic fraction is Rm (A2), the catalyst laminate is Rm (A1)> Rm (A2). The catalyst laminate according to claim 1, wherein the Rm (A1) is 0.1 or more and 1.0 or less. The catalyst laminate according to claim 1 or 2 , wherein the Rm (A2) is 0.01 or more and 0.45 or less. The catalyst laminate according to any one of claims 1 to 3, wherein the average thickness of the first catalyst layer is thicker than the average thickness of the second catalyst layer. Catalyst laminate according to any one of claims 1 to 4 average thickness of the first catalyst layer is 4nm or 35nm or less. The catalyst laminate according to any one of claims 1 to 5, wherein the average thickness of the second catalyst layer is 2 nm or more and 34 nm or less. The catalyst laminate according to any one of claims 1 to 6 , wherein a pillar connecting the first catalyst layers is present in the second catalyst layer. The catalyst laminate according to any one of claims 1 to 7 , wherein the proportion of the catalyst not present in the first catalyst layer is 30% or more and less than 90%. The noble metal or an oxide thereof contains at least one selected from the group consisting of Ir, Pt, Ru, Rh, Os, Pd and Au, and the non-precious metal or an oxide thereof contains Fe, Co, Ni, Mn and Al. , Zn, Ta, W, Hf , Si, Mo, Ti, Zr, Nb, V, Cr, Sn, and according to at least any one of claims 1 to 8 comprising one of which is selected from the group consisting of Sr Catalyst laminate. A membrane electrode complex comprising the catalyst laminate according to any one of claims 1 to 9. An electrochemical cell comprising the membrane electrode complex according to claim 10. A stack comprising the electrochemical cell according to claim 11. A water electrolyzer using the stack according to claim 12. Water use system using the water electrolysis apparatus according to the stack or claim 13, wherein the electrochemical cell according to claim 12 to claim 11.

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