JP2019167620A - Catalyst laminate, membrane electrode assembly, electrochemical cell, stack, water electrolysis device and water utilization system - Google Patents

Abstract

To provide a catalyst laminate, a membrane electrode assembly, an electrochemical cell, and a stack which are capable of achieving a laminated structure ensuring strength and substance transport efficiency and are capable of realizing sufficient durability and water electrolysis performance even with a small amount of noble metal.SOLUTION: A catalyst laminate in an embodiment comprises a plurality of catalyst layers containing at least one of a noble metal and an oxide of the noble metal and at least one of a non-noble metal and an oxide of the non-noble metal. The catalyst laminate comprises two or more of a first catalyst layers and two or more of a second catalyst layers. In the atomic composition fraction of the noble metal obtained using line analysis by an 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 maximum value and the minimum value of the atomic composition fraction of the noble metal, and the second catalyst layer is equal to or larger than the average of the maximum value and the minimum value of the atomic composition fraction of the noble metal. The second catalyst layer lies between the first catalyst layers.SELECTED DRAWING: Figure 2

Description

  Embodiments described herein relate generally to a catalyst laminate, a membrane electrode assembly, an electrochemical cell, a stack, a water electrolysis device, and a water utilization system.

  In recent years, electrochemical cells have been actively studied. Among electrochemical cells, for example, Polymer Electrolyte Water Electrolysis Cell (PEEC) is excellent in 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 noble metal catalyst used. In general, in order to ensure sufficient durability and water electrolysis performance, a Pt nanoparticle catalyst is used as the cathode of PEEC, and a particulate Ir-based catalyst is used as the anode. In particular, the anode was made of Ir black or Ir oxide powder, and the powder was slurried with a solvent and applied onto the substrate, and then the solvent was removed by a drying process or the like and supported on the substrate. Since the contact between the catalyst layer and the substrate is insufficient, the catalyst particles gradually desorb in a high load environment where the substrate is corroded or operated at a high current density for a long time. As a result, there was a serious problem in durability. Furthermore, Ir fine particles are aggregated, the specific surface area is reduced, and mass transport indispensable for the electrode reaction is inhibited, so that sufficient water electrolysis efficiency cannot be obtained.

  On the other hand, in the catalyst technology of the present inventors, a catalyst is sputtered on a base material by a vacuum film forming method, thereby ensuring adhesion strength with a substrate and obtaining relatively high durability with a small amount of catalyst. I can do it. In addition, the layered structure in which pores are introduced into the catalyst layer and pore layers that do not contain catalyst are alternately stacked using a pore former increases the specific surface area contributing to the electrolytic reaction and the mass transport efficiency, and reduces the amount of noble metals However, sufficient electrolysis efficiency is obtained.

JP 2012-204221 A JP 2010-33759 A JP-A-2006-62857

  The problem to be solved by the present invention is to realize a laminated structure that secures higher strength and mass transport efficiency, and provides a catalyst laminated body, membrane electrode composite, electric, which can obtain sufficient durability and water electrolysis performance even with a small amount of noble metal It is to provide chemical cells and stacks.

  The catalyst stack of the embodiment is a catalyst stack including a plurality of catalyst layers including 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 two or more first catalysts A first catalyst in the atomic composition fraction of the noble metal obtained using line analysis by energy dispersive X-ray spectroscopy in the thickness direction of the catalyst stack. The layer is below 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 is present between the first catalyst layers.

The SEM image of the conventional catalyst laminated body. FIG. 3 is a diagram illustrating an example of an EDS line analysis according to the first embodiment. 1 is an HAADF image according to Example 1; FIG. 4 is a partially enlarged view of FIG. 3. The binarized image of FIG. The catalyst amount measurement schematic in a catalyst layer. Sectional drawing of the membrane electrode assembly (MEA) which concerns on 2nd Embodiment. Explanatory drawing which shows the manufacturing method of the catalyst laminated body and electrode which concern 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. In addition, the same code | symbol shall be attached | subjected to a common structure through embodiment, and the overlapping description is abbreviate | omitted. Each figure is a schematic diagram for promoting explanation and understanding of the embodiment, and its shape, dimensions, ratio, etc. are different from the actual device, but these are the following explanations and known techniques. The design can be changed as appropriate.

(First embodiment)
FIG. 1 is an SEM image of a conventional catalyst laminate. A catalyst laminate structure in which two or more void layers 122 and catalyst layers 121 are alternately laminated as shown in FIG. 1 has been developed as an electrode having relatively high durability and high specific surface area. However, regarding the anode for water electrolysis, the ends of the catalyst layer 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 by the base material. Thereby, it becomes a stable structure in which deformation is suppressed with respect to the pressure in the stacking direction, and relatively high durability can be obtained. However, the load on the structure is large when continuously exposed to high current, high temperature, and high pressure, and there is room for improvement in improving durability while maintaining mass transport efficiency.

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

  According to this embodiment, a catalyst laminate 10 is provided. The catalyst stack 10 is a catalyst stack 10 including a plurality of catalyst layers including 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.

  This catalyst layer is the highest and lowest compositional fractions of noble metal atoms measured in a cross section of the catalyst laminate 10 in an energy dispersive X-ray spectroscopy (EDS) line analysis described later. A layer having a composition fraction lower than the average (first catalyst layer: A1 layer 11), and a layer having a composition fraction higher than the average of the highest and lowest composition fractions of noble metal atoms (second catalyst). Layer: A2 layer including 12).

  The catalyst stack 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 alternately arranged. The second catalyst layer 12 is disposed between the first catalyst layers 11. The first catalyst layer 11 and the second catalyst layer 12 are preferably in direct contact with each other.

  FIG. 2 is an example of a chart (figure) obtained by EDS line analysis, where the horizontal axis represents the distance in the depth direction (nm), the vertical axis represents the atomic composition fraction (atom%), 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 it is a laminated structure in which the A2 layers 12 are alternately stacked between the A1 layers 11, the catalyst laminated body 10 can be prevented from being deformed and high strength can be secured, and Even a small amount of noble metal can exist stably in a high load environment of high current, high temperature and high pressure. In FIG. 2, the measurement depth shows a part of the result up to about 70 nm in the chart. Even in a region deeper than 70 nm, the A1 layers 11 and the A2 layers 12 are alternately present.

  Furthermore, since both the A1 layer 11 and the A2 layer 12 have a structure with a gap on the order of nm, and the specific surface area can be increased, the material transport can be performed smoothly and the catalytic activity can be improved.

The catalyst layer will be described in detail.
As the catalyst material employed in the catalyst layer of the present embodiment, other additives can be appropriately selected according to the electrode reaction. From the viewpoint of catalytic activity and durability, a noble metal or noble metal oxide catalyst is included, 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's it. Further, from the viewpoint of forming a stable and strong laminated structure, non-noble metals or oxides thereof are included, and non-noble metal elements contained in the catalyst layer are Fe, Co, Ni, Mn, Al, Zn, Ta, W, Hf. , Si, Mo, Ti, Zr, Nb, V, Cr, Sn, and Sr.

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

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

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

  In order to perform observation using a HAADF image, the sample is embedded in a resin and processed to a thickness of 0.1 μm. 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. In FIG. 4, a plurality of pillars 13 can be observed in the A2 layer 12. Details of the pillar 13 will be described later.

  In order to obtain the non-noble metal atomic composition fraction (atom%) and the noble metal atomic composition fraction (atom%) of the catalyst layer, elemental composition analysis is performed by EDS line analysis. 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 noble metals and non-noble metals is measured. First, HAADF images for 20 samples are prepared. For each of the samples thus obtained, EDS line analysis is performed 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 from the HAADF image. Based on the result of each line, the maximum value and the minimum value of the composition fraction of the noble metal atoms are obtained, and the layer having a composition fraction less than the average of them is designated as A1 layer 11, and the maximum value and the minimum value of the composition fraction are A layer having a composition fraction higher than the average is defined as A2 layer 12, and the boundary line between A1 layer 11 and A2 layer 12 is clarified by connecting the boundaries. Even when a catalyst laminate is produced using two or more kinds of noble metals and non-noble metals, the maximum value of the atomic composition fraction of noble metals in the EDS line analysis is the sum of the noble metals (for example, the maximum of noble metals A). Value + maximum value of precious metal B). This is calculated in the same way for the minimum value of the atomic composition fraction of the noble metal.

  From the EDS line analysis, the ratio of non-noble metal Rm in each layer, that is, the ratio of (non-noble metal composition fraction) / (noble metal composition fraction) of each of the A1 layer 11 and A2 layer Rm (A1), Rm (A2) Ask for. Rm (A1) is preferably between 0.1 and 1.0. This is because cocatalysis occurs due to the remaining non-noble metal, and the activity increases. However, if the proportion of non-noble metals is too small (Rm (A1) is smaller than 0.1), the effect of the promoter is small and it becomes difficult to maintain a structure having appropriate voids (portions where no catalyst is present). Therefore, it is not preferable, and if the ratio of non-noble metal is too large (Rm (A1) is greater than 1.0), noble metal dissolves into the electrolyte membrane 23 in the membrane electrode assembly 20, and proton conduction of the electrolyte membrane 23 is prevented. Since it inhibits, it is not preferable. 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. Rm (A2) is preferably in the range of 0.01 to 0.45. If the ratio of non-noble metals is too small (Rm (A2) is smaller than 0.01), the amount of voids is small and the diffusion of substances such as water and oxygen is slow, and the ratio of non-noble metals is large (Rm (A2) is This is because the non-noble metal melts during operation of the electrochemical cell, and the A2 layer 12 is crushed and the mass transport performance is lowered. The range of Rm (A2) is more preferably 0.05 or more and 0.4 or less. If this is 0.05 or more, the catalytic activity increases due to the cocatalyst action of the non-noble metal and the overall characteristics are improved. It is possible to improve the durability.

  From the viewpoint of stability, the average thickness of the A1 layer 11 is preferably larger than the average thickness of the A2 layer 12. From the same viewpoint, the average thickness of the A1 layer 11 is more preferably 1.5 times or more and 2.0 times or less than the average thickness of the A2 layer 12. Further, as the A1 layer 11 becomes thicker, the diffusibility of the substance moving inside the A1 layer 11 becomes worse. On the other hand, if the A1 layer 11 is too thin, it is easily deformed and long-term stability cannot be secured. The thickness is preferably 4 nm or more and 35 nm or less.

  The thicker the A2 layer 12 is, the better the diffusibility of the substance moving inside the A2 layer 12 is. On the other hand, if the A2 layer 12 is too thick, the A2 layer 12 is crushed during electrochemical cell operation or hot pressing, resulting in poor stability. 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 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 diffusibility 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 determined by EDS line analysis. In addition, the average thickness of the A1 layer 11 is an average value of the thickness per one layer of the A1 layer 11 calculated from the boundary line obtained from the line analysis. Moreover, the average thickness of the A2 layer 12 is an average value of the thickness per one layer of the A2 layer 12 calculated from the boundary line obtained from the line analysis.

  In order to promote the material transport 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 material transport, the catalyst on the substrate side can be used, and the activity of the entire catalyst stack 10 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 stack 10 is constant, it is preferable to increase the thickness of one layer of the A1 layer 11 having a large amount of noble metal serving as a catalyst. The moving distance of the substance that diffuses through the laminate 10 to the base material can be shortened, and the activity of the catalyst laminate 10 as a whole can be improved. However, as described above, if the thickness per layer of the A1 layer 11 is increased, the material diffusibility is suppressed, which is not preferable.

  Therefore, in this embodiment, since the A1 layer 11 can be made to have a thickness that can improve the activity and the substance diffusibility as the catalyst laminate 10, and the A2 layer 12 can be made the minimum thickness that does not inhibit the substance transport, The overall thickness of the catalyst stack 10 can be reduced while improving the overall activity of the body 10.

Although details of the manufacturing method of the catalyst stack 10 will be described later, these stacked structures can be manufactured by laminating a mixed layer of noble metal and non-noble metal by multi-source sputtering and then washing away some non-noble metal by etching. Although the structure before etching is proportional to the output ratio at the time of sputtering and the sputtering time, non-noble metals are eluted by etching, and the A1 layer 11 and the A2 layer 12 tend to collapse and contract. When the proportion of non-noble metal is large, the non-noble metal ratio (Rm) of the non-noble metal A1 layer 11 and A2 layer 12 is high in both the A1 layer 11 and the A2 layer 12. However, since non-noble metals are easily dissolved by etching, even when there are too many non-noble metals in each layer, the ratio of non-noble metals does not continue to increase and does not exceed a certain level.
However, if a large amount of non-noble 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 performed sufficiently and the A1 layer 11 and the A2 layer 12 The non-noble metal ratio (Rm) tends to increase. Further, when the concentration of the solution used for etching is increased or when the etching time is increased, the non-noble 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 stack 10 while suppressing the overall thickness of the catalyst stack 10, the thickness ranges of the A1 layer 11 and the A2 layer 12 described above, More preferably, Rm (A1)> Rm (A2). By satisfying Rm (A1)> Rm (A2), since rapid deformation can be suppressed, it is possible to contribute to improving durability.

Next, a method for 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 locations within 10% are observed from where the long side and short side of the substrate of the membrane electrode assembly intersect. The observation unit appropriately sets the magnification so that the field of view becomes 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 obtained in this way, it is effective to obtain the black and white contrast ratio. By obtaining the black-and-white contrast ratio in the TEM image, as shown in FIG. 5, it is shown that the catalyst is present in a region close to white, and the portion where no catalyst is present is shown in black. Analysis using the TEM image described below is performed to clarify the structural features. The apparatus and analysis conditions used for TEM observation and the software used for image analysis are as follows.
[TEM measurement conditions]
InstructName = TalosF200X (made by FEI)
AcceleratingVoltage = 200,000V
Magnification = 320,000
[TEM image analysis software]
PhotoImpact (COREL product)
Image-Pro plus (Media Cybernetics)

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

  At this time, as shown in FIG. 6, the ranges of the A1 layer 11 and the A2 layer 12 are the thickness of each layer obtained by EDS line analysis and a straight line orthogonal to the thickness, and are “enclosed” by the width of the TEM image. Is the range indicated by.

  In the TEM image, the portion of each A1 layer 11 where the catalyst is not present is preferably 30% or more and less than 90% by area ratio. This is because if 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 suppress the diffusion resistance of the substance moving in the A1 layer 11 and to achieve both structural durability more efficiently.

  In the A2 layer 12, the area where the catalyst is not present is preferably 30% or more and 95% or less by area ratio. This is because, if it is less than 30%, the portion where the catalyst does not exist is small, and the transport of water necessary for the reaction and the generated oxygen is slowed, resulting in an increase in overvoltage. Further, if the portion where the catalyst is not present is larger than 95%, the structure is brittle, the structure is crushed in a long-term operation, the substance diffusion is delayed, and an overvoltage rise is caused. In the A2 layer 12, the portion where the catalyst is not present is more preferably 35% or more and 70% or less. By being in this range, it is possible to more efficiently suppress an overvoltage increase caused by slowing of material transport.

  As shown in FIG. 5, a catalyst may exist in the A2 layer 12 so as to connect the A1 layers 11 together. This catalyst portion is called a pillar 13. The presence of this pillar 13 allows the pillar 13 to play a role like a support in the A2 layer 12 in long-term operation, so that the thickness of the A2 layer 12 can be maintained, and the A1 layers 11 are connected to each other. Therefore, peeling of the A1 layer 11 can be prevented.

  In the catalyst laminate 10 provided by the present embodiment, the A1 layer 11 controls the composition of noble metal atoms and maintains an optimum thickness, while the A2 layer 12 is thin to the minimum thickness that allows reaction and product to diffuse. Furthermore, 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 that ensures strength and mass transport efficiency even with a small amount of noble metal.

(Second Embodiment)
In 2nd Embodiment, as shown in FIG. 7, the membrane electrode assembly (Membrane Electrode Assembly: MEA) 20 provided with the catalyst laminated body 10 which concerns on 1st Embodiment is provided. The MEA 20 includes a first electrode 21 and a second electrode 22 and an electrolyte membrane 23 disposed therebetween.

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

  First, the base material and the electrolyte membrane constituting the MEA 20 will be described in order.

<Base material>
The electrode substrate is generally required to be porous and conductive. When used as an anode of a water electrolysis cell, a titanium material is generally employed to ensure durability. Although it does not specifically limit about the form of a base material, The close which consists of a titanium mesh and a titanium fiber, a titanium nonwoven fabric, a titanium sintered compact, etc. are mentioned. The water electrolysis performance may be improved by adjusting the aperture ratio of the porous substrate, particularly the structure of the portion in contact with the catalyst laminate 10, or the surface treatment of the substrate such as blasting. This is probably because water supply to the catalyst stack 10 and discharge of the electrode reaction product were smoothed, and the electrode reaction in the catalyst stack 10 was promoted. You may attach another coating layer on a base material. In some cases, the durability of the electrode is greatly improved by the dense conductive layer. Although a coating layer is not specifically limited, Ceramic materials, such as a metal material, an oxide, and nitride, carbon, etc. can be used.

<Electrolyte membrane>
The electrolyte membrane is often required to have ionic conductivity. Examples of the electrolyte membrane having proton conductivity include a fluororesin having a sulfonic acid group (for example, Nafion (manufactured by DuPont), Flemion (manufactured by Asahi Kasei Co., Ltd.), and Ashiblek (manufactured by Asahi Glass Co., Ltd.)), a hydrocarbon membrane, 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, dissolution resistance and MEA output characteristics, the thickness of the electrolyte membrane when dried is preferably 10 μm or more and 200 μm or less.

  Hereafter, the manufacturing method of the electrode which has the catalyst laminated body 10 concerning this embodiment, and the structure and manufacturing method of MEA are demonstrated using FIG.

  As for the anode, a material including a catalyst material and a pore former material are formed on the Ti base material 21B using a vacuum apparatus, and a precursor of the catalyst laminate 10 is produced. For the production of the Ir oxide-based catalyst laminate 10, a reactive sputtering method such as adding oxygen gas to a 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 source power and substrate temperature during sputtering (step 1).

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

  Basically, as the precursor of the catalyst laminate 10, a catalyst material mainly composed of a noble metal and a pore former material composed of a non-noble metal are simultaneously formed on a base by sputtering or vapor deposition. In the film formation, the composition ratio, the number of layers, the layer thickness, etc., of the noble metal and the non-noble metal of each layer before etching of the catalyst laminate 10 are determined according to the power source power, gas pressure, catalyst material and pore forming material at the time of precursor film formation. It can be adjusted by the deposition rate. More specifically, the thickness of the A1 layer 11 and the A2 layer 12 decreases as the noble metal output decreases, and the thickness of the A1 layer 11 and the A2 layer 12 increases as the noble metal output increases. Furthermore, the catalyst layer thickness, shape, composition ratio in the catalyst layer, and the structure of the catalyst laminate 10 can also be adjusted in the etching process of the pore forming material using a chemical solution such as acid or alkali.

  Further, after removing the pore former, the structure of the catalyst laminate 10 can be adjusted by performing a post-treatment such as a heat treatment as necessary, and the catalyst activity can be adjusted by arbitrarily adjusting the laminate structure. And durability can be improved (step 3).

  For example, control of Rm (A1) and Rm (A2) by washing with acid aqueous solution such as nitric acid, hydrochloric acid, sulfuric acid or the like or alkaline aqueous solution such as sodium hydroxide, potassium hydroxide, ammonia, etc. 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, and the catalytic activity and durability can be improved.
Although the manufacturing method of the oxide-based catalyst stack 10 has been described so far, when the catalyst stack 10 containing no oxide is manufactured, it is manufactured by the same method except that oxygen is not used for the environment during sputtering. be able to.

  Further, one layer of the catalyst laminate 10 includes a noble metal, a noble metal oxide, and a non-noble metal, but the other layer also includes a catalyst laminate 10 having different compositions such as a noble metal and a non-noble metal. It can be similarly produced by changing the sputtering environment.

  In many cases, depending on the substrate, the catalyst laminate 10 is directly formed. However, by the process of forming directly, a dense interface layer can be formed between the catalyst laminate 10 and the substrate. It is possible to greatly suppress the deterioration of the base material.

  The MEA 20 according to this embodiment is manufactured by using the above-described catalyst laminate 10 as at least one of the first and second catalyst laminates 21A and 22A in FIG.

  In general, the catalyst laminate 10 and the electrolyte membrane 23 are joined by heating and pressurizing to produce the MEA 20. Both electrodes of the ME 20 are laminated and bonded as shown in FIG. 7 with the electrolyte membrane 23 sandwiched between electrodes including the catalyst laminate 21A and the catalyst laminate 22A when the base material of the catalyst laminate 10 is a gas diffusion layer. As a result, MEA 20 is obtained. When the formation substrate of the catalyst laminate 10 is a transfer substrate, the catalyst laminate 10 is transferred from the transfer substrate to the electrolyte membrane 23 by heating and pressing, and then gas diffusion is performed on the catalyst laminate 10. The MEA 20 can be fabricated by arranging the layers and bonding them to the counter electrode.

Joining of each member as described above is generally performed using a hot press machine. The pressing temperature is higher than the glass transition temperature of the polymer electrolyte used as the 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 pressing pressure and the pressing time depend on the hardness of the first electrode 21 and the second electrode 22, but generally the pressure is 5 kg / cm ² or more and 200 kg / cm ² or less, and the time is 5 seconds. 20 minutes.

It should be noted that the following process may be employed for joining the catalyst laminate 10 and the electrolyte membrane 23. The electrolyte membrane 23 is formed on the substrate with the catalyst laminate 10, and the counter electrode catalyst laminate 10 is attached thereon. If a base material is a gas diffusion layer, it can be used as MEA20 as it is. When the substrate is a transfer substrate, the gas diffusion layer is replaced before use as the MEA 20.
The MEA provided by the present embodiment includes the catalyst laminate according to the first embodiment, thereby ensuring strength and material transport efficiency, and providing sufficient durability and water electrolysis performance even with a small amount of noble metal. it can.

(Third embodiment)
According to 3rd Embodiment, an electrochemical cell provided with MEA which concerns on 2nd Embodiment is provided.

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

  By including the MEA according to the second embodiment, the electrochemical cell according to the present embodiment can provide sufficient durability and water electrolysis performance even with a small amount of noble 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 this embodiment. The stack 400 has a configuration in which a plurality of electrochemical cells 41 are connected in series. A clamping plate 42 is attached to both ends of the electrochemical cell, and a stack is produced by clamping with an appropriate pressure.

  The stack according to the present embodiment includes the electrochemical cell according to the third embodiment, so that sufficient durability and water electrolysis performance can be provided even with a small amount of noble metal. Since the amount of hydrogen produced in the water electrolysis cell 300 composed of one MEA 200 is small, a large amount of hydrogen can be obtained by configuring a stack 400 in which a plurality of water electrolysis cells 300 (41) are connected in series.

(Fifth embodiment)
FIG. 11 is a diagram illustrating a water electrolysis apparatus according to a fifth embodiment.
In the fifth embodiment, a stack 400 is used for the water electrolysis apparatus 500. As shown in FIG. 9, a water electrolysis stack 400 is formed by stacking water electrolysis cells in series. A power source 51 is attached to the water electrolysis stack 400, and a voltage is applied between the anode and the cathode. The anode side of the water electrolysis stack 400 is connected to a gas-liquid separation device 52 and a mixing tank 53 for separating the generated gas and unreacted water. The solution is fed from the device 54 by the pump 55, mixed from the gas-liquid separator 52 through the check valve 56, mixed in the mixing tank 53 and circulated to the anode. Oxygen produced at the anode is passed through a gas-liquid separator 52 to obtain oxygen gas. On the other hand, on the cathode side, a hydrogen purifier 58 is connected continuously to the gas-liquid separator 57 to obtain high purity hydrogen. Impurities are discharged through a path having a valve 59 connected to the hydrogen purifier 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 during pyrolysis, and the like. The water electrolysis apparatus 500 can use the MEA 200 or the electrochemical cell 300 in addition to the stack 400.

  The water electrolysis apparatus according to the present embodiment includes the stack according to the fourth embodiment, so that sufficient durability and water electrolysis performance can be provided even with a small amount of noble metal.

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

(Seventh embodiment)
FIG. 13 is a diagram illustrating a hydrogen utilization system 700 according to the seventh embodiment.
In the seventh embodiment, a reversible fuel cell (URFC) in which hydrogen production by water electrolysis and power generation are switched is mounted. A water electrolysis stack 400 is used for the reversible fuel cell. As shown in FIG. 13, a water electrolysis stack 400 in which water electrolysis cells 300 are stacked in series is used. A power source 71 such as solar power generation or wind power generation is attached to the water electrolysis stack 400, and a voltage is applied between the anode and cathode in the hydrogen production mode. The anode side of the water electrolysis stack 400 is connected to a gas-liquid separator 72 and a mixing tank 73a for separating generated gas and unreacted water. Liquid is fed from the device 74 by the pump 75a, mixed from the gas-liquid separation device 72 through the check valve 75b, mixed by the mixing tank 73a, and circulated to the anode. Oxygen generated at the anode is passed through a gas-liquid separator 72 to obtain oxygen gas. On the other hand, on the cathode side, a hydrogen purifier 77 is connected continuously to the gas-liquid separator 76 to obtain high purity hydrogen. High purity hydrogen gas is stored in the hydrogen gas tank 73b. Impurities are discharged through a path having a valve 78 connected to the gas-liquid separator 76.

  On the other hand, in the power generation mode, high-purity hydrogen stored in the hydrogen tank 73b is supplied to the water electrolysis stack 400 and reacts with external air, so that it is converted into electricity by the fuel cell reaction and used as power for the drive device 79. be able to. Examples of the driving device 79 include cars, home appliances, and industrial devices. By using the electrode of the present invention, it is possible to construct the hydrogen utilization system of Embodiment 7 that is small and compact, consumes less power, and has high durability.

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

Example 1
<Production of electrode>
(PEEC standard cathode)
As a base material, carbon paper Toray060 (made by Toray Industries, Inc.) having a carbon layer with a thickness of 25 μm was prepared. On this substrate, a catalyst layer having a laminated structure including a void layer was formed by a sputtering method so that the loading density of the Pt catalyst was 0.1 mg / cm ² to obtain an electrode having a porous catalyst layer. This electrode was used as a standard cathode in Examples and Comparative Examples.

(PEEC anode fabrication)
A titanium mesh substrate was prepared as the substrate.
On this base material, a laminate of a catalyst precursor made of a mixture of a noble metal and a non-noble metal or an oxide thereof was obtained by reactive sputtering. In the film formation, the precious metal and non-noble metal composition ratio, the oxygen atom and metal atom composition ratio, the number of layers, and the layer thickness of each precursor layer are obtained at the time of simultaneous sputtering of the noble metal and non-noble metal. The output (W) and sputtering time (s) were adjusted as shown in Table 1.

  More specifically, sputtering is performed in oxygen-argon for 180 seconds with an RF output of noble metal Ir of 100 W and a non-noble metal Ni DC output of 750 W. Subsequently, sputtering is performed for 180 seconds with an Ir RF output of 25 W and a Ni DC output of 50 W. Further, sputtering is performed for 180 seconds with the RF output of the noble metal Ir being 100 W and the DC output of the non-noble metal Ni being 750 W. Subsequently, sputtering is performed for 180 seconds with an Ir RF output of 25 W and a Ni DC output of 50 W. 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 and A2 layers of a catalyst aggregate that is a mixture of Ir and Ni is produced, and then heat treatment is performed to obtain an electrode composed of the catalyst laminate. The amount of noble metal catalyst is all 0.1 mg / cm ² .

A necessary 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 measurement method is as described in the first embodiment.
The analysis results of the produced electrodes are shown in Table 2. Moreover, the pillar was confirmed from the cross-sectional HAADF image of Example 1.

<Production of MEA for PEEC>
A 5 cm × 5 cm square section was cut from the PEEC standard cathode and each anode. A standard cathode, an electrolyte membrane (Nafion 115 (manufactured by DuPont)), and an anode were combined and thermocompression bonded to obtain various PEEC MEAs.

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

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

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

(Examples 2 to 11)
A catalyst laminate was produced by the reactive 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 1-11)
A catalyst laminate was produced by the reactive 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 electrolysis voltage (V) and higher durability than the single cell incorporating the MEA of Comparative Examples 1 to 11.

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

Further, under the conditions for producing the precursor by the reactive sputtering of Ir and Ni in Example 1, the sputtering output is adjusted using a target having a noble metal amount of Ir 30% and Ru 70%, and IrRu and Ni are simultaneously sputtered. It was. The sputtering conditions are shown in Table 3 (Examples 12 to 22, Comparative Examples 12 to 23). The sample subjected to the simultaneous sputtering in this manner was subjected to the same acid treatment and heat treatment as in Example 1 and converted to MEA, and the electrolytic performance was evaluated using an evaluation cell. Table 4 shows the obtained results.
Since the catalytic activity is improved by about 50 mV by adding Ru, the evaluation standard at this time is less than 1.85 V ... A, 1.85 to 1.95 V ... B, more than 1.95 V ... C , And. The durability time evaluation was performed as described above. As a result, the same performance as in Example 1 was obtained.

  As described above, according to some of the embodiments described above, it is possible to provide a catalyst laminate and a membrane electrode assembly that are structurally stable and have high durability even during long-term operation with a small amount of noble metal. . At the same time, the electrochemical cell, stack, and water electrolysis apparatus employing the catalyst layer laminate and the membrane electrode assembly can exhibit high stability and high durability.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

10: catalyst laminate, 11: A1 layer, 12: A2 layer, 13: pillar, 200: membrane electrode composite, 21: first electrode, 21A: first catalyst laminate, 21B: first substrate, 22 : Second electrode, 22A: second catalyst laminate, 22B: second substrate, 23: electrolyte membrane, 300: electrochemical cell, 31: first electrode, 31A: first catalyst layer, 31B: first Substrate, 32: second electrode, 32A: second catalyst layer, 32B: second substrate, 33: electrolyte membrane, 234, 35: gasket, 36, 37: current collector plate, 38, 39: clamping plate, 38A, 39A: flow path, 400: stack, 41: electrochemical cell, 42, 43: clamping plate, 51: power supply, 52: mixing tank, 53, 57: gas-liquid separator, 54: ion-exchange water production device, 55: pump, 56: check valve, 58: hydrogen purifier, 59: valve; 1 0: electrode, 121: catalyst layer, 122: void layer, 600: hydrogen utilization system, 61: power source, 62: hydrogen power generation device, 63: hydrogen gas tank, 64: driving device, 700: hydrogen utilization system, 71: power Source: 72: Gas-liquid separation device, 73a: Mixing tank, 73b: Hydrogen gas tank, 74: Ion exchange water production device, 75a: Pump, 75b: Check valve, 76: Gas-liquid separation device, 77: Hydrogen purification device, 78: Valve, 79: Drive device

Claims (15)

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,
Comprising two or more first catalyst layers and two or more second catalyst layers;
In the atomic composition fraction of the noble metal obtained 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;
The second catalyst layer has an atomic composition fraction of the noble metal equal to or higher than an average of the highest value and the lowest value,
A catalyst laminate in which the second catalyst layer is present between the first catalyst layers.   A value obtained by dividing the atomic composition fraction of the non-noble metal of the first catalyst layer by the atomic fraction of the noble metal of the first catalyst layer is Rm (A1), and the noble metal of the second catalyst layer 2. The catalyst laminate according to claim 1, wherein Rm (A1)> Rm (A2), where Rm (A2) is a value obtained by dividing the atomic composition fraction of the non-noble metal of the second catalyst layer by the atomic fraction. .   The catalyst laminate according to claim 1 or 2, wherein the Rm (A1) is 0.1 or more and 1.0 or less.   The catalyst laminate according to any one of claims 1 to 3, wherein the Rm (A2) is 0.01 or more and 0.45 or less.   5. The catalyst laminate according to claim 1, wherein an average thickness of the first catalyst layer is thicker than an average thickness of the second catalyst layer.   6. The catalyst laminate according to claim 1, wherein an average thickness of the first catalyst layer is 4 nm or more and 35 nm or less.   The catalyst laminate according to any one of claims 1 to 6, wherein an 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 7, wherein pillars that connect the first catalyst layers are present in the second catalyst layer.   The catalyst laminate according to any one of claims 1 to 8, wherein a proportion of the catalyst not present in the first catalyst layer is 30% or more and less than 90%.   The noble metal or oxide thereof includes at least one selected from the group consisting of Ir, Pt, Ru, Rh, Os, Pd and Au, and the non-noble metal or oxide thereof is Fe, Co, Ni, Mn, Al 10. At least one selected from the group consisting of Zn, Ta, W, Hf, Si, Mo, Ti, Zr, Nb, V, Cr, Sn, and Sr. Catalyst laminate.   The membrane electrode assembly containing the catalyst laminated body of any one of Claims 1 thru | or 10.   An electrochemical cell comprising the membrane electrode assembly according to claim 11.   A stack comprising the electrochemical cell according to claim 12.   A water electrolysis apparatus using the stack according to claim 13. A water utilization system using the electrochemical cell according to claim 12, the stack according to claim 13, or the water electrolysis apparatus according to claim 14.