Electrode catalyst layer for electrochemical cell, membrane electrode assembly for electrochemical cell, and electrochemical cell

Abstract

An electrode catalyst layer for an electrochemical cell has a first catalyst layer and a second catalyst layer. The cell resistance of the first catalyst layer measured at 80°C and 40% RH is lower than the cell resistance of the second catalyst layer. The electrode catalyst layer for the electrochemical cell is used in a manner that the first catalyst layer is disposed closer to the electrolyte membrane side than the second catalyst layer. It is preferable that the first catalytically active component included in the first catalyst layer and the second catalytically active component included in the second catalyst layer each independently include at least one element selected from the group consisting of platinum, palladium, ruthenium, and iridium.

Description

Technical Field

[0001] This invention relates to an electrode catalyst layer for electrochemical cells, a membrane electrode assembly for electrochemical cells, and an electrochemical cell. Background Technology

[0002] In electrochemical cells such as solid polymer fuel cells and water electrolysis devices, catalyst supports on which precious metal catalysts such as platinum are loaded are used as electrode catalyst layers. From the perspective of efficient catalyst utilization, carbonaceous materials, which have a large specific surface area, are mostly used as catalyst supports.

[0003] In recent years, research has been conducted to improve the catalytic activity of electrochemical cells operating in the intermediate temperature range of 100°C to 300°C. However, even in this temperature range or at temperatures around 80°C lower, carbonaceous supports tend to oxidize and disappear, contributing to catalyst detachment and electrolyte membrane degradation. As a method to improve the durability of carbonaceous supports, the use of highly crystalline carbonaceous materials is being investigated, but even this is insufficient to significantly enhance durability. Therefore, research is underway to replace carbonaceous supports with those formed from metal oxides.

[0004] On the other hand, the aforementioned electrochemical cell undergoes an electrode reaction at the three-phase interface, generating water within the catalyst layer. While the generated water dissipates from the catalyst layer, it can accumulate in some cases. If this accumulation becomes excessive, the catalyst layer becomes unable to fully contain the water, causing a phenomenon known as overflow. Patent documents 1 and 2 propose methods to prevent this overflow phenomenon.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2004-171847

[0008] Patent Document 2: US2017 / 141407A1 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] Because the aforementioned supports formed from metal oxides have higher polarity than those made from carbonaceous materials, electrode reactions can become difficult to proceed smoothly in extreme environments such as high humidity (leading to overflow) or low humidity (leading to low humidity). As mentioned above, techniques for improving electrode reactions under high humidity conditions have been proposed in the past, but no techniques have been proposed to improve electrode reactions under both low and high humidity conditions.

[0011] Therefore, the objective of this invention is to provide an electrode catalyst layer for an electrochemical battery that is durable and allows for smooth electrochemical reactions under both low-humidity and high-humidity conditions.

[0012] This invention provides an electrode catalyst layer for an electrochemical battery, which comprises a first catalyst layer and a second catalyst layer.

[0013] The first catalyst layer includes a first catalyst support, which is formed by loading the first catalytically active component onto a support containing a first metal oxide.

[0014] The second catalyst layer includes a second catalyst support, which is formed by loading the second catalytically active component onto a support containing a second metal oxide.

[0015] The cell resistance of the first catalyst layer, measured by the current interruption method at 80℃ and 40%RH, is lower than that of the second catalyst layer.

[0016] The electrode catalyst layer for the electrochemical cell is used in such a manner that the first catalyst layer is positioned closer to the electrolyte membrane than the second catalyst layer.

[0017] This invention provides an electrode catalyst layer for an electrochemical battery, which comprises a first catalyst layer and a second catalyst layer.

[0018] The first catalyst layer includes a first catalyst support, which is formed by loading a first catalytically active component onto a support containing a first metal oxide.

[0019] The second catalyst layer includes a second catalyst support, which is formed by loading the second catalytically active component onto a support containing a second metal oxide.

[0020] The cumulative volumetric particle size D at 50% capacity of the first catalyst support was determined by laser diffraction / scattering particle size distribution method. 50 The cumulative volumetric particle size D at 50% capacity of the second catalyst support was determined by laser diffraction / scattering particle size distribution method. 50 big,

[0021] In the pore size distribution determined by mercury porosimetry,

[0022] Peaks were observed in the first catalyst layer in the range of 0.005 μm to less than 0.1 μm and in the range of 0.1 μm to less than 1 μm.

[0023] At least one peak was observed in the second catalyst layer in the range above 0.005 μm and below 0.1 μm.

[0024] The electrode catalyst layer for the electrochemical cell is used in such a manner that the first catalyst layer is positioned closer to the electrolyte membrane than the second catalyst layer. Detailed Implementation

[0025] The present invention will now be described based on its preferred embodiments. The present invention relates to an electrode catalyst layer for an electrochemical cell. The electrode catalyst layer comprises at least two layers: a first catalyst layer and a second catalyst layer. The first catalyst layer and the second catalyst layer are preferably in direct contact. In this case, no other catalyst layer or layer other than a catalyst layer is intentionally formed between the two catalyst layers. In the following description, the term "electrode catalyst layer" is used to refer to both the first catalyst layer and the second catalyst layer.

[0026] When the electrode catalyst layer of the present invention is assembled in an electrochemical cell, the electrode catalyst layer is used such that the first catalyst layer is positioned closer to the electrolyte membrane than the second catalyst layer. For example, it is positioned such that the first catalyst layer is in direct contact with the electrolyte membrane. In this case, it is preferable that no other catalyst layer or other layer besides a catalyst layer is intentionally formed between the first catalyst layer and the electrolyte membrane. Of course, other catalyst layers or other layers besides a catalyst layer may also be disposed between the first catalyst layer and the electrolyte membrane as needed.

[0027] Regarding the second catalyst layer, it can be used in a manner where the second catalyst layer is in direct contact with the gas diffusion layer, or other layers such as a microporous layer can be sandwiched between the second catalyst layer and the gas diffusion layer.

[0028] The first catalyst layer comprises a first catalyst support, which is formed by loading a first catalytically active component onto a support containing a first metal oxide. Conversely, the second catalyst layer comprises a second catalyst support, which is formed by loading a second catalytically active component onto a support containing a second metal oxide. The first and second catalyst layers can be distinguished, for example, by the particle size of the catalyst support (e.g., the volumetric cumulative particle size D). 50 Alternatively, the first and second catalyst layers can be distinguished by the type of catalytically active component or the type of support. Or, the first and second catalyst layers can be distinguished by their physical properties, such as battery resistance.

[0029] In this invention, the first catalyst layer and the second catalyst layer constituting the electrode catalyst layer are each endowed with different functions. Specifically, the first catalyst layer has the function of suppressing the reduction of electrochemical reaction even when the electrode catalyst layer is in a low-wet state.

[0030] On the other hand, the second catalyst layer has the function of suppressing the reduction of electrochemical reaction even when the electrode catalyst layer is in a highly humid state. As a result, the electrode catalyst layer of the present invention can smoothly carry out electrochemical reactions in either a low-humidity state or a high-humidity state.

[0031] In addition, in this invention, metal oxides are used as carriers for catalytically active components, thus resulting in high durability during power generation.

[0032] In this invention, "low humidity state" refers to a state where the humidity inside the electrode catalyst layer is below approximately 40% RH. On the other hand, "high humidity state" refers to a state where the humidity inside the electrode catalyst layer is above approximately 90% RH.

[0033] It is known that varying humidity levels within the electrode catalyst layer affect the proton mobility of the electrolyte membrane and ionomers, thereby impacting electrochemical reactions. Proton mobility tends to decrease, especially under low humidity conditions. From the viewpoint of suppressing the decrease in proton mobility of the electrode catalyst layer under low humidity conditions, the inventors conducted in-depth research and found that constructing each catalyst layer in a manner that makes the cell resistance of the first catalyst layer lower than that of the second catalyst layer is effective.

[0034] The elements constituting battery resistance include the resistance of the electrolyte membrane, the resistance of the constituent components, contact resistance, and other factors, but the main factor is proton mobility. Therefore, in this invention, battery resistance is used as a standard for proton mobility, and the battery resistance of each catalyst layer is adjusted to ensure that electrochemical reactions can proceed smoothly under both low-humidity and high-humidity conditions.

[0035] From the viewpoint that electrochemical reactions can be carried out more smoothly under either low or high humidity conditions, at 80°C and 40% RH, the battery resistance R1 of the first catalyst layer is preferably 50% or more and less than 100% of the battery resistance R2 of the second catalyst layer, more preferably 70% or more and less than 95%, and even more preferably 80% or more and less than 92%.

[0036] The cell resistance of the first and second catalyst layers was measured under low humidity conditions of 80°C and 40% RH. The cell resistance was measured using the current interruption method. Regarding cell resistance, a single cell was fabricated using either the first or second catalyst layer as the cathode electrode catalyst and platinum-supported carbon as the anode electrode catalyst, and this single cell was used as the object for measurement. Detailed methods for measuring cell resistance are described in the examples described later.

[0037] As described above, it is preferable that the cell resistance of the first catalyst layer is lower than that of the second catalyst layer under low humidity conditions (80°C, 40% RH). From the perspective of enabling smoother electrochemical reactions under both low and high humidity conditions, it is also advantageous that the cell resistance of the first catalyst layer is lower than that of the second catalyst layer under high humidity conditions (80°C, 90% RH). Particularly at 80°C, 90% RH, the cell resistance R1 of the first catalyst layer is preferably 50% or more and less than 100% of the cell resistance R2 of the second catalyst layer, more preferably 70% or more and less than 95%, and even more preferably 80% or more and less than 92%.

[0038] Hereinafter, the first catalyst layer and the second catalyst layer constituting the electrode catalyst layer of the present invention will be described.

[0039] The first catalyst layer contains a first catalyst support. The first catalyst support is formed by loading the first catalytically active component onto a support containing the first metal oxide.

[0040] As the first metal oxide, a conductive metal oxide is preferred. Furthermore, as the first metal oxide, a metal oxide that does not readily dissolve in the metal constituting the first metal oxide under the operating conditions of an electrochemical cell is preferred.

[0041] The first metal oxide preferably has a volume resistivity of, for example, below 100 kΩcm. The volume resistivity is measured, for example, using a powder resistivity measuring system (Mitsubishi Chemical Analytech Co., Ltd. PD-51) and a resistivity meter (Mitsubishi Chemical Analytech Co., Ltd. MCP-T610). Specifically, 1 g of sample is added to a probe syringe, and the probe unit is mounted on the PD-51. A load of 18 kN is applied using a hydraulic lift to produce cylindrical granules with a diameter of 20 mm. The resistivity of the resulting granules is measured using the MCP-T610.

[0042] Examples of the first metal oxide include one or more selected from indium oxide, tin oxide, titanium oxide, zirconium oxide, cerium oxide, molybdenum oxide, tungsten oxide, zinc oxide, vanadium oxide, tantalum oxide, niobium oxide, and rhenium oxide. Particularly from the perspective of excellent acid resistance, the first metal oxide is preferably tin oxide, titanium oxide, or zirconium oxide. More preferably, inorganic oxides containing one or more elements selected from indium, niobium, tantalum, antimony, and tungsten can be listed. Additionally, inorganic oxides containing halogen elements can also be listed. Specifically, examples include indium-containing tin oxides, antimony-containing tin oxides, fluorine-containing tin oxides, fluorine-tungsten-containing tin oxides, tantalum-containing tin oxides, tantalum-antimony-containing tin oxides, tungsten-containing tin oxides, and niobium-containing tin oxides containing (doped) metals and / or non-metals.

[0043] As a carrier formed of tin oxide, the carriers described in WO2016 / 98399 and WO2020 / 31479 may be used. The contents of these publications are incorporated herein by reference.

[0044] From the perspective of increasing the specific surface area of ​​the support and highly dispersing the catalyst, it is preferable that the primary particle size of the first metal oxide is 10 nm or more and 100 nm or less, particularly 10 nm or more and 50 nm or less, and especially 12 nm or more and 50 nm or less. The particle size of the first metal oxide is determined as follows: the particles of the metal oxide are observed by electron microscopy, and the maximum span length of 500 or more particles is measured and the average value is calculated. The observation magnification is set to 100,000x, and at this magnification, the smallest unit considered as the particle is determined based on its geometric morphology.

[0045] The first catalytically active component supported on a carrier formed of a first metal oxide can be the same material used in this art to date. For example, various noble metals can be used as the first catalytically active component. In particular, from the perspective of high catalytic activity, at least one element selected from the group consisting of platinum, palladium, ruthenium, osmium, and iridium is preferred as the first catalytically active component, and platinum is more preferred.

[0046] When using platinum as the primary catalytic active ingredient, elemental platinum or platinum alloys can be used. Examples of platinum alloys include alloys of platinum with other precious metals, and alloys of platinum with transition metals. Examples of precious metals other than platinum include palladium, ruthenium, rhodium, osmium, and iridium. Examples of transition metals include nickel, cobalt, iron, manganese, chromium, molybdenum, lanthanum, cerium, gadolinium, copper, and titanium.

[0047] When using platinum as the first catalytic active component, especially considering that the catalytic activity is high even when the electrode catalyst layer is in a low-wetting state, elemental platinum is preferred.

[0048] From the perspective of efficiently exhibiting catalytic activity, the first catalytically active component preferably has an average particle size of 1 nm or more and 10 nm or less on the surface of the support. The particle size of the catalyst can be determined in the same way as the particle size of the first metal oxide. The observation magnification is set to 500,000 times.

[0049] The cumulative volumetric particle size D at 50% capacity of the first catalyst support was determined by laser diffraction / scattering particle size distribution method. 50 Preferably, the micrometer is 0.1 μm or more and 8 μm or less, more preferably 0.2 μm or more and 5 μm or less, and even more preferably 0.3 μm or more and 3 μm or less.

[0050] The first catalyst support can be used in powder form or it can be granulated. Granulation methods include spray drying, extrusion granulation, and rotary granulation.

[0051] It should be noted that the above D 50 The determination can be performed as follows: For example, a catalyst layer containing a catalyst support and an ionomer such as Nafion (registered trademark, described later) is dispersed in a composition to obtain a dispersion; the dispersion is diluted with ethanol; and the resulting liquid is measured using a laser diffraction / scattering particle size distribution device. Alternatively, instead of the method targeting the dispersion, the catalyst can be peeled off from a coated Teflon (registered trademark) sheet or an electrolyte membrane (hereinafter also referred to as "CCM") covering the catalyst layer, and the peeled catalyst support is dispersed in ethanol for determination.

[0052] In particular, using the first catalyst support in a granulated state offers the following advantages: the amount of water present in the first catalyst layer becomes easier to control, and proton mobility is not easily reduced even in a low-wetting state within the electrode catalyst layer. From this perspective, the volumetric cumulative particle size D of the granulated first catalyst support... 50 The preferred range is the one described above.

[0053] Next, the second catalyst layer will be described. The second catalyst layer contains a second catalyst support. The second catalyst support is formed by loading the second catalytically active component onto a support containing the second metal oxide.

[0054] As the second metal oxide, a conductive metal oxide is preferred. Furthermore, as the second metal oxide, a metal oxide that does not readily dissolve in the metal constituting the second metal oxide during the operation of an electrochemical cell is preferred. Specifically, the second metal oxide can be a substance of the same kind as or a different kind of substance exemplified as the first metal oxide. For example, tin oxide, titanium oxide, or zirconium oxide can be used independently as both the first and second metal oxides.

[0055] The second catalytically active component, supported on a carrier formed of a second metal oxide, can be the same material used in the art to date. For example, various noble metals can be used as the second catalytically active component. Specifically, the second catalytically active component can be a material of the same kind as or a different kind from the material exemplified as the first catalytically active component. More specifically, it is preferable that both the first and second catalytically active components independently comprise at least one element selected from the group consisting of platinum, palladium, ruthenium, osmium, and iridium.

[0056] In particular, using a platinum transition metal alloy as the second catalytic active component makes it easier to adjust the cell resistance of the first catalyst layer to be lower than that of the second catalyst layer, which is therefore preferred. From the perspective of high catalytic activity, using a platinum transition metal alloy is also preferred. Platinum transition metal alloys have higher catalytic activity than elemental platinum, making them a preferred material. However, on the other hand, a decrease in catalyst activity under low-humidity conditions is sometimes observed. However, by placing the platinum transition metal alloy in the second catalyst layer, i.e., on the side relatively far from the electrolyte membrane, water supply from the first catalyst layer is facilitated (i.e., proton mobility does not decrease), thus the catalytic activity is less likely to decrease.

[0057] From the viewpoint of maximizing catalytic activity, the ratio of platinum to transition metal in platinum transition metal alloys is preferably set to 20 mol% or more and 40 mol% or less relative to 100 mol% platinum.

[0058] The preferred particle size of the second catalyst support is the same as that of the first catalyst layer. The second catalyst support can be used in powder form or in a granulated form.

[0059] To make the cell resistance of the first catalyst layer lower than that of the second catalyst layer, one or more of the following methods can be used: (i) making the second catalytic active component different from the first catalytic active component; (ii) making the particle size of the first catalyst support larger than that of the second catalyst support; (iii) adjusting the pore size distribution of the first and second catalyst layers; (iv) making the amount of ionomer contained in the first catalyst layer different from that contained in the second catalyst layer.

[0060] In case (i), it is preferable, for example, to use elemental platinum as the first catalytic active ingredient on the one hand, and a platinum transition metal alloy as the second catalytic active ingredient on the other hand.

[0061] In case (ii), the cumulative volumetric particle size D of the first catalyst support at 50% capacity based on laser diffraction / scattering particle size distribution determination is determined. 50 The cumulative volumetric particle size D at 50% capacity of the second catalyst support was determined by laser diffraction / scattering particle size distribution method. 50 It is advantageous to be large.

[0062] In case (iii), it is advantageous to produce a substance in which, in the pore size distribution determined by mercury intrusion porosimetry, at least one peak is observed in the first catalyst layer in the range of 0.005 μm or more and less than 0.1 μm and in the range of 0.1 μm or more and less than 1 μm, and in the second catalyst layer in the range of 0.005 μm or more and less than 0.1 μm.

[0063] For purposes of (ii) and (iii), it is preferred to use a granulated material as the first catalyst support and a powdered material as the second catalyst support.

[0064] In case (iv), it is preferable that the amount of ionomer contained in the first catalyst layer is greater than the amount of ionomer contained in the second catalyst layer.

[0065] The methods described in (i) to (iv) above can be applied whether the first metal oxide and the second metal oxide are the same or different, but they are particularly effective when the first metal oxide and the second metal oxide are the same substance. This is especially true when both the first metal oxide and the second metal oxide are tin oxides.

[0066] The first and second catalyst layers may contain other components on the basis of the catalyst support. The first and / or second catalyst layers may contain, for example, ionomers. The ionomers preferably have proton conductivity. By including ionomers in the first and / or second catalyst layers, the performance of these catalyst layers is further improved. As ionomers, for example, polymeric materials with a structure consisting of perfluoroether side chains with terminal sulfonic acid groups bonded to the polytetrafluoroethylene backbone can be used. Examples of such ionomers include Nafion (registered trademark), FLEMION (registered trademark), Aciplex (registered trademark), and Fumion F (registered trademark).

[0067] When ionomers are included in the first catalyst layer and / or the second catalyst layer, adjusting the amount of the ionomer and the amount of the support is advantageous from the viewpoint of making the cell resistance of the first catalyst layer lower than that of the second catalyst layer. For example, in the first catalyst layer and / or the second catalyst layer, from the viewpoint of covering the catalytically active component with ionomers and making the catalyst-supported support easier to cope with humidity changes, it is preferable that the ratio of the mass I of the ionomer to the mass M of the support in the first catalyst layer or the second catalyst layer, i.e., the value of I / M, is independently set to 0.06 or more, more preferably 0.07 or more. On the other hand, from the viewpoint of minimizing the increase in cell resistance caused by a higher proportion of ionomers, it is preferable that the value of I / M is independently set to 0.25 or less, more preferably 0.22 or less, and even more preferably 0.20 or less. It should be noted that the ionomers are mostly provided in the form of a dispersion, and in this case, the aforementioned mass I of the ionomer refers to the mass of the solid component in the dispersion.

[0068] The thickness t1 of the first catalyst layer is preferably 0.2 μm or more and 10 μm or less. By setting the thickness t1 of the first catalyst layer within this range, the catalyst layer can be made low-resistivity not only under low-humidity conditions, but also effectively prevents overflow under high-humidity conditions. From this point of view, the thickness t1 of the first catalyst layer is more preferably 0.5 μm or more and 7.5 μm or less, and even more preferably 1 μm or more and 5 μm or less.

[0069] On the other hand, the thickness t2 of the second catalyst layer is preferably 0.5 μm or more and 15 μm or less. By setting the thickness t2 of the second catalyst layer within this range, overflow under high humidity conditions can be prevented, which is preferable in terms of obtaining good catalytic activity. From this point of view, the thickness t2 of the second catalyst layer is more preferably 2 μm or more and 10 μm or less, and even more preferably 2 μm or more and 8 μm or less.

[0070] The relative relationship between the thickness t1 of the first catalyst layer and the thickness t2 of the second catalyst layer is related to the smooth progress of electrochemical reactions under both low-humidity and high-humidity conditions. From this perspective, it is preferable to set the ratio of the thickness t1 of the first catalyst layer to the thickness t2 of the second catalyst layer, i.e., t1 / t2, to be 0.05 or more and 2 or less, more preferably 0.1 or more and 1.5 or less, even more preferably 0.2 or more and 1 or less, and even more preferably 0.4 or more and 0.9 or less.

[0071] The thicknesses of the first and second catalyst layers were determined as follows: The first and second catalyst layers were sequentially formed on a solid electrolyte membrane, and their cross-sections were observed using a scanning electron microscope at, for example, a magnification of 5000x. Within the field of view of this image, the thicknesses of the first and second catalyst layers were measured at 20 points at arbitrary intervals. Next, cross-sectional images of two different fields of view were taken, and the average thicknesses of the first and second catalyst layers were calculated for each of the 20 points. Finally, the arithmetic mean of the thicknesses of the first and second catalyst layers measured during the three image observations was calculated to determine the thicknesses of the first and second catalyst layers.

[0072] To ensure that the cell resistance of the first catalyst layer is lower than that of the second catalyst layer, it is also advantageous to adjust the pore size distribution in these catalyst layers. Specifically, regarding the first catalyst layer, it is preferable that at least one peak is observed in the pore size distribution determined by mercury porosimetry in the range of 0.005 μm or greater and less than 0.1 μm. Particularly preferred is the observation of a single peak within this pore size range.

[0073] For the first catalyst layer, it is preferable that, in addition to the aforementioned range, at least one peak is also observed in the range of 0.1 μm to 1 μm. Particularly preferred is that a single peak is observed in this pore size range.

[0074] To ensure that the pore size distribution of the first catalyst layer has peaks in the aforementioned ranges, it is advantageous, for example, to use a first metal oxide with a particle size of 10 nm or more and 100 nm or less as the first metal oxide constituting the first catalyst support, and to use the first catalyst support in a granulated state. The peaks in the range of 0.005 μm or more and less than 0.1 μm mainly correspond to the pores between the primary particles of the first catalyst support. The peaks in the range of 0.1 μm or more and less than 1 μm mainly correspond to the pores between the granules.

[0075] On the other hand, regarding the second catalyst layer, it is preferable that at least one peak is observed in the range of 0.005 μm or more and 0.1 μm or less in the pore size distribution determined by mercury intrusion porosimetry, and more preferably a single peak is observed.

[0076] In order to make the pore size distribution of the second catalyst layer have a single peak in the aforementioned range, it is advantageous to use a second metal oxide with a particle size of 10 nm or more and 100 nm or less as the second metal oxide constituting the second catalyst support, and to use the second catalyst support in powder form (i.e., without granulation).

[0077] Pore ​​size distribution based on mercury intrusion porosimetry is measured using, for example, the Auto Pore IV Model 9520 manufactured by Shimadzu Corporation. Specifically, the sample is immersed in a sample cell, and pressure is continuously applied from 0 psi to 60,000 psi (413,700 kPa). The amount of mercury intruded into the pores of the sample is estimated based on capacitance, thus obtaining the relationship between pore size and pore volume.

[0078] The electrode catalyst layer of the present invention can be used as a CCM in an electrochemical cell. The CCM comprises a solid electrolyte membrane and an electrode catalyst layer disposed on the surface of the solid electrolyte membrane. In the electrode catalyst layer of the CCM, a first catalyst layer is disposed closer to the solid electrolyte membrane than a second catalyst layer.

[0079] Examples of solid electrolyte membranes include proton conductor membranes based on perfluorosulfonic acid polymers, membranes obtained by doping inorganic acids such as phosphoric acid into hydrocarbon polymers, organic / inorganic hybrid polymers in which some functional groups of the proton conductor are replaced, and proton conductors obtained by impregnating a phosphoric acid solution or a sulfuric acid solution into a polymer matrix.

[0080] To obtain a catalyst membrane (CCM) by forming an electrode catalyst layer having a first catalyst layer and a second catalyst layer on the surface of a solid electrolyte membrane, firstly, a dispersion containing a first catalyst support is prepared, and this dispersion is coated onto one side of a release liner to form a coating of the first catalyst layer. Next, the coated surface of the dispersion on the release liner is overlapped with the solid electrolyte membrane, and hot pressing is performed in this state to transfer the first catalyst layer onto the solid electrolyte membrane. Next, a dispersion containing a second catalyst support is coated onto one side of the release liner to form a coating of the second catalyst layer. Then, the coated surface of the dispersion on the release liner is overlapped with the surface of the solid electrolyte membrane where the first catalyst layer is formed, and hot pressing is performed in this state to transfer the second catalyst layer onto the first catalyst layer. This yields the CCM.

[0081] Primary alcohols are preferably used as the liquid medium for preparing the dispersion of the catalyst support. Examples of primary alcohols include those with 1 or more but less than 10 carbon atoms. Among these, saturated aliphatic alcohols are preferred. Examples include methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, and decanol. Saturated aliphatic alcohols with 1 or more but less than 4 carbon atoms are particularly preferred. One primary alcohol can be used alone or in combination of two or more. Other solvents besides the aforementioned primary alcohols can also be used, such as aliphatic monohydric alcohols like 2-propanol, aromatic hydrocarbons like toluene and benzene, aliphatic hydrocarbons like hexane, other ketones, esters, ethers, and other organic solvents, as well as water.

[0082] The electrode catalyst layer of the present invention can also be used as a membrane electrode assembly (hereinafter also referred to as "MEA"). The MEA comprises: a solid electrolyte membrane, an electrode catalyst layer disposed on the surface of the solid electrolyte membrane, and a gas diffusion layer disposed on the surface of the electrode catalyst layer. In the electrode catalyst layer of the MEA, the first catalyst layer is disposed closer to the solid electrolyte membrane than the second catalyst layer.

[0083] As a gas diffusion layer, carbon paper or carbon cloth, which are porous materials, can be used, for example. Specifically, it can be formed from carbon cloth, which is obtained by weaving together carbon fibers with a surface coated with polytetrafluoroethylene and uncoated carbon fibers in a specified ratio.

[0084] The MEA described above can be used to assemble electrochemical cells. In the case of an electrochemical cell that is a battery, such as a fuel cell or a metal-air battery, the electrode catalyst layer of the present invention is preferably used as the cathode. In the case of an electrochemical cell that is a water electrolysis device, the electrode catalyst layer of the present invention is preferably used as the anode. This operation allows for smooth electrochemical processes under both low and high humidity conditions, which is preferable.

[0085] Example

[0086] The present invention will now be described in more detail through embodiments. However, the scope of the present invention is not limited to these embodiments. Unless otherwise specified, "%" refers to "mass %".

[0087] [Example 1]

[0088] (1) Manufacturing of the first metal oxide

[0089] 5.47 g of sodium hydroxide and 0.56 g of Na₂WO₄·2H₂O were dissolved in 495 g of pure water to prepare an alkaline aqueous solution, which was designated as solution A. Separately, 489 g of pure water was added to a beaker, and 11.55 g of tin difluoride was dissolved in it to obtain a tin aqueous solution, which was designated as solution B. While stirring solution B with a paddle at room temperature (25 °C), the entire amount of the previously prepared solution A was added. After the addition of solution A was complete, the mixture was allowed to mature at room temperature with stirring for 5 minutes. Subsequently, the mixture was decanted and washed with pure water until the viscosity dropped below 100 μS / cm, yielding a slurry of the precursor.

[0090] Add pure water to the obtained slurry to adjust the concentration to 1%, and measure 200g of it. Add 1.07g of 30% hydrogen peroxide solution to it. Then, let it mature at room temperature while stirring for 5 minutes.

[0091] Hydrothermal synthesis was performed using the apparatus shown in Figure 1 of Publication No. WO2016 / 98399. The set temperature of reactor 10 in the figure was 600°C. The pressure in reactor 10 was set to 25 MPa. This temperature / pressure condition represents the supercritical conditions for water. Furthermore, the piping length from mixing section 8 to the outlet of reactor 10 and the pump flow rate were adjusted to ensure a reaction time of 5 minutes. This yielded tin oxide particles containing fluorine and tungsten. These tin oxide particles were used as the first metal oxide. Electron microscopy revealed that the primary particle size of the tin oxide particles was 15 nm.

[0092] (2) Granulation of the first metal oxide

[0093] The first metal oxide obtained in (1) was granulated by spray drying. The operating conditions of the spray dryer are as follows.

[0094] • Slurry concentration: 40g / L

[0095] • Slurry feed rate: 3.3 mL / min

[0096] • Inlet temperature: 220℃

[0097] The cumulative particle size D of the obtained granules 50 It is 2.45μm.

[0098] (3) Manufacturing of the first catalyst support

[0099] 5 mL of H2PtCl6 solution (equivalent to 1 g of Pt) was dissolved in 295 mL of distilled water. 15.3 g of NaHSO3 was added, and the solution was diluted with 1400 mL of distilled water. 5% NaOH aqueous solution was added, and while adjusting the pH to approximately 5, 120 mL of 35% hydrogen peroxide solution was added dropwise to obtain a liquid containing platinum colloids. At this point, 5% NaOH aqueous solution was added to maintain the pH of the liquid at approximately 5. 5.67 g of tin oxide particles obtained in (2) was added, and the mixture was stirred at 90 °C for 3 hours. Subsequently, the liquid was cooled, and solid-liquid separation was performed. In order to remove chloride ions from the water-containing powder obtained through solid-liquid separation, the solution was diluted again with 1500 mL of distilled water, boiled at 90 °C for 1 hour, and the liquid was cooled for solid-liquid separation. This washing operation was performed 4 times. Finally, after solid-liquid separation, the solution was dried at 60 °C for 12 hours under atmospheric conditions. Thus, the surface of the tin oxide particles was loaded with platinum oxide in a manner deviating from the stoichiometric ratio. Next, the tin oxide particles were heat-treated at 80°C for 2 hours under a 4 vol% H₂ / N₂ atmosphere to reduce the platinum. The platinum loading, determined by ICP emission spectroscopy, was 14% relative to the platinum-loaded tin oxide particles. This yielded the first catalyst support.

[0100] (4) Formation of the first catalyst layer

[0101] 1.46 g of the first catalyst support formed by granulation was added to a container, followed by the sequential addition of pure water, ethanol, and 2-propanol at a mass ratio of 35:45:20 (3.06 g of the mixture). The resulting dispersion was ultrasonically dispersed for 3 minutes. Next, 10 mm diameter yttrium-stabilized zirconia pellets were placed in the container and stirred at 800 rpm for 20 minutes using a planetary ball mill (THINKY ARE310). Then, 5% Nafion (registered trademark) (274704-100 mL, manufactured by Sigma-Aldrich) was added to the dispersion, and the mixture was dispersed ultrasonically and stirred using a planetary ball mill in the same manner as described above. The amount of Nafion added was set to a Nafion / (first support) mass ratio of 0.074.

[0102] The resulting dispersion was applied onto a polytetrafluoroethylene sheet using a bar coater, and the coating was dried at 60°C.

[0103] (5) Manufacturing of the second metal oxide

[0104] It is produced using the same procedures as the production of the first metal oxide.

[0105] (6) Manufacturing of the second catalyst support

[0106] Add 337 mL of N,N-dimethylformamide (hereinafter also referred to as "DMF". Manufactured by FUJIFILM Wako Pure Chemical Corporation, 049-32363) to a 500 mL volumetric flask, and then add the following ingredients in the manner shown below to achieve the concentrations indicated.

[0107] • Bis(acetylacetone)platinum(II) (Pt(acac)2, 028-16853, manufactured by FUJIFILM Wako Pure Chemical Corporation): 9.87 × 10⁻⁶ -3 mol / L -DMF

[0108] • Bis(2,4-pentanedione)nickel(II) dihydrate (Ni(acac)2·2H2O, 343-01981, manufactured by Dojin Chemical Research Institute Co., Ltd.): 3.62 × 10 -3 mol / L -DMF

[0109] Benzoic acid (204-00985, FUJIFILM Wako Pure Chemical Corporation): 2.49 × 10 - 1 mol / L -DMF

[0110] The second metal oxide obtained in (5) is 7.49 g / L. -DMF

[0111] The liquid containing the aforementioned components was dispersed using an ultrasonic disperser at room temperature for 30 minutes to prepare a dispersion. The volumetric flask containing the dispersion was purged with argon gas while being pre-stirred at room temperature and 400 rpm for 20 hours using a rugby ball-shaped stir bar with a major diameter of approximately 2 cm and a minor diameter of approximately 1 cm.

[0112] Next, while purging the volumetric flask containing the pre-stirred dispersion with argon gas, the flask was immersed in an oil bath at 160°C to heat the dispersion. The time required for the solvent in the volumetric flask to boil was approximately 7 minutes. After boiling, the mixture was refluxed for 12 hours at an oil bath temperature of 160°C. The oil bath was then removed, and the mixture was cooled to room temperature before filtration to obtain the solid component.

[0113] The obtained solid component was washed five times with a mixed solvent of acetone and ethanol (1:1 by volume), followed by a single wash with a mixed solvent of water and ethanol (1:1 by volume) and then dried. The resulting dried powder was dispersed in 400 mL of 0.5 mol / L perchloric acid, heated and stirred at 60 °C for 2 hours, and then filtered, washed, and dried. This yielded the second catalyst support loaded with platinum-nickel alloy.

[0114] The loading of platinum-nickel alloy in the second catalyst support is 20% platinum and 1.6% nickel relative to the second catalyst support (containing nickel at a ratio of 26.6 mol% relative to 100 mol% platinum).

[0115] (7) Formation of the second catalyst layer

[0116] 1.0 g of the second catalyst support was placed in a container, and then pure water, ethanol, and 2-propanol were added sequentially at a mass ratio of 33:50:17 (2 g of the mixture). The resulting dispersion was ultrasonically dispersed for 3 minutes. Next, glass balls with a diameter of 2 mm were placed in the container and stirred at 100 rpm for 30 minutes using a planetary ball mill (PM 200, Retsch). Then, 5% Nafion (registered trademark) (274704-100 mL, Sigma-Aldrich) was added to the dispersion, and the mixture was dispersed ultrasonically and stirred using a planetary ball mill in the same manner as before. The amount of Nafion added was set to a Nafion / (second support) mass ratio of 0.074.

[0117] The resulting dispersion was applied onto a polytetrafluoroethylene sheet using a bar coater, and the coating was dried at 60°C.

[0118] (8) Formation of the electrode catalyst layer for the anode

[0119] 1.00 g of platinum-loaded carbon black (TEC10E50E) manufactured by Tanaka Precious Metals Industry Co., Ltd. was added to a container, followed by the addition of pure water, ethanol, and 2-propanol in a mass ratio of 45:35:20 (12.8 g of the mixture). The resulting dispersion was ultrasonically dispersed for 3 minutes. Next, 10 mm diameter yttrium-stabilized zirconia balls were added to the container, and the mixture was stirred at 800 rpm for 20 minutes using a planetary ball mill (THINKY ARE310). Then, 5% Nafion (registered trademark) (274704-100 ml, manufactured by Sigma-Aldrich) was added to the dispersion, and the mixture was dispersed ultrasonically and stirred in the same manner as before using a planetary ball mill. The amount of Nafion added was set to a Nafion / platinum-loaded carbon black mass ratio of 0.70. The resulting dispersion was coated onto a polytetrafluoroethylene sheet using a rod coater, and the coating was dried at 60°C.

[0120] (9) CCM manufacturing

[0121] A sheet of polytetrafluoroethylene (PTFE) with the first catalyst layer and a sheet of PTFE with the anode electrode catalyst layer were cut into 54 mm squares and overlapped with an electrolyte membrane of Nafion (registered trademark) (NRE-211, manufactured by DuPont). The membranes were then subjected to an induction heating process at 140°C and 20 kgf / cm². 2 Under atmospheric conditions, hot pressing and transfer were performed for 2 minutes. Next, the PTFE sheet with the first catalyst layer was peeled off to expose the first catalyst layer. Then, the PTFE sheet with the second catalyst layer was overlapped on top of the first catalyst layer, and the process was carried out at 140°C and 20 kgf / cm². 2 Under atmospheric conditions, hot pressing and transfer are performed for 2 minutes. In this way, a cathode catalyst layer consisting of a first catalyst layer and a second catalyst layer is formed on one side of the solid polymer electrolyte membrane formed by Nafion, and an anode catalyst layer is formed on the other side.

[0122] (10) Assembly of solid polymer fuel cells

[0123] The CCM obtained in (9) was used to assemble a solid polymer fuel cell. SIGRACET 29BC (manufactured by SGL Corporation) was used as the gas diffusion layer.

[0124] [Example 2]

[0125] In the formation step of the first catalyst layer in (4) of Example 1, the diameter of the spheres was set to 5 mm, the stirring time before adding 5% Nafion was set to 90 minutes, and the stirring time after adding Nafion was set to 60 minutes. The first catalyst support granulated in this way was then pulverized. Otherwise, the same procedure as in Example 1 was followed to obtain a solid polymer fuel cell.

[0126] [Comparative Example 1]

[0127] In Example 1, the granulation process of the first metal oxide (2) was omitted, and the process was otherwise the same as in Example 1 to obtain a solid polymer fuel cell.

[0128] [Comparative Example 2]

[0129] The process of (9) in Example 1 is performed as follows. Otherwise, the same procedure as in Example 1 is followed to obtain a solid polymer fuel cell.

[0130] The polytetrafluoroethylene (PTFE) sheet with the second catalyst layer and the PTFE sheet with the anode electrode catalyst layer prepared in Example 1 were cut into 54 mm square shapes and overlapped with the Nafion (registered trademark) (NRE-211, manufactured by DuPont) electrolyte membrane. The membranes were then subjected to an induction heating at 140°C and 20 kgf / cm². 2 Under atmospheric conditions, the transfer was performed for 2 minutes. Next, the polytetrafluoroethylene sheet with the first catalyst layer prepared in Example 1 was overlapped onto the second catalyst layer and subjected to heat pressing at 140°C and 20 kgf / cm². 2 Under atmospheric conditions, hot pressing is performed for 2 minutes to transfer the catalyst. This process creates a cathode catalyst layer consisting of a second catalyst layer and a first catalyst layer on one side of the solid polymer electrolyte membrane formed from Nafion, and an anode catalyst layer on the other side.

[0131] [Comparative Example 3]

[0132] In this comparative example, the same catalyst layer as the anode catalyst layer was formed as the cathode catalyst layer. That is, the cathode catalyst layer contained a catalyst support formed of platinum-loaded carbon black. Otherwise, the process was the same as in Example 1 to obtain a solid polymer fuel cell.

[0133] [Evaluation 1]

[0134] The particle size distribution of the catalyst support for the first and second catalyst layers obtained in the examples and comparative examples was determined by the following method.

[0135] The dispersions used in the formation of the first and second catalyst layers were diluted with ethanol. The resulting liquids were then used as the target material, and the particle size distribution was determined using a laser diffraction / scattering particle size distribution measuring device (HORIBA, Ltd. LA-920). The results are shown in Table 1.

[0136] [Evaluation 2]

[0137] The cross-sections of the CCMs obtained in the examples and comparative examples were observed using an electron microscope to determine the thicknesses of the first and second catalyst layers in the cathode catalyst layer. Furthermore, the pore size distribution based on mercury intrusion porosimetry was determined using the above method. For the pore size distribution, the polytetrafluoroethylene sheets with the first catalyst layer and the polytetrafluoroethylene sheets with the second catalyst layer obtained in (4) and (7) above were individually tested at 140°C and 20 kgf / cm². 2 Under atmospheric conditions, the catalyst was hot-pressed for 2 minutes, and the first and second catalyst layers, formed separately, were measured. The results are shown in Table 1. It should be noted that for Comparative Example 3, which was designed with only one catalyst layer, the pore size distribution measurement was omitted.

[0138] [Evaluation 3]

[0139] The cell resistance of the first and second catalyst layers obtained in the examples and comparative examples was measured using the following method. The results are shown in Table 2.

[0140] To eliminate factors other than the characteristics of the catalyst support used in each catalyst layer that affect battery resistance under low humidity conditions, the Pt coating weight of the polytetrafluoroethylene sheet was adjusted to 0.2 mg / cm². 2 .

[0141] Next, using a sheet with the coating amount adjusted, a single cell for measuring battery resistance is prepared as follows.

[0142] A sheet of polytetrafluoroethylene coated with the first catalyst layer and a sheet of polytetrafluoroethylene with the anode electrode catalyst layer were cut into 54 mm square shapes and overlapped with an electrolyte membrane of Nafion (registered trademark) (NRE-211, manufactured by DuPont). The membranes were then subjected to an induction heating process at 140°C and 20 kgf / cm². 2 Under atmospheric conditions, the mixture was hot-pressed for 2 minutes and then transferred. Using the resulting CCM, a single cell for measuring the resistance of the first catalyst layer was assembled. SIGRACET 29BC (manufactured by SGL Corporation) was used as the gas diffusion layer.

[0143] Alternatively, a polytetrafluoroethylene sheet with a second catalyst layer is used instead of a polytetrafluoroethylene sheet with a first catalyst layer, and a single cell for measuring the battery resistance of the second catalyst layer is assembled using the same steps as described above.

[0144] The obtained single cells were used to generate electricity, and the cell resistance at 0.6V was measured using the current interruption method. A Scrinber Associates 890e FC electronic load instrument was used for the measurements. Power generation was conducted under both high humidity (80°C and 90% RH for both cathode and anode) and low humidity (80°C and 40% RH for both cathode and anode). Hydrogen was supplied to the anode at a rate of 5 L / min, and air was supplied to the cathode at a rate of 25 L / min.

[0145] [Evaluation 4]

[0146] The high-temperature durability of the fuel cells obtained in the examples and comparative examples was determined using the following methods. The results are shown in Table 2.

[0147] Power generation was conducted for 16 hours under low humidity conditions (cathode and anode both 110°C, 30% RH). The surface area of ​​the platinum catalyst in the electrode catalyst layer before and after power generation was measured using ECSA. Based on (S... F -S A ) / S A The residual rate (%) of the platinum catalyst is calculated by multiplying by 100, and this value is used as the standard for durability at high temperatures. A S represents the surface area of ​​the platinum catalyst before power generation. F This indicates the surface area of ​​the platinum catalyst after power generation.

[0148] [Evaluation 5]

[0149] Using the CCM obtained in the examples and comparative examples, a single cell for battery resistance measurement was assembled. SIGRACET 29BC (manufactured by SGL Corporation) was used as the gas diffusion layer.

[0150] The power generation of each obtained single cell was evaluated under both high humidity (80°C and 90% RH for both cathode and anode) and low humidity (80°C and 40% RH for both cathode and anode). For the gas supply to the anode and cathode, a hydrogen supply rate of 5 L / min was set for the anode, and an air supply rate of 25 L / min was set for the cathode. Here, the current density (A / cm²) was calculated when the voltage was set to 0.6 V. 2 The results are shown in Table 2.

[0151] [Table 1]

[0152]

[0153] [Table 2]

[0154]

[0155] The results shown in Table 2 clearly demonstrate that the fuel cells obtained in each embodiment exhibit excellent durability when generating electricity under high temperature / low humidity conditions. Furthermore, it is clear that the fuel cells obtained in each embodiment show good power generation characteristics under both low and high humidity conditions.

[0156] Industrial availability

[0157] The electrode catalyst layer for electrochemical batteries using the present invention has durability and can carry out electrochemical reactions smoothly under both low and high humidity conditions.

Claims

1. An electrode catalyst layer for an electrochemical battery, comprising a first catalyst layer and a second catalyst layer, The first catalyst layer includes a first catalyst support, which is formed by loading the first catalytically active component onto a support containing a first metal oxide. The second catalyst layer includes a second catalyst support, which is formed by loading the second catalytically active component onto a support containing a second metal oxide. The first catalytically active component contained in the first catalyst layer is elemental platinum. The second catalyst layer contains a platinum transition metal alloy as the second catalytically active component. The cumulative volumetric particle size D at 50% capacity of the first catalyst support was determined by laser diffraction / scattering particle size distribution method. 50 The cumulative volumetric particle size D at 50% capacity of the second catalyst support was determined by laser diffraction / scattering particle size distribution method. 50 big, In the pore size distribution determined by mercury porosimetry, Peaks were observed in the first catalyst layer in the range of 0.005 μm to less than 0.1 μm and in the range of 0.1 μm to less than 1 μm. At least one peak was observed in the second catalyst layer in the range above 0.005 μm and below 0.1 μm. The electrode catalyst layer for the electrochemical cell is used in such a manner that the first catalyst layer is positioned closer to the electrolyte membrane than the second catalyst layer. The ratio of the thickness t1 of the first catalyst layer to the thickness t2 of the second catalyst layer, i.e., t1 / t2, is greater than 0.05 and less than 2.

2. The electrode catalyst layer according to claim 1, wherein the cell resistance of the first catalyst layer, measured by the current interruption method at 80°C and 40%RH, is more than 70% and less than 95% of the cell resistance of the second catalyst layer.

3. The electrode catalyst layer according to claim 1 or 2, wherein, The first metal oxide and the second metal oxide are each independently tin oxide, titanium oxide, or zirconium oxide.

4. The electrode catalyst layer according to claim 1 or 2, wherein, The thickness t1 of the first catalyst layer is greater than 0.2 μm and less than 10 μm. The thickness t2 of the second catalyst layer is greater than 0.5 μm and less than 15 μm.

5. A membrane electrode assembly for an electrochemical battery, comprising: A solid electrolyte membrane, a catalyst layer disposed on the surface of the solid electrolyte membrane, and a gas diffusion layer disposed on the surface of the catalyst layer. The catalyst layer is the electrode catalyst layer according to any one of claims 1 to 4.

6. An electrochemical battery comprising the membrane electrode assembly as described in claim 5.

7. The electrochemical battery according to claim 6 is a solid polymer fuel cell.

8. The electrochemical battery according to claim 6 is a metal-air battery.

9. The electrochemical cell according to claim 6, wherein it is a water electrolysis device.

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