Water electrolysis cell, and water electrolysis cell stack

Abstract

To provide an anode catalyst layer exhibiting high catalytic activity and capable of maintaining stable catalytic activity.SOLUTION: The anode catalyst layer includes an oxide catalyst of a perovskite-type structure, including an alkali earth metal ion in an A site ion and at least one species selected from the group consisting of an iridium ion and a ruthenium ion, and a metal ion in a B site ion, and an ionomer.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure , water relates to an electrolytic cell and a water electrolysis cell stack.

Background Art

[0002] The electrolysis of water (hereinafter sometimes referred to as "water electrolysis") is a method of producing hydrogen and oxygen from water by electrolysis. For example, in technologies that utilize hydrogen as an energy source, water electrolysis is a promising technology for sustainable hydrogen production.

[0003] The water electrolysis cell used for water electrolysis includes an anode separator, an anode gas diffusion layer, an anode catalyst, an electrolyte membrane, a cathode catalyst, a cathode gas diffusion layer, a cathode separator, etc. Regarding the anode catalyst and the cathode catalyst, catalysts suitable for water electrolysis have been studied.

[0004] For example, Patent Document 1 discloses an oxygen generation reaction electrode including nanostructured whiskers, having an oxygen generation reaction electrolysis catalyst including at least one layer, and any layer of the oxygen generation reaction electrolysis catalyst containing a total of at least 95 atomic percent of Ir and 5 atomic percent or less of Pt with respect to the total content of cations and elemental metals in each layer.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Anode catalysts containing elements with anode activity such as iridium and ruthenium have high catalytic activity. However, since the anode catalyst is exposed to a strong oxidation atmosphere during water electrolysis, elements such as ruthenium and iridium are liable to dissolve, and the anode catalyst containing such elements is liable to be destabilized.

[0007] For example, in the catalyst containing iridium as in Patent Document 1, iridium is liable to dissolve, and the catalyst may be destabilized.

[0008] An object of the present disclosure is to provide a water electrolysis cell and a water electrolysis cell stack including an anode catalyst that exhibits high catalytic activity and can maintain stable catalytic activity. layer

Means for Solving the Problems

[0009] The present disclosure includes the following aspects. <1> An oxide catalyst having a perovskite-type structure, which contains alkaline earth metal ions in the A-site ions and at least one selected from the group consisting of iridium ions and ruthenium ions and metal ions (excluding iridium ions and ruthenium ions) in the B-site ions, an ionomer, and an anode catalyst layer containing the same. <2> The anode catalyst layer according to <1>, wherein the logarithmic value (log(X / Y)) of the mass ratio of the content (X) of the ionomer to the total content (Y) of the iridium ions and ruthenium ions contained in the B-site ions is -0.860 to 0.060. <3> The anode catalyst layer according to <2>, wherein the logarithmic value (log(X / Y)) of the mass ratio of the content (X) of the ionomer to the total content (Y) of the iridium ions and ruthenium ions contained in the B-site ions is -0.620 to -0.090. <4> ​The anode catalyst layer according to <3>, wherein the logarithm value (log(X / Y)) of the mass ratio between the content (X) of the ionomer and the total content (Y) of the iridium ions and ruthenium ions contained in the B-site ions is -0.500 to -0.180. <5> The alkaline earth metal ions include at least one selected from the group consisting of calcium ions, strontium ions, and barium ions. The metal ions include at least one selected from the group consisting of titanium ions, zirconium ions, and tin ions. The anode catalyst layer according to any one of <1> to <4>, wherein the total molar concentration of the iridium ions and ruthenium ions in the B-site ions is 5 mol% or more and 67 mol% or less. <6> The anode catalyst layer according to any one of <1> to <5>, wherein the alkaline earth metal ions include strontium ions and the metal ions include titanium ions. <7> The anode catalyst layer according to any one of <1> to <5>, wherein the alkaline earth metal ions include strontium ions and the metal ions include zirconium ions. <8> The anode catalyst layer according to any one of <1> to <7>, wherein the ionomer contains a perfluorosulfonic acid group. <9> A water electrolysis cell comprising an anode gas diffusion layer, the anode catalyst layer according to any one of <1> to <8>, an electrolyte membrane, a cathode catalyst layer, a cathode gas diffusion layer, and a separator. <10> A water electrolysis cell stack in which the water electrolysis cells according to <9> are stacked.

Advantages of the Invention

[0010] According to the present disclosure, there are provided a water electrolysis cell and a water electrolysis cell stack including an anode catalyst that exhibits high catalytic activity and can maintain stable catalytic activity. layer ​

Brief Description of the Drawings

[0011] [Figure 1] It is a schematic cross-sectional view of a water electrolysis cell. [Figure 2] It is a graph showing the relationship between log(X / Y) and log{current density (A / mg-Ir) per iridium mass at 1.8 V}.

Modes for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present disclosure will be described. The present disclosure is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the object of the present disclosure. The ratio of dimensions in the drawings does not necessarily represent the ratio of actual dimensions.

[0013] In the present disclosure, a numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value.

[0014] In the numerical ranges described stepwise in the present disclosure, the upper limit value described in a certain numerical range may be replaced with the upper limit value of the numerical range described in other stepwise descriptions, and the lower limit value described in a certain numerical range may be replaced with the lower limit value of the numerical range described in other stepwise descriptions. In the numerical ranges described stepwise in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples.

[0015] In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.

[0016] <Anode Catalyst Layer> The anode catalyst layer of the present disclosure contains an alkaline earth metal ion in the A-site ion and at least one selected from the group consisting of iridium ions and ruthenium ions and a metal ion (excluding iridium ions and ruthenium ions) in the B-site ion, and includes an oxide catalyst having a perovskite structure. Further, the anode catalyst layer of the present disclosure contains an ionomer.

[0017] According to the present disclosure, an anode catalyst layer showing high catalytic activity and capable of maintaining stable catalytic activity can be obtained. Although the reason for this effect is not necessarily clear, it is presumed as follows. The anode catalyst layer of the present disclosure can maintain stable catalytic activity by including an oxide catalyst having a perovskite structure. Further, by including at least one of iridium ions and ruthenium ions as the B-site ions of the perovskite structure and the A-site ions and B-site ions being the above ions, it becomes possible to increase the current density of the water electrolysis cell including the anode catalyst layer, and high catalytic activity is shown. Further, by including an ionomer, excellent ion conductivity is obtained, and high catalytic activity is shown. From the above, it is presumed that it shows high catalytic activity and can maintain stable catalytic activity.

[0018] (Oxide catalyst) First, an oxide catalyst having a perovskite structure, which contains an alkaline earth metal ion in the A-site ion and at least one selected from the group consisting of iridium ions and ruthenium ions and a metal ion in the B-site ion, will be described. The oxide catalyst can be produced by a conventionally known method. For example, the oxide catalyst having the perovskite structure can be produced by a conventionally known solid-phase method, liquid-phase method, etc. Examples of the solid-phase method include a method by direct reaction of solid raw materials, and examples of the liquid-phase method include the Pechini method, complex polymerization method, hydrothermal synthesis method, etc.

[0019] The oxide catalyst having a perovskite structure is generally ABO 3It is represented by the chemical formula. Some perovskite-structured oxide catalysts have oxygen non-stoichiometry. The oxygen content may be deficient or excessive compared to 3. Also, the A-site ions and B-site ions may be partially substituted with different elements, respectively.

[0020] · Alkaline earth metal ions (A-site ions) The A-site ions of the perovskite structure include alkaline earth metal ions. Examples of the alkaline earth metal ions include calcium ions, strontium ions, barium ions, radium ions, etc. The alkaline earth metal ions preferably include at least one selected from the group consisting of calcium ions, strontium ions, and barium ions, and more preferably include strontium ions. The A-site ions may be one kind of alkaline earth metal ion or two or more kinds of alkaline earth metal ions.

[0021] · Iridium ions and ruthenium ions (B-site ions) The B-site ions of the perovskite structure include at least one selected from the group consisting of iridium ions and ruthenium ions. The iridium ions and ruthenium ions may include only one of them or both of them. Preferably, iridium ions are included.

[0022] From the viewpoint of being able to sustain stable catalytic activity, the logarithmic value (log(X / Y)) of the mass ratio of the content (X) of the ionomer and the total content (Y) of iridium ions and ruthenium ions contained in the B-site ions is preferably -0.860 to 0.060, more preferably -0.620 to -0.090, and even more preferably -0.500 to -0.180. Here, from the perspective of reducing the internal resistance of the cell and enhancing the efficiency of the water electrolysis reaction, in the anode catalyst layer, it is preferable to highly disperse the catalyst particles to increase the reaction area while adjusting the amount of the ionomer responsible for ion conduction to an appropriate amount. By setting the ratio of the ionomer to iridium ions and ruthenium ions within a range that is not too small, a sufficient ion conduction path can be obtained, the internal resistance of the cell can be reduced, and the efficiency of the water electrolysis reaction can be enhanced. On the other hand, by setting the ratio of the ionomer to iridium ions and ruthenium ions within a range that is not too large, it is possible to suppress the ionomer from covering the catalyst surface and reducing the reaction area, reduce the internal resistance of the cell, and enhance the efficiency of the water electrolysis reaction.

[0023] Regarding the anode catalyst layer of the present disclosure, the total molar concentration of iridium ions and ruthenium ions as B-site ions is preferably 5 mol% or more and 67 mol% or less, more preferably 7 mol% or more and 60 mol% or less, and even more preferably 10 mol% or more and 50 mol% or less from the perspective of maintaining stable catalytic activity.

[0024] · Metal ions (B-site ions) The B-site ions of the perovskite structure contain metal ions (excluding iridium ions and ruthenium ions). Examples of the metal ions include ions of metals such as titanium (Ti), zirconium (Zr), tin (Sn), scandium (Sc), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), indium (In), antimony (Sb), etc. Among them, from the viewpoint of the metal ions being stable elements and being able to maintain the stable catalytic activity of the anode catalyst layer, it is preferable to contain at least one selected from the group consisting of titanium ions, zirconium ions, and tin ions, and it is more preferable to contain at least one selected from the group consisting of titanium ions and zirconium ions. The metal ions in the B-site ions may be only one kind of metal ion or two or more kinds of metal ions.

[0025] The combination of the alkaline earth metal ions in the A-site ions and the metal ions in the B-site ions will be described. The combination of the alkaline earth metal ions and the metal ions is not particularly limited, but from the viewpoint of being able to maintain the stable catalytic activity of the anode catalyst layer, it is preferable to contain strontium ions as the alkaline earth metal ions and titanium ions as the metal ions. Also, from the viewpoint of being able to maintain the stable catalytic activity of the anode catalyst layer, it is preferable to contain strontium ions as the alkaline earth metal ions and zirconium ions as the metal ions.

[0026] The molar concentration of the metal ions contained in the A-site ions, the molar concentration of the metal ions contained in the B-site ions, and the molar concentration of the iridium ions and ruthenium ions contained in the B-site ions can be determined by analyzing the anode catalyst by high-frequency inductively coupled plasma (ICP).

[0027] In the anode catalyst layer of the present disclosure, the content of the above oxide catalyst (oxide catalyst having a perovskite structure) is not particularly limited, and it is preferably 70% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and most preferably 100% by mass with respect to the total amount of the anode catalyst layer.

[0028] (Ionomer) Next, the ionomer will be described. An ionomer is, for example, a resin having an ion-crosslinked ethylene skeleton as a basic structure. From the viewpoint of obtaining excellent ion conduction, it is preferable that the ionomer contains a perfluorosulfonic acid group in the skeleton.

[0029] Typical examples of the ionomer containing a perfluorosulfonic acid group include the ionomer represented by the following formula (1).

[0030] [Chemical formula]

[0031] (In formula (1), m represents 0 to 10, n represents 1 to 10, x represents 1 to 20, and y represents 100 or more.)

[0032] For example, Nafion (registered trademark) 117 has a structure of (m≧1, n = 2, x = 5 to 13.5, y = 1000) in formula (1). The chemical structure of the ionomer can be evaluated by using solid-state NMR (nuclear magnetic resonance) measurement and CHN analysis (carbon C, hydrogen H, nitrogen N atom analysis) in combination to separate the anode catalyst layer from the catalyst. Furthermore, the ratio of the catalyst to the ionomer can be evaluated by ICP (inductively coupled plasma) analysis.

[0033] The anode catalyst layer of the present disclosure contains alkaline earth metal ions in A-site ions and at least one selected from the group consisting of iridium ions and ruthenium ions and metal ions (excluding iridium ions and ruthenium ions) in B-site ions, and is an oxide catalyst having a perovskite structure, and may contain components other than the ionomer. For example, components having catalytic activity other than the oxide catalyst having a perovskite structure, unreacted components of raw materials used for the production of the oxide catalyst having a perovskite structure, side reaction components, carriers, and the like can be mentioned. Examples of the carrier include titanium oxide and tin oxide that are stable under water electrolysis conditions.

[0034] <Water electrolysis cell> The water electrolysis cell of the present disclosure includes an anode gas diffusion layer, the anode catalyst layer of the present disclosure described above, an electrolyte membrane, a cathode catalyst layer, a cathode gas diffusion layer, and a separator.

[0035] As the anode gas diffusion layer, electrolyte membrane, cathode catalyst layer, cathode gas diffusion layer, and separator, members used in conventionally known water electrolysis cells may be applied.

[0036] The water electrolysis cell may further include other components. The other components may be selected from the components of known water electrolysis cells. Examples of the other components include gaskets, sealing materials, and the like.

[0037] For example, as the anode gas diffusion layer and the cathode gas diffusion layer, independently of each other, a porous body, a powder sintered body, a fiber sintered body, a metal mesh, a felt, or the like, a substance through which a fluid can flow in the layer can be used.

[0038] The anode gas diffusion layer may be coated with a corrosion-resistant conductive material from the viewpoint of suppressing an increase in resistance due to oxidation. Examples of the coating material include platinum, gold, silver, titanium nitride, titanium carbide, titanium carbonitride, and the like.

[0039] The electrolyte membrane may be selected from known electrolyte membranes (which may be ion exchange membranes) used in water electrolysis. The electrolyte membrane preferably has the property of selectively permeating protons (H + +). Examples of the electrolyte membrane include polymer electrolyte membranes (PEMs). Examples of the polymer electrolyte membrane include perfluorocarbon membranes having sulfonic acid groups. Examples of the perfluorocarbon membrane having sulfonic acid groups include Nafion membranes.

[0040] The electrolyte membrane is a polymer having proton conductivity by having ionic groups, and may be, for example, either a fluorine-based polymer electrolyte or a hydrocarbon-based polymer electrolyte.

[0041] Here, the fluorine-based polymer electrolyte means one in which most or all of the hydrogen in the alkyl group and / or alkylene group in the polymer is substituted with fluorine atoms. Representative examples of the fluorine-based polymer electrolyte having ionic groups include commercially available products such as "Nafion" (registered trademark) (manufactured by Chemours Co., Ltd.), "Aquivion" (registered trademark) (manufactured by Solvay), "Flemion" (registered trademark) (manufactured by AGC Inc.), and "Aciplex" (registered trademark) (manufactured by Asahi Kasei Corporation).

[0042] As the hydrocarbon-based electrolyte, an aromatic hydrocarbon-based polymer having an aromatic ring in the main chain is preferable. Here, the aromatic ring may include not only hydrocarbon-based aromatic rings composed only of carbon atoms and hydrogen atoms such as benzene rings and naphthalene skeletons, but also hetero rings such as pyridine rings, imidazole rings, and thiol rings. Further, a part of aliphatic units may constitute the polymer together with the aromatic ring units.

[0043] Specific examples of the aromatic hydrocarbon-based polymer include polymers having a structure selected from polysulfone, polyethersulfone, polyphenylene oxide, polyarylene ether, polyphenylene sulfide, polyphenylene sulfide sulfone, polyparaphenylene, polyarylene, polyarylene ketone, polyether ketone, polyarylene phosphine oxide, polyether phosphine oxide, polybenzoxazole, polybenzothiazole, polybenzimidazole, polyamide, polyimide, polyetherimide, and polyimide sulfone in the main chain together with an aromatic ring. Here, polysulfone, polyethersulfone, polyether ketone, etc. mentioned herein are general terms for structures having a sulfone bond, an ether bond, a ketone bond, etc. in their molecular chains, and include polyether ketone ketone, polyether ether ketone, polyether ether ketone ketone, polyether ketone ether ketone ketone, polyether ketone sulfone, etc. The aromatic hydrocarbon-based polymer may have a plurality of these structures. Among these, as the aromatic hydrocarbon-based polymer, a polymer having a polyether ketone skeleton, that is, a polyether ketone-based polymer is particularly preferable.

[0044] The electrolyte membrane may be combined with a reinforcing material. By using a reinforcing material, for example, when joining the electrolyte membrane and the electrode by a hot press method, gas leakage and short circuit in the electrode due to membrane breakage are less likely to occur.

[0045] Specific examples of the reinforcing material include fluorine-based polymers such as PTFE (polytetrafluoroethylene), PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PVDF (polyvinylidene fluoride), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), etc., or thermoplastic resins such as PE (polyethylene), PP (polypropylene), etc., and engineering plastics such as PI (polyimide), PSF (polysulfone), PES (polyethersulfone), PEEK (polyetheretherketone), PPSS (polyphenylene sulfide sulfone), PPO (polyphenylene oxide), PEK (polyetherketone), PBI (polybenzimidazole), PPS (polyphenylene sulfide), PPP (polyp - paraphenylene), PPQ (polyphenylquinoxaline), polybenzoxazole (PBO), polybenzothiazole (PBT), poly - paraphenylene terephthalamide (PPTA), etc., and homogeneous porous membranes composed of these.

[0046] The cathode catalyst may be selected from known catalysts used in water electrolysis. Examples of the catalyst components include, for example, platinum, gold, silver, palladium, iridium, rhodium, ruthenium, tin, iron, cobalt, nickel, molybdenum, tungsten, vanadium, and alloys thereof, oxides thereof, etc. The form of the catalyst may be particles. The cathode catalyst may include a catalyst supported on a carrier. Examples of the carrier include carbon black, etc.

[0047] The water electrolysis cell includes an anode catalyst layer according to the present disclosure containing an oxide catalyst (an anode catalyst, preferably oxide catalyst particles) and an ionomer. Further, it may include a cathode catalyst layer containing a cathode catalyst (preferably cathode catalyst particles) and an ionomer. Thereby, since the contact area between the catalyst and the ionomer in the catalyst layer increases, the reaction tends to be promoted.

[0048] The primary particle diameter of the oxide catalyst (anode catalyst) is preferably from 1 nm to 10 μm, more preferably from 2 nm to 1 μm, and even more preferably from 5 nm to 100 nm. When the primary particle diameter of the oxide catalyst (anode catalyst) is 1 nm or more, the mixing ratio of the ionomer required to increase the contact area does not become too large, and many electron conduction paths can be secured inside the anode catalyst layer, so that the tendency to increase the resistance is reduced. When the primary particle diameter of the anode catalyst is 10 μm or less, the decrease in the contact area with the ionomer is suppressed, so that the tendency to increase the resistance is reduced. The particle diameter of the catalyst can be evaluated by a scanning electron microscope or a transmission electron microscope.

[0049] Examples of the separator include an anode separator disposed on the anode gas diffusion layer side and a cathode separator disposed on the cathode gas diffusion layer side. Examples of the material of the separator include titanium, stainless steel, carbon, and the like. From the viewpoint of suppressing oxidation by oxygen generated on the anode side, the anode separator preferably contains titanium.

[0050] The anode separator may be coated with a corrosion-resistant conductive material in order to suppress an increase in resistance due to oxidation. Examples of the coating material include platinum, gold, silver, titanium nitride, titanium carbide, titanium carbonitride, and the like.

[0051] The arrangement of each component in the water electrolysis cell may be determined with reference to a known water electrolysis cell. In the water electrolysis cell, the electrolyte membrane is preferably located between the anode catalyst layer and the cathode catalyst layer. In the water electrolysis cell, the electrolyte membrane, the anode catalyst layer, and the cathode catalyst layer are preferably located between the anode gas diffusion layer and the cathode gas diffusion layer. In the water electrolysis cell, the electrolyte membrane, the anode catalyst layer, the cathode catalyst layer, the anode gas diffusion layer, and the cathode gas diffusion layer are preferably located between the two separators.

[0052] An example of a water electrolysis cell is shown in FIG. 1. FIG. 1 is a schematic cross-sectional view of the water electrolysis cell. As shown in FIG. 1, the water electrolysis cell 100 includes, in order from the upper side of FIG. 1, an anode separator 60, an anode gas diffusion layer 20, an anode catalyst layer 12, an electrolyte membrane 11, a cathode catalyst layer 13, a cathode gas diffusion layer 30, and a cathode separator 70. Further, a gasket 40 is disposed between the anode separator 60 and the electrolyte membrane 11, and a gasket 50 is disposed between the cathode separator 70 and the electrolyte membrane 11.

[0053] <Water electrolysis device> The water electrolysis device of the present disclosure may be a water electrolysis cell stack formed by laminating a plurality of the above-described water electrolysis cells of the present disclosure, or may be a device including the water electrolysis cell stack or the water electrolysis cell of the present disclosure and other components.

[0054] The other components may be selected from the components of known water electrolysis devices. Examples of the other components include auxiliary devices such as a power conditioner, a water pump, an ion exchange resin, a heat exchanger, and a dehumidifier.

Example

[0055] Hereinafter, the present disclosure will be described in detail with reference to examples. However, the present disclosure is not limited to the following examples. The matters shown in the following examples may be appropriately changed without departing from the gist of the present disclosure. Note that Examples 11 to 14 are shown as reference examples of the present disclosure.

[0056] <Example 1> By the Pechini method, a catalyst powder containing an oxide having a perovskite structure in which iridium ions are incorporated into the B site of strontium titanate (SrTiO 3 ) was obtained. The starting materials were strontium nitrate (Sr(NO 3 ) 2 ), titanium tetrabutoxide (C 16 H 36 O 4 Ti) and potassium hexachloroiridate (K 2 IrCl 6 ). Sr(NO3 ) 2 30.2 g of 2 KIrCl 6 5.7 g of citric acid monohydrate (C 6 H 8 O 7 ·H 2 O) and 20.1 g of each were weighed and put into 750 mL of pure water, mixed, and stirred at room temperature for 1 hour or more to dissolve. This mixed solution was designated as solution A. C 16 H 36 O 4 8.1 g of C 2 H 6 O 2 Ti was weighed and mixed with 300 mL of ethylene glycol (C 2 H 6 O 2 ) and stirred for 1 hour or more to mix. This mixed solution was designated as solution B. After solution A was put into solution B, a hot stirrer was used and the mixture was stirred and mixed at 70 °C for 3 hours or more. Then, the mixed solution was transferred to a zirconia crucible and heat-treated at 180 °C for 12 hours, 200 °C for 6 hours, 300 °C for 6 hours, 500 °C for 3 hours, and 600 °C for 6 hours. The powder after heat treatment was recovered, put into a beaker together with 500 mL of 1 M hydrochloric acid aqueous solution, and stirred for 6 hours or more to remove unreacted components. The obtained mixed solution was washed with water using a suction filter and dried in an oven at 60 °C to obtain catalyst powder. When X-ray diffraction measurement was performed on the synthesized catalyst powder, a diffraction pattern derived from a perovskite-type structure was obtained. When the obtained powder was dissolved in aqua regia and analyzed by high-frequency inductively coupled plasma (ICP), the molar concentration of iridium ions at the B site was 67 mol%.

[0057] Using the synthesized catalyst powder, a test anode catalyst layer for current density measurement was prepared. 10 g of the obtained catalyst powder, a 5 mass% Nafion dispersion solution (manufactured by Sigma-Aldrich, 70160) corresponding to an ionomer, were weighed so that log(X / Y) (the logarithmic value of the mass ratio of the content (X) of the ionomer to the total content (Y) of iridium ions and ruthenium ions contained in the B-site ions) was -0.662, transferred to a glass container together with 2-propanol and pure water, and mixed with a homogenizer for 30 minutes or more to obtain an anode slurry. A commercially available Pt / C (platinum / carbon) was used as the cathode catalyst and mixed with the ionomer to obtain a cathode slurry. The anode slurry and the cathode slurry were each sprayed onto a polytetrafluoroethylene (Teflon (registered trademark)) sheet with both the vertical and horizontal lengths of 5 cm, and transferred onto the electrolyte membrane using a hot press to fabricate an electrolyte membrane with a catalyst layer. The amount of the anode catalyst was determined from the mass difference before and after coating on the Teflon sheet, and the amount of iridium coating was calculated from the ratio of the metal elements of the catalyst. When comparing the masses of the Teflon sheets before and after transfer, the transfer rate of the anode catalyst layer was 100%.

[0058] The fabricated electrolyte membrane with a catalyst layer was cut into a 2 cm square, the anode catalyst was peeled off with a spatula and scraped off, dissolved in aqua regia, and analyzed by ICP (manufactured by Hitachi High-Technologies Corporation, PS3520VDDII). As a result of analyzing the composition and coating amount of the catalyst, it was consistent with the composition and coating amount of the catalyst charge. Also, solid 19 19F-NMR analysis (manufactured by Bruker, AVANCE NEO400) was performed. The test was carried out by the single pulse method, with a spectral width of 200 kHz, a pulse width of 2.4 μsec, and a sample rotation speed of 20 kHz to obtain a spectrum. Furthermore, the fluorine and sulfur components were analyzed by ion chromatography to estimate the structure of the ionomer. As a result, it was consistent with the composition of the charged ionomer. From the estimated structure of the ionomer and the results of elemental analysis by ion chromatography, the mass of the ionomer contained in the catalyst layer was estimated, and the ionomer coating amount per unit area was calculated. As a result, it was consistent with the charged coating amount.

[0059] An electrolytic cell with a catalyst layer, an anode gas diffusion layer, a separator on the anode side, a cathode gas diffusion layer, a separator on the cathode side, an end plate on the anode side, a current collector plate on the anode side, an insulating sheet disposed between the end plate and the current collector plate on the anode side, an end plate on the cathode side, a current collector plate on the cathode side, and an insulating sheet disposed between the end plate and the current collector plate on the cathode side was fabricated. The separator on the anode side was made of titanium plated with Pt, with the vertical and horizontal lengths of the electrode installation part being 5 cm each, and 26 parallel flow channels with a width of 1 mm and a depth of 2 mm for both the grooves and ridges within a 5 cm side range. The separator on the cathode side was made of carbon, with the vertical and horizontal lengths of the electrode installation part being 5 cm each, and 26 parallel flow channels with a width of 1 mm and a depth of 2 mm for both the grooves and ridges within a 5 cm side range. The anode gas diffusion layer used a sintered body of titanium fibers plated with Pt. The cathode gas diffusion layer was made of a carbon material (manufactured by SGL Carbon Japan Co., Ltd.) and was cut to have vertical and horizontal lengths of 5 cm each. The gaskets for the anode and cathode used sheets of polytetrafluoroethylene (Teflon (registered trademark)) with the electrode installation parts cut out. The electrode layer was disposed on the part of the gasket where the electrode installation part was cut out, and further, the separator on the anode side, the anode gas diffusion layer, the electrolyte membrane with a catalyst layer, the cathode gas diffusion layer, and the separator on the cathode side were laminated so that the electrode installation part and the flow channel parts of the anode and cathode overlapped. The separators on the anode side and the cathode side were laminated in the order of the current collector plate, the insulating sheet, and the end plate, and fastened with bolts to fabricate the electrolytic cell. A water inlet and a pipe for discharging the generated oxygen and unreacted water were installed on the separator on the anode side, and a pipe for discharging the generated hydrogen was installed on the separator on the cathode side. The current collector plates on the anode side and the cathode side were each connected to an external power source (manufactured by Kikusui Electronics Industry Co., Ltd., PWR1201L). After connecting an external power source to the water electrolysis cell, the temperature of the water electrolysis cell was raised to 60 °C, and water was supplied to the water electrolysis cell at a flow rate of 100 ml / min. From 1.50 V to 1.90 V, it was held for 2 minutes at intervals of 0.1 V under constant voltage control. After reaching 1.90 V, it was held for 2 minutes at intervals of 0.1 V down to 1.50 V. This was defined as one cycle, and a total of 10 cycles of conditioning were performed. Subsequently, the voltage of the water electrolysis cell was held at 2.3 V for 100 hours under constant voltage control, and then the current value at a voltage of 1.8 V was measured to calculate log{current density (A / mg-Ir) per iridium mass at 1.8 V}, which was 0.891.

[0060] <Example 2> As starting materials, 62.4 g of Sr(NO 3 ) 2 , 11.9 g of K 2 IrCl 6 , 4.2 g of C 16 H 36 O 4 Ti, 41.6 g of C 6 H 8 O 7 ·H 2 O, 1500 mL of pure water, and 600 mL of C 2 H 6 O 2 were used. A catalyst powder containing an oxide having a perovskite structure was prepared in the same manner as in Example 1. The molar concentration of iridium ions at the B site was 33 mol%. Furthermore, a Nafion dispersion solution was mixed so that log(X / Y) became -0.438 to obtain an anode slurry. Thereafter, an electrolyte membrane with a catalyst layer was prepared in the same manner as in Example 1. log{current density (A / mg-Ir) per iridium mass at 1.8 V} was 1.073.

[0061] <Example 3> An anode slurry was obtained in the same manner as in Example 2, except that log(X / Y) was adjusted to -0.137. Thereafter, an electrolyte membrane with a catalyst layer was obtained in the same manner as in Example 1. log{current density (A / mg-Ir) per iridium mass at 1.8 V} was 0.843.

[0062] <Example 4> An anode slurry was obtained in the same manner as in Example 2, except that log(X / Y) was adjusted to 0.039. Thereafter, an electrolyte membrane with a catalyst layer was produced in the same manner as in Example 1. log{current density per iridium mass at 1.8 V (A / mg-Ir)} was 0.808.

[0063] <Example 5> As starting materials, Ba(NO 3 ) 2 , K 2 IrCl 6 and C 16 H 36 O 4 Ti were used. 58.7 g of Ba(NO 3 ) 2 , 5.5 g of K 2 IrCl 6 , 4.8 g of C 16 H 36 O 4 Ti, 19.3 g of C 6 H 8 O 7 ·H 2 O, 700 mL of pure water, and 300 mL of C 2 H 6 O 2 were used. A catalyst powder containing an oxide having a perovskite structure was produced in the same manner as in Example 1, except for the above. The molar concentration of iridium ions at the B site was 45 mol%. Furthermore, a Nafion dispersion solution was mixed so that log(X / Y) became -0.463 to obtain an anode slurry. Thereafter, an electrolyte membrane with a catalyst layer was produced in the same manner as in Example 1. log{current density per iridium mass at 1.8 V (A / mg-Ir)} was 1.037.

[0064] <Example 6> The starting materials were Sr(NO 3 ) 2 , K 2 IrCl 6 and zirconium oxychloride octahydrate (ZrOCl 2 ·8H 2O) was used. Sr(NO 3 ) 2 was weighed at 86.8 g, K 2 IrCl 6 was weighed at 14.1 g, ZrOCl 2 ·8H 2 O was weighed at 14.4 g, C 6 H 8 O 7 ·H 2 O was weighed at 345 g, and each was weighed and put into 1500 mL of pure water together with 600 mL of C 2 H 6 O 2 and mixed. The mixture was stirred at room temperature for 1 hour or more. Then, using a hot stirrer, the mixture was stirred and mixed at 75 °C for 3 hours or more. Then, the mixed solution was transferred to a zirconia crucible and heat-treated at 180 °C for 12 hours, 200 °C for 6 hours, 300 °C for 6 hours, 500 °C for 3 hours, 600 °C for 6 hours, and 700 °C for 6 hours. The powder after heat treatment was recovered, and the subsequent operations were carried out in the same manner as in Example 1 to prepare catalyst powder. The molar concentration of iridium ions at the B site was 40 mol%. Further, a Nafion dispersion solution was mixed so that log(X / Y) became -0.459 to obtain an anode slurry. Then, in the same manner as in Example 1, an electrolyte membrane with a catalyst layer was prepared. log{current density per iridium mass at 1.8 V (A / mg-Ir)} was 1.049.

[0065] <Example 7> An anode slurry was obtained in the same manner as in Example 6 except that log(X / Y) was adjusted to -0.158. Then, in the same manner as in Example 1, an electrolyte membrane with a catalyst layer was prepared. log{current density per iridium mass at 1.8 V (A / mg-Ir)} was 0.792.

[0066] <Example 8> An anode slurry was obtained in the same manner as in Example 6 except that log(X / Y) was adjusted to 0.018. Then, in the same manner as in Example 1, an electrolyte membrane with a catalyst layer was prepared. log{current density per iridium mass at 1.8 V (A / mg-Ir)} was 0.732.

[0067] <Example 9> As starting materials, Ba(NO 3 ) 2 , K 2 IrCl 6 and ZrOCl 2 ·8H 2 O were used. 97.6 g of Ba(NO 3 ) 2 , 12.8 g of K 2 IrCl 6 , 8.5 g of ZrOCl 2 ·8H 2 O, 315 g of C 6 H 8 O 7 ·H 2 O were weighed respectively and added to 1400 mL of pure water together with 550 mL of C 2 H 6 O 2 to synthesize catalyst powder in the same manner as in Example 6. The molar concentration of iridium ions at the B site was 50 mol%. Furthermore, a Nafion dispersion solution was mixed so that log(X / Y) became -0.468 to obtain an anode slurry. Then, an electrolyte membrane with a catalyst layer was produced in the same manner as in Example 1. log{current density (A / mg-Ir) per iridium mass at 1.8 V} was 1.041.

[0068] <Example 10> As starting materials, calcium carbonate (CaCO 3 ), K 2 IrCl 6 and ZrOCl 2 ·8H 2 O were used. 52.0 g of CaCO 3 , 16.0 g of K 2 IrCl 6 , 25.0 g of ZrOCl 2 ·8H 2 O, 400 g of C 6 H 8 O 7 ·H 2 O were weighed respectively and added to 70 mL of nitric acid and 700 mL of C 2 H 6 O 2It was put into 1700 mL of pure water, and catalyst powder was synthesized in the same manner as in Example 6. The molar concentration of iridium ions at site B was 50 mol%. Furthermore, a Nafion dispersion solution was mixed so that log(X / Y) became -0.440 to obtain an anode slurry. Thereafter, an electrolyte membrane with a catalyst layer was produced in the same manner as in Example 1. log{Current density (A / mg-Ir) per iridium mass at 1.8 V} was 1.009.

[0069] <Example 11> An anode slurry was obtained in the same manner as in Example 2 except that log(X / Y) was adjusted to be 0.261. Thereafter, an electrolyte membrane with a catalyst layer was produced in the same manner as in Example 1. log{Current density (A / mg-Ir) per iridium mass at 1.8 V} was -0.398.

[0070] <Example 12> An anode slurry was obtained in the same manner as in Example 2 except that log(X / Y) was adjusted to be -1.137. Thereafter, an electrolyte membrane with a catalyst layer was produced in the same manner as in Example 1. log{Current density (A / mg-Ir) per iridium mass at 1.8 V} was 0.146.

[0071] <Example 13> An anode slurry was obtained in the same manner as in Example 6 except that log(X / Y) was adjusted to be -1.158. Thereafter, an electrolyte membrane with a catalyst layer was produced in the same manner as in Example 1. log{Current density (A / mg-Ir) per iridium mass at 1.8 V} was 0.079.

[0072] <Example 14> An anode slurry was obtained in the same manner as in Example 6 except that log(X / Y) was adjusted to be 0.240. Thereafter, an electrolyte membrane with a catalyst layer was produced in the same manner as in Example 1. log{Current density (A / mg-Ir) per iridium mass at 1.8 V} was -0.523.

[0073] <Comparative Example 1> For the anode catalyst, commercially available RuO 2 was used. Furthermore, a Nafion dispersion solution was mixed so that log(X / Y) became -1.000 to obtain an anode slurry. Thereafter, in the same manner as in Example 1, an electrolyte membrane with a catalyst layer was obtained. log{current density per ruthenium mass at 1.8 V (A / mg-Ru)} was -0.843.

[0074] <Comparative Example 2> In the same manner as in Example 2, a catalyst powder containing an oxide (SrTi 0.67 Ir 0.33 O 3 ) having a perovskite structure was prepared. Next, when obtaining the anode slurry, polyvinylidene fluoride (PVdF) (Kureha Corporation, L#1120) dissolved in N-methylpyrrolidone (NMP) was used as a binder. The catalyst powder and PVdF were weighed so that the mass ratio of the solid content was 95:5, NMP was added to adjust the viscosity of the slurry, and an anode slurry was obtained. An electrolyte membrane with a catalyst layer was obtained by the method described in Example 1, except that the anode slurry was coated on a Teflon sheet with a bar coater so as to be 1.0 mg / cm 2 in terms of the total mass of the catalyst powder and the binder. log{current density per iridium mass at 1.8 V (A / mg-Ir)} was -0.907.

[0075]

Table 1

[0076] In all of Examples 1 to 14, the value of log{current density per iridium mass at 1.8 V (A / mg-Ir)} was larger than the value of log{current density per ruthenium mass at 1.8 V (A / mg-Ru)} of Comparative Example 1. RuO 2It is known that elution progresses at high potentials. This indicates that the catalyst eluted and deactivated during constant voltage operation at 2.3V. After the test, the water electrolysis cell was disassembled, and scanning electron microscopy and energy-dispersive X-ray spectroscopy were used in combination to perform microstructure and elemental analysis on the cross-section of the electrolyte membrane with the catalyst layer. As a result, it was confirmed that there are precipitates of oxides containing Ru in the electrolyte near the anode catalyst layer. On the other hand, among Examples 1 to 14, in Example 2 where log{current density per iridium mass at 1.8V (A / mg-Ir)} was the largest, elution of the constituent elements of the catalyst into the electrolyte membrane as seen in Comparative Example 1 was not observed. This indicates that the catalyst having a perovskite-type structure is stable even at high potentials.

[0077] In all of Examples 1 to 14, log{current density per iridium mass at 1.8V (A / mg-Ir)} was larger compared to Comparative Example 2. In Examples 1 to 14, protons can move in the catalyst layer and it contains an ionomer necessary for the formation of active sites for the water electrolysis reaction, whereas in Comparative Example 2, it contains PVdF, which does not contribute to proton movement in the catalyst layer or the formation of active sites for the water electrolysis reaction, as a binder. From this, it is considered that in Comparative Example 2, proton paths and reaction active sites were not formed inside the anode catalyst layer, which was the factor that the performance of the catalyst could not be elicited.

[0078] In Examples 1 to 14, in the range where log(X / Y) is less than -0.3, as log(X / Y) increases, log{current density per iridium mass at 1.8 V (A / mg-Ir)} tended to increase. This may be because by increasing the mass of the ionomer per iridium mass, a proton path was efficiently formed inside the anode catalyst layer, resulting in improved performance. Also, in the range where log(X / Y) is greater than -0.3, as log(X / Y) decreases, log{current density per iridium mass at 1.8 V (A / mg-Ir)} tended to increase. When the amount of the ionomer per iridium mass increases, it is considered that the catalyst surface is covered with the ionomer, and as a result, the amount of active sites for the water electrolysis reaction decreases. However, in this range, as log(X / Y) decreases, the excess ionomer decreases, and it is considered that the active sites for the water electrolysis reaction are efficiently introduced inside the anode catalyst layer, resulting in improved performance.

[0079] Also, as shown in FIG. 2, in a water electrolysis cell including an anode catalyst layer containing a perovskite-type structure anode catalyst and an ionomer, when log(X / Y) is defined as P and log{current density per iridium mass at 1.8 V (A / mg-Ir)} is defined as Q, the relationship between P and Q does not depend on the constituent elements of the anode catalyst and the concentration of iridium ions contained in the B site. Q = -2.1232P 3 -5.2892P 2 -2.7969P + 0.6662 It was found that it is represented by this. From this, it was found that when P is -0.860 or more and 0.060 or less, Q is 0.5 or more, and it is a high-performance water electrolysis cell. When P is -0.620 or more and -0.090 or less, Q is 0.86 or more, and it was found that it is a more high-performance water electrolysis cell. Further, when P is -0.500 or more and -0.180 or less, Q is 1 or more, and it was found that it is a more high-performance water electrolysis cell.

Explanation of Symbols

[0080] 11: Electrolyte membrane 12: Anode catalyst layer 13: Cathode catalyst layer 20: Anode gas diffusion layer 30: Cathode gas diffusion layer 40: Gasket 50: Gasket 60: Anode separator 70: Cathode separator 100: Water electrolysis cell

Claims

1. A water electrolysis cell comprising an anode gas diffusion layer, an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, a cathode gas diffusion layer, a separator, and water used for water electrolysis, wherein the anode catalyst layer contains an alkaline earth metal ion in A-site ions and at least one selected from the group consisting of iridium ions and ruthenium ions and a metal ion (excluding iridium ions and ruthenium ions) in B-site ions, and is an oxide catalyst having a perovskite-type structure, an ionomer, and contains, wherein the metal ion contains at least one selected from the group consisting of zirconium ions and tin ions, a water electrolysis cell in which a logarithmic value (log(X / Y)) of a mass ratio of the content (X) of the ionomer to the total content (Y) of the iridium ions and ruthenium ions contained in the B-site ions is -0.860 to 0.

060.

2. The water electrolysis cell according to claim 1, wherein a logarithmic value (log(X / Y)) of a mass ratio of the content (X) of the ionomer to the total content (Y) of the iridium ions and ruthenium ions contained in the B-site ions is -0.620 to -0.

090.

3. The water electrolysis cell according to claim 2, wherein a logarithmic value (log(X / Y)) of a mass ratio of the content (X) of the ionomer to the total content (Y) of the iridium ions and ruthenium ions contained in the B-site ions is -0.500 to -0.

180.

4. wherein the alkaline earth metal ion contains at least one selected from the group consisting of calcium ions, strontium ions, and barium ions, wherein the metal ion contains at least one selected from the group consisting of zirconium ions and tin ions, The water electrolysis cell according to claim 1, wherein a total molar concentration of the iridium ions and ruthenium ions in the B-site ions is 5 mol% or more and 67 mol% or less.

5. The water electrolysis cell according to claim 1, wherein the alkaline earth metal ion contains strontium ions.

6. The water electrolysis cell according to claim 1, wherein the alkaline earth metal ion contains strontium ions and the metal ion contains zirconium ions.

7. The water electrolysis cell according to claim 1, wherein the ionomer contains a perfluorosulfonic acid group.

8. A water electrolysis cell stack in which the water electrolysis cells according to any one of Claims 1 to 7 are stacked.

Images