Patent Application
20250207274
The present disclosure relates to an electrode for water electrolysis cell, a water electrolysis cell, a water electrolysis device, and a method for manufacturing an electrode for water electrolysis cell.
In recent years, there has been an expectation for development of electrodes to be used in water electrolysis devices.
JP 2020-12171 A describes an electrode for electrolysis of water, the electrode including an electrode substrate as a nickel foam on which NiO and a layered double hydroxide of Ni and Fe are formed.
JP 2021-139027 A describes an anode for oxygen evolution. In this anode for oxygen evolution, a catalyst layer composed of NiFe-ns (nanosheet) is formed on a surface of a predetermined intermediate. The intermediate includes an intermediate layer having a composition of Li0.5Ni1.5O2, which is formed on a surface of an anode substrate being a nickel-expanded mesh.
In Seyeong Lee et al, “Operational durability of three-dimensional Ni—Fe layered double hydroxide electrocatalyst for water oxidation,” Electrochimica Acta, 2019, Vol. 315, p. 94-101N, activity of oxygen evolution reaction (OER) of a Ni—Fe layered double hydride (Ni—Fe LDH) electrode is examined.
In Jiande Chen et al, “Interfacial Interaction between FeOOH and Ni—Fe LDH to Modulate the Local Electronic Structure for Enhanced OER Electrocatalysis,” ACS Catalysis, 2018, Vol. 8, p. 11342-11351, it is described that the local electronic structure of Ni—Fe LDH is adjusted by an interfacial interaction between FeOOH and the Ni—Fe LDH, which enhances the OER electrode-catalytic activity. In an alkaline water electrolysis, outflow of an electrode catalyst or an electrode substrate from the electrode is an issue, where the outflow is caused by redox of the electrode substrate and the electrode due to a reverse current generated by a repeated operation-suspension cycle.
The description in the above literatures need to be reconsidered from the viewpoint of durability of the electrodes used in the water electrolysis devices.
Therefore, the present disclosure provides a novel electrode for water electrolysis cell, the electrode being advantageous from the viewpoint of durability.
The present disclosure provides an electrode for water electrolysis cell, where the electrode includes:
According to the present disclosure, it is possible to provide a novel electrode for water electrolysis cell, the electrode being advantageous from the viewpoint of durability.
(Findings on which the Present Disclosure is Based)
Use of renewable energy sources such as solar power and wind power has been attracting attention as a measure against global warming. Power generation using such renewable energy sources may lead to a problem of surplus electricity being wasted. For this reason, the efficiency of renewable energy use is not necessarily sufficient. Therefore, methods of making effective use of surplus electricity by producing and storing hydrogen using surplus electricity are being considered.
Electrolysis of water is a possible method for producing hydrogen using surplus electricity. In order to produce hydrogen affordably and stably, there is a demand for development of a highly efficient, long-life water electrolysis device.
In a water electrolysis device, oxygen is evolved at the anode and hydrogen is evolved at the cathode. The reaction in which oxygen is evolved at the anode may be called an anode reaction, and the reaction in which hydrogen is evolved at the cathode may be called a cathode reaction. In order to provide a highly efficient water electrolysis device, it is desirable that the overpotential is low, especially at the anode. In addition, it is desirable that the overpotential is low at the cathode as well. Therefore, there is a demand for development of a high-performance electrode for the anode reaction or the cathode reaction of water electrolysis.
For example, an LDH is considered to be a promising material for electrodes for water electrolysis cell from the viewpoint of its large specific surface area and various combinations of metal ions. In this case, it is thought that the LDH can be supported on a base having electric conductivity. For example, as described in JP 2020-12171 A or the like, it is conceivable to support the LDH on a base such as nickel foam. However, this technique may need to be reconsidered from the viewpoint of durability with regard to electrode reaction in water-splitting. As a result of diligent studies, the inventors have newly discovered that the durability of electrode for water electrolysis cell is enhanced by the presence of a predetermined layer between the layer including the LDH and the conductive base, and the inventors have completed an electrode for water electrolysis cell of the present disclosure.
Embodiments of the present disclosure are described below with reference to the attached drawings. The present disclosure is not limited to the following embodiments. The embodiments described below are all intended to provide comprehensive or specific examples. Therefore, the numerical values, the shapes, the materials, the components, the arrangement or the positions of the components, the connection forms or the like shown in the following embodiments are simply intended to demonstrate examples, but are not intended to limit the present disclosure. Among the components in the following embodiments, the components that are not described in the independent claims indicating the highest-level concept are described as optional components. Descriptions of components with the same reference numerals in the drawings may be omitted. The drawings show each component schematically to facilitate understanding, so that the shapes, the dimensional ratios and the like may not be accurately depicted.
In the electrode 1 for water electrolysis cell, the thickness of the first layer 11 is not limited to a specific value. For example, the first layer 11 has a thickness of 10 nm or less. Thereby, the electrode 1 for water electrolysis cell is likely to exhibit high durability and the electrode 1 is likely to have high electrode activity. The thickness of the first layer 11 can be determined, for example, by performing a TEM-EDX line analysis in a region including the second layer 12, the first layer 11, and the conductive base 10 in a TEM image of the cross-section of the electrode 1 for water electrolysis cell. The thickness of the first layer 11 can be determined by noting the counts of the first transition metal, the second transition metal, and the oxygen in the TEM-EDX line analysis results. The thickness of the first layer 11 is, for example, 1 nm or more.
In the electrode 1 for water electrolysis cell, the first transition metal and the second transition metal are not limited to particular metals. The first transition metal is, for example, Ni. The second transition metal is, for example, a transition metal selected from the group consisting of V, Cr, Mn, Fe, Co, Cu, W, and Ru. With this configuration, the electrode 1 for water electrolysis cell is more likely to exhibit high durability while having high electrode activity.
In the electrode 1 for water electrolysis cell, the second transition metal is preferably Fe. In this case, the electrode 1 for water electrolysis cell is more likely to have high electrode activity and to exhibit high durability. In addition, the cost for manufacturing the electrode 1 for water electrolysis cell can be easily reduced.
The conductive base 10 is not limited to a specific base as long as it includes a first transition metal and has electric conductivity. The conductive base 10 may include a metal other than the first transition metal, or it may include a resin. The entire conductive base 10 may be composed of a metal. The conductive base 10 may have a structure in which a surface layer including a metal is formed on a member of a resin such as polypropylene or polyethylene. In this case, the surface layer including the metal may be a plated film or a sputtered film. The metal included in the conductive base 10 may be a pure metal such as nickel, or an alloy such as stainless steel or Inconel. Inconel is a registered trademark.
The surface of the conductive base 10 preferably includes at least one selected from the group consisting of nickel and nickel oxide. In this case, the conductive base 10 is likely to have high alkali resistance. In the case where the surface of the conductive base 10 includes at least one selected from the group consisting of nickel and nickel oxide, the conductive base 10 may be entirely composed of nickel. The conductive base 10 may have a surface layer including at least one selected from the group consisting of nickel and nickel oxide. The surface layer is, for example, a sputtered film or a plated film.
In the case where the surface of the conductive base 10 includes at least one selected from the group consisting of nickel and nickel oxide, the nickel and nickel oxide may have a predetermined orientation.
The shape of the conductive base 10 is not limited to a specific shape. The conductive base 10 may have, for example, a non-porous structure such as a plate or a foil, or may have a porous structure, such as a mesh, a foamed body and a non-woven fabric. The conductive base 10 may be composed of particles such as metal particles. The conductive base 10 preferably has a porous structure. In this case, the surface area of the conductive part of the conductive base 10 is likely to increase, and the electrode 1 for water electrolysis cell is likely to have high electrode activity. In addition, escape of gas evolved during the water electrolysis reaction can be prevented easily.
The thickness of the conductive base 10 is not limited to a specific value. The conductive base 10 is, for example, 0.02 mm or more in thickness. In this case, the conductive base 10 can be handled easily. The thickness of the conductive base 10 is, for example, 10 mm or less.
As described above, the second layer 12 includes the LDH.
The LDH 20 has a composition represented by the following Formula (1), for example. In Formula (1), M12+ is a divalent transition metal ion. M23+ is a trivalent transition metal ion. An− is an interlayer anion. x is a rational number that satisfies a requirement 0<x<1. y is a number that corresponds to the required amount of charge balance. n is an integer. And m is a suitable rational number.
[M12+1−xM23+x(OH)2][yAn−·mH2O] Formula (1)
The two or more transition metals in the LDH 20 are not limited to specific transition metals. In other words, M1 and M2 in the composition shown in Formula (1) are not limited to specific transition metals. The two or more transition metals include, for example, at least two selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. In this case, the electrode 1 for water electrolysis cell is likely to have high electrode activity.
The two or more transition metals in the LDH 20 include Ni and Fe, for example. In the composition shown in Formula (1), for example, M1 may be Ni and M2 may be Fe. In this case, the electrode 1 for water electrolysis cell is more likely to have high electrode activity.
An− as an interlayer anion may be an inorganic ion or an organic ion. Examples of the inorganic ion include CO32−, NO3−, Cl−, SO42−, Br−, OH−, F−, I−, Si2O52−, B4O5(OH)42−, and PO43−. Examples of the organic ion include CH3(CH2)nSO4−, CH3(CH2)nCOO−, CH3(CH2)nPO4−, and CH3(CH2)nNO3−. An− can be inserted between layers of metal hydroxide together with water molecules. The charge and ion size of An− are not limited to specific values. The LDH 20 may include one kind of An− or multiple kinds of An−.
As shown in
The second layer 12 may include a chelating agent. The chelating agent may coordinate with the transition metal ions included in the LDH 20. Thereby in formation of the second layer 12, the LDH 20 is likely to be synthesized to have a small particle diameter. As a result, the specific surface area of the LDH 20 is likely to increase, and thus, the electrode 1 for water electrolysis cell is likely to have high electrode activity. The chelating agent is a ligand with multiple coordination sites, i.e., a multidentate ligand.
The chelating agent is not limited to a specific chelating agent. The chelating agent is, for example, an organic compound capable of coordinating with a transition metal ion in the LDH 20. The chelating agent may be at least one selected from the group consisting of a bidentate organic ligand and a tridentate organic ligand. Examples of the chelating agents include β-diketone, β-ketoester, hydroxycarboxylic acid, and hydroxycarboxylate. Examples of the β-diketones include acetylacetone (ACAC), trifluoroacetylacetone, hexafluoroacetylacetone, benzoylacetone, tenoyl trifluoroacetone, dipyrrovalyl methane, dibenzoylmethane, and ascorbic acid. Examples of the β-keto esters include methyl acetoacetate, ethyl acetoacetate, allyl acetoacetate, benzyl acetoacetate, n-propyl acetoacetate, iso-propyl acetoacetate, n-butyl acetoacetate, iso-butyl acetoacetate, tert-butyl acetoacetate, 2-methoxyethyl acetoacetate, and methyl 3-oxopentanoate. Examples of the hydroxycarboxylic acids and their salts include tartaric acid, citric acid, malic acid, gluconic acid, ferulic acid, lactic acid, glucuronic acid, and their salts.
The chelating agent preferably includes at least one selected from the group consisting of acetylacetone and a citrate. In this case, the electrode 1 for water electrolysis cell is more likely to have high electrode activity. An example of the citrate is trisodium citrate.
The thickness of the second layer 12 is not limited to a specific value. The second layer 12 has a thickness of 35 nm or more, for example. With this configuration, the electrode 1 for water electrolysis cell is more likely to have high electrode activity. The second layer 12 includes a part having a thickness of 35 nm or more, for example. The thickness of the second layer 12 can be determined by, for example, a TEM observation of a cross-section of the electrode 1 for water electrolysis cell. The thickness of the second layer 12 is, for example, 210 nm or less.
The second layer 12 covers, for example, a surface of the conductive base 10. A coverage of the second layer 12 on the surface of the conductive base 10 is not limited to a specific value. The coverage is preferably 99% or more. In this case, the electrode 1 for water electrolysis cell is likely to have high electrode activity. In addition, the electrode 1 for water electrolysis cell is likely to have high durability. The coverage can be determined, for example, in accordance with the method described in Examples.
The method for manufacturing the electrode 1 for water electrolysis cell is not limited to a specific method. The electrode 1 for water electrolysis cell can be manufactured in accordance with a method including the following steps (I) and (II), for example.
(I) Promoting mixing of a solution S in which a conductive base 10 including a first transition metal is immersed, where the solution S includes a chloride ion and a second transition metal different from the first transition metal.
(II) Forming a layer including LDH including the second transition metal and a third transition metal different from the second transition metal on a surface of the conductive base 10.
In the step (I), there can be an interaction between the first transition metal included in the conductive base 10 and the second transition metal and chloride included in the solution S. This facilitates formation of a layer to firmly fix the layer including LDH formed in the step (II) to the conductive base 10. As a result, the electrode 1 for water electrolysis cell is likely to exhibit high durability.
The promoting of mixing of the solution S in the step (I) can be performed, for example, by vibrating the conductive base 10, shaking the container in which the solution S and the conductive base 10 are enclosed, or stirring the solution S using a stirrer piece and a stirrer. With this method, a forced convection of the solution S occurs, and mixing of the solution S can be promoted.
The temperature of the solution S in the step (I) is not limited to a specific temperature. For example, the temperature of the solution S in the step (I) is 20° C.±15° C. In this case, an electrode 1 for water electrolysis cell having high electrode activity can be obtained easily.
The solvent of the solution S may be water, an organic solvent, or a mixture of water and an organic solvent.
The solution S may further include, for example, a chelating agent. Thereby, the LDH 20 being synthesized in the step (II) is likely to have a small particle size, and the specific surface area of the LDH 20 is likely to increase. The electrode 1 for the water electrolysis cell is more likely to have high electrode activity.
In the case where the solution S includes a chelating agent, the solution S may further include a third transition metal. In this case, a complex formed by the third transition metal and the chelating agent included in the solution S may contribute to the synthesis of LDH 20.
In the case where the solution S includes a chelating agent, the third transition metal may be the same transition metal as the first transition metal. In this case, the method for manufacturing the electrode 1 for water electrolysis cell can be simplified.
The chelating agent included in the solution S may be selected with reference to the above examples of the chelating agents to be included in the second layer 12. The chelating agent included in the solution S preferably includes at least one selected from the group consisting of acetylacetone and a citrate. This improves the dispersion stability of the complex in the solution S, and facilitates formation of the second layer 12 in the electrode 1 for water electrolysis cell in the desired state. As a result, the electrode 1 for water electrolysis cell is more likely to have high electrode activity.
In the step (II), the method of forming a layer including the LDH is not limited to a specific method. The layer including the LDH can be formed, for example, by adjusting the solution S to be alkaline. Thereby, the electrode 1 for water electrolysis cell is more likely to exhibit high durability.
The method of adjusting the solution S to be alkaline is not limited to a specific method. For example, the solution S may be adjusted to be alkaline by mixing the above solution S with an alkaline solution. Alternatively, the solution may be adjusted to be alkaline by adding a pH booster to the solution. In this case, the pH booster is not limited to a specific compound. The pH booster is, for example, a compound having an epoxy group. Examples of the pH booster include propylene oxide, ethylene oxide, and butylene oxide.
When a pH booster having an epoxy group such as propylene oxide is added to the solution S, in the presence of a nucleophile such as a chloride ion, the pH booster can capture hydrogen ions present in the solution S, following the ring-opening reaction of the epoxy group. As a result, the pH of the solution S rises, and the solution S can be alkaline. The pH of the solution S is 1, for example. When the pH booster is added to the solution S, the pH of the solution S rises gradually from 1, for example, and eventually the solution S can be alkaline. The final pH of the solution S is, for example, in a range of 8 to 12. Addition of the pH booster to the solution promotes the reaction in which hydrogen ions in the solution S is captured. Thereby, the pH of the solution S gradually rises. The time period from the addition of the pH booster to the solution S until the pH of the solution S reaches a steady state is not limited to a specific time period. That time period can be, for example, more than 24 hours, or several days.
The temperature of the solution S when adjusting the solution S to be alkaline is not limited to a specific temperature. The temperature of the solution S is, for example, room temperature 20° C.±15° C. In this case, an electrode 1 for water electrolysis cell with high electrode activity can be obtained easily.
In the above-mentioned manufacturing method, the first transition metal and the second transition metal are not limited to specific transition metals. For example, the first transition metal is Ni and the second transition metal is a transition metal selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. In this case, an electrode for water electrolysis cell, which is more likely to exhibit high durability while having high electrode activity, can be manufactured easily.
The second transition metal ion is preferably an Fe ion. In this case, an electrode for water electrolysis cell, which is more likely to exhibit high durability while having high electrode activity, can be manufactured easily.
In the case where the first transition metal is Ni and the second transition metal is Fe, for example, the reaction represented by the following Formula (2) can occur in the step (I). As a result, the conductive base 10 can be etched. In addition, in the step (I), it is considered that Fe3+ included in the solution S can diffuse near the surface of the conductive base 10 to form a layer including Ni, Fe, and oxygen on the surface of the conductive base 10 together with some of Fe3+ and Ni2+ and oxygen. A layer including the LDH is then formed on this layer in the step (II). The thus obtained electrode 1 for water electrolysis cell includes a layer including Ni, Fe and oxygen formed between the conductive base 10 and the layer including the LDH.
4Ni2+Cl−2+2Fe3+Cl−3+2Ni→5Ni2+Cl−2+2Fe2+Cl−2+1Ni Formula (2)
In the case where the first transition metal is Ni and the second transition metal is Fe, in manufacturing the electrode 1 for water electrolysis cell, a molar ratio of a content of Fe ion to a content of Ni included in the conductive base 10 is not limited to a specific value. For example, the molar ratio is 0.75 or less. In this case, it is possible to prevent the nickel included in the conductive base 10 from dissolving to make it difficult to manufacture the electrode 1 for water electrolysis cell, where the dissolution may be caused by the reaction shown by Formula (2).
The molar ratio is preferably in a range of 0.05 to 0.25. In this case, a layer including Ni, Fe and oxygen can be formed easily on the surface of the conductive base 10 in the desired state, and an electrode 1 for water electrolysis cell with high durability can be obtained easily. In addition, the second layer 12 can be easily formed uniformly on the conductive base 10, and an electrode 1 for water electrolysis cell with high electrode activity can be manufactured easily.
In the case where the first transition metal is Ni and the second transition metal is Fe, in manufacturing the electrode 1 for water electrolysis cell, a value obtained by dividing the content of Fe ion on a molar basis by the surface area of the conductive base 10 is not limited to a specific value. For example, this value is 0.29 mmol/cm2 or less. In this case, it is possible to prevent the nickel included in the conductive base 10 from dissolving to make it difficult to manufacture the electrode 1 for water electrolysis cell, where the dissolution may be caused by the reaction represented by Formula (2).
The above-described value, which is obtainable by dividing the content of Fe ions on a molar basis by the surface area of the conductive base 10, is preferably in a range of 0.01 mmol/cm2 to 0.1 mmol/cm2. In this case, a layer including Ni, Fe and oxygen is formed easily on the surface of the conductive base 10 in a desired state, and an electrode 1 for water electrolysis cell having high durability is easily obtained. In addition, the second layer 12 can be easily formed uniformly on the conductive base 10, and an electrode 1 for water electrolysis cell having high electrode activity can be manufactured more easily.
The electrode 1 for water electrolysis cell according to the present embodiment can be used, for example, as an electrode for water electrolysis cell of an alkaline water electrolysis device or an anion-exchange membrane type water electrolysis device. The electrode 1 for water electrolysis cell is used, for example, in at least one selected from the group consisting of the anode and the cathode in the water electrolysis device. Thereby, the activity of the anode reaction or the cathode reaction in a water electrolysis is likely to increase.
The water electrolysis cell 2 is, for example, an alkaline water electrolysis cell for which an alkaline aqueous solution is used. The alkaline aqueous solution used in the water electrolysis cell 2 is not limited to a specific alkaline aqueous solution. Examples of the alkaline aqueous solution include a potassium hydroxide aqueous solution and a sodium hydroxide aqueous solution.
As shown in
The separator 2p is, for example, a separator for alkaline water electrolysis. The separator 2p is, for example, a sheet-shaped porous membrane. The separator 2p has a thickness, for example, in a range of 100 μm to 500 μm and has pores that serve as a passage for ions or an electrolytic solution. Materials for the separator 2p are not limited to a specific material. Examples of the material for the separator 2p include asbestos, polymer-reinforced asbestos, potassium titanate bonded with polytetrafluoroethylene (PTFE), zirconia bonded with PTFE, and antimonic acid and antimony oxide bonded with polysulfone. Other examples of materials for the separator 2p include sintered nickel, nickel coated with ceramics and nickel oxide, and polysulfone. The separator 2p may be Zirfon Perl UTP 500 manufactured by AGFA.
The anode 2a may be arranged in a state of zero gap, namely, in a state where the anode 2a is in contact with the separator 2p, or the anode 2a may be arranged in a state in which there is a gap between the anode 2a and the separator 2p. The cathode 2b may be arranged in a state being in contact with the separator 2p, or the cathode 2b may be arranged in a state in which there is a gap between the cathode 2b and the separator 2p.
The water electrolysis cell 2 electrolyzes an alkaline aqueous solution to produce hydrogen and oxygen. An aqueous solution including a hydroxide of an alkali metal or alkaline earth metal is supplied to the first chamber 2m. In addition, an alkaline aqueous solution may be supplied to the second chamber 2n. Electrolysis is carried out while an alkaline aqueous solution of a predetermined concentration is discharged from the first chamber 2m and the second chamber 2n, whereby hydrogen and oxygen are produced.
In the case where the anode 2a includes the electrode 1 for water electrolysis cell, the cathode 2b may include, for example, an electrode material known as a cathode for an alkaline water electrolysis cell.
In the water electrolysis cell 2, in the case where the cathode 2b includes the electrode 1 for water electrolysis cell, the anode 2a may include the electrode material known as the anode for the alkaline water electrolysis cell. In the water electrolysis cell 2, both the anode 2a and the cathode 2b may include the electrode 1 for water electrolysis cell.
With the above configuration, at least one selected from the group consisting of the anode 2a and the cathode 2b includes the electrode 1 for water electrolysis cell, and thus, the water electrolysis cell 2 can exhibit high durability.
The voltage applicator 40 is electrically connected to the anode 2a and the cathode 2b. The voltage applicator 40 causes the potential of the anode 2a to become higher than the potential of the cathode 2b. The voltage applicator 40 is not limited to a specific type of voltage applicator as long as the voltage applicator 40 is capable of applying a voltage between the anode 2a and the cathode 2b. The voltage applicator 40 may be a device to adjust the voltage applied between the anode 2a and the cathode 2b. In the case where the voltage applicator 40 is connected to a direct current power source such as a battery, a solar cell and a fuel cell, the voltage applicator 40 includes a DC/DC converter, for example. In the case where the voltage applicator 40 is connected to an alternating current power source such as a commercial power source, the voltage applicator 40 is equipped with an AC/DC converter, for example. The voltage applicator 40 may be an electric power type power source, for example. In the electric power type power source, the voltage to be applied between the anode 2a and the cathode 2b, and the current to flow between the anode 2a and the cathode 2b, are adjusted such that the electric power supplied to the water electrolysis device 3 will be a predetermined set value.
With the above configuration, the water electrolysis device 3 can exhibit high durability.
The water electrolysis cell is, for example, an anion-exchange membrane (AEM) type water electrolysis cell. As shown in
The anion-exchange membrane 4p is not limited to a specific type of anion-exchange membrane. The anion-exchange membrane 4p has conductivity for anions such as hydroxide ions. The anion-exchange membrane 4p is capable of preventing mixing of the oxygen gas generated at the anode 4a with the hydrogen gas generated at the cathode 4b. The oxygen gas passes through the gas diffusion layer 4n and is led outside the anode 4a. The hydrogen gas passes through the gas diffusion layer 4k and is led outside the cathode 4b.
In the water electrolysis cell 4, in the case where the anode 4a includes the electrode 1 for water electrolysis cell, the cathode 4b may be a known cathode in an AEM-type water electrolysis cell.
In the water electrolysis cell 4, in the case where the cathode 4b includes the electrode 1 for water electrolysis cell, the anode 4a may be the known anode of the AEM-type water electrolysis cell. In the water electrolysis cell 4, both the anode 4a and the cathode 4b may include the electrode 1 for water electrolysis cell.
With the above configuration, at least one selected from the group consisting of the anode 4a and the cathode 4b includes the electrode 1 for water electrolysis cell, whereby the water electrolysis cell 4 can exhibit high durability.
The metallic particles composing the conductive base 10 include one or more transition metals. Examples of the transition metals include V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. The metal particles may include Ni, and the metal particles may be Ni particles. The transition metal included in the metal particles 11 may be the same metal as the two or more transition metals included in the LDH of the second layer 12.
The shape of the metal particles composing the conductive base 10 is not limited to a specific shape. For example, the shape of the metal particles is granular. In the case where the shape of the metal particles is granular, the average particle diameter of the metal particles is not limited to a specific value. The average particle diameter of the metal particles may be 100 nm or less, or may be 50 nm or less. The average particle diameter of the metal particles may be 10 nm or more, or 20 nm or more. The metal particles may, for example, have an average particle size to support a sufficient amount of LDH. As a result, even in the case where a voltage is applied to the electrode 1 for water electrolysis cell, the second layer 12 including the LDH and the metal particles composing the conductive base 10 are less likely to separate, and the electrode 1 for water electrolysis cell will have high durability. In addition, with such a configuration, the electrode 1 for water electrolysis cell can more reliably have high durability, for example, in the anode reaction of water electrolysis. The average particle diameter of the metal particles can be determined, for example, by observing the metal particles with a transmission electron microscope (TEM). Specifically, the average of the maximum and minimum diameters of fifty metal particles observable as a whole is defined as the particle size of each metal particle, and the average particle size can then be determined as the arithmetic mean of the particle sizes.
The voltage applicator 40 is electrically connected to the anode 4a and to the cathode 4b. Due to the voltage applicator 40, the potential of the anode 4a becomes higher than the potential of the cathode 4b. The voltage applicator 40 is not limited to a specific type of voltage applicator as long as the voltage applicator 40 is capable of applying a voltage between the anode 4a and the cathode 4b. The voltage applicator 40 may be a device to adjust the voltage applied between the anode 4a and the cathode 4b. In the case where the voltage applicator 40 is connected to a direct current power source such as a battery, solar cell, or fuel cell, the voltage applicator 40 includes a DC/DC converter, for example. In the case where the voltage applicator 40 is connected to an alternating current power source such as a commercial power source, the voltage applicator 40 includes an AC/DC converter, for example. The voltage applicator 40 may be an electric power type power source, for example. In the electric power type power source, the voltage applied between the anode 4a and the cathode 4b and the current flowing between the anode 4a and the cathode 4b are adjusted such that the power supplied to the water electrolysis device 5 becomes a predetermined set value.
With the above configuration, the water electrolysis device 5 can exhibit high durability.
From the above description, the following techniques are disclosed.
An electrode for water electrolysis cell, the electrode including:
The electrode according to Technique 1, wherein
The conductive base has a porous structure.
The electrode according to Technique 1 or 2, wherein
The electrode according to any one of Techniques 1 to 3, wherein
The electrode according to any one of Techniques 1 to 4, wherein
The electrode according to Technique 5, wherein
The electrode according to any one of Techniques 1 to 6, wherein
The electrode according to Technique 7, wherein
A water electrolysis cell including:
A water electrolysis cell including:
A water electrolysis device including:
A method for manufacturing an electrode for water electrolysis cell, the method including:
The method according to Technique 12, wherein
The method according to Technique 12, wherein
The method according to any one of Techniques 12 to 14, wherein
The method according to any one of Techniques 12 to 15, wherein
The method according to Technique 16, wherein
The method according to Technique 17, wherein
The method according to Technique 16, wherein
The method according to Technique 19, wherein
The method according to Technique 13 or 14, wherein
The present disclosure is further explained in detail by referring to Examples. The following Examples demonstrate a part of the present disclosure, and the present disclosure is not limited to the Examples.
A mixed solvent was prepared by mixing 6.688 milliliters (mL) of water and 10.032 mL of ethanol. The ethanol was a product purchased from FUJIFILM Wako Pure Chemical Corporation. In the mixed solvent, a volume ratio of the water to the ethanol was 2:3. In this mixed solvent, 0.5685 g of nickel chloride hexahydrate and 0.3233 g of iron chloride hexahydrate were dissolved to prepare a solution. The nickel chloride hexahydrate and the iron chloride hexahydrate were products purchased from FUJIFILM Wako Pure Chemical Corporation. To this solution, 0.113 mL of acetylacetone (ACAC) as a chelating agent was added to obtain a chelating agent solution. The ACAC was a product purchased from Sigma-Aldrich Corporation. An amount of substance of the ACAC in the chelating agent solution was 1/3.25 of a total amount of substance of Ni ions and Fe ions. The chelating agent solution was acidic.
Five Ni meshes manufactured by Nilaco Corporation were washed with acetone for 10 minutes and then washed with a 1M HCl aqueous solution for 10 minutes for degreasing the Ni meshes and removing impurities. The Ni meshes each had a wire diameter of 0.1 mm, the number of meshes of a Ni mesh was 60, and each Ni mesh was shaped circular with a diameter of 15 mm in a plan view. The total weight of the five Ni meshes was 0.281 g. Next, the Ni meshes were washed with water and dried to complete the washing treatment of the Ni mesh.
After completion of the washing process, the Ni meshes were then immersed in the chelating agent solution described above. In this state, the chelating agent solution including the Ni meshes was shaken and stirred at 25° C. for 24 hours. At this time, the outermost surface of the Ni mesh was etched in accordance with the reaction in the above Formula (2). In this case, a molar ratio of the Fe ion content to the Ni content in the Ni mesh was 0.25. In addition, a value obtained by dividing the content of the Fe ions on a molar basis by the surface area of the Ni mesh was 0.0942 millimoles (mmol)/cm2. The surface area of the Ni mesh was determined by taking into account the geometric shape of the Ni mesh based on the wire diameter, the mesh count and the diameter.
Next, 1.216 mL of propylene oxide (POX) as a pH booster was added to the chelating agent solution. The amount of POX added was adjusted such that a ratio of an amount of substance of the POX to an amount of substance of the chloride ions in the mixed solution was 2. The resulting mixed solution was shaken and stirred at 25° C. for 72 hours. It is understood that during the shaking and stirring of the mixed solution, the POX gradually captured the hydrogen ions in the mixed solution, and that the pH of the mixed solution gradually increased and became alkaline. After 72 hours of shaking and stirring, the Ni meshes were collected, and the Ni meshes was washed with water and dried. In this way, the electrode according to Example 1 was obtained.
An electrode according to Example 2 was produced in the same way as in Example 1, except for the following points. In preparing a mixed solvent, 0.535 mL of water and 0.803 mL of ethanol were mixed. In the mixed solvent, a volume ratio of the water to the ethanol was 2:3. The amount of nickel chloride hexahydrate dissolved in the mixed solvent was 0.0455 g, and the amount of iron chloride hexahydrate dissolved in the mixed solvent was 0.0259 g. The amount of the ACAC added in the preparation of the chelating agent solution was 0.009 mL, and the amount of substance of the ACAC in the chelating agent solution was 1/3.25 of a total amount of substance of Ni ions and Fe ions. Two Ni meshes were used, and the total mass of the two Ni meshes was 0.112 g. The molar ratio of the content of Fe ions to the content of Ni in the Ni meshes during the shaking and stirring of the chelating agent solution including the Ni meshes was 0.05. In addition, a value obtained by dividing the content of Fe ions on a molar basis by the surface area of the Ni meshes was 0.0188 mmol/cm2.
An electrode according to Example 3 was prepared in the same way as Example 1, except for the following points. In preparing a mixed solvent, 6.900 mL of water and 10.351 mL of ethanol were mixed. In the mixed solvent, a volume ratio of the water to the ethanol was 2:3. The amount of nickel chloride hexahydrate dissolved in the mixed solvent was 5.8654 g, and the amount of iron chloride hexahydrate dissolved in the mixed solvent was 3.3351 g. The amount of the ACAC added in the preparation of the chelating agent solution was 1.164 mL, and the amount of substance of the ACAC in the chelating agent solution was 1/3.25 of the total amount of substance of Ni ions and Fe ions. Four Ni meshes were used, and the total mass of the four Ni meshes was 0.96 g. Each Ni mesh was a square with a side length of 20 mm in a plan view. The amount of the POX added to the chelating agent solution was 12.545 mL. A molar ratio of the content of Fe ions to the content of Ni in the Ni mesh during the shaking and stirring of the chelating agent solution including the Ni mesh was 0.75. In addition, a value obtained by dividing the content of Fe ions on a molar basis by the surface area of the Ni mesh was 0.2844 mmol/cm2. An amount of the POX added was adjusted such that the ratio of the amount of substance of the POX to the amount of substance of the chloride ions in the mixed solution of the chelating agent solution and the POX would be 2.
A mixed solvent was prepared by mixing 6.900 mL of water and 10.351 mL of ethanol. The ethanol was a product purchased from FUJIFILM Wako Pure Chemical Corporation. In the mixed solvent, a volume ratio of the water to the ethanol was 2:3. In this mixed solvent, 5.8654 g of nickel chloride hexahydrate and 3.3351 g of iron chloride hexahydrate were dissolved to prepare a solution. The nickel chloride hexahydrate and the iron chloride hexahydrate were products purchased from FUJIFILM Wako Pure Chemical Corporation. To this solution, 1.164 mL of acetylacetone (ACAC) as a chelating agent was added to obtain a chelating agent solution. The ACAC was a product purchased from Sigma-Aldrich Corporation. The amount of substance of the ACAC in the chelating agent solution was 1/3.25 of the total amount of substance of the Ni ions and the Fe ions. The pH of the chelating agent solution was 1.
One Ni mesh manufactured by Nilaco Corporation was washed with acetone for 10 minutes and then washed with a 1 M HCl aqueous solution for 10 minutes for degreasing the Ni mesh and removing impurities. The Ni mesh had a wire diameter of 0.1 mm, the number of meshes of the Ni mesh was 60, and the Ni mesh was a square with a side length of 20 mm in a plan view. The weight of the Ni mesh was 0.25 g. Next, the Ni mesh was washed with water and dried to complete the washing process for the Ni mesh.
After completion of the washing process, the Ni mesh was then immersed in the chelating agent solution. In this state, the chelating agent solution including the Ni mesh was shaken and stirred at 25° C. for 24 hours. At this time, in accordance with the reaction in the above Formula (2), the Ni mesh was entirely etched and dissolved. As a result, no evaluable electrode was obtained in Comparative Example 1. The molar ratio of the content of Fe ions to the content of Ni in the Ni mesh was 2.9. Further, a value obtained by dividing the content of Fe ions on a molar basis by the surface area of the Ni mesh was 1.0919 mmol/cm2.
Five Ni meshes were used as the electrodes according to Comparative Example 2, after completion of washing in the same way as in Example 1.
An electrode according to Comparative Example 3 was prepared in the same way as in Example 1, except for the following points. A Ni mesh after completion of the washing process was placed in the aforementioned chelating agent solution, and immediately thereafter, POX was added to the chelating agent solution. In other words, in Comparative Example 3, the chelating agent solution including the Ni mesh was not shaken or stirred before the addition of POX.
Samples for morphological observation were picked up and processed using a focused ion beam (FIB) system (FB-2200 manufactured by Hitachi High-Technologies Corporation). Next, the samples for morphological observation were sliced using FIB NX5000 manufactured by Hitachi High-Tech Science. The structure of the electrode according to each Example and each Comparative Example was identified, and the morphology of the electrode was observed, by performing a cross-sectional observation and an electron beam diffraction of the thus obtained samples, using a transmission electron microscope (TEM) JEM-F200 manufactured by JEOL Ltd. In this way, the states of the LDH in the electrodes according to Examples and Comparative Examples were evaluated.
A TEM-EDX line analysis was performed from the layer including the LDH to the Ni mesh of the electrode according to Example 1.
As shown in
A TEM-EDX line analysis was performed from the layer including the LDH to the Ni mesh of the electrode according to Comparative Example 3.
The oxygen evolution reaction (OER) overpotentials of the electrode according to the respective Examples and Comparative Examples 2 and 3 were evaluated. The following equipment was used for the measurements: a VersaSTAT4, potentiostat manufactured by Princeton Applied Research; an alkali sample vial (200 ml) manufactured by BAS Inc.; a Teflon (registered trademark) cap (200 ml) manufactured by BAS Inc.; and a plate electrode AE-2 manufactured by EC FRONTIER CO., LTD., as a working electrode jig. The electrodes as working electrodes according to the respective Examples and Comparative Examples 2 and 3 were fixed to the jig. As the counter electrode, a double platinum wire counter electrode (D.6.0305.200J) manufactured by Metrohm AG was used. The current derived from the anode reaction of the water electrolysis cell was measured using the three-electrode method under the following measurement conditions. The anode reaction is the oxygen evolution reaction.
The OER overpotential was determined by subtracting a theoretical potential of 1.229 V required to drive the oxygen evolution reaction from the voltage corresponding to the current density of 10 mA/cm2 in the fifth cycle. The results are shown in Table 1. Table 1 shows a molar ratio of the Fe ion content to the Ni content in the Ni mesh in production of an electrode, as well as a value obtained by dividing a content of the Fe ion on a molar basis by the surface area of the Ni mesh. Table 1 also shows whether the chelating agent solution including the Ni mesh was shaken/stirred before the addition of POX, and whether the electrode was successfully produced.
From the measurement results for evaluation of the OER overpotential, the coverage of the layer including the LDH to the surface of the Ni mesh was determined based on the following Formula (3). The results are shown in Table 1. In Formula (3), SNiOx is an integral value of the current density at a potential in a range of 1.38 V to 1.48 V, and SNi is an integral value of the current density at a potential in a range of 1.35 V to 1.38 V. The peak in the current density at potentials in a range of 1.38 V to 1.48 V is a peak derived from the hydroxides of iron and nickel, while the peak in the current density in a range of 1.35 V to 1.38 V is a peak derived from pure nickel.
As shown in Table 1, the OER overpotentials of the electrodes according to Examples 1 to 3 are lower than the OER overpotential of the electrode according to Comparative Example 2, whereby it is understood that an electrode including a layer including the LDH has high electrode activity. In the meantime, comparing each Example with Comparative Example 1, if the molar ratio of the content of the Fe ions to the content of Ni in the Ni mesh is high, a chemical reaction to dissolve the Ni becomes intense, and the entire Ni mesh dissolves, making it impossible to produce an electrode. For this reason, it is understood that the molar ratio of the content of Fe ions to the content of Ni in the Ni mesh is desirably 0.75 or less. In addition, it is understood that the value obtained by dividing the content of Fe ions on a molar basis by the surface area of the Ni mesh is desirably 0.29 mmol/cm2 or less.
As shown in Table 1, the OER overpotentials of the electrodes according to Examples 1 and 2 are particularly low. Therefore, from the viewpoint of electrode activity, it was suggested that the molar ratio of the content of Fe ions to the content of Ni included in the Ni mesh be more desirably in a range of 0.05 to 0.25. In addition, it was suggested that the value obtained by dividing the content of Fe ions on a molar basis by the surface area of the Ni mesh be more desirably in a range of 0.01 mmol/cm2 to 0.1 mmol/cm2.
The OER overpotentials of the electrodes according to of Example 1 and Comparative Examples 2 and 3 were measured for 1000 cycles to evaluate the durability of the electrodes. The following equipment was used for the measurements: a VersaSTAT4 potentiostat manufactured by Princeton Applied Research; an alkali sample vial (200 ml) manufactured by BAS Inc.; a Teflon (registered trademark) cap (200 ml) manufactured by BAS Inc.; and a plate electrode AE-2 manufactured by EC FRONTIER CO., LTD. as the working electrode jig. The electrodes as working electrodes according to Example 1 and Comparative Examples 2 and 3 were fixed to the jig. As the counter electrode, a double platinum wire counter electrode (D.6.0305.200J) manufactured by Metrohm AG was used. The current derived from the anode reaction of the water electrolysis cell was measured using the three-electrode method under the following measurement conditions. The anode reaction is the oxygen evolution reaction.
Comparing Example 1 with Comparative Example 2 and Comparative Example 3, the OER overpotential of the electrode according to Example 1 does not rise by the 50th cycle. On the other hand, the OER overpotentials of the electrodes according to Comparative Examples 2 and 3 rise before the 50th cycle. Therefore, from the viewpoint of electrode durability, it is apparently important to promote mixing of the chelating agent solution with the Ni mesh immersed therein by shaking and stirring the chelating agent solution with the Ni mesh, before adjusting the solution to be alkaline.
Many modifications and other embodiments of the present disclosure will be apparent to those skilled in the art with reference to the above description. Therefore, the above description should be interpreted only as an example, and is provided for the purpose of teaching those skilled in the art the best manner to carry out the present disclosure. The operating conditions, the composition, the structure and/or the function can be substantially modified without departing from the spirit of the present disclosure.
An electrode for water electrolysis cell of the present disclosure can be used as an anode or a cathode for water electrolysis.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-148620 | Sep 2022 | JP | national |
This application is a continuation of PCT/JP2023/026693 filed on Jul. 20, 2023, which claims foreign priority of Japanese Patent Application No. 2022-148620 filed on Sep. 16, 2022, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2023/026693 | Jul 2023 | WO |
| Child | 19075248 | US |
