Water electrolysis anode catalyst, composite member including water electrolysis anode catalyst, and water electrolysis apparatus including composite member

Abstract

To provide a novel water electrolysis anode catalyst having sufficient catalyst performance and sufficient durability even if Ir is not contained.SOLUTION: At least one compound selected from the group consisting of carbides, nitrides, and borides containing at least one element selected from the group consisting of Group IV, V, and VI elements in the fourth to sixth periods and Group XIV elements in the second to sixth periods.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a water electrolysis anode catalyst, a composite member including the water electrolysis anode catalyst, and a water electrolysis device including the composite member. [Background technology]

[0002] Water electrolysis is a fundamental technology that will support the next-generation hydrogen society. One of the essential components for water electrolysis is the water electrolysis electrode catalyst, which promotes the electrolysis reaction of water molecules. In particular, if water electrolysis electrode catalysts can promote the electrolysis of liquid water molecules, it will be possible to produce "green hydrogen," which does not involve the atmospheric release of carbon dioxide during production. Green hydrogen is highly sought after as an alternative energy source to fossil fuels. For this reason, water electrolysis electrode catalysts are required to have high catalytic performance that can promote the electrolysis of liquid water molecules. Furthermore, water electrolysis electrode catalysts must be highly durable in order to achieve highly efficient, long-term stable water electrolysis.

[0003] Water electrolysis catalysts include anode catalysts for oxygen generation and cathode catalysts for hydrogen generation. Iridium (Ir)-based catalysts are often used as anode catalysts because of their high catalytic performance, which can promote the electrolysis of water molecules in a liquid state. Ir is a mineral resource with low production volume and is unevenly distributed across regions, so its material price is extremely high and is prone to volatility due to influences from the international market. Patent Document 1 discloses a water electrolysis anode catalyst with a reduced amount of Ir. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2017-115232 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, with the expected global demand for large-scale, inexpensive green hydrogen, there is a demand for water electrolysis anode catalysts that do not need to contain Ir.

[0006] The present disclosure has been made in light of these circumstances, and one of its objectives is to provide a novel water electrolysis anode catalyst that does not contain Ir but has sufficient catalytic performance and durability. [Means for solving the problem]

[0007] Aspect 1 of the present invention is The water electrolysis anode catalyst comprises at least one compound selected from the group consisting of carbides, nitrides, and borides containing at least one element selected from the group consisting of Group IV, V, and VI elements of the fourth period or more and the sixth period or less and Group XIV elements of the second period or more and the sixth period or less.

[0008] Aspect 2 of the present invention is Aspect 1 is the anode catalyst for water electrolysis according to Aspect 1, wherein the compound is any one selected from the group consisting of a carbide, a nitride, and a boride containing any one element selected from the group consisting of Si, Zr, Nb, Hf, Ta, and W, or boron carbide.

[0009] Aspect 3 of the present invention is The electrical resistivity of the compound at 300 K is 1×10 5 The water electrolysis anode catalyst according to aspect 1 or 2, wherein the electrical conductivity is Ω·m or less.

[0010] A fourth aspect of the present invention is Aspect 4 is the anode water electrolysis catalyst according to any one of Aspects 1 to 3, wherein the compound has a standard enthalpy of formation of −10 kJ / mol or less.

[0011] A fifth aspect of the present invention is The composite member includes a solid electrolyte and the water electrolysis anode catalyst according to any one of Aspects 1 to 4 in contact with the solid electrolyte.

[0012] A sixth aspect of the present invention is A water electrolysis device including the composite member according to embodiment 5. [Effects of the Invention]

[0013] According to an embodiment of the present invention, it is possible to provide a novel water electrolysis anode catalyst that does not contain Ir but has sufficient catalytic performance and durability. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present inventors have conducted extensive research to develop a novel water electrolysis anode catalyst that has sufficient catalytic performance and durability even without containing Ir. As a result, they have found that sufficient catalytic performance and durability can be achieved by including at least one compound selected from the group consisting of carbides, nitrides, and borides containing at least one element selected from the group consisting of Groups IV, V, and VI elements from the fourth period to the sixth period and Group XIV elements from the second period to the sixth period, which have not previously been known to have water electrolysis anode catalytic performance. The reason for this is believed to be as follows. Boron, carbon, and nitrogen are all small elements with small atomic radii (85–65 pm). These small elements, along with elements from Periods IV, V, VI, and XIV (hereinafter referred to as "large elements"), which have large atomic radii (155–135 pm) and small electronegativity differences with the small elements, form a group of solid compounds called "interstitial compounds" (note that the electronegativity of the small elements is 2.0–3.0; the electronegativity of the large elements is 1.3–2.5). Interstitial compounds have a unique crystalline structure in which small elements are embedded in the gaps in the lattice of the large elements. Many interstitial compounds are known to have high thermal and chemical stability due to the strong chemical bonds between the small and large elements (i.e., high exothermic enthalpy of formation). In fact, the melting points of the tungsten carbide, niobium nitride, and tantalum boride included in this embodiment reach 2870°C, 2573°C, and 3000°C or higher, respectively, and they also have a high level of chemical corrosion resistance, such as being resistant to molten sodium hydroxide. Borides, carbides, and nitrides of large elements share a common property: the electronegativity difference between the small and large elements is small, and the atomic charge imbalance is weak. As a result, the chemical bonds that form the compounds have a strong covalent character. In addition to compounds containing both large and small elements, carbides, nitrides, and borides containing silicon (third period, group XIV), which has an electronegativity roughly equal to that of the small elements, and boron carbides and carbon nitrides (i.e., nitrides and borides of carbon (second period, group XIV)), which are composed exclusively of small elements, are all highly thermally and chemically stable and are thought to have similar catalytic properties. It should be noted that the above mechanism does not limit the technical scope of the embodiments of the present invention. The following provides details of each requirement stipulated by the embodiment of the present invention.

[0015] <1. Water electrolysis anode catalyst> A water electrolysis anode catalyst according to an embodiment of the present invention comprises at least one compound selected from the group consisting of carbides, nitrides, and borides containing at least one element selected from the group consisting of Group IV, V, VI elements of the fourth period or more and the sixth period or less and Group XIV elements of the second period or more and the sixth period or less. The water electrolysis anode catalyst according to an embodiment of the present invention has sufficient catalytic performance and durability by containing at least one compound specified as above.

[0016] The compound is preferably boron carbide or any one selected from the group consisting of carbides, nitrides, and borides containing any one element selected from the group consisting of Si, Zr, Nb, Hf, Ta, and W, as these exhibit excellent durability. Furthermore, the compound is more preferably boron carbide or any one selected from the group consisting of carbides and borides containing any one element selected from the group consisting of Si, Zr, Nb, Hf, Ta, and W, as these exhibit even more excellent durability. Furthermore, the compound is even more preferably selected from the group consisting of SiC, HfC, TaC, WC, and TaB2, as these exhibit even more excellent durability. The carbide is preferably any one selected from the group consisting of SiC, ZrC, NbC, HfC, TaC, and WC, more preferably any one selected from the group consisting of SiC, ZrC, HfC, TaC, and WC, and even more preferably any one selected from the group consisting of SiC, HfC, TaC, and WC. The boride is preferably any one selected from the group consisting of ZrB2, TaB2, and WB, more preferably any one selected from the group consisting of TaB2 and WB, and even more preferably TaB2. The nitride is preferably NbN. The presence or absence of the above compound can be identified, for example, by obtaining an X-ray diffraction pattern of the water electrolysis anode catalyst.

[0017] The electrical resistivity of the above compound at 300 K is 1×10 5 It is preferable that the electrical resistivity is 1×10 Ω·m or less. This can further promote the oxygen generation reaction in water electrolysis. -2 It is more preferable that it is Ω·m or less, and 1×10 -5 The lower limit of the electrical resistivity is not particularly limited, but is, for example, 1×10 -7 The electrical resistivity can be measured by the four-terminal method (four-probe method), and literature values ​​may be used.

[0018] The above compound preferably has a standard enthalpy of formation of -10 kJ / mol or less. This can result in a more stable structure and improved durability. The standard enthalpy of formation is more preferably -20 kJ / mol or less. The lower limit of the standard enthalpy of formation is not particularly limited, but can be, for example, -200 kJ / mol or more or -160 kJ / mol or more. The standard enthalpy of formation can be measured by known methods such as calorimetry and thermoelectric power analysis, and literature values ​​may also be used.

[0019] The water electrolysis anode catalyst according to an embodiment of the present invention contains at least one of the above compounds, and the total content thereof is preferably 50 mass% or more, 60 mass% or more, 70 mass% or more, 80 mass% or more, and 90 mass% or more, in that order, and is most preferably 100 mass%.

[0020] The water electrolysis anode catalyst according to an embodiment of the present invention has sufficient catalytic performance and durability even without containing Ir. The water electrolysis anode catalyst according to an embodiment of the present invention may contain Ir, but the content thereof is preferably low, for example, preferably 10 mass% or less, more preferably 1 mass% or less, and most preferably does not contain Ir.

[0021] The shape, size, and manufacturing method of the water electrolysis anode catalyst according to the embodiment of the present invention are not particularly limited. In one embodiment of the present invention, the water electrolysis anode catalyst may be a powder having an average particle size (D50) of 100 nm to 10 μm.

[0022] <2. Composite material containing water electrolysis anode catalyst> The water electrolysis anode catalyst according to this embodiment can be used in a water electrolysis device (such as a water electrolysis cell). Examples of water electrolysis devices include alkaline water electrolysis devices, solid polymer water electrolysis devices, and solid oxide water electrolysis devices. In these devices, the water electrolysis anode catalyst is used together with a solid electrolyte. The composite member according to this embodiment includes a solid electrolyte and the water electrolysis anode catalyst according to this embodiment in contact with the solid electrolyte. This composite member can be suitably used in the above device. Examples of solid electrolytes include known ion exchange membranes such as Nafion (registered trademark) membranes and solid oxide electrolytes.

[0023] <3.Water electrolysis device> The water electrolysis device according to this embodiment includes the composite member. Examples of the water electrolysis device include an alkaline water electrolysis device, a solid polymer water electrolysis device, and a solid oxide water electrolysis device. [Example]

[0024] The present embodiment will be described in more detail below with reference to examples. The present embodiment is not limited to the following examples, and can be implemented with appropriate modifications within the scope of the above-mentioned and below-mentioned aims, and all such modifications are included in the technical scope of the present embodiment.

[0025] <Preparation of water electrolysis cell> A Nafion (registered trademark) membrane N-115 (127 μm thick) was prepared as a solid electrolyte (ion exchange membrane). PtC powder (Tanaka Kikinzoku K.K., TEC10E50E) was applied at a concentration of 12.5 mg / cm on one side of the ion exchange membrane (corresponding to the cathode side of water electrolysis). 2 After uniformly spreading, 0.05 mL of Nafion (registered trademark) dispersion (5% dispersion solution DE520 CS type 328-86713) was added and dried. The compound powders (commercially available products) shown in Table 1 were prepared. The powders were applied to the other side of the ion exchange membrane (corresponding to the water electrolysis anode side) at a concentration of 6.3 mg / cm. 2 After uniformly spreading, 0.067 mL of the Nafion (registered trademark) dispersion was added and the mixture was dried to obtain a solid polymer water electrolysis cell. Regarding the literature values ​​of electrical resistivity in Table 1, the values ​​of Test Nos. 2 and 8 are values ​​measured at 300 K. As for the others, the values ​​of Test Nos. 1 and 3 were measured at room temperature, the values ​​of Test Nos. 5, 6, and 10 were measured at 298 K, the value of Test No. 9 was measured at 295 K, and the value of Test No. 4 was measured at 288 K. All of these are considered to be equivalent to the electrical resistivity at 300 K, and are considered to be equivalent to the 1×10 5 In addition, for Test No. 7, the conduction electrons of the sixth period metal borides are mainly composed of the 5d electrons of the sixth period metal, so the electrical resistivity value of the pure sixth period metal, ρ~10 -7 Ω·m (at 300K), and according to the following literature, the electrical resistivity of WB2 is about 10 -7 Therefore, the electrical resistivity (at 300K) of the compound WB is 1×10 5The preferred requirement is Ω·m or less (even more preferred requirement is 1×10 -2 Ω·m or less): Reference: Changchun Wang et al., "Mechanical and Electrical Characteristics of WB2 Synthesized at High Pressure and High Temperature", Materials, (2020), 13, 1212.

[0026] [Table 1]

[0027] <Catalyst characteristic evaluation> A current collector (titanium, Pt-plated) with multiple openings was placed in contact with both sides of the solid polymer water electrolysis cell. Water was brought into contact with only the anode side of the water electrolysis cell through the multiple openings, and the IV curve of the cell was measured. Measurements were performed with and / or without water circulation, and in at least one case, the current flow rate was 2.0 A / cm , compared with Test No. 13 (without anode catalyst for water electrolysis). 2 The catalysts in which the applied voltage (V) decreased by 0.2 V or more (i.e., the oxygen evolution reaction was predominantly promoted) were evaluated as having sufficient catalytic performance.

[0028] <Durability evaluation> A current collector (titanium, Pt-plated) with multiple openings was placed in contact with both sides of the solid polymer water electrolysis cell. Water (circulated) was brought into contact with only the anode side of the water electrolysis cell through the multiple openings, and a current of 1.5 A / cm 2 for 1000 min was applied. 2 The voltage was continuously applied and measured at regular intervals. Those whose "voltage value after 1000 minutes / voltage value after 10 minutes" ratio was 2.5 or less were evaluated as having sufficient durability.

[0029] The evaluation results are shown in Table 2.

[0030] [Table 2]

[0031] The following can be seen from Table 2. Test Nos. 1 to 10 are examples that satisfy all the requirements of this embodiment and had sufficient catalytic performance and durability even without containing Ir. In particular, Test Nos. 1 to 9, in which the compound was any one selected from the group consisting of carbides, nitrides, and borides containing any one element selected from the group consisting of Si, Zr, Nb, Hf, Ta, and W, or boron carbide, had a low "voltage value after 1000 minutes / voltage value after 10 minutes" value (e.g., 2.0 or less), which was a preferable result. Furthermore, Test Nos. 1 to 7 and 9, in which the compound was any one selected from the group consisting of carbides and borides containing any one element selected from the group consisting of Si, Zr, Nb, Hf, Ta, and W, or boron carbide, had a lower "voltage value after 1000 minutes / voltage value after 10 minutes" value (e.g., 1.3 or less), which was a more preferable result. Furthermore, Test Nos. 1 and 3 to 6, in which the compound was selected from the group consisting of SiC, HfC, TaC, WC, and TaB2, had a "voltage value after 1000 minutes / voltage value after 10 minutes" ratio lower than that of IrO2 in Test No. 11, which was a more favorable result. Also, Test Nos. 2 to 10 had an electrical resistivity of 1×10 at 300 K. -2 This meets the more desirable requirement of Ω·m or less, and is 2.0 A / cm compared to Test No. 13. 2 The applied voltage (V) further decreased (for example, by 0.8 V or more). On the other hand, Test No. 12 did not satisfy the requirements of this embodiment, and the catalytic performance was insufficient.

Claims

1. A water electrolysis anode catalyst comprising at least one compound selected from the group consisting of carbides, nitrides, and borides containing at least one element selected from the group consisting of Group IV, V, and VI elements of the fourth period or more and the sixth period or less and Group XIV elements of the second period or more and the sixth period or less.

2. 2. The water electrolysis anode catalyst according to claim 1, wherein the compound is any one selected from the group consisting of a carbide, a nitride, and a boride containing any one element selected from the group consisting of Si, Zr, Nb, Hf, Ta, and W, or boron carbide.

3. The electrical resistivity of the compound at 300 K is 1×10 ５ The water electrolysis anode catalyst according to claim 1, having a resistance of Ω·m or less.

4. 2. The water electrolysis anode catalyst according to claim 1, wherein the compound has a standard enthalpy of formation of −10 kJ / mol or less.

5. A composite member comprising: a solid electrolyte; and the water electrolysis anode catalyst according to any one of claims 1 to 4 in contact with the solid electrolyte.

6. A water electrolysis device comprising the composite member according to claim 5 .

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