Catalyst for hydrogen generation, and method for producing catalyst for hydrogen generation

Abstract

Provided is a catalyst for hydrogen generation comprising a mixture of tungsten carbide and cobalt, the catalyst for hydrogen generation being characterized in that the absolute value of the cathode current per mg of the catalyst is 0.10 mA / mg or more when the catalyst for hydrogen generation is loaded on a glassy carbon electrode and subjected to potential scanning at -1.2 V with respect to a silver / silver chloride reference electrode under nitrogen bubbling in a 1 mol / L sodium hydroxide aqueous solution.

Description

Catalyst for generating hydrogen and method for producing catalyst for generating hydrogen

[0001] The present invention relates to a hydrogen generation catalyst used to promote a hydrogen generation reaction, and a method for producing the hydrogen generation catalyst. This application claims priority based on Japanese Patent Application No. 2023-204122, filed on December 1, 2023, the contents of which are incorporated herein by reference.

[0002] An example of a means for generating hydrogen is a polymer electrolyte membrane (PEM). The above-mentioned polymer electrolyte membrane (PEM) includes a water electrolysis cell having an anode and a cathode arranged opposite each other, and an ion-permeable membrane arranged between the anode and the cathode. A catalyst layer is formed on each of the two surfaces of the ion-permeable membrane (the surface in contact with the anode and the surface in contact with the cathode). In a water electrolysis device (water electrolysis cell) configured as described above, oxygen (O ) is produced on the anode side by decomposing water. ２ ) is generated on the cathode side, and hydrogen (H ２ ) will occur.

[0003] Here, platinum (Pt) is widely used as a hydrogen generation catalyst used in the cathode (hydrogen generation electrode). Platinum (Pt) is usually used in a state supported on nanocarbon. However, platinum (Pt) is a precious metal and is very expensive, which has led to a problem of significantly increasing the operating costs of the water electrolysis device.

[0004] Therefore, as a catalyst for generating hydrogen that can replace platinum (Pt), those disclosed in Patent Documents 1 and 2 have been proposed, for example. Patent Document 1 discloses a tungsten carbide catalyst, ２ C ０．８５ In addition, Patent Document 2 proposes tungsten-nickel carbide (W—Ni—C) formed on a carbon support.

[0005] Japanese Patent Publication No. 2016-163861 (A) Japanese Special Publication No. 2018-528141 (A)

[0006] However, the above-mentioned hydrogen generating catalyst is required to be able to promote hydrogen generation more efficiently and stably. Furthermore, the above-mentioned hydrogen generating catalyst is required to have low production costs so that hydrogen generation can be performed inexpensively. However, Patent Documents 1 and 2 require a heat treatment at a high temperature after mixing the raw materials, which raises the problem of high production costs.

[0007] The present invention has been made in view of the above-mentioned circumstances, and aims to provide a hydrogen generation catalyst that can be produced at low cost and is capable of generating hydrogen efficiently, and a method for producing the hydrogen generation catalyst.

[0008] In order to solve the above problems, a catalyst for generating hydrogen according to a first aspect of the present invention is a catalyst for generating hydrogen comprising a mixture of tungsten carbide and cobalt, characterized in that the absolute value of the cathode current per mg of catalyst when the catalyst for generating hydrogen is supported on a glassy carbon electrode and subjected to potential scanning at −1.2 V against a silver-silver chloride standard electrode under nitrogen bubbling in a 1 mol / L aqueous sodium hydroxide solution is 0.10 mA / mg or more.

[0009] According to the catalyst for hydrogen generation of Aspect 1 of the present invention, since it is composed of a mixture of tungsten carbide and cobalt, electron transfer at the interface between tungsten carbide and cobalt is promoted, thereby improving catalytic activity. Furthermore, the coexistence of tungsten carbide improves the oxidation resistance of cobalt, contributing to improved catalytic activity in the reaction solution. As described above, when the catalyst for hydrogen generation is supported on a glassy carbon electrode and subjected to potential scanning at −1.2 V against a silver-silver chloride standard electrode in a 1 mol / L aqueous sodium hydroxide solution with nitrogen bubbling, the absolute value of the cathode current per 1 mg of catalyst is 0.10 mA / mg or more, thereby enabling efficient and stable promotion of hydrogen generation.

[0010] The catalyst for generating hydrogen according to Aspect 2 of the present invention is characterized in that, in the catalyst for generating hydrogen according to Aspect 1, the cobalt content is in the range of 1.0 mass% or more and 50.0 mass% or less. According to the catalyst for generating hydrogen according to Aspect 2 of the present invention, the cobalt content is in the range of 1.0 mass% or more and 50.0 mass% or less, so that catalytic activity can be reliably improved and oxidation resistance can be sufficiently improved. Therefore, hydrogen generation can be promoted more efficiently and stably.

[0011] A catalyst for generating hydrogen according to Aspect 3 of the present invention is characterized in that the tungsten carbide has a hexagonal crystal structure in the catalyst for generating hydrogen according to Aspect 1 or Aspect 2. According to the catalyst for generating hydrogen according to Aspect 3 of the present invention, the tungsten carbide has a hexagonal crystal structure, which improves chemical resistance and makes the catalyst more stable in the reaction solution, thereby ensuring improved catalytic activity.

[0012] The catalyst for generating hydrogen according to Aspect 4 of the present invention is characterized in that the tungsten carbide and the cobalt are present on the outermost surface of the catalyst for generating hydrogen according to any one of Aspects 1 to 3. According to the catalyst for generating hydrogen according to Aspect 4 of the present invention, the tungsten carbide and the cobalt are present on the outermost surface, which ensures that an interface between the tungsten carbide and the cobalt is present on the outermost surface, thereby reliably promoting electron transfer and further improving catalytic activity.

[0013] A catalyst for generating hydrogen according to a fifth aspect of the present invention is a catalyst for generating hydrogen according to any one of the first to fourth aspects, wherein the BET specific surface area is 0.5 m ２ / g or more 20.0m ２ According to the catalyst for generating hydrogen of aspect 5 of the present invention, the BET specific surface area is in the range of 0.5 m / g or less. ２ / g or more 20.0m ２ / g or less, the surface area is sufficiently large and the catalytic activity can be reliably improved.

[0014] The method for producing a catalyst for generating hydrogen according to Aspect 6 of the present invention is a method for producing a catalyst for generating hydrogen according to any one of Aspects 1 to 5, and is characterized in that tungsten carbide powder and cobalt powder are mechanically mixed. According to the method for producing a catalyst for generating hydrogen according to Aspect 6 of the present invention, the catalyst for generating hydrogen according to any one of Aspects 1 to 5 is produced by mechanically mixing tungsten carbide powder and cobalt powder, so that the catalyst for generating hydrogen can be easily produced by a relatively simple procedure, and the production cost of the catalyst for generating hydrogen can be significantly reduced.

[0015] According to the present invention, it is possible to provide a hydrogen generation catalyst that can be produced at low cost and that is capable of generating hydrogen efficiently, and a method for producing the hydrogen generation catalyst.

[0016] 1 is a diagram showing the results of XRD analysis of Inventive Example 1 in the Examples, 2 is an observation photograph of Inventive Example 1 in the Examples, and 3 is a diagram showing the results of component analysis of Inventive Example 1 in the Examples.

[0017] A hydrogen generating catalyst according to one embodiment of the present invention and a method for producing the hydrogen generating catalyst will be described below. The hydrogen generating catalyst according to one embodiment of the present invention is used as a hydrogen generating catalyst disposed in a cathode (hydrogen generating electrode) of a water electrolysis cell constituting a polymer electrolyte membrane (PEM) water electrolysis device.

[0018] The hydrogen generating catalyst of this embodiment is made of a mixture of tungsten carbide and cobalt, and has a structure in which the surface of the tungsten carbide is partially modified with cobalt. In the hydrogen generating catalyst of this embodiment, the hydrogen generating catalyst is supported on a glassy carbon electrode, and when the catalyst is subjected to potential scanning at −1.2 V against a silver-silver chloride standard electrode in a 1 mol / L aqueous sodium hydroxide solution with nitrogen bubbling, the absolute value of the cathode current per 1 mg of catalyst is 0.10 mA / mg or more.

[0019] In the catalyst for generating hydrogen according to this embodiment, the cobalt content is preferably in the range of 1.0 mass % or more and 50.0 mass % or less. In the catalyst for generating hydrogen according to this embodiment, it is preferable that tungsten carbide has a hexagonal crystal structure. Furthermore, in the catalyst for generating hydrogen according to this embodiment, it is preferable that tungsten carbide and cobalt are present on the outermost surface. In the catalyst for generating hydrogen according to this embodiment, it is preferable that the BET specific surface area is 0.5 m ２ / g or more 20.0m ２ It is preferable that the range is 1 / g or less.

[0020] The reasons for specifying the structure, the absolute value of the cathode current per 1 mg of catalyst, the cobalt content, the tungsten carbide crystal structure, the outermost surface structure of the catalyst, and the BET specific surface area as described above for the hydrogen generation catalyst of this embodiment will be explained below.

[0021] (Structure) As described above, the hydrogen generation catalyst of this embodiment is made of a mixture of tungsten carbide and cobalt, and has a structure in which the surface of the tungsten carbide is partially modified with cobalt. By adopting such a structure, an interface between the tungsten carbide and cobalt is present, and electron transfer is promoted at the interface between the tungsten carbide and cobalt, thereby improving catalytic activity. Furthermore, the coexistence of cobalt with tungsten carbide improves oxidation resistance, and the catalytic activity is also improved in the reaction solution.

[0022] (Cathode Current per 1 mg of Catalyst) In the hydrogen generation catalyst of this embodiment, when the catalyst is supported on a glassy carbon electrode and subjected to potential scanning at −1.2 V against a silver-silver chloride standard electrode in a 1 mol / L aqueous sodium hydroxide solution with nitrogen bubbling, the absolute value of the cathode current per 1 mg of catalyst is 0.10 mA / mg or more, and therefore the catalyst has catalytic activity sufficient for practical use as a hydrogen generation catalyst. The absolute value of the cathode current per 1 mg of catalyst is preferably 0.30 mA / mg or more, and more preferably 0.50 mA / mg or more. Although not particularly limited, the absolute value of the cathode current per 1 mg of catalyst may be 5000 mA / mg or less, 2000 mA / mg or less, or 1000 mA / mg or less.

[0023] (Cobalt Content) In the catalyst for generating hydrogen according to this embodiment, when the cobalt content is 1.0% by mass or more, electron transfer at the interface between tungsten carbide and cobalt is sufficiently promoted, resulting in a reliable improvement in catalytic activity. On the other hand, when the cobalt content is 50.0% by mass or less, the entire catalyst for generating hydrogen has excellent oxidation resistance, enabling more stable use. The cobalt content is more preferably 5.0% by mass or more, and even more preferably 10.0% by mass or more. The cobalt content is more preferably 40.0% by mass or less, and even more preferably 30.0% by mass or less.

[0024] (Crystal structure of tungsten carbide) In the catalyst for generating hydrogen of this embodiment, when tungsten carbide has a hexagonal crystal structure, the chemical resistance of the entire catalyst for generating hydrogen is further improved, and the catalyst is more stable in the reaction solution, resulting in a reliable improvement in catalytic activity.

[0025] (Structure of the outermost surface of the catalyst) In the hydrogen generation catalyst of this embodiment, when tungsten carbide and cobalt are present on the outermost surface, an interface between tungsten carbide and cobalt is present on the outermost surface of the catalyst, and electron transfer is promoted at the interface between tungsten carbide and cobalt, resulting in a reliable improvement in catalytic activity.

[0026] (BET specific surface area) In the hydrogen generation catalyst of this embodiment, the BET specific surface area is 0.5 m ２ On the other hand, when the BET specific surface area of ​​the hydrogen generation catalyst is 20.0 m / g or more, the surface area is sufficiently large and the catalytic activity is reliably improved. ２ It is practically difficult to produce a material with a BET specific surface area exceeding 1.0 m / g. ２ / g or more, and 2.0m ２ / g or more. The BET specific surface area is 19.0 m ２ / g or less, and more preferably 18.0m ２ It is more preferable that the SiO2 content is 1 / g or less.

[0027] Next, a method for producing a hydrogen generation catalyst according to this embodiment will be described. First, tungsten carbide powder and cobalt powder are prepared. The tungsten carbide powder and cobalt powder are weighed to a predetermined mass ratio. The weighed tungsten carbide powder and cobalt powder are then mechanically mixed using an attritor or the like. In this embodiment, the tungsten carbide powder and cobalt powder are introduced into an alcohol dispersion medium and mixed using an attritor. A cemented carbide alloy of tungsten carbide and cobalt was used as the medium. The mixing conditions were a rotation speed of 500 rpm to 1200 rpm and a mixing time of 1 hour to 48 hours. After mixing, it is preferable to volatilize the alcohol dispersion medium. Note that the BET specific surface area can be increased by reducing the particle size of the starting materials or by extending the mechanical mixing time.

[0028] As described above, the catalyst for generating hydrogen according to this embodiment can be produced by mechanically mixing tungsten carbide powder and cobalt powder.

[0029] The hydrogen generating catalyst of this embodiment configured as described above is made of a mixture of tungsten carbide and cobalt, and the surface of the tungsten carbide is partially modified with cobalt, which promotes electron transfer at the interface between the tungsten carbide and cobalt, thereby improving catalytic activity. Furthermore, the coexistence of cobalt with tungsten carbide improves the oxidation resistance of cobalt, which contributes to improving catalytic activity in the reaction solution. Therefore, by using the hydrogen generating catalyst of this embodiment, hydrogen can be generated efficiently and stably.

[0030] The hydrogen generation catalyst of this embodiment has an absolute value of 0.10 mA / mg or more of cathode current per 1 mg of catalyst when supported on a glassy carbon electrode and subjected to potential scanning at −1.2 V against a silver-silver chloride standard electrode in a 1 mol / L aqueous sodium hydroxide solution with nitrogen bubbling. Therefore, the catalyst can be used practically as a hydrogen generation catalyst for water electrolysis devices.

[0031] In the hydrogen generation catalyst of this embodiment, when the cobalt content is in the range of 1.0 mass % or more and 50.0 mass % or less, the catalytic activity can be reliably improved and the oxidation resistance can be sufficiently improved, thereby promoting hydrogen generation more efficiently and stably.

[0032] In the hydrogen generation catalyst of this embodiment, when tungsten carbide has a hexagonal crystal structure, chemical resistance is improved, the catalyst is more stable in the reaction solution, and catalytic activity can be reliably improved.

[0033] In the hydrogen generation catalyst of this embodiment, when tungsten carbide and cobalt are present on the outermost surface, an interface between tungsten carbide and cobalt is present on the outermost surface of the catalyst, which reliably promotes electron transfer and further reliably improves catalytic activity.

[0034] In the hydrogen generation catalyst of this embodiment, the BET specific surface area is 0.5 m ２ / g or more 20.0m ２When the surface area is within the range of 1 / g or less, the surface area is sufficiently large and the catalytic activity can be reliably improved.

[0035] According to the method for producing a catalyst for generating hydrogen of this embodiment, the catalyst for generating hydrogen of this embodiment is produced by mechanically mixing tungsten carbide powder and cobalt powder, so that the catalyst for generating hydrogen can be produced easily by a relatively simple procedure, and the production cost of the catalyst for generating hydrogen can be significantly reduced.

[0036] Although the embodiment of the present invention has been described above, the present invention is not limited to this and can be modified as appropriate within the scope of the technical idea of ​​the invention.

[0037] The results of experiments conducted to confirm the effectiveness of the present invention will be described below.

[0038] Hexagonal tungsten carbide powder (Japan New Metals Co., Ltd.: average particle size 6.0 μm) and cobalt powder (Umicore Japan Co., Ltd.: average particle size 0.5 μm) were prepared as raw materials. These raw materials were weighed out to the mass ratio shown in Table 1. The tungsten carbide powder and cobalt powder weighed out to the predetermined mass ratio were added to an ethanol dispersion medium and mechanically mixed using an attritor. WC+Co cemented carbide ball material (diameter 3 mm) was used as the media. The attritor rotation speed was set to 1000 rpm, and mechanical mixing was performed for the mixing time shown in Table 1. After mixing, the ethanol dispersion medium was evaporated in a vacuum dryer under conditions of 80°C x 6 hours, and hydrogen generation catalysts of Invention Examples 1 to 9 were produced.

[0039] In Comparative Example 1, a catalyst was used that consisted only of hexagonal tungsten carbide powder (Japan New Metals Co., Ltd.), and in Comparative Example 2, a catalyst was used that consisted only of cobalt powder (Umicore Japan Co., Ltd.).

[0040] The thus obtained invention examples 1 to 9 and comparative examples 1 and 2 were evaluated for each item according to the following procedures.

[0041] (Evaluation of Water Electrolysis Activity) 30 mg of the prepared catalyst was weighed and placed in a sample bottle. 1 mL of ion-exchanged water, 0.85 mL of ethanol, and 0.15 mL of 5 vol% Nafion dispersion were added, and ultrasonic irradiation was performed for 30 minutes. 10 μL of the resulting suspension (at this time, the catalyst amount in the suspension was 0.15 mg) was removed and dropped onto a 5 mmφ glassy carbon electrode and allowed to air dry. Cyclic voltammetry was performed using a Solartron potentiostat (SI-1287) in a 1 M aqueous sodium hydroxide solution under nitrogen bubbling (100 mL / min) with the prepared catalyst-supported electrode as the working electrode, a silver-silver chloride electrode as the standard electrode, and a platinum black electrode as the counter electrode. The sweep rate was 10 mV / s, the potential sweep range was −1.4 V to 0.4 V, and the cathode current was calculated by normalizing the current value at a potential of −1.2 V by the catalyst amount (0.15 mg) (unit: mA / mg). The evaluation results are shown in Table 1.

[0042] (XRD analysis) Measurement was performed using an Empyrean X-ray diffractometer manufactured by PANalytical. A Cu tube (1.54 angstroms) was used as the X-ray source. Measurement was performed in the range of 2θ = 10 to 90° to confirm the crystalline phase of tungsten carbide in the catalyst material. The evaluation results are shown in Table 1. Figure 1 shows the measurement results for Inventive Example 1. The appearance of peaks corresponding to the hexagonal phase of tungsten carbide (WC) was confirmed. (Peaks derived from (001) around 2θ = 31.5°, (100) around 35.6°, (101) around 48.3°, and (110) around 64.0°, respectively.)

[0043] (AES Analysis) The elemental state on the outermost surface of the catalyst was confirmed using a scanning Auger electron spectrometer PHI-700xi manufactured by ULVAC-PHI. Since the outermost surface was analyzed, sputtering with Ar was not performed. Measurements were performed at magnifications of 5,000x and 50,000x. At 5,000x, elemental mapping of W and Co was performed, and at 50,000x, point analysis was performed at four representative points to perform semi-quantitative analysis of the elements present. The evaluation results are shown in Table 1. FIG. 2 shows an observation photograph and elemental mapping of Inventive Example 1 at 5,000x. FIG. 3 shows an observation photograph and semi-quantitative analysis results of Inventive Example 1 at 50,000x. In the elemental mapping at 5,000x, W and Co signals were detected evenly across the entire particle surface. Furthermore, in semi-quantitative elemental analysis at 50,000x magnification, significant concentrations of all elements W, C, and Co were detected at every point, confirming that both WC and Co were present on the outermost surface of the catalyst.

[0044] (BET Specific Surface Area) The specific surface area of ​​the catalyst was measured using an AUTOSORB-iQ2 manufactured by QUANTACHROME Inc. After degassing at 200°C for 60 minutes, the measurement was carried out using nitrogen gas. The evaluation results are shown in Table 1.

[0045]

[0046] Comparative Example 1 was composed only of tungsten carbide, and had a low catalytic activity of 0.078 mA / mg, making it unsuitable for practical use as a catalyst for generating hydrogen in water electrolysis. Comparative Example 2 was composed only of cobalt, and had a low catalytic activity of 0.040 mA / mg, making it unsuitable for practical use as a catalyst for generating hydrogen in water electrolysis.

[0047] In contrast, Inventive Examples 1 to 9 contained tungsten carbide and cobalt, and had a structure in which the surface of the tungsten carbide was partially modified with cobalt. The absolute value of the cathode current per mg of catalyst was 0.10 mA / mg or more, which indicated sufficiently high catalytic activity and made them practical for use as catalysts for generating hydrogen in water electrolysis.

[0048] From the above, it was confirmed that the present invention can provide a hydrogen generation catalyst that can be manufactured at low cost and that can generate hydrogen efficiently, and a method for manufacturing the hydrogen generation catalyst.

[0049] According to the present invention, it is possible to provide a hydrogen generation catalyst that can be produced at low cost and that can generate hydrogen efficiently, and a method for producing the hydrogen generation catalyst.

Claims

1. A catalyst for generating hydrogen comprising a mixture of tungsten carbide and cobalt, characterized in that the catalyst for generating hydrogen is supported on a glassy carbon electrode and, when placed in a 1 mol / L aqueous sodium hydroxide solution with nitrogen bubbling, subjected to potential scanning at -1.2 V against a silver-silver chloride standard electrode, the absolute value of the cathode current per 1 mg of catalyst is 0.10 mA / mg or more.

2. The hydrogen generation catalyst according to claim 1, characterized in that the cobalt content is within the range of 1.0 mass % or more and 50.0 mass % or less.

3. The hydrogen generation catalyst according to claim 1, wherein the tungsten carbide has a hexagonal crystal structure.

4. The hydrogen generation catalyst according to claim 1, wherein the tungsten carbide and the cobalt are present on the outermost surface.

5. BET specific surface area is 0.5m ２ / g or more 20.0m ２ The hydrogen generation catalyst according to claim 1, characterized in that the molecular weight of the catalyst is in the range of 0.1 to 1.0 g / g or less.

6. A method for producing a catalyst for generating hydrogen according to any one of claims 1 to 5, comprising mechanically mixing tungsten carbide powder and cobalt powder.

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