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

Abstract

To provide a catalyst for hydrogen generation that can be manufactured at low cost and enables efficient hydrogen generation, and a method for producing the catalyst for hydrogen generation.SOLUTION: A catalyst for hydrogen generation comprises a mixture of tungsten carbide and cobalt, characterized in that the absolute value of a 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.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a hydrogen generation catalyst used for promoting a hydrogen generation reaction and a method for manufacturing the hydrogen generation catalyst.

Background Art

[0002] As a means for generating hydrogen, for example, a polymer electrolyte water electrolysis device (PEM) can be mentioned. The above-described polymer electrolyte water electrolysis device (PEM) includes a water electrolysis cell including an anodic electrode and a cathodic electrode arranged opposite to each other and an ion permeable membrane arranged between these anodic electrode and cathodic electrode. Note that catalyst layers are respectively formed on both surfaces (contact surfaces with the anodic electrode and contact surfaces with the cathodic electrode) of the ion permeable membrane. In a water electrolysis device (water electrolysis cell) having such a configuration, oxygen (O 2 ) is generated on the anodic electrode side by decomposing water, and hydrogen (H 2 ) is generated on the cathodic electrode side.

[0003] Here, as the hydrogen generation catalyst used in the cathodic electrode (hydrogen generation electrode), platinum (Pt) is widely used. Platinum (Pt) is usually used in a state supported on a single nano-carbon. However, since platinum (Pt) is a noble metal and very expensive, there has been a problem that the operating cost of the water electrolysis device is significantly increased.

[0004] Therefore, as a hydrogen generation catalyst to replace platinum (Pt), for example, those disclosed in Patent Documents 1 and 2 have been proposed. In Patent Document 1, a tungsten carbide-based catalyst in which the XRD peak ratio of W 2 C 0.85 / W is specified has been proposed. Further, in Patent Document 2, tungsten-nickel carbide (W-Ni-C) formed on a carbon carrier has been proposed.

Prior Art Documents

Patent Document

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] By the way, in the above-mentioned catalyst for hydrogen generation, it is required that hydrogen generation can be promoted more efficiently and stably. In addition, in the above-mentioned catalyst for hydrogen generation, it is required that the production cost is low in order to generate hydrogen at low cost. However, in Patent Documents 1 and 2, there is a problem that after mixing the raw materials, it is necessary to perform heat treatment at a high temperature, resulting in a high production cost.

[0007] This invention has been made in view of the above circumstances, and an object thereof is to provide a catalyst for hydrogen generation that can be manufactured at low cost and can efficiently generate hydrogen, and a method for manufacturing the catalyst for hydrogen generation.

Means for Solving the Problems

[0008] In order to solve the above problems, the catalyst for hydrogen generation according to Embodiment 1 of the present invention is a catalyst for hydrogen generation comprising a mixture of tungsten carbide and cobalt, wherein the catalyst for hydrogen generation is supported on a glassy carbon electrode and in a 1 mol / L aqueous sodium hydroxide solution under nitrogen bubbling, when the potential is scanned to -1.2 V with respect to a silver-silver chloride standard electrode, the absolute value of the cathodic current per 1 mg of the catalyst is 0.10 mA / mg or more.

[0009] According to the hydrogen generation catalyst of Aspect 1 of the present invention, since it is composed of a mixture of tungsten carbide and cobalt, electron transfer is promoted at the interface between tungsten carbide and cobalt, improving the catalytic activity. In addition, coexisting with tungsten carbide improves the oxidation resistance of cobalt, contributing to the improvement of the catalytic activity in the reaction solution. And as described above, when the hydrogen generation catalyst is supported on a glassy carbon electrode and subjected to potential scanning to -1.2 V with respect to a silver-silver chloride standard electrode under nitrogen bubbling in a 1 mol / L aqueous sodium hydroxide solution, the absolute value of the cathodic current per 1 mg of the catalyst is 0.10 mA / mg or more, so that hydrogen generation can be promoted efficiently and stably.

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

[0011] The hydrogen generation catalyst of Aspect 3 of the present invention is characterized in that, in the hydrogen generation catalyst of Aspect 1 or Aspect 2, the tungsten carbide has a hexagonal crystal structure. According to the hydrogen generation catalyst of Aspect 3 of the present invention, since the tungsten carbide has a hexagonal crystal structure, the chemical resistance is improved, it becomes more stable in the reaction solution, and the catalytic activity can be surely improved.

[0012] The hydrogen generation catalyst of Aspect 4 of the present invention is characterized in that, in any one of the hydrogen generation catalysts of Aspect 1 to Aspect 3, the tungsten carbide and the cobalt are present on the outermost surface. According to the hydrogen generation catalyst of Aspect 4 of the present invention, since the tungsten carbide and the cobalt are present on the outermost surface, an interface between the tungsten carbide and the cobalt exists on the outermost surface, and the electron transfer is surely promoted, so that the catalytic activity can be further surely improved.

[0013] The hydrogen generation catalyst of Aspect 5 of the present invention is any one of the hydrogen generation catalysts of Aspects 1 to 4, wherein the BET specific surface area is 0.5 m 2 / g or more and 20.0 m 2 / g or less. According to the hydrogen generation catalyst of Aspect 5 of the present invention, since the BET specific surface area is in the range of 0.5 m 2 / g or more and 20.0 m 2 / g or less, the surface area is sufficiently large and the catalytic activity can be surely improved.

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

Advantages of the Invention

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

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0017] Hereinafter, a hydrogen generation catalyst which is an embodiment of the present invention, and a method for manufacturing the hydrogen generation catalyst will be described. The hydrogen generation catalyst which is an embodiment of the present invention is used as a hydrogen generation catalyst disposed at the cathode electrode (hydrogen generation electrode) of a water electrolysis cell constituting a polymer electrolyte type water electrolysis device (PEM).

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

[0019] Here, in the hydrogen generation catalyst of the present embodiment, the cobalt content is preferably in the range of 1.0 mass% or more and 50.0 mass% or less. Further, in the hydrogen generation catalyst of the present embodiment, tungsten carbide preferably has a hexagonal crystal structure. Furthermore, in the hydrogen generation catalyst of the present embodiment, tungsten carbide and cobalt are preferably present on the outermost surface. Also, in the hydrogen generation catalyst of the present embodiment, the BET specific surface area is preferably in the range of 0.5 m 2 / g or more and 20.0 m 2 / g or less.

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

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

[0022] (Cathode current per 1 mg of the catalyst) In the hydrogen generation catalyst of the present embodiment, when the potential is scanned to -1.2 V with respect to the silver-silver chloride standard electrode while supported on a glassy carbon electrode and under nitrogen bubbling in a 1 mol / L aqueous sodium hydroxide solution, the absolute value of the cathode current per 1 mg of the catalyst is 0.10 mA / mg or more, indicating that it has sufficient catalytic activity to be practically used as a hydrogen generation catalyst. Note that the absolute value of the cathode current per 1 mg of the above-mentioned catalyst is preferably 0.30 mA / mg or more, and more preferably 0.50 mA / mg or more.

[0023] (Cobalt content) In the hydrogen generation catalyst of the present embodiment, when the cobalt content is 1.0 mass% or more, electron transfer at the interface between tungsten carbide and cobalt is sufficiently promoted, and the catalytic activity is surely improved. On the other hand, when the cobalt content is 50.0 mass% or less, the entire hydrogen generation catalyst has excellent oxidation resistance, and it can be used more stably. Incidentally, the cobalt content is more preferably 5.0% by mass or more, and even more preferably 10.0% by mass or more. Further, 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 hydrogen generation catalyst of the present embodiment, when tungsten carbide has a hexagonal crystal structure, the chemical resistance of the entire hydrogen generation catalyst is further improved, it becomes more stable even in the reaction solution, and the catalyst activity is surely improved.

[0025] (Structure of the outermost surface of the catalyst) In the hydrogen generation catalyst of the present embodiment, when tungsten carbide and cobalt are present on the outermost surface, an interface between tungsten carbide and cobalt exists on the outermost surface of the catalyst, and electron transfer is promoted at this interface between tungsten carbide and cobalt, and the catalyst activity is surely improved.

[0026] (BET specific surface area) In the hydrogen generation catalyst of the present embodiment, when the BET specific surface area is 0.5 m 2 / g or more, the surface area is sufficiently large, and the catalyst activity is surely improved. On the other hand, it is substantially difficult to produce a hydrogen generation catalyst having a BET specific surface area exceeding 20.0 m 2 / g. Incidentally, the BET specific surface area is more preferably 1.0 m 2 / g or more, and even more preferably 2.0 m 2 / g or more. Further, the BET specific surface area is more preferably 19.0 m 2 / g or less, and even more preferably 18.0 m 2 / g or less.

[0027] Next, a method for manufacturing the hydrogen generation catalyst of the present embodiment will be described. First, prepare tungsten carbide powder and cobalt powder. Weigh the tungsten carbide powder and cobalt powder so that they have a predetermined mass ratio. Then, mechanically mix the weighed tungsten carbide powder and cobalt powder using an attritor or the like. Here, in this embodiment, the tungsten carbide powder and cobalt powder are put into an alcohol dispersion medium and mixed by an attritor. At this time, a cemented carbide of tungsten carbide and cobalt is used as the media. The mixing conditions were a rotation speed of 500 rpm or more and 1200 rpm or less, and a mixing time of 1 hour or more and 48 hours or less. After mixing, it is preferable to volatilize the alcohol dispersion medium. Note that by reducing the particle size of the starting materials or increasing the mechanical mixing time, it is possible to increase the BET specific surface area.

[0028] As described above, by mechanically mixing tungsten carbide powder and cobalt powder, it becomes possible to produce the catalyst for hydrogen generation according to this embodiment.

[0029] According to the catalyst for hydrogen generation of this embodiment configured as described above, it is composed of a mixture of tungsten carbide and cobalt, and since cobalt is partially modified on the surface of tungsten carbide, electron transfer is promoted at the interface between tungsten carbide and cobalt, and the catalytic activity is improved. In addition, by coexisting with tungsten carbide, the oxidation resistance of cobalt is improved, which contributes to the improvement of the catalytic activity in the reaction solution. Therefore, by using the catalyst for hydrogen generation of this embodiment, hydrogen can be generated efficiently and stably.

[0030] And in the catalyst for hydrogen generation of this embodiment, when supported on a glassy carbon electrode and subjected to potential scanning to -1.2 V with respect to a silver-silver chloride standard electrode under nitrogen bubbling in a 1 mol / L aqueous sodium hydroxide solution, the absolute value of the cathodic current per 1 mg of the catalyst is 0.10 mA / mg or more, so it is practical as a catalyst for hydrogen generation in a water electrolysis device.

[0031] In the hydrogen generation catalyst according to the present 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 surely improved, and the oxidation resistance can be sufficiently improved. Therefore, hydrogen generation can be promoted more efficiently and stably.

[0032] In the hydrogen generation catalyst according to the present embodiment, when tungsten carbide has a hexagonal crystal structure, the chemical resistance is improved, it becomes more stable in the reaction solution, and the catalytic activity can be surely improved.

[0033] In the hydrogen generation catalyst according to the present embodiment, when tungsten carbide and cobalt are present on the outermost surface, an interface between tungsten carbide and cobalt exists on the outermost surface of the catalyst, electron transfer is surely promoted, and the catalytic activity can be more surely improved.

[0034] In the hydrogen generation catalyst according to the present embodiment, when the BET specific surface area is in the range of 0.5 m 2 / g or more and 20.0 m 2 / g or less, the surface area is sufficiently large and the catalytic activity can be surely improved.

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

[0036] As described above, the embodiments of the present invention have been described, but the present invention is not limited thereto, and can be appropriately changed without departing from the technical idea of the invention.

Examples

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

[0038] As raw materials, hexagonal tungsten carbide powder (Shin-Etsu Metal Co., Ltd.: average particle size 6.0 μm) and cobalt powder (UMICORE Japan Co., Ltd.: average particle size 0.5 μm) were prepared. These raw materials were weighed so as to have the mass ratios shown in Table 1. The weighed tungsten carbide powder and cobalt powder at a predetermined mass ratio were put into an ethanol dispersion medium and mechanically mixed using an attritor. At this time, WC+Co cemented carbide ball materials (diameter 3 mm) were used as media. The rotation speed of the attritor 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 using a vacuum dryer under the conditions of 80 °C × 6 hours to produce the hydrogen generation catalysts of Examples 1 to 9 of the present invention.

[0039] Note that Comparative Example 1 was a catalyst composed only of hexagonal tungsten carbide powder (Shin-Etsu Metal Co., Ltd.). Comparative Example 2 was a catalyst composed only of cobalt powder (UMICORE Japan Co., Ltd.).

[0040] In Examples 1 to 9 of the present invention and Comparative Examples 1 and 2 obtained as described above, each item was evaluated by the following procedure.

[0041] (Hydroelectrolysis activity evaluation) 30 mg of the prepared catalyst was weighed and put into 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 was taken out from the obtained suspension (at this time, the amount of catalyst in the suspension was 0.15 mg), dropped onto a 5 mmφ glassy carbon electrode, and naturally dried. Using the prepared catalyst-supported electrode as the working electrode, a silver-silver chloride electrode as the reference electrode, and a platinum black electrode as the counter electrode, cyclic voltammetry was performed in a 1 M aqueous sodium hydroxide solution under nitrogen bubbling (100 mL / min) using a potentiostat (SI-1287) manufactured by Solartron. The sweep rate was 10 mV / s, the potential sweep range was -1.4 V to 0.4 V, and the cathodic current was calculated by normalizing the current value at a potential of -1.2 V with the amount of catalyst (0.15 mg) (unit: mA / mg). The evaluation results are shown in Table 1.

[0042] (XRD analysis) Measurement was carried out using a PANalytical X-ray diffractometer Empyrean. A Cu tube target (1.54 Å) was used as the X-ray source. Measurement was performed in the range of 2θ = 10 to 90°, and the crystal phase of tungsten carbide in the catalyst material was confirmed. The evaluation results are shown in Table 1. Fig. 1 shows the measurement results of Example 1 of the present invention. 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, Inc. For the outermost surface analysis, analysis was performed without sputtering with Ar. Measurements were carried out at magnification ratios of 5000 times and 50000 times. At 5000 times, elemental mapping of W and Co was performed, and at 50000 times, point analysis was carried out at four representative points, and semi-quantitative analysis of the existing elements was performed. The evaluation results are shown in Table 1. Fig. 2 shows the observation photograph and elemental mapping at 5000 times of Example 1 of the present invention. Fig. 3 shows the observation photograph and semi-quantitative analysis results at 50000 times of Example 1 of the present invention. In the elemental mapping at 5000 times, W and Co signals were detected uniformly from the surface of all particles. In addition, in the semi-quantitative elemental analysis at 50000 times, significant concentrations of all elements of W, C, and Co were detected from any point, and from this, it was confirmed that both WC and Co are 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. After treatment at 200 °C for 60 minutes for degassing, measurement was carried out using nitrogen gas. The evaluation results are shown in Table 1.

[0045]

Table 1

[0046] In Comparative Example 1, it was composed only of tungsten carbide, the absolute value of the cathode current per 1 mg of the catalyst was 0.078 mA / mg, the catalytic activity was low, and it was not practical as a catalyst for hydrogen generation in water electrolysis. In Comparative Example 2, it was composed only of cobalt, the absolute value of the cathode current per 1 mg of the catalyst was 0.040 mA / mg, the catalytic activity was low, and it was not practical as a catalyst for hydrogen generation in water electrolysis.

[0047] On the other hand, in Examples 1 to 9 of the present invention, it contained tungsten carbide and cobalt, and had a structure in which cobalt was partially modified on the surface of tungsten carbide. The absolute value of the cathode current per 1 mg of the catalyst was 0.10 mA / mg or more, the catalytic activity was sufficiently high, and it was practical as a catalyst for hydrogen generation in water electrolysis.

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

Claims

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

2. The hydrogen generation catalyst according to claim 1, wherein the cobalt content is in the range of 1.0% by mass or more and 50.0% by 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. The BET specific surface area is 0.5 m ２ / g or more and 20.0 m ２ / g or less, and the hydrogen generation catalyst according to claim 1, characterized in that it is within this range.

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

Images