Catalyst, method for producing catalyst, and fuel cell

Abstract

To provide a catalyst that exhibits superior properties.SOLUTION: A catalyst 1 includes rods 2 comprising an alloy of platinum and one or more of Group 8, Group 9, or Group 10 elements, and bundle-shaped carbon nanotubes 3 carrying the rods 2, wherein at least some of the rods 2 exist in grooves between the carbon nanotubes 3.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a catalyst, a method for producing the catalyst, and a fuel cell. [Background technology]

[0002] Catalysts are used to promote chemical reactions in fuel cells and other devices. To improve energy efficiency, there is a need to develop technologies to improve the properties of catalysts. Nanoparticles and nanorods, which are sized at the nanometer level, are attracting attention as such technologies. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] "Gold Nanorods: Properties and Applications", Christian Schoen, [online], Internet <URL:https: / / www.sigmaaldrich.com / JP / ja / technical-documents / technical-article / materials-science-and-engineering / biosensors-and-imaging / gold-nanostructures Summary of the Invention [Problem to be solved by the invention]

[0004] The present inventors have conducted extensive research to further improve the properties of catalysts and have succeeded in developing a novel catalyst containing nanorods.

[0005] The present disclosure has been made in view of such problems, and its object is to provide a catalyst having excellent properties. [Means for solving the problem]

[0006] In order to solve the above problems, a catalyst according to one embodiment of the present disclosure includes rods containing an alloy of platinum and one or more of a Group 8 element, a Group 9 element, and a Group 10 element, and bundles of carbon nanotubes supporting the rods, with at least some of the rods existing in grooves between the carbon nanotubes.

[0007] Another aspect of the present disclosure is a method for producing a catalyst, the method comprising heating a solution containing a source of metallic material and a carbon material treated with an acid.

[0008] Yet another aspect of the present disclosure is a fuel cell, which includes the above-described catalyst and an electrode. [Effects of the Invention]

[0009] According to the present disclosure, a catalyst having excellent properties can be provided. [Brief explanation of the drawings]

[0010] [Figure 1] 1 shows an electron microscope photograph of a catalyst of the present disclosure. [Figure 2] FIG. 1 is a diagram schematically illustrating the structure of a catalyst according to the present disclosure. [Figure 3] FIG. 2 is a view showing an electron microscope photograph of a catalyst. [Figure 4] FIG. 1 is a diagram showing the analysis results of a catalyst obtained by an energy dispersive X-ray analyzer. [Figure 5] FIG. 1 is a diagram showing the measurement results of catalytic properties. [Figure 6] FIG. 1 is a diagram showing the measurement results of catalytic properties. [Figure 7] FIG. 2 is a view showing an electron microscope photograph of a catalyst. [Figure 8] FIG. 2 is a view showing an electron microscope photograph of a catalyst. [Figure 9] FIG. 2 is a view showing an electron microscope photograph of a catalyst. DETAILED DESCRIPTION OF THE INVENTION

[0011] 1 shows an electron microscope photograph of a catalyst of the present disclosure. Catalyst 1 includes bundles of carbon nanotubes 3 and nanorods 2 supported in the grooves between the bundles of carbon nanotubes 3.

[0012] The nanorods 2 include a metallic material having catalytic properties. The metallic material may include platinum, palladium, or an alloy of platinum or palladium with one or more of Group 8 elements, Group 9 elements, and Group 10 elements. The metallic material may also include an alloy of platinum with palladium, iron, cobalt, nickel, etc.

[0013] The diameter (width) of the nanorods 2 may be 0.2 nm or more. The diameter of the nanorods 2 may be 0.3 nm or more, 0.4 nm or more, 0.5 nm or more, 0.6 nm or more, 0.7 nm or more, or 0.8 nm or more. The diameter of the nanorods 2 may be 50 nm or less. The diameter of the nanorods 2 may be 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, 15 nm or less, 10 nm or less, 9 nm or less, 8 nm or less, 7 nm or less, 6 nm or less, 5 nm or less, 4 nm or less, 3 nm or less, 2 nm or less, 1 nm or less, 0.9 nm or less, 0.8 nm or less, 0.7 nm or less, 0.6 nm or less, 0.5 nm or less, 0.4 nm or less, or 0.3 nm or less. The diameter of the nanorods 2 may be measured using an electron microscope photograph.

[0014] The length of the nanorods 2 may be 1 nm or more. The length of the nanorods 2 may be 2 nm or more, 3 nm or more, 4 nm or more, 5 nm or more, 6 nm or more, 7 nm or more, 8 nm or more, 9 nm or more, 10 nm or more, 20 nm or more, 30 nm or more, 40 nm or more, 50 nm or more, 60 nm or more, 70 nm or more, 80 nm or more, 90 nm or more, 100 nm or more, 110 nm or more, or 120 nm or more. The length of the nanorods 2 may be 50 nm or less. The length of the nanorods 2 may be 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, 15 nm or less, 10 nm or less, 9 nm or less, 8 nm or less, 7 nm or less, 6 nm or less, 5 nm or less, 4 nm or less, 3 nm or less, 2 nm or less, or 1 nm or less. The length of the nanorods 2 may be measured using an electron microscope photograph.

[0015] The aspect ratio (ratio of length to width) of nanorods 2 may be 2 or greater. The aspect ratio of nanorods 2 may be 3 or greater, 4 or greater, 5 or greater, 6 or greater, 7 or greater, 8 or greater, 9 or greater, 10 or greater, 11 or greater, 12 or greater, 13 or greater, 14 or greater, 15 or greater, 16 or greater, 17 or greater, 18 or greater, 19 or greater, or 20 or greater.

[0016] Nanorods with diameters of approximately tens to hundreds of nanometers exhibit continuous size effects, such as a shift in absorption peak with changes in aspect ratio, and catalytic efficiency improves as the size decreases due to an increase in surface area. However, sub-nanorods with diameters of a few nanometers or less have diameters of the order of a few atoms, so the size effect becomes discontinuous and the development of unique catalytic properties can be expected. As will be explained in the examples below, the catalysts of the present disclosure have excellent catalytic properties.

[0017] The carbon nanotubes 3 may be single-walled carbon nanotubes, multi-walled carbon nanotubes, or a mixture thereof. This can improve the durability, electrical conductivity, and thermal conductivity of the catalyst 1. Furthermore, when the catalyst 1 of the present disclosure is used in a polymer electrolyte fuel cell or the like, the proportion of voids in the catalyst layer can be increased, thereby improving gas diffusibility and suppressing concentration polarization at the output point. The carbon nanotubes 3 may be single-walled carbon nanotubes synthesized by the enhanced direct injection pyrolytic synthesis method (e-DIPS). Single-walled carbon nanotubes synthesized by the e-DIPS method have significantly higher purity and crystallinity, and can therefore further improve the oxidation resistance of the catalyst 1 in high-temperature, high-potential environments. For example, the G / D ratio of MEIJO eDIPS single-walled carbon nanotubes manufactured by Meijo Nano Carbon Co., Ltd., which is an index for evaluating crystallinity, is 224, which is significantly higher than the 65 of the single-walled carbon nanotubes manufactured by KH Chemicals, the 39 of the single-walled carbon nanotubes manufactured by OCSiAl TUBALL, the 5 of the single-walled carbon nanotubes manufactured by Zeon Corporation, and the 1 of general multi-walled carbon nanotubes. The G / D ratio can be calculated by the Raman spectrum of carbon nanotubes at 1590 cm -1 The intensity of the G-band originating from the graphite structure that appears near 1350 cm -1 The G / D ratio of the carbon nanotube 3 is the ratio of the intensity of the D-band derived from defects appearing near the carbon nanotube 3. The G / D ratio of the carbon nanotube 3 may be 70 or more, 80 or more, 90 or more, 100 or more, 110 or more, 120 or more, 130 or more, 140 or more, 150 or more, 160 or more, 170 or more, 180 or more, 190 or more, 200 or more, 210 or more, or 220 or more.

[0018] The active surface area (ECSA) of catalyst 1 is 60 m 2 / g or more, 65m 2 / g or more, 70m 2 / g or more, 75m 2 / g or more, 80m 2 / g or more, 85m 2 / g or more, 90m 2 / g or more, 95m 2 / g or more, 100m 2 / g or more, 105m 2 / g or more, 110m 2 / g or more, 115m 2 / g or more, 120m 2 / g or more, 125m 2 / g or more, 130m 2 / g or more.

[0019] The mass activity (MA) of catalyst 1 may be 70 A / g or greater, 80 A / g or greater, 90 A / g or greater, 100 A / g or greater, 110 A / g or greater, 120 A / g or greater, 130 A / g or greater, 140 A / g or greater, 150 A / g or greater, 160 A / g or greater, 170 A / g or greater, 180 A / g or greater, 190 A / g or greater, 200 A / g or greater, 21 A / g or greater, 220 A / g or greater, 230 A / g or greater, 240 A / g or greater, 250 A / g or greater, 260 A / g or greater, or 270 A / g or greater.

[0020] The surface activity (SA) of catalyst 1 was 110 μA / cm 2 More than 120μA / cm 2 More than 130μA / cm 2 More than 140μA / cm 2 More than 150μA / cm 2 More than 160μA / cm 2 More than 170μA / cm 2 More than 180μA / cm 2 More than 190μA / cm 2 More than 200μA / cm 2 More than 250μA / cm 2 More than 300μA / cm 2 More than 350μA / cm 2 It may be more than that.

[0021] The amount of platinum used per unit power of catalyst 1 may be 0.4 g / kW or less, 0.39 g / kW or less, 0.38 g / kW or less, 0.37 g / kW or less, 0.36 g / kW or less, 0.35 g / kW or less, 0.34 g / kW or less, 0.33 g / kW or less, 0.32 g / kW or less, 0.31 g / kW or less, 0.3 g / kW or less, 0.29 g / kW or less, or 0.28 g / kW or less.

[0022] The fuel cell of the present disclosure includes the catalyst 1 and an electrode. The fuel cell may be a polymer electrolyte fuel cell (PEFC). The fuel cell may include an ion exchange membrane such as Nafion (registered trademark).

[0023] The method for producing catalyst 1 of the present disclosure includes a step of heating a solution containing a raw material metal material and a carbon material treated with an acid.

[0024] The raw material of the metallic material may include a platinum or palladium compound. The raw material of the metallic material may include a platinum or palladium compound and a compound of one or more of a Group 8 element, a Group 9 element, and a Group 10 element. The raw material of the metallic material may include a platinum compound and a compound of palladium, iron, cobalt, nickel, or the like.

[0025] The carbon material may include carbon nanotubes, which may be single-walled carbon nanotubes, multi-walled carbon nanotubes, or a mixture thereof.

[0026] The acid may include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, etc. The acid may include organic acids such as carboxylic acids, sulfonic acids, etc.

[0027] The method for producing catalyst 1 of the present disclosure may further include a step of crushing the carbon material. The step of crushing the carbon material may include a step of irradiating a solution containing the carbon material with ultrasonic waves. The carbon material may be crushed by any known technique.

[0028] 2 shows a schematic diagram of the structure of the catalyst of the present disclosure. Carbon nanotubes 3 are tubular carbon materials with a diameter of approximately 0.4 to 50 nm. Several to several tens of layers of metal material are deposited in the gaps between adjacent tubular carbon nanotubes 3 in a rod-like shape, forming nanorods 2 with a diameter of approximately 0.2 to 50 nm.

[0029] In the manufacturing method of the catalyst 1 described above, it is thought that by treating the carbon material with acid in advance, protons are adsorbed onto the surface of the grooves between the bundled carbon nanotubes 3, and then metal ions are adsorbed in place of the protons at the positions where the protons had been adsorbed, thereby forming nanorods 2 of the metal material using the grooves of the carbon nanotubes 3 as a template.

[0030] Therefore, the length, width, aspect ratio, etc. of nanorods 2 can be controlled by the type, length, width, aspect ratio, and amount of carbon nanotubes, the degree of acid treatment of the carbon nanotubes, the type, amount, and concentration of acid treatment agent, the type, extent, and time of disintegration of the carbon nanotubes in the solution, the degree of dispersion of the carbon nanotubes in the solution, etc. In addition, the length, width, aspect ratio, etc. of nanorods 2 can be controlled by the type of metal material, the ratio of elements contained in the metal material, the type, amount, and concentration of the raw material of the metal material, and its solubility in the solution, etc. By adjusting the length, width, and aspect ratio of nanorods 2, the properties of catalyst 1 can be suitably adjusted to suit the application of catalyst 1.

[0031] [Example] [Catalyst Preparation] Catalysts were prepared in which nanorods containing platinum alone (Example 1), a platinum-palladium alloy with an atomic ratio of platinum to palladium of 1:1 (Example 2), and a platinum-palladium alloy with an atomic ratio of platinum to palladium of 0.7:1.3 (Example 3) were supported on single-walled carbon nanotubes.

[0032] An 8 wt% HPtCl6 aqueous solution was prepared by dissolving HPtCl6·6H2O in water. A 2.8 wt% PdCl2 aqueous solution was prepared by dissolving PdCl2 (28 mg) and HCl (300 mg) in water. 8 wt% HPtCl6 (100 μL) and 2.8 wt% PdCl2 (100 μL) were dissolved in DMF (12 mL), and ethylene glycol (8 mL) was added to the solution. The resulting solution was stirred at room temperature for over 8 hours until it became clear. e-DIPS single-walled carbon nanotubes (12 mg), which had previously been treated with sonication in hydrochloric acid, were added to the stirred solution, and ultrasonic waves were applied for 15 minutes using a horn-type ultrasonicator to disperse the single-walled carbon nanotubes. The solution containing the single-walled carbon nanotubes was placed in a Teflon-lined autoclave and reacted at 170°C for 8 hours. After the reaction, the solution was collected, filtered through a membrane filter, and washed with acetone, methanol, and purified water in that order. The catalyst on the membrane filter was dried overnight at 80°C.

[0033] [Electron microscope photograph] 3(a), (b), and (c) show electron microscope photographs of the catalysts of Examples 1 to 3, respectively. The catalysts of Examples 1 and 3 contain many nanoparticles, while the catalyst of Example 2 contains many nanorods. It was shown that many nanorods can be formed when the atomic ratio of platinum to palladium is close to 1:1. This suggests that the atomic ratio of platinum to palladium may be 0.4:1.6 to 1.6:0.4.

[0034] [Nanorod size] The nanorods in the catalyst of Example 2 had an average length of 19.36 nm, an average width of 1.53 nm, and an average aspect ratio of 13.29. The nanorods in the catalyst of Example 3 had an average length of 7.59 nm, an average width of 1.70 nm, and an average aspect ratio of 4.55. This indicates that the aspect ratio of the nanorods is higher when the atomic ratio of platinum to palladium is closer to 1:1. This demonstrates that the length, width, and aspect ratio of the nanorods can be controlled by the ratio of elements contained in the metal material.

[0035] [Elemental analysis] Figures 4(a), (b), and (c) show the results of analysis of the catalyst of Example 2 using an energy dispersive X-ray analyzer (EDS). Figure 4(a) shows an electron microscope image of nanorods contained in the catalyst of Example 2. Figures 4(b) and (c) show elemental maps of platinum and palladium, respectively, in the catalyst of Example 2. It was shown that platinum and palladium were mixed in the nanorods. The platinum to palladium content ratio was Pt:Pd = 2.3 to 3.7:1.

[0036] [Catalytic properties] 5(a) and (b) show the results of cyclic voltammetry measurements using a commercially available Pt / C catalyst and the catalyst of Example 2, respectively. The amount of platinum supported on the Pt / C catalyst was 20.4 μg / cm 2 The amount of platinum supported in the catalyst of Example 2 was 6.8 μg / cm 2 Figure 5(c) shows the results of convective voltammetry measurements using a commercial Pt / C catalyst and the catalyst of Example 2. Figure 5(d) shows the active surface area (ECSA), mass activity (MA), and surface activity (SA) calculated from the measurement results of the commercial Pt / C catalyst and the catalyst of Example 2. The catalyst of Example 2 was shown to be superior in these catalytic properties.

[0037] FIG. 6(a) shows the current density-voltage curves of a commercially available Pt / C catalyst, a catalyst containing platinum nanoparticles supported on single-walled carbon nanotubes, and the catalyst of Example 2. FIG. 6(b) shows the results of cyclic voltammetry measurements of a commercially available Pt / C catalyst, a catalyst containing platinum nanoparticles supported on single-walled carbon nanotubes, and the catalyst of Example 2. FIG. 6(c) shows the active surface area (ECSA) and platinum usage per unit power calculated from the measurement results of a commercially available Pt / C catalyst, a catalyst containing platinum nanoparticles supported on single-walled carbon nanotubes, and a catalyst containing the sample of Example 2. The catalyst of Example 2, which has the lowest platinum loading, was shown to be superior in these catalytic properties.

[0038] [Processing time dependency] Using the above-described catalyst preparation method, we prepared two catalysts by reacting a solution containing single-walled carbon nanotubes at 170°C for 4 hours and 8 hours, respectively. The average nanoparticle size and the average nanorod diameter and length for each catalyst were calculated. Figure 7(a) shows an electron microscope image of the catalyst prepared after 4 hours of reaction, Figure 7(b) shows an electron microscope image of the catalyst prepared after 8 hours of reaction, and Figure 7(c) shows the nanoparticle size, nanorod length, diameter, aspect ratio, and maximum length for each catalyst. The catalyst prepared after 8 hours of reaction had larger nanoparticle size, nanorod length, diameter, maximum length, and aspect ratio than the catalyst prepared after 4 hours of reaction.

[0039] [Acid treatment dependency] Using the catalyst preparation method described above, we prepared catalysts using single-walled carbon nanotubes pretreated in hydrochloric acid and catalysts using single-walled carbon nanotubes without acid pretreatment. The pretreatment consisted of stirring the single-walled carbon nanotubes for 23 hours, followed by stirring in hydrochloric acid for 4 days and 23 hours. Figure 8(a) shows electron micrographs of the catalyst prepared using single-walled carbon nanotubes with acid pretreatment and the catalyst prepared using single-walled carbon nanotubes without acid pretreatment. The catalyst prepared using single-walled carbon nanotubes with acid pretreatment had longer nanorods than the catalyst prepared using single-walled carbon nanotubes without acid pretreatment. As shown in Figures 9(a) and 9(b), nanorods over 100 nm in length were observed.

[0040] As described above, the technology of the present disclosure can provide a catalyst that has excellent catalytic properties such as active surface area, mass activity, and surface activity. Furthermore, the amount of expensive metals such as platinum used can be reduced, thereby reducing the production cost of the catalyst.

[0041] The present disclosure has been described above based on examples. These examples are merely illustrative, and it will be understood by those skilled in the art that various modifications are possible in the combination of the components and processing steps, and that such modifications are also within the scope of the present disclosure. [Explanation of symbols]

[0042] 1 Catalyst, 2 Nanorods, 3 Carbon nanotubes.

Claims

1. a rod containing an alloy of platinum and one or more of a Group 8 element, a Group 9 element, and a Group 10 element; a bundle of carbon nanotubes supporting the rod; Including, At least some of the rods are present in the grooves between the carbon nanotubes. catalyst.

2. The diameter of the rod is 0.2 nm or more and 0.8 nm or less. The catalyst of claim 1.

3. The rod comprises an alloy of platinum and palladium. The catalyst according to claim 1 or 2.

4. The carbon nanotubes include single-walled carbon nanotubes. The catalyst according to claim 1 or 2.

5. The method includes heating a solution containing a metal material raw material and an acid-treated carbon material. Catalyst manufacturing method.

6. The catalyst includes rods including the metal material supported on the carbon material. The method of claim 5.

7. The rods are located in the grooves between the carbon materials. The method of claim 6.

8. The diameter of the rod is 0.2 nm or more and 0.8 nm or less.

8. The method according to claim 6 or 7.

9. The metal material includes platinum or an alloy of platinum with one or more of a Group 8 element, a Group 9 element, and a Group 10 element.

8. The method according to any one of claims 5 to 7.

10. The metal material is an alloy of platinum and palladium.

10. The method of claim 9.

11. The carbon material includes carbon nanotubes. The method of claim 7.

12. The carbon material includes single-walled carbon nanotubes. The method of claim 11.

13. The diameter of the rod is controlled by at least one of the type, length, width, aspect ratio, and amount of the carbon nanotubes, the degree of acid treatment of the carbon nanotubes, the type, amount, and concentration of the acid used in the acid treatment, the details, degree, and time of crushing the carbon nanotubes in the solution, the degree of dispersion of the carbon nanotubes in the solution, the type of the metal material, the ratio of elements contained in the metal material, the type, amount, and concentration of the raw material of the metal material, and the solubility in the solution. The method of claim 11.

14. The catalyst according to claim 1 or 2; An electrode; A fuel cell comprising:

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