Method for producing metal nanowire catalyst
By carrying metal nanowires on the carbon support and cleaning with hydride reducing agent solution, the problem of impurities covering the surface of the metal nanowire catalyst is solved, the catalytic activity is maintained and the coagulation is avoided, and efficient catalytic performance is achieved.
Patent Information
- Application Number
- CN202510155715.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2024-02-13
- Filing Date
- 2025-02-12
- Publication Date
- 2025-08-15
AI Technical Summary
In the prior art, when the metal nanowire catalyst is not cleaned sufficiently, the surface will be covered with impurities, resulting in a decrease in catalytic activity, and high-temperature treatment will cause the carbon support and metal nanowire to condense, reducing surface area and catalytic activity.
By carrying metal nanowires on the carbon support, and in the cleaning process, the metal nanowires are carried on the carbon support, and in the cleaning process, a solution containing a hydride reducing agent is used to contact the support, and then centrifuge and multiple cleanings are performed to remove impurities, including the use of cleaning solutions such as sodium borohydride, pure water and organic solvents, to ensure that the shape of the metal nanowires remains unchanged.
It effectively removes impurities on the surface of metal nanowires, maintains catalytic activity, avoids aggregation caused by high temperature treatment, and improves the catalytic activity and stability of the catalyst.
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Figure CN120479416A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a method for preparing a metal nanowire catalyst. Background Art
[0002] Metal nanowires, due to their large surface area relative to mass (specific surface area), offer excellent catalytic activity. Their relatively stable surface also provides excellent durability, making them highly anticipated as catalyst materials. These metal nanowires are synthesized by reducing metal salts in a solvent containing a dispersant and a protective agent. Examples of metal nanowires synthesized include gold, silver, copper, platinum, and nickel.
[0003] "Synthesis of Platinum Alloy Nanowire Catalysts and Their Oxygen Reduction Reaction Activity," Yoshimi Iguchi et al., PDF Abstracts of the Battery Symposium (CD-ROM), Vol. 61, ROMBUN NO. 3G02, published in 2020, describes the synthesis of metal nanowires composed of platinum-nickel alloy and their catalytic activity. Summary of the Invention
[0004] The metal nanowires synthesized as described above are mixed with a carbon support in a solvent and supported on the carbon support, thereby obtaining a metal nanowire catalyst. A dispersant is used when supporting the metal nanowires on the carbon support. The dispersant adsorbs on the surface of the metal nanowires to prevent agglomeration of the metal nanowires in the solvent. However, if the metal nanowires are not cleaned sufficiently, the surface of the metal nanowires may be covered with impurities, resulting in a decrease in catalytic activity.
[0005] To remove impurities attached to such metal nanowires, the present inventors attempted washing with organic solvents and water. However, it became clear that conventional washing did not sufficiently remove impurities, and the catalytic activity did not improve as expected.
[0006] Furthermore, the inventors of this application focused on the use of organic substances in dispersants and protective agents. They heated metal nanowire catalysts to several hundred degrees Celsius, attempting to remove impurities through volatilization or oxidation (combustion). Furthermore, they determined that high-temperature treatment of the metal nanowire catalysts resulted in agglomeration (agglomeration due to sintering) between the carbon support and the metal nanowire catalyst, reducing the surface area and, in turn, lowering catalytic activity.
[0007] The purpose of the present invention is to solve the above technical problems.
[0008] The present disclosure provides a method for producing a metal nanowire catalyst, comprising a loading step and a washing step, wherein, in the loading step, a carbon support is loaded with metal nanowires; after the loading step, impurities are removed from the support formed by the carbon support loaded with the metal nanowires in the washing step, and the washing step comprises a first mixing step and a first separation step, wherein, in the first mixing step, a solution containing a hydride reducing agent is brought into contact with the support; and in the first separation step, a first impurity separated from the support in the first mixing step is removed from the first mixture obtained in the first mixing step.
[0009] According to the above-mentioned method for producing a metal nanowire catalyst, impurities attached to the metal nanowires can be removed while maintaining the shape of the metal nanowires, thereby improving catalytic activity.
[0010] The above-mentioned objects, features and advantages can be easily understood from the following description of the embodiments with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Figure 1 This is an explanatory diagram of a method for producing a metal nanowire catalyst.
[0012] Figure 2 This is an explanatory diagram of the synthesis process of metal nanowires.
[0013] Figure 3 It is an explanatory diagram of the step of making a carbon support support metal nanowires.
[0014] Figure 4 It is an explanatory diagram of the washing step of the carbon support (support) supporting metal nanowires.
[0015] Figure 5 It means that the Figure 4 The metal nanowire catalyst (Comparative Example 1) and the Figure 4 A graph showing the results of measuring the weight change of the metal nanowire catalyst (Example) during the cleaning process.
[0016] Figure 6A is a transmission electron microscope photograph of the metal nanowire catalyst of Comparative Example 1. Figure 6B is a transmission electron microscope photograph of the metal nanowire catalyst according to Comparative Example 2 that was heat-treated at 450°C. Figure 6C This is a transmission electron microscope photograph of the metal nanowire catalyst according to the example after being cleaned with a cleaning solution containing sodium borohydride.
[0017] Figure 7This table shows the results of measuring the surface atomic concentrations of the metal nanowire catalysts according to Comparative Example 1, Comparative Example 2, and Examples by X-ray photoelectron spectroscopy (XPS).
[0018] Figure 8 This is a graph showing the results of measuring the mass activity ratios of the metal nanowire catalysts according to Comparative Example 1, Comparative Example 2, and Examples using a rotating disk electrode method (RDE). DETAILED DESCRIPTION
[0019] like Figures 6A to 6C As shown, the metal nanowire catalyst 10 has a structure in which short-fibered metal nanowires 14 are dispersed and supported on the surface of a granular fine carbon support 12 (carbon particles). Such a metal nanowire catalyst 10 is used, for example, in electrodes of electrochemical cells such as fuel cells and water electrolysis devices.
[0020] The carbon support 12 is not particularly limited as long as it can support the metal nanowires 14. For example, CA250 (trade name) manufactured by Denka Co., Ltd., OSAB (trade name) manufactured by Denka Co., Ltd., Vulcan (trade name) manufactured by Cabot Corporation, Ketjenblack (registered trademark) manufactured by Ketjen Black International, Inc., Norit (trade name) manufactured by Norit Corporation, BLACK PEARL manufactured by Cabot Corporation, Acetylene Black (trade name) manufactured by Chevron Corporation, and VGCF (registered trademark) manufactured by Resonac Corporation can be used as the carbon support 12. Furthermore, the carbon support 12 is not limited to a granular form and may be in a one-dimensional or two-dimensional form, such as carbon nanotubes, carbon nanohorns, carbon nanowalls, or carbon nanofibers.
[0021] The carbon carrier 12 is dispersed in the solvent in the form of particles in the supporting step described below. In the solvent, the carbon carrier 12 may form an aggregate formed by agglomerating a plurality of particles.
[0022] The metal elements constituting the metal nanowires 14 can be appropriately selected from any metal elements according to the purpose. The metal elements can be, for example, base metal elements such as nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), tin (Sn), aluminum (Al), zinc (Zn), titanium (Ti), niobium (Nb), tungsten (W), molybdenum (Mo), chromium (Cr) or vanadium (V). In addition, the metal elements can also be precious metal elements such as platinum (Pt), silver (Ag), gold (Au), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru) or osmium (Os). The above elements can include single elements or compounds with other elements, or the metal nanowires 14 can also include multiple elements listed above. In addition, the metal nanowires 14 can also be composed of an alloy combining several of the above elements. As a catalyst for the electrodes of fuel cells, metal nanowires 14 composed of platinum or a platinum alloy are preferred.
[0023] Generally, the diameter of the metal nanowires 14 is approximately 1 nm to 10 nm. The length of the metal nanowires 14 varies depending on the material and manufacturing method, but is typically between several hundred nm and several μm. Because their total length is longer than their diameter, the metal nanowires 14 have an elongated linear shape. For example, the metal nanowires 14 can be used in the metal nanowire catalyst 10 in a short, fiber-like state, shorter than immediately after synthesis.
[0024] In one embodiment, the metal nanowires 14 can be intentionally shortened to a length that allows them to be supported by the carbon support 12. When the average length of the metal nanowires 14 in the metal nanowire catalyst 10 is equal to or smaller than the particle size of the carbon support 12 or its aggregates (secondary particles), the metal nanowires 14 have improved dispersibility, enabling good support by the carbon support 12. Furthermore, if the length of the metal nanowires 14 immediately after synthesis is sufficiently short, a shortening step is unnecessary.
[0025] The metal nanowire catalyst 10 of this embodiment is produced by the following method.
[0026] like Figure 1 As shown, the method for producing the metal nanowire catalyst 10 of the present embodiment includes, in order of steps, a synthesis step ( S10 ), a supporting step ( S20 ), and a washing step ( S30 ).
[0027] The method for producing the metal nanowire catalyst 10 starts with the synthesis step (S10). The synthesis step (S10) is a step for synthesizing the metal nanowire 14, including Figure 2 The synthesis step (S10) starts with the metal salt solution preparation step (S11). The metal salt solution preparation step (S11) includes the step of mixing the metal salt, glucose, octadecene and oleylamine as precursors.
[0028] The precursor used in the metal salt solution preparation step (S11) is a salt of the metal element. The precursor is selected from substances that can be reduced to a metal by reacting with the mixture in the synthesis step described below. For example, when synthesizing platinum nanowires, platinum (II) acetylacetonate can be used as the precursor. Octadecene is used as the solvent. Other solvents can also be used instead of octadecene.
[0029] Oleylamine acts as a reducing agent and stabilizer in subsequent steps. Specifically, at high temperatures, oleylamine becomes an electron donor, reducing the precursor metal salt and precipitating the metal. Furthermore, oleylamine inhibits the growth of the precipitated metal particles by coating their surfaces, stopping their growth at nanometer size and allowing more metal salt to be used for the growth of metal nanowires 14.
[0030] Glucose also acts as a reducing agent for the precursor. A polyol can also be used instead of glucose. The polyol can be hexadecanediol, tetraethylene glycol, propylene glycol, trimethylene glycol, diethylene glycol, ethylene glycol, or stearyl glycol.
[0031] In the metal salt solution preparation step ( S11 ), the mixture is mixed by a stirrer or the like, and then further uniformly dispersed by an ultrasonic homogenizer or the like.
[0032] Next, the synthesis step (S10) enters the catalyst addition step (S12) of adding a protective agent and a catalyst. The protective agent is, for example, polyvinyl pyrrolidone (PVP). Polyvinyl pyrrolidone has multiple carbonyl groups (CO bond groups) in the molecule. The carbonyl group of polyvinyl pyrrolidone is adsorbed on the precipitated metal, so that the polyvinyl pyrrolidone molecules extending in a chain form surround the precipitated metal. Accordingly, the spherical growth of the metal is hindered, and the precipitated metal grows in a one-dimensional (linear) shape. The catalyst is added to promote the growth of the metal nanowires 14. The catalyst can be, for example, a tungsten (W) complex, a chromium (Cr) complex, or a molybdenum (Mo) complex. Tungsten hexacarbonyl can be suitably used when synthesizing platinum nanowires.
[0033] Next, the synthesis step (S10) enters the heat treatment step (S13). The heat treatment step (S13) heats the mixed solution prepared in the catalyst addition step (S12) to a predetermined reaction temperature (e.g., 110°C to 140°C) to grow the metal nanowires 14. The heat treatment step (S13) is performed over a period of several tens of minutes to several tens of hours. In addition, the heat treatment step (S13) includes a heating step of heating from room temperature to a predetermined temperature and a cooling step of cooling from a predetermined temperature to room temperature. The heating step and the cooling step are performed at a predetermined heating rate or cooling rate, respectively. The heating treatment step can be performed while stirring the mixed solution.
[0034] Next, the synthesis step ( S10 ) proceeds to the filtration step ( S14 ). In the filtration step ( S14 ), the metal nanowires 14 are extracted from the mixed solution by filtration or other methods.
[0035] Next, the synthesis step (S10) enters the separation step (S15). In the separation step (S15), a cleaning solvent is added to the metal nanowires 14 recovered by filtration. For example, a mixture of acetone, cyclohexane, and ethanol can be used as the cleaning solvent. The addition of the cleaning solvent removes some impurities adhering to the metal nanowires 14. The cleaning solvent and the metal nanowires 14 are mixed by stirring and applying ultrasonic waves.
[0036] Next, in a separation step (S15), centrifugation is performed to separate the mixture containing the cleaning solvent and the metal nanowires 14 into a precipitate layer and a supernatant layer. The precipitate layer contains the metal nanowires 14, while the supernatant layer is composed of the cleaning solvent. The supernatant layer is then removed, and the metal nanowires 14 in the precipitate layer are recovered.
[0037] Then, a washing solvent may be further added to the recovered precipitate layer, and centrifugal separation may be performed, thereby repeating the separation step (S15) multiple times.
[0038] The metal nanowires 14 obtained in the above-mentioned separation step (S15) are surrounded by impurities including polyvinyl pyrrolidone and oleylamine. The impurities surrounding the plurality of metal nanowires 14 easily form hydrophobic bonds due to the interaction of non-polar groups with each other. Therefore, if the metal nanowires 14 are dried, the metal nanowires 14 will be more likely to aggregate, making it difficult for the metal nanowires 14 to disperse on the carbon support 12. Therefore, after the separation step (S15), a preservation solvent addition step (S16) is performed to add a preservation solvent to the metal nanowires 14. As the preservation solvent, ethanol (alcohol) can be used, for example. In the preservation solvent addition step (S16), a treatment can also be performed to disperse the metal nanowires 14 in the preservation solvent by applying ultrasonic waves. The preservation solvent addition step (S16) can obtain a metal nanowire dispersion in which the metal nanowires 14 are dispersed in the preservation solvent.
[0039] The synthesis step ( S10 ) is completed through the above steps. The metal nanowires 14 synthesized in the synthesis step ( S10 ) are used as a metal nanowire dispersion in the supporting step ( S20 ).
[0040] Next, the method for producing the metal nanowire catalyst 10 enters the loading step (S20). Figure 3As shown, the supporting step (S20) proceeds to the carrier mixing step (S21) for mixing the carbon carrier 12 with the metal nanowires 14. In the carrier mixing step (S21), the carbon carrier 12, the metal nanowire dispersion, and the dispersion solvent are mixed. The dispersion solvent is a mixture of a polar solvent and a non-polar solvent. For example, an organic solvent mixed with ethanol and cyclohexane can be used as the dispersion solvent. In addition, oleylamine can be added as a dispersant in the carrier mixing step (S21). Oleylamine effectively disperses the metal nanowires 14, which have been aggregated into bundles by polyvinyl pyrrolidone, in the solvent.
[0041] Next, the loading process (S20) enters the ultrasonic treatment process (S22). In the ultrasonic treatment process (S22), ultrasonic waves are applied to the mixed solution prepared in the carrier mixing process (S21) by an ultrasonic homogenizer. The ultrasonic treatment process (S22) is performed, for example, for tens of minutes to several hours. Through the ultrasonic treatment process (S22), the metal nanowires 14 condensed into bundles are separated, and the separated metal nanowires 14 are short-fibered and shortened. The length of the metal nanowires 14 becomes a value corresponding to the frequency and output of the applied ultrasonic waves. The short-fibered metal nanowires 14 are attached to the surface of the carbon support 12 in a dispersed state, and a support in which the metal nanowires 14 are supported by the carbon support 12 is obtained.
[0042] Next, the support step (S20) enters the concentration step (S23). In the concentration step (S23), the mixed solution subjected to the ultrasonic treatment step (S22) is separated by centrifugation into a precipitate layer containing the support and a supernatant layer containing the dispersion solvent. In the concentration step (S23), the supernatant layer is removed and the precipitate layer containing the concentrated support is recovered.
[0043] Next, the support step (S20) enters the drying step (S24). In the drying step (S24), the precipitate layer (suspension) obtained in the concentration step (S23) is dried. The drying step (S24) is performed, for example, by drying under reduced pressure. The drying step (S24) removes the solvent from the support, obtaining a solid support.
[0044] After the support step (S20), the support enters the calcination step (S25). The calcination step (S25) is performed, for example, by heating the support to a calcination temperature of 200°C to 300°C in an inert gas atmosphere containing approximately 3% hydrogen. A calcination temperature of approximately 250°C in the calcination step (S25) is preferred because it promotes the removal of impurities adhering to the surface of the metal nanowires 14 and prevents shrinkage (sintering) caused by sintering.
[0045] Next, the method for manufacturing the metal nanowire catalyst 10 enters the cleaning step (S30). Figure 4 As shown, the cleaning step (S30) includes the steps shown in the figure. The cleaning step (S30) starts with the first mixing step (S31). The first mixing step (S31) includes mixing the support and the first cleaning solution to form a first mixture. The first impurity is separated from the support by the first mixing step (S31). The first cleaning solution is a solution containing a hydride reducing agent and a solvent. The solvent used in the first cleaning solution includes, for example, alcohol and water.
[0046] The hydride reducing agent used in the first cleaning solution hydrogenates carbon double bonds in organic matter remaining on the metal nanowire support. Furthermore, the hydride reducing agent reduces carbonyl compounds such as ketones and aldehydes in the organic matter into alcohols. By chemically altering the organic matter, the hydride reducing agent reduces its adsorption to the metal nanowires 14. Furthermore, by chemically altering the organic matter as an impurity, the hydride reducing agent increases its affinity for the solvent.
[0047] As a hydride reducing agent, at least one of sodium borohydride, lithium aluminum hydride, lithium borohydride, borane, sodium cyanoborohydride, and sodium triacetoxyborohydride can be used. Sodium borohydride is safe to handle and is preferred in terms of operability. However, the cleaning effect of hydride reducing agents is not limited to sodium borohydride.
[0048] In the first mixing step (S31), oleylamine, polyvinylpyrrolidone, and the like used in the loading step are believed to adhere to the surface of the metal nanowires 14 as impurities. Oleylamine receives hydride ions from the hydride reducing agent and becomes octadecylamine. For example, when sodium borohydride is used as the hydride reducing agent, oleylamine and sodium borohydride react as follows. C 18 H 37 N+NaBH4→C 18 H 37 NH2+NaBo2+H2(Reaction 1) C 18 H 37 N+2NaBH4→C 18 H 37 NH2+2NaB(OH)2+H2 (Reaction Formula 2)
[0049] In addition, a portion of the sodium borohydride also reacts with water to produce sodium tetrahydroborate and hydrogen (Reaction Formula 2). The above reaction is an example of a reductive amination reaction that utilizes the reducing power of a hydride reducing agent. This reaction converts unsaturated functional groups such as carbonyl compounds and imines into amines.
[0050] The first cleaning liquid is prepared before the first mixing step (S31). Since the hydride reducing agent also decomposes when it comes into contact with water, the first cleaning liquid is preferably prepared immediately before the first mixing step (S31).
[0051] Next, the washing step (S30) proceeds to the first centrifugation step (S32). In the first centrifugation step, the first mixture obtained in the first mixing step (S31) is centrifuged. The first centrifugation step (S32) separates the first mixture into a first sedimentation layer containing the support and a first supernatant layer containing impurities separated from the support.
[0052] Next, the washing step (S30) enters the first supernatant removal step (S33). In the first supernatant removal step (S33), the first supernatant layer separated in the first centrifugal separation step (S32) is removed. Thus, the first sedimentation layer containing the support is recovered.
[0053] If necessary, the process may return to the first mixing step ( S31 ) and repeat the first mixing step ( S31 ) to the first supernatant removal step ( S33 ) on the first precipitation layer.
[0054] Afterwards, the cleaning process (S30) enters the second mixing process (S34). In the second mixing process (S34), the first precipitation layer and the second cleaning liquid are mixed to prepare a second mixture. Pure water (ion exchange water) is used as the second cleaning liquid. The second cleaning liquid removes the second impurities composed of ionic substances from the support. Examples of the second impurities include calcium ions, magnesium ions, sodium ions, potassium ions, chloride ions, bicarbonate ions, sulfate ions, nitrate ions, etc. In this embodiment, the second mixing process (S34) is also effective for removing nitrate ions from oleylamine oxidation.
[0055] Next, the washing step (S30) proceeds to the second centrifugation step (S35). The second centrifugation step (S35) centrifuges the second mixture obtained in the second mixing step (S34). The second centrifugation step (S35) separates the second mixture into a second sedimentation layer containing the support and a second supernatant layer containing the second impurities separated from the support.
[0056] Next, the washing step (S30) enters the second supernatant removal step (S36). In the second supernatant removal step (S36), the second supernatant layer is removed and the second sedimentation layer is recovered.
[0057] The second mixing step ( S34 ) to the second supernatant removal step ( S36 ) may be performed once or repeatedly a plurality of times as necessary.
[0058] Afterwards, the cleaning step (S30) enters the third mixing step (S37). In the third mixing step (S37), a third mixture mixed with a third cleaning liquid is prepared relative to the second precipitation layer. The third cleaning liquid is an organic solvent, for example, a polar solvent can be used. For example, the third cleaning liquid can be any one of acetone, methanol, ethanol, acetic acid, ethyl acetate, chloroform, toluene, xylene, methyl ethyl ketone, or a mixture thereof. In addition, if acetone, a polar solvent with a high affinity for water, is used as the third cleaning liquid, it is possible to remove not only fat-soluble impurities but also water-soluble impurities, and is therefore preferred.
[0059] The third impurity is removed from the support in the third mixing step (S37). Examples of the third impurity include fat, oil, wax, resin, rubber, polymer, etc. The third impurity may include the protective agent used in the synthesis step (S10) and the dispersant used in the support step (S20).
[0060] Next, the washing step (S30) proceeds to the third centrifugal separation step (S38). In the third centrifugal separation step (S38), the third mixture is separated into a third supernatant layer and a third sediment layer.
[0061] Next, the washing step (S30) proceeds to the third supernatant removal step (S39). In the third supernatant removal step (S39), the third supernatant layer is removed. The support is recovered together with the third precipitated layer.
[0062] If necessary, the third mixing step ( S37 ) to the third supernatant removal step ( S39 ) may be repeated.
[0063] Next, the washing step (S30) proceeds to the drying step (S40). The drying step (S40) is performed by drying the third precipitated layer under reduced pressure. The reduced pressure drying is performed by heating at 50°C for 72 hours in a reduced pressure atmosphere.
[0064] The washing step ( S30 ) is completed through the above steps, and the metal nanowire catalyst 10 of this embodiment is completed.
[0065] Next, as an example of an actual metal nanowire catalyst 10 , the results of producing and evaluating a platinum nanowire catalyst will be described.
[0066] (Synthesis of Platinum Nanowires) 18.75 mmol of platinum (II) acetylacetonate (Pt(acac)2), 22.5 mmol of glucose, 30 ml of 1-octadecene, and 45 ml of oleylamine were mixed with a stirrer to prepare a metal salt solution (S11). The metal salt solution was then subjected to ultrasonic waves for 10 minutes for further stirring and mixing.
[0067] Next, as a catalyst addition step (S12), 0.225 mmol of polyvinyl pyrrolidone and 0.15 mmol of tungsten hexacarbonyl (W(CO)6) were added to the above-mentioned metal salt solution. Then, as a heat treatment step (S13), the metal salt solution was heat treated. The heat treatment step (S13) was performed at 120°C for 3 hours while the metal salt solution was stirred.
[0068] Next, the heat-treated metal salt solution is filtered (S14) to recover the platinum nanowires. Next, a separation step (S15) is performed. Specifically, a mixture of acetone, cyclohexane, and ethanol is added to the recovered platinum nanowires. The suspension containing the platinum nanowires is then centrifuged, and the supernatant layer is removed, allowing the platinum nanowires to be recovered along with the precipitate.
[0069] Ethanol was added to the precipitate obtained by centrifugation as a storage solution, and ultrasonic waves were applied for 15 minutes. This process prepared a platinum nanowire dispersion in which platinum nanowires were dispersed in ethanol. The thus prepared platinum nanowire dispersion was transferred to a bottle for storage.
[0070] (Loading process) Next, a step ( S20 ) of loading the synthesized platinum nanowires onto the carbon support 12 was performed. A platinum nanowire dispersion containing 107 mg of platinum nanowires, 200 ml of ethanol, 200 ml of cyclohexane, and 20 ml of oleylamine were added to 9630 mg of the carbon support 12 and mixed, thereby performing a support mixing step ( S21 ).
[0071] Next, as an ultrasonic treatment step (S22), ultrasonic waves are applied to the mixed solution prepared in the carrier mixing step (S21) by an ultrasonic homogenizer. The ultrasonic treatment step (S22) is performed for 60 minutes. Next, as a concentration step (S23), the mixed solution that has undergone the ultrasonic treatment step (S22) is centrifuged. Then, the supernatant layer of the mixed solution is removed as a precipitated layer, and the support is recovered. Then, as a drying step (S24), the support is dried under reduced pressure. Then, as a calcination step (S25), the support is calcined at 250°C for 12 hours in an inert gas atmosphere containing 3% hydrogen.
[0072] (Comparative Example 1) The metal nanowire catalyst 10 of Comparative Example 1 is the support obtained in the above-mentioned calcination step ( S25 ).
[0073] (Comparative Example 2) The metal nanowire catalyst 10 of Comparative Example 2 was prepared by subjecting the support obtained in the calcination step ( S25 ) to an additional calcination treatment at 450° C. in order to remove organic matter.
[0074] (Example) The metal nanowire catalyst 10 of the embodiment is prepared by performing the following washing process on the support obtained in the above-mentioned calcination process (S25). First, as the first mixing process (S31), 3.33g of sodium borohydride is mixed with the first washing liquid to prepare the first mixture. The first washing liquid is a mixture of 83ml of water and 83ml of ethanol. Next, 250mg of the support obtained in the above-mentioned calcination process (S25) and 166ml of the above-mentioned first washing liquid are put into a prescribed container and mixed. Through this operation, foaming is generated from the support. After the foaming from the support stops, centrifugation is performed as the first centrifugation process (S32), and the supernatant layer of the first mixture is removed as the first supernatant removal process (S33). The addition of the first washing liquid (the first mixing process (S31)), the first centrifugation process (S32) and the first supernatant removal process (S33) are repeated 5 times. The first washing liquid is appropriately prepared and used.
[0075] Next, as a second mixing step (S34), the first precipitate layer was transferred to a 50 ml centrifuge tube, 40 ml of pure water (ion-exchanged water) was added, and manual mixing was performed for 1 minute. Thereafter, a second centrifugation step (S35) and a second supernatant removal step (S36) were performed. The second mixing step (S34), second centrifugation step (S35), and second supernatant removal step (S36) were repeated three times.
[0076] Next, as a third mixing step (S37), 40 ml of acetone as a third washing solution was added to the second precipitate layer and manually mixed for 1 minute. Thereafter, a third centrifugation step (S38) and a third supernatant removal step (S39) were performed. The third mixing step (S37), third centrifugation step (S38), and third supernatant removal step (S39) were repeated three times.
[0077] Then, as a drying step ( S40 ), the suspension of the third precipitation layer was dried under reduced pressure at 50° C. for 72 hours to obtain the metal nanowire catalyst 10 of the example.
[0078] Next, the metal nanowire catalysts 10 according to Comparative Example 1, Comparative Example 2, and Examples were evaluated.
[0079] (Based on TG evaluation results) like Figure 5As shown, the weight change of the metal nanowire catalyst 10 of Comparative Example 1 and the metal nanowire catalyst 10 of the Example was measured using the thermobalance method (TG). The measurement was performed in a nitrogen atmosphere at a heating rate of 10°C / minute. As shown in the figure, as the temperature increased, impurities attached to the metal nanowire catalyst 10 were volatilized and removed, resulting in a weight decrease. The result showed that the weight change of the metal nanowire catalyst 10 of the Example was approximately 0.3% smaller than that of the metal nanowire catalyst 10 of Comparative Example 1. This result indicates that the metal nanowire catalyst 10 of the Example, which had undergone the cleaning step (S30), had a reduced amount of impurities.
[0080] (Based on TEM observations) Then, if Figures 6A to 6C As shown in FIG, the metal nanowire catalysts 10 of each of Comparative Example 1, Comparative Example 2 and Example were observed using a transmission electron microscope. Figure 6A (Comparative Example 1) and Figure 6C As shown in the Example, in the metal nanowire catalyst 10 of Comparative Example 1 and the Example, the carbon support 12 and the platinum nanowires are dispersed, maintaining a high surface area. Figure 6B As shown, the carbon support 12 and platinum nanowires of the metal nanowire catalyst 10 of Comparative Example 2 sintered and shrank (agglomerated) during the heat treatment at 450° C. In Comparative Example 2, the porosity of the carbon support 12 decreased, and the platinum nanowires aggregated into agglomerates.
[0081] (Atomic concentration measurement based on XPS) like Figure 7 As shown, the surface atomic concentrations of the metal nanowire catalysts 10 of Comparative Examples 1, 2, and Examples were measured using X-ray photoelectron spectroscopy. The nitrogen atomic concentration is derived from the dispersant and protective agent (oleylamine). Furthermore, the oxygen atomic concentration reflects the reduction state of the platinum nanowire surfaces; a lower value promotes reduction and enhances catalytic activity. A higher platinum atomic concentration indicates that more platinum nanowires are present on the surface of the metal nanowire catalyst 10.
[0082] In the metal nanowire catalyst 10 of Comparative Example 1, which did not undergo a washing step, the atomic concentrations of nitrogen and oxygen were higher than those of Comparative Example 2 and the Examples, indicating that more impurities were attached to the surface. Furthermore, it was confirmed that the amount of platinum nanowires exposed on the surface of the metal nanowire catalyst 10 of Comparative Example 1 was less than that of Comparative Example 2 and the Examples.
[0083] In the case of the metal nanowire catalyst 10 of Comparative Example 2 (after heat treatment at 450°C), the atomic concentration of nitrogen from the dispersant and protective agent was reduced, minimizing residual impurities. Furthermore, the atomic concentration of oxygen was minimized, confirming that reduction of the platinum nanowire surfaces was progressing. Furthermore, the atomic concentration of platinum was maximized, confirming that more platinum nanowires were exposed on the surface compared to Comparative Example 1.
[0084] In the case of the metal nanowire catalyst 10 of the Example, the nitrogen atomic concentration was lower than that of Comparative Example 1, confirming that the impurity concentration was reduced by the cleaning process. Compared to the oxygen atomic concentration of Comparative Example 1, the oxygen atomic concentration of the metal nanowire catalyst 10 of the Example was lower, confirming that reduction of the platinum nanowire surface was still progressing. Furthermore, the platinum atomic concentration of the Example was higher than that of Comparative Example 1, confirming that more platinum nanowires were exposed on the surface.
[0085] (Mass activity ratio based on RDE method) Then, if Figure 8 The mass activity ratio was measured using the RDE (Rotating Disc Electrode) method. The Pt / C catalyst is used for comparison and represents the measurement results of a conventional platinum catalyst in which platinum particles are supported on a carbon support 12 . Figure 8 The mass activity ratio is a value (relative value) expressed as the ratio of the catalytic activity per gram of platinum in the catalyst to be measured to the catalytic activity per gram of platinum in the Pt / C catalyst.
[0086] The mass activity ratio of the metal nanowire catalyst 10 of Comparative Example 1 was 1.7, and a higher catalytic activity was obtained than in the case of supporting platinum particles.
[0087] The mass activity ratio of the metal nanowire catalyst 10 of Comparative Example 2 was 0.4, which was lower than that of the Pt / C catalyst. Figure 7 The impurity concentration of the metal nanowire catalyst 10 of Comparative Example 2 is reduced, but Figure 6B As shown in FIG, it is believed that the catalytic activity is reduced due to the agglomeration of the platinum nanowires, which results in a reduction in surface area.
[0088] In contrast, the metal nanowire catalyst 10 according to the example exhibited a mass activity ratio twice that of the Pt / C catalyst, and its mass activity ratio was improved compared to Comparative Example 1. The metal nanowire catalyst 10 according to the example was effectively cleaned with a hydride reducing agent to remove impurities. Furthermore, the metal nanowire catalyst 10 according to the example prevented agglomeration. Furthermore, the metal nanowire catalyst 10 according to the example reduced the surface of the platinum nanowires using the hydride reducing agent, thereby enhancing catalytic activity. Consequently, the metal nanowire catalyst 10 according to the example exhibited excellent catalytic activity.
[0089] Regarding the above-mentioned embodiment, the following supplementary notes are further disclosed.
[0090] (Note 1) The method for producing a metal nanowire catalyst (10) disclosed herein includes a loading step (S20) and a washing step (S30), wherein, in the loading step, a carbon support (12) is loaded with metal nanowires (14); after the loading step, impurities are removed from the support formed by the carbon support loaded with the metal nanowires in the washing step, and the washing step includes a first mixing step (S31) and a first separation step, wherein, in the first mixing step, a solution containing a hydride reducing agent is brought into contact with the support; and in the first separation step, the first impurities separated from the support in the first mixing step are removed from the first mixture obtained in the first mixing step.
[0091] (Note 2) According to the method for producing a metal nanowire catalyst described in Appendix 1, the first separation step may include a first centrifugal separation step (S32) and a first supernatant removal step (S33), wherein, in the first centrifugal separation step, the first mixture is separated into a first precipitate layer containing the support and a first supernatant layer containing the first impurity by centrifuging; and in the first supernatant removal step, the first supernatant layer is removed.
[0092] (Note 3) According to the method for manufacturing a metal nanowire catalyst described in Note 2, the washing step may further include a second mixing step (S34) and a second separation step after the first separation step, wherein, in the second mixing step, pure water is added to the first precipitation layer and mixed; and in the second separation step, the second impurities separated from the support in the second mixing step are removed from the second mixture obtained in the second mixing step.
[0093] (Note 4) According to the method for producing a metal nanowire catalyst described in Appendix 3, the second separation step may include a second centrifugal separation step (S35) and a second supernatant removal step (S36), wherein, in the second centrifugal separation step, the second mixture is separated into a second precipitate layer containing the support and a second supernatant layer containing the second impurities by centrifuging; and in the second supernatant removal step, the second supernatant layer is removed.
[0094] (Note 5) According to the method for manufacturing a metal nanowire catalyst described in Note 4, the washing step may further include a third mixing step (S37) and a third separation step after the second separation step, wherein, in the third mixing step, an organic solvent is added to the second precipitated layer and mixed; and in the third separation step, the third impurity separated from the support in the third mixing step is removed from the third mixture obtained in the third mixing step.
[0095] (Note 6) According to the method for manufacturing a metal nanowire catalyst described in Note 5, the third separation step may include a third centrifugal separation step (S38) and a third supernatant removal step (S39), wherein, in the third centrifugal separation step, the third mixture is separated into a third precipitate layer containing the support and a third supernatant layer containing the third impurities by centrifuging; and in the third supernatant removal step, the third supernatant layer is removed.
[0096] (Note 7) The method for producing a metal nanowire catalyst according to Supplementary Note 6 may further include a drying step ( S40 ) after the third separation step, wherein the third precipitation layer is dried in the drying step.
[0097] (Note 8) The method for producing a metal nanowire catalyst according to any one of Appendixes 1 to 7 may be such that the hydride reducing agent includes at least one of sodium borohydride, lithium aluminum hydride, lithium borohydride, borane, sodium cyanoborohydride, and sodium triacetoxyborohydride.
[0098] (Note 9) The method for producing a metal nanowire catalyst according to any one of Supplementary Notes 5 to 7 may be such that the organic solvent comprises at least one of acetone, toluene, xylene, methyl ethyl ketone, ethyl acetate, ethanol, methanol, acetic acid, and chloroform. These organic solvents can efficiently remove fat-soluble impurities from the metal nanowire catalyst.
[0099] The present disclosure has been described in detail, but the present disclosure is not limited to the above-mentioned embodiments. These embodiments can be supplemented, replaced, changed, partially deleted, etc. without departing from the scope of the main purpose of the present disclosure, or without departing from the scope of the main purpose of the present disclosure derived from the contents recorded in the technical solution and its equivalents. In addition, these embodiments can also be implemented in combination. For example, in the above-mentioned embodiments, the order of each operation and the order of each processing are shown as an example only and are not limited to this. In addition, the same applies to the use of numerical values or formulas in the description of the above-mentioned embodiments.
Claims
1. A method for producing a metal nanowire catalyst, characterized in that: It includes a loading process and a cleaning process, wherein: In the supporting step, the carbon support supports the metal nanowires; After the supporting step, impurities are removed from the support formed by the carbon support supporting the metal nanowires in the washing step. The cleaning process includes a first mixing process and a first separation process, wherein: In the first mixing step, a solution containing a hydride reducing agent is brought into contact with the support; In the first separation step, the first impurities separated from the support in the first mixing step are removed from the first mixture obtained in the first mixing step.
2. The method for producing a metal nanowire catalyst according to claim 1, wherein: The first separation step includes a first centrifugation step and a first supernatant removal step, wherein: In the first centrifugation step, the first mixture is centrifuged to separate into a first precipitate layer containing the support and a first supernatant layer containing the first impurities; In the first supernatant liquid removal step, the first supernatant layer is removed.
3. The method for producing a metal nanowire catalyst according to claim 2, wherein: The cleaning process further includes a second mixing process and a second separation process after the first separation process, wherein: In the second mixing step, pure water is added to the first precipitation layer and mixed; In the second separation step, the second impurities separated from the support in the second mixing step are removed from the second mixture obtained in the second mixing step.
4. The method for producing a metal nanowire catalyst according to claim 3, wherein: The second separation step includes a second centrifugation step and a second supernatant removal step, wherein: In the second centrifugal separation step, the second mixture is centrifuged to separate into a second precipitate layer containing the support and a second supernatant layer containing the second impurities; In the second supernatant liquid removal step, the second supernatant layer is removed.
5. The method for producing a metal nanowire catalyst according to claim 4, wherein: The cleaning process further includes a third mixing process and a third separation process after the second separation process, wherein: In the third mixing step, an organic solvent is added to the second precipitation layer and mixed; In the third separation step, the third impurities separated from the support in the third mixing step are removed from the third mixture obtained in the third mixing step.
6. The method for producing a metal nanowire catalyst according to claim 5, wherein: The third separation step includes a third centrifugation step and a third supernatant removal step, wherein: In the third centrifugation step, the third mixture is centrifuged to separate into a third precipitate layer containing the support and a third supernatant layer containing the third impurities; In the third supernatant liquid removal step, the third supernatant layer is removed.
7. The method for producing a metal nanowire catalyst according to claim 6, wherein: The third separation step is followed by a drying step, in which the third precipitation layer is dried.
8. The method for producing a metal nanowire catalyst according to any one of claims 1 to 7, wherein: The hydride reducing agent includes at least one of sodium borohydride, lithium aluminum hydride, lithium borohydride, borane, sodium cyanoborohydride and sodium triacetoxyborohydride.
9. The method for producing a metal nanowire catalyst according to any one of claims 5 to 7, wherein: The organic solvent includes at least one of acetone, toluene, xylene, methyl ethyl ketone, ethyl acetate, ethanol, methanol, acetic acid and chloroform.