Ruthenium-based catalyst as well as preparation method and application thereof

Abstract

The invention relates to a ruthenium-based catalyst and a preparation method and application thereof, and belongs to the technical field of seawater electrolysis catalysts. The preparation method of the ruthenium-based catalyst comprises the following steps: dissolving a ruthenium source, a metal salt and a reducing agent in a mixed solvent, heating and stirring to obtain a mixed solution, uniformly dispersing the mixed solution to the surface of a hard template, and carrying out vacuum drying to obtain precursor powder; and calcining the precursor powder, and carrying out suction filtration, centrifugation and drying on the calcined product to obtain the ruthenium-based catalyst. The catalyst also has excellent stability, and can be continuously electrolyzed for more than 100 hours under the condition of neutral seawater and high current density; and an excellent chlorine inhibition effect is realized. The preparation method provided by the invention is simple and efficient, has the characteristic of universality, is easy for large-scale production, and is beneficial to development of marine resources.

Description

Technical Field

[0001] The present application relates to the technical field of catalysts for electrolyzing seawater, and in particular to a ruthenium-based catalyst and a preparation method and application thereof. Background Art

[0002] As a new energy source, hydrogen energy is gradually becoming the key to the transformation of the global energy structure. Hydrogen production technology is an important part of the hydrogen economy, among which green and sustainable water electrolysis is considered to be one of the most promising methods of hydrogen production. Compared with limited freshwater resources, the widespread existence of seawater makes seawater electrolysis hydrogen production particularly important. However, the presence of chloride ions (Cl-) and microorganisms in seawater can cause corrosion and clogging of the catalyst, significantly affecting its activity and stability.

[0003] At present, ruthenium (Ru)-based catalysts are widely considered to be the most effective oxygen evolution reaction (OER) catalysts. However, ruthenium (RuO2)-based catalysts have attracted widespread attention due to their excellent catalytic properties and relatively low cost. RuO2 has a low overpotential in the process of water electrolysis, exhibits good catalytic activity, and can effectively promote the OER reaction. However, in the electrolysis environment, the stability of RuO2 is challenged, and long-term electrolysis reactions may lead to a decrease in its catalytic performance, especially in seawater containing Cl-, where the risk of corrosion and loss increases. Therefore, the development of highly active and stable Ru-based catalysts is of great significance in the field of hydrogen production. In recent years, many inspiring strategies have been proposed to improve the electrocatalytic performance. For example, multi-metal structures with unique electronic properties are used, and different metals are combined and matched, hoping to use their synergistic effects to optimize the electrocatalytic process; organic modification of metal surfaces, using the unique functional groups of organic matter to form specific chemical bonds with the metal surface, etc., in an attempt to change the electronic environment and properties of the metal surface; and regulating the interaction between metal and support, using the mutual influence between support and metal to adjust the state of the active sites of the metal, etc.

[0004] However, these strategies also have many defects. For the method of using multi-metal structures, the ratio between different metals is difficult to control accurately. Once the ratio is out of balance, not only will the synergistic effect fail to be exerted, but new active sites may be inhibited, and even structural instability problems caused by factors such as differences in lattice parameters between different metals may occur, thereby affecting the long-term stability of electrocatalytic performance. As for the strategy of modifying metal surfaces with organic matter, the adsorption stability of organic matter on the metal surface is greatly affected by environmental factors. For example, under extreme reaction conditions such as high temperature, strong acid and alkali, organic matter is easily desorbed from the metal surface, which greatly reduces the modification effect. At the same time, the difference in conductivity of the organic matter itself may also hinder the electron transfer process in the overall electrocatalytic reaction.

[0005] In terms of regulating the interaction between metal and support, although this interaction particularly emphasizes its importance, neither the regulation of reaction intermediates nor the stability has been well improved. This interaction can change the d-band structure of the metal catalyst, enhance the adsorption of reaction intermediates, thereby lowering the energy barrier and promoting the progress of the reaction. However, in reality, when solely relying on regulating the metal-support interaction to change the d-band structure, it is often difficult to precisely adjust the d-band center to the most suitable position, resulting in either too strong or too weak adsorption of reaction intermediates. Too strong adsorption will make it difficult for the intermediates to desorb, hindering the progress of subsequent reaction steps, while too weak adsorption cannot fully utilize the intermediates to promote the efficient development of the reaction, ultimately affecting the overall electrocatalytic efficiency. Moreover, this conventional regulation method is difficult to maintain the stability of the d-band structure for a long time. During the long-term reaction process, the d-band structure is prone to shift, causing the adsorption performance of reaction intermediates to change accordingly, thereby affecting the stability of the electrocatalytic reaction.

[0006] However, through in-depth research, regulating the d-band center can, to a certain extent, solve these defects. Using Lewis acid metal oxides with electron buffering ability as supports. They can form stable interactions with metals, effectively restricting the migration and aggregation of metal atoms, thereby maintaining the long-term stability of the d-band structure and ensuring that the electrocatalytic reaction can proceed stably and efficiently for a long time. Summary of the Invention

[0007] In view of this, the present application provides a ruthenium-based catalyst, its preparation method and application. This ruthenium-based catalyst exhibits performance superior to that of commercial RuO2 catalysts, not only reducing the loading of noble metal catalysts but also reducing the cost of electrolytic seawater catalysts, which is of great significance for promoting the commercialization process of electrolytic seawater catalysts and can effectively overcome the defects existing in the above-mentioned prior art.

[0008] The first aspect of the present application provides a preparation method of a ruthenium-based catalyst, comprising the following steps:

[0009] Dissolve a ruthenium source, a metal salt and a reducing agent in a mixed solvent, heat and stir to obtain a mixed solution, uniformly disperse the mixed solution on the surface of a hard template, and vacuum dry to obtain a precursor powder; calcine the precursor powder, and after suction filtration, centrifugation and drying of the calcined product, a ruthenium-based catalyst is obtained.

[0010] This application utilizes the layer repulsion effect of Lewis acid to inhibit the influence of chloride ions. By modifying the surface of the Ru-based catalyst with a layer of material with Lewis acid properties, the contact of Cl- ions can be effectively repelled, thereby reducing its interference with the catalytic activity. This Lewis acid layer can not only reduce the activity of chloride ions, but also promote the dissociation of water molecules and the oxygen evolution reaction (OER) by changing the electron density of the reaction environment, thus enhancing the overall electrocatalytic performance. In addition, in order to further improve the activity and stability of the catalyst, this application will use Nb2O5 as the carrier. This material, with its excellent stability and corrosion resistance, can provide stable support for RuO2. By controlling the loading amount of RuO2, the design of an ultra-low loading catalyst can be achieved, reducing costs while maintaining catalytic performance. This application will provide a new design idea for the OER catalyst for electrolyzing neutral seawater. Through the repulsion effect of the Lewis acid layer, it is expected to significantly improve the activity and stability of the catalyst in a chloride ion environment, contributing to a sustainable hydrogen energy economy.

[0011] Preferably, it specifically includes the following steps:

[0012] (1) Dissolve ruthenium chloride, metal salt and reducing agent in a mixed solvent of ethanol and water. After heating and stirring, a mixed solution is obtained. Disperse the mixed solution evenly on the surface of the hard template and vacuum dry to obtain precursor powder;

[0013] Among them, the reducing agent is selected from one of glucose, ethanol, and isopropanol;

[0014] (2) Calcinate the precursor powder, and after filtration, centrifugation, and drying of the calcined product, a Ru-based catalyst is obtained.

[0015] Preferably, the specific conditions for the calcination are: place the precursor powder in a muffle furnace and keep it calcined at 350 - 600 °C for 1 - 4 h.

[0016] Preferably, in step (1), the specific process of evenly dispersing the mixed solution on the surface of the hard template is: disperse the mixed solution evenly on the surface of the hard template at a speed of adding 3 ml every 10 min.

[0017] Preferably, in step (2), the specific processes of filtration, centrifugation, and drying are: dissolve the calcined product in water, and remove the hard template by filtration and centrifugation. The rotation speed of centrifugation is 6000 - 15000 rpm, and the centrifugation time is 5 - 15 min; take the supernatant after centrifugation, add ethanol to the supernatant and centrifuge, the rotation speed of centrifugation is 6000 - 15000 rpm, and the centrifugation time is 5 - 15 min to remove impurities, and take the supernatant after centrifugation; finally, vacuum dry for 1 - 3 h to obtain a Ru-based catalyst.

[0018] Preferably, the molar ratio of ruthenium chloride to metal salt is (1 - 4):(1 - 4); or

[0019] The ratio of the total molar amount of ruthenium chloride and metal salt to the volume of the mixed solvent is 0.2 mmol:(20 - 50) ml, wherein the volume ratio of ethanol to water in the mixed solvent is (3:4):1; or

[0020] The ratio of the total molar amount of ruthenium chloride, metal salt and glucose to the molar mass of the hard template is (1 - 3) mmol:(5 - 10) mol.

[0021] Preferably, in step (1), the temperature of the heating and stirring is 40 - 70 °C, and the time of the heating and stirring is 0.5 - 1 h; or

[0022] In step (1), the time of the vacuum drying is 2 - 5 h.

[0023] Preferably, the metal salt is ammonium niobate oxalate hydrate or sodium chromate; the hard template is sodium chloride or potassium chloride particles.

[0024] The second aspect of the present application also provides a ruthenium-based catalyst, which is the ruthenium-based catalyst prepared by the above method.

[0025] The third aspect of the present application also provides the application of the above ruthenium-based catalyst in the electrolysis of seawater. Specifically, the ruthenium-based catalyst is used as an anode catalyst for the oxygen evolution reaction in the electrolysis of seawater.

[0026] Compared with the prior art, the present application has the following beneficial effects:

[0027] 1. The method of the present application uses sodium chloride (NaCl) or potassium chloride (KCl) particles as the hard template, ruthenium chloride as the ruthenium source, and ammonium niobate oxalate hydrate as the niobium source. The ruthenium chloride, metal salt and glucose are dissolved in a mixed solvent of ethanol and water to prepare a mixed solution, which is uniformly dropped onto the surface of the hard template. After calcination in a muffle furnace, the calcined product is dissolved in water, and the sodium chloride (NaCl) or potassium chloride (KCl) template and impurities are removed by suction filtration and centrifugation, and then vacuum dried to form a RuO2@Nb2O5 catalyst with a nanosheet structure. The strong interaction between the Nb2O5 support and RuO2, the activity and stability tested in a neutral seawater system, and the hydrogen evolution overpotential is only 318 mV at 10 mA cm -2 which is better than 342 mV of the commercial RuO2 catalyst.

[0028] 2. The catalyst of the present application also has excellent stability and can continuously electrolyze for more than 100 hours under the conditions of neutral seawater at a large current density; moreover, excellent chlorine inhibition effect is achieved. The preparation method of the present application is simple, efficient and has the characteristics of universality, easy for mass production, and is conducive to the development of marine resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the present application or the prior art, the following will briefly introduce the drawings required for the description of the present application or the prior art. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0030] Figure 1 XRD patterns of RuO2@Nb2O5, RuO2 and Nb2O5 prepared in Example 1 of the present application;

[0031] Figure 2 SEM image of RuO2@Nb2O5 prepared in Example 1 of the present application;

[0032] Figure 3 TEM image of RuO2@Nb2O5 prepared in Example 1 of the present application;

[0033] Figure 4 LSV test diagrams of RuO2@Nb2O5, m-RuO2, c-RuO2 and Nb2O5 prepared in Example 1 of the present application;

[0034] Figure 5 Long-term stability diagrams of RuO2@Nb2O5 and c-RuO2 prepared in Example 1 of the present application;

[0035] Figure 6 By-products of ClO generated from the stability tests of RuO2@Nb2O5 and RuO2 prepared in Example 1 of the present application - DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] To make the objectives, technical solutions and advantages of the present application clearer, the following will clearly and completely describe the technical solutions in the present application in conjunction with the drawings in the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments in the present application fall within the scope of protection of the present application.

[0037] Unless otherwise specified, the experimental methods used in the embodiments of the present application are all conventional methods.

[0038] In the following examples and comparative examples, unless otherwise specified, all raw materials can be obtained through commercial purchase or conventional methods.

[0039] In the following examples and comparative examples, the Chinese name of seawater is seawater; in m-RuO2 and c-RuO2, c- represents commercial and m- represents synthetic.

[0040] Example 1

[0041] 1. The method for one-step synthesis and self-assembly of the heterojunction RuO2@Nb2O5 catalyst in this example includes the following steps:

[0042] (1) Prepare a mixed solution by dissolving 0.1 mmol of ruthenium chloride (RuCl3·3H2O), 0.1 mmol of ammonium niobate oxalate hydrate (C4H4NNbO9·nH2O), and 1.0 mmol of glucose (C6H 12 O6) in a mixed solvent of ethanol and water (10 ml of water + 30 ml of ethanol). After stirring evenly at 60 °C for 1 h, a mixed solution is obtained. Disperse the mixed solution evenly on the surface of 500 g of KCl particles (disperse the mixed solution evenly on the surface of the hard template at a rate of 3 ml every 10 min), and vacuum dry for 2 h to obtain the precursor powder.

[0043] (2) Calcinate the precursor powder in a muffle furnace at 550 °C for 1 h to obtain the catalyst precursor.

[0044] (3) After fully dissolving the catalyst precursor in water, dissolve the hard template in water. Separate the hard template and the catalyst by filtration and centrifugation (centrifugation speed: 10000 rpm, centrifugation time: 10 min). Take the supernatant after centrifugation, add ethanol to the supernatant and centrifuge (centrifugation speed: 10000 rpm, centrifugation time: 10 min) to remove impurities existing during the calcination process. Take the supernatant after centrifugation, and finally vacuum dry for 2 h to obtain the finally purified RuO2@Nb2O5 catalyst.

[0045] 2. All the above drugs are of analytical purity.

[0046] 3. The above Nb2O5 combines with low-loading RuO2 particles in the form of a support of a Lewis acid metal oxide to form a strong interaction between the metal and the support.

[0047] Example 2: RuO2@Cr2O3 catalyst

[0048] 1. The preparation method provided in this example can refer to Example 1, except that ammonium niobate oxalate hydrate is replaced with sodium chromate to prepare the RuO2@Cr2O3 catalyst.

[0049] 2. The preparation process of the RuO2@Cr2O3 catalyst is the same as that in Example 1, and this catalyst is applied to the oxygen evolution reaction system of electrolyzing seawater.

[0050] Example 3

[0051] The preparation method provided in this example can refer to Example 1, the difference is that in step (1), the KCl particles are replaced by NaCl particles.

[0052] Example 4

[0053] The preparation method provided in this example can refer to Example 1, the difference is that in step (1), the ratio of the total molar amount of ruthenium chloride and sodium chromate to the volume of the mixed solvent (ethanol - water) is 0.2 mmol: 20 ml.

[0054] Example 5

[0055] The preparation method provided in this example can refer to Example 1, the difference is that in step (1), the volume concentration of ethanol in the mixed solvent is 80%.

[0056] Example 6

[0057] The preparation method provided in this example can refer to Example 1, the difference is that in step (1), the ratio of the total molar amount of ruthenium chloride and sodium chromate to the mass of KCl particles is 0.2 mmol: 400 g.

[0058] Example 7

[0059] The preparation method provided in this example can refer to Example 1, the difference is that in step (1), the molar ratio of ruthenium chloride to sodium chromate is 1:2.

[0060] Example 8

[0061] The preparation method provided in this example can refer to Example 1, the difference is that in step (1), the heating and stirring time is 0.8 h.

[0062] Example 9

[0063] The preparation method provided in this example can refer to Example 1, the difference is that in step (1), the vacuum drying time is 3 h.

[0064] Example 10

[0065] The preparation method provided in this example can refer to Example 1, the difference is that in step (3), the centrifugation speed is 15000 rpm and the centrifugation time for each time is 12 min.

[0066] Example 11

[0067] The preparation method provided in this example can refer to Example 1, with the difference that the vacuum drying time in step (3) is 3 h.

[0068] Comparative Example 1

[0069] The preparation method provided in this comparative example can refer to Example 1, with the difference that the calcination temperature is adjusted to 700 °C. At this temperature, the hard template (KCl) will dissolve and it is impossible to form the RuO2@Nb2O5 catalyst.

[0070] Comparative Example 2

[0071] The preparation method provided in this comparative example can refer to Example 1, with the difference that the calcination temperature is adjusted to 300 °C. At this temperature, Ru does not start to nucleate and it is impossible to form the RuO2@Nb2O5 catalyst.

[0072] Comparative Example 3

[0073] The method for one-step synthesis and self-assembly of the heterojunction RuO2@Nb2O5 catalyst in this example includes the following steps:

[0074] (1) Prepare a solution by dissolving 0.1 mmol of ruthenium chloride (RuCl3·3H2O), 0.1 mmol of ammonium niobate oxalate hydrate (C4H4NNbO9·nH2O), and 1.0 mmol of glucose (C6H 12 O6) in a mixed solvent of ethanol and water (10 ml of water + 30 ml of ethanol). After stirring evenly at 60 °C for 1 h, a mixed solution is obtained. The mixed solution is evenly dispersed on the surface of 500 g of KCl particles (the mixed solution is evenly dispersed on the surface of the hard template at a rate of 3 ml per 10 min), and vacuum dried for 2 h to obtain the precursor powder.

[0075] (2) Calcinate the precursor powder in a muffle furnace at 550 °C for 1 h to obtain the catalyst precursor after calcination.

[0076] (3) After fully dissolving the catalyst precursor in water to dissolve the hard template in water, separate the hard template and the catalyst by suction filtration and centrifugation (centrifugation speed: 10000 rpm, centrifugation time: 10 min). After centrifugation, take the supernatant, add ethanol to the supernatant and centrifuge (centrifugation speed: 10000 rpm, centrifugation time: 10 min) to remove the impurities existing during the calcination process. After centrifugation, take the supernatant, and finally vacuum dry for 2 h to obtain the finally purified RuO2@Nb2O5 catalyst.

[0077] Test Example

[0078] 1. Perform X-ray diffraction (XRD) analysis on the finally purified RuO2@Nb2O5 catalyst to obtain the RuO2@Nb2O5 phase as Figure 1 shown.

[0079] 2. The scanning electron microscope (SEM) was used to characterize the microscopic morphology of the product obtained in step 1. As Figure 2 shown, RuO2@Nb2O5 presents a two-dimensional nanosheet structure.

[0080] 3. The field emission electron microscope (TEM) was used to characterize the microscopic morphology of the product obtained in step 1. As Figure 3 shown, RuO2@Nb2O5 presents a two-dimensional nanosheet structure.

[0081] 4. As Figure 4 shown, the catalytic performance of the product of Example 1 was tested in a neutral seawater electrolyte system. It can be seen from Figure 4 that at 10 mA cm -2 , RuO2@Nb2O5 only requires an overpotential of 318 mV, showing optimal performance compared to the c-RuO2 (342 mV) catalyst.

[0082] 5. As Figure 5 shown, the stability of the RuO2@Nb2O5 catalyst was tested in a neutral seawater system. It can be seen that after 100 h of long-term continuous electrolysis at 100 mA cm -2 , the activity did not show a significant decline.

[0083] 6. As Figure 6 shown, the stability of the catalyst was tested in a neutral seawater system. After electrolysis using the RuO2@Nb2O5 catalyst, the measured ClO - concentration was about 7.566×10 -8 mol L -1 , significantly lower than the corresponding concentration of the c-RuO2 catalyst (5.662×10 -7 mol L -1 ). This indicates that the RuO2@Nb2O5 catalyst has excellent selectivity and chlorine inhibition performance.

[0084] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A preparation method of a ruthenium-based catalyst, characterized in that, It includes the following steps: Dissolve a ruthenium source, a metal salt, and a reducing agent in a mixed solvent. After heating and stirring, a mixed solution is obtained. Disperse the mixed solution evenly on the surface of a hard template and conduct vacuum drying to obtain a precursor powder. Calcinate the precursor powder, and after filtration, centrifugation, and drying of the calcined product, a ruthenium-based catalyst is obtained.

2. The preparation method of the ruthenium-based catalyst according to claim 1, wherein, Specifically, it includes the following steps: (1) Dissolve ruthenium chloride, a metal salt, and a reducing agent in a mixed solvent of ethanol and water. After heating and stirring, a mixed solution is obtained. Disperse the mixed solution evenly on the surface of a hard template and conduct vacuum drying to obtain a precursor powder. Among them, the reducing agent is selected from one of glucose, ethanol, and isopropanol. (2) Calcinate the precursor powder, and after filtration, centrifugation, and drying of the calcined product, a ruthenium-based catalyst is obtained.

3. The preparation method of the ruthenium-based catalyst according to claim 1 or 2, characterized in that, The specific conditions for the calcination are: Place the precursor powder in a muffle furnace and keep it calcined at 350 - 600 °C for 1 - 4 h.

4. The preparation method of the ruthenium-based catalyst according to claim 2, characterized in that, In step (1), the specific process of dispersing the mixed solution evenly on the surface of the hard template is: Disperse the mixed solution evenly on the surface of the hard template at a rate of adding 3 ml every 10 min.

5. The preparation method of the ruthenium-based catalyst according to claim 2, wherein, In step (2), the specific processes of filtration, centrifugation, and drying are: Dissolve the calcined product in water, and then remove the hard template by filtration and centrifugation. The rotation speed of centrifugation is 6000 - 15000 rpm, and the centrifugation time is 5 - 15 min. After centrifugation, take the supernatant, add ethanol to the supernatant and conduct centrifugation. The rotation speed of centrifugation is 6000 - 15000 rpm, and the centrifugation time is 5 - 15 min to remove impurities. After centrifugation, take the supernatant. Finally, conduct vacuum drying for 1 - 3 h to obtain a ruthenium-based catalyst.

6. The preparation method of the ruthenium-based catalyst according to claim 2, wherein, The molar ratio of the ruthenium chloride to the metal salt is (1 - 4):(1 - 4); or The ratio of the total molar amount of the ruthenium chloride and the metal salt to the volume of the mixed solvent is 0.2 mmol:(20 - 50) ml, where the volume ratio of ethanol to water in the mixed solvent is (3:4):1; or The ratio of the total molar amount of the ruthenium chloride, the metal salt, and glucose to the molar mass of the hard template is (1 - 3) mmol:(5 - 10) mol.

7. The preparation method of the ruthenium-based catalyst according to claim 2, wherein, In step (1), the temperature of heating and stirring is 40 - 70 °C, and the time of heating and stirring is 0.5 - 1 h; or In step (1), the time of vacuum drying is 2 - 5 h.

8. The preparation method of the ruthenium-based catalyst according to claim 1 or 2, characterized in that, The metal salt is ammonium niobate oxalate hydrate or sodium chromate; the hard template is sodium chloride or potassium chloride particles.

9. A ruthenium-based catalyst, characterized in that, A ruthenium-based catalyst prepared by the method according to any one of claims 1 - 8.

10. The application of the ruthenium-based catalyst according to claim 9 in electrolyzing seawater.

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