A ruthenium-based catalyst, its preparation method and use

Abstract

The present application relates to the technical field of electrocatalytic water splitting, in particular to a ruthenium-based catalyst and a preparation method and application thereof. The present application provides a ruthenium-based catalyst, which comprises a core and a shell covering the core, the material of the core comprises metallic ruthenium, and the material of the shell comprises ruthenium oxide. In the core-shell structure obtained by the present application, the RuO2 shell layer and the metal core present a preferred orientation and expose a specific crystal face (101). When used as an anode catalyst for proton exchange membrane water electrolysis, the ruthenium-based catalyst has more reaction sites, high catalytic activity and strong stability.

Description

Technical Field

[0001] This invention relates to the field of electrocatalytic water splitting technology, specifically to a ruthenium-based catalyst, its preparation method, and its application. Background Technology

[0002] Ruthenium-based catalysts, as acidic water oxidation catalysts, are excellent electrocatalysts due to their lower cost, larger reserves, and better activity compared to yttrium oxide. Core-shell structured nanocatalysts can effectively increase the reactive sites of the catalyst, reduce the reaction potential, and thus extend the lifespan of ruthenium-based catalysts. Conventional synthesis methods for ruthenium-based core-shell structured nanocatalysts require the use of surfactants, sodium borohydride reducing agents or template agents, organic solvents, etc., resulting in high preparation costs, complex processes, and the generation of large amounts of organic wastewater. Existing technologies for preparing ruthenium-based core-shell structured nanocatalysts include preparing ruthenium-based alloys through co-reduction, followed by purification and separation and then calcination to obtain the core-shell structure; or using template-etching methods to control the core-shell thickness; or using surfactants to construct the core-shell structure. However, these methods still have the problem of introducing and removing impurities (such as carbon), making it difficult to efficiently obtain the ideal core-shell structure. Furthermore, template etching and post-processing increase the complexity of the reaction, and the use of surfactants poses a risk of industrial wastewater discharge. Furthermore, the stability of ruthenium-based core-shell catalysts obtained through these methods has not seen a significant breakthrough, and their service life needs further improvement. Summary of the Invention

[0003] Therefore, the technical problem to be solved by the present invention is to overcome the deficiency of insufficient stability of ruthenium-based catalysts in the prior art, thereby providing a ruthenium-based catalyst, its preparation method and application.

[0004] In a first aspect, the present invention provides a ruthenium-based catalyst comprising a core and a shell covering the core, wherein the core is made of metallic ruthenium and the shell is made of ruthenium oxide.

[0005] In one alternative embodiment, the shell further comprises a first doped metal; The first doped metal includes at least one of nickel, cobalt, manganese, iron, and chromium; In one alternative embodiment, the shell further comprises a second doped metal; In one alternative embodiment, the second doped metal includes at least one of nickel, cobalt, manganese, iron, and chromium; In one alternative embodiment, the ruthenium oxide comprises ruthenium dioxide.

[0006] Secondly, the present invention provides a method for preparing a ruthenium-based catalyst, comprising the following steps: heating an aqueous solution containing ruthenium salt to 150-200 °C within 3-5 min and holding it at that temperature, followed by a first cooling, a second cooling to room temperature, and filtration to obtain an intermediate; The intermediate is calcined to obtain the ruthenium-based catalyst. The first cooling includes the step of cooling to a first temperature at a rate of 25-50℃ / min; The first temperature is 90~100℃; The second cooling process includes the process of cooling from the first temperature to room temperature; The second cooling method has no requirement for the cooling rate; it can cool naturally to room temperature or cool down to room temperature at the rate of the first cooling method. The aqueous solution containing ruthenium salt also contains alkali metal chloride salts and / or alkaline earth metal chloride salts; In one optional embodiment, the alkali metal chloride salt includes at least one of sodium chloride and potassium chloride; In one alternative embodiment, the alkaline earth metal chloride salt includes magnesium chloride; In one optional embodiment, the concentration of ruthenium salt in the aqueous solution containing ruthenium salt is 1 wt%-10 wt%; In one alternative embodiment, the ruthenium salt is selected from ruthenium chloride trihydrate; In one optional embodiment, the concentration of alkali metal chloride or alkaline earth metal chloride in the aqueous solution containing ruthenium salt is 1 wt%-10 wt%.

[0007] In some embodiments of the present invention, the aqueous solution containing ruthenium salt further includes a doped metal salt; In one optional embodiment, the mass ratio of the doped metal salt to the ruthenium salt in the aqueous solution containing ruthenium salt is (0.01-0.2):1; In one optional embodiment, the doped metal salt is at least one selected from nickel salt, cobalt salt, manganese salt, iron salt, and chromium salt; In one alternative embodiment, the doped metal salt is at least one of nickel chloride, cobalt chloride, manganese nitrate, ferric nitrate, and chromium nitrate.

[0008] In one alternative implementation, the insulation process is carried out at 70-200 psi.

[0009] In one alternative implementation, the heating is performed by microwave heating.

[0010] In one optional implementation, the process further includes washing and drying the intermediate. The washing process involves multiple rinses with water and ethanol, respectively. In one optional embodiment, the calcination step includes: heating to 220-350 °C at a heating rate of 4-7 °C / min and holding at that temperature for 2-4 h.

[0011] In an optional embodiment, the method further includes adding the substrate to an aqueous solution containing ruthenium salt. The type of substrate is not specifically limited in this invention, as long as it does not affect the heating method. Examples include glass substrates such as ATO, ITO, and FTO; carbon materials such as carbon cloth, carbon fiber paper, graphene, and graphylene; and titanium-based materials such as titanium mesh, titanium felt, and titanium plates.

[0012] Thirdly, the present invention provides an application of the above-mentioned ruthenium-based catalyst or the ruthenium-based catalyst prepared by the above preparation method in the electrocatalytic splitting of water.

[0013] The technical solution of this invention has the following advantages: 1. The ruthenium-based catalyst provided by the present invention comprises a core and a shell covering the core, wherein the core is made of metallic ruthenium and the shell is made of ruthenium oxide.

[0014] The core-shell structure obtained in this invention exhibits a preferred orientation between the RuO2 shell and the metal core, and exposes a specific crystal plane (101). When used as an anode catalyst for proton exchange membrane water electrolysis, it has more reaction sites, higher catalytic activity, and stronger stability.

[0015] 2. The method for preparing ruthenium-based core-shell nanocatalysts provided by this invention increases the nucleation probability of metallic ruthenium by adjusting the concentration of chloride ions in the mixed salt solution, thereby obtaining a nanocatalyst with a core-shell structure. The catalyst preparation process does not require the addition of surfactants, redox agents, acids, bases, templates, or other auxiliaries, simplifying the catalyst preparation method. Furthermore, the ruthenium-based core-shell nanocatalysts prepared by the method described in this invention have a ruthenium-based metal core and a ruthenium-based oxide shell, with the oxide uniformly dispersed on the surface of the metal core. When used as an anode catalyst for proton exchange membrane water electrolysis, it has more reaction sites, higher catalytic activity, and stronger stability.

[0016] 3. The present invention provides a method for preparing a ruthenium-based catalyst, preferably using microwave heating with simultaneous stirring, which helps to increase the nucleation rate. Controlling the rotation speed during separation can prevent irreversible agglomeration of nanoparticles. Doping with metal salts during catalyst preparation helps to further enhance the catalyst's activity. Attached Figure Description

[0017] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the preparation method proposed in this invention; Figure 2 These are stability test graphs of Example 1 and Comparative Example 1 of the present invention, as well as two commercially available ruthenium dioxide catalysts; Figure 3 This is a transmission electron microscope image of the catalyst prepared in Example 1 of the present invention; Figure 4 This is a transmission electron microscopy (TEM) energy dispersive spectroscopy (EDS) spectrum of the catalyst prepared in Example 1 of this invention; Figure 5 This is a transmission electron microscope (TEM) characterization image of the catalyst prepared in Example 1 of the present invention; Figure 6 This is the XRD pattern of the catalyst prepared in Example 1 of this invention. Detailed Implementation

[0019] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0020] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0021] Example 1 This embodiment provides a method for preparing a ruthenium-based catalyst, as shown in the schematic diagram. Figure 1 As shown, it includes the following steps: 13 mL of an aqueous solution of 1.5 wt% ruthenium chloride trihydrate (containing 6.7 wt% sodium chloride) was stirred at 600 rpm. Simultaneously, the aqueous solution was heated to 160 °C over 3.2 min using microwave heating and held at that temperature for 10 min. The pressure during the holding period was controlled at approximately 90 psi. After the holding period, the temperature was reduced to 90 °C at a rate of 45 °C / min and then allowed to cool naturally to room temperature to obtain a ruthenium-based precursor suspension.

[0022] The ruthenium-based precursor suspension was then centrifuged to separate solids and liquids (centrifugation speed was 13000 rpm). The solids obtained from the solid-liquid separation were washed with deionized water and ethanol by centrifugation and ultrasonication, and then dried in a vacuum oven to obtain a black powder. The black powder was transferred to a magnetic boat and heated to 300°C at a heating rate of 5°C / min in air atmosphere, and then calcined for 4 hours. After the heating was completed, the furnace was naturally cooled to obtain the ruthenium-based catalyst.

[0023] The stability of the prepared catalyst was tested according to the stability test method described in the following experimental examples, at 500 mA / cm. 2 The tank pressure is 1.51 V, and it can operate stably for over 230 hours.

[0024] Example 2 This embodiment provides a method for preparing a ruthenium-based catalyst, including the following steps: 13 mL of an aqueous solution of 1.5 wt% ruthenium chloride trihydrate (with magnesium chloride concentration of 6.7 wt%) was stirred at 900 rpm. Simultaneously, the aqueous solution was heated to 160 °C over 3.2 min using microwave heating and held at that temperature for 10 min. The pressure during the holding period was controlled at approximately 90 psi. After the holding period, the temperature was reduced to 90 °C at a rate of 45 °C / min and then allowed to cool naturally to room temperature to obtain a ruthenium-based precursor suspension.

[0025] The ruthenium-based precursor suspension was then centrifuged at 13,000 rpm to separate solids and liquids. The solids obtained from the solid-liquid separation were washed with deionized water and ethanol by centrifugation and ultrasonication, and then dried in a vacuum oven to obtain a black powder.

[0026] The black powder was transferred to a magnetic boat and heated to 300°C at a heating rate of 5°C / min in air atmosphere, and then calcined for 4 hours. After the heating was completed, the furnace was naturally cooled to obtain the ruthenium-based catalyst.

[0027] Example 3 This embodiment provides a method for preparing a ruthenium-based catalyst, including the following steps: 13 mL of an aqueous solution of 1.0 wt% ruthenium chloride trihydrate (containing 9 wt% potassium chloride) was stirred at 600 rpm. Simultaneously, the aqueous solution was heated to 150 °C over 3.2 min using microwave heating and held at that temperature for 10 min. The pressure during the holding period was controlled at approximately 90 psi. After the holding period, the temperature was reduced to 90 °C at a rate of 45 °C / min and then allowed to cool naturally to room temperature to obtain a ruthenium-based precursor suspension.

[0028] The ruthenium-based precursor suspension was then centrifuged at 13,000 rpm to separate solids and liquids. The solids obtained from the solid-liquid separation were washed with deionized water and ethanol by centrifugation and ultrasonication, and then dried in a vacuum oven to obtain a black powder.

[0029] The black powder was transferred to a magnetic boat and heated to 250°C at a heating rate of 5°C / min in air atmosphere, and then calcined for 4 hours. After the heating was completed, the furnace was naturally cooled to obtain the ruthenium-based catalyst.

[0030] Example 4 This embodiment provides a method for preparing a ruthenium-based catalyst, including the following steps: 13 mL of an aqueous solution of 1.0 wt% ruthenium chloride trihydrate (in which the concentration of sodium chloride in the aqueous solution is 9 wt%) was stirred at a speed of 900 rpm. Simultaneously, the aqueous solution was heated to 200 °C in 3.8 min by microwave heating and held at that temperature for 10 min. The pressure during the holding period was controlled at approximately 90 psi. After the holding period, the temperature was reduced to 90 °C at a rate of 45 °C / min and then allowed to cool naturally to room temperature to obtain a ruthenium-based precursor suspension.

[0031] The ruthenium-based precursor suspension was then centrifuged at 13,000 rpm to separate solids and liquids. The solids obtained from the solid-liquid separation were washed with deionized water and ethanol by centrifugation and ultrasonication, and then dried in a vacuum oven to obtain a black powder.

[0032] The black powder was transferred to a magnetic boat and heated to 350°C at a heating rate of 5°C / min in air atmosphere, and then calcined for 2 hours. After the heating was completed, the furnace was naturally cooled to obtain the ruthenium-based catalyst.

[0033] Comparative Example 1 This comparative example provides a method for preparing a catalyst, which differs from Example 1 in that the aqueous solution does not contain sodium chloride salt, but is otherwise the same as Example 1.

[0034] The stability of the prepared catalyst was tested according to the stability test method described in the following experimental examples, at 500 mA / cm. 2 The power-off stability does not exceed 100 hours of operation.

[0035] Experimental Example 1 This experimental example provides the performance tests and results of the ruthenium-based catalysts provided in the examples and comparative examples, as follows: 1. Stability testing method: The prepared catalyst was dispersed in a solvent of water and isopropanol in a volume ratio of 1:5, and 12% (by mass) of Nafion 117 (20% concentration) solution was added as a binder to bring the total solid content of the solution to 1.2%. The prepared dispersion was sonicated in an ice-water bath for 2 hours to obtain the anode catalyst dispersion. A cathode catalyst dispersion was prepared using the same method with 75% Pt / C. Both dispersions were sprayed onto both sides of a Nafion 115 membrane and hot-pressed at 400 kg and 60 °C for 3 min to form a membrane electrode, wherein the anode catalyst loading was 2 mg·cm³. -2 The cathode catalyst loading is 0.4 mg·cm³. -2 After assembling the membrane electrode into a proton exchange membrane water electrolysis device, the electrolysis rate was 30 mL / min. -1 Ultrapure water is introduced into it at a flow rate of 60°C, and the overall temperature of the control device is maintained at 500 mA·cm⁻¹. -2 The current density was measured to test its stability.

[0036] Following the test methods described above, the catalysts prepared in Example 1 and Comparative Example 1, as well as two commercially available ruthenium dioxide catalysts, were used as anode catalysts during proton exchange membrane water electrolysis. The stability of each catalyst was tested, and the results are as follows: Figure 2 As shown.

[0037] Depend on Figure 2 It can be seen that the catalyst prepared in Example 1 has a much better stability than the catalyst prepared in Comparative Example 1. This is because the addition of sodium chloride to the mixed aqueous solution in Example 1 changed the concentration of chloride ions, increased the nucleation probability of ruthenium metal, and made it easier for nanoparticles to form a core-shell structure.

[0038] 2. Transmission electron microscopy (TEM) testing The morphology and elemental composition of the ruthenium-based core-shell nanocatalyst prepared in Example 1 were characterized using transmission electron microscopy. The morphology characterization results are as follows: Figure 3 As shown. Figure 4 This is a transmission electron microscopy (TEM) energy dispersive spectroscopy (EDS) image of a ruthenium-based core-shell nanocatalyst. Green represents the ruthenium signal, and blue represents the oxygen signal. Figure 4 It can be seen that the catalyst prepared in Example 1 has a distinct core-shell structure. Figure 5 Figure a shows the morphology of the ruthenium-based core-shell nanocatalyst. Figure 5 In the diagram, b represents the diffraction pattern at position 1. Figure 5 In the diagram, c represents the diffraction pattern at position 2. Figure 5 In the diagram, d and e represent the crystal structure model of the catalyst. Figure 5 f is the transmission electron microscopy (TEM) energy dispersive spectroscopy (EDS) spectrum of the ruthenium-based core-shell catalyst. Figure 5 In the image, g represents the energy spectrum of oxygen. Figure 5 In the diagram, h represents the energy spectrum of ruthenium. From... Figure 5 As can be seen from b and c, the ruthenium-based catalyst with a core-shell structure obtained in this invention exhibits a preferred orientation between the shell and the metal core, and exposes a specific crystal plane (101).

[0039] 3. X-ray diffraction test X-ray diffraction tests were performed on the catalyst prepared in Example 1 of this invention, and the results are as follows: Figure 6 As shown.

[0040] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A ruthenium-based catalyst, characterized in that, The ruthenium-based catalyst comprises a core and a shell covering the core, wherein the core is made of metallic ruthenium and the shell is made of ruthenium oxide.

2. The ruthenium-based catalyst according to claim 1, characterized in that, The shell also contains a first doped metal; The first doped metal includes at least one of nickel, cobalt, manganese, iron, and chromium; Preferably, the shell further comprises a second doped metal; Preferably, the second doped metal includes at least one selected from nickel, cobalt, manganese, iron, and chromium; Preferably, the ruthenium oxide comprises ruthenium dioxide.

3. A method for preparing a ruthenium-based catalyst, characterized in that, The process includes the following steps: heating an aqueous solution containing ruthenium salt to 150-200 °C within 3-5 minutes and holding it at that temperature, followed by a first cooling, a second cooling to room temperature, and then filtration to obtain an intermediate. The intermediate is calcined to obtain the ruthenium-based catalyst. The first cooling includes the step of cooling to a first temperature at a rate of 25-50℃ / min; The first temperature is 90~100℃; The second cooling process includes the process of cooling from the first temperature to room temperature; The aqueous solution containing ruthenium salt also contains alkali metal chloride salts and / or alkaline earth metal chloride salts; Preferably, the alkali metal chloride salt includes at least one of sodium chloride and potassium chloride; Preferably, the alkaline earth metal chloride salt includes magnesium chloride.

4. The preparation method according to claim 3, characterized in that, The concentration of ruthenium salt in the aqueous solution containing ruthenium salt is 1 wt%-10 wt%; Preferably, the ruthenium salt is selected from ruthenium chloride trihydrate; Preferably, the concentration of alkali metal chloride or alkaline earth metal chloride in the aqueous solution containing ruthenium salt is 1 wt%-10 wt%.

5. The preparation method according to any one of claims 3 or 4, characterized in that, The aqueous solution containing ruthenium salt also includes doped metal salts; Preferably, the mass ratio of the doped metal salt to the ruthenium salt in the aqueous solution containing ruthenium salt is (0.01-0.2):1; Preferably, the doped metal salt is at least one selected from nickel salt, cobalt salt, manganese salt, iron salt, and chromium salt; Preferably, the doped metal salt is at least one selected from nickel chloride, cobalt chloride, manganese nitrate, ferric nitrate, and chromium nitrate.

6. The preparation method according to any one of claims 3-5, characterized in that, The insulation process is carried out under conditions of 70-200 psi.

7. The preparation method according to any one of claims 3-6, characterized in that, The heating is performed using microwave heating.

8. The preparation method according to any one of claims 3-7, characterized in that, The calcination step includes: heating to 220-350 ℃ at a heating rate of 4-7 ℃ / min, and holding at that temperature for 2-4 h.

9. The preparation method according to any one of claims 3-7, characterized in that, The aqueous solution containing ruthenium salt also includes a substrate.

10. The application of a ruthenium-based catalyst according to any one of claims 1-2 or a ruthenium-based catalyst prepared by any one of claims 3-9 in the electrocatalytic splitting of water.

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