Preparation method of micro-nano hierarchical structure ruthenium dioxide self-assembled hollow spheres

Abstract

The application discloses a preparation method of micro-nano hierarchical structure ruthenium dioxide self-assembled hollow spheres, which comprises the following steps: dissolving a soluble ruthenium salt in water, adding the soluble ruthenium salt into a water solution in which a sulfonic acid type surfactant is dissolved, stirring uniformly, carrying out a hydrothermal reaction, centrifuging, drying and calcining at a certain temperature, and obtaining rutile RuO2 self-assembled hollow sphere structures with uniform size and controllable morphology. The application has the advantages that raw materials are easy to obtain, the synthesis process is environment-friendly (water is used as a solvent), the process is simple, the product morphology is controllable, the hollow sphere structure has an electrolyte accessible inner and outer surface, and the stability of the micro-nano three-dimensional building structure, and can be used in the fields of catalysis, electrochemical energy storage, sensing and the like.

Description

Technical Field

[0001] This invention relates to a method for preparing self-assembled hollow spheres of ruthenium dioxide with a micro / nano hierarchical structure; it belongs to the field of material micro / nano structure control technology. Background Technology

[0002] RuO2 materials exist in both crystalline and amorphous structures. Due to their high cost, they are currently mainly used in important fields such as military and aerospace. RuO2 possesses excellent electrical conductivity and pseudocapacitive properties, making it a promising candidate for energy storage. RuO2 is the best oxygen evolution electrocatalyst among acidic electrolytes and can be used in industrial hydrogen production technologies (electrolysis of water) and regenerative fuel cells. RuO2 exhibiting small size effects or modified forms also demonstrates excellent catalytic activity in ethanol oxidation, hydrogen evolution reaction, and electrochemical ammonia synthesis (nitrogen reduction to ammonia).

[0003] Current research on RuO2 materials focuses on two aspects: First, designing novel structures to give RuO2 both micron and nanoscale characteristics, such as small size effect and 3D structural stability, thereby improving the utilization efficiency of active sites and electrochemical stability, and to some extent reducing the amount of precious metal materials used, thus saving costs. Second, combining RuO2 with other materials to combine the advantages of both and provide composite materials with better overall performance. For example, patent "CN 104909352B" provides a method for preparing ruthenium-based composite hollow oxide, but it involves using reduced metal particles as seeds to form a hollow structure, making the preparation process relatively complex. Traditionally, hard template methods are used to construct hollow microstructures, but the template removal process may damage the hollow structure, making it difficult to obtain an ideal hollow structure.

[0004] In fields such as electrocatalysis and energy storage, the performance of materials is closely related to their microstructure, grain size, crystallinity, and pore structure. Existing methods for preparing crystalline RuO2 often involve annealing in an open oxygen source. Prolonged annealing or excessively high temperatures can cause significant grain growth, leading to the loss of the electrocatalytic and electrochemical activity inherent in the material at the micro- and nano-scale. The method proposed in this invention combines a hydrothermal process and employs a sulfonic acid-based surfactant to regulate the morphology of RuO2. After high-temperature calcination, RuO2 retains its micro- and nano-scale characteristics, and its hierarchical self-assembled structure is beneficial for improving the long-term electrochemical stability of the material during application. Furthermore, compared to the precipitation method used in conventional RuO2 production, the hydrothermal method reduces the use of large amounts of alkali solution.

[0005] In summary, no existing methods have been reported on combining sulfonic acid surfactants with hydrothermal synthesis techniques to regulate the RuO2 crystal structure and form micro / nano hierarchical hollow sphere structures. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention is the first to employ hydrothermal synthesis. By controlling the concentrations of sulfonic acid surfactants and ruthenium salts, as well as the hydrothermal synthesis conditions, ruthenium dioxide self-assembled hollow spheres with micro-nano hierarchical hollow sphere structures are obtained without the participation of organic solvents.

[0007] RuO2 typically operates in acidic electrolytes, and for both electrocatalysis and energy storage applications, the electrochemical stability of its structure and its high efficiency are two crucial metrics. The product of this invention possesses a micro-nano hierarchical 3D structure, providing a framework for long-term stable operation. Furthermore, the hollow spheres have internal and external surfaces accessible to the electrolyte, enhancing the efficiency of the active material.

[0008] The preparation process of the RuO2 micro / nano structure of this invention is relatively simple, does not require the participation of organic solvents in the reaction, is environmentally friendly, and produces a unique product structure.

[0009] This invention discloses a method for preparing self-assembled hollow spheres of ruthenium dioxide with a micro / nano hierarchical structure, comprising the following steps:

[0010] (1) Dissolve the sulfonic acid surfactant in water and stir evenly to obtain solution A; the concentration of the sulfonic acid surfactant in solution A is 0.1 x 10⁻⁶. -5 ~1x10 -4 mol / L;

[0011] (2) Dissolve ruthenium salt in water and stir evenly to obtain solution B; the concentration of ruthenium in solution B is 0.1-1 mol / L;

[0012] (3) Take an appropriate amount of solution B and add it to solution A. After stirring evenly, transfer the mixture into a hydrothermal reactor and perform a hydrothermal reaction for a period of time. The temperature of the hydrothermal reaction is 80-250℃ and the reaction time is 2-30h.

[0013] (4) After centrifuging and washing the sample obtained from the hydrothermal reaction, it was calcined to obtain a uniform and controllable RuO2 self-assembled hollow sphere structure.

[0014] This invention uses water as a solvent, making the preparation process relatively environmentally friendly, as it eliminates the need for toxic organic solvents in the reaction environment. The introduction of an appropriate concentration of sulfonic acid-based surfactant can regulate the microstructure of the synthesized RuO2 material and inhibit grain merging and growth during calcination, resulting in a self-assembled hollow sphere structure with micro- and nano-sized characteristics.

[0015] In step (1) above, the sulfonic acid surfactant is at least one of partially sulfonated polystyrene, benzenesulfonic acid formaldehyde condensate, naphthalenesulfonic acid formaldehyde condensate, sulfonated polybutadiene, polyacrylic acid propylene ester sulfonate, lignin sulfonate, and polystyrene sulfonate. The polystyrene sulfonate is preferably sodium polystyrene sulfonate.

[0016] Furthermore, in step (1) above, the sulfonic acid surfactant, typically an anionic polymeric surfactant, has an aqueous solution concentration of 0.1 x 10⁻⁶. -5 ~1x10 -4 mol / L. Preferably 0.5 x 10⁻⁶ mol / L. -5 ~8x10 -5 mol / L.

[0017] To obtain self-assembled RuO2 hollow spheres with a particle size of 150 nm to 800 nm, the concentration of the sulfonic acid surfactant needs to be controlled at 1 x 10⁻⁶. -5 ~5x10 -5 mol / L.

[0018] Meanwhile, when the concentration of the sulfonic acid surfactant is 2.8 x 10⁻⁶ -5 ~5x10 -5 At mol / L, the constituent units of the self-assembled RuO2 hollow spheres have nanoscale characteristics, with a particle size of 10–30 nm.

[0019] Furthermore, in step (2) above, the soluble ruthenium salt is hydrated ruthenium chloride.

[0020] Furthermore, in step (2) above, the concentration of the ruthenium salt aqueous solution is 0.1 to 1 mol / L.

[0021] To obtain self-assembled RuO2 hollow spheres with a particle size of 150 nm to 800 nm, the concentration of ruthenium in the ruthenium solution needs to be controlled at 0.2 to 0.3 mol / L.

[0022] Furthermore, in step (3) above, the temperature of the hydrothermal reaction is 80–250°C, preferably 100–200°C. Excessively high hydrothermal temperatures will result in uneven product particle size, while excessively low temperatures will lead to adverse effects such as low sphericity and low sphericity.

[0023] Furthermore, in step (3) above, the hydrothermal reaction time is 2 to 20 hours, preferably 15 to 18 hours. Too long a hydrothermal time will result in uneven particle size of the product, while too short a time will prevent the formation of a stable spherical structure.

[0024] Furthermore, in step (4) above, the heating rate of the calcination treatment is 5-10℃ / min, from room temperature to 300-800℃. Excessive calcination temperature will cause sphere breakage and a decrease in active surface area, while excessively low temperature will result in high impurity content in the product.

[0025] Furthermore, in step (4) above, the heat preservation time of the calcination treatment is 0.5 to 2 hours.

[0026] Furthermore, in step (4) above, the calcination temperature is preferably 600-800℃ and the time is 1-2h.

[0027] According to the above method, the product obtained is a rutile phase RuO2 self-assembled hollow sphere with a diameter of 0.5 to 5 μm. Its structural unit is a granular structure with adjustable size, and the size of the granular structure is 10 to 50 nm.

[0028] When the concentration of sodium polystyrene sulfonate in solution A is 4.2–4.3 x 10⁻⁶ -5 In solution B, the concentration of ruthenium is 0.19–0.21 mol / L, the hydrothermal reaction temperature is 175–185 °C, and the hydrothermal reaction time is 14–16 h. After the hydrothermal reaction, the product is washed, centrifuged, and calcined at 595–605 °C for 110–130 min to obtain self-assembled RuO2 hollow spheres with a diameter of about 200–300 nm. The constituent units of the self-assembled RuO2 hollow spheres have nanoscale characteristics, about 10–20 nm.

[0029] When the concentration of sodium polystyrene sulfonate in solution A is 2.8–2.9 x 10⁻⁶ -5 In solution B, the concentration of ruthenium is 0.19–0.21 mol / L, the hydrothermal reaction temperature is 195–205 °C, and the hydrothermal reaction time is 15–17 h. After the hydrothermal reaction, the product is washed, centrifuged, and calcined at 795–805 °C for 50–65 min to obtain self-assembled RuO2 hollow spheres with a diameter of approximately 720–780 nm. The constituent units of the self-assembled RuO2 hollow spheres have nanoscale characteristics, approximately 18–32 nm.

[0030] This invention precipitates the product through a hydrothermal reaction, eliminating the need for an alkaline solution. The addition of a sulfonic acid surfactant provides a soft template for the self-assembly of RuO2 hollow spheres. Specifically, after the sulfonic acid surfactant adsorbs to saturation on the solution surface, it forms stable micelles within the solution, associated with molecular or ionic dispersions. Due to electrostatic interactions, the "micelle-water" interface adsorbs a large amount of ruthenium cations (Ru3+), forming a metastable structure. Under the action of the hydrothermal reaction, the metastable structure transforms into a stable structure. In the subsequent calcination process, the nonpolar hydrocarbon chains forming the micelle centers are carbonized and oxidized, forming a hollow structure. The RuO2 grains merge and grow according to the Oswald mechanism, forming the walls of the hollow spheres. Under the regulation of the sulfonic acid surfactant, even after high-temperature calcination (300–800℃), the grain size of rutile RuO2 remains at the nanoscale, forming a self-assembled structure with micro-nano hierarchical characteristics.

[0031] This invention utilizes a hydrothermal method to first prepare a stable precursor structure by controlling the ratio of sulfonic acid surfactant and ruthenium salt. Then, the structure-directing agent (sulfonic acid surfactant) is removed through washing and calcination, resulting in uniformly sized self-assembled microspheres. The method is simple, and the product morphology is unique and controllable, facilitating large-scale production and possessing potential application value in high-efficiency catalysis and electrochemical energy storage. Attached Figure Description

[0032] Figure 1 SEM image of RuO2 synthesized in Example 1 of this invention.

[0033] Figure 2 SEM image of RuO2 synthesized in Example 2 of this invention.

[0034] Figure 3 TEM image of RuO2 synthesized in Example 2 of this invention.

[0035] Figure 4 TEM image of RuO2 synthesized in Example 3 of this invention.

[0036] Figure 5 TEM image of RuO2 synthesized in Example 4 of this invention.

[0037] Figure 6 HRTEM image of the surface of the self-assembled RuO2 hollow spheres synthesized in Example 4 of this invention.

[0038] Figure 7 SEM image of RuO2 synthesized in Comparative Example 1

[0039] Figure 8 SEM image of RuO2 synthesized in Comparative Example 2 Detailed Implementation

[0040] The present invention will be further illustrated by the following embodiments. The following description is for the purpose of explaining the present invention and does not limit its content.

[0041] Example 1

[0042] Dissolve 0.25g of sodium polystyrene sulfonate powder (average molecular weight: 70000) in 300ml of water (1.19x10⁻⁶). -5 Add 50 ml of sodium polystyrene sulfonate aqueous solution to a beaker, then add 3 g of RuCl3 aqueous solution (0.15 mol / L). Transfer the solution to a hydrothermal reactor and maintain at 250 °C for 25 h. Wash and centrifuge the sample. Observe the surface morphology of the product using scanning electron microscopy. Figure 1 As shown.

[0043] Depend on Figure 1It can be seen that if no calcination treatment is performed, the spherical surface is very smooth and no fine grain structure appears. The diameter of the spheres is about 0.5 to 5 μm. This indicates that the hydrothermal temperature is too high or the hydrothermal time is too long. Due to the influence of Oswald ripening, the diameter of the product spheres is not uniform.

[0044] Example 2

[0045] Dissolve 0.2g of sodium polystyrene sulfonate powder in 200ml of water (1.43x10). -5 Add 60 ml of sodium polystyrene sulfonate aqueous solution to a beaker, then add 2 g of RuCl3 aqueous solution (0.2 mol / L). Transfer the solution to a hydrothermal reactor and maintain at 100 °C for 18 h. Wash and centrifuge the sample. Observe the surface morphology of the product using scanning electron microscopy. Figure 2 As shown. The surface morphology of the product was observed using transmission electron microscopy, as follows. Figure 3 As shown.

[0046] Depend on Figure 2 and Figure 3 It can be seen that without calcination, the spherical surface is very smooth, without fine grain structure, and... Figure 1 The SEM description is consistent. Under these reaction conditions, the diameter of the stable precursor spheres is approximately 200–300 nm.

[0047] contrast Figure 1 and Figure 2 It is known that adjusting the ratio of sulfonic acid surfactants and ruthenium salts, as well as the hydrothermal reaction conditions, can change the diameter of the stable precursor RuO2 spheres.

[0048] Example 3

[0049] Dissolve 0.3g of sodium polystyrene sulfonate powder in 100ml of water (4.29x10). -5 Take 70 ml of sodium polystyrene sulfonate aqueous solution and add it to a beaker. Add 3 g of RuCl3 aqueous solution (0.2 mol / L), transfer to a hydrothermal reactor, and maintain at 180℃ for 15 h. Wash the sample, centrifuge, and calcine (600℃, 2 h). Observe the surface morphology of the product using transmission electron microscopy, such as... Figure 4 As shown.

[0050] Depend on Figure 4 It is known that the diameter of the self-assembled RuO2 hollow sphere structure is about 200-300 nm (the constituent units of the self-assembled RuO2 hollow sphere have nanoscale characteristics, about 10-20 nm). It has a rough surface composed of nanoparticles, which increases the specific area. The pores between the particles facilitate the entry of electrolytes and can enhance the catalytic and energy storage activities of the material.

[0051] Example 4

[0052] Dissolve 0.2g of sodium polystyrene sulfonate powder in 100ml of water (2.86x10). -5 Add 50 ml of sodium polystyrene sulfonate aqueous solution to a beaker, then add 2 g of RuCl3 aqueous solution (0.2 mol / L). Transfer the solution to a hydrothermal reactor and maintain at 200℃ for 16 h. Wash and centrifuge the sample, then calcine it (800℃, 1 h). Observe the surface morphology of the product using transmission electron microscopy, such as... Figure 5 As shown, the edges of the structure are magnified for observation, such as... Figure 6 As shown.

[0053] Depend on Figure 5 It is known that the diameter of the self-assembled RuO2 hollow sphere structure is approximately 750 nm.

[0054] Depend on Figure 6 It is known that the constituent units of the self-assembled RuO2 hollow spheres have nanoscale characteristics, approximately 20–30 nm.

[0055] contrast Figure 4 and Figure 5 It is known that adjusting the ratio of sulfonic acid surfactants and ruthenium salts, as well as the time and temperature of hydrothermal reaction and calcination, can alter the dimensional characteristics of the self-assembled hollow sphere structure.

[0056] Comparative Example 1

[0057] Add 60 ml of deionized water and 10 g (0.1 mol / L) of RuCl3 aqueous solution to a beaker, stir well, and then transfer to a hydrothermal reactor. Maintain the temperature at 200 °C for 15 h. Wash and centrifuge the sample. Observe the surface morphology of the product using a scanning electron microscope, such as... Figure 7 As shown.

[0058] Depend on Figure 7 It can be seen that without sulfonic acid surfactants as structure directing agents, the resulting products have irregular shapes, smooth and compact particle surfaces, and lack porous structures.

[0059] Comparative Example 2

[0060] All other conditions were the same as in Example 4, except for the concentration of the sodium polystyrene sulfonate aqueous solution prepared. 2.06 g of sodium polystyrene sulfonate powder was dissolved in 100 ml of water (2.94 x 10⁻⁶ g / ml). -4 50 ml of sodium polystyrene sulfonate aqueous solution was added to a beaker, followed by 2 g of RuCl3 aqueous solution (0.2 mol / L). The mixture was then transferred to a hydrothermal reactor and kept at 200 °C for 16 h. The product was gel-like. Scanning electron microscopy revealed the following morphology: Figure 8 As shown, the structure is a mixture of spherical and plate-like structures, indicating that excessively high concentrations of sulfonic acid surfactants affect the yield of spherical products.

Claims

1. A method for preparing self-assembled hollow spheres of ruthenium dioxide with a micro / nano hierarchical structure, characterized in that: Dissolve 0.3g of sodium polystyrene sulfonate powder in 100ml of water according to the ratio. Take out 70ml of sodium polystyrene sulfonate aqueous solution and add it to a beaker. Add 3g of 0.2mol / L RuCl3 aqueous solution and transfer it to a hydrothermal reactor. Maintain the temperature at 180℃ for 15h. Wash the sample, centrifuge it, and calcine it at 600℃ for 2h.

2. A method for preparing self-assembled hollow spheres of ruthenium dioxide with micro / nano hierarchical structure, characterized in that: Dissolve 0.2g of sodium polystyrene sulfonate powder in 100ml of water according to the ratio. Take out 50ml of sodium polystyrene sulfonate aqueous solution and add it to a beaker. Add 2g of 0.2mol / L RuCl3 aqueous solution and transfer it to a hydrothermal reactor. Maintain the temperature at 200℃ for 16h. Wash the sample, centrifuge it, and calcine it at 800℃ for 1h.

Images