Core-shell structure metal aerogel with high porosity and preparation method thereof

Abstract

The invention belongs to the field of nano material preparation and catalysis, and discloses core-shell structure metal aerogel with high porosity and a preparation method of the core-shell structure metal aerogel. The metal aerogel comprises the following components: a reducing agent, a Ru salt precursor and a ligand, in the metal aerogel, the molar ratio of the reducing agent to the Ru salt precursor to the ligand is (2-4): 1: 1. According to the method, the types of reactants and reaction conditions are systematically regulated and controlled, and the single-metal ruthenium (Ru) aerogel with the high specific surface area is synthesized through a one-pot method. Then, the proportion (Ru / RuO2) of core-shell components in the aerogel is accurately adjusted by regulating and controlling the heat treatment time and temperature in a muffle furnace, and then the metal aerogel with the high porosity and the Ru / RuO2 core-shell structure is successfully constructed. Experimental results show that the prepared material shows excellent electro-catalytic hydrogen evolution and oxygen evolution performance under the condition of full pH. The invention provides a new strategy for designing the metal aerogel electrocatalyst with the core-shell structure.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of nanomaterial preparation and catalysis, and particularly relates to a core-shell structure metal aerogel with high porosity and a preparation method thereof BACKGROUND

[0002] Under the background of continuous growth of energy demand and increasingly serious environmental problems, hydrogen energy has been regarded as an important strategic direction for realizing sustainable development due to its high energy density, environmental friendliness, and utilization efficiency. Among many hydrogen production technologies, the water electrolysis method driven by renewable energy has attracted much attention. Generally, the water electrolysis process includes two catalytic half-reactions: a cathode hydrogen evolution reaction (HER) and an anode oxygen evolution reaction (OER). Both of the two half-reactions have a high energy barrier, resulting in slow reaction kinetics, and therefore a catalyst is usually needed to reduce the overpotential. At present, Ru, Ir and Pt-based materials are considered to be commercial electrocatalysts, but they usually only exhibit excellent performance for one of OER or HER in a specific electrolyte. If a full water splitting system is constructed in the same medium, the overall efficiency is low. Therefore, it is of great significance to develop a catalyst with dual-function HER and OER electrocatalytic performance in a wide pH range.

[0003] CN 117414845 A core-shell or hollow structure metal aerogel and a preparation method thereof. The core-shell hollow structure is constructed by dynamic shell formation and replacement. The core layer uses non-noble metals such as Fe, Co, Ni and Cu, and the hydroxide or oxide gel structure of the core layer itself is unstable in air and is easily damaged by subsequent washing, solvent exchange or drying process. When the shell layer metal salt is introduced, the core layer acts as a "sacrificial template", and its structure dynamically changes during the etching process, which is difficult to accurately control, resulting in the formation of incomplete hollow structure due to the residual of part of the solid core.

[0004] In summary, the current preparation of core-shell or hollow structure metal aerogel has certain preparation technology in the field of nanomaterial preparation and catalysis, but there are still problems such as incomplete hollow structure, fragile shell layer and the like. Therefore, it is of great significance to develop a core-shell structure metal aerogel with stable structure, controllable process and complete characterization. SUMMARY

[0005] The purpose of the present application is to provide a core-shell structure metal aerogel with high porosity. The metal aerogel can not only inhibit excessive growth and prevent agglomeration by adsorbing ligands on the ruthenium crystal face to form a larger specific surface area, but also can be connected and attached directionally with ruthenium salt precursors to form a solid and continuous three-dimensional network, realize hierarchical pore structure, improve porosity, and ensure that the surface of the aerogel is rich in high-activity catalysts.

[0006] Another object of the present application is to provide a preparation method of a core-shell structure metal aerogel with high porosity. The method controls the nucleation and growth of ligands, guides the Ru to form a metal hydrogel, self-assembles to form a network structure, supercritical drying removes the solvent completely above the critical point, eliminates the capillary force that destroys the structure, converts the wet gel structure into an aerogel, and forms a surface-oxidized solid core-shell through controlled heat treatment, without consuming the inner core, to form a core-shell structure metal aerogel with stable structure and excellent performance.

[0007] The object of the present application is achieved by the following scheme: A core-shell structure metal aerogel with high porosity comprises the following components: a reducing agent, a Ru salt precursor, and a ligand; and the molar ratio of the reducing agent, the Ru salt precursor, and the ligand in the metal aerogel is (2-4): 1: 1.

[0008] The Ru salt precursor provides metal ruthenium elements, provides a high-speed electron conduction path for the subsequent formed three-dimensional network, and the Ru metal has good chemical stability and mechanical strength, and can build a stable aerogel skeleton; the reducing agent provides electrons, forcibly and quickly reduces the Ru ions to Ru atoms, and drives the nucleation process; the ligand is selectively adsorbed on the specific crystal face of Ru, inhibits the excessive growth of particles to prevent agglomeration, forms an open and connected three-dimensional network structure, creates high porosity and hierarchical pore structure of the material, and stabilizes the internal structure of the colloid.

[0009] Preferably, the Ru salt precursor is one or more of ruthenium chloride, ruthenium acetylacetone, or ruthenium nitrate.

[0010] Preferably, the concentration of the Ru salt precursor aqueous solution is 0.2-0.4M.

[0011] The binding ability of anions or organic ligands to Ru central ions determines the stability of the precursor and the reduction difficulty, Cl - can form stable coordination ions with Ru 3+ , is beneficial to the formation of smaller and more uniform nanoparticles, has a slower reduction rate, and is beneficial to the formation of a more ordered and more solid three-dimensional network system; NO3 - ligand is weaker, and the reducing agent is more likely to attack Ru 3+ , the reaction is rapid, and the gel can be quickly formed to improve the synthesis efficiency; acetylacetone is a strong chelating ligand, forms a stable neutral molecular complex with Ru center, significantly changes the van der Waals force and spatial repulsive force between nanoparticles, and forms a more solid three-dimensional network system.

[0012] Preferably, the reducing agent is one or more of sodium borohydride, sodium carbonate, or sodium hypophosphite.

[0013] Preferably, the concentration of the reducing agent aqueous solution is 0.6-1.2M.

[0014] Sodium borohydride has extremely strong reducing properties, providing hydride anions and enabling rapid, irreversible electron transfer of Ru ions. This can instantly generate a large number of crystal nuclei, consuming a large amount of precursors, resulting in fast gelation and the construction of aerogel frameworks with high specific surface area. Sodium carbonate creates an alkaline environment by regulating the pH of the reaction, under which the ruthenium precursor hydrolyzes, reducing its stability and making it easier to reduce. Sodium hypophosphite undergoes a relatively slow but controllable surface catalytic reaction, which is conducive to directional adhesion and can form more robust three-dimensional network nodes. Phosphates can cross-link particles, enhancing gel stability.

[0015] Preferably, the ligand is one or more of sodium deoxycholate, polyvinylpyrrolidone, 2-mercaptopropionic acid, or sodium citrate.

[0016] Preferably, the concentration of the ligand in the Ru salt aqueous solution is 0.2-0.4M.

[0017] The steric hindrance effect of ligands can cause their macromolecular chains to form a barrier around the particles, guiding the nanoparticle path. Sodium deoxycholate has hydrophilic carboxyl groups and hydrophobic steroid rings, which can guide the nucleation, growth and assembly of ruthenium nanoparticles at the surface or interface, optimizing the pore structure of the aerogel. Polyvinylpyrrolidone long molecular chain barrier effect stabilizes and effectively inhibits excessive particle growth, forming uniform nanoparticles. 2-Mercaptopropionic acid can form strong Ru-S covalent bonds, and its surface passivation effect can lock particle growth, enabling the preparation of stable colloids. Sodium citrate itself has weak reducing ability, which can participate in and regulate the reduction process. Multiple carboxyl groups can provide multi-level coordination, achieving colloidal stability through Coulomb repulsion.

[0018] A method for preparing a core-shell structured metal aerogel with high porosity includes the following steps: S1, freshly prepared reducing agent aqueous solution, Ru salt aqueous solution precursor and ligand are added to the reaction vessel. After reaction at room temperature, the solid and solution are separated to form Ru metal hydrogel. S2, the obtained Ru metal hydrogel was repeatedly washed with deionized water to remove the impurities remaining in the reaction process, and then supercritical drying was performed to obtain a high specific surface area Ru metal aerogel. S3. The pre-prepared Ru aerogel was heated in a tube furnace in an air atmosphere to obtain a metal aerogel sample with high porosity and a Ru / RuO2 core-shell structure.

[0019] Preferably, the heating temperature in step S3 is 250-550℃ and the heating time is 0.5-5h.

[0020] When ruthenium oxide is oxidized at low temperature for a short time, a thin core-shell structure with high specific surface area and excellent conductivity can be obtained. When ruthenium oxide is oxidized at low temperature for a long time, a shell of medium thickness is formed with more active sites and good stability. When ruthenium oxide is oxidized at high temperature for a short time, a crystalline thick shell can be formed, which enhances mechanical stability. When ruthenium oxide is oxidized at high temperature for a long time, a highly crystalline shell with high mechanical strength is obtained.

[0021] The present invention also provides an application of a core-shell structured metal aerogel with high porosity, which is applied in the field of electrocatalytic water splitting.

[0022] The beneficial effects of this invention are as follows: (1) Select appropriate types of Ru salt precursors, reducing agents and ligands, and systematically regulate reaction conditions to obtain metal Ru aerogels with high porosity and specific surface area, so as to provide active sites for catalytic reactions and effectively improve efficiency. (2) Metal aerogel materials with Ru / RuO2 core-shell structure were successfully prepared by taking advantage of the easy oxidation of metal Ru. Through the electronic interaction at the metal-oxide interface, the electronic structure of the active site was effectively regulated, the adsorption energy of the reaction intermediate was optimized, and the catalytic performance of water electrolysis was improved. Attached Figure Description

[0023] Figure 1 SEM images of Examples 3-4 and Comparative Examples 1-4.

[0024] Figure 2 XRD spectra of Examples 3-4 and Comparative Examples 1-4.

[0025] Figure 3 Examples 3-4 and Comparative Example 1: HER and OER linear polarization curves under different pH conditions.

[0026] Figure 4 Example 4, Comparative Examples 2-4: HER and OER linear polarization curves under different pH conditions.

[0027] Figure 5 Example 4: Linear polarization curves of total hydrolysis under acidic conditions.

[0028] Figure 6 Example 4: Linear polarization curves of total hydrolysis under alkaline conditions.

[0029] Figure 7 Example 4: Total hydrolysis it curve under acidic conditions.

[0030] Figure 8 Example 4: Total hydrolysis it curve under alkaline conditions. Detailed Implementation

[0031] Example 1: S1, 5 mL of freshly prepared NaBH4 aqueous solution (0.4 M) and 5 mL of RuCl3 aqueous solution precursor (0.1 M) were mixed and added to a 20 mL glass bottle. After reacting at room temperature for 5 h, the solid separated from the solution and Ru metal hydrogel was formed at the bottom of the bottle. S2, the obtained Ru metal hydrogel was repeatedly washed 5 times with deionized water to remove impurities remaining in the reaction process, and then supercritical drying was performed for 12 hours to obtain a high-porosity Ru metal aerogel.

[0032] Example 2: S1, 5 mL of freshly prepared NaBH4 aqueous solution (0.2 M) and 5 mL of RuCl3 aqueous solution precursor (0.1 M) were mixed and added to a 20 mL glass bottle, and then 0.5 mmol of sodium citrate was added. After reacting at room temperature for 5 h, the solid separated from the solution and Ru metal hydrogel was formed at the bottom of the bottle. S2, the obtained Ru metal hydrogel was repeatedly washed 5 times with deionized water to remove impurities remaining in the reaction process, and then supercritical drying was performed for 12 hours to obtain a high-porosity Ru metal aerogel.

[0033] Example 3: S1, 5 mL of freshly prepared NaBH4 aqueous solution (0.3 M) and 5 mL of RuCl3 aqueous solution precursor (0.1 M) were mixed and added to a 20 mL glass bottle, and then 0.5 mmol of sodium citrate was added. After reacting at room temperature for 5 h, the solid separated from the solution and Ru metal hydrogel was formed at the bottom of the bottle. S2, the obtained Ru metal hydrogel was repeatedly washed 5 times with deionized water to remove impurities remaining in the reaction process, and then supercritical drying was performed for 12 hours to obtain a high-porosity Ru metal aerogel.

[0034] Example 4: S1, 5 mL of freshly prepared NaBH4 aqueous solution (0.3 M) and 5 mL of RuCl3 aqueous solution precursor (0.1 M) were mixed and added to a 20 mL glass bottle, and then 0.5 mmol of sodium citrate was added. After reacting at room temperature for 5 h, the solid separated from the solution and Ru metal hydrogel was formed at the bottom of the bottle. S2, the obtained Ru metal hydrogel was repeatedly washed with deionized water 5 times to remove the impurities remaining in the reaction process, and then supercritical drying for 12 hours was performed to obtain a high porosity Ru metal aerogel. S3. The pre-prepared Ru aerogel was placed in a tube furnace in an air atmosphere and heated at 350°C for 30 min to obtain a sample with Ru-30 (350°C).

[0035] Comparative Example 1: S1, 5 mL of freshly prepared NaBH4 aqueous solution (0.3 M) and 5 mL of RuCl3 aqueous solution precursor (0.1 M) were mixed and added to a 20 mL glass bottle, and then 0.5 mmol of sodium citrate was added. After reacting at room temperature for 5 h, the solid separated from the solution and Ru metal hydrogel was formed at the bottom of the bottle. S2, the obtained Ru metal hydrogel was repeatedly washed with deionized water 5 times to remove the impurities remaining in the reaction process, and then supercritical drying for 12 hours was performed to obtain a high porosity Ru metal aerogel. S3. The pre-prepared Ru aerogel was placed in a tube furnace in an air atmosphere and heated at 350°C for 60 min to obtain a sample with Ru-60 (350°C).

[0036] The difference between this comparative example and Example 4 is that the conditions in step S3 are heating at 350°C for 60 minutes.

[0037] Comparative Example 2: S1, 5 mL of freshly prepared NaBH4 aqueous solution (0.3 M) and 5 mL of RuCl3 aqueous solution precursor (0.1 M) were mixed and added to a 20 mL glass bottle, and then 0.5 mmol of sodium citrate was added. After reacting at room temperature for 5 h, the solid separated from the solution and Ru metal hydrogel was formed at the bottom of the bottle. S2, the obtained Ru metal hydrogel was repeatedly washed with deionized water 5 times to remove the impurities remaining in the reaction process, and then supercritical drying for 12 hours was performed to obtain a high porosity Ru metal aerogel. S3. The pre-prepared Ru aerogel was placed in a tube furnace in an air atmosphere and heated at 250°C for 30 min to obtain a sample with Ru-30 (250°C).

[0038] The difference between this comparative example and Example 4 is that the condition in step S3 is heating at 250°C for 30 minutes.

[0039] Comparative Example 3: S1, 5 mL of freshly prepared NaBH4 aqueous solution (0.3 M) and 5 mL of RuCl3 aqueous solution precursor (0.1 M) were mixed and added to a 20 mL glass bottle, and then 0.5 mmol of sodium citrate was added. After reacting at room temperature for 5 h, the solid separated from the solution and Ru metal hydrogel was formed at the bottom of the bottle. S2, the obtained Ru metal hydrogel was repeatedly washed with deionized water 5 times to remove the impurities remaining in the reaction process, and then supercritical drying for 12 hours was performed to obtain a high porosity Ru metal aerogel. S3. The pre-prepared Ru aerogel was placed in a tube furnace in an air atmosphere and heated at 450°C for 30 min to obtain a sample with Ru-30 (450°C).

[0040] The difference between this comparative example and Example 4 is that the condition in step S3 is heating at 450°C for 30 minutes.

[0041] Comparative Example 4: S1, 5 mL of freshly prepared NaBH4 aqueous solution (0.3 M) and 5 mL of RuCl3 aqueous solution precursor (0.1 M) were mixed and added to a 20 mL glass bottle, and then 0.5 mmol of sodium citrate was added. After reacting at room temperature for 5 h, the solid separated from the solution and Ru metal hydrogel was formed at the bottom of the bottle. S2, the obtained Ru metal hydrogel was repeatedly washed with deionized water 5 times to remove the impurities remaining in the reaction process, and then supercritical drying for 12 hours was performed to obtain a high porosity Ru metal aerogel. S3. The pre-prepared Ru aerogel was placed in a tube furnace in an air atmosphere and heated at 550°C for 30 min to obtain a sample with Ru-30 (550°C).

[0042] The difference between this comparative example and Example 4 is that the condition in step S3 is heating at 550°C for 30 minutes.

[0043] Experimental Example 1: This experimental example is the specific surface area test of Examples 1-3, and the results are shown in Table 1.

[0044] The sample was accurately weighed and degassed in a vacuum for an extended period. The treated sample was then placed in a liquid nitrogen environment at -196°C. The amount of nitrogen adsorbed by the sample under different relative pressures was accurately measured using a physical adsorption instrument to obtain the adsorption-desorption isotherm. A linear range of 0.05-0.35 for P / P0 on the adsorption isotherm was selected, and the specific surface area of ​​the sample was calculated by fitting the BET equation. The average value of the three sets of measurements was taken.

[0045] Table 1: The following table shows the specific surface area test results for Examples 1-3.

[0046] Catalyst BET surface area (m2 / ) Example 1 33.9596 Example 2 29.2518 Example 3 40.2508 Example 1 (molar ratio of reducing agent to Ru salt precursor is 4:1) used a high concentration of NaBH4, which created a high reduction potential and reduction rate. The solution instantly reached extremely high supersaturation, resulting in explosive nucleation and the instantaneous generation of a large number of tiny Ru crystal nuclei, forming a high specific surface area. However, without the steric hindrance of ligands, the newly generated nanoparticles tended to aggregate and grow rapidly and disorderly. Small particles dissolved and redeposited onto the surface of large particles, reducing surface energy. The high concentration of reducing agent made the reaction too fast, resulting in local concentration unevenness and causing the network structure to be partially dense and non-porous.

[0047] Example 2 (molar ratio of reducing agent, Ru salt precursor, and ligand was 2:1:1) introduced sodium citrate as a ligand. The carboxyl groups of sodium citrate can adsorb onto the surface of Ru nanoparticles, effectively inhibiting excessive growth and aggregation of particles through electrostatic repulsion and steric hindrance. However, the NaBH4 concentration was too low, the total amount of reducing agent was insufficient, the nucleation rate was slow, and the number of nuclei was reduced, resulting in incomplete reduction of the Ru³⁺ precursor. The resulting primary nanoparticles were large in size, and the three-dimensional gel network structure was loose.

[0048] In Example 3 (the molar ratio of reducing agent, Ru salt precursor, and ligand was 3:1:1), the concentration of NaBH4 was moderate, with 0.3M falling between that of Examples 1 and 2. It can effectively nucleate, generating a large number of fine primary nanoparticles. The addition of sodium citrate adsorbs onto the surface of the newly formed particles, preventing disordered aggregation through electrostatic repulsion and steric hindrance, stabilizing the high surface energy fine particles, and forming a more porous and structurally stable three-dimensional network.

[0049] Experimental Example 2: This experimental example is the SEM test of Examples 3-4 and Comparative Examples 1-4.

[0050] Samples were taken from aerogels and firmly adhered to a SEM stage using conductive adhesive. Observations were performed under high vacuum mode, with appropriate accelerating voltage and low beam current. Initially, representative regions with intact structures were identified at low magnification, then the magnification was gradually increased to over 100,000 times. Secondary electron signals were used to clearly capture the three-dimensional porous network morphology, the assembly method of nanoparticles, and the overall outline of the core-shell structure, thus comprehensively characterizing its microstructure. Figure 1 ).

[0051] Figure 1 Example 3 illustrates a Ru aerogel, an untreated aerogel whose structure is formed by the reduction of Ru salt precursors to Ru atoms, which then form an open, interconnected three-dimensional network under the action of sodium citrate and NaBH4. Figure 1 The material has abundant pores and a distinct hierarchical pore structure, resulting in good particle dispersion. However, it has not undergone heat treatment and therefore suffers from insufficient thermal stability.

[0052] Figure 1 In Example 4, Ru-30 (350℃) was heat-treated at 350℃ for 30 minutes. This temperature promotes the crystallinity of Ru particles, enhances chemical stability and mechanical strength. Figure 1 As a result, the three-dimensional network remains open and connected, with high porosity and uniform Ru particle dispersion. Compared with Example 3, Example 4 has better structural stability, more complete pore structure, and more dispersed particles.

[0053] Figure 1 In Comparative Example 1, Ru-60 (350℃) was used. Compared to Example 4, the heat treatment time at the same temperature was extended to 60 minutes. Excessive heat treatment leads to excessive growth and agglomeration of Ru particles. Because the inhibitory effect of the ligands on agglomeration gradually fails under prolonged heat treatment, Ru atoms migrate and sinter. Figure 1 As a result, the pore structure is destroyed, the dispersion between particles deteriorates, and ultimately the connectivity and porosity of the three-dimensional network decrease, which is detrimental to electron conduction and mass transport.

[0054] Figure 1 In Comparative Example 2, Ru-30 (250℃) was heat-treated at 250℃ for 30 min. The temperature was relatively low, and the effect of heat treatment on structural regulation was limited. Compared to Example 3 without heat treatment, the pore structure and particle dispersion did not change significantly. Due to insufficient temperature, the crystallinity and structural compactness of the Ru particles did not improve significantly.

[0055] Figure 1 In Comparative Example 3, Ru-30 (450℃) was heat-treated at 450℃ for 30 minutes. The excessively high temperature caused severe sintering and agglomeration of Ru particles. From... Figure 1 As a result, a large number of particles aggregate, the original open three-dimensional network is destroyed, and the porosity decreases. High temperature increases the crystallinity of Ru, but excessive structural damage reduces mechanical strength. At this high temperature, the ligands completely lose their ability to inhibit agglomeration, and Ru atoms migrate rapidly and undergo large-scale sintering, leading to a deterioration in material properties.

[0056] Figure 1 In Comparative Example 4, Ru-30 (550℃) was used; at a higher temperature of 550℃, Ru particles melted and agglomerated. Figure 1 As you can see, it exhibits a dense, blocky structure. The original three-dimensional network of aerogel has been completely destroyed. Ru has extremely poor dispersion, and the electron conduction pathway is severely blocked, resulting in a significant decrease in chemical stability and mechanical strength.

[0057] In summary, Example 4 is the best. Heat treatment at 350℃ for 30 minutes enhances the crystallinity of Ru particles, improves chemical stability and mechanical strength, maintains an open and interconnected three-dimensional network and high porosity, and avoids insufficient structural stability at low temperatures, excessive sintering at high temperatures, and pore collapse.

[0058] Experimental Example 3: This experimental example is the XRD test of Examples 3-4 and Comparative Examples 1-4.

[0059] The prepared sample was placed in an X-ray diffractometer. At room temperature, a Cu target Kα ray source (wavelength λ=1.5406Å) was used. The operating voltage was set to 40kV and the current to 40mA. Continuous scanning mode was used to collect diffraction data in the range of 10° to 90° (2θ) with a step size of 0.02° and a scanning speed of 2° per second.

[0060] Figure 1 The Ru aerogel in Example 3 is insufficient because it is reduced by a reducing agent and its aggregation is inhibited by ligands without high-temperature heat treatment to promote grain growth. Therefore, only the broadened characteristic peak of metallic Ru appears, and the absence of RuO2 peak indicates that Ru exists in the metallic state without heat treatment.

[0061] Figure 2 In Example 4, Ru-30 (350℃) showed a significantly sharpened characteristic peak of metallic Ru, a substantial increase in crystallinity, and the absence of RuO2 characteristic peaks. High temperature promoted the orderly growth of Ru grains, improved crystallinity, enhanced electron conduction and structural stability, and prevented the oxidation of Ru to form RuO2, thus maintaining the pure phase of metallic Ru.

[0062] Figure 2 In Comparative Example 1, Ru-60 (350℃) still has the peak of metallic Ru, but the peak shape is slightly wider than that of Ru-30 (350℃), and a weak RuO2 characteristic peak appears. The heat treatment time at 350℃ is extended to 60 min. Excessive heat treatment leads to the destruction of Ru grain growth. In the long-term air atmosphere, Ru undergoes slight oxidation to generate RuO2, which reduces the effective content of metallic Ru and affects the electronic conduction performance.

[0063] Figure 2 In Comparative Example 2, Ru-30 (250℃) was dominated by the broadened peak of metallic Ru, with no obvious RuO2 peak, but the peak shape was slightly sharper than that of Example 3. The heat treatment temperature of 250℃ was relatively low, which only slightly improved the crystallinity of Ru and did not cause significant oxidation. However, the improvement in crystallinity was limited, and the electronic conductivity of metallic Ru was not significantly improved.

[0064] Figure 2 In Comparative Example 3, Ru-30 (450℃) showed a sharper Ru peak (high crystallinity) and a distinct RuO2 characteristic peak. The temperature of 450℃ was too high. Although it further improved the crystallinity of Ru, a large amount of Ru in the air was oxidized to RuO2, the proportion of the metallic Ru phase decreased, and the electron conduction path was weakened.

[0065] Figure 2In the case of Ru-30 (550℃) as Comparative Example 4, the characteristic peak of RuO2 is very strong, and the characteristic peak of metallic Ru is almost masked. At the extremely high temperature of 550℃, Ru is almost completely oxidized to RuO2 in the air atmosphere, and the metallic Ru phase basically disappears.

[0066] In summary, Example 4 is the best, containing only the metallic Ru phase and no RuO2 impurities. The diffraction peaks of metallic Ru are sharp, the grains grow in an orderly manner, and the chemical stability and mechanical strength are excellent. The electronic conductivity of the three-dimensional framework is enhanced.

[0067] Experimental Example 4: This experimental example is Examples 3-4, and the linear polarization curves of HER and OER under different pH conditions for Comparative Example 1 are shown in [link to example]. Figure 2 ).

[0068] 5 mg of sample (Examples 3, 4, and Comparative Example 1) was uniformly dispersed in Nafion / alcohol solution and then drop-coated onto a glassy carbon electrode as the working electrode. Together with the reference electrode Hg / HgO and platinum wire, this formed a standard three-electrode system, placed in electrolytes of different pH values. Before HER testing, high-purity nitrogen or oxygen was continuously introduced into the electrolyte to eliminate interference from dissolved oxygen and achieve saturation (for OER testing, high-purity oxygen was continuously introduced into the electrolyte). A linear voltammetric scan was performed at a scan rate of 3.5 mV / s. HER testing was performed in the cathode potential window near zero potential, while OER testing was performed in the anodic potential window above 1.0 V vs. RHE. The current density-potential relationship curves were recorded.

[0069] HER analysis: Under alkaline conditions, the current density of Ru-30 (Example 4) reached -100 mA·cm⁻¹. -2 At this time, the overpotential was significantly lower than that of Ru (Example 3) and Ru-60 (Comparative Example 1), and the reaction kinetics were the fastest. The overpotential of Ru (Example 3) was higher than that of Ru-30, but the lack of heat treatment resulted in low crystallinity, insufficient electron conduction and utilization efficiency of reaction sites. The overpotential of Ru-60 (Comparative Example 1) was higher than that of Ru-30, and long-term heat treatment led to particle agglomeration, destruction of pore structure, and reduction of reaction sites. Under acidic conditions, Ru-30 (Example 4) at a current density of -10 mA·cm -2 In the same range, the overpotential is the most negative, and the kinetic advantage is significant. The overpotential of Ru (Example 3) is higher than that of Ru-30. Insufficient crystallinity leads to a lower number of reactive sites. The overpotential of Ru-60 (Comparative Example 1) is higher than that of Ru-30. Structural defects caused by long-term heat treatment limit the hydrogen evolution kinetics.

[0070] ORE analysis: Under alkaline conditions, the current density of Ru-30 (Example 4) reached 50 mA·cm⁻¹. -2At this time, the overpotential was significantly lower than that of Ru and Ru-60, and the reaction kinetics were the fastest. The overpotential of Ru (Example 3) was higher than that of Ru-30. The low crystallinity led to insufficient efficiency in electron conduction and lattice oxygen participation in the reaction. The overpotential of Ru-60 (Comparative Example 1) was higher than that of Ru-30. The structural agglomeration resulted in insufficient exposure of active sites, which limited the kinetics. Under acidic conditions, the current density of Ru-30 (Example 4) reached 100 mA·cm. -2 At that time, the overpotential was much lower than that of Ru and Ru-60, and the OER kinetics were optimal. Ru (Example 3) had a high overpotential, and insufficient crystallinity led to poor reactivity. Ru-60 (Comparative Example 1) had a high overpotential, and structural defects limited the OER kinetics.

[0071] Experimental Example 5: This experimental example is the linear polarization curves of HER and OER under different pH conditions for Examples 4 and Comparative Examples 2-4 (see...). Figure 3 ).

[0072] 5 mg of sample (Example 4, Comparative Example 2, Comparative Example 3, Comparative Example 4) was uniformly dispersed in Nafion / alcohol solution and then drop-coated onto a glassy carbon electrode as the working electrode. Together with the reference electrode Hg / HgO and platinum wire, this formed a standard three-electrode system, placed in electrolytes of different pH values. Before HER testing, high-purity nitrogen or oxygen was continuously introduced into the electrolyte to eliminate interference from dissolved oxygen and achieve saturation (for OER testing, high-purity oxygen was continuously introduced into the electrolyte). A linear voltammetric scan was performed at a scan rate of 3.5 mV / s. HER testing was performed in the cathode potential window near zero potential, while OER testing was performed in the anodic potential window above 1.0 V vs. RHE. The current density-potential relationship curves were recorded.

[0073] HER analysis: Under alkaline conditions, heat treatment of Ru-350 (Example 4) at 350°C improved the crystallinity of Ru, inhibited ligand aggregation, maintained high porosity, and achieved a current density of -100 mA·cm⁻¹. -2 At this temperature, the overpotential was significantly lower than that of Ru-250, Ru-450, and Ru-550, indicating the fastest reaction kinetics. The overpotential of Ru-250 (Comparative Example 2) was higher than that of Ru-350 because the temperature of 250℃ was too low, resulting in insufficient Ru crystallinity and low efficiency in electron conduction and active site utilization. The overpotential of Ru-450 (Comparative Example 3) was higher than that of Ru-350 because the high temperature of 450℃ caused excessive sintering and agglomeration of Ru particles, destroying the pore structure and insufficient exposure of active sites. The overpotential of Ru-550 (Comparative Example 4) was the highest because at 550℃, a large amount of Ru was oxidized (generating RuO2), drastically reducing the proportion of metallic Ru phase and destroying the core pathway of electron conduction. Under acidic conditions, Ru-350 (Example 4) exhibited strong resistance to acid corrosion due to its high crystallinity and open pores, ensuring the efficient utilization of H₂. +Transport and contact with active sites, at a current density of -10 mA·cm -2 In the same range, the overpotential is the most negative, and the kinetic advantage is significant. The overpotential of Ru-250 (Comparative Example 2) is higher than that of Ru-350. Insufficient crystallinity leads to poor reaction activity. The overpotential of Ru-450 (Comparative Example 3) is higher than that of Ru-350. Particle agglomeration masks the active sites and limits hydrogen evolution kinetics. The overpotential of Ru-550 (Comparative Example 4) is the highest. RuO2 has poor stability in acidic conditions and the proportion of metallic Ru is extremely low, resulting in a significant decrease in catalytic activity.

[0074] ORE analysis: Under alkaline conditions, Ru-350 (Example 4), with its highly crystalline metallic Ru, provides efficient electron conduction. The open pores facilitate OH⁻ transport and lattice oxygen participation in the reaction, while being free of RuO₂ impurities. A current density of 50 mA·cm⁻¹ is achieved. -2 At this time, the overpotential was significantly lower than that of other samples, and the reaction kinetics were the fastest. The overpotential of Ru-250 (Comparative Example 2) was higher than that of Ru-350. Insufficient crystallinity led to low electron conduction and low activation efficiency of reaction sites. The overpotential of Ru-450 (Comparative Example 3) was higher than that of Ru-350. Particle agglomeration resulted in insufficient exposure of active sites, limiting OER kinetics. The overpotential of Ru-550 (Comparative Example 4) was the highest. Although the large amount of RuO2 generated had some activity for OER, the lack of metallic Ru phase led to a decrease in electron conduction and structural stability. Its overall performance was inferior to that of Ru-350 with pure metallic Ru phase. Under acidic conditions, Ru-350 (Example 4) metallic Ru had good chemical stability in acidic conditions. High crystallinity and open channels ensured charge transfer and mass transport in the reaction, and the current density reached 100 mA·cm. -2 When the overpotential is much lower than that of other samples, the OER kinetics are optimal. Ru-250 (Comparative Example 2) has a high overpotential, and insufficient crystallinity leads to poor reactivity. Ru-450 (Comparative Example 3) has a high overpotential, and severe particle agglomeration restricts the utilization of active sites. Ru-550 (Comparative Example 4) has a high overpotential, and RuO2 is easily soluble in acid, with an extremely low proportion of metallic Ru.

[0075] In summary, based on the linear polarization curves of HER and OER under different pH conditions, Example 4 showed the best performance. Therefore, the following experiments will be conducted using Example 4.

[0076] Experimental Example 6: This experimental example is the linear polarization curve of total hydrolysis under acidic conditions in Example 4 (see...). Figure 4 ).

[0077] 5 mg of the sample from Example 4 was uniformly dispersed in a Nafion / alcohol solution and then drop-coated onto a glassy carbon electrode as the working electrode. Together with the Hg / HgO reference electrode and the platinum wire counter electrode, this formed a three-electrode system. The electrolyte was a nitrogen-saturated 0.5 M H₂SO₄ alkaline solution. A linear voltammetric scan was performed at a scan rate of 3.5 mV / s, starting near the open-circuit potential and scanning towards the anode to 1.8 V vs. RHE. The scan simultaneously covered the potential windows of both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), and the current density-potential relationship curve was recorded.

[0078] Experimental Example 7: This experimental example is the linear polarization curve of total hydrolysis under alkaline conditions in Example 4 (see...). Figure 5 ).

[0079] 5 mg of the sample from Example 4 was uniformly dispersed in a Nafion / alcohol solution and then drop-coated onto a glassy carbon electrode as the working electrode. This, along with a Hg / HgO reference electrode and a platinum wire counter electrode, constituted a three-electrode system. The electrolyte was a nitrogen-saturated 1.0 M KOH alkaline solution. A linear voltammetric scan was performed at a scan rate of 3.5 mV / s, starting near the open-circuit potential and scanning towards the anode towards 1.8 V vs. RHE. The scan simultaneously covered the potential windows of both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), and the current density-potential relationship curves were recorded.

[0080] Experimental Example 8: This experimental example is the total hydrolysis it curve of Example 4 under acidic conditions (see...). Figure 6 ).

[0081] 5 mg of the sample from Example 4 was uniformly dispersed in a Nafion / alcohol solution and then drop-coated onto a glassy carbon electrode as the working electrode. Together with the Hg / HgO reference electrode and the platinum wire counter electrode, this formed a three-electrode system. The electrolyte was a nitrogen-saturated 0.5 M H₂SO₄ electrolyte. A chronoamperometric method was used, applying a constant potential of 1.23 V, higher than that required for water decomposition, and continuously recording the change in current density over time to obtain the total hydrolysis it curve.

[0082] Experimental Example 9: This experimental example is the total hydrolysis it curve of Example 4 under alkaline conditions (see...). Figure 7 ).

[0083] 5 mg of the sample from Example 4 was uniformly dispersed in a Nafion / alcohol solution and then drop-coated onto a glassy carbon electrode as the working electrode. Together with the Hg / HgO reference electrode and the platinum wire counter electrode, this formed a three-electrode system. The electrolyte was a nitrogen-saturated 0.5 M H₂SO₄ electrolyte. A chronoamperometric method was used, applying a constant potential of 1.23 V, higher than that required for water decomposition, and continuously recording the change in current density over time to obtain the total hydrolysis it curve.

[0084] Comprehensive test examples 6-9, Figure 8 Figures 5-8It can be seen that Example 4 exhibits excellent and stable kinetics in both acid-base hydrolysis, adapts to a wide pH range, and has the best performance, making it the optimal formulation and method for preparing metal aerogels.

Claims

1. A core-shell structured metal aerogel with high porosity, characterized in that, The metal aerogel comprises the following components: reducing agent, Ru salt precursor, and ligand; In the metal aerogel, the molar ratio of reducing agent, Ru salt precursor, and ligand is (2-4):1:

1.

2. The core-shell structured metal aerogel with high porosity according to claim 1, characterized in that, The Ru salt precursor is one or more of ruthenium chloride, ruthenium acetylacetonate, or ruthenium nitrate.

3. The core-shell structured metal aerogel with high porosity according to claim 1 or 2, characterized in that, The concentration of the Ru salt precursor aqueous solution is 0.2-0.4 M.

4. The core-shell structured metal aerogel with high porosity according to claim 1, characterized in that, The reducing agent is one or more of sodium borohydride, sodium carbonate, or sodium hypophosphite.

5. The core-shell structured metal aerogel with high porosity according to claim 1 or 4, characterized in that, The concentration of the reducing agent aqueous solution is 0.6-1.2 M.

6. The core-shell structured metal aerogel with high porosity according to claim 1, characterized in that, The ligand is one or more of sodium deoxycholate, polyvinylpyrrolidone, 2-mercaptopropionic acid, or sodium citrate.

7. The core-shell structured metal aerogel with high porosity according to claim 1 or 6, characterized in that, The concentration of the ligand in the Ru salt aqueous solution is 0.2-0.4 M.

8. A method for preparing a core-shell structured metal aerogel with high porosity as described in any one of claims 1-7, characterized in that, Includes the following steps: S1, freshly prepared reducing agent aqueous solution, Ru salt aqueous solution precursor and ligand are added to the reaction vessel. After reaction at room temperature, the solid and solution are separated to form Ru metal hydrogel. S2, the obtained Ru metal hydrogel was repeatedly washed with deionized water to remove the impurities remaining in the reaction process, and then supercritical drying was performed to obtain a high specific surface area Ru metal aerogel. S3, the pre-prepared Ru aerogel is heated in a tube furnace in an air atmosphere to obtain a metal aerogel sample with high porosity and a Ru / RuO2 core-shell structure.

9. The method for preparing core-shell structured metal aerogel according to claim 8, characterized in that, In step S3, the heating temperature is 250-550℃ and the heating time is 0.5-5h.

10. An application of a core-shell structured metal aerogel with high porosity as described in any one of claims 1-9, characterized in that, The core-shell structured metal aerogel is applied in the field of electrocatalytic water splitting.

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