A gradient complex-plasma assisted preparation method and application of iridium-ruthenium bimetallic oxide

Abstract

The application belongs to the technical field of electrocatalytic materials, and discloses a gradient complexation-plasma assisted preparation method and application of iridium-ruthenium bimetallic oxide. The method adopts stepwise ultrasonic assisted double complexing agent gradient complexation to realize molecular level pre-mixing of Ir and Ru ions; the method precisely controls nucleation and growth rates of the two kinds of ions through reverse dropping and pH step precipitation; and the method first introduces low-temperature plasma treatment of the precipitation suspension to improve particle dispersibility and pre-locate oxygen vacancies; and the method combines freeze drying and two-stage calcination to obtain iridium-ruthenium bimetallic oxide with high specific surface area and atomic level uniform mixing. The method overcomes the problems of Ir and Ru ion precipitation kinetics mismatch and serious particle agglomeration in the traditional coprecipitation method, and the iridium-ruthenium bimetallic oxide catalyst prepared by the method exhibits excellent activity in an acid oxygen evolution reaction and can be applied to a proton exchange membrane water electrolyzer. The application has novel process, good reproducibility and significant industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic materials technology, specifically relating to a gradient complexation-plasma-assisted preparation method and application of iridium-ruthenium bimetallic oxide. Background Technology

[0002] Proton exchange membrane electrolysis (PEMWE) is a key technology for green hydrogen production. Its anodic oxygen evolution reaction (OER) kinetics are slow, thus requiring highly efficient and stable electrocatalysts. Iridium-based and ruthenium-based oxides are recognized as the best-performing OER catalysts. However, ruthenium oxide (RuO2) is easily dissolved and deactivated at acidic high potentials, while iridium oxide (IrO2) is expensive and has relatively low activity. Therefore, combining iridium and ruthenium to form solid solutions or mixed oxides is the mainstream strategy that balances activity and stability.

[0003] Currently, the main methods for preparing iridium-ruthenium composite catalysts include: Adams melting method, coprecipitation method, sol-gel method, template method, electrodeposition method, and atomic layer deposition method. Among them, the coprecipitation method has attracted much attention due to its simplicity and ease of industrialization. However, the traditional coprecipitation method has two inherent drawbacks: one is that Ir... 3+ / Ir 4+ With Ru 3+ / Ru 4+ The inconsistent pH windows for hydrolysis precipitation (Ru ions begin to precipitate at pH≈4, while Ir ions require pH>7 to precipitate completely) lead to elemental segregation; secondly, local supersaturation during precipitation can easily cause uneven particle size.

[0004] To address these issues, researchers attempted to add a single complexing agent (such as citric acid or EDTA), but a single complexing agent cannot simultaneously match the precipitation kinetics of both ions. Furthermore, existing techniques generally employ conventional heating and stirring precipitation, oven drying, and one-step calcination, which limits the means to control the micro-mixing and precursor morphology during the precipitation process.

[0005] In summary, there is an urgent need to develop a novel method for preparing iridium-ruthenium bimetallic oxides that can achieve atomic-level uniform mixing of iridium and ruthenium, controllable particle size, and high process repeatability. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a gradient complexation-plasma-assisted preparation method for iridium-ruthenium bimetallic oxides. This method solves the problem of mismatched precipitation rates of the two ions in the traditional co-precipitation method by controlling the kinetics of the two complexing agents, thereby achieving atomic-level uniform mixing. Furthermore, the morphology of the precursor during the precipitation process is controlled by a synergistic process of "pH gradient reverse precipitation + low-temperature plasma-assisted aging + tert-butanol freeze-drying + two-stage calcination", which improves dispersibility and specific surface area.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a gradient complexation-plasma-assisted preparation method for iridium-ruthenium bimetallic oxides, comprising the following steps: (1) Stepwise gradient complexation: Iridium precursor and ruthenium precursor are dissolved in water to obtain a mixed solution. First complexing agent is added to the mixed solution and sonicated once to allow the first complexing agent to preferentially form a stable Ru-citric acid complex with ruthenium ions. Then, a second complexing agent is added and sonicated a second time to allow the second complexing agent to simultaneously form a bimetallic chelate complex with Ir and Ru ions, resulting in a clear dark red or brownish-yellow bimetallic complex solution.

[0008] (2) pH gradient reverse precipitation: The bimetallic complex solution obtained in step (1) is added dropwise to the alkaline precipitant aqueous solution under vigorous stirring. During the dropwise addition, dilute alkali solution is added synchronously by a peristaltic pump so that the pH value of the reaction system is controlled according to the stepwise procedure. After the staged precipitation is completed, stirring and aging are continued to obtain a uniform precipitate suspension.

[0009] (3) Low-temperature plasma-assisted aging: The precipitated suspension obtained in step (2) is transferred to a low-temperature plasma reactor and subjected to dielectric barrier discharge plasma treatment. The active species (such as ·OH, ·H) generated by the plasma in this process can promote the condensation of hydroxyl groups on the surface of the precipitated particles, improve particle dispersibility and introduce oxygen vacancy precursors.

[0010] (4) Freeze-drying: The precipitate suspension after step (3) is centrifuged to obtain the precipitate, which is washed twice with deionized water and anhydrous ethanol. The washed precipitate is ultrasonically dispersed and then transferred to a freeze dryer for freeze-drying to obtain fluffy iridium-ruthenium bimetallic hydroxide precursor powder.

[0011] (5) Two-stage calcination: The precursor powder obtained in step (4) is placed in a tube furnace and calcined in two stages under an air or oxygen atmosphere. After calcination, it is naturally cooled to room temperature to obtain iridium-ruthenium bimetallic oxide.

[0012] Preferably, in step (1), the iridium precursor is one of chloroiridic acid, iridium trichloride, or potassium chloroiridate, and the ruthenium precursor is one of ruthenium trichloride, chlororuthenic acid, or potassium chlororuthenate; the total metal ion concentration of Ir and Ru in the mixed solution is 0.01 to 0.1 mol / L, and the molar ratio of Ir to Ru in the mixed solution is (1 to 9): (9 to 1).

[0013] Preferably, in step (1), the first complexing agent is citric acid or citrate, and the amount added is 1.5 to 4 times the amount of ruthenium ions in the mixed solution; the second complexing agent is L-aspartic acid, L-glutamic acid or glycine, and the amount added is 1 to 3 times the amount of total metal ions in the mixed solution.

[0014] Preferably, the conditions for the first ultrasonic treatment in step (1) are: power of 100-300 W, frequency of 40 kHz, temperature of 20-50 ℃, and time of 20-40 min; the conditions for the second ultrasonic treatment are: power of 100-300 W, frequency of 40 kHz, temperature of 50-80 ℃, and time of 30-50 min.

[0015] Preferably, the concentration of the alkaline precipitant aqueous solution in step (2) is 0.1 to 2 mol / L; the precipitant is one or more of ammonia, ammonium carbonate, and ammonium bicarbonate; when the precipitant is multiple of ammonia, ammonium carbonate, and ammonium bicarbonate, the components can be mixed in any proportion.

[0016] As a further preferred option, ammonium bicarbonate is used as the precipitant, which decomposes and releases CO2 during the precipitation process, thus buffering the pH and creating pores.

[0017] As a further preferred option, the dilute alkali solution is an ammonia solution with a mass fraction of 5%.

[0018] Preferably, in step (2), the reverse dropwise addition rate is 0.5–5 mL / min, and the stirring rate is 500–1000 rpm. The pH step program conditions are as follows: first, maintain the pH at 4.5–5.5 for 5–15 min. During this stage, Ru will not form a large amount of hydroxide precipitate, but will slowly and uniformly nucleate due to the complexation effect of citric acid. Then, linearly increase the pH to 7.0–8.0 at a rate of 0.1–0.3 pH / min and maintain it for 10–30 min to allow Ir and Ru to precipitate completely at the same time. The temperature of the entire process is 30–60 °C.

[0019] Preferably, in step (3), the low-temperature plasma treatment is dielectric barrier discharge with a discharge power of 50-150 W, a temperature of 40-70 °C, and a treatment time of 10-60 min; the atmosphere is oxygen or air; when the atmosphere is oxygen, the flow rate is 50-200 mL / min; when the atmosphere is air, the flow rate can be set.

[0020] Preferably, the ultrasonic dispersion step in step (4) is as follows: the washed precipitate is dispersed in an aqueous solution of tert-butanol with a mass fraction of 10-20%, and ultrasonically treated for 20-40 min at a power of 100-300 W and a frequency of 40 kHz; the freeze-drying temperature is below -50 ℃, the vacuum degree is below 10 Pa, and the time is 24-48 h.

[0021] Preferably, the two-stage calcination step (5) is as follows: in the first stage, the temperature is raised to 200-300 ℃ at a rate of 1-3 ℃ / min and held for 1-2 h to decompose the complexing agent and residual organic matter in the precursor; in the second stage, the temperature is raised to 350-550 ℃ at a rate of 2-5 ℃ / min and held for 2-5 h to convert the hydroxide into oxide and form a uniform iridium-ruthenium solid solution structure.

[0022] This invention also provides an application of the iridium-ruthenium bimetallic oxide prepared by the above method in the acidic oxygen evolution reaction.

[0023] The iridium-ruthenium bimetallic oxide prepared by the method of the present invention can be supported on a carbon-based support or an oxide support to prepare a supported Ir-Ru bimetallic catalyst.

[0024] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention combines the stepwise regulation of dual complexing agents with a multi-step synergistic process of "pH gradient reverse precipitation + low temperature plasma-assisted aging + tert-butanol-assisted freeze drying + two-stage calcination", which achieves the effects of high particle uniformity, good dispersibility and high specific surface area, as follows: This invention employs dual complexing agent kinetic control, preferentially complexing ruthenium with a citric acid-based complexing agent, followed by simultaneous complexing of iridium and ruthenium with an amino acid-based complexing agent. Then, a reverse-dropping method and a pH stepwise program are used to control the precise nucleation in stages, ensuring the simultaneous and complete precipitation of Ir and Ru. This fundamentally solves the problem of mismatched precipitation rates between the two ions in traditional co-precipitation methods, achieving atomically uniform mixing. Furthermore, this invention introduces low-temperature plasma-assisted aging into the post-precipitation treatment of iridium and ruthenium. The active species generated by the plasma (such as ·OH and ·H) promote the condensation of hydroxyl groups on the surface of the precipitated particles, improving particle dispersibility and introducing oxygen vacancy precursors. Combined with tert-butanol-assisted freeze-drying and two-stage calcination, this significantly improves dispersibility and specific surface area.

[0025] (2) The iridium-ruthenium bimetallic oxide prepared by the method of the present invention can be applied to the field of electrocatalytic oxygen evolution. The prepared iridium-ruthenium composite catalyst has excellent comprehensive performance: the overpotential is as low as 225mV (@10mA / cm). 2 The specific surface area reaches 20 m². 2 / g or more.

[0026] (3) The process of this invention is simple, has a wide range of applications, and has good prospects for industrialization. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1 A method for preparing an iridium-ruthenium bimetallic oxide catalyst is as follows: (1) Stepwise gradient complexation: Weigh 0.258 g of chloroiridium acid (H2IrCl6·6H2O, containing 0.5 mmol of Ir) and 0.261 g of ruthenium trichloride (RuCl3·3H2O, containing 1.0 mmol of Ru) and dissolve them in 100 mL of deionized water to obtain a mixed solution. The molar ratio of Ir to Ru in the mixed solution is 1:2, and the total metal ion concentration is 0.015 mol / L. Add 0.576 g of citric acid (3.0 mmol) and sonicate at 40 ℃, 150 W, and 40 kHz for 20 min. Then add 0.450 g of L-aspartic acid (3.38 mmol), heat to 60 ℃, and sonicate at 200 W and 40 kHz for 30 min to obtain a clear bimetallic complex solution.

[0029] (2) pH gradient reverse precipitation: Take 200 mL of ammonium bicarbonate solution (1.0 mol / L) and place it in a beaker. Stir in a water bath at 50 ℃ and 800 rpm. Add the bimetallic complex solution obtained in step (1) dropwise to the ammonium bicarbonate solution at a rate of 1 mL / min. At the same time, add ammonia water (mass fraction of 5%) dropwise through a peristaltic pump to maintain the pH of the system at 5.0±0.01 for 10 min. Then raise the pH to 7.5 at a rate of 0.2 pH / min and maintain it for 30 min. Continue stirring and aging for 30 min to obtain a precipitate suspension. Fine bubbles (CO2) escape during the precipitation process.

[0030] (3) Low-temperature plasma-assisted aging: The precipitate suspension obtained in step (2) was transferred into a plasma reactor (quartz tube with an inner diameter of 25 mm), oxygen was introduced at a flow rate of 100 mL / min, dielectric barrier discharge was applied, and the mixture was treated for 30 min at a temperature of 55℃, a discharge power of 100 W, and a frequency of 10 kHz.

[0031] (4) Freeze-drying: The precipitate suspension after step (3) was centrifuged at 10,000 rpm for 10 min to separate the precipitate, washed twice with deionized water, and then washed twice with ethanol. The washed precipitate was dispersed in a 15% tert-butanol aqueous solution and ultrasonically treated for 30 min at a power of 200 W and a frequency of 40 kHz. Then, it was freeze-dried at -50 ℃ and a vacuum degree of less than 10 Pa for 48 h to obtain the precursor powder.

[0032] (5) Two-stage calcination: The precursor powder obtained in step (4) is placed in a tube furnace and calcined in two stages under an air atmosphere. In the first stage, the temperature is raised to 250 ℃ at a rate of 1 ℃ / min and held for 1 h. In the second stage, the temperature is raised to 450 ℃ at a rate of 3 ℃ / min and held for 4 h. After calcination, the powder is naturally cooled to room temperature to obtain black iridium-ruthenium bimetallic oxide powder.

[0033] Example 2 A method for preparing an iridium-ruthenium bimetallic oxide catalyst is as follows: (1) Stepwise gradient complexation: Weigh 0.386 g of chloroiridium acid (H2IrCl6·6H2O, containing 0.75 mmol of Ir) and 0.131 g of ruthenium trichloride (RuCl3·3H2O, containing 0.5 mmol of Ru) and dissolve them in 100 mL of deionized water to obtain a mixed solution. The molar ratio of Ir to Ru in the mixed solution is 3:2, and the total metal ion concentration is 0.0125 mol / L. Add 0.288 g of citric acid (1.5 mmol) and sonicate at 40 ℃, 150 W, and 40 kHz for 20 min. Then add 0.376 g of L-glutamic acid (2.56 mmol), heat to 60 ℃, and sonicate at 150 W and 40 kHz for 40 min to obtain a clear bimetallic complex solution.

[0034] (2) pH gradient reverse precipitation: Take 200 mL of ammonium bicarbonate solution (1.0 mol / L) and place it in a beaker. Stir in a water bath at 50 ℃ and 800 rpm. Add the bimetallic complex solution obtained in step (1) dropwise to the ammonium bicarbonate solution at a rate of 1 mL / min. At the same time, add ammonia water (mass fraction of 5%) dropwise through a peristaltic pump to maintain the pH of the system at 5.0±0.01 for 10 min. Then raise the pH to 7.8 at a rate of 0.2 pH / min and maintain it for 30 min. Continue stirring and aging for 30 min to obtain a precipitate suspension. Fine bubbles (CO2) escape during the precipitation process.

[0035] (3) Low-temperature plasma-assisted aging: The precipitate suspension obtained in step (2) was transferred into a plasma reactor (quartz tube with an inner diameter of 25 mm), oxygen was introduced at a flow rate of 100 mL / min, dielectric barrier discharge was applied, and the mixture was treated for 20 min at a temperature of 55℃, a discharge power of 120 W, and a frequency of 10 kHz.

[0036] (4) Freeze-drying: The precipitate suspension after step (3) was centrifuged at 10,000 rpm for 10 min to separate the precipitate, washed twice with deionized water, and then washed twice with ethanol. The washed precipitate was dispersed in a 15% tert-butanol aqueous solution and ultrasonically treated for 30 min at a power of 200 W and a frequency of 40 kHz. Then, it was freeze-dried at -50 ℃ and a vacuum degree of less than 10 Pa for 48 h to obtain the precursor powder.

[0037] (5) Two-stage calcination: The precursor powder obtained in step (4) is placed in a tube furnace and calcined in two stages under an air atmosphere. In the first stage, the temperature is raised to 250 ℃ at a rate of 1 ℃ / min and held for 1 h. In the second stage, the temperature is raised to 450 ℃ at a rate of 3 ℃ / min and held for 4 h. After calcination, the powder is naturally cooled to room temperature to obtain black iridium-ruthenium bimetallic oxide powder.

[0038] Example 3 A method for preparing an iridium-ruthenium bimetallic oxide catalyst is as follows: (1) Stepwise gradient complexation: Weigh 0.129 g of chloroiridium acid (H2IrCl6·6H2O, containing 0.25 mmol of Ir) and 0.261 g of ruthenium trichloride (RuCl3·3H2O, containing 1 mmol of Ru) and dissolve them in 100 mL of deionized water to obtain a mixed solution. The molar ratio of Ir to Ru in the mixed solution is 1:4, and the total metal ion concentration is 0.0125 mol / L. Add 0.720 g of citric acid (3.75 mmol) and sonicate at 30 ℃, 150 W, and 40 kHz for 40 min. Then add 0.341 g of L-aspartic acid (2.56 mmol), heat to 60 ℃, and sonicate at 150 W and 40 kHz for 50 min to obtain a clear bimetallic complex solution.

[0039] (2) pH gradient reverse precipitation: Take 200 mL of ammonium bicarbonate solution (1.5 mol / L) and place it in a beaker. Stir in a water bath at 50 ℃ and 800 rpm. Add the bimetallic complex solution obtained in step (1) dropwise to the ammonium bicarbonate solution at a rate of 1 mL / min. At the same time, add ammonia water (mass fraction of 5%) dropwise through a peristaltic pump to maintain the pH of the system at 5±0.01 for 10 min. Then raise the pH to 7.5 at a rate of 0.2 pH / min and maintain it for 30 min. Continue stirring and aging for 30 min to obtain a precipitate suspension. Fine bubbles (CO2) escape during the precipitation process.

[0040] (3) Low-temperature plasma-assisted aging: The precipitated suspension obtained in step (2) is transferred into a plasma reactor (quartz tube with an inner diameter of 25 mm), air is introduced, dielectric barrier discharge is applied, and the mixture is treated for 50 min at a temperature of 55 ℃, a discharge power of 100 W, and a frequency of 10 kHz.

[0041] (4) Freeze-drying: The precipitate suspension after step (3) was centrifuged at 10,000 rpm for 10 min to separate the precipitate, washed twice with deionized water, and then washed twice with ethanol. The washed precipitate was dispersed in a 15% tert-butanol aqueous solution and ultrasonically treated for 35 min at a power of 200 W and a frequency of 40 kHz. Then, it was freeze-dried at -50 ℃ and a vacuum degree of less than 10 Pa for 48 h to obtain the precursor powder.

[0042] (5) Two-stage calcination: The precursor powder obtained in step (4) is placed in a tube furnace and calcined in two stages under an air atmosphere. In the first stage, the temperature is raised to 250 ℃ at a rate of 1 ℃ / min and held for 1 h. In the second stage, the temperature is raised to 450 ℃ at a rate of 3 ℃ / min and held for 4 h. After calcination, the powder is naturally cooled to room temperature to obtain black iridium-ruthenium bimetallic oxide powder.

[0043] Example 4 A method for preparing an iridium-ruthenium bimetallic oxide catalyst is as follows: (1) Stepwise gradient complexation: Weigh 0.0515 g of chloroiridium acid (H2IrCl6·6H2O, containing 0.1 mmol of Ir) and 0.235 g of ruthenium trichloride (RuCl3·3H2O, containing 0.9 mmol of Ru) and dissolve them in 100 mL of deionized water to obtain a mixed solution. The molar ratio of Ir to Ru in the mixed solution is 1:9 and the total metal ion concentration is 0.01 mol / L. Add 0.929 g of sodium citrate (3.6 mmol) and sonicate at 20 ℃, 300 W, and 40 kHz for 30 min. Then add 0.225 g of glycine (3 mmol), heat to 50 ℃, and sonicate at 300 W and 40 kHz for 30 min to obtain a clear bimetallic complex solution.

[0044] (2) pH gradient reverse precipitation: Take 200 mL of ammonia solution (0.1 mol / L) and place it in a beaker. Stir in a water bath at 60 ℃ and 500 rpm. Add the bimetallic complex solution obtained in step (1) dropwise to the ammonia solution at a rate of 0.5 mL / min. At the same time, add ammonia water (mass fraction of 5%) dropwise through a peristaltic pump to maintain the pH of the system at 4.5±0.01 for 5 min. Then raise the pH to 7.0 at a rate of 0.1 pH / min and maintain it for 20 min. Continue stirring and aging for 30 min to obtain a precipitate suspension. Fine bubbles (CO2) escape during the precipitation process.

[0045] (3) Low-temperature plasma-assisted aging: The precipitate suspension obtained in step (2) was transferred into a plasma reactor (quartz tube with an inner diameter of 25 mm), oxygen was introduced at a flow rate of 200 mL / min, dielectric barrier discharge was applied, and the mixture was treated for 10 min at a temperature of 70℃, a discharge power of 150 W, and a frequency of 10 kHz.

[0046] (4) Freeze-drying: The precipitate suspension after step (3) was centrifuged at 10,000 rpm for 10 min to separate the precipitate, washed twice with deionized water, and then washed twice with ethanol. The washed precipitate was dispersed in a 10% tert-butanol aqueous solution and ultrasonically treated for 20 min at a power of 100 W and a frequency of 40 kHz. Then, it was freeze-dried at -50 ℃ and a vacuum degree of less than 10 Pa for 24 h to obtain the precursor powder.

[0047] (5) Two-stage calcination: The precursor powder obtained in step (4) is placed in a tube furnace and calcined in two stages under an air atmosphere. In the first stage, the temperature is raised to 200 ℃ at a rate of 2 ℃ / min and held for 2 h. In the second stage, the temperature is raised to 350 ℃ at a rate of 2 ℃ / min and held for 5 h. After calcination, the powder is naturally cooled to room temperature to obtain black iridium-ruthenium bimetallic oxide powder.

[0048] Example 5 A method for preparing an iridium-ruthenium bimetallic oxide catalyst is as follows: (1) Stepwise gradient complexation: Weigh 4.635 g of chloroiridium acid (H2IrCl6·6H2O, containing 9 mmol of Ir) and 0.192 g of ruthenium trichloride (RuCl3·3H2O, containing 1 mmol of Ru) and dissolve them in 100 mL of deionized water to obtain a mixed solution. The molar ratio of Ir to Ru in the mixed solution is 9:1 and the total metal ion concentration is 0.1 mol / L. Add 0.339 g of ammonium citrate (1.5 mmol) and sonicate at 50 ℃, 100 W, and 40 kHz for 20 min. Then add 1.471 g of L-glutamic acid (10 mmol), heat to 80 ℃, and sonicate at 100 W and 40 kHz for 30 min to obtain a clear bimetallic complex solution.

[0049] (2) pH gradient reverse precipitation: Take 200 mL of ammonium carbonate solution (2 mol / L) and place it in a beaker. Stir in a water bath at 30 ℃ and 1000 rpm. Add the bimetallic complex solution obtained in step (1) dropwise to the ammonium carbonate solution at a rate of 5 mL / min. At the same time, add ammonia water (mass fraction of 5%) dropwise through a peristaltic pump to maintain the pH of the system at 5.5±0.01 for 15 min. Then raise the pH to 8.0 at a rate of 0.3 pH / min and maintain it for 10 min. Continue stirring and aging for 30 min to obtain a precipitate suspension. Fine bubbles (CO2) escape during the precipitation process.

[0050] (3) Low-temperature plasma-assisted aging: The precipitated suspension obtained in step (2) was transferred into a plasma reactor (quartz tube with an inner diameter of 25 mm), oxygen was introduced at a flow rate of 50 mL / min, dielectric barrier discharge was applied, and the mixture was treated for 60 min at a temperature of 40℃, a discharge power of 50 W, and a frequency of 10 kHz.

[0051] (4) Freeze-drying: The precipitate suspension after step (3) was centrifuged at 10,000 rpm for 10 min to separate the precipitate, washed twice with deionized water, and then washed twice with ethanol; the washed precipitate was dispersed in a 20% tert-butanol aqueous solution and ultrasonically treated for 40 min at a power of 300 W and a frequency of 40 kHz; then freeze-dried at -50 ℃ and a vacuum degree of less than 10 Pa for 48 h to obtain the precursor powder.

[0052] (5) Two-stage calcination: The precursor powder obtained in step (4) is placed in a tube furnace and calcined in two stages under an air atmosphere. In the first stage, the temperature is raised to 300 ℃ at a rate of 3 ℃ / min and held for 2 h. In the second stage, the temperature is raised to 550 ℃ at a rate of 5 ℃ / min and held for 2 h. After calcination, the powder is naturally cooled to room temperature to obtain black iridium-ruthenium bimetallic oxide powder.

[0053] Comparative Example 1 This comparative example is used to verify the necessity of a multi-step synergistic process of "pH gradient reverse precipitation + low-temperature plasma-assisted aging + tert-butanol-assisted freeze-drying + two-stage calcination" for controlling the morphology of the precipitation process. This comparative example uses the traditional co-precipitation method, as detailed below: (1) Preparation of precursor solution: Weigh 0.258 g of chloroiridium acid (H2IrCl6·6H2O, containing 0.5 mmol of Ir) and 0.261 g of ruthenium trichloride (RuCl3·3H2O, containing 1.0 mmol of Ru) and dissolve them in 100 mL of deionized water to obtain a mixed solution. The molar ratio of Ir to Ru in the mixed solution is 1:2, and the total metal ion concentration is 0.015 mol / L. The solution is ultrasonically treated for 40 min at a temperature of 60 ℃, a power of 150 W, and a frequency of 40 kHz to obtain a clear bimetallic solution.

[0054] (2) Coprecipitation: Take 200 mL of ammonium bicarbonate solution (1.0 mol / L) and place it in a beaker. Stir in a water bath at 50 °C and 1000 rpm. Add the bimetallic solution obtained in step (1) dropwise to the ammonium bicarbonate solution at a rate of 5 mL / min. Add ammonia water (mass fraction of 5%) dropwise through a peristaltic pump until the pH of the system reaches 7.5. During the dropwise addition, local precipitation occurs. Continue stirring and aging for 60 min to obtain a precipitate suspension.

[0055] (3) Washing and drying: The precipitate suspension obtained in step (2) is filtered to separate the precipitate, washed three times with deionized water, and then washed twice with ethanol; the washed precipitate is placed in an oven and dried at 80 °C for 12 h to obtain precursor powder.

[0056] (4) Calcination: The precursor powder obtained in step (3) is placed in a muffle furnace and heated to 450 °C at a rate of 5 °C / min in an air atmosphere. It is then calcined at a constant temperature for 4 h. After calcination, it is naturally cooled to room temperature to obtain black iridium-ruthenium bimetallic oxide powder.

[0057] Comparative Example 2 This comparative example is used to verify the necessity of stepwise complexation by a dual complexing agent for regulating metal complexation. The difference between this comparative example and Example 1 is that a single complexing agent (citric acid) is used; the remaining steps and processes are the same as in Example 1, as detailed below: (1) Complexation: Weigh 0.258 g of chloroiridium acid (H2IrCl6·6H2O, containing 0.5 mmol of Ir) and 0.261 g of ruthenium trichloride (RuCl3·3H2O, containing 1.0 mmol of Ru) and dissolve them in 100 mL of deionized water to obtain a mixed solution. The molar ratio of Ir to Ru in the mixed solution is 1:2 and the total metal ion concentration is 0.015 mol / L. Add 1.225 g of citric acid (6.38 mmol) and sonicate at 40 ℃, 150 W, and 40 kHz for 20 min to obtain a bimetallic complex solution.

[0058] (2) pH gradient reverse precipitation: Take 200 mL of ammonium bicarbonate solution (1.0 mol / L) and place it in a beaker. Stir in a water bath at 50 ℃ and 800 rpm. Add the bimetallic complex solution obtained in step (1) dropwise to the ammonium carbonate solution at a rate of 1 mL / min. At the same time, add ammonia water (mass fraction of 5%) dropwise through a peristaltic pump to maintain the pH of the system at 5.0±0.01 for 10 min. Then raise the pH to 7.5 at a rate of 0.2 pH / min and maintain it for 30 min. Continue stirring and aging for 30 min to obtain a precipitate suspension. Fine bubbles (CO2) escape during the precipitation process.

[0059] (3) Low-temperature plasma-assisted aging: The precipitate suspension obtained in step (2) was transferred into a plasma reactor (quartz tube with an inner diameter of 25 mm), oxygen was introduced at a flow rate of 100 mL / min, dielectric barrier discharge was applied, and the mixture was treated for 30 min at a temperature of 55℃, a discharge power of 100 W, and a frequency of 10 kHz.

[0060] (4) Freeze-drying: The precipitate suspension after step (3) was centrifuged at 10,000 rpm for 10 min to separate the precipitate, washed twice with deionized water, and then washed twice with ethanol. The washed precipitate was dispersed in a 15% tert-butanol aqueous solution and ultrasonically treated for 30 min at a power of 200 W and a frequency of 40 kHz. Then, it was freeze-dried at -50 ℃ and a vacuum degree of less than 10 Pa for 48 h to obtain the precursor powder.

[0061] (5) Two-stage calcination: The precursor powder obtained in step (4) is placed in a tube furnace and calcined in two stages under an air atmosphere. In the first stage, the temperature is raised to 250 ℃ at a rate of 1 ℃ / min and held for 1 h. In the second stage, the temperature is raised to 450 ℃ at a rate of 3 ℃ / min and held for 4 h. After calcination, the powder is naturally cooled to room temperature to obtain black iridium-ruthenium bimetallic oxide powder.

[0062] The iridium-ruthenium bimetallic oxides prepared in the embodiments and comparative examples of this invention were applied to supported Ir-Ru bimetallic catalysts, and the comprehensive performance of the catalysts was tested. The results are shown in Table 1. Table 1 As shown in Table 1, compared with the comparative examples, the supported Ir-Ru bimetallic catalyst prepared by the method of the present invention has excellent comprehensive performance. Among them, the overpotential of the supported Ir-Ru bimetallic catalyst prepared in Example 3 is as low as 225 mV @ 10 mA·cm -2 The supported Ir-Ru bimetallic catalyst prepared in Example 1 has a high specific surface area of ​​34 m². 2 / g.

[0063] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A gradient complexation-plasma-assisted preparation method for iridium-ruthenium bimetallic oxides, characterized in that, Includes the following steps: (1) Dissolve the iridium precursor and the ruthenium precursor in water to obtain a mixed solution. Add the first complexing agent to the mixed solution and perform a sonication treatment. Then add the second complexing agent and perform a second sonication treatment to obtain a bimetallic complex solution. (2) The bimetallic complex solution obtained in step (1) is added dropwise to an alkaline precipitant aqueous solution, and a precipitate suspension is obtained by staged precipitation through a pH step program; (3) Low-temperature plasma treatment of the precipitated suspension; (4) The precipitate suspension after step (3) is centrifuged to obtain the precipitate, and then washed, ultrasonically dispersed and freeze-dried to obtain the precursor powder; (5) The precursor powder obtained in step (4) is subjected to two-stage calcination to obtain iridium-ruthenium bimetallic oxide.

2. The gradient complexation-plasma-assisted preparation method of iridium-ruthenium bimetallic oxide according to claim 1, characterized in that, In step (1), the iridium precursor is one of chloroiridium acid, iridium trichloride, or potassium chloroiridium, and the ruthenium precursor is one of ruthenium trichloride, chlororuthenium acid, or potassium chlororuthenium; the total metal ion concentration of Ir and Ru in the mixed solution is 0.01 to 0.1 mol / L, and the molar ratio of Ir to Ru in the mixed solution is (1 to 9): (9 to 1).

3. The gradient complexation-plasma-assisted preparation method of iridium-ruthenium bimetallic oxide according to claim 1, characterized in that, In step (1), the first complexing agent is citric acid or citrate, and the amount added is 1.5 to 4 times the amount of ruthenium ions in the mixed solution; the second complexing agent is L-aspartic acid, L-glutamic acid or glycine, and the amount added is 1 to 3 times the amount of total metal ions in the mixed solution.

4. The gradient complexation-plasma-assisted preparation method of iridium-ruthenium bimetallic oxide according to claim 1, characterized in that, The conditions for the first ultrasonic treatment in step (1) are: power of 100-300 W, frequency of 40 kHz, temperature of 20-50 ℃, and time of 20-40 min; the conditions for the second ultrasonic treatment are: power of 100-300 W, frequency of 40 kHz, temperature of 50-80 ℃, and time of 30-50 min.

5. The gradient complexation-plasma-assisted preparation method of iridium-ruthenium bimetallic oxide according to claim 1, characterized in that, In step (2), the concentration of the alkaline precipitant aqueous solution is 0.1–2 mol / L; the precipitant is one or more of ammonia, ammonium carbonate, and ammonium bicarbonate.

6. The gradient complexation-plasma-assisted preparation method of iridium-ruthenium bimetallic oxide according to claim 1, characterized in that, In step (2), the reverse drop rate is 0.5–5 mL / min, and the stirring rate is 500–1000 rpm. The pH step program conditions are: first, maintain pH 4.5–5.5 for 5–15 min, then increase it to pH 7.0–8.0 at a rate of 0.1–0.3 pH / min and maintain it for 10–30 min. The temperature of the entire process is 30–60 °C.

7. The gradient complexation-plasma-assisted preparation method of iridium-ruthenium bimetallic oxide according to claim 1, characterized in that, In step (3), the low-temperature plasma treatment is a dielectric barrier discharge with a discharge power of 50-150 W, a temperature of 40-70 °C, and a treatment time of 10-60 min. The atmosphere is oxygen or air. When the atmosphere is oxygen, the flow rate is 50-200 mL / min. When the atmosphere is air, the flow rate does not need to be set.

8. The gradient complexation-plasma-assisted preparation method of iridium-ruthenium bimetallic oxide according to claim 1, characterized in that, The ultrasonic dispersion step in step (4) is as follows: the washed precipitate is dispersed in an aqueous solution of tert-butanol with a mass fraction of 10-20%, and ultrasonically treated for 20-40 min at a power of 100-300 W and a frequency of 40 kHz; the freeze-drying temperature is below -50 ℃, the vacuum degree is below 10 Pa, and the time is 24-48 h.

9. The gradient complexation-plasma-assisted preparation method of iridium-ruthenium bimetallic oxide according to claim 1, characterized in that, The two-stage calcination process in step (5) is as follows: in the first stage, the temperature is increased to 200-300 ℃ at a rate of 1-3 ℃ / min and held for 1-2 h; in the second stage, the temperature is increased to 350-550 ℃ at a rate of 2-5 ℃ / min and held for 2-5 h.

10. The application of the iridium-ruthenium bimetallic oxide prepared by any one of claims 1 to 9 in the acidic oxygen evolution reaction.

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