A method for magnetic regulation of iridium-based oxides and an iridium-based oxide catalyst material obtained thereby

Abstract

The application discloses a kind of magnetic regulation methods of iridium-based oxides and obtained iridium-based oxide catalyst materials, the strategy of hetero-element doping is first realized in the magnetic regulation of metal iridium in the oxide of co-edge structure, so as to optimize the electrocatalytic water oxidation performance of iridium-based oxide in strong acidic environment, experimental operation is simple, and economic cost is greatly reduced, effectively solve the current low catalytic activity of iridium-based oxide, the problem of poor stability, conducive to realizing large-scale industrial application.Compared with commercial iridium dioxide catalyst, the composite iridium-based oxide material synthesized by the application has high catalytic unit point activity and strong catalytic stability.The magnetic regulation method proposed in the application can be applied to the regulation of other properties.

Description

Technical Field

[0001] This invention belongs to the field of iridium-based oxide material modification, specifically relating to a method for magnetic control of iridium-based oxides and the obtained iridium-based oxide catalyst material. Background Technology

[0002] Hydrogen energy is considered the most ideal green energy carrier for solving the current energy crisis. Hydrogen production through electrochemical water splitting is simple, environmentally friendly, and produces high-purity hydrogen with few impurities. Among these technologies, proton exchange membrane electrolysis (PEM) in acidic aqueous solutions has attracted widespread attention due to its advantages such as high current density, high water splitting efficiency, fast response, and small footprint. The water electrolysis process involves two half-reactions: hydrogen production and oxygen production. The anodic water oxidation reaction for oxygen production is a four-electron process that requires significant energy, severely limiting the overall reaction efficiency of the electrolyzer and representing a bottleneck in the development of current proton exchange membrane hydrolysis technology. Currently, the electrocatalysts with application potential in acidic oxygen production reactions are mainly noble metal-based materials. However, the scarcity and high cost of noble metal materials, along with their high overpotential and limited stability, hinder the commercial application of oxygen production catalysts. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides a method for magnetic modulation of iridium-based oxides and the resulting iridium-based oxide catalyst material. Research has shown that regulating the spin configuration of metal sites can effectively improve the intrinsic electrochemical activity of water oxidation electrocatalysts. This invention introduces magnetic cobalt atoms to alter the magnetism of the iridium-based oxide material, optimizing its magnetic structure and ultimately leading to improved electrocatalytic water oxidation performance in acidic solvent environments.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] The first objective of this invention is to provide a method for controlling the magnetic properties of iridium-based oxides, comprising the following steps:

[0006] (1) Dissolve citric acid monohydrate and calcium salt in water to obtain reaction solution A; dissolve iridium salt and cobalt salt in ethylene glycol to obtain reaction solution B. The role of ethylene glycol is to promote the dissolution of iridium salt. After thoroughly mixing reaction solution A and reaction solution B, a multi-metal-organic hybrid material precursor solution is obtained. Then, the precursor solution is placed in a constant temperature environment of 120-180℃ for constant temperature dehydration and drying for 12-24 hours to obtain a precursor solid. Preferably, the calcium salt is calcium nitrate or calcium carbonate, the cobalt salt is cobalt nitrate or cobalt carbonate, and the iridium salt is potassium hexachloroiridate or iridium trichloride. It should be noted that the specific temperature for constant temperature dehydration and drying can be 120℃, 150℃, or 180℃, and the time can be 12h, 15h, 18h, or 24h.

[0007] (2) The obtained precursor solid was placed in an air atmosphere at 1-2℃ for 1 minute. -1 The heating rate is adjusted, and solid oxide powder is obtained through sequential high-temperature annealing; preferably, the high-temperature annealing program is performed sequentially at 200℃ for 6 hours, 300℃ for 6 hours, 500℃ for 3 hours, and 700℃ for 6 hours; high-temperature annealing can promote the gradual decomposition of organic molecules to achieve a stable phase and crystal structure of the target material, and the heating rate to reach the high temperature can specifically be 1.0, 1.5, or 2.0℃ / min. -1 For those skilled in the art, appropriate choices can be made based on the actual situation, and all of them can achieve the purpose of this invention.

[0008] (3) The obtained solid oxide powder is soaked in a strong acid solution for 10-20 hours. The sample is collected by centrifugation and washed multiple times with deionized water and alcohol solution, respectively, and then dehydrated and dried in an air drying oven for storage. Preferably, the strong acid solution is 1M hydrochloric acid; the soaking time can be 10 hours, 15 hours, or 20 hours, etc. For those skilled in the art, appropriate selection can be made according to the actual situation, and all of them can achieve the purpose of the present invention.

[0009] The second objective of this invention is to provide an iridium-based oxide catalyst material with optimized magnetic structure, which is prepared by the method described in the first objective; the iridium-based oxide is a mixed metal oxide composed of the noble metal iridium and non-noble metals; the magnetic change of this oxide material is caused by the magnetic atom cobalt, which has an optimized spin state, thus exhibiting moderate adsorption and desorption strength for intermediates and high energy conversion efficiency.

[0010] The reaction principle involved in this invention is as follows:

[0011] This invention obtains a uniform multi-metallic element organic complex precursor through a chemical solvent method; after a high-temperature annealing process, the organic framework is slowly decomposed in sequence to obtain a stable iridium-based oxide crystal structure; the annealing product contains non-iridium oxide impurities, which can be completely removed with hydrochloric acid solution, leaving no residue even on the nanolayer of the target catalyst surface.

[0012] The beneficial effects of this invention are as follows:

[0013] This invention obtains the reaction precursor through a chemical solvent method, promoting full reaction between multiple metal sources. A high-temperature annealing process controls the degradation and separation sequence of the organic molecular framework in the precursor, thereby promoting oxide crystallization. Hydrochloric acid solution effectively removes oxide impurities. This invention, for the first time, employs a heteroelement doping strategy, introducing magnetic cobalt atoms to alter the magnetism of iridium-based oxide materials. This achieves magnetic modulation of metallic iridium in edge-structured oxides, thus optimizing the electrocatalytic water oxidation performance of iridium-based oxides in strongly acidic environments. This invention features simple experimental operation, significantly reduced economic costs, and effectively solves the current problems of low catalytic activity and poor stability of iridium-based oxides, facilitating large-scale industrial applications. Compared with commercial iridium dioxide catalysts, the composite iridium-based oxide material synthesized in this invention exhibits high catalytic activity per unit point and strong catalytic stability. Attached Figure Description

[0014] Figure 1 Magnetic characteristic maps of the products prepared for comparative examples and embodiments;

[0015] Figure 2 Graphs showing the theoretical calculation verification of the magnetic structure of the products prepared in the comparative examples and embodiments;

[0016] Figure 3 Electrocatalytic oxygen production activity and stability of the products prepared in the comparative examples and examples; Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0018] Example 1

[0019] A method for preparing an iridium-based oxide material containing highly spin-iridium active sites includes the following steps:

[0020] (1) 312 mg of calcium nitrate and 280 mg of citric acid monohydrate are mixed with 5 ml of water to form solution A.

[0021] 72 mg potassium hexachloroiridate and 4.8 mg cobalt nitrate were dissolved in 4 mL of ethylene glycol to form solution B; at room temperature, reaction solution A was added dropwise to reaction solution B and stirred thoroughly until completely dissolved to obtain a multi-metal-organic hybrid material precursor solution C; solution C was dried at 150 °C to obtain a solid product as the precursor.

[0022] (2) The precursor was heated in air at 200℃ (6h), 300℃ (6h), 500℃ (3h) and 700℃ (6h) sequentially, with a heating rate of 1.7℃ / min. -1 Finally, solid oxide powder is obtained.

[0023] (3) Finally, the obtained solid oxide powder was treated with 1M hydrochloric acid solution for 6 hours to remove impurities. The solid product was obtained by centrifugation and washed multiple times with deionized water and alcohol solution, respectively. Then it was dried at a constant temperature of 60°C in an oven to obtain a 10 at% Co-doped Ca2IrO4 sample, labeled as 0.1Co-CIO.

[0024] Example 2

[0025] A method for preparing an iridium-based oxide material containing a central spin iridium active site includes the following steps:

[0026] (1) 312 mg of calcium nitrate and 280 mg of citric acid monohydrate are mixed with 5 ml of water to form solution A.

[0027] 80 mg potassium hexachloroiridate and 9.6 mg cobalt nitrate were dissolved in 4 mL of ethylene glycol to form solution B; at room temperature, reaction solution A was added dropwise to reaction solution B and stirred thoroughly until completely dissolved to obtain a multi-metal-organic hybrid material precursor solution C; solution C was dried at 150 °C to obtain a solid product as the precursor.

[0028] (2) The precursor was heated in air at 200℃ (6h), 300℃ (6h), 500℃ (3h) and 700℃ (6h) sequentially, with a heating rate of 1.7℃ / min. -1 Finally, solid oxide powder is obtained.

[0029] (3) Finally, the obtained solid oxide powder was treated with 1M hydrochloric acid solution for 6 hours to remove impurities. The solid product was obtained by centrifugation and washed multiple times with deionized water and alcohol solution, and then dried at a constant temperature of 60°C in an oven to obtain a 20 at% Co-doped Ca2IrO4 sample, labeled as 0.2Co-CIO.

[0030] Example 3

[0031] A method for preparing an iridium-based oxide material containing low-spin iridium active sites includes the following steps:

[0032] (1) 312 mg of calcium nitrate and 280 mg of citric acid monohydrate are mixed with 5 ml of water to form solution A.

[0033] 80 mg potassium hexachloroiridate and 19.2 mg cobalt nitrate were dissolved in 4 mL of ethylene glycol to form solution B. At room temperature, reaction solution A was added dropwise to reaction solution B and stirred thoroughly until completely dissolved to obtain a multi-metal-organic hybrid material precursor solution C. Solution C was dried at 150 °C to obtain a solid product as the precursor.

[0034] (2) The precursor was heated in air at 200℃ (6h), 300℃ (6h), 500℃ (3h) and 700℃ (6h) sequentially, with a heating rate of 1.7℃ / min. -1 Finally, solid oxide powder is obtained.

[0035] (3) Finally, the obtained solid oxide powder was treated with 1M hydrochloric acid solution for 6 hours to remove impurities. The solid product was obtained by centrifugation and washed multiple times with deionized water and alcohol solution, and then dried at a constant temperature of 60℃ in an oven to obtain a 40 at% Co-doped Ca2IrO4 sample, labeled as 0.4Co-CIO.

[0036] Comparative Example 1

[0037] Inert iridium dioxide materials for conventional electrocatalytic reactions are commercial catalysts, labeled IrO2.

[0038] Comparative Example 2

[0039] A method for preparing uncontrolled magnetic iridium-based oxide materials includes the following steps:

[0040] (1) 312 mg of calcium nitrate and 280 mg of citric acid monohydrate are mixed with 5 ml of water to form solution A.

[0041] 80 mg of potassium hexachloroiridate was dissolved in 4 mL of ethylene glycol to form solution B; at room temperature, reaction solution A was added dropwise to reaction solution B and stirred thoroughly until completely dissolved to obtain a multi-metal-organic hybrid material precursor solution C; solution C was dried at 150 °C to obtain a solid product as the precursor.

[0042] (2) The precursor was heated in air at 200℃ (6h), 300℃ (6h), 500℃ (3h) and 700℃ (6h) sequentially, with a heating rate of 1.7℃ / min. -1 Finally, solid oxide powder is obtained.

[0043] (3) Finally, the obtained solid oxide powder was treated with 1M hydrochloric acid solution for 6 hours to remove impurities. The solid product was obtained by centrifugation and washed multiple times with deionized water and alcohol solution, respectively. Then, it was dried in an oven at a constant temperature of 60°C to obtain sample Ca2IrO4, labeled as CIO.

[0044] Structural characterization

[0045] The products prepared in the above embodiments and comparative examples were structurally characterized. Figure 1 Figure a shows the magnetic characterization structure of the products prepared in the comparative example and the embodiment. It can be seen that the magnetic susceptibility gradually increases with the increase of Co doping concentration. Figure 1Figure b shows the Co L3 edge X-ray absorption spectrum of the product prepared in the example. It can be seen that the doped Co elements in the examples have different spin distribution structures, among which 0.2Co-CIO has the optimal cobalt spin state. Figure 1 Figure c shows the OK edge X-ray absorption spectra of the products prepared in the comparative example and the embodiment. Figure 1 Figure d shows the active Ir site spin distribution structure of the products prepared in the comparative example and the embodiment, in which 0.2Co-CIO has the optimal spin state in iridium. Figure 2 The magnetic structure of the products prepared in the comparative examples and embodiments is shown in the theoretical calculation verification diagram. From left to right, they correspond to CIO, 0.1Co-CIO, 0.2Co-CIO and 0.4Co-CIO, respectively. It can be seen that as the cobalt doping concentration increases, the spin density of the doping element cobalt gradually decreases, while the spin density of the active site iridium gradually increases. Therefore, the spin density of the coordinated oxygen changes significantly, thus significantly affecting its performance.

[0046] Performance testing

[0047] The materials prepared in the comparative examples and embodiments described above were subjected to electrocatalytic oxygen production performance testing in a strongly acidic environment (sulfuric acid solution with pH = 0). The electrocatalytic oxygen production performance testing was performed using the standard three-electrode method, with a silver chloride electrode as the reference electrode and a platinum mesh as the counter electrode. The test results are as follows: Figure 3 As shown. From Figure 3 Figures a and b in the table show that the product prepared in the example has a lower electrocatalytic oxygen production overpotential and higher iridium mass activity than the product in the comparative example. Figure 3 Figure c shows that Example 0.2Co-CIO exhibits superior acid-resistant electrocatalytic stability. These results demonstrate that the present invention obtains iridium-based oxide materials with magnetically regulated structures through heteroatomic Co doping, with 0.2Co-CIO showing significantly optimized catalytic performance.

[0048] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method of magnetic control of iridium-based oxides, characterized by: The method comprises the following steps: (1) dissolving citric acid and calcium salt in water to obtain reaction liquid A; dissolving iridium salt and cobalt salt in ethylene glycol to obtain reaction liquid B; mixing reaction liquid A and reaction liquid B uniformly to obtain a multi-metal-organic hybrid material precursor solution, and then drying to obtain a precursor solid; (2) annealing the precursor solid at high temperature to obtain a solid oxide powder; (3) soaking the obtained solid oxide powder in an acid solution to remove impurities, and finally cleaning and dehydrating and drying to obtain an iridium-based oxide catalyst material with optimized magnetic structure; In step (1), the calcium salt is calcium nitrate or calcium carbonate; the cobalt salt is cobalt nitrate or cobalt carbonate; and the iridium salt is potassium hexachloroiridate or iridium trichloride. In step (2), the high-temperature annealing method is as follows: placing the precursor solid in an air atmosphere, and sequentially annealing at 200 DEG C for 6 h, at 300 DEG C for 6 h, at 500 DEG C for 3 h, and at 700 DEG C for 6 h in a high-temperature furnace.

2. The method of claim 1, wherein the method is performed at a temperature of 300 K or less. In step (1), the drying temperature is 120-180 DEG C.

3. The method of claim 1, wherein the method is performed at a temperature of 300- 400 °C. In step (1), the drying time is 12-24 h.

4. The method of claim 1, wherein the method is performed at a temperature of 300- 400 °C. In step (3), the acid solution is a hydrochloric acid solution.

5. The method of claim 1, wherein the method is performed at a temperature of 300- 400 °C. In step (3), the soaking time is 10-20 h.

6. An iridium-based oxide catalyst material characterized by: It is obtained by using the magnetic regulation method according to any one of claims 1 to 5.

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