Porous metastable state iridium oxide composite catalyst and preparation method thereof

Abstract

The invention discloses a preparation method of a porous metastable state iridium oxide composite catalyst, which comprises the following steps: uniformly mixing iridium salt, inorganic salt, metal salt, a dispersant and pre-ground sodium nitrate in a solvent, and adjusting the pH value of the solution to 1-3 to obtain a uniformly mixed solution; removing the solvent from the mixed solution to obtain a uniform powder mixture; uniformly grinding the powder mixture, and performing high-temperature roasting in a muffle furnace to obtain a composite metal oxide; and fully washing and drying the composite metal oxide to obtain the porous metastable iridium oxide composite catalyst. The iridium oxide is doped and compositely modified by adopting the inorganic salt, the metal salt and the pore-forming agent, the internal lattice structure, the electronic state and the void structure of the iridium oxide are adjusted, the catalytic activity and the stability are improved, and the method is simple, easy to implement, high in yield, capable of achieving large-scale mass production and beneficial to industrial application.

Description

Technical Field

[0001] The invention relates to the field of electrochemical catalysis, and in particular to a porous metastable iridium oxide composite catalyst with high activity and durability for use in the electrolysis of water to produce hydrogen and oxygen evolution reaction, and a preparation method thereof. Background Art

[0002] As an important part of the future national energy system, hydrogen has high calorific value, abundant resources, is clean and carbon-free, can be used for power generation, heating, long-term long-distance energy storage and transportation, has both energy and energy storage properties, and has a wide range of application scenarios. It is an important carrier for energy users to achieve green and low-carbon transformation. "Green hydrogen" produced by sustainable clean energy electrolysis of water is the cornerstone for achieving low-carbon development of the hydrogen energy industry chain.

[0003] In the field of hydrogen production by electrolysis of water using PEM (Proton Exchange Membrane), iridium oxide, as a conventional commercial oxygen evolution catalyst, has the characteristics of high catalytic activity and good stability. The preparation methods include Adamas Fusion method, alkali precipitation method, liquid phase reduction method, soft and hard template method, spray deposition method and mechanochemical method. Among them, Adamas Fusions method can directly generate nano-sized iridium metal oxide by simply mixing and oxidizing iridium salt and sodium nitrate, which has the characteristics of simple synthesis process, adjustable structure and easy production and scale-up.

[0004] For example, CN 114540871 A discloses a method for preparing an amorphous iridium-manganese binary catalyst for a PEM water electrolysis anode, comprising dispersing iridium tetrachloride hydrate, manganese salt and sodium nitrate in a solvent, mixing them uniformly, evaporating them to dryness and calcining them at a constant temperature; washing them after ultrasonic treatment in an acid solution, collecting black precipitates, drying and grinding them to obtain an amorphous iridium-manganese binary catalyst.

[0005] For example, CN 116695159 A discloses a method of dissolving an iridium source, adding ammonia water, ultrasonically stirring, and adding nitrate, and then stirring at 50-100° C. for 0.5-5 h to evaporate the water to obtain an iridium dioxide precursor powder, and keeping the iridium dioxide precursor powder in an air atmosphere at a constant temperature of 300-800° C. for 0.5-5 h to obtain the catalyst.

[0006] For example, CN 116272971 A discloses a method for preparing a flaky porous iridium oxide catalyst, which comprises mixing an iridium source, a metal salt and a surfactant in an alcohol / water solution to obtain a uniform mixed solution, drying to remove the solvent and directly calcining at a high temperature to obtain a flaky porous iridium oxide nanomaterial.

[0007] For another example, CN 114164458 A discloses a method for preparing an iridium-ruthenium oxygen evolution catalyst, wherein an iridium precursor and a ruthenium precursor are dissolved in a solvent to obtain a mixed solution; a pore-forming agent and sodium nitrate are added to the mixed solution, and the mixed solution is heated and calcined and washed to obtain a crude iridium-ruthenium oxide product; the crude iridium-ruthenium oxide product is pre-leached with an acid solution, and washed and dried to obtain an iridium-ruthenium-based oxygen evolution catalyst.

[0008] The iridium oxide catalyst prepared by the Adamas Fusions method is mostly in the rutile phase, and its lattice is relatively complete, but its catalytic activity and stability are poor. Researchers have added pore-forming agents or small molecules to regulate the morphology and porosity of iridium oxide, or added metal ions to form iridium alloys or complexes to regulate the valence state or crystal form of iridium metal to improve catalytic activity, but the above strategies still have limited improvement effects. Therefore, how to obtain an oxygen evolution catalyst with high catalytic activity and high stability has become a technical problem that needs to be solved urgently in this field. Summary of the invention

[0009] In order to solve the above technical problems, the present invention provides a porous metastable iridium oxide composite catalyst and a preparation method thereof.

[0010] In a first aspect, the present invention provides a method for preparing a porous metastable iridium oxide composite catalyst, which is achieved by adopting the following technical scheme.

[0011] A method for preparing a porous metastable iridium oxide composite catalyst comprises the following steps:

[0012] S1. The iridium salt, the inorganic salt, the metal salt, the dispersant and the pre-ground sodium nitrate are uniformly mixed in a solvent, and the pH of the solution is adjusted to 1 to 3 to obtain a uniform mixed solution;

[0013] S2. removing the solvent from the mixed solution obtained in step S1 to obtain a uniform powder mixture;

[0014] S3. The powder mixture obtained in step S2 is ground uniformly and calcined at high temperature in a muffle furnace to obtain a composite metal oxide;

[0015] S4. The composite metal oxide obtained in step S3 is fully washed and dried to obtain a porous metastable iridium oxide composite catalyst.

[0016] Furthermore, in step S1, the iridium salt is selected from one or more combinations of chloroiridic acid, iridium acetate, iridium acetylacetonate, iridium trichloride, sodium hexachloroiridate, and potassium hexachloroiridate.

[0017] Furthermore, in step S1, the inorganic salt is selected from one or more combinations of sodium borate, sodium phosphate, and sodium acetate.

[0018] Furthermore, in step S1, the metal salt is selected from one or more combinations of nickel chloride, nickel nitrate, nickel acetylacetonate, cobalt chloride, cobalt nitrate, tantalum chloride and titanium boride.

[0019] Furthermore, in step S1, the dispersant is selected from one or more combinations of ammonium carbonate, ammonium bicarbonate, sodium carbonate, potassium carbonate, ammonium oxalate, and ammonium acetate.

[0020] Furthermore, in step S1, the solvent is selected from an aqueous solution of one or more of methanol, ethanol, isopropanol, ethylene glycol, and polyethylene glycol.

[0021] Furthermore, in step S1, the molar ratio of iridium salt, inorganic salt, metal salt and dispersant is 1:(0.01-0.1):(0.1-0.3):(5-80), the amount of sodium nitrate added is 10-30 times the mass of iridium salt, and the amount of solvent used is 20-30 times the mass of iridium salt.

[0022] Furthermore, in step S1, the materials are uniformly mixed in the solvent by stirring at room temperature or by ultrasonication in an ice bath, and an inert gas (nitrogen or argon) is filled during the mixing process to isolate the air.

[0023] Furthermore, in step S2, the method for removing the solvent from the mixed solution is freeze drying or reduced pressure distillation; during the freeze drying process, the cold trap temperature is -60 to -75°C, the sublimation temperature is 0 to 20°C, the sublimation negative pressure range is -0.7 to -0.95Mpa, and the total freeze drying time is 24 to 48h; the reduced pressure distillation negative pressure is -0.7 to -0.95Mpa, and the distillation temperature is 20 to 50°C.

[0024] Furthermore, in step S3, the mixed powder is calcined at a temperature of 300 to 550°C, a heating rate of 2 to 10°C / min, and a constant temperature calcination time of 0.5 to 3h.

[0025] Furthermore, in step S4, the washing method is to sequentially use 10wt% nitric acid, ultrapure water and ethanol solution for washing and filtering.

[0026] Furthermore, in step S4, the drying method is circulating fan heating drying or vacuum drying, and the drying temperature is 50-80°C.

[0027] In a second aspect, the present invention provides a porous metastable iridium oxide composite catalyst, which is achieved by adopting the following technical solution.

[0028] A porous metastable iridium oxide composite catalyst prepared by the above preparation method.

[0029] This application has the following beneficial effects.

[0030] (1) The present invention uses a low-valent iridium salt as a catalyst precursor, and uses freeze drying or reduced pressure distillation to dry the precursor mixed solution, strictly controlling the valence of iridium during sample mixing and pretreatment, thereby achieving fine control of the iridium valence and electron cloud density in the iridium oxide catalyst;

[0031] (2) The present invention adopts inorganic salt, metal salt and pore-forming agent to dope and compositely modify iridium oxide, adjust the internal lattice structure, electronic state and void structure of iridium oxide, and improve the catalytic activity and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic diagram of the TEM test results of the oxygen evolution catalyst of Example 1 of the present invention;

[0033] Figure 2 is the linear voltammetry (LSV) curve of the oxygen evolution catalyst of Example 1 of the present invention;

[0034] Figure 3 It is the chronoamperometry curve (CP) of the oxygen evolution catalyst of Example 1 of the present invention. DETAILED DESCRIPTION

[0035] The present patent application is further described below in conjunction with embodiments.

[0036] Example 1

[0037] A method for preparing a porous metastable iridium oxide composite catalyst comprises the following steps:

[0038] (1) Dissolve 1 g of iridium acetate, 0.01 g of sodium borate, 0.08 g of tantalum chloride, 5.9 g of ammonium carbonate, and 20 g of ground sodium nitrate in 16 mL of isopropanol aqueous solution (V). (异丙醇) :V (水) =3:1), in a nitrogen atmosphere, ultrasonically treating the mixed solution in an ice bath until it is completely dissolved, and adjusting the pH of the solution to 1.5 to obtain a mixed solution;

[0039] (2) freezing the mixed solution at a temperature below -65°C for 12 h, and then freeze-drying the mixture at 10°C and a negative pressure of -0.89 MPa for 12 h to obtain a mixed powder;

[0040] (3) transferring the mixed powder to a muffle furnace and calcining at 450° C. for 30 minutes at a heating rate of 10° C. / min to obtain a mixed metal oxide;

[0041] (4) washing and filtering the mixed metal oxide with 10 wt % nitric acid, ultrapure water and ethanol solution in sequence;

[0042] (5) Drying the filter residue at 60° C. to obtain a porous metastable iridium oxide composite catalyst.

[0043] Comparative Example 1

[0044] A method for preparing an iridium oxide catalyst, which differs from Example 1 in that sodium borate and tantalum chloride are not added during the preparation process.

[0045] Comparative Example 2

[0046] A method for preparing an iridium oxide catalyst, which differs from Example 1 in that: during the preparation process, after iridium acetate, sodium borate, tantalum chloride, ammonium carbonate and sodium nitrate are added to an isopropanol aqueous solution, heating and stirring at 50° C. in an air atmosphere are used to promote the dissolution of each reaction raw material, and the solvent pH is not adjusted.

[0047] Comparative Example 3

[0048] A method for preparing an iridium oxide catalyst is different from Example 1 in that during the preparation process, the mixed solution is kept in a constant temperature water bath at 80° C. until the solvent is evaporated to dryness to obtain a mixed powder.

[0049] Comparative Example 4

[0050] A method for preparing an iridium oxide catalyst is different from Example 1 in that during the preparation process, the mixed oxide obtained after calcination is not washed with 10wt% nitric acid, but only washed and filtered with water and anhydrous ethanol.

[0051] Comparative Example 5

[0052] A method for preparing an iridium oxide catalyst, which differs from Example 1 in that: in an air atmosphere, iridium acetate is dissolved in an isopropanol aqueous solution under stirring at room temperature, without adding inorganic salts, metal salts and pore-forming agents, and then the solvent is evaporated, the solid powder is calcined, washed with pure water, and dried to obtain iridium oxide.

[0053] Performance Testing

[0054] The electrolysis life of the oxygen evolution catalysts prepared in Example 1 and Comparative Examples 1-5 was evaluated respectively, and the specific parameters were as follows:

[0055] The electrocatalytic activity and durability were evaluated using a potentiostat with a standard three-electrode electrochemical cell. A graphite rod and a saturated calomel electrode were used as the counter electrode and reference electrode, respectively. The catalyst loading on the glassy carbon rod was 0.1 mg Ir / cm 2 , all potentials were converted to the potential of the reversible hydrogen electrode (RHE). The OER polarization curves were measured in Ar-saturated 0.1 M HClO4 solution at a scan rate of 5 mV / s at 1600 rpm, and the catalyst durability was measured at 10 mA / cm 2The results were obtained by chronopotentiometry at 200 rpm and 1600 rpm.

[0056] By the same electrolysis life evaluation method, the comparison results of the electrolysis life of Example 1 and Comparative Examples 1-5 are obtained, as shown in Table 1:

[0057] Table 1 Electrolysis life list

[0058] <![CDATA[Overpotential η 10 (mV)]]> Electrolysis life (h) Example 1 292 20 Comparative Example 1 305 12 Comparative Example 2 312 4 Comparative Example 3 330 2 Comparative Example 4 320 6 Comparative Example 5 345 2

[0059] In Table 1, it can be seen from the comparison between Example 1 and Comparative Example 1 that under the same preparation conditions, the addition of inorganic salts and metal salts can improve the structure of iridium oxide, form a metastable iridium oxide complex, reduce the catalyst overpotential and significantly improve the catalyst stability. It can be seen from the comparison between Example 1, Comparative Example 2 and Comparative Example 3 that in the process of material preparation, the air atmosphere, 50°C heating to promote the dissolution of raw materials and 80°C constant temperature evaporation will change the valence state of iridium, so that the iridium mixture has undergone valence changes before calcination, thereby significantly reducing the catalyst performance and stability. It can be seen from the comparison between Example 1 and Comparative Example 4 that the composite metal oxide after calcination is not treated with dilute nitric acid, and the excess inorganic salts, metal salts and pore-forming agents in the composite metal oxide cannot be completely removed, which will also affect the catalyst performance and stability. It can be seen from the comparison between Example 1 and Comparative Example 5 that by innovatively introducing inorganic salts, metal salts and pore-forming agents, and strictly controlling the valence state of iridium during the synthesis process, the iridium-containing mixture is prevented from undergoing significant valence changes before calcination, which can significantly improve the catalytic performance and stability of iridium oxide prepared by the Aadmas Fusion method.

[0060] The embodiments of this specific implementation method are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a porous metastable iridium oxide composite catalyst, characterized in that: The following steps are involved: S1. The iridium salt, the inorganic salt, the metal salt, the dispersant and the pre-ground sodium nitrate are uniformly mixed in a solvent, and the pH of the solution is adjusted to 1 to 3 to obtain a uniform mixed solution; S2. removing the solvent from the mixed solution obtained in step S1 to obtain a uniform powder mixture; S3. The powder mixture obtained in step S2 is ground uniformly and calcined at high temperature in a muffle furnace to obtain a composite metal oxide; S4. The composite metal oxide obtained in step S3 is fully washed and dried to obtain a porous metastable iridium oxide composite catalyst.

2. The method for preparing a porous metastable iridium oxide composite catalyst according to claim 1, characterized in that: In step S1, the iridium salt is selected from one or more of chloroiridic acid, iridium acetate, iridium acetylacetonate, iridium trichloride, sodium hexachloroiridate, and potassium hexachloroiridate.

3. The method for preparing a porous metastable iridium oxide composite catalyst according to claim 1, characterized in that: In step S1, the inorganic salt is selected from one or more combinations of sodium borate, sodium phosphate, and sodium acetate.

4. The method for preparing a porous metastable iridium oxide composite catalyst according to claim 1, characterized in that: In step S1, the metal salt is selected from one or more combinations of nickel chloride, nickel nitrate, nickel acetylacetonate, cobalt chloride, cobalt nitrate, tantalum chloride and titanium boride.

5. The method for preparing a porous metastable iridium oxide composite catalyst according to claim 1, characterized in that: In step S1, the dispersant is selected from one or more combinations of ammonium carbonate, ammonium bicarbonate, sodium carbonate, potassium carbonate, ammonium oxalate, and ammonium acetate.

6. The method for preparing a porous metastable iridium oxide composite catalyst according to claim 1, characterized in that: In step S1, the molar ratio of iridium salt, inorganic salt, metal salt and dispersant is 1:(0.01-0.1):(0.1-0.3):(5-80), the amount of sodium nitrate added is 10-30 times the mass of iridium salt, and the amount of solvent used is 20-30 times the mass of iridium salt.

7. The method for preparing a porous metastable iridium oxide composite catalyst according to claim 1, characterized in that: In step S2, the method for removing the solvent from the mixed solution is freeze drying or reduced pressure distillation; during the freeze drying process, the cold trap temperature is -60 to -75°C, the sublimation temperature is 0 to 20°C, the sublimation negative pressure range is -0.7 to -0.95MPa, and the total freeze drying time is 24 to 48h; the reduced pressure distillation negative pressure is -0.7 to -0.95Mpa, and the distillation temperature is 20 to 50°C.

8. The method for preparing a porous metastable iridium oxide composite catalyst according to claim 1, characterized in that: In step S3, the mixed powder is calcined at a temperature of 300 to 550°C, a heating rate of 2 to 10°C / min, and a constant temperature calcination time of 0.5 to 3 hours.

9. The method for preparing a porous metastable iridium oxide composite catalyst according to claim 1, characterized in that: In step S4, the washing method is to use 10wt% nitric acid, ultrapure water and ethanol solution in sequence for washing and filtering.

10. A porous metastable iridium oxide composite catalyst prepared by the preparation method according to any one of claims 1 to 9.

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