Iron-tantalum bimetal organic framework catalyst and preparation method and application thereof

Abstract

The invention belongs to the technical field of catalysts, and discloses an iron-tantalum bimetal organic framework catalyst and a preparation method and application thereof. The iron-tantalum bimetal organic framework catalyst takes foamed nickel as a substrate, and a needle-shaped iron-tantalum bimetal organic framework material is uniformly loaded on the foamed nickel substrate. The preparation method comprises the following steps: carrying out acid etching on foamed nickel, then washing with ethanol and water in sequence, and drying; the preparation method comprises the following steps: uniformly dispersing water-soluble ferric salt and tantalum chloride in water to obtain a solution A; 2-hydroxyterephthalic acid is dissolved in a mixed solvent composed of absolute ethyl alcohol and N, N-dimethylformamide, and a solution B is obtained; dropwise adding the solution B into the solution A to obtain a solution C; obliquely placing foamed nickel into a hydrothermal reaction kettle, adding the solution C, completely soaking the foamed nickel, and reacting at 80-125 DEG C for 8-12 hours; and taking out the foamed nickel, washing with water, and drying to obtain the target catalyst. The catalyst prepared by the invention can realize low overpotential and excellent stability when being used for water electrolysis oxygen evolution reaction.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to an iron-tantalum bimetallic organic framework catalyst, its preparation method, and its application. Background Technology

[0002] Hydrogen energy, due to its high energy density and pollution-free combustion products, is considered the most promising next-generation clean energy source. Among various hydrogen production technologies, water electrolysis can convert intermittent renewable energy sources (such as solar and wind power) into high-purity hydrogen, achieving the production of "green hydrogen" and serving as a crucial bridge connecting renewable energy and hydrogen energy. The water electrolysis process involves two half-reactions: the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. The OER is a complex process involving four electron transfers, characterized by slow kinetics and high overpotential, becoming a bottleneck restricting the overall efficiency of water electrolysis. Therefore, developing efficient and stable OER electrocatalysts is crucial for reducing electrolyzer energy consumption and improving hydrogen production efficiency. Currently, noble metal-based catalysts (such as ruthenium oxide and iridium oxide) are recognized as the most advanced OER catalysts. However, the scarcity and high cost of noble metals severely limit their prospects for large-scale industrial applications.

[0003] Therefore, developing alternative catalysts with non-precious metal or low-precious metal content has become a research hotspot. Among them, catalysts based on 3d transition metals such as iron have shown great application potential due to their abundant resources, low cost, and tunable electronic structure. However, despite significant progress in the research of iron-based metal catalysts, their performance (especially activity and stability) still lags far behind that of precious metal catalysts. Summary of the Invention

[0004] To address the issues of poor stability and activity in existing catalysts for hydrogen production and oxygen evolution reaction via water electrolysis, the present invention aims to provide an iron-tantalum bimetallic organic framework catalyst, its preparation method, and its applications.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A bimetallic organic framework catalyst based on nickel foam, wherein the bimetallic organic framework material is uniformly loaded on the nickel foam substrate and the bimetallic organic framework material is needle-shaped; in the bimetallic organic framework material, the molar ratio of iron (Fe): tantalum (Ta) is 2:3 to 4:1.

[0006] The preparation method of the iron-tantalum bimetallic organic framework catalyst includes the following steps: (1) The nickel foam is acid etched, then cleaned with ethanol and water in sequence, dried and set aside; (2) Disperse water-soluble iron salt and tantalum chloride evenly in water to obtain solution A; (3) Dissolve 2-hydroxyterephthalic acid in a mixed solvent of anhydrous ethanol and N,N-dimethylformamide to obtain solution B; (4) Add solution B dropwise to solution A. After the addition is complete, stir well to obtain solution C. (5) Place the nickel foam obtained in step (1) into a hydrothermal reactor at an angle, then add solution C to the hydrothermal reactor and completely immerse the nickel foam, and then react at 80~125℃ for 8~12h; after the reaction is completed, cool to room temperature, take out the nickel foam, rinse its surface impurities with water, dry, and obtain the iron-tantalum bimetallic organic framework catalyst. In this context, the amount of water-soluble iron salt and tantalum chloride used in the molar ratio ensures that the ratio of iron to tantalum is 2:3~4:1, and the ratio of (iron + tantalum) to water in the solution of step (2) is 2-hydroxyterephthalic acid to anhydrous ethanol to N,N-dimethylformamide = (0.6~1) mmol / L to (8~12) mL to (120~180) mg to (3~6) mL to (3~6) mL.

[0007] Preferably, in step (1), the nickel foam is acid-etched in 1-3 mol / L hydrochloric acid for 10-30 min.

[0008] Preferably, in step (2), the water-soluble iron salt is ferric nitrate, ferric chloride, or ferric sulfate.

[0009] Preferably, in step (4), solution B is added dropwise to solution A at a rate of 0.05~0.5 mL / s.

[0010] Application of the iron-tantalum bimetallic organic framework catalyst: used as an anodic oxygen evolution reaction catalyst in water electrolysis for hydrogen production.

[0011] The preparation principle of this invention is as follows: This invention controllably incorporates a high-valence transition metal (Ta) into an iron-based organic framework material, which can adjust the electronic structure of iron atoms, optimize the adsorption energy of iron sites for oxygen-containing intermediates, and reduce the valence state of iron atoms to avoid excessive oxidation and dissolution of iron, thereby enhancing OER performance and activity and stability at high current densities. With appropriate doping of Ta, the iron-tantalum bimetallic organic framework material of this invention has a relatively moderate MOF structure. The unique periodic structure of MOFs combined with the porous and conductive foam nickel substrate provides abundant metal active sites and conductivity for the catalytic material, and also provides effective space for gas escape during the oxygen evolution reaction. At the same time, the bimetallic synergistic effect between Fe and Ta can enhance the intrinsic activity of the catalyst, producing advantages in thermodynamics and reaction kinetics, making the material have excellent electrochemical performance.

[0012] Beneficial effects: This invention not only has the advantages of simple synthesis, low equipment requirements and cost, short processing time, and convenient operation, but also the iron-tantalum bimetallic organic framework catalyst prepared by this invention can achieve low overpotential and excellent stability in the oxygen evolution reaction of water electrolysis: in a 1 M potassium hydroxide solution system, only an overpotential of 253 mV is required to reach 100 mA·cm⁻¹. -2 The current density, and at 100 mA·cm -2 It exhibited electrochemical stability for at least 2200 hours. Attached Figure Description

[0013] Figure 1 SEM images of the catalysts obtained in Example 1 (ab) and Comparative Example 2 (cd) of this invention.

[0014] Figure 2 : Elemental mapping diagram of the catalyst obtained in Example 1 of this invention.

[0015] Figure 3 : Elemental mapping diagram of the catalyst obtained in Comparative Example 2 of this invention.

[0016] Figure 4 XPS analysis diagrams of the catalysts obtained in Example 1 and Comparative Example 2 of this invention.

[0017] Figure 5 Cyclic voltammetric performance test diagrams of the catalysts obtained in Examples 1-4 of this invention.

[0018] Figure 6 : Cyclic voltammetric performance test diagrams of the catalysts obtained in Comparative Examples 1-3 of this invention.

[0019] Figure 7 The constant current stability test diagram of the catalysts obtained in Example 1 and Comparative Example 2 of this invention. Detailed Implementation

[0020] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the described embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0021] Example 1

[0022] A method for preparing an iron-tantalum bimetallic organic framework catalyst, comprising the following steps: (1) A foam nickel with a thickness of 1 mm, a length of 3 cm and a width of 3 cm was acid etched in 2M hydrochloric acid for 15 min. Then it was placed in anhydrous ethanol and deionized water for ultrasonic cleaning for 10 min each. The foam nickel was then taken out and placed in a petri dish and dried in a constant temperature drying oven (60℃) to obtain pretreated foam nickel. (2) According to the total molar amount of ferric nitrate nonahydrate and tantalum pentachloride being 1 mmol and the molar ratio of ferric nitrate nonahydrate to tantalum pentachloride being 3:2, weigh ferric nitrate nonahydrate, tantalum pentachloride and 160 mg of organic ligand 2-hydroxyterephthalic acid; add the weighed ferric nitrate nonahydrate and tantalum pentachloride to 10 mL of deionized water and stir for 40 min to obtain a homogeneous solution A; add 2-hydroxyterephthalic acid to a mixed solvent consisting of 5 mL of anhydrous ethanol and 5 mL of N,N-dimethylformamide, and place it in an ultrasonic device and sonicate for 30 min to fully disperse it to obtain a homogeneous solution B; add solution B dropwise to solution A at a rate of 0.1 mL / s, and stir for 1 h after the addition is complete to obtain a homogeneous solution C; (3) Place the pretreated nickel foam from step (1) into the hydrothermal reactor at an angle and slowly pour solution C into the hydrothermal reactor. At this time, solution C should completely immerse the nickel foam. Then, place the hydrothermal reactor in the hydrothermal reaction chamber at 125°C for 12 hours. After the reaction is completed, wait for the temperature of the hydrothermal reactor to drop to room temperature, remove the nickel foam with the product attached, rinse off the surface impurities with deionized water, place it in a petri dish, and dry it in a constant temperature drying oven to obtain the iron-tantalum bimetallic organic framework catalyst.

[0023] Example 2 The difference from Example 1 is that in step (2), the molar ratio of ferric nitrate nonahydrate to tantalum pentachloride is adjusted to 1:4; all other aspects are the same as in Example 1.

[0024] Example 3 The difference from Example 1 is that in step (2), the molar ratio of ferric nitrate nonahydrate to tantalum pentachloride is adjusted to 2:3; all other aspects are the same as in Example 1.

[0025] Example 4 The difference from Example 1 is that in step (2), the molar ratio of ferric nitrate nonahydrate to tantalum pentachloride is adjusted to 4:1; all other aspects are the same as in Example 1.

[0026] Comparative Example 1 The difference from Example 1 is that no metal-organic framework material was grown on the nickel foam substrate. The specific preparation steps are as follows: nickel foam with a thickness of 1 mm, a length of 3 cm, and a width of 3 cm was acid-etched in 2M hydrochloric acid for 15 min, and then placed in anhydrous ethanol and deionized water for ultrasonic cleaning for 10 min each. Then the nickel foam was taken out and placed in a petri dish and dried in a constant temperature drying oven (60°C) to obtain pretreated nickel foam, which was directly used as a catalyst.

[0027] Comparative Example 2 The difference from Example 1 is that in step (2), tantalum pentachloride was not added, that is, the molar ratio of ferric nitrate nonahydrate to tantalum pentachloride was adjusted to 5:0, and the amount of ferric nitrate nonahydrate was 1 mmol; everything else was the same as in Example 1.

[0028] The catalyst prepared in this comparative example is an iron single-metal organic framework catalyst.

[0029] Comparative Example 3 The difference from Example 1 is that in step (2), tantalum pentachloride is replaced with niobium oxalate, and the total molar amount of ferric nitrate nonahydrate and niobium oxalate is 1 mmol and the molar ratio of ferric nitrate nonahydrate to niobium oxalate is 3:2; all other aspects are the same as in Example 1.

[0030] The catalyst prepared in this comparative example is an iron-niobium bimetallic organic framework catalyst.

[0031] Product structure characterization Figure 1 These are SEM images of the catalysts obtained in Example 1 (ab) and Comparative Example 2 (cd) of the present invention. Figure 1 As can be seen from a, the iron-tantalum bimetallic organic framework material is distributed in needle-like shapes on the nickel foam substrate, by... Figure 1 c indicates that the iron single-metal organic framework material is distributed in a thick layer on the nickel foam substrate; it is evident that the doping of Ta atoms can effectively change the morphology of the iron single-metal organic framework material, and the needle-like material can effectively increase the active area of ​​the chemical reaction during the catalytic reaction, providing more adsorption / desorption sites for the four-electron transfer of the oxygen evolution reaction (OER), thereby increasing the density of active sites of the product.

[0032] Figure 2 This is an elemental mapping diagram of the catalyst obtained in Example 1 of the present invention. Figure 2 It can be clearly seen that the uniform distribution of Fe, Ta, C and O elements in the iron-tantalum bimetallic organic framework catalyst proves the successful doping of Ta element.

[0033] Figure 3 This is an elemental mapping diagram of the catalyst obtained in Comparative Example 2 of the present invention. Figure 3It can be clearly seen that the Fe, C, and O elements are evenly distributed in the iron single-metal organic framework catalyst.

[0034] Figure 4 The images show the elemental XPS analysis of the catalysts obtained in Example 1 and Comparative Example 2 of this invention. Figure 4 As shown, it can be clearly seen that with the doping of Ta, the Fe2p peak shifts to lower energies, proving that Ta doping can effectively reduce the valence state of Fe. The reduction in the valence state of Fe can effectively prevent the active site Fe from being over-oxidized during the oxygen evolution reaction at high potential, effectively improving the stability of the catalyst at high current density. At the same time, the binding energy between the low valence state Fe and oxygen-containing intermediates (*O, *OH, *OO) is weakened, which is conducive to the release of oxygen and enhances the activity of the catalyst.

[0035] Performance testing (a) Cyclic Volt-Ampere Performance Test The catalysts obtained in Examples 1-4 and Comparative Examples 1-3 of this invention are all self-supporting catalysts (with a nickel foam substrate as support), and therefore can be directly used as working electrodes. A three-electrode system was used, with the catalysts obtained in Examples 1-4 and Comparative Examples 1-3 of this invention as working electrodes, a carbon rod as a counter electrode, and silver chloride as a reference electrode. Cyclic voltammetry performance was tested in 1M KOH solution at a scan rate of 5 mV / s.

[0036] Figure 5 These are cyclic voltammetric test graphs of the catalysts obtained in Examples 1-4 of this invention. Figure 5 It can be seen that when the electrode current density of the oxygen evolution reaction is 100 mA·cm -2 At that time, the overpotentials (relative to reversible hydrogen, the same below) of the catalysts in Examples 1 to 4 were 253mV, 390mV, 270mV, and 260mV, respectively. It can be seen that as the proportion of Ta atoms increases, the overpotential of the catalyst first decreases and then increases. Except for iron:tantalum = 1:4 (Example 2), the overpotentials of the iron-tantalum bimetallic organic framework catalysts (Examples 1, 3, and 4) prepared based on other iron-tantalum ratios are lower than those of the noble metal IrO and RuO2 catalysts reported so far. In particular, the performance is optimal when iron:tantalum = 3:2 (Example 1).

[0037] Figure 6 The figures show the cyclic voltammetric performance test results of the catalysts obtained in Comparative Examples 1-3 of this invention. Figure 6 It can be seen that when the electrode current density of the oxygen evolution reaction is 100 mA·cm -2At that time, the overpotentials of the catalysts in Comparative Examples 1 to 3 were 485mV, 287mV, and 270mV, respectively. It can be seen that the catalyst in Example 1 has a much higher activity than the catalysts in Comparative Examples 1 to 3, which proves the superiority of Ta doping. Pure nickel foam (Comparative Example 1) is difficult to work at high current densities.

[0038] (II) Constant Current Stability Test A three-electrode system was used, with the catalysts obtained in Example 1 and Comparative Example 2 of this invention as the working electrode, a carbon rod as the counter electrode, and silver chloride as the reference electrode, in 1M KOH solution at 100 mA·cm⁻¹. -2 Constant current stability test was performed under the specified conditions.

[0039] Figure 7 The graphs show the constant current stability test results of the catalysts obtained in Example 1 and Comparative Example 2 of this invention. Figure 7 It can be seen that: the catalyst in Example 1 at 100 mA·cm -2 At a current density of 100 mA·cm⁻¹, the overpotential did not increase significantly after 2400 h of testing, therefore it can be tested at a current density of 100 mA·cm⁻¹. -2 Under the same conditions, the catalyst in Example 1 operated stably for at least 2400 hours; however, the catalyst in Comparative Example 2 only maintained stable operation for less than 120 hours at the same current density before its voltage increased significantly, indicating that the catalyst had deactivated. Constant current stability testing clearly demonstrates that Ta doping effectively improves the stability of the catalyst.

Claims

1. A bimetallic organic framework catalyst made of iron and tantalum, characterized in that: The iron-tantalum bimetallic organic framework catalyst uses nickel foam as a substrate, on which iron-tantalum bimetallic organic framework material is uniformly loaded, and the iron-tantalum bimetallic organic framework material is needle-shaped; in the iron-tantalum bimetallic organic framework material, the molar ratio of iron to tantalum is 2:3 to 4:

1.

2. A method for preparing the iron-tantalum bimetallic organic framework catalyst as described in claim 1, characterized in that, The steps are as follows: (1) The nickel foam is acid etched, then cleaned with ethanol and water in sequence, dried and set aside; (2) Disperse water-soluble iron salt and tantalum chloride evenly in water to obtain solution A; (3) Dissolve 2-hydroxyterephthalic acid in a mixed solvent of anhydrous ethanol and N,N-dimethylformamide to obtain solution B; (4) Add solution B dropwise to solution A. After the addition is complete, stir well to obtain solution C. (5) Place the nickel foam obtained in step (1) into a hydrothermal reactor at an angle, then add solution C to the hydrothermal reactor and completely immerse the nickel foam, and then react at 80~125℃ for 8~12h; after the reaction is completed, cool to room temperature, take out the nickel foam, rinse its surface impurities with water, dry, and obtain the iron-tantalum bimetallic organic framework catalyst. In this context, the amount of water-soluble iron salt and tantalum chloride used in the molar ratio ensures that the ratio of iron to tantalum is 2:3~4:1, and the ratio of (iron + tantalum) to water in the solution of step (2) is 2-hydroxyterephthalic acid to anhydrous ethanol to N,N-dimethylformamide = (0.6~1) mmol / L to (8~12) mL to (120~180) mg to (3~6) mL to (3~6) mL.

3. The method for preparing the iron-tantalum bimetallic organic framework catalyst as described in claim 1, characterized in that: In step (1), the nickel foam is acid-etched in 1~3 mol / L hydrochloric acid for 10~30 min.

4. The method for preparing the iron-tantalum bimetallic organic framework catalyst as described in claim 1, characterized in that: In step (2), the water-soluble iron salt is ferric nitrate, ferric chloride, or ferric sulfate.

5. The method for preparing the iron-tantalum bimetallic organic framework catalyst as described in claim 1, characterized in that: In step (4), solution B is added dropwise to solution A at a rate of 0.05~0.5 mL / s.

6. The application of the iron-tantalum bimetallic organic framework catalyst as described in claim 1, characterized in that: It is used as a catalyst for the oxygen evolution reaction at the anode in water electrolysis to produce hydrogen.

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