Nickel ferrite electrocatalyst as well as preparation method and application thereof
The nickel ferrite catalyst addresses the inefficiencies of oxide iron catalysts by improving conductivity and stability, enhancing ammonia production and enabling easy recovery, thus offering a more efficient and sustainable nitrogen reduction process.
Patent Information
- Application Number
- CN202510685409.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-27
- Publication Date
- 2025-07-08
AI Technical Summary
Existing electrocatalysts for nitrogen reduction to ammonia face challenges such as slow nitrogen adsorption and activation kinetics, low ammonia yield, and instability under high current densities, particularly with oxide iron catalysts due to poor conductivity, limited active sites, and difficulty in recovery and reuse.
A nickel ferrite catalyst (NixFe2O4) is synthesized via a hydrothermal method, optimizing the molar ratios of nickel and iron salts with sodium hydroxide and polyvinylpyrrolidone, enhancing conductivity, active sites, and stability, and enabling magnetic recovery.
The nickel ferrite catalyst exhibits improved conductivity, active site density, and stability, increasing ammonia production rates and reducing resource waste and environmental impact by facilitating easy recovery.
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Figure CN120272953A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of electrocatalysis, and particularly relates to a nickel ferrite electrocatalyst, a preparation method thereof, and an application thereof. Background Art
[0002] Ammonia (NH3), as an important chemical raw material, is widely used in the fields of agriculture, industry, and energy. Traditional ammonia synthesis mainly relies on the Haber - Bosch process, which requires high temperature (400 - 500 °C) and high pressure (15 - 30 MPa), consuming a large amount of energy and generating a large amount of greenhouse gases, imposing a burden on the environment. With the increasing global demand for green and sustainable development, developing an energy - saving and environmentally friendly ammonia synthesis technology has become an urgent task.
[0003] The electrocatalytic nitrogen reduction reaction for ammonia synthesis has received extensive attention due to its green, sustainable, and mild reaction conditions (room temperature and atmospheric pressure). However, the main challenges faced by this technology are the slow kinetics of the nitrogen adsorption and activation process, resulting in low ammonia production rate, and the hydrogen evolution reaction that reduces the selectivity of electrochemical reduction for ammonia production. Therefore, developing efficient electrocatalysts is the key to achieving a breakthrough in the electrocatalytic nitrogen reduction reaction for ammonia synthesis.
[0004] Iron oxide (Fe2O3) is considered a potential ammonia synthesis catalyst due to its abundant reserves, low cost, and good electrochemical properties. However, there are still some limitations in the electrocatalytic nitrogen reduction process of iron oxide. First, the poor conductivity of iron oxide limits its application efficiency in electrocatalytic reactions. Second, it is difficult to recycle iron oxide after the catalytic reaction, which not only increases the use cost but also may lead to resource waste and environmental pollution. In addition, the limited number of active sites of iron oxide results in insufficient adsorption and activation ability for nitrogen, leading to low ammonia production rate; and at high current densities, the active sites of the catalyst are easily reduced, resulting in a decrease in the stability and activity of the catalyst. Therefore, how to improve the conductivity, stability, and recyclability of iron oxide through modification is the key to achieving its efficient application in the field of ammonia synthesis. Summary of the Invention
[0005] In order to improve the conductivity, stability, and recyclability of the electrocatalyst for nitrogen reduction to ammonia, the present invention proposes a nickel ferrite electrocatalyst, a preparation method thereof, and an application thereof.
[0006] The technical solution of the present invention is as follows:
[0007] A preparation method of a nickel ferrite electrocatalyst, comprising the following steps:
[0008] Disperse nickel salt, iron salt, sodium hydroxide, and polyvinylpyrrolidone in deionized water, and carry out a hydrothermal reaction to obtain the nickel ferrite electrocatalyst;
[0009] The molar ratio of the nickel salt to the iron salt is 0.7 to 1.1:2.
[0010] Preferably, the nickel salt in the solution system is Ni(NO3)2·6H2O, and the iron salt is Fe(NO3)3·9H2O.
[0011] Preferably, the molar ratio of the iron salt to sodium hydroxide is 0.2 to 0.4:1.
[0012] Preferably, the mass ratio of the iron salt to polyvinylpyrrolidone is 0.1 to 0.3:1.
[0013] Preferably, the temperature of the hydrothermal reaction is 120 to 180 °C, and the reaction time is 5 to 10 h.
[0014] The present invention also provides a nickel ferrite electrocatalyst prepared by using the above preparation method. The chemical formula of the nickel ferrite electrocatalyst is Ni x Fe2O4, where x = 0.7 to 1.1.
[0015] The present invention also provides an application of the above nickel ferrite electrocatalyst in electrocatalytic nitrogen reduction for ammonia synthesis.
[0016] Compared with the prior art, the specific beneficial effects of the present invention are as follows:
[0017] The present invention uses a hydrothermal reaction method to prepare spinel-type Ni x Fe2O4. By precisely controlling parameters such as the molar ratio of the nickel salt to the iron salt, the molar ratio of the iron salt to sodium hydroxide, and the mass ratio of the iron salt to PVP, as well as the temperature and time of the hydrothermal reaction, the structure and properties of Ni x Fe2O4 can be regulated. The obtained Ni x Fe2O4 has better conductivity, the number of active sites, and stability compared with the existing electrocatalysts, thereby improving its performance in electrocatalytic nitrogen reduction for ammonia synthesis. Specifically, Ni x Fe2O4 prepared by regulating the metal ratio and the like improves the conductivity and enhances the electrocatalytic reaction efficiency; the product has more active sites, enhances the adsorption and activation ability of nitrogen, and improves the ammonia yield; the optimized preparation process enhances the stability of the catalyst during the electrocatalytic reaction, and the activity is not easily decreased; it has been verified that the product of the present invention has strong magnetism, which is convenient for recycling by magnetic attraction after the catalytic reaction, reduces the use cost, and reduces resource waste and environmental pollution.
[0018] The present invention provides an efficient, environmentally friendly, and recyclable electrocatalyst and its application solution for electrocatalytic nitrogen reduction for ammonia synthesis. The preparation process is simple and the cost is low, and it has broad application prospects. Description of the Drawings
[0019] Figure 1 Scanning electron microscope (SEM) image of the nickel ferrite (Ni 0.9 Fe2O4) electrocatalyst prepared in Example 1;
[0020] Figure 2 Scanning electron microscope (SEM) image of the nickel ferrite (Ni 0.7 Fe2O4) electrocatalyst prepared in Example 2;
[0021] Figure 3 Scanning electron microscope (SEM) image of the nickel ferrite (Ni 1.1 Fe2O4) electrocatalyst prepared in Example 3;
[0022] Figure 4 Scanning electron microscope (SEM) image of the iron oxide (Fe2O3) electrocatalyst prepared in the comparative example;
[0023] Figure 5 Diagram of the metal atom ratio of Ni and Fe obtained by inductively coupled plasma (ICP) testing of the catalysts prepared in Examples 1 to 3;
[0024] Figure 6 Diagram of the ammonia production rate and Faraday efficiency of each catalyst prepared in Examples 1 to 3 and the comparative example at a potential of -0.4 V vs. RHE;
[0025] Figure 7 Result diagram of the I-t test on different catalysts in the effect example;
[0026] Figure 8 Result diagram of the electrochemical impedance spectroscopy (EIS) test on different catalysts in the effect example;
[0027] Figure 9 Schematic diagram of the catalyst recovery test in the effect example. Detailed Description of the Invention
[0028] To make the technical solutions of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention. It should be noted that the following embodiments are only used to better understand the technical solutions of the present invention and should not be construed as a limitation of the present invention.
[0029] Example 1.
[0030] A preparation method of a nickel ferrite (Ni 0.9 Fe2O4) electrocatalyst, the specific steps are as follows:
[0031] Dissolve Ni(NO3)2·6H2O and Fe(NO3)3·9H2O in an appropriate amount of deionized water according to a molar ratio of 0.9:2. Subsequently, add sodium hydroxide to the solution so that the molar ratio of iron salt to sodium hydroxide is 0.3:1, and then add PVP so that the mass ratio of iron salt to PVP is 0.2:1. Place the above mixed solution in a hydrothermal reaction kettle and react at a temperature of 170 °C for 8 h to obtain Ni 0.9 Fe2O4.
[0032] Example 2.
[0033] A preparation method of a nickel ferrite (Ni 0.7 Fe2O4) electrocatalyst is as follows:
[0034] Dissolve Ni(NO3)2·6H2O and Fe(NO3)3·9H2O in an appropriate amount of deionized water according to a molar ratio of 0.7:2. Then add sodium hydroxide to the solution so that the molar ratio of iron salt to sodium hydroxide is 0.2:1, and then add PVP so that the mass ratio of iron salt to PVP is 0.1:1. Place the above mixed solution in a hydrothermal reaction kettle and react at a temperature of 160 °C for 10 h to obtain Ni 0.7 Fe2O4.
[0035] Example 3.
[0036] A preparation method of a nickel ferrite (Ni 1.1 Fe2O4) electrocatalyst is as follows:
[0037] Dissolve Ni(NO3)2·6H2O and Fe(NO3)3·9H2O in an appropriate amount of deionized water according to a molar ratio of 1.1:2. Then add sodium hydroxide to the solution so that the molar ratio of iron salt to sodium hydroxide is 0.4:1, and then add PVP so that the mass ratio of iron salt to PVP is 0.3:1. Place the above mixed solution in a hydrothermal reaction kettle and react at a temperature of 180 °C for 5 h to obtain Ni 1.1 Fe2O4.
[0038] Comparative example.
[0039] A preparation method of an iron oxide (Fe2O3) electrocatalyst is as follows:
[0040] Dissolve Fe(NO3)3·9H2O in an appropriate amount of deionized water without adding a nickel source. Add sodium hydroxide to the solution so that the molar ratio of iron salt to sodium hydroxide is 0.3:1, and then add PVP so that the mass ratio of iron salt to PVP is 0.2:1. Place the above mixed solution in a hydrothermal reaction kettle and react at a temperature of 170 °C for 8 h to form a Fe(OH)3 precipitate. Dry the formed precipitate to obtain a Fe(OH)3 precursor. Place the Fe(OH)3 precursor in a muffle furnace and calcine it at 300 °C for 2 h to obtain Fe2O3.
[0041] Characterization example.
[0042] Characterize the products generated in Examples 1 to 3. Their scanning electron microscope images are respectively as Figures 1 to 3 shown. Characterize the product generated in the comparative example. Its scanning electron microscope image is as Figure 4 shown. The morphological differences between pure iron oxide and nickel ferrite indicate that the doping of nickel plays a dominant role in the crystal growth mode. The regulation of the nickel-iron ratio significantly affects the microstructure and particle arrangement of nickel ferrite. An increase in the nickel content may affect the formation of a regular cubic structure.
[0043] Test the prepared catalysts in Examples 1 to 3 by inductively coupled plasma (ICP) to obtain the metal atom ratios of Ni and Fe. The results are shown in Figure 5 shown, clearly showing the feeding ratios and actual atomic ratios of Ni and Fe in each example. Therefore, it should be noted that the chemical formulas in the embodiments of the present application specification are all written according to the feeding ratios. The value of x in the actual chemical formula Ni x Fe2O4 has a slight fluctuation compared to the feeding ratio.
[0044] Effect example.
[0045] Test the electrochemical performance of the electrocatalysts in Examples 1 to 3 and the comparative example. The specific operation process is as follows:
[0046] 1. Catalyst dispersion and electrode preparation:
[0047] Respectively take 3 mg of the electrocatalysts prepared in Examples 1 to 3 and the comparative example, and disperse them in 0.8 mL of deionized water. Add 200 μL of 5% Nafion solution to the dispersion and ultrasonically treat it for 30 min to uniformly disperse the catalyst. Drop 10 μL of the dispersion on a glassy carbon electrode with a diameter of 5 mm and let it dry naturally for later use.
[0048] 2. Ammonia production rate and Faraday efficiency test:
[0049] Using an electrochemical workstation, continuous electrolysis was carried out at -0.4 V vs. RHE for 2 h. During the electrolysis process, high-purity nitrogen gas (99.999%) was continuously introduced to exclude dissolved oxygen, and the solution was kept stirred. The ammonia production rate and Faraday efficiency diagrams are shown in Figure 6 As shown, the ammonia production performance and electrocatalytic selectivity of different catalysts were compared. The results show that for the catalyst in Example 1 at -0.4 V vs. RHE potential, the ammonia production rate reached 75.6 μg h -1 mg -1 , and the Faraday efficiency reached 13.6%. For the catalyst in Example 2 at -0.4 V vs. RHE potential, the ammonia production rate reached 52.7 μg h -1 mg -1 , and the Faraday efficiency reached 9.8%. For the catalyst in Example 3 at -0.4 V vs. RHE potential, the ammonia production rate reached 45.3 μg h -1 mg -1 , and the Faraday efficiency reached 10.4%. For the iron oxide catalyst in the comparative example at -0.4 V vs. RHE potential, the ammonia production rate was 23.6 μg h -1 mg -1 , and the Faraday efficiency was only 4.2%. It can be proved that the nickel ferrite electrocatalyst provided by the present invention has significantly better performance than the pure iron oxide catalyst.
[0050] 3. I-t test (chronoamperometry test):
[0051] Chronoamperometry test was carried out using an electrochemical workstation. The test adopted a three-electrode system, and the test electrolyte was 0.1 M sodium sulfate solution. Nitrogen gas was continuously introduced before and during the test. Chronoamperometry test was carried out at a potential of -0.4 V vs. RHE, and the change curve of current with time was recorded, as shown in Figure 7 .
[0052] The test results show that the current of Example 1 (Ni 0.9 Fe2O4) remained stable during the long-term test, showing excellent stability. The currents of Example 2 (Ni 0.7 Fe2O4) and Example 3 (Ni 1.1 Fe2O4) fluctuated slightly, but the overall stability was good. The current of the comparative example (Fe2O3) decreased rapidly within a short time, indicating its poor stability and easy deactivation.
[0053] 4. EIS test (electrochemical impedance spectroscopy test):
[0054] Electrochemical impedance spectroscopy test was carried out using an electrochemical workstation, and the charge transfer resistances of each catalyst were compared. The results are shown in Figure 8 . The test results show that: Example 1 (Ni 0.9The charge transfer resistance (R of Fe2O4) ct ) is significantly lower than that of other samples, indicating excellent conductivity. Example 2 (Ni 0.7 Fe2O4) and Example 3 (Ni 1.1 Fe2O4) also have relatively low charge transfer resistances, but are still higher than that of Example 1. The charge transfer resistance of the comparative example (Fe2O3) is the highest, indicating poor conductivity and limiting the electrocatalytic performance.
[0055] 5. Catalyst recovery test:
[0056] The nickel ferrite (Ni 0.9 Fe2O4) catalyst prepared in Example 1 was dispersed in 8 mL of deionized water to form a uniform suspension. A magnet was placed outside the beaker and left standing for 10 min. It was found that the nickel ferrite was quickly attracted by the magnet and the solution gradually became clear. As Figure 9 shown, the left side is the state of the nickel ferrite catalyst dispersed in the solution, and the right side is the state of the clear solution after the catalyst is attracted by the magnet, proving that the catalyst has good magnetism and is convenient for recovery.
[0057] In summary, the catalyst claimed in the present invention has made significant progress in terms of stability, conductivity and recyclability, is significantly superior to the iron oxide catalyst, solves the main problems existing in iron oxide, and has a broader application prospect.
[0058] Obviously, the above examples are only for clear illustration and not a limitation of the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.
Claims
1. A preparation method of a nickel ferrite electrocatalyst, characterized in that, It includes the following steps: Disperse nickel salt, iron salt, sodium hydroxide and polyvinylpyrrolidone in deionized water, and carry out hydrothermal reaction to obtain nickel ferrite electrocatalyst; The molar ratio of the nickel salt to the iron salt is 0.7-1.1:
2.
2. The preparation method of the nickel ferrite electrocatalyst according to claim 1, wherein The nickel salt in the solution system is Ni(NO3)2·6H2O, and the iron salt is Fe(NO3)3·9H2O.
3. The preparation method of the nickel ferrite electrocatalyst according to claim 1, wherein, The molar ratio of the iron salt to sodium hydroxide is 0.2-0.4:
1.
4. The preparation method of the nickel ferrite electrocatalyst according to claim 1, characterized in that, The mass ratio of the iron salt to polyvinylpyrrolidone is 0.1-0.3:
1.
5. The preparation method of the nickel ferrite electrocatalyst according to claim 1, wherein, The temperature of the hydrothermal reaction is 120-180°C, and the reaction time is 5-10 h.
6. A nickel ferrite electrocatalyst, characterized in that, Prepared by using the preparation method described in any one of claims 1 to 5, and the chemical formula of the nickel ferrite electrocatalyst is Ni x Fe2O4, where x = 0.7 to 1.
1.
7. Application of a nickel ferrite electrocatalyst as described in claim 6 in electrocatalytic reduction of nitrogen to synthesize ammonia.