Fe3O4 / Fe2O3 electrocatalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of electrocatalysts, and particularly relates to a Fe3O4 / Fe2O3 electrocatalyst and a preparation method and application thereof. The preparation method comprises the following steps: dissolving the mesoporous molecular sieve and ferric nitrate in an organic solvent, adding alkali to adjust the pH value, evaporating to dryness, and calcining to prepare the Fe3O4 / Fe2O3 electrocatalyst. According to the Fe3O4 / Fe2O3 electrocatalyst disclosed by the invention, the specific surface area of the catalyst is remarkably increased through the multistage pore and nanoflower / skeleton design, more active sites and better mass transfer characteristics are provided for oxygen reduction reaction, and the electrocatalytic performance of the material is further improved. The preparation of the Fe3O4 / Fe2O3 electrocatalyst only needs two steps of hydrothermal reaction and high-temperature calcination, does not need complex equipment or harsh conditions, and is easy for large-scale production. As an electrocatalyst for oxygen reduction, the Fe3O4 / Fe2O3 electrocatalyst disclosed by the invention has relatively special morphology and relatively excellent performance.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalyst technology, and particularly relates to a Fe3O4 / Fe2O3 electrocatalyst, its preparation method, and its application. Background Technology

[0002] In the field of energy conversion and storage, highly efficient electrocatalysts are crucial. The oxygen evolution reaction (OER) is a key reaction step in many important energy technologies, such as fuel cells and metal-air batteries. Currently, commercial catalysts used for these reactions are mainly based on precious metals such as platinum. However, precious metal catalysts suffer from high cost, resource scarcity, and poor durability, which severely limit their large-scale application.

[0003] Non-precious metal-based catalysts, especially iron-based catalysts, have become a research hotspot due to their relatively abundant raw material sources, low cost, and good catalytic potential. However, traditional iron oxide catalysts have shortcomings in terms of active site exposure and mass transfer efficiency, resulting in room for improvement in their catalytic performance. For example, the catalyst structure is not conducive to oxygen transport and electrolyte diffusion, which limits reaction kinetics and makes it difficult to meet the needs of practical applications. Therefore, developing iron oxide catalysts with unique structures and excellent performance is of significant practical importance. Summary of the Invention

[0004] The purpose of this invention is to provide a Fe3O4 / Fe2O3 electrocatalyst, its preparation method, and its application, in order to solve the problem of how to provide a Fe3O4 / Fe2O3 catalyst with high exposure of active sites and promoting the transport of oxygen and electrolytes.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A method for preparing a Fe3O4 / Fe2O3 electrocatalyst, comprising:

[0007] The Fe3O4 / Fe2O3 electrocatalyst was prepared by dissolving mesoporous molecular sieve and ferric nitrate in an organic solvent, adjusting the pH with alkali, evaporating to dryness, and then calcining.

[0008] Preferably, the mass ratio of the mesoporous molecular sieve to the ferric nitrate is 0.5 to 1.5:3.

[0009] Preferably, the mesoporous molecular sieve is SBA-15.

[0010] Preferably, the organic solvent is ethanol.

[0011] Preferably, the ratio of the mesoporous molecular sieve to the organic solvent is 1g mesoporous molecular sieve: 40-80ml organic solvent.

[0012] Preferably, the pH adjustment by adding alkali includes adjusting the pH to 7.5-8.5 by adding potassium hydroxide.

[0013] Preferably, the calcination temperature is 700–900°C.

[0014] Preferably, the calcination temperature is 775–825°C.

[0015] Preferably, the calcination temperature is 800°C.

[0016] A Fe3O4 / Fe2O3 electrocatalyst is prepared by the method described above.

[0017] Application of the Fe3O4 / Fe2O3 electrocatalyst in electrochemical oxygen reduction reaction.

[0018] Compared with the prior art, the present invention has the following advantages and technical effects:

[0019] In this invention, the Fe3O4 / Fe2O3 electrocatalyst, through its hierarchical pore structure and nanoflower / framework design, significantly increases the specific surface area of ​​the catalyst, providing more active sites and better mass transport characteristics for the oxygen reduction reaction, thereby improving the electrocatalytic performance of the material.

[0020] The preparation of the Fe3O4 / Fe2O3 electrocatalyst of the present invention only requires two steps: hydrothermal reaction and high-temperature calcination. It does not require complex equipment or harsh conditions and is easy to scale up for production.

[0021] The Fe3O4 / Fe2O3 electrocatalyst of the present invention has a unique morphology and superior performance as an oxygen reduction electrocatalyst. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 X-ray diffraction data for Fe3O4 / Fe2O3 catalyst materials;

[0024] Figure 2 This is a scanning electron microscope (SEM) image of the SBA-15.

[0025] Figure 3 SEM image of the Fe3O4 / Fe2O3 catalyst at 700℃;

[0026] Figure 4 SEM image of the 800℃ Fe3O4 / Fe2O3 catalyst;

[0027] Figure 5 SEM image of the 900℃ Fe3O4 / Fe2O3 catalyst;

[0028] Figure 6 a is the SEM image of Fe3O4 without a template. Figure 6 b is the SEM image of Fe2O3 without a template;

[0029] Figure 7 The specific surface area diagrams of Fe-NC at 700℃, 800℃, and 900℃ are shown.

[0030] Figure 8 The LSV curves of ORR for Fe3O4 / Fe2O3 catalysts at 700℃, 800℃, and 900℃ are shown.

[0031] Figure 9 The ORR of Fe3O4 / Fe2O3 catalyst at 800℃ is shown as LSV curve at different rotation speeds.

[0032] Figure 10 The ORR curve of the Fe3O4 / Fe2O3 catalyst at 800℃ is a 20-cycle test curve.

[0033] Figure 11 The graph shows the ORR of the Fe3O4 / Fe2O3 catalyst after 20 cycles at 900℃. Detailed Implementation

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] Example 1

[0037] S1. Preparation of SBA-15

[0038] 6.0 g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) was weighed and dissolved in water. The pH of the solution was adjusted to 1 with hydrochloric acid and kept at 40°C for 3 h. Then, tetraethoxysilane (TEOS) was added and stirred for 24 h. After aging for 24 h, the solution was filtered, washed, and dried. Finally, it was calcined in a muffle furnace at 550°C for 8 h to obtain the final sample SBA-15.

[0039] S2. Prepare the evaporated sample

[0040] Weigh 0.50g of SBA-15 and a certain amount of ferric nitrate and dissolve them in 30mL of ethanol. Adjust the pH of the solution to 8 with potassium hydroxide and evaporate the solution to dryness at 60℃.

[0041] S3, calcination

[0042] The evaporated sample obtained from S2 was calcined at high temperature in a tube furnace at 700℃.

[0043] S4. Remove the template to obtain the target product.

[0044] The template was then removed with 1.0M NaOH to obtain a three-dimensional coral-like Fe3O4 / Fe2O3 structure.

[0045] Example 2

[0046] The only difference between this embodiment and Embodiment 1 is that the high-temperature calcination temperature in S3 is 800°C; all other conditions are exactly the same.

[0047] Example 3

[0048] The only difference between this embodiment and Embodiment 1 is that the high-temperature calcination temperature in S3 is 900°C; all other conditions are exactly the same.

[0049] Comparative Example 1

[0050] S1. Weigh 1.65g of ferric nitrate and dissolve it in 30mL of ethanol, then adjust the pH of the solution to 8 with potassium hydroxide. Evaporate the solution to dryness at 60℃.

[0051] S2. The sample obtained in S1 is calcined at high temperature in a tube furnace to obtain Fe3O4 / Fe2O3 with a granular structure.

[0052] Test Example 1

[0053] This experimental example confirms the electrocatalyst material, specifically including:

[0054] S1. The catalyst material in Example 1 was detected by X-ray (XRD) diffraction technology to obtain the diffraction pattern.

[0055] S2. Compare the obtained diffraction pattern with the PDF card (Powder Diffraction File).

[0056] from Figure 1 As can be seen from the data, the XRD data of the catalyst material in Example 1 matches the PDF card, proving that the catalyst material in Example 1 is a Fe3O4 / Fe2O3 catalyst material.

[0057] Test Example 2

[0058] This experimental example involves the observation of electrocatalyst materials using scanning electron microscopy imaging, specifically including:

[0059] Scanning electron microscopy (SEM) was used to observe SBA-15, the catalyst materials in Examples 1-3, and Fe3O4 / Fe2O3 without template, respectively. The images obtained are shown below. Figure 2-6 As shown.

[0060] contrast Figure 2 and Figure 3 It can be seen that, Figure 3 SEM images of the catalyst material in Example 1 and Figure 2 The SEM image of SBA-15 still retains the shape of the template.

[0061] from Figure 4 As can be seen from the above, a thin layer of nanoflowers grew on the surface of the catalyst material in Example 2, and the template morphology gradually disappeared and turned into a lotus root shape.

[0062] from Figure 5 As can be seen, the morphology of the catalyst material in Example 3 changes to a three-dimensional (3D) coral-like nanostructure.

[0063] from Figure 6 a and Figure 6 As can be seen in b, the SEM images of Fe3O4 without template and Fe2O3 without template both show that the morphology of the materials is nanoparticle-like.

[0064] Experimental Example 3

[0065] This experimental example measures the specific surface area of ​​an electrocatalyst material, specifically including:

[0066] This experimental example uses the BET (Brunauer-Emmett-Teller) method, a standard method for measuring the specific surface area of ​​materials, especially suitable for nanomaterials such as electrocatalysts. Specifically, it includes:

[0067] S1. Sample preparation: Weigh 1.0g of each of the three powder samples (Fe3O4 / Fe2O3-700 in Example 1, Fe3O4 / Fe2O3-800 in Example 2, and Fe3O4 / Fe2O3-900 in Example 3).

[0068] S2. Sample pretreatment (degassing): at a temperature of 150-200℃ for 12 hours, with a vacuum degree <10. -2 Torr(1.3×10 -4 Under the condition of Pa), degassing is performed to remove moisture, volatile substances and other impurities adsorbed on the sample surface, so as to ensure that the measured specific surface area is the true specific surface area of ​​the material itself.

[0069] S3. After degassing is complete, perform BET adsorption measurement:

[0070] First, set the instrument conditions as follows: nitrogen as the adsorbate (purity ≥ 99.999%); measurement temperature: 77K (liquid nitrogen temperature); relative pressure (p / p0) range: 0.05-0.35 (optimal range); measure 10-15 data points (covering the 0.05-0.35p / p0 range). Then, install the degassed sample tube at the measurement station and allow it to reach thermal equilibrium at the measurement temperature for pre-adsorption (vacuuming to low pressure). Gradually introduce nitrogen and measure the adsorption amount at different relative pressures.

[0071] S4. Data Acquisition: The instrument automatically records the adsorption amount at each pressure point and simultaneously measures the dead volume (used to calculate the absolute adsorption amount). The data acquisition time is 30-90 minutes.

[0072] S5. Data Analysis and Calculation:

[0073] BET equation:

[0074] 1 / (V[(p0 / p)-1])=(1 / VmC)+[(C-1) / VmC](p / p0)

[0075] Where V is the adsorption amount at p / p0 pressure, Vm is the monolayer adsorption amount, and C is the BET constant (related to the heat of adsorption).

[0076] Linear fitting:

[0077] The experimental data are converted into BET linear form, typically using data points in the range of relative pressure 0.05-0.35, and then subjected to least squares linear fitting.

[0078] Parameter calculation:

[0079] Calculate Vm and C values ​​from the slope and intercept of the fitted straight line, and then calculate the specific surface area.

[0080] S=(Vm×N×σ) / M

[0081] Where S is the specific surface area (m²) 2 / g), Vm is the monolayer adsorption capacity (cm²) 3 / gSTP), where N is Avogadro's constant (6.022×10⁻⁶ gSTP). 23 mol⁻¹), σ is the cross-sectional area of ​​nitrogen molecules (0.162 nm). 2 M is the molar volume of nitrogen (22414 cm³). 3 / molSTP).

[0082] Data verification:

[0083] Check the linear correlation (R) of the BET plot 2 The value should generally be >0.99. Confirm that the C value is reasonable (usually C>2; negative or extremely low C values ​​may indicate that the data is not applicable to the BET model). Check whether it is within the applicable range (avoid using data with p / p0>0.35).

[0084] By following the steps above, the specific surface area of ​​materials such as electrocatalysts can be accurately measured, providing reliable data support for catalytic performance research and material optimization.

[0085] Experimental results from Figure 7 As can be seen, the catalyst with the 700℃ process in Example 1 has the lowest specific surface area, while the catalyst with the 800℃ process in Example 2 has the highest specific surface area. This indicates that the nanosheet structure grown at this temperature increases the specific surface area of ​​the material. The catalyst with the 900℃ process in Example 3 has a lower specific surface area, indicating that the material has become a coral-like structure and most of the mesopores have become macropores.

[0086] Test Example 4

[0087] This experimental example involves performance testing of the electrode material, specifically including:

[0088] S1. Configure electrode materials

[0089] 0.3 mg of each of the Fe3O4 / Fe2O3 catalysts from Examples 1-3 and Comparative Example 1 were dispersed in a 300 μL mixture of isopropanol and water (isopropanol to water volume ratio of 1:1). Two drops of Nafion ionomer were added to the mixture, and the mixture was sonicated for 15-20 min to obtain four uniform inks.

[0090] S2. Prepare ORR electrolytes

[0091] Prepare a 0.1 mol / L potassium hydroxide solution, then measure 250 mL of the potassium hydroxide solution and pour it into a beaker to use as the electrolyte for the next test.

[0092] S3, spin-coated catalyst material

[0093] Using a spin coater, the four inks containing different catalyst materials prepared in step S1 were uniformly dropped onto their respective platinum-carbon electrodes to ensure that the surface catalyst material was fully and uniformly spread.

[0094] S4. Install electrodes

[0095] A spin-coated platinum-carbon electrode containing the catalyst of Example 1 was selected and connected to a rotating disk as the working electrode, an Ag / AgCl electrode as the reference electrode, and a graphite rod as the counter electrode, and connected to an electrochemical workstation.

[0096] S5, Start the experiment

[0097] After confirming that all parameters are set correctly, begin the experiment.

[0098] The electrochemical workstation is controlled to perform potential scanning or apply current according to the set parameters, and the response current of the electrode system is recorded in real time. Each set of data is tested multiple times until the data is stable.

[0099] S6. Conduct experiments on other electrodes.

[0100] The experiments in steps S4-S5 were performed on the spin-coated platinum-carbon electrodes containing the catalysts from Examples 2, 3, and Comparative Example 1.

[0101] The experimental results are as follows Figure 8-10 As shown in the image.

[0102] from Figure 8 It can be seen that the electrocatalyst material prepared at 800℃ in Example 2 has the highest half-wave potential and initial potential, indicating that its performance is optimal. The initial potential at 800℃ is 0.89V, significantly better than that at 700℃ and 900℃. Furthermore, we also observe that the ORR curves of the material at 700℃ and 900℃ show two steps, indicating that in the oxygen reduction reaction, O2 molecules are reduced to H2O2 via a two-electron pathway, but at 900℃, the material tends to be reduced to H2O via a four-electron pathway.

[0103] S7. Perform a rotation experiment on the catalyst material in Example 2.

[0104] The platinum-carbon electrode with the catalyst spin-coated in Example 2 was selected, and its performance at different rotation speeds was tested and recorded.

[0105] from Figure 9 As can be seen, the performance of the Fe3O4 / Fe2O3 catalyst material with nanoflower structure prepared in Example 2 at 800℃ gradually increases with the increase of rotation speed.

[0106] S8. Perform a 20-cycle test on the platinum-carbon electrode with the catalyst spin-coated in Implementation 2.

[0107] from Figure 10 As can be seen from the data, the LSV curve of the Fe3O4 / Fe2O3 catalyst material with nanoflower structure prepared in Example 2 at 800℃ basically overlaps with the curve of the first cycle after 20 cycles of testing. This indicates that the performance of this material remains unchanged after 20 cycles of testing, proving that the material has good stability.

[0108] S9. Perform a spin-coating test on the catalyst in Example 3 following steps S7-S8, followed by 20 cycles.

[0109] Experimental results from Figure 11 As can be seen, the LSV curve of the Fe3O4 / Fe2O3 catalyst material with nanoflower structure prepared in Example 3 at 900℃ could not coincide with the curve of the first cycle after 20 cycles of testing, and the current density showed a significant decrease, indicating that the performance of this material decreased after 20 cycles of testing.

[0110] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a Fe3O4 / Fe2O3 electrocatalyst, characterized in that, include: The Fe3O4 / Fe2O3 electrocatalyst was prepared by dissolving mesoporous molecular sieve and ferric nitrate in an organic solvent, adjusting the pH with alkali, evaporating to dryness, and then calcining.

2. The method for preparing a Fe3O4 / Fe2O3 electrocatalyst according to claim 1, characterized in that: The mass ratio of the mesoporous molecular sieve to the ferric nitrate is 0.5~1.5:

3.

3. The method for preparing a Fe3O4 / Fe2O3 electrocatalyst according to claim 1, characterized in that: The mesoporous molecular sieve is SBA-15.

4. The method for preparing a Fe3O4 / Fe2O3 electrocatalyst according to claim 1, characterized in that: The organic solvent is ethanol.

5. The method for preparing a Fe3O4 / Fe2O3 electrocatalyst according to claim 1, characterized in that: The ratio of the mesoporous molecular sieve to the organic solvent is 1g mesoporous molecular sieve: 40~80ml organic solvent.

6. The method for preparing a Fe3O4 / Fe2O3 electrocatalyst according to claim 1, characterized in that: The pH adjustment by adding alkali includes adjusting the pH to 7.5-8.5 by adding potassium hydroxide.

7. The method for preparing a Fe3O4 / Fe2O3 electrocatalyst according to claim 1, characterized in that: The calcination temperature is 700~900℃.

8. The method for preparing a Fe3O4 / Fe2O3 electrocatalyst according to claim 7, characterized in that: The calcination temperature is 775~825℃.

9. A Fe3O4 / Fe2O3 electrocatalyst, characterized in that, It is prepared by the method of any one of claims 1-8 for the preparation of Fe3O4 / Fe2O3 electrocatalyst.

10. The application of the Fe3O4 / Fe2O3 electrocatalyst as described in claim 9 in the electrochemical oxygen reduction reaction.

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