A ferroelectric Bi 2 Fe 4 O 9 Preparation method of nanosheet catalyst

Abstract

The present invention discloses a preparation method of a ferroelectric Bi2Fe4O9 nanosheet catalyst and its application in an electrocatalytic hydrogen evolution reaction. By means of hydrothermal and calcination methods, the d-band center of the ferroelectric metal is adjusted to obtain a Bi2Fe4O9 nanosheet ferroelectric material with switchable ferroelectric polarization. The preparation method is green, simple and economical, and is suitable for large-scale industrial production. The ferroelectric Bi2Fe4O9 nanosheets prepared by the present invention have a two-dimensional structure, high atomic utilization rate and large surface area, showing rich active centers, large hydrogen adsorption energy and low reaction barrier, and showing high catalytic activity for the hydrogen evolution reaction, opening up a new application field for the development of ferroelectric Bi2Fe4O9 nanosheet catalysts.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy catalysis, and particularly relates to a preparation method of a ferroelectric Bi 2 Fe 4 O 9 nanosheet catalyst. The ferroelectric Bi 2 Fe 4 O 9 nanosheets exhibit high catalytic activity as catalysts in the catalytic electrolytic water hydrogen production reaction. Background Art

[0002] Ferroelectric materials with strong inversion symmetry and spontaneous polarization of mechanical vibration will undergo transformation under the action of an external electric field. In this process, the piezoelectric effect will be generated, thereby inducing electrocatalytic behavior. After piezoelectric treatment, the ferroelectric material can reduce the overpotential of electrolytic water hydrogen production and promote the generation of hydrogen. However, under the piezoelectric effect, the common ferroelectric nanocatalysts such as PbTiO 3 , BaTiO 3 etc. cannot reach the critical Gibbs free energy threshold (1.23 eV) of the water decomposition reaction. Therefore, it is necessary to design and manufacture more effective ferroelectric catalysts. It has been found that in addition to the chemical composition of the material, its morphology also plays an important role in performance. The morphological structure, chemical composition, and electronic structure of metal materials are key parameters to effectively improve the relevant catalytic performance by controlling their size, shape, and composition. In this work, the influence of morphology engineering and ferroelectric polarization on ferroelectric catalytic performance was utilized, and a ferroelectric Bi 2 Fe 4 O 9 nanomaterials were prepared by combining hydrothermal method and calcination method. It has a typical 2D nanosheet morphology and has excellent ferroelectric properties, simple chemical composition, and environmental friendliness.

[0003] In the hydrogen evolution reaction (HER) process, noble metal catalysts such as platinum catalysts show high kinetic reaction rates and stabilities as commercial catalysts. Although noble metal catalysts such as platinum-based electrocatalysts and palladium-based catalysts exhibit excellent catalytic performance, these noble metal cathode electrocatalysts still have the disadvantages of high cost and low activity, which prompts us to explore more advanced and efficient hydrogen evolution reaction catalysts. 2D nanosheets can effectively increase the specific surface area of the catalyst and the number of exposed active sites. However, there are few reports on the use of ferroelectric nanosheets for electrocatalysis at present, mainly because ferroelectric nanocatalysts have weak activity and stability for the hydrogen evolution reaction under untreated conditions. Therefore, there is an urgent need for a simple and effective method to prepare two-dimensional porous and easily piezopolarized ferroelectric nanoelectrocatalysts. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing ferroelectric Bi 2 Fe 4 O 9 nanosheets.

[0005] For the above object, the technical solution adopted by the present invention is: A method for preparing ferroelectric Bi 2 Fe 4 O 9 nanosheets, characterized in that: Bi(NO 3 )·5H 2 O and FeCl 3 ·6H 2 O are added to an ethylene glycol solvent, mixed evenly, the pH of the solution is adjusted to 10-11 with NaOH, and the mixture is kept warm at 180 °C for 48 hours. After the reaction, the obtained solid is centrifugally washed with deionized water and dried in vacuum. The obtained black solid is further calcined at 500 °C in an air atmosphere for 2 hours to obtain Bi 2 Fe 4 O 9 nanosheets. 0.05 g of Bi 2 Fe 4 O 9 nanosheets are evenly coated on a negative disk-shaped copper electrode with a voltage of 20 kV and an area of about 3 cm 2 . The distance between the two electrodes is 1 cm, and the duration is 30 minutes to obtain a polarized sample.

[0006] In the above preparation method, the concentration of Bi(NO 3 )·5H 2 O is 1-4 mM, preferably 2 mM.

[0007] In the above preparation method, the concentration of FeCl 3 ·6H 2 O is 1-4 mM, preferably 2 mM.

[0008] In the above preparation method, the pH range of the mixed solution is 9-12, preferably 10.

[0009] In the above preparation method, the temperature of the first solvothermal reaction is 140-200 °C, preferably 180 °C.

[0010] In the above preparation method, the time of the first solvothermal reaction is 40-60 h, preferably 48 h.

[0011] In the above preparation method, the temperature of the second calcination is 400-700 °C, preferably 500 °C.

[0012] In the above preparation method, the time for the second-step dissolution and calcination is 1.5 - 5 °C, preferably 2 °C.

[0013] The beneficial effects of the present invention are as follows:

[0014] 1. Compared with other chemical methods, the preparation method of the present invention is simple. The reaction is carried out in a closed container, the required conditions are safer, and the yield is high, making it easy to scale up production. Secondly, the obtained material is two-dimensional porous ferroelectric Bi 2 Fe 4 O 9 nanosheets. The pore size of the ferroelectric Bi 2 Fe 4 O 9 nanosheets is between 2 and 50 nm, and its activity for the hydrogen evolution reaction is significantly improved.

[0015] 2. The ferroelectric Bi 2 Fe 4 O 9 nanomaterials of the present invention as electrocatalysts for the hydrogen evolution reaction not only solve the problem of poor stability of commercial Pt / C, but also avoid the use of precious metals to reduce the cost of the reaction, and have high hydrogen evolution catalytic activity and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is an XRD picture of the ferroelectric Bi 2 Fe 4 O 9 nanomaterials prepared in Example 1.

[0017] Figure 2 is a TEM picture of the ferroelectric Bi 2 Fe 4 O 9 nanomaterials prepared in Example 1.

[0018] Figure 3 is an AFM photo of the ferroelectric Bi 2 Fe 4 O 9 nanomaterials prepared in Example 1.

[0019] Figure 4 is a BET picture of the ferroelectric Bi 2 Fe 4 O 9 nanomaterials prepared in Example 1.

[0020] Figure 5 is a polarization curve graph of the electrocatalytic hydrogen evolution reaction of the ferroelectric Bi 2 Fe 4 O 9 nanomaterials prepared in Example 1 and the commercial Pt / C catalyst.

[0021] Figure 6 is a graph of the ferroelectric Bi 2 Fe 4 O9 Comparison diagram of the stability of nanomaterials and commercial Pt / C in 1M KOH solution. Detailed implementation manners

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0023] Embodiment 1

[0024] Add Bi(NO 3 )·5H 2 O and FeCl 3 ·6H 2 O into ethylene glycol solvent, mix evenly, adjust the pH of the solution to 10 - 11 with NaOH, keep warm at 180 °C for 48 hours, and after the reaction, the obtained solid is centrifugally washed with deionized water and vacuum dried. The obtained black solid is further calcined in air atmosphere at 500 °C for 2 hours to obtain Bi 2 Fe 4 O 9 nanosheets. Coat 0.05 g of Bi 2 Fe 4 O 9 nanosheets evenly on the negative disk-shaped copper electrode with a voltage of 20 kV and an area of about 3 cm 2 . The distance between the two electrodes is 1 cm, and the duration is 30 minutes to obtain a polarized sample. As can be seen from Figure 1, the obtained product is Bi 2 Fe 4 O 9 , and polarization does not change the crystal structure of the substance. As can be seen from Figure 2, the obtained product is a nanoscale sheet structure. It can be seen from the atomic force microscope image in Figure 3 the thickness of the Bi 2 Fe 4 O 9 nanosheets, and the BET pore size diagram in Figure 4 shows that the pores of the Bi 2 Fe 4 O 9 nanosheets are mesopores.

[0025] Embodiment 2

[0026] Add Bi(NO 3 )·5H 2 O into ethylene glycol solvent, mix evenly, add FeCl 3 ·6H 2 O solution to the obtained mixed solution, then adjust the pH to 10 - 11, and perform hydrothermal reaction at 160 °C for 48 h under strong alkaline conditions. After the reaction, it is centrifugally washed with deionized water and vacuum dried to obtain Bi 2 Fe 4 O 9Precursor. Then it was calcined in air at 500 °C for 2 h to obtain Bi 2 Fe 4 O 9 nanosheets.

[0027] Example 3

[0028] Bi(NO 3 )·5H 2 O was added to ethylene glycol solvent and mixed evenly. FeCl 3 ·6H 2 O solution was added to the obtained mixed solution, and then the pH was adjusted to 10 - 11. Hydrothermal reaction was carried out at 180 °C for 48 h under strong alkaline conditions. After the reaction, it was centrifugally washed with deionized water and dried in vacuum to obtain Bi 2 Fe 4 O 9 precursor. Then it was calcined in air at 400 °C for 2 h to obtain Bi 2 Fe 4 O 9 nanosheets.

[0029] Example 4

[0030] Ferroelectric Bi 2 Fe 4 O 9 Application of nanomaterials as electrocatalysts in hydrogen evolution reaction

[0031] 4 mg of the ferroelectric Bi 2 Fe 4 O 9 nanomaterials obtained in Example 1 were respectively formulated into a solution with 400 μL of isopropanol, 1600 μL of deionized water, and 100 μL of naphthol. Then 4 μL of the solution was dropped on a glassy carbon electrode. Using a carbon rod, a calomel electrode, and a glassy carbon electrode as the counter electrode, reference electrode, and working electrode respectively, tests were carried out in 1 M KOH solution using a Shanghai Chenhua electrochemical 760 workstation, and the stability and hydrogen evolution reaction of the ferroelectric Bi 2 Fe 4 O 9 nanomaterials and commercial Pt / C were tested. The LSV test conditions in the hydrogen evolution reaction were: a scanning rate of 5 mV / s.

[0032] As can be seen from Figures 5 and 6, the comparison of the stability and catalytic activity between the ferroelectric Bi 2 Fe 4 O 9 nanomaterials obtained in Example 1 and commercial Pt / C. The ferroelectric Bi 2 Fe 4 O 9 nanomaterials have better hydrogen evolution activity under alkaline conditions, and at a voltage of 0.16 V (vs RHE), the ferroelectric Bi2 Fe 4 O 9 The nanomaterial does not substantially decay after 30 h of cycling, while commercial Pt / C decays by 46% after 30 h of cycling.

Claims

1. A preparation method of a ferroelectric Bi 2 Fe 4 O 9 nanosheet catalyst It is characterized in that: Dissolve Bi(NO 3 )·5H 2 O and FeCl 3 ·6H 2 O in ethylene glycol solvent, mix evenly, adjust the pH of the solution to 10 - 11 with NaOH, carry out solvothermal reaction at 140 - 200 °C for 40 - 60 hours. After the reaction, the obtained solid is centrifugally washed with deionized water and dried in vacuum; the obtained solid is further calcined in air atmosphere at 400 - 700 °C for 2 hours to obtain Bi 2 Fe 4 O 9 nanosheets; evenly coat 0.05 g of Bi 2 Fe 4 O 9 nanosheets on a negative disk-shaped copper electrode with a voltage of 20 kV and an area of about 3 cm 2 . The distance between the two electrodes is 1 cm, and the duration is 30 minutes. The obtained polarized Bi 2 Fe 4 O 9 nanosheet sample is the ferroelectric Bi 2 Fe 4 O 9 nanosheet catalyst.

2. The preparation method of the ferroelectric Bi 2 Fe 4 O 9 nanosheet catalyst, It is characterized in that: The concentration of Bi(NO 3 )·5H 2 O is 1 - 4 mM.

3. The preparation method of the ferroelectric Bi 2 Fe 4 O 9 nanosheet catalyst It is characterized in that: The concentration of the FeCl 3 ·6H 2 O is 1 - 4 mM.

4. The preparation method of the ferroelectric Bi 2 Fe 4 O 9 nanosheet catalyst, It is characterized in that: The temperature of the solvothermal reaction is 180 °C.

5. The preparation method of the ferroelectric Bi 2 Fe 4 O 9 nanosheet catalyst, It is characterized in that: The time of the solvothermal reaction is 48 hours.

6. The preparation method of the ferroelectric Bi 2 Fe 4 O 9 nanosheet catalyst It is characterized in that: The calcination temperature is 500 °C.

Images