Bi / Bi2O2CO3 nanoflower sheet reconstructed and derived from Bi / BiOBr as well as preparation method and application of Bi / Bi2O2CO3 nanoflower sheet

Abstract

The invention belongs to the field of catalysts, and particularly relates to a Bi / Bi2O2CO3 nanoflower sheet reconstructed and derived from Bi / BiOBr as well as a preparation method and application of the Bi / Bi2O2CO3 nanoflower sheet. The preparation method comprises the following steps: carrying out thermal reaction to generate Bi-MOF; carrying out bromination on the Bi-MOF to obtain brominated Bi-MOF; the brominated Bi-MOF is subjected to pyrolysis, and a Bi / BiOBr precursor is formed; and preparing the Bi / BiOBr precursor into a working electrode, and reconstructing and reducing the working electrode under the condition of external voltage to obtain the Bi / Bi2O2CO3 composite material. Brominated Bi-MOF is synthesized through a simple solvothermal method, part of Bi < 3 + > is reduced into Bi0 through high-temperature pyrolysis under the inert gas condition by means of the C element contained in a Bi-MOF ligand, a Bi / BiOBr structure is generated in one step, and the Bi / BiOBr structure is further reconstructed through an electrochemical reduction method to form the nano flower sheet of the Bi / Bi2O2CO3 composite structure.

Description

Technical Field

[0001] The invention belongs to the field of catalysts, and in particular relates to a Bi / Bi2O2CO3 nano flower sheet derived from Bi / BiOBr reconstruction, and a preparation method and application thereof. Background Art

[0002] In recent years, electrocatalytic carbon dioxide reduction technology (CO2RR) has become one of the important ways to realize CO2 resource utilization due to its advantages such as environmental friendliness, energy efficiency and low raw material cost.

[0003] Among the many CO2 reduction products, although we intuitively want to control the selectivity to obtain higher value products such as ethylene, ethanol and n-propanol, economic and technical analysis clearly points out that after comprehensive evaluation, those C2+ products cannot achieve the greatest economic benefits, and the two-electron products of electrochemical CO2RR such as CO or HCOOH are the most economically feasible. Formic acid is an important chemical intermediate in many industrial processes and is widely used in leather, pesticides, medicine, dyes and rubber industries. It can also be directly used as a chemical fuel for formic acid (or formate) fuel cells. The industrial production of formic acid is usually achieved by carbonylation of methanol and subsequent hydrolysis of methyl formate. However, this process is energy intensive and is usually limited by reaction rate, by-products and investment costs. Therefore, direct electrochemical CO2 reduction to formic acid under mild conditions with high energy conversion efficiency is very attractive. In recent years, bismuth (Bi) electrocatalysts have attracted much attention due to their excellent formate selectivity, high hydrogen evolution reaction (HER) overpotential, low toxicity and low cost. However, there are also some problems with bismuth-based catalysts. Although bismuth-based catalysts have high selectivity, their high selectivity potential range is narrow and the partial current density is low. In addition, bismuth-based catalysts are prone to reconstruction during the electrocatalytic carbon dioxide reduction process, and active sites are difficult to identify. Therefore, designing and preparing low-cost bismuth-based catalysts with high selectivity and high activity under a wide potential range and clarifying their active sites are of great significance to promote the practical application of electrocatalytic carbon dioxide reduction technology on an industrial scale. Summary of the invention

[0004] The object of the present invention is to provide a Bi / Bi2O2CO3 nano flower sheet derived from Bi / BiOBr reconstruction and a preparation method and application thereof.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for preparing Bi / Bi2O2CO3 nanoflower sheets derived from Bi / BiOBr reconstruction comprises the following steps:

[0007] Step 1: Disperse the bismuth source and the ligand in a solvent, stir and mix them evenly, and perform a thermal reaction to generate Bi-MOF;

[0008] Step 2: Add the obtained Bi-MOF to a bromination reagent for hydrothermal bromination to obtain the brominated Bi-MOF;

[0009] Step 3: Pyrolyze the brominated Bi-MOF in an inert gas atmosphere to form a Bi / BiOBr precursor;

[0010] Step 4: Prepare the Bi / BiOBr precursor into a working electrode, reconstruct and reduce it under an applied voltage to obtain a Bi / Bi2O2CO3 composite material.

[0011] The molar ratio of the bismuth source to the ligand in step 1 is 1:(9-13); preferably 1:11.7;

[0012] Preferably, the temperature of the thermal reaction is 100-150°C; preferably 120°C;

[0013] Preferably, the bismuth source is one of bismuth nitrate, bismuth chloride, or bismuth acetate, or a mixture thereof; preferably, the ligand is 1,3,5-trimethylbenzene trimesic acid.

[0014] In step 2, the mass ratio of Bi-MOF to bromination reagent is 1:(1-3); preferably 1:1.6;

[0015] Preferably, the bromination reagent is NH4Br;

[0016] The preferred heating temperature is 80-100°C; preferably 90°C.

[0017] In step 3, the pyrolysis temperature is 400-700° C., and the pyrolysis time is 1-2 hours.

[0018] Preferably, the pyrolysis temperature is 500°C.

[0019] The specific steps in step 4 are: prepare the obtained Bi / BiOBr into an ink solution (5mg Bi / BiOBr+1000μL water+960μL isopropanol+40μL nafion solution), spray 200μL ink solution onto the electrode, and perform cyclic voltammetry scanning CV in a CO2-saturated 0.5M KHCO3 electrolyte with a potential range of 0.68 to -1.22Vvs.RHE, and electrolyze at -0.72 to -1.12Vvs.RHE for 0 to 30min to obtain Bi / Bi2O2CO3 nanoflower sheets.

[0020] Preferably, electrolysis is performed at -0.82 V vs. RHE for 0 to 30 min.

[0021] The present invention also includes a Bi / Bi2O2CO3 nano flower sheet obtained by the preparation method.

[0022] The present invention also includes an application of the Bi / Bi2O2CO3 nano flower sheet.

[0023] Applied to the electrocatalytic reduction of carbon dioxide to produce formic acid.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention synthesizes the brominated Bi-MOF by a simple solvent thermal method, and utilizes the C element contained in the Bi-MOF ligand to pyrolyze part of the Bi under inert gas conditions at high temperature. 3+ Reduction to Bi 0 , a Bi / BiOBr structure is generated in one step, which is then reconstructed into a Bi / Bi2O2CO3 composite structure nanosheet by electrochemical reduction.

[0026] The present invention explores the structural evolution of Bi-based catalysts during the research process, and mainly records the changes in its reconstruction through XRD and SEM, which provides a certain reference for the speculation of the evolution mechanism of Bi-based materials during the electrocatalytic carbon dioxide reduction process.

[0027] The invention can stably catalyze the reduction of carbon dioxide into formate in a wide potential window and at a high current density. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the synthesis of Bi / Bi2O2CO3 nanoflower sheets derived from Bi / BiOBr reconstruction;

[0029] Figure 2 This is a scanning electron microscopy image of Bi / Bi2O2CO3 nanoflower sheets (reduced at -0.82V vs. RHE for 30min);

[0030] Figure 3 Transmission electron microscopy image of Bi / Bi2O2CO3 nanoflower sheet (reduced at -0.82V vs. RHE for 30min);

[0031] Figure 4 The XRD structure diagram of Bi-MOF precursor after thermal decomposition and bromination at different temperatures;

[0032] Figure 5 is the XRD pattern of the precursor after calcination at 500°C in Example 2;

[0033] Figure 6 This is a scanning electron microscope image of the precursor after calcination at 500° C. in Example 2;

[0034] Figure 7 is a transmission electron microscope image of the precursor after calcination at 500° C. in Example 2;

[0035] Figure 8 Scanning electron microscope images of samples prepared for Examples 1, 2, 3-6, recording the changes in the morphology of the precursor Bi / BiOBr with the reduction time under the potential condition of -0.82V vs. RHE;

[0036] Fig. 9 The crystal structure diagram of the sample catalyst prepared in Examples 1, 2, 3-6;

[0037] Fig.10 Scanning electron microscope images of sample catalysts prepared for Comparative Examples 1-6;

[0038] Fig.11 XRD patterns of the sample catalysts prepared for Comparative Examples 1-6.

[0039] Fig.12 The Raman spectra of Bi / Bi2O2CO3 nanoflower flakes derived from Bi / BiOBr reconstruction before and after derivatization and the comparison sample;

[0040] Fig.13 A comparison of the electrochemical active area of ​​Bi / Bi2O2CO3 nanoflowers derived from Bi / BiOBr reconstruction and that of the control sample;

[0041] Fig.14 LSV curve and formic acid partial current density curve of Bi / Bi2O2CO3 nanoflower derived from Bi / BiOBr reconstruction;

[0042] Fig.15 The product Faraday efficiency diagram of Bi / Bi2O2CO3 nanoflowers derived from Bi / BiOBr reconstruction;

[0043] Fig.16 This is a stability test diagram of Bi / Bi2O2CO3 nanoflowers derived from Bi / BiOBr reconstruction. DETAILED DESCRIPTION

[0044] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and the best embodiments.

[0045] Example 1

[0046] The Bi / Bi2O2CO3 nanoflower sheets were prepared by combining the pyrolysis Bi-MOF strategy and electrochemical reduction method. The preparation process includes the following steps: Figure 1 Showing a flow chart):

[0047] Step 1: Dissolve 0.15g Bi(NO3)3·5H2O and 0.75g H3BTC (1,3,5-benzene trimesic acid) in 60ml methanol solution, put into the lining of a 100ml reactor and stir for 20min, hydrothermal at 120℃ for 24h, wash the obtained white powder with methanol three times, and put it in a vacuum oven at 60℃ for 9h. The obtained product is recorded as Bi-MOF.

[0048] Step 2: 600 mg Bi-MOF was immersed in 60 mL deionized water, stirred, and then 0.012 mol (1 g) NH4Br was added thereto, stirred for 20 min, and then heated to 90 ° C and stirred for 1 h, taken out and filtered, and vacuum dried at 60 ° C for 9 h to obtain the brominated Bi-MOF.

[0049] Step 3: The brominated Bi-MOF was directly placed in a tubular furnace and pyrolyzed at 500 °C for 2 h under Ar (100 ml / min) conditions to obtain the final product Bi / BiOBr.

[0050] Step 4: The obtained Bi / BiOBr was prepared into an ink solution (5 mg Bi / BiOBr + 1000 μL water + 960 μL isopropanol + 40 μL nafion solution), 200 μL ink was sprayed onto the electrode, and 6 cycles of cyclic voltammetry (CV) were performed in a CO2-saturated 0.5 M KHCO3 electrolyte with a potential range of 0.68 to -1.22 V vs. RHE, and electrolysis was performed at -0.82 V vs. RHE for 30 min to obtain Bi / Bi2O2CO3 nanoflower sheets.

[0051] The material prepared in Example 1 was characterized by morphology, and the results are shown in Figure 2 and Figure 3 ,Depend on Figure 2 and Figure 3 It can be seen that Example 1 prepared a catalyst having a nano flower-like shape, and the flower-like shape has abundant wrinkles.

[0052] Example 2

[0053] Only step 3 of Example 1 was performed, and the pyrolysis temperature conditions were changed to 400, 500, 600, and 700° C. to explore the generated precursor structure.

[0054] The crystal structure of the Bi-based compounds prepared by different pyrolysis temperatures in Example 2 was identified. Figure 4 , Figure 4The XRD structure diagram of Bi-MOF precursor after pyrolysis and bromination at different temperatures shows that when the pyrolysis temperature is low, Bi / BiOBr structure is generated, and most of it will be converted into Bi when the temperature exceeds 600℃. 24 Br 10 O 31 Mutually.

[0055] Figure 5 This is the XRD pattern of the precursor after calcination at 500°C in Example 2. It can be seen that the crystal phase of the precursor after calcination at 500°C is composed only of Bi and BiOBr.

[0056] Figure 6 This is a scanning electron microscope image of the precursor after calcination at 500° C. in Example 2. It can be seen that the precursor after calcination at 500° C. presents an irregular nanosheet shape.

[0057] Figure 7 Figure 2 is a transmission electron micrograph of the precursor calcined at 500°C in Example 2. It can be seen that the precursor Bi / BiOBr calcined at 500°C exhibits a porous nanosheet morphology, which may be due to the reduction of Bi by the C ligand in the MOF during the pyrolysis process. 3+ And formed.

[0058] Example 3

[0059] On the basis of Example 1, the step of electroreduction at a potential of -0.82 V vs. RHE was removed, and only the CV step was retained.

[0060] Example 4

[0061] On the basis of Example 1, only the electro-reduction time was changed to 2 min.

[0062] Example 5

[0063] On the basis of Example 1, only the electro-reduction time was changed to 5 min.

[0064] Example 6

[0065] On the basis of Example 1, only the electro-reduction time was changed to 15 min.

[0066] Figure 8 The scanning electron microscope images of the samples corresponding to Example 1 (30 min), Example 2 (500°C pyrolysis), and Examples 3-6 record the changes in the morphology of the precursor Bi / BiOBr with the reduction time under the potential condition of -0.82 V vs. RHE. It can be seen from the figure that after CV, the morphology of the catalyst changes, and the irregular nanosheets become leaf-shaped nanosheets, until 15 min when the leaf-shaped nanosheets are connected to each other and become nanoflower-shaped.

[0067] Fig. 9 The crystal structures of the prepared sample catalysts corresponding to Example 1 (30 min), Example 2 (500 ° C pyrolysis), and Examples 3-6 record the crystal structure changes of the initial Bi / BiOBr precursor under CV and electrolysis conditions of different time. It can be seen from the figure that after CV, Bi / BiOBr is immediately reconstructed and evolves into a mixed phase of Bi and Bi2O2CO3, and these two crystal structures are maintained during the subsequent electrolysis process.

[0068] Comparative Example 1

[0069] Step 1: Dissolve 0.15g Bi(NO3)3·5H2O and 0.75g H3BTC (1,3,5-benzene trimesic acid) in 60ml methanol solution, put into the lining of a 100ml reactor and stir for 20min, hydrothermal at 120℃ for 24h, wash the obtained white powder with methanol three times, and put it in a vacuum oven at 60℃ for 9h. The obtained product is recorded as Bi-MOF.

[0070] Step 2: The Bi-MOF formed in step 1 was directly pyrolyzed at 600°C for 1 h in an Ar (100 ml / min) atmosphere to generate a comparative sample Bi / Bi2O3.

[0071] Comparative Example 2

[0072] The sample in Comparative Example 1 was prepared into an ink solution (same as above), sprayed onto the electrode, and subjected to 6 cycles of cyclic voltammetry (CV) in a CO2-saturated 0.5M KHCO3 electrolyte, with a potential range of 0.68 to -1.22 V vs. RHE.

[0073] Comparative Example 3

[0074] The sample in Comparative Example 1 was prepared into an ink solution, sprayed onto the electrode, and subjected to 6 cycles of cyclic voltammetry (CV) in a CO2-saturated 0.5M KHCO3 electrolyte with a potential range of 0.68 to -1.22 V vs. RHE, and electrolyzed at a potential of -0.82 V vs. RHE for 10 min.

[0075] Comparative Example 4

[0076] The sample in Comparative Example 1 was prepared into an ink solution, sprayed onto the electrode, and subjected to 6 cycles of cyclic voltammetry (CV) in a CO2-saturated 0.5M KHCO3 electrolyte with a potential range of 0.68 to -1.22 V vs. RHE, and electrolyzed at a potential of -1.5 V vs. RHE for 20 min.

[0077] Comparative Example 5

[0078] The sample in Comparative Example 1 was prepared into an ink solution, sprayed onto the electrode, and subjected to 6 cycles of cyclic voltammetry (CV) in a CO2-saturated 0.5M KHCO3 electrolyte with a potential range of 0.68 to -1.22 V vs. RHE, and electrolyzed at a potential of -0.82 V vs. RHE for 30 min.

[0079] Comparative Example 6

[0080] The sample in Comparative Example 1 was prepared into an ink solution, sprayed onto the electrode, and subjected to 6 cycles of cyclic voltammetry (CV) in a CO2-saturated 0.5M KHCO3 electrolyte with a potential range of 0.68 to -1.22 V vs. RHE, and electrolyzed at a potential of -0.82 V vs. RHE for 1 h.

[0081] Fig.10 Scanning electron microscope of sample catalysts prepared in Comparative Examples 1-6, recording the changes in the morphology of the precursor Bi / Bi2O3 with reduction time at a potential of -0.82 V vs. RHE. It can be seen from the figure that after CV and electrolysis for different time periods, its morphology has basically not changed.

[0082] Fig.11 The XRD diagram of the sample catalyst prepared in Comparative Examples 1-6 records the change of the crystal structure of the precursor Bi / Bi2O3 with the reduction time at a potential of -0.82V vs. RHE. It can be seen from the figure that after CV and electrolysis for different time periods, its crystal structure has basically not changed.

[0083] Fig.12 The Raman spectra of the Bi / Bi2O2CO3 nanoflower sheet (Example 1) derived from Bi / BiOBr (calcined at 500°C in Example 2) before and after derivatization and the comparative sample (Comparative Example 1) are shown in Figure 1. It can be seen that after CV and electrochemical reduction, the Bi / BiOBr precursor evolves into the structure of Bi and Bi2O2CO3.

[0084] Fig.13 The figure is a comparison of the electrochemically active area of ​​the Bi / Bi2O2CO3 nanoflower sheet derived from Bi / BiOBr reconstruction (Example 1) and the comparative sample (Comparative Example 1). It can be seen that the derived Bi / Bi2O2CO3 nanoflower sheet has a larger electrochemically active area than Bi / Bi2O3 and commercial Bi powder.

[0085] Fig.14The LSV curve and partial current density curve of the Bi / Bi2O2CO3 nanoflower sheet (Example 1) derived from Bi / BiOBr reconstruction are shown in Figure 1. It can be seen that the derived Bi / Bi2O2CO3 nanoflower sheet has higher electrocatalytic reaction activity and higher CO2 catalytic efficiency than Bi / Bi2O3 and commercial Bi powder.

[0086] Fig.15 The product Faraday efficiency diagram of Bi / Bi2O2CO3 nanoflowers derived from Bi / BiOBr reconstruction. It can be seen that the Bi / Bi2O2CO3 nanoflowers derived from Bi / BiOBr reconstruction can maintain more than 90% of the formic acid Faraday efficiency under a wide potential.

[0087] Fig.16 The stability test diagram of Bi / Bi2O2CO3 nanoflowers derived from Bi / BiOBr reconstruction. It can be seen that the catalyst can be recycled for 100 hours or more, and the current is maintained at 18mA / cm in the H cell at -0.82V vs.RHE. -2 With excellent stability.

[0088] In summary, it can be seen that the present invention provides a Bi / Bi2O2CO3 nanoflower sheet with a high electrochemical active area, which can provide a large number of exposed active sites and significantly improve the efficiency of electrocatalytic CO2 production of formic acid. In the process of preparing the examples, we mainly used XRD and SEM characterization to explore the evolution of the catalyst by changing parameters such as electrolysis time. In addition, the catalyst has the following advantages in the catalytic process:

[0089] 1. Bi / Bi2O2CO3 nanoflowers have a higher electrochemically active area (ECSA), thus providing more reaction sites and promoting the CO2 reduction reaction.

[0090] 2. The Faradaic efficiency of formic acid of Bi / Bi2O2CO3 nanoflower sheets exceeds 90% under a wide potential, so it has excellent formic acid selectivity.

[0091] 3. Bi / Bi2O2CO3 nanoflowers can be quickly reconstructed by Bi / BiOBr. After CV and 15 minutes of point reduction, complete reconstruction can occur.

[0092] 4. Bi / Bi2O2CO3 nanoflowers have high stability and can be recycled for more than 100 hours.

[0093] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing Bi / Bi2O2CO3 nanoflower sheets derived from Bi / BiOBr reconstruction, characterized in that: The steps include: Step 1: Disperse the bismuth source and the ligand in a solvent, stir and mix them evenly, and perform a solvothermal reaction to generate Bi-MOF; Step 2: Add the obtained Bi-MOF to a bromination reagent for hydrothermal bromination to obtain the brominated Bi-MOF; Step 3: Pyrolyze the brominated Bi-MOF in an inert gas atmosphere to form a Bi / BiOBr precursor; Step 4: Prepare the Bi / BiOBr precursor into a working electrode, reconstruct and reduce it under an applied voltage to obtain a Bi / Bi2O2CO3 composite material.

2. The method for preparing Bi / Bi2O2CO3 nanoflower sheets derived from Bi / BiOBr reconstruction according to claim 1, characterized in that: The molar ratio of the bismuth source to the ligand in step 1 is 1:(9-13); preferably 1:11.7; Preferably, the temperature of the thermal reaction is 100-150°C; preferably 120°C; Preferably, the bismuth source is one or a mixture of bismuth nitrate, bismuth chloride, or bismuth acetate; Preferably, the ligand is 1,3,5-trimethylbenzene carboxylic acid.

3. The method for preparing Bi / Bi2O2CO3 nanoflower sheets derived from Bi / BiOBr reconstruction according to claim 1, characterized in that: In step 2, the mass ratio of Bi-MOF to bromination reagent is 1:(1-3); preferably 1:1.6; Preferably, the bromination reagent is NH4Br; The preferred heating temperature is 80-100°C; preferably 90°C.

4. The method for preparing Bi / Bi2O2CO3 nanoflower sheets derived from Bi / BiOBr reconstruction according to claim 1, characterized in that: In step 3, the pyrolysis temperature is 400-700° C., and the pyrolysis time is 1-2 hours.

5. The method for preparing Bi / Bi2O2CO3 nanoflower sheets derived from Bi / BiOBr reconstruction according to claim 4, characterized in that: The pyrolysis temperature is 500°C.

6. The method for preparing Bi / Bi2O2CO3 nanoflower sheets derived from Bi / BiOBr reconstruction according to claim 1, characterized in that: The specific steps in step 4 are: configure the obtained Bi / BiOBr into an ink solution and spray it onto the electrode, perform cyclic voltammetry scanning CV in a CO2-saturated 0.5M KHCO3 electrolyte with a potential range of 0.68 to -1.22V vs.RHE, and electrolyze at -0.72 to -1.12V vs.RHE for 0 to 30min to obtain Bi / Bi2O2CO3 nanoflower sheets.

7. The method for preparing Bi / Bi2O2CO3 nanoflower sheets derived from Bi / BiOBr reconstruction according to claim 6, characterized in that: The electrolysis was performed at -0.82 V vs. RHE for 0 to 30 min.

8. A Bi / Bi2O2CO3 nanoflower sheet obtained by the preparation method according to any one of claims 1 to 7.

9. An application of the Bi / Bi2O2CO3 nano flower sheet as claimed in claim 9.

10. The use according to claim 9, characterized in that: Applied to the electrocatalytic reduction of carbon dioxide to produce formic acid.

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