A bismuth-doped Co 3 O 4 nanosheet electrocatalyst, its preparation method and application

Abstract

The present invention provides a bismuth-doped Co3O4 nanosheet electrocatalyst, a preparation method thereof, and an application thereof, including the following steps: 1) placing nickel foam in a mixed solution containing metal ions and ligands, and performing a solvothermal reaction to obtain a BiCo-MOF precursor; the metal ions include Co 2+ and Bi 3+ ; the ligand is 2-methylimidazole; 2) calcining the BiCo-MOF precursor to obtain the bismuth-doped Co3O4 nanosheet electrocatalyst. The preparation process of the present invention is simple, the preparation conditions are mild, and the preparation equipment is simple, which is conducive to industrial production; the obtained bismuth-doped Co3O4 nanosheet electrocatalyst has a high specific surface area, many reaction active sites, and easy reaction; it has low-potential GOR performance, and high-value-added glucose oxidation products can be produced at the anode. Bismuth doping effectively regulates the internal electronic structure of the catalyst, thereby improving the intrinsic activity of the catalyst and promoting the electrolysis efficiency of the catalyst as an anode for glucose solution, and is expected to be applied to the electrocatalytic oxidation reaction of glucose.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalytic oxidation of glucose, and particularly to a bismuth-doped Co 3 O 4 nanosheet electrocatalyst and its preparation method and application. Background Art

[0002] The electrolytic water hydrogen production technology is an extremely attractive hydrogen production method. However, the slow kinetics of the oxygen evolution reaction and the high overpotential required on the anode of this technology seriously hinder the overall water decomposition and limit its large-scale industrial application. Moreover, the O 2 produced at the anode will inevitably react with the H 2 produced at the cathode to form an explosive mixture gas, bringing great potential safety hazards. In addition, the anode product O 2 is a by-product with low added value. Replacing the oxygen evolution reaction (OER) with the glucose oxidation reaction (GOR) can not only reduce the anodic oxidation potential and produce high-added-value products (such as gluconic acid, arabinose, etc.), but also assist in hydrogen production, which is a promising and feasible strategy.

[0003] In recent years, noble metal-based materials (such as Au, Ir, Pt-based materials) can be seen everywhere in the field of glucose oxidation. Such materials generally exhibit excellent GOR performance, but the disadvantages of high price and scarce resources limit their wide application in the market. Therefore, it is urgent to find catalysts with low cost and rich reserves. Cobalt-based materials are a type of non-noble metal-based materials with low cost and rich resources, and are favored by researchers in the field of glucose oxidation. However, their GOR performance is still far from satisfactory, and the overpotential required for the complete oxidation of glucose aqueous solution is also not ideal enough. Summary of the Invention

[0004] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a bismuth-doped Co 3 O 4 nanosheet electrocatalyst and its preparation method and application, which are used to solve the problems of high GOR potential and high overall electrolysis potential energy.

[0005] To achieve the above purpose and other related purposes, the present invention provides a preparation method of a bismuth-doped Co 3 O 4 nanosheet electrocatalyst, including the following steps:

[0006] 1) Placing nickel foam in a mixed solution containing metal ions and ligands, and performing a solvothermal reaction to obtain a BiCo-MOF precursor; the metal ions include Co 2+ and Bi 3+ ; the ligand is 2-methylimidazole;

[0007] 2) Calcinate the BiCo-MOF precursor to obtain bismuth-doped Co 3 O 4 nanosheet electrocatalyst (Bi-Co 3 O 4 / NF catalyst).

[0008] In the above technical solution of the present invention, by in-situ growing the BiCo-MOF precursor on nickel foam and then successfully converting it into Bi-Co 3 O 4 / NF catalyst through calcination. The incorporation of high-valence metal bismuth improves the intrinsic activity of the catalyst, enabling the catalyst to have excellent glucose oxidation performance. The significant reduction of the anodic oxidation potential of the catalyst and the improvement of the overall electrolysis efficiency are conducive to the hydrogen evolution reaction on the cathode.

[0009] Preferably, in step 1), the nickel foam is pretreated by a method including the following steps: ultrasonically treating the nickel foam successively with hydrochloric acid, absolute ethanol, and acetone, rinsing with methanol, and finally immersing it in methanol for standby. The pretreatment can remove the surface oxide layer and surface organic substances of the nickel foam, which is more conducive to the firm self-growth of the catalyst on the nickel foam surface.

[0010] Preferably, in step 1), the solvent of the mixed solution is selected from one or both of methanol and water.

[0011] Preferably, in step 1), the molar ratio of the total amount of metal ions to the amount of ligand in the mixed solution is 1:(1.5 - 2).

[0012] Preferably, in step 1), the concentration of Co 2+ in the mixed solution is 10 - 20 mol / L, the concentration of Bi 3+ is 0.1 - 0.2 mol / L, and the concentration of 2-methylimidazole is 0.2 - 0.3 mol / L.

[0013] Preferably, in step 1), the molar ratio of Bi 3+ to Co 2+ in the mixed solution is 1:(5 - 10); Co 2+ is derived from Co(NO 3 ) 2 ·6H 2 O, Bi 3+ is derived from Bi(NO 3 ) 3 ·5H 2 O, BiCl 3 or NaBiO 3 ·2H 2O; The BiCo-MOF precursor has a two-dimensional nanosheet array structure, which is beneficial to forming a three-dimensional array structure during the calcination stage and increasing the contact area between the catalyst and the electrolyte.

[0014] Preferably, in step 1), the solvothermal reaction temperature is 100-150 °C, such as specifically 100-120 °C, 120-140 °C, 140-150 °C, and the reaction time is 1-6 h, such as specifically 1-3 h, 3-4 h, 4-6 h.

[0015] Preferably, in step 1), after the reaction, washing and drying processes are further included.

[0016] More preferably, washing is carried out with a liquid consistent with the solvent; the drying is vacuum drying, and the drying temperature is 60-70 °C.

[0017] Preferably, in step 2), the calcination temperature is 300-400 °C, such as specifically 300-350 °C, 350-400 °C; the calcination time is 1-4 h, such as specifically 1-2 h, 2-3 h, 3-4 h; during the calcination process, the heating rate is controlled at 3-5 °C / min; such as specifically 3-4 °C / min, 4-5 °C / min; the calcination atmosphere is air.

[0018] The present invention also provides a bismuth-doped Co 3 O 4 nanosheet electrocatalyst prepared by the above preparation method.

[0019] Preferably, the bismuth-doped Co 3 O 4 nanosheet electrocatalyst has a three-dimensional array structure assembled by two-dimensional nanosheets.

[0020] The present invention also provides an application of a bismuth-doped Co 3 O 4 nanosheet electrocatalyst prepared by the above preparation method in the electrocatalytic oxidation reaction of glucose.

[0021] The bismuth-doped Co 3 O 4 nanosheet electrocatalyst prepared by the present invention has a three-dimensional array structure assembled by two-dimensional nanosheets. When applied to the electrocatalytic oxidation reaction of glucose, it can increase the contact area between the catalyst and the electrolyte, have more reactive sites, improve the glucose oxidation performance of the catalyst, and effectively assist in the preparation of hydrogen. The anodic oxidation potential of the catalyst is greatly reduced, and the overall electrolysis efficiency is improved, which is beneficial to the hydrogen evolution reaction on the cathode.

[0022] As described above, the bismuth-doped Co 3 O 4The nanosheet electrocatalyst, its preparation method and application have the following beneficial effects: the preparation process is simple, the preparation conditions are mild, the preparation equipment is simple, which is conducive to industrial production; the prepared bismuth-doped Co 3 O 4 The nanosheet electrocatalyst has a high specific surface area, many reactive sites, and the reaction is easy to proceed; it has low-potential GOR performance, and high-value-added glucose oxidation products such as arabinose and gluconic acid can be produced at the anode. The two-electrode system assembled by this catalyst has a low battery voltage and is easy to carry out overall electrolysis; it has a relatively high glucose conversion rate (31%), with an arabinose selectivity of 78.6% and a gluconic acid selectivity of 21.4%; bismuth doping effectively regulates the internal electronic structure of the catalyst, thereby improving the intrinsic activity of the catalyst and promoting the electrolysis efficiency of the catalyst as an anode for glucose solution, and is expected to be applied to the electrocatalytic oxidation reaction of glucose. Description of the Drawings

[0023] Figure 1 are the SEM images of the BiCo-MOF precursor (a) and Bi-Co 3 O 4 / NF catalyst (b) prepared in Example 1.

[0024] Figure 2 are the TEM images (a, b) and TEM mapping image (c) of the Bi-Co 3 O 4 / NF catalyst prepared in Example 1.

[0025] Figure 3 are the SEM images of the Co-MOF precursor (a) and Co 3 O 4 / NF catalyst (b) prepared in Comparative Example 1.

[0026] Figure 4 are the XRD patterns of the BiCo-MOF precursor and Bi-Co 3 O 4 / NF catalyst prepared in Example 1.

[0027] Figure 5 are the XRD patterns of the Co 3 O 4 / NF catalyst prepared in Comparative Example 1.

[0028] Figure 6 are the HER (a) and GOR (b) of the Bi-Co 3 O 4 / NF catalyst prepared in Example 1, the Co 3 O 4 / NF catalyst prepared in Comparative Example 1 and the blank sample NF.

[0029] Figure 7 is the Bi-Co prepared in Example 1 3 O 4 / NF catalyst assembled two-electrode system catalytic performance diagram.

[0030] Figure 8 is the Bi-Co prepared in Example 1 3 O 4 Mass spectrometry analysis diagram of the electrolyte after 15h of overall electrolysis of the two-electrode system assembled with / NF catalyst. In the figure, A is the mass spectrometry diagram corresponding to glucose, B is the mass spectrometry diagram corresponding to lactic acid, C is the mass spectrometry diagram corresponding to arabinose, and D is the mass spectrometry diagram corresponding to gluconic acid. Detailed implementation manners

[0031] The following specific examples illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0032] It should be noted that the process equipment or devices not specifically noted in the following examples all adopt conventional equipment or devices in the art.

[0033] In addition, it should be understood that one or more method steps mentioned in the present invention do not exclude the existence of other method steps before and after the combined steps or the insertion of other method steps between these clearly mentioned steps, unless otherwise stated; it should also be understood that the combined connection relationship between one or more devices / devices mentioned in the present invention does not exclude the existence of other devices / devices before and after the combined devices / devices or the insertion of other devices / devices between these two clearly mentioned devices / devices, unless otherwise stated. Moreover, unless otherwise stated, the numbers of the method steps are only convenient tools for identifying the method steps, rather than limiting the arrangement order of the method steps or the scope in which the present invention can be implemented. The change or adjustment of their relative relationship, without substantial change in technical content, should also be regarded as the scope in which the present invention can be implemented.

[0034] In the following examples of the present application, the nickel foam is pretreated by a method including the following steps:

[0035] Select nickel foam with a specification of 200×300×2.0mm and a pore diameter of 110PPI, cut out 3×3cm 2 , ultrasonically clean with 3mol / L dilute hydrochloric acid, absolute ethanol, and acetone for 5 minutes respectively, then rinse with methanol, and finally immerse the nickel foam in methanol for standby.

[0036] Example 1

[0037] (1) Weigh 1.02 g of Co(NO 3 ) 2 ·6H 2 O, 0.243 g of Bi(NO 3 ) 3 ·5H 2 O, dissolve them together in 15 mL of methanol to form Solution A; weigh 0.616 g of 2-methylimidazole, dissolve it in 15 mL of methanol to form Solution B; mix the above Solutions A and B evenly to form Solution C, pour it into a reaction kettle, vertically insert the treated nickel foam, and carry out a hydrothermal reaction at 120 °C for 4 h; after the reaction is completed, naturally cool it to room temperature, then wash it 3 times with methanol, and dry it in a vacuum oven at 60 °C for 6 h to prepare the BiCo-MOF precursor;

[0038] (2) Put the BiCo-MOF precursor prepared in step (1) into a tube furnace, under an air atmosphere, heat it up to 350 °C at a rate of 5 °C / min, calcine it at 350 °C for 2 h, and naturally cool it to obtain the Bi-Co 3 O 4 / NF catalyst, which is the bismuth-doped Co 3 O 4 nanosheet electrocatalyst.

[0039] Comparative Example 1

[0040] (1) Weigh 1.164 g of Co(NO 3 ) 2 ·6H 2 O, dissolve it in 15 mL of methanol to form Solution A; weigh 0.616 g of 2-methylimidazole, dissolve it in 15 mL of methanol to form Solution B; mix the above Solutions A and B evenly to form Solution C, pour it into a reaction kettle, vertically insert the treated nickel foam, and carry out a solvothermal reaction at 120 °C for 4 h; after the reaction is completed, naturally cool it to room temperature, then wash it 3 times with methanol, and dry it in a vacuum oven at 60 °C for 6 h to prepare the Co-MOF precursor;

[0041] (2) Put the Co-MOF precursor prepared in step (1) into a tube furnace, under an air atmosphere, heat it up to 350 °C at a rate of 5 °C / min, calcine it at 350 °C for 2 h, and naturally cool it to obtain the Co 3 O 4 / NF catalyst.

[0042] Characterization tests were carried out on the Bi-Co 3 O 4 / NF catalyst prepared in Example 1 and the Co 3 O 4 / NF catalyst prepared in Comparative Example 1:

[0043] (1) Morphology characterization:

[0044] SEM characterization: It was carried out on a HITACHI S-4700 scanning electron microscope. The sample preparation method used is as follows: The prepared Bi-Co 3 O 4 / NF was cut into 2×2 mm 2 , placed on the surface of the support stage with conductive adhesive, and then put into the SEM chamber for testing.

[0045] High-resolution TEM analysis: It was carried out on a JEOL 2010F transmission electron microscope. The sample preparation method used is as follows: Bi-Co 3 O 4 / NF was cut into 2×2 mm 2 , about 5 mL of ethanol was added dropwise, ultrasonically dispersed for 5 min, and a small amount of the dispersion was dropped onto the surface of a copper grid with a microgrid (including a microporous carbon support film) by the dropwise method, and left to dry naturally at room temperature.

[0046] The SEM of the BiCo-MOF precursor obtained in Example 1 is as shown in Figure 1 (a), it can be seen that the BiCo-MOF precursor has a two-dimensional nanosheet array structure; Bi-Co 3 O 4 / NF catalyst's SEM is as shown in Figure 1 (b), TEM is as shown in Figure 2 . Figure 1 In (b), it can be seen that the morphology of the Bi-Co 3 O 4 / NF catalyst is a three-dimensional array structure assembled by two-dimensional nanosheets. It can be seen from Figure 2 that the Bi-Co 3 O 4 / NF catalyst has a uniform composition and a stable structure, and the lattice spacings of 0.24 nm and 0.46 nm correspond to the (311) and (111) planes of Co 3 O 4 respectively. The SEM of the Co-MOF precursor obtained in Comparative Example 1 is as shown in Figure 3 (a), and the SEM of the Co 3 O 4 / NF catalyst is as shown in Figure 3 (b), it can be seen that the morphology of the Co 3 O 4 / NF catalyst is a three-dimensional array structure assembled by two-dimensional nanosheets.

[0047] (2) Wide-angle XRD analysis:

[0048] XRD tests were carried out on a Bruker D8 Advance X-ray diffractometer. The samples to be tested were prepared as follows: Take the BiCo-MOF precursor and Bi-Co 3 O 4 / NF catalyst in Example 1, cut it into 1×1 cm 2 , add about 5 mL of ethanol, disperse it ultrasonically for 3 min until homogeneous, drop the dispersion onto a silicon wafer drop by drop, dry it with an infrared lamp, and then place the silicon wafer in a square frosted groove above a quartz wafer for testing. Figure 4 The wide-angle XRD patterns of the BiCo-MOF precursor and Bi-Co 3 O 4 / NF catalyst in Example 1 are given. It can be seen that the XRD information obtained from the samples matches the standard card (PDF#761802) of Co 3 O 4 . Figure 5 The wide-angle XRD pattern of the Co 3 O 4 / NF catalyst in Comparative Example 1 is given. It can be seen that the XRD information obtained from the samples matches the standard card (PDF#761802) of Co 3 O 4 .

[0049] (3) Electrochemical performance test:

[0050] The electrochemical performance test was carried out on a CHI760e electrochemical workstation. The samples to be tested were prepared as follows: Cut the Bi-Co 3 O 4 / NF catalyst and the comparative sample into 1×2 cm 2 , prepare an electrolyte of 1 M KOH + 0.15 M glucose, and immerse a 1 cm 2 area sample in the electrolyte to test HER and GOR. Figure 6 (a) and (b) are the HER and GOR of the Bi-Co 3 O 4 / NF catalyst and the comparative sample, Figure 7 is the performance curve of the Bi-Co 3 O 4 / NF catalyst two-electrode system. It can be obtained from the figure that the HER and GOR performances of the Bi-Co 3 O 4 / NF catalyst are the most excellent, and the battery voltage of the two-electrode system assembled from it in alkaline glucose solution is much lower than that in alkaline aqueous solution, indicating that the Bi-Co 3 O 4 / NF catalyst has excellent glucose catalytic oxidation performance.

[0051] (4) Mass spectrometry analysis:

[0052] The mass spectrometry test was carried out on a SCIEX X500R QTOF MS mass spectrometer, and the test conditions were as follows:

[0053] Ion source: electrospray ionization source (EIS); ionization mode: droplet

[0054] Ion source gas 1: 50 psi; ion source gas 2: 50 psi; curtain gas (N 2 ) : 35 psi

[0055] Ion spray voltage (V): -4500; temperature (°C): 550

[0056] Preparation of the sample to be tested: Assemble Bi-Co 3 O 4 / NF into a two-electrode system, prepare 1M KOH + 0.5M glucose as the electrolyte, react at a current density of 50 mA cm -2 for 15 h, and take 5 mL of the electrolyte after the reaction as the sample to be tested.

[0057] Figure 6 The following is the test result. The upper and lower parts are the mass spectrometry diagrams of various extracted organic substances and their corresponding mass-to-charge ratio diagrams respectively. It can be analyzed from the figure that there are glucose (A) with a mass fraction M = 180, lactic acid (B) with M = 90, arabinose (C) with M = 150, and gluconic acid (D) with M = 196 in the electrolyte.

[0058] Conversion route of glucose: First, isomerization occurs under alkaline conditions, a part is transformed into lactic acid, and then it is further oxidized to arabinose and gluconic acid through electrolysis.

[0059] In addition, the conversion rate of glucose and the selectivity of various organic substances can be further calculated according to the change in the area of the mass spectrometry diagram. The calculation method is as follows:

[0060]

[0061]

[0062]

[0063] Example 2

[0064] (1) Weigh 1.02 g of Co(NO 3 ) 2 ·6H 2 O, 1.02 g of Bi(NO 3 ) 3 ·5H 2Weigh 0.243 g of O and dissolve it in 15 mL of methanol together to form Solution A; weigh 0.616 g of 2-methylimidazole and dissolve it in 15 mL of methanol to form Solution B; mix the above Solutions A and B evenly to form Solution C, pour it into a reaction kettle, vertically insert the treated nickel foam, and carry out a solvothermal reaction at 100 °C for 6 h; after the reaction is completed, cool it naturally to room temperature, then wash it 3 times with methanol, and dry it in a vacuum oven at 60 °C for 6 h to prepare a BiCo-MOF precursor;

[0065] (2) Put the BiCo-MOF precursor prepared in step (1) into a tubular furnace, under an air atmosphere, heat it to 300 °C at a rate of 5 °C / min, calcine it at 300 °C for 4 h, and cool it naturally to obtain a Bi-Co 3 O 4 / NF catalyst, which is a bismuth-doped Co 3 O 4 nanosheet electrocatalyst.

[0066] Example 3

[0067] (1) Weigh 1.02 g of Co(NO 3 )2·6H 2 O and 0.243 g of BiCl 3 , dissolve them in 15 mL of deionized water together to form Solution A; weigh 0.616 g of 2-methylimidazole and dissolve it in 15 mL of deionized water to form Solution B; mix the above Solutions A and B evenly to form Solution C, pour it into a reaction kettle, vertically insert the treated nickel foam, and carry out a solvothermal reaction at 140 °C for 2 h; after the reaction is completed, cool it naturally to room temperature, then wash it 3 times with deionized water, and dry it in a vacuum oven at 60 °C for 6 h to prepare a BiCo-MOF precursor;

[0068] (2) Put the BiCo-MOF precursor prepared in step (1) into a tubular furnace, under an air atmosphere, heat it to 400 °C at a rate of 5 °C / min, calcine it at 400 °C for 1 h, and cool it naturally to obtain a Bi-Co 3 O 4 / NF catalyst, which is a bismuth-doped Co 3 O 4 nanosheet electrocatalyst.

[0069] Example 4

[0070] (1) Prepare a mixed solvent of methanol and deionized water with a volume ratio of 1:1; weigh 1.092 g of Co(NO 3 ) 2 ·6H 2 O and 1.092 g of NaBiO 3 ·2H 2O 0.057g, dissolved in 15mL of the above mixed solvent to form a solution A; weigh 0.616g of 2-methylimidazole, dissolved in 15mL of the above solvent to form a solution B; mix the above solutions A and B evenly to form a solution C, pour it into a reactor, vertically insert the treated nickel foam, and perform a solvent thermal reaction at 120°C for 6h; after the reaction is completed, naturally cool to room temperature, then wash with excess solvent 3 times, and bake in a vacuum oven at 60°C for 6h to prepare a BiCo-MOF precursor;

[0071] (2) The BiCo-MOF precursor prepared in step (1) was placed in a tube furnace, heated to 350°C at 5°C / min in an air atmosphere, calcined at 350°C for 2h, and cooled naturally to obtain Bi-Co 3 O 4 / NF catalyst, namely bismuth-doped Co 3 O 4 Nanosheet electrocatalysts.

[0072] Example 5

[0073] (1) Weigh Co(NO 3 ) 2 6H 2 O 1.092g, Bi(NO 3 ) 3 ·5H 2 O 0.057g, dissolved in 15mL methanol to form solution A; weigh 0.616g of 2-methylimidazole, dissolved in 15mL methanol to form solution B; mix the above solutions A and B evenly to form solution C, pour it into a reactor, vertically insert the treated nickel foam, and perform solvent thermal reaction at 120℃ for 4h; after the reaction, naturally cool to room temperature, then wash with methanol 3 times, and bake in a vacuum oven at 60℃ for 6h to prepare a BiCo-MOF precursor;

[0074] (2) The BiCo-MOF precursor prepared in step (1) was placed in a tube furnace, heated to 400°C at 5°C / min in an air atmosphere, calcined at 400°C for 2h, and cooled naturally to obtain Bi-Co 3 O 4 / NF catalyst, namely bismuth-doped Co 3 O 4 Nanosheet electrocatalysts.

[0075] The bismuth-doped Co 3 O 4 The performance of the nanosheet electrocatalyst is comparable to that of Example 1 and will not be described in detail here.

[0076] The above embodiments are intended to illustrate the embodiments disclosed in the present invention and should not be construed as limiting the present invention. In addition, various modifications listed herein and changes in the methods and compositions of the invention will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. Although the present invention has been specifically described in connection with various specific preferred embodiments of the present invention, it should be understood that the present invention should not be limited to these specific embodiments. In fact, all such modifications that are obvious to those skilled in the art as described above to obtain the invention should be included within the scope of the present invention.

Claims

1. Application of bismuth-doped Co 3 O 4 nanosheet electrocatalyst in electrocatalytic oxidation reaction of glucose It is characterized in that The bismuth-doped Co 3 O 4 nanosheet electrocatalyst is prepared by a preparation method including the following steps: 1) Place nickel foam in a mixed solution containing metal ions and ligands, and carry out a solvothermal reaction to obtain a BiCo-MOF precursor; the metal ions include Co 2+ and Bi 3+ ; the ligand is 2-methylimidazole; 2) Calcinate the BiCo-MOF precursor to obtain the bismuth-doped Co 3 O 4 nanosheet electrocatalyst.

2. The application according to claim 1, it is characterized in that: in step 1), the solvent of the mixed solution is selected from one or both of methanol and water.

3. The application according to claim 1, it is characterized in that: in step 1), the molar ratio of the total amount of metal ions to the amount of ligand in the mixed solution is 1:(1.5 - 2).

4. The application according to claim 1, it is characterized in that: In step 1), the concentration of Co in the mixed solution 2+ is 10 - 20 mol / L, the concentration of Bi 3+ is 0.1 - 0.2 mol / L, and the concentration of 2-methylimidazole is 0.2 - 0.3 mol / L.

5. The application according to claim 1, it is characterized in that: In step 1), Bi in the mixed solution 3+ and Co 2+ have a molar ratio of 1:(5 - 10); Co 2+ is sourced from Co(NO 3 ) 2 ·6H 2 O, Bi 3+ is sourced from Bi(NO 3 ) 3 ·5H 2 O, BiCl 3 or NaBiO 3 ·2H 2 O; the BiCo-MOF precursor has a two-dimensional nanosheet array structure.

6. The application according to claim 1, it is characterized in that: in step 1), the solvothermal reaction temperature is 100 - 150 °C, and the reaction time is 1 - 6 h.

7. The application according to claim 1, it is characterized in that: in step 2), the calcination temperature is 300 - 400 °C, and the calcination time is 1 - 4 h; during the calcination process, the heating rate is controlled at 3 - 5 °C / min; the calcination atmosphere is air.

8. The application according to claim 1, it is characterized in that: The bismuth-doped Co 3 O 4 nanosheet electrocatalyst has a three-dimensional array structure assembled by two-dimensional nanosheets.

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