A modified Co-MOF composite electrocatalytic oxygen evolution material and its preparation method

Abstract

The present invention discloses a modified Co-MOF composite electrocatalytic oxygen evolution material and a preparation method thereof. The catalyst comprises flaky Co-MOF and pine needle-shaped MoSe2 loaded on the surface of Co-MOF. The preparation method is as follows: Selenium powder is dissolved in hydrazine hydrate and stirred until the solution becomes dark red-brown, then an aqueous molybdate solution and trisodium citrate are added, and stirred until the solid dissolves, followed by a hydrothermal reaction to obtain black powder, which is pine needle-shaped MoSe2; Cobalt salt and 4,4'-biphenyldicarboxylic acid are respectively dissolved in N,N-dimethylformamide solvent, the 4,4'-biphenyldicarboxylic acid solution is adjusted to be alkaline, then mixed with the cobalt salt solution, MoSe2 is added, dispersed evenly, and a hydrothermal reaction is carried out to obtain the final product; By modifying pine needle-shaped MoSe2 onto layered Co-MOF, an electronic interaction is formed between the two materials, which promotes the rapid migration of electrons and improves the electrocatalytic oxygen evolution reaction activity.

Description

Technical Field

[0001] The present invention relates to an electrocatalytic oxygen evolution material and a preparation method thereof, and particularly relates to a modified Co-MOF composite electrocatalytic oxygen evolution material and a preparation method thereof. Background Art

[0002] Hydrogen is considered a promising clean energy source with advantages such as high energy density and renewability, and is regarded as a substitute for future fossil fuels. Splitting water into hydrogen using electricity is a simple and efficient method. In electrochemistry, water splitting occurs through two independent half-cell reactions. The hydrogen evolution reaction (HER) at the cathode of the electrolyzer produces gaseous H 2 , and the oxygen evolution reaction (OER) at the anode produces O 2 . Among them, the OER process has slow kinetics and involves multiple electron transfers, which is the key limitation in the water splitting process. This technical barrier urgently requires an OER electrocatalyst with a high current density driven by a low overpotential. IrO 2 and RuO 2 currently perform well in the oxygen evolution reaction, but their high prices, limited reserves, and poor stability limit their large-scale applications in actual production. Therefore, exploring a highly efficient, durable, and abundant hydroelectric hydrogen production catalyst is a major challenge.

[0003] Metal-organic frameworks (MOFs) are two-dimensional or three-dimensional porous crystalline materials synthesized from metal cation salts or clusters and multidentate organic ligands with coordination bonds. Due to their large specific surface area, abundant adjustable pores, and structural flexibility, MOFs are considered promising candidates for electrocatalysis. Among them, Co-based MOFs have rich properties and high economic benefits, and have great potential in replacing noble metal-based (RuO 2 and IrO 2 ) materials in the electrocatalytic oxygen evolution reaction (OER). Most Co-MOFs have a large number of metal active sites and structural variability, but their poor electrical conductivity and chemical stability greatly hinder their direct use as potential OER electrocatalysts. Summary of the Invention

[0004] Object of the Invention: The present invention aims to provide a modified Co-MOF composite electrocatalytic oxygen evolution material that improves the electrical conductivity and chemical stability of Co-MOF materials; the second object of the present invention is to provide a preparation method for the modified Co-MOF composite electrocatalytic oxygen evolution material.

[0005] Technical Solution: The modified Co-MOF composite electrocatalytic oxygen evolution material of the present invention includes sheet-like Co-MOF and pine needle-like MoSe 2 loaded on the surface of Co-MOF.

[0006] Preferably, the mass ratio of the Co-MOF to MoSe 2 is 1:0.06 to 0.33. As the proportion of MoSe 2 increases, the catalytic activity of the composite electrocatalytic oxygen evolution material first increases and then decreases, showing a volcano shape. Because as the content of MoSe 2 increases, the conductivity of the composite material gradually increases, and the catalytic performance also increases accordingly. However, when the content of MoSe 2 is too high, it will accumulate on the surface of Co-MOF, reducing the active sites, thereby leading to a decrease in catalytic activity.

[0007] Preferably, the ligand of the Co-MOF is 4,4'-biphenyldicarboxylic acid. Due to the larger conjugated structure and more flexible structure of 4,4'-biphenyldicarboxylic acid, the Co-MOF has higher conductivity, larger pore size, more active sites, and chemical stability, etc.

[0008] The preparation method of the modified Co-MOF composite electrocatalytic oxygen evolution material of the present invention includes the following steps:

[0009] (1) Dissolve selenium powder in hydrazine hydrate and stir until the solution becomes dark red-brown, then add an aqueous molybdate solution and trisodium citrate, stir until the solid dissolves, and then carry out a hydrothermal reaction to obtain a black powder, which is needle-like MoSe 2 ;

[0010] (2) Dissolve cobalt salt and 4,4'-biphenyldicarboxylic acid in N,N-dimethylformamide solvent respectively, adjust the 4,4'-biphenyldicarboxylic acid solution to be alkaline, then mix it with the cobalt salt solution, add the MoSe 2 prepared in step (1), disperse it evenly, and then carry out a hydrothermal reaction to obtain MoSe 2 / Co-MOF composite electrocatalytic oxygen evolution material.

[0011] In the step (1), trisodium citrate is a structure-directing agent, which promotes the formation of needle-like molybdenum diselenide and is beneficial to the structural stability. Preferably, in step (1), the molar ratio of selenium powder, molybdenum in the molybdate to trisodium citrate is 1.2 to 4:1:1.

[0012] Preferably, in step (1), the temperature of the hydrothermal reaction is 180 to 220 °C and the time is 3 to 8 hours.

[0013] Preferably, in step (2), the temperature of the hydrothermal reaction is 80 to 120 °C and the time is 12 to 20 hours.

[0014] During the solvothermal reaction in step (2), the composite material synthesized by the hydrothermal reaction can well retain the structure of the original Co-MOF, utilize a large number of active sites of the original MOF, and the two materials are closely connected to form a strong interaction.

[0015] Invention mechanism: Co-MOF has a large number of metal active sites and structural variability, and its structure and properties can be adjusted by changing the organic linker. Co-MOF is synthesized with 4,4'-biphenyldicarboxylic acid (BPDC) as the organic ligand. The biphenyl structure of the organic ligand BPDC has a larger conjugated structure and a more flexible structure, making Co-MOFs have higher conductivity, larger pore size and more variable structures.

[0016] MoSe 2 With high conductivity and electron migration characteristics, it promotes the rapid transmission of electrons. The pine needle-like molybdenum diselenide is more tightly bound and more conducive to electron transmission. In addition, the pine needle-like structure has a larger specific surface area and more active sites, which promotes its catalytic activity. Using pine needle-like MoSe 2 Modify the layered Co-MOF, and add MoSe 2 to the precursor solution of Co-MOF will not destroy the structure of Co-MOF, retain the structure of the original MOF, and can maximize the utilization of the large specific surface area, rich active sites, etc. of the original Co-MOF, which is more conducive to the electrocatalytic oxygen evolution reaction (OER). Utilize a large number of active sites of Co-MOF to modify MoSe 2 onto its surface. The high conductivity and electron migration characteristics of MoSe 2 can improve the conductivity of Co-MOF, improve and promote the rapid transmission of electrons, and the large specific surface area of Co-MOF makes MoSe 2 more dispersed, further increasing the active sites. The combination of Co-MOF and MoSe 2 can give full play to the advantages of both materials, form a strong interaction, further improve the stability of the composite material, and improve the electrocatalytic oxygen evolution reaction (OER) activity.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: (1) By using pine needle-like MoSe 2It is modified onto the layered Co-MOF, forming an electronic interaction between the two materials, promoting the rapid migration of electrons, improving the electrocatalytic oxygen evolution reaction (OER) activity, and maintaining high stability and good catalytic hydrogen evolution activity during long-term oxygen production tests; (2) The ligand of Co-MOF is 4,4'-biphenyldicarboxylic acid, which has a larger conjugated structure and a more flexible structure, making Co-MOF have higher conductivity, larger pore size, more active sites, and chemical stability, etc.; (3) The preparation method is simple and easy to industrialize. Description of the Drawings

[0018] Figure 1 MoSe prepared in Example 1 2 / Co-MOF composite electrocatalytic oxygen evolution material, needle-like MoSe prepared in Comparative Example 1 2 monomer and X-ray diffraction pattern of the Co-MOF powder monomer prepared in Comparative Example 2;

[0019] Figure 2 MoSe prepared in Example 1 2 / Co-MOF composite electrocatalytic oxygen evolution material, needle-like MoSe prepared in Comparative Example 1 2 monomer and scanning electron micrograph of the Co-MOF powder monomer prepared in Comparative Example 2;

[0020] Figure 3 MoSe prepared in Example 1 2 Transmission electron micrograph of the transmission electron microscope for the / Co-MOF composite electrocatalytic oxygen evolution material;

[0021] Figure 4 MoSe prepared in Comparative Example 3 2 and MoSe 2 Transmission electron micrograph of the transmission electron microscope for the / Co-MOF composite electrocatalytic oxygen evolution material;

[0022] Figure 5 MoSe prepared in Example 1 2 / Co-MOF composite electrocatalytic oxygen evolution material, needle-like MoSe prepared in Comparative Example 1 2 monomer, Co-MOF powder monomer prepared in Comparative Example 2 and commercial RuO 2 electrocatalytic water splitting oxygen production diagram and corresponding Tafel diagram;

[0023] Figure 6 Electrocatalytic water splitting oxygen production diagram of the composite electrocatalytic oxygen evolution materials prepared in Examples 1 to 4;

[0024] Figure 7 Electrocatalytic water splitting oxygen production diagram of the composite electrocatalytic oxygen evolution materials prepared in Example 1 and Comparative Example 3;

[0025] Figure 8 The MoSe prepared for Example 1 2 / Co-MOF composite electrocatalytic oxygen evolution material, the needle-like MoSe prepared in Comparative Example 1 2 monomer and the CV diagram of the Co-MOF powder monomer prepared in Comparative Example 2;

[0026] Figure 9 The MoSe prepared for Example 1 2 / Co-MOF composite electrocatalytic oxygen evolution material, the needle-like MoSe prepared in Comparative Example 1 2 monomer and the C dl diagram;

[0027] Figure 10 The MoSe prepared for Example 1 2 / Co-MOF composite electrocatalytic oxygen evolution material, the needle-like MoSe prepared in Comparative Example 1 2 monomer and the impedance diagram of the Co-MOF powder monomer prepared in Comparative Example 2;

[0028] Figure 11 The MoSe prepared for Example 1 2 / Co-MOF composite electrocatalytic oxygen evolution material's 20h stability diagram and 1000CV stability diagram. Detailed implementation mode

[0029] The technical solution of the present invention will be further described below in conjunction with the embodiments.

[0030] Example 1

[0031] The modified Co-MOF composite electrocatalytic oxygen evolution material of the present invention, its preparation method includes the following steps:

[0032] (1) Dissolve 0.24 g of sodium molybdate dihydrate in 25 mL of deionized water with ultrasonic waves, and dissolve 0.16 g of selenium powder in 5 mL of hydrazine hydrate (NH 4 H 2 O) solution, stir vigorously for 30 min until the solution is dark red-brown. Mix the above two solutions, add 0.3 g of trisodium citrate, stir until uniform, transfer to a 50 mL sealed reactor, carry out the reaction at 200 °C for 4 h, cool after the reaction ends, centrifuge the reaction solution, wash and dry to obtain needle-like MoSe 2 black powder;

[0033] (2) First, dissolve 1 mmol of cobalt nitrate hexahydrate in 10 mL of DMF solvent, and dissolve 1 mmol of 4,4'-biphenyldicarboxylic acid (H 2 BPDC) in 10 mL of DMF solvent. Then in H2 Add 2 mL of 0.4 M sodium hydroxide solution dropwise to the BPDC solution. Mix the above two solutions, then add 50 mg of the molybdenum diselenide powder prepared in step (1) and stir ultrasonically to obtain a homogeneous solution. Finally, transfer the solution to a Teflon-lined (40 mL) stainless steel autoclave and carry out the reaction at 100 °C for 15 hours. At the end of the reaction, remove the suspension, naturally cool to room temperature, centrifuge to collect the precipitate, wash it three times with DMF and ethanol, and dry the product in a vacuum drying oven at 60 °C to obtain MoSe 2 / Co-MOF composite electrocatalytic oxygen evolution material.

[0034] By weighing the mass of the final product MoSe 2 / Co-MOF composite electrocatalytic oxygen evolution material and the mass of the initially added MoSe 2 The mass of MoSe 2 In the / Co-MOF composite electrocatalytic oxygen evolution material, the mass ratio of Co-MOF to MoSe 2 is 1:0.06.

[0035] Example 2

[0036] For the modified Co-MOF composite electrocatalytic oxygen evolution material of the present invention, its preparation method includes the following steps:

[0037] (1) Dissolve 0.24 g of sodium molybdate dihydrate in 25 mL of deionized water with ultrasonic waves, and dissolve 0.16 g of selenium powder in 5 mL of hydrazine hydrate (NH 4 H 2 O) solution. Stir vigorously for 30 min until the solution becomes dark red-brown. Mix the above two solutions, add 0.3 g of trisodium citrate, stir until homogeneous, transfer to a 50 mL sealed reactor, and react at 200 °C for 4 h. After the reaction is completed, cool, centrifuge the reaction solution, wash and dry to obtain needle-like MoSe 2 black powder;

[0038] (2) Dissolve 1 mmol of cobalt nitrate hexahydrate in 10 mL of DMF solvent, and dissolve 1 mmol of 4,4'-biphenyldicarboxylic acid (H 2 BPDC) in 10 mL of DMF solvent. Then add 2 mL of 0.4 M sodium hydroxide solution dropwise to the H 2 BPDC solution. Mix the above two solutions, then add 20 mg of the molybdenum diselenide powder prepared in step (1) and stir ultrasonically to obtain a homogeneous solution. Finally, transfer the solution to a Teflon-lined (40 mL) stainless steel autoclave and react at 100 °C for 15 hours. At the end of the reaction, remove the suspension, and naturally cool to room temperature, centrifuge to collect the precipitate, wash it three times with DMF and ethanol, and dry the product in a vacuum drying oven at 60 °C to obtain MoSe2 / Co-MOF composite electrocatalytic oxygen evolution material.

[0039] MoSe 2 In the MoSe 2 / Co-MOF composite electrocatalytic oxygen evolution material, the mass ratio of Co-MOF to MoSe

[0040] Example 3

[0041] The preparation method of the modified Co-MOF composite electrocatalytic oxygen evolution material of the present invention includes the following steps:

[0042] (1) Dissolve 0.24 g of sodium molybdate dihydrate in 25 mL of deionized water by ultrasonic wave, and dissolve 0.16 g of selenium powder in 5 mL of hydrazine hydrate (NH 4 H 2 O) solution. Stir vigorously for 30 min until the solution becomes dark red-brown. Mix the above two solutions, add 0.3 g of trisodium citrate, stir until homogeneous, transfer to a 50 mL sealed reactor, react at 200 °C for 4 h, cool after the reaction, centrifuge the reaction solution, wash and dry to obtain needle-like MoSe 2 black powder;

[0043] (2) Dissolve 1 mmol of cobalt nitrate hexahydrate in 10 mL of DMF solvent, and dissolve 1 mmol of 4,4'-biphenyldicarboxylic acid (H 2 BPDC) in 10 mL of DMF solvent. Then add 2 mL of 0.4 M sodium hydroxide solution dropwise to the H 2 BPDC solution, mix the above two solutions, and then add 80 mg of the molybdenum diselenide powder prepared in step (1) and stir ultrasonically to obtain a homogeneous solution. Finally, transfer the solution to a Teflon-lined (40 mL) stainless steel autoclave and react at 100 °C for 15 hours. At the end of the reaction, remove the suspension, cool naturally to room temperature, centrifuge to collect the precipitate, wash 3 times with DMF and ethanol, and dry the product in a vacuum drying oven at 60 °C to obtain MoSe 2 / Co-MOF composite electrocatalytic oxygen evolution material.

[0044] MoSe 2 In the MoSe 2 / Co-MOF composite electrocatalytic oxygen evolution material, the mass ratio of Co-MOF to MoSe

[0045] Example 4

[0046] The preparation method of the modified Co-MOF composite electrocatalytic oxygen evolution material of the present invention includes the following steps:

[0047] (1) Dissolve 0.24 g of sodium molybdate dihydrate in 25 mL of deionized water using ultrasound, and dissolve 0.16 g of selenium powder in 5 mL of hydrazine hydrate (NH 4 H 2 O) solution. Stir vigorously for 30 min until the solution becomes dark red-brown. Mix the above two solutions, add 0.3 g of trisodium citrate, stir until homogeneous, transfer to a 50 mL sealed reactor, react at 200 °C for 4 h, cool after the reaction, centrifuge the reaction solution, wash and dry to obtain needle-like MoSe 2 black powder;

[0048] (4) Dissolve 1 mmol of cobalt nitrate hexahydrate in 10 mL of DMF solvent, and dissolve 1 mmol of 4,4'-biphenyldicarboxylic acid (H 2 BPDC) in 10 mL of DMF solvent. Then add 2 mL of 0.4 M sodium hydroxide solution dropwise to the H 2 BPDC solution. Mix the above two solutions, and then add 100 mg of the molybdenum diselenide powder prepared in step (1) and stir ultrasonically to obtain a homogeneous solution. Finally, transfer the solution to a Teflon-lined (40 mL) stainless steel autoclave and react at 100 °C for 15 h. At the end of the reaction, remove the suspension, cool naturally to room temperature, centrifuge to collect the precipitate, wash 3 times with DMF and ethanol, and dry the product in a vacuum drying oven at 60 °C to obtain the MoSe 2 / Co-MOF composite electrocatalytic oxygen evolution material.

[0049] MoSe 2 / Co-MOF composite electrocatalytic oxygen evolution material, the mass ratio of Co-MOF to MoSe 2 is 1:0.33.

[0050] Comparative Example 1

[0051] Only perform step (1) on the basis of Example 1 to obtain needle-like MoSe 2 black powder.

[0052] Comparative Example 2

[0053] Dissolve 1 mmol of cobalt nitrate hexahydrate in 10 mL of DMF solvent, and dissolve 1 mmol of 4,4'-biphenyldicarboxylic acid (H 2 BPDC) in 10 mL of DMF solvent. Then in H 2Add 2 mL of 0.4 M sodium hydroxide solution dropwise to the BPDC solution. Stir the above two solutions for 10 min to mix them evenly. Transfer the solution to a Teflon-lined (40 mL) stainless steel autoclave and carry out the reaction at 100 °C for 15 hours. After the reaction is completed, naturally cool it to room temperature, centrifuge to collect the precipitate, wash it 3 times with DMF and ethanol, and dry it in a vacuum drying oven at 60 °C to obtain the Co-MOF powder monomer.

[0054] Comparative Example 3

[0055] On the basis of Example 1, in step (1), trisodium citrate is not added, and the other conditions remain unchanged.

[0056] Structure Characterization

[0057] For the MoSe prepared in Example 1 2 / Co-MOF composite electrocatalytic oxygen evolution material, the pine needle-shaped MoSe prepared in Comparative Example 1 2 monomer and the Co-MOF powder monomer prepared in Comparative Example 2 were subjected to X-ray diffraction detection, and the results are shown in Figure 1 , and by Figure 1 comparing the crystal diffraction data of the composite with those of the two monomers and the standard cards, it can be seen that the two materials were successfully synthesized and successfully compounded.

[0058] For the MoSe prepared in Example 1 2 / Co-MOF composite electrocatalytic oxygen evolution material, the pine needle-shaped MoSe prepared in Comparative Example 1 2 monomer and the Co-MOF powder monomer prepared in Comparative Example 2 were subjected to scanning electron microscopy detection, and the results are shown in Figure 2 . Figure 2 (a) is the Co-MOF monomer, Figure 2 (b) is MoSe 2 , Figure 2 (c) and Figure 2 (d) are MoSe 2 / Co-MOF. From Figure 2 (a), it can be seen that Co-MOF is lamellar. From Figure 2 (b), it can be seen that the prepared MoSe 2 is pine needle-shaped. From Figure 2 (c) and 2(d), it can be seen the close contact between MoSe 2 and the Co-MOF material.

[0059] For the MoSe prepared in Example 1 2 / Co-MOF composite electrocatalytic oxygen evolution material was subjected to transmission electron microscopy detection, and the results are shown in Figure 3 . From Figure 3 it can be seen that MoSe 2In close contact with the surface of Co-MOF, a strong interaction is formed, and it can be seen that the (101) crystal plane of MoSe 2 indicates the successful composite of the two materials.

[0060] For the MoSe 2 synthesized in Comparative Example 3 and the MoSe 2 / Co-MOF composite material, scanning electron microscopy detection was carried out, and the results are as Figure 4 shown. As can be seen from Figure 4 (a), due to the absence of trisodium citrate, the synthesized MoSe 2 shows a granular shape and does not have a pine needle-like structure.

[0061] Performance testing

[0062] (1) Performance testing of electrocatalytic water splitting for oxygen evolution

[0063] Testing method: (1) Take a piece of nickel foam (3 cm × 2 cm), wash it with 3M HCl, acetone, ethanol, and deionized water in an ultrasonic bath for 15 minutes, and place it in a vacuum drying oven at 60 °C for drying to make it clean and in an activated state for standby; (2) During the synthesis of the catalyst, when transferring the reaction solution of the last step to the reaction kettle, place a piece of nickel foam, and then put it into the oven for hydrothermal reaction to obtain the catalyst grown on the nickel foam. The performance testing of electrocatalytic water splitting for oxygen evolution is completed on a CHI760D workstation. A three-electrode system at room temperature is used, with a platinum sheet as the counter electrode, Ag / AgCl as the reference electrode, the nickel foam loaded with the sample as the working electrode, and a KOH solution (1.0 M) as the electrolyte. Linear sweep voltammetry (LSV) is used to test the overpotential of the material at a scanning rate of 5 mV / s. According to the following Tafel equation for the Tafel slope, η = b log j + a, where b is the Tafel slope and j is the current density.

[0064] For the MoSe 2 / Co-MOF composite electrocatalytic oxygen evolution material prepared in Example 1, the pine needle-like MoSe 2 monomer prepared in Comparative Example 1, the Co-MOF powder monomer prepared in Comparative Example 2, and commercial RuO 2 for electrocatalytic water splitting for oxygen evolution were tested, plotted, and the corresponding Tafel plots were obtained. The results are shown in Figure 5 .

[0065] As can be seen from Figure 5 , the MoSe 2 / Co-MOF composite electrocatalytic oxygen evolution material, MoSe 2 monomer, Co-MOF powder monomer, and commercial RuO 2The overpotentials are 273 mV, 450 mV, 340 mV, 297 mV and 582 mV respectively. MoSe 2 The electrocatalytic oxygen evolution activity of the MoSe 2 monomer, Co-MOF powder monomer and commercial RuO 2 .

[0066] For the MoSe 2 loaded with different amounts of pine needle-like MoSe prepared in Examples 1 to 4 2 The electrocatalytic water splitting oxygen evolution of the MoSe Figure 6 / Co-MOF composite electrocatalytic oxygen evolution materials was tested, and the results are as

[0067] shown. Figure 6 It can be seen that as the proportion of MoSe 2 increases, the catalytic activity of the composite electrocatalytic oxygen evolution material first increases and then decreases, showing a volcano shape. Because as the content of MoSe 2 increases, the conductivity of the composite material gradually increases, and the catalytic performance also increases accordingly. When the content of MoSe 2 is too high, it will accumulate on the surface of Co-MOF, reducing the active sites, resulting in a decrease in catalytic activity.

[0068] The electrocatalytic water splitting oxygen evolution of the composite electrocatalytic oxygen evolution materials prepared in Example 1 and Comparative Example 1 was tested, and the results are as Figure 7 shown.

[0069] It can be seen from Figure 7 that at a current density of 50 mA cm -2 , the overpotentials of the pine needle-like MoSe 2 and Co-MOF composite material in Example 1 are 273 mV, which is significantly lower than the overpotential of 301 mV of the composite material of ordinary non-pine needle-like MoSe2 and Co-MOF in Comparative Example 3. It shows that the pine needle-like MoSe 2 synthesized by adding a structure directing agent with a large surface area can indeed improve the electrocatalytic oxygen evolution activity of the composite material.

[0070] (2) CV test

[0071] Test method: Completed on a CHI 760D workstation. Using a three-electrode system at room temperature, a platinum sheet as the counter electrode, Ag / AgCl as the reference electrode, the foam nickel loaded with the sample as the working electrode, and a KOH solution (1.0 M) as the electrolyte. CV curves were obtained at different scanning rates (20 - 100 mV / s) in the non-Faraday region (1.23 - 1.33 V vs. RHE). The electrochemically active surface area (ECSA) of the catalyst can be obtained through the double-layer capacitance (Cdl ) to evaluate, where C dl is obtained from the CV curve. The test results are shown in Figure 8 and Figure 9 .

[0072] From Figure 8 and Figure 9 it can be seen that the electrochemically active surface area (ECSA) is a key parameter to measure the number of exposed active sites. By measuring the CV results in the non-Faradaic region at different scan rates through cyclic voltammetry (as shown in Figure 8 ), the ECSA is obtained from the double-layer capacitance (Cdl) (as shown in Figure 9 ). From Figure 9 it can be seen that the Cdl value in the MoSe 2 / Co-MOF sample is greater than that of the Co-MOF monomer and MoSe 2 monomer, indicating that there are more active sites in the MoSe 2 / Co-MOF composite. The results further show that the introduction of MoSe2 increases the ECSA or active sites, greatly improving the catalytic activity.

[0073] (3) Impedance detection

[0074] Test method: Test on a CHI 760D workstation. A three-electrode system at room temperature is used, with a platinum sheet as the counter electrode, Ag / AgCl as the reference electrode, nickel foam loaded with the sample as the working electrode, and a KOH solution (1.0 M) as the electrolyte. The test is carried out in the frequency range of 0.1 - 100 kHz at open circuit voltage.

[0075] By detecting the impedance of the MoSe 2 / Co-MOF composite electrocatalytic oxygen evolution material, MoSe 2 monomer, and Co-MOF powder monomer, the results are shown in Figure 10 .

[0076] From Figure 10 it can be seen that by fitting the electrochemical impedance of the catalyst material, the equivalent circuit consists of an ohmic resistance (R s ) and two parallel combinations, where R ct represents the charge transfer resistance. The R 2 value of the MoSe ct / Co-MOF composite material (R ct = 7.45 Ω) is less than that of Co MOF (R ct = 9.13 Ω) and MoSe2 (R ct = 10.03 Ω). Generally, the smaller the R ct value, the more effective and faster the charge transfer, and the better the OER performance. It also strongly proves that the incorporation of MoSe2 Introduced into Co-MOF, it is beneficial to improve the conductivity of Co-MOF, further reduce the resistance, and achieve more efficient charge transfer and electron transfer between electrolyte ions during the OER process.

[0077] (4) Stability test

[0078] By testing the stability of the MoSe 2 / Co-MOF composite electrocatalytic oxygen evolution material, the results are shown in Figure 11 .

[0079] As can be seen from Figure 11 , the 20h stability test and 1000CV stability test indicate that the composite material has high stability.

Claims

1. A modified Co-MOF composite electrocatalytic oxygen evolution material, characterized in that, It includes flaky Co-MOF and pine needle-like MoSe loaded on the surface of Co-MOF 2 , and the ligand of the Co-MOF is 4,4'-biphenyldicarboxylic acid.

2. The modified Co-MOF composite electrocatalytic oxygen evolution material according to claim 1, characterized in that, The mass ratio of the Co-MOF to MoSe 2 is 1:0.06 to 0.

33.

3. A preparation method of the modified Co-MOF composite electrocatalytic oxygen evolution material according to claim 1 or 2, characterized in that, comprising the following steps: (1) Dissolve selenium powder in hydrazine hydrate and stir until the solution becomes dark red-brown. Then add an aqueous solution of molybdate and trisodium citrate, and stir until the solid dissolves. Then carry out a hydrothermal reaction to obtain a black powder, which is needle-like MoSe 2 ; (2) Dissolve cobalt salt and 4,4'-biphenyldicarboxylic acid in N,N-dimethylformamide solvent respectively, adjust the 4,4'-biphenyldicarboxylic acid solution to be alkaline, then mix it with the cobalt salt solution, add MoSe prepared in step (1) 2 , disperse it evenly, and then carry out hydrothermal reaction to obtain MoSe 2 / Co-MOF composite electrocatalytic oxygen evolution material.

4. The preparation method of the material according to claim 3, characterized in that, In step (1), the molar ratio of molybdenum in selenium powder and molybdate to trisodium citrate is 1.2-4:1:

1.

5. The preparation method of the material according to claim 3, characterized in that, In step (1), the temperature of the hydrothermal reaction is 180-220 °C and the time is 3-8 hours.

6. The preparation method of the material according to claim 3, characterized in that, In step (2), the temperature of the hydrothermal reaction is 80-120 °C and the time is 12-20 h.

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