A self-supporting cobalt oxide composite electrode, a preparation method thereof, and its application in seawater electrolysis

Abstract

The present invention discloses a self-supporting cobalt oxide composite electrode, a preparation method thereof, and an application in seawater electrolysis, belonging to the field of battery technology; using melamine formaldehyde-polyethyleneimine resin as an adhesive, a cobalt-based coordination polymer is combined with activated carbon fiber paper, and a composite electrode is obtained after high-temperature annealing, and the composite electrode is applied to seawater electrolysis. In the composite electrode, a nitrogen-doped carbon layer is formed after high-temperature annealing of the melamine formaldehyde-polyethyleneimine resin, which has good electrical conductivity and certain electrocatalytic performance, effectively solving the problem of low electrical conductivity of seawater itself. At the same time, the carbon layer can also protect the electrocatalytic active components wrapped therein, reduce the corrosion of chloride ions in seawater to the electrode, and slow down the precipitation of calcium and magnesium ions on the electrode surface. Compared with the electrode material prepared by the traditional in situ growth method, the electrode prepared by the present invention has better stability and anti-interference ability and longer service life.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a self-supporting cobalt tetroxide composite electrode, a preparation method thereof, and application thereof in seawater electrolysis. Background Art

[0002] With the depletion of traditional fossil fuels and the intensification of the greenhouse effect, people are searching for low-cost, environmentally friendly, clean energy. Hydrogen, the 21st century's most promising clean energy source, can be produced through methods such as fossil fuel refining, methane recombination, photocatalytic water splitting, and water electrolysis. Seawater is one of Earth's most abundant natural water sources, accounting for 96.5% of the world's total water resources. Therefore, water electrolysis is widely considered the most promising carbon-free and efficient strategy for hydrogen production.

[0003] Generally speaking, water electrolysis involves two half-reactions: the oxygen evolution reaction (OER) at the anode and the hydrogen evolution reaction (HER) at the cathode. Both reactions require effective electrocatalysts to reduce energy consumption. While commercial noble metal catalysts have high activity, their high price and scarce reserves in the Earth's crust limit their practical applications. Therefore, researchers have turned their attention to the development of non-noble metal electrocatalysts.

[0004] However, in actual research and development, hydrogen production from seawater remains a significant challenge due to the low electrical conductivity of seawater itself, the tendency of calcium and magnesium ions in it to form precipitates that inactivate active sites, and the corrosion of electrodes caused by high concentrations of chloride ions. Therefore, it is urgent to develop a catalytic electrode with high catalytic activity, low overpotential, high stability, and immunity to interference from chloride ions and other plasmas in seawater. Summary of the Invention

[0005] The purpose of the present invention is to provide a self-supporting cobalt oxide composite electrode, a preparation method thereof, and an application in seawater electrolysis. The composite electrode has high catalytic activity, low overpotential, high stability, and is not affected by chloride ions in seawater. It can be used for hydrogen and oxygen production reactions in alkaline seawater.

[0006] The object of the present invention is achieved through the following technical solutions:

[0007] A self-supporting cobalt oxide composite electrode is constructed by combining a cobalt-based coordination polymer with activated carbon fiber paper using a melamine formaldehyde-polyethyleneimine resin as a binder, followed by high-temperature annealing. The activated carbon fiber paper is activated to enhance its hydrophilicity.

[0008] In this solution, a nitrogen-doped carbon layer is formed after high-temperature annealing of a melamine formaldehyde-polyethyleneimine resin. This layer exhibits excellent electrical conductivity and electrocatalytic properties, effectively addressing the inherently low conductivity of seawater. The carbon layer also protects the encapsulated electrocatalytically active components, mitigating corrosion of the electrode by chloride ions in seawater and slowing the precipitation of calcium and magnesium ions on the electrode surface. Compared to electrode materials prepared using traditional in-situ growth methods, the electrodes produced in this method exhibit improved stability, improved anti-interference capabilities, and a longer service life.

[0009] The self-supporting cobalt tetroxide composite electrode provided by the present invention can solve the problems encountered when using seawater as the electrolyte, such as being unaffected by interference from chloride ions and other plasmas in seawater. It also has high catalytic activity, low overpotential, and high stability, and can be widely used in alkaline seawater hydrogen and oxygen production reactions.

[0010] In addition, to achieve the above object, the present invention also provides a method for preparing a self-supporting cobalt oxide composite electrode, comprising the following steps:

[0011] S1. Preparation of raw materials:

[0012] Preparation of activated carbon fiber paper: First, mix the carbon fiber paper with HNO3 solution and dry it; then wash it, mix it with NaOH solution and dry it; finally, take it out, wash it, and dry it to obtain CP, that is, activated carbon fiber paper;

[0013] Synthesis of melamine formaldehyde-polyethyleneimine resin: Melamine, deionized water, and formaldehyde are mixed and stirred until clear to obtain oligomeric melamine formaldehyde resin; the oligomeric melamine formaldehyde resin is then mixed with polyethyleneimine and thoroughly ground to obtain MP, i.e., melamine formaldehyde-polyethyleneimine resin;

[0014] Synthesis of ZIF-67 nanoparticles: First, cobalt nitrate was added to methanol and fully dissolved, which was recorded as Solution A. 2-methylimidazole was added to methanol and fully dissolved, which was recorded as Solution B. Solution B was then poured into Solution A, and after thorough stirring, the mixture was centrifuged, washed, and dried to obtain ZIF-67 nanoparticles, i.e., cobalt-based coordination polymer particles.

[0015] S2. Preparation of composite electrodes:

[0016] S21. Weigh a certain amount of ZIF-67 nanoparticles and melamine formaldehyde-polyethyleneimine resin, mix them thoroughly, and then apply them to the surface of activated carbon fiber paper. After drying, apply the same method to the reverse side to obtain ZIF-67 / MP / CP after drying.

[0017] S22. Place ZIF-67 / MP / CP in a tube furnace and raise the temperature to 500-900°C under an inert gas atmosphere. Keep at this temperature for 2 hours and then cool naturally to obtain ZIF-67 / MP / CP-T, i.e., a composite electrode.

[0018] The preparation method provided by the present invention has the advantages of simplicity, high repeatability, low cost, etc.

[0019] Preferably, in the preparation of activated carbon fiber paper in step S1, the temperature of the first two dryings is 92-98° C., and the drying time is 10-15 hours.

[0020] Preferably, in the synthesis of the melamine formaldehyde-polyethyleneimine resin in step S1, the mass ratio of the oligomeric melamine formaldehyde resin to the polyethyleneimine is 1:(0.2-2).

[0021] Preferably, in the synthesis of ZIF-67 nanoparticles in step S1, the mass ratio of cobalt nitrate to 2-methylimidazole is (0.1-1): (0.1-1).

[0022] Preferably, in step S21, the mass ratio of ZIF-67 to melamine formaldehyde-polyethyleneimine resin is (1-30):100.

[0023] Preferably, in step S22, the heating rate is 2-10°C / min.

[0024] In addition, to achieve the above-mentioned purpose, the present invention also provides an application of a self-supporting cobalt tetroxide composite electrode in seawater electrolysis.

[0025] The composite electrode prepared by the present invention can be directly used as the cathode and anode of an electrolytic cell to produce hydrogen and oxygen by electrolyzing water.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The present invention uses melamine formaldehyde-polyethyleneimine resin as a binder to combine a cobalt-based coordination polymer with activated carbon fiber paper, and then annealing at high temperature to obtain a composite electrode. In this electrode, the melamine formaldehyde-polyethyleneimine resin forms a nitrogen-doped carbon layer after high-temperature annealing. This layer has good electrical conductivity and certain electrocatalytic properties, effectively solving the problem of low electrical conductivity of seawater itself. At the same time, the carbon layer can also protect the electrocatalytically active components encapsulated therein, reduce the corrosion of chloride ions in seawater on the electrode, and slow the precipitation of calcium and magnesium ions on the electrode surface. Compared with electrode materials prepared by traditional in situ growth methods, the electrodes prepared by the present invention have better stability, anti-interference ability, and longer service life.

[0028] 2. The self-supporting cobalt tetroxide composite electrode provided by the present invention has good dual catalytic function in the hydrogen evolution reaction and oxygen evolution reaction of water electrolysis, which can simplify the reaction system design and reduce the catalyst synthesis cost, thereby achieving more efficient, sustainable and economical energy conversion; at the same time, it has good catalytic stability and long service life, and can maintain high and long-term stable operation at high current density. For example, in alkaline seawater, it can run continuously for more than 13 hours and maintain an industrial-grade current density (500mA / cm 2 ).

[0029] 3. In the self-supporting cobalt tetroxide composite electrode provided by the present invention, the current density generated under the same overpotential of cobalt tetroxide catalytic activity is higher, and the current density can reach up to 800mA / cm 2 .

[0030] 4. The self-supporting cobalt tetroxide composite electrode provided by the present invention has good anti-interference performance and can be used in the hydrogen and oxygen production reaction processes of alkaline seawater without being interfered with or affected by the presence of various ions such as chloride ions in seawater.

[0031] 5. The self-supporting cobalt oxide composite electrode provided by the present invention is an integrated composite electrode material. Based on its high specific surface area and good conductivity, the material has high catalytic activity, as well as strong stability, anti-interference and corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 : Scanning electron microscope images of activated carbon fiber paper, ZIF-67, ZIF-67 / MP / CP, and ZIF-67 / MP / CP-T;

[0033] in, Figure 1 a in the figure is a scanning electron microscope image of carbon fiber paper; Figure 1 b is the scanning electron microscope image of ZIF-67; Figure 1 c is the scanning electron microscope image of ZIF-67 / MP / CP; Figure 1 Figures d, e, f, g, and h are scanning electron microscope images of ZIF-67 / MP / CP-T (T is 500℃, 600℃, 700℃, 800℃, and 900℃, respectively);

[0034] Figure 2 : LSV curves of HER and OER of ZIF-67 / MP / CP-700 composite electrode material in seawater at pH = 14;

[0035] Figure 3 : LSV curves of HER and OER of ZIF-67 / MP / CP-800 composite electrode material in seawater at pH = 14;

[0036] Figure 4: LSV curves of HER and OER of ZIF-67 / MP / CP-900 composite electrode material in seawater at pH = 14;

[0037] Figure 5 :ZIF-67 / MP / CP-800 in seawater with pH=14 at 500mA / cm -2 The IT test is performed at the potential corresponding to the current density. DETAILED DESCRIPTION

[0038] Example 1

[0039] S1. Preparation of raw materials.

[0040] Cut the carbon fiber paper into 1cm×2cm pieces, mix it with 50mL of 1mol / L HNO3, and place it in a 95℃ oven to react for 12 hours. Remove it and rinse it with deionized water until it is neutral. Then mix it with 50mL of 1mol / L NaOH and place it in a 95℃ oven to react for 12 hours. Remove it and rinse it with deionized water until it is neutral. Then dry it to obtain activated carbon fiber paper.

[0041] Dissolve 1.455g of cobalt nitrate in 50mL of methanol and stir thoroughly until dissolved (Solution A). Dissolve 1.6446g of 2-methylimidazole in 50mL of methanol and stir thoroughly until dissolved (Solution B). Pour Solution B into Solution A and stir under medium-speed magnetic stirring for 1 hour. After the reaction is complete, separate the mixture by centrifugation at 9000rpm for 3 minutes, wash three times with methanol, and dry in a 75°C oven to obtain ZIF-67 nanoparticles.

[0042] 3.0 g of melamine, 5.4 mL of deionized water, and 6.9 mL of formaldehyde were mixed and stirred in an 80°C water bath with magnetic stirring until clear to obtain an oligomeric melamine-formaldehyde resin. The obtained oligomeric melamine-formaldehyde resin was then mixed with polyethyleneimine at a mass ratio of 1:1 and thoroughly ground to obtain a melamine-formaldehyde-polyethyleneimine resin.

[0043] S2. Preparation of composite electrodes.

[0044] Weigh 10 mg of ZIF-67 and mix it with MP at a mass ratio of 1:5. After mixing evenly, apply it to the surface of activated carbon fiber paper, dry it in an oven, and apply the same method to the reverse side. After drying, ZIF-67 / MP / CP is obtained. ZIF-67 / MP / CP is placed in a tube furnace under an inert gas atmosphere and heated to 700°C at a rate of 5°C / min. After holding for 2 hours and then cooling naturally, ZIF-67 / MP / CP-700 is obtained.

[0045] The scanning electron microscope images of the activated carbon fiber paper, ZIF-67, ZIF-67 / MP / CP and ZIF-67 / MP / CP-T in Example 1 are as follows: Figure 1 shown.

[0046] in, Figure 1 a in the figure is a scanning electron microscope image of carbon fiber paper;

[0047] Figure 1 b in the figure is the synthesized ZIF-67 nanoparticles. The image shows that the particles are polyhedral in morphology and the particle size is 200-800 nm.

[0048] Figure 1 c in the figure is the scanning electron microscope image of ZIF-67 / MP / CP. Figure 1 As can be observed in Figure c, ZIF-67 / MP / CP is prepared by mixing ZIF-67 nanoparticles into melamine formaldehyde-polyethyleneimine resin, coating it on carbon fiber paper and curing it. The ZIF-67 nanoparticles are uniformly dispersed in the melamine formaldehyde-polyethyleneimine resin cured layer, and the resin cured layer is firmly bonded to the carbon fiber paper.

[0049] Figure 1 dh in the figure is a scanning electron microscope image of ZIF-67 / MP / CP-T. In addition to the annealing treatment at 700℃, ZIF-67 / MP / CP was also annealed at 500, 600, 800, and 900℃ in a nitrogen atmosphere. Figure 1 As can be seen from the dh in the figure, the melamine formaldehyde-polyethyleneimine resin was successfully converted into a black nitrogen-doped carbon layer and firmly loaded on the carbon fiber paper. Cobalt tetroxide nanoparticles were observed on the surface of the composite electrode. From the cross-section of the carbon layer, polyhedral carbon particles transformed from ZIF-67 were seen, with a particle size of about 200-800nm.

[0050] In order to test the electrocatalytic performance of ZIF-67 / MP / CP-700 composite electrode materials in alkaline seawater environment, electrochemical tests were carried out in alkaline seawater with pH = 14, such as Figure 2 As shown in the HER test, ZIF-67 / MP / CP-700 has ηHER@10mA / cm 2 =0.061V,ηHER@50mA / cm 2 =0.266V,ηHER@100mA / cm 2 =0.336V,ηHER@500mA / cm 2 =0.636V performance; in the OER test, ZIF-67 / MP / CP-700 has ηOER@10mA / cm 2 =0.054V,ηOER@50mA / cm2 =0.181V,ηOER@100mA / cm 2 =0.273V,ηOER@300mA / cm 2 =0.447V performance.

[0051] In summary, ZIF-67 / MP / CP-700 can effectively catalyze hydrogen and oxygen evolution reactions in alkaline seawater (pH = 14), with the HER current density reaching up to 700 mA / cm 2 , the OER current density can reach up to 300mA / cm 2 .

[0052] Example 2

[0053] S1. Preparation of raw materials.

[0054] Cut the carbon fiber paper into 1cm×2cm pieces, mix it with 50mL of 1mol / L HNO3, and place it in a 95℃ oven to react for 12 hours. Remove it and wash it with deionized water until it is neutral, then mix it with 50mL of 1mol / L NaOH and place it in a 95℃ oven to react for 12 hours. Remove it and wash it with deionized water until it is neutral, and dry it to obtain activated carbon fiber paper.

[0055] Dissolve 1.455g of cobalt nitrate in 50mL of methanol and stir thoroughly until dissolved (Solution A). Dissolve 1.6446g of 2-methylimidazole in 50mL of methanol and stir thoroughly until dissolved (Solution B). Pour Solution B into Solution A and stir under medium-speed magnetic stirring for 1 hour. After the reaction is complete, separate the mixture by centrifugation at 9000rpm for 3 minutes, wash three times with methanol, and dry in a 75°C oven to obtain ZIF-67 nanoparticles.

[0056] 3.0 g of melamine, 5.4 mL of deionized water, and 6.9 mL of formaldehyde were mixed and stirred in an 80°C water bath with magnetic stirring until clear to obtain an oligomeric melamine-formaldehyde resin. The obtained oligomeric melamine-formaldehyde resin was then mixed with polyethyleneimine at a mass ratio of 1:1 and thoroughly ground to obtain a melamine-formaldehyde-polyethyleneimine resin.

[0057] S2. Preparation of composite electrodes.

[0058] Weigh 10 mg of ZIF-67 and mix it with MP at a mass ratio of 1:5. After mixing evenly, apply it to the surface of the activated carbon fiber paper, dry it in an oven, and apply the same method to the reverse side. After drying, ZIF-67 / MP / CP is obtained. The ZIF-67 / MP / CP is placed in a tube furnace under an inert gas atmosphere and heated at a rate of 5°C / min to 800°C. After holding for 2 hours and then cooling naturally, ZIF-67 / MP / CP-800 is obtained.

[0059] In order to test the electrocatalytic performance of ZIF-67 / MP / CP-800 composite electrode materials in alkaline seawater environment, electrochemical tests were carried out in alkaline seawater with pH = 14. Figure 3 As shown in the HER test, ZIF-67 / MP / CP-800 has ηHER@10mA / cm 2 =0.057V,ηHER@50mA / cm 2 =0.220V,ηHER@100mA / cm 2 =0.285V,ηHER@500mA / cm 2 =0.535V performance; in the OER test, ZIF-67 / MP / CP-800 has ηOER@10mA / cm 2 =0.076V,ηOER@50mA / cm 2 =0.226V,ηOER@100mA / cm 2 =0.313V,ηOER@300mA / cm 2 =0.464V performance.

[0060] In summary, ZIF-67 / MP / CP-800 can also effectively catalyze hydrogen and oxygen evolution reactions in alkaline seawater (pH = 14), with the HER current density reaching up to 800 mA / cm 2 , the OER current density can reach up to 300mA / cm 2 ; and its catalytic activity for HER is better than that of ZIF-67 / MP / CP-700, and the energy (overpotential) required to achieve the same current density is lower than that of ZIF-67 / MP / CP-700.

[0061] Example 3

[0062] S1. Preparation of raw materials.

[0063] Cut the carbon fiber paper into 1cm×2cm pieces, mix it with 50mL of 1mol / L HNO3, and place it in a 95℃ oven to react for 12 hours. Remove it and wash it with deionized water until it is neutral, then mix it with 50mL of 1mol / L NaOH and place it in a 95℃ oven to react for 12 hours. Remove it and wash it with deionized water until it is neutral, and dry it to obtain activated carbon fiber paper.

[0064] Dissolve 1.455g of cobalt nitrate in 50mL of methanol and stir thoroughly until dissolved (Solution A). Dissolve 1.6446g of 2-methylimidazole in 50mL of methanol and stir thoroughly until dissolved (Solution B). Pour Solution B into Solution A and stir under medium-speed magnetic stirring for 1 hour. After the reaction is complete, separate the mixture by centrifugation at 9000rpm for 3 minutes, wash three times with methanol, and dry in a 75°C oven to obtain ZIF-67 nanoparticles.

[0065] 3.0 g of melamine, 5.4 mL of deionized water, and 6.9 mL of formaldehyde were mixed and stirred in an 80°C water bath with magnetic stirring until clear to obtain an oligomeric melamine-formaldehyde resin. The obtained oligomeric melamine-formaldehyde resin was then mixed with polyethyleneimine at a mass ratio of 1:1 and thoroughly ground to obtain a melamine-formaldehyde-polyethyleneimine resin.

[0066] S2. Preparation of composite electrodes.

[0067] Weigh 10 mg of ZIF-67 and mix it with MP at a mass ratio of 1:5. After mixing evenly, apply it to the surface of the activated carbon fiber paper, dry it in an oven, and apply the same method to the reverse side. After drying, ZIF-67 / MP / CP is obtained. The ZIF-67 / MP / CP is placed in a tube furnace under an inert gas atmosphere and heated to 900°C at a rate of 5°C / min. After holding for 2 hours and then cooling naturally, ZIF-67 / MP / CP-900 is obtained.

[0068] In order to test the electrocatalytic performance of ZIF-67 / MP / CP-900 composite electrode materials in alkaline seawater environment, electrochemical tests were carried out in alkaline seawater with pH = 14. Figure 4 As shown in the HER test, ZIF-67 / MP / CP-800 has ηHER@10mA / cm 2 =0.085V,ηHER@50mA / cm 2 =0.310V,ηHER@100mA / cm 2 =0.373V,ηHER@500mA / cm 2 =0.648V performance; in the OER test, ZIF-67 / MP / CP-800 has ηOER@10mA / cm 2 =0.096V,ηOER@50mA / cm 2 =0.252V,ηOER@100mA / cm 2 =0.333V,ηOER@300mA / cm 2 =0.465V performance.

[0069] In summary, ZIF-67 / MP / CP-900 can also effectively catalyze hydrogen and oxygen evolution reactions in alkaline seawater (pH = 14), with the HER current density reaching up to 720 mA / cm 2 , the OER current density can reach up to 300mA / cm 2 .

[0070] Application example: Self-supporting cobalt tetroxide composite electrode ZIF-67 / MP / CP-800 electrolyzes water to produce hydrogen in alkaline seawater at pH = 14.

[0071] The present invention simulates the real industrial electrolysis water hydrogen production environment, and the composite electrode material ZIF-67 / MP / CP-800, graphite electrode, silver / silver chloride electrode and alkaline seawater with pH=14 form an electrolytic cell system. Figure 5 As shown in Figure 2, when the hydrogen evolution reaction in alkaline seawater electrolysis is driven by a constant voltage, ZIF-67 / MP / CP-800 can maintain a constant current of 500 mA / cm -2 The current density output of the commercial platinum carbon catalyst (Pt / C) decays to 300mA / cm after 2 hours of continuous operation. -2 This result shows that the composite electrode material ZIF-67 / MP / CP-800 exhibits good stability and anti-interference ability, and the catalytic performance is not affected.

Claims

1. A self-supporting cobalt oxide composite electrode, characterized in that: Using melamine formaldehyde-polyethyleneimine resin as a binder, a cobalt-based coordination polymer was combined with activated carbon fiber paper, and a composite electrode was obtained after high-temperature annealing. The cobalt-based coordination polymer is ZIF-67 nanoparticles; and the high-temperature annealing temperature is 500-900°C.

2. The method for preparing a self-supporting cobalt tetroxide composite electrode according to claim 1, characterized in that: The steps include: S1. Preparation of raw materials: Preparation of activated carbon fiber paper: First, mix the carbon fiber paper with HNO3 solution and dry it; then wash it, mix it with NaOH solution and dry it; finally, take it out, wash it, and dry it to obtain CP, that is, activated carbon fiber paper; Synthesis of melamine formaldehyde-polyethyleneimine resin: Melamine, deionized water, and formaldehyde are mixed and stirred until clear to obtain oligomeric melamine formaldehyde resin; the oligomeric melamine formaldehyde resin is then mixed with polyethyleneimine and thoroughly ground to obtain MP, i.e., melamine formaldehyde-polyethyleneimine resin; Synthesis of ZIF-67 nanoparticles: First, cobalt nitrate was added to methanol and fully dissolved, which was recorded as Solution A. 2-methylimidazole was added to methanol and fully dissolved, which was recorded as Solution B. Solution B was then poured into Solution A, and after thorough stirring, the mixture was centrifuged, washed, and dried to obtain ZIF-67 nanoparticles, i.e., cobalt-based coordination polymer particles. S2. Preparation of composite electrodes: S21. Weigh a certain amount of ZIF-67 nanoparticles and melamine formaldehyde - polyethyleneimine resin, mix them thoroughly, and then apply them to the surface of activated carbon fiber paper. After drying, apply the same method to the reverse side, and dry to obtain ZIF-67 / MP / CP. S22. Place ZIF-67 / MP / CP in a tube furnace and, under an inert gas atmosphere, raise the temperature to 500-900°C. Maintain the temperature for 2 hours and then cool naturally to obtain ZIF-67 / MP / CP-T, a composite electrode.

3. The method for preparing a self-supporting cobalt oxide composite electrode according to claim 2, wherein: In the preparation of activated carbon fiber paper in step S1, the temperature of the first two dryings is 92-98° C., and the drying time is 10-15 hours.

4. The method for preparing a self-supporting cobalt oxide composite electrode according to claim 2, wherein: In the synthesis of the melamine-formaldehyde-polyethyleneimine resin in step S1, the mass ratio of the oligomeric melamine-formaldehyde resin to the polyethyleneimine is 1:(0.2-2).

5. The method for preparing a self-supporting cobalt tetroxide composite electrode according to claim 2, characterized in that: In the synthesis of step S1ZIF-67 nanoparticles, the mass ratio of cobalt nitrate and 2-methylimidazole is (0.1 ~ 1): (0.1 ~ 1).

6. The method for preparing a self-supporting cobalt oxide composite electrode according to claim 2, wherein: In step S21, the mass ratio of ZIF-67 to melamine formaldehyde-polyethyleneimine resin is (1-30):

100.

7. The method for preparing a self-supporting cobalt tetroxide composite electrode according to claim 2, characterized in that: In step S22, the heating rate is 2-10°C / min.

8. The use of the self-supporting cobalt tetroxide composite electrode in seawater electrolysis according to claim 1, characterized in that: The composite electrode is directly used as the cathode or anode of an electrolytic cell.

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