Preparation method of metal atom doped cobaltosic oxide electrolyzed water catalyst

Abstract

The invention discloses a preparation method of a metal atom doped cobaltosic oxide electrolyzed water catalyst, and relates to a preparation method of an electrolyzed water catalyst. The invention aims to solve the problems of high cost, slow reaction in an acid environment and relatively high overpotential of the existing electrolytic water oxygen evolution catalyst prepared from noble metals and compounds thereof. The preparation method comprises the following steps: 1, dissolving cobalt nitrate in a solvent, and uniformly stirring; 2, adding the metal salt into the solvent, and uniformly stirring; and 3, sequentially dropwise adding to the surface of the carbon cloth, then heating and preserving heat, and cooling in air after heat preservation. The method is used for preparing the metal atom doped cobaltosic oxide electrolyzed water catalyst.

Description

Technical Field

[0001] The invention relates to a method for preparing a water electrolysis catalyst. Background Art

[0002] Energy is the cornerstone of social progress, and social development is accompanied by the replacement of different energy forms. Carbon-based fossil energy such as coal, oil, and natural gas is the main energy source in today's society. The combustion of these fossil energy sources also releases a large amount of carbon dioxide, exacerbating the greenhouse effect.

[0003] my country has vigorously promoted the adjustment of energy structure and developed clean energy, such as wind energy, solar energy, hydropower and geothermal energy. However, these clean energy sources have problems such as low energy density and discontinuous energy supply, which have brought difficulties to the collection and utilization of energy. Therefore, how to effectively use renewable energy has become a major issue in the current energy field. Hydrogen energy has the advantages of no pollution and high energy density. It is considered to be an ideal green energy and has great potential to become an ideal clean energy for commercial use. Building an energy industry chain with hydrogen as an energy conversion carrier is the key to developing green energy and promoting energy conversion. Among the many energy conversion methods, the method of producing hydrogen by electrolysis of water has attracted widespread attention. The hydrogen produced by this method has high purity and no pollutants are discharged during the preparation process. In particular, the proton exchange membrane water electrolysis hydrogen production technology has the characteristics of high current density, small equipment size, no corrosive liquid and fast response speed. The water electrolysis hydrogen production technology has a fast response speed and is easy to combine with renewable energy. It has greater scale potential, is cleaner and more sustainable, and is the most promising way to supply green hydrogen. Therefore, the water electrolysis hydrogen production technology coupled with renewable energy is regarded as an ideal way to obtain clean energy.

[0004] Water electrolysis consists of two half reactions, namely the cathode reaction dominated by the cathode electrode and the anode reaction dominated by the anode electrode. The cathode electrode material and the anode electrode material act as catalysts for the reactions on both sides, respectively. Due to the limitations of electrode reaction kinetics, a high overpotential needs to be overcome in the process of water electrolysis. In actual production, excessive overpotential will consume a lot of electrical energy, increase the cost of hydrogen energy, and limit the industrial development of water electrolysis technology.

[0005] In order to further reduce energy loss, a highly active catalyst is needed to reduce the overpotential of the reaction, thereby promoting the reaction. Precious metals such as platinum (Pt), ruthenium (Ru), iridium (Ir) and their compounds are considered to be catalysts for water electrolysis with high theoretical activity and have been applied in some electrocatalytic scenarios. The oxygen evolution reaction mainly occurs on the anode side. Due to its complex four-electron transfer process and highly oxidizing environment, the requirements for the catalyst are more stringent. The OER (2H2O→O2+4H + +4e -) is generally recognized as the determining factor of water electrolysis efficiency, because OER is kinetically slower than cathode HER. Iridium dioxide (IrO2) is often used as a catalyst for oxygen evolution reaction. Due to the slow kinetics of oxygen evolution reaction in water electrolysis and the OH - The lack of precious metal catalysts results in high overpotential, slow reaction, and high preparation cost, which limits the development of acidic water electrolysis oxygen evolution catalysts. Summary of the invention

[0006] The present invention aims to solve the problems of high cost, slow reaction in acidic environment and high overpotential of the existing water electrolysis oxygen evolution catalyst prepared by using precious metals and their compounds, and further provides a preparation method of metal atom doped cobalt tetroxide water electrolysis catalyst.

[0007] A method for preparing a metal atom-doped cobalt tetroxide water electrolysis catalyst is carried out according to the following steps:

[0008] 1. Dissolve cobalt nitrate in a solvent and stir evenly to obtain solution A;

[0009] 2. Add the metal salt to the solvent and stir evenly to obtain solution B;

[0010] 3. Solution A and solution B are sequentially added dropwise onto the surface of the carbon cloth, and then placed in a muffle furnace, kept warm at a temperature of 100°C to 300°C, and then cooled in air to complete the preparation method of the metal atom-doped cobalt tetroxide water electrolysis catalyst.

[0011] The beneficial effects of the present invention are:

[0012] The present invention uses common metal salt solution and cobalt nitrate solution as raw materials for the reaction. The catalyst is prepared by thermal decomposition in air. The introduction of heterogeneous elements greatly optimizes the adsorption free energy of the reaction intermediates, reasonably regulates the adsorption of the catalyst to each reaction intermediate, and improves the catalytic activity of the catalyst.

[0013] 1. When the metal element in the metal salt is Fe, the present invention dopes Fe into the cobalt tetroxide catalyst and uses the introduced Fe element to adjust the electronic structure of the catalyst. The introduction of Fe element causes the electrons to transfer from Co element to Fe element, which weakens the effect on OH - The adsorption is beneficial to the subsequent steps and improves the catalytic activity of the material. It solves the problem of slow oxygen evolution reaction kinetics and high overpotential in an acidic environment.

[0014] 2. The raw materials of the present invention are widely available, and chloride, acetate, sulfate and nitrate can all be used as raw materials, which is more feasible. Compared with traditional precious metal catalysts, the selected raw materials are cheaper, which further reduces the preparation cost of the catalyst.

[0015] 3. The present invention introduces heterogeneous elements into the catalyst surface by simple means, regulates the adsorption of the catalyst to the reaction intermediates, and provides new active sites. The catalyst prepared by the present invention has a self-supporting substrate and can be used as an electrode without additional coating. At the same time, the catalyst has excellent catalytic performance and broad prospects.

[0016] 4. The present invention has a simple process, easy operation, green reaction process, short synthesis cycle, and is conducive to rapid large-scale preparation of catalysts. At the same time, the reaction temperature is low, which saves a lot of energy.

[0017] Instruction Manual

[0018] Figure 1 This is a microscopic SEM image of the metal atom-doped cobalt tetroxide water electrolysis catalyst prepared in Example 1;

[0019] Figure 2 The LSV diagram of the metal atom-doped cobalt tetroxide water electrolysis catalyst prepared in Example 1 during the process of water electrolysis and oxygen evolution in an acidic electrolyte;

[0020] Figure 3 The LSV diagram of the metal atom-doped cobalt tetroxide water electrolysis catalyst prepared in Example 1 during the process of water electrolysis and oxygen evolution in an alkaline electrolyte;

[0021] Figure 4 This is a first principle calculation diagram of the metal atom-doped cobalt tetroxide water electrolysis catalyst prepared in Example 1;

[0022] Figure 5 XRD diagrams of the metal atom-doped cobalt tetroxide water electrolysis catalyst and the undoped cobalt tetroxide water electrolysis catalyst prepared in Example 1:

[0023] Figure 6 The Raman graphs of the metal atom-doped cobalt tetroxide water electrolysis catalyst and the undoped cobalt tetroxide water electrolysis catalyst prepared in Example 1 are as follows:

[0024] Figure 7 High-resolution XPS images of the metal atom-doped cobalt tetroxide water electrolysis catalyst and the undoped cobalt tetroxide water electrolysis catalyst prepared in Example 1;

[0025] Figure 8 This is a stability test diagram of the metal atom-doped cobalt tetroxide water electrolysis catalyst prepared in Example 1;

[0026] Fig. 9 The LSV diagram of the metal atom-doped cobalt tetroxide water electrolysis catalyst prepared in Example 1 and Comparative Experiment 1;

[0027] Fig.10 LSV diagram of the metal atom-doped cobalt tetroxide water electrolysis catalyst prepared in Example 1 and Comparative Experiment 2. DETAILED DESCRIPTION

[0028] Specific implementation method 1: This implementation method is a method for preparing a metal atom-doped cobalt tetraoxide water electrolysis catalyst, which is carried out according to the following steps:

[0029] 1. Dissolve cobalt nitrate in a solvent and stir evenly to obtain solution A;

[0030] 2. Add the metal salt to the solvent and stir evenly to obtain solution B;

[0031] 3. Solution A and solution B are sequentially added dropwise onto the surface of the carbon cloth, and then placed in a muffle furnace, kept warm at a temperature of 100°C to 300°C, and then cooled in air to complete the preparation method of the metal atom-doped cobalt tetroxide water electrolysis catalyst.

[0032] The beneficial effects of this embodiment are:

[0033] This embodiment uses common metal salt solution and cobalt nitrate solution as raw materials for the reaction. The catalyst is prepared by thermal decomposition in air. The introduction of heterogeneous elements greatly optimizes the adsorption free energy of the reaction intermediates, reasonably regulates the adsorption of the catalyst to each reaction intermediate, and improves the catalytic activity of the catalyst.

[0034] 1. When the metal element in the metal salt is Fe, the present embodiment dopes Fe into the cobalt oxide catalyst, and uses the introduced Fe element to adjust the electronic structure of the catalyst. The introduction of Fe element causes the electrons to transfer from Co element to Fe element, which weakens the effect of OH - The adsorption is beneficial to the subsequent steps and improves the catalytic activity of the material. It solves the problem of slow oxygen evolution reaction kinetics and high overpotential in an acidic environment.

[0035] 2. The raw materials of this embodiment are widely available, and chloride, acetate, sulfate, and nitrate can all be used as raw materials, which is more feasible. Compared with traditional precious metal catalysts, the selected raw materials are cheaper, further reducing the preparation cost of the catalyst.

[0036] 3. This embodiment introduces heterogeneous elements into the catalyst surface by simple means, regulates the adsorption of the catalyst to the reaction intermediates, and provides new active sites. The catalyst prepared in this embodiment has a self-supporting substrate and can be used as an electrode without additional coating. At the same time, the catalyst has excellent catalytic performance and broad prospects.

[0037] 4. The present embodiment has a simple process, easy operation, green reaction process, short synthesis cycle, and is conducive to the rapid large-scale preparation of catalysts. At the same time, the reaction temperature is low, which saves a lot of energy.

[0038] Specific embodiment 2: This embodiment is different from specific embodiment 1 in that the concentration of cobalt nitrate in solution A described in step 1 is 0.1 g / mL to 1 g / mL; the concentration of metal salt in solution B described in step 2 is 0.01 g / mL to 0.03 g / mL. Others are the same as specific embodiment 1.

[0039] Specific implementation method 3: This implementation method is different from specific implementation method 1 or 2 in that the solvent in step 1 and step 2 is anhydrous ethanol or deionized water. The rest is the same as specific implementation method 1 or 2.

[0040] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the metal salt in step 2 is chloride, acetate, acetic acid salt, sulfate or nitrate. Other aspects are the same as specific embodiments 1 to 3.

[0041] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the metal element in the metal salt in step 2 is one or a combination of Fe, Ni, Ce and Zn. The rest is the same as specific embodiments 1 to 4.

[0042] Specific embodiment 6: This embodiment is different from the specific embodiments 1 to 5 in that the amount of solution A added in step 3 is 0.1 mL / cm 2 ~0.2mL / cm 2 The rest is the same as the specific implementation modes 1 to 5.

[0043] Specific embodiment 7: This embodiment differs from the specific embodiments 1 to 6 in that the amount of solution B added in step 3 is 0.05 mL / cm 2 ~0.15mL / cm 2 The rest is the same as the specific implementation modes 1 to 6.

[0044] Specific embodiment 8: This embodiment differs from specific embodiments 1 to 7 in that: in step 3, the temperature is raised to 100°C to 300°C at a heating rate of 4°C / min to 8°C / min, and then the temperature is kept at 100°C to 300°C. The rest is the same as specific embodiments 1 to 7.

[0045] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that: in step 3, the temperature is kept at 100° C. to 300° C. for 0.5 h to 3 h. The rest is the same as specific embodiments 1 to 8.

[0046] Specific embodiment 10: This embodiment differs from specific embodiments 1 to 9 in that: in step 3, the temperature is raised to 200°C to 300°C at a heating rate of 6°C / min to 8°C / min, and then the temperature is kept at 200°C to 300°C for 1h to 3h. The rest is the same as specific embodiments 1 to 9.

[0047] The following examples are used to verify the beneficial effects of the present invention:

[0048] Embodiment 1:

[0049] A method for preparing a metal atom-doped cobalt tetroxide water electrolysis catalyst is carried out according to the following steps:

[0050] 1. Dissolve cobalt nitrate in anhydrous ethanol and stir evenly to obtain solution A;

[0051] The concentration of cobalt nitrate in the solution A is 0.5 g / mL;

[0052] 2. Add the metal salt to anhydrous ethanol and stir evenly to obtain solution B;

[0053] The metal salt is ferric chloride; the concentration of the metal salt in solution B is 0.025 g / mL;

[0054] 3. Solution A and solution B were sequentially added dropwise onto the surface of a carbon cloth of size 2 cm × 5 cm, and then placed in a muffle furnace, and the temperature was raised to 200°C at a heating rate of 6°C / min, and then kept at 200°C for 1 hour, and then cooled in air to obtain a metal atom-doped cobalt tetroxide water electrolysis catalyst, named Fe-Co3O4;

[0055] The amount of solution A added was 0.125 mL / cm 2 ;

[0056] The amount of solution B added was 0.1 mL / cm 2 .

[0057] The carbon cloth described in step 3 was purchased from Taiwan Carbon Energy Technology Co., Ltd., model number W0S1011.

[0058] Figure 1 This is a microscopic SEM image of the metal atom-doped cobalt tetroxide water electrolysis catalyst prepared in Example 1; as can be seen from the image, the catalyst prepared in Example 1 is composed of tiny nanoparticles, and the nanoparticles are attached to the carbon fibers.

[0059] The oxygen evolution reaction (OER) of water electrolysis was carried out using a three-electrode test system, wherein the metal atom-doped cobalt tetroxide water electrolysis catalyst prepared in Example 1 was used as the working electrode, the carbon rod pair was used as the counter electrode, the saturated calomel electrode was used as the reference electrode, and a 0.5 M H2SO4 solution was used as the electrolyte; Figure 2 This is the LSV diagram of the metal atom-doped cobalt tetroxide electrolytic water catalyst prepared in Example 1 during the electrolysis of water and oxygen evolution in an acidic electrolyte; as can be seen from the figure, the current density is 10 mA / cm 2 The required overpotential is 259 mV, indicating excellent catalytic activity.

[0060] The oxygen evolution reaction (OER) of water electrolysis was carried out using a three-electrode test system, wherein the metal atom-doped cobalt tetroxide water electrolysis catalyst prepared in Example 1 was used as a working electrode, a carbon rod pair was used as a counter electrode, a saturated calomel electrode was used as a reference electrode, and a 1 M KOH solution was used as an electrolyte; Figure 3 This is the LSV diagram of the metal atom-doped cobalt tetroxide electrolytic water catalyst prepared in Example 1 during the electrolysis of water and oxygen evolution in an alkaline electrolyte; as can be seen from the figure, the current density is 10 mA / cm 2 The required overpotential is 203 mV, indicating excellent catalytic activity.

[0061] Figure 2 and Figure 3 It is proved that the metal atom-doped cobalt tetroxide water electrolysis catalyst prepared in Example 1 has excellent OER catalytic activity in both acidic and alkaline environments.

[0062] Figure 4 This is the first principle calculation diagram of the metal atom-doped cobalt tetroxide water electrolysis catalyst prepared in Example 1; it can be seen from the figure that the introduction of Fe element optimizes the electron distribution on the catalyst surface. Compared with the original matrix Co3O4, the introduction of Fe element reduces the catalyst's OH - The introduction of Fe element is more conducive to the conversion of *OH to *O, optimizes the adsorption of the catalyst to the reaction intermediates, and improves the electrocatalytic activity of the material.

[0063] Figure 5The XRD graphs of the metal atom-doped cobalt tetroxide water electrolysis catalyst and the undoped cobalt tetroxide water electrolysis catalyst prepared in Example 1: As can be seen from the graph, the introduction of the Fe element reduces the diffraction peak of the catalyst XRD, which means that the crystallinity of the material is reduced. The introduction of metal atoms successfully regulates the crystallinity of the catalyst. The low-crystallinity material increases its contact area with the electrolyte due to a large number of grain boundaries and more diffusion channels, thereby improving the catalytic performance of the catalyst.

[0064] Figure 6 Raman graphs of the metal atom-doped cobalt tetroxide water electrolysis catalyst and the undoped cobalt tetroxide water electrolysis catalyst prepared in Example 1: As can be seen from the figure, the introduction of the Fe element makes the Raman diffraction peak of the catalyst broaden, which means that the introduction of the Fe element reduces the crystallinity of the material, provides more channels for liquid exchange and diffusion, exposes more activity of the catalyst, and improves the catalytic performance of the catalyst.

[0065] Figure 7 High-resolution XPS images of the metal atom-doped cobalt tetroxide water electrolysis catalyst and the undoped cobalt tetroxide water electrolysis catalyst prepared in Example 1; the Fe element can effectively adjust the electronic structure of the catalyst, and the electrons are transferred from the Co element to the Fe element. The electron enrichment around the Fe element weakens the OH - The adsorption Figure 4 It has been proved in.

[0066] The oxygen evolution reaction (OER) of water electrolysis was carried out using a three-electrode test system, wherein the metal atom-doped cobalt tetroxide water electrolysis catalyst prepared in Example 1 was used as the working electrode, the carbon rod pair was used as the counter electrode, the saturated calomel electrode was used as the reference electrode, and a 0.5 M H2SO4 solution was used as the electrolyte. Figure 8 This is a stability test diagram of the metal atom-doped cobalt tetroxide water electrolysis catalyst prepared in Example 1. At a current density of 10 mA / cm 2 The catalyst can work stably for 35,000 seconds and has excellent stability.

[0067] Comparative Experiment 1: The difference between this comparative experiment and Example 1 is that in step 2, ferric chloride is replaced by strontium chloride, and strontium chloride is dissolved in deionized water and stirred evenly to obtain solution B; the concentration of strontium chloride in the solution B is 0.0125 g / mL; the amount of solution B added in step 3 is 0.05 mL / cm 2 The metal atom-doped cobalt tetraoxide water electrolysis catalyst prepared in step 3 is named Sr-Co3O4. The rest is the same as in Example 1.

[0068] The oxygen evolution reaction (OER) of water electrolysis was carried out using a three-electrode test system, wherein the metal atom-doped cobalt tetroxide water electrolysis catalyst prepared in Example 1 or Comparative Experiment 1 was used as the working electrode, the carbon rod pair was used as the counter electrode, the saturated calomel electrode was used as the reference electrode, and a 0.5M H2SO4 solution was used as the electrolyte; Fig. 9 The LSV diagram of the metal atom-doped cobalt tetroxide water electrolysis catalyst prepared in Example 1 and Comparative Experiment 1. As can be seen from the figure, the current density is 10mA / cm 2 The overpotential required for the catalyst prepared in Example 1 is 259 mV, while the overpotential required for the catalyst prepared in Comparative Experiment 1 is 370 mV, which proves that the difference in doping elements will greatly affect the catalytic activity of the material.

[0069] Comparative Experiment 2: The difference between this comparative experiment and Example 1 is that the amount of solution B added in step 3 is 0.025 mL / cm 2 The metal atom-doped cobalt tetraoxide water electrolysis catalyst prepared in step 3 is named Fe-Co3O4-1. The rest is the same as in Example 1.

[0070] The oxygen evolution reaction (OER) of water electrolysis was carried out using a three-electrode test system, wherein the metal atom-doped cobalt tetroxide water electrolysis catalyst prepared in Example 1 or Comparative Experiment 2 was used as the working electrode, the carbon rod pair was used as the counter electrode, the saturated calomel electrode was used as the reference electrode, and a 0.5M H2SO4 solution was used as the electrolyte; Fig.10 The LSV diagram of the metal atom-doped cobalt tetroxide water electrolysis catalyst prepared in Example 1 and Comparative Experiment 2. As can be seen from the figure, the current density is 10mA / cm 2 The overpotential required for the catalyst prepared in Example 1 is 259 mV, while the overpotential required for the catalyst prepared in Comparative Experiment 2 is 290 mV, which proves that different addition amounts will greatly affect the catalytic activity of the material.

Claims

1. A method for preparing a metal atom-doped cobalt tetroxide water electrolysis catalyst, characterized in that It is carried out in the following steps:

1. Dissolve cobalt nitrate in a solvent and stir evenly to obtain solution A; 2. Add the metal salt to the solvent and stir evenly to obtain solution B; 3. Solution A and solution B are sequentially added dropwise onto the surface of the carbon cloth, and then placed in a muffle furnace, kept warm at a temperature of 100°C to 300°C, and then cooled in air to complete the preparation method of the metal atom-doped cobalt tetroxide water electrolysis catalyst.

2. The method for preparing a metal atom-doped cobalt tetroxide water electrolysis catalyst according to claim 1, characterized in that The concentration of cobalt nitrate in solution A described in step 1 is 0.1 g / mL to 1 g / mL; the concentration of metal salt in solution B described in step 2 is 0.01 g / mL to 0.03 g / mL.

3. The method for preparing a metal atom-doped cobalt tetroxide water electrolysis catalyst according to claim 1, characterized in that The solvent in step 1 and step 2 is anhydrous ethanol or deionized water.

4. The method for preparing a metal atom-doped cobalt tetraoxide water electrolysis catalyst according to claim 1, characterized in that The metal salt described in step 2 is chloride, acetate, acetic acid salt, sulfate or nitrate.

5. The method for preparing a metal atom-doped cobalt tetraoxide water electrolysis catalyst according to claim 4, characterized in that The metal element in the metal salt described in step 2 is one of Fe, Ni, Ce and Zn or a combination of several thereof.

6. The method for preparing a metal atom-doped cobalt tetraoxide water electrolysis catalyst according to claim 1, characterized in that The amount of solution A added in step 3 is 0.1 mL / cm 2 ~0.2mL / cm 2 .

7. The method for preparing a metal atom-doped cobalt tetraoxide water electrolysis catalyst according to claim 1, characterized in that The amount of solution B added in step 3 is 0.05 mL / cm 2 ~0.15mL / cm 2 .

8. The method for preparing a metal atom-doped cobalt tetraoxide water electrolysis catalyst according to claim 1, characterized in that In step 3, the temperature is raised to 100°C to 300°C at a heating rate of 4°C / min to 8°C / min, and then kept at 100°C to 300°C.

9. The method for preparing a metal atom-doped cobalt tetraoxide water electrolysis catalyst according to claim 1, characterized in that In step 3, the temperature is kept at 100° C. to 300° C. for 0.5 h to 3 h.

10. The method for preparing a metal atom-doped cobalt tetraoxide water electrolysis catalyst according to claim 1, characterized in that In step 3, the temperature is raised to 200°C to 300°C at a heating rate of 6°C / min to 8°C / min, and then kept at 200°C to 300°C for 1h to 3h.

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