CN113584512B - A kind of preparation method of cobalt/cobalt oxide/molybdenum oxide in-situ electrode - Google Patents

Abstract

The invention provides a preparation method of a cobalt/cobalt oxide/molybdenum oxide in-situ electrode. First prepare a precursor solution containing cobalt/molybdenum oxide or cobalt/molybdenum hydroxide, attach it to the surface of nickel foam (NF), and then use the electrochemical reduction method to apply a constant potential in a specific electrolyte. Reduction, reducing the precursor substances attached to the surface of the nickel foam (NF) to cobalt and generating cobalt oxide and molybdenum oxide. The raw materials required by the technical solution of the present invention have many advantages, such as non-polluting, low cost, simple operation, and quick preparation; the prepared molybdenum oxide passivated cobalt/cobalt oxide in-situ electrode is used as hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) The bifunctional electrocatalysts exhibit excellent catalytic activity and have promising applications in electrocatalytic water splitting.

Description

A kind of preparation method of cobalt/cobalt oxide/molybdenum oxide in-situ electrode

technical field

The invention relates to the preparation of multi-component multifunctional materials, and the application belongs to the field of electrocatalysis and energy conversion materials and devices.

Background technique

Energy consumption is a bottleneck restricting world development. As traditional fossil fuels are increasingly exhausted, energy shortages and global environmental pollution have become increasingly serious. To alleviate such problems, it is extremely urgent to develop efficient, economical and renewable green energy. Hydrogen energy is regarded as a new type of high-efficiency energy carrier due to its high energy conversion efficiency, clean and renewable energy, and zero carbon emissions. one of the ways). Water splitting involves two half-reactions, the oxygen evolution reaction (OER) at the anode and the oxygen evolution reaction (HER) at the cathode. At present, the most efficient HER and OER catalysts are platinum-based materials and iridium and ruthenium noble metal oxides, respectively, but the high price, rare reserves and poor stability of these materials severely limit their large-scale commercial applications. Therefore, finding and preparing non-polluting, low-cost, stable and efficient non-precious metal-based materials has become an important research direction in the field of electrocatalytic water splitting. Among them, cobalt and nickel-based non-precious all-metal materials are not only cheap and abundant, but also exhibit excellent performance in water splitting, showing huge commercial application prospects.

Molybdenum-based compounds are important materials in many fields (as electro, photocatalysts and other catalysts). The tuned value state of molybdenum and its easy combination with various anions make the application of molybdenum-based materials diversified in different fields (Catalysis Science & Technology, 2016, 6(7): 2403-2412..). So far, various cobalt-based materials have been reported for HER, such as metallic Co, CoS2, CoP and _CoSe , showing high catalytic activity. Cobalt oxide/(oxy)hydroxide showed better catalytic activity for OER. This means that cobalt-based materials with different cobalt active species are able to complete the full water splitting to produce hydrogen and oxygen. However, metallic Co or _{CoxOy materials} have many disadvantageous characteristics, such as easy accumulation and low electrical conductivity. (Chemical communications, 2016, 52(35): 5946-5949.).

Based on the above investigation, the patent of the present invention adopts the method of electrochemical reduction to prepare molybdenum oxide passivated cobalt/cobalt oxide in-situ electrode, and uses a large negative potential to convert the attached hydroxide into oxide, and reduce cobalt oxide or cobalt salt. For metal cobalt, more active sites are exposed at the same time, and the ratio of metal cobalt and cobalt oxide in the electrode is optimized by adjusting the time of electrochemical reduction. The prepared molybdenum oxide passivated cobalt/cobalt oxide in situ electrode is expected to have high HER and OER electrocatalytic activity and high stability.

SUMMARY OF THE INVENTION

In view of this, the present invention provides a method for preparing a molybdenum oxide passivation cobalt/cobalt oxide in-situ electrode, the preparation comprising the following steps:

S1. Prepare the precursor of cobalt/molybdenum oxide or cobalt/molybdenum hydroxide: dissolve cobalt chloride of decrystallized water in a mixed solution of ethanol and glacial acetic acid, then add molybdenum acetylacetonate while stirring, then Add a mixture of water-ethanol, continue to stir until the solution is clear to form a cobalt/cobalt (hydro)oxide solution, place the solution in a hydrothermal box for a period of time, and after cooling, immerse nickel foam (NF) in it, and then Take out and shake off excess solution with a glue homogenizer, and dry it for later use.

S2. Electroreduction: The NF attached to the precursor is placed in the electrolyte of sodium sulfate and boric acid, and the NF is electroreduced for a period of time by using an electrochemical workstation by means of constant electricity. The surface electrolyte was then rinsed with UP water and dried.

S3. The electrode is obtained after the steps of attaching and electrochemical reduction are cycled for many times, or the molybdenum oxide passivation cobalt/cobalt oxide in-situ electrode is obtained by electrochemical reduction after cycling the attaching step for many times.

Further, in S1, the concentration of cobalt chloride is 0.5~1 mol/L, and the molar ratio of cobalt chloride to molybdenum acetylacetonate is 1:0.1~0.2.

Further, in S1, the first solvent is the mixed solution of ethanol and glacial acetic acid, wherein the volume ratio of ethanol and glacial acetic acid is 1:0.02～0.04, and the second solvent is the mixed solution of water-ethanol, wherein ethanol and water The volume ratio of the solvent is 1:0.03~0.07, and the volume ratio of the first solvent to the second solvent is 1:0.1~0.3.

Further, the heat preservation temperature of the hydrothermal box described in S1 is 80°C to 120°C, and the heat preservation time is 4 hours.

Further, the drying described in S1 and S2 is 70°C to 90°C.

Further, in S2, the potential range is -2.5~-3.0 V relative to the saturated calomel electrode.

Further, the time in S2 is 600-3000 seconds.

Further, the cycle times mentioned in S3 are all 0 to 5 times.

The invention also relates to the application of the material obtained by the preparation method in the HER/OER bifunctional catalytic electrolysis of water.

The present invention has the following beneficial effects:

1. In the preparation of molybdenum oxide passivation cobalt/cobalt oxide in-situ electrode materials, the present invention first configures a precursor solution, and the Co and Mo elements are mixed at the molecular level. On the one hand, it is beneficial to refine the particle size of the product and expose more On the other hand, it is convenient for the subsequent generation of molybdenum oxide passivated cobalt/cobalt oxide in-situ electrodes to uniformly disperse the Co, CoO _x , and MoO _y phases (or components), thereby facilitating the synergy Improve HER and OER electrocatalytic activity and stability.

2. The NF after the attached precursor is placed in a mixture of sodium sulfate and boric acid, and the NF is electroreduced for a certain period of time by a potentiostatic method using an electrochemical workstation. The hydroxide attached to the surface of NF is converted into oxide by electroreduction, and the cobalt oxide or cobalt salt is reduced to metallic cobalt.

3. Multiple attachment steps are to increase its loading in NF to increase the number of active sites, thereby increasing the

HER and OER electrocatalytic activity and stability.

Description of drawings

Figure 1 shows the HER linear voltammetry curve and the OER linear voltammetry scan measured by the sample prepared in Example 1, wherein a is the HER linear voltammetry scan (LSV), and b is the OER linear voltammetry scan (LSV).

Figure 2 shows the HER linear voltammetry curve and the OER linear voltammetry scan measured by the sample prepared in Example 2, where a is the HER linear voltammetry scan (LSV), and b is the OER linear voltammetry scan (LSV).

3 is the HER linear voltammetry curve and the OER linear voltammetry scan measured by the sample prepared in Example 3, wherein a is the HER linear voltammetry scan (LSV), and b is the OER linear voltammetry scan (LSV).

FIG. 4 is the HER linear voltammetry curve measured by the sample prepared in Example 4. FIG.

Figure 5 shows the HER linear voltammetry curve and the OER linear voltammetry scan measured by the sample prepared in Example 5, wherein a is the HER linear voltammetry scan (LSV), and b is the OER linear voltammetry scan (LSV).

Figure 6 shows the HER linear voltammetry curve and the OER linear voltammetry scan measured by the sample prepared in Example 6, wherein a is the HER linear voltammetry scan (LSV), and b is the OER linear voltammetry scan (LSV).

FIG. 7 is an SEM image of the sample prepared in Example 3, a is an SEM image of a magnification of 11000, and b is an SEM image of a magnification of 50000.

FIG. 8 is an SEM image of the sample prepared in Example 5, a is an SEM image of a magnification of 10,000, and b is an SEM image of a magnification of 50,000.

FIG. 9 is an SEM image of the sample prepared in Example 6, a is an SEM image of a magnification of 10,000, and b is an SEM image of a magnification of 50,000.

Characterization condition

In the embodiment of the invention, the HER and OER test methods are as follows: the nickel foam is used as the working electrode, the carbon rod is used as the counter electrode, and the saturated Hg/HgO electrode is used as the reference electrode, the electrolyte used is: 1 M KOH aqueous solution, and the scanning speed is 5~ 10 mV/s. Nitrogen was injected in the HER test, and oxygen was injected in the OER test. Oxygen and nitrogen were naturally saturated in 1 M aqueous KOH with stirring at 200 rpm during the test. The saturated Hg/HgO electrode is calibrated with a reversible hydrogen electrode, and the potentials described below are relative to the reversible hydrogen electrode. In the LSV test, the potential ( IR ) compensation was automatically performed by Shanghai Chenhua workstation. X-ray diffraction (SEM) patterns of the samples were obtained using a SMART LAB-9 X-ray diffractometer. Scanning electron microscope (XRD) images were acquired using an Inspect F50 scanning electron microscope (FEI America).

Example 1

At room temperature, 2.475 _g of CoCl was dissolved in a mixture of 21.99 mL of ethanol and 0.72 mL of glacial acetic acid, then 0.877 g of molybdenum acetylacetonate was added while stirring, and then a mixture of 6 mL of ethanol and 0.3 mL of water was added dropwise , continue to stir until the solution is clear and a solution is formed. It was then sealed and kept in a hydrothermal box at 80°C for 4 hours. After cooling, the nickel foam (NF) was immersed for ten minutes, taken out, and the excess solution was thrown out with a glue spinner, followed by drying at 80°C. Weigh 7.102 g of sodium sulfate and 3.0915 g of boric acid to prepare 100 mL of electrolyte, and the solvent is UP water. The treated NF was electroreduced by an electrochemical workstation. The reference electrode was a calomel electrode, and the counter electrode was a platinum sheet. The potential was set at -2.5 V for 600 seconds. Rinse off the surface electrolyte with UP water and dry.

FIG. 1 shows the measured HER and OER linear voltammetry (LSV) scans of the samples prepared in Example 1. It can be seen from Figure 1(a) that when the current density passing through the electrode is 10 mA/cm ² , the overpotential corresponding to the HER reaction in the alkaline aqueous solution is 106 mV; it can be seen from Figure 1(b) that the current density passing through the electrode is 10 mV. The overpotential corresponding to the OER reaction in alkaline aqueous solution is 280 mV at mA/cm ² .

Example 2

At room temperature, 2.475 _g of CoCl was dissolved in a mixture of 21.99 mL of ethanol and 0.72 mL of glacial acetic acid, then 0.877 g of molybdenum acetylacetonate was added while stirring, and then a mixture of 6 mL of ethanol and 0.3 mL of water was added dropwise , continue to stir until the solution is clear and a solution is formed. It was then sealed and kept in a hydrothermal box at 80°C for 4 hours. After cooling, the nickel foam (NF) was immersed for ten minutes, taken out, and the excess solution was thrown out with a glue spinner, followed by drying at 80°C. Weigh 7.102 g of sodium sulfate and 3.0915 g of boric acid to prepare 100 mL of electrolyte, and the solvent is UP water. The treated NF was electroreduced by an electrochemical workstation. The reference electrode was a calomel electrode, and the counter electrode was a platinum sheet. The potential was set at -3.0 V for 600 seconds. Rinse off the surface electrolyte with UP water and dry. The electrode is obtained by cycling the adhesion solution and the electroreduction process once again.

FIG. 2 shows the measured HER and OER linear voltammetry (LSV) scans of the samples prepared in Example 2. It can be seen from Fig. 2(a) that the overpotential corresponding to the HER reaction in the alkaline aqueous solution is 124 mV when the current density passing through the electrode is 10 mA/cm ² ; The overpotential corresponding to the OER reaction in alkaline aqueous solution is 280 mV at mA/cm ² .

Example 3

At room temperature, 2.475 _g of CoCl was dissolved in a mixture of 21.99 mL of ethanol and 0.72 mL of glacial acetic acid, then 0.877 g of molybdenum acetylacetonate was added while stirring, and then a mixture of 6 mL of ethanol and 0.3 mL of water was added dropwise , continue to stir until the solution is clear and a solution is formed. It was then sealed and kept in a hydrothermal box at 80°C for 4 hours. After cooling, the nickel foam (NF) was immersed for ten minutes, taken out, and the excess solution was thrown out with a glue spinner, followed by drying at 80°C. Weigh 7.102 g of sodium sulfate and 3.0915 g of boric acid to prepare 100 mL of electrolyte, and the solvent is UP water. The treated NF was electroreduced by an electrochemical workstation. The reference electrode was a calomel electrode, and the counter electrode was a platinum sheet. The potential was set at -3.0 V for 600 seconds. Rinse off the surface electrolyte with UP water and dry.

FIG. 3 shows the measured HER and OER linear voltammetry (LSV) scans of the samples prepared in Example 3. FIG. It can be seen from Fig. 3(a) that when the current density passing through the electrode is 10 mA/cm ² , the overpotential corresponding to the HER reaction in the alkaline aqueous solution is 210 mV; from Fig. 3(b), it can be seen that the current density passing through the electrode is 10 mV. The overpotential corresponding to the OER reaction in alkaline aqueous solution is 280 mV at mA/cm ² .

FIG. 7 is the SEM image of Example 3. It can be seen from the figure that the prepared sample is attached to the nickel foam, and it is observed at high magnification that it is in a state of small particle connection, and the surface is uniformly distributed.

Example 4

At room temperature, 2.475 _g of CoCl was dissolved in a mixture of 21.99 mL of ethanol and 0.72 mL of glacial acetic acid, then 0.877 g of molybdenum acetylacetonate was added while stirring, and then a mixture of 6 mL of ethanol and 0.3 mL of water was added dropwise , continue to stir until the solution is clear to form a precursor solution. It was then sealed and kept in a hydrothermal box at 120 °C for 4 hours. After cooling, 2 mL of the precursor solution was taken out and all dropped on the nickel foam (NF), and the whole process was dried at 90 °C. Weigh 7.102 g of sodium sulfate and 3.0915 g of boric acid to prepare 100 mL of electrolyte, and add 2 mL of precursor solution to it. The treated NF was electroreduced by an electrochemical workstation. The reference electrode was a calomel electrode, and the counter electrode was a platinum sheet. The potential was set at -3.0 V for 1800 seconds. Rinse off the surface electrolyte with UP water and dry. It was annealed at 350°C for 1 hour in a tube furnace with Ar gas as protective gas.

4 is the HER linear voltammetry (LSV) measured for the sample prepared in Example 4. It can be seen from the figure that when the current density through the electrode is 10 mA/cm ² , the overpotential corresponding to the HER reaction in the alkaline aqueous solution is 11 mV;

Example 5

At room temperature, 2.475 _g of CoCl was dissolved in a mixture of 21.99 mL of ethanol and 0.72 mL of glacial acetic acid, then 0.877 g of molybdenum acetylacetonate was added while stirring, and then a mixture of 6 mL of ethanol and 0.3 mL of water was added dropwise , continue to stir until the solution is clear and a solution is formed. It was then sealed and kept in a hydrothermal box at 80°C for 4 hours. After cooling, the nickel foam (NF) was immersed for ten minutes, taken out, and the excess solution was thrown out with a glue spinner, followed by drying at 80°C. Weigh 7.102 g of sodium sulfate and 3.0915 g of boric acid to prepare 100 mL of electrolyte, and the solvent is UP water. The treated NF was electroreduced by an electrochemical workstation. The reference electrode was a calomel electrode, and the counter electrode was a platinum sheet. The potential was set at -3.0 V for 600 seconds. Rinse off the surface electrolyte with UP water and dry. The electrode was obtained by cycling the attachment solution and electroreduction steps twice again.

FIG. 5 shows the HER and OER linear voltammetry (LSV) scans of the samples prepared in Example 5. FIG. It can be seen from Fig. 5(a) that when the current density passing through the electrode is 10 mA/cm ² , the overpotential corresponding to oxygen production by the HER reaction in the alkaline aqueous solution is only 22 mV; When it is 10 mA/cm ² , the overpotential corresponding to oxygen production by OER reaction in alkaline aqueous solution is 280 mV.

FIG. 8 is the SEM image of Example 5. It can be seen from the figure that the prepared sample is attached to the nickel foam, and it is observed that it is spherical and evenly distributed on the surface under high magnification.

Example 6

At room temperature, 2.475 _g of CoCl was dissolved in a mixture of 21.99 mL of ethanol and 0.72 mL of glacial acetic acid, then 0.877 g of molybdenum acetylacetonate was added while stirring, and then a mixture of 6 mL of ethanol and 0.3 mL of water was added dropwise , continue to stir until the solution is clear and a solution is formed. It was then sealed and kept in a hydrothermal box at 80°C for 4 hours. After cooling, the nickel foam (NF) was immersed for 10 minutes, taken out, and the excess solution was thrown out with a glue spinner, followed by drying at 80°C, and the step was repeated. The solution was attached twice during the operation, and the solution was attached three times on the NF. Weigh 7.102 g of sodium sulfate and 3.0915 g of boric acid to prepare 100 mL of electrolyte, and the solvent is UP water. The treated NF was electroreduced by an electrochemical workstation. The reference electrode was a calomel electrode, and the counter electrode was a platinum sheet. The potential was set at -3.0 V for 1800 seconds. Rinse off the surface electrolyte with UP water and dry.

FIG. 6 shows the measured HER and OER linear voltammetry (LSV) scans of the samples prepared in Example 6. FIG. It can be seen from Fig. 6(a) that when the current density passing through the electrode is 10 mA/cm ² , the overpotential corresponding to the HER reaction in the alkaline aqueous solution is 150 mV; it can be seen from Fig. 6(b) that the current density passing through the electrode is 10 mV. The overpotential corresponding to the OER reaction in alkaline aqueous solution is 290 mV at mA/cm ² .

FIG. 9 is the SEM image of Example 6. It is shown in the figure that the prepared sample is attached to the nickel foam, and it is observed at high magnification that it is spherical, and the surface is evenly distributed with holes.

Claims (4)

1. A preparation method of a cobalt/cobalt oxide/molybdenum oxide in-situ electrode is characterized by comprising the following specific preparation methods:

s1, preparing a precursor of cobalt/molybdenum oxide or cobalt/molybdenum hydroxide: dissolving cobalt chloride without crystal water in a first solvent, adding molybdenum acetylacetonate while stirring, adding a second solvent, continuously stirring until the solution is clear to form an oxide or hydroxide solution of cobalt/molybdenum, placing the solution in a hydrothermal tank, keeping the temperature at 80-120 ℃ for 4 hours, immersing foam nickel NF in the solution after cooling, taking out the solution, throwing the solution out by using a homogenizer, and drying the solution for later use;

the first solvent is a mixed solution of ethanol and glacial acetic acid, wherein the volume ratio of the ethanol to the glacial acetic acid is 1: 0.02-0.04, wherein the second solvent is a water-ethanol mixed solution, and the volume ratio of ethanol to water is 1: 0.03-0.07, wherein the volume ratio of the first solvent to the second solvent is 1: 0.1 to 0.3;

the concentration of the cobalt chloride is 0.5-1 mol/L, and the molar ratio of the cobalt chloride to the molybdenum acetylacetonate is 1: 0.1 to 0.2;

s2, electroreduction: placing NF attached with the precursor in electrolyte of sodium sulfate and boric acid, performing electro-reduction on the NF for a period of time by using an electrochemical workstation in a constant potential mode, wherein the constant potential is in a range of-2.5V to-3.0V relative to a saturated calomel electrode, and then flushing the electrolyte on the surface by using UP water and drying;

s3, cycling the step S1 and the step S2 for multiple times to prepare the electrode, or cycling the step S1 for multiple times to prepare the cobalt/cobalt oxide/molybdenum oxide in-situ electrode by electrochemical reduction.

2. The method of claim 1, wherein the drying process of the cobalt/cobalt oxide/molybdenum oxide in-situ electrode is 70-90 ℃ in S1 and S2.

3. The method for preparing the cobalt/cobalt oxide/molybdenum oxide in-situ electrode according to claim 1, wherein the time in S2 is 600-3000 seconds.

4. The method for preparing the cobalt/cobalt oxide/molybdenum oxide in-situ electrode according to claim 1, wherein the number of cycles in S3 is 1-5.

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