High-entropy hydroxide oxygen evolution catalyst with cation vacancy and preparation method thereof

Abstract

The invention belongs to the technical field of electrolyzed water oxygen evolution catalysts, and discloses a high-entropy hydroxide oxygen evolution catalyst with cation vacancies and a preparation method thereof. According to the catalyst disclosed by the invention, cation vacancies are introduced into the high-entropy hydroxide, so that the electronic structure of the high-entropy hydroxide is optimized, and the oxygen evolution catalytic activity is improved; and meanwhile, the stability of the catalyst is also effectively improved by the high-entropy structure of the quinary material. The high-entropy hydroxide precursor is prepared through the hydrothermal reaction, then cation vacancies are introduced through the alkali etching means, the high-entropy hydroxide oxygen evolution catalyst with the cation vacancies is obtained, the synthesis method is simple and efficient, and large-scale production is easy to achieve.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrolytic water oxygen evolution catalysts, and particularly relates to a high-entropy hydroxide oxygen evolution catalyst with cation vacancies and a preparation method thereof. Background Art

[0002] With the rapid development of the economy, energy resources are becoming increasingly important in supporting social development and human life. At present, a large part of energy comes from traditional resources such as oil and natural gas, which leads to serious environmental pollution problems. Therefore, there is an urgent need to develop sustainable energy conversion and storage systems to reduce dependence on fossil fuels. Hydrogen, as a renewable clean energy, can effectively alleviate the energy crisis and environmental pollution. Among them, hydrogen production by water electrolysis is an effective means of producing green hydrogen. However, the kinetic process of its oxygen evolution reaction (OER) is slow, which limits the improvement of the efficiency of the water electrolysis reaction. Therefore, it is very necessary to develop OER catalysts with low cost, high activity and long-term stability.

[0003] In recent years, transition metal hydroxide catalysts have been widely used, among which nickel iron hydrotalcite NiFe-LDHs is the most promising transition metal-based OER catalyst. However, due to the problems of insufficient exposure of NiFe-LDHs active sites and weak adsorption of reaction intermediates, the catalytic activity and stability need to be further improved. In the literature (1) Angew.Chem.Int.Ed., 2021, 60, 24612-24619, Peng et al. introduced cation vacancies in NiFe-LDHs by alkaline etching, thereby improving the stability of NiFe-LDHs catalysts in the alkaline OER process. After the introduction of cation vacancies, the metal cations (Ni 2+ and Fe 3+ ) is enhanced, the lattice distortion is reduced, and the metal dissolution in NiFe-LDHs under alkaline OER conditions is significantly inhibited, thereby improving the electrocatalytic stability. However, the introduced cation vacancies did not significantly improve the catalytic activity of NiFe-LDHs. In the literature (2) Journal of Energy Chemistry, 2021, 60: 121-126, Gu et al. successfully prepared a new type of Fe-Cr-Co-Ni-Cu HE-LDHs by a hydrothermal method, and stripped it into ultra-thin HE-LDHs with rich defect sites by plasma etching. The ultra-thin defect-rich Fe-Cr-Co-Ni-Cu HE-LDHs-Ar-20 nanosheets have uniform surface atomic distribution and exhibit excellent OER performance. However, the equipment required for the use of plasma etching technology is relatively high, and the material does not maintain good stability. Therefore, the development of oxygen evolution catalysts with simple preparation methods and coexisting activity and stability is the current research focus. Summary of the Invention

[0004] To solve the above problems, one of the objects of the present invention is to provide a high-entropy hydroxide oxygen evolution catalyst with cation vacancies. The catalyst is in the form of nanoflowers composed of nanosheets, with a nanoflower diameter of 6 to 10 μm, a radial dimension of the nanosheets of 800 to 1200 nm, and a thickness of the nanosheets of 50 to 150 nm. The catalyst contains five metal elements, Mg, Co, Ni, Zn and Fe, which are evenly distributed, and the molar percentages of each metal element in all metal elements are: 13 to 19 mol%, 21 to 27 mol%, 27 to 34 mol%, 4 to 10 mol%, and 17 to 23 mol%, respectively.

[0005] A second object of the present invention is to provide a method for preparing a high-entropy hydroxide oxygen evolution catalyst having cation vacancies, comprising the following process steps:

[0006] (1) Magnesium salt, cobalt salt, nickel salt, zinc salt, and iron salt were weighed in a molar ratio of (1-2):(1-2):(1-2):2:2, and then dissolved in deionized water and ultrasonically mixed until completely dissolved, to prepare a total metal ion concentration of 0.15-0.25 mol·L -1 ammonium fluoride and urea were weighed in a molar ratio of 2:5, dissolved in deionized water, and ultrasonicated until completely dissolved to prepare an ammonium fluoride concentration of 0.2-0.6 mol·L -1 The urea concentration is 0.8~1.2mol·L -1 Solution B. Solution B is then added to solution A, ultrasonicated until completely mixed to form solution C, and solution C is transferred to a polytetrafluoroethylene reactor containing a catalyst carrier for hydrothermal reaction at a reaction temperature of 110-130°C for 5-7 hours. After the reaction solution is cooled, the product is taken out and washed with deionized water, and then placed in a 50-70°C blast oven to dry for 5-7 hours to obtain a high entropy hydroxide oxygen evolution catalyst precursor; wherein the magnesium salt is one or more of magnesium sulfate, magnesium nitrate, magnesium chloride or magnesium acetate, the cobalt salt is one or more of cobalt sulfate, cobalt nitrate, cobalt chloride or cobalt acetate, the nickel salt is one or more of nickel sulfate, nickel nitrate, nickel chloride or nickel acetate, the zinc salt is one or more of zinc sulfate, zinc nitrate, zinc chloride or zinc acetate, the iron salt is one or more of ferric sulfate, ferric nitrate, ferric chloride or ferric acetate, and the catalyst carrier is one of nickel foam, carbon cloth, and carbon paper.

[0007] (2) Place the high entropy hydroxide oxygen evolution catalyst precursor obtained in step (1) into 1.5-2.5 mol·L -1The Zn ions were partially removed by etching in a KOH solution for 6 to 18 hours, and the product was then taken out and washed with deionized water. It was then placed in a 50 to 70 ° C forced air oven and dried for 5 to 7 hours to obtain a high entropy hydroxide oxygen evolution catalyst with cation vacancies.

[0008] Figure 1 The XRD spectrum of Example 2 corresponds well to the characteristic peaks of NiFe-LDHs, indicating that high entropy hydroxide was successfully prepared. Figure 2 This is the TEM electron microscope image of Comparative Example 1, from which it can be seen that its structure is a nanoflower composed of nanosheets. Figure 3 The TEM electron microscope image of Example 2 shows that after alkali etching, the original morphology is still maintained. The electrochemical properties of the products prepared in Example 2 and Comparative Example 1 were tested by linear voltammetry scanning to obtain the electrolytic water oxygen evolution performance, as shown in FIG. Figure 4 As shown. Figure 4 From the linear sweep voltammetry curve, at the same current density, the oxygen evolution overpotential of Example 2 is much smaller than that of Comparative Example 1, which indicates that the cation vacancies can significantly improve the activity of the oxygen evolution catalyst. Figure 5 This is the stability test diagram of Example 2. It can be seen that the catalytic material is -2 The current density can be maintained stably for 300 hours, proving that the high entropy hydroxide material has excellent stability.

[0009] The beneficial effects and advantages of the present invention are as follows: the high-entropy hydroxide oxygen evolution catalyst with cation vacancies proposed by the present invention optimizes the electronic structure of the high-entropy hydroxide and improves the catalytic activity for oxygen evolution; at the same time, the high-entropy structure of the high-entropy catalyst effectively improves the stability of the catalyst. Therefore, the catalyst has excellent catalytic activity and stability in alkaline electrolysis of water. The present invention uses a hydrothermal method to grow the high-entropy hydroxide in situ on the catalyst support, and then uses an alkaline etching method to simply and effectively introduce cation vacancies into the high-entropy hydroxide, which has the characteristics of simple production process and easy large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is the X-ray diffraction pattern of the sample in Example 2, where the horizontal axis is twice the angle (2θ), the unit is degree (°), and the vertical axis is the diffraction intensity, the unit is absolute unit (au).

[0011] Figure 2 This is the transmission electron microscope image of the sample in comparative example 1.

[0012] Figure 3 This is a transmission electron microscope image of the sample in Example 2.

[0013] Figure 4The linear sweep voltammetry curves of the samples in Example 2 and Comparative Example 1 are shown. The test potential range is 1.0-1.9 V (vs. RHE) and the scan rate is 5 mV·s. -1 The horizontal axis is the voltage in volts relative to the reversible hydrogen electrode (Vvs.RHE), and the vertical axis is the current density in milliamperes per square centimeter (mA / cm 2 ).

[0014] Figure 5 This is the electrocatalytic stability test diagram of the sample in Example 2, the test current density is 100 mA cm -2 , the horizontal axis is time, the unit is hour (h), and the vertical axis is voltage, the unit is volt, relative to the reversible hydrogen electrode (V vs. RHE). DETAILED DESCRIPTION

[0015] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings, specific embodiments and comparative examples, but the present invention is not limited thereto.

[0016] Example 1

[0017] (1) Weigh 0.0271g of anhydrous MgSO4, 0.0349g of anhydrous CoSO4, 0.0348g of anhydrous NiSO4, 0.0727g of anhydrous ZnSO4, and 0.1800g of anhydrous Fe2(SO4)3 and dissolve them in 10mL of deionized water. Ultrasonic mixing is performed until they are completely dissolved to form solution A. Weigh 0.148g of NH4F and 0.601g of urea and dissolve them in 10mL of deionized water. Ultrasonic mixing is performed until they are completely dissolved to form solution B. Solution B is then added to solution A and ultrasonic mixing is performed until they are completely mixed to form solution C. Solution C is then transferred to a 50mL reactor containing nickel foam and lined with polytetrafluoroethylene and subjected to hydrothermal reaction at 110°C for 7h. After the reaction solution is cooled, the product is removed and washed with deionized water. It is then placed in a 50°C forced air oven and dried for 7h to obtain a high entropy hydroxide oxygen evolution catalyst precursor.

[0018] (2) Place the high entropy hydroxide precursor in 2.5 mol·L -1 The product was etched in a KOH solution for 6 h, then taken out and washed with deionized water, and then placed in a 50°C forced air oven to dry for 7 h to obtain a high entropy hydroxide oxygen evolution catalyst with cation vacancies.

[0019] The MgCoNiZnFe-LDHs-V prepared in this example Zn -6h material is used in electrolysis of water for oxygen evolution reaction. -1 The linear sweep voltammetry curve test was carried out in KOH, and it was found that the material-2 Under this condition, the overpotential is 227mV.

[0020] Example 2

[0021] (1) 0.1154 g Mg(NO3)2·6H2O, 0.1310 g Co(NO3)2·6H2O, 0.1309 g Ni(NO3)2·6H2O, 0.1339 g Zn(NO3)2·6H2O, and 0.1818 g Fe(NO3)3·9H2O were dissolved in 10 mL of deionized water and ultrasonically mixed until completely dissolved to form solution A. 0.148 g NH4F and 0.601 g urea were dissolved in 10 mL of deionized water and ultrasonically mixed until completely dissolved to form solution B. Solution B was then added to solution A and ultrasonically mixed until completely mixed to form solution C. Solution C was then transferred to a 50 mL reactor containing carbon cloth and lined with polytetrafluoroethylene and subjected to hydrothermal reaction at 120°C for 6 h. After the reaction solution was cooled, the product was taken out and washed with deionized water, and then placed in a 60° C. forced air oven to dry for 6 h to obtain a high entropy hydroxide oxygen evolution catalyst precursor.

[0022] (2) Place the high entropy hydroxide precursor in 2 mol·L -1 The product was etched in a KOH solution for 12 h, and then taken out and washed with deionized water, and then placed in a 60 ° C forced air oven to dry for 6 h to obtain a high entropy hydroxide oxygen evolution catalyst with cation vacancies.

[0023] The material was subjected to XRD test, such as Figure 1 As shown, it corresponds well to the characteristic peaks of NiFe-LDHs, indicating that high entropy hydroxide was successfully prepared. Figure 3 As shown, it is in the shape of nanosheets. Zn -12h material is used in electrolysis of water for oxygen evolution reaction. -1 The electrochemical performance of the test was tested in KOH. Figure 4 As shown, the material is 10mA·cm -2 Under the condition of 100mA·cm, the overpotential is 202mV, and under the condition of 100mA·cm -2 Under the condition of high temperature, it can maintain stability for 300h.

[0024] Example 3

[0025] (1) Weigh 0.0321g of anhydrous MgCl2, 0.0438g of anhydrous CoCl2, 0.0437g of anhydrous NiCl2, 0.0613g of anhydrous ZnCl2, and 0.0730g of anhydrous FeCl3 and dissolve them in 10mL of deionized water. Ultrasonic mixing is performed until completely dissolved to form solution A. Weigh 0.148g of NH4F and 0.601g of urea and dissolve them in 10mL of deionized water. Ultrasonic mixing is performed until completely dissolved to form solution B. Solution B is then added to solution A and ultrasonic mixing is performed until completely mixed to form solution C. Solution C is then transferred to a 50mL reactor containing carbon paper and lined with polytetrafluoroethylene and subjected to hydrothermal reaction at 130°C for 5h. After the reaction solution is cooled, the product is removed and washed with deionized water. It is then placed in a forced air oven at 70°C and dried for 5h to obtain a high-entropy hydroxide oxygen evolution catalyst precursor.

[0026] (2) Place the high entropy hydroxide precursor in 1.5 mol·L -1 The product was etched in a KOH solution for 18 h, and then taken out and washed with deionized water, and then placed in a 70 ° C forced air oven to dry for 5 h to obtain a high entropy hydroxide oxygen evolution catalyst with cation vacancies.

[0027] The MgCoNiZnFe-LDHs-V prepared in this example Zn -18h material is used in electrolysis of water for oxygen evolution reaction. -1 The linear sweep voltammetry curve test was carried out in KOH, and it was found that the material -2 Under this condition, the overpotential is 223mV.

[0028] Comparative Example 1

[0029] (1) 0.0641 g of anhydrous Mg(CH3COO)2, 0.0797 g of anhydrous Co(CH3COO)2, 0.0796 g of anhydrous Ni(CH3COO)2, 0.0826 g of anhydrous Zn(CH3COO)2, and 0.0873 g of anhydrous Fe(OH)(CH3COO)2 were dissolved in 10 mL of deionized water and ultrasonically mixed until completely dissolved to form solution A. 0.148 g of NH4F and 0.601 g of urea were dissolved in 10 mL of deionized water and ultrasonically mixed until completely dissolved to form solution B. Solution B was then added to solution A and ultrasonically mixed until completely mixed to form solution C. Solution C was then transferred to a 50 mL reactor containing carbon cloth and lined with polytetrafluoroethylene and subjected to hydrothermal reaction at 120°C for 6 h. After the reaction solution was cooled, the product was taken out and washed with deionized water, and then placed in a 60° C. forced air oven to dry for 6 h to obtain a high entropy hydroxide oxygen evolution catalyst.

[0030] The material morphology is Figure 2At the same time, the MgCoNiZnFe-LDHs material prepared in this comparative example was applied to the electrolysis of water and oxygen evolution reaction. -1 The electrochemical performance of the test was tested in KOH. Figure 4 As shown, the material is 10mA·cm -2 Under this condition, the overpotential is 272mV.

Claims

1. A high entropy hydroxide oxygen evolution catalyst with cation vacancies, characterized in that: The catalyst is in the form of nanoflowers composed of nanosheets with a diameter of 6 to 10 μm, a radial dimension of 800 to 1200 nm, and a thickness of 50 to 150 nm. The catalyst contains evenly distributed metal elements: Mg, Co, Ni, Zn, and Fe. The molar percentages of Mg, Co, Ni, Zn, and Fe in the total metal elements are 13 to 19 mol%, 21 to 27 mol%, 27 to 34 mol%, 4 to 10 mol%, and 17 to 23 mol%, respectively.

2. A method for preparing the high entropy hydroxide oxygen evolution catalyst with cation vacancies according to claim 1, characterized in that: The process steps include: (1) Magnesium salt, cobalt salt, nickel salt, zinc salt, and iron salt were weighed in a molar ratio of (1-2):(1-2):(1-2):2:2, and then dissolved in deionized water and ultrasonically mixed until completely dissolved, to prepare a total metal ion concentration of 0.15-0.25 mol·L -1 ammonium fluoride and urea were weighed in a molar ratio of 2:5, dissolved in deionized water, and ultrasonicated until completely dissolved to prepare an ammonium fluoride concentration of 0.2-0.6 mol·L -1 The urea concentration is 0.8~1.2mol·L -1 Solution B. Solution B is then added to Solution A and ultrasonicated until completely mixed to form Solution C. Solution C is then transferred to a polytetrafluoroethylene reactor containing a catalyst support for a hydrothermal reaction at a temperature of 110-130°C for 5-7 hours. After the reaction solution cools, the product is removed and washed with deionized water, then dried in a forced air oven at 50-70°C for 5-7 hours to obtain a high-entropy hydroxide oxygen evolution catalyst precursor. (2) Place the high entropy hydroxide oxygen evolution catalyst precursor obtained in step (1) into 1.5-2.5 mol·L -1 The Zn ions were partially removed by etching in a KOH solution for 6 to 18 hours, and the product was then taken out and washed with deionized water. It was then dried in a 50 to 70 ° C forced air oven for 5 to 7 hours to obtain a high entropy hydroxide oxygen evolution catalyst with cation vacancies.

3. The preparation method according to claim 2, characterized in that The magnesium salt in step (1) is one or more of magnesium sulfate, magnesium nitrate, magnesium chloride or magnesium acetate.

4. The preparation method according to claim 2, characterized in that The cobalt salt in step (1) is one or more of cobalt sulfate, cobalt nitrate, cobalt chloride or cobalt acetate.

5. The preparation method according to claim 2, characterized in that The nickel salt in step (1) is one or more of nickel sulfate, nickel nitrate, nickel chloride or nickel acetate.

6. The preparation method according to claim 2, characterized in that The zinc salt in step (1) is one or more of zinc sulfate, zinc nitrate, zinc chloride or zinc acetate.

7. The preparation method according to claim 2, characterized in that The iron salt in step (1) is one or more of ferric sulfate, ferric nitrate, ferric chloride or ferric acetate.

8. The preparation method according to claim 2, characterized in that The catalyst carrier in step (1) is one of nickel foam, carbon cloth and carbon paper.

Images