A layered double metal hydroxide composite material and its preparation method and application

Abstract

The present invention discloses a layered double hydroxide composite material, its preparation method, and application. The preparation method comprises the following steps: adding cobalt nitrate hexahydrate, nickel nitrate hexahydrate, and urea to deionized water, mixing them uniformly, immersing them in carbon cloth, performing a hydrothermal reaction, cooling, washing, and vacuum drying, then adding sodium hypophosphite, heating and maintaining the heat, and cooling to produce NiCoP@CC; adding nickel nitrate hexahydrate, ferrous sulfate heptahydrate, and urea to deionized water, immersing the prepared NiCoP@CC in the mixture, performing a hydrothermal reaction, and then cooling, washing, and drying to produce NiCoP / NiFe LDH@CC, i.e., a layered double hydroxide composite material. The composite material prepared by the present invention exhibits high catalytic activity as an oxygen evolution catalyst. Furthermore, when used as a positive electrode catalyst in zinc-air batteries, it can stably cycle for approximately 240 hours, with a charge-discharge voltage difference of approximately 0.80V and a charge-discharge efficiency of approximately 60%.

Description

Technical Field

[0001] The present invention relates to the technical field of layered double hydroxide preparation, and in particular to a layered double hydroxide composite material, a preparation method and an application thereof. Background Art

[0002] Water electrolysis technology is an important way to produce hydrogen energy in a green way and has huge development potential. The thermodynamic equilibrium potential of water electrolysis is 1.23V vs. RHE. Under alkaline conditions, the water electrolysis process includes the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) electrochemical reactions. In practical applications, the large overpotential makes the voltage driving water electrolysis much higher than the equilibrium potential (1.23V vs. RHE), which brings about the problems of high energy consumption and low efficiency in the water electrolysis process. The main source of overpotential is the OER process, because its four-electron proton reaction is slower and more complex than the HER process (two-electron reaction). Therefore, the research on highly active OER catalysts is crucial to reducing the overpotential of water electrolysis and improving its energy efficiency. In addition, compared to common battery systems such as lead-acid batteries, alkaline batteries, and lithium-ion batteries, rechargeable zinc-air batteries have significant advantages in energy density, safety, environmental protection, and cost. They are a new type of metal-air battery that releases or stores energy through redox reactions between the zinc negative electrode and the oxygen at the positive electrode. They use aqueous electrolytes and a semi-open cell design, which have absolute advantages in battery safety. At the same time, they have extremely high theoretical energy density, which makes them significantly superior to other secondary batteries in terms of battery weight and volume. Although rechargeable zinc-air batteries have so many advantages, their problems in discharge power, charge and discharge efficiency, and cycle life have greatly hindered their large-scale commercial application. To solve the existing problems of rechargeable zinc-air batteries, the most important thing is to find a superior cathode catalyst.

[0003] Layered double hydroxides (LDHs), also known as hydrotalcite, are a type of natural mineral material with a two-dimensional structure. Its structure consists of a main layer of positively charged metal cations (M 2+ 1-x M 3+ x (OH)2) and negatively charged hydrated anions ((A n- ) x / n·zH2O) interlayer. Among LDHs, NiFe LDH is considered to be the most promising oxygen evolution catalyst and is expected to replace commercial precious metal catalysts (such as IrO2 and RuO2). However, its intrinsic activity is relatively low, and the particle size or thickness of NiFe LDH is large (>20nm). The OER process occurs on the surface or near the surface of the electrocatalyst, which leads to an extremely limited number of active sites in NiFe LDH that can effectively participate in the OER. Therefore, it is of great significance to study a new layered double hydroxide composite material. Summary of the Invention

[0004] In order to solve the above technical problems, the purpose of the present invention is to provide a layered double hydroxide composite material and its preparation method and application, so as to solve the problems of low activity and poor stability of the existing oxygen evolution catalyst NiFe LDH.

[0005] The present invention solves the above technical problems with the following technical solution: a method for preparing a layered double hydroxide composite material is provided, comprising the following steps:

[0006] (1) Cobalt nitrate hexahydrate, nickel nitrate hexahydrate, and urea were added to deionized water in sequence, mixed evenly, and then immersed in the pretreated carbon cloth for hydrothermal reaction for 6-10 hours, followed by cooling, washing, and vacuum drying. Sodium hypophosphite was then added, heated and kept warm for 1.5-2.5 hours, and cooled naturally to room temperature to obtain NiCoP@CC.

[0007] (2) Nickel nitrate hexahydrate, ferrous sulfate heptahydrate and urea are added to deionized water in sequence, mixed evenly, and then immersed in the NiCoP@CC prepared in step (1), hydrothermally reacted for 2-5 hours, and then cooled, washed and dried to obtain NiCoP / NiFe LDH@CC, i.e., a layered double hydroxide composite material.

[0008] The beneficial effects of the present invention are as follows: when the composite material prepared by the present invention is used as an oxygen evolution catalyst, the electronic structure of the catalyst is regulated by the heterojunction interface, thereby changing the physicochemical properties of the catalyst, thereby optimizing its oxygen electrocatalytic electrochemical performance, and improving the catalytic conversion efficiency of zinc-air battery energy storage.

[0009] On the basis of the above technical solution, the present invention can also be improved as follows:

[0010] Furthermore, in step (1), the molar volume ratio of cobalt nitrate hexahydrate, nickel nitrate hexahydrate, urea, sodium hypophosphite and deionized water is 0.8-1.2 mmol: 0.8-1.2 mmol: 5-7 mmol: 0.9-1.1 mmol: 30-40 mL.

[0011] Furthermore, in step (1), the pretreated carbon cloth is prepared by the following method: the carbon cloth is sequentially ultrasonicated with 4-6wt% hydrochloric acid solution, deionized water and ethanol for 5-15 minutes, then immersed in 60-80wt% nitric acid solution for 1.5-2.5 hours, and then washed and dried to obtain the pretreated carbon cloth.

[0012] Furthermore, in step (1), a hydrothermal reaction is carried out at 100-150°C.

[0013] Furthermore, in step (1), heating and heat preservation are carried out in an inert atmosphere.

[0014] Furthermore, in step (1), the temperature is heated to 300-380°C at a heating rate of 4-6°C / min.

[0015] Furthermore, in step (2), the molar volume ratio of nickel nitrate hexahydrate, ferrous sulfate heptahydrate, urea and deionized water is 0.5-1 mmol: 0.1-0.3 mmol: 2-6 mmol: 25-35 mL.

[0016] The beneficial effects of adopting the above further technical solution are: the process of preparing NiFe LDH by the hydrothermal reaction preparation method is simple and easy to scale up, wherein urea is used as a growth agent, which is conducive to the formation of uniform NiFe LDH nanosheets at this ratio.

[0017] Furthermore, in step (2), a hydrothermal reaction is carried out at 80-120°C.

[0018] Furthermore, in steps (1)-(2), the mixture is mixed uniformly by electromagnetic stirring for 25-35 minutes.

[0019] Furthermore, in steps (1)-(2), the mixture is naturally cooled to room temperature.

[0020] Furthermore, in steps (1)-(2), deionized water and ethanol are used for alternating washing.

[0021] Furthermore, in steps (1)-(2), vacuum drying is performed at 50-70° C. for 6-10 h.

[0022] The present invention also provides a composite material prepared by the preparation method of the layered double metal hydroxide composite material.

[0023] The present invention also provides the use of the layered double metal hydroxide composite material as an oxygen evolution catalyst.

[0024] The present invention has the following beneficial effects:

[0025] 1. The preparation method of the present invention is simple, easy to operate and easy to promote.

[0026] 2. The composite material NiCoP / NiFe LDH@CC prepared in the present invention is a nanoflower-like structure composed of nanosheets, the diameter of the nanosheets is about 1 μm, and the thickness of the nanosheets is about 10-15 nm.

[0027] 3. The composite material NiCoP / NiFe LDH@CC prepared in the present invention has high catalytic activity as an oxygen evolution catalyst.

[0028] 4. When the composite material NiCoP / NiFe LDH@CC prepared by the present invention is used as a cathode catalyst for zinc-air batteries, it can stably cycle for about 240 hours, with a charge-discharge voltage difference of about 0.80 V and a charge-discharge efficiency of about 60%, fully demonstrating that NiCoP / NiFeLDH@CC has good prospects as a cathode catalyst for zinc-air batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is the XRD pattern of the composite material prepared in Example 1;

[0030] Figure 2 is a SEM image of the composite material prepared in Example 1;

[0031] Figure 3 The OER polarization curves of the composite materials prepared in Example 1 and Comparative Examples 1-2 are shown;

[0032] Figure 4 for Figure 3 Tafel slope corresponding to the middle curve;

[0033] Figure 5 The discharge and charge cycle curve of the composite material of Example 1 as a positive electrode catalyst of a zinc-air battery. DETAILED DESCRIPTION

[0034] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples are only used to explain the present invention and are not intended to limit the scope of the invention. In the embodiments, if specific conditions are not specified, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0035] Example 1:

[0036] A layered double hydroxide composite material, the preparation method of which comprises the following steps:

[0037] (1) Cut the carbon cloth into 3×3cm 2 The large and small squares were sequentially ultrasonicated with 5wt% hydrochloric acid solution, deionized water and ethanol for 10 minutes, then soaked in 70wt% nitric acid solution for 2 hours, then cleaned with deionized water and finally dried to obtain pretreated carbon cloth;

[0038] (2) Cobalt nitrate hexahydrate, nickel nitrate hexahydrate and urea were added to deionized water in sequence, and after being mixed uniformly by electromagnetic stirring at room temperature for 30 minutes, the pretreated carbon cloth prepared in step (1) was immersed in the mixture, and the mixture was transferred to a stainless steel high-pressure reactor, and hydrothermally reacted at 120°C for 8 hours, and then naturally cooled to room temperature, and washed alternately with deionized water and ethanol, and vacuum dried at 60°C for 8 hours, and then transferred to a tube furnace, and sodium hypophosphite was added. In an inert atmosphere, the mixture was heated to 350°C at a heating rate of 5°C / min and kept warm for 2 hours, and then naturally cooled to room temperature to prepare NiCoP@CC; wherein the molar volume ratio of cobalt nitrate hexahydrate, nickel nitrate hexahydrate, urea, sodium hypophosphite and deionized water was 1mmol:1mmol:6mmol:1mmol:35mL;

[0039] (3) Nickel nitrate hexahydrate, ferrous sulfate heptahydrate and urea were added to deionized water in sequence, and after being mixed uniformly by electromagnetic stirring at room temperature for 30 minutes, the NiCoP@CC prepared in step (2) was immersed in the water, and the mixture was transferred to a stainless steel high-pressure reactor, and hydrothermally reacted at 100°C for 4 hours, and then naturally cooled to room temperature, washed alternately with deionized water and ethanol, and vacuum dried at 60°C for 8 hours to obtain NiCoP / NiFe LDH@CC, i.e., a layered double hydroxide composite material; wherein the molar volume ratio of nickel nitrate hexahydrate, ferrous sulfate heptahydrate, urea and deionized water is 0.8 mmol:0.2 mmol:4 mmol:30 mL.

[0040] Example 2:

[0041] A layered double hydroxide composite material, the preparation method of which comprises the following steps:

[0042] (1) Cut the carbon cloth into 3×3cm 2 The large and small squares were sequentially ultrasonicated with 4wt% hydrochloric acid solution, deionized water and ethanol for 15 minutes, then soaked in 60wt% nitric acid solution for 2.5 hours, then cleaned with deionized water and finally dried to obtain pretreated carbon cloth;

[0043] (2) Cobalt nitrate hexahydrate, nickel nitrate hexahydrate and urea were added to deionized water in sequence, and after being mixed uniformly by electromagnetic stirring for 25 minutes at room temperature, the pretreated carbon cloth prepared in step (1) was immersed in the mixture, and the mixture was transferred to a stainless steel high-pressure reactor, and hydrothermally reacted at 100°C for 10 hours, and then naturally cooled to room temperature, and washed alternately with deionized water and ethanol, and vacuum dried at 50°C for 10 hours, and then transferred to a tube furnace, and sodium hypophosphite was added. In an inert atmosphere, the mixture was heated to 300°C at a heating rate of 4°C / min and kept warm for 2.5 hours, and then naturally cooled to room temperature to prepare NiCoP@CC; wherein the molar volume ratio of cobalt nitrate hexahydrate, nickel nitrate hexahydrate, urea and deionized water was 0.8mmol:0.8mmol:5mmol:0.9mmol:30mL;

[0044] (3) Nickel nitrate hexahydrate, ferrous sulfate heptahydrate and urea were added to deionized water in sequence, and after being uniformly mixed by electromagnetic stirring at room temperature for 25 minutes, the NiCoP@CC prepared in step (2) was immersed in the mixture, and the mixture was transferred to a stainless steel high-pressure reactor, and hydrothermally reacted at 80°C for 5 hours, and then naturally cooled to room temperature, washed alternately with deionized water and ethanol, and vacuum dried at 70°C for 10 hours to obtain NiCoP / NiFe LDH@CC, i.e., a layered double hydroxide composite material; wherein the molar volume ratio of nickel nitrate hexahydrate, ferrous sulfate heptahydrate, urea, sodium hypophosphite and deionized water is 0.5mmol:0.1mmol:2mmol:25mL.

[0045] Example 3:

[0046] A layered double hydroxide composite material, the preparation method of which comprises the following steps:

[0047] (1) Cut the carbon cloth into 3×3cm 2 The large and small squares were sequentially ultrasonicated with 6wt% hydrochloric acid solution, deionized water and ethanol for 5 minutes, then soaked in 80wt% nitric acid solution for 1.5 hours, then cleaned with deionized water and finally dried to obtain pretreated carbon cloth;

[0048] (2) Cobalt nitrate hexahydrate, nickel nitrate hexahydrate and urea were added to deionized water in sequence, and after being uniformly mixed by electromagnetic stirring at room temperature for 35 minutes, the pretreated carbon cloth prepared in step (1) was immersed in the mixture, and the mixture was transferred to a stainless steel high-pressure reactor, and hydrothermally reacted at 150°C for 6 hours, and then naturally cooled to room temperature, and washed alternately with deionized water and ethanol, and vacuum dried at 70°C for 6 hours, and then transferred to a tube furnace, and sodium hypophosphite was added. In an inert atmosphere, the mixture was heated to 380°C at a heating rate of 6°C / min and kept warm for 1.5 hours, and then naturally cooled to room temperature to prepare NiCoP@CC; wherein the molar volume ratio of cobalt nitrate hexahydrate, nickel nitrate hexahydrate, urea, sodium hypophosphite and deionized water was 1.2mmol:1.2mmol:7mmol:1.1mmol:40mL;

[0049] (3) Nickel nitrate hexahydrate, ferrous sulfate heptahydrate and urea were added to deionized water in sequence, and after being uniformly mixed by electromagnetic stirring at room temperature for 35 minutes, the NiCoP@CC prepared in step (2) was immersed in the mixture, and the mixture was transferred to a stainless steel high-pressure reactor, and hydrothermally reacted at 120°C for 2 hours, and then naturally cooled to room temperature, washed alternately with deionized water and ethanol, and vacuum dried at 70°C for 6 hours to obtain NiCoP / NiFe LDH@CC, i.e., a layered double hydroxide composite material; wherein the molar volume ratio of nickel nitrate hexahydrate, ferrous sulfate heptahydrate, urea and deionized water is 1mmol:0.3mmol:6mmol:35mL. Comparative Example 1:

[0050] A NiCoP@CC composite material, the preparation method of which comprises the following steps:

[0051] Same as steps (1)-(2) in the embodiment.

[0052] Comparative Example 2:

[0053] A NiFe LDH@CC composite material, the preparation method of which comprises the following steps:

[0054] (1) Cut the carbon cloth into 3×3cm 2 The large and small squares were sequentially ultrasonicated with 5wt% hydrochloric acid solution, deionized water and ethanol for 10 minutes, then soaked in 70wt% nitric acid solution for 2 hours, then cleaned with deionized water and finally dried to obtain pretreated carbon cloth;

[0055] (2) Nickel nitrate hexahydrate, ferrous sulfate heptahydrate and urea were added to deionized water in sequence, and after being uniformly mixed by electromagnetic stirring at room temperature for 30 minutes, the mixture was immersed in the pretreated carbon cloth obtained in step (1), and transferred to a stainless steel high-pressure reactor. The mixture was hydrothermally reacted at 100°C for 4 hours, and then naturally cooled to room temperature. The mixture was washed alternately with deionized water and ethanol, and vacuum-dried at 60°C for 10 hours to obtain NiFe LDH@CC; wherein the molar volume ratio of nickel nitrate hexahydrate, ferrous sulfate heptahydrate, urea and deionized water was 0.8 mmol: 0.2 mmol: 4 mmol: 30 mL.

[0056] Test example

[0057] The characterization and performance of the layered double hydroxide composite materials prepared in Examples 1-3 are basically consistent. The following tests are performed using the composite material prepared in Example 1 as an example.

[0058] 1. Characterization and testing

[0059] 1. The layered double hydroxide composite material obtained in Example 1 was tested by X-ray diffractometer (XRD, Rigaku D / max-2500). The results are shown in Figure 1 .Depend on Figure 1 It can be seen that hydrotalcite-like NiFe LDH@CC is generated in the composite material prepared by the present invention.

[0060] 2. The layered double hydroxide composite material obtained in Example 1 was tested by focused ion beam scanning electron microscopy (Zeiss Auriga FIB / SEM, 5kV). Figure 2 .Depend on Figure 2 It can be seen that the microscopic morphology of the composite material prepared in the present invention is a nanoflower-like structure composed of nanosheets, the diameter of the nanosheets is about 1 μm, and the thickness of the nanosheets is about 10-15 nm.

[0061] 2. Performance Testing

[0062] 1. The composite materials prepared in Example 1 and Comparative Examples 1-2 were used as oxygen evolution catalysts to test their catalytic performance. The specific method was as follows: using a three-electrode test method, the NiCoP@CC prepared in Comparative Example 1, the NiFe LDH@CC prepared in Comparative Example 2, and the NiCoP / NiFe LDH@CC prepared in Example 1 (effective area of ​​1×1 cm 2 ) as the working electrode, Pt wire electrode as the counter electrode, Ag / AgCl electrode (filled with 10wt% KNO3 solution) as the reference electrode, and 0.1mol / L potassium hydroxide solution as the electrolyte. Oxygen was introduced for 20min before the test until the entire system was saturated with O2, and the entire test process continued to be in an O2 saturated state.

[0063] The reversible hydrogen electrode potential of the catalyst potential is calculated according to the following formula:

[0064] E (RHE) =E (Ag / AgCl) +E 0 (Ag / AgCl,0.199V) +0.0591×pH

[0065] Among them, E (RHE) is the reversible hydrogen electrode potential, E (Ag / AgCl) is the potential read out with Ag / AgCl as the reference electrode, E 0 (Ag / AgCl,0.199V) is the potential at the Ag / AgCl reference electrode, and pH is the acidity or alkalinity of the electrolyte.

[0066] The polarization curve of oxygen evolution reaction (OER) was tested by linear voltammetry (LSV) with a scan rate of 1 mV / s. The Tafel slope was obtained from the polarization curve. Figure 3-4 .Depend on Figure 3-4 It can be seen that the current density is 10mA / cm 2 When the overpotential of NiCoP / NiFe LDH@CC prepared in Example 1 is 340 mV, the overpotential of NiCoP@CC prepared in Comparative Example 1 is 470 mV. It can be seen that the overpotential and Tafel slope performance parameters of the composite material of the present invention are improved compared with those of Comparative Examples 1-2, indicating that the catalytic activity of the composite material NiCoP / NiFeLDH@CC prepared in the present invention as an oxygen evolution catalyst is improved.

[0067] 2. The composite material NiCoP / NiFe LDH@CC prepared in Example 1 was used as a cathode catalyst for zinc-air batteries to perform performance testing. The specific test method was as follows: the zinc-air battery test used a typical two-electrode system, including a NiCoP / NiFe LDH@CC cathode catalyst that allows O2 to enter the system and a zinc metal anode, 6 mol / L KOH solution and 0.2 mol / L Zn(Ac)2 as electrolytes (to ensure reversible Zn anode reaction). The results are shown in FIG. Figure 5 .Depend on Figure 5 It can be seen that when the composite material NiCoP / NiFe LDH@CC prepared by the present invention is used as a cathode catalyst for zinc-air batteries, it can stably cycle for about 240 hours, with a charge-discharge voltage difference of about 0.80V and a charge-discharge efficiency of about 60%, fully demonstrating that NiCoP / NiFe LDH@CC has good prospects as a cathode catalyst for zinc-air batteries.

[0068] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a layered double hydroxide composite material, characterized in that: The following steps are involved: (1) Cobalt nitrate hexahydrate, nickel nitrate hexahydrate and urea were added to deionized water in sequence, mixed evenly, and then immersed in the pretreated carbon cloth for hydrothermal reaction for 6-10 hours, followed by cooling, washing and vacuum drying. Sodium hypophosphite was then added, heated and kept warm for 1.5-2.5 hours, and cooled naturally to room temperature to obtain NiCoP@CC. (2) nickel nitrate hexahydrate, ferrous sulfate heptahydrate and urea are added to deionized water in sequence, mixed evenly, and then immersed in the NiCoP@CC prepared in step (1), hydrothermally reacted for 2-5 hours, and then cooled, washed and dried to obtain NiCoP / NiFe LDH@CC, i.e., a layered double hydroxide composite material; In step (1), the pretreated carbon cloth is prepared by the following method: the carbon cloth is sequentially ultrasonicated with a 4-6 wt% hydrochloric acid solution, deionized water, and ethanol for 5-15 minutes, then immersed in a 60-80 wt% nitric acid solution for 1.5-2.5 hours, and then washed and dried to obtain the pretreated carbon cloth; In step (1), a hydrothermal reaction is carried out at 100-150°C; In step (1), heating to 300-380°C at a heating rate of 4-6°C / min; In step (2), a hydrothermal reaction is carried out at 80-120°C.

2. The method for preparing the layered double hydroxide composite material according to claim 1, wherein: In step (1), the molar volume ratio of cobalt nitrate hexahydrate, nickel nitrate hexahydrate, urea, sodium hypophosphite and deionized water is 0.8-1.2 mmol: 0.8-1.2 mmol: 5-7 mmol: 0.9-1.1 mmol: 30-40 mL.

3. The method for preparing the layered double hydroxide composite material according to claim 1, wherein: In step (1), heating and heat preservation are carried out in an inert atmosphere.

4. The method for preparing the layered double hydroxide composite material according to claim 1, wherein: In step (2), the molar volume ratio of nickel nitrate hexahydrate, ferrous sulfate heptahydrate, urea and deionized water is 0.5-1 mmol: 0.1-0.3 mmol: 2-6 mmol: 25-35 mL.

5. A layered double hydroxide composite material obtained according to the method for preparing a layered double hydroxide composite material according to any one of claims 1 to 4.

6. Use of the layered double hydroxide composite material according to claim 5 as an oxygen evolution catalyst.

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