Preparation and application of composite layered double-metal hydroxide with low oxygen evolution overpotential

Abstract

The invention discloses preparation and application of a Co (OH) 2-based composite layered double-metal hydroxide, and belongs to the technical field of electro-catalytic oxygen evolution. According to the preparation method, Co (NO3) 2.6 H2O, NH4F and CO (NH2) 2 react on foamed nickel to prepare Co (OH) 2 / NF, then NiCl2. 6H2O, metal salt, urea and hexamethylenetetramine serve as raw materials, Co (OH) 2 coated Ni-Mn LDHs and Co (OH) 2 coated Ni-Co LDHs are prepared on the Co (OH) 2 / NF through a simple hydrothermal reaction, and the Co (OH) 2 coated Ni-Mn LDHs and the Co (OH) 2 coated Ni-Co LDHs can serve as electrode materials to be used for the anodic oxidation reaction of ethyl alcohol, methyl alcohol and N, N-dimethylformamide.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalytic oxygen evolution, and specifically relates to the preparation of a composite layered double metal hydroxide based on Co(OH)2 and its application as an electrode material for anodic oxidation reactions of ethanol, methanol and N,N-dimethylformamide. Background Art

[0002] With the depletion of energy and environmental degradation, the search for clean energy is urgent. Green hydrogen energy produced by electrolytic water decomposition is considered an effective means to solve the current environmental crisis. Electrolytic water decomposition produces hydrogen evolution reaction (HER) at the cathode and oxygen evolution reaction (OER) at the anode. However, the slow kinetics of OER limit the rate of hydrogen evolution at the cathode. Therefore, the use of other small molecules such as methanol (CH3OH), ethanol (C2H5OH) and N, N-dimethylformamide (DMF) to replace OER in the anodic oxidation reaction to reduce the potential and energy consumption has attracted widespread attention.

[0003] At present, some studies have explored the addition of small molecules such as N2H4, urea, 5-hydroxymethylfurfural and alcohols to water-soluble electrolytes to replace traditional OER catalysts, thereby reducing the oxygen evolution overpotential and energy consumption of electrode materials. However, according to existing literature reports, the effect of these additives in reducing the oxygen evolution overpotential is usually between 0.05 V and 0.1 V, and more effective strategies are still needed to further improve performance. Summary of the invention

[0004] The purpose of the present invention is to provide a preparation method of a composite layered double hydroxide (LDHs) composite material based on Co(OH)2 and its application as an anode electrode material, wherein the composite material can significantly reduce the peroxide potential in the anodic oxidation reaction of CH3OH, EtOH and DMF.

[0005] To achieve the above object, the present invention adopts the following technical solution: A method for preparing a composite layered double metal hydroxide based on Co(OH)2 comprises the following steps: 1) Co(NO3)2·6H2O, NH4F and urea (CO(NH2)2) were stirred and dissolved in deionized water to form a uniform solution; 2) The solution obtained in step 1) is transferred to a stainless steel reactor lined with polytetrafluoroethylene, and clean nickel foam is placed therein for reaction, and then the nickel foam is taken out, washed, and dried to obtain Co(OH)2 / NF; 3) NiCl2·6H2O, metal salt, urea and hexamethylenetetramine (HMT) were stirred and dissolved in deionized water to form a uniform solution; 4) The solution obtained in step 3) is transferred to a stainless steel reactor lined with polytetrafluoroethylene, and Co(OH)2 / NF is placed therein for hydrothermal reaction to obtain the composite layered double metal hydroxide based on Co(OH)2.

[0006] Furthermore, the molar ratio of Co(NO3)2·6H2O, NH4F and urea used in step 1) is 2:1:4.

[0007] Furthermore, the reaction temperature in step 2) is 80° C. and the reaction time is 12 h.

[0008] Furthermore, the metal salt in step 3) is MnCl2·4H2O or CoCl2·6H2O.

[0009] Furthermore, the molar ratio of NiCl2·6H2O, metal salt, urea and hexamethylenetetramine used in step 3) is 1:1:2:1.

[0010] Furthermore, the temperature of the hydrothermal reaction in step 4) is 100° C. and the time is 10 h.

[0011] The obtained composite layered double hydroxide is specifically Co(OH)2@Ni-Mn LDHs or Co(OH)2@Ni-CoLDHs, which can be used as an anode electrode material in anodization reactions of ethanol, methanol, N,N-dimethylformamide, etc.

[0012] The beneficial effects of the present invention are: The Co(OH)2@Ni-Mn LDHs and Co(OH)2@Ni-Co LDHs active materials prepared by the present invention are based on lamellar Co(OH)2, so that Ni-Mn LDHs and Ni-Co LDHs are uniformly distributed on Co(OH)2 nanosheets in the form of continuous and continuous sheets, which can provide a large number of active sites and significantly reduce the peroxide potential in the anodic oxidation reaction of CH3OH, EtOH and DMF.

[0013] The results show that the Co(OH)2@Ni-Mn LDHs and Co(OH)2@Ni-Co LDHs prepared by the present invention have good thermal conductivity at a current density of 40 mA cm -2 Under the conditions of , the oxygen evolution potentials are 1.60 V and 1.56 V, respectively, which are better than the existing records (patent CN113604834A provides a core-shell structure NiCo-LDH / (Ni, Fe)(OH)2 / nickel foam composite electrode composed of NiCo-LDH uniformly coated on a needle-like (Ni, Fe)(OH)2, which has a current density of 40 mA cm -2 Under the condition of , the oxygen evolution potential is only 1.64 V). BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 SEM images of Co(OH)2 / NF (a), Co(OH)2@Ni-Mn LDHs / NF (b) and Co(OH)2@Ni-CoLDHs / NF (c) prepared in the examples.

[0015] Figure 2 XRD patterns of Co(OH)2, Co(OH)2@Ni-Mn LDHs and Co(OH)2@Ni-Co LDHs prepared in the examples.

[0016] Figure 3 Linear sweep voltammetry (LSV) curves of Co(OH)2@Ni-Mn LDHs / NF (a) and Co(OH)2@Ni-Co LDHs / NF (b) electrode materials prepared in the examples.

[0017] Figure 4 Cyclic voltammetry (CV) curves of Co(OH)2@Ni-Mn LDHs / NF (a) and Co(OH)2@Ni-Co LDHs / NF (b) electrode materials prepared in the examples in different electrolytes.

[0018] Figure 5 Linear sweep voltammetry (LSV) curves of Co(OH)2@Ni-Mn LDHs / NF (a) and Co(OH)2@Ni-Co LDHs / NF (b) electrode materials prepared in different electrolytes. DETAILED DESCRIPTION

[0019] A method for preparing a composite layered double metal hydroxide based on Co(OH)2 comprises the following steps: 1) Add Co(NO3)2·6H2O, NH4F and CO(NH2)2 in a molar ratio of 2:1:4 into deionized water and stir to dissolve to form a uniform solution; 2) The solution obtained in step 1) was transferred to a stainless steel reactor lined with polytetrafluoroethylene, clean nickel foam was placed in it, and the reaction was carried out at 80°C for 12 hours. After that, the nickel foam was taken out, washed, and dried to obtain Co(OH)2 / NF; 3) Add NiCl2·6H2O, metal salt, CO(NH2)2 and HMT into deionized water at a molar ratio of 1:1:2:1 and stir to dissolve to form a uniform solution; 4) The solution obtained in step 3) was transferred to a stainless steel reactor lined with polytetrafluoroethylene, and Co(OH)2 / NF was added and reacted at 100°C for 10 h. Then, the nickel foam was taken out, washed, and dried to obtain a composite layered double hydroxide based on Co(OH)2 with an electrode loading of 2.0-3.0 mg / cm 2 .

[0020] Wherein, the metal salt in step 3) is MnCl2·4H2O or CoCl2·6H2O.

[0021] In order to make the contents of the present invention easier to understand, the technical solution of the present invention is further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0022] Example 1 (1) Clean the nickel foam (2 cm × 3 cm) with acetone, hydrochloric acid, deionized water and anhydrous ethanol in sequence, and then dry it at 60 °C for 10 h; (2) Dissolve 0.58 g Co(NO3)2·6H2O, 0.37 g NH4F, and 0.24 g CO(NH2)2 in 35 mL of deionized water and stir for 15 min to form a homogeneous solution; (3) The solution of step (2) was transferred to a stainless steel reactor lined with polytetrafluoroethylene, and the treated nickel foam was placed in the reactor. The reactor was placed in an oven at 80°C for reaction for 12 hours. After that, the nickel foam was taken out, rinsed with deionized water and anhydrous ethanol, and dried at 60°C for 10 hours to obtain Co(OH)2 / NF; (4) Dissolve 0.47 g NiCl2·6H2O, 0.39 g MnCl2·4H2O, 0.24 g CO(NH2)2, and 0.28 g HMT in 35 mL deionized water and stir for 15 min to form a homogeneous solution. (5) The solution was transferred to a stainless steel reactor lined with polytetrafluoroethylene, and Co(OH)2 / NF was placed in the reactor. The reactor was placed in an oven at 100°C for 10 h. The nickel foam was then taken out, rinsed with deionized water and anhydrous ethanol, and dried at 60°C for 10 h to obtain Co(OH)2@Ni-Mn LDHs / NF.

[0023] Example 2 (1) Clean the nickel foam (2 cm × 3 cm) with acetone, hydrochloric acid, deionized water and anhydrous ethanol in sequence, and then dry it at 60 °C for 10 h; (2) Dissolve 0.58 g Co(NO3)2·6H2O, 0.37 g NH4F, and 0.24 g CO(NH2)2 in 35 mL of deionized water and stir for 15 min to form a homogeneous solution; (3) The solution of step (2) was transferred to a stainless steel reactor lined with polytetrafluoroethylene, and the treated nickel foam was placed in the reactor. The reactor was placed in an oven at 80°C for reaction for 12 hours. After that, the nickel foam was taken out, rinsed with deionized water and anhydrous ethanol, and dried at 60°C for 10 hours to obtain Co(OH)2 / NF; (4) Dissolve 0.47 g NiCl2·6H2O, 0.47 g CoCl2·4H2O, 0.24 g CO(NH2)2, and 0.28 g HMT in 35 mL of deionized water and stir for 15 min to form a uniform solution. (5) The solution was transferred to a stainless steel reactor lined with polytetrafluoroethylene, and Co(OH)2 / NF was placed in the reactor. The reactor was placed in an oven at 100°C for 10 h. The nickel foam was then taken out, rinsed with deionized water and anhydrous ethanol, and dried at 60°C for 10 h to obtain Co(OH)2@Ni-Co LDHs / NF.

[0024] Figure 1 The SEM images of the prepared Co(OH)2 / NF (a), Co(OH)2@Ni-Mn LDHs / NF (b) and Co(OH)2@Ni-CoLDHs / NF (c). The SEM image of Co(OH)2 / NF shows that the foamed nickel skeleton is densely covered with layered Co(OH)2, and these layers have numerous needle-like protrusions growing on them. The SEM images of Co(OH)2@Ni-Mn LDHs / NF and Co(OH)2@Ni-CoLDHs / NF show that Ni-Mn LDHs and Ni-Co LDHs both use layered Co(OH)2 as carriers and grow along the needle-like protrusions to form a unique microstructure. This structure not only enhances the mechanical stability of the material, but also greatly expands the distribution of reactive active sites, providing a richer contact area for the catalytic reaction.

[0025] Figure 2 The XRD patterns of the prepared Co(OH)2, Co(OH)2@Ni-Mn LDHs and Co(OH)2@Ni-Co LDHs are shown in Figure 1. There are no other impurity peaks in the spectrum, indicating that the prepared active materials are of high purity.

[0026] Figure 3The LSV curves of Co(OH)2@Ni-Mn LDHs (a) and Co(OH)2@Ni-Co LDHs (b) electrode materials in 1 M KOH electrolyte. As can be seen from the figure, the peroxide potential of the material is significantly reduced after the composite Co(OH)2, which indicates that Co(OH)2 as a carrier promotes the expansion and growth of Ni-Mn LDHs and Ni-Co LDHs, avoiding their existence in a single aggregate state, thereby increasing the active sites.

[0027] Figure 4 The CV curves of the prepared Co(OH)2@Ni-Mn LDHs (a) and Co(OH)2@Ni-Co LDHs (b) electrode materials at a scan rate of 50 mV / s. As can be seen from the figure, an obvious oxidation peak can be observed in pure 1 M KOH electrolyte. When different additives are introduced into the electrolyte, polarization begins to appear earlier, and the order of polarization is EtOH, DMF and CH3OH.

[0028] Figure 5 LSV curves of the prepared Co(OH)2@Ni-Mn LDHs (a) and Co(OH)2@Ni-Co LDHs (b) electrode materials in different electrolytes. As can be seen from the figure, EOR shows the earliest starting point, followed by NOR and finally MOR; and compared with OER, the starting potentials of these oxidation reactions are significantly reduced. Among them, the average decrease in the peroxygen potential of Co(OH)2@Ni-Mn LDHs is 0.19, while the average decrease in the peroxygen potential of Co(OH)2@Ni-Co LDHs is 0.18. These results show that the prepared Co(OH)2@Ni-Mn LDHs and Co(OH)2@Ni-Co LDHs can significantly reduce the overpotential of the oxidation reaction and have good electrocatalytic activity.

[0029] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing a composite layered double metal hydroxide based on Co(OH)2, characterized in that: The following steps are involved: 1) Co(NO3)2·6H2O, NH4F and urea were stirred and dissolved in deionized water to form a uniform solution; 2) The solution obtained in step 1) is transferred to a stainless steel reactor lined with polytetrafluoroethylene, and clean nickel foam is placed therein for reaction, and then the nickel foam is taken out, washed, and dried to obtain Co(OH)2 / NF; 3) NiCl2·6H2O, metal salt, urea and hexamethylenetetramine are stirred and dissolved in deionized water to form a uniform solution; 4) The solution obtained in step 3) is transferred to a stainless steel reactor lined with polytetrafluoroethylene, and Co(OH)2 / NF is placed therein for hydrothermal reaction to obtain the composite layered double metal hydroxide based on Co(OH)2.

2. The composite layered double metal hydroxide based on Co(OH)2 according to claim 1, characterized in that: The molar ratio of Co(NO3)2·6H2O, NH4F and urea used in step 1) is 2:1:

4.

3. The composite layered double hydroxide based on Co(OH)2 according to claim 1, characterized in that: The reaction temperature in step 2) is 80°C and the reaction time is 12 hours.

4. The composite layered double hydroxide based on Co(OH)2 according to claim 1, characterized in that: The metal salt in step 3) is MnCl2·4H2O or CoCl2·6H2O.

5. The composite layered double hydroxide based on Co(OH)2 according to claim 1, characterized in that: The molar ratio of NiCl2·6H2O, metal salt, urea and hexamethylenetetramine used in step 3) is 1:1:2:

1.

6. The composite layered double hydroxide based on Co(OH)2 according to claim 1, characterized in that: The temperature of the hydrothermal reaction in step 4) is 100°C and the time is 10 hours.

7. Use of the composite layered double metal hydroxide prepared by the method of claim 1 as an anode electrode material.

8. The use according to claim 7, characterized in that: The anode electrode material is used in the anode oxidation reaction of ethanol, methanol or N,N-dimethylformamide.

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