Persulfate radical induced nickel-iron layered hydroxide catalytic material as well as preparation method and application thereof

Abstract

The invention discloses a preparation method of a persulfate-induced ferro-nickel layered hydroxide catalytic material, which comprises the following steps: preparing a precursor solution containing persulfate, the precursor solution containing persulfate comprises persulfate, nickel salt, iron salt, urea and ammonium fluoride; a self-supporting conductive substrate is placed in the precursor solution to be subjected to a hydrothermal reaction, and the persulfate radical induced ferronickel layered hydroxide catalytic material is obtained. The invention also discloses the persulfate-induced nickel-iron layered hydroxide catalytic material obtained by the preparation method and application of the persulfate-induced nickel-iron layered hydroxide catalytic material in an electrode material. According to the preparation method provided by the invention, direct synthesis of high intrinsic active species in the preparation process is realized, and a subsequent slow electrochemical activation reconstruction process is avoided; the prepared catalytic material has excellent electro-catalytic oxygen evolution performance.

Description

Technical Field

[0001] The invention belongs to the field of nano material technology and electrochemical energy conversion, and specifically relates to a persulfate-induced nickel-iron layered hydroxide catalytic material and a preparation method and application thereof. Background Art

[0002] In the field of electrochemical energy conversion, the oxygen evolution reaction (OER) is the anodic half-reaction of water splitting, and its efficient catalysis is crucial to improving the overall water splitting efficiency. Currently, noble metal oxides such as IrO2 and RuO2 are widely studied due to their excellent OER catalytic activity, but their high cost and resource scarcity limit large-scale commercial applications. Therefore, the development of low-cost, high-performance non-noble metal OER catalysts has become a research hotspot.

[0003] Nickel-iron layered hydroxide (NiFe LDH), as a type of non-precious metal catalyst, has attracted much attention due to its low cost, adjustable structure, and environmental friendliness. In the application process, NiFe LDH usually needs to reconstruct its surface structure through multiple cyclic voltammetry (CV) activation to show excellent performance. Its real active sites are high-oxidation state Ni and Fe after electrochemical activation and reconstruction. However, current research mainly focuses on strategies such as morphology regulation, heteroatom doping, and defect engineering to solve problems such as insufficient exposure of active sites and poor conductivity of NiFe LDH. For example, the Chinese patent with publication number CN118360618A discloses a method for preparing a highly active self-supporting alkaline oxygen evolution electrode, which uses Zn doping to prepare a NiFeZn LDH precursor, and removes Zn by strong alkali etching, thereby changing the morphology of conventional NiFe LDH and obtaining a nanosheet structure with a defect-rich surface to improve OER performance. These studies still have problems such as the need for a slow electrochemical activation process for the catalyst.

[0004] Effectively regulating nickel iron to a high oxidation state and directly synthesizing a highly active NiFe LDH catalyst is a major technical bottleneck in the development of its industrial application. Chinese patent publication number CN111686736A discloses a NiFe-LDH / NF three-dimensional self-supporting electrolytic water oxygen evolution catalyst containing highly active high-valent iron, which is prepared by a two-step hydrothermal and electrochemical method. Chinese patent publication number CN118771541A discloses a NiFeOOH@TiN-V heterostructure catalyst, which is prepared by plasma enhanced atomic layer deposition and has high equipment requirements. Therefore, the development of a NiFe LDH catalytic material with a simple process and direct synthesis of highly active species is of great significance to promoting the commercial application of water electrolysis hydrogen production technology. Summary of the invention

[0005] The present invention aims to provide a persulfate-induced nickel-iron layered hydroxide catalytic material, a preparation method and an application thereof; the preparation method provided by the present invention realizes the direct synthesis of highly intrinsically active species during the preparation process, avoiding the subsequent slow electrochemical activation reconstruction process; the catalytic material prepared by the present invention has excellent electrocatalytic oxygen evolution performance.

[0006] The present invention provides the following technical solutions:

[0007] The first aspect of the present invention provides a method for preparing a persulfate-induced nickel-iron layered hydroxide catalytic material, the preparation method comprising: preparing a persulfate-containing precursor solution, the persulfate-containing precursor solution comprising persulfate, nickel salt, iron salt, urea and ammonium fluoride; placing a self-supporting conductive substrate in the precursor solution for a hydrothermal reaction to obtain a persulfate-induced nickel-iron layered hydroxide catalytic material.

[0008] The invention adopts persulfate to directly regulate the high intrinsic active sites of nickel-iron layered hydroxide in a hydrothermal system, and realizes the in-situ growth of modified nickel-iron layered hydroxide on a self-supporting conductive substrate through a simple one-step hydrothermal method, thereby enriching the synthesis and preparation technology of nickel-iron layered hydroxide, overcoming the problems of slow electrochemical activation process and poor activity of nickel-iron layered hydroxide (NiFe LDH) in the prior art, and at the same time, the simple preparation process also greatly broadens its commercial application value.

[0009] Preferably, the persulfate is selected from at least one of ammonium persulfate or sodium persulfate;

[0010] Preferably, the molar concentration of persulfate in the precursor solution is 0.01 mol / L to 0.1 mol / L;

[0011] Preferably, the nickel salt is selected from but not limited to nickel chloride, nickel sulfate, and nickel nitrate;

[0012] Preferably, the molar concentration of nickel in the precursor solution is 0.02 mol / L to 0.05 mol / L;

[0013] Preferably, the iron salt is selected from but not limited to ferric chloride, ferric sulfate, and ferric nitrate;

[0014] Preferably, the molar concentration of the iron element in the precursor solution is 0.001 mol / L to 0.05 mol / L;

[0015] Preferably, the molar concentration of the urea is 0.1 mol / L to 0.5 mol / L;

[0016] Preferably, the molar concentration of ammonium fluoride is 0.05 mol / L to 0.2 mol / L;

[0017] Preferably, the hydrothermal reaction temperature is 100-150° C. and the reaction time is 5-20 h.

[0018] The present invention limits the above concentration range and reaction temperature and time, so as to realize the direct synthesis of species with high intrinsic activity.

[0019] Further preferably, the molar concentration of the persulfate is 0.03 mol / L to 0.05 mol / L, the molar concentration of the nickel element is 0.035 mol / L, the molar concentration of the iron element is 0.01 mol / L, the molar concentration of the urea is 0.2 mol / L, and the molar concentration of the ammonium fluoride is 0.1 mol / L. The present invention improves the electrocatalytic oxygen evolution performance of the material by further regulating the concentration of the precursor solution.

[0020] Further preferably, the hydrothermal reaction temperature is 120-140° C., which is beneficial to improving the electrocatalytic oxygen evolution performance of the material.

[0021] The self-supporting conductive substrate is selected from at least one of nickel foam, nickel iron foam, copper foam, nickel mesh, nickel felt, iron mesh, iron felt, nickel iron mesh, nickel iron felt, carbon paper, graphite, carbon cloth or carbon felt.

[0022] The second aspect of the present invention provides a persulfate-induced nickel-iron layered hydroxide catalytic material obtained by the above preparation method, comprising a self-supporting conductive substrate and persulfate-induced nickel-iron layered hydroxide nanosheets grown in situ on the surface of the substrate.

[0023] The present invention provides a persulfate-induced nickel-iron layered hydroxide catalytic material. The persulfate optimizes the electronic structure of the nickel-iron layered hydroxide, promoting the conversion of nickel / iron into highly intrinsically active species in a high oxidation state. The self-supporting conductive substrate improves the conductivity of the material. The nanosheet staggered array morphology increases the exposed specific surface area, which can accelerate the charge transfer rate in the catalytic process and the adsorption and desorption of gases. When used as an electrode material, it can show excellent electrochemical performance.

[0024] The nickel-iron layered hydroxide comprises nickel, iron and sulfur elements, wherein the nickel and iron elements are both in high oxidation states: the valence state of the nickel element is greater than +2, the valence state of the iron element is greater than +3, and the valence state of the sulfur element is between +4 and +6.

[0025] The molar ratio of nickel, iron and sulfur in the nickel-iron layered hydroxide is (0.70-0.80):(0.20-0.25):(0.01-0.05). The present invention adjusts the molar ratio of the three elements to make the nickel-iron layered hydroxide have excellent electrocatalytic oxygen evolution performance.

[0026] Preferably, the molar ratio of nickel, iron and sulfur in the nickel-iron layered hydroxide is (0.72-0.75): (0.22-0.25): 0.03. The nickel-iron layered hydroxide with the above molar ratio has better electrocatalytic oxygen evolution performance.

[0027] The third aspect of the present invention provides an application of the above-mentioned persulfate-induced nickel-iron layered hydroxide as a catalytic material for oxygen evolution reaction in electrolysis of water; further, an application directly as an oxygen evolution reaction in electrolysis of water (as an anode material) under alkaline conditions.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention uses a simple one-step hydrothermal method to modify nickel-iron layered hydroxide using persulfate induction. This method not only simplifies the process flow of catalyst preparation, but also realizes the direct synthesis of highly intrinsically active species during the preparation process, avoids the subsequent slow electrochemical activation reconstruction process, and greatly improves the process efficiency.

[0030] 2. The catalytic material provided by the present invention has excellent electrocatalytic oxygen evolution performance. Through the induction of persulfate, nickel and iron species are converted to high oxidation states, which enhances the intrinsic activity of nickel-iron layered hydroxides, thereby effectively reducing the reaction overpotential and improving the energy conversion efficiency.

[0031] 3. The catalytic material provided by the present invention is in situ grown on a self-supporting conductive substrate (such as nickel foam) and can be directly used as a working electrode without the need for secondary preparation using polymer adhesives that are not conducive to conductivity. This not only further improves the process efficiency, but also further enhances the conductivity and stability of the catalyst and improves its electrocatalytic performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a scanning electron microscope image of the persulfate-induced nickel-iron layered hydroxide catalytic material prepared in Example 1.

[0033] Figure 2 It is the full X-ray photoelectron spectrum of the persulfate-induced nickel-iron layered hydroxide catalytic material prepared in Example 1-4.

[0034] Figure 3 It is a detailed X-ray photoelectron spectrum of sulfur element in the persulfate-induced nickel-iron layered hydroxide catalytic material prepared in Example 1 and the nickel-iron layered hydroxide catalytic material prepared in Comparative Example 1.

[0035] Figure 4It is a detailed X-ray photoelectron spectrum of nickel element in the persulfate-induced nickel-iron layered hydroxide catalytic material prepared in Example 1 and the nickel-iron layered hydroxide catalytic material prepared in Comparative Example 1.

[0036] Figure 5 It is a detailed X-ray photoelectron spectrum of iron element in the persulfate-induced nickel-iron layered hydroxide catalytic material prepared in Example 1 and the nickel-iron layered hydroxide catalytic material prepared in Comparative Example 1.

[0037] Figure 6 It is a linear sweep voltammetric performance test graph of the persulfate-induced nickel-iron layered hydroxide catalytic material prepared in Examples 1-4, the nickel-iron layered hydroxide nanosheet catalytic material prepared in Comparative Example 1, and the pure nickel foam material prepared in Comparative Example 2 without undergoing an electrochemical activation process.

[0038] Figure 7 It is a comparison chart of linear sweep voltammetric performance tests of the persulfate-induced nickel-iron layered hydroxide catalytic material prepared in Example 1 and the nickel-iron layered hydroxide nanosheet catalytic material prepared in Comparative Example 1 before and after electrochemical activation. DETAILED DESCRIPTION

[0039] The present invention is further described below in conjunction with specific embodiments.

[0040] Example 1

[0041] (1) 0.001 mol of ammonium persulfate, 0.0007 mol of nickel nitrate hexahydrate, 0.0002 mol of ferric nitrate nonahydrate, 0.004 mol of urea and 0.002 mol of ammonium fluoride were dissolved in 20 mL of deionized water and stirred thoroughly to obtain a uniform precursor solution.

[0042] (2) The homogeneously mixed precursor solution was transferred to a 50 mL polytetrafluoroethylene reactor, and the pretreated nickel foam was added, and the mixture was hydrothermally reacted at 120° C. for 12 h. After being naturally cooled to room temperature, the mixture was taken out, repeatedly washed with deionized water, and then dried in a vacuum drying oven at 50° C. for 8 h to obtain a persulfate-induced nickel-iron layered hydroxide catalytic material, which was recorded as Example 1.

[0043] Example 2

[0044] (1) 0.0006 mol of ammonium persulfate, 0.0007 mol of nickel nitrate hexahydrate, 0.0002 mol of ferric nitrate nonahydrate, 0.004 mol of urea and 0.002 mol of ammonium fluoride were dissolved in 20 mL of deionized water and stirred thoroughly to obtain a uniform precursor solution.

[0045] (2) The homogeneously mixed precursor solution was transferred to a 50 mL polytetrafluoroethylene reactor, and the pretreated nickel foam was added, and the mixture was hydrothermally reacted at 120° C. for 12 h. After being naturally cooled to room temperature, the mixture was taken out, repeatedly washed with deionized water, and then dried in a vacuum drying oven at 50° C. for 8 h to obtain a persulfate-induced nickel-iron layered hydroxide catalytic material, which was recorded as Example 2.

[0046] Example 3

[0047] (1) 0.001 mol of ammonium persulfate, 0.0007 mol of nickel nitrate hexahydrate, 0.0002 mol of ferric nitrate nonahydrate, 0.004 mol of urea and 0.002 mol of ammonium fluoride were dissolved in 20 mL of deionized water and stirred thoroughly to obtain a uniform precursor solution.

[0048] (2) The homogeneously mixed precursor solution was transferred to a 50 mL polytetrafluoroethylene reactor, and the pretreated nickel foam was added, and the mixture was hydrothermally reacted at 140° C. for 12 h. After being naturally cooled to room temperature, the mixture was taken out, repeatedly washed with deionized water, and then dried in a vacuum drying oven at 50° C. for 8 h to obtain a persulfate-induced nickel-iron layered hydroxide catalytic material, which was recorded as Example 3.

[0049] Example 4

[0050] (1) 0.001 mol of sodium persulfate, 0.0007 mol of nickel nitrate hexahydrate, 0.0002 mol of ferric nitrate nonahydrate, 0.004 mol of urea and 0.002 mol of ammonium fluoride were dissolved in 20 mL of deionized water and stirred thoroughly to obtain a uniform precursor solution.

[0051] (2) The homogeneously mixed precursor solution was transferred to a 50 mL polytetrafluoroethylene reactor, and the pretreated nickel foam was added, and the mixture was hydrothermally reacted at 120° C. for 12 h. After being naturally cooled to room temperature, the mixture was taken out, repeatedly washed with deionized water, and then dried in a vacuum drying oven at 50° C. for 8 h to obtain a persulfate-induced nickel-iron layered hydroxide catalytic material, which was recorded as Example 4.

[0052] Comparative Example 1

[0053] (1) 0.0007 mol of nickel nitrate hexahydrate, 0.0002 mol of ferric nitrate nonahydrate, 0.004 mol of urea and 0.002 mol of ammonium fluoride were dissolved in 20 mL of deionized water and stirred thoroughly to obtain a uniform precursor solution free of persulfate.

[0054] (2) The homogeneously mixed precursor solution was transferred to a 50 mL polytetrafluoroethylene reactor, and the pretreated nickel foam was added, and the mixture was hydrothermally reacted at 120° C. for 12 h. After being naturally cooled to room temperature, the mixture was taken out, repeatedly washed with deionized water, and then dried in a vacuum drying oven at 50° C. for 8 h to obtain a conventional nickel-iron layered hydroxide catalytic material, which was recorded as Comparative Example 1.

[0055] Comparative Example 2

[0056] Pretreated nickel foam: The nickel foam was cut into 3*1 cm sheets, and ultrasonically cleaned in acetone solution, 1 mol dilute hydrochloric acid solution, deionized water, and ethanol solution for 15 min each, and then dried in a vacuum drying oven to obtain pretreated nickel foam, which is recorded as Comparative Example 2.

[0057] Material structure analysis:

[0058] Figure 1 is a scanning electron microscope image of Example 1. Figure 1 It can be seen that these nickel-iron layered hydroxide nanosheets are uniformly and densely loaded on the nickel foam substrate skeleton, indicating that the self-supporting electrode material of nickel-iron layered hydroxide was successfully prepared.

[0059] Figure 2 It is the full spectrum of X-ray photoelectron spectra of Examples 1-4. Figure 2 It shows that there is sulfur in the materials of Examples 1-4. According to the analysis of the full spectrum results of X-ray photoelectron spectroscopy, the molar ratio of nickel, iron and sulfur in the nickel-iron layered hydroxide prepared in Example 1 is about 0.75:0.22:0.03, the molar ratio of nickel, iron and sulfur in the nickel-iron layered hydroxide prepared in Example 2 is about 0.75:0.22:0.03, the molar ratio of nickel, iron and sulfur in the nickel-iron layered hydroxide prepared in Example 3 is about 0.73:0.24:0.03, and the molar ratio of nickel, iron and sulfur in the nickel-iron layered hydroxide prepared in Example 4 is about 0.72:0.25:0.03.

[0060] Figure 3 The X-ray photoelectron spectrum of sulfur in Example 1 and Comparative Example 1 is detailed. Figure 3 It can be seen that there is no sulfur peak in Comparative Example 1, and a sulfur peak is detected at 167.6 eV in Example 1, and the valence state of sulfur is between +4 and +6.

[0061] Figure 4 The X-ray photoelectron spectroscopy fine spectra of nickel element in Example 1 and Comparative Example 1 are shown in FIG. Figure 5 The X-ray photoelectron spectroscopy of the iron element in Example 1 and Comparative Example 1 is detailed. Figure 4 and Figure 5It can be seen that after sulfate induction, the nickel and iron in the nickel-iron layered hydroxide catalytic material are shifted to high binding energy. Therefore, the Ni>+2 and Fe>+3 in the nickel-iron layered hydroxide catalytic material prepared in Example 1 proves the formation of highly active high-valent nickel and iron species.

[0062] The above results show that compared with traditional nickel-iron layered hydroxide catalytic materials, persulfate-induced nickel-iron layered hydroxide catalytic materials were successfully prepared and modified. Their characteristics are that nickel and iron exist in highly active high-valent states, the valence state of sulfur element is between +4 and +6, and the molar ratio between nickel element, iron element and sulfur element is approximately 0.75:0.22:0.03.

[0063] Oxygen evolution performance test and analysis:

[0064] The catalysts prepared in Examples 1-4 and Comparative Examples 1-2 were used as working electrodes for electrochemical performance tests. The electrochemical performance evaluation used a three-electrode system, with a mercury oxide electrode as a reference electrode, a graphite rod electrode as a counter electrode, and a 1.0 M potassium hydroxide solution as an electrolyte solution. A linear voltammetric scan test was performed in a CHI 760e electrochemical workstation with a voltage range of 0.2 to 1.0 V (vs. Hg / HgO) and a scan rate of 5.0 mV / s.

[0065] Figure 6 The linear voltammetric scanning diagrams of the persulfate-induced nickel-iron layered hydroxide catalytic materials of Examples 1-4, the unmodified nickel-iron layered hydroxide catalytic materials of Comparative Example 1, and the nickel foam substrate material of Comparative Example 2 without undergoing the electrochemical activation process. Figure 6 It can be seen that the performance of the catalysts prepared in Examples 1-4 is better than that of the catalysts prepared in Comparative Examples 1-2, indicating that the persulfate induction can improve the intrinsic activity of nickel-iron layered hydroxide. Figure 6 It can also be found that the type and concentration of persulfate and the hydrothermal temperature in the preparation process of Examples 1-4 have an impact on the material properties, among which the electrocatalytic oxygen evolution performance of the material under the synthesis conditions of Example 1 is the best.

[0066] Figure 7 The linear voltammetric scanning diagrams of the persulfate-induced nickel-iron layered hydroxide catalyst material of Example 1 and the unmodified nickel-iron layered hydroxide catalyst material of Comparative Example 1 before and after the electrochemical activation process. The electrochemical activation process is specifically to perform cyclic voltammetric scanning activation on the material, with a scanning voltage range of 0.2 to 1.0 V (vs. Hg / HgO), a scanning speed of 50.0 mV / s, and a scanning number of 20 circles. Figure 7It can be seen that the material prepared in Comparative Example 1 needs to undergo an electrochemical activation process to improve its performance, while the material prepared in Example 1 can directly achieve excellent electrocatalytic performance. After undergoing the electrochemical activation process, the performance of the material prepared in Example 1 is still better than that of the material prepared in Comparative Example 1, showing excellent electrocatalytic oxygen evolution performance and stability.

[0067] In summary, the persulfate-induced nickel-iron layered hydroxide catalytic material provided by the present invention has a simple synthesis process, has high intrinsic electrocatalytic oxygen evolution activity without undergoing a slow electrochemical activation process, and can be directly used as an electrocatalytic oxygen evolution anode material in the field of water electrolysis.

[0068] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing a persulfate-induced nickel-iron layered hydroxide catalyst material, characterized in that: The preparation method comprises: preparing a precursor solution containing persulfate, wherein the precursor solution containing persulfate comprises persulfate, nickel salt, iron salt, urea and ammonium fluoride; placing a self-supporting conductive substrate in the precursor solution for hydrothermal reaction to obtain a persulfate-induced nickel-iron layered hydroxide catalytic material.

2. The preparation method according to claim 1, characterized in that: The persulfate is selected from at least one of ammonium persulfate or sodium persulfate.

3. The preparation method according to claim 1, characterized in that: In the precursor solution, the molar concentration of persulfate is 0.01mol / L to 0.1mol / L, the molar concentration of nickel element is 0.02mol / L to 0.05mol / L, the molar concentration of iron element is 0.001mol / L to 0.05mol / L, the molar concentration of urea is 0.1mol / L to 0.5mol / L, and the molar concentration of ammonium fluoride is 0.05mol / L to 0.2mol / L.

4. The preparation method according to claim 1, characterized in that: The temperature of the hydrothermal reaction is 100-150° C., and the time is 5-20 hours.

5. The preparation method according to claim 1, characterized in that: The self-supporting conductive substrate is selected from at least one of nickel foam, nickel iron foam, copper foam, nickel mesh, nickel felt, iron mesh, iron felt, nickel iron mesh, nickel iron felt, carbon paper, graphite, carbon cloth or carbon felt.

6. A persulfate-induced nickel-iron layered hydroxide catalytic material obtained by the preparation method according to any one of claims 1 to 5, characterized in that: The catalytic material comprises a self-supporting conductive substrate and nickel-iron layered hydroxide nanosheets induced by persulfate radicals in-situ grown on the surface of the substrate.

7. The persulfate-induced nickel-iron layered hydroxide catalytic material according to claim 6, characterized in that: The nickel-iron layered hydroxide comprises nickel, iron and sulfur elements, wherein the nickel and iron elements are both in high oxidation states: the valence state of the nickel element is greater than +2, the valence state of the iron element is greater than +3, and the valence state of the sulfur element is between +4 and +6.

8. The persulfate-induced nickel-iron layered hydroxide catalytic material according to claim 6, characterized in that: The molar ratio of nickel element, iron element and sulfur element in the nickel-iron layered hydroxide is (0.70-0.80):(0.20-0.25):(0.01-0.05).

9. Use of the persulfate-induced nickel-iron layered hydroxide catalyst material according to claim 6 in electrode materials.

10. The use according to claim 9, characterized in that: The persulfate-induced nickel-iron layered hydroxide catalytic material is directly used as an anode material for electrolyzing water and evolving oxygen, without the need for an electrochemical activation process.

Images