Defect-rich S-FeAl LDHet catalyst and preparation method and application thereof

Abstract

The invention relates to the technical field of sulfur-doped iron-aluminum bimetallic materials, in particular to a defect-rich S-FeAl LDHet catalyst and a preparation method and application thereof. A non-noble metal electrocatalyst S-FeAl LDH growing on a foamed nickel substrate in situ is synthesized through a hydrothermal method, then CV selective etching of Al sites is conducted on the catalyst S-FeAl LDH under the alkaline condition, the morphology and the electronic structure of the catalyst are regulated and controlled, and the defect-rich S-FeAl LDHet catalyst is formed. According to the invention, Al etching is carried out on the electrochemical window of the OER, so that the morphology of the catalyst does not change, and the mechanical strength of the catalyst is also retained. According to the method for constructing the defect by electrochemical in-situ etching of Al, the catalytic performance can be intuitively obtained through a CV curve. The optimal etching amount is determined according to the number of CV etching turns, and complete exposure of active sites is ensured. Meanwhile, the conductivity of the catalyst can also be optimized.

Description

Technical Field

[0001] The present invention relates to the technical field of sulfur-doped iron-aluminum bimetallic materials, and in particular to a defect-rich S-FeAlLDH et Catalyst and its preparation method and application. Background Art

[0002] The oxygen evolution reaction (OER) is a core reaction in the electrolysis of water to produce hydrogen, which determines the efficiency of hydrogen production. Through electrocatalytic water splitting, discontinuous renewable energy (such as solar and wind energy) can be converted into clean hydrogen, thereby realizing large-scale and stable storage of hydrogen energy. In recent years, a large number of non-precious metal water oxidation catalytic materials have been reported, including transition metal oxides, hydroxides, sulfides, phosphides, and metal-organic framework materials. These materials are expected to replace precious metal-based catalysts due to their unique electronic structure and relatively high crustal reserves. Catalyst design requires excellent catalytic activity and long-term stability in the OER process. Therefore, its morphology design, active site construction, and electronic structure regulation are hot issues that scientific researchers are concerned about.

[0003] In electrocatalytic OER, defect engineering mainly includes the introduction of point defects (such as vacancies, substitutional atoms, etc.), line defects (such as dislocations), and surface defects (such as grain boundaries). Introducing defect engineering in the design of OER electrocatalysts has great advantages. First, improving electrocatalytic activity: by introducing defects, the electronic structure and physicochemical properties of the catalyst can be changed, the activation energy of the reaction can be reduced, and thus its catalytic activity can be optimized. Second, improving the stability of the catalyst: by forming a stable defect structure, the catalyst can be prevented from agglomerating or falling off during the reaction, thereby increasing its service life. Third, changing the reaction path and regulating the OER reaction mechanism.

[0004] Recently, researchers have used chemical reagents such as strong acids, strong bases or oxidants to etch catalysts to introduce different types of defects. This method is simple and easy, but it may cause certain damage to the structure and performance of the catalyst. In addition, defects can also be introduced on the surface of the catalyst through physical vapor deposition technology. For example, defects such as substitutional atoms or vacancies can be introduced into the catalyst through methods such as ion implantation or sputtering. This method can achieve precise control of defects, but the cost is relatively high. These two strategies for constructing defects have both advantages and disadvantages. Therefore, there is an urgent need to develop a stable and low-cost defect construction method. Summary of the invention

[0005] The present invention provides a defect-rich S-FeAl LDH to solve the technical problems that the current method of introducing defects on the catalyst surface is high in cost or easily causes certain damage to the structure and performance of the catalyst. etPreparation method of catalyst. The present invention uses an electrochemical etching scheme to construct defects, which can greatly control the cost problem and retain the original structure of the catalyst. Excellent catalytic performance and excellent stability can be obtained through a simple preparation process.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a defect-rich S-FeAl LDH et The preparation method of the catalyst is to synthesize the non-precious metal electrocatalyst S-FeAlLDH grown in situ on the nickel foam substrate by a hydrothermal method, and then the catalyst S-FeAl LDH is subjected to CV selective etching of the Al site under alkaline conditions to regulate the morphology and electronic structure of the catalyst to form a defect-rich S-FeAl LDH et catalyst.

[0007] As a further limitation of the technical solution of the present invention, the preparation method specifically comprises the following steps: (1) Treatment of nickel foam NF The NF was ultrasonicated in 0.1 mol / L HCl, acetone, anhydrous ethanol and deionized water for 10 min in sequence, and then dried in a vacuum drying oven at 60 °C. The dried NF was taken out and sealed for later use; (2) Synthesis of S-FeAl LDH catalyst Dissolve ferric nitrate nonahydrate, aluminum nitrate nonahydrate, ammonium fluoride and urea in deionized water and stir for 30 min, then add sodium thiosulfate and H2O2 and stir for 20 min; finally, put the mixed solution and the NF substrate treated in step (1) into a reactor for reaction. After the reaction, wash with deionized water and anhydrous ethanol in turn, and dry in a vacuum drying oven to obtain S-FeAl LDH catalyst.

[0008] (3) Defect-rich S-FeAl LDH et Catalyst synthesis In KOH electrolyte, the S-FeAl LDH prepared in step (2) was used as the working electrode, the graphite rod was used as the counter electrode, and the Hg / HgO electrode was used as the reference electrode. Cyclic voltammetry was performed in the potential range of 0.2-0.7 V for 20 cycles at a scan rate of 20 mV s -1 Then, it was rinsed with deionized water and dried in a vacuum oven to obtain defect-rich S-FeAl LDH et catalyst.

[0009] One of the problems faced in solving the technical problem of the present invention is that for designing catalysts with defects, it is necessary to introduce substances that can construct defects. Amphoteric oxide Al2O3 is one of the substances selected by the present invention to assist in the synthesis of catalysts. The Al2O3 site is etched to obtain the desired defect structure. Layered double hydroxides are selected and heteroatom doped as Al2O3 carriers to synthesize S-doped FeAl layered double hydroxide (S-FeAl LDH) catalysts. It can exhibit high activity and stability in the OER process.

[0010] One of the problems faced in solving the technical problem of the present invention is: defect construction method. The Al site etching scheme needs to avoid chemical etching with strong acids and strong bases, because this method has too many uncontrollable factors, and it is impossible to guarantee the etching degree of the Al site and whether it will destroy the intrinsic structure of the catalyst. Therefore, an electrochemical method is adopted to perform CV etching in the OER potential range. This electrochemical etching method can observe the changes in the electrocatalytic OER performance of the catalyst during the etching process. When the optimal OER performance is achieved, the active sites are fully exposed and the catalytic performance is greatly improved.

[0011] As a further limitation of the technical solution of the present invention, in step (1), the size of the NF is 2 × 3 cm 2 .

[0012] As a further limitation of the technical solution of the present invention, in step (2), the mass ratio of ferric nitrate nonahydrate, aluminum nitrate nonahydrate, ammonium fluoride, urea and sodium thiosulfate is 6.87:11.49:36:9.1:3-7.

[0013] As a further limitation of the technical solution of the present invention, the mass volume ratio of sodium thiosulfate, deionized water and H2O2 in step (2) is 3-7 mg: 3 mL: 20 µL.

[0014] As a further limitation of the technical solution of the present invention, it is characterized in that the reaction conditions in the reaction kettle in step (2) are at a temperature of 100-140 o C for 10-14 h.

[0015] As a further limitation of the technical solution of the present invention, the concentration of the KOH electrolyte in step (3) is 1 mol / L, and the size of the S-FeAl LDH as the working electrode is 1 cm × 1 cm -2 .

[0016] The present invention also provides defect-rich S-FeAl LDH obtained by the above preparation method et catalyst.

[0017] In addition, the present invention also provides the above-mentioned defect-rich S-FeAl LDHet Application of catalysts in metal-air batteries and oxygen evolution catalytic reactions at water electrolysis oxidation electrodes.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The design inspiration of the catalyst of the present invention comes from the fact that the hydroxide or oxide of Al can be dissolved in acid or alkali. Therefore, the Al element is introduced into the catalyst and Al2O3 is generated by a hydrothermal method. Since the electrolyte of OER is a strong base, Al2O3 will be continuously etched as OER proceeds, and finally Al defects will be constructed. The electrochemical method is used to construct Al defects, which has the following advantages: (1) Avoid complex preparation processes such as physical vapor deposition technology and high production costs.

[0019] (2) Avoid using chemical reagents such as strong acids, strong bases or oxidants to etch the catalyst and destroy the catalyst structure; by performing Al etching in the electrochemical window of OER, the catalyst morphology can remain unchanged and the mechanical strength of the catalyst can be retained.

[0020] (3) The method of electrochemical in-situ etching of Al to construct defects can intuitively obtain the catalytic performance through the CV curve. That is, the optimal etching amount is determined by the number of CV etching cycles to ensure that the active sites are completely exposed. At the same time, the conductivity of the catalyst can also be optimized. The defect-rich S-FeAl LDH prepared by the present invention et The catalyst showed good application prospects in the process of electrocatalytic oxygen evolution. The etching of Al2O3 species generated a large number of defect vacancies, which fully exposed the active sites, greatly increased the electrochemical active surface area, and improved the intrinsic activity of S-FeAl LDH. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 For FeAl LDH, S-Fe LDH, S-FeAl LDH and S-FeAl LDH et Scanning electron microscope image of .

[0022] Figure 2 LSV diagrams of different catalysts in 1 mol / L KOH electrolyte.

[0023] Figure 3 Overpotential diagrams of different catalysts.

[0024] Figure 4 Tafel slope plots of different catalysts.

[0025] Figure 5 C of different catalysts dl picture.

[0026] Figure 6 Electrochemical impedance spectroscopy of different catalysts.

[0027] Figure 7 S-FeAl LDH et Timing curve of the catalyst in 1 mol / L KOH electrolyte. DETAILED DESCRIPTION

[0028] The present invention is further described below in conjunction with specific embodiments. Example 1

[0029] A defect-rich S-FeAl LDH et Preparation method of catalyst: (1) Treatment of nickel foam (NF) NF (2 × 3 cm 2 ) were ultrasonically treated in 0.1 mol / L HCl, acetone, anhydrous ethanol and deionized water for 10 min respectively, and then dried in a vacuum drying oven at 60 °C. The dried NF was taken out and sealed for later use.

[0030] (2) Synthesis of S-FeAl LDH catalyst 34.35 mg of ferric nitrate nonahydrate, 57.45 mg of aluminum nitrate nonahydrate, 180 mg of ammonium fluoride, and 44.5 mg of urea were dissolved in 15 mL of deionized water and stirred for 30 min. Then 25 mg of sodium thiosulfate and 100 µL of H2O2 were added and stirred for 20 min. Finally, the above solution and the NF substrate were placed in a 20 mL reactor and heated at 120 °C. o C for 12 h. After the reaction, the catalyst was washed with deionized water and anhydrous ethanol in turn and dried in a vacuum drying oven. The obtained catalyst was recorded as S-FeAl LDH.

[0031] Note: Screening of synthesis conditions of S-FeAl LDH catalyst. The mass of Na2S2O3 (15 mg and 35 mg), the mass ratio of ferric nitrate nonahydrate to aluminum nitrate nonahydrate (1:2 and 2:1), the reaction temperature (100 o C and 140 o C), reaction time (10 h and 14 h), and the same method was used to prepare the comparative catalyst, and the LSV curve of the oxygen evolution reaction was measured to select the optimal precursor synthesis conditions.

[0032] (3) Defect-rich S-FeAl LDH et Catalyst synthesis The S-FeAl LDH (1 cm × 1 cm -2) as the working electrode, graphite rod as the counter electrode, and Hg / HgO electrode as the reference electrode were scanned 20 times in the potential range of 0.2-0.7 V by cyclic voltammetry at a scan rate of 20 mV s -1 Then rinse with deionized water, put into a vacuum drying oven to dry, and the prepared catalyst is recorded as S-FeAl LDH et .

[0033] Scanning electron microscopy and electrochemical tests were performed on the defect-rich catalyst prepared in this example, and the structure is as follows: FeAl LDH, S-Fe LDH, S-FeAl LDH and S-FeAl LDH were studied by scanning electron microscopy (SEM). et The microscopic morphology, such as Figure 1 ad shown. FeAl LDH, S-Fe LDH, S-FeAl LDH and S-FeAl LDH et The SEM images of the NF substrates show that many vertical nanosheet arrays are in situ grown on the NF substrate, which will provide more active sites for the oxygen evolution reaction. The surface of FeAlLDH nanosheets is relatively rough and has many small particles attached, while S-Fe LDH, S-FeAl LDH and S-FeAl LDH et The surface of the nanosheets is relatively smooth, indicating that the introduction of S element is conducive to the orderly growth of the catalyst to form a smooth surface. The electrochemical etching scheme makes the catalyst morphology intact without any change.

[0034] The non-precious metal electrocatalyst S-FeAl LDH grown in situ on nickel foam substrate was successfully synthesized through hydrothermal reaction and subsequent electrochemical etching. et . It has shown good application prospects in the process of electrocatalytic oxygen evolution. The etching of Al2O3 species generates a large number of defect vacancies, which fully exposes the active sites, greatly increases the electrochemical active surface area, and improves the intrinsic activity of S-FeAl LDH. Electrochemical testing was used to evaluate the S-FeAl LDH et The electrocatalytic oxygen evolution activity and stability of Figure 2-7 As shown, at 100 mA cm -2 The overpotential of oxygen evolution reaction is only 271 mV at the current density of 1.37 V, and it can run stably for 50 h at this current density, showing that S-FeAl LDH etThe catalyst has excellent electrocatalytic oxygen evolution performance and long-term stability. This study demonstrates the great potential of defect-rich layered double hydroxide materials as electrocatalysts to replace precious metal oxides for efficient water electrolysis, and proves that the defect-rich catalyst synthesized by electrochemical etching has excellent electrocatalytic oxygen evolution activity and good stability in alkaline media. The results emphasize the importance of defects formed by electrochemical etching in the development of electrocatalysts.

Claims

1. A defect-rich S-FeAl LDH et The method for preparing a catalyst is characterized in that: The non-precious metal electrocatalyst S-FeAl LDH grown in situ on a nickel foam substrate was synthesized by a hydrothermal method. Then, the catalyst S-FeAl LDH was subjected to CV selective etching of the Al site under alkaline conditions to regulate the morphology and electronic structure of the catalyst to form a defect-rich S-FeAl LDH. et catalyst.

2. A defect-rich S-FeAl LDH according to claim 1 et The method for preparing a catalyst is characterized in that: The following steps are involved: (1) Treatment of nickel foam NF The NF was ultrasonicated in 0.1 mol / L HCl, acetone, anhydrous ethanol and deionized water for 10 min in sequence, and then dried in a vacuum drying oven at 60 °C. The dried NF was taken out and sealed for later use; (2) Synthesis of S-FeAl LDH catalyst Dissolve ferric nitrate nonahydrate, aluminum nitrate nonahydrate, ammonium fluoride and urea in deionized water and stir for 30 min, then add sodium thiosulfate and H2O2 and stir for 20 min; finally, put the mixed solution and the NF substrate treated in step (1) into a reactor for reaction, and after the reaction, wash with deionized water and anhydrous ethanol in turn, and put into a vacuum drying oven for drying to obtain S-FeAl LDH catalyst; (3) Defect-rich S-FeAl LDH et Catalyst synthesis In KOH electrolyte, the S-FeAl LDH prepared in step (2) was used as the working electrode, the graphite rod was used as the counter electrode, and the Hg / HgO electrode was used as the reference electrode. Cyclic voltammetry was performed in the potential range of 0.2-0.7 V for 20 cycles at a scan rate of 20 mVs -1 Then, it was rinsed with deionized water and dried in a vacuum oven to obtain defect-rich S-FeAl LDH et catalyst.

3. A defect-rich S-FeAl LDH according to claim 2 et The method for preparing a catalyst is characterized in that: Step (1) The size of NF is 2 × 3 cm 2 .

4. A defect-rich S-FeAl LDH according to claim 2 et The method for preparing a catalyst is characterized in that: In step (2), the mass ratio of ferric nitrate nonahydrate, aluminum nitrate nonahydrate, ammonium fluoride, urea and sodium thiosulfate is 6.87:11.49:36:9.1:3-7.

5. A defect-rich S-FeAl LDH according to claim 3 et The method for preparing a catalyst is characterized in that: The mass volume ratio of sodium thiosulfate, deionized water and H2O2 in step (2) is 3-7 mg: 3 mL: 20 µL.

6. A defect-rich S-FeAl LDH according to claim 2 et The method for preparing a catalyst is characterized in that: The reaction conditions in the reactor in step (2) are as follows: o C for 10-14 h.

7. A defect-rich S-FeAl LDH according to claim 2 et The method for preparing a catalyst is characterized in that: Step (3) The concentration of KOH electrolyte is 1 mol / L, and the size of S-FeAl LDH as working electrode is 1 cm × 1 cm -2 .

8. Defect-rich S-FeAl LDH obtained by the preparation method according to any one of claims 1 to 6 et catalyst.

9. The defect-rich S-FeAl LDH according to claim 7 et Application of catalysts in metal-air batteries and oxygen evolution catalytic reactions at water electrolysis oxidation electrodes.

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