Preparation method and application of a CoNi-LDH catalyst

Abstract

The application discloses a preparation method of in-situ electrodeposition growth of CoNi-LDH nanosheet catalyst on a titanium oxide sheet substrate and application thereof. Layered double hydroxide (LDH) is a kind of two-dimensional layered anion intercalation clay mineral, and due to the fact that the layered double hydroxide is rich in hydroxyl, has adjustable surface electronic structure and alkalinity and coordination unsaturated active sites, the layered double hydroxide shows great application prospect in numerous catalysts. Based on this, the application utilizes a titanium sheet as a carrier, firstly carries out oxidation and annealing on the titanium sheet, then loads CoNi-LDH nanosheets on the titanium sheet substrate after oxidation through an electrodeposition method, and directly uses the titanium sheet as a cathode for electrocatalytic reduction of NO2 ‑ Ammonia is synthesized, and good effects are obtained.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial synthesis and electrocatalysis technology, specifically referring to a method for preparing a layered bimetallic hydroxide nanosheet catalyst by in-situ electrodeposition on a titanium dioxide substrate and its application in the electrocatalytic reduction of NO2. - Applications in ammonia synthesis. Background Technology

[0002] Nitrite (NO2) - NO2 plays a vital role in plant growth as an essential nutrient, but it is also a harmful pollutant in the environment, food, and industrial systems. - It is highly toxic, and excessive exposure to NO2 can cause health problems and even death. Therefore, to ensure food and water safety, people are striving to find effective methods to control NO2. - Methods for removal. However, currently commonly used methods such as reverse osmosis, ion exchange, and electrodialysis can only remove NO2. - Concentration and separation cannot completely eliminate NO2, which will lead to serious secondary pollution and expensive subsequent treatment costs. Therefore, electrochemical catalysis of NO2... - Ammonia synthesis can convert NO2 - These methods stand out due to their significant advantages, such as conversion into valuable ammonia (NH3) and the ability to couple renewable electricity to reduce process carbon emissions.

[0003] Layered bimetallic hydroxides (LDHs) are widely used in electrocatalytic energy conversion fields, such as the oxygen evolution reaction (OER), carbon dioxide reduction reaction (CO2RR), and hydrogen evolution reaction (HER), due to their tunable layered structure, flexible elemental composition, abundant active sites, and good structural stability. Transition metal-based layered LDH catalysts have attracted widespread attention due to their excellent performance and low cost, with Co and Ni-based LDH catalysts showing particularly broad application prospects. Furthermore, the tubular structure of TiO2 nanotubes provides excellent adhesion, making them suitable as substrates for electrodeposition to support catalysts. This in-situ loading of catalysts onto the surface of oxidized and annealed titanium sheets not only results in uniform distribution and good conductivity but also avoids the problems of detachment and reactant contamination associated with traditional powder catalysts that require binders for drop-coating onto electrodes.

[0004] However, current research on the electrocatalytic reduction of NO2 using layered bimetallic hydroxides supported on TiO2 nanotubes as catalysts is lacking. - No research has been reported on the ammonia synthesis reaction. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a cobalt-nickel double hydroxide nanosheet catalyst grown in situ on oxidized titanium sheets and its application in the electrocatalytic reduction of NO2. - Ammonia synthesis specifically refers to the process of using titanium sheets as a substrate, first oxidizing and annealing the titanium sheets, then using an electrodeposition method to in-situ load cobalt-nickel double hydroxide nanosheets on the surface of TiO2 nanotubes, and directly using them for electrocatalytic ammonia synthesis, which has achieved good results.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] A method for preparing a layered double hydroxide nanosheet catalyst includes the following steps:

[0008] ① A three-electrode system was adopted, in which the oxidized and annealed titanium sheet, saturated calomel electrode (SCE) and platinum sheet electrode were used as the working electrode, reference electrode and counter electrode, respectively, and the prepared solution was used as the electrolyte. Layered double hydroxide nanosheets were loaded onto the substrate surface in situ by electrodeposition.

[0009] ② The product was rinsed and dried to obtain TiO2 nanotubes loaded with layered double hydroxide nanosheets in situ.

[0010] The specific preparation method is as follows:

[0011] ① The titanium sheet was ultrasonically cleaned for 10-30 minutes with acetone, acid solution (HF:HNO3:H2O), and ultrapure water to remove surface organic matter and oxides. It was then rinsed with deionized water and ethanol, and vacuum dried for later use. ② A 35 ml ammonium fluoride (NH4F)-ethylene glycol solution was prepared, containing 0.5% NH4F by mass and 2% ultrapure water by volume. TiO2 nanotubes were grown in situ on the titanium sheet using electrochemical anodic oxidation. ③ The TiO2-grown titanium sheet was placed in a tube furnace and annealed under an argon atmosphere at 5℃ for 1 minute. -1 The sample was heated to 500℃ and held for 3 hours at a controlled heating rate, then cooled to room temperature. The argon flow rate was maintained at a constant 100 mL / min throughout the process. -1 ④ Dissolve appropriate amounts of cobalt salt and nickel salt in deionized water; ⑤ Use a three-electrode system for electrodeposition, with the oxidized and annealed titanium sheet, saturated calomel electrode (SCE), and platinum sheet electrode serving as the working electrode, reference electrode, and counter electrode, respectively. The solution prepared in step ④ is used as the electrolyte. Constant voltage deposition yields the working electrode loaded with the catalyst. The prepared electrode is washed with deionized water and dried at room temperature.

[0012] The metal solution is a cobalt and nickel salt solution in different proportions.

[0013] By using the processing method of the present invention, and by controlling parameters such as different oxidation voltages, different annealing temperatures, and different metal salt contents, it is beneficial to obtain CoNi-LDH nanosheet arrays loaded on TiO2 nanotubes.

[0014] In step ①, the total amount of metal salt added is 0.3 mmol;

[0015] Preferably, in step ①, the metal salt-ligand solution is prepared by weighing 0.09 mmol of nickel salt and 0.21 mmol of cobalt salt, dissolving them in 50 ml of deionized water and stirring until homogeneous.

[0016] In step ①, the deposition voltage is -1V (vs. SCE);

[0017] In step ①, the deposition time is 300 seconds.

[0018] The cleaning described in step ② refers to rinsing three times each with deionized water and anhydrous ethanol;

[0019] In step ②, drying refers to drying in a 60℃ electric heating drying oven for 12 hours;

[0020] The present invention provides an application of a layered bimetallic hydroxide nanosheet catalyst for the electrocatalytic synthesis of ammonia.

[0021] The specific method for using the layered bimetallic hydroxide nanosheet catalyst provided by this invention for electrocatalytic ammonia synthesis is as follows:

[0022] The CoNi-LDH / TiO2 prepared above was directly used as a cathode for electrocatalytic ammonia synthesis.

[0023] This invention utilizes CoNi-LDH / TiO2 as an electrode for electrocatalytic ammonia synthesis, exhibiting a significant ammonia production rate and high Faradaic efficiency (FE). The layered bimetallic hydroxide nanosheet catalyst synthesis method provided by this invention is simple, low-cost, and yields nanosheets with stable properties, uniform size, and a significant ammonia production promotion effect.

[0024] Compared with the prior art, the present invention has the following advantages and effects:

[0025] 1. The green preparation method of layered bimetallic hydroxide nanosheets disclosed in this invention is simple, requires no expensive instruments or equipment, and is easy to operate, economical and environmentally friendly.

[0026] 2. The layered bimetallic hydroxide nanosheet catalyst prepared in this invention exhibits stable performance, uniform size, and good electrical conductivity and electrochemical stability. Its application in the electrocatalytic synthesis of ammonia has yielded significant results. Attached Figure Description

[0027] Figure 1 The image shows the X-ray photoelectron spectroscopy (XPS) spectrum of the CoNi-LDH / TiO2 catalyst prepared in Example 1 of this invention.

[0028] Figure 2 The image shows the X-ray energy dispersive spectroscopy (EDS) pattern of the CoNi-LDH / TiO2 catalyst prepared in Example 1 of this invention.

[0029] Figure 3 The image shows a scanning electron microscope (SEM) image of the CoNi-LDH / TiO2 catalyst prepared in Example 1 of this invention.

[0030] Figure 4 Transmission electron microscopy (TEM) image of the CoNi-LDH / TiO2 catalyst prepared in Example 1 of this invention;

[0031] Figure 5 The image shows a scanning electron microscope (SEM) image of the CoNi-LDH / TiO2 catalyst prepared in Example 2 of this invention.

[0032] Figure 6 This is a scanning electron microscope (SEM) image of the CoNi-LDH / TiO2 catalyst prepared in Example 3 of the present invention;

[0033] Figure 7 The image shows a scanning electron microscope (SEM) image of the Co(OH)2 / TiO2 catalyst prepared in Example 4 of this invention.

[0034] Figure 8 This is a scanning electron microscope (SEM) image of the Ni(OH)2 / TiO2 catalyst prepared in Example 5 of the present invention;

[0035] Figure 9 This is a scanning electron microscope (SEM) image of the TiO2 catalyst prepared in Example 6 of the present invention;

[0036] Figure 10 This is a graph showing the efficiency of the catalyst prepared in Example 1 of this invention for electrocatalytic ammonia synthesis. Detailed Implementation

[0037] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0038] Example 1

[0039] The preparation of a CoNi-LDH nanosheet catalyst in situ supported on TiO2 nanotubes includes the following steps: ① Titanium sheets are ultrasonically cleaned for 15 min with acetone, acid solution (HF:HNO3:H2O), and ultrapure water to remove surface organic matter and oxides, then rinsed with deionized water and ethanol, and vacuum dried for later use; ② An ammonium fluoride-ethylene glycol solution is prepared, and TiO2 nanotubes are grown in situ on the titanium sheets using an electrochemical anodic oxidation method; ③ The titanium sheets with grown TiO2 are placed in a tube furnace and annealed under an argon atmosphere to transform them into anatase-type TiO2 nanotubes rich in oxygen vacancies. iO2; ④ Dissolve 0.21 mmol of cobalt chloride hexahydrate (CoCl2·6H2O) and 0.15 mmol of nickel chloride hexahydrate (NiCl2·6H2O) in 50 mL of deionized water; ⑤ Electrodeposition is performed using a three-electrode system. The oxidized and annealed titanium sheet, saturated calomel electrode (SCE), and platinum sheet electrode are used as the working electrode, reference electrode, and counter electrode, respectively. The solution prepared in step ④ is used as the electrolyte. CoNi-LDH / TiO2 is obtained by deposition at a constant voltage of -1V (vs. SCE) for 300 s. The prepared electrode is washed with deionized water and dried at room temperature.

[0040] Characterization of the CoNi-LDH / TiO2 catalyst prepared above:

[0041] The prepared CoNi-LDH / TiO2 catalyst was characterized, and the X-ray photoelectron spectroscopy (XPS) spectrum is shown below. Figure 1 As shown, in the Ni2p region, the two peaks at 874.0 and 856.8 eV are attributed to Ni2p. 1 / 2 and Ni2p 3 / 2 The two satellite peaks at 880.3 and 862.6 eV correspond to Ni. 2+ The two peaks at 796.8 and 781.0 eV are attributed to Co2p, respectively. 1 / 2 and Co2p 3 / 2 The two satellite peaks at 803.1 and 786.5 eV correspond to Co. 2+ The results showed that Ni and Co in the prepared catalyst were mainly Ni. 2+ and Co 2+ Existing in the form of

[0042] Figure 2 The EDS diagram confirmed that the prepared material contained only four elements: Ni, Co, Ti, and O. Figure 3 and Figure 4 The images are SEM and TEM images of the CoNi-LDH / TiO2 nanosheets, which show a nanosheet structure based on their surface morphology.

[0043] Example 2

[0044] The preparation of a CoNi-LDH nanosheet catalyst in situ supported on TiO2 nanotubes includes the following steps: ① Titanium sheets are ultrasonically cleaned for 15 min with acetone, acid solution (HF:HNO3:H2O), and ultrapure water to remove surface organic matter and oxides, then rinsed with deionized water and ethanol, and vacuum dried for later use; ② An ammonium fluoride-ethylene glycol solution is prepared, and TiO2 nanotubes are grown in situ on the titanium sheets using an electrochemical anodic oxidation method; ③ The titanium sheets with grown TiO2 are placed in a tube furnace and annealed under an argon atmosphere to transform them into anatase-type TiO2 nanotubes rich in oxygen vacancies. iO2; ④ Dissolve 0.15 mmol of cobalt chloride hexahydrate (CoCl2·6H2O) and 0.15 mmol of nickel chloride hexahydrate (NiCl2·6H2O) in 50 mL of deionized water; ⑤ Electrodeposition is performed using a three-electrode system. The oxidized and annealed titanium sheet, saturated calomel electrode (SCE), and platinum sheet electrode are used as the working electrode, reference electrode, and counter electrode, respectively. The solution prepared in step ④ is used as the electrolyte. CoNi-LDH / TiO2 is obtained by deposition at a constant voltage of -1V (vs. SCE) for 300 s. The prepared electrode is washed with deionized water and dried at room temperature.

[0045] Characterization of the CoNi-LDH / TiO2 catalyst prepared above:

[0046] The prepared CoNi-LDH / TiO2 catalyst was characterized, and the SEM images are shown below. Figure 5 As shown.

[0047] Example 3

[0048] The preparation of a CoNi-LDH nanosheet catalyst in situ supported on TiO2 nanotubes includes the following steps: ① Titanium sheets are ultrasonically cleaned for 15 min with acetone, acid solution (HF:HNO3:H2O), and ultrapure water to remove surface organic matter and oxides, then rinsed with deionized water and ethanol, and vacuum dried for later use; ② An ammonium fluoride-ethylene glycol solution is prepared, and TiO2 nanotubes are grown in situ on the titanium sheets using an electrochemical anodic oxidation method; ③ The titanium sheets with grown TiO2 are placed in a tube furnace and annealed under an argon atmosphere to transform them into anatase-type TiO2 nanotubes rich in oxygen vacancies. iO2; ④ Dissolve 0.09 mmol of cobalt chloride hexahydrate (CoCl2·6H2O) and 0.21 mmol of nickel chloride hexahydrate (NiCl2·6H2O) in 50 mL of deionized water; ⑤ Electrodeposition is performed using a three-electrode system. The oxidized and annealed titanium sheet, saturated calomel electrode (SCE), and platinum sheet electrode are used as the working electrode, reference electrode, and counter electrode, respectively. The solution prepared in step ④ is used as the electrolyte. CoNi-LDH / TiO2 is obtained by deposition at a constant voltage of -1V (vs. SCE) for 300 s. The prepared electrode is washed with deionized water and dried at room temperature.

[0049] Characterization of the CoNi-LDH / TiO2 catalyst prepared above:

[0050] The prepared CoNi-LDH / TiO2 catalyst was characterized, and the SEM images are shown below. Figure 6 As shown.

[0051] Example 4

[0052] The preparation of a Co(OH)₂ nanosheet catalyst in situ supported on TiO₂ nanotubes includes the following steps: ① Titanium sheets are ultrasonically cleaned for 15 min each with acetone, acid solution (HF:HNO₃:H₂O), and ultrapure water to remove surface organic matter and oxides, then rinsed with deionized water and ethanol, and vacuum dried for later use; ② An ammonium fluoride-ethylene glycol solution is prepared, and TiO₂ nanotubes are grown in situ on the titanium sheets using an electrochemical anodic oxidation method; ③ The titanium sheets with grown TiO₂ are placed in a tube furnace and annealed under an argon atmosphere to... It transforms into anatase TiO2 rich in oxygen vacancies; ④ Dissolve 0.3 mmol of cobalt chloride hexahydrate (CoCl2·6H2O) in 50 mL of deionized water; ⑤ Electrodeposition is performed using a three-electrode system, with the oxidized and annealed titanium sheet, saturated calomel electrode (SCE), and platinum sheet electrode serving as the working electrode, reference electrode, and counter electrode, respectively. The solution prepared in step ④ is used as the electrolyte, and Co(OH)2 / TiO2 is obtained by deposition at a constant voltage of -1V (vs. SCE) for 300 s. The prepared electrode is then washed with deionized water and dried at room temperature.

[0053] Characterization of the Co(OH)2 / TiO2 catalyst prepared above:

[0054] The prepared Co(OH)₂ / TiO₂ catalyst was characterized, and the SEM images are shown below. Figure 7 As shown.

[0055] Example 5

[0056] The preparation of a Ni(OH)₂ nanosheet catalyst in situ supported on TiO₂ nanotubes includes the following steps: ① Titanium sheets are ultrasonically cleaned for 15 min each with acetone, acid solution (HF:HNO₃:H₂O), and ultrapure water to remove surface organic matter and oxides, then rinsed with deionized water and ethanol, and vacuum dried for later use; ② An ammonium fluoride-ethylene glycol solution is prepared, and TiO₂ nanotubes are grown in situ on the titanium sheets using an electrochemical anodic oxidation method; ③ The TiO₂-grown titanium sheets are placed in a tube furnace and annealed under an argon atmosphere to... It transforms into anatase TiO2 rich in oxygen vacancies; ④ Dissolve 0.3 mmol of nickel chloride hexahydrate (NiCl2·6H2O) in 50 mL of deionized water; ⑤ Electrodeposition is performed using a three-electrode system, with the oxidized and annealed titanium sheet, saturated calomel electrode (SCE), and platinum sheet electrode serving as the working electrode, reference electrode, and counter electrode, respectively. The solution prepared in step ④ is used as the electrolyte, and Ni(OH)2 / TiO2 is obtained by deposition at a constant voltage of -1V (vs. SCE) for 300 s. The prepared electrode is then washed with deionized water and dried at room temperature.

[0057] Characterization of the Ni(OH)2 / TiO2 catalyst prepared above:

[0058] The prepared Ni(OH)₂ / TiO₂ catalyst was characterized, and the SEM images are shown below. Figure 8 As shown.

[0059] Example 6

[0060] The preparation of a TiO2 nanotube catalyst includes the following steps: ① Titanium sheets are ultrasonically cleaned for 15 min with acetone, acid solution (HF:HNO3:H2O), and ultrapure water to remove surface organic matter and oxides, then rinsed with deionized water and ethanol, and vacuum dried for later use; ② An ammonium fluoride-ethylene glycol solution is prepared, and TiO2 nanotubes are grown in situ on the titanium sheets using an electrochemical anodic oxidation method; ③ The titanium sheets with grown TiO2 are placed in a tube furnace and annealed under an argon atmosphere to transform them into anatase TiO2 rich in oxygen vacancies.

[0061] Characterization of the TiO2 catalyst prepared above:

[0062] The prepared TiO2 catalyst was characterized, and the SEM images are shown below. Figure 9 As shown.

[0063] Example 7

[0064] The CoNi-LDH / TiO2 prepared in Example 1 was used as an electrode for the cathode electrocatalytic reduction of nitrite to synthesize ammonia.

[0065] The specific application method is as follows: Place a 1×1cm... 2CoNi-LDH / TiO2 was used directly as the working electrode, a mercury oxide electrode as the reference electrode, and a platinum sheet as the counter electrode. The electrolytic cell was a typical H-type electrolytic cell, the electrochemical workstation was a Chenhua CHI760E, and the electrolyte was 1 mol / L potassium nitrite solution. -1 A potassium hydroxide solution was used. Electrocatalytic reduction of nitrite to ammonia was performed using the catalysts prepared above as electrodes, and the catalytic effects were as follows: Figure 10 As shown. During the electrolysis process, high-purity argon gas with a purity of 99.999% was continuously introduced, and electrolysis was carried out for 1 hour by applying different potentials.

[0066] After electrolysis, samples were taken and the ammonia production was tested using the indophenol blue method.

[0067] Plot the ammonia production and Faraday efficiency at different potentials. Figure 10 This reflects the selectivity of nitrogen reduction at different potentials, with the maximum Faraday efficiency achieved when the applied potential is -0.5V (vs. SCE).

Claims

1. The application of a CoNi-LDH nanosheet catalyst grown in situ on a titanium dioxide substrate by electrodeposition in the electrocatalytic synthesis of ammonia from nitrite, characterized in that... A method for preparing a CoNi-LDH nanosheet catalyst by in-situ electrodeposition growth of CoNi-LDH nanosheets uniformly grown on the surface of anatase titanium dioxide includes the following steps: ① The titanium sheet is ultrasonically cleaned with acetone, acid solution and ultrapure water for 10-30 minutes to remove organic matter and oxides on the surface, then rinsed with deionized water and ethanol, and vacuum dried for later use. ② Prepare an ammonium fluoride-ethylene glycol solution and use electrochemical anodic oxidation to grow TiO2 nanotubes in situ at a voltage of 40V-60V on titanium sheets; ③ Place the titanium sheet with TiO2 growth into a tube furnace and anneal it at 400℃-600℃ under an argon atmosphere to transform it into anatase TiO2 rich in oxygen vacancies. ④ Dissolve 0.21 mmol of cobalt chloride hexahydrate and 0.15 mmol of nickel chloride hexahydrate in 50 ml of deionized water to form a mixed solution; ⑤ Electrodeposition was performed using a three-electrode system. The oxidized and annealed titanium sheet, saturated calomel electrode, and platinum sheet electrode were used as the working electrode, reference electrode, and counter electrode, respectively. The solution prepared in step ④ was used as the electrolyte. The working electrode loaded with the catalyst was obtained by deposition at a constant voltage of -1V vs. SCE for 300s. The prepared electrode was washed with deionized water and dried at room temperature.

2. The application according to claim 1, characterized in that, The thickness of the titanium substrate is 0.1mm-0.5mm.

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