Co-based electrocatalyst and preparation method and application thereof

Abstract

The invention discloses a Co-based electrocatalyst and a preparation method and application thereof, and belongs to the technical field of electrocatalytic material preparation, and the preparation method of the Co-based electrocatalyst comprises the following steps: (1) carrying out ultrasonic cleaning on foamed nickel, and drying for later use; (2) placing the dried foamed nickel in a cobalt nitrate plating solution for electroplating to obtain an intermediate product; and (3) dipping the intermediate product in a silver nitrate solution for chemical deposition, and taking out to obtain the Co-based electrocatalyst, the electrocatalyst shows efficient conversion rate and product selectivity for catalytic oxidation of benzyl alcohol, can promote effective activation of benzyl alcohol, and can convert benzyl alcohol into benzoic acid products with high selectivity under high current density, so that a new idea is provided for selection of electrocatalytic benzyl alcohol catalysts, and the electrocatalyst has wide application prospects. And more references are provided for a benzoic acid preparation process.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of electrocatalyst materials, and particularly relates to a Co-based electrocatalyst, a preparation method thereof, and an application thereof. Background Art

[0002] With the deepening of the concept of global green and sustainable development, the development of efficient and low-carbon chemical synthesis technologies has become a common goal in the academic and industrial fields. Electrochemical catalysis technology provides an innovative path for traditional high-energy-consuming and highly polluting organic synthesis by virtue of its advantages such as driving reactions using clean electric energy, mild reaction conditions, and precise regulation of product selectivity. This technology has been widely applied in the field of energy conversion (such as oxygen reduction reaction ORR, oxygen evolution reaction OER, hydrogen evolution reaction HER, carbon dioxide reduction reaction CO2RR, etc.). Among them, significant progress has been made in the technology of hydrogen production by electrolyzing water in recent years: the cathode HER reaction realizes efficient hydrogen production by optimizing the noble metal loading strategy, but the anodic OER process at the other end is limited by slow kinetics and low-value oxygen products, restricting the overall energy efficiency. Therefore, researchers have proposed to utilize the characteristics of the relatively low oxidation potential of organic small molecules to replace the anodic reaction with the oxidation of organic small molecules, and form a green technology system of "dual production in one cell" through the coupling of hydrogen production by electrolyzing water and the synthesis of high-value chemicals, showing great economic potential.

[0003] The electrooxidation of benzyl alcohol is one of the representative reactions in the electrocatalytic organic small molecule oxidation reaction system. Its selectively oxidized products (benzaldehyde / benzoic acid), as key intermediates in the pharmaceutical, perfume, and dye industries, have a continuously growing market demand. However, this system still faces multiple challenges: 1) The competition between anodic OER and benzyl alcohol oxidation (BAOR) leads to reduced reaction selectivity and increased energy consumption; 2) The oxidation path of organic molecules is complex, and product separation and purification are difficult; 3) The existing catalysts have insufficient ability to activate C-H bonds, resulting in a high overpotential (>1.5V vs. RHE) and limited current density (<50mA / cm 2 ) Summary of the Invention

[0004] Aiming at at least one of the problems existing in the oxidation of benzyl alcohol by the existing catalysts, such as weak adsorption and activation ability, low product selectivity, and slow reaction kinetics, the present invention provides an electrocatalyst capable of realizing efficient adsorption-activation and directional conversion of benzyl alcohol molecules, so as to provide an electrocatalyst with excellent catalytic performance, good stability, rich raw material resources, simple, controllable and environmentally friendly preparation process, low cost, and easy for industrial mass production for the oxidation of benzyl alcohol.

[0005] The object of the present invention is achieved by the following technical solutions:

[0006] A preparation method of a Co-based electrocatalyst, comprising the following steps:

[0007] (1) Ultrasonically clean the nickel foam and dry it for later use;

[0008] (2) Electroplate the dried nickel foam in a cobalt nitrate plating solution to obtain an intermediate product;

[0009] (3) Immerse the intermediate product in a silver nitrate solution for chemical deposition, and take it out to obtain the Co-based electrocatalyst.

[0010] In some preferred embodiments, the nickel foam in step (1) is ultrasonically cleaned successively with acetone, hydrochloric acid solution, deionized water, and ethanol.

[0011] In some preferred embodiments, the concentration of cobalt nitrate in the cobalt nitrate plating solution in step (2) is 0.2 - 0.4 mol / L.

[0012] In some preferred embodiments, the electroplating in step (2) is carried out in an electrolytic cell, and the electroplating potential with reference to the calomel electrode is -1 V.

[0013] In some preferred embodiments, the electroplating time is 400 s.

[0014] In some preferred embodiments, the concentration of the silver nitrate solution in step (3) is 10 mmol / L.

[0015] In some preferred embodiments, the impregnation time for the chemical deposition is 20 min.

[0016] Another aspect of the present invention lies in providing a Co-based electrocatalyst, which is prepared by the aforementioned preparation method.

[0017] Yet another aspect of the present invention lies in providing a method for applying the Co-based electrocatalyst, specifically for catalyzing the oxidation reaction of alcohols.

[0018] In some preferred embodiments, the Co-based electrocatalyst is used to catalyze the selective conversion of benzyl alcohol to benzoic acid.

[0019] The beneficial effects of the present invention are as follows:

[0020] (1) Aiming at the problems existing in the oxidation of benzyl alcohol by existing catalysts, such as weak adsorption activation ability, low product selectivity, and slow reaction kinetics, the present invention designs a transition metal-based catalyst with a specific d-electron orbital structure to further optimize the reactant adsorption energy, stabilize the oxygen-containing intermediate, and at the same time inhibit the OER side reaction, improving the selectivity of catalytic oxidation. The electrocatalyst of the present invention is a synergistic catalyst with silver (Ag) as the adsorption site and cobalt hydroxide (Co(OH)2) nanosheets as the catalytic site; the electrocatalyst can promote the effective activation of benzyl alcohol and selectively convert benzyl alcohol into benzoic acid products at a relatively high current density, which provides a new idea for the selection of electrocatalytic benzyl alcohol catalysts and also provides more references for the preparation process of benzoic acid.

[0021] (2) The electrocatalyst of the present invention shows high conversion rate and product selectivity in the catalytic oxidation of benzyl alcohol. Among them, the following two factors play a key role in regulating the electrocatalytic activity of the electrocatalyst of the present invention: one is that the Co(OH)2 nanosheets have a large specific surface area and are easily oxidized to form cobalt oxyhydroxide (CoOOH) with higher activity in the alcohol oxidation reaction, which helps the progress of the oxidation reaction; the other is that after Ag is modified on the surface of the Co(OH)2 nanosheets, the adsorption of the reactant benzyl alcohol is enhanced, and at the same time the aldehyde intermediate is stabilized, thereby improving the reaction selectivity.

[0022] (3) The electrocatalyst of the present invention is prepared by one-step electrodeposition and one-step chemical deposition method. Due to its advantages of low raw material cost, simple and effective preparation method, controllable and environmentally friendly synthesis process, etc., it is very conducive to the large-scale production of this material and has considerable practical application prospects in electrocatalytic alcohol oxidation. Description of the Drawings

[0023] The present invention is further described with the accompanying drawings, but the embodiments in the drawings do not constitute any limitation to the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to the following drawings without creative work.

[0024] Figure 1 is a schematic diagram of the preparation process of the Co-based electrocatalyst of the present invention;

[0025] Figure 2 is the XRD pattern of the intermediate product and the Co-based electrocatalyst prepared from cobalt nitrate plating solutions with different concentrations;

[0026] Figure 3 is the SEM image of the intermediate product and the Co-based electrocatalyst described in Example 1; among them, a and b are SEM images of the intermediate product at different magnifications; c and d are SEM images of the Co-based electrocatalyst at different magnifications;

[0027] Figure 4It is the XPS spectrogram of the Co-based electrocatalyst described in Example 1;

[0028] Figure 5 a, Figure 5 b are the linear sweep voltammetry (LSV) curves of the intermediate product (Co(OH)2) and the Co-based electrocatalyst (Ag / Co(OH)2) described in Example 1 tested in 1 M KOH solution with / without benzyl alcohol respectively; Figure 5 c is the current density of Co(OH)2 and Ag / Co(OH)2 at different potentials;

[0029] Figure 6 It is the mass spectrogram of the products when the intermediate product (Co(OH)2) and the Co-based electrocatalyst (Ag-Co(OH)2) described in Example 1 react for 12 h in 1 M KOH solution containing 0.1 M benzyl alcohol under the condition of a constant voltage of 1.4 V vs. RHE;

[0030] Figure 7 It is the conversion rate curve of benzyl alcohol and the benzoic acid yield curve during the reaction of the Co-based electrocatalyst described in Example 1 at 1.4 V vs. RHE for 24 h;

[0031] Figure 8 It is the LSV performance diagram of the oxidation of benzyl alcohol tested for different transition metal hydroxides described in Comparative Examples 1-4 in 1 M KOH solution;

[0032] Figure 9 It is a comparison diagram of the LSV performance of the oxidation of benzyl alcohol when the intermediate product Co(OH)2 described in Example 1 grows on nickel foam and carbon cloth respectively. Detailed implementation method

[0033] The present invention will be further described in conjunction with the following examples.

[0034] Example 1

[0035] This example relates to a Co-based electrocatalyst, and its preparation method includes the following steps:

[0036] (1) Take a piece of nickel foam (NF), and ultrasonically clean it successively with acetone, 3 mol / L hydrochloric acid solution, deionized water and ethanol. After cleaning, store it in ethanol solution for later use and dry it before use;

[0037] (2) Dissolve 14.6 g of cobalt nitrate hexahydrate in water, make up the volume to obtain 250 mL of cobalt nitrate plating solution. Take 20 mL of the cobalt nitrate plating solution into the electrolytic cell, place the nickel foam dried in step (1) in the electrolytic cell, and electroplate for 400 s at room temperature in a three-electrode system. The electroplating potential is set to -1 V vs. SCE. After electroplating, take out the nickel foam and wash it with deionized water, and dry it to obtain the intermediate product;

[0038] (3) Dissolve silver nitrate in deionized water to prepare a silver nitrate solution with a concentration of 10 mmol / L. Immerse the intermediate product prepared in step (2) in the silver nitrate solution, impregnate it for 20 min at room temperature and a rotation speed of 150 rpm, take it out and wash it with deionized water to obtain the Co-based electrocatalyst.

[0039] 1. Characterization experiments

[0040] (1) XRD characterization

[0041] To avoid the interference of the NF substrate on the XRD characterization (its strong Ni characteristic peaks will cover the intrinsic diffraction signals of the material), a carbon cloth with low background interference is used as the carrier substrate for XRD characterization. See the appendix Figure 2 When Co and Ag / Co are deposited on the carbon cloth using the same process, the characteristic peak of the (100) crystal plane of Co(OH)2 (2θ = 33.1°) can be clearly observed, and new diffraction peaks (2θ = 38.1°, 44.3°) belonging to the cubic phase Ag(111) and (200) crystal planes appear after Ag modification, confirming that the synthesized product is the loading of Ag / Co(OH)2. To further explore the influence of the precursor concentration on the crystal plane regulation, the concentration of the cobalt nitrate solution is increased to 0.4 mol / L for a control experiment. The XRD results show that there are no significant changes in the positions and relative intensity ratios of the characteristic peaks, indicating that the crystal growth orientation is mainly affected by the interfacial energy rather than the concentration drive.

[0042] (2) SEM characterization

[0043] The morphologies of the intermediate product and the Co-based electrocatalyst are characterized by SEM. The characterization results are shown in the appendix Figure 3 , Figure 3 a, Figure 3 b are SEM images of the intermediate product magnified at different multiples. It can be seen that Co(OH)2 is closely packed on the nickel foam in the form of nanosheets; Figure 3 c, Figure 3 d are SEM images of Ag / Co(OH)2 magnified at different multiples, clearly showing that Ag is uniformly distributed on the surface of the Co(OH)2 nanosheets.

[0044] (3) XPS characterization

[0045] The changes in the electronic valence states of Co before and after Ag modification are analyzed by XPS. The X-ray photoelectron spectroscopy (XPS) spectrogram of the Co-based electrocatalyst is shown in the appendix Figure 4 , appendix Figure 4 It can be clearly confirmed that after Ag is modified on Co(OH)2, Co 3+ / Co 2+ The increase in the proportion of Co indicates that the valence state of Co has increased, which will help form more active sites in the subsequent oxidation of benzyl alcohol.

[0046] 2. Performance detection experiments

[0047] (1) Electrochemical performance test

[0048] Using an H-type electrolytic cell, in 1 M KOH solution, the intermediate product (Co(OH)2) prepared in Example 1 and the Co-based electrocatalyst (Ag / Co(OH)2) were used as the working electrode, Hg / HgO as the reference electrode, and Pt as the counter electrode. An electrochemical workstation was used to evaluate the electrocatalytic performance of the prepared samples.

[0049] Within the potential window of 0.4 V - 1.6 V vs. RHE, 1 M KOH solutions with / without 0.1 M benzyl alcohol (BA) were used as the electrolyte respectively, and linear sweep voltammograms (LSV) were performed on the obtained Co(OH)2 and Ag / Co(OH)2 electrodes. The results are shown in Appendix Figure 5 , According to Figure 5 Figures 5a and 5b, it can be seen that both catalysts have good responses to BA. To better compare the effects of Ag modification on the oxidation of benzyl alcohol, Figure 5 Figure 5c reads the oxidation current density corresponding to the two electrodes at 1.2 V - 1.6 V vs. RHE respectively, confirming that the introduction of Ag significantly increases the oxidation current density.

[0050] (2) Detection of oxidation products

[0051] To clarify the regulatory effect of Ag modification on the oxidation path of benzyl alcohol, at a working potential of 1.4 V vs. RHE, the intermediate product (Co(OH)2) and the Co-based electrocatalyst (Ag / Co(OH)2) were used as the working electrode respectively, and the reaction was continued for 12 hours in 1 M KOH electrolyte containing 0.1 M benzyl alcohol. The products of the diluted electrolyte were analyzed by gas chromatography-mass spectrometry (GC-MS). The results are shown in Appendix Figure 6 , It was found that the Co(OH)2 electrode produced both benzaldehyde and benzoic acid, while the Ag / Co(OH)2 electrode significantly improved the product selectivity, with benzoic acid as the main product, indicating that Ag modification effectively inhibited the desorption of intermediate products and could achieve the highly selective oxidation of benzyl alcohol to benzoic acid.

[0052] To further explore the catalytic stability and reaction process of the Ag / Co(OH)2 system, the reaction was extended to 24 hours at the same potential, and samples were taken every 3 hours for GC detection. Based on the linear relationship between the characteristic peak area and concentration of benzoic acid, a time-conversion curve was constructed. The results are shown in AppendixFigure 7 The results showed that: 1) The conversion rate of benzyl alcohol increased gradually with time, and 90.6% had been converted after 24 hours; 2) From the change in the characteristic peak area of benzoic acid, it could be seen that it was rapidly generated in the first 12 hours and then gradually slowed down due to the decrease in the concentration of reactants, which confirmed that the catalyst still maintained its activity during the long-term reaction.

[0053] Comparative Example 1

[0054] The preparation of Ni(OH)2-NF includes the following steps:

[0055] (1) Take a piece of nickel foam (NF), and ultrasonically clean it successively with acetone, 3 mol / L hydrochloric acid solution, deionized water and ethanol. After cleaning, keep it in ethanol solution for later use and dry it before use.

[0056] (2) Prepare Ni(OH)2-NF: Dissolve 11.6 g of nickel nitrate in water, make up the volume to obtain 100 mL of nickel nitrate plating solution. Take 10 mL of the nickel nitrate plating solution, dilute it with 10 mL of distilled water and add it to the electrolytic cell. Place the dried nickel foam in step (1) into the electrolytic cell, and electroplate for 400 s under room temperature conditions and in a three-electrode system. Set the electroplating potential to -1 V vs. SCE. After electroplating, take out the nickel foam and wash and dry it with deionized water.

[0057] Comparative Example 2

[0058] The preparation of CoFe(OH)2-NF includes the following steps:

[0059] (1) The same as Comparative Example 1;

[0060] (2) Dissolve 9.7 g of ferric nitrate nonahydrate in water, make up the volume to obtain 100 mL of 0.4 M ferric nitrate plating solution. Dissolve 11.6 g of cobalt nitrate hexahydrate in water, make up the volume to obtain 100 mL of 0.4 M cobalt nitrate plating solution. Take 15 mL of each of the two plating solutions and mix them evenly in a clean and dry beaker. Then take 20 mL of the mixed solution and add it to the electrolytic cell. Place the dried nickel foam in step (1) into the electrolytic cell, and the electroplating method is the same as that in step (2) of Comparative Example 1.

[0061] Comparative Example 3

[0062] The preparation of CoNi(OH)2-NF includes the following steps:

[0063] (1) The same as Comparative Example 1;

[0064] (2) Take 15 mL of the nickel nitrate plating solution described in Comparative Example 1 and 15 mL of the cobalt nitrate plating solution described in Comparative Example 2 and mix them evenly in a clean and dry beaker. Then take 20 mL of the mixed solution and add it to the electrolytic cell. Place the dried nickel foam in step (1) into the electrolytic cell, and the electroplating method is the same as that in step (2) of Comparative Example 1.

[0065] Comparative Example 4

[0066] Preparation of NiFe(OH)2-NF includes the following steps:

[0067] (1) The same as Comparative Example 1;

[0068] (2) Take 15 mL each of the nickel nitrate plating solution described in Comparative Example 1 and the iron nitrate plating solution described in Comparative Example 2 and mix them evenly in a clean and dry beaker. Then take 20 mL of the mixed solution and add it to the electrolytic cell. Place the nickel foam dried in step (1) into the electrolytic cell, and the electroplating method is the same as step (2) of Comparative Example 1.

[0069] Figure 8 Shows the LSV curves of several different hydroxides before and after adding 0.1 M benzyl alcohol. Compared with Figure 5 Co(OH)2-NF of a, the response of these hydroxides to benzyl alcohol is weak, proving that the unique electronic structure and better reaction kinetics of Co(OH)2 make it show significant superiority in the electrocatalytic oxidation of benzyl alcohol.

[0070] Comparative Example 5

[0071] Deposit Co(OH)2 in Example 1 on carbon cloth by the same electroplating steps for comparison. Its preparation method includes the following steps:

[0072] (1) Take a piece of carbon cloth (CF), calcine it in a tube furnace at 600 °C for 2 hours for cleaning with water. After the temperature returns to room temperature, ultrasonically clean it with ethanol, and store it in an ethanol solution for later use. Dry it before use;

[0073] (2) Dissolve 14.6 g of cobalt nitrate hexahydrate in water, make up the volume to obtain 250 mL of cobalt nitrate plating solution. Take 20 mL of the cobalt nitrate plating solution and put it into the electrolytic cell. Place the carbon cloth dried in step (1) into the electrolytic cell, electroplate for 400 s at room temperature and in a three-electrode system, set the electroplating potential to -1 V vs. SCE. After electroplating, take out the nickel foam and wash it with deionized water, and dry it to obtain Co(OH)2-CF.

[0074] As Figure 9 shown, at a large potential (1.4 V - 1.6 V vs. RHE), when using NF as the support material, the current density is significantly greater than that of CF, which will provide higher catalytic reaction efficiency, more excellent charge transfer ability and stronger structural stability support for the oxidation reaction, fully proving that NF has significant advantages as a carrier in the electrocatalytic oxidation system of benzyl alcohol.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a Co-based electrocatalyst, characterized in that: The following steps are involved: (1) ultrasonically cleaning the nickel foam and drying it for later use; (2) electroplating the dried nickel foam in a cobalt nitrate plating solution to obtain an intermediate product; (3) Immersing the intermediate product in a silver nitrate solution for chemical deposition, and taking it out to obtain the Co-based electrocatalyst.

2. The method for preparing a Co-based electrocatalyst according to claim 1, characterized in that: The nickel foam in step (1) is ultrasonically cleaned in acetone, hydrochloric acid solution, deionized water and ethanol in sequence.

3. The method for preparing a Co-based electrocatalyst according to claim 1, characterized in that: The concentration of cobalt nitrate in the cobalt nitrate plating solution in step (2) is 0.2-0.4 mol / L.

4. The method for preparing a Co-based electrocatalyst according to claim 1, characterized in that: The electroplating in step (2) is carried out in an electrolytic cell, and the plating potential relative to the calomel electrode is -1V.

5. The method for preparing a Co-based electrocatalyst according to claim 4, characterized in that: The electroplating time is 400s.

6. The method for preparing a Co-based electrocatalyst according to claim 1, characterized in that: The concentration of the silver nitrate solution in step (3) is 10 mmol / L.

7. The method for preparing a Co-based electrocatalyst according to claim 6, characterized in that: The immersion time of the chemical deposition is 20 min.

8. A Co-based electrocatalyst, characterized in that Prepared according to any one of claims 1 to 7.

9. The use of a Co-based electrocatalyst according to claim 8, characterized in that: Used to catalyze the oxidation reaction of alcohols.

10. The use according to claim 9, characterized in that: Used to catalyze the selective conversion of benzyl alcohol into benzoic acid.

Images