Co (OH) 2-based electrocatalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of electrocatalysis, and particularly relates to a Co (OH) 2-based electrocatalyst and a preparation method and application thereof. The Co (OH) 2-based electrocatalyst comprises a conductive substrate and a Co (OH) 2 active layer loaded on the surface of the conductive substrate, the Co (OH) 2 active layer is used for generating a corresponding hydrogenation reduction product from a nitrogen heterocyclic ring organic compound through electrochemical hydrogenation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrocatalysis, and particularly relates to a Co(OH)2-based electrocatalyst and a preparation method and application thereof. BACKGROUND

[0002] With the transformation of global energy structure towards clean and low-carbon, developing efficient and safe energy storage and conversion technology has become a key challenge in the forefront of science and technology. Liquid organic hydrogen storage technology can realize safe and efficient storage and transportation of hydrogen energy at room temperature and pressure by reversible catalytic hydrogenation and dehydrogenation between unsaturated organic compounds (such as nitrogen-containing heterocyclic compounds) and their hydrogenation products, and has shown great application prospects. In addition, the core reaction of this technology system, selective hydrogenation, also has important value in the field of fine chemical industry such as synthesis of pharmaceutical intermediates.

[0003] The key to realizing the above-mentioned technology lies in efficient catalysts. Traditional hydrogenation processes mostly use thermal catalytic pathways, relying on high-temperature and high-pressure conditions and noble metal catalysts such as platinum and palladium, which not only have high energy consumption and high cost, but also have significant safety hazards. As a more attractive alternative, electrocatalytic hydrogenation technology can directly utilize electrical energy to drive water and other proton sources to react under mild conditions at room temperature and pressure, and to react with organic substrates to realize the integration of hydrogen utilization and hydrogenation process, significantly simplifying the process and improving energy utilization efficiency. Therefore, developing inexpensive and efficient non-noble metal electrocatalysts has become the focus of research in this field, among which transition metal hydroxides / oxides have attracted much attention due to their low cost and abundant reserves.

[0004] However, existing non-noble metal-based electrocatalysts still face many technical problems in practical application. First, the catalytic activity is generally insufficient, which requires a higher overpotential to drive the reaction, causing energy waste; second, the product selectivity is poor, and by-products are easily produced during the reaction, reducing the efficiency of hydrogen storage-hydrogen release cycle and the purity of the product; third, the stability of the catalyst is poor, and the binding force between the active material and the conductive substrate is weak, which can easily collapse or peel off from the electrode substrate after long-term work in the electrolyte, resulting in rapid decay of catalytic performance. Therefore, there is an urgent need in the art to provide a new type of electrocatalyst that can form a stable integrated structure with the conductive substrate and simultaneously solve the technical problems of low activity, poor selectivity and insufficient stability of existing technology in catalyzing nitrogen-containing heterocyclic organic compounds. SUMMARY

[0005] The purpose of the present application is to solve the above-mentioned problems, and provide a Co(OH)2-based electrocatalyst and a preparation method and application thereof.

[0006] In a first aspect, a Co(OH)2-based electrocatalyst is provided, which adopts the following technical scheme: A Co(OH)2-based electrocatalyst, comprising a conductive substrate and a Co(OH)2 active layer loaded on the surface of the conductive substrate; the Co(OH)2 active layer is used for generating corresponding hydrogenated reduction products of nitrogen-containing heterocyclic organic compounds by electrochemical hydrogenation.

[0007] Further, the conductive substrate is selected from one of foamed nickel and carbon paper.

[0008] Further, the conductive substrate is carbon paper.

[0009] In a second aspect, a preparation method of a Co(OH)2-based electrocatalyst adopts the following technical scheme: A preparation method of a Co(OH)2-based electrocatalyst comprises the following steps: In a three-electrode electrolytic cell, a cobalt salt solution is used as an electrolyte, the conductive substrate is used as a working electrode, a platinum electrode is used as a counter electrode, and a saturated mercury-mercury electrode is used as a reference electrode for in-situ electrodeposition, the Co(OH)2 active layer is deposited on the surface of the conductive substrate, and then the Co(OH)2-based electrocatalyst is obtained after cleaning and drying.

[0010] Further, the in-situ electrodeposition adopts constant potential electrodeposition by chronoamperometry at a constant potential of -1.1~-1.7 V vs. SCE for 30 min -120 min.

[0011] In a third aspect, an application of a Co(OH)2-based electrocatalyst adopts the following technical scheme: An application of the Co(OH)2-based catalyst in a hydrogenation reaction of nitrogen-containing heterocyclic organic compounds, wherein the Co(OH)2-based electrocatalyst is used as a cathode for electrocatalytic hydrogenation reaction.

[0012] Further, in the hydrogenation reaction, the electrolyte in the cathode chamber comprises ≤3 mol / L of a strong alkali aqueous solution and ≤0.5 mol / L of the nitrogen-containing heterocyclic organic compound.

[0013] Further, a platinum electrode or a carbon electrode is used as an anode for electrocatalytic hydrogenation reaction, and the electrolyte in the anode chamber comprises ≤3 mol / L of a strong alkali aqueous solution.

[0014] Further, the nitrogen-containing heterocyclic organic compound is selected from one or more of pyrazine, quinoline, isoquinoline, quinoxaline and derivatives thereof.

[0015] Further, the nitrogen-containing heterocyclic organic compound is quinoxaline, and the corresponding hydrogenated reduction product thereof is tetrahydroquinoxaline.

[0016] The beneficial effects of the present application are: This invention provides a Co(OH)₂-based electrocatalyst. By directly loading a Co(OH)₂ active layer onto the surface of a conductive substrate, a robust and structurally stable integrated electrode is formed. This effectively avoids the problems of aggregation, dissolution, or stripping from the substrate of the catalytic active material due to insufficient physical adsorption during the electrochemical reaction, thus endowing the catalyst with excellent long-term operational stability. The constructed Co(OH)₂ active layer itself exhibits excellent catalytic activity and product selectivity for the electrochemical hydrogenation reaction of nitrogen-containing heterocyclic organic compounds. It can achieve a high catalytic current density at a low overpotential and efficiently convert reactants into the target hydrogenation reduction product, significantly suppressing the occurrence of side reactions. Attached Figure Description

[0017] Figure 1 SEM measurements of Co(OH)2 / CP provided in Example 1: (a) 500 μm, (b) 100 μm, (c) 100 μm, (d) 50 μm.

[0018] Figure 2 LSV test was performed in 1 M KOH with or without 0.015 M quinoxaline when Co(OH)2 / CP provided in Example 1 was used as the working electrode.

[0019] Figure 3 When the working electrode provided in Example 1 is Co(OH)2 / CP, it exhibits a constant potential of -0.2V in the presence of 10 mM quinoxaline. vs GC spectrum of RHE hydrogenation reaction after 12 h. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the present application will be further described in detail below with reference to the accompanying drawings. The described embodiments should not be regarded as limitations on the present invention. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] In the following description, references to "some embodiments" refer to a subset of all possible embodiments; however, it is understood that "some embodiments" may be the same or different subsets of all possible embodiments and may be combined with each other without conflict. Unless otherwise defined, all technical and scientific terms used in the embodiments of the invention have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments of the invention pertain. The terminology used in the embodiments of the invention is for the purpose of describing the embodiments of the invention only and is not intended to limit the invention.

[0022] It should be understood by those skilled in the art that, in the following description of the embodiments of the present application, the order of the serial numbers does not mean the order of execution, and part or all of the steps can be executed in parallel or in sequence, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0023] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0024] Those skilled in the art should understand that the numerical range in the embodiments of the present application should be understood as also specifically disclosing each intermediate value between the upper limit and the lower limit of the range. Each smaller range between any stated value and stated range of intermediate values and any other stated value or intermediate value within the stated range is also included in the present application. The upper limit and lower limit of these smaller ranges can be included or excluded independently from the range.

[0025] Unless otherwise specified, the technical / scientific terms used herein have the same meaning as generally understood by those skilled in the art of the present application. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can also be used in the embodiments or tests of the present application. All documents mentioned in this specification are generally incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of any conflict between the contents of the present application and any incorporated document, the contents of the present application shall prevail.

[0026] It should be noted that all raw materials and / or reagents in the embodiments of the present application are purchased on the market or prepared according to conventional methods well known to those skilled in the art.

[0027] The present embodiment provides a Co(OH)2-based electrocatalyst, comprising a conductive substrate and a Co(OH)2active layer loaded on the surface of the conductive substrate; the Co(OH)2active layer is used to generate the corresponding hydrogenated reduction product by electrochemically hydrogenating the nitrogen-containing heterocyclic organic compound.

[0028] In some embodiments, the conductive substrate is selected from one of foamed nickel, carbon paper.

[0029] In some embodiments, the conductive substrate is carbon paper.

[0030] The present embodiment provides a Co(OH)2-based electrocatalyst, which has a typical structure of an integrated electrode mainly comprising a conductive substrate with good electrical conductivity and a Co(OH)2active layer directly loaded on the surface of the conductive substrate by in-situ growth. This close loading mode ensures excellent physical bonding force and electrical contact between the active layer and the substrate, thereby improving the overall stability and electron transport efficiency of the catalyst. The Co(OH)2active layer serves as a catalytic center in the electrochemical reaction system, which is used to convert nitrogen-containing heterocyclic organic compounds (such as quinoxaline) into their corresponding hydrogenated reduction products (such as tetrahydroquinoxaline) through electrochemical hydrogenation reaction with high efficiency and high selectivity. In specific embodiments, in order to balance good electrical conductivity, chemical stability and provide high specific surface area loading sites for active substances, the conductive substrate can be preferably selected from various porous conductive materials, such as but not limited to nickel foam or carbon paper. In a preferred embodiment, carbon paper (CP) is selected as the conductive substrate to prepare the Co(OH)2 / CP electrocatalyst.

[0031] The present embodiment provides a method for preparing a Co(OH)2-based electrocatalyst, comprising the following steps: In a three-electrode electrolytic cell, a cobalt salt solution is used as the electrolyte, the conductive substrate is used as the working electrode, the platinum electrode is used as the counter electrode, and the saturated calomel electrode is used as the reference electrode for in-situ electrodeposition. The Co(OH)2active layer is deposited on the surface of the conductive substrate, washed, dried, and the Co(OH)2-based electrocatalyst is obtained.

[0032] In some embodiments, the in-situ electrodeposition is performed by chronoamperometry for constant potential electrodeposition at -1.1~-1.7 V vs. SCE for 30 min -120 min.

[0033] The Co(OH)2-based electrocatalyst provided in this embodiment can be prepared by a simple and controllable in-situ electrodeposition method. The specific preparation process is carried out in a standard three-electrode electrolytic cell. The pretreated conductive substrate (such as a 2 cm × 3 cm carbon paper) is used as the working electrode, a platinum (Pt) sheet or platinum mesh is used as the counter electrode, and a saturated calomel electrode (SCE) is used as the reference electrode. The electrolyte is an aqueous solution containing a soluble cobalt salt, for example, cobalt acetate ((CH3COO)2Co) is used as the cobalt source, and the concentration can be adjusted in the range of 0.01 M to 0.4 M, and a specific example is to use a 40 mM cobalt acetate solution. After immersing the above electrodes in the electrolyte, a constant cathodic potential is applied by the chronoamperometry method of the electrochemical workstation for electrodeposition. The constant potential can be set in the range of -1.1 V to -1.7 V (vs. SCE), and the deposition time is adjusted to 30 minutes to 120 minutes according to the required loading amount. After the deposition is completed, the conductive substrate loaded with the Co(OH)2active layer is taken out, washed with a large amount of deionized water to remove the residual electrolyte, and finally placed in a vacuum drying box for sufficient drying (for example, 8 hours) at a temperature of 50°C to 80°C (for example, 60°C), to obtain the final Co(OH)2-based electrocatalyst integrated electrode.

[0034] The application provides a Co(OH)2-based catalyst in the hydrogenation reaction of nitrogen-containing heterocyclic organic compounds, and the Co(OH)2-based electrocatalyst is used as a cathode for electrocatalytic hydrogenation reaction.

[0035] In some embodiments, in the hydrogenation reaction, the electrolyte in the cathode chamber contains a strong alkali aqueous solution with a concentration of ≤3 mol / L, and a nitrogen-containing heterocyclic organic compound with a concentration of ≤0.5 mol / L.

[0036] In some embodiments, a platinum electrode or a carbon electrode is used as an anode for electrocatalytic hydrogenation reaction, and the electrolyte in the anode chamber contains a strong alkali aqueous solution with a concentration of ≤3 mol / L.

[0037] In some embodiments, the nitrogen-containing heterocyclic organic compound is selected from one or more of pyrazine, quinoline, isoquinoline, quinoxaline, and derivatives thereof.

[0038] In some embodiments, the nitrogen-containing heterocyclic organic compound is quinoxaline, and the corresponding hydrogenated reduction product is tetrahydroquinoxaline.

[0039] The Co(OH)2-based electrocatalyst provided in this embodiment exhibits excellent application performance in the electrocatalytic hydrogenation reaction of nitrogen-containing heterocyclic organic compounds. In a specific application, the Co(OH)2-based electrocatalyst is used as a cathode (working electrode) for the electrocatalytic hydrogenation reaction. The reaction is usually carried out in an H-type electrolytic cell separated by an anion exchange membrane. The cathode chamber is filled with a cathode electrolyte composed of a strong alkali aqueous solution and a nitrogen-containing heterocyclic organic compound, wherein the concentration of the strong alkali (such as KOH or NaOH) can be as high as 3 mol / L, and the concentration of the organic compound as the reaction substrate does not exceed 0.5 mol / L. For example, in a specific test, the cathode electrolyte can be composed of 1 M KOH and 0.015 M quinoxaline solution. The anode chamber is filled with an anode electrolyte, usually a strong alkali aqueous solution (such as 1 M KOH) of the same concentration as the cathode chamber, and a platinum electrode is used as the anode. The Co(OH)2-based electrocatalyst is suitable for a wide range of nitrogen-containing heterocyclic organic compounds, which can be selected from one or more of pyrazine, quinoline, isoquinoline, quinoxaline, and various derivatives containing alkyl or carboxyl groups. In a typical application example, when quinoxaline is used as the reactant, the electrocatalytic hydrogenation system can efficiently convert it into the corresponding hydrogenated product, tetrahydroquinoxaline.

[0040] General pretreatment steps for substrates in the following examples: The conductive substrate was cut into a specific size (actually cut to 2 cm x 3 cm), and sequentially ultrasonically cleaned in anhydrous ethanol, 2 M hydrochloric acid, and deionized water for 30 min each to remove surface oil and impurities, and dried in a 60°C vacuum drying oven for 2 h for standby use.

[0041] Example Example 1 Example 1 provides a Co(OH)2-based electrocatalyst, which includes a foam nickel and a Co(OH)2 active layer supported on the surface of the foam nickel; an electron microscope is used to observe the morphology of the Co(OH)2 active layer of Example 1, as shown in Figure 1 .

[0042] Example 1 also provides a method for preparing a Co(OH)2-based electrocatalyst, which includes the following steps: In a three-electrode electrolytic cell, a solution of 40 mM (CH3COOH)2Co was used as the electrolyte, the pretreated CP was used as the working electrode, a Pt plate was used as the counter electrode, and a saturated calomel electrode was used as the reference electrode for in-situ electrodeposition. Chronoamperometry was used for constant potential electrodeposition at -1.65 V vs. SCE for 30 minutes to obtain the Co(OH)2 / CP electrocatalyst. After the reaction, the Co(OH)2 / CP electrocatalyst was washed with a large amount of deionized water and dried in a 60°C vacuum drying oven for 8 h.

[0043] Example 2 Example 2 provides a Co(OH)2-based electrocatalyst, comprising carbon paper and a Co(OH)2 active layer supported on the surface of the carbon paper.

[0044] Example 2 also provides a method for preparing a Co(OH)2-based electrocatalyst, comprising the following steps: In a three-electrode electrolytic cell, the pretreated NF was used as the working electrode, a Pt plate was used as the counter electrode, and a saturated calomel electrode was used as the reference electrode for in-situ electrodeposition with a 10 mM (CH3COOH)2Co solution as the electrolyte. Chronoamperometry was used for constant potential electrodeposition, and a Co(OH)2 / NF electrocatalyst was obtained at -1.5 V vs. SCE for 60 minutes. After the reaction, the Co(OH)2 / NF electrocatalyst was washed with a large amount of deionized water and dried in a vacuum drying oven at 60°C for 8 h.

[0045] Example 3 Example 3 provides a Co(OH)2-based electrocatalyst, comprising foamed copper and a Co(OH)2 active layer supported on the surface of the foamed copper.

[0046] Example 3 also provides a method for preparing a Co(OH)2-based electrocatalyst, comprising the following steps: In a three-electrode electrolytic cell, the pretreated CP was used as the working electrode, a Pt plate was used as the counter electrode, and a saturated calomel electrode was used as the reference electrode for in-situ electrodeposition with a 0.4 M (CH3COOH)2Co solution as the electrolyte. Chronoamperometry was used for constant potential electrodeposition, and a Co(OH)2 / CP electrocatalyst was obtained at -1.1 V vs. SCE for 120 minutes. After the reaction, the Co(OH)2 / CP electrocatalyst was washed with a large amount of deionized water and dried in a vacuum drying oven at 60°C for 8 h.

[0047] Performance test Performance test of Co(OH)2 / CP catalyst for electrocatalytic hydrogenation of pyrazine Two H-type glass electrolytic cells with Nafion 117 proton exchange membranes separating the negative and positive chambers were used as the experimental group and the control group, respectively.

[0048] Experimental group: Cathode chamber (working electrode chamber): 35.0 mL of electrolyte was added, which was composed of 1.0 M KOH aqueous solution and 0.015 M quinoline; anode chamber (counter electrode chamber): 35.0 mL of 1.0 M KOH aqueous solution was added.

[0049] Control group: Cathode compartment (working electrode compartment): 35.0 mL of electrolyte was added, which was 1.0 M KOH aqueous solution; anode compartment (counter electrode compartment): 35.0 mL of 1.0 M KOH aqueous solution was added.

[0050] Electrode installation and electrochemical test setup: The Co(OH)2 / CP catalyst prepared in Example 1 was installed in the cathode (working electrode) of two electrolytic cells, respectively; platinum sheets were installed as anodes (counter electrodes), respectively; the saturated calomel electrode (SCE) with a Luggin capillary tip was placed close to the surface of the working electrode (about 2-3 mm) as a reference electrode in the cathode compartment.

[0051] The electrochemical workstation was connected. Electrochemical activation: the above two groups of electrolytic cells were scanned in the range of 0~ -1.5V at a speed of 0.005V / s, and the linear sweep voltammetry test results are shown in Figure 2 , it can be seen that without the addition of quinoline, the hydrogen evolution current density at -0.2 V (vs. RHE) is -11 mA, and the current density after the addition of quinoline is significantly improved, and the catalytic hydrogenation current reaches -32 mA, which proves that the catalyst not only has good hydrogen evolution activity, but also has excellent catalytic hydrogenation activity. Figure 2 vs After activation, the constant potential electrolysis mode was set, and the constant potential -0.2 V (vs. RHE) was applied for the electrocatalytic hydrogenation reaction of quinoline, and the electrolysis time was 12 hours. After 12 hours of electrolysis, a small amount of electrolyte sample was carefully taken out from the cathode compartment; according to the needs, the sample can be diluted by a certain multiple with an appropriate amount of solvent, and filtered through a 0.22 μm filter membrane to remove solid particles.

[0052] The pretreated sample was injected into the gas chromatograph, and by comparing the retention time and peak area with the previously calibrated quinoline (raw material) and tetrahydroquinoline (main product) standard samples, the residual amount of quinoline and the generation amount of tetrahydroquinoline in the reaction liquid were quantitatively analyzed, and the results are shown in , it can be seen that after 12 hours of hydrogenation, the initial concentration of quinoline is 10 mM, and the initial concentration should be converted to 1.3 mg mL -1 , and after 12 hours of reaction, the product was detected by GC, the conversion rate was 82.5%, and the selectivity was 80.8%.

[0053] Figure 3 Figure 3

[0054] ​​​The above merely illustrates the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A Co(OH)2-based electrocatalyst, characterized in that, The Co(OH)2-based electrocatalyst comprises a conductive substrate and a Co(OH)2 active layer loaded on the surface of the conductive substrate; the Co(OH)2 active layer is used for generating corresponding hydrogenated reduction products of nitrogen-containing heterocyclic organic compounds by electrochemical hydrogenation.

2. The Co(OH)2-based electrocatalyst of claim 1, wherein, The conductive substrate is selected from one of foamed nickel and carbon paper.

3. The Co(OH)2-based electrocatalyst of claim 2, wherein, The conductive substrate is carbon paper.

4. A method for preparing the Co(OH)2-based electrocatalyst according to any one of claims 1 to 3, characterized in that, The method comprises the following steps: The Co(OH)2 active layer is deposited on the surface of the conductive substrate in a three-electrode electrolytic cell with a cobalt salt solution as an electrolyte, the conductive substrate as a working electrode, a platinum electrode as a counter electrode, and a saturated calomel electrode as a reference electrode; the Co(OH)2 active layer is washed and dried to obtain the Co(OH)2-based electrocatalyst.

5. The method of claim 4, wherein, The in-situ electrodeposition is carried out by constant potential electrodeposition by chronocoulometry at a constant potential of -1.1 to -1.7 V vs. SCE for 30 to 120 min.

6. Use of the Co(OH)2-based catalyst according to any one of claims 1 to 3 in the hydrogenation of nitrogen-containing heterocyclic organic compounds, characterized in that, The Co(OH)2-based electrocatalyst is used as a cathode for electrocatalytic hydrogenation reaction.

7. Use according to claim 6, characterized in that, In the hydrogenation reaction, the electrolyte in the cathode chamber comprises ≤3 mol / L of a strong alkali aqueous solution and ≤0.5 mol / L of the nitrogen-containing heterocyclic organic compound.

8. Use according to claim 7, characterized in that, A platinum electrode or a carbon electrode is used as an anode for electrocatalytic hydrogenation reaction, and the electrolyte in the anode chamber comprises ≤3 mol / L of a strong alkali aqueous solution.

9. Use according to claim 8, characterized in that, The nitrogen-containing heterocyclic organic compound is selected from one or more of pyrazine, quinoline, isoquinoline, quinoxaline and derivatives thereof.

10. Use according to claim 9, characterized in that, The nitrogen-containing heterocyclic organic compound is quinoxaline, and the corresponding hydrogenated reduction product thereof is tetrahydroquinoxaline.

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