Cobalt-doped nickel-based coordination polymer catalyst as well as preparation method and application thereof

Abstract

The invention provides a cobalt-doped nickel-based coordination polymer catalyst and a preparation method and application thereof.The preparation method comprises the following steps that S1, Schiff base and 4, 4 '-dipyridyl are placed in a mixed solvent to be mixed, acid is added into the mixed solvent to obtain a precursor solution, the precursor solution and foamed nickel are mixed, a coordination reaction is conducted through a hydrothermal method, and a nickel-based coordination polymer is obtained; and S2, dissolving cobalt salt in an organic solvent, adding into the nickel-based coordination polymer, mixing, and carrying out a hydrothermal method to obtain the cobalt-doped nickel-based coordination polymer catalyst. The preparation method is simple in process, low in cost and good in repeatability.

Description

Technical Field

[0001] The present invention relates to the field of electrocatalysis technology, and in particular to a cobalt-doped nickel-based coordination polymer catalyst and a preparation method and application thereof. Background Art

[0002] Currently, hydrogen production by water electrolysis is an ideal energy conversion method. It has attracted widespread attention due to its clean products and flexible system. The oxygen evolution reaction (OER) is a key step that restricts its efficiency. Therefore, the development of efficient, stable and cost-controlled oxygen evolution electrocatalysts has important scientific research significance and practical application value. Nickel foam-supported electrode is a material with a unique three-dimensional porous structure and nickel metal properties. Its highly interconnected porous network (porosity often exceeds 95%) provides a huge specific surface area, which can efficiently load a large number of catalyst nanoparticles, thereby greatly exposing active sites and significantly improving the overall catalytic activity. At the same time, the metal nickel skeleton itself constitutes an excellent interconnected conductive network, ensuring the rapid and low-resistance transmission of electrons inside the electrode and between the catalyst / substrate interface, effectively reducing energy consumption and improving reaction kinetics. However, the main component, nickel metal itself, has a low inherent catalytic activity for many important electrocatalytic reactions (such as oxygen evolution reaction OER, hydrogen evolution reaction HER, carbon dioxide reduction CO2RR, etc.), and its efficiency is insufficient. Furthermore, nickel can dissolve, oxidize, or undergo structural collapse under harsh electrochemical conditions (especially high potential or strong acid / alkaline electrolytes), leading to activity decay and decreased stability. Therefore, in situ growth on the surface of nickel foam is an effective means to reduce the overpotential and increase catalyst stability.

[0003] Coordination polymer materials have received great attention in the field of hydrogen production by water electrolysis due to their regular pores. However, they are prone to structural collapse during the synthesis process, which greatly weakens their advantages of large specific surface area. For example, the Zhong team (Doi.org / 10.1021 / acscatal.5b00524) combined CoNi-MOFs / rGO into CoNi-MOFs and prepared a catalyst by chemically crosslinking CoNi-MOFs and rGO. The catalyst's insufficient conductivity and poor structural stability limit the charge transfer efficiency, resulting in slow reaction kinetics. It is also prone to structural collapse during the synthesis process, which greatly weakens its advantages of large specific surface area and leads to poor catalytic activity. Summary of the Invention

[0004] The technical problem to be solved by the present invention is how to improve the catalytic activity of the catalyst.

[0005] The present invention solves the above technical problems through the following technical means:

[0006] The first aspect of the present invention provides a cobalt-doped nickel-based coordination polymer catalyst, comprising the following steps:

[0007] S1: Schiff base and 4,4'-bipyridine are placed in a mixed solvent, an acid is added thereto to obtain a precursor solution, the precursor solution is mixed with nickel foam, and a coordination reaction is carried out by a hydrothermal method to obtain a nickel-based coordination polymer;

[0008] S2 dissolves cobalt salt in an organic solvent and adds it to a nickel-based coordination polymer, and then performs a hydrothermal method to prepare a cobalt-doped nickel-based coordination polymer catalyst.

[0009] Beneficial effect: The nickel foam of the present application is etched by acid so that nickel ions generated by the nickel foam are coordinated with Schiff base, 4,4'-bipyridine and nickel ions generated by the nickel foam by a hydrothermal method to generate nickel-based coordination polymers.

[0010] This application uses highly conductive nickel foam as a carrier and grows a coordination polymer on it, which can increase the stability of the catalyst while producing more nickel active sites, thereby improving the catalytic activity; 4,4'-bipyridine is used as a co-ligand, allowing the Schiff base to better coordinate with nickel ions.

[0011] This application uses a hydrothermal method to dope cobalt onto the surface of a nickel-based coordination polymer to produce a cobalt-doped nickel-based coordination polymer catalyst. The addition of cobalt to metallic nickel alters the nickel's lattice structure, making it easier to restructure the nickel into nickel oxyhydroxide, facilitating electron transport and increasing the catalyst's reactivity. The preparation method is simple, low-cost, and highly reproducible.

[0012] Preferably, in S1, the pH of the precursor solution is 3-4.

[0013] Beneficial effects: In the present application, nickel foam is etched by acid to produce nickel ions in the nickel foam. When the pH of the precursor solution is lower than 3, the nickel foam is subjected to transition etching to reduce the conductivity of the nickel foam. When the pH of the precursor solution is higher than 4, the nickel foam is etched to produce fewer nickel ions, resulting in less nickel-based coordination polymer generated in the later coordination reaction, affecting the stability of the catalyst and the reaction activity of the catalyst.

[0014] Preferably, the nickel foam needs to be cleaned before the reaction. The specific operation is to place the nickel foam in acetone, hydrochloric acid, and deionized water for ultrasonic cleaning, and finally blow dry with nitrogen.

[0015] Preferably, the ultrasonic cleaning time is 20 minutes.

[0016] Preferably, in S1, the mass ratio of Schiff base to 4,4'-bipyridine is 10:3.

[0017] Preferably, the structural formula of the Schiff base is as follows:

[0018]

[0019] Preferably, in S1, the mixed solvent is N'N-dimethylformamide and methanol, and the volume ratio of N'N-dimethylformamide to methanol is 1:1.

[0020] Preferably, in S1, the acid is an inorganic acid, which includes one or more of hydrochloric acid, sulfuric acid or nitric acid.

[0021] Preferably, in S1, the reaction temperature of the hydrothermal method is 70-110° C., and the reaction time is 12-24 h.

[0022] Preferably, in S2, the organic solvent is N'N-dimethylformamide.

[0023] Preferably, in S2, the reaction temperature of the hydrothermal method is 100-140° C., and the reaction time is 10-18 h.

[0024] Preferably, in S2, the mass of the cobalt salt is 0.01-0.1 g.

[0025] Preferably, in S2, the cobalt salt is a soluble cobalt salt, and the soluble cobalt salt is cobalt chloride or cobalt nitrate.

[0026] The second aspect of the present invention provides a cobalt-doped nickel-based coordination polymer catalyst, which is prepared according to the above-mentioned preparation method of the cobalt-doped nickel-based coordination polymer catalyst.

[0027] A third aspect of the present invention provides an application of a cobalt-doped nickel-based coordination polymer catalyst as an oxygen evolution catalyst. The cobalt-doped nickel-based coordination polymer catalyst is prepared according to the above-mentioned preparation method of the cobalt-doped nickel-based coordination polymer catalyst.

[0028] Beneficial effect: When a voltage is applied to the cobalt-doped nickel-based coordination polymer catalyst of the present application, part of the coordination polymer is reconstructed to generate linear and irregular tiny particles. The linear and irregular tiny particles contain nickel oxyhydroxide, which is a true catalytically active substance, thereby improving the catalytic activity of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the preparation method of the cobalt-doped nickel-based coordination polymer catalyst in Example 1;

[0030] Figure 2High-resolution scanning electron micrographs (SEM) of the nickel foam, nickel-based coordination polymer, and cobalt-doped nickel-based coordination polymer catalyst of Example 1; the left image is an SEM image of the nickel foam, the middle image is an SEM image of the nickel-based coordination polymer, and the right image is an SEM image of the cobalt-doped nickel-based coordination polymer catalyst;

[0031] Figure 3 Transmission electron microscopy (TEM) images of the cobalt-doped nickel-based coordination polymer catalyst (right) and the nickel-based coordination polymer (left) of Example 1;

[0032] Figure 4 Surface scanning element distribution map (Mapping) of the cobalt-doped nickel-based coordination polymer catalyst of Example 1; wherein Figures a and e correspond to the element distribution maps of C, Co, O, N, and Ni, respectively;

[0033] Figure 5 Fourier transform infrared spectroscopy (FT-IR) of the cobalt-doped nickel-based coordination polymer catalyst, nickel-based coordination polymer, Schiff base and 4,4'-bipyridine of Example 1;

[0034] Figure 6 The confocal microscopic Raman spectra (Raman) of the cobalt-doped nickel-based coordination polymer catalyst and the nickel-based coordination polymer of Example 1;

[0035] Figure 7 1 is the LSV curve of the cobalt-doped nickel-based coordination polymer catalyst of Example 1 and the nickel-based coordination polymer catalyst of Comparative Example 1; wherein NF represents foamed nickel, which is used as a standard catalyst;

[0036] Figure 8 The Tafel slopes of the cobalt-doped nickel-based coordination polymer catalyst of Example 1 and the nickel-based coordination polymer catalyst of Comparative Example 1 in 1 M KOH solution; wherein NF represents nickel foam, which is used as a standard catalyst;

[0037] Figure 9 It curves of the cobalt-doped nickel-based coordination polymer catalyst of Example 1 and the nickel-based coordination polymer catalyst of Comparative Example 1 in 1M KOH solution; wherein NF represents foamed nickel, which is used as a standard catalyst;

[0038] Figure 10 This is a SEM image of the cobalt-doped nickel-based coordination polymer catalyst of Example 1 after high voltage oxygen evolution catalysis is applied. DETAILED DESCRIPTION

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0040] Unless otherwise specified, the test materials and reagents used in the following examples can be obtained from commercial sources.

[0041] If no specific techniques or conditions are specified in the examples, they can be carried out according to the techniques or conditions described in the literature in the field or according to the product instructions.

[0042] Example 1

[0043] according to Figure 1 As shown, this embodiment provides a cobalt-doped nickel-based coordination polymer catalyst and a preparation method thereof, which specifically includes the following steps:

[0044] S1: The nickel foam is placed in acetone, 2 mol / L dilute hydrochloric acid, and deionized water for ultrasonic cleaning for 20 minutes respectively, and the cleaned nickel foam is blown dry with nitrogen to obtain clean nickel foam.

[0045] S2: 25 mL of N,N-dimethylformamide and 25 mL of methanol were mixed to obtain a mixed solvent, and then 0.5 g of Schiff base and 0.15 g of 4,4'-bipyridine were added thereto and stirred evenly. Then, 8.55 μL of 2 mol / L hydrochloric acid was added to the solution and stirred and ultrasonically mixed to obtain a precursor solution. The pH of the precursor solution was 3.5.

[0046] S3 places clean nickel foam in a polytetrafluoroethylene reactor, slowly injects the precursor solution along the inner wall of the polytetrafluoroethylene reactor, seals it with a stainless steel hydrothermal reactor, and reacts at 100°C for 14 hours. After the reaction is completed, it is cooled to room temperature. The obtained product is washed 5 times with a mixed solvent of N,N-dimethylformamide and methanol, and blown dry with nitrogen to obtain a nickel-based coordination polymer.

[0047] S4: 0.0214 g of cobalt chloride hexahydrate was dissolved in N,N-dimethylformamide to obtain a cobalt chloride solution. The cobalt chloride solution was then injected into a polytetrafluoroethylene liner and mixed with a nickel-based coordination polymer. The mixture was sealed and placed in a 120°C oven for reaction for 18 hours. After the reaction was completed, the mixture was cooled to room temperature to obtain a cobalt-doped nickel-based coordination polymer catalyst.

[0048] according to Figure 2-3It can be seen that nickel-based coordination polymers grow on the surface of nickel foam and cover the contour of nickel foam. Figure 4 It can be seen that cobalt was successfully doped into the nickel-based coordination polymer to obtain a cobalt-doped nickel-based coordination polymer catalyst.

[0049] according to Figure 5 As shown, the characteristic peaks of C=N of Schiff base and a series of characteristic peaks of 4,4'-bipyridine were detected in both the cobalt-doped nickel-based coordination polymer catalyst and the nickel-based coordination polymer, indicating that the coordination polymer was successfully synthesized.

[0050] according to Figure 6 It can be seen that no new Raman peak is generated in the nickel-based coordination polymer, while a new characteristic peak is generated in the cobalt-doped nickel-based coordination polymer catalyst, indicating that cobalt is doped on the surface of the nickel-based coordination polymer. This example successfully prepares the cobalt-doped nickel-based coordination polymer catalyst.

[0051] Example 2

[0052] This embodiment provides a cobalt-doped nickel-based coordination polymer catalyst and a preparation method thereof. This embodiment differs from Example 1 in that: in S2, hydrochloric acid is replaced by nitric acid, and all other steps are the same.

[0053] Characterization showed that the cobalt-doped nickel-based coordination polymer catalyst was successfully prepared in this example. It had a heterogeneous structure and the size was consistent with that of Example 1.

[0054] Example 3

[0055] This embodiment provides a cobalt-doped nickel-based coordination polymer catalyst and a preparation method thereof. This embodiment differs from Example 1 in that in S4, cobalt chloride hexahydrate is replaced with cobalt nitrate hexahydrate, and all other conditions are the same.

[0056] Characterization showed that the cobalt-doped nickel-based coordination polymer catalyst was successfully prepared in this example. It had a heterogeneous structure and the size was consistent with that of Example 1.

[0057] Example 4

[0058] This embodiment provides a cobalt-doped nickel-based coordination polymer catalyst and a preparation method thereof. This embodiment differs from Example 1 in that: in S4, the mass of cobalt chloride hexahydrate is 0.0107 g.

[0059] Characterization showed that the cobalt-doped nickel-based coordination polymer catalyst was successfully prepared in this example. It had a heterogeneous structure and the size was consistent with that of Example 1.

[0060] Example 5

[0061] This embodiment provides a cobalt-doped nickel-based coordination polymer catalyst and a preparation method thereof. This embodiment differs from Example 1 in that: in S4, the mass of cobalt chloride hexahydrate is 0.0963 g.

[0062] Characterization showed that the cobalt-doped nickel-based coordination polymer catalyst was successfully prepared in this example. It had a heterogeneous structure and the size was consistent with that of Example 1.

[0063] Comparative Example 1

[0064] This comparative example provides a nickel-based coordination polymer catalyst and a preparation method thereof. Compared with Example 1, this comparative example differs in that step S4 is omitted to obtain a nickel-based coordination polymer catalyst, and all other aspects are the same.

[0065] Comparative Example 2

[0066] This comparative example provides a cobalt-doped nickel-based coordination polymer catalyst and a preparation method thereof. Compared with Example 1, this comparative example differs in that: no acid is added to S2, the pH of the precursor solution is 5.86, and all other conditions are the same.

[0067] Comparative Example 3

[0068] This comparative example provides a cobalt-doped nickel-based coordination polymer catalyst and a preparation method thereof. This comparative example provides a cobalt-doped nickel-based coordination polymer catalyst and a preparation method thereof. Compared with Example 1, this comparative example differs in that: in S2, hydrochloric acid is replaced by citric acid, and everything else is the same.

[0069] Comparative Example 4

[0070] This comparative example provides a cobalt-doped nickel-based coordination polymer catalyst and a preparation method thereof. This comparative example provides a cobalt-doped nickel-based coordination polymer catalyst and a preparation method thereof. Compared with Example 1, this comparative example differs in that: in S2, hydrochloric acid is replaced by acetic acid, and everything else is the same.

[0071] Comparative Example 5

[0072] This comparative example provides a cobalt-doped nickel-based coordination polymer catalyst and a preparation method thereof. Compared with Example 1, this comparative example differs in that: 4,4'-bipyridine is not added to S2, and all other aspects are the same.

[0073] Comparative Example 6

[0074] This comparative example provides a cobalt-doped nickel-based coordination polymer catalyst and a preparation method thereof. The only difference between this comparative example and Example 1 is that in S2, 20 mL of N,N-dimethylformamide and 30 mL of methanol are evenly mixed to obtain a mixed solvent, and the rest are the same.

[0075] Experimental example

[0076] The catalysts prepared in Examples 1-5 and Comparative Examples 1-6 were subjected to electrochemical tests, as follows:

[0077] 1. Using a three-electrode system with 75% iR compensation, 1M KOH was used as the electrolyte, mercuric oxide was used as the reference electrode, and a platinum sheet was used as the counter electrode. The catalysts prepared in Examples 1-5 and Comparative Examples 1-6 were used as the working electrodes. The LSV curves were obtained from the test results of Example 1 and Comparative Example 1. Figure 7 The specific data are shown in Table 1.

[0078] 2. According to Figure 7 The LSV curves of Example 1 and Comparative Example 1 were obtained by further data processing, as shown in FIG. Figure 8 shown.

[0079] 3. According to Figure 7 The catalyst stability lines of Example 1 and Comparative Example 1 obtained by further data processing of the LSV curve are as follows: Figure 9 shown.

[0080] 4. The SEM image of the cobalt-doped nickel-based coordination polymer catalyst of Example 1 after high voltage oxygen evolution catalysis is as follows: Figure 10 shown.

[0081]

[0082]

[0083] according to Figure 7 As shown, the overpotential of the cobalt-doped nickel-based coordination polymer catalyst of Example 1 is significantly lower than that of nickel foam, while the overpotential of the nickel-based coordination polymer catalyst of Comparative Example 1 is between that of Example 1 and nickel foam, indicating that the cobalt-doped nickel-based coordination polymer catalyst of Example 1 has the best catalytic activity and efficiency.

[0084] according to Figure 8 As shown, the cobalt-doped nickel-based coordination polymer catalyst of Example 1 has the smallest Tafel slope value, followed by Comparative Example 1, and finally nickel foam. Therefore, it can be seen that the catalyst of Example 1 has the best catalytic activity.

[0085] according to Figure 9 As shown, the current density of the cobalt-doped nickel-based coordination polymer catalyst of Example 1 and the nickel-based coordination polymer catalyst of Comparative Example 1 can be maintained without obvious decay within 180 minutes, indicating that the cobalt-doped nickel-based coordination polymer catalyst and the nickel-based coordination polymer catalyst prepared by nickel foam have good stability.

[0086] according to Figure 10As shown, after applying voltage to catalyze oxygen evolution, the cobalt-doped nickel-based coordination polymer catalyst of Example 1 can obviously be seen to be partially reconstructed to generate linear and irregular tiny particles. The linear and irregular tiny particles contain nickel oxyhydroxyl, which is a real catalytically active substance, thereby improving the catalytic activity of the catalyst.

[0087] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a cobalt-doped nickel-based coordination polymer catalyst, characterized in that: The following steps are involved: S1: nickel foam, Schiff base and 4,4'-bipyridine are placed in a mixed solvent, acid is added thereto to obtain a precursor solution, and the precursor solution is subjected to a coordination reaction by a hydrothermal method to obtain a nickel-based coordination polymer; S2 dissolves cobalt salt in an organic solvent and adds it to a nickel-based coordination polymer to prepare a cobalt-doped nickel-based coordination polymer catalyst by a hydrothermal method.

2. The method for preparing a cobalt-doped nickel-based coordination polymer catalyst according to claim 1, wherein: In S1, the mass ratio of Schiff base to 4,4'-bipyridine is 10:

3.

3. The method for preparing a cobalt-doped nickel-based coordination polymer catalyst according to claim 1 or 2, characterized in that: The structural formula of Schiff base is as follows:

4. The method for preparing a cobalt-doped nickel-based coordination polymer catalyst according to claim 1, wherein: In S1, the mixed solvent is N'N-dimethylformamide and methanol, and the volume ratio of N'N-dimethylformamide to methanol is 1:

1.

5. The method for preparing a cobalt-doped nickel-based coordination polymer catalyst according to claim 1, wherein: In S1, the acid is an inorganic acid, which includes one or more of hydrochloric acid, sulfuric acid or nitric acid.

6. The method for preparing a cobalt-doped nickel-based coordination polymer catalyst according to claim 1, characterized in that: In S1, the reaction temperature of the hydrothermal method is 70-110° C., and the reaction time is 12-24 h.

7. The method for preparing a cobalt-doped nickel-based coordination polymer catalyst according to claim 1, characterized in that: In S2, the reaction temperature of the hydrothermal method is 100-140°C, and the reaction time is 10-18h.

8. The method for preparing a cobalt-doped nickel-based coordination polymer catalyst according to claim 1, wherein: In S2, the mass of the cobalt salt is 0.01-0.1 g, the cobalt salt is a soluble cobalt salt, and the soluble cobalt salt is cobalt chloride or cobalt nitrate.

9. A cobalt-doped nickel-based coordination polymer catalyst, characterized in that: The cobalt-doped nickel-based coordination polymer catalyst is prepared according to the preparation method of the cobalt-doped nickel-based coordination polymer catalyst according to any one of claims 1 to 8.

10. Use of a cobalt-doped nickel-based coordination polymer catalyst as an oxygen evolution catalyst, characterized in that: The cobalt-doped nickel-based coordination polymer catalyst is prepared according to the preparation method of the cobalt-doped nickel-based coordination polymer catalyst according to any one of claims 1 to 8.

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