Preparation method of unsaturated coordination boron-doped nickel-based metal organic framework material, product and application thereof

Abstract

The application discloses a preparation method of an unsaturated coordination boron-doped nickel-based metal organic framework material, which comprises the following steps: (1) stirring and dissolving a nickel salt, 1,4-benzenedicarboxylic acid and 4-carboxyphenylboronic acid in a solvent to obtain a precursor solution; and (2) adding triethylamine into the precursor solution obtained in the step (1) to obtain the unsaturated coordination boron-doped nickel-based metal organic framework material. The application further discloses the unsaturated coordination boron-doped nickel-based metal organic framework material prepared by the preparation method and application of the unsaturated coordination boron-doped nickel-based metal organic framework material in an electric reduction O2 production H2O2 reaction. The application of the catalytic material as an electric catalyst in the electric reduction O2 production H2O2 reaction in an alkaline electrolyte. The catalytic material exhibits excellent two-electron electric reduction O2 production H2O2 activity and selectivity in the alkaline electrolyte, and has good catalytic stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrocatalytic materials, in particular to a preparation method of unsaturated coordination boron-doped nickel-based metal organic framework material, and products and applications thereof. BACKGROUND

[0002] Hydrogen peroxide (H2O2) as a green and environmentally friendly inorganic oxidant has been widely used in various chemical production processes, such as chemical synthesis, paper industry, sewage treatment, medical disinfection and other application scenarios. At present, the preparation of H2O2 still mainly relies on the traditional anthraquinone hydrogenation production technology. However, the anthraquinone process for preparing H2O2 requires large equipment investment and energy consumption and will discharge a large amount of waste liquid. In order to reduce transportation costs, the concentration of prepared H2O2 is usually increased to 70wt.%, which will significantly increase the explosion risk during transportation.

[0003] The electrocatalytic two-electron oxygen reduction (2e - ORR) technology can realize green on-site production of H2O2 and solve the problems faced by the traditional anthraquinone process. Although Pd, Pt and other noble metal-based electrocatalysts have the advantages of small overpotential and high two-electron ORR selectivity, their further development is limited due to the scarcity of their crustal content, so it is necessary to develop non-noble metal-based two-electron ORR electrocatalysts with high activity and selectivity. In recent years, metal organic framework (MOF) materials have been widely used as precursors due to their adjustable metal coordination and porous structure, and after high-temperature calcination, nanocarbon-based two-electron ORR electrocatalysts are prepared.

[0004] A preparation method of an iron-doped porous carbon oxygen reduction catalyst is disclosed in Chinese patent document CN114150333A. The method uses an iron-based MOF material as a precursor, and through high-temperature carbonization treatment in an inert atmosphere, then washes off the excess iron with sulfuric acid, and the obtained material has excellent acidic two-electron ORR H2O2 production performance. A preparation method of an electro-synthetic H2O2 catalyst is disclosed in Chinese patent document CN116043266A. The method uses MOF material ZIF-67 as a precursor, and through high-temperature annealing carbonization, vacuum solid-phase phosphorization and selenization, a CoPSe catalyst is finally obtained, which has excellent acidic two-electron ORR H2O2 production activity and selectivity. Erhuan Zhang et al. prepared a single-atom In-loaded hollow nanocarbon rod catalyst with N, S first coordination and B second coordination by high-temperature pyrolysis of heteroatom-modified In-based MOF material coupled with acid washing strategy, which has excellent alkaline two-electron ORR H2O2 production selectivity (Angew. Chem. Int. Ed. 2022, 61, e202117347).

[0005] However, the MOF material is used as a precursor template to prepare a nano-carbon-based electrocatalyst through high-temperature pyrolysis, which completely destroys the MOF skeleton structure, causes serious agglomeration of the metal sites therein, and cannot utilize the structural advantages of the original MOF material. However, the selectivity and activity of the MOF material directly used as an electrocatalyst for the electro-reduction of O2 to produce H2O2 are still weak.

[0006] Therefore, how to improve the catalytic activity and selectivity of the MOF material is a research hotspot in the field. SUMMARY

[0007] The purpose of the present application is to provide a preparation method of an unsaturated coordination boron-doped nickel-based metal organic framework material, and an application of the unsaturated coordination boron-doped nickel-based metal organic framework material prepared by the above preparation method as an electrode material for electrocatalytic reduction of oxygen to produce H2O2 in an alkaline electrolyte. The electrode material has excellent catalytic activity and selectivity for a two-electron oxygen reduction reaction under alkaline conditions, and also has good catalytic stability.

[0008] To achieve the above purpose, the present application provides the following technical scheme:

[0009] A preparation method of an unsaturated coordination boron-doped nickel-based metal organic framework material, comprising the following steps:

[0010] (1) Dissolving nickel salt, 1,4-benzenedicarboxylic acid and 4-carboxyphenylboronic acid in a solvent by stirring to obtain a precursor solution;

[0011] (2) Adding triethylamine to the precursor solution obtained in step (1) to obtain an unsaturated coordination boron-doped nickel-based metal organic framework material.

[0012] The preparation principle of the unsaturated coordination boron-doped nickel-based metal organic framework material provided by the present application is as follows: 1,4-benzenedicarboxylic acid is used as an organic ligand, 4-carboxyphenylboronic acid is used as a boron-containing ligand doping regulator, and triethylamine is added to cause deprotonation of the carboxylic acid / hydroxyl groups of the organic linker, thereby initiating self-assembly coordination polymerization of divalent nickel ions with the oxygen sites of 1,4-benzenedicarboxylic acid and 4-carboxyphenylboronic acid, and finally preparing a non-metallic boron-doped nickel-based metal organic framework material with a two-dimensional nanosheet morphology, which can expose more reactive sites. Triethylamine can also generate a small amount of OH - anions in water, thereby stabilizing the layered structure of the two-dimensional metal organic framework and preventing three-dimensional agglomeration.

[0013] The doping of non-metallic boron can not only regulate the electronic structure of the metal-organic framework material, but also reduce the coordination number of the Ni-O coordination configuration, generate more unsaturated coordination Ni center sites in the framework, accelerate the dissociation of water molecules more effectively, enhance the proton-coupled electron transfer process in ORR, and ultimately synergistically improve the two-electron ORR H2O2 production activity and selectivity of the metal-organic framework material.

[0014] The nickel salt in step (1) is a soluble salt, selected from nickel chloride, nickel nitrate, nickel sulfate, and hydrates thereof, etc. Preferably, the nickel salt is nickel chloride hexahydrate.

[0015] The solvent in step (1) is a mixed solvent of water, ethanol, and DMF. The mixed solvent is water:ethanol:DMF = 0.5-2:0.5-2:12-18 mL (volume ratio). Since the organic ligand is dissolved in DMF, but the OH group in water and alcohol is needed for its full coordination, a mixed solvent is needed.

[0016] The stirring time in step (1) is 20-60 min. Magnetic stirring or ultrasonic dispersion can be used to uniformly disperse the nickel salt, 1,4-benzenedicarboxylic acid, and 4-carboxyphenylboronic acid in the mixed solvent.

[0017] In step (1), the mass concentration of the nickel salt is 4-8 g / L, the mass concentration of 1,4-benzenedicarboxylic acid is 2-4 g / L, and the mass concentration of 4-carboxyphenylboronic acid is 0.3-1.4 g / L. When the amount of boron-containing ligand is too low, the doping amount is too small, the influence on the electronic structure of the overall material is small, and the catalytic activity is not significantly improved. When the amount is too high, the boron-containing ligand will preferentially coordinate with the metal ions, causing the material to aggregate and reduce the specific surface area, thereby affecting the activity of the catalyst.

[0018] Preferably, the mass concentration of 4-carboxyphenylboronic acid is 0.7-1.4 g / L. At this time, the doping amount of boron in the product can be ensured to be in a more appropriate range, further improving the two-electron ORR electrocatalytic activity and selectivity, and making the selectivity of electro-reducing O2 to produce H2O2 in alkaline electrolyte at least 87%.

[0019] In step (2), the volume fraction of triethylamine is 2-4%, and the stirring time is 24-48 h. The addition amount of triethylamine is too low or too high, which will affect the coordination rate of the material, and the length of the stirring reaction time will affect the polymerization degree of the material, thereby affecting the micro two-dimensional morphology and unsaturated coordination of the material.

[0020] More preferably, the mixed solvent is water:ethanol:DMF = 1:1:16 mL (volume ratio). The mass concentration of nickel salt is 4.9 g / L, the mass concentration of 1,4-phthalic acid is 2.8 g / L, and the mass concentration of 4-carboxyphenylboronic acid is 0.7 g / L; the volume fraction of triethylamine is 2.2%, and the stirring time is 24 h. Under these conditions, the prepared boron-doped nickel-based metal-organic framework electrode material exhibits high electrocatalytic activity and selectivity in the electroreduction of O2 to H2O2 in an alkaline electrolyte.

[0021] The present invention also provides an unsaturated coordinated boron-doped nickel-based metal-organic framework material prepared by the above preparation method, which can be represented by the chemical formula: B-NiBDC, wherein B is boron doping; and NiBDC is nickel-based metal-organic framework material.

[0022] The unsaturated coordinated boron-doped nickel-based metal-organic framework material has a two-dimensional nanosheet structure.

[0023] This invention also provides the application of the above-mentioned unsaturated coordinated boron-doped nickel-based metal-organic framework material in the electroreduction of O2 to H2O2 reaction in alkaline electrolyte.

[0024] This invention effectively modulates the electronic structure of MOF materials through in-situ non-metallic boron doping and unsaturated site modulation strategies, thereby significantly improving the catalytic activity and selectivity of their two-electron ORR. Specifically, this invention prepares the aforementioned unsaturated coordinated boron-doped nickel-based metal-organic framework material through a ligand regulation strategy, enabling effective rational design of the metal-organic framework structure and thus optimizing its electronic structure. The boron-doped nickel-based metal-organic framework material provided by this invention possesses abundant unsaturated coordinated nickel centers, which can modulate the material's electronic structure while enhancing the rate-controlled proton-coupled electron transfer elementary reaction steps, thereby improving electrocatalytic reaction activity and selectivity.

[0025] When the unsaturated coordinated boron-doped nickel-based metal-organic framework material provided by this invention is used as an electrocatalyst in the electroreduction of O2 to H2O2 in an alkaline electrolyte, it serves as a cathode material for the electrocatalytic generation of H2O2. This catalyst exhibits excellent electrochemical performance and stability.

[0026] In the electroreduction reaction of O2 to produce H2O2, a three-electrode system is adopted. Specifically, an Ag / AgCl electrode is used as the reference electrode, a carbon rod is used as the counter electrode, a rotating ring disk electrode made of boron-doped nickel-based metal-organic framework material provided by the present invention is used as the working electrode, and 0.1 MkOH solution is used as the electrolyte.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The unsaturated coordination boron-doped nickel-based metal organic framework material provided by the application has high efficient electrocatalytic activity and selectivity in the production of H2O2 by the electro-reduction of O2 in an alkaline electrolyte. For example, the selectivity of H2O2 is at least 75% in the potential range of 0-0.55V, and the optimal selectivity is above 95% at the initial potential of 0.74V, which provides the possibility for the realization of green electro-synthesis of H2O2 technology;

[0029] (2) The unsaturated coordination boron-doped nickel-based metal organic framework material provided by the application has a micro two-dimensional nanosheet morphology, which can expose more reaction active sites and is conducive to the electro-catalytic cathodic two-electron ORR;

[0030] (3) The unsaturated coordination boron-doped nickel-based metal organic framework material provided by the application optimizes the electronic structure of the nickel-based metal organic framework material through the doping of boron-containing ligands, generates more unsaturated coordination nickel sites in the metal organic framework, accelerates the reaction kinetics of the proton-coupled electron process, and finally improves the activity and selectivity of the production of H2O2 by the electro-reduction of O2. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 A scanning electron microscope (SEM) image of the B-NiBDC catalytic material prepared in Example 1;

[0032] Figure 2 A transmission electron microscope (TEM) image of the catalyst B-NiBDC catalytic material prepared in Example 1;

[0033] Figure 3 An X-ray diffraction (XRD) image of the catalyst B-NiBDC catalytic material prepared in Example 1;

[0034] Figure 4 Polarization curve images of the catalytic materials prepared in Examples 1-4 and Comparative Example 1 in the production of H2O2 by the electro-reduction of O2 in application examples;

[0035] Figure 5 Polarization curve images of the B-NiBDC catalytic material prepared in Example 1 before and after the CV cycle accelerated aging in the production of H2O2 by the electro-reduction of O2. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical scheme and advantages of the application more clear and understandable, the application will be further described in detail below in combination with examples. It should be understood that the specific examples described herein are only used to explain the application and not to limit the application. Those skilled in the art can modify or replace the equivalent without departing from the spirit and scope of the technical scheme of the application, which should be covered within the protection scope of the application. The raw materials used in the following specific embodiments are all purchased from the market.

[0037] Example 1

[0038] (1) 178 mg of solid particles of nickel chloride hexahydrate, 99.7 mg of solid particles of 1,4-benzenedicarboxylic acid, and 25 mg of solid particles of 4-carboxyphenylboronic acid were weighed and dissolved in a mixed solvent of 2 mL of ethanol, 2 mL of deionized water, and 32 mL of DMF, and stirred at room temperature for 20 min until completely dissolved to obtain a green clear solution;

[0039] (2) 0.8 mL of triethylamine was quickly added to the obtained clear solution, and stirring was continued for 24 h. After centrifugation and washing with DMF and ethanol for several times, the unsaturated coordination boron-doped nickel-based metal organic framework material was finally dried in a vacuum oven at 60°C for 12 h, and was recorded as B-NiBDC.

[0040] Figure 1 The scanning electron microscope (SEM) image of the unsaturated coordination boron-doped nickel-based metal organic framework material prepared in this example is shown in FIG. 1. Figure 2 The transmission electron microscope (TEM) image of the unsaturated coordination boron-doped nickel-based metal organic framework material prepared in this example is shown in FIG. 2. Figures 1-2 It can be seen that the obtained catalytic material has a two-dimensional nanosheet morphology. The X-ray diffraction pattern of the unsaturated coordination boron-doped nickel-based metal organic framework material prepared in this example is shown in FIG. 3. Figure 3 It shows obvious diffraction peaks at positions of 8.7°, 15.5°, 18.2°, and 24.0°, which are consistent with the characteristic peak positions of the nickel-based metal organic framework material obtained by fitting, proving that the doping of non-metallic boron does not change the crystal structure of the nickel-based metal organic framework material, and also does not form a metal compound.

[0041] Example 2

[0042] According to the preparation process of Example 1, the addition amounts of 1,4-benzenedicarboxylic acid and 4-carboxyphenylboronic acid in step (1) were changed to 112.1 mg and 12.4 mg, respectively, to obtain a catalytic material.

[0043] Example 3

[0044] According to the preparation process of Example 1, the addition amounts of 1,4-benzenedicarboxylic acid and 4-carboxyphenylboronic acid in step (1) were changed to 87.2 mg and 37.2 mg, respectively, to obtain a catalytic material.

[0045] Example 4

[0046] According to the preparation process of Example 1, the addition amounts of 1,4-benzenedicarboxylic acid and 4-carboxyphenylboronic acid in step (1) were changed to 74.8 mg and 50 mg, respectively, to obtain a catalytic material.

[0047] Comparative Example 1

[0048] According to the process of Example 1, the difference is that no 4-carboxyphenylboronic acid is added in step (1) to obtain a nickel-based metal organic framework electrode material, denoted as NiBDC.

[0049] Application Example

[0050] (1) Using a three-electrode system, the dispersion liquid drop configured with the catalytic material prepared in Examples 1-4 or Comparative Example 1 is coated on a rotating ring-disk electrode with a platinum ring, and after natural drying, it is used as a working electrode, the counter electrode is a carbon rod, the reference electrode is a saturated Ag / AgCl electrode, and the electrolyte is 0.1M KOH;

[0051] (2) Using a Shanghai Chenhua CHI 760E electrochemical workstation, oxygen is introduced into the electrolyte for 20 min before testing. The CV program is used, and the test interval is 1.0-0V vs. reversible hydrogen electrode (RHE) with a scan rate of 50mV s -1 , and the catalytic material is cycled for 20 cycles to reach a stable state. Linear sweep voltammetry (LSV) test is performed on the catalysts prepared in Examples 1-4 and Comparative Example 1. After CV activation, the program is switched to LSV program, and the test interval is 1.0-0V vs. RHE, the working electrode rotation speed is 1600rpm, the scan rate is 5mV / s, and the platinum ring is applied with a constant voltage of 1.2V vs. RHE. The polarization curve of the catalytic material provided by Examples 1-4 and Comparative Example 1 for the electro-reduction of O2 to produce H2O2 in oxygen-saturated 0.1M KOH solution is shown in Figure 4 , and it can be seen from Figure 4 that the catalytic materials prepared in each example have good performance for the electro-reduction of O2 to produce H2O2 in alkaline electrolyte. The starting potential of the catalytic material of Example 1 is only 0.74V, and the H2O2 selectivity is >95%, which has excellent activity and selectivity. The starting potential of the catalytic material of Comparative Example 1 is 0.70V, and the H2O2 selectivity is only about 70%, which proves that the doping of non-metallic boron can significantly improve the catalytic performance of the nickel-based metal organic framework electrode material.

[0052] Among them, the selectivity of the catalysts prepared in Examples 2-4 is 81%, 75% and 87% respectively.

[0053] The ring current Ir and the disk current Id and the electron collection rate N of the rotating ring-disk electrode can be calculated according to the following formula: Figure 4 Selectivity% = 2*Ir / (NId+Ir)*100%.

[0054] Stability test of the catalyst prepared in Example 1

[0055] The stability of the catalytic material is tested by 5000-cycle CV cycle aging test. As Figure 5As shown, the polarization curves of the unsaturated coordinated boron-doped nickel-based metal-organic frameworks after CV aging did not change significantly, and still maintained excellent H2O2 production activity and selectivity, proving its superior catalytic stability.

Claims

1. An application of an unsaturated coordinated boron-doped nickel-based metal-organic framework material, characterized in that, Application of the unsaturated coordinated boron-doped nickel-based metal-organic framework material in the electroreduction of O2 to H2O2 reaction in alkaline electrolyte; The preparation method of the unsaturated coordinated boron-doped nickel-based metal-organic framework material includes the following steps: (1) Dissolve nickel salt, 1,4-phthalic acid and 4-carboxyphenylboronic acid in a solvent at room temperature to obtain a precursor solution; (2) Triethylamine was added to the precursor solution obtained in step (1), and the reaction was continued at room temperature to obtain an unsaturated coordinated boron-doped nickel-based metal-organic framework material. The precursor solution in step (1) has a nickel salt concentration of 4–8 g / L, a 1,4-phthalic acid concentration of 2–4 g / L, and a 4-carboxyphenylboronic acid concentration of 0.3–1.4 g / L. The triethylamine in step (2) accounts for 2-4% of the volume of the precursor solution; The unsaturated coordinated boron-doped nickel-based metal-organic framework material has a two-dimensional nanosheet structure.

2. The application of the unsaturated coordinated boron-doped nickel-based metal-organic framework material according to claim 1, characterized in that, The nickel salt mentioned in step (1) is a soluble salt selected from nickel chloride, nickel nitrate, nickel sulfate and their hydrates.

3. The application of the unsaturated coordinated boron-doped nickel-based metal-organic framework material according to claim 1, characterized in that, The solvent is a mixture of water, ethanol and DMF.

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