Preparation method of cobalt-based molecular catalyst and application of cobalt-based molecular catalyst in electrocatalytic preparation of hydrogen peroxide

Abstract

The invention particularly relates to a preparation method of a cobalt-based molecular catalyst and application of the cobalt-based molecular catalyst in electrocatalytic preparation of hydrogen peroxide. The preparation method of the cobalt-based molecular catalyst comprises the following steps: mixing boron nitride and cobalt phthalocyanine in acetonitrile, carrying out ultrasonic treatment, stirring, standing, calcining the sediment, and grinding to obtain the CBN catalyst. According to the CBN catalyst, when the ratio of m (BN) to m (CoPc) is 6: 1, the hydrogen peroxide production effect of CBN is the best, the selectivity of two-electron oxygen reduction is as high as 97% only in ambient air under the voltage of-0.3 V vs Ag / AgCl, and the yield of hydrogen peroxide is 0.847 mmol / L / cm < 2 >. A novel catalyst material is provided for generating hydrogen peroxide through electro-catalysis of oxygen.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic hydrogen peroxide production technology, and specifically relates to a method for preparing a cobalt-based molecular catalyst and its application in the electrocatalytic production of hydrogen peroxide. Background Technology

[0002] Hydrogen peroxide (H2O2) is a chemically valuable oxidant widely used in various fields, such as water treatment, medical disinfection, chemical synthesis, textile / paper bleaching, and the electronics industry. In recent years, total H2O2 consumption has been growing rapidly at a rate exceeding 50% annually. Therefore, developing efficient and simple methods to produce H2O2 is crucial to meeting its increasing demand. Industrially, H2O2 is produced via the energy-intensive anthraquinone process, which involves the oxidation and reduction of large amounts of anthraquinone. To date, the anthraquinone process accounts for 95% of global and 99% of domestic hydrogen peroxide production. While this method is important for large-scale H2O2 production, it has several drawbacks, such as the need for large plants and infrastructure, high energy input, and costly purification. Furthermore, H2O2 is relatively unstable and hazardous at high concentrations, posing safety concerns during storage and transportation.

[0003] Therefore, exploring convenient and effective alternative methods for producing H2O2 is imperative. Among these, electrochemical methods are an environmentally friendly and economical way to achieve on-site H2O2 production, especially when powered by renewable electricity. This approach not only avoids the safety issues associated with H2O2 production, storage, and transportation, but also eliminates the need for large-scale equipment. Electrocatalysis is used to convert oxygen into hydrogen peroxide (2e⁻). - The ORR process has proven to be a feasible research method. However, due to the uncontrollable adsorption of the intermediate species *OOH by the catalyst, 2e... - The low selectivity of ORR leads to the conversion of oxygen into the four-electron reduction product—water. Therefore, a method for reducing 2e-electron oxygen is designed. - Catalysts with high ORR selectivity are very important. Summary of the Invention

[0004] To address the above problems, this invention provides a method for preparing a cobalt-based molecular catalyst and its application in the electrocatalytic preparation of hydrogen peroxide.

[0005] The technical solution adopted in this invention is:

[0006] A method for preparing a cobalt-based molecular catalyst includes the following steps:

[0007] 1) Mix boron nitride (BN) and cobalt phthalocyanine (CoPc) and add them to a beaker, then pour acetonitrile into the beaker and sonicate.

[0008] 2) Add the rotor to the beaker, stir, let stand, pour off the supernatant, put the sediment into the crucible, and calcine it in the muffle furnace;

[0009] 3) Grind the product obtained after calcination to obtain a cobalt-based molecular catalyst.

[0010] Furthermore, in the above preparation method, in step 1), the mass ratio of boron nitride to cobalt phthalocyanine is 4:1, 6:1, or 8:1.

[0011] Preferably, the mass ratio of boron nitride to cobalt phthalocyanine is 6:1.

[0012] Furthermore, in the above preparation method, in step 1), the amount of acetonitrile used is 60 mL.

[0013] Furthermore, in the above preparation method, step 1), the ultrasonic time is 3 hours.

[0014] Furthermore, in the above preparation method, step 2), the stirring time is 12 hours.

[0015] Furthermore, in the above preparation method, step 2), the standing time is 12 hours.

[0016] Furthermore, in the above preparation method, step 2), the calcination conditions are: heating to 300 ℃ at a heating rate of 5 ℃ / min, and calcining at 300 ℃ for 2 h.

[0017] Application of cobalt-based molecular catalysts prepared by any of the above methods in the electrocatalytic preparation of hydrogen peroxide.

[0018] The beneficial effects of this invention are as follows: This invention combines a cobalt-based molecular catalyst—cobalt phthalocyanine (CoPc)—with boron nitride (BN) through ultrasonic exfoliation followed by calcination to form a thin-layer composite material, named CBN. This composite structure maintains the structure of both boron nitride and the cobalt-based molecular catalyst. Ultrasonic exfoliation of the layered two-dimensional material is achieved. The introduction of boron nitride ensures the stability of cobalt phthalocyanine during sintering and promotes the integrity of the crystal structure of the generated CBN catalyst. Adjusting the feed ratio revealed that when m(BN):m(CoPc) = 6:1, CBN exhibits the best hydrogen peroxide production effect. Under ambient air conditions and at a voltage of -0.3 V vs Ag / AgCl, the selectivity for two-electron oxygen reduction reaches as high as 97%, and the hydrogen peroxide yield is 0.847 mmol / L / cm³. 2 This provides a novel catalyst material for the electrocatalytic production of hydrogen peroxide from oxygen. Attached Figure Description

[0019] Figure 1This is the XRD pattern of the CBN catalyst.

[0020] Figure 2 LSV curves for CBN catalyst tested on a rotating disk electrode.

[0021] Figure 3 Selectivity and electron transfer number of CBN catalyst for hydrogen peroxide production.

[0022] Figure 4 The LSV curves of CBN catalysts formed under different feed amounts are shown.

[0023] Figure 5 The bar chart shows the hydrogen peroxide yield of CBN catalysts formed under different feed amounts. Detailed Implementation

[0024] Example 1

[0025] (I) Preparation method of cobalt-based molecular catalysts

[0026] A mixture of BN and CoPc was added to a beaker at ratios of m(BN):m(CoPc) of 4:1, 6:1, and 8:1, respectively. Then, 60 mL of acetonitrile solvent was added to the beaker, and the mixture was sonicated for 3 hours. A rotor was then added to the beaker, and the mixture was stirred overnight. After standing for 12 hours, the supernatant was discarded. The deposit was placed in a crucible and calcined in a muffle furnace at a heating rate of 5 °C / min to 300 °C for 2 hours. Finally, the calcined product was ground to obtain the CBN catalyst.

[0027] (ii) Material Characterization

[0028] Figure 1 The XRD pattern of the CBN catalyst is shown below. Figure 1 As shown, structural peaks of both BN and cobalt phthalocyanine can be identified on CBN (m(BN):m(CoPc) = 6:1), and no structural change occurs. This demonstrates the successful preparation of the CBN catalyst.

[0029] (III) Performance Testing

[0030] 1. The oxygen reduction reaction (ORR) performance of the catalyst was investigated using a rotating ring-disk electrode (RRDE, AFMSRCE type, Pine Corporation, Hong Kong). First, 2 mg of catalyst powder was mixed with 1 mL of anhydrous ethanol and 20 μL of Nafion solution (5 wt%), and ultrasonically dispersed for 30 min to prepare a homogeneous catalyst ink. A three-electrode system was constructed using a platinum counter electrode and an Ag / AgCl reference electrode, combined with the RRDE. The catalyst was reacted in air-saturated 0.1 M Na₂SO₄ solution (pH 7.2) at a rate of 10 mV s⁻¹. -1 The scan rate and rotation speed were 1600 rpm, the polarization current of the collecting disk electrode and the H2O2 oxidation current of the platinum ring electrode (fixed potential of 1.3 Vvs RHE) were determined. The collection efficiency (N) of the platinum ring electrode for H2O2 was 37% by calibration using the single-electron reversible redox reaction of potassium ferrocyanide / potassium ferricyanide. Based on the corrected current value, the H2O2 selectivity was calculated using formula (1):

[0031] (1)

[0032] Secondly, the formula (2) for calculating the number of electrons transferred is as follows:

[0033] (2)

[0034] In the formula, I R I is the loop current test value. D This is the disk current test value.

[0035] The linear sweep cyclic voltammetry (LSV) curve obtained by rotating ring electrode (RRDE) testing is shown below. Figure 2 As shown, the catalytic behavior of materials BN+CoPc and CoPc in the oxygen reduction reaction (ORR) was compared. In the RRDE test, the disk current (Ic) was... D This mainly reflects the total current of oxygen reduction (including 2e). - The path generates H2O2 and 4e. - The path generates H2O), while the loop current (I) R This was used to detect the oxidation current of the intermediate product H₂O₂. Experimental results showed that the ring current of material BN+CoPc was significantly higher than that of material CoPc, indicating that it was more likely to be affected by the 2e⁻ oxidation process. - H2O2 is generated via the pathway; however, the disk current of material BN+CoPc is lower than that of material CoPc, indicating that its overall ORR activity is lower, but its selectivity is higher. At a potential of -0.3 V vs Ag / AgCl, the H2O2 selectivity of material BN+CoPc is as high as 97%, and the electron transfer number (n) is close to 2 ( Figure 3 Formula (2) shows that it almost perfectly follows 2e- The ORR pathway. In contrast, the electron transfer number of the material CoPc is close to 4, indicating that it dominates the 4e electron transfer pathway. - The path directly generates H2O.

[0036] 2. The current and rate of hydrogen peroxide production via two-electron oxygen reduction using the Shanghai Chenhua electrochemical workstation were tested. The testing method was as follows: 1 mg of CBN catalyst was added to 1 mL of anhydrous ethanol and ultrasonically dispersed until homogeneous. Then, 5 μL of Nafion solution was added dropwise and ultrasonically dispersed again until homogeneous. 50 μL of the dispersion was then taken and dropped onto carbon paper in four portions. The carbon paper loaded with the CBN catalyst was used as the working electrode, Ag / AgCl as the reference electrode, platinum wire as the working electrode, and 0.1 M Na₂SO₄ as the electrolyte. An H-type electrolytic cell was used, which was not sealed, and air was introduced into the electrolyte.

[0037] The effect of different CoPc loadings on the ORR performance of BN-based catalysts was systematically studied. LSV curves measured using the Chenhua electrochemical workstation showed that, when the feed ratios were 4:1, 6:1, and 8:1, although the overall current density of the catalyst did not change significantly with different feed ratios (…),… Figure 4 However, their hydrogen peroxide yields differ significantly. For example... Figure 5 As shown, when the feed ratio is 6:1, the formed CBN catalyst exhibits a superior H2O2 yield of 0.847 mmol / L / cm³ at a potential of -0.3 V vs Ag / AgCl. 2 .

Claims

1. A method for preparing a cobalt-based molecular catalyst, characterized by, The method comprises the following steps: 1) mixing boron nitride and cobalt phthalocyanine into a beaker, then pouring acetonitrile into the beaker and ultrasonicating; 2) adding a rotor into the beaker, stirring, standing, pouring off the supernatant, and placing the deposit into a crucible and calcining in a muffle furnace; 3) grinding the product obtained after calcining to obtain a cobalt-based molecular catalyst.

2. The production method according to claim 1, characterized by, In step 1), the mass ratio of the boron nitride and the cobalt phthalocyanine is 4:1, 6:1 or 8:

1.

3. The production method according to claim 2, characterized by, In step 1), the mass ratio of the boron nitride and the cobalt phthalocyanine is 6:

1.

4. The method of claim 1, wherein, In step 1), the amount of the acetonitrile is 60 mL.

5. The preparation method according to claim 1, characterized in that, In step 1), the ultrasonicating time is 3 h.

6. The method of claim 1, wherein, In step 2), the stirring time is 12 h.

7. The preparation method according to claim 1, characterized in that, In step 2), the standing time is 12 h.

8. The method of claim 1, wherein, In step 2), the calcining condition is: increasing the temperature to 300 ℃ at a temperature increasing rate of 5 ℃ / min, and calcining at 300 ℃ for 2 h.

9. Use of the cobalt-based molecular catalyst prepared by the preparation method in any one of claims 1-8 in electrocatalytic preparation of hydrogen peroxide.

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