A supported catalyst for electrocatalytic oxygen reduction to hydrogen peroxide, its preparation method and application.

Abstract

This invention relates to the field of electrosynthesis of high-value-added products, and more particularly to a supported catalyst for the electrocatalytic reduction of oxygen to produce hydrogen peroxide, its preparation method, and its application. The catalyst is represented by the formula NiTPP@CNT-ox, wherein oxygen-doped carbon nanotubes (CNT-ox) serve as the support, and nickel tetraphenylporphyrin (NiTPP) serves as the active site. This invention utilizes a dispersion-adsorption method to adsorb NiTPP onto CNT-ox, obtaining the supported catalyst NiTPP@CNT-ox. The NiTPP@CNT-ox prepared by this invention exhibits high catalytic activity, selectivity, and excellent stability in the electrocatalytic reduction of oxygen to produce hydrogen peroxide, showing promising application prospects.

Description

Technical Field

[0001] This invention relates to the field of electrosynthesis of high value-added products, and more particularly to a supported catalyst for electrocatalytic oxygen reduction to produce hydrogen peroxide, its preparation method, and its application. Background Technology

[0002] Hydrogen peroxide is a promising green chemical with applications in numerous fields, including medicine, textiles, papermaking, caprolactam processes, semiconductors, and aerospace. Traditional production methods, such as the anthraquinone process, suffer from high equipment and production costs, environmental pollution from organic solvents, and safety hazards related to the transportation and storage of high-concentration hydrogen peroxide due to centralized production. Electrochemical synthesis of hydrogen peroxide offers milder reaction conditions, is environmentally friendly, produces high-purity products, and has low production costs. Its hydrogen-oxygen separation design and dispersed equipment avoid some of the difficulties and dangers associated with production, transportation, and storage, making it a promising candidate for practical applications.

[0003] Electrocatalytic oxygen reduction to hydrogen peroxide can be categorized into acidic, neutral, and alkaline reactions based on the pH of the reaction system. Under acidic conditions, the oxygen reduction reaction kinetics are slow, and the hydrogen evolution side reaction is severe. Hydrogen peroxide produced under alkaline conditions has narrower applications and is more prone to self-decomposition, which is exothermic and produces gas, increasing the risks during transportation and storage. Neutral hydrogen peroxide offers greater flexibility in applications and is easier to store, making it suitable for large-scale applications.

[0004] Catalysts are crucial for the industrial application of electrocatalytic oxygen reduction to hydrogen peroxide. Catalyst performance also exhibits a correlation with the pH value of the reaction system, specifically in the following ways (including but not limited to): 1) Reaction mechanism: Acidity is O2 + 2H+ + +2e - →H₂O₂; alkaline reaction: O₂ + H₂O + 2e⁻ - →HO2 - 2) Reaction pathway: The reduction of oxygen can proceed via a four-electron (4e) reaction. - ) or two electrons (2e - The reaction proceeds via a transfer pathway, generating either water or H2O2. Changes in pH affect the adsorption pattern of oxygen molecules on the catalyst surface, thus determining the reaction pathway. 3) Reaction kinetics: Changes in pH affect the electrochemical bilayer (EDL) structure and surface adsorption energy, thereby influencing the kinetics of the entire electrochemical process. Therefore, the design principles and performance of catalysts vary significantly across different systems, necessitating the specialized research and development of catalysts for neutral conditions. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a supported catalyst for electrocatalytic oxygen reduction to hydrogen peroxide and its preparation method. A highly active transition metal-nitrogen-carbon catalyst is obtained through a simple and environmentally friendly preparation process, enabling high-selectivity electrocatalytic oxygen reduction to hydrogen peroxide under neutral conditions. This invention improves the spin state and charge distribution of nickel atoms in tetraphenylporphyrin nickel molecules adsorbed on the carbon nanotube surface by oxygen doping, thereby regulating the adsorption energy of key oxygen reduction intermediates and enhancing H2O2 production performance. The prepared catalyst exhibits high activity at 1000 mA cm⁻¹. -2 It has a Faraday efficiency of 85.3% at high current densities.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] In one aspect, the present invention provides a supported catalyst, wherein the catalyst is a tetraphenylporphyrin nickel supported on oxygen-doped carbon nanotubes; the catalyst is represented by the formula NiTPP@CNT-ox, wherein the oxygen-doped carbon nanotube CNT-ox is the support and the tetraphenylporphyrin nickel NiTPP is the active site.

[0008] In the above technical solution, the loading of nickel in the catalyst is further 1-3 wt%.

[0009] Another aspect of the present invention provides a method for preparing the above-mentioned catalyst, wherein oxygen-doped carbon nanotubes are dispersed in a solvent, tetraphenylporphyrin nickel is added, the dispersion is ultrasonically dispersed uniformly, the dispersion is separated and dried to obtain the supported catalyst NiTPP@CNT-ox.

[0010] In the above technical solution, the mass ratio of the oxygen-doped carbon nanotubes to tetraphenylporphyrin nickel is 1:1 to 10:1; the solvent is N,N-dimethylformamide.

[0011] Furthermore, in the above technical solution, the method for preparing the oxygen-doped carbon nanotubes is as follows:

[0012] Step S1: Add carbon nanotubes to nitric acid solution and disperse evenly to obtain a dispersion;

[0013] Step S2: Add the dispersion obtained in step S1 to the polytetrafluoroethylene liner and place it in a hydrothermal reactor;

[0014] Step S3: Heat the hydrothermal reactor containing the dispersion obtained in step S2 to 120~200℃ and keep it at that temperature for 1~8 hours to obtain the hydrothermally treated dispersion.

[0015] Step S4: The dispersion obtained in step S3 is centrifuged, washed with water, and vacuum dried to obtain oxygen-doped carbon nanotubes.

[0016] In the above technical solution, further, in step S1, the mass ratio of the carbon nanotube to the volume of nitric acid is 1~30mg:1mL; the concentration of the nitric acid is 0.1~3mol / L.

[0017] In the above technical solution, further, in step S2, the filling degree of the dispersion in the polytetrafluoroethylene liner is 30~80%.

[0018] The present invention also provides an application of the above-mentioned catalyst in the electrocatalytic oxygen reduction to hydrogen peroxide reaction, wherein the electrolyte system in the electrocatalytic oxygen reduction to hydrogen peroxide reaction is a neutral solution.

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

[0020] (1) This invention uses oxygen-doped carbon nanotubes as a support, which can improve the spin state and charge distribution of nickel atoms in the adsorbed active molecule NiTPP, regulate the adsorption energy of the key ORR intermediate, avoid the problem of slow reaction rate caused by weak adsorption energy, and avoid the problem of low selectivity caused by the difficulty of desorption of intermediates with strong adsorption energy, thus improving the production performance of H2O2 in neutral electrolyte. The supported catalyst NiTPP@CNT-ox was tested in neutral electrolyte (0.1 M K2SO4) using a rotating ring-disk electrode system. The test results showed that NiTPP@CNT-ox had a selectivity of 82.7-99.7% in the potential range of 0.1~0.4 V (vs RHE), proving that it has high hydrogen peroxide selectivity.

[0021] (2) The active adsorbent molecule NiTPP of the catalyst of the present invention has low catalytic activity for the reduction of hydrogen peroxide, which makes the selectivity of hydrogen peroxide high. In addition, NiTPP has high turnover efficiency and can maintain high Faraday efficiency at high current density. Attached Figure Description

[0022] Figure 1 Linear sweep voltammetric curves of the catalysts prepared in Example 1 and Comparative Example 1, obtained by rotating ring disk testing, in neutral electrolyte (0.1 MK2SO4);

[0023] Figure 2 The total X-ray photoelectron spectra of NiTPP@CNT-ox and CNT-ox in Example 1;

[0024] Figure 3 The fine Ni 2p spectra of the X-ray photoelectron spectroscopy of NiTPP@CNT-ox in Example 1, NiTPP@CNT-re in Comparative Example 1, and NiTPP are shown.

[0025] Figure 4Linear sweep voltammetry curves of the catalysts prepared in Example 1, Comparative Example 2 and Comparative Example 3 in neutral electrolyte (0.1 M K2SO4) obtained by rotating ring disk testing;

[0026] Figure 5 Hydrogen peroxide selectivity-potential curves of the catalysts prepared in Examples 1, 2, and 3, obtained by rotating ring disk testing, in neutral electrolyte (0.1 M K2SO4);

[0027] Figure 6 Linear sweep voltammetric curves of the catalysts prepared in Example 1, Comparative Example 2 and Comparative Example 3 in alkaline electrolyte (0.1 M KOH) obtained by rotating ring disk testing;

[0028] Figure 7 Hydrogen peroxide selectivity-potential curves of the catalysts prepared in Example 1, Comparative Example 2 and Comparative Example 3 in alkaline electrolyte (0.1 M KOH) obtained by rotating ring disk testing;

[0029] Figure 8 The variation of Faraday efficiency of NiTPP@CNT-ox in Example 1 under different current densities was tested in a flowing electrolyzer. Detailed Implementation

[0030] The following examples further illustrate the above-described content of the present invention, but it should not be construed as limiting the scope of the subject matter of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention.

[0031] Unless otherwise specified, the materials used in the embodiments of the present invention can be obtained commercially or prepared according to conventional methods known to those skilled in the art.

[0032] Example 1

[0033] (1) Add 1 g of carbon nanotubes to 60 ml of nitric acid solution with a concentration of 2 M and disperse evenly to obtain a dispersion;

[0034] (2) Add the dispersion obtained in step (1) to a polytetrafluoroethylene liner with a volume of 100 mL and place it in a hydrothermal reactor;

[0035] (3) Heat the hydrothermal reactor containing the dispersion obtained in step (2) to 120°C and keep it at that temperature for 2 hours to obtain the hydrothermal treated dispersion.

[0036] (4) The dispersion obtained in step (3) is centrifuged, washed with water and vacuum dried to obtain oxygen-doped multi-walled carbon nanotubes (CNT-ox).

[0037] (5) Take 300 mg of CNT-ox obtained in step (4) and disperse it in the solvent N,N-dimethylformamide. Add 100 mg of nickel tetraphenylporphyrin (NiTPP) and ultrasonically disperse it evenly. After separation and drying, the dispersion is used to obtain the supported catalyst NiTPP@CNT-ox.

[0038] Comparative Example 1

[0039] (1) Add 1 g of carbon nanotubes to 60 ml of nitric acid solution with a concentration of 2 M and disperse evenly to obtain a dispersion;

[0040] (2) Add the dispersion obtained in step (1) to a polytetrafluoroethylene liner with a volume of 100 mL and place it in a hydrothermal reactor;

[0041] (3) Heat the hydrothermal reactor containing the dispersion obtained in step (2) to 120°C and keep it at that temperature for 2 hours to obtain the hydrothermal treated dispersion.

[0042] (4) The dispersion obtained in step (3) is centrifuged, washed with water and vacuum dried to obtain oxygen-doped multi-walled carbon nanotubes (CNT-ox).

[0043] (5) Take 300 mg of CNT-ox obtained in step (4) and put it into the quartz tube of the tube furnace. Pass in a hydrogen-argon mixture with a hydrogen volume content of 5%. Heat the tube furnace to 900 °C and hold for 1 hour. After the tube furnace is cooled down, take out the sample and name it CNT-re.

[0044] (6) Take 300 mg of CNT-re obtained in step (5) and disperse it in the solvent N,N-dimethylformamide. Add 100 mg of nickel tetraphenylporphyrin (NiTPP) and ultrasonically disperse it evenly. After separation and drying, the dispersion is used to obtain the supported catalyst NiTPP@CNT-re.

[0045] Comparative Example 2

[0046] (1) Add 1 g of carbon nanotubes to 60 ml of nitric acid solution with a concentration of 2 M and disperse evenly to obtain a dispersion;

[0047] (2) Add the dispersion obtained in step (1) to a polytetrafluoroethylene liner with a volume of 100 mL and place it in a hydrothermal reactor;

[0048] (3) Heat the hydrothermal reactor containing the dispersion obtained in step (2) to 120°C and keep it at that temperature for 2 hours to obtain the hydrothermal treated dispersion.

[0049] (4) The dispersion obtained in step (3) is centrifuged, washed with water and vacuum dried to obtain oxygen-doped multi-walled carbon nanotubes (CNT-ox).

[0050] (5) Take 300 mg of CNT-ox obtained in step (4) and disperse it in the solvent N,N-dimethylformamide. Add 100 mg of tetraphenylporphyrin cobalt (CoTPP) and ultrasonically disperse it evenly. After separation and drying, the dispersion is used to obtain the supported catalyst CoTPP@CNT-ox.

[0051] Comparative Example 3

[0052] (1) Add 1 g of carbon nanotubes to 60 ml of nitric acid solution with a concentration of 2 M and disperse evenly to obtain a dispersion;

[0053] (2) Add the dispersion obtained in step (1) to a polytetrafluoroethylene liner with a volume of 100 mL and place it in a hydrothermal reactor;

[0054] (3) Heat the hydrothermal reactor containing the dispersion obtained in step (2) to 120°C and keep it at that temperature for 2 hours to obtain the hydrothermal treated dispersion.

[0055] (4) The dispersion obtained in step (3) is centrifuged, washed with water and vacuum dried to obtain oxygen-doped multi-walled carbon nanotubes (CNT-ox).

[0056] (5) Take 300 mg of CNT-ox obtained in step (4) and disperse it in the solvent N,N-dimethylformamide. Add 100 mg of tetraphenylporphyrin iron (FeTPP) and ultrasonically disperse it evenly. After separation and drying, the dispersion is used to obtain the supported catalyst FeTPP@CNT-ox.

[0057] from Figure 1 The linear sweep voltammetry curves of Example 1 and Comparative Example 1 show that NiTPP@CNT-ox prepared by loading NiTPP with oxygen-doped carbon nanotubes exhibits the highest hydrogen peroxide oxidation current. j ring This indicates that it has the highest catalytic activity for producing hydrogen peroxide. In addition, in Example 1 and Comparative Example 1, NiTPP@CNT-ox has the highest hydrogen peroxide selectivity, with a selectivity of 82.7% to 99.7% in the potential range of 0.1 to 0.4 V (vs RHE).

[0058] from Figure 2 The overall X-ray photoelectron spectroscopy spectrum showed that NiTPP@CNT-ox exhibited additional N 1s and Ni 2p peaks compared to CNT-ox, indicating that NiTPP was successfully adsorbed onto CNT-ox. From... Figure 3A comparison of the fine Ni 2p X-ray photoelectron spectroscopy spectra of Example 1 and Comparative Example 1 shows that Ni has a higher binding energy, indicating that the oxygen atoms in CNT-ox have an electronic control effect on Ni. Furthermore, among NiTPP@CNT-ox, CoTPP@CNT-ox, and FeTPP@CNT-ox, NiTPP@CNT-ox exhibits the lowest catalytic activity for hydrogen peroxide reduction (H2O2RR), demonstrating that the generated hydrogen peroxide is further reduced at the lowest rate on its surface. This also explains the high selectivity of NiTPP@CNT-ox for hydrogen peroxide production. Figure 4 and Figure 5 The performance of FeTPP and CoTPP as active molecules was compared, and FeTPP showed lower catalytic selectivity. Figure 6 and Figure 7 The catalytic performance of NiTPP@CNT-ox, CoTPP@CNT-ox and FeTPP@CNT-ox under alkaline conditions (0.1 M KOH solution) was evaluated. Under low potential conditions (0.1~0.3 V), the selectivity was lower than that under neutral conditions. Figure 8 This shows the variation of the Faradaic efficiency of NiTPP@CNT-ox at different current densities during flow electrolysis. The Faradaic efficiency of NiTPP@CNT-ox ranges from 200 to 600 mA cm⁻¹. -2 Within the range, it is higher than 93.2%, 1000mA cm -2 It can also reach 85.3%.

[0059] Table 1 shows the elemental content of CNT-ox, NiTPP@CNT-ox, CNT-re, NiTPP@CNT-re, and NiTPP obtained by X-ray photoelectron spectroscopy and inductively coupled plasma optical emission spectroscopy (ICP-OES). As can be seen from Table 1, compared to CNT-ox, the oxygen content of CNT-re after high-temperature hydrogen reduction treatment is significantly reduced. The lack of interaction between oxygen and nickel leads to a decrease in hydrogen peroxide selectivity in NiTPP@CNT-re.

[0060] Table 1

[0061]

[0062] In summary, on the one hand, compared to NiTPP@CNT-re that has undergone reduction treatment, the method of this invention, by incorporating oxygen atoms, regulates the spin state and charge distribution of nickel atoms, achieving the goal of adjusting the adsorption energy of the key ORR intermediate, thereby obtaining a catalyst NiTPP@CNT-ox with high H2O2 production efficiency, which demonstrates the importance of oxygen doping; on the other hand, compared to CoTPP@CNT-ox and FeTPP@CNT-ox with CoTPP and FeTPP as active centers, NiTPP@CNT-ox exhibits the lowest catalytic activity for hydrogen peroxide reduction (H2O2RR), which demonstrates the importance of selecting NiTPP as the active center.

[0063] The above embodiments are merely preferred examples of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. The application of a supported catalyst in the electrocatalytic reduction of oxygen to hydrogen peroxide, characterized in that, The electrolyte system in the electrocatalytic oxygen reduction to hydrogen peroxide reaction is a neutral solution. The catalyst is oxygen-doped carbon nanotubes supported on tetraphenylporphyrin nickel. The preparation method is as follows: oxygen-doped carbon nanotubes are dispersed in a solvent, tetraphenylporphyrin nickel is added, ultrasonically dispersed evenly, and the dispersion is separated and dried to obtain oxygen-doped carbon nanotubes supported on tetraphenylporphyrin nickel. The oxygen-doped carbon nanotubes are prepared as follows: Step S1: Add carbon nanotubes to nitric acid solution and disperse evenly to obtain a dispersion; Step S2: Add the dispersion obtained in step S1 to the polytetrafluoroethylene liner and place it in a hydrothermal reactor; Step S3: Heat the hydrothermal reactor containing the dispersion obtained in step S2 to 120~200℃ and keep it at that temperature for 1~8 hours to obtain the hydrothermally treated dispersion. Step S4: The dispersion obtained in step S3 is centrifuged, washed with water, and vacuum dried to obtain oxygen-doped carbon nanotubes.

2. The application according to claim 1, characterized in that, The catalyst contains 1-3 wt% nickel.

3. The application according to claim 1, characterized in that, The mass ratio of the oxygen-doped carbon nanotubes to tetraphenylporphyrin nickel is 1:1 to 10:

1.

4. The application according to claim 1, characterized in that, The solvent is N,N-dimethylformamide.

5. The application according to claim 1, characterized in that, In step S1, the mass ratio of the carbon nanotubes to the volume of nitric acid is 1~30 mg: 1 mL; The concentration of the nitric acid is 0.1~3 mol / L.

6. The application according to claim 1, characterized in that, In step S2, the dispersion is filled to 30-80% in the polytetrafluoroethylene liner.

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