A method for preparing a bimetallic oxide heterojunction electrocatalyst having lewis acid sites

Abstract

The application belongs to the technical field of catalysts, and discloses a preparation method of a bimetallic oxide heterojunction with Lewis acid sites, and the bimetallic oxide heterojunction is used for preparing H2O2 in an electrocatalytic oxygen reduction reaction. The preparation steps are as follows: an Al metal salt, a non-Al metal salt and an organic base are mixed, a layered bimetallic hydroxide is generated in a hydrothermal environment, and then the bimetallic oxide heterojunction electrocatalyst is obtained through programmed calcination. In an alkaline electrolyte, in a voltage range of 0.2-0.6 V vs. RHE, the bimetallic oxide heterojunction electrocatalyst synthesized has a high hydrogen peroxide yield, the number of transferred electrons is close to 2, has ideal 2-electron process selectivity of the oxygen reduction reaction, and meanwhile, the bimetallic oxide heterojunction electrocatalyst has excellent cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology and relates to a method for preparing a bimetallic oxide heterojunction electrocatalyst with Lewis acid sites that utilizes the 2-electron process of oxygen reduction reaction to generate H2O2. Background Technology

[0002] Hydrogen peroxide (H2O2), as an important green energy source, is widely used in bleaching, textile mills, chemical synthesis, medical disinfection, wastewater treatment, and semiconductor manufacturing. Currently, H2O2 production mainly employs the industrial anthraquinone process and the direct mixing reaction of H2-O2. However, these methods are characterized by high labor and storage costs, severe pollution, and high transportation risks. Therefore, an economical, environmentally friendly, and safe method for synthesizing H2O2 is needed. In fact, H2O2 can be synthesized via a two-electron electrocatalytic oxygen reduction reaction (ORR). The ORR process is mainly divided into two pathways: the four-electron pathway with H2O as the final product and the two-electron pathway with H2O2 as the final product. The four-electron and two-electron pathways primarily depend on the bond breaking mode in the key reaction intermediate *OOH. Therefore, the electrocatalytic ORR synthesis of H2O2 requires a highly efficient electrocatalyst to improve the selectivity and catalytic activity of the two-electron pathway. Platinum-based catalysts are currently the most commonly used and recognized ORR catalysts. Noble metal catalysts used for the two-electron pathway are typically noble metal alloys. However, the scarcity and high cost of noble metal materials make the development of non-noble metal catalysts particularly important. The diversity and controllability of transition metal catalysts are beneficial for improving H2O2 yield and reducing costs. Cobalt oxide catalysts, with their abundant resources, low cost, and environmental friendliness, are considered promising alternatives to noble metal catalysts. However, the electrocatalytic activity and selectivity of cobalt oxide catalysts in the oxygen reduction reaction are difficult to regulate. Among electrocatalysts synthesized by conventional methods, cobalt oxide catalysts possess a high coordination structure, which facilitates the breaking of the OO bond in *OOH during oxygen reduction, favoring the 4-electron ORR process. The main factors affecting the electronic pathway of oxygen reduction in electrocatalysts are the catalyst's geometry and electronic structure. Lewis acid theory proves that the introduction of Lewis acid Al can regulate the electronic structure of the electrocatalyst, promoting the retention of the OO bond in the reaction intermediate *OOH, which is beneficial for the 2-electron pathway of oxygen reduction. Doping cobalt oxide with Lewis acid sites Al is a feasible strategy to adjust the electron redistribution of oxygen-containing active sites, improve electronic structure and conductivity, and further optimize the adsorption and desorption of the key reaction intermediate *OOH. The formation of bimetallic heterojunction structures with Lewis acid sites can improve catalyst selectivity and H2O2 yield. Summary of the Invention

[0003] This invention discloses a method for preparing a bimetallic oxide heterojunction electrocatalyst that utilizes the two-electron process of the oxygen reduction reaction to generate excess H2O2. This catalyst exhibits high selectivity for the two-electron oxygen reduction process and a high H2O2 yield. Simultaneously, the catalyst possesses excellent stability.

[0004] A method for preparing a bimetallic oxide heterojunction electrocatalyst that utilizes the 2-electron process of the oxygen reduction reaction to generate hydrogen peroxide includes the following steps:

[0005] (1) Weigh out Al metal salt, non-Al metal salt and organic base in a certain proportion, dissolve them in water, and stir at room temperature for 40-60 minutes.

[0006] (2) Transfer the solution obtained in step (1) to a steel autoclave lined with polytetrafluoroethylene and place it in an oven to heat and react. After the reaction is completely cooled, collect the precipitate by centrifugation and wash it several times with deionized water and ethanol respectively. Then centrifuge and dry it in a vacuum oven at a constant temperature of 60-90℃.

[0007] (3) After grinding the sample from step (2), transfer it to a crucible, place the crucible in a tube furnace, seal it, introduce inert gas, and anneal it at 700-900℃ for 1-3 hours. After naturally cooling to room temperature, take the calcined sample out of the quartz tube to obtain a bimetallic oxide heterojunction electrocatalyst with Lewis acid sites.

[0008] In step (1), the non-Al metal salt used is any one of Fe, Co, Ni, Cu, Zn, Mo, W, or Mg.

[0009] In step (1), the organic base used is any one of urea, m-phenylenediamine, hexamethylenetetramine, triethylenediamine or triphenylamine.

[0010] In step (1), the molar ratio of the metal salt mixture to the organic base is 6.0–8.0: 2.5–4.0.

[0011] In step (2), the temperature of the heating reaction is 120-180℃ and the reaction time is 18-30h.

[0012] In step (3), the inert gas is argon or nitrogen.

[0013] The application of the bimetallic oxide heterojunction electrocatalyst with Lewis acid sites prepared in this invention for the preparation of hydrogen peroxide via redox reactions.

[0014] The bimetallic oxide heterojunction electrocatalysts prepared in the above synthesis scheme were mainly evaluated for their performance in the electrocatalytic oxygen reduction reaction using an electrochemical workstation. The evaluation criteria for oxygen reduction performance included the calculated hydrogen peroxide yield, the number of transferred electrons, and stability. These three factors were considered comprehensively to evaluate the electrocatalytic oxygen reduction performance.

[0015] The beneficial effects of this invention:

[0016] (1) The bimetallic oxide heterojunction catalyst prepared by the present invention has high selectivity for the 2-electron process of oxygen reduction reaction, which can replace the high-risk and high-cost anthraquinone synthesis method to synthesize hydrogen peroxide.

[0017] (2) The raw materials used in this invention are abundant and readily available, mainly metal salts and organic bases. The synthesis process is pollution-free and low-cost, achieving the goal of reducing research costs while ensuring no impact on the environment.

[0018] (3) This invention only involves conventional synthesis methods that are easy to operate, such as stirring, vacuum drying and calcination, which not only reduces costs but also facilitates large-scale production and provides convenience for future applications.

[0019] (4) The material prepared by the present invention has excellent catalytic performance. Attached Figure Description

[0020] Figure 1 CoAl2O in Example 1 4 / (a) Scanning electron microscope (SEM) image, (bc) Transmission electron microscope (TEM) image and (d) High-power transmission electron microscope (HRTEM) image of CoO catalyst;

[0021] Figure 2 The X-ray diffraction (XRD) pattern of the CoAl2O4 / CoO catalyst in Example 1;

[0022] Figure 3 (a) shows the CoAl2O4 / CoO catalyst in Example 1 in an O2-saturated atmosphere of 0.1 mol L⁻¹ -1 (a) ORR activity diagram in KOH electrolyte (electrode rotation speed: 1600 rpm); (b) is the ORR activity diagram in Example 1 based on the CoAl2O4 / CoO catalyst in O2-saturated 0.1 mol L -1 Hydrogen peroxide yield and number of transferred electrons were calculated from the ring current and disk current in the KOH electrolyte.

[0023] Figure 4 The CoAl2O4 / CoO catalyst in Example 1 was in O2-saturated 0.1 mol L -1 CV cycle stability test in KOH electrolyte. Detailed Implementation

[0024] This invention provides a method and application for modifying a ring disk electrode with a bimetallic oxide heterojunction electrocatalyst. The invention will be further explained below with reference to the accompanying drawings and specific embodiments to enable those skilled in the art to better understand the operation process of the invention. However, the scope of protection of this invention is not limited to the following embodiments.

[0025] Example 1:

[0026] (1) Weigh out cobalt nitrate: aluminum nitrate: hexamethylenetetramine = 2.5 mmol: 4.5 mmol: 3.5 mmol in a certain ratio, dissolve in water, and stir at room temperature for 50 min;

[0027] (2) The solution obtained in step (1) was transferred to a steel autoclave lined with polytetrafluoroethylene and placed in an oven to heat the reaction at 150°C for 24 hours. After the reaction was completely cooled, the precipitate was collected by centrifugation and washed several times with deionized water and ethanol, respectively. Then it was centrifuged and dried in a vacuum oven at a constant temperature of 60°C.

[0028] (3) After grinding the sample from step (2), transfer it to a crucible, place the crucible in a tube furnace, seal it, introduce argon gas, heat it to 800℃ for annealing for 2 hours, and cool it naturally to room temperature. Then take the calcined sample out of the quartz tube to obtain the bimetallic oxide heterojunction electrocatalyst, named CoAl2O4 / CoO.

[0029] Modification, testing, and assembly of electrode materials:

[0030] (1) Modification of the working electrode:

[0031] 5 mg of CoAl2O4 / CoO catalyst was ultrasonically dispersed in a mixed solution of 1 mL of water and ethanol, and 10 μL of naphthol was added and ultrasonicated to obtain a suspension. 10 μL of the suspension was drop-coated onto a pretreated ring-disk electrode and dried at room temperature for later use.

[0032] (2) Electrochemical testing methods and conditions:

[0033] Electrochemical tests were performed using a CHI 760E electrochemical workstation (Shanghai Chenhua Instruments Co., Ltd.), employing a traditional three-electrode system: a modified electrode as the working electrode, a platinum wire electrode as the counter electrode, and a silver / silver chloride (Ag / AgCl) electrode as the reference electrode (all potentials are relative to the Ag / AgCl electrode). Electrochemical tests were conducted at room temperature and at 0.1 mol / L... -1 In KOH alkaline electrolyte, the potential is -0.2 to -1.0 V (vs. Ag / AgCl).

[0034] Example 2:

[0035] (1) Weigh out nickel chloride: aluminum sulfate: urea in a certain ratio of 2.0 mmol: 5.0 mmol: 4.0 mmol, dissolve in water, and stir at room temperature for 40 min;

[0036] (2) The solution obtained in step (1) was transferred to a steel autoclave lined with polytetrafluoroethylene and placed in an oven for heating at 140°C for 30 hours. After the reaction was completely cooled, the precipitate was collected by centrifugation and washed several times with deionized water and ethanol, respectively. Then it was centrifuged and dried in a vacuum oven at a constant temperature of 70°C.

[0037] (3) After grinding the sample from step (2), transfer it to a crucible, place the crucible in a tube furnace, seal it, introduce nitrogen gas, heat it to 700℃ for annealing for 3 hours, and cool it naturally to room temperature. Then take the calcined sample out of the quartz tube to obtain the bimetallic oxide heterojunction electrocatalyst, named NiAl2O4 / NiO.

[0038] Modification and testing of electrode materials:

[0039] (1) Modification of the working electrode:

[0040] 5 mg of NiAl2O4 / NiO catalyst was ultrasonically dispersed in a mixed solution of 1 mL of water and ethanol, and 10 μL of naphthol was added and ultrasonicated to obtain a suspension. 10 μL of the suspension was drop-coated onto a pretreated ring-disk electrode and dried at room temperature for later use.

[0041] (2) Electrochemical testing methods and conditions:

[0042] Electrochemical tests were performed using a CHI 760E electrochemical workstation (Shanghai Chenhua Instruments Co., Ltd.), employing a traditional three-electrode system: a modified electrode as the working electrode, a platinum wire electrode as the counter electrode, and a silver / silver chloride (Ag / AgCl) electrode as the reference electrode (all potentials are relative to the Ag / AgCl electrode). Electrochemical tests were conducted at room temperature and at 0.1 mol / L... -1 In KOH alkaline electrolyte, the potential is -0.2 to -1.0 V (vs. Ag / AgCl).

[0043] Example 3:

[0044] (1) Weigh out magnesium sulfate: aluminum chloride: m-phenylenediamine in a certain ratio of 3.0 mmol: 4.5 mmol: 4.0 mmol, dissolve in water, and stir at room temperature for 60 min;

[0045] (2) The solution obtained in step (1) was transferred to a steel autoclave lined with polytetrafluoroethylene and placed in an oven to heat the reaction at 160°C for 18 hours. After the reaction was completely cooled, the precipitate was collected by centrifugation and washed several times with deionized water and ethanol, respectively. Then it was centrifuged and dried in a vacuum oven at a constant temperature of 80°C.

[0046] (3) After grinding the sample from step (2), transfer it to a crucible, place the crucible in a tube furnace, seal it, introduce argon gas, heat it to 900℃ for annealing for 1 hour, and cool it naturally to room temperature. Then take the calcined sample out of the quartz tube to obtain the bimetallic oxide heterojunction electrocatalyst, named MgAl2O4 / MgO.

[0047] Modification and testing of electrode materials:

[0048] (1) Modification of the working electrode:

[0049] 5 mg of MgAl2O4 / MgO catalyst was ultrasonically dispersed in a mixed solution of 1 mL of water and ethanol, and 10 μL of naphthol was added and ultrasonicated to obtain a suspension. 10 μL of the suspension was drop-coated onto a pretreated ring-disk electrode and dried at room temperature for later use.

[0050] (2) Electrochemical testing methods and conditions:

[0051] Electrochemical tests were performed using a CHI 760E electrochemical workstation (Shanghai Chenhua Instruments Co., Ltd.), employing a traditional three-electrode system: a modified electrode as the working electrode, a platinum wire electrode as the counter electrode, and a silver / silver chloride (Ag / AgCl) electrode as the reference electrode (all potentials are relative to the Ag / AgCl electrode). Electrochemical tests were conducted at room temperature and at 0.1 mol / L... -1 In KOH alkaline electrolyte, the potential is -0.2 to -1.0 V (vs. Ag / AgCl).

[0052] Figure 1 In example a, the SEM image of the CoAl2O4 / CoO catalyst in Example 1 shows the plate-like structure of CoAl2O4 and the particle structure of CoO. Figure 1 As can be seen from b and c, the CoAl2O4 / CoO catalyst is composed of both CoO particles and CoAl2O4 sheets. Figure 1 The heterojunction interface formed by CoAl2O4 and CoO can be seen in d, which proves the successful synthesis of bimetallic heterojunction.

[0053] Figure 2In Example 1, the XRD pattern of the CoAl2O4 / CoO catalyst showed obvious characteristic peaks of the CoAl2O4 (220), (311), (400), (422), (511), and (440) crystal planes, as well as obvious characteristic peaks of the CoO (111), (200), and (220) crystal planes. This indicates that the metallic phase in the catalyst has good crystallinity and is mainly distributed in the form of CoAl2O4 and CoO; this is consistent with the SEM and TEM results.

[0054] Figure 3 The results of a show that the disk current and ring current of the CoAl2O4 / CoO catalyst in Example 1 are... Figure 3 The results showed that the hydrogen peroxide yield of CoAl2O4 / CoO was around 85% in the voltage range of 0.2–0.6 V vs. RHE, and the number of transferred electrons was close to 2, indicating that the catalyst has ideal selectivity for the 2-electron oxygen reduction reaction.

[0055] Figure 4 The results show that the CV curve of the CoAl2O4 / CoO catalyst did not change significantly after 1000 CV cycles, demonstrating the excellent stability of the CoAl2O4 / CoO catalyst.

[0056] Note: The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Therefore, although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention. All technical solutions and improvements that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. The use of a bimetallic oxide heterojunction electrocatalyst with Lewis acid sites for the oxygen reduction reaction to prepare H2O2, characterized in that, The preparation steps of the electrocatalyst are as follows: (1) Weigh out Al metal salt, non-Al metal salt and organic base in a certain proportion, dissolve them in water and stir at room temperature; The non-Al metal salt used is any one of Fe, Co, Ni, or Mg. (2) Transfer the solution obtained in step (1) to a steel autoclave lined with polytetrafluoroethylene and place it in an oven to heat and react. After the reaction is completely cooled, collect the precipitate by centrifugation and wash it several times with deionized water and ethanol respectively. Then centrifuge and dry it in a constant temperature vacuum oven. (3) After grinding the sample from step (2), transfer it to a crucible, place the crucible in a tube furnace, seal it, introduce an inert gas, heat it to 700~900℃ for annealing for 1~3 h, and cool it naturally to room temperature. Then, take the calcined sample out of the quartz tube to obtain a bimetallic oxide heterojunction electrocatalyst with Lewis acid sites.

2. The use according to claim 1, characterized in that, In step (1), the organic base used is any one of urea, m-phenylenediamine, hexamethylenetetramine, triethylenediamine or triphenylamine.

3. The use according to claim 1, characterized in that, In step (1), the molar ratio of the metal salt mixture to the organic base is 6.0~8.0:2.5~4.

0.

4. The use according to claim 1, characterized in that, In step (1), the stirring time at room temperature is 40~60 min.

5. The use according to claim 1, characterized in that, In step (2), the heating temperature is 120~180℃ and the reaction time is 18~30 h; the drying temperature is 60~90℃.

6. The use according to claim 1, characterized in that, In step (3), the inert gas is argon or nitrogen.

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