A method for preparing a catalyst for electrocatalytic preparation of hydrogen peroxide and products and uses thereof

Abstract

The application discloses a preparation method of a catalyst for electrocatalytic preparation of hydrogen peroxide, and a product and application thereof. The application adopts a hydrothermal method to prepare a precursor NiS2 by using nickel sulfate hexahydrate, anhydrous sodium thiosulfate and sublimed sulfur as raw materials, then adopts CVD deposition and high-temperature pyrolysis treatment to prepare C-coated Ni3S2 by using anhydrous ethanol as a carbon source, and the NiS2-CVD-600-40 has very excellent two-electron oxygen reduction selectivity, when the disc electrode voltage is-0.5V, the electron transfer number is close to 2, and the H2O2 selectivity can reach 93%; when the NiS2-CVD-600-40 is used as a catalyst to assemble H pool and flow pool to produce H2O2, the H2O2 production rates are 846mmol.gcat ‑1 ·h ‑1 and 2860mmol.gcat ‑1 ·h ‑1 respectively.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically relating to a method for preparing a catalyst for the electrocatalytic preparation of hydrogen peroxide, its products, and applications. Background Technology

[0002] Electrocatalytic oxygen reduction is a broad field with two pathways: four-electron ORR and two-electron ORR. The products of these two pathways are H2O and H2O2, respectively. The process of generating H2O through four-electron ORR is mainly studied in fuel cells or metal-air batteries, while generating H2O2 through two-electron ORR is considered an effective strategy for the green production of hydrogen peroxide.

[0003] H2O2 is a multifunctional and environmentally friendly oxidant, a crucial chemical in modern industry, with wide applications in bleaching, textiles, chemical synthesis, wastewater treatment, disinfection, and semiconductor manufacturing. Currently, 95% of H2O2 is synthesized via the anthraquinone process, but this process is energy-intensive, complex, requires precious metal catalysts, and produces many toxic byproducts. Furthermore, the anthraquinone process requires large-scale equipment, making decentralized H2O2 production difficult and posing significant storage and transportation safety risks. Direct synthesis of H2O2 from H2 and O2 is an alternative strategy, but H2 / O2 mixtures have a large explosive range (4–94 mol% H2), posing substantial safety hazards. Against this backdrop, electrocatalytic two-electron oxygen reduction (2e2O2) has attracted increasing attention due to its safety, environmental friendliness, and ability to achieve decentralized H2O2 production. However, due to the 2e2O2 production process… - The ORR path is always subject to 4e, which is thermodynamically more likely to occur. - Competition exists along the ORR pathway, therefore developing highly selective and stable catalysts is crucial for promoting 2e- ... - ORR production of H2O2 is crucial.

[0004] Noble metals typically possess high catalytic activity, selectivity, and stability for the electroreduction of O2 to H2O2, making them a promising class of catalysts, especially Pd-based catalysts, which exhibit high two-electron selectivity. However, the scarcity and high cost of Pd limit its application in the 2e-electron phase. - Large-scale application of ORR in producing H2O2. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0006] As one aspect of the present invention, the present invention provides a method for preparing a catalyst for the electrocatalytic preparation of hydrogen peroxide, which comprises the following steps:

[0007] (1) Preparation of precursor NiS2: Nickel sulfate hexahydrate and sodium thiosulfate pentahydrate were dissolved in water and mixed to form a solution. Sulfur powder was added, and the mixture was stirred and transferred to a hydrothermal reactor with a polytetrafluoroethylene liner. The reaction was carried out in a forced-air drying oven at 130-150°C. After cooling to room temperature, the mixture was filtered, washed, and dried to obtain NiS2 powder.

[0008] (2) Spread the NiS2 powder evenly in a flat magnetic boat, then place the magnetic boat in a quartz tube, place it on a tube furnace connected to a chemical vapor deposition generator, introduce inert gas to exhaust air, heat the tube furnace to 400-600°C at a heating rate of 4-5°C / min, and at the same time, draw anhydrous ethanol into the chemical vapor deposition generator and maintain for 2 hours to obtain a catalyst for the electrocatalytic preparation of hydrogen peroxide.

[0009] As a preferred embodiment of the preparation method of the catalyst for the electrocatalytic preparation of hydrogen peroxide according to the present invention: In step (1), 0.01 mol of nickel sulfate hexahydrate and 0.01 mol of sodium thiosulfate pentahydrate are dissolved in a beaker containing 40 mL of water, and ultrasonically mixed for 5 min in an ultrasonic cleaner to form a homogeneous solution. 0.01 mol of sulfur powder is added, and after stirring and mixing, it is transferred to a hydrothermal reactor with a polytetrafluoroethylene liner. The reaction is carried out in a forced-air drying oven at 140°C. After cooling to room temperature, the mixture is filtered, washed, and dried to obtain NiS2 powder.

[0010] As a preferred embodiment of the preparation method of the catalyst for the electrocatalytic preparation of hydrogen peroxide according to the present invention: in step (1), the stirring and mixing is carried out at a speed of 400 r / min for 30 min.

[0011] As a preferred embodiment of the preparation method of the catalyst for the electrocatalytic preparation of hydrogen peroxide according to the present invention: in step (1), the reaction is carried out in the drying oven at 130-150°C for 24 hours.

[0012] As a preferred embodiment of the preparation method of the catalyst for the electrocatalytic preparation of hydrogen peroxide according to the present invention: in step (1), the washing is performed by washing with anhydrous ethanol, CS2, 1M HCl and deionized water in sequence.

[0013] As a preferred embodiment of the preparation method of the catalyst for the electrocatalytic preparation of hydrogen peroxide according to the present invention: in step (1), the drying is vacuum drying at 80°C for 10 hours.

[0014] As a preferred embodiment of the preparation method of the catalyst for the electrocatalytic preparation of hydrogen peroxide according to the present invention: in step (2), the inert gas, including argon, is introduced.

[0015] As a preferred embodiment of the preparation method of the catalyst for the electrocatalytic preparation of hydrogen peroxide according to the present invention: in step (2), anhydrous ethanol is drawn into a chemical vapor deposition generator, wherein the amount of anhydrous ethanol injected is 30-40 mL of anhydrous ethanol per 100 mg NiS2 powder.

[0016] The beneficial effects of this invention are as follows: This invention uses nickel sulfate hexahydrate, anhydrous sodium thiosulfate, and sublimed sulfur as raw materials to prepare the precursor NiS2 via a hydrothermal method. Subsequently, using anhydrous ethanol as the carbon source, C-coated Ni3S2 is prepared from the precursor NiS2 through simultaneous CVD deposition and high-temperature pyrolysis treatment, named NiS2-CVD-XY (X is the pyrolysis temperature, Y is the amount of anhydrous ethanol added). Electrochemical tests show that the optimal pyrolysis temperature is 600℃ and the optimal ethanol injection volume is 40mL. Further electrochemical tests and structural characterization confirm that the Ni3S2 phase in NiS2-CVD-600-40 is 2e-. - The main source of activity for ORR (Orthogonal Oxygen Reduction), and the carbon deposited on the CVD catalyst can effectively improve the conductivity of the catalyst material and increase the current density of ORR. Furthermore, DFT calculations show that the deposited carbon can effectively adjust the electron cloud density of Ni in the Ni3S2 phase, thereby adjusting the adsorption degree of O2 molecules and some oxygen-containing intermediates by Ni3S2 and improving two-electron selectivity. Simultaneously, the free energy spectrum shows that electrochemical tests also indicate that NiS2-CVD-600-40 has excellent two-electron oxygen reduction selectivity. When the disk electrode voltage is -0.5V, its electron transfer number is close to 2, and the H2O2 selectivity can reach 93%. When NiS2-CVD-600-40 is used as a catalyst to assemble H2O2 production in both the H-cell and flow cell, the H2O2 yield is 846 mmol·gcat. -1 ·h -1 and 2860 mmol·gcat -1 ·h -1 . Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below, wherein:

[0018] Figure 1 This is a schematic diagram of the preparation of NiS2-CVD-600-40.

[0019] Figure 2XRD diffraction patterns of NiS2, NiS2-600 and NiS2-CVD-600-40 catalysts.

[0020] Figure 3 Raman spectra are shown for (a) NiS2, (b) NiS2-600, and (c) NiS2-CVD-600-40 catalysts.

[0021] Figure 4 For morphological characterization, SEM images of (a) NiS2, (b) NiS2-600 and (c) NiS2-CVD-600-40 catalysts are shown; (d) transmission electron microscopy image of NiS2-CVD-600-40, (e) high-resolution transmission electron microscopy image, and (f) mapping image are shown.

[0022] Figure 5 (a) X-ray photoelectron spectra of NiS2, NiS2-600 and NiS2-CVD-600-40 catalysts; (b) C1s high-resolution photoelectron spectrum of NiS2-CVD-600-40; (c) Ni 2p high-resolution photoelectron spectrum of NiS2-600 and NiS2-CVD-600-40; (d) S 2p high-resolution photoelectron spectrum of NiS2-CVD-600-40.

[0023] Figure 6 The CV curves of NiS2-CVD-600-40 catalyst in different gases are shown.

[0024] Figure 7 (a) disk current density, (b) ring current, (c) number of electrons transferred per O2 molecule, and (d) H2O2 selectivity of NiS2, NiS2-600, NiS2-CVD-600-40, and carbon black-CVD-600-40 catalysts obtained by RRDE testing.

[0025] Figure 8 (a) disk current density, (b) ring current, (c) number of electrons transferred per O2 molecule, and (d) H2O2 selectivity of NiS2-CVD-500-40, NiS2-CVD-600-40, and NiS2-CVD-700-40 catalysts obtained by RRDE testing.

[0026] Figure 9 (a) disk current density, (b) ring current, (c) number of electrons transferred per O2 molecule, and (d) H2O2 selectivity of NiS2-CVD-600-20, NiS2-CVD-600-40, NiS2-CVD-600-60, and NiS2-CVD-600-80 catalysts obtained by RRDE testing.

[0027] Figure 10 The graph shows the electrochemical stability of the NiS2-CVD-600-40 catalyst.

[0028] Figure 11 (a) Schematic diagram of the H cell structure; (b) NiS2-CVD-600-40 catalyst in the H cell at -50 mA·cm -2 (c) Electrolysis curves at current density; (d) UV spectrum of electrolyte for testing electrogenerated H2O2 by NiS2-CVD-600-40 catalyst in H cell; (e) Schematic diagram of flow cell structure; (f) Electrolysis curves of NiS2-CVD-600-40 catalyst in flow cell at -50 mA·cm⁻¹. -2 Electrolysis curves at current density; (f) UV spectrum of electrolyte for testing electrogenerated H2O2 by NiS2-CVD-600-40 catalyst in H cell.

[0029] Figure 12 (a) disk current density, (b) ring current, (c) number of electrons transferred in a single O2 molecule, and (d) H2O2 selectivity for NiS2-CVD-glucose catalyst.

[0030] Figure 13 (a) disk current density, (b) ring current, (c) number of electrons transferred in a single O2 molecule, and (d) H2O2 selectivity for NiS2@C catalyst.

[0031] Figure 14 (a) disk current density, (b) ring current, (c) number of electrons transferred in a single O2 molecule, and (d) H2O2 selectivity for the NiS2-CO2-600 catalyst. Detailed Implementation

[0032] To make the above-mentioned objectives, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to specific examples.

[0033] Example 1:

[0034] Catalyst preparation:

[0035] (1) Preparation of precursor NiS2: First, 0.01 mol nickel sulfate hexahydrate and 0.01 mol sodium thiosulfate pentahydrate were dissolved in a beaker containing 40 mL of deionized water. Then, the mixture was ultrasonicated for 5 min in an ultrasonic cleaner to form a homogeneous solution. Then, 0.01 mol sulfur (S) powder was added to the solution and stirred at 400 r / min for 30 min to uniformly disperse the S powder in the solution. After stirring, the above dispersion was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and reacted at 140 °C for 24 h in a forced-air drying oven. After cooling to room temperature, the mixture was filtered and washed successively with anhydrous ethanol, CS2, 1M HCl and deionized water to remove residual S powder and impurities. Finally, the mixture was vacuum dried at 80 °C for 10 h to obtain NiS2 powder.

[0036] (2) CVD deposition: Using anhydrous ethanol as the carbon source, a carbon layer is deposited on the surface of the NiS2 powder prepared in step (1) by chemical vapor deposition. The specific operation method is as follows: First, weigh 100mg NiS2 powder was spread evenly in a flat magnetic boat. The magnetic boat containing NiS2 powder was then placed in a quartz tube and placed on a tube furnace connected to a CVD gas generator (Hefei Kejing Materials Technology Co., Ltd., LVD-F1). Before heating, high-purity argon gas was purged into the tube furnace for 30 minutes to remove residual air from the quartz tube, with the purging rate maintained at approximately 50 ml / min. The tube furnace was then heated to 600°C at a heating rate of 5°C / min and held at this temperature for 2 hours. During the high-temperature calcination process, when the temperature reached 560°C, the CVD generator was turned on, and its heating switch was also turned on, raising the temperature to 110°C. When the tube furnace temperature reached 600°C, the pump was turned on to draw anhydrous ethanol into the CVD generator. When the anhydrous ethanol injection volume reached 40 mL, the CVD generator was turned off. After the tube furnace heating program ended and the temperature cooled to room temperature, NiS2-CVD-600-40 was obtained. In addition, NiS2-CVD-XY (X = 500, 600, 700; Y = 20, 40, 60, 80) were prepared by changing the pyrolysis temperature and the amount of anhydrous ethanol added, respectively. X is the pyrolysis temperature and Y is the amount of anhydrous ethanol added.

[0037] (3) Preparation of control samples: Ni3S2 without C was prepared by directly calcining NiS2 prepared in step (1) at 600℃ without CVD deposition. The materials obtained by CVD deposition using carbon black (CB) as a precursor and anhydrous ethanol as a carbon source according to the method in step (2) (anhydrous ethanol injection amount of 40mL, pyrolysis temperature of 600℃) were used as control samples. They were named NiS2-600 and CB-CVD-600-40 respectively.

[0038] Analysis and characterization:

[0039] The crystal form and phase composition of the material were analyzed by X-ray diffraction (XRD); the microstructure of the material was observed by scanning electron microscopy (SEM); the internal structure of the material was observed by transmission electron microscopy (TEM), and the composition of the material was further analyzed by high-resolution transmission electron microscopy (HRTEM); the elemental distribution of the material was analyzed by mapping test; the elemental composition and valence state of the material surface were studied by X-ray photoelectron spectroscopy (XPS); the specific surface area, pore size distribution and pore volume of the material were analyzed by N2 adsorption-desorption method; and the material composition, graphitization degree or defect degree of the material were studied by Raman spectroscopy.

[0040] Material structure and characterization:

[0041] Material crystal form analysis:

[0042] First, X-ray diffraction (XRD) was used to analyze the phase composition of the prepared precursor and catalyst. The results are as follows: Figure 2 As shown, the precursor exhibits major peaks at 2θ = 27.058°, 31.468°, 35.224°, 38.736°, 45.105°, 53.353°, 55.966°, 58.416°, and 60.866°, corresponding to the NiS2 θ values ​​of (1-11), (200), (0-12), (-1-12), and (-202), respectively. The presence of (-1-31), (-2-22), (-320), and (2-31) crystal planes indicates that the precursor composition is NiS2. Materials obtained by direct calcination at 600℃ exhibit crystal planes at 2θ = 21.797°, 31.099°, 37.785°, 38.221°, 44.325°, 49.776°, 50.067°, 54.572°, and 55.154°. A major peak appeared at 55.444°, corresponding to the (010), (-110), (111), (-111), (020), (120), (-120), (121), (-121), and (-211) crystal planes of Ni3S2, indicating that NiS2 was transformed into Ni3S2 after direct calcination at 600℃. In addition to having the same diffraction peaks as Ni3S2 obtained by direct calcination at 600℃, the material obtained by simultaneous high-temperature calcination at 600℃ also showed a diffraction peak of the amorphous carbon (002) crystal plane at 2θ = 25.373°, indicating that the surface of Ni3S2 was successfully coated with a carbon layer after CVD deposition, and the crystal form of Ni sulfide is the same as that of NiS2 obtained by direct calcination at 600℃, both being Ni3S2.

[0043] Raman spectral analysis:

[0044] Raman spectroscopy can not only be used to study the degree of graphitization or defects in carbon materials, but also to determine the composition of materials based on certain characteristic peaks. Figure 3 The image shows the Raman spectrum of a material obtained by simultaneously performing NiS2 precursor, direct calcination of NiS2 at 600℃, high-temperature calcination at 600℃, and CVD deposition. Figure 3 (a) Shows precursors at 270.3 and 476.2 cm. -1 There are two characteristic peaks at the point, which correspond to the Eg and Ag photons of NiS2, respectively, which further proves the successful synthesis of the precursor NiS2; Figure 3 (b) is the Raman spectrum of the material obtained by direct calcination of NiS2 at 600℃, showing that it reaches a peak value of 185.4 cm⁻¹. -1 324.2cm -1 198.1cm -1 222.2cm -1 305.7cm -1 and 349.0cm -1 Characteristic peaks appeared at the point, corresponding to the two A1 and four E vibrational models of Ni3S2, respectively, further indicating that NiS2 was transformed into the Ni3S2 crystalline phase after direct calcination at 600℃. Figure 3 (c) The Raman spectrum of the material obtained by simultaneous high-temperature calcination at 600℃ and CVD deposition only shows the region at 1340 cm⁻¹. -1 and 1587cm -1 The D and G peaks of the carbon skeleton at the location were not found, and the characteristic peaks of Ni3S2 were not found. This is because Raman spectroscopy is a surface analysis method, and the surface of the material obtained by simultaneous high-temperature calcination at 600℃ and CVD deposition is coated with carbon. Therefore, only the D and G peaks appeared in its Raman spectrum.

[0045] Morphological characteristics:

[0046] The microstructures of the precursors NiS2, NiS2-600, and NiS2-CVD-600-40 were observed using scanning electron microscopy (SEM). The results are as follows: Figure 4 As shown. Figure 4 (a) shows that the precursor NiS2 is a microsphere composed of many nanosheets of varying sizes, with a thickness of about 30 nm and a relatively smooth surface; Figure 4 (b) is a SEM image of NiS2-600, which shows that it has lost its nanosheet morphology; Figure 4(c) indicates that the surface of NiS2-CVD-600-40 material is a loose and rough carbon layer with mutual cross-linking. The structure of the deposited carbon layer significantly changes the original smooth and complete surface of NiS2 and NiS2-600. This makes NiS2-CVD-600-40 have more exposed sites and specific surface area than NiS2 and NiS2-600, which is beneficial to ORR. Figure 4 The TEM image of NiS2-CVD-600-40 in (d) also shows the successful coating of the carbon layer. The 0.287 nm interplanar spacing in the HRTEM image corresponds to the (110) crystal plane of Ni3S2. This further indicates that after high-temperature calcination and CVD deposition, NiS2 was successfully transformed into the Ni3S2 phase and a thin carbon layer was successfully coated on its surface. Figure 4 (f) is a TEM-Mapping image of NiS2-CVD-600-40, which shows that the material contains four elements: C, O, S, and Ni, and they are evenly distributed in the material.

[0047] XPS Analysis:

[0048] The surface elemental composition and chemical valence state of NiS2, NiS2-600 and NiS2-CVD-600-40 catalysts were analyzed by X-ray photoelectron spectroscopy (XPS). Figure 5 (a) shows the total XPS spectrum of NiS2, NiS2-600 and NiS2-CVD-600-40, where the peaks at 163eV, 284eV, 533eV and 853eV belong to the four elements S, C, O and Ni, respectively. Table 1 shows the elemental content on the surface of NiS2, NiS2-600, and NiS2-CVD-600-40 catalysts. It can be seen that the surface C atom content of the NiS2-CVD-600-40 catalyst is as high as 92.04%. This is because the anhydrous ethanol vaporized in the CVD generator is carbonized at a high temperature of 600 degrees Celsius, forming porous amorphous carbon coating on the Ni sulfide surface. Carbon was still detected on the surfaces of NiS2-600 and NiS2, which did not undergo CVD carbon deposition, with carbon atom percentages of 24.6% and 28.07%, respectively. This is because during XPS sample preparation, the sample comes into contact with air, inevitably causing some contaminating carbon components to adsorb onto the sample surface, which are then detected in the XPS. Meanwhile, the table also shows that the atomic ratio of Ni to S on the surface of NiS2-600 and NiS2-CVD-600-40 catalysts is approximately 3:2. This further illustrates that whether it is direct calcination at 600℃ or CVD deposition followed by high-temperature calcination, NiS2 is transformed into Ni3S2, which is consistent with the previous XRD results. Figure 5(b) shows the high-resolution Ni 2p XPS spectra of NiS2-600 and NiS2-CVD-600-40. Fitting analysis reveals that the peaks at 853.55 eV and 870.75 eV in NiS2-600 belong to Ni 2+ The peaks at 856.40 eV and 874.30 eV belong to Ni. 3+ The peaks at 861.55 eV and 880.35 eV are both satellite peaks; compared with NiS2-600, Ni in NiS2-CVD-600-40 2+ The binding energies of the peaks are 852.90 eV and 870.25 eV, Ni 3+ The binding energies of the peaks are 856.1 eV and 874.06 eV, both shifting towards lower binding energies, indicating an increase in the electron cloud density around Ni in NiS2-CVD-600-40. Furthermore, the peak area ratio suggests that Ni in NiS2-CVD-600-40 exhibits a higher electron cloud density. 2+ The peak area ratio of Ni is higher than that of NiS2-600, which indicates that Ni 3+ To Ni 2+ The transformation. In the high-resolution S 2p XPS spectrum of NiS2-CVD-600-40, the peaks at 162.25 eV and 163.45 eV match S-Ni, the peak at 169.03 eV belongs to SO, and the peaks at 163.78 eV and 164.95 eV belong to satellite peaks. Figure 5 (d) is the high-resolution XPS spectrum of C1s in NiS2-CVD-600-40. The peak at 284.62 eV corresponds to the C-Ni bond, indicating that the outer carbon layer is bonded to Ni in the inner nickel sulfide.

[0049] Table 1. Elemental content of NiS2, NiS2-600 and NiS2-CVD-600-40 catalysts

[0050]

[0051] Specific surface area and pore size distribution:

[0052] Electrochemical testing:

[0053] Except for the H2O2 yield test, all other electrochemical tests were performed on a rotating ring-disc electrode (RRDE). Similar to the 4e-ORR electrochemical test method, the electrode system was a traditional three-electrode system (the catalyst-coated RRDE was the working electrode, the saturated Ag / AgCl electrode was the reference electrode, and the Pt column electrode was the counter electrode). The electrolyte was a 0.1M KOH aqueous solution. Before the test, O2 was bubbled into the electrolyte for 30 minutes to saturate it. The rotation speed of the rotating ring-disc electrode remained at 1600 rpm.

[0054] Figure 6 The figures show the CV curves of the NiS2-CVD-600-40 catalyst under saturated Ar and saturated O2 atmospheres, respectively. It can be seen that an oxygen reduction peak appeared at 0.574 V under saturated O2 atmosphere, while no oxygen reduction peak was observed under saturated Ar atmosphere, indicating that the NiS2-CVD-600-40 catalyst can catalyze ORR well.

[0055] Linear sweep voltammetry (LSV) tests were performed on the precursors NiS2, NiS2-600, and NiS2-CVD-600-40 catalysts. Figure 7 (ab) represent the disk current density and ring current of NiS2, NiS2-600, NiS2-CVD-600-40, and respectively. It can be seen that NiS2-CVD-600-40 has the largest disk current density and ring current. This is because the surface of NiS2-CVD-600-40 is coated with a carbon layer, which can improve the conductivity of the material and thus increase the limiting current. Figure 7 (cd) represents the electron transfer number and H2O2 selectivity of several materials in the voltage range of 0.165–0.5 V (vs. RHE). It can be seen that in this range, the average electron transfer number of the precursor NiS2 is 2.81, and the highest H2O2 selectivity is only 66.9%, while the average electron transfer number of NiS2-600 is 2.26, and the highest H2O2 selectivity can reach 90.3%. This indicates that the two-electron ORR selectivity of NiS2-600 is much better than that of NiS2. Combined with the previous XRD phase analysis and Raman spectroscopy analysis, it is inferred that this is due to the transformation of the NiS2 phase to the Ni3S2 phase. Compared to NiS2-600, the average electron transfer number of NiS2-CVD-600-40 is reduced to 2.18, closer to 2. Its H2O2 selectivity reaches a maximum of 93.7%, and remains above 90% over a wide voltage range. This indicates that the ORR under NiS2-CVD-600-40 catalyst is more biased towards the two-electron pathway. Combined with the previous XPS analysis, this may be because the coated carbon layer bonds with Ni in Ni3S2, effectively regulating the electron cloud density around Ni, thereby altering the selectivity of Ni3S2 for O2 and... ＊ The adsorption of oxygen-containing intermediates such as OOH alters the ORR pathway. Using anhydrous ethanol as the carbon source and carbon black as the substrate, the material obtained by CVD deposition showed an average electron transfer number of 2.88 within a voltage range of 0.165–0.5 V (vs. RHE), with the highest H2O2 selectivity at 66.6%. This is significantly lower than the close 2 of NiS2-600 and NiS2-CVD-600-40, indicating that the Ni3S2 crystalline phase within the porous carbon layer is the main active source for 2e-ORR.

[0056] To investigate the effect of calcination temperature on material properties, CVD deposition was performed at 500℃ and 700℃, respectively, while ensuring the same carbon coating amount (i.e., ensuring that the amount of anhydrous ethanol entering the CVD generator was 40 mL). Electrochemical tests were then conducted, and the results are as follows: Figure 8 As shown, within the voltage range of 0.165–0.5V, the average electron transfer numbers of the material at calcination temperatures of 500℃, 600℃, and 700℃ are 2.41, 2.18, and 2.40, respectively, with the highest H2O2 selectivity being 83.6%, 93.7%, and 82.7%, respectively. This indicates that 600℃ is the optimal calcination temperature for catalytic two-electron ORR.

[0057] Next, while maintaining the calcination temperature at 600℃, the amount of carbon coating was varied by changing the amount of anhydrous ethanol entering the CVD generator, and the effect of carbon coating on the material's catalytic activity against 2e⁻ was investigated. - The impact of ORR performance. Figure 9 The data represent the LSV, electron transfer number, and H2O2 selectivity of the material when the ethanol injection volume into the CVD generator is 20 mL, 40 mL, 60 mL, and 80 mL, respectively. When the ethanol injection volume increases from 20 mL to 40 mL, both disk current density and loop current increase, the average electron transfer number within the 0.165–0.5 V range decreases from 2.23 to 2.18, and the H2O2 selectivity also improves to some extent. When the injection volume continues to increase to 60 mL and 80 mL, both disk current density and loop current further increase, but the average electron transfer number is still higher than that at 40 mL, and the H2O2 selectivity decreases slightly, indicating that 40 mL is the optimal ethanol injection volume.

[0058] High-performance two-electron ORR catalysts must not only have good oxygen reduction catalytic activity and high two-electron selectivity, but also good electrochemical stability. Therefore, stability tests were conducted on NiS2-CVD-600-40. Figure 10 The it curves show that the disk current and ring current decayed very little within 12 hours, indicating that NiS2-CVD-600-40 has good electrocatalytic ORR stability.

[0059] To evaluate the performance of the NiS2-CVD-600-40 catalyst in producing H2O2 in a practical device, the yield of H2O2 produced by NiS2-CVD-600-40 electrocatalysis was measured in an H cell and a flow cell, respectively. Figure 11(a) is a schematic diagram of H2O2 production in an H-cell. The left side is the anode chamber, and the right side is the cathode chamber, separated by a proton exchange membrane. A three-electrode system was used in the test, with the working electrode being hydrophobic carbon paper supported on NiS2-CVD-600-40 catalyst. (First, 2 mg of catalyst was weighed and placed in a small centrifuge tube, then 800 μL of anhydrous ethanol was added as a dispersant, and 5 μL of Nafion 117 solution was added as a binder. The mixture was sonicated for 30 min to obtain a uniformly dispersed catalyst ink. Finally, the catalyst ink was uniformly drop-coated onto a 1.5 cm...) 2 The working electrode was obtained by air-drying on hydrophobic carbon paper with a catalyst loading of 1.33 mg·cm³. -2 The reference electrode was a saturated Ag / AgCl electrode, the counter electrode was a titanium mesh supported on iridium dioxide, and the electrolyte was a 0.1M KOH aqueous solution. Before the test, O2 was passed through the cathode chamber for 30 minutes to saturate the electrolyte with O2. Figure 11 (b) is at -50 mA·cm -2 Electrolysis curves over 1800 s at a given current density. After the reaction, Ce was used... 4+ The yield of H2O2 was determined by titration and UV-Vis spectrophotometry, and the yield was 846 mmol·gcat. -1 ·h -1 .

[0060] Although 2e under NiS2-CVD-600-40 catalysis in H pool - The ORR achieved a high H2O2 yield, but the H2O2 generation rate in the H-cell was still limited by mass diffusion. To further improve the H2O2 yield, a three-phase flow cell reactor was employed. The flow cell can significantly reduce mass transfer limitations, thereby generating a larger H2O2 current. Figure 11 (d) is a schematic diagram of a three-phase flow tank reactor. After O2 enters the gas flow channel from the inlet, part of it is discharged from the outlet, and the other part passes through the PTFE hydrophobic and permeable layer and the gas diffusion layer in sequence. Finally, under the action of NiS2-CVD-600-40 catalyst, two-electron ORR is generated to produce H2O2. Figure 11 (e) is at -50mA·cm- 2 The electrolysis curve of the reaction at a current density for 1800 s, after Ce 4+ Titration and UV-Vis spectrophotometry showed that the yield of H2O2 in the flow cell was 2860 mmol·gcat. -1 ·h -1 It far exceeds the H pool. NiS2-CVD-600-40 has great potential in the actual production of H2O2.

[0061] This invention prepares NiS2 via a one-step hydrothermal method, and then uses NiS2 as a precursor and anhydrous ethanol as a carbon source to prepare C-coated Ni3S2 using a strategy of simultaneous high-temperature pyrolysis and CVD deposition. Electrochemical tests show that NiS2-CVD-600-40, with a pyrolysis temperature of 600℃ and an anhydrous ethanol injection volume of 40 mL, exhibits excellent 2e2 oxidation state. - ORR performance showed a H2O2 selectivity of 93.7%; when NiS2-CVD-600-40 was used as a catalyst to assemble H2O2 production in both the H-cell and flow cell, the H2O2 yields were 846 mmol·gcat. -1 ·h -1 and 2860 mmol·gcat -1 ·h -1 .

[0062] Electrochemical tests and structural characterization revealed that the Ni3S2 phase in NiS2-CVD-600-40 is the main source of activity for 2e-ORR. The C deposited on the CVD effectively improves the conductivity of the catalytic material and increases the ORR current density. Furthermore, XPS analysis showed that the deposited C effectively modulates the electron cloud density of Ni in the Ni3S2 phase, which may adjust the adsorption degree of O2 molecules and some oxygen-containing intermediates by Ni3S2, thereby improving two-electron selectivity.

[0063] Compare with Example 1:

[0064] Catalyst preparation:

[0065] (1) Preparation of precursor NiS2: First, 0.01 mol nickel sulfate hexahydrate and 0.01 mol sodium thiosulfate pentahydrate were dissolved in a beaker containing 40 mL of deionized water. Then, the mixture was ultrasonicated for 5 min in an ultrasonic cleaner to form a homogeneous solution. Then, 0.01 mol sulfur (S) powder was added to the solution and stirred at 400 r / min for 30 min to uniformly disperse the S powder in the solution. After stirring, the above dispersion was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and reacted at 140 °C for 24 h in a forced-air drying oven. After cooling to room temperature, the mixture was filtered and washed successively with anhydrous ethanol, CS2, 1M HCl and deionized water to remove residual S powder and impurities. Finally, the mixture was vacuum dried at 80 °C for 10 h to obtain NiS2 powder.

[0066] (2) CVD deposition: Using glucose as a carbon source, a carbon layer is deposited on the surface of the NiS2 powder prepared in step (1) by chemical vapor deposition. The specific operating method is as follows: First, weigh 100 mg of NiS2 powder and spread it evenly in a flat magnetic boat; then place the magnetic boat containing NiS2 powder in a quartz tube and place it on a tube furnace connected to a CVD gas phase generator. Before heating, purge the tube furnace with high-purity argon gas for 30 min to remove residual air from the quartz tube, maintaining a purge rate of about 50 ml / min. Next, heat the tube furnace to 600°C at a heating rate of 5°C / min and maintain this temperature for 2 h. During the high-temperature calcination process, when the temperature reaches 560°C, turn on the CVD generator and simultaneously turn on its heating switch to raise the temperature to 110°C. When the tube furnace temperature reaches 600°C, turn on the pump to draw glucose (1 M glucose aqueous solution) into the CVD generator. When the glucose injection volume is 40 mL, turn off the CVD generator. After the tube furnace heating program ends and the temperature drops to room temperature, NiS2-CVD-glucose is obtained.

[0067] As attached Figure 12 As shown, the disk current density and ring current of NiS2-CVD-glucose, as well as the number of electrons transferred and H2O2 selectivity in the voltage range of 0.165 to 0.5 V (vs. RHE), show that the average number of electrons transferred in NiS2-CVD-glucose is 2.43 in this range, and the H2O2 selectivity reaches the highest of 81.1%, while the hydrogen peroxide selectivity is much lower than that of NiS2-CVD-600-40.

[0068] Compare with Example 2:

[0069] Catalyst preparation:

[0070] (1) Preparation of precursor NiS2: First, 0.01 mol nickel sulfate hexahydrate and 0.01 mol sodium thiosulfate pentahydrate were dissolved in a beaker containing 40 mL of deionized water. Then, the mixture was ultrasonicated for 5 min in an ultrasonic cleaner to form a homogeneous solution. Then, 0.01 mol sulfur (S) powder was added to the solution and stirred at 400 r / min for 30 min to uniformly disperse the S powder in the solution. After stirring, the above dispersion was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and reacted at 140 °C for 24 h in a forced-air drying oven. After cooling to room temperature, the mixture was filtered and washed successively with anhydrous ethanol, CS2, 1M HCl and deionized water to remove residual S powder and impurities. Finally, the mixture was vacuum dried at 80 °C for 10 h to obtain NiS2 powder.

[0071] (2) Impregnation method: Using glucose as the carbon source, a layer of carbon is coated onto the outside of NiS2 through impregnation. After pyrolysis and carbonization, NiS2@C material is obtained. The specific method is as follows: First, prepare a 1M glucose solution. Accurately weigh 18.198g of glucose and add it to a 200mL beaker. Then, accurately measure 100mL of deionized water and pour it into the beaker. Then, place the beaker in an ultrasonic water bath to accelerate dissolution and obtain a 1M glucose solution. Accurately weigh 50mg of NiS2 and add it to the 1M glucose solution. Stir at room temperature for 8 hours. This completely impregnates the surface of NiS2 with a layer of glucose. After impregnation, remove excess aqueous solution by filtration and then place it in a vacuum drying oven and dry it overnight at 80℃. After drying, pyrolyze and carbonize the sample in an inert gas N2 at 600℃ for 2 hours to obtain the product NiS2@C. The heating rate during the heating process is maintained at 5℃ / min.

[0072] As attached Figure 13 As shown, the disk current density and ring current of NiS2@C, as well as the number of electrons transferred and H2O2 selectivity in the voltage range of 0.165–0.5 V (vs. RHE), show that the disk current and ring current of NiS2-CVD-glucose are much lower than those of NiS2-CVD-600-40, with an average number of electrons transferred of 2.77 and a maximum H2O2 selectivity of only 68.7%. This indicates that the conductivity and hydrogen peroxide selectivity of the catalyst treated by impregnation with carbon coating are significantly lower than those of the CVD-coated catalyst.

[0073] Compare with Example 3:

[0074] Catalyst preparation:

[0075] (1) Preparation of precursor NiS2: First, 0.01 mol nickel sulfate hexahydrate and 0.01 mol sodium thiosulfate pentahydrate were dissolved in a beaker containing 40 mL of deionized water. Then, the mixture was ultrasonicated for 5 min in an ultrasonic cleaner to form a homogeneous solution. Then, 0.01 mol sulfur (S) powder was added to the solution and stirred at 400 r / min for 30 min to uniformly disperse the S powder in the solution. After stirring, the above dispersion was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and reacted at 140 °C for 24 h in a forced-air drying oven. After cooling to room temperature, the mixture was filtered and washed successively with anhydrous ethanol, CS2, 1M HCl and deionized water to remove residual S powder and impurities. Finally, the mixture was vacuum dried at 80 °C for 10 h to obtain NiS2 powder.

[0076] (2) Chemical vapor deposition: Using carbon dioxide as the carbon source, a carbon layer is deposited on the surface of the NiS2 powder prepared in step (1) by chemical vapor deposition. The specific operation method is as follows: First, weigh 100mg of NiS2 powder and spread it evenly in a flat magnetic boat; then place the magnetic boat containing NiS2 powder in a quartz tube. Before heating, first pass high-purity carbon dioxide gas into the tube furnace for 30min to remove the residual air in the quartz tube. The gas flow rate is maintained at about 50ml / min. Next, heat the tube furnace to 600℃ at a heating rate of 5℃ / min and maintain it at this temperature for 2h. After the tube furnace heating program ends and cools to room temperature, NiS2-CO2-600 is obtained.

[0077] As attached Figure 14 As shown, the disk current density and ring current of NiS2-CO2-600, as well as the number of electrons transferred and H2O2 selectivity in the voltage range of 0.165–0.5 V (vs. RHE), reveal that the average number of electrons transferred in NiS2-CVD-glucose is 2.63 within this range, and the highest H2O2 selectivity only reaches 73.9%. This indicates that the carbon encapsulation effect using CO2 as the carbon source is significantly worse than that using ethanol. Therefore, ethanol is preferred as the carbon source.

[0078] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a catalyst for the electrocatalytic production of hydrogen peroxide, characterized in that: It consists of the following steps, (1) Preparation of precursor NiS2: Nickel sulfate hexahydrate and sodium thiosulfate pentahydrate were dissolved in water and mixed to form a solution. Sulfur powder was added, and the mixture was stirred and transferred to a hydrothermal reactor with a polytetrafluoroethylene liner. The reaction was carried out in a forced-air drying oven at 130~150℃. After cooling to room temperature, the mixture was filtered, washed, and dried to obtain NiS2 powder. (2) Spread the NiS2 powder evenly in a flat magnetic boat, then place the magnetic boat in a quartz tube and place it on a tube furnace connected to a chemical vapor deposition generator. Inert gas is introduced to remove air. The tube furnace is heated to 400-600°C at a heating rate of 4-5°C / min. At the same time, anhydrous ethanol is drawn into the chemical vapor deposition generator. The amount of anhydrous ethanol injected is 30-40 mL of anhydrous ethanol per 100 mg NiS2 powder. Keep for 2 h to obtain the catalyst for the electrocatalytic preparation of hydrogen peroxide.

2. The method for preparing the catalyst for electrocatalytic preparation of hydrogen peroxide according to claim 1, characterized in that: In step (1), 0.01 mol of nickel sulfate hexahydrate and 0.01 mol of sodium thiosulfate pentahydrate are dissolved in a beaker containing 40 mL of water and ultrasonicated for 5 min in an ultrasonic cleaner to form a homogeneous solution. 0.01 mol of sulfur powder is added, and after stirring and mixing, the mixture is transferred to a hydrothermal reactor with a polytetrafluoroethylene liner. The mixture is reacted at 140°C in a forced-air drying oven. After cooling to room temperature, the mixture is filtered, washed, and dried to obtain NiS2 powder.

3. The method for preparing the catalyst for electrocatalytic preparation of hydrogen peroxide according to claim 1 or 2, characterized in that: In step (1), the stirring and mixing is carried out at a speed of 400 r / min for 30 min.

4. The method for preparing the catalyst for electrocatalytic preparation of hydrogen peroxide according to claim 1 or 2, characterized in that: In step (1), the reaction is carried out in the forced-air drying oven at 130~150℃ for 24 h.

5. The method for preparing the catalyst for electrocatalytic preparation of hydrogen peroxide according to claim 1 or 2, characterized in that: In step (1), the washing is performed by sequentially washing with anhydrous ethanol, CS2, 1M HCl and deionized water.

6. The method for preparing the catalyst for electrocatalytic preparation of hydrogen peroxide according to claim 1 or 2, characterized in that: In step (1), the drying is vacuum drying at 80°C for 10 h.

7. The method for preparing the catalyst for electrocatalytic preparation of hydrogen peroxide according to claim 1 or 2, characterized in that: In step (2), an inert gas, including argon, is introduced.

8. The catalyst obtained by the preparation method according to claim 1.

9. The application of the catalyst according to claim 8 in the electrocatalytic preparation of hydrogen peroxide.

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