A sulfur-defect heterojunction molybdenum disulfide and a light-induced preparation method and application thereof

Abstract

This invention relates to the field of catalyst technology, specifically to a sulfur-defect heterojunction molybdenum disulfide and its photo-induced preparation method and application. The invention provides a method for photo-induced preparation of sulfur-defect heterojunction molybdenum disulfide, comprising: stirring a molybdenum source, a sulfur source, and deionized water until homogeneous, then transferring the mixture to a high-pressure reactor containing carbon cloth, and performing a hydrothermal reaction to obtain carbon cloth uniformly grown with a MoS2 precursor; irradiating the carbon cloth uniformly grown with the MoS2 precursor under a mixed atmosphere of hydrogen and inert gas with a xenon lamp to obtain sulfur-defect-containing heterojunction molybdenum disulfide. This invention proposes using xenon lamp irradiation instead of high-temperature calcination to prepare molybdenum disulfide with S vacancies. Furthermore, the molybdenum disulfide obtained by this method is a heterojunction form with a blend of two crystal phases, which can provide new ideas for subsequent research on crystalline heterojunctions and related methods for creating defects in sulfides.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a sulfur-defect heterojunction molybdenum disulfide, its photo-induced preparation method, and its application. Background Technology

[0002] In today's world, problems such as energy depletion, air pollution, and greenhouse gas emissions continue to plague humanity, prompting the exploration and utilization of clean and renewable energy sources. Hydrogen energy, as a clean, efficient, safe, and sustainable new energy source, is a secondary energy source, making hydrogen production technology one of the core issues in its utilization. Among numerous hydrogen production technologies, electrochemical water splitting (water decomposition into hydrogen and oxygen) shows promising development prospects, and the preparation of highly efficient catalysts for its cathode electrocatalytic hydrogen evolution reaction (HER) is a key technology.

[0003] Molybdenum sulfide (MoS2) possesses high melting point and hardness, good thermal stability, mechanical stability, and excellent corrosion resistance, making it widely used in various fields requiring high temperature resistance, abrasion resistance, and chemical corrosion resistance. Furthermore, its graphene-like structure and excellent physicochemical properties have led to its extensive application in electrocatalytic hydrogen evolution research. Simultaneously, it exhibits electronic structures and catalytic properties similar to noble metals, making it widely applicable as a catalyst for reactions involving hydrogen, such as alkane isomerization, hydrogenation of unsaturated hydrocarbons, hydrodesulfurization, and denitrogenation. Moreover, its catalytic performance is comparable to that of noble metals platinum and iridium, making it a promising electrocatalyst often referred to as a "platinum-like catalyst."

[0004] Edge sites of MoS2 are its main active centers, and these sites possess a low hydrogen evolution reaction free energy barrier, which helps improve the efficiency of HER. The electrocatalytic performance of MoS2 in HER is affected by a variety of factors, including its morphology, crystal phase, and defect structure. Li et al. (ACS nano 13.6(2019):6824-6834.) pointed out that sulfur vacancy defects in metal sulfides are key to improving their HER performance. Sulfur vacancies can provide more active sites for the reaction and improve electron transport pathways, thereby significantly reducing the overpotential of the reaction and enhancing catalytic activity.

[0005] Currently, the preparation of S-defects mainly relies on high-temperature thermal reduction and chemical reduction. For example, S-defects can be produced by calcining at a high temperature above 600℃ for 2 hours using hydrogen as the reducing gas (ACS nano 13.6(2019):6824-6834.). However, this method requires high temperature and continuous hydrogen gas supply, resulting in high energy consumption and long reaction time. The crystal phase transformation of the catalyst also often requires high energy consumption to achieve (Advanced Materials 32.33(2020):2001889.).

[0006] Therefore, how to prepare sulfur-vacancy molybdenum disulfide materials in a mild and rapid manner remains to be explored. Summary of the Invention

[0007] This invention provides a sulfur-defect heterojunction molybdenum disulfide, its photo-induced preparation method, and its application. The method produces a MoS2 heterojunction containing S vacancies with a synergistic crystalline phase, increasing the number of reactive sites and effectively improving the electrocatalytic hydrogen production performance of MoS2.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] This invention provides a method for photo-induced preparation of molybdenum disulfide with sulfur defects, comprising:

[0010] S1. After the molybdenum source, sulfur source and deionized water are stirred evenly, they are transferred into a high-pressure reactor containing carbon cloth. The hydrothermal reaction is carried out to obtain carbon cloth with uniformly grown MoS2 precursor.

[0011] S2. Under a mixed atmosphere of hydrogen and inert gas, carbon cloth uniformly grown with MoS2 precursor prepared in S1 is irradiated with a xenon lamp to obtain a heterojunction molybdenum disulfide with sulfur defects.

[0012] This invention utilizes carbon cloth as the growth substrate for MoS2 and prepares the MoS2 precursor via a hydrothermal reaction. Taking advantage of the instability of the MoS2 precursor, hydrogen gas is used to remove some sulfur from the MoS2 under xenon lamp irradiation. This removed sulfur leaves as H2S gas, thus forming S vacancies on the MoS2. Simultaneously, under xenon lamp irradiation, electron escape causes some 1T-type MoS2 to transform into 2H-type MoS2. The resulting MoS2 is actually a mixture of 1T-type and 2H-type MoS2, and a heterojunction of these two different crystalline forms occurs. The final product obtained by this invention is a heterojunction molybdenum disulfide (a heterojunction of 1T-type and 2H-type MoS2) containing sulfur defects (S vacancies).

[0013] Furthermore, the sulfur-deficient heterojunction molybdenum disulfide obtained in this invention exhibited catalytic activity far exceeding that of single MoS2 in electrocatalytic hydrogen production performance testing.

[0014] It is worth noting that the S-vacancy in MoS2 precursor is usually created by high temperature, which requires calcination at a temperature above 600°C, and this requires a high heat output. However, the xenon lamp irradiation method proposed in this invention requires a lower heat output. The surface temperature of the MoS2 precursor is generally around 200°C. By taking advantage of the strong light absorption properties of the black powder of the MoS2 precursor, light energy is converted into heat energy on the powder surface, and the defect is created with only a lower heat output.

[0015] Preferably, in step S1, the temperature of the hydrothermal reaction is 180–220°C, and the time of the hydrothermal reaction is 18–24 hours.

[0016] More preferably, the hydrothermal reaction temperature is 200°C and the hydrothermal reaction time is 18 hours.

[0017] Preferably, in S1, the molybdenum source is ammonium molybdate or ammonium tetrathiomolybdate, and the sulfur source is thiourea, thioacetamide, or L-cysteine.

[0018] More preferably, the molybdenum source is ammonium molybdate, and the sulfur source is thiourea.

[0019] Preferably, in step S1, the carbon cloth is pre-cleaned with an organic solvent and naturally dried before being placed in a high-pressure reactor.

[0020] More preferably, the carbon cloth is cleaned with acetone, then cleaned with deionized water and anhydrous ethanol, and then naturally dried before being transferred into a high-pressure reactor.

[0021] Preferably, in step S2, the inert gas is argon and / or nitrogen.

[0022] More preferably, the inert gas is argon.

[0023] Preferably, in step S2, the volume ratio of hydrogen to inert gas is 1:(6-9).

[0024] More preferably, the volume ratio of hydrogen to inert gas is 1:9.

[0025] Preferably, in step S2, the xenon lamp irradiation current is 18–20 A, the xenon lamp irradiation time is 10–20 min, and the xenon lamp irradiation intensity is 3–13 sun, where 1 sun ≈ 100 mW / cm². 2 .

[0026] More preferably, the xenon lamp irradiation current is 18–19 A, the xenon lamp irradiation time is 12–18 min, and the xenon lamp irradiation intensity is 5–10 sun, where 1 sun ≈ 100 mW / cm². 2 .

[0027] More preferably, the xenon lamp irradiation current is 19A, the xenon lamp irradiation time is 15min, and the xenon lamp irradiation intensity is 6sun, where 1sun ≈ 100mW / cm². 2 .

[0028] The present invention also provides a sulfur-defect heterojunction molybdenum disulfide prepared by the above method.

[0029] Preferably, the sulfur-defect heterojunction molybdenum disulfide contains a heterojunction of IT-type molybdenum disulfide and 2H-type molybdenum disulfide.

[0030] The present invention also provides the application of the sulfur-deficient heterojunction molybdenum disulfide prepared by the above method or the above sulfur-deficient heterojunction molybdenum disulfide in electrocatalytic hydrogen production.

[0031] Therefore, the present invention has the following beneficial effects:

[0032] (1) This invention proposes to prepare molybdenum disulfide with S vacancies by replacing high-temperature calcination with xenon lamp irradiation. At the same time, the molybdenum disulfide prepared by this method is a heterojunction form with two crystal forms, which can provide new ideas for subsequent research on crystal phase heterojunctions and related methods for creating defects in sulfides.

[0033] (2) The sulfur-defect heterojunction molybdenum disulfide prepared by the present invention has a heterojunction containing both IT-type molybdenum disulfide and 2H-type molybdenum disulfide while having S defects, and exhibits ultra-high electrocatalytic hydrogen production activity.

[0034] (3) The method provided by the present invention greatly simplifies the preparation process of defects represented by molybdenum sulfide, which is accompanied by crystal phase transformation. The entire production process does not require the use of precision instruments and has the characteristics of simple and easy synthesis operation and short reaction time (10-20 min).

[0035] (4) The method provided by the present invention does not require the long-term introduction of expensive or dangerous gases such as ammonia and methane, thus overcoming the problem of long-term high-temperature operation of high-temperature furnaces in traditional methods, and has broad application prospects. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the xenon lamp illumination of the present invention;

[0037] Figure 2 EPR comparison chart;

[0038] Figure 3 XRD comparison chart;

[0039] Figure 4 Raman comparison chart;

[0040] Figure 5 XPS Mo 3D image;

[0041] Figure 6 Image for XPS S2p;

[0042] Figure 7 The graph shows the evaluation data of LSV for electrocatalytic hydrogen production under 1M KOH.

[0043] Figure 8 The graph shows the LSV evaluation data for electrocatalytic hydrogen production using 0.5M H2SO4. Detailed Implementation

[0044] The present invention will be further described below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0045]

Example

[0046] Example 1

[0047] S1. After cleaning the carbon cloth with acetone, it is then cleaned with deionized water and anhydrous ethanol and allowed to air dry for later use.

[0048] S2. Accurately weigh 0.206g of ammonium molybdate tetrahydrate ((NH4)6Mo7O 24 0.3806 g of thiourea (CH4N2S) and 0.4 H2O were dissolved in 30 mL of deionized water under magnetic stirring to form a homogeneous solution. The solution was then transferred to a 50 mL Teflon-lined stainless steel high-pressure reactor, and a cleaned carbon cloth was immersed in the mixture as a growth substrate. The high-pressure reactor was placed in an electric furnace at 200 °C, and the reaction was carried out for 18 h. The reaction system was then cooled to room temperature. The final product was washed several times with deionized water and anhydrous ethanol to remove any possible ions; it was then air-dried at room temperature to obtain a carbon cloth with uniformly grown MoS2. The MoS2-grown carbon cloth was cut into pieces with dimensions of 0.5 x 1 cm. 2 The cut carbon cloth with MoS2 growth was subjected to xenon lamp irradiation in an H2 atmosphere (a mixture of 10 vol% H2 and 90 vol% Ar). The xenon lamp irradiation current was 19 A, the irradiation time was 15 min, and the xenon lamp irradiation intensity was 6 sun. This yielded a sulfur-defect heterojunction molybdenum disulfide material.

[0049] Comparative Example 1

[0050] This comparative example is basically the same as Example 1, except that the xenon lamp irradiation step is omitted and molybdenum disulfide material is obtained after hydrothermal treatment.

[0051] Comparative Example 2

[0052] This comparative example is basically the same as Example 1, except that the 10 vol% H2 and 90 vol% Ar mixture is replaced with a pure argon atmosphere to obtain molybdenum disulfide material.

[0053] [Performance Testing]

[0054] 1. Empty seat

[0055] The catalyst materials prepared in Example 1 and Comparative Examples 1-2 were subjected to EPR testing to verify whether S vacancies appeared. The results are as follows: Figure 2 As shown. Observation Figure 2 It can be seen that no vacancy signal was observed in Comparative Examples 1 and 2, while a strong vacancy signal was observed in Example 1. This result indicates that only the catalyst material prepared in Example 1 exhibited sulfur defects.

[0056] 2. Morphology and structure

[0057] To verify the EPR results and further analyze the material structure, the catalyst materials prepared in Example 1 and Comparative Examples 1-2 were subjected to XRD, Raman, and XPS structural analysis.

[0058] Figure 3 The image is an XRD pattern, where... The markings correspond to the 2H phase MoS2 standard card of JPDS number 37-1492; the "∮" marking corresponds to the IT phase MoS2. Observation shows that the molybdenum disulfide material prepared in Comparative Example 1 is IT phase MoS2, while the molybdenum disulfide material prepared in Comparative Example 2 is 2H phase MoS2. Combining the EPR and XRD results, it can be clearly inferred that the molybdenum disulfide material in Comparative Example 1 is a single-phase IT phase MoS2 without sulfur defects, while the molybdenum disulfide material in Comparative Example 2 is a single-phase 2H phase MoS2 without sulfur defects. However, the spectrum corresponding to Example 1 shows both IT and 2H phases, suggesting the possible formation of a mixed-phase heterojunction structure of sulfur-defective molybdenum disulfide.

[0059] Figure 4 The Raman spectrum is shown; the spectrum corresponding to Comparative Example 1 is at 151.4 cm⁻¹. -1 233.1cm -1 and 345.8cm -1 The peaks appearing at 280cm correspond to the J1, J2, and J3 bands of the 1T phase MoS2, respectively; -1 The peak at that location corresponds to E1g This indicates the presence of octahedral coordination in 1T-MoS2. The Raman peak in Comparative Example 2 only reaches 377 cm⁻¹. -1 and 403cm -1 The two peaks correspond to the E of 2H-MoS2, respectively. 1 2g and A 1g The Raman peaks in Example 1 not only exhibit the typical J1, J2, and J3 band peaks of 1T phase MoS2, but also the typical E peaks of 2H-MoS2. 1 2g and A 1g The peak, this result verifies the existence of 1T-MoS2 and 2H-MoS2 heterojunctions.

[0060] Figure 5 and Figure 6 XPS images of the catalyst materials prepared in Example 1, Comparative Example 1, and Comparative Example 2. Observation Figure 5 It can be seen that the two peaks at 229 eV and 232.3 eV in Comparative Example 1 correspond to Mo on 1T-MoS2, respectively. 4+ 3D 5 / 2 and 3D 3 / 2 Comparative Example 2 shows two peaks at 229.9 eV and 232.9 eV corresponding to 2H-MoS2Mo. 4+ 3D 5 / 2 and 3D 3 / 2 Peaks. In Example 1, characteristic peaks corresponding to 1T-MoS2 and 2H-MoS2 appeared.

[0061] Figure 6 In the examples, the S2p spectra of Example 1, Comparative Example 1, and Comparative Example 2 are quite similar. However, compared to Comparative Example 1, Comparative Example 2 shows a different S2p spectrum. 2- 2p 1 / 2 The peak shifts towards higher energies; from 162.1 eV in Comparative Example 1 to 163.1 eV in Comparative Example 2.

[0062] XPS results further confirm the coexistence of the 1T and 2H phases of MoS2 in Example 1. Combining the XRD, Raman, and XPS results, the structure of Example 1 can be determined to be a mixed-phase heterojunction structure with sulfur defects.

[0063] 3. Electrocatalytic hydrogen production

[0064] Catalytic performance testing methods:

[0065] ① Using a CHI660D electrochemical workstation, linear sweep voltammetry (LSV) was performed with the following parameters: Init E = -0.159V, Final E = 0.659V, Scan Rate = 0.005V / s, Sample Interval = 0.001V, Quiet Time = 2, Sensitivity = 1.e-002A / V. The electrolyte was a 0.5M sulfuric acid solution, and the saturated calomel electrode (SCE) and carbon rod were used as the reference and counter electrodes, respectively.

[0066] ② Using a CHI660D electrochemical workstation, linear sweep voltammetry (LSV) was performed with the following parameters: Init E = -0.784V, Final E = -1.684V, ScanRate = 0.005V / s, Sample Interval = 0.001V, Quiet Time = 2, Sensitivity = 1.e-002A / V. The electrolyte was a 1M potassium hydroxide solution, and the saturated calomel electrode (SCE) and carbon rod were used as the reference and counter electrodes, respectively.

[0067] The catalyst materials prepared in Example 1 and Comparative Examples 1-2 were tested for electrocatalytic hydrogen production, and the results are as follows: Figures 7-8 As shown. To verify the effect of xenon lamp irradiation-induced S-vacancy synergistic heterostructure on electrocatalytic performance, LSV was performed in alkaline and acidic media to evaluate the HER performance of the catalyst.

[0068] LSV was performed in 1M KOH to evaluate the HER activity of the catalyst, and the results are as follows: Figure 7 As shown. Figure 7 In the case where the current density is fixed at 10 mA·cm -2 At the same time, the overpotential of the 1T phase MoS2 prepared in Comparative Example 1 was 253 mV, the overpotential of the 2H phase MoS2 prepared in Comparative Example 2 was 192 mV, and the overpotential of the sulfur-defect heterojunction molybdenum disulfide material prepared in Example 1 was 155 mV. Analysis shows that the catalytic material containing the 2H phase MoS2 has a lower overpotential than the 1T phase MoS2; this indicates that the 2H phase MoS2 has a greater impact on HER performance. Specifically, the overpotential of the sulfur-defect heterojunction molybdenum disulfide material is significantly lower than that of the single-phase MoS2 material without sulfur defects. This suggests that the formation of the S-vacancy synergistic heterojunction induced by xenon lamp irradiation generates more active sites, thereby improving the HER performance of MoS2 materials in alkaline media.

[0069] observe Figure 8It can be seen that the overpotentials of the catalyst materials prepared in Comparative Example 1 and Example 1 are 232 mV and 192 mV, respectively; at the same time, it can be found that the overpotentials are ordered from smallest to largest as follows: Example 1, Comparative Example 2, Comparative Example 1. These results demonstrate that the S-vacancy synergistic crystalline heterojunction significantly improves the HER activity of MoS2 material in acidic (0.5 M H2SO4) medium, and its performance is similar to that of the S-vacancy synergistic crystalline heterojunction in alkaline HER.

Claims

1. A method for photo-induced preparation of sulfur-defect heterojunction molybdenum disulfide, characterized in that, include: S1. After the molybdenum source, sulfur source and deionized water are stirred evenly, they are transferred into a high-pressure reactor containing carbon cloth. The hydrothermal reaction is carried out to obtain carbon cloth with uniformly grown MoS2 precursor. S2. Under a mixed atmosphere of hydrogen and inert gas, carbon cloth uniformly grown with MoS2 precursor prepared in S1 was irradiated with a xenon lamp to obtain a heterojunction molybdenum disulfide containing sulfur defects. The xenon lamp irradiation current was 18-20 A, the irradiation time was 10-20 min, and the irradiation intensity was 3-13 sun, where 1 sun ≈ 100 mW / cm². 2 .

2. The method as described in claim 1, characterized in that, In S1, the hydrothermal reaction temperature is 180~220℃, and the hydrothermal reaction time is 18~24 h.

3. The method as described in claim 1 or 2, characterized in that, In S1, the molybdenum source is ammonium molybdate or ammonium tetrathiomolybdate, and the sulfur source is thiourea, thioacetamide, or L-cysteine.

4. The method as described in claim 1, characterized in that, In step S1, the carbon cloth is pre-cleaned with an organic solvent and naturally dried before being placed in a high-pressure reactor.

5. The method as described in claim 1, characterized in that, In step S2, the inert gas is argon and / or nitrogen.

6. The method as described in claim 1 or 5, characterized in that, In S2, the volume ratio of hydrogen to inert gas is 1:(6~9).

7. The sulfur-defect heterojunction molybdenum disulfide prepared by the method according to any one of claims 1 to 6, characterized in that, The sulfur-defect heterojunction molybdenum disulfide is a sulfur-defect-containing heterojunction molybdenum disulfide; the sulfur-defect-containing heterojunction molybdenum disulfide contains IT-type molybdenum disulfide and 2H-type molybdenum disulfide heterojunctions.

8. The application of the sulfur-deficient heterojunction molybdenum disulfide prepared by the method of any one of claims 1 to 6, or the sulfur-deficient heterojunction molybdenum disulfide as described in claim 7, in electrocatalytic hydrogen production.

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