Preparation method of ru-doped molybdenum disulfide-based nanomaterial for electrochemical synthesis of ammonia

Abstract

The present application relates to the field of electrocatalytic energy storage, and aims to provide a preparation method of Ru-doped MoS2-based nanomaterial for electrochemical synthesis of ammonia.The method comprises the following steps: adding ruthenium trichloride, sodium molybdate dihydrate and thioacetamide into a hydrothermal reaction kettle and mixing uniformly; reacting at 190 DEG C for 20h, and after natural cooling to room temperature, washing and drying the reaction product to obtain a silver gray powder, which is the Ru-doped MoS2-based nanomaterial.The 2H phase to 1T phase transition of MoS2 is realized by Ru doping, and the conductivity of the material is optimized; the Ru-Mo-S synergistic center promotes the activation of N2 and the bonding ability of NHx, thereby improving the activity of electrocatalytic reduction of N2 to NH3.A large number of catalytically active sites are provided by the atomically dispersed Ru in the catalyst, and high atom utilization is realized.The one-step hydrothermal method is adopted, the raw material reserves of the precursors used are abundant and the cost is low, and the method is suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to a method for preparing Ru-doped MoS2-based nanomaterials for biomimetic electrochemical nitrogen fixation, belonging to the field of electrocatalytic energy storage. Background Technology

[0002] Ammonia (NH3), as an important chemical raw material and the optimal hydrogen storage carrier, is widely used in chemical, pharmaceutical, and energy fields. The industrial-scale Harber-Bosch process for ammonia synthesis, developed since the early 20th century, has greatly promoted the fertilizer industry and contributed to population growth. However, the traditional high-temperature, high-pressure Harber-Bosch process (N2 + H2 → NH3, 450-550℃, 20-50 MPa) leads to high energy consumption and greenhouse gas emissions. In recent years, electrocatalytic nitrogen fixation (ENRR), using water (H2O) and nitrogen (N2) as raw materials to produce ammonia at ambient temperature and pressure, is considered a promising ammonia synthesis technology. This efficient, clean, and low-energy ammonia synthesis technology is of great significance to human societal development. However, due to the low solubility of N2 and the high dissociation energy of N≡N (941 kJ / mol), this process faces challenges. -1 The presence of hydrogen evolution reaction (HER) at the cathode competes with the ENRR reaction, resulting in low yield and energy efficiency bottlenecks. Therefore, developing highly active and selective ENRR catalysts is crucial.

[0003] Among numerous ENRR catalysts, transition metals such as Ru, Fe, Pt, and Pd exert a strong attraction on electrons in N≡N, and the antibonding π orbitals of N≡N can accept outer electrons from these elements. Furthermore, MoS₂ has attracted widespread attention due to its inclusion of Mo and S, two important elements in biological nitrogenases, and its ENRR activity has been verified (CN 112844420A, CN 112473698 A). However, these catalysts are still limited by bottlenecks such as low catalytic selectivity and low catalytic yield. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for preparing Ru-doped MoS2-based nanomaterials for electrochemical ammonia synthesis.

[0005] To solve the technical problem, the solution of the present invention is:

[0006] A method for preparing Ru-doped MoS2-based nanomaterials for electrochemical ammonia synthesis is provided, comprising the following steps:

[0007] (1) Weigh ruthenium trichloride, sodium molybdate dihydrate and thioacetamide in a molar ratio of 0.2:1:5 and add them to a hydrothermal reactor and mix them evenly.

[0008] (2) After reacting at 190℃ for 20h and naturally cooling to room temperature, the reactants were washed and dried to obtain a silver-gray powder, which is the Ru-doped MoS2-based nanomaterial.

[0009] As a preferred embodiment of the present invention, the hydrothermal reactor is placed in a hydrothermal oven for heating.

[0010] As a preferred embodiment of the present invention, deionized water and ethanol are used as washing liquids, and the reactants are washed multiple times by vacuum filtration.

[0011] As a preferred embodiment of the present invention, the reactants are dried by freeze drying.

[0012] This invention further provides a method for applying Ru-doped MoS2-based nanomaterials prepared by the aforementioned method in electrochemical ammonia synthesis, comprising the following steps:

[0013] (1) Powdered Ru-doped MoS2-based nanomaterials were dispersed in a dispersion to obtain a slurry; the slurry was coated on hydrophobic carbon paper and dried to obtain a Ru-MoS2 electrode sheet.

[0014] (2) A three-electrode H-type electrolytic cell was constructed using Ru-MoS2 electrode sheet as working electrode, metal Pt sheet as counter electrode, Ag / AgCl electrode as reference electrode, and 0.25M LiClO4 solution as electrolyte.

[0015] (3) N2 is first introduced into the electrolyte in a bubbling manner for 30 minutes, and then the H-type electrolytic cell is energized. During the energizing process, N2 is continuously introduced at a flow rate of 20 sccm. At the Ru-MoS2 electrode, N2 is catalytically reduced to NH3.

[0016] As a preferred embodiment of the present invention, the dispersion is a mixture of deionized water, ethylene glycol and Nafion in a volume ratio of 47:2:1, and the mass concentration of Nafion in the solution is 1 wt‰.

[0017] As a preferred embodiment of the present invention, the mass-to-volume ratio of Ru-doped MoS2-based nanomaterials in the slurry to the dispersion is 2 mg: 1 mL.

[0018] As a preferred embodiment of the present invention, the voltage applied to the working electrode is in the range of -0.2V to -0.8V vs. RHE.

[0019] Description of the invention principle:

[0020] Natural nitrogenases contain elements such as Fe, Mo, and S, and possess a Fe-Mo-S center with synergistic catalytic activity. In industrial ammonia synthesis, Fe and Ru are optimal element choices for catalysts because they can form appropriate bonds with intermediate species NHx (x = 0, 1, 2, 3). This invention utilizes a biomimetic design of the Fe-Mo-S center and optimizes the coordination structure through heteroatomic Ru doping. On the one hand, it retains the unoccupied d orbitals of Mo, enabling it to adsorb N2; on the other hand, it optimizes the bonding ability of NHx through Ru atoms, thereby obtaining a high-performance ENRR electrocatalyst.

[0021] This invention utilizes a hydrothermal one-pot method to prepare a biomimetic Ru-MoS2 electrocatalyst. By doping with Ru atoms, not only is the MoS2 phase optimized from 2H to 1T, but the synergistic active sites of Ru-Mo-S are also beneficial to the activation of N2 and the bonding ability of NHx, thereby improving the efficiency of catalytic reduction of N2 to NH3.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] (1) The present invention realizes the transformation of MoS2 from the 2H phase to the 1T phase through Ru doping, thereby optimizing the conductivity of the material; the Ru-Mo-S synergistic center promotes the activation of N2 and the bonding ability of NHx, thereby improving the activity of electrocatalytic reduction of N2 to NH3.

[0024] (2) The Ru-MoS2 catalyst prepared in this invention can achieve 57.47 mg h⁻¹ at -0.6 V vs. RHE and -0.2 V vs. RHE, respectively. -1 mg -1 Ammonia production rate and Faraday efficiency of 46.38%. Atomically dispersed Ru provides a large number of catalytically active sites, achieving high atom utilization.

[0025] (3) The present invention adopts a one-step hydrothermal method, and the raw materials of the precursors used are abundant and low in cost, which is suitable for large-scale industrial production. Attached Figure Description

[0026] Figure 1 This is a TEM image of Ru-MoS2 in Embodiment 1 of the present invention.

[0027] Figure 2 This is a STEM image of Ru-MoS2 in Embodiment 1 of the present invention.

[0028] Figure 3 This is the EDS diagram of Ru-MoS2 in Embodiment 1 of the present invention.

[0029] Figure 4This is the Raman displacement diagram of Ru-MoS2 in Embodiment 1 of the present invention.

[0030] Figure 5 This is the high-resolution S 2p spectrum of Ru-MoS2 in XPS in Example 1 of the present invention.

[0031] Figure 6 This is an XAFS diagram of Ru-MoS2 in Embodiment 1 of the present invention.

[0032] Figure 7 This is a schematic diagram of the atomic structure of Ru-MoS2 in Embodiment 1 of the present invention.

[0033] Figure 8 This is a comparison chart of ammonia yield between the example Ru-MoS2 and the comparative example MoS2 at different potentials.

[0034] Figure 9 The graph shows a comparison of the Faraday efficiency of the example Ru-MoS2 and the comparative example MoS2 at different potentials.

[0035] Figure 10 This example compares ammonia production by Ru-MoS2 at different potentials. Detailed Implementation

[0036] The present invention will now be described in detail with reference to specific embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0037] The ferric chloride, sodium molybdate dihydrate, and thioacetamide used in the following examples were all purchased from Sigma-Aldrich Ltd. and were of analytical grade.

[0038] Part 1: Preparation and Application of Catalysts

[0039] Example 1: Preparation of Ru-MoS2

[0040] The preparation method of Ru-doped MoS2-based nanomaterials includes the following steps:

[0041] (1) Weigh out 32 mg of ruthenium chloride (RuCl3), 242 mg of sodium molybdate dihydrate (Na2MoO4.2H2O) and 376 mg of thioacetamide (C2H5NS) in a molar ratio of 0.2:1:5.

[0042] (2) Add each reactant to the hydrothermal reactor and mix evenly. Then place it in a hydrothermal oven and heat it to 190°C for 20 hours.

[0043] (3) After the reaction is complete, let it cool naturally to room temperature, take out the reaction product, and wash it by filtration multiple times with deionized water and ethanol.

[0044] (4) The powder obtained by filtration is freeze-dried to recover silver-gray powder, which is Ru-doped MoS2-based nanomaterial, or simply Ru-MoS2.

[0045] Application method example:

[0046] The Ru-MoS2 prepared in Example 1 can be used for biomimetic electrochemical nitrogen fixation. Examples of its applications include:

[0047] (1) Take 1 mL of Nafion, add 2 mL of ethylene glycol and 47 mL of deionized water, and sonicate for 5 min to obtain 50 mL of 1 wt‰ Nafion solution.

[0048] (2) Take 2 mg of the prepared Ru-MoS2 into 1 mL of 1 wt‰ Nafion solution and sonicate for 2 h to obtain a uniformly dispersed catalyst slurry of 2 mg / mL.

[0049] (3) Cut a 1.5cm × 1cm piece of hydrophobic carbon paper, and drop 100uL of the prepared catalyst slurry onto a 1cm piece. 2 On hydrophobic carbon paper, after natural drying, 0.2 mg / cm³ was obtained. 2 Electrode plates for the catalyst;

[0050] (4) A three-electrode system was constructed in an H-type tank for the electroreduction of N2 to synthesize NH3:

[0051] The working electrode (catalyst electrode) and the reference electrode (Ag / AgCl electrode) are placed in the cathode tank, and the counter electrode (Pt sheet) is placed in the anode tank. The electrolyte is a 0.25M LiClO4 solution. N2 is continuously introduced into the electrolytic cell during operation. The voltage applied to the working electrode is in the range of -0.2V to -0.8V vs. RHE.

[0052] Part Two: Catalyst Performance Testing and Analysis

[0053] 1. Preparation of Comparative Example 1 MoS2

[0054] Following the preparation method of Ru-MoS2 in Example 1, 242 mg of sodium molybdate dihydrate (Na2MoO4.2H2O) and 376 mg of thioacetamide (C2H5NS) were placed in a hydrothermal reactor; the subsequent processing steps were the same, and the final reaction product was a black powder, namely MoS2.

[0055] 2. Performance testing methods:

[0056] (1) Following the steps in the application example of Example 1, carbon paper electrodes coated with Ru-MoS2 catalyst and carbon paper electrodes coated with MoS2 catalyst were prepared respectively.

[0057] (2) Referring to the application example of Example 1, two kinds of carbon paper electrodes were used as working electrodes, and electrochemical tests were carried out in the H-type groove three-electrode system respectively.

[0058] (3) The electrochemical ammonia synthesis performance was evaluated using the CHI 660E electrochemical workstation;

[0059] (4) Electrochemical N2 to NH3 reduction performance was tested in a three-electrode system using working electrodes coated with different catalysts. During the test, the Ag / AgCl electrode was converted to a standard hydrogen electrode (RHE), and the conversion relationship was: E RHE =E Ag / AgCl +0.0591*pH+0.198, pH=6.8. The ENRR voltage test is performed at 0.2V intervals, with the test range being -0.2V to -0.8V vs. RHE.

[0060] (5) Before the test, N2 was introduced into the electrolyte at 50 sccm for 30 minutes. During the test, N2 was continuously introduced at 20 sccm. The voltage range of -0.2V to -0.8V vs. RHE was applied at 0.2V intervals for 30 minutes using the constant voltage method. The electrolyte was replaced and N2 was introduced to test the new voltage.

[0061] (6) The electrolyte of the constant voltage test was retained and the content of NH3 in the reaction solution was quantified by ultraviolet spectrophotometry. The Faraday efficiency of N2 to NH3 conversion is calculated as follows:

[0062]

[0063] In the formula, n is the number of electrons transferred; F is the Faraday constant, 96485 C mol. -1 C: NH3 concentration; V: electrolyte volume; M: relative mole fraction of NH3, NH3 in solution exists as NH4+. + It exists in the form of , so the relative molecular weight is 18; Q: is the total electrolytic charge.

[0064] The formula for calculating the yield of NH3 is as follows:

[0065]

[0066] C: NH3 concentration; V: electrolyte volume; T: reaction time; m: catalyst mass.

[0067] 3. Analysis and Conclusion

[0068] Figure 1 The structural morphology of the catalyst material Ru-MoS2 was characterized. TEM images show that the synthesized Ru-MoS2 nanoparticles exhibit a two-dimensional structure. Further analysis using dark-field transmission electron microscopy (STEM) revealed the morphology. Figure 2 It can be seen that there are defects on the surface of the two-dimensional structure. Atomic Ru replaces part of the surface of the two-dimensional material MoS2 with a 1T structure.

[0069] Figure 3 The EDS elemental distribution of the catalyst Ru-MoS2 is shown, revealing strong signals from Mo and S, while the Ru signal is weaker, and Ru is uniformly distributed on MoS2. Further analysis using Raman spectroscopy of MoS2 and Ru-MoS2... Figure 4 It can be seen that, compared to MoS2, Ru-MoS2, in addition to having the original 2H characteristic peak, also has the J1 (150 cm⁻¹) characteristic peak of the 1T phase. -1 ) and J3 (344cm -1 The two characteristic peaks indicate that Ru atom doping causes the phase transition from the 2H phase to the 1T phase of MoS2. This finding is consistent with... Figure 2 The structure is consistent with the STEM characterization.

[0070] Based on XPS analysis, it can be found that Ru doping optimizes the electronic structure of S. Figure 5 Compared to the S atom in MoS2, the S atom in Ru-MoS2 shifts towards higher binding energies, indicating that the S atom either loses electrons or bonds with the more electronegative Ru. To further investigate the coordination structure of Ru, XAFS analysis of Ru-MoS2 was performed using... Figure 6 It can be observed that Ru-MoS2 only contains Ru-S bonds and does not contain Ru-Ru or Ru-Mo bonds, which is consistent with... Figure 5 The redshift results for the binding energy of S 2p are consistent. Fitting analysis revealed that the coordination number of Ru is 5.5, indicating that Ru replaced some of the Mo sites, with five S atoms coordinated around it, and formed an S defect indirectly connected to the Mo atom. Figure 7 ).

[0071] Figure 8 , 9 The ammonia production efficiency and Faradaic efficiency of Ru-MoS2 and MoS2 catalysts for N2 reduction at different potentials were statistically analyzed. It can be seen that the ammonia production efficiency and Faradaic efficiency of Ru-MoS2 are significantly higher than those of MoS2. Ru-MoS2 achieved its maximum Faradaic efficiency (46.38%) and maximum yield at -0.2V vs. RHE and -0.6V vs. RHE, respectively. Its Faraday efficiency and yield are both greater than those of the currently reported precious metal Pd / C catalyst (CN112647093 A) and Ni-based catalyst (CN 113388858 A).

[0072] Figure 10The figure shows a comparison of ammonia production at different potentials for Ru-MoS2 in Example 1. As can be seen from the figure, the color of the -0.6V vs. RHE potential is darker than that of other potentials, indicating that the yield of N2 to NH3 is the highest under this potential.

[0073] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing Ru-doped MoS2-based nanomaterials for electrochemical ammonia synthesis, characterized in that, Includes the following steps: (1) Weigh ruthenium trichloride, sodium molybdate dihydrate and thioacetamide in a molar ratio of 0.2:1:5 and add them to a hydrothermal reactor and mix them evenly; (2) After reacting at 190℃ for 20h and naturally cooling to room temperature, the reactants were washed and dried to obtain a silver-gray powder, which is the Ru-doped MoS2-based nanomaterial. In the Ru-doped MoS2-based nanomaterial, Ru is doped into MoS2 in an atomically dispersed manner, realizing the transformation of the 2H phase to the 1T phase of MoS2. Only Ru-S bonds exist in the material, and Ru-Ru bonds and Ru-Mo bonds do not exist.

2. The method according to claim 1, characterized in that, The hydrothermal reactor is placed in a hydrothermal oven for heating.

3. The method according to claim 1, characterized in that, The reactants were washed multiple times using deionized water and ethanol as washing liquids by vacuum filtration.

4. The method according to claim 1, characterized in that, The reactants were dried by freeze drying.

5. The method for applying the Ru-doped MoS2-based nanomaterials prepared by the method of claim 1 in the electrochemical synthesis of ammonia, characterized in that, Includes the following steps: (1) Disperse powdered Ru-doped MoS2-based nanomaterials in a dispersion to obtain a slurry; coat the slurry onto hydrophobic carbon paper and dry it to obtain a Ru-MoS2 electrode sheet. (2) A three-electrode H-type electrolytic cell was constructed using Ru-MoS2 electrode sheet as working electrode, metal Pt sheet as counter electrode, Ag / AgCl electrode as reference electrode, and 0.25M LiClO4 solution as electrolyte. (3) N2 is first introduced into the electrolyte in a bubbling manner for 30 minutes, and then the H-type electrolytic cell is energized; during the energizing process, N2 is continuously introduced at a flow rate of 20 sccm; at the Ru-MoS2 electrode, N2 is catalytically reduced to NH3.

6. The method according to claim 5, characterized in that, The dispersion is a mixture of deionized water, ethylene glycol, and Nafion in a volume ratio of 47:2:1, and the mass concentration of Nafion in the solution is 1 wt‰.

7. The method according to claim 5, characterized in that, The mass-to-volume ratio of Ru-doped MoS2-based nanomaterials to dispersion in the slurry was 2 mg: 1 mL.

8. The method according to claim 5, characterized in that, The voltage applied to the working electrode ranges from -0.2V to -0.8V. vs .RHE.

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