Electrocatalytic material and preparation method thereof

Abstract

The application belongs to the technical field of electrocatalysis, and particularly relates to an electrocatalytic material and a preparation method thereof. Existing catalytic materials are unstable in the process of electrocatalytic hydrogen evolution. The application provides an electrocatalytic material, which is prepared from 2H-MoS2 and alkali metal carbonate through high-temperature calcination. Through a method of facilitating phase transition of 2H-MoS2 by means of molten alkali metal carbonate assisted intercalation, a ternary 1T'-MMoS2 (A=Na, K) material is prepared. The 1T'-MMoS2 is a stable ternary compound, so that the product avoids reverse transition from the 1T' phase to the 2H phase in the process of electrocatalytic hydrogen evolution, thereby exhibiting excellent stability.

Description

Technical Field

[0001] This application belongs to the field of electrocatalysis technology, and in particular relates to an electrocatalytic material and its preparation method. Background Technology

[0002] In recent years, due to the cleanliness of hydrogen energy and the high cost of precious metal catalysts such as platinum and palladium, the search for inexpensive hydrogen evolution catalysts has become a research focus for many researchers (Nano Energy 42 (2017) 69–89). Transition metal chalcogenides (TMDs) with graphite-like structures have attracted widespread attention due to their unique physicochemical properties. Studies have found that the excellent performance of TMDs in the field of electrocatalysis makes them a promising alternative to precious metal catalysts such as platinum and palladium in the electrocatalytic hydrogen evolution reaction (HER).

[0003] TMDs typically exhibit multiphase structures, primarily consisting of three phases: 1T, 2H, and 3R. Most naturally occurring TMDs exist in their stable 2H phase (Chem. Soc. Rev., 2015, 44, 2702–2712). The 2H phase is a semiconductor phase with limited active sites, resulting in poor HER performance; while the 1T phase possesses metal-like conductivity and more active sites. Therefore, transforming the 2H phase into the 1T phase is a significant research topic. Summary of the Invention

[0004] 1. Technical problems to be solved

[0005] To address the instability of existing catalytic materials during electrocatalytic hydrogen evolution, this application provides an electrocatalytic material and its preparation method.

[0006] 2. Technical Solution

[0007] To achieve the above objectives, this application provides an electrocatalytic material prepared by high-temperature calcination of 2H-MoS2 and alkali metal carbonate.

[0008] Another embodiment provided in this application is that the 2H-MoS2 is a commercial molybdenum disulfide powder crystal with a purity greater than 99%.

[0009] Another embodiment provided in this application is that the alkali metal carbonate is sodium carbonate, potassium carbonate, sodium bicarbonate, or potassium bicarbonate.

[0010] Another embodiment provided in this application is that the molar ratio of 2H-MoS2 to the alkali metal carbonate is 2:2, 2:3 or 2:4.

[0011] Another embodiment provided in this application is: the method includes:

[0012] Step S1: Grind 2H-MoS2 and alkali metal carbonate evenly in an agate mortar;

[0013] Step S2: Transfer the uniformly mixed solid powder to a corundum boat, place it in a tube furnace, and calcine it at high temperature under an inert atmosphere.

[0014] Step S3: After the tube furnace cools to room temperature, remove the sample, transfer it to a centrifuge tube with distilled water, and perform ultrasonic dispersion.

[0015] Step S4: After the sample is fully dispersed in distilled water, centrifuge to wash away the unreacted alkali metal carbonates in the mixture, and finally dry it in an oven to obtain 1T′-MMoS2.

[0016] Another embodiment provided in this application is that the grinding time is 10 min to 30 min.

[0017] Another embodiment provided in this application is as follows: the inert atmosphere is nitrogen, argon or a hydrogen-argon mixture, the calcination temperature is 650℃~950℃, and the calcination time is 6~10h.

[0018] Another embodiment provided in this application is that the ultrasound time is 3 to 5 hours.

[0019] Another embodiment provided in this application is as follows: the centrifugal washing method is to alternate between ethanol and distilled water, the centrifugal washing speed is 8000-10000 r / min, and the single centrifugation time is 2-10 min.

[0020] Another embodiment provided in this application is: the sample after centrifugation and washing is vacuum dried at 60-120°C.

[0021] 3. Beneficial effects

[0022] Compared with existing technologies, the beneficial effects of the electrocatalytic material and its preparation method provided in this application are as follows:

[0023] The electrocatalytic material provided in this application is a method for preparing a highly stable ternary transition metal chalcogenide electrolysis hydrogen evolution catalyst. The ternary 1T′-MMoS2 (A=Na、K) material was prepared by using a molten alkali metal carbonate-assisted intercalation method to induce a phase transformation of 2H-MoS2.

[0024] The electrocatalytic material provided in this application has a 1T′ phase that is a distorted 1T phase with similar structure and physical and chemical properties.

[0025] The electrocatalytic material provided in this application is a ternary 1T′-MMoS2 electrocatalytic material with excellent electrocatalytic performance.

[0026] The method for preparing the electrocatalytic material provided in this application employs a high-temperature calcination-assisted intercalation method. Alkali metal ions are inserted into 2H-MoS2 through high-temperature calcination. This is because Na2CO3 has a melting point of 851℃ and tends to decompose at high temperatures; MoS2 has a melting point of 2375℃. When the temperature of the tube furnace rises to 950℃, Na2CO3 becomes molten. At this point, MoS2 remains dispersed as a solid powder within the molten Na2CO3. Some of the Na2CO3 decomposes at this temperature, and the resulting elemental Na exhibits strong reducing properties at high temperatures. The highly dispersed fine droplets of elemental Na in the molten Na2CO3 undergo a redox reaction with the 2H-phase MoS2 powder, and intercalation is completed with the assistance of the molten alkali, generating the 1T′-phase ternary bimetallic sulfide NaMoS2. Possible decomposition reactions are as follows:

[0027] Na₂CO₃→Na₂O+CO₂↑ (high temperature) (3-1)

[0028] 2Na₂O→2Na+Na₂O₂ (high temperature) (3-2)

[0029] 2Na₂O₂→2Na₂O+O₂↑ (high temperature) (3-3)

[0030] Na+MoS2→NaMoS2 (high temperature) (3-4)

[0031] Different purities of 1T′-MMoS2 can be controlled through high-temperature calcination, achieving the preparation of a high-purity 1T′ phase. 1T′-MMoS2 is a stable ternary compound, preventing the reverse transition from the 1T′ phase to the 2H phase during electrocatalytic hydrogen evolution, thus exhibiting excellent stability. Furthermore, this method is simple to operate and holds promise for industrial-scale production. Attached Figure Description

[0032] Figure 1 These are the XRD spectra of commercial molybdenum disulfide (2H-MoS2) and highly stable metallic ternary transition metal chalcogenide (1T′-NaMoS2) in Example 1 of this application;

[0033] Figure 2 This is a scanning electron microscope image of the highly stable metallic phase ternary transition metal chalcogenide (1T′-NaMoS2) in Example 1 of this application;

[0034] Figure 3 These are XPS images of commercial molybdenum disulfide (2H-MoS2) and highly stable metallic ternary transition metal chalcogenide (1T′-NaMoS2) in Example 1 of this application;

[0035] Figure 4 These are linear sweep voltammetric curves of a rotating disk electrode containing commercial molybdenum disulfide (2H-MoS2) and a highly stable metallic ternary transition metal chalcogenide (1T′-NaMoS2) as described in Example 1 of this application.

[0036] Figure 5 These are linear sweep voltammetric curves of a rotating disk electrode containing commercial molybdenum disulfide (2H-MoS2) and a highly stable metallic ternary transition metal chalcogenide (1T′-KMoS2) as described in Example 1 of this application. Detailed Implementation

[0037] In the following, specific embodiments of this application will be described in detail with reference to the accompanying drawings. Based on these detailed descriptions, those skilled in the art will be able to clearly understand and implement this application. Without departing from the principles of this application, features from various embodiments can be combined to obtain new implementations, or certain features from some embodiments can be substituted to obtain other preferred implementations.

[0038] See Figures 1-5 This application provides that a certain mass of 2H-MoS2 and alkali metal carbonate are first weighed and ground thoroughly in a mortar. After the two are mixed evenly, they are transferred to a corundum boat and placed in a tube furnace for high-temperature calcination under an inert atmosphere. After calcination, the mixture is then ultrasonically and centrifugally washed, and finally dried for later use.

[0039] The specific preparation steps are as follows:

[0040] Step S1: First, grind 2H-MoS2 and alkali metal carbonate in a mortar at a molar ratio of 1:1 to 1:2 (preferably 2:3) for 10 to 30 minutes, and then transfer the mixed powder to a corundum boat.

[0041] Step S2: Place the corundum boat into a tube furnace and calcine it at a temperature of 650℃~950℃ in a nitrogen atmosphere for 6~10 hours;

[0042] Step S3: After the furnace temperature drops to room temperature, transfer the sample to a centrifuge tube with distilled water, and then sonicate it in an ultrasonic cleaner for 1-2 hours.

[0043] Step S4: Wash the product by alternating centrifugation with distilled water and ethanol at a speed of 8000-10000 r / min, with a single centrifugation time of 2-10 min; finally, dry it in a vacuum oven at 60℃-120℃.

[0044] Figure 1 XRD patterns of MoS2, NaMoS2, and KMoS2; Figure 2 SEM image of NaMoS2; Figure 3(a) Fine spectrum of Mo 3d for MoS2 and NaMoS2 / MoS2; (b) Fine spectrum of S2p for S2. Figure 4 Polarization curves for MoS2 and NaMoS2; Figure 5 The polarization curves for MoS2 and KMoS2 are shown. Specific Implementation Example 1:

[0046] First, grind 0.32g of 2H-MoS2 and 0.32g of Na2CO3 in a mortar for 20 minutes, then transfer the mixed powder to an alumina boat; place the alumina boat in a tube furnace and calcine at 950℃ for 8 hours under a nitrogen atmosphere; after the furnace temperature drops to room temperature, transfer the sample to a centrifuge tube with distilled water, first place it in an ultrasonic cleaner and sonicate for 4 hours, then wash it three times alternately with distilled water and ethanol, and finally dry it in a vacuum oven at 60℃.

[0047] The ternary 1T′-NaMoS2 material with excellent electrocatalytic performance prepared in Example 1 was tested by X-ray diffraction (XRD) as follows: Figure 1 As shown, the XRD pattern of MoS2 before calcination shows strong diffraction peaks at 14.5°, 39.7° and 50.0°, which correspond to the (002), (103) and (105) crystal planes of commercial 2H-MoS2 (PDF#37-1492), respectively. After the Na2CO3 intercalation reaction, the characteristic peaks of commercial 2H-MoS2 disappeared as shown by the red dashed line, and strong characteristic peaks appeared at 9.8° and 19.4°, indicating that 1T′-NaMoS2 (PDF#18-1257) appeared in the calcined product, that is, the intercalation of Na atoms into 2H-MoS2 was successfully achieved.

[0048] The ternary 1T′-MMoS2 material with excellent electrocatalytic performance prepared in Example 1 was tested using scanning electron microscopy (SEM) as follows: Figure 2 As shown, commercial MoS2 exhibits a significant delamination and curling phenomenon after intercalation. This is because the intercalation of Na atoms increases the interatomic spacing at the microscopic level, causing the microsheets to delaminate and curl.

[0049] The ternary 1T′-NaMoS2 material with excellent electrocatalytic performance prepared in Example 1 was tested using X-ray photoelectron spectroscopy (XPS) as follows: Figure 3 As shown, Figure (a) is the fine spectrum of Mo 3d, and the Mo 3d of +3 valence Mo atoms in 1T′-NaMoS2. 5 / 2 and Mo 3d 3 / 2Compared with the XPS spectrum of Mo 3d in 2H-MoS2, it shifted 1.4 eV towards the direction of lower binding energy, indicating that under molten alkaline conditions, the intercalation process of molten elemental Na has a reducing effect on MoS2, which reduces the oxidation state of Mo atoms and finally yields 1T′-NaMoS2. Figure 3 (b) shows the fine XPS spectrum of S2p. Peak fitting revealed two singlets at 162.6 eV and 163.7 eV in commercial MoS2, corresponding to S2p in MoS2, respectively. 3 / 2 and S2p 1 / 2 S2p in calcined products 3 / 2 and S2p 1 / 2 The positions of the two characteristic peaks are 161.2 eV and 162.3 eV, respectively, both shifted by 1.4 eV towards lower binding energies. This is because the electron cloud density of the S atom increases after the insertion of the less electronegative alkali metal and its bonding with the S atom, thus lowering its electron binding energy. This further confirms that the Na atom completed the intercalation reaction in the form of bonding, resulting in the excellent stability of the 1T′ phase product.

[0050] Linear sweep voltammetry (LSV) of the ternary 1T′-NaMoS2 material with excellent electrocatalytic performance prepared in Example 1 was performed by... Figure 4 It can be known that at 10mA cm -2 At the given current density, the overpotential of NaMoS2 was 315.45 mV, which was nearly half that of commercial MoS2, indicating that the introduction of Na significantly improved the electrocatalytic hydrogen evolution performance. Specific Implementation Example 2:

[0052] First, grind 0.32g of 2H-MoS2 and 0.25g of NaHCO3 in a mortar for 20 minutes, then transfer the mixed powder to an alumina boat. Place the alumina boat in a tube furnace and calcine it at 950℃ for 8 hours under a nitrogen atmosphere. After the furnace temperature drops to room temperature, transfer the sample to a centrifuge tube with distilled water, sonicate it in an ultrasonic cleaner for 4 hours, wash it alternately with distilled water and ethanol, and finally dry it in an oven at 60℃. Specific Implementation Example 3:

[0054] First, grind 0.32g of 2H-MoS2 and 0.276g of K2CO3 in a mortar for 20 minutes, then transfer the mixed powder to an alumina boat; place the alumina boat in a tube furnace and calcine at 750℃ for 8 hours under a nitrogen atmosphere; after the furnace temperature drops to room temperature, transfer the sample to a centrifuge tube with distilled water, first place it in an ultrasonic cleaner and sonicate for 4 hours, then wash it alternately with distilled water and ethanol, and finally dry it in an oven at 60℃.

[0055] The ternary 1T′-KMoS2 material with excellent electrocatalytic performance prepared in Example 3 was tested by X-ray diffraction (XRD) as follows: Figure 1 As shown, the blue dashed line indicates that the characteristic peak of commercial 2H-MoS2 has disappeared, and strong characteristic peaks have appeared at 9.5° and 19.1°, indicating that 1T′-KMoS2 (PDF#18-1064) has appeared in the calcined product, that is, the intercalation of K atoms into commercial 2H-MoS2 has been successfully achieved by the molten alkali metal potassium intercalation method.

[0056] Linear sweep voltammetry (LSV) of the ternary 1T′-KMoS2 material with excellent electrocatalytic performance prepared in Example 3 was performed by... Figure 5 It can be known that at 10mA cm -2 At the given current density, the overpotential of KMoS2 is more than twice that of commercial MoS2, indicating that the introduction of K significantly improves the electrocatalytic hydrogen evolution performance.

[0057] The phase transformation of 2H-MoS2 was successfully achieved using high-temperature molten alkali metal carbonate-assisted intercalation, resulting in the preparation of ternary 1T′-MMoS2. For example, 1T′-NaMoS2 and 1T′-KMoS2 are often described in the literature as intermediates: sodium ions intercalate into 2H-MoS2 materials during sodium battery charging to form intermediate NaMoS2 (Adv. Mater. 2021, 33, 2007090); intermediates are formed by the intercalation of alkali metal ions in alkali metal intercalation and exfoliation methods (ACS Catal. 2018, 8, 2774-2781). Although 1T′-NaMoS2 and 1T′-KMoS2 exhibit superior electrocatalytic performance compared to the 2H phase molybdenum disulfide, the 1T′ phase formed by these methods is unstable in practical applications and easily degenerates into the 2H phase: in the former, lithium and sodium ions leave the 2H-MoS2 material during discharge, and in the latter, the alkali metal ions detach during the exfoliation process. In the product 1T′-MMoS2 of this application, the alkali metal forms a chemical bond with the 2H-MoS2 material, which has high stability and can therefore be used as an excellent electrocatalytic material.

[0058] Although this application has been described above with reference to specific embodiments, those skilled in the art will understand that many modifications can be made to the configurations and details disclosed in this application within the principles and scope of the disclosure. The scope of protection of this application is determined by the appended claims, and the claims are intended to cover all modifications included in the literal meaning or scope of equivalents of the technical features in the claims.

Claims

1. An electrocatalytic material, characterized in that: The material is prepared by high-temperature calcination of 2H-MoS2 and alkali metal carbonate; the alkali metal carbonate is sodium carbonate, potassium carbonate, sodium bicarbonate or potassium bicarbonate. The molar ratio of 2H-MoS2 to the alkali metal carbonate is 2:2, 2:3, or 2:4; The calcination temperature is 650 ℃~950 ℃, and the calcination time is 6~10 h; The material is a ternary 1T'-MMoS2, where M is Na or K.

2. The electrocatalytic material as described in claim 1, characterized in that: The 2H-MoS2 is a commercial molybdenum disulfide powder crystal with a purity greater than 99%.

3. The method for preparing the electrocatalytic material according to any one of claims 1 to 2, characterized in that: The method includes: Step S1: Grind 2H-MoS2 and alkali metal carbonate evenly in an agate mortar; Step S2: Transfer the uniformly mixed solid powder to a corundum boat, place it in a tube furnace, and calcine it at high temperature under an inert atmosphere. The calcine temperature is 650 ℃~950 ℃ and the calcine time is 6~10 h. Step S3: After the tube furnace cools to room temperature, remove the sample, transfer it to a centrifuge tube with distilled water, and perform ultrasonic dispersion. Step S4: After the sample is fully dispersed in distilled water, centrifuge and wash away the unreacted alkali metal carbonates in the mixture, and finally dry it in an oven to obtain 1T′-MMoS2.

4. The method for preparing the electrocatalytic material as described in claim 3, characterized in that: The grinding time is 10 min to 30 min.

5. The method for preparing the electrocatalytic material as described in claim 3, characterized in that: The inert atmosphere is nitrogen, argon, or a mixture of hydrogen and argon.

6. The method for preparing the electrocatalytic material as described in claim 3, characterized in that: The ultrasound duration is 3–5 hours.

7. The method for preparing the electrocatalytic material as described in claim 3, characterized in that: The centrifugal washing method involves alternating washing with ethanol and distilled water, with a centrifugal speed of 8000–10000 r / min and a single centrifugation time of 2–10 min.

8. The method for preparing the electrocatalytic material as described in claim 3, characterized in that: The samples after centrifugation and washing were then vacuum dried at 60–120°C.

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