Self-supporting molybdenum nitride / nickel sulfide composite catalyst and preparation method and application thereof

Abstract

The invention discloses a self-supporting molybdenum nitride / nickel sulfide composite catalyst and a preparation method and application thereof. The preparation method comprises the following steps: placing carbon cloth in a mixed solution containing Mo salt and thiourea by using a solvothermal method, carrying out solvothermal treatment to obtain a self-supporting MoS2 nanosheet grown on the carbon cloth, dipping the self-supporting MoS2 nanosheet in a nickel acetate solution to form a MoS2 precursor of Ni ion intercalation, and carrying out vacuum drying on the MoS2 precursor to obtain the self-supporting MoS2 nanosheet. And after drying, nitriding in an ammonia gas atmosphere to obtain the two-dimensional Mo5N6 / Ni3S2 self-supporting composite catalyst growing on the carbon cloth. The in-situ coupling interface remarkably enhances the effect of an interface electronic structure, so that adsorption and desorption of adsorbed hydrogen are optimized, enhanced hydrogen evolution kinetics are obtained, and meanwhile, the self-supporting two-dimensional nanosheet structure facilitates exposure of a large number of catalytic active sites, so that excellent hydrogen evolution performance is obtained; the preparation method is simple, convenient to operate and suitable for popularization and application.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional material preparation, and particularly relates to a self-supporting molybdenum nitride / nickel sulfide composite catalyst, a preparation method thereof and an application thereof. Background Art

[0002] Ni 3 S 2 As a naturally occurring nickel sulfide mineral, due to the continuous Ni-Ni network in its crystal structure, it exhibits good metallic conductivity, and the multivalent Ni species in Ni 3 S 2 can promote the adsorption and dissociation of water molecules and is widely used in the field of electrocatalytic hydrogen evolution. However, the practical application of Ni 3 S 2 is still limited by its poor hydrogen evolution activity, which is caused by its rough morphology and lack of effective proton adsorption sites. To address this issue, combining Ni 3 S 2 with other active materials to form a heterostructure has been proven to be an effective strategy to improve its hydrogen evolution activity. Nevertheless, developing complex Ni 3 S 2 -based composite electrocatalysts with high hydrogen evolution activity and strong stability is still a formidable challenge. For example, Patent CN202410798698.X discloses a nickel compound-phosphide sub-nano hybrid self-supporting electrode, a preparation method thereof and an application thereof. A layer of amorphous nickel phosphide thin layer is covered on the surface of carbon cloth fibers by electroless plating, and heat treatment is carried out under different atmospheres to in-situ crystallize and transform the amorphous thin layer to obtain different nickel compound-phosphide sub-nano hybrid structures. Although the hydrogen evolution activity is improved to a certain extent, the hydrogen adsorption activities of nickel phosphide and nickel sulfide phases are both insufficient, which limits the further improvement of hydrogen evolution kinetics. Moreover, the number of active sites of the chemical plating layer with a sub-nano size particle structure is limited, resulting in a low catalytic hydrogen evolution efficiency. In contrast, two-dimensional structures have attracted much attention from researchers due to their anisotropic conductivity, large specific surface area, and abundant reaction active sites. Moreover, when the nanosheets are thinned to the atomic layer thickness, more highly active coordinatively unsaturated atoms will be exposed on the surface to form a highly active surface, thus greatly increasing the hydrogen evolution activity. For example, Patent CN202310427273.3 discloses a MoS 2 / Ni 3 S 2 @N-rGO nanosheet array electrocatalyst and a preparation method thereof. A nitrogen-doped reduced graphene oxide is coated on a nickel foam substrate by a two-step hydrothermal method, and then MoS 2 / Ni 3 S 2The nanosheet array has a high hydrogen evolution activity due to the significantly increased number of hydrogen evolution active sites in the two-dimensional structure. However, in this structure, MoS 2 is a semiconductor material with low conductivity, and the catalytic activity mainly comes from the edge S sites. The density of active S sites is low, resulting in difficulty in further improving the catalytic hydrogen production efficiency. Therefore, developing a simple, efficient, and stable two-dimensional Ni 3 S 2 -based electrolytic water hydrogen production catalyst has become an urgent problem to be solved currently. Summary of the Invention

[0003] The present invention provides a self-supporting molybdenum nitride / nickel sulfide composite catalyst, a preparation method thereof, and its electrocatalytic hydrogen production application to simultaneously enhance the water dissociation and hydrogen desorption processes and achieve simple and efficient alkaline water decomposition.

[0004] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] A preparation method of a self-supporting molybdenum nitride / nickel sulfide composite catalyst includes the following steps:

[0006] 1) Immerse the carbon cloth in a mixed solution of molybdate and thiourea, perform a solvothermal reaction, and wash and dry to obtain MoS 2 nanosheets grown on the carbon cloth;

[0007] 2) Immerse the product of step 1) in an aqueous solution of nickel acetate tetrahydrate, keep it warm and static, and take it out and dry to obtain the Ni-ion intercalated MoS 2 precursor;

[0008] 3) Keep the precursor obtained in step 2) warm in an ammonia-containing atmosphere, and naturally cool to obtain the self-supporting Mo 5 N 6 / Ni 3 S 2 composite catalyst.

[0009] In the above solution, the molybdate is ammonium molybdate or sodium molybdate or a mixture thereof.

[0010] In the above solution, the concentration of the molybdate is 3-10 mmol / L, and the concentration of the thiourea is 80-150 mmol / L.

[0011] In the above solution, the solvothermal reaction temperature is 160-200 °C, and the time is 12-24 h.

[0012] In the above solution, the concentration of the nickel acetate tetrahydrate is 20-50 mmol / L, the static temperature is 80-90 °C, and the static time is 6-12 h.

[0013] In the above solution, the volume ratio of ammonia in the ammonia-containing atmosphere is 20-100%.

[0014] In the above solution, in step 3), the heat preservation temperature is 550°C - 650°C, the heat preservation time is 1.5 - 2.5 h, and the heating rate is 5°C / min -1 , and the gas flow rate is 100 - 300 sccm.

[0015] The self-supporting molybdenum nitride / nickel sulfide composite catalyst prepared by the described preparation method, the composite catalyst includes carbon cloth and two-dimensional Mo 5 N 6 / Ni 3 S 2 heterojunction.

[0016] In the above solution, the two-dimensional Mo 5 N 6 / Ni 3 S 2 heterojunction is a nanosheet with a two-dimensional layered structure.

[0017] In the above solution, the selected carbon cloth is hydrophilic carbon cloth.

[0018] The application of the described composite catalyst in water electrolysis for hydrogen production.

[0019] The reaction principle of the present invention is: by heat-preserving and impregnating the hydrothermally synthesized MoS 2 @CC in a nickel acetate solution to form Ni ion intercalated MoS 2 . The intercalated Ni ions provide the Ni source for the NiS 3 S 2 phase and can also significantly reduce the temperature and time required to obtain Mo 5 N 6 . Finally, through nitridation conversion, a two-dimensional Mo 5 N 6 / Ni 3 S 2 heterostructure is formed. At the interface of the heterostructure, Ni 3 S 2 provides electrons for Mo 5 N 6 , increasing the charge density on the surface of Mo 5 N 6 to form an interfacial electric field, thereby regulating the adsorption strength of Ni 3 S 2 for hydrogen and significantly reducing the charge transfer resistance of the catalyst material. The two-dimensional structure greatly increases the number of catalytic active sites. Therefore, Mo 5 N 6 / Ni 3S 2 @CC has more excellent electrocatalytic hydrogen evolution performance compared with pure MoS 2 @CC and pure Mo 5 N 6 @CC has more excellent electrocatalytic hydrogen evolution performance compared with pure MoS -2 At a current density of 10 mA cm 2 SO 4 The overpotentials in 1 M KOH and 0.5 M H -1 SO -1 solutions are 51 mV and 204 mV respectively, and the corresponding Tafel slopes are 80 mV dec

[0020] The beneficial effects of the present invention are as follows: The present invention uses ultrathin two-dimensional MoS 2 (with a thickness of 20-70 nanometers) grown hydrothermally on carbon cloth as a precursor, and further intercalates Ni ions into MoS 2 and nitriding in an ammonia-containing atmosphere to prepare two-dimensional Mo 5 N 6 / Ni 3 S 2 heterojunction nanosheets. On the one hand, the intercalated Ni ions can act as a desulfurizer for MoS 2 to in-situ react to form Ni 3 S 2 , significantly reducing the nitridation conversion temperature of MoS 2 , which also effectively avoids the collapse of the two-dimensional structure at high temperatures. On the other hand, the nitridation conversion of MoS 2 forms a highly conductive nitrogen-rich phase Mo 5 N 6 and Ni 3 S 2 couples in-situ to form a two-dimensional heterojunction interface, which promotes the rearrangement of the electronic structure of Ni 3 S 2 , significantly enhancing the adsorption of hydrogen. At the same time, the two-dimensional structure exposes sufficient catalytic active sites, thus obtaining high hydrogen evolution performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic diagram of the preparation process of the electrochemical catalyst material described in the present invention;

[0022] Figure 2 is the scanning electron microscope image of each step of the corresponding nickel mesh electrode in Example 1 and Comparative Example 1 of the present invention;

[0023] Figure 3 is the X-ray diffraction pattern of the final products prepared in Example 1 and Comparative Example 1 of the present invention;

[0024] Figure 4 This is the EDS element distribution diagram of the final product prepared in Example 1 of the present invention;

[0025] Figure 5 This is a transmission electron microscope image of the final product prepared in Example 1 of the present invention;

[0026] Figure 6 This is a high-resolution XPS spectrum of the final product prepared in Example 1 of the present invention;

[0027] Figure 7 This is an electrochemical polarization curve diagram of the catalyst prepared in Example 1 of the present invention;

[0028] Figure 8 The scanning electron microscope image and X-ray diffraction pattern of the corresponding catalyst in Comparative Example 2 of the present invention;

[0029] Figure 9 This is the X-ray diffraction pattern of the final product prepared in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] Example 1

[0032] A method for preparing a self-supporting molybdenum nitride / nickel sulfide composite catalyst, the schematic diagram of the preparation process is shown in Figure 1 , the specific preparation method comprises the following steps:

[0033] 1) The carbon cloth (abbreviated as CC) is ultrasonically cleaned, dried and set aside;

[0034] 2) The carbon cloth obtained in step 1) was immersed in a mixed solution of 3 mmol / L ammonium molybdate tetrahydrate and 135 mmol / L thiourea, kept at 200°C in a reactor for 24 h, cooled to room temperature, washed and dried to obtain MoS grown on the carbon cloth. 2 @CC;

[0035] 3) MoS obtained in step 2) 2 @CC was placed in a 30mmol / L nickel acetate tetrahydrate aqueous solution and allowed to stand for 6h;

[0036] 4) The precursor in step 3) was kept at 600°C in ammonia for 2 h, with a heating rate of 5°C min -1 After natural cooling, Mo loaded on carbon cloth was obtained. 5 N 6 / Ni 3 S2 sample.

[0037] Comparative Example 1

[0038] A method for preparing a molybdenum nitride / nickel sulfide heterojunction composite catalyst, the specific preparation method comprising the following steps:

[0039] 1) The carbon cloth is ultrasonically cleaned, dried and set aside;

[0040] 2) The carbon cloth obtained in step 1) was immersed in a mixed solution of 3 mmol / L ammonium molybdate tetrahydrate and 135 mmol / L thiourea, kept at 200°C in a reactor for 24 h, cooled to room temperature, washed and dried to obtain MoS grown on the carbon cloth. 2 @CC;

[0041] 3) MoS obtained in step 2) 2 @CC was placed in a 30mmol / L nickel acetate tetrahydrate aqueous solution and allowed to stand for 6h;

[0042] 4) The precursor in step 3) was kept at 500℃ and 700℃ in ammonia for 2h, with a heating rate of 5℃min -1 After natural cooling, Mo loaded on carbon cloth was obtained. 5 N 6 / Ni 3 S 2 sample.

[0043] Comparative Example 2

[0044] A method for preparing a molybdenum nitride / nickel sulfide heterojunction composite catalyst, the specific preparation method comprising the following steps:

[0045] The other steps are the same as those in Example 1, except that the ammonia nitridation time in step 4 is changed to 1 h and 3 h.

[0046] Figure 2 (ab) are MoS synthesized by hydrothermal method 2 @CC,MoS 2 The nanosheets are uniformly coated on the carbon cloth fibers to form a nanosheet array. 2 @CC was impregnated with 0.03M nickel acetate solution and then 3 The SEM images of the nitrided samples at 500℃, 600℃ and 700℃ are shown in Figure 2. Figure 2 (ch) shows the morphology of the sample after nitridation at 500℃ and the original MoS 2 @CC has no obvious difference; when the temperature rises to 600℃, the nanosheets on the surface of the carbon fiber change from the original curled nanosheets to plate-like nanosheets. This is because at 600℃, MoS 2 Nitrided to Mo5 N 6 ; When the temperature reaches 700 °C, serious sintering appears on the sample surface.

[0047] Figure 3 XRD patterns of the products obtained in Example 1 and Comparative Example 1 are shown, which display the XRD patterns of the samples obtained by nitriding at different temperatures. It can be clearly seen from the figure that after hydrothermal treatment, the four strong peaks of the MoS 2 @CC sample at 14.13°, 32.91°, 33.70° and 58.92° respectively correspond to the (002), (100), (101) and (008) crystal planes of 2H-phase MoS 2 (JCPDS#75-1539). After impregnation with nickel acetate solution and nitriding, when the nitriding temperature is 500 °C, new characteristic peaks appear at 21.77°, 31.13°, 37.78°, 44.37°, 49.73°, 50.16° and 55.20°, corresponding to the (101), (110), (003), (202), (113), (211) and (122) crystal planes of Ni 3 S 2 (JCPDS#76-1870); when the nitriding temperature is 600 °C, the characteristic peaks of MoS 2 disappear, and the new peaks appearing at 22.41°, 32.40°, 36.71°, 40.26°, 49.71°, 66.12°, 75.51°, 79.60° and 86.98° respectively correspond to the (101), (004), (110), (112), (114), (300), (304), (118) and (224) crystal planes of Mo 5 N 6 (JCPDS#51-1326), indicating that when the temperature is 600 °C, MoS 2 is nitrided to Mo 5 N 6 , and at the same time, the presence of the Ni 3 S 2 phase can be clearly seen through the XRD pattern, and there are no other impurity peaks; when the nitriding temperature rises to 700 °C, it can be clearly seen from the XRD that the crystallinity of Mo 5 N 6 and Ni 3 S 2 is significantly improved. In summary, the hydrothermally synthesized MoS 2 @CC is impregnated with nickel acetate solution and then nitrided in NH 3 : when the temperature reaches 500 °C, part of the nickel acetate reacts with MoS 2 to generate Ni 3 S 2phase, and its morphology did not change significantly; when the temperature reached 600 °C, MoS 2 was completely nitrided to form Mo 5 N 6 and Ni 3 S 2 two phases, and its morphology was transformed from nanosheets with curled edges into an array of plate-like nanosheets; when the temperature was increased to 700 °C, Mo 5 N 6 and Ni 3 S 2 two phases had significantly improved crystallinity, and severe sintering appeared on the surface of the sample;

[0048] Figure 4 shows the EDS element distribution map of the Mo 5 N 6 / Ni 3 S 2 @CC sample. Figure a shows the uniform arrangement of S, Ni, C, Mo, and N. Figures (b - f) respectively show the uniform distribution of S, Ni, C, Mo, and N in Mo 5 N 6 / Ni 3 S 2 @CC, which is consistent with the XRD results, indicating the successful preparation of Mo 5 N 6 and Ni 3 S 2 two phases.

[0049] Figure 5 is the transmission electron microscopy image of the product obtained in Example 1, which is the TEM image of the Mo 5 N 6 / Ni 3 S 2 @CC sample, and the microscopic morphology and crystal structure of the material can be observed. Figure a is the low-resolution TEM image of the Mo 5 N 6 / Ni 3 S 2 @CC after ultrasonic dispersion. The size of the Mo 5 N 6 / Ni 3 S 2 nanosheets can be seen from the figure, and the size of the Mo 5 N 6 / Ni 3 S 2 nanosheets is about 100 - 300 nm. Figure b is the Mo 5 N 6 / Ni 3 S 2High-resolution TEM lattice images, where the lattice spacing of 0.40 nm corresponds to Mo 5 N 6 for the (101) crystal plane, and the lattice spacing of 0.24 nm corresponds to Ni 3 S 2 for the (003) crystal plane, which is consistent with the XRD results. At the same time, Mo 5 N 6 and Ni 3 S 2 interfaces of the two phases can be clearly observed, indicating the successful synthesis of the heterostructure. Figure c shows the TEM image of a single Mo 5 N 6 / Ni 3 S 2 nanosheet, with a diameter of about 300 nm. Figure d shows the corresponding EDS elemental distribution, where Mo, N, S, and Ni are uniformly distributed in the nanosheet, consistent with the SEM results.

[0050] Figure 6 Figure 28 is the high-resolution XPS spectrum of Example 1. As shown in Figure a, the XPS fine spectrum of Mo 3d of the obtained sample. The peaks at 232.06 eV, 228.86 eV, and 226.06 eV in the MoS 2 @CC sample correspond to MoS 2 's Mo 3d 3 / 2 , Mo3d 5 / 2 , and S2s respectively. The two peaks at 233.24 eV and 229.11 eV in the Mo 5 N 6 / Ni 3 S 2 @CC sample correspond to Mo 5 N 6 's Mo3d 3 / 2 and Mo 3d 5 / 2 , which is consistent with previous reports. This indicates that the MoS 2 in the sample has been completely nitrided to Mo 5 N 6 , consistent with the XRD results. Compared with Mo 5 N 6 @CC, the Mo 3d 5 N 6 / Ni 3 S 2 @CC's Mo 3d 3 / 2 and Mo 3d 5 / 2 double peaks are negatively shifted by about 0.34 eV, which means that electrons transfer from Ni 3 S 2 to Mo 5 N6 , Mo 5 N 6 and Ni 3 S 2 The electronic interaction between them leads to the redistribution of charges at their interface. In addition, the two peaks of Mo 5 N 6 @CC at 232.77 eV and 235.68 eV are attributed to the partial oxidation of the sample. Figure b shows the XPS fine spectra of S2p of MoS 2 @CC and Mo 5 N 6 / Ni 3 S 2 @CC samples. Among them, the peaks at 161.70 eV and 162.95 eV in the MoS 2 @CC sample correspond to S2p 2 of MoS 3 / 2 and S2p 1 / 2 . For the Mo 5 N 6 / Ni 3 S 2 @CC sample, the two spin - orbit peaks at 161.91 eV and 163.00 eV are attributed to S2p 3 S 2 of Ni 3 / 2 and S2p 1 / 2 . Specifically, the peak at 161.91 eV is related to low - coordinated sulfide ions, and the peak at 163.00 eV originates from the sulfur - metal bond. Due to surface oxidation, the additional peak at 168.55 eV is related to the high oxidation state of sulfur in air. Figure c shows the XPS fine spectra of Ni 2p of Mo 5 N 6 / Ni 3 S 2 @CC samples. Among them, the peaks at 852.77 eV and 869.95 eV are the characteristic peaks of Ni 3 S 2 and can be attributed to Ni(0) - related. In addition, the peaks at 855.88 eV and 873.61 eV are related to Ni 3 S 2 of Ni(+2). The other two peaks at 861.61 eV and 880.49 eV are satellite peaks.

[0051] Figure 7 For the catalyst material obtained in Example 1, the comparison of catalytic hydrogen evolution performance in 1M KOH and 0.5M H 2 SO 4 . As shown in Figures a and d, the prepared Mo 5 N 6 / Ni3 S 2 @CC catalyst in 1 M KOH and 0.5 M H 2 SO 4 electrolyte, the overpotentials at a current density of 10 mA cm -2 are 51 mV and 204 mV respectively. This is significantly better than that of MoS 2 @CC (151 mV and 210 mV), Mo 5 N 6 @CC (155 mV and 289 mV) in electrocatalytic hydrogen evolution activity. The Tafel curves (Figs. b and e) were obtained by taking the logarithm of the current in the LSV curves and linearly fitting the linear part (the formula is: η = b×log j + a, where η is the potential, b is the Tafel slope, a is the transfer coefficient, and j is the current). The Tafel slopes of Pt / C in 1 M KOH and 0.5 M H 2 SO 4 electrolyte are 35.72 mV dec -1 and 33.38 mV dec -1 , which conforms to the Volmer-Tafel process. While the Tafel slopes of Mo 5 N 6 / Ni 3 S 2 @CC in alkaline and acidic environments are 80 mV dec -1 and 74 mV dec -1 , respectively, conforming to the Volmer-Heyrovsky process. At the same time, the Tafel slopes of MoS 2 @CC are 127 mV dec -1 and 102 mV dec -1 , and the Tafel slopes of Mo 5 N 6 @CC are 82 mV dec -1 and 92 mV dec -1 . The above shows that after nitridation and the formation of heterojunctions, MoS 2 significantly changes the mechanism of the hydrogen evolution reaction, making the reaction easier to occur.

[0052] Stability is an important criterion for evaluating the ability to maintain catalytic activity during long-term operation under different electrolyte conditions. We studied Mo 5 N 6 / Ni 3 S 2 @CC catalyst in acid and alkali electrolytes at 10 mAcm -2The constant current test was performed with a current density of 1000 Ω (Figures c and f). Before and after the 12-hour stability test, the LSV curves almost overlapped, and the potential did not change significantly during the test, showing that Mo 5 N 6 / Ni 3 S 2 @CC catalyst has excellent stability.

[0053] Figure 8 The scanning electron microscope image and X-ray diffraction pattern of the electrode obtained in Comparative Example 2. When the nitridation time is 1 h, the XRD spectrum shows that Ni 3 S 2 The characteristic peak of , and the strong peak at 36.71° is attributed to Mo 5 N 6 The (110) crystal plane of MoS 2 It begins to be nitrided, and its morphology is better than that of the original MoS 2 @CC did not change significantly (Figure a, d); when the nitriding time was 2h, MoS 2 Completely nitrided, XRD shows only Mo 5 N 6 and Ni 3 S 2 Two phases, and the nanosheets change from edge curling to plate shape (Figure b, d); when the nitridation time is 3h, Mo 5 N 6 and Ni 3 S 2 The crystallinity of the two phases is improved, and the nanosheets on the surface of the carbon fiber are sintered. 2 @CC in NH 3 Mo is prepared by nitriding at 550-650℃ for 1.5-3.5h under atmosphere 5 N 6 / Ni 3 S 2 @CC Sample.

[0054] Comparative Example 3

[0055] A method for preparing a molybdenum nitride catalyst, the specific preparation method comprising the following steps:

[0056] 1) The carbon cloth is ultrasonically cleaned, dried and set aside;

[0057] 2) The carbon cloth obtained in step 1) was immersed in a mixed solution of 3 mmol / L ammonium molybdate tetrahydrate and 135 mmol / L thiourea, kept at 200°C in a reactor for 24 h, cooled to room temperature, washed and dried to obtain MoS grown on the carbon cloth. 2 @CC;

[0058] 3) The precursor in step 2) was kept at 600 °C for 2 h and 850 °C for 5 h in ammonia gas and then cooled naturally to obtain Mo supported on carbon cloth. 5 N 6 sample.

[0059] Figure 9 It is the X-ray diffraction pattern of the electrode obtained in Comparative Example 3. As Figure 9 shown, it is the XRD patterns of the original MoS 2 @CC and the nitridation treatment directly in NH 3 without the adsorption of nickel acetate. When we nitrided MoS 5 N 6 / Ni 3 S 2 @CC samples under the same conditions (600 °C, 2 h), it can be found from the XRD pattern that the characteristic peaks of MoS 2 do not show obvious changes, indicating that MoS 2 cannot undergo nitridation reaction under the same conditions. In order to obtain the Mo 2 N 5 phase, we increased the temperature to 850 °C and the nitridation time was 5 h. It is obvious from the XRD pattern that after nitridation at 850 °C for 5 h in ammonia gas, the characteristic peaks of MoS 6 disappeared and were completely nitrided into Mo 2 N 5 N 6 to obtain the Mo 5 N 6 @CC sample. This further shows that the intercalated Ni ions can act as a desulfurizer for MoS 2 to in-situ react to form Ni 3 S 2 and significantly reduce the nitridation conversion temperature of MoS 2 , which also effectively avoids the collapse of the two-dimensional structure at high temperatures.

[0060] It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of this invention patent shall be subject to the appended claims.

Claims

1. A method for preparing a self-supporting molybdenum nitride / nickel sulfide composite catalyst, characterized in that: The steps include: 1) immersing the carbon cloth in a mixed solution of molybdenum salt and thiourea to perform a solvothermal reaction, and then washing and drying to obtain MoS2 nanosheets grown on the carbon cloth; 2) immersing the product of step 1) in a nickel acetate tetrahydrate aqueous solution and keeping it warm and standing, taking it out and drying it to obtain a MoS2 precursor with Ni ion intercalation; 3) The precursor obtained in step 2) is kept warm in an atmosphere containing ammonia, and the self-supporting Mo5N6 / Ni3S2 composite catalyst is obtained after natural cooling.

2. The preparation method according to claim 1, characterized in that: The molybdenum salt is ammonium molybdate or sodium molybdate or a mixture thereof.

3. The preparation method according to claim 1, characterized in that: The molybdenum salt concentration is 3-10 mmol / L, and the thiourea concentration is 80-150 mmol / L.

4. The preparation method according to claim 1, characterized in that: The solvent thermal reaction temperature is 160-200° C. and the time is 12-24 hours.

5. The preparation method according to claim 1, characterized in that: The nickel acetate tetrahydrate has a concentration of 20 to 50 mmol / L, a standing temperature of 80 to 90° C., and a standing time of 6 to 12 hours.

6. The preparation method according to claim 1, characterized in that: The volume concentration of ammonia in the ammonia-containing atmosphere is 20-100%.

7. The preparation method according to claim 6, characterized in that: In the step 3), the holding temperature is 550° C.-650° C., the holding time is 1.5-2.5 hours, and the gas flow rate is 100-300 sccm.

8. A self-supporting molybdenum nitride / nickel sulfide composite catalyst prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The composite catalyst comprises carbon cloth and a two-dimensional Mo5N6 / Ni3S2 heterojunction grown on the surface of the carbon cloth.

9. The composite catalyst according to claim 8, characterized in that The two-dimensional Mo5N6 / Ni3S2 heterojunction is a nanosheet with a two-dimensional layered structure.

10. Use of the composite catalyst according to claim 8 or 9 in producing hydrogen by electrolysis of water.

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