Cd-Ni3S2 / NF composite materials, their preparation methods, and applications.

Abstract

The application provides a Cd-Ni3S2 / NF composite material and a preparation method and application thereof. By adopting the preparation method provided in the application, by regulating the molar quantity of a cadmium source, a nickel salt, an alkali salt, ammonium fluoride and a sulfur source within the range of the application, and the reaction temperature and time in steps (2)-(3), the Cd-Ni3S2 / NF composite material obtained has HER and OER dual-function electrocatalytic activity.

Description

Technical Field

[0001] This application relates to the field of catalyst technology, and in particular to Cd-Ni3S2 / NF composite materials, their preparation methods, and applications. Background Technology

[0002] The use of non-renewable fossil fuels has made environmental pollution and the energy crisis two major problems hindering human development. Therefore, finding renewable and clean energy sources to replace traditional energy sources has become an urgent problem to solve. Hydrogen has a high calorific value and energy density, and its combustion product is only water, making it a truly green energy source. Electrolysis of water is one of the main methods for obtaining hydrogen energy. It can be divided into two half-reactions: the oxygen evolution reaction (OER) at the anode and the hydrogen evolution reaction (HER) at the cathode. However, these two half-reactions require high overpotentials and have slow kinetics, severely limiting the application of water electrolysis in practical production and daily life. Therefore, finding suitable catalysts to reduce the overpotentials of these two reactions is particularly important.

[0003] Currently, Ru / Ir-based and Pt-based noble metal catalysts are the most effective commercial catalysts for OER and HER reactions, respectively, but their scarcity and high cost limit their large-scale industrial application. Non-noble metal catalysts, on the other hand, mostly lack practicality due to poor catalytic performance or their ability to catalyze only HER or OER reactions alone, making it difficult to achieve large-scale hydrogen production through water electrolysis. Summary of the Invention

[0004] The purpose of this application is to provide a Cd-Ni3S2 / NF composite material, its preparation method and application, to achieve bifunctional electrocatalytic activity of HER and OER.

[0005] The first aspect of this application provides a method for preparing Cd-Ni3S2 / NF composite materials, which includes the following steps:

[0006] (1) Dissolve nickel salt, cadmium source, alkali source and ammonium fluoride in water to form a mixed solution; wherein the molar ratio of the cadmium source, the nickel salt and the alkali source is 1:(2-6):(10-30), the molar ratio of the alkali source and the ammonium fluoride is (1-3):1, and the ratio of the number of moles of ammonium fluoride to the volume of water is 1 mmol:(5-9) mL;

[0007] (2) Place the nickel foam and the mixed solution into a reaction vessel, seal it, control the temperature at 140℃~180℃, react for 6h~10h, and after the reaction is complete, clean and dry to obtain hydroxide precursor material.

[0008] (3) The sulfur source solution and the hydroxide precursor material are placed in a reaction vessel, sealed, and the temperature is controlled at 130℃~170℃. The reaction is carried out for 4h~8h. After the reaction is completed, the mixture is cleaned and dried to obtain the Cd-Ni3S2 / NF composite material. The ratio of the number of moles of sulfur source to the volume of water in the sulfur source solution is 1mmol∶(25~30)mL, and the molar ratio of sulfur source to nickel salt is 1∶(1.0~2.0).

[0009] In some embodiments of this application, the nickel salt is selected from at least one of nickel nitrate, nickel sulfate, and nickel chloride.

[0010] In some embodiments of this application, the cadmium source is selected from at least one of cadmium nitrate, cadmium sulfate, and cadmium chloride.

[0011] In some embodiments of this application, the alkali source is selected from at least one of urea and hexamethylenetetramine.

[0012] In some embodiments of this application, the sulfur source is selected from at least one of sodium sulfide, thiourea, and thioacetamide.

[0013] The second aspect of this application provides a Cd-Ni3S2 / NF composite material, which is prepared according to the preparation method of any of the foregoing embodiments.

[0014] A third aspect of this application provides the use of the Cd-Ni3S2 / NF composite material in any of the foregoing embodiments for electrocatalytic HER, electrocatalytic OER, and electrocatalytic total water splitting.

[0015] The beneficial effects of this application are:

[0016] This application provides a Cd-Ni3S2 / NF composite material, its preparation method, and its application. Using nickel foam as a substrate, the Cd-Ni3S2 / NF composite material is synthesized via a two-step hydrothermal method. In the structure of the Cd-Ni3S2 / NF composite material, Ni→S electron transfer leads to the formation of Ni on the surface of the Cd-Ni3S2 / NF composite material. 3+ An increased species ratio is beneficial for improving OER catalytic activity. Doping Cd-Ni3S2 / NF composites with cadmium, which has a larger ionic radius, distorts the Ni3S2 lattice, exposing more nickel active sites and thus improving electrocatalytic activity, achieving efficient and stable electrocatalytic activity. DFT calculations show that after Cd doping, the adsorbed hydrogen atoms are closer to the surface of Ni3S2, and the Gibbs free energy (ΔG) is higher. H* The reduced current density significantly improves the HER catalytic activity. The Cd-Ni3S2 / NF composite material prepared in this application achieves efficient and stable dual catalytic activity for both HER and OER in an alkaline electrolyte (current density of 10 mA / cm²).2 At that time, the overpotentials of HER and OER were 140mV and 197mV, respectively; in the total water splitting test, the required cell voltage was 1.489V, which is very low, indicating excellent catalytic performance for total water splitting, and this performance was achieved at a current density of 10mA / cm². 2 It can stably electrolyze for more than 50 hours, demonstrating high stability. As an excellent catalyst for the total water electrolysis process, it has high application value and good economic prospects.

[0017] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0019] Figure 1 The XRD patterns of the products obtained in Examples 1-3 and Comparative Example 1 of this application are shown below.

[0020] Figure 2 SEM images of the products obtained in Examples 1-3 and Comparative Example 1 of this application;

[0021] Figure 3 The SEM-EDS elemental distribution map and TEM image of the product obtained in Example 2 of this application are shown.

[0022] Figure 4 XPS images of the products prepared in Examples 1-3 and Comparative Example 1 of this application;

[0023] Figure 5 The graphs show the HER performance of the products prepared in Examples 1-3 and Comparative Example 1 of this application and the commercial catalyst Pt-C / NF.

[0024] Figure 6 The products prepared in Examples 1-3 and Comparative Example 1 of this application, and the commercial catalyst RuO 2 / NF's OER performance test chart;

[0025] Figure 7 The graphs show the total water hydrolysis performance test results of the products prepared in Examples 1-3 and Comparative Example 1 of this application.

[0026] Figure 8 The DFT calculation process and results of the products prepared in Example 2 and Comparative Example 1 of this application are shown below.

[0027] Figure 9 These are the structural models of Example 2 and Comparative Example 1 of this application after structural optimization in the OER four-step reaction;

[0028] Figure 10 This is the total density of states diagram of the products prepared in Example 2 and Comparative Example 1 of this application. Detailed Implementation

[0029] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0030] The first aspect of this application provides a method for preparing Cd-Ni3S2 / NF composite materials, which includes the following steps:

[0031] (1) Dissolve nickel salt, cadmium source, alkali source and ammonium fluoride in water to form a mixed solution; wherein the molar ratio of the cadmium source, the nickel salt and the alkali source is 1:(2-6):(10-30), the molar ratio of the alkali source and the ammonium fluoride is (1-3):1, and the ratio of the number of moles of ammonium fluoride to the volume of water is 1 mmol:(5-9) mL;

[0032] (2) Place the nickel foam and the mixed solution into a reaction vessel, seal it, control the temperature at 140℃~180℃, react for 6h~10h, and after the reaction is complete, clean and dry to obtain hydroxide precursor material.

[0033] (3) The sulfur source solution and the hydroxide precursor material are placed in a reaction vessel, sealed, and the temperature is controlled at 130℃~170℃. The reaction is carried out for 4h~8h. After the reaction is completed, the mixture is cleaned and dried to obtain the Cd-Ni3S2 / NF composite material. The ratio of the number of moles of sulfur source to the volume of water in the sulfur source solution is 1mmol∶(25~30)mL, and the molar ratio of sulfur source to nickel salt is 1∶(1.0~2.0).

[0034] Transition metal sulfides (TMS) exhibit high conductivity and catalytic activity, especially nickel-based catalysts with nickel sulfides as the main component, such as NiS, NiS2, and Ni3S2. Ni3S2, in particular, is a rhombic crystal with Ni atoms located in distorted tetrahedral positions within a cubic sulfur lattice approximately at its volume center. Ni3S2 exhibits strong Ni-Ni bond interactions and pronounced intrinsic metallic behavior. However, nickel-based sulfides cannot simultaneously possess high HER and OER activities during catalysis. The inventors discovered that doping Ni3S2 with Cd can, on the one hand, modulate the coordination valence state and chemical environment of the electrolyte, thus improving HER and OER activities; on the other hand, it can distort the Ni3S2 lattice, exposing more Ni sites, thereby enhancing the HER and OER performance of Ni3S2. This application uses cadmium source, nickel salt, alkali salt, ammonium fluoride and sulfur source within the above molar range, as well as the reaction temperature and time in steps (2)-(3), to form a favorable Cd-Ni3S2 / NF morphology structure, expose more active sites, and thus improve the HER and OER electrocatalytic performance of Cd-Ni3S2 / NF.

[0035] Nickel foam (NF) is used as a substrate material in this application and can be directly used as an electrode to improve the conductivity of the catalyst. The unique three-dimensional framework of NF allows for the construction of composite materials with specific morphologies. Nickel foam has a high specific surface area, which enables good dispersion of the synthesized Cd-Ni3S2, fully exposing the electrocatalytic active sites. Furthermore, using NF as a substrate allows for closer interaction between the active material and the substrate, enhancing the mechanical stability and conductivity of the material. Cd-Ni3S2 exhibits a crisscrossing morphology on NF, which has a larger specific surface area and more exposed active sites, facilitating electron transfer and the release of generated gases, thereby achieving highly efficient and stable electrocatalytic HER and OER performance.

[0036] In step (1) of this application, when the molar ratio of cadmium source to nickel salt is too low, the formed Cd-Ni3S2 / NF nanosheets are relatively thin and elongated, but the electrocatalytic activity of HER or OER is poor due to the low Cd doping amount. When the molar ratio of cadmium source to nickel salt increases, the thickness of the formed Cd-Ni3S2 / NF nanosheets increases, the stability of the material is enhanced, and many pores appear on the surface of the nanosheets, increasing the specific surface area. Due to the appropriate Cd doping amount and nanosheet array structure, the electrocatalytic activity of HER or OER reaches its optimal level. However, when the molar ratio of cadmium source to nickel salt is too high, the morphology of the composite material changes drastically, transforming from a nanosheet morphology to a large bulk morphology, which reduces the exposed active sites of the composite material and worsens the electrocatalytic activity of HER or OER. Therefore, this application controls the molar ratio of cadmium source to nickel salt to be 1:(2-6), preferably 1:(3-5), which is beneficial to expose more electrocatalytic active sites and thus improve the electrocatalytic performance of HER and OER.

[0037] Before use, the nickel foam in step (2) of this application is pretreated. The pretreatment includes ultrasonic cleaning with 1 mol / L hydrochloric acid for 10-20 minutes, followed by cleaning with acetone, deionized water and anhydrous ethanol, and vacuum drying.

[0038] This application does not impose any particular restrictions on the reactor in steps (2) and (3), as long as it achieves the purpose of this application. For example, the reactor can be a polytetrafluoroethylene stainless steel high-pressure reactor. This application does not impose any particular restrictions on the cleaning and drying in steps (2) and (3) above, as long as it achieves the purpose of this application. For example, cleaning can be done by sequentially using distilled water and anhydrous ethanol, and the drying temperature can be 30℃-60℃.

[0039] In some embodiments of this application, the nickel salt is selected from at least one of nickel nitrate, nickel sulfate, and nickel chloride. Selecting the aforementioned nickel salt is more advantageous for obtaining Cd-Ni3S2 / NF composite materials with high HER and OER electrocatalytic performance.

[0040] In some embodiments of this application, the cadmium source is selected from at least one of cadmium nitrate, cadmium sulfate, and cadmium chloride. Selecting the aforementioned cadmium source is more advantageous for obtaining Cd-Ni3S2 / NF composite materials with high HER and OER electrocatalytic performance.

[0041] In some embodiments of this application, the alkali source is selected from at least one of urea and hexamethylenetetramine. By selecting the above-mentioned alkali source, it is more advantageous to obtain Cd-Ni3S2 / NF composite materials with high HER and OER electrocatalytic performance.

[0042] In some embodiments of this application, the sulfur source is selected from at least one of sodium sulfide, thiourea, and thioacetamide. Selecting the above-mentioned sulfur source is more advantageous for obtaining Cd-Ni3S2 / NF composite materials with high HER and OER electrocatalytic performance.

[0043] A second aspect of this application provides a Cd-Ni3S2 / NF composite material prepared according to the preparation method in any of the foregoing embodiments. The Cd-Ni3S2 / NF composite material prepared by the above method has a plate-like nanostructure, which can generate more Ni active sites, thereby achieving efficient and stable dual catalytic performance for HER and OER.

[0044] A third aspect of this application provides the use of the Cd-Ni3S2 / NF composite material in any of the foregoing embodiments for electrocatalytic HER, electrocatalytic OER, and electrocatalytic total water splitting. The Cd-Ni3S2 / NF composite material provided in this application has bifunctional electrocatalytic activity for both HER and OER, and can be applied to electrocatalytic total water splitting.

[0045] This application provides a Cd-Ni3S2 / NF composite material and its preparation method. Using nickel foam as a substrate, a two-step hydrothermal method is employed to synthesize the Cd-Ni3S2 / NF composite material. In the structure of the Cd-Ni3S2 / NF composite material, Ni→S electron transfer leads to the formation of Ni in Cd-Ni3S2 / NF. 3+ An increased proportion of cadmium (Cd) is beneficial for improving OER activity. Doping Ni3S2 with cadmium, which has a larger ionic radius, can distort the crystal lattice, exposing more nickel active sites, thereby improving electrocatalytic activity and achieving efficient and stable electrocatalytic activity. DFT calculations show that after Cd doping, H atoms are closer to the surface of Ni3S2, and the Gibbs free energy (ΔG) is higher. H* The reduced oxygen content significantly improves HER catalytic activity. Furthermore, the Cd-Ni3S2 / NF composite material prepared in this application demonstrates efficient and stable dual HER and OER catalytic performance in a complete water splitting test with an alkaline electrolyte, exhibiting high application value and promising economic prospects. The Cd-Ni3S2 / NF composite material provided in this application uses nickel foam as a support, which can be directly used as an electrode, thus saving raw material costs. This application employs a two-step hydrothermal method to synthesize the Cd-Ni3S2 / NF composite material, a simple and low-cost preparation method suitable for industrial production.

[0046] Example 1

[0047] (1) Nickel foam pretreatment

[0048] The surface NiO layer was removed by ultrasonic cleaning with 1 mol / L hydrochloric acid solution for 15 minutes. Then, it was cleaned with acetone, deionized water and ethanol for 30 minutes each, and then vacuum dried at 40°C for 12 hours to obtain pretreated nickel foam.

[0049] (2) Preparation of Cd-Ni3S2 / NF composite precursor

[0050] A hydrothermal method was used to dissolve 2 mmol of Ni(NO3)3·6H2O, 1 mmol of Cd(NO3)2·4H2O, 10 mmol of urea, and 5 mmol of ammonium fluoride in 35 mL of deionized water and stir to form a clear and transparent precursor solution. The precursor solution and the pretreated nickel foam were transferred to a 50 mL polytetrafluoroethylene stainless steel hydrothermal reactor, sealed, and placed in an oven at 160 °C for 8 h. After the reaction was completed, the mixture was cooled to room temperature, washed with distilled water and anhydrous ethanol, and dried at 40 °C for 12 h to obtain the Cd-Ni3S2 / NF composite material precursor.

[0051] (3) Preparation of Cd-Ni3S2 / NF composite material

[0052] Using a hydrothermal method, 0.3 g of Na2S·9H2O was dissolved in 35 mL of deionized water and stirred to form a transparent and homogeneous solution. The solution and the above-mentioned Cd-Ni3S2 / NF composite material precursor were transferred to a 50 mL polytetrafluoroethylene stainless steel hydrothermal reactor, sealed, and placed in an oven at 150 °C for 6 h. After the reaction was completed, the mixture was cooled to room temperature, washed with distilled water and anhydrous ethanol, and dried at 40 °C for 12 h. The product was designated as Cd-Ni3S2 / NF-1 / 2.

[0053] Example 2

[0054] Except for the molar ratio of Cd(NO3)2·4H2O to Ni(NO3)3·6H2O being 1:4, everything else was the same as in Example 1, and the obtained product was denoted as Cd-Ni3S2 / NF-1 / 4.

[0055] Example 3

[0056] Except for the molar ratio of Cd(NO3)2·4H2O to Ni(NO3)3·6H2O being 1:6, everything else was the same as in Example 1, and the obtained product was denoted as Cd-Ni3S2 / NF-1 / 6.

[0057] Comparative Example 1

[0058] Except for step (2) where Cd(NO3)2·4H2O is not added, the rest is the same as in Example 1, and the product Ni3S2 / NF nanosheets are obtained, denoted as Ni3S2 / NF.

[0059] Structural analysis and performance testing

[0060] Characterization of Cd-Ni3S2 / NF composite materials

[0061] 1. X-ray diffraction (XRD) analysis

[0062] The XRD analysis results of the products of Examples 1-3 and Comparative Example 1 of this application are as follows: Figure 1 As shown, where, Figure 1 Curves (a)-(d) in the figure are the XRD spectra of the products prepared in Comparative Example 1, Example 3, Example 2 and Example 1, respectively.

[0063] from Figure 1 It can be seen that all products exhibit strong diffraction peaks at 44.5°, 51.8°, and 76.4°, corresponding to elemental Ni, respectively. 0 The (111), (200), and (220) crystal planes of (JCPDS card number 04-0850) indicate that the products are all grown on NF; all products show diffraction peaks at 21.7°, 31.1°, 37.8°, 50.1°, 55.2°, and 55.4°, corresponding to the (101), (110), (003), (211), (122), and (300) crystal planes of Ni3S2 (JCPDS card number 44-1418), respectively, indicating the formation of Ni3S2. Furthermore, from... Figure 1 It can be seen that, compared with Comparative Example 1 without Cd doping, the Cd-Ni3S2 / NF composite materials obtained in Examples 1-3 of this application, apart from the diffraction peaks of Ni3S2, did not show diffraction peaks of other Cd-based compounds, indicating that the Cd doping in Examples 1-3 of this application did not form a new phase. However, from Figure 1 As can be seen in (B), compared with Comparative Example 1 (without Cd doping), the peak positions of Cd-Ni3S2 / NF obtained in Examples 1-3 of this application are shifted to the left, and the degree of deviation of the diffraction peak positions increases with the increase of Cd addition. This is because the radius of Cd ions is larger than that of Ni ions, and the doping of Cd leads to an increase in the interplanar spacing (leftward shift of the diffraction peak, and a decrease in the 2θ angle). It can be seen that Cd ions have been successfully doped into the Ni3S2 lattice.

[0064] 2. Analysis of electron microscopy results

[0065] Scanning electron microscope (SEM) images of the products of Examples 1-3 and Comparative Example 1 of this application are shown below. Figure 2 As shown, where, Figure 2 The (a)-(d) and (a')-(d') images in the figure are SEM images of the products prepared in Comparative Example 1, Example 3, Example 2 and Example 1 at different magnifications.

[0066] from Figure 2 It can be seen that the Ni3S2 / NF nanosheets of Comparative Example 1 without Cd doping are relatively thin and have a petal-like shape. However, the thickness of the Cd-Ni3S2 / NF nanosheets in Examples 2 and 3 after Cd doping changed significantly. In Example 1, with a higher Cd doping concentration, as shown... Figure 2 As shown in (d) and (d'), the nanosheet structure of the product disappears. Compared to the pure phase Ni3S2 / NF nanosheets, the thickness of the Cd-Ni3S2 / NF nanosheets doped with Cd increases, indicating that the Cd doping in Examples 2-3 of this application alters the morphology of the Ni3S2 / NF nanosheets. Specifically, when the molar ratio of Cd to Ni is 1:6 (Example 3), the thickness of the Cd-Ni nanosheets increases. Figure 2 Figures (b) and (b') show that the Cd-Ni3S2 / NF nanosheets are elongated and have surface protrusions; when the molar ratio of Cd to Ni increases to 1:4 (Example 2), the... Figure 2 Figures (c) and (c') show that as the thickness of the Cd-Ni3S2 / NF nanosheets increases, an uneven surface with pores appears; when the molar ratio of Cd to Ni continues to increase to 1:2 (Example 1), the thickness of the Cd-Ni3S2 / NF nanosheets increases, and an uneven surface with pores appears; when the molar ratio of Cd to Ni continues to increase to 1:2 (Example 1), the thickness of the Cd-Ni3 Figure 2 As can be seen from the (d) and (d') figures, Cd-Ni3S2 / NF no longer exhibits a nanosheet morphology, but rather a continuous blocky morphology with undulating surfaces. Furthermore, the Cd-Ni3S2 / NF nanosheets obtained in Example 2 of this application show significant surface porosity, resulting in an increased specific surface area and allowing for sufficient contact with the electrolyte solution, thus further enhancing electrocatalytic performance.

[0067] The SEM-EDS elemental distribution map and transmission electron microscope (TEM) image of the product Cd-Ni3S2 / NF-1 / 4 in Example 2 of this application are as follows: Figure 3 As shown, (a) is an SEM image, (b) to (d) are elemental distribution maps of S, Ni, and Cd elements in the corresponding region of (a), respectively, (e) is a TEM image, and (f) is a high-resolution transmission electron microscope (HRTEM) image. Figure 3 As shown in diagrams (b)-(d), Cd-Ni3S2 / NF-1 / 4 contains Ni, S, and Cd elements, and these three elements are evenly distributed. Figure 3 As can be seen from Figure (e), the Cd-Ni3S2 / NF-1 / 4 nanosheets have a crystal plane spacing of 0.29 nm, which is basically corresponding to the (110) crystal plane of Ni3S2.

[0068] 3. X-ray photoelectron spectroscopy (XPS) analysis

[0069] This application uses XPS analysis to determine the valence states of Cd, Ni, and S in the products of Example 2 and Comparative Example 1. The results are as follows: Figure 4 As shown, (a) is the XPS full spectrum of Cd-Ni3S2 / NF-1 / 4 in Example 2 of this application, (b) is the Ni 2p XPS spectrum of Cd-Ni3S2 / NF-1 / 4 in Example 2 of this application and Ni3S2 / NF in Comparative Example 1, (c) is the S 2p XPS spectrum of Cd-Ni3S2 / NF-1 / 4 in Example 2 of this application and Ni3S2 / NF in Comparative Example 1, and (d) is the Cd 3d XPS spectrum of Cd-Ni3S2 / NF-1 / 4 in Example 2 of this application.

[0070] from Figure 4 As shown in Figure (a), Cd, Ni, and S elements are present on Cd-Ni3S2 / NF-1 / 4 in Example 2 of this application. Figure (b) shows that after Cd doping Ni3S2, the binding energies of 855.0 eV and 872.7 eV correspond to Ni... 2+ 2p 3 / 2 and Ni 2+ 2p 1 / 2 The higher binding energies of 856.8 eV and 874.8 eV correspond to Ni 3+ 2p 3 / 2 and Ni 3+ 2p 1 / 2 The peak values ​​of 861.1 eV and 879.7 eV are their satellite peaks, generated by the spin-orbit double peaks. Calculations based on the integral area of ​​the fitted curves indicate that Ni in the pure-phase Ni3S2... 3+ with Ni 2+ The peak area ratio is 0.33, while after Cd doping, Ni... 3+ with Ni 2+ The ratio of peak areas becomes 0.59, indicating that after Cd doping, trivalent Ni... 3+ The content increased. As can be seen from Figure (c), in the Cd-Ni3S2 / NF-1 / 4 prepared in Example 2 of this application, the peaks with binding energies of 162.4 and 163.8 eV belong to S, respectively. 2- 2p 3 / 2 and S 2- 2p 1 / 2 The signal peak at 168.3 eV corresponds to oxidized sulfur species (SO), which is due to the surface oxidation of sulfur in the air. Furthermore, compared to pure Ni3S2, the S 2p binding energy of Cd-Ni3S2 / NF-1 / 4 decreased by 0.3 eV after Cd doping in Example 2 of this application, indicating that Cd doping causes electron transfer to the S element, binding Ni... 3+The increase in content is inferred to be due to electron transfer from Ni to S. As can be seen from the (d) figure, the peaks at 411.8 eV and 405.8 eV correspond to Cd. 2+ 3D 3 / 2 and Cd 2+ 3D 5 / 2 This proves that Cd is doped into Ni3S2.

[0071] Therefore, in Embodiment 2 of this application, in Cd 2+ After ions replace some Ni sites, an electron transfer from Ni to S occurs within Ni3S2, causing Ni in Cd-doped Ni3S2 to... 3+ / Ni 2+ The proportion is higher, while Ni 3+ Increasing the proportion of Ni helps improve OER activity; simultaneously, compared to Ni, Cd has a larger ionic radius, which leads to lattice distortion in Ni3S2, exposing more Ni sites and thus further increasing the number of electrocatalytic active sites. Therefore, Example 2 of this application contains more Ni. 3+ The Cd-Ni3S2 / NF-1 / 4 structure is conducive to the electrocatalytic reaction.

[0072] Electrocatalytic performance test

[0073] 1. HER test

[0074] The HER performance of the products prepared in Examples 1-3 and Comparative Example 1 of this application was tested, and the commercial catalyst Pt / C loaded on NF was used as a control, with a Pt / C loading of 1.32 mg / cm³. 2 This is denoted as Pt / C / NF. A standard three-electrode system was used for testing. The products prepared in Examples 1-3 and Comparative Example 1 of this application were directly used as electrodes. A 1×2cm product obtained in Examples 1-3 and Comparative Example 1 was clamped onto an electrode holder as the working electrode. The counter electrode was a platinum sheet electrode, and the reference electrode was a Hg / HgO electrode. The electrolyte was a 1M KOH solution. The polarization curve was measured using linear sweep voltammetry (LSV) at a scan rate of 5 mV / s. The results are as follows: Figure 5 As shown, (a) is the polarization curve, (b) is the Tafel slope plot, and (c) is the current density at 10 mA / cm². -2 At the same time, the overpotential comparison diagrams of the products prepared in Examples 1-3 and Comparative Example 1 of this application are shown in Figure (d), which is a Nernst curve; Figure (e) is a linear fitting diagram of the change in capacitive current density versus the sweep rate; and Figure (f) is a diagram showing the overpotential of the products prepared at a current density of 10 mA / cm². -2 Stability testing of the sample prepared in Example 2 of this application.

[0075] from Figure 5As shown in Figures (a) and (c), compared to the pure-phase Ni3S2 / NF in Comparative Example 1, the overpotentials of Cd-Ni3S2 / NF in Examples 1-3 of this application all decreased, indicating that the Cd-Ni3S2 / NF prepared in these examples has higher HER activity. Specifically, in Examples 1-3 of this application, with the increase of Cd doping amount, the overpotential shows a trend of first decreasing and then increasing, that is, the HER activity first increases and then decreases. Among them, the Cd-Ni3S2 / NF-1 / 4 prepared in Example 2 of this application has better performance, with a current density of 10 mA cm⁻¹. -2 At that time, only an overpotential of 140mV is needed, i.e., η 10 =140mV, indicating that its HER electrocatalytic activity is the highest. Furthermore, although the morphology of Cd-Ni3S2 / NF-1 / 2 in Example 1 of this application is not nanosheet-like, its overpotential is still lower than that of pure-phase Ni3S2 / NF nanosheets. Therefore, in the preparation of Cd-Ni3S2 / NF in this application, the molar ratio of Cd to Ni is 1:(2-6), preferably 1:(3-5). It can be seen that when Cd-Ni3S2 / NF formed by controlled Cd doping in Examples 1-3 of this application is used as an electrode material, it can improve the HER electrocatalytic activity. From... Figure 5 As can be seen from Figure (b), compared to the pure-phase Ni3S2 / NF nanosheets in Comparative Example 1, the Cd-Ni3S2 / NF in Examples 1-3 of this application have lower Tafel slope values, and the Cd-Ni3S2 / NF prepared in Example 2 of this application has an even lower Tafel slope value, only 144 mV dec. -1 This indicates that it has excellent HER dynamic performance.

[0076] Electrochemical impedance spectroscopy was used to study the kinetic process of the electrode. The Nernst curve of the electrode was measured using the IMP-ACImpedance program on an electrochemical workstation. The parameters were set as follows: voltage 1.43 V, frequency range 100 kHz to 0.01 Hz, and perturbation 5 mV. The test results are as follows: Figure 5 As shown in Figure (d), based on the fitted model, the series resistance (Rs) and charge transfer resistance (R) are... ct The HER value was calculated, and the results are shown in Table 1. (Reference) Figure 5 Figure (d) and Table 1 show that, by comparing the radius and resistance value of the low-frequency semicircle, it can be seen that, compared to the pure-phase Ni3S2 / NF nanosheets in Comparative Example 1, the charge transfer resistance (R) of the Cd-Ni3S2 / NF prepared in Examples 1-3 of this application is significantly lower. ct The Ri of the Cd-Ni3S2 / NF-1 / 4 composite material prepared in Example 2 of this application is relatively small. ctThe smaller size indicates a faster electron transfer rate in the HER reaction. Specifically, Examples 1-3 of this application yielded Ri of Cd-Ni3S2 / NF. ct The Ω values ​​were 7.82Ω, 4.63Ω, and 11.37Ω, respectively, while the RΩ of the nanosheets prepared in Comparative Example 1 was... ct It is 12.27Ω. From Figure 5 As can be seen in Figure (e), compared to the pure-phase Ni3S2 / NF nanosheets in Comparative Example 1, the Cd-Ni3S2 / NF nanosheets prepared in Examples 1-3 of this application have higher C content. dl The values ​​all increased, indicating an increase in specific surface area and improved electrocatalytic effect. In particular, the Cd-Ni3S2 / NF-1 / 4 composite material prepared in Example 2 of this application has the largest C value. dl The value is 44.03 mF cm. -2 This indicates that it has the largest electrocatalytic active surface area.

[0077] Using the chronoamperometry method, the Cd-Ni3S2 / NF-1 / 4 composite material prepared in Example 2 of this application was subjected to a current density of 10 mA·cm⁻¹. -2 The following HER stability test was performed, and the results are as follows: Figure 5 As shown in Figure (f). From Figure 5 As can be seen from Figure (f), the current density did not change significantly after 48 hours of continuous electrolysis, indicating that it has good HER electrocatalytic stability.

[0078] Table 1

[0079]

[0080]

[0081] 2. OER Test

[0082] The OER performance of the products prepared in Examples 1-3 and Comparative Example 1 of this application was tested, and the commercial catalyst RuO2 loaded on NF was used as a control, with a RuO2 loading of 1.35 mg / cm³. 2 This is denoted as RuO2 / NF. A standard three-electrode system was used for testing. The products obtained in Examples 1-3 and Comparative Example 1 of this application were directly used as electrodes. A 1×2 cm product obtained in Examples 1-3 and Comparative Example 1 was clamped onto an electrode holder as the working electrode. The counter electrode was a platinum sheet electrode, the reference electrode was a Hg / HgO electrode, and the electrolyte was a 1M KOH solution. The polarization curve was measured using linear sweep voltammetry (LSV) at a scan rate of 5 mV / s. The results are as follows: Figure 6 As shown, (a) is the polarization curve, (b) is the Tafel slope diagram, and (c) is the current density at 10 mA / cm².-2 At the same time, the overpotential comparison diagrams of the products prepared in Examples 1-3 and Comparative Example 1 of this application are shown in Figure (d), which is a Nernst curve; Figure (e) is a linear fitting diagram of the change in capacitive current density versus the sweep rate; and Figure (f) is a diagram showing the overpotential of the products prepared at a current density of 10 mA cm⁻¹. -2 At that time, the stability test of the composite material prepared in Example 2 of this application was conducted.

[0083] from Figure 6 As shown in Figures (a) and (c), compared to the pure-phase Ni3S2 / NF in Comparative Example 1, the overpotentials of Cd-Ni3S2 / NF in Examples 1-3 of this application all decreased, indicating that the Cd-Ni3S2 / NF prepared in these examples has higher HER activity. Specifically, in Examples 1-3 of this application, with the increase of Cd doping amount, the overpotential shows a trend of first decreasing and then increasing, that is, the OER catalytic activity first increases and then decreases. Among them, the Cd-Ni3S2 / NF-1 / 4 composite material prepared in Example 2 of this application has better performance, when the current density is 10 mA cm⁻¹. -2 At that time, only an overpotential of 197mV is needed, that is, the η of OER. 10 =197mV, the OER electrocatalytic activity is higher, even lower than the overpotential η of noble metal catalyst supported on NF, i.e., RuO2 / NF. 10 =280mV. Therefore, in the preparation of Cd-Ni3S2 / NF in this application, the molar ratio of Cd to Ni is 1:(2-6), preferably 1:(3-5). It can be seen that when Cd-doped Cd-Ni3S2 / NF in Examples 1-3 of this application is used as an electrode material, it is beneficial to improve the morphology and structure, expose more suitable active sites, and thus improve the electrocatalytic activity of OER.

[0084] In addition, the η of the commercial catalyst RuO2 loaded onto NF is... 10 =280mV, which is greater than the Cd-Ni3S2 / NF prepared in Examples 1-3 of this application. It can be seen that the OER electrocatalytic activity of the Cd-Ni3S2 / NF prepared in this application is better than that of the commercial catalyst RuO2. Moreover, the cost of the Cd-Ni3S2 / NF prepared in this application is much lower than that of the noble metal RuO2, and it has good commercial application prospects.

[0085] from Figure 6 As can be seen from Figure (b), compared to the pure-phase Ni3S2 / NF nanosheets in Comparative Example 1, the Cd-Ni3S2 / NF in Examples 1-3 of this application have lower Tafel slope values, and the Cd-Ni3S2 / NF composite material prepared in Example 2 of this application has an even lower Tafel slope value, only 54 mV dec. -1This indicates that it has excellent OER kinetic performance, which in turn proves its excellent electrocatalytic performance.

[0086] Electrochemical impedance spectroscopy was used to study the kinetic process of the electrode. The Nernst curve of the electrode was measured using the IMP-ACImpedance program on an electrochemical workstation. The parameters were set as follows: voltage 1.43 V, frequency range 100 kHz to 0.01 Hz, perturbation 5 mV. The test results are as follows: Figure 6 As shown in Figure (d). Based on the fitting model, it can be known that the series resistance (R) s ) and charge transfer resistance (R ct The OER (Output Efficiency) value is shown in Table 2. (Reference) Figure 6 Figure (d) and Table 2 show that, by comparing the radius and resistance of the low-frequency semicircle, the Cd-Ni3S2 / NF composite materials prepared in Examples 1-3 of this application have higher resistance than the pure-phase Ni3S2 / NF nanosheets in Comparative Example 1. ct The Rc of the Cd-Ni3S2 / NF-1 / 4 composite material prepared in Example 2 of this application is relatively small. ct The smaller impedance indicates a faster electron transfer rate in the HER reaction. Specifically, the impedances of the products obtained in Examples 1-3 of this application were 2.99Ω, 2.48Ω, and 3.52Ω, respectively, while the impedance of the composite material prepared in Comparative Example 1 was 8.55Ω.

[0087] from Figure 6 As can be seen in Figure (e), compared to the pure-phase Ni3S2 / NF nanosheets in Comparative Example 1, the Cd-Ni3S2 / NF nanosheets prepared in Examples 1-3 of this application have higher C content. dl The increased values ​​indicate an increase in specific surface area and improved electrocatalytic performance. In particular, the Cd-Ni3S2 / NF-1 / 4 composite material prepared in Example 2 of this application exhibits a larger C... dl The value is 22.11 mF cm. -2 This indicates that it has a larger electrocatalytic active surface area.

[0088] Electrochemical stability is another important factor in evaluating the performance of electrocatalysts. Using a chronoamperometric method, the Cd-Ni3S2 / NF-1 / 4 composite material prepared in Example 2 of this application was tested at a current density of 10 mA·cm⁻¹. -2 The OER stability test was performed, and the results are as follows: Figure 6 As shown in Figure (f). From Figure 6 As can be seen from Figure (f), the current density remained essentially unchanged after 48 hours of continuous electrolysis, indicating that it has good OER electrocatalytic stability.

[0089] Table 2

[0090] Example 1 2.31 2.99 Example 2 2.48 2.48 Example 3 1.98 3.52 Comparative Example 1 1.95 8.55

[0091] 3. Complete water electrolysis performance test

[0092] The products prepared in Examples 1-3 and Comparative Example 1 of this application were used simultaneously as anode and cathode materials to construct a dual-electrode electrolyzer for complete water splitting. A standard dual-electrode system was used for testing. The self-supporting materials prepared in Examples 1-3 and Comparative Example 1 of this application were directly used as electrodes. A 1×2 cm piece of the aforementioned material was clamped onto the electrode holder as the cathode and anode for electrolysis. The electrolyte was 1 MkOH solution. The polarization curve was tested using linear sweep voltammetry (LSV) at a scan rate of 5 mV / s. The results are as follows: Figure 7 As shown, (a) is the polarization curve of the products prepared in Examples 1-3 and Comparative Example 1 of this application, and (b) is the time-current density curve of the product prepared in Example 2 of this application for electrocatalytic water splitting.

[0093] from Figure 7 As shown in Figure (a), compared to the pure-phase Ni3S2 / NF in Comparative Example 1, the Cd-Ni3S2 / NF in Examples 1-3 of this application have lower cell voltages, indicating that the Cd-Ni3S2 / NF prepared in this application has high electrocatalytic activity, and the Cd-Ni3S2 / NF composite material prepared in Example 2 of this application has an even lower cell voltage. Specifically, at a current density of 10 mA·cm⁻¹ -2 At that time, the cell voltages of the Cd-Ni3S2 / NF prepared in Examples 1-3 of this application were 1.518V, 1.489V, and 1.562V, respectively. The cell voltage of Cd-Ni3S2 / NF-1 / 4 was the lowest, at 1.489V, indicating that it has the best overall water-saving catalytic performance. In contrast, the cell voltage of the pure-phase Ni3S2 / NF nanosheets prepared in Comparative Example 1 was 1.60V, and its overall water-splitting performance was inferior to that of the Cd-Ni3S2 / NF composite material.

[0094] Using the chronoamperometry method, the Cd-Ni3S2 / NF-1 / 4 composite material prepared in Example 2 of this application was subjected to a current density of 10 mA·cm⁻¹. -2 The stability test of electrocatalytic water splitting was carried out, and the results are as follows: Figure 7 As shown in Figure (b) of the table. From Figure 7 As can be seen from Figure (b), the current density remained essentially unchanged after 50 hours of continuous electrolysis, indicating that the Cd-Ni3S2 / NF-1 / 4 composite material prepared in this application has good electrochemical stability when applied to electrocatalytic water splitting.

[0095] 4. DFT Calculation

[0096] To verify the influence of electron transfer and elemental electronic structure on the electrocatalytic performance of the Cd-Ni3S2 / NF prepared in this application, first-principles calculations were performed. To achieve structural optimization and static self-consistent calculations for Ni3S2 and Cd-Ni3S2, theoretical calculations were performed using the Vienna ab-into simulation package (VASP) program based on density functional theory (DFT). Simultaneously, the projection-enhanced wave (PAW) method was used to describe the electron-ion interaction, and the Perdew-Burke-Ernzerhof (PBE) exchange correlation function was demonstrated under the generalized gradient approximation (GGA). For the Brillouin region sampling of the Cd-Ni3S2 / NF prepared in Example 2 of this application and the pure-phase Ni3S2 / NF prepared in Comparative Example 1, a 3×3×1 Monkhorst-pack grid was used. The Cd-Ni3S2 / NF-1 / 4 prepared in Example 2 of this application was determined by EDS to have an atomic ratio of approximately 1:49 between Cd and Ni. A 3×3×2 Ni3S2 unit cell (54 Ni atoms) was selected as the computational unit cell. In the expanded unit cell, one Ni atom was replaced with a Cd atom. To avoid interactions between adjacent periodic units, the vacuum thickness was set to... The DFT calculation results are as follows: Figure 8 As shown, (a) is the Gibbs free energy of hydrogen adsorption of the products prepared in Example 2 and Comparative Example 1 of this application at U = 0V, and (b) is the DFT calculation of the Gibbs free energy of the four-step OER process of the products prepared in Example 2 and Comparative Example 1 of this application. The symbol * indicates the adsorption active site.

[0097] from Figure 8 As can be seen from Figure (a), in the Cd-Ni3S2 / NF of Example 2 of this application, H atoms are closer to the surface of Ni3S2 after Cd atoms are doped, and the overpotential ΔG H* The value decreased from 0.56 eV to 0.31 eV, indicating that the incorporation of Cd can significantly reduce the ΔG of Ni3S2. H* This results in Cd-Ni3S2 / NF exhibiting higher HER electrocatalytic activity.

[0098] Meanwhile, the Gibbs free energies of the O*, OH*, and OOH* intermediates on the Ni3S2 surface before and after doping were calculated during the four-electron transfer process of OER (2H2O→O2+4H++4e-). Figure 8Figure (b) shows the top view of the optimized OER ball-and-bar model of Ni3S2 and Cd-Ni3S2 and its step diagram of energy barrier changes. The dashed line represents the calculated Ni3S2 step diagram, and the solid line represents the calculated Cd-Ni3S2 step diagram. The value of each step corresponds to the adsorption Gibbs free energy of different steps in the OER reaction, with the largest value corresponding to the maximum adsorption Gibbs free energy. The step in which this value is located is the rate-determining step of the OER process. Theoretical calculations show that the doping of Cd atoms does not change the rate-determining step; the rate-determining step for both is the second step of the four-electron transfer (*OH to *O). In the pure-phase Ni3S2 / NF nanosheets obtained in Comparative Example 1, the second step involves the adsorption of OH... - The Gibbs free energy of the original sample is 1.62 eV, and the calculated overpotential for the entire process is 0.39 V. However, the energy barrier of the Cd-Ni3S2 prepared in Example 2 of this application is significantly reduced, and the required overpotential for the entire process is reduced to 0.22 V. This demonstrates that with the incorporation of Cd, Ni3S2 adsorbs OH... - The free energy changes, the overpotential decreases, and the OER performance of the material is improved.

[0099] Figure 9 The figures shown are the structural models of Example 2 and Comparative Example 1 after structural optimization in the four-step OER reaction. Figure (a1) is a top view of the original Cd-Ni3S2 model; Figures (b1), (c1), and (d1) are top views of the Cd-Ni3S2 model after adsorption of *OH, O*, and *OOH intermediates, respectively; Figure (a2) is a test diagram of the original Cd-Ni3S2 model; Figures (b2), (c2), and (d2) are test diagrams of the Cd-Ni3S2 model after adsorption of *OH, O*, and *OOH intermediates, respectively. 2. Side view of the model for adsorbing *OH, O*, and *OOH intermediates; Figure (e1) is the top view of the original model of Ni3S2, and Figures (f1), (g1), and (h1) are the top views of the model for adsorbing *OH, O*, and *OOH intermediates of Ni3S2, respectively; Figure (e2) is the side view of the original model of Ni3S2, and Figures (f2), (g2), and (h2) are the side views of the model for adsorbing *OH, O*, and *OOH intermediates of Ni3S2, respectively. From Figure 9 It can be seen that, after structural optimization, the active site of each adsorption intermediate is Ni connected to Cd.

[0100] Figure 10 The total density of states of the products prepared in Example 2 and Comparative Example 1 of this application is shown. Compared with pure phase Ni3S2, Cd-Ni3S2 at the Fermi level (E) f The peak value near the α value is higher, and the intensity increases with Cd doping. The results indicate that introducing Cd can improve carrier density and intrinsic metallic properties, thereby obtaining better electrocatalytic performance.

[0101] DFT theoretical calculations confirmed the experimental results, showing that the Cd-Ni3S2 / NF composite material prepared in this application exhibits higher electrocatalytic activity than the pure-phase Ni3S2 / NF nanosheets prepared in the comparative example. Therefore, the Cd-Ni3S2 / NF composite material prepared in this application can achieve dual catalytic activity for both electrocatalytic OER and electrocatalytic HER.

[0102] It should be noted that, in this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0103] The various embodiments in this specification are described in a related manner. For the same or similar parts between the various embodiments, please refer to each other. Each embodiment focuses on describing the differences from other embodiments.

[0104] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application are included within the scope of protection of this application.

Claims

1. A method for preparing a Cd-Ni3S2 / NF composite water electrolysis catalyst, comprising the following steps: (1) Dissolve nickel salt, cadmium source, alkali source and ammonium fluoride in water to form a mixed solution; wherein the molar ratio of the cadmium source, the nickel salt and the alkali source is 1:(2~6):(10~30), the molar ratio of the alkali source and the ammonium fluoride is (1~3):1, and the ratio of the number of moles of ammonium fluoride to the volume of water is 1 mmol:(5~9) mL; (2) Place the nickel foam and the mixed solution into a reaction vessel, seal it, control the temperature at 140℃~180℃, react for 6h~10h, and after the reaction is complete, clean and dry to obtain hydroxide precursor material; (3) The sulfur source solution and the hydroxide precursor material are placed in a reaction vessel, sealed, and the temperature is controlled at 130℃~170℃. The reaction is carried out for 4h~8h. After the reaction is completed, the mixture is cleaned and dried to obtain the Cd-Ni3S2 / NF composite material hydrolysis catalyst. The ratio of the number of moles of sulfur source to the volume of water in the sulfur source solution is 1mmol:(25~30)mL, and the molar ratio of sulfur source to nickel salt is 1:(1.0~2.0).

2. The preparation method according to claim 1, wherein, The nickel salt is selected from at least one of nickel nitrate, nickel sulfate, and nickel chloride.

3. The preparation method according to claim 1, wherein, The cadmium source is selected from at least one of cadmium nitrate, cadmium sulfate, and cadmium chloride.

4. The preparation method according to claim 1, wherein, The alkali source is selected from at least one of urea and hexamethylenetetramine.

5. The preparation method according to claim 1, wherein, The sulfur source is selected from at least one of sodium sulfide, thiourea, and thioacetamide.

6. A Cd-Ni3S2 / NF composite water electrolysis catalyst prepared by the preparation method according to any one of claims 1-5.

7. The use of the Cd-Ni3S2 / NF composite water electrocatalyst according to claim 6 for electrocatalytic HER, electrocatalytic OER and electrocatalytic water electrolysis.

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