Oxygen-doped cobalt-iron sulfide composite material, method for preparing same, and use thereof

Abstract

The application discloses an oxygen-doped cobalt-iron sulfide composite material and a preparation method and application thereof, wherein the oxygen-doped cobalt-iron sulfide composite material comprises: a conductive substrate and an oxygen-doped cobalt-iron sulfide grown on the conductive substrate. The conductive substrate can be directly used as an electrode while increasing the conductivity of the material, facilitating the electrocatalytic hydrogen evolution reaction of the catalyst; the introduction of the Fe element causes the electron transfer of Co to Fe, regulates the electronic structure of CoS2, improves the conductivity of the catalyst, the further doping of O causes the electron redistribution, increases the electron density of S, promotes the adsorption of H at the S site, and significantly reduces the S site of the catalyst H* , thereby reducing the energy barrier of HER and accelerating the hydrogen evolution reaction. Tests prove that the oxygen-doped cobalt-iron sulfide composite material has excellent HER catalytic activity and persistent electrochemical stability.

Description

Technical Field

[0001] This application relates to the field of electrocatalyst technology, and in particular to oxygen-doped cobalt iron sulfide composite materials, their preparation methods, and applications. Background Technology

[0002] With the increasing depletion of traditional fossil fuels, there is an urgent need to develop efficient and sustainable new energy sources. Hydrogen energy, due to its advantages of being clean, renewable, and having high energy density, has become an ideal energy carrier. Electrolysis of water is the most efficient method for hydrogen production, yielding high-purity and recyclable hydrogen energy through the hydrogen evolution reaction (HER) at its cathode. However, the HER reaction requires a high activation energy barrier, necessitating the addition of a suitable catalyst to reduce the overpotential. Currently, Pt-based materials are the most active electrocatalysts, but their high cost and limited reserves severely restrict their industrial application. Therefore, developing efficient and low-cost non-precious metal-based HER electrocatalysts is of great significance.

[0003] Patent document 202110448410.2 discloses a triangular nanoarray assembled from iron-doped cobalt sulfide and molybdenum sulfide nanosheets. The array uses carbon cloth as a substrate, with iron-doped cobalt sulfide grown on the carbon cloth to form a triangular nanoarray, and molybdenum sulfide nanosheets grown on the triangular nanoarray formed by the iron-doped cobalt sulfide. This triangular nanoarray assembled from iron-doped cobalt sulfide and molybdenum sulfide nanosheets exhibits excellent HER catalytic activity and long-lasting electrochemical stability.

[0004] The inventors of this application, through analysis, concluded that the superior performance of this iron-doped cobalt sulfide and molybdenum sulfide nanosheet composite material mainly originates from the introduction of molybdenum sulfide nanosheets. This is also evidenced by the description in the patent document. For example, the patent document describes that the prepared iron-doped cobalt sulfide and molybdenum sulfide nanosheet composite material achieves 10 mA / cm². 2 The required overpotential at a current density of η is 10 =68mV, but the iron-doped cobalt sulfide material obtained without the introduction of molybdenum sulfide nanosheets reaches 10mA / cm. 2 The required overpotential η at the current density 10 =202mV. This indicates that the HER catalytic activity of iron-doped cobalt sulfide materials without composite molybdenum sulfide nanosheets is not ideal.

[0005] Therefore, further exploration of iron-doped cobalt sulfide materials without the introduction of a second HER catalyst to improve their HER catalytic activity is of great significance, whether for use as a standalone HER catalyst or for combining them with other catalytic materials to obtain catalytic materials with superior performance. Summary of the Invention

[0006] The objective of the first aspect of this application is to provide an oxygen-doped cobalt iron sulfide composite material.

[0007] The second aspect of this application aims to provide a method for preparing oxygen-doped cobalt iron sulfide composite materials.

[0008] The purpose of the third aspect of this application is to provide the use of oxygen-doped cobalt iron sulfide composite materials in the catalytic hydrogen evolution reaction.

[0009] To achieve the above objectives, the first aspect of this application provides an oxygen-doped cobalt iron sulfide composite material, comprising:

[0010] Conductive substrate, and

[0011] Oxygen-doped cobalt iron sulfide grown on the conductive substrate.

[0012] In some embodiments of this application, the oxygen-doped cobalt iron sulfide has a triangular nanosheet array morphology composed of nanoparticles.

[0013] In some embodiments of the application, gaps exist between the nanoparticles.

[0014] In some embodiments of the application, the conductive substrate is selected from carbon cloth or carbon paper.

[0015] In some embodiments of the application, the cobalt-iron sulfide of the composite material has the following chemical composition:

[0016] (Co 0.75 Fe 0.25 )S2.

[0017] In this application, the nanosheet or nanoparticle refers to at least one dimension of the sheet or particle, such as the thickness of the sheet, and the particle size is in the nanometer range, i.e., between 1 and 1000 nanometers.

[0018] The second aspect of this application provides a method for preparing the aforementioned oxygen-doped cobalt iron sulfide composite material, comprising:

[0019] Step (1): Mix the aqueous solution of divalent cobalt salt with the aqueous solution of 2-methylimidazole to obtain a reaction solution. Immerse the conductive substrate in the solution and let it stand for 2-6 hours to obtain Co-MOF (cobalt-based metal-organic framework) grown on the conductive substrate. The molar concentration ratio of divalent cobalt salt to 2-methylimidazole in the reaction solution is 1:(4-12).

[0020] Step (2): Immerse the conductive substrate along with the Co-MOF grown thereon in an aqueous solution of K4[Fe(CN)6] and let it stand for 6-10 hours to obtain a CoFe Prussian blue analog formed on the conductive substrate, wherein the molar concentration of K4[Fe(CN)6] in its aqueous solution to the molar concentration of the divalent cobalt salt in the reaction solution is (0.5-1.5):1, preferably 1:1;

[0021] Step (3): The conductive substrate together with the CoFe Prussian blue analogue grown thereon is calcined in an oxygen-containing atmosphere to obtain an oxide precursor;

[0022] Step (4): The obtained oxide precursor is reacted with sulfur powder in an inert atmosphere to sulfide it, thereby obtaining an oxygen-doped cobalt iron sulfide composite material.

[0023] In some embodiments of the application, before step (1), the carbon cloth or carbon paper is ultrasonically cleaned for 20-40 minutes each with concentrated nitric acid, deionized water and ethanol respectively.

[0024] In some embodiments of the application, the calcination in step (3) is carried out at 250-400°C for 1-3 hours.

[0025] In some embodiments of this application, the oxygen-containing atmosphere may be air.

[0026] In some embodiments of the application, the vulcanization of step (4) includes reacting with sulfur powder at 400-600°C in an inert atmosphere for 1-3 hours.

[0027] In some embodiments of the application, in step (4), vulcanization is carried out by reacting with an excess of sulfur powder.

[0028] In some embodiments of the application, the inert atmosphere is selected from at least one of nitrogen, helium, neon, and argon.

[0029] In some embodiments of the application, the divalent cobalt salt is selected from at least one of cobalt nitrate, cobalt chloride, and cobalt sulfate.

[0030] In some embodiments of the application, the method for preparing the oxygen-doped cobalt iron sulfide composite material includes:

[0031] Step (1): Mix the aqueous solution of divalent cobalt salt with the aqueous solution of 2-methylimidazole to obtain a reaction solution. Immerse the carbon cloth in the solution and let it stand for 4 hours to obtain a Co-MOF (cobalt-based metal-organic framework) grown on a conductive substrate. The molar ratio of divalent cobalt salt to 2-methylimidazole in the reaction solution is 1:8.

[0032] Step (2): Immerse the conductive substrate along with the Co-MOF grown thereon in an aqueous solution of K4[Fe(CN)6] and let it stand for 8 hours to obtain the CoFe Prussian blue analogue (PBA) formed on the conductive substrate, wherein the molar concentration of K4[Fe(CN)6] in its aqueous solution is 1:1 to the molar concentration of the divalent cobalt salt in the reaction solution.

[0033] Step (3): The conductive substrate and the CoFe Prussian blue analogue grown thereon are heated to 300°C in air at a heating rate of 5°C / min and held at that temperature for 2 hours to obtain the oxide precursor.

[0034] Step (4): The obtained oxide precursor is sulfided with excess sulfur powder in an inert atmosphere at 500°C for 2 hours to obtain oxygen-doped cobalt iron sulfide composite material.

[0035] In some embodiments of this application, the molar amount of sulfur powder is greater than twice the molar amount of cobalt salt used in step (1).

[0036] The third aspect of this application provides the application of the aforementioned oxygen-doped cobalt iron sulfide composite material in electrocatalytic hydrogen evolution, especially in water electrolysis for hydrogen evolution.

[0037] Beneficial effects

[0038] This application provides a composite material for growing oxygen-doped cobalt iron sulfide on a conductive substrate. The conductive substrate, such as carbon cloth or carbon paper, increases the material's conductivity and can also be directly used as an electrode, facilitating the electrocatalytic hydrogen evolution reaction of the catalyst. The introduction of Fe leads to electron transfer from Co to Fe, modulating the electronic structure of CoS2 and improving the catalyst's conductivity. Further doping with O causes electron redistribution, increasing the electron density of S, promoting H adsorption at S sites, and significantly reducing the ΔG at S sites. H* This lowers the energy barrier for the hydrogen evolution reaction (HER) and accelerates the reaction. Testing has shown that the oxygen-doped cobalt-iron sulfide composite material provided in this application exhibits excellent HER catalytic activity and long-lasting electrochemical stability. Attached Figure Description

[0039] Figure 1 Figure (A) shows the XRD patterns of the intermediate CC@CoFeO-0.025 and the final product CC@O-CoFeS-0.025 prepared in step (3) of Example 1, as well as CC@(CoFe)S2 prepared in Comparative Example 3. Figure 1 (B) is an enlarged view of regions I and II in (A);

[0040] Figure 2 The XRD patterns of CC@O-CoS2 prepared in Comparative Example 1 and CC@CoS2 prepared in Comparative Example 2 are shown.

[0041] Figure 3 A comparison of the XRD patterns of the final products CC@O-CoFeS-0.025, CC@O-CoFeS-0.015, and CC@O-CoFeS-0.033 prepared in Examples 1-3 is shown.

[0042] Figure 4 SEM images of the intermediate CC@CoFeO-0.025 (a) prepared in step (3) of Example 1, the final product CC@O-CoFeS-0.025 (b), CC@O-CoFeS-0.015 (c) prepared in Example 2, CC@O-CoFeS-0.033 (d) prepared in Example 3, CC@(CoFe)S2 (e) prepared in Comparative Example 3, and CC@O-CoS2 (f) prepared in Comparative Example 1 are shown.

[0043] Figure 5 The elemental distribution of CC@O-CoFeS-0.025 is shown, where (a) is a SEM image of CC@O-CoFeS-0.025, (b)-(e) are the elemental distribution corresponding to (a), and (f) is the atomic percentage of the elements contained in CC@O-CoFeS-0.025.

[0044] Figure 6 The XPS spectrum of CC@O-CoFeS-0.025 prepared in Example 1 is shown;

[0045] Figure 7 XPS spectra of CC@(CoFe)S2 prepared in Comparative Example 3, CC@O-CoS2 prepared in Comparative Example 1, and CC@CoS2 prepared in Comparative Example 2 are shown.

[0046] Figure 8 The polarization curves of the HER reaction of CC@O-CoFeS-(0.025, 0.015, 0.033) prepared in Examples 1-3 are shown.

[0047] Figure 9 The HER performance of each sample in 0.5M H2SO4 solution is shown;

[0048] Figure 10 The characterization results of CC@O-CoFeS-0.025 after stability testing are shown. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments in this application are within the scope of protection of this application.

[0050] Preparation of oxygen-doped cobalt-iron sulfide composite materials

[0051] Example 1

[0052] Before preparing the composite material, the carbon cloth is first pretreated using the following method to remove surface impurities.

[0053] Cut out 2×3cm 2 The carbon cloth was ultrasonically cleaned for 30 minutes in sequence with concentrated nitric acid, deionized water and ethanol to remove surface impurities.

[0054] Step (1): Growing Co-MOF on carbon cloth

[0055] 0.582 g (2 mmol) of Co(NO3)2·6H2O was dissolved in 40 mL of deionized water to obtain a 0.05 mol / L cobalt nitrate aqueous solution. 1.313 g of 2-methylimidazole was dissolved in 40 mL of deionized water to obtain a 0.4 mol / L 2-methylimidazole aqueous solution. The two solutions were mixed, and the pretreated carbon cloth was added. After standing at room temperature for 4 hours, the mixture was removed, washed with deionized water, and vacuum dried to obtain a Co-MOF grown on the carbon cloth, denoted as CC@Co-MOF.

[0056] Step (2): Formation of CoFe Prussian blue analogue on carbon cloth

[0057] CC@Co-MOF was immersed in 0.025 mol L -1 The product was left to stand in an aqueous solution of K4[Fe(CN)6] for 8 hours, washed with deionized water, and dried under vacuum to obtain a CoFe Prussian blue analogue formed on carbon cloth, denoted as CC@CoFe PBA-0.025 (the 0.025 is used to identify products obtained using different concentrations of K4[Fe(CN)6]).

[0058] Step (3): The product CC@CoFe PBA-0.025 prepared in step (2) is placed in air and heated to 300°C at a heating rate of 5°C / min and kept at that temperature for 2 hours to obtain the oxide precursor, denoted as CC@CoFeO-0.025.

[0059] Step (4): Place the CC@CoFe-0.025 prepared in step (3) downwind in a nitrogen atmosphere and place 0.4g of sulfur powder upwind. Keep it at 500℃ for 2 hours for sulfidation. After natural cooling, oxygen-doped cobalt iron sulfide composite material is obtained, denoted as CC@O-CoFeS-0.025.

[0060] Example 2

[0061] The only difference between Example 2 and Example 1 is that the concentration of the K4[Fe(CN)6] aqueous solution in step (2) is 0.015 mol / L. -1 .

[0062] The other steps and conditions are the same as in Example 1, and the final composite material is denoted as CC@O-CoFeS-0.015.

[0063] Example 3

[0064] The only difference between Example 3 and Example 1 is that the concentration of the K4[Fe(CN)6] aqueous solution in step (2) is 0.033 mol / L. -1 .

[0065] The other steps and conditions are the same as in Example 1, and the final composite material is denoted as CC@O-CoFeS-0.033.

[0066] Example 4

[0067] The only difference between Example 4 and Example 1 is that in step (1), 40 mL of 0.05 mol / L cobalt chloride aqueous solution is used instead of 40 mL of 0.05 mol / L cobalt nitrate aqueous solution in Example 1.

[0068] Comparative Example 1: Preparation of oxygen-doped cobalt sulfide composite material (denoted as CC@O-CoS2)

[0069] The preparation process of CC@O-CoS2 is carried out in accordance with the preparation steps of Example 1. The main difference between CC@O-CoS2 and Example 1 is that step (2) is omitted. After obtaining CC@Co-MOF, it is directly calcined and oxidized, and then sulfided to obtain CC@O-CoS2.

[0070] Comparative Example 2: Preparation of Cobalt Sulfide Composite Material (denoted as CC@CoS2)

[0071] First, CC@Co-MOF was prepared according to step (1) of Example 1. Then, it was directly vulcanized according to step (4) of Example 1 to obtain CC@CoS2.

[0072] Preparation of Comparative Example 3: Cobalt-Iron Sulfide Composite Material (CC@(CoFe)S2)

[0073] First, CC@CoFe PBA-0.025 was prepared according to steps (1) and (2) of Example 1. Then, it was directly vulcanized according to step (4) of Example 1 to obtain CC@(CoFe)S2.

[0074] <Performance Analysis and Testing>

[0075] 1. X-ray diffraction (XRD) analysis

[0076] After removing the carbon cloth, the products obtained in Examples 1-3 and Comparative Examples 1-3, as well as the intermediate CC@CoFeO-0.025 prepared in step (3) of Example 1, were subjected to XRD analysis. The XRD patterns obtained are shown below. Figures 1-3 As shown. In Figure 1 The image shows the XRD patterns of the intermediate CC@CoFeO-0.025 and the final product CC@O-CoFeS-0.025 prepared in step (3) of Example 1, as well as CC@(CoFe)S2 prepared in Comparative Example 3. Figure 2 The XRD patterns of CC@O-CoS2 prepared in Comparative Example 1 and CC@CoS2 prepared in Comparative Example 2 are shown in the figure. Figure 3 The XRD patterns of the final products CC@O-CoFeS-(0.015, 0.025, 0.033) prepared in Examples 1-3 are shown.

[0077] like Figure 1 As shown in curve a of (A), the oxide CoFeO-0.025 (Fe content is 0.025 mol L) -1 The diffraction peaks at 36.3°, 58.8°, and 64.8° are close to the (311), (511), and (440) crystal planes of CoFe2O4 (JCPDS No. 22-1086). Compared with the CoFe2O4 standard card, the diffraction peaks are shifted to the left, corresponding to an increased interplanar spacing. Compared with pure CoFe2O4, this may be due to the presence of a greater amount of Co in CoFeO-0.025. 2+ (Radius is 0.065 nm), its ionic radius is greater than Fe. 2+ The radius (0.061 nm). For CC@O-CoFeS-0.025 (see...) Figure 1 Curve b) of (A) shows diffraction patterns at 28.1°, 32.6°, 36.5°, 40.1°, 46.7°, 55.2°, 57.9°, 60.5°, and 63.1°, which correspond to the (111), (200), (210), (211), (220), (311), (222), (230), and (321) crystal planes of CoS2 (JCPDS No. 41-1471) or FeS2 (JCPDS No. 65-3321). Figure 1As shown in the magnified image (B), compared to pure CoS2, the diffraction peak of CC@O-CoFeS-0.025 shifts to the right, indicating that the smaller Fe radius... 2+ Co with a larger partial substitution radius 2+ This results in a narrower lattice. Similarly, compared to pure FeS2, the diffraction peak of CC@O-CoFeS-0.025 shifts to the left, indicating that the Co has a larger radius. 2+ The presence of O leads to lattice expansion. To demonstrate the doping of O, O-free CC@(CoFe)S2 was used as a control. Compared with CC@(CoFe)S2 ( Figure 1 Compared to curve c) in (A), the diffraction peak of CC@O-CoFeS-0.025 is observed to shift to a higher angle, which means that the lattice is narrower, indicating that the ionic radius is smaller than S. 2- O 2- The presence of [something]. Moreover, a similar phenomenon was found in the control samples CC@O-CoS2 and CC@CoS2. Figure 2 The diffraction peaks of CC@O-CoS2 (O-doped phase) are shifted to the right compared to pure CoS2 (JCPDS No. 41-1471). Figure 3 As can be seen, with the increase of Fe content, the diffraction peak of CC@O-CoFeS shifts to a higher angle and gradually approaches the peak position of FeS2.

[0078] 2. Scanning electron microscopy analysis

[0079] Scanning electron microscopy (SEM) analysis was performed on the intermediate CC@CoFeO-0.025 prepared in step (3) of Example 1, the final product CC@O-CoFeS-0.025, CC@O-CoFeS-0.015 prepared in Example 2, CC@O-CoFeS-0.033 prepared in Example 3, CC@(CoFe)S2 prepared in Comparative Example 3, and CC@O-CoS2 prepared in Comparative Example 1. The results are as follows: Figure 4 As shown.

[0080] Figure 4 Images (a), (b), (c), (d), (e), and (f) are scanning electron microscope (SEM) images of CC@CoFeO-0.025, CC@O-CoFeS-0.025, CC@O-CoFeS-0.015, CC@O-CoFeS-0.033, CC@(CoFe)S2, and CC@O-CoS2, respectively.

[0081] Depend on Figure 4As shown in (a), a triangular nanosheet array of oxide CC@CoFeO-0.025 is vertically grown on the carbon fibers of the carbon cloth, and the surface of this nanosheet array is rough. Interestingly, the CC@O-CoFeS-0.025 obtained after vulcanization still maintains the triangular nanosheet array morphology, but the nanosheets become thinner. Figure 4 (b)). From Figure 4 As can be observed in the magnified image in (b), the CC@O-CoFeS-0.025 nanosheets are composed of interconnected nanoparticles with numerous gaps between them. In contrast, when the Fe content is 0.015 mol / L... -1 At that time, the product CC@O-CoFeS-0.015 ( Figure 4 (c) also exhibits a triangular nanoarray morphology, but the nanosheets are relatively thicker. When the Fe dosage increases to 0.033 mol / L... -1 hour( Figure 4 In the middle (d) section, the obtained triangular nanosheets were thinner than those of CC@O-CoFeS-0.015, but still thicker than those of CC@O-CoFeS-0.025. The unique porosity-rich triangular nanoarray structure of CC@O-CoFeS-0.025 not only exposes more active sites but also facilitates sufficient contact between the catalyst and the electrolyte. In contrast, the control sample CC@(CoFe)S2 (without O) only exhibited a thicker triangular array morphology, with no gaps on the nanosheets. Figure 4 (e)). For CC@O-CoS2 (Fe-free), the triangular plate-like morphology is not obvious and the edges are curled. Figure 4 The significant difference in morphology of CC@O-CoS2 is likely due to the lack of Fe. The elemental distribution of CC@O-CoFeS-0.025 (f) Figure 5 The results show that Co, Fe, S, and O elements are uniformly distributed throughout the nanosheets. Furthermore, the atomic percentages of Co, Fe, S, and O are 25.23%, 8.19%, 53.4%, and 13.18%, respectively. Considering the possibility of trace air ingress during the testing process leading to inaccurate O content measurements, the composition of CC@O-CoFeS-0.025 can be determined based on the molar ratio of Co, Fe, and S as follows: (Co...) 0.75 Fe 0.25 (S) x O y )2, or written as O-doped (Co) 0.75 Fe 0.25 )S2.

[0082] 3. X-ray photoelectron spectroscopy (XPS) analysis

[0083] XPS analysis was performed on CC@O-CoFeS-0.025 prepared in Example 1, and the results are as follows: Figure 6As shown, (a) is the Co 2p spectrum, (b) is the Fe 2p spectrum, (c) is the S 2p spectrum, and (d) is the O 1s spectrum.

[0084] XPS analysis was performed on CC@O-CoS2 prepared in Comparative Example 1, CC@CoS2 prepared in Comparative Example 2, and CC@(CoFe)S2 prepared in Comparative Example 3. The results are as follows: Figure 7 As shown, (a) Co 2p spectrum, (b) Fe 2p spectrum, and (c) S 2p spectrum are the spectra of CC@(CoFe)S2, (a') Co 2p and (b') S 2p are the spectra of CC@O-CoS2, and (a”) Co 2p and (b”) S 2p are the spectra of CC@CoS2.

[0085] The elemental valence states of CC@O-CoFeS-0.025 were analyzed using XPS. The Co 2p spectrum was analyzed. Figure 6 In (a)), the two peaks at binding energies of 797.9 and 782.4 eV are attributed to Co, respectively. 2+ Co 2p 1 / 2 and Co 2p 3 / 2 The two peaks at 794.3 and 779.1 eV correspond to Co, respectively. 3+ Co 2p 1 / 2 and Co 2p 3 / 2 The two peaks are relatively weak, indicating that Co 3+ The content is low. Figure 6 (b) shows the Fe 2p spectrum, with binding energies of 707.8 and 720.9 eV corresponding to Fe 2+ Fe 2p 3 / 2 and Fe 2p 1 / 2 The two peaks at 712.1 and 725.2 eV belong to Fe, respectively. 3+ Fe 2p 3 / 2 and Fe 2p 1 / 2 Fe 3+ The presence of this may be due to surface oxidation and oxidation treatment of the material. Regarding S 2p ( Figure 6 In the middle (c), the two peaks with binding energies at 164.1 and 162.9 eV correspond to S2 in O-(CoFe)S2, respectively. 2- S2p 1 / 2 and S 2p 3 / 2 The peaks at 167.0 and 168.8 eV belong to SO4. 2- Its presence is due to oxidation of the material surface. In the O 1s spectrum ( Figure 6 In the middle (d)), the peak with a binding energy of 530.7 eV belongs to the metal-O bond (O). LThis proves that O exists in the crystal lattice and bonds with metal ions. The two peaks at 531.5 eV and 532.1 eV correspond to oxygen vacancies (O₂, O₂, O₃ ... V Oxygen adsorbed at the surface and oxygen (O) adsorbed by water molecules on the material surface ads ).

[0086] To further investigate the effects of Fe and O, XPS tests were performed on control samples CC@(CoFe)S2, CC@O-CoS2, and CC@CoS2. Compared with CC@(CoFe)S2, the Co 2p and Fe 2p values ​​were... Figure 7 (a) and (b)), CC@O-CoFeS-0.025 Figure 6 The peak positions in (a) and (b) shift towards higher binding energy (Co). 2+ 2p shift +0.5eV, Fe 2+ The 2p shift (+0.5 eV) indicates that the oxidation states of both Co and Fe increase after O doping. This means that doping with highly electronegative O heteroatoms reduces the electron density around Co and Fe. Furthermore, CC@O-CoFeS-0.025 ( Figure 6 The S 2p binding energy of (c) is lower than that of CC@(CoFe)S2. Figure 7 (c) indicates that doping with highly electronegative O increases the electron density of S, which can promote the adsorption of H at S sites. Therefore, O doping can modulate the electronic structure of Co-Fe sulfides.

[0087] With CC@CoS2 ( Figure 7 Compared to (a”) and (b”)), in CC@O-CoS2 ( Figure 7 Similar phenomena of increased Co 2p binding energy and decreased S 2p binding energy were also observed in (a') and (b') (Co 2p shift +0.4 eV, S 2p shift -0.2 eV). Compared with CC@O-CoS2 (Fe-free) ( Figure 7 In (a') and (b'), the Co 2p peak of CC@O-CoFeS-0.025 (containing Fe) shifts to a higher binding energy by 0.3 eV, while the S 2p peak position remains unchanged. This indicates that the introduction of Fe causes electrons to transfer from Co to Fe, but has no effect on S.

[0088] In summary, Fe and O doping helps to modulate the electronic structure of CoS2. The introduction of Fe leads to electron transfer from Co to Fe, thereby increasing the catalyst's conductivity. O doping increases the electron density of S and promotes the adsorption of H at S sites, both of which are beneficial to improving the HER activity of the catalyst.

[0089] 4. Electrocatalytic performance test

[0090] The electrocatalytic hydrogen evolution performance of CC@O-CoFeS-0.025, CC@O-CoFeS-0.015, CC@O-CoFeS-0.033 prepared in Examples 1-3, and the control sample prepared in the comparative example, was tested. A standard three-electrode system was used. The material synthesized on carbon cloth could be directly used as the electrode. The obtained 1×2 cm sample was clamped on the electrode holder as the working electrode, the counter electrode was a graphite electrode, and the reference electrode was a saturated Ag / AgCl electrode. The electrolyte was 0.5 M H2SO4. The polarization curve was tested by linear sweep voltammetry (LSV) at a scan rate of 5 mV / s. The results are as follows. Figure 8-9 As shown.

[0091] Figure 8 The polarization curves of HER for CC@O-CoFeS-0.025, CC@O-CoFeS-0.015, and CC@O-CoFeS-0.033 prepared in Examples 1-3 are shown.

[0092] Figure 9 The HER performance of each sample in 0.5 M H2SO4 solution is shown, including (A) HER polarization curves of CC@O-CoFeS-0.025, CC@(CoFe)S2, CC@O-CoS2 and CC@CoS2, and (B) HER polarization curves at a current density of 10 mA cm⁻¹. -2 Comparison of overpotentials for different samples, (C) Comparison of Tafel slopes, (D) Nyquist (impedance) plot, (E) Linear fitting of current density changes of CC@O-CoFeS-0.025, CC@(CoFe)S2, CC@O-CoS2 and CC@CoS2 with scan rate, (F) Stability test of CC@O-CoFeS-0.025 at an overpotential of 140mV (It plot).

[0093] from Figure 8 It can be seen from this that when the current density is 10 mA / cm² -2 At that time, the required overpotential (η) for CC@O-CoFeS-0.025 10 The value is 105 mV, which is much lower than CC@O-CoFeS-0.015(η). 10 =153mV) and CC@O-CoFeS-0.033(η 10 The overpotential value was 122 mV. The excellent HER performance of CC@O-CoFeS-0.025 may be attributed to its unique interstitial triangular nanosheet array morphology. To further evaluate the HER performance of CC@O-CoFeS-0.025, the HER performance of the control samples CC@(CoFe)S2, CC@O-CoS2, and CC@CoS2 was tested. Figure 9From (A) and (B), it can be seen that CC@O-CoFeS-0.025(η) 10 =105mV) The HER performance of the sample CC@(CoFe)S2(η) was significantly better than that of the control sample. 10 =148mV), CC@O-CoS2(η 10 =206mV) and CC@CoS2(η 10 =398mV). The electrocatalytic HER activity trend of the control samples is as follows: CC@(CoFe)S2>CC@O-CoS2>CC@CoS2. Compared with CC@CoS2, the high electronegativity of O doping in CC@O-CoS2 increases the electron density of S, which is beneficial to the adsorption of H at S sites, thereby improving HER activity. Compared with CC@O-CoS2 and CC@CoS2, CC@(CoFe)S2 has significantly enhanced HER performance, possibly because the introduction of Fe modulates the electronic structure of CoS2 and improves the conductivity of the catalyst. The Fe / O co-doped product CC@O-CoFeS-0.025 has the best catalytic performance.

[0094] Furthermore, the Tafel slope of CC@O-CoFeS-0.025 is very small (62 mV / dec), much lower than that of CC@(CoFe)S2 (78 mV / dec). -1 ),CC@O-CoS2(92mV dec -1 ) and CC@CoS2(118mV dec -1 The value of ) Figure 9 (C) The lower Tafel slope value indicates that the HER reaction kinetics of CC@O-CoFeS-0.025 are faster. It is evident that the CC@O-CoFeS-0.025 synthesized in this invention possesses rapid reaction kinetics and high electrocatalytic activity, showing promising commercial application prospects.

[0095] Electrochemical impedance spectroscopy (EIS) was used to study the interfacial electron transfer kinetics. The quister spectra of CC@O-CoFeS-0.025 and the control sample were measured in the frequency range of 0.01 Hz to 100 kHz. The electrochemical kinetics between the electrocatalyst and the electrolyte can be analyzed using charge transfer resistance (R). ct R is represented by ) ct The smaller the value, the faster the charge transfer kinetics. For example... Figure 9 As shown in (D), CC@O-CoFeS-0.025(R) ct The charge transfer impedance of (0.4Ω) is much smaller than that of CC@(CoFe)S2(R). ct =1.1Ω),CC@O-CoS2(R ct =2.2Ω) and CC@CoS2(R ct=18.1Ω), indicating that CC@O-CoFeS-0.025 has a faster electron transfer rate in the hydrogen evolution reaction. It is evident that the CC@O-CoFeS-0.025 synthesized in this application possesses a very high charge transfer rate. From Figure 9 As can be seen in (E), CC@O-CoFeS-0.025(9.13mF cm) -2 C dl Greater than CC@(CoFe)S2(7.66mF cm) -2 ), CC@O-CoS2(6.00mF cm -2 ) and CC@CoS2(2.95mF cm -2 The results indicate that CC@O-CoFeS-0.025 has the largest catalytic active surface area, which can expose more catalytic active sites and help improve electrocatalytic performance.

[0096] Furthermore, stability is also an important criterion for evaluating catalyst performance. The It curve of CC@O-CoFeS-0.025 at a potential of 140 mV was tested, and the results are as follows: Figure 9 As shown in Figure (F), the current density of the catalyst did not decrease significantly after 24 hours of catalytic reaction, indicating that it has good electrochemical stability in acidic solution.

[0097] The electrode material after stability testing was characterized, and the results are as follows: Figure 10 As shown, (a) is the XRD pattern of CC@O-CoFeS-0.025 before and after the stability test (24 hours), (b)-(c) are the SEM images of CC@O-CoFeS-0.025 before and after the stability test, and (d)-(g) are the XPS spectra of CC@O-CoFeS-0.025 before and after the stability test: (d) Co 2p, (e) O1s, (f) Fe 2p and (g) S 2p.

[0098] XRD patterns confirm that the diffraction peaks corresponding to the original O-CoFeS-0.025 are basically present (the diffraction peaks at 26° and 44° correspond to Cd, see [reference]). Figure 10 (a) indicates that the structure remains unchanged. The morphology of the sample after the stability test ( Figure 10 (c) and before test ( Figure 10 (b) is very similar. XPS spectrum ( Figure 10 The results (d-g) demonstrate that the elemental composition and chemical state of the samples remained unchanged before and after the stability test. These results prove that the catalyst exhibits excellent HER stability in acidic electrolytes.

[0099] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. An oxygen-doped cobalt iron sulfide composite material, characterized in that, include: A conductive substrate, and an oxygen-doped cobalt-iron sulfide grown on the conductive substrate; The cobalt-iron sulfide in the composite material has the following chemical composition: (Co 0.75 Fe 0.25 S2; and The oxygen-doped cobalt-iron sulfide composite material is prepared by the following method: Step (1): Mix the aqueous solution of divalent cobalt salt with the aqueous solution of 2-methylimidazole to obtain a reaction solution. Immerse the conductive substrate in the solution and let it stand for 2-6 hours to obtain Co-MOF grown on the conductive substrate. The molar concentration ratio of divalent cobalt salt to 2-methylimidazole in the reaction solution is 1:(4-12). Step (2): Immerse the conductive substrate along with the Co-MOF grown thereon in an aqueous solution of K4[Fe(CN)6] and let it stand for 6-10 hours to obtain a CoFe Prussian blue analog formed on the conductive substrate, wherein the molar concentration of K4[Fe(CN)6] in its aqueous solution and the molar concentration of the divalent cobalt salt in the reaction solution are (0.5-1.5):1; Step (3): The conductive substrate together with the CoFe Prussian blue analogue grown thereon is calcined in an oxygen-containing atmosphere to obtain an oxide precursor; Step (4): The obtained oxide precursor is reacted with sulfur powder in an inert atmosphere to obtain oxygen-doped cobalt iron sulfide composite material.

2. The oxygen-doped cobalt-iron sulfide composite material according to claim 1, characterized in that, The oxygen-doped cobalt iron sulfide has a triangular nanosheet array morphology composed of nanoparticles.

3. The oxygen-doped cobalt iron sulfide composite material according to claim 1, characterized in that, There are gaps between the nanoparticles.

4. The oxygen-doped cobalt iron sulfide composite material according to claim 1, characterized in that, The conductive substrate is selected from carbon cloth or carbon paper.

5. The oxygen-doped cobalt-iron sulfide composite material according to claim 1, characterized in that, The molar concentration of K4[Fe(CN)6] in its aqueous solution is 1:1 to the molar concentration of the divalent cobalt salt in the reaction solution.

6. The oxygen-doped cobalt-iron sulfide composite material according to claim 1, characterized in that, The calcination in step (3) is carried out at 250-400 ℃ for 1-3 hours.

7. The oxygen-doped cobalt-iron sulfide composite material according to claim 1, characterized in that, The vulcanization in step (4) includes reacting with sulfur powder at 400-600 °C in an inert atmosphere for 1-3 hours.

8. The oxygen-doped cobalt-iron sulfide composite material according to claim 1, characterized in that, The divalent cobalt salt is selected from at least one of cobalt nitrate, cobalt chloride, and cobalt sulfate.

9. The application of the oxygen-doped cobalt iron sulfide composite material according to any one of claims 1-8 in electrocatalytic hydrogen evolution.

10. The application according to claim 9, characterized in that, The electrocatalytic hydrogen evolution is hydrogen evolution through water electrolysis.

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