Transition metal element doped copper-based sulfide and preparation method and application thereof

Abstract

The invention relates to the field of hydrogen production through water electrolysis assisted by small molecule oxidation, and discloses transition metal element doped Cu7S4 and a preparation method and application thereof.The copper-based sulfide comprises a Cu7S4 material and transition metal elements doped in the Cu7S4 material, the transition metal elements comprise nickel and / or iron, and the transition metal elements are doped in the Cu7S4 material. The copper-based sulfide provided by the invention has relatively low overpotential and excellent catalytic activity under an alkaline condition.

Description

Technical Field

[0001] The present invention relates to the field of small molecule oxidation-assisted electrolytic water hydrogen production, and particularly to a transition metal element-doped copper-based sulfide, a preparation method thereof, and an application thereof. Background Art

[0002] As the most promising clean energy carrier, hydrogen energy has high calorific value, zero carbon emissions, and a wide range of application scenarios. However, currently, about 95% of the world's hydrogen energy still relies on fossil fuel reforming for production, which is accompanied by a large amount of CO2 emissions, contrary to the sustainable development goal. The electrolytic water hydrogen production technology decomposes water into hydrogen (H2) and oxygen (O2) by electric energy, and theoretically can achieve large-scale production of green hydrogen, but its industrialization is still restricted by the bottlenecks of high energy consumption and high cost. The anodic oxygen evolution reaction (OER) of traditional alkaline electrolytic water needs to overcome a relatively high thermodynamic overpotential (theoretical 1.23 V, actually often requires 1.8 - 2.0 V), resulting in an overall energy efficiency of less than 70%. In addition, the high cost (the unit price of Ir exceeds 1000 US dollars / g) and scarcity (the global annual output is less than 10 tons) of noble metal catalysts (such as IrO2, RuO2) further limit the technology promotion. Therefore, developing an efficient and low-cost electrolytic water hydrogen production system has become an urgent need in the field of energy chemistry.

[0003] In recent years, the small molecule oxidation-assisted electrolytic water hydrogen production technology has received extensive attention due to its revolutionary potential. This technology uses the oxidation reaction of organic small molecules (such as urea, methanol, ethylene glycol) or sulfur-containing compounds (such as sulfides, sulfites) to replace the traditional oxygen evolution reaction (OER), and significantly reduces the hydrogen production energy consumption through the thermodynamically more favorable small molecule oxidation reaction. Taking sulfide oxidation (SOR) as an example, its theoretical potential (about 0.3 - 0.5 V vs. RHE) is significantly lower than that of OER (1.23 V), which can effectively reduce the working voltage of the electrolytic cell, and at the same time combine the anodic reaction with the resource utilization of sulfur-containing waste, having both environmental and economic benefits. In this context, copper-based sulfides have emerged due to their unique electronic structure and catalytic properties, but the existing copper-based sulfides still have problems of relatively high overpotential and insufficient catalytic activity. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problems of relatively high overpotential and insufficient catalytic activity existing in the prior art, and provide a transition metal element-doped Cu7S4, a preparation method thereof, and an application thereof. The transition metal element-doped Cu7S4 has a lower overpotential and excellent catalytic activity under alkaline conditions.

[0005] To achieve the above object, a first aspect of the present invention provides a transition metal element-doped copper-based sulfide, wherein the copper-based sulfide comprises a Cu7S4 material and a transition metal element doped in the Cu7S4 material, and the transition metal element comprises nickel and / or iron.

[0006] A second aspect of the present invention provides a preparation method of a transition metal element-doped copper-based sulfide, wherein the preparation method comprises: Immersing copper hydroxide nanosheets in a solution containing a transition metal element to carry out a first reaction to obtain a precursor, wherein the transition metal element comprises nickel and / or iron; Immersing the precursor in a solution containing sulfur element to carry out a second reaction to obtain a copper-based sulfide.

[0007] A third aspect of the present invention provides an application of the copper-based sulfide described in the first aspect of the present invention or the copper-based sulfide prepared by the preparation method described in the second aspect of the present invention in hydrogen production by electrolyzing water.

[0008] The preparation method provided by the invention constructs a Cu7S4 hierarchical structure doped with transition metal elements rich in sulfur vacancies on copper foam by adopting chemical bath deposition method and sulfidation method, which has the following advantages: (1) It has a lower overpotential under alkaline conditions and excellent catalytic activity; (2) It has smaller Tafel slope values in both HER and SOR reactions, and the reaction kinetics is fast; (3) It has a small charge transfer resistance during the process of small molecule oxidation electrolysis of water; (4) It has a large electrochemical surface area and double-layer capacitance C dl , and a large electrochemically active area; (5) It has persistent stability, and the constant electrolysis during the HER reaction process lasts at least 48 h; (6) It produces products with certain added value such as polysulfide S8 during the process of sulfide oxidation electrolysis of water; (7) It can be used in a two-electrode electrolytic cell device, providing a good preparation route and strategy for the development of new high-efficiency non-precious metal catalysts, and providing a new way for low-cost and high-efficiency hydrogen production and the removal and reuse of toxic sulfide waste. Description of the Drawings

[0009] Figure 1 It is a SEM image of the prepared copper-based sulfide; Figure 2 It is a TEM image of the prepared copper-based sulfide; Figure 3 It is an XRD pattern of the prepared copper-based sulfide; Figure 4is the XPS graph of the prepared copper-based sulfide; Figure 5 is the EPR graph of the prepared copper-based sulfide; Figure 6 is the linear sweep voltammetry (LSV) graph of the prepared copper-based sulfide; Figure 7 is the Tafel slope (Tafel) graph of the prepared copper-based sulfide; Figure 8 is the electrochemical impedance spectroscopy (EIS) graph of the prepared copper-based sulfide; Figure 9 is the cyclic voltammetry (CV) graph of the prepared copper-based sulfide; Figure 10 is the stability test graph of the prepared copper-based sulfide; Figure 11 is the CP curve of the prepared copper-based sulfide before and after injecting 1 M Na2S in 1 M KOH electrolyte; Figure 12 is the X-ray diffraction (XRD) graph of the S8 product in the SOR reaction of the prepared copper-based sulfide; Figure 13 UV-visible spectrum graph of polysulfide generated in the SOR reaction of the copper-based sulfide of Example 1; Figure 14 is the two-electrode performance graph of the alkaline electrolyzer (HER-SOR) assembled with the prepared copper-based sulfide. Detailed implementation manners

[0010] The following further elaborates on the detailed implementation manners of the present invention with reference to the accompanying drawings. It should be understood that the detailed implementation manners described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.

[0011] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0012] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the values between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0013] In addition, the term "and / or" in the specification and claims is used to describe the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. The character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0014] The first aspect of the present invention provides a transition metal element-doped copper-based sulfide, wherein the copper-based sulfide includes a Cu7S4 material and a transition metal element doped in the Cu7S4 material, and the transition metal element includes nickel and / or iron.

[0015] Copper, as one of the transition metals with the highest crust abundance (content about 50 ppm), its sulfides (such as Cu2S, CuS) have metallic-like conductivity (conductivity 10³ - 10 4 S / m) and adjustable surface oxidation states, showing significant advantages in the SOR reaction.

[0016] The 3d electron orbital characteristics of nickel give it a strong affinity for sulfur species, which can effectively promote the adsorption and oxidation of S 2- For the transition metal element-doped copper-based sulfide provided by the present invention, especially when the doped transition metal element is nickel, through the synergistic optimization strategy of the composition and structure between Cu and Ni, not only the catalytic performance is significantly improved, but also the hydrogen production cost can be reduced by the in-situ utilization of industrial sulfur-containing waste liquid (such as Na2S in refinery wastewater), providing an innovative solution for constructing an efficient and low-energy hydrogen production system.

[0017] Preferably, the copper-based sulfide has a hierarchical structure, including a first-level structure in the shape of nanorods and a second-level structure formed by nanoparticles attached thereto. The attached nanoparticle material composition is the same as that of the copper-based sulfide, and they form a hierarchical structure from the same material.

[0018] Preferably, the copper-based sulfide has sulfur vacancies.

[0019] The second aspect of the present invention provides a preparation method of a transition metal element-doped copper-based sulfide, wherein the preparation method includes: The copper hydroxide nanosheets are immersed in a solution containing a transition metal element to carry out a first reaction to obtain a precursor, wherein the transition metal element includes nickel and / or iron; The precursor is immersed in a solution containing sulfur element to carry out a second reaction to obtain a copper-based sulfide.

[0020] The preparation method provided by the present invention is simple and convenient, with less reagent consumption, low raw material cost, and relatively low required preparation conditions, which is convenient for commercial application.

[0021] Preferably, the molar ratio of the transition metal element in the solution containing the transition metal element to the copper hydroxide nanosheets is 0.05 - 5:1. The molar ratio of the transition metal element to the copper hydroxide nanosheets can be any value between any two of 0.05:1, 0.1:1, 0.3:1, 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1.

[0022] Preferably, the mass ratio of the sulfur element in the solution containing the sulfur element to the precursor is 0.1 - 0.6:1. The molar ratio of the sulfur element to the precursor can be any value between any two of 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1.

[0023] Preferably, the time of the first reaction is 15 - 25 min, and the temperature is 20 - 30 °C. The temperature of the first reaction is generally room temperature, that is, 20 °C, 25 °C, 30 °C, etc., and the reaction time can be 5 min, 10 min, 15 min, etc.

[0024] Preferably, the time of the second reaction is 10 - 40 min, and the temperature is 20 - 30 °C. The temperature of the second reaction is generally room temperature, that is, 20 °C, 25 °C, 30 °C, etc., and the reaction time can be 10 min, 20 min, 30 min, 40 min, etc.

[0025] Preferably, the preparation method of the solution containing the transition metal element includes: Dissolve the salt of the transition metal element in water to obtain solution I; Dissolve potassium persulfate in water to obtain solution II, and the molar ratio of the potassium element in the solution II to the transition metal element in the solution I is 0.3 - 0.6:1; Mix the solution I and solution II to obtain solution III; Add ammonia water to the solution III to obtain the solution containing the transition metal element, and the volume ratio of the ammonia water to the solution III is 1:8 - 10.

[0026] The concentration of ammonia water can be 25%-28%.

[0027] Preferably, the preparation method further includes: taking out the copper hydroxide nanosheets after the first reaction and drying them to obtain the precursor, wherein the drying temperature is 30-80 °C.

[0028] Preferably, the salt of the transition metal element is selected from one or more of nickel sulfate, nickel chloride, nickel nitrate, nickel acetate, nickel sulfamate, iron sulfate, iron chloride, iron nitrate and their respective hydrates.

[0029] Preferably, the solute of the sulfur element solution is selected from one or more of sodium sulfide, thioacetamide, thiourea, L-cysteine, sulfur and their respective hydrates.

[0030] Preferably, the raw materials for preparing the copper hydroxide nanosheets include copper foam.

[0031] The preparation method of the copper hydroxide nanosheets includes: Soaking the copper foam in the mixed solution and reacting for 10-20 min to obtain the copper hydroxide nanosheets, wherein the mixed solution includes sodium hydroxide and ammonium persulfate, and the molar ratio of sodium hydroxide to ammonium persulfate is 20-30:1.

[0032] The third aspect of the present invention provides an application of the copper-based sulfide described in the first aspect of the present invention or the copper-based sulfide prepared by the preparation method described in the second aspect of the present invention in the electrolysis of water to produce hydrogen.

[0033] The present invention also provides a particularly preferred preparation method, which includes: Soaking the copper hydroxide nanosheets in the solution containing the transition metal element and performing the first reaction to obtain the precursor, wherein the transition metal element includes nickel and / or iron; Soaking the precursor in the solution containing the sulfur element and performing the second reaction to obtain the copper-based sulfide; The molar ratio of the transition metal element in the solution containing the transition metal element to the copper hydroxide nanosheets is 0.2-0.4:1; The mass ratio of the sulfur element in the solution containing the sulfur element to the precursor is 0.1-0.2:1.

[0034] The present invention will be further described below in conjunction with specific embodiments.

[0035] In the following specific embodiments, unless otherwise specified, the reagents or instruments used without indicating the manufacturer can be conventional products obtained by commercial purchase. For those not indicating specific conditions in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer.

[0036] I. Preparation of copper hydroxide nanosheets is as follows: S1. Cut a 3 cm × 3 cm piece of copper foam (obtained commercially), place it in a 1 mol / L HCl solution, ultrasonically treat it for 15 min, then ultrasonically clean it with anhydrous ethanol and deionized water for 3 min each, and dry it in an oven at 60 °C; S2. Dissolve 6 g of NaOH in 30 mL of deionized water to obtain a 5 mol / L NaOH solution; Dissolve 1.368 g of (NH4)2S2O8 in 30 mL of deionized water to obtain a 0.2 mol / L (NH4)2S2O8 solution; Mix the NaOH solution and the (NH4)2S2O8 solution at room temperature, ultrasonically treat it for 10 min to obtain a mixed solution; S3. Place the copper foam treated in S1 into the mixed solution, react at room temperature for 15 min, take it out, wash it with ethanol and deionized water respectively, and dry it in an oven at 60 °C to obtain Cu(OH)2 nanosheets.

[0037] II. Preparation of copper-based sulfide (1) Preparation of the precursor Dissolve 3.943 g of NiSO4·6H2O in 15 mL of deionized water to obtain a 1 mol / L NiSO4 solution, namely solution I.

[0038] Dissolve 0.811 g of K2S2O8 in 12 mL of deionized water to obtain a 0.25 mol / L K2S2O8 solution, namely solution II.

[0039] Mix the NiSO4 solution and the K2S2O8 solution evenly at room temperature (25 °C) to obtain solution III; Add 3 mL of 25% ammonia water to solution III, ultrasonically treat it for 10 min to mix evenly to obtain a solution containing transition metal elements, named solution IV.

[0040] Immerse the prepared Cu(OH)2 nanosheets in solution IV, where the molar ratio of Cu(OH)2 nanosheets to the transition metal elements in solution IV is 1:0.3, react at room temperature for 20 min, take it out, wash it with ethanol and deionized water respectively, and dry it in an oven at 60 °C to obtain a Ni-Cu(OH)2 nanorod precursor.

[0041] (2) Preparation of copper-based sulfide Dissolve 0.368 g of Na2S·9H2O in 30 mL of deionized water to obtain a Na2S solution with a concentration of 0.05 mol / L.

[0042] Immerse the prepared Ni-Cu(OH)2 nanorods in a 0.05 M Na2S solution, where the mass ratio of sulfur element in the Na2S solution to the Ni-Cu(OH)2 nanorods is 0.15:1. React at 25 °C for 20 min, take out the sample, wash it with ethanol and deionized water respectively, and dry it in an oven at 60 °C to obtain a transition metal element-doped copper-based sulfide, named Ni-Cu7S4 hierarchical structure.

[0043] III. Preparation of comparative catalysts Immerse the Cu(OH)2 nanosheets prepared in step (I) in a 0.05 M Na2S solution, where the mass ratio of sulfur element in the Na2S solution to the Cu(OH)2 nanorods is 0.15:1. React at 25 °C for 20 min, take out the sample, wash it with ethanol and deionized water respectively, and dry it in an oven at 60 °C. The obtained product is named Cu7S4 catalyst.

[0044] IV. Test the prepared Ni-Cu7S4 as follows: 1. Conduct scanning electron microscopy (SEM). The results are as Figure 1 shown. It can be seen from Figure 1 that the prepared Ni-Cu7S4 is nanorods, and dense nanoparticles are covered on it. Combining with the Figure 2 TEM image, it can be seen that the components of the nanoparticles are the same as those of the nanorod structure, both being Ni-Cu7S4, that is, the two are homogeneous hierarchical nanomaterials. It can be seen that the Ni-Cu7S4 hierarchical structure is successfully prepared.

[0045] 2. Conduct transmission electron microscopy (TEM) scanning. The results are as Figure 2 shown. It can be seen that the morphology of the Ni-Cu7S4 prepared in the present invention is in the form of a nanorod structure. Among them, high-resolution lattice fringes of 0.323 nm and 0.305 nm are observed ( Figure 2 the enlarged square area in c), corresponding to the (6 0 4) and (8 0 4) crystal planes of Cu7S4 respectively. Element mapping analysis shows that Ni, Cu, and S elements are evenly distributed on the surface of the nanorod structure.

[0046] 3. Conduct X-ray diffraction (XRD). The results are as Figure 3 shown. It can be seen that there are no diffraction peaks of Ni metal or composite phases in the Ni-Cu7S4 prepared in the present invention. This result indicates that Ni is doped into Cu7S4 as an ion and no independent phase is formed.

[0047] 4. X-ray photoelectron spectroscopy (XPS) was performed, and the results are as follows: Figure 4 As can be seen, the binding energies at Cu 2p 3 / 2 and Cu 2p 1 / 2 in the Ni-Cu7S4 prepared by the present invention are 932.6 / 934.5 eV and 952.5 / 954.8 eV respectively, indicating that Cu exists in the form of Cu + and Cu 2+ . The deconvoluted S 2p spectrum clearly shows that the binding energies of S 2p 3 / 2 and S 2p 1 / 2 are 162.05 and 163.2 eV respectively, indicating a close correlation of the Cu-S bond. The peak at a binding energy of 167.2 eV is attributed to the S-O bond, which may be caused by partial oxidation of the surface sulfide exposed to air. Ni 2p has two characteristic peaks at 855.9 and 873.4 eV, which belong to Ni 2p 3 / 2 and Ni 2p 1 / 2 respectively, indicating that Ni is successfully doped in the Cu7S4 catalyst.

[0048] 5. Electron paramagnetic resonance spectroscopy (EPR) was performed, and the results are as follows: Figure 5 As can be seen, a strong signal peak was found at g = 2.003 for the Ni-Cu7S4 catalyst prepared by the present invention, indicating the generation of sulfur vacancy defects in the catalyst. The sulfur vacancies increase the number of unpaired electrons in the catalyst, providing more active sites and improving the intrinsic catalytic activity of the catalyst.

[0049] 6. HER reaction and SOR reaction were carried out At room temperature, the HER reaction was carried out in a 1 mol / L KOH electrolyte solution using a three-electrode system. The working electrode was the copper-based sulfide prepared by the present invention with a geometric area of 1×1 cm 2 , the counter electrode was a platinum sheet, and the reference electrode was a saturated calomel electrode Hg / Hg2Cl2 / KCl. The scanning rate was 5 mV s -1 , and the correction rate was 100%. The potential was corrected for iR according to the formula where i is the current and R is the electrolyte resistance in the electrochemical impedance test.

[0050] At room temperature, the SOR reaction was carried out in a 1 mol / L KOH + 1 mol / L Na2S electrolyte solution using a three-electrode system. The working electrode for the SOR reaction was the copper-based sulfide with a geometric area of 1×1 cm 2 prepared by the present invention, the counter electrode was a platinum sheet, and the reference electrode was a saturated calomel electrode Hg / Hg2Cl2 / KCl. The scanning rate was 5 mV s-1 , the correction rate is 100%. According to the formula Perform iR correction on the potential, where i is the current and R is the electrolyte resistance in the electrochemical impedance test.

[0051] In addition, the pretreated copper foam (code CF in the figure) and the prepared Cu7S4 catalyst were used as the working electrodes respectively, and the commercially available Pt / C electrode and RuO2 electrode were used as the working electrodes to carry out the above HER and SOR reactions.

[0052] Figure 6 In, a is the LSV curve of HER, and b is the LSV curve of SOR. The horizontal axis in the figure represents the potential, and the vertical axis represents the current. It can be seen from the figure that the Ni-Cu7S4 prepared by the present invention has an overpotential of 106 mV for HER at a current density of 10 mA·cm -2 Under the condition, while its voltage potential for SOR at the same current density of 10 mA·cm -2 Under the condition is 0.30 V. In addition, the overpotentials of Cu7S4, CF, and Pt / C electrodes for HER at a current density of 10 mA·cm -2 Under the condition are 226.5, 457.7, and 19.8 mV respectively, while their voltage potentials for SOR at the same current density of 10 mA·cm -2 Under the condition are 0.31, 0.32, and 0.53 V respectively. The voltage potential of RuO2 for SOR at a current density of 10 mA·cm -2 Under the condition is 0.47 V. It shows that the Ni-Cu7S4 catalyst prepared by the present invention has excellent catalytic activity.

[0053] Through Figure 6 The LSV curve in, the Tafel slope value is further calculated, and the results are as Figure 7 Shown, where a in the figure is the Tafel slope of HER. Compared with Cu7S4 (139.4 mV·dec −1 ), and CF (175.8 mV·dec −1 ), the Tafel slope of Ni-Cu7S4 (115.8 mV·dec −1 ) is much smaller, proving that the electron transfer kinetics of Ni-Cu7S4 is faster during the HER process. In the figure, b is the Tafel slope of SOR, and the value of the Ni-Cu7S4 electrode is the smallest at 24.6 mV·dec −1 , lower than Cu7S4 (35.5 mV·dec −1 ), CF (49.9 mV·dec −1 ), RuO2 (151.5 mV·dec−1 ), and Pt / C (253 mV·dec −1 ), indicating that the SOR kinetics catalyzed by Ni-Cu7S4 is faster. This indicates that the Ni-Cu7S4 catalyst prepared in the present invention has faster reaction kinetics in the electrolytic water system.

[0054] Further analysis was carried out by electrochemical impedance testing, and the results are as Figure 8 shown. In the figure, a is the impedance diagram of HER, and the R of Ni-Cu7S4 ct is significantly lower than that of other comparative catalysts and is close to Pt / C. In the figure, b is the impedance diagram of SOR. Compared with Cu7S4, CF, RuO2 and Pt / C, the charge transfer resistance (R ct ) of Ni-Cu7S4 is the lowest. It can be seen from the figure that the Ni-Cu7S4 catalyst prepared in the present invention has a small impedance, indicating that the Ni-Cu7S4 catalyst prepared in the present invention has a small charge transfer impedance in the electrolytic water system, thus achieving a faster electron transfer rate.

[0055] As Figure 9 shown, cyclic voltammetry (CV) was carried out in a 1 mol / L KOH electrolyte using the above three-electrode system for the HER reaction at different scan rates (20 mV·s −1 , 40 mV·s −1 , 60 mV·s −1 , 80 mV·s −1 and 100 mV·s −1 ) to test the Ni-Cu7S4 catalyst. In the figure, a is the CV curve and b is the double-layer capacitance C dl calculated using this curve. The C dl value of the Ni-Cu7S4 catalyst prepared in the present invention is 10.42 mF·cm -2 , indicating that the Ni-Cu7S4 prepared in the present invention has a large active specific surface area, which can not only promote charge transfer but also provide more active sites.

[0056] As Figure 10 shown, chronopotentiometry (CP) testing was carried out in a 1 mol / L KOH electrolyte using the HER three-electrode system to evaluate the long-term stability of the catalyst. The working electrode is the prepared copper-based sulfide with a geometric area of 1×1 cm 2 , the counter electrode is a platinum sheet, and the reference electrode is a saturated calomel electrode Hg / Hg2Cl2 / KCl. The Ni-Cu7S4 catalyst prepared in the present invention at 50 mA·cm -2The lower constant electrolysis remained stable for at least 48 h, indicating that the Ni-Cu7S4 catalyst prepared by the present invention has good long-term stability under alkaline conditions.

[0057] As Figure 11 shown, the CP test of the Ni-Cu7S4 prepared by the present invention was carried out using a SOR three-electrode system. First, it reacted in 1 mol / L KOH electrolyte for 600 s, and then 1 mol / L Na2S solution was added to the electrolyte and reacted for another 600 s. It can be seen from the figure that the potential of the prepared Ni-Cu7S4 catalyst decreased significantly after adding 1 mol / L Na2S solution in 1 mol / L KOH electrolyte, indicating that the prepared Ni-Cu7S4 catalyst has good sulfur adsorption ability and good catalytic activity in the SOR reaction.

[0058] 7. Perform the determination of low-added-value S8 products The CP test was carried out using a SOR three-electrode system in an electrolyte of 1 M KOH + 1 M Na2S (the ratio of the two is 1:1) for 24 h, and the current density was 10 mA·cm -2 . The anode electrolyte after the test was placed in an ice bath, and concentrated sulfuric acid was gradually added to the electrolyte until the pH value became 1.0 to form a yellow precipitate. Then the solid yellow product was collected by filtration, washed with deionized water, and dried in an oven at 60 °C to obtain a yellow powder.

[0059] The yellow powder was subjected to X-ray diffraction (XRD pattern), and the results were as Figure 12 shown. The results showed that the yellow powder was a low-added-value product of polysulfide S8, which was consistent with the standard card of monomer sulfur (S8) (PDF# 78-1888).

[0060] The prepared Ni-Cu7S4 was subjected to constant current electrolysis for more than 25 h at a current density of 10 mA·cm -2 in an electrolyte of 1 mol / L KOH + 1 mol / L Na2S (the ratio of the two is 1:1) using a SOR three-electrode system. A certain amount of anode electrolyte was taken at 0 h, 2 h, 5 h, 8 h, 10 h, 15 h, and 25 h respectively, and its ultraviolet-visible spectrum was measured.

[0061] The results were as Figure 13 shown. It can be seen from the figure that as the electrolysis time increased, the color of the electrolyte gradually changed from transparent to dark yellow, the signal intensity at 300 nm increased significantly, and a new peak appeared at 370 nm. The peaks at 300 nm and 370 nm were due to short-chain polysulfides (S2 2- -S42- ). The increase in intensity indicates the conversion of soluble polysulfides from short chains to long chains. The presence of these peaks proves the formation of polysulfides in the electrolyte.

[0062] 8. Perform two-electrode performance tests Cut the Ni-Cu7S4 prepared by the present invention into 1×1 cm 2 , and assemble them into an H-type electrolytic cell device as the cathode and anode electrodes respectively for two-electrode performance tests. The cathode is an electrolyte of 1 mol / L KOH solution, and the anode is an electrolyte of 1 mol / L KOH + 1 mol / L Na2S (the ratio of the two is 1:1).

[0063] The results are as Figure 14 shown. The H-type electrolytic cell device (HER-SOR) assembled with the Ni-Cu7S4 catalyst prepared by the present invention only requires a voltage of 0.33 V to obtain a current density of 10 mA·cm -2 at room temperature. It shows that the prepared Ni-Cu7S4 catalyst reacts violently during the electrolytic water reaction and has excellent catalytic activity.

[0064] The preferred embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited thereto. Within the technical concept scope of the present invention, various simple modifications can be made to the technical solutions of the present invention, including the combination of each specific technical feature in any suitable way. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods. But these simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A transition metal element-doped copper-based sulfide, characterized in that, The copper-based sulfide includes a Cu7S4 material and transition metal elements doped in the Cu7S4 material, wherein the transition metal elements include nickel and / or iron.

2. The copper-based sulfide according to claim 1, wherein, The copper-based sulfide has a hierarchical structure, including a first-level structure in the shape of nanorods and a second-level structure formed by nanoparticles attached thereto.

3. The copper-based sulfide according to claim 1 or 2, wherein The copper-based sulfide has sulfur vacancies.

4. A preparation method of a transition metal element-doped copper-based sulfide, characterized in that, The preparation method includes: Immersing copper hydroxide nanosheets in a solution containing transition metal elements to carry out a first reaction to obtain a precursor, wherein the transition metal elements include nickel and / or iron; Immersing the precursor in a solution containing sulfur elements to carry out a second reaction to obtain the copper-based sulfide.

5. The preparation method according to claim 4, wherein, The molar ratio of the transition metal elements in the solution containing transition metal elements to the copper hydroxide nanosheets is 0.05 - 5:1; And / or, the mass ratio of the sulfur elements in the solution containing sulfur elements to the precursor is 0.1 - 0.6:

1.

6. The preparation method according to claim 4 or 5, wherein The time of the first reaction is 15 - 25 min, and the temperature is 20 - 30 °C; And / or, the time of the second reaction is 10 - 40 min, and the temperature is 20 - 30 °C.

7. The preparation method according to claim 6, wherein, The preparation method of the solution containing transition metal elements includes: Dissolving a salt of a transition metal element in water to obtain solution I; Dissolving potassium persulfate in water to obtain solution II, and the molar ratio of the potassium element in solution II to the transition metal element in solution I is 0.3 - 0.6:1; Mixing solution I and solution II to obtain solution III; Adding ammonia water to solution III to obtain the solution containing transition metal elements, and the volume ratio of the ammonia water to solution III is 1:8 - 10.

8. The preparation method according to claim 7, wherein, The preparation method further includes: taking out the copper hydroxide nanosheets after the first reaction and drying them to obtain the precursor, wherein the drying temperature is 30 - 80 °C.

9. The preparation method according to claim 7, wherein, The salt of the transition metal element is selected from one or more of nickel sulfate, nickel chloride, nickel nitrate, nickel acetate, nickel sulfamate, iron sulfate, iron chloride, iron nitrate and their respective hydrates; And / or, the solute of the solution of sulfur elements is selected from one or more of sodium sulfide, thioacetamide, thiourea, L-cysteine, sulfur and their respective hydrates; And / or, the raw materials for preparing the copper hydroxide nanosheets include copper foam.

10. Application of the copper-based sulfide according to any one of claims 1 - 3 or the copper-based sulfide prepared by the preparation method according to any one of claims 4 - 9 in hydrogen production by electrolyzing water.

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