Doped CuCo2S4 and preparation method thereof

Abstract

The invention provides doped CuCo2S4 and a preparation method of the doped CuCo2S4. The preparation method comprises the following steps: mixing a copper source, a cobalt source and a solvent to form an intermediate mixture; adding a sulfur source and a doping agent into the intermediate mixture, and carrying out hydrothermal reaction to obtain doped CuCo2S4; wherein the dopant comprises a selenium source and / or a tellurium source; the molar ratio of the copper source to the cobalt source to the sulfur source is 1: (2-2.5): (2-10). The invention also provides the doped CuCo2S4 obtained by the preparation method, and an electrolyzed water catalyst containing the doped CuCo2S4 or prepared from the doped CuCo2S4. The doped CuCo2S4 can be applied to an OER reaction and an HER reaction, and has relatively high catalytic activity and stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrolytic water, and particularly relates to a doped CuCo2S4 and a preparation method thereof. Background Art

[0002] Electrocatalytic water splitting for hydrogen production is considered an efficient and environmentally friendly renewable resource strategy. The electrolytic water reaction consists of two half-reactions, namely the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. Both of these reactions require catalysts to improve the efficiency of electrolytic water and reduce the overpotential of the reaction. Currently, noble metal platinum-based and ruthenium-based nanocatalysts have high HER and OER activities, but the high cost and scarcity of noble metals hinder their large-scale application in the field of electrolytic water. In recent years, a large number of low-cost transition metal sulfides, selenides, phosphides, carbides, nitrides, alloys, oxides, hydroxides, phosphates, etc. have been developed and applied to HER and OER. Among them, the spinel sulfide CuCo2S4 catalyst can not only capture protons during the HER process but also promote the formation of peroxides in the OER, so it has excellent HER and OER activities. However, the existing CuCo2S4 catalysts need to be prepared by multiple-step reactions, and their catalytic performance is single and the application range is narrow. The complex preparation process and the catalytic performance that still need to be further improved limit their commercialization. Summary of the Invention

[0003] In order to solve the above problems, the purpose of the present invention is to provide a doped CuCo2S4 and a preparation method thereof. The doped CuCo2S4 can be applied to the OER reaction and the HER reaction, and has high catalytic activity and stability.

[0004] To achieve the above object, the present invention provides a preparation method of a doped CuCo2S4, which includes: mixing a copper source, a cobalt source, and a solvent to form an intermediate mixture; adding a sulfur source and a dopant to the intermediate mixture, and performing a hydrothermal reaction to obtain the doped CuCo2S4; wherein, the dopant includes a selenium source and / or a tellurium source; the molar ratio of the copper source to the cobalt source is 1:2 - 2.5; the molar ratio of the copper source to the sulfur source is 1:2 - 10.

[0005] In the above preparation method, by doping selenium and / or tellurium in CuCo2S4, on the one hand, the structure and morphology of the catalyst can be regulated, the specific surface area of the material can be increased, and more active sites of the material can be exposed; on the other hand, the doping of selenium and / or tellurium can increase the vacancies in the material, and the doping elements can have a synergistic effect with copper and cobalt elements, thereby improving the catalytic activity of the material.

[0006] In the above preparation method, the copper source generally includes soluble copper salts, specifically, it may include one or a combination of two or more of copper chloride, copper nitrate, and copper acetate.

[0007] In the above preparation method, the cobalt source generally includes soluble cobalt salts, specifically, it may include one or a combination of two or more of cobalt chloride, cobalt nitrate, and cobalt acetate.

[0008] In the above preparation method, the sulfur source generally may include one or a combination of two or more of thiourea, sodium sulfide, and C2H5NS (thioacetamide).

[0009] In the above preparation method, the molar ratio of the copper source to the cobalt source can be controlled to be 1:2 - 2.5. For example, it can be specific values such as 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, etc., and the range with any two of the above specific values as endpoints.

[0010] In the above preparation method, the molar ratio of the copper source to the sulfur source can be controlled to be 1:2 - 10. For example, it can be specific values such as 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, etc., and the range with any two of the above specific values as endpoints. The molar ratio of the copper source to the sulfur source can be further controlled to be 1:4 - 6.

[0011] In the above preparation method, the molar ratio of the copper source, cobalt source, and sulfur source can be 1:2 - 2.5:2 - 10, and can be further controlled to be 1:2:2 - 10, and can be further controlled to be 1:2:4 - 6.

[0012] In the above preparation method, the molar ratio of the dopant to the copper source can be controlled to be 0.1 - 0.8:1. Specifically, it can be specific values such as 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, etc., and the range with any two of the above specific values as endpoints.

[0013] In the above preparation method, by doping Se and Te into CuCo2S4, the conductivity of the material can be improved and the electronic structure can be optimized, thereby enhancing the inherent HER and OER performance of CuCo2S4, facilitating the capture / release of oxygen intermediates, and thus promoting the fast kinetics of OER and HER. The doping of Se and Te can generate abundant sulfur vacancies in CuCo2S4, thereby providing abundant active sites, effectively promoting charge transfer and mass transfer, reducing the kinetic barrier and activation energy, and thus improving the overall intrinsic catalytic performance of the above material as a catalyst.

[0014] In the above preparation method, the selenium source may include selenium oxides and / or selenium salts, and specifically may include one or a combination of two or more of selenium dioxide, selenium tetrachloride, selenium dichloride, and sodium selenite.

[0015] In the above preparation method, the tellurium source may include tellurium salts, and specifically may include one or a combination of two or more of potassium tellurite, sodium tellurite, and ammonium tellurite.

[0016] In the above preparation method, the temperature of the hydrothermal reaction is 80 - 200 °C, for example, specific values such as 80 °C, 90 °C, 100 °C, 110 °C, 120 °C, 130 °C, 140 °C, 150 °C, 160 °C, 170 °C, 180 °C, 190 °C, 200 °C, and ranges with any two of the above specific values as endpoints. The temperature of the hydrothermal reaction may further be 100 - 160 °C or 120 - 180 °C. By controlling the temperature of the hydrothermal reaction, the morphology and structure of CuCo2S4 can be controlled.

[0017] In the above preparation method, the time of the hydrothermal reaction is 6 - 20 h, for example, specific values such as 6 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, and ranges with any two of the above specific values as endpoints. The time of the hydrothermal reaction may further be 10 - 20 h, and more specifically may be 10 - 18 h.

[0018] In the above preparation method, the solvent may include one or a combination of two or more of water, methanol, and ethanol; specifically, the solvent may include one or a combination of two or more of deionized water, anhydrous methanol, and anhydrous ethanol.

[0019] According to a specific embodiment of the present invention, the above preparation method may include:

[0020] Mixing a copper source, a cobalt source, and a solvent to form an intermediate mixture; adding a sulfur source and a dopant to the intermediate mixture, and performing a hydrothermal reaction at 80 - 200 °C for 6 - 20 h to obtain doped CuCo2S4; wherein, the molar ratio of the copper source, the cobalt source, and the sulfur source is 1:2 - 2.5:2 - 10, and the molar ratio of the dopant to the copper source is 0.1 - 0.8:1.

[0021] The present invention also provides a doped CuCo2S4, which is obtained by the above preparation method. In some specific embodiments, Se and / or Te are doped in the CuCo2S4.

[0022] In some specific embodiments, the doped CuCo₂S₄ can exhibit a nano-flower-like morphology, that is, the material has nano-sheets, several nano-sheets form a cluster, and the nano-sheets in the same cluster cross-connect at the same point to form a nano-flower-like structure. Among them, the three-dimensional nano-sheets in the above material can provide a large number of active sites and diffusion channels for the catalytic reaction, thereby improving the catalytic activity of the material.

[0023] In the above doped CuCo₂S₄, the particle size of the doped CuCo₂S₄ is 1 μm - 5 μm, and the specific surface area of the doped CuCo₂S₄ is 5 m 2 g -1 -20 m 2 g -1 。

[0024] The present invention also provides an electrolytic water catalyst, which includes the above doped CuCo₂S₄, or is made of the above doped CuCo₂S₄. The present invention provides a flower-like structure composed of nano-sheets, which has a relatively high specific surface area, can expose more active sites, and improve the catalytic activity.

[0025] In some specific embodiments, the above doped CuCo₂S₄ as an electrolytic water catalyst can be applied to electrolytic water hydrogen production reactions such as OER and HER, with a low required voltage and showing high catalytic activity. In some other specific embodiments, the above doped CuCo₂S₄ as an electrolytic water catalyst can also be applied to other alkaline electrolytic water hydrogen production reactions and show high catalytic activity.

[0026] In some specific embodiments, when the above doped CuCo₂S₄ is used as an electrolytic water catalyst in OER, the overpotential at a current density of 10 mA cm -2 can be controlled below 320 mV, and further can reach below 260 mV.

[0027] In some specific embodiments, when the above doped CuCo₂S₄ is used as an electrolytic water catalyst in HER, the overpotential at a current density of 10 mA cm -2 can be controlled below 130 mV, and further can reach below 90 mV.

[0028] In some specific embodiments, when the above doped CuCo₂S₄ is used as an electrolytic water catalyst in the electrolytic water process, only a voltage of 1.68 V, or even below 1.58 V, is required at a current density of 10 mA cm -2 , showing high catalytic activity.

[0029] The beneficial effects of the present invention include:

[0030] The preparation method provided by the present invention prepares doped CuCo2S4 through a one-step hydrothermal reaction. The doped CuCo2S4 has a high specific surface area, can expose more active sites, and the catalytic activity and chemical stability are significantly improved; the process is simple and energy-consuming is less, and it has practical application prospects. Description of the Drawings

[0031] Figure 1a XRD pattern of the doped CuCo2S4 catalyst of Example 1.

[0032] Figure 1b XPS full spectrum of the doped CuCo2S4 catalyst of Example 1.

[0033] Figure 2 SEM image of the doped CuCo2S4 catalyst of Example 1.

[0034] Figure 3 LSV graph of the OER performance of the doped CuCo2S4 catalyst of Example 1 in a three-electrode system.

[0035] Figure 4 LSV graph of the HER performance of the doped CuCo2S4 catalyst of Example 1 in a three-electrode system.

[0036] Figure 5 LSV graph of the water electrolysis performance of the doped CuCo2S4 catalyst of Example 1 in a two-electrode system.

[0037] Figure 6 EPR pattern of the doped CuCo2S4 catalyst of Example 1. Detailed Description of the Invention

[0038] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solutions of the present invention will be described in detail below, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0039] The sources of the raw materials or equipment used in the following experiments are as follows: cobalt chloride (CoCl2·2H2O), copper chloride (CuCl2·2H2O), absolute ethanol, thiourea (CH4N2S), sodium tellurite (Na2O3Te), sodium selenite (Na2O3Se), selenium dioxide (SeO2) were all purchased from Aladdin Reagent Company. Nafion solution (mass concentration 5 wt%, Sigma Aldrich). Analytical balance (Precisa, XJ220A), ultrasonic cleaner (Kunshan Shumei, KQ-500E), forced air drying oven (Shanghai Jinghong, DFG-9076A), electrochemical workstation (Shanghai Chenhua, CHI 760E).

[0040] Evaluation and analysis method: All electrochemical tests were carried out at room temperature using a CHI 760E electrochemical workstation and a standard three-electrode system. In an alkaline solution, Hg / HgO and a graphite rod were used as the reference electrode and the counter electrode, respectively. Preparation method of the working electrode: 4.0 mg of the sample and 20 μL of Nafion (5 wt%) were dissolved in a solution containing 360 μL of absolute ethanol and 120 μL of deionized water. The resulting slurry was ultrasonically treated for 1 hour to obtain a uniform suspension. Then, 50 μL of the above dispersion was dropped onto a carbon paper of 1×1 cm 2 and dried at room temperature. In a 1 M KOH solution, linear voltammetry curves were scanned at a scanning rate of 5 mV s -1 to obtain the electrochemical performance of the catalyst.

[0041] Example 1

[0042] This example provides a doped CuCo2S4 catalyst, and its preparation method includes:

[0043] Weigh 1 mmol of CuCl2·2H2O and 2 mmol of CoCl2·6H2O and dissolve them in 40 mL of absolute ethanol. Stir magnetically at room temperature to dissolve into a uniform solution; add 4 mmol of CH4N2S and 0.1 mmol of SeO2 to the above solution, and continue magnetic stirring at room temperature; transfer the mixed solution to a hydrothermal reaction kettle and carry out hydrothermal reaction at 160 °C for 20 h, and then naturally cool. The obtained solid powder can be obtained as doped CuCo2S4 after washing and drying.

[0044] Calculated according to the feeding ratio, the molar ratio of Cu, Co, S, and Se in the raw materials is 1:2:3.68:0.32.

[0045] Figure 1a is the XRD pattern of the doped CuCo2S4 catalyst prepared in this example. Phase analysis shows that its main component is CuCo2S4. Figure 1b is the XPS pattern of the doped CuCo2S4 catalyst prepared in this example. From Figure 1b it can be seen that the catalyst contains Cu, Co, S, and Se elements. Combining Figure 1a , Figure 1b results, it can be seen that Se exists in the catalyst in a doped form.

[0046] Figure 2 is the SEM pattern of the doped CuCo2S4 catalyst prepared in this example. The doped CuCo2S4 presents a flower-like structure with a diameter of 3-4 μm, which is formed by the interconnection of nanosheets to form a three-dimensional nano-flower structure, which is beneficial to increasing the specific surface area of the catalyst and exposing more active sites.

[0047] Figure 3 ,Figure 4 OER and HER performance graphs of the doped CuCo2S4 catalyst prepared in this example. At a current density of 10 mA cm -2 , the overpotentials of OER and HER are 226 mV and 65 mV respectively.

[0048] Figure 5 Two-electrode water electrolysis performance graph of the doped CuCo2S4 catalyst prepared in this example. It can be seen from Figure 5 that during the water electrolysis process of the doped CuCo2S4 catalyst, the voltage at a current density of 10 mA cm -2 is 1.52 V, showing high catalytic activity.

[0049] Figure 6 EPR graph of the doped CuCo2S4 catalyst prepared in this example. It can be seen from Figure 6 that there are vacancies in this catalyst.

[0050] Example 2

[0051] This example provides a doped CuCo2S4 catalyst, and its preparation method includes:

[0052] Weigh 1 mmol of CuCl2·2H2O and 2 mmol of CoCl2·6H2O and dissolve them in 40 mL of absolute ethanol. Stir magnetically at room temperature to dissolve into a homogeneous solution; add 6 mmol of CH4N2S and 0.5 mmol of SeO2 to the above solution, and continue magnetic stirring at room temperature; transfer the mixed solution to a hydrothermal reaction kettle and carry out hydrothermal reaction at 140 °C for 15 h, and then cool naturally. The obtained solid powder can be obtained as doped CuCo2S4 after washing and drying.

[0053] In the electrochemical performance test, using a three-electrode system, the overpotentials of OER and HER at a current density of 10 mA cm -2 are 259 mV and 86 mV respectively. Using a two-electrode system, the voltage during the water electrolysis process at a current density of 10 mA cm -2 is 1.57 V.

[0054] Example 3

[0055] This example provides a doped CuCo2S4 catalyst, and its preparation method includes:

[0056] Weigh 1 mmol of CuCl2·2H2O and 2 mmol of CoCl2·6H2O and dissolve them in 40 mL of absolute ethanol. Stir magnetically at room temperature to dissolve into a homogeneous solution. Add 6 mmol of CH4N2S and 0.5 mmol of Na2O3Te to the above solution and continue magnetic stirring at room temperature. Transfer the mixed solution to a hydrothermal reaction kettle and carry out hydrothermal reaction at 100 °C for 10 h. Cool naturally. The obtained solid powder can be obtained as doped CuCo2S4 after washing and drying.

[0057] In the electrochemical performance test, using a three-electrode system, the overpotentials of OER and HER at a current density of 10 mA cm -2 are 280 mV and 106 mV respectively. Using a two-electrode system, the voltage at a current density of 10 mA cm during the electrolysis of water is 1.62 V. -2

[0058] Example 4

[0059] This example provides a doped CuCo2S4 catalyst, and its preparation method includes:

[0060] Weigh 1 mmol of CuCl2·2H2O and 2 mmol of CoCl2·6H2O and dissolve them in 40 mL of absolute ethanol. Stir magnetically at room temperature to dissolve into a homogeneous solution. Add 7 mmol of CH4N2S and 0.3 mmol of Na2O3Te to the above solution and continue magnetic stirring at room temperature. Transfer the mixed solution to a hydrothermal reaction kettle and carry out hydrothermal reaction at 100 °C for 10 h. Cool naturally. The obtained solid powder can be obtained as doped CuCo2S4 after the reaction after washing and drying.

[0061] In the electrochemical performance test, using a three-electrode system, the overpotentials of OER and HER at a current density of 10 mA cm -2 are 299 mV and 126 mV respectively. Using a two-electrode system, the voltage at a current density of 10 mA cm during the electrolysis of water is 1.66 V. -2

[0062] Example 5

[0063] This example provides a doped CuCo2S4 catalyst, and its preparation method includes:

[0064] ​​Weigh 1 mmol of CuCl2·2H2O and 2 mmol of CoCl2·6H2O and dissolve them in 40 mL of absolute ethanol. Stir magnetically at room temperature until a homogeneous solution is formed; add 8 mmol of CH4N2S and 0.8 mmol of Na2O3Se to the above solution and continue magnetic stirring at room temperature; transfer the mixed solution to a hydrothermal reactor and carry out hydrothermal reaction at 100 °C for 10 h, and then cool it naturally. The obtained solid powder can be obtained as the doped CuCo2S4 after washing and drying.

[0065] In the electrochemical performance test, the overpotentials of OER and HER at a current density of 10 mA cm -2 are 320 mV and 118 mV respectively measured by a three-electrode system, and the voltage at a current density of 10 mA cm -2 during the electrolysis of water is 1.67 V measured by a two-electrode system.

[0066] Comparative Example 1

[0067] This comparative example provides a CuCo2S4 catalyst, and its preparation method includes:

[0068] Weigh 1 mmol of CuCl2·2H2O and 2 mmol of CoCl2·6H2O and dissolve them in 40 mL of absolute ethanol. Stir magnetically at room temperature until a homogeneous solution is formed; add 4 mmol of CH4N2S to the above solution and continue magnetic stirring at room temperature; transfer the mixed solution to a hydrothermal reactor and carry out hydrothermal reaction at 160 °C for 20 h, and then cool it naturally. The obtained solid powder can be obtained as CuCo2S4 after washing and drying.

[0069] In the electrochemical performance test, the overpotentials of OER and HER at a current density of 10 mA cm -2 are 342 mV and 290 mV respectively measured by a three-electrode system, and the voltage at a current density of 10 mA cm -2 during the electrolysis of water is 1.83 V.

[0070] Comparing the test results of Example 1 with those of Comparative Example 1, it can be seen that compared with the CuCo2S4 catalyst without doping elements, the present invention can reduce the overpotential and voltage in the electrolysis of water by doping in the catalyst, and has better catalytic activity.

[0071] From the above test results, it can be seen that the preparation method provided by the present invention can directly synthesize a doped CuCo2S4 catalyst with a flower-like morphology formed by the assembly of nanosheets through a one-step hydrothermal reaction. The morphological characteristics of the doped CuCo2S4 catalyst endow it with a high specific surface area, and provide a large number of active sites and diffusion channels for the catalytic reaction, thereby improving the catalytic activity of the material.

[0072] In the doped CuCo2S4 catalyst of the present invention, the vacancies generated by doping serve as abundant active sites, which can promote charge transfer and mass transfer, reduce the kinetic barrier and activation energy, thereby improving the overall intrinsic catalytic performance of the catalyst; by doping Se and / or Te, the conductivity of the material can be increased and the electronic structure in the material can be optimized, enhancing the HER and OER performance of the CuCo2S4 catalyst, facilitating the capture / release of oxygen intermediates, and thus promoting the fast kinetics of OER and HER.

Claims

1. A preparation method of doped CuCo2S4, the preparation method comprising: Mixing a copper source, a cobalt source, a solvent, a sulfur source and a dopant, and performing a hydrothermal reaction to obtain doped CuCo2S4; wherein the dopant comprises a selenium source and / or a tellurium source; the molar ratio of the copper source to the cobalt source is 1:2 - 2.5; the molar ratio of the copper source to the sulfur source is 1:2 - 10.

2. The preparation method according to claim 1, wherein The copper source comprises one or more combinations of copper chloride, copper nitrate and copper acetate.

3. The preparation method according to claim 1, wherein The cobalt source comprises one or more combinations of cobalt chloride, cobalt nitrate and cobalt acetate.

4. The preparation method according to claim 1, wherein The sulfur source comprises one or more combinations of thiourea, sodium sulfide, and C2H5NS.

5. The preparation method according to claim 1, wherein The molar ratio of the copper source, the cobalt source and the sulfur source is 1:2:2 - 1:2:10, preferably 1:2:4 - 1:2:

6.

6. The preparation method according to claim 1, wherein, The molar ratio of the dopant to the copper source is 0.1 - 0.8:

1.

7. The preparation method according to claim 1, wherein, The selenium source comprises one or more combinations of selenium dioxide, selenium tetrachloride, selenium dichloride, and sodium selenite.

8. The preparation method according to claim 1, wherein, The tellurium source comprises one or more combinations of potassium tellurite, sodium tellurite, and ammonium tellurite.

9. According to the preparation method described in claim 1, wherein The temperature of the hydrothermal reaction is 80 - 200 °C; preferably 120 - 180 °C; The time of the hydrothermal reaction is 6 - 20 h, preferably 10 - 20 h.

10. A doped CuCo2S4, which is obtained by the preparation method according to any one of claims 1 - 9.

11. An electrolytic water catalyst, which comprises the doped CuCo2S4 according to claim 10, or is made of the doped CuCo2S4 according to claim 10.

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