A sulfur-modified copper / cuprous oxide electrode material and its preparation method

Abstract

This invention provides a sulfur-modified copper / cuprous oxide electrode material and its preparation method. The invention utilizes a low-concentration NaBH4 solution to chemically reduce Cu9S5, causing copper ions in Cu9S5 to be reduced in situ to cuprous oxide and a small amount of elemental copper. Most of the anionic sulfur in Cu9S5 escapes as H2S gas, while the sulfur inside the material exists by occupying oxygen sites, thus obtaining anion-modified S-Cu / Cu2O material. This preparation method is simple to operate, has low requirements for reaction conditions and equipment, low raw material costs, and produces green and pollution-free reaction products. The prepared S-Cu / Cu2O material exhibits excellent capacitance performance, with a specific capacitance of 1800-2408 F / g and a rate capability of 55%-67%. Therefore, it is expected to be widely used as a working electrode material in supercapacitors and other energy storage devices.

Description

Technical fields:

[0001] This invention relates to the field of electrode material preparation, specifically to anion-modified copper / cuprous oxide electrode materials and their preparation methods. This material is suitable for use as an electrode material in energy storage devices such as supercapacitors. Background technology:

[0002] With the depletion of fossil fuels, people are increasingly concerned about the impact of global warming on the Earth. Therefore, the search for sustainable clean energy has become a perpetual theme in the modern era. For a long time, in the process of developing clean energy, we have urgently sought an efficient, low-cost, and safe energy storage device. Compared to hybrid capacitors, other low-cost metal-ion batteries, such as sodium-ion and potassium-ion batteries, suffer from low charge / discharge rates and safety issues. Based on this, hybrid capacitors are a very promising energy storage device that can replace batteries. In terms of energy storage mechanism, compared to double-layer electrode materials where energy storage only occurs through adsorption and desorption on the electrode surface, battery-type electrode materials are materials that store energy through redox reactions between the electrode surface and electrolyte ions. However, in the past decade of research, many high-performance cathode materials have been reported, but in comparison, anode materials are severely limited by their very low specific capacitance, making it difficult to match them with cathodes. Based on this problem, it is hoped that a high-performance anode material can be prepared to promote the widespread application of hybrid capacitors.

[0003] Among transition metal oxide materials, copper-based oxide materials possess advantages such as low cost, environmental friendliness, unique electronic structure, and high specific capacitance. Therefore, copper-based oxide materials are among the most promising electrode materials, with CuO and Cu2O being extensively studied in the field of supercapacitors. For example, the literature *Applied Surface Science*, 2019, 449, 474-484, successfully constructed a Cu2O-CuO / reduced graphene oxide nanocomposite material using a hydrothermal method. The specific process involved dispersing copper chloride and pre-synthesized graphene oxide separately in deionized water. Then, an aqueous solution of sodium hydroxide was added to the copper chloride aqueous solution and mixed thoroughly. This mixture was then combined with the graphene oxide dispersion and subjected to a hydrothermal reaction at 140℃ for 24 hours. After washing and drying at 80℃, the Cu2O-CuO / reduced graphene oxide nanocomposite material was obtained. The preparation method requires high temperature and high pressure, which increases the energy consumption of production. Moreover, the voltage range of the obtained electrode material is very small, only -0.7-0V (vs. Ag / AgCl), and the specific capacity at a current density of 1A / g is also not high, only 436.6F / g.

[0004] The literature *Journal of Alloys and Compounds*, 2021, 856, 157466, describes a two-step process for constructing a Cu₂O / Cu@C nanosheet supercapacitor cathode material. The first step involves a hydrothermal reaction of copper nitrate, 4-(pyridin-4-yl)phthalic acid, and 1,4-bis(benzimidazol-1-yl)benzene in a mixed solution of dimethylacetamide, acetonitrile, and water at 100°C for 48 hours. After washing and drying, a copper-containing metal-organic framework (Cu-MOF) precursor is obtained. The second step involves calcining the Cu-MOF precursor at 600°C for 2 hours under a nitrogen atmosphere, thus obtaining the Cu₂O / Cu@C material, which exhibits a capacity of 665 F / g at 0.5 A / g. This preparation method uses flammable dimethylacetamide, posing a safety risk, and requires high-temperature calcination, increasing energy consumption and cost, while also resulting in low synthesis efficiency.

[0005] Therefore, existing copper-based oxide electrode materials still suffer from low specific capacitance. To improve the conductivity and specific capacitance of electrode materials, anion modification can be employed. The resulting special electronic structure can enhance the capacitance performance of the material. For example, the literature Nano Energy, 2017, 39, 162-171 describes a hydrothermal sulfidation method to obtain an S-doped CoP nanorod array on carbon cloth as a positive electrode material for a supercapacitor. The specific steps are as follows: First, a hydrothermal reaction of cobalt nitrate, ammonium fluoride, and urea on carbon cloth at 100°C for 4 hours was carried out. After washing and drying, a Co-OH precursor was obtained on the carbon cloth. Second, sodium hypophosphite was placed upstream of a tube furnace, and the Co-OH / carbon cloth precursor was placed downstream. Under a nitrogen atmosphere, the tube furnace was phosphating at 300°C for 2 hours to obtain CoP on the carbon cloth. Third, under a nitrogen atmosphere, the tube furnace was further sulfided at 400°C using sulfur powder for 1 hour to obtain S-doped CoP nanorod materials on the carbon cloth. The sulfur-doped metal phosphide material prepared by this method has a high capacity of 610 F / g at 1 A / g, which is 1.78 times that of the undoped CoP material. However, the preparation method is cumbersome and requires harsh conditions, including multiple high-temperature calcinations, high reaction temperatures, and long cycles. These factors increase energy consumption and cost, and result in low synthesis efficiency, limiting the large-scale preparation of this method.

[0006] The literature *Nature Communications*, 2022, 13, 1965, reports an Ag,S dual-doped Cu₂O / Cu nanowire material for the electrochemical reduction of carbon dioxide. The specific preparation process is as follows: First, Ag-doped Cu₂S precursor is obtained by in-situ electrodeposition on copper foam. Second, under continuous carbon dioxide gas flow, an electrochemical reduction is performed for 30 min using a 1:3 molar ratio of 1-butyl-3-methylimidazolium tetrafluoroborate / water-saturated carbon dioxide solution and a 0.5M H₂SO₄ solution as the cathode and anolyte, respectively, to obtain the final Ag,S-doped Cu₂O / Cu electrode material. This material, used as a catalyst for the electrochemical reduction of carbon dioxide, exhibits excellent performance, reaching 122.7 mA / cm². 2 The current density and Faraday efficiency are 67.4%. The drawbacks of this preparation method are the need for continuous carbon dioxide gas flow and the complexity of the electrolyte solution used, which increases production energy consumption and cost.

[0007] The aforementioned literature indicates that conventional methods for preparing anion-modified materials generally require stringent conditions, leading to complex processes and high costs. Therefore, this patent proposes a simple, green method for preparing anion-modified metal oxides at room temperature and pressure. In this method, the metal sulfide Cu9S5 is selected as both the sulfur and copper source. Anion-modified Cu / Cu2O nanowire materials are obtained through a simple and rapid one-step wet chemical reduction method at room temperature and pressure. These materials exhibit excellent charge-discharge capacity and can be used as anode materials in supercapacitors. Furthermore, the preparation method is simple, low-cost, and suitable for large-scale production. Summary of the Invention:

[0008] The purpose of this invention is to provide a sulfur-modified copper / cuprous oxide composite electrode material and its preparation method, which is suitable for use as an electrode material for energy storage devices such as supercapacitors.

[0009] In this invention, a low-concentration NaBH4 solution is used as a reducing agent, with Cu9S5 serving as both a copper and sulfur source. NaBH4 hydrolyzes to produce a large amount of reducing gas H2, creating an alkaline environment. During the vigorous reduction reaction, copper ions are reduced to cuprous oxide and a small amount of elemental copper. Most of the anionic sulfur escapes as H2S gas. The residual sulfur inside the material exists in Cu / Cu2O by occupying oxygen sites, resulting in an anionicly modified S-Cu / Cu2O material. Modifying metal oxide materials with anionic sulfur improves both the conductivity and specific capacitance of the metal oxide.

[0010] The present invention provides a sulfur-modified copper / cuprous oxide composite electrode material, with the chemical formula S-Cu / Cu₂O. Its microstructure consists of nanowires approximately 10-30 nm wide, with curved shapes and stacked wires forming voids, placing the material in a mesoporous state. The specific surface area of ​​this electrode material is 53.06 m². 2 g -1 The specific capacitance is 1800-2408 F / g, and the rate capability is 55%-67%.

[0011] The preparation method of the S-Cu / Cu2O electrode material provided by this invention includes the following specific steps:

[0012] A. Dissolve copper acetate and thiourea in ethylene glycol and stir at room temperature for 1-3 hours to prepare a mixed solution, wherein the molar ratio of copper acetate to thiourea is 1:1.5-2 and the concentration of copper acetate is 0.05-0.1M. Perform hydrothermal reaction at 160-180℃ for 8-12 hours. After natural cooling, wash and dry to obtain Cu9S5 nanosphere precursor.

[0013] B. Prepare a 0.8-1.2 M NaBH4 solution at room temperature;

[0014] C. Add 0.1-0.15 L of NaBH4 solution per gram of Cu9S5 to a container containing Cu9S5 powder. Stir and react for 15-35 min at room temperature (22-33℃) and 99-100 kPa. Rinse thoroughly with deionized water until the pH reaches 7. Pre-freeze at -58 to -62℃ for 12-18 h, then freeze-dry under vacuum for 10-24 h to obtain anionic sulfur-modified S-Cu / Cu2O composite material with a nanowire structure 10-30 nm wide and a specific surface area of ​​45.18-53.06 m². 2 g -1 This electrode material exhibits good supercapacitor performance, with a specific capacitance of 1800-2408 F / g and a rate capability of 55-67%.

[0015] The invention is characterized by utilizing the low-concentration NaBH4 hydrolysis to generate a large amount of reducing gas H2, and the resulting alkaline environment, which reduces Cu9S5 copper ions to cuprous oxide and a small amount of elemental copper. Cu9S5 also serves as both a copper source and a sulfur source, with most of the anionic sulfur escaping as H2S gas. The sulfur remaining inside the material exists in the Cu / Cu2O structure by occupying oxygen sites, resulting in S-Cu / Cu2O nanowire materials.

[0016] The obtained S-Cu / Cu2O material was characterized and its application performance was tested. The results are shown in the table below. Figure 1-8

[0017] Figure 1 The image shows the scanning electron microscope (SEM) characterization of the S-Cu / Cu2O material prepared in Example 1. As can be seen from the image, it is a nanowire material with curved and stacked layers, and its diameter is about 20 nm.

[0018] Figure 2 The figure shows the X-ray diffraction (XRD) characterization of the S-Cu / Cu2O material prepared in Example 1. As can be seen from the figure, the relevant diffraction peaks of Cu and Cu2O appear respectively, indicating that the material is an S-Cu / Cu2O material.

[0019] Figure 3 The figure shows the transmission electron microscopy (TEM) characterization of the S-Cu / Cu2O material prepared in Example 1. As can be seen from the figure, the S-Cu / Cu2O material has a linear structure of about 20 nm.

[0020] Figure 4 The image shows the scanning electron microscope (SEM) characterization of the S-Cu / Cu2O material prepared in Example 3. As can be seen from the figure, it is a nanowire material with a diameter of about 20 nm.

[0021] Figure 5 The image shows the scanning electron microscope (SEM) characterization of the S-Cu / Cu2O material prepared in Example 4. As can be seen from the figure, it is a nanowire material with a diameter of about 30 nm.

[0022] Figure 6 The figure shows the cyclic voltammetry curves of the S-Cu / Cu2O electrode prepared in Example 1 in a 1 mol / L KOH electrolyte. As can be seen from the figure, there are obvious redox characteristic peaks, and the curve shape remains consistent at each scan rate, indicating that the material has good reversibility.

[0023] Figure 7These are the charge-discharge curves of the S-Cu / Cu2O electrode prepared in Example 1 at different current densities in a 1 mol / L KOH electrolyte. At current densities of 1 A / g, 2 A / g, 3 A / g, 4 A / g, 5 A / g, 6 A / g, 7 A / g, 8 A / g, 9 A / g, and 10 A / g, the specific capacitances were 2408 F / g (668.9 mAh / g), 2138 F / g (593.9 mAh / g), 2010 F / g (558.3 ​​mAh / g), 2000 F / g (555.6 mAh / g), 1895 F / g (526.4 mAh / g), 1890 F / g (525 mAh / g), 1834 F / g (509.4 mAh / g), 1792 F / g (497.8 mAh / g), 1728 F / g (480 mAh / g), and 1620 F / g (450 mAh / g) (electrode active component was 0.003 g). The results show that the material has excellent specific capacitance.

[0024] Figure 8 The figure shows the charge-discharge rate curves of the S-Cu / Cu2O electrode prepared in Example 1 in a 1 mol / L KOH electrolyte. As can be seen from the figure, the specific capacitance decreases with the increase of current density. As the current density increases from 1 A / g to 10 A / g, the specific capacitance drops to 67% of the initial value. This indicates that the electrode material still has a relatively ideal specific capacitance under high charge-discharge rate conditions, which shows that the synergistic effect of the composite structure improves the electrochemical performance of the material.

[0025] The beneficial effects of this invention are:

[0026] (1) In this invention, Cu9S5 is chemically reduced by a low-concentration NaBH4 solution, so that the copper ions in Cu9S are reduced in situ to cuprous oxide and a small amount of elemental copper. Most of the anionic sulfur in Cu9S escapes in the form of H2S gas, while the sulfur inside the material exists in the form of occupying oxygen sites, thereby obtaining anionic S-modified Cu / Cu2O material.

[0027] (2) According to the UV-Vis diffuse reflectance spectrum and first-principles calculation results, the electronic structure of Cu / Cu2O was optimized by sulfide ion modification, the band gap of the material was reduced, the conductivity of the material was increased, thereby promoting the charge transport efficiency and reducing the adsorption energy of hydroxide ions, which helped to improve the overall electrochemical performance of the material.

[0028] (3) The prepared S-Cu / Cu2O material has good supercapacitor anode performance, with a specific capacitance of 1800-2408 F / g and a rate capability of 55%-67%. Therefore, it is expected to be widely used as an anode material in supercapacitors and even other energy storage devices.

[0029] (4) The preparation method used in this invention is simple to operate and has low requirements for reaction conditions and equipment. It can be carried out at room temperature. With Cu9S5 as the precursor raw material, there is no need to add copper source and sulfur source. The raw material cost is low and the reaction product is green and pollution-free, which fully reflects the concept of low-carbon economy and sustainable development. Attached Figure Description

[0030] Figure 1 The scanning electron microscope (SEM) characterization of the S-Cu / Cu2O prepared in Example 1 is shown.

[0031] Figure 2 The X-ray diffraction (XRD) characterization of S-Cu / Cu2O prepared in Example 1 is shown.

[0032] Figure 3 The transmission electron microscope (TEM) characterization of S-Cu / Cu2O prepared in Example 1 is shown.

[0033] Figure 4 The image shows the scanning electron microscope (SEM) characterization of the S-Cu / Cu2O prepared in Example 3.

[0034] Figure 5 The image shows the scanning electron microscope (SEM) characterization of the S-Cu / Cu2O prepared in Example 4.

[0035] Figure 6 The image shows the cyclic voltammetry curve of the S-Cu / Cu2O electrode prepared in Example 1.

[0036] Figure 7 These are the charge-discharge curves of the S-Cu / Cu2O electrode prepared in Example 1 at different current densities.

[0037] Figure 8 This is the charge-discharge rate curve of the S-Cu / Cu2O electrode prepared in Example 1. Detailed Implementation

[0038] Example 1

[0039] A. Weigh 4 mmol of copper acetate and 6 mmol of thiourea and dissolve them in 40 mL of ethylene glycol. Stir at room temperature for 3 h to form a homogeneous solution. Perform hydrothermal reaction at 180 °C for 10 h. After natural cooling, wash and dry to obtain Cu9S5 nanosphere precursor.

[0040] B. Prepare a 1M NaBH4 solution at room temperature;

[0041] C. Adding 0.1 L of NaBH4 solution per gram of Cu9S5, the NaBH4 solution was added to a container containing Cu9S5 powder. The mixture was stirred and reacted for 20 min at 25°C and 100 kPa. After rinsing with a large amount of deionized water until the pH reached 7, the mixture was pre-frozen at -60°C for 12 h, followed by vacuum freeze-drying for 10 h to obtain anionic sulfur-modified S-Cu / Cu2O composite material with a 20 nm wide nanowire structure and a specific surface area of ​​53.06 m². 2 g -1 The electrode material has a specific capacitance of 2408 F / g and a rate capability of 67%.

[0042] Electrochemical performance tests were performed on the obtained S-Cu / Cu2O:

[0043] Mix 3 mg S-Cu / Cu2O thoroughly with 20–40 μL of 5% Nafion solution (adhesive) and 0.5 ml of ethanol, and coat the mixture onto a 1 × 1 cm substrate. 2 The electrode material was obtained by drying on a titanium mesh. In a three-electrode testing system, using this electrode material as the working electrode, cyclic voltammetry, charge-discharge, and charge-discharge rate tests were performed in a 1 mol / L KOH electrolyte within a voltage window of -1 to 0 V (vs Hg / HgO). The results are shown in [Figure number missing]. Figure 6-8 .

[0044] Example 2

[0045] A. Weigh 4 mmol of copper acetate and 6 mmol of thiourea and dissolve them in 40 mL of ethylene glycol. Stir at room temperature for 3 h to form a homogeneous solution. Perform hydrothermal reaction at 170 °C for 11 h. After natural cooling, wash and dry to obtain Cu9S5 nanosphere precursor.

[0046] B. Prepare a 1M NaBH4 solution at room temperature;

[0047] C. Adding 0.12 L of NaBH4 solution per gram of Cu9S5, the NaBH4 solution was added to a container containing Cu9S5 powder. The mixture was stirred and reacted for 15 min at room temperature (26°C) and 99.9 kPa. After rinsing with a large amount of deionized water until the pH reached 7, the mixture was pre-frozen at -60°C for 12 h, followed by vacuum freeze-drying for 10 h to obtain anionic sulfur-modified S-Cu / Cu2O composite material with a 20 nm wide nanowire structure and a specific surface area of ​​48.60 m². 2 g -1 The electrode material has a specific capacitance of 2142 F / g and a rate capability of 64%.

[0048] Example 3

[0049] A. Weigh 2 mmol copper acetate and 4 mmol thiourea and dissolve them in 40 mL ethylene glycol. Stir at room temperature for 1 h to form a homogeneous solution. Perform hydrothermal reaction at 160 °C for 12 h. After natural cooling, wash and dry to obtain Cu9S5 nanosphere precursor.

[0050] B. Prepare a 1.2M NaBH4 solution at room temperature;

[0051] C. Adding 0.13 L of NaBH4 solution per gram of Cu9S5, the NaBH4 solution was added to a container containing Cu9S5 powder. The mixture was stirred and reacted for 20 min at 27°C and 100 kPa. After rinsing with a large amount of deionized water until the pH reached 7, the mixture was pre-frozen at -60°C for 12 h, followed by vacuum freeze-drying for 10 h to obtain anionic sulfur-modified S-Cu / Cu2O composite material with a 20 nm wide nanowire structure and a specific surface area of ​​50.34 m². 2 g -1 The electrode material has a specific capacitance of 1986.3 F / g and a rate capability of 58%.

[0052] Example 4

[0053] A. Weigh 4 mmol of copper acetate and 6 mmol of thiourea and dissolve them in 40 mL of ethylene glycol. Stir at room temperature for 3 h to form a homogeneous solution. Perform hydrothermal reaction at 180 °C for 11 h. After natural cooling, wash and dry to obtain Cu9S5 nanosphere precursor.

[0054] B. Prepare a 0.8 M NaBH4 solution at room temperature;

[0055] C. Adding 0.1 L of NaBH4 solution per gram of Cu9S5, the NaBH4 solution was added to a container containing Cu9S5 powder. The mixture was stirred and reacted for 30 min at 25°C and 100 kPa. After rinsing with a large amount of deionized water until the pH reached 7, the mixture was pre-frozen at -60°C for 12 h, followed by vacuum freeze-drying for 10 h to obtain anionic sulfur-modified S-Cu / Cu2O composite material with a 30 nm wide nanowire structure and a specific surface area of ​​48.81 m². 2 g -1 The electrode material has a specific capacitance of 1987 F / g and a rate capability of 63%.

[0056] Example 5

[0057] A. Weigh 3 mmol copper acetate and 5 mmol thiourea and dissolve them in 40 mL ethylene glycol. Stir at room temperature for 2 h to form a homogeneous solution. Perform hydrothermal reaction at 170 °C for 12 h. After natural cooling, wash and dry to obtain Cu9S5 nanosphere precursor.

[0058] B. Prepare a 1M NaBH4 solution at room temperature;

[0059] C. Adding 0.1 L of NaBH4 solution per gram of Cu9S5, the NaBH4 solution was added to a container containing Cu9S5 powder. The mixture was stirred and reacted for 35 min at 26°C and 100 kPa. After rinsing with a large amount of deionized water until the pH reached 7, the mixture was pre-frozen at -60°C for 12 h, followed by vacuum freeze-drying for 10 h to obtain anionic sulfur-modified S-Cu / Cu2O composite material with a 30 nm wide nanowire structure and a specific surface area of ​​42.13 m². 2 g -1 The electrode material has a specific capacitance of 2214.5 F / g and a rate capability of 55%.

Claims

1. A method for preparing a sulfur-modified copper / cuprous oxide electrode material, characterized in that: Prepare according to the following specific steps: A. Dissolve copper acetate and thiourea in ethylene glycol and stir at room temperature for 1-3 h to prepare a mixed solution, wherein the molar ratio of copper acetate to thiourea is 1:1.5-2 and the concentration of copper acetate is 0.05-0.1M. Perform hydrothermal reaction at 160-180℃ for 8-12 h. After natural cooling, wash and dry to obtain Cu9S5 nanosphere precursor. B. Prepare a 0.8-1.2 M NaBH4 solution at room temperature; C. Add 0.1-0.15 liters of NaBH4 solution per gram of Cu9S5 to a container containing Cu9S5 powder. Stir and react for 15-35 min at room temperature (22-33℃) and 99-100 kPa. Rinse thoroughly with deionized water until pH 7. Pre-freeze at -58 to -62℃ for 12-18 h, and then freeze-dry under vacuum for 10-24 h to obtain anionic sulfur-modified S-Cu / Cu2O composite material.

2. A sulfur-modified copper / cuprous oxide electrode material prepared according to claim 1, characterized in that, The electrode material has the chemical formula S-Cu / Cu₂O. Its microstructure consists of nanowires 10-30 nm wide. The nanowires are curved and stacked, creating voids that place the material in a mesoporous state. The specific surface area of ​​this electrode material is 53.06 m². 2 g -1 The specific capacitance is 1800-2408 F / g, and the rate performance is 55%-67%.

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