Preparation method and application of copper oxide nanowire loaded three-dimensional electrode

Abstract

The application discloses a preparation method and application of a three-dimensional electrode loaded with copper oxide nanowires. The method comprises the following steps: firstly, cleaning the copper foam; then, placing the copper foam into a solution to perform an oxidation reaction to obtain a copper hydroxide nanowire / copper foam composite material; and finally, taking the above-mentioned precursor as a template to prepare a copper oxide nanowire / copper foam composite material rich in oxygen vacancies through a hydrothermal reaction. The one-dimensional copper oxide nanowire structure rich in oxygen vacancies can significantly improve the specific surface area and adsorption capacity of a catalytic electrode, optimize the active species generation rate and charge transfer capacity, so that the catalytic electrode has a lower initial potential and Tafel slope in glycerol electro-oxidation reaction, and has excellent formate selectivity.

Description

Technical Field

[0001] This invention belongs to the field of catalyst synthesis and application technology, and relates to a method for preparing a three-dimensional electrode supported on copper oxide nanowires, specifically a method for preparing oxygen-vacancy-rich copper oxide nanowires grown on a copper foam three-dimensional current collector. This invention also relates to the application of this material as a catalytic electrode in the electro-oxidation reaction of glycerol. Background Technology

[0002] With social progress and industrial development, human demand for energy and bulk chemicals continues to grow, leading to the gradual depletion of finite fossil fuels such as crude oil, coal, and natural gas. Furthermore, carbon emissions and environmental degradation caused by fossil fuel use have become urgent global problems that need to be addressed. Developing and utilizing renewable biomass resources holds promise for achieving a sustainable supply of energy and chemicals. Electrocatalytic glycerol oxidation (GOR) is an emerging method for producing formate, which can serve as a complementary strategy to existing industrial formate production methods such as formate methyl ester hydrolysis and CO2 hydrogenation. Simultaneously, anodic GOR coupled with cathodic hydrogen evolution reaction (HER) is considered an energy-saving, low-cost, and efficient hybrid water electrolysis system that can simultaneously produce high-purity hydrogen and formate. However, the GOR reaction involves the adsorption of active hydroxyl species and glycerol (GLY) molecules at limited active sites. Insufficient supply of active hydroxyl species and weak glycerol adsorption capacity hinder the improvement of reaction efficiency. In addition, the competitive oxygen evolution reaction (OER) greatly limits the selectivity of GOR. Therefore, developing highly active and selective electrocatalysts with optimized adsorption sites is key to achieving efficient value-added conversion of glycerol.

[0003] Compared to traditional precious metal powder catalysts, copper-based catalytic electrodes supported on copper foam offer advantages such as low cost, simple preparation methods, and the elimination of the need for binders, making them an excellent alternative catalyst in the catalysis field. However, due to insufficient electrochemical active sites and weak adsorption capacity for glycerol molecules, the GOR performance of copper-based catalysts falls far short of the requirements for practical applications, hindering their widespread adoption. Therefore, there is an urgent need in this field for a highly efficient and stable method for preparing copper-based electrode materials. Summary of the Invention

[0004] Based on the above scientific questions, this invention proposes a method for preparing a three-dimensional electrode supported on copper oxide nanowires, considering both increasing the active surface area and improving the adsorption of active species. Nanowires are one-dimensional materials with high orientation and designable dimensions, possessing high aspect ratios and specific surface areas, as well as self-supporting mechanical properties, making them easy to directly load onto substrates in arrays for catalytic reactions. Researchers constructed copper hydroxide nanowires on a copper foam support using liquid-phase chemical deposition, and then, based on a defect engineering strategy, converted them into oxygen-vacancy-rich copper oxide nanowires via a hydrothermal method. Experimental results show that vacancies can serve as adsorption sites for active hydroxyl species, thereby greatly increasing the number of adsorption sites and enhancing reaction efficiency. Furthermore, vacancies can modulate the d-band center of the catalytic material, promoting the adsorption of active hydroxyl species and glycerol molecules, thus optimizing GOR kinetics.

[0005] The purpose of this invention is to provide a method for preparing a three-dimensional electrode loaded with copper oxide nanowires;

[0006] Another object of the present invention is to provide the application of the catalytic electrode in the electrocatalytic oxidation of glycerol.

[0007] I. Fabrication of Three-Dimensional Electrodes Loaded with Copper Oxide Nanowires

[0008] The method for preparing a three-dimensional electrode supported on copper oxide nanowires proposed in this invention specifically includes the following steps:

[0009] (1) The cut copper foam is placed in ethanol and acetone solutions and ultrasonically treated for 5 min respectively. Then it is ultrasonically treated in 0.5-5.0M hydrochloric acid aqueous solution for 10-60 min. Finally, it is washed with deionized water and used directly for the preparation of catalytic electrode. The thickness of the copper foam is 0.2-2.0 mm, the porosity is 96%, and the pore density is 5-60 PPI.

[0010] (2) Dissolve 80 mmol NaOH and 1–10 mmol K₂S₂O₈ in 30 mL of ultrapure water to obtain a precursor solution. Place the copper foam obtained in step (2) into the solution and maintain it at 0–100 °C for 10–60 min to grow copper hydroxide nanowires. Afterward, wash and dry the prepared sample to obtain a copper hydroxide nanowire / copper foam composite material, denoted as Cu(OH)₂NWs / CF.

[0011] (3) The precursor obtained in step (2) is placed in a hydrothermal reactor for hydrothermal treatment at a temperature of 100–300°C for 1–4 hours. After the temperature drops to room temperature, it is removed to obtain a copper oxide nanowire / copper foam composite material, denoted as V. O -CuO xNWs / CF. The hydrothermal solution is one of H2SO4 solution, ultrapure water or KOH solution, with a pH of 1 to 14.

[0012] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0013] Preferably, the thickness of the copper foam is 0.5 to 1 mm. If the thickness of the copper foam is less than 0.2 mm, its mechanical strength and chemical stability are poor and it is easy to break. If the thickness of the copper foam is greater than 2.0 mm, it will increase the resistance to charge transfer and lead to a decrease in the catalytic activity of the electrode.

[0014] Preferably, the pore density of the copper foam is 20–40 PPI, such as 20 PPI, 25 PPI, 30 PPI, 35 PPI, or 40 PPI. If the pore density of the copper foam is less than 5 PPI, its specific surface area is small, which is not conducive to improving catalytic activity; if the pore density of the copper foam is greater than 60 PPI, its mechanical properties are poor, it is easy to break, resulting in poor catalytic stability.

[0015] Preferably, the concentration of hydrochloric acid in step (1) is 1.0–4.0 M, such as 1.0 M, 1.5 M, 2.0 M, 2.5 M, 3.0 M, 3.5 M, or 4.0 M. If the concentration of hydrochloric acid is less than 0.5 M, it is insufficient to remove the oxide layer on the copper surface, resulting in uneven distribution of the growth material or poor bonding with the carrier; if the concentration of hydrochloric acid is higher than 5.0 M, it may damage the inherent three-dimensional structure of the copper foam, reducing the specific surface area and electron transport capacity.

[0016] Preferably, step (1) involves sonicating in hydrochloric acid solution for 20–40 minutes, such as 20 minutes, 25 minutes, 30 minutes, 35 minutes, or 40 minutes. If the sonication time is less than 10 minutes, it is insufficient to fully remove the oxide layer on the surface of the copper foam, resulting in uneven material growth on the inner surface of the copper foam. If the sonication time is greater than 60 minutes, the three-dimensional structure of the copper foam will deform and collapse to a certain extent, leading to a decrease in its mechanical properties and a reduction in its specific surface area, which is detrimental to subsequent preparation and testing processes.

[0017] Preferably, the amount of K2S2O8 in step (2) is 2-5 mmol. K2S2O8 is a strong oxidizing agent, and its function is to oxidize Cu to Cu. 2+ If the amount of substance is less than 1 mmol, it is difficult to form a dense nanowire structure with a suitable length; if the amount of substance is greater than 10 mmol, the growth rate is too fast, which will form other three-dimensional structures and reduce the specific surface area of ​​the material.

[0018] Preferably, the growth temperature of copper hydroxide nanowires / copper foam in step (2) is 10 to 30°C, such as 10°C, 15°C, 20°C, 25°C or 30°C.

[0019] Preferably, the growth time of copper hydroxide nanowires / copper foam in step (2) is 30-60 min, such as 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, or 60 min. If the reaction time is less than 10 min, the material growth is insufficient and its performance advantages are difficult to demonstrate; if the reaction time is greater than 60 min, larger grains may grow, resulting in uneven morphology and thus reducing the reactivity.

[0020] Preferably, the drying method in step (2) is vacuum drying.

[0021] Preferably, the hydrothermal solution in step (3) is either ultrapure water or KOH solution.

[0022] Preferably, the hydrothermal treatment temperature in step (3) is 180–220°C, such as 180°C, 190°C, 200°C, 210°C, or 220°C. If the hydrothermal temperature is less than 100°C, the precursor copper hydroxide cannot be completely converted into copper oxide; if the hydrothermal temperature is greater than 300°C, the preparation time will be prolonged, which is not conducive to practical application.

[0023] Preferably, the hydrothermal treatment time in step (3) is 1.6 to 2.2 hours, for example, 1.6 hours, 1.8 hours, 2.0 hours or 2.2 hours.

[0024] Preferably, the pH of the hydrothermal treatment solution in step (3) is 7 to 14 h, such as 7, 8, 9, 10, 11, 12, 13 or 14.

[0025] As a further preferred embodiment of the method described in this invention, the method includes the following steps:

[0026] (1) The cut copper foam is placed in ethanol and acetone solutions and ultrasonically treated for 5 min respectively. Then it is ultrasonically treated in 1.0-4.0M hydrochloric acid aqueous solution for 20-40 min. Finally, it is washed with deionized water and used directly for the preparation of catalytic electrode. The thickness of the copper foam is 0.5-1 mm, the porosity is 96%, and the pore density is 20-40 PPI.

[0027] (2) Dissolve 80 mmol NaOH and 2–5 mmol K₂S₂O₈ in 30 mL of ultrapure water to obtain a precursor solution. Place the copper foam obtained in step (2) into the solution and maintain it at 10–30 °C for 30–60 min to grow copper hydroxide nanowires. Afterward, wash and dry the prepared sample to obtain a copper hydroxide nanowire / copper foam composite material, denoted as Cu(OH)₂NWs / CF.

[0028] (3) The precursor obtained in step (2) is placed in a hydrothermal reactor for hydrothermal treatment at a temperature of 180–220°C for 1.6–2.2 h. After the temperature drops to room temperature, it is removed to obtain a copper oxide nanowire / copper foam composite material rich in oxygen vacancies, denoted as V. O -CuO x NWs / CF. The hydrothermal solution is either ultrapure water or KOH solution, with a pH of 7–14.

[0029] II. Characterization of three-dimensional electrodes loaded with copper oxide nanowires.

[0030] 1. X-ray diffraction pattern

[0031] Figure 1 It is the Cu(OH)2NWs / CF and V prepared in Example 1 O -CuO x X-ray diffraction pattern of NWs / CF. From the standard card, it can be seen that the diffraction peaks of Cu(OH)2NWs / CF are attributed to Cu(OH)2 (PDF#80-0656) and Cu (PDF#70-3038), V O -CuO x The diffraction peaks of NWs / CF are attributed to CuO (PDF#89-5898), Cu2O (PDF#65-3288), and Cu (PDF#70-3038). Among them, Cu is derived from copper foam as a support, and the fabricated nanowires are composed of CuO and Cu2O.

[0032] 2. Scanning electron microscope image

[0033] Figure 2 It is the Cu(OH)2NWs / CF and V prepared in Example 1 O -CuO x Scanning electron microscope image of NWs / CF. From Figure 2 It can be seen that Cu(OH)₂NWs / CF consists of uniformly long and evenly distributed nanowires supported on a copper foam framework. After the hydrothermal reaction, V O -CuO x In NWs / CF, the nanowires intertwine and are partially reconstructed into nanosheets.

[0034] 3. Transmission electron microscopy image

[0035] Figure 3 V prepared in Example 1 O -CuO x Transmission electron microscopy mapping of NWs / CF, from Figure 3 As can be seen from the data, Cu and O elements are evenly distributed in V. O -CuO x NWs / CF nanowires.

[0036] 4. X-ray photoelectron spectroscopy image

[0037] Figure 4 It is the Cu(OH)2NWs / CF prepared in Example 1, CuO x NWs / CF and V O -CuO x X-ray photoelectron spectroscopy image of NWs / CF, in which CuO x NWs / CF is a comparative sample obtained by annealing Cu(OH)2NWs / CF at the same temperature for 2 hours. Its oxygen vacancy content is significantly lower than that of V. O -CuO x NWs / CF. From Figure 4 As can be seen from a, the main peaks at 933.40 eV and 935.00 eV belong to Cu, respectively. 0 / Cu + 2p 3 / 2 and Cu 2+ 2p 3 / 2 It can be seen that the prepared sample contains Cu. 0 / Cu + and Cu 2+ This is consistent with the results of the X-ray diffraction pattern. Figure 4 As can be seen from Figure a, the fitted peaks at 529.80, 531.45, and 532.70 eV are attributed to lattice oxygen, oxygen vacancies, and oxygen in adsorbed water, respectively. O -CuO x The oxygen vacancy content in NWs / CF is 72%, indicating a high oxygen vacancy content, while CuO... x The oxygen vacancy content of NWs / CF is 36%.

[0038] III. Electrochemical Performance Testing of Three-Dimensional Electrodes Loaded with Copper Oxide Nanowires

[0039] 1. Step A: Using Ag / AgCl electrode and Pt sheet as reference electrode and counter electrode respectively, and the prepared three-dimensional electrode supported on copper oxide nanowires as working electrode, a three-electrode electrocatalytic glycerol oxidation reaction was carried out. First, the voltage range was set, and cyclic voltammetry (CV) was performed to activate the electrode. After the performance stabilized, the linear voltammetry (LSV) curve was tested.

[0040] Step B: Electrocatalytic oxidation of glycerol was carried out at different potentials using chronoamperometry, followed by product analysis using liquid chromatography to calculate the selectivity of formate at different potentials.

[0041] 2. In step A, the voltage range is 1–2 V vs. RHE (relative to the reversible hydrogen electrode), and the CV scan rate is 0.1 Vs. -1 The LSV scan rate is 5 mV / s. -1 .

[0042] 3. The voltage range in step B is 1.2 to 1.8 V vs. RHE, and the amount of reaction charge is kept constant.

[0043] 4. Electrochemical performance of the working electrode

[0044] The working electrode described above was immersed in a solution of 1 M KOH and 0.3 M GLY, and its electrochemical performance was characterized by LSV curves and Tafel slope. The Cu(OH)₂NWs / CF and V prepared in Example 1... O -CuO x LSV of NWs / CF such as Figure 5 As shown in the figure. It can be seen from the figure that V O -CuO x NWs / CF has the lowest reaction initiation potential of 1.10 V vs. RHE and a current density of 100 mA cm⁻¹. -2 At that time, V O -CuO x The NWs / CF reaction potential is the lowest. This indicates that the V is rich in oxygen vacancies. O -CuO x NWs / CF exhibits optimal electrocatalytic glycerol oxidation performance, attributed to its excellent active species generation rate and charge transfer capability. Figure 6 It can be seen that the V prepared in Example 1 O -CuO x NWs / CF has the lowest Tafel slope of 94.4 mV dec -1 This indicates that the synthesized electrocatalyst V O -CuO x NWs / CF exhibited the best catalytic kinetics, consistent with LSV test results. Figure 7V prepared in Example 1 O -CuO x The product test chromatograms of NWs / CF at different potentials show that formate is the main product of the reaction. 1.60V vs. RHE is the optimal potential for formate production, and the formate selectivity at this potential is calculated to be 95%.

[0045] In summary, this invention first cleans the copper foam, then oxidizes it in a NaOH and K2S2O8 solution to obtain a copper hydroxide nanowire / copper foam composite material Cu(OH)2NWs / CF. Finally, using this precursor as a template, a copper oxide nanowire / copper foam composite material V rich in oxygen vacancies is prepared via a hydrothermal reaction. O -CuO x The oxygen vacancy-optimized one-dimensional copper oxide nanowire structure can significantly improve the specific surface area and adsorption capacity of the catalytic electrode, optimize the generation rate of active species and charge transfer ability. Therefore, this catalytic electrode has a low onset potential and Tafel slope in the electro-oxidation reaction of glycerol, and exhibits excellent formate selectivity. Attached Figure Description

[0046] Figure 1 Cu(OH)₂NWs / CF and V prepared in Example 1 O -CuO x X-ray diffraction pattern of NWs / CF.

[0047] Figure 2 Cu(OH)₂NWs / CF and V prepared in Example 1 O -CuO x Scanning electron microscope image of NWs / CF.

[0048] Figure 3 for Figure 3 V prepared in Example 1 O -CuO x Transmission electron microscopy mapping of NWs / CF.

[0049] Figure 4 Cu(OH)₂NWs / CF and V prepared in Example 1 O -CuO x X-ray photoelectron spectroscopy images of NWs / CF, a for Cu and b for O.

[0050] Figure 5 Cu(OH)₂NWs / CF and V prepared in Example 1 O -CuO x LSV plot of NWs / CF in 1M KOH and 0.3M GLY solutions.

[0051] Figure 6 For the Cu(OH)2NWs / CF and V prepared in Example 1 O -CuO x Tafel slope plot of NWs / CF in 1M KOH and 0.3M GLY solutions.

[0052] Figure 7 V prepared in Example 1 O -CuO x Product test patterns at different potentials of NWs / CF. Detailed Implementation

[0053] The preparation and performance of a three-dimensional electrode supported on copper oxide nanowires according to the present invention will be further illustrated below through specific embodiments.

[0054] Example 1

[0055] (1) The cut copper foam was placed in ethanol and acetone solutions and ultrasonically treated for 5 min each. Then it was ultrasonically treated in 3.0 M hydrochloric acid aqueous solution for 20 min. Finally, it was washed with deionized water and used directly for the preparation of catalytic electrode. The copper foam had a thickness of 0.5 mm, a porosity of 96%, and a pore density of 30 PPI.

[0056] (2) Dissolve 80 mmol NaOH and 4 mmol K2S2O8 in 30 mL of ultrapure water to obtain a precursor solution. Place the copper foam obtained in step (2) into the solution and keep it at 25 °C for 45 min to grow copper hydroxide nanowires. Afterwards, wash and dry the prepared sample to obtain the copper hydroxide nanowire / copper foam composite material Cu(OH)2NWs / CF.

[0057] (3) The precursor obtained in step (2) was placed in a hydrothermal reactor for hydrothermal treatment at a temperature of 200℃ for 2 hours. After the temperature dropped to room temperature, it was removed to obtain a copper oxide nanowire / copper foam composite material rich in oxygen vacancies, denoted as V. O -CuO x NWs / CF. The hydrothermal solution is ultrapure water with a pH of 7.

[0058] (4) Electrochemical performance testing, at a current density of 10 mA / cm² -2 The potential of this catalyst is 1.15 V vs. RHE, and the Tafel slope is 94 mV dec. -1 The formate selectivity was 95% at 1.6V vs. RHE potential.

[0059] Example 2

[0060] The difference from Example 1 is that the hydrochloric acid concentration in step (1) is 4.5M and the ultrasonic time is 40min, while the rest of the steps are the same as in Example 1.

[0061] Electrochemical performance testing was conducted at a current density of 10 mA / cm². -2 The potential of this catalyst is 1.20 V vs. RHE, and the Tafel slope is 105 mV dec. -1 At a potential of 1.6V vs. RHE, the formate selectivity is 90%.

[0062] Example 3

[0063] Unlike Example 1, the thickness of the copper foam in step (1) is 1.5 mm and the pore density is 40 PPI. The remaining steps are the same as in Example 1.

[0064] Electrochemical performance testing was conducted at a current density of 10 mA / cm². -2 The potential of this catalyst is 1.23 V vs. RHE, and the Tafel slope is 113 mV dec. -1 The formate selectivity was 89% at 1.6V vs. RHE potential.

[0065] Example 4

[0066] Unlike Example 1, the amount of K2S2O8 in step (2) is 8 mmol, while the rest of the steps are the same as in Example 1.

[0067] Electrochemical performance testing was conducted at a current density of 10 mA / cm². -2 The potential of this catalyst is 1.19 V vs. RHE, and the Tafel slope is 101 mV dec. -1 The formate selectivity was 92% at 1.6V vs. RHE potential.

[0068] Example 5

[0069] The difference from Example 1 is that the growth temperature in step (2) is 40°C and the growth time is 60 min, while the rest of the steps are the same as in Example 1.

[0070] Electrochemical performance testing was conducted at a current density of 10 mA cm⁻¹. -2 The potential of this catalyst is 1.28 V vs. RHE, and the Tafel slope is 134 mV dec. -1 The formate selectivity was 88% at 1.6V vs. RHE potential.

[0071] Example 6

[0072] Unlike Example 1, the hydrothermal treatment temperature in step (3) is 250°C and the treatment time is 2.2h. The remaining steps are the same as in Example 1.

[0073] Electrochemical performance testing was conducted at a current density of 10 mA / cm². -2 The potential of this catalyst is 1.19 V vs. RHE, and the Tafel slope is 100 mV dec. -1 The formate selectivity was 93% at 1.6V vs. RHE potential.

[0074] Example 7

[0075] Unlike Example 1, the hydrothermal solution in step (3) is an aqueous solution of KOH with pH = 13, while the rest of the steps are the same as in Example 1.

[0076] Electrochemical performance testing was conducted at a current density of 10 mA / cm². -2 The potential of this catalyst is 1.24 V vs. RHE, and the Tafel slope is 109 mV dec. -1 The formate selectivity was 88% at 1.6V vs. RHE potential.

[0077] The above are preferred embodiments of the present invention. Any changes made to the technical solution of the present invention that do not exceed the scope of the technical solution of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a three-dimensional electrode supported on copper oxide nanowires, comprising the following steps: (1) Sonicate the copper foam in ethanol and acetone solutions respectively; The sample was then sonicated in hydrochloric acid solution and finally washed with deionized water before being used directly for the preparation of subsequent catalytic electrodes. (2) Add the copper foam obtained in step (1) to NaOH and K2S2O8 solution to carry out oxidation reaction. Then, wash and dry the sample to obtain copper hydroxide nanowire / copper foam composite material. (3) The precursor obtained in step (2) is subjected to hydrothermal treatment to obtain copper oxide nanowires / copper foam composite material loaded on copper foam.

2. The preparation method according to claim 1, characterized in that: In step (1), the thickness of the copper foam is 0.2 to 2.0 mm, the porosity is 96%, and the pore density is 5 to 60 PPI (average number of pores per unit inch).

3. The preparation method according to claim 1, characterized in that: In step (1), the concentration of HCl in the hydrochloric acid solution is 0.5–5.0 M.

4. The preparation method according to claim 1, characterized in that: In step (2), the amount of K2S2O8 dissolved in 30 mL of ultrapure water is 1 to 10 mmol.

5. The preparation method according to claim 1, characterized in that: In step (3), the temperature of the hydrothermal reaction is 100-300℃.

6. The preparation method according to claim 1, characterized in that: In step (3), the hydrothermal solution is one of H2SO4 solution, ultrapure water or KOH solution, with a pH of 1 to 14.

7. The three-dimensional electrode with copper oxide nanowires prepared by the method described in claim 1 is used in electrocatalytic reactions.

8. The application as described in claim 7, wherein the electrocatalytic reaction is an electrocatalytic glycerol oxidation reaction.

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