A copper cobalt oxide electrode, a preparation method and application thereof in preparation of 2,5-furan dicarboxylic acid

Abstract

The application belongs to the technical field of electrocatalytic oxidation of 5-hydroxymethylfurfural, and particularly relates to a copper-cobalt oxide electrode, a preparation method thereof and application of the electrode in preparation of 2,5-furan dicarboxylic acid. The preparation method of the copper-cobalt oxide electrode comprises the following steps: providing a mixed salt solution in which copper salt and cobalt salt are dissolved, wherein the total concentration of copper ions and cobalt ions contained in the mixed salt solution is 0.1-0.2 mol / L; using the mixed salt solution as an electrolyte, using purified carbon fiber felt as a working electrode, and using Pt as a counter electrode to perform constant potential deposition at room temperature; after the electrodeposition is completed, an electrode precursor with the carbon fiber felt as a matrix is obtained, and copper-cobalt hydroxide is coated on the electrode precursor; and the electrode precursor is calcined in an air atmosphere at 300-310 DEG C to obtain the copper-cobalt oxide electrode. The electrode can be used for electrocatalytic oxidation of 5-hydroxymethylfurfural to prepare 2,5-furan dicarboxylic acid, and the process conditions are mild, the electrode material is low in cost, and the synthesis process is environmentally friendly, so the electrode has a good industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of 5-hydroxymethylfurfural electrocatalytic oxidation technology, specifically relating to a copper-cobalt oxide electrode, its preparation method, and its application in the preparation of 2,5-furandicarboxylic acid. Background Technology

[0002] With the depletion of oil, natural gas, and other fossil fuels, biomass resources have become a major competitor due to their renewability and vast reserves. 5-Hydroxymethylfurfural (HMF) is considered a compound with wide applications, obtainable from biomass resources and possessing significant industrial potential. For example, 2,5-furandicarboxylic acid (FDCA) can be prepared by the oxidation of HMF, a method that promises to be a green alternative to the existing petroleum-based monomer terephthalic acid. Although the oxidation of HMF has been studied for many years, most reports involve high-temperature thermocatalytic conversion using various heterogeneous catalysts containing noble metals (such as Pt, Au, and Pd) under high-pressure O2 conditions. This synthesis method is not only costly and energy-intensive but also poses significant safety risks. Therefore, developing a new FDCA synthesis method with high catalytic activity, high selectivity, and low energy remains a considerable challenge.

[0003] Electrocatalytic oxidation is a green and efficient method that can generate FDCA with high selectivity and high yield at ambient temperature and pressure, and can also simultaneously achieve hydrogen production through low-voltage water electrolysis. This method avoids the explosion hazard caused by excessive O2 use under high temperature and pressure. Furthermore, the electrochemical conversion under ambient temperature and pressure conditions can utilize clean and sustainable water as an oxygen source, transferring active oxygen species from the oxidizing electrocatalyst, thus significantly reducing O2 consumption. Currently, transition metal oxides are widely used in the electrooxidation of small molecules due to their unique eg hybrid orbitals and abundant 3d electrons. CuO, in particular, is a promising electrocatalyst for HMF catalytic oxidation. However, due to the weak adsorption and activation capabilities of OH- and HMF molecules, the inherent HMF oxidation activity of CuO still falls far short of practical requirements. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a copper cobalt oxide electrode, a preparation method, and its application in the preparation of 2,5-furandicarboxylic acid. CuCo2O4 is deposited on a carbon fiber substrate using an electrodeposition method to obtain a dual transition metal composite oxide electrode. This electrode is used for the electrocatalytic oxidation of HMF to prepare FDCA, achieving an HMF conversion rate of up to 97%, an FDCA yield of up to 90%, a selectivity of up to 93%, and a Faradaic efficiency of over 86%. Therefore, the present invention provides a highly catalytically active, highly selective, and low-energy FDCA synthesis method, solving the technical problems of high cost, high energy consumption, and safety hazards existing in the current HMF oxidation process.

[0006] (II) Technical Solution

[0007] In a first aspect, the present invention provides a method for preparing a copper-cobalt oxide electrode, comprising the following steps:

[0008] S1. Provide a mixed salt solution containing dissolved copper and cobalt salts, wherein the total concentration of copper and cobalt ions in the mixed salt solution is 0.1-0.2 mol / L;

[0009] S2. Using a mixed salt solution as the electrolyte, at room temperature, using purified carbon fiber felt as the working electrode and Pt as the counter electrode, constant potential deposition is performed; after electrode deposition, an electrode precursor with carbon fiber felt as the substrate is obtained, and the electrode precursor is coated with copper cobalt hydroxide.

[0010] S3. The electrode precursor is calcined in air at 300-310°C. After calcination, a copper-cobalt oxide electrode is obtained.

[0011] According to a preferred embodiment of the present invention, in S1, the copper salt in the mixed salt solution is copper nitrate, and the cobalt salt is cobalt nitrate; preferably, the molar ratio of copper ions to cobalt ions is 2-8:8-2, more preferably 3:7; the total concentration of copper ions and cobalt ions in the mixed salt solution is 0.1 mol / L. For example, the copper ion concentration is 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, or 0.08 mol / L, more preferably 0.03 mol / L; the cobalt ion concentration is 0.07 mol / L.

[0012] According to a preferred embodiment of the present invention, in S2, the conditions for constant potential deposition are as follows: the stirring speed of the electrolyte is set to 750-850 rpm; using an Ag / AgCl electrode and saturated KCl as reference electrodes, constant potential deposition is performed for 5-10 minutes under conditions where the potential is kept constant at 1.5V-2.5V vs. Ag / AgCl; then the carbon fiber felt is removed to obtain the electrode precursor. By comparing with the reference electrode, the potential on the working electrode can be precisely set and maintained. This ensures that the deposition process proceeds at the predetermined potential, thereby achieving precise control over the type, structure, and morphology of the deposit.

[0013] According to a preferred embodiment of the present invention, in S2, the purified carbon fiber felt refers to the carbon fiber felt being treated as follows: the carbon fiber felt is cut to an appropriate size, ultrasonically cleaned with deionized water, acetone, and anhydrous ethanol for 5-10 minutes each, and then vacuum dried for later use.

[0014] According to a preferred embodiment of the present invention, in S3, the calcination process is as follows: in an air atmosphere, the temperature is raised to 300-310°C at a rate of 2-2.5°C, and calcined at that temperature for 2.5-3.5 hours, and then lowered to room temperature at a rate of 3-4°C to obtain a copper-cobalt oxide electrode.

[0015] Secondly, the present invention provides a copper-cobalt oxide electrode for the electrocatalytic oxidation of HMF to prepare FDCA, which is prepared using any of the above embodiments.

[0016] Thirdly, the present invention also provides a method for preparing FDCA by electrocatalytic oxidation of HMF, comprising: using a copper cobalt oxide electrode prepared in any of the above embodiments as a working electrode, an Hg / HgO electrode as a reference electrode, assembling a three-electrode electrolytic cell with Pt as the counter electrode, and separating the anodic electrolytic cell and the cathode electrolytic cell by an anion exchange membrane.

[0017] A potassium hydroxide solution containing HMF is added to the anolyte, and a potassium hydroxide solution of the same concentration as the anolyte is added to the cathode; the working electrode is installed in the anolyte.

[0018] Under normal pressure, the voltage between the working electrode and the counter electrode is maintained at 1.0-1.5V to carry out the electrolytic reaction and FDCA is obtained in the anodic electrolytic cell; during the electrolytic reaction, the electrolyte temperature in the electrolytic cell is maintained at 20-60℃.

[0019] According to a preferred embodiment of the present invention, the anion exchange membrane is Fumasep FAA-3-PK-130.

[0020] According to a preferred embodiment of the present invention, the initial concentration of potassium hydroxide solution in the anodic and cathodic electrolytic cells is 1.0 mol / L.

[0021] According to a preferred embodiment of the present invention, hydrogen gas is also generated in the cathode electrolyzer.

[0022] According to a preferred embodiment of the present invention, during the electrolysis reaction, the electrolyte temperature in the electrolytic cell is maintained at 20-60°C by continuous stirring and a water bath. Continuous stirring ensures uniform phase distribution and temperature distribution in the solution within the three-electrode electrolytic cell, while the water bath maintains a constant electrolyte temperature. Preferably, the stirring speed is 800-1000 rpm. Controlling this reaction temperature significantly reduces side reactions, improves process safety, and ensures the yield of the target product.

[0023] According to a preferred embodiment of the present invention, the initial concentration of HMF in the anodic electrolyzer is 10-40 mmol / L.

[0024] According to a preferred embodiment of the present invention, during the electrolysis reaction, the electrolyte temperature is maintained at 40°C, the electrolysis voltage is 1.1V, and the electrolysis time is 3 hours or more, preferably 3-5 hours.

[0025] (III) Beneficial Effects

[0026] This invention employs an electrodeposition method to prepare a copper-cobalt oxide electrode with a carbon fiber felt substrate, and applies it to the electrocatalytic oxidation of HMF to prepare the high-value-added fine chemical FDCA. The electrocatalytic oxidation of HMF to FDCA exhibits excellent electrocatalytic oxidation performance, achieving a maximum FDCA yield of 90%, an HMF conversion rate of 97%, a selectivity of 93%, and a Faraday efficiency of 86%. Compared to existing technologies using heterogeneous catalysts with noble metals under high-pressure O2 conditions, the electrocatalytic oxidation method of HMF to FDCA in this invention is not only low-cost and low-energy-consumption, but also boasts high reactant conversion and selectivity, as well as high process safety, making it suitable for large-scale production applications.

[0027] In the copper-cobalt oxide electrode of this invention, copper oxide and cobalt oxide are uniformly intercalated at the nanoscale to form an integral structure in which each serves as both a dissolved and dispersed phase. This composite oxide can provide a large number of interfacial contact areas, which is beneficial for electron transfer and the increase of catalytic active sites, thus helping to improve catalytic efficiency and promote electron transfer (the interface between different materials can optimize the electron transfer path and reduce resistance), thereby increasing the electrochemical reaction rate, promoting synergistic effects, and further improving catalytic performance.

[0028] The high-performance copper-cobalt oxide electrode prepared by this invention combines the excellent properties of transition metal oxides and carbon fiber felt, exhibiting advantages such as good oxidation performance, good corrosion resistance, low cost, and high temperature resistance. The electrode deposition method for electrode preparation offers advantages such as simple operation, mature and controllable process, and readily available and inexpensive raw materials. The process conditions for preparing the copper-cobalt oxide electrode and FDCA using this invention are mild, the electrode materials are inexpensive, and the synthesis process is environmentally friendly, demonstrating excellent prospects for industrial application. Attached Figure Description

[0029] Figure 1 The image shows a SEM image of the copper-cobalt oxide electrode prepared in Example 1.

[0030] Figure 2 The image shows the EDS diagram of the copper-cobalt oxide electrode prepared in Example 1.

[0031] Figure 3 A schematic diagram of an electrolytic reaction cell for the electrocatalytic oxidation of HMF to prepare FDCA. Detailed Implementation

[0032] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] Currently, CuO is commonly used as a catalyst for the catalytic oxidation of HMF. However, due to the weak adsorption and activation capabilities of OH- and HMF molecules, the inherent HMF oxidation activity of CuO is far from meeting practical requirements. Compared to monometallic oxides, bimetallic oxides exhibit synergistic effects, larger specific surface areas, and more active sites, often resulting in higher catalytic activity. Therefore, this invention develops an HMF catalytic oxidation electrode based on copper-cobalt oxide. Existing technologies often employ co-deposition or combustion methods for composite metal oxides. However, for applications requiring precise control of fine structures or composition, co-deposition and combustion methods struggle to achieve ideal accuracy. Co-deposition involves significant randomness, making it almost impossible to obtain composite metal oxides with a predetermined atomic ratio. Combustion methods require strict safety measures due to high temperatures and potential explosion risks. Furthermore, some materials are not suitable for combustion preparation, especially carbon-supported composite materials. Therefore, this invention employs an electrodeposition method to prepare copper-cobalt oxide electrodes. The advantages of electrodeposition are: high controllability: the thickness and composition of the deposited layer can be precisely controlled by adjusting factors such as current density and deposition time; the atomic ratio of different metals in the composite metal oxide electrode can be precisely controlled by preparing an electrolyte with a predetermined composition; good material uniformity: a relatively uniform and smooth surface can be obtained; strong adaptability: applicable to a variety of material systems, including metallic and non-metallic materials; and high flexibility: easy to achieve the deposition of complex shaped parts.

[0034] In selecting the substrate material for the copper-cobalt oxide electrode, this invention uses carbon fiber felt. Compared to other porous and conductive metal foam materials, carbon fiber felt offers the following advantages: High specific surface area: Carbon fiber felt has a very high specific surface area, which is beneficial for increasing the catalyst loading and thus enhancing catalytic activity. The network of pores throughout the carbon fiber felt helps increase the electrolyte contact area and provides channels for gas diffusion. Good conductivity: Carbon fiber felt itself is an excellent conductor, effectively promoting electron transfer and improving electrochemical reaction efficiency. High mechanical strength: Carbon fiber felt possesses excellent mechanical properties, including high strength and lightweight characteristics. Good corrosion resistance: Compared to metal foam materials, carbon fiber felt exhibits superior stability and durability against many chemicals. Easy processing: Complex structures can be formed through weaving, winding, etc., facilitating the design of electrodes of different shapes (such as O-type or U-type electrodes) and sizes. It has strong bonding with specific types of catalysts. Currently, only nickel metal foam materials have a relatively mature preparation process and low cost, while other metal foams are expensive. Furthermore, the high density of metal foam can increase the overall electrode weight. Although metal foam is porous, it cannot form a through-network of pores, resulting in poor electrolyte contact and gas diffusion. The metal foam substrate also presents potential corrosion problems, which can reduce its service life. In terms of application flexibility, metal foam materials are not very flexible and cannot be easily shaped into various forms as needed, limiting their ability for customized design. Therefore, this invention chooses carbon fiber felt as the electrode substrate material to prepare a copper-cobalt oxide electrode.

[0035] The present invention will be described below with reference to preferred embodiments. The anion exchange membrane Fumasep FAA-3-PK-130 used in the embodiments was purchased from Shanghai Zijun Technology Co., Ltd.

[0036] Example 1

[0037] This embodiment uses hydrophilic carbon fiber felt as a substrate and prepares a copper-cobalt oxide catalytic electrode by constant potential electrodeposition. This catalytic electrode is then used as the anode for the electrolytic synthesis of FDCA from HMF. This embodiment includes the following steps:

[0038] (1) Preparation of copper-cobalt oxide catalytic electrode

[0039] Cut the hydrophilic carbon fiber felt into 1cm×1.5cm pieces, clean them sequentially with 20mL each of deionized water, acetone, and anhydrous ethanol in an ultrasonic bath for 10min, and then dry them in a vacuum desiccator for later use.

[0040] A constant potential deposition process was performed using carbon fiber felt as the working electrode, an Ag / AgCl electrode (saturated KCl) as the reference electrode, and a Pt sheet as the counter electrode. The electrolyte contained 0.03 mol / L Cu(NO3)2·3H2O and 0.07 mol / L Co(NO3)2·6H2O dissolved in it. During electrodeposition, the electrolyte was continuously stirred at 800 rpm, and deposition was carried out at a constant potential of 2.0 V vs. Ag / AgCl for 5 min to obtain the Cu-Co hydroxide electrode precursor.

[0041] The electrode precursor was placed in a quartz boat and then placed in a tube furnace. Under air atmosphere, the heating rate was controlled at 2℃ / min. When the temperature reached 300℃, it was calcined for 3 hours. After the reaction was complete, the cooling rate was controlled at 3℃ / min until the temperature reached room temperature, finally obtaining the copper-cobalt oxide electrode. Figure 1 and Figure 2 The images shown are SEM and EDS images of the copper-cobalt oxide electrode prepared in this embodiment. The images show that various different atoms are intercalated to form an overall structure in which the dissolved phase and the dispersed phase are mutually integrated.

[0042] (2) Electrocatalytic oxidation of HMF to synthesize FDCA

[0043] Using the copper-cobalt oxide electrode prepared in the above steps as the working electrode, the Hg / HgO electrode as the reference electrode, and the Pt electrode as the counter electrode, a three-electrode electrolytic cell is assembled (e.g., Figure 3 (See schematic diagram). The anolyte and catholyte are separated by an anion exchange membrane. A potassium hydroxide solution containing 20 mmol / L HMF (potassium hydroxide concentration 1.0 mol / L) is added to the anolyte, and a 1.0 mol / L potassium hydroxide solution is added to the catholyte. The working electrode is installed in the anolyte, and the counter electrode is installed in the catholyte. The voltage between the working and counter electrodes is maintained at 1.1 V under normal pressure for 3 hours, yielding FDCA in the anolyte. During the electrolysis, the electrolyte is continuously stirred at 800 rpm, and both the anolyte and catholyte are kept at a constant temperature of 40°C using a water bath. After 3 hours of electrolysis, the yield of FDCA in the anolyte is quantitatively determined by liquid chromatography. The yield, selectivity, and Faraday efficiency of FDCA were measured to be 91%, 97%, and 89%, respectively.

[0044] Example 2

[0045] This embodiment uses hydrophilic carbon fiber felt as a substrate and prepares a copper-cobalt oxide catalytic electrode by constant potential electrodeposition. This catalytic electrode is then used as the anode for the electrolytic synthesis of FDCA from HMF. Specifically, the process includes the following steps:

[0046] (1) Preparation of copper-cobalt oxide catalytic electrode

[0047] Cut the hydrophilic carbon fiber felt into 1cm×1.5cm pieces, clean them sequentially with 20mL each of deionized water, acetone, and anhydrous ethanol in an ultrasonic bath for 10min, and then dry them in a vacuum desiccator for later use.

[0048] A constant potential deposition process was performed using carbon fiber felt as the working electrode, an Ag / AgCl electrode (saturated with KCl) as the reference electrode, and a Pt sheet as the counter electrode. The electrolyte contained 0.06 mol / L Cu(NO3)2·3H2O and 0.04 mol / L Co(NO3)2·6H2O dissolved in it. During electrodeposition, the electrolyte was continuously stirred at 800 rpm, and deposition was carried out at a constant potential of 2.0 V vs. Ag / AgCl for 5 min to obtain the Cu-Co hydroxide electrode precursor.

[0049] The electrode precursor was placed in a quartz boat and then placed in a tube furnace. Under air atmosphere, the heating rate was controlled at 2℃ / min. When the temperature reached 300℃, it was calcined for 3 hours. After the reaction was completed, the cooling rate was controlled at 3℃ / min until the temperature dropped to room temperature, finally obtaining the copper-cobalt oxide electrode.

[0050] (2) Electrocatalytic oxidation of HMF to synthesize FDCA

[0051] Following the method and conditions for the electrocatalytic oxidation of HMF to synthesize FDCA in Example 1, FDCA was finally obtained in the anolyte. After electrolysis, the yield of FDCA in the anolyte was quantitatively determined by liquid chromatography. The yield, selectivity, and Faraday efficiency of FDCA were measured to be 73%, 88.2%, and 79.3%, respectively.

[0052] Example 3

[0053] This embodiment uses hydrophilic carbon fiber felt as a substrate and prepares a copper-cobalt oxide catalytic electrode by constant potential electrodeposition. This catalytic electrode is then used as the anode for the electrolytic synthesis of FDCA from HMF. Specifically, the process includes the following steps:

[0054] (1) Preparation of copper-cobalt oxide catalytic electrode

[0055] The copper-cobalt oxide catalytic electrode was prepared according to the same method and conditions as step (1) in Example 1.

[0056] (2) Electrocatalytic oxidation of HMF to synthesize FDCA

[0057] A three-electrode electrolytic cell was assembled using the copper-cobalt oxide electrode prepared in the above steps as the working electrode, an Hg / HgO electrode as the reference electrode, and a Pt electrode as the counter electrode. An anion exchange membrane separated the anolyte and cathode electrolytic cells. A potassium hydroxide solution containing 30 mmol / L HMF (potassium hydroxide concentration 1.0 mol / L) was added to the anolyte, and a 1.0 mol / L potassium hydroxide solution was added to the cathode electrolytic cell. The working electrode was installed in the anolyte, and the counter electrode was installed in the cathode electrolytic cell. The voltage between the working and counter electrodes was maintained at 1.5 V under normal pressure for 3 hours, yielding FDCA in the anolyte. During the electrolysis, the electrolyte was continuously stirred at 800 rpm, and the anolyte and cathode electrolytic cells were kept at a constant temperature of 30°C using a water bath. After 3 hours of electrolysis, the yield of FDCA in the anolyte was quantitatively determined by liquid chromatography. The yield, selectivity, and Faraday efficiency of FDCA were measured to be 70%, 81%, and 70.7%, respectively.

[0058] Example 4

[0059] This embodiment uses hydrophilic carbon fiber felt as a substrate and prepares a copper-cobalt oxide catalytic electrode by constant potential electrodeposition. This catalytic electrode is then used as the anode for the electrolytic synthesis of FDCA from HMF. Specifically, the process includes the following steps:

[0060] (1) Preparation of copper-cobalt oxide catalytic electrode

[0061] Cut the hydrophilic carbon fiber felt into 1cm×1.5cm pieces, clean them sequentially with 20mL each of deionized water, acetone, and anhydrous ethanol in an ultrasonic bath for 10min, and then dry them in a vacuum desiccator for later use.

[0062] A constant potential deposition process was performed using carbon fiber felt as the working electrode, an Ag / AgCl electrode (saturated KCl) as the reference electrode, and a Pt sheet as the counter electrode. The electrolyte contained 0.02 mol / L Cu(NO3)2·3H2O and 0.08 mol / L Co(NO3)2·6H2O dissolved in it. During electrodeposition, the electrolyte was continuously stirred at 800 rpm, and deposition was carried out at a constant potential of 2.0 V vs. Ag / AgCl for 5 min to obtain the Cu-Co hydroxide electrode precursor. The electrode precursor was placed in a quartz boat and then placed in a tube furnace. Under air atmosphere, the heating rate was controlled at 2 °C / min. After the temperature reached 300 °C, calcination was carried out for 3 h. After the reaction was completed, the cooling rate was controlled at 3 °C / min until the temperature reached room temperature, finally yielding the copper-cobalt oxide electrode.

[0063] (2) Electrocatalytic oxidation of HMF to synthesize FDCA

[0064] Following the method and conditions for the electrocatalytic oxidation of HMF to synthesize FDCA in Example 1, FDCA was finally obtained in the anolyte. After electrolysis, the yield of FDCA in the anolyte was quantitatively determined by liquid chromatography. The yield, selectivity, and Faraday efficiency of FDCA were measured to be 84%, 90.3%, and 86.6%, respectively.

[0065] Example 5

[0066] This embodiment uses hydrophilic carbon fiber felt as a substrate and prepares a copper-cobalt oxide catalytic electrode by constant potential electrodeposition. This catalytic electrode is then used as the anode for the electrolytic synthesis of FDCA from HMF. Specifically, the process includes the following steps:

[0067] (1) Preparation of copper-cobalt oxide catalytic electrode

[0068] Cut the hydrophilic carbon fiber felt into 1cm×1.5cm pieces, clean them sequentially with 20mL each of deionized water, acetone, and anhydrous ethanol in an ultrasonic bath for 10min, and then dry them in a vacuum desiccator for later use.

[0069] A constant potential deposition process was performed using carbon fiber felt as the working electrode, an Ag / AgCl electrode (saturated KCl) as the reference electrode, and a Pt sheet as the counter electrode. The electrolyte contained 0.05 mol / L Cu(NO3)2·3H2O and 0.05 mol / L Co(NO3)2·6H2O. During electrodeposition, the electrolyte was continuously stirred at 800 rpm, and deposition was carried out at a constant potential of 2.0 V vs. Ag / AgCl for 5 min to obtain the Cu-Co hydroxide electrode precursor. The electrode precursor was placed in a quartz boat and then placed in a tube furnace. Under air atmosphere, the heating rate was controlled at 2 °C / min. When the temperature reached 300 °C, calcination was carried out for 3 h. After the reaction was completed, the cooling rate was controlled at 3 °C / min until the temperature reached room temperature, finally obtaining the copper-cobalt oxide electrode.

[0070] (2) Electrocatalytic oxidation of HMF to synthesize FDCA

[0071] Following the method and conditions for the electrocatalytic oxidation of HMF to synthesize FDCA in Example 1, FDCA was finally obtained in an anolyte. After electrolysis, the yield of FDCA in the anolyte was quantitatively determined by liquid chromatography. The yield, selectivity, and Faraday efficiency of FDCA were measured to be 82%, 87.8%, and 78.5%, respectively.

[0072] Example 6

[0073] This embodiment uses hydrophilic carbon fiber felt as a substrate and prepares a copper-cobalt oxide catalytic electrode by constant potential electrodeposition. This catalytic electrode is then used as the anode for the electrolytic synthesis of FDCA from HMF. Specifically, the process includes the following steps:

[0074] (1) Preparation of copper-cobalt oxide catalytic electrode

[0075] The copper-cobalt oxide catalytic electrode was prepared according to the same method and conditions as step (1) in Example 1.

[0076] (2) Electrocatalytic oxidation of HMF to synthesize FDCA

[0077] Using the copper-cobalt oxide electrode prepared in the above steps as the working electrode, an Hg / HgO electrode as the reference electrode, and a Pt electrode as the counter electrode, a three-electrode electrolytic cell was assembled. The anolyte and cathode electrolytic cells were separated by an anion exchange membrane. A potassium hydroxide solution containing 20 mmol / L HMF (potassium hydroxide concentration 1.0 mol / L) was added to the anolyte, and a 1.0 mol / L potassium hydroxide solution was added to the cathode electrolytic cell. The working electrode was installed in the anolyte, and the counter electrode was installed in the cathode electrolytic cell. The voltage between the working and counter electrodes was maintained at 1.2 V under normal pressure for 4 hours, yielding FDCA in the anolyte. During the electrolysis reaction, the electrolyte was continuously stirred at 800 rpm, and the anolyte and cathode electrolytic cells were kept at a constant temperature of 60℃ using a water bath. After 3 hours of electrolysis, the yield of FDCA in the anolyte was quantitatively determined by liquid chromatography. The yield, selectivity, and Faraday efficiency of FDCA were measured to be 76%, 83.4%, and 73.9%, respectively.

[0078] The comparison of the above examples reveals that when preparing the copper-cobalt oxide electrode, the optimal electrocatalytic efficiency is achieved when the molar ratio of copper ions to cobalt ions is 3:7 and the total concentration of copper and cobalt ions in the mixed salt solution is 0.1 mol / L, with the electrodeposition potential constant at 2.0 V vs. Ag / AgCl for 300 s. Furthermore, when using this cobalt oxide electrode to electrocatalyze the oxidation of HMF to prepare FDCA, the anolyte consisted of a 1.0 mol / L potassium hydroxide solution and a 20 mmol / L HMF solution. The electrolysis temperature was constant at 40 °C, and the voltage was 1.1 V for 3 h. This resulted in the highest yield, selectivity, and Faraday efficiency of the final target product, FDCA.

[0079] Comparative Example 1

[0080] This comparative example replaces the carbon fiber felt with copper foam of the same size, based on Example 1. The copper foam was then cleaned sequentially with 20 mL each of deionized water, acetone, and anhydrous ethanol in an ultrasonic bath for 10 min, and dried in a vacuum desiccator for later use. Next, the method and conditions for preparing the copper-cobalt oxide electrode in Example 1 were followed to prepare a copper-cobalt oxide electrode based on copper foam. Using the prepared copper-cobalt oxide electrode as the anode, electrocatalytic oxidation of HMF to FDCA was performed according to step (2) in Example 1. After electrolysis, the yield of FDCA in the anolyte was quantitatively detected by liquid chromatography. The yield, selectivity, and Faradaic efficiency of FDCA were measured to be 84.2%, 87.8%, and 79.9%, respectively. During the preparation of the copper-cobalt oxide electrode from the calcined electrode precursor, the conductivity of the copper foam decreased significantly due to the formation of a large amount of cuprous oxide on its surface, resulting in a significant decrease in the catalytic performance and Faradaic efficiency of the electrode.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a copper-cobalt oxide electrode, characterized in that, Includes the following steps: S1. Provide a mixed salt solution containing dissolved copper and cobalt salts, wherein the total concentration of copper and cobalt ions in the mixed salt solution is 0.1 mol / L and the molar ratio of copper ions to cobalt ions is 3:7; S2. Using a mixed salt solution as the electrolyte, at room temperature, using purified carbon fiber felt as the working electrode and Pt as the counter electrode, constant potential deposition is performed; after electrode deposition, an electrode precursor with carbon fiber felt as the substrate is obtained, and the electrode precursor is coated with copper cobalt hydroxide. The conditions for constant potential deposition are as follows: using Ag / AgCl electrode and saturated KCl as reference electrodes, constant potential deposition is performed for 5-10 min under the condition of constant potential deposition at 1.5V-2.5V vs. Ag / AgCl, and then the carbon fiber felt is removed to obtain the electrode precursor. S3. The electrode precursor is calcined in air at 300-310°C. After calcination, a copper-cobalt oxide electrode is obtained.

2. The preparation method according to claim 1, characterized in that, In S2, the stirring speed of the electrolyte during the constant potential deposition process is 750-850 rpm.

3. The preparation method according to claim 1, characterized in that, In S2, the purified carbon fiber felt refers to the carbon fiber felt being treated as follows: cut the carbon fiber felt to an appropriate size, ultrasonically clean it for 5-10 minutes each with deionized water, acetone, and anhydrous ethanol, and then vacuum dry it for later use.

4. The preparation method according to claim 1, characterized in that, In S3, the calcination process is as follows: in an air atmosphere, the temperature is raised to 300-310℃ at a rate of 2-2.5℃, and calcined at that temperature for 2.5-3.5h. Then, the temperature is lowered to room temperature at a rate of 3-4℃ to obtain a copper-cobalt oxide electrode.

5. A copper-cobalt oxide electrode for the electrocatalytic oxidation of 5-hydroxymethylfurfural to prepare 2,5-furandicarboxylic acid, which is prepared by the preparation method according to any one of claims 1-4.

6. A method for preparing 2,5-furandicarboxylic acid by electrocatalytic oxidation of 5-hydroxymethylfurfural, characterized in that, include: Using the copper-cobalt oxide electrode as described in claim 5 as the working electrode, the Hg / HgO electrode as the reference electrode, and Pt as the counter electrode, a three-electrode electrolytic cell is assembled, with an anion exchange membrane separating the anode electrolytic cell and the cathode electrolytic cell. A potassium hydroxide solution containing HMF is added to the anolyte, and a potassium hydroxide solution of the same concentration as the anolyte is added to the cathode; the working electrode is installed in the anolyte. Under normal pressure, the voltage between the working electrode and the counter electrode is maintained at 1.0-1.5V to carry out the electrolytic reaction and FDCA is obtained in the anodic electrolytic cell; during the electrolytic reaction, the electrolyte temperature in the electrolytic cell is maintained at 20-60℃.

7. The method according to claim 6, characterized in that, The initial concentration of potassium hydroxide solution in the anodic and cathodic electrolytic cells is 1.0 mol / L.

8. The method according to claim 6, characterized in that, During the electrolysis reaction, the electrolyte temperature in the electrolytic cell is maintained at 20-60℃ by continuous stirring and constant water bath temperature; the stirring speed is 800-1000 rpm.

9. The method according to claim 6, characterized in that, The initial concentration of HMF in the anodic electrolyzer is 10-40 mmol / L; a hydrogen collection device is installed in the cathode electrolyzer.

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