Ni-Co LDH redox mediator, modular electrochemical synthesis system and construction method thereof

Abstract

The present invention provides a Ni-Co LDH redox medium, a modular electrochemical synthesis system and a construction method thereof. The preparation of the redox medium comprises: dissolving nickel nitrate hexahydrate and cobalt chloride hexahydrate in a methanol-ultrapure water mixed solution and stirring vigorously, adding hexadecyltrimethylammonium bromide and stirring, and performing hydrothermal reaction, cooling, washing and drying to obtain the Ni-Co LDH redox medium. The present invention synthesizes Ni-Co LDH as a solid redox medium through one-step hydrothermal synthesis, and constructs a system for modular synthesis of H2O2 and FDCA in an alkaline electrolyte. The Ni-Co LDH redox medium electrode converts between a reduced state and an oxidized state through a reversible redox reaction, accompanied by OH ‑ Ion adsorption / desorption. The Ni-Co LDH redox mediator electrode selectively stores and transports hydroxide ions involved in the target half-reaction through reversible conversion with NiOOH and CoOOH. This enables modular production of higher-value chemicals, H2O2 and FDCA, while maintaining ionic balance.

Description

Technical Field

[0001] The present invention relates to the technical field of modular electrochemical synthesis systems, and in particular to a Ni-Co LDH redox medium, a modular electrochemical synthesis system and a construction method thereof. Background Art

[0002] "Paired electrolysis" refers to the production of valuable products at both the anode and cathode. Paired electrolysis methods have been deployed industrially on both large and small scales. Electrochemical production of chemicals using renewable electricity offers sustainability advantages over traditional chemical manufacturing, particularly for small-scale, distributed, on-site production of high-value chemicals. This modular electrochemical synthesis model decouples the cathode and cathode of traditional electrochemical synthesis reactions by pairing a solid reversible redox mediator with the anodic oxidation reaction and the cathodic reduction reaction, respectively. If the solid redox mediator is in a high-valent state, it can couple with the anodic reaction in the first step to produce the anodic product and the reduced form of the mediator. Subsequently, the reduced redox mediator couples with the cathodic reaction, providing the necessary electrons to drive the cathodic reduction reaction. Conversely, coupling the original low-valent redox mediator with the cathode can first produce the cathodic reduction product, which is then reduced to its original state by coupling with the anodic reaction. This allows the cathode and anodic reactions to occur at different times and even locations, and the cathode reaction rate is not limited by the anode. This also avoids the use of expensive ion exchange membranes and allows for flexibility in adapting to the volatility of renewable clean energy.

[0003] Solid redox mediators consist of charge-carrying redox-active materials that can reversibly store and release electrons and ions (e.g., Na + 、H + OH - ) to realize complete electrochemical reactions using independent half-reactions of our choice. Key to modular electrochemical synthesis is the use of solid redox mediators. Similar to reservoirs used in pumped-storage power plants, redox reservoirs allow for the temporary storage of electrons and chemical ions, redirecting their activity to execute electrochemical half-reactions at varying times, locations, and scales. Currently, research has shown that sodium nickel hexacyanoferrate (NaNiHCF) can serve as a stable and reversible solid redox mediator, pairing with oxidation and reduction half-reactions to enable modular electrochemical synthesis of diverse chemical species. For example, sodium nickel hexacyanoferrate can be used as a stable and reversible solid redox mediator in combination with different anode and cathode electrochemical reactions to modularly produce several strong oxidants (hydrogen peroxide (H2O2), sodium persulfate, or active chlorine). Hydrogen peroxide, a strong oxidant, is suitable for medical wound disinfection, environmental disinfection, and food sterilization in its aqueous solution.

[0004] Furthermore, the growing demand for petrochemicals and the widespread depletion of fossil fuels have stimulated significant interest in developing sustainable alternatives. Biomass, an abundant renewable resource, is considered a promising alternative to fossil fuels for the production of sustainable chemicals. 5-Hydroxymethylfurfural (HMF) is one of the most extensively studied biomass-derived platform molecules, widely used in the production of pharmaceutical intermediates, polymer monomers, and agrochemicals. 2,5-Furancarboxylic acid (FDCA), the oxidation product of 5-HMF, is an important polymer monomer. FDCA is a favorable building block for the synthesis of polyethylene, thereby replacing petroleum-based polyethylene terephthalate (PET), possessing significant economic and environmental value. Therefore, achieving modular production of higher-value chemicals such as H2O2 and FDCA is of great significance. Summary of the Invention

[0005] The purpose of the present invention is to provide a Ni-Co LDH redox mediator, a modular electrochemical synthesis system and a construction method thereof, firstly synthesizing the Ni-Co LDH redox mediator by a one-step hydrothermal method, and then constructing a modular system for synthesizing H2O2 and FDCA in an alkaline electrolyte. The Ni-Co LDH redox mediator electrode converts between the reduced state and the oxidized state through a reversible redox reaction, accompanied by OH - The adsorption / desorption of ions enables modular production of higher value chemicals H2O2 and FDCA.

[0006] The present invention solves the technical problem by adopting the following technical solutions.

[0007] The present invention provides a method for preparing a Ni-Co LDH redox medium, comprising the following steps:

[0008] Nickel nitrate hexahydrate and cobalt chloride hexahydrate were dissolved in a methanol-ultrapure water mixed solution and stirred vigorously for 15-25 minutes, and then hexadecyltrimethylammonium bromide was added and stirred for 50-70 minutes. After hydrothermal reaction, cooling, washing, and drying, a Ni-Co LDH redox medium was obtained.

[0009] The present invention provides a Ni-Co LDH redox medium, which is prepared according to the preparation method of the Ni-Co LDH redox medium.

[0010] The present invention provides a method for constructing a modular electrochemical synthesis system, wherein the modular electrochemical synthesis system includes a H2O2 electrolytic cell and a 2,5-furancarboxylic acid electrolytic cell, and comprises the following steps:

[0011] S1. Dispersing the Ni-Co LDH redox medium in a nitrogen methyl pyrrolidone solution, then adding a polyvinylidene fluoride binder and an acetylene black solution to obtain a mixed solution, and finally dropping the mixed solution onto nickel foam, drying, and pressing to obtain the Ni-Co LDH redox medium electrode;

[0012] S2. Dispersing nickel acetate tetrahydrate, ferrous sulfate heptahydrate, and terephthalic acid in a mixed solution of N,N-dimethylacetamide and deionized water, subjecting the mixture to a hydrothermal reaction at 140-160° C. for 2.5-3.5 h after ultrasonic treatment, cooling, washing, drying, grinding, and pyrolysis to obtain Ni-Fe-MOF NSs-300, and then dispersing the Ni-Fe-MOF NSs-300 and carbon black in an isopropyl alcohol and Nafion solution, subjecting the mixture to ultrasonic treatment for 25-35 min to obtain ink, and finally adding the ink dropwise onto carbon paper and drying to obtain a Ni-Fe-MOF NSs-300 electrode;

[0013] S3, adding nickel chloride hexahydrate and vanadium chloride to deionized water and stirring, adding urea and then ultrasonically treating, then placing together with nickel foam in a stainless steel autoclave for hydrothermal reaction at 110-130° C. for 11-13 hours, cooling, washing, and drying to obtain a NiV-LDH / NF electrode;

[0014] S4. Using the Ni-Co LDH redox mediator electrode as a counter electrode, the Ni-Fe-MOF NSs-300 electrode as a working electrode, and a NaOH solution as an electrolyte, a H2O2 electrolytic cell is obtained; then taking out the Ni-Co LDH redox mediator electrode that is charged and oxidized in the H2O2 electrolytic cell as a counter electrode, the NiV-LDH / NF electrode as a working electrode, and a mixed solution of KOH and 5-hydroxymethylfurfural as an electrolyte to obtain a 2,5-furancarboxylic acid electrolytic cell.

[0015] The present invention provides a modular electrochemical synthesis system, which is prepared according to the construction method.

[0016] The beneficial effects of the Ni-Co LDH redox mediator, modular electrochemical synthesis system, and construction method thereof according to the embodiments of the present invention are:

[0017] The present invention synthesizes Ni-Co LDH as a solid redox medium through one-step hydrothermal synthesis and constructs a modular system for synthesizing H2O2 and FDCA in an alkaline electrolyte. The Ni-Co LDH redox medium electrode transforms between the reduced state and the oxidized state through a reversible redox reaction, accompanied by OH -Ion adsorption / desorption. The modular electrochemical synthesis system for H2O2 and FDCA involves a two-step EC-(EC / C) cycle. The reversible redox reaction of the Ni-Co LDH redox mediator electrode is first coupled with the H2O2 electrosynthesis reaction (HPR) and then with the HMF electrosynthesis of FDCA reaction (HMFOR). The Ni-Co LDH redox mediator electrode selectively stores and transports hydroxide ions involved in the target half-reaction through reversible conversion with NiOOH and CoOOH. This enables modular production of higher-value chemicals, H2O2 and FDCA, while maintaining ionic balance. Furthermore, when the Ni-Co LDH redox mediator electrode is oxidized to NiOOH and CoOOH and paired with FDCA synthesis, the NiOOH and CoOOH themselves exhibit significant spontaneous direct chemical oxidation of HMF to FDCA. The Ni-Co LDH redox mediator electrode, while serving as a redox mediator to construct an efficient modular electrochemical synthesis system, can also spontaneously and directly oxidize HMF to FDCA. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 is a flow chart of the modular electrochemical synthesis system of the present invention;

[0020] Figure 2 is a schematic diagram of the modular electrochemical synthesis system of the present invention;

[0021] Figure 3 This is the XRD pattern of the Ni-Co LDH redox medium of Example 1 of the present invention;

[0022] Figure 4 This is a SEM image of the Ni-Co LDH redox medium of Example 1 of the present invention;

[0023] Figure 5 CV curves of the Ni-Co LDH redox mediator electrode of Example 2 of the present invention at different scan rates in a 1.0 M NaOH aqueous solution;

[0024] Figure 6 This is a representative constant current discharge curve of the Ni-Co LDH redox mediator electrode in 1 M NaOH solution according to Example 2 of the present invention;

[0025] Figure 7 This is a rate performance diagram of the Ni-Co LDH redox mediator electrode of Example 2 of the present invention;

[0026] Figure 8 Graph showing the cycling stability of the Ni-Co LDH redox mediator electrode according to Example 2 of the present invention;

[0027] Figure 9 Graphs showing the constant current charge curve of the Ni-Co LDH redox mediator electrode in Example 2 of the present invention in a 1 M NaOH solution at the cathode and the constant current discharge curve in a 1 M KOH + 10 mM HMF solution at the anode;

[0028] Figure 10 20 cycles of constant current charge and discharge of the Ni-Co LDH redox mediator electrode according to Example 2 of the present invention;

[0029] Figure 11 The chronopotentiometry curves of the electrodes in the H2O2 electrolytic cell and the FDCA electrolytic cell during the modular electrochemical synthesis process are shown;

[0030] Figure 12 The average potential of the Ni-Co LDH redox mediator electrode and the corresponding average cell voltage of the H2O2 electrolysis cell and the FDCA electrolysis cell during 20 modular electrochemical syntheses;

[0031] Figure 13 The Coulombic efficiency of the Ni-Co LDH redox mediator electrode during 20 modular electrochemical syntheses and the voltage efficiency diagram of the modular electrosynthesis system;

[0032] Figure 14 The H2O2 production and Faraday efficiency diagram during 20 modular electrochemical synthesis processes;

[0033] Figure 15 Figure 2 shows the FDCA yield and the amount of electricity applied in each cycle during the 20 modular electrochemical syntheses. DETAILED DESCRIPTION

[0034] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0035] The following is a detailed description of the Ni-Co LDH redox medium, modular electrochemical synthesis system, and construction method thereof according to the embodiments of the present invention.

[0036] The present invention provides a method for preparing a Ni-Co LDH redox medium, comprising the following steps:

[0037] Nickel nitrate hexahydrate and cobalt chloride hexahydrate are dissolved in a methanol-ultrapure water mixture and stirred vigorously for 15-25 minutes. Cetyltrimethylammonium bromide is then added and stirred for 50-70 minutes. The mixture undergoes a hydrothermal reaction, is cooled, cleaned, and dried to obtain a Ni-Co LDH redox medium. The hydrothermal reaction is carried out in a 50 mL Teflon-lined stainless steel autoclave, and the product is cooled naturally to room temperature. The substrate is then centrifuged and washed multiple times with ultrapure water and anhydrous ethanol to remove excess impurities. The resulting precipitate is then dried in a vacuum drying oven at 60°C overnight to obtain the Ni-Co LDH redox medium.

[0038] Furthermore, in a preferred embodiment of the present invention, the mass-to-volume ratio of the nickel nitrate hexahydrate, the cobalt chloride hexahydrate, the methanol-ultrapure water mixed solution, and the cetyltrimethylammonium bromide is 1.8-1.9:1:550-650:14-16 (g / g / mL / g), wherein the volume ratio of methanol to ultrapure water in the methanol-ultrapure water mixed solution is 3.5-4.5:1. Preferably, the volume ratio of methanol to ultrapure water in the methanol-ultrapure water mixed solution is 4:1.

[0039] Furthermore, in a preferred embodiment of the present invention, the hydrothermal reaction temperature is 170-190° C., and the reaction time is 22-26 hours. Preferably, the hydrothermal reaction temperature is 180° C., and the reaction time is 24 hours.

[0040] The present invention also provides a Ni-Co LDH redox medium, which is prepared according to the preparation method of the Ni-Co LDH redox medium.

[0041] The present invention also provides a method for constructing a modular electrochemical synthesis system, wherein the modular electrochemical synthesis system comprises a H2O2 electrolytic cell (Cell H2O2 ) and 2,5-furancarboxylic acid electrolytic cell (Cell FDCA ), including the following steps:

[0042] S1. Disperse the Ni-Co LDH redox mediator in a nitrogen-methyl pyrrolidone solution, then add a polyvinylidene fluoride (PVDF) binder and an acetylene black solution to obtain a mixed solution. Finally, dropwise add the mixed solution onto a pretreated nickel foam (10×10 mm), dry, and press to obtain the Ni-Co LDH redox mediator electrode. The acetylene black solution of the present invention is prepared by dispersing acetylene black in a nitrogen-methyl pyrrolidone solution, wherein the concentration of the acetylene black solution is 10 mg / mL. The mass-to-volume ratio of the Ni-Co LDH redox mediator, nitrogen-methyl pyrrolidone solution, PVDF binder, and acetylene black solution is 1:75-85:6-6.5:12-13. The pressing pressure is 5 MPa.

[0043] Furthermore, in a preferred embodiment of the present invention, in the Ni-Co LDH redox mediator electrode, the loading amount of the Ni-Co LDH redox mediator is 3-9 mg cm -2 .

[0044] S2. Nickel acetate tetrahydrate, ferrous sulfate heptahydrate, and terephthalic acid were dispersed in a mixture of N,N-dimethylacetamide and deionized water. After ultrasonic treatment, the mixture was hydrothermally reacted at 140–160°C for 2.5–3.5 h. The mixture was cooled, washed, dried, ground, and pyrolyzed to obtain Ni-Fe-MOF NSs-300. The Ni-Fe-MOF NSs-300 and carbon black were then dispersed in a 5 wt% Nafion solution of isopropyl alcohol and ultrasonically treated for 25–35 min to obtain an ink. Finally, the ink was dropwise added to carbon paper (10 × 10 mm) and dried to obtain a Ni-Fe-MOF NSs-300 electrode. The hydrothermal reaction was carried out in a 30 mL Teflon-lined stainless steel autoclave. The reaction was allowed to cool naturally to room temperature. The substrate was removed, centrifuged, and washed three times with anhydrous ethanol to remove impurities. The resulting precipitate was dried in a vacuum oven at 70°C for 24 h. Finally, the dried precipitate was ground into a fine powder. The temperature was then raised to 300°C in a tube furnace under an argon atmosphere at a heating rate of 2°C / min and held at 300°C for 1 hour. After pyrolysis, Ni-Fe-MOF NSs-300 was obtained.

[0045] Furthermore, in a preferred embodiment of the present invention, the mass volume ratio of the nickel acetate tetrahydrate, the ferrous sulfate heptahydrate, the terephthalic acid, and the N,N-dimethylacetamide-deionized water mixed solution is 6-6.5:0.3-0.4:0.3-0.4:1 (mg / mg / mg / mL).

[0046] Furthermore, in a preferred embodiment of the present invention, in the Ni-Fe-MOF NSs-300 electrode, the loading amount of the Ni-Fe-MOF NSs-300 is 0.8-1.2 mg cm -2 .

[0047] S3. Add nickel chloride hexahydrate and vanadium chloride to deionized water and stir. After adding urea, ultrasonic treatment is performed. The mixture is then placed in a stainless steel autoclave together with the pretreated nickel foam and hydrothermally reacted at 110-130°C for 11-13 hours. The mixture is cooled, washed, and dried to obtain a NiV-LDH / NF electrode. Preferably, the nickel foam has a size of 1×3 cm. After the hydrothermal reaction, the nickel foam is removed and washed with a large amount of water and ethanol, followed by drying at 60°C overnight to obtain NiV-LDH grown in situ on the nickel foam.

[0048] Furthermore, in a preferred embodiment of the present invention, the mass volume ratio of the nickel chloride hexahydrate, the vanadium chloride, the deionized water, and the urea is 6.5-7:1:0.8-1.2:8-9 (mg / mg / mL / mg).

[0049] S4. Using the Ni-Co LDH redox mediator electrode as a counter electrode, the Ni-Fe-MOF NSs-300 electrode as a working electrode, and a NaOH solution as an electrolyte, a H2O2 electrolytic cell is obtained; then taking out the Ni-Co LDH redox mediator electrode that is charged and oxidized in the H2O2 electrolytic cell as a counter electrode, the NiV-LDH / NF electrode as a working electrode, and a mixed solution of KOH and 5-hydroxymethylfurfural as an electrolyte to obtain a 2,5-furancarboxylic acid electrolytic cell.

[0050] Specifically, the present invention uses an H2O2 electrolytic cell containing 60 mL of 1 mol / L NaOH solution and an FDCA electrolytic cell containing 10 mL of 1 mol / L KOH + 10 mmol / L HMF solution, with a size of 2 × 3 cm 2 , Ni-Co LDH redox mediator electrode with an active material loading of 54 mg was used as a Cell H2O2 Take out the counter electrode in the Cell H2O2 The Ni-Co LDH redox medium electrode after oxidation in the electrolytic cell serves as the cell FDCA The counter electrode. H2O2 In the experiment, Ni-Fe-MOF NSs-300 electrode (catalyst loading of about 0.1 mg) and Hg / HgO electrode were used as working electrode and reference electrode. O2 gas was continuously bubbled into the electrolyte to ensure O2 saturation. FDCA In the NiV-LDH / NF electrode (1 × 3 cm2 ) and Hg / HgO electrodes were used as working electrode and reference electrode, respectively. Figure 1 As shown, H2O2 was first electrosynthesized at a current density of 35 mA. H2O2 The Ni-Co LDH redox mediator electrode in the middle is changed from reduced state to oxidized state. Then the oxidized Ni-Co LDH redox mediator electrode is rinsed with 1 M KOH + 10 mM HMF solution and then placed in the right cell. FDCA Electrosynthesis of FDCA was performed at a current density of 15 mA. The Ni-Co LDH redox mediator electrode was reduced and the left cell H2O2 After a typical mode cycle, the Ni-Co LDH redox mediator electrode was washed with 1 M NaOH solution and used again for continuous HPR reaction.

[0051] To facilitate understanding of the present invention, the mechanism of synthesis of H2O2 and FDCA by the modular electrochemical synthesis system of the present invention is described in detail below.

[0052] The modular electrochemical synthesis system involves a two-step EC-(EC / C) cycle process. Figure 2 In the left module, Ni-Co LDH is oxidized to NiOOH and CoOOH, which then pair with HPR to generate H2O2. NiOOH and CoOOH are then reduced to their original states and paired with HMFOR to produce FDCA in the right module. Ni-Co LDH transforms between reduced and oxidized states through a reversible redox reaction, accompanied by the adsorption / desorption of OH ions. Furthermore, NiOOH and CoOOH exhibit spontaneous direct chemical promotion when paired with HMFOR. Therefore, the generation of H2O2 and FDCA is effectively separated in time and space.

[0053] The present invention also provides a modular electrochemical synthesis system, which is prepared according to the construction method. The present invention uses a one-step hydrothermal synthesis of Ni-Co LDH as a solid redox medium to construct a modular synthesis system of H2O2 and FDCA in an alkaline electrolyte. The Ni-Co LDH redox medium electrode converts between the reduced state and the oxidized state through a reversible redox reaction, accompanied by OH -Adsorption / desorption of ions. The modular electrochemical synthesis system of H2O2 and FDCA involves a two-step EC-(EC / C) cycle. The reversible redox reaction of Ni-Co LDH is first paired with the H2O2 electrosynthesis reaction, and then paired with the HMF electrosynthesis FDCA reaction. The Ni-Co LDH redox mediator electrode selectively stores and transports hydroxide ions involved in the target half-reaction through reversible conversion with NiOOH and CoOOH. While ensuring ion balance, modular production of higher-value chemicals H2O2 and FDCA is achieved. At the same time, when the Ni-Co LDH redox mediator electrode is oxidized to NiOOH and CoOOH and paired with the synthesis of FDCA, NiOOH and CoOOH themselves have a great spontaneous direct chemical oxidation effect on the conversion of HMF to FDCA. While Ni-Co LDH serves as a redox mediator to construct an efficient modular electrochemical synthesis system, it can also spontaneously and directly chemically oxidize HMF to FDCA.

[0054] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0055] Example 1

[0056] This embodiment provides a Ni-Co LDH redox mediator, which is prepared according to the following method:

[0057] Using an analytical balance, 0.0611 g of nickel nitrate hexahydrate (Ni(NO₃)₂·6H₂O) and 0.0333 g of cobalt chloride hexahydrate (CoCl₂·6H₂O) were dissolved in 20 mL of a methanol-ultrapure water mixture (the volume ratio of methanol to ultrapure water was 4:1). After vigorous stirring for 20 minutes, 0.5 g of cetyltrimethylammonium bromide (CTAB) was added to the clear solution. After stirring for one hour, the solution was transferred to a 50 mL Teflon-lined stainless steel autoclave and maintained at 180°C for 24 hours before cooling naturally to room temperature. The substrate was centrifuged and washed multiple times with ultrapure water and anhydrous ethanol to remove excess impurities. The resulting precipitate was dried in a vacuum oven at 60°C overnight to obtain the Ni-Co LDH redox mediator.

[0058] Example 2

[0059] This embodiment provides a Ni-Co LDH redox mediator electrode, which is prepared by the following method:

[0060] First, 2 mg of acetylene black was dispersed in 200 μL of nitrogen-methyl pyrrolidone solution to obtain an acetylene black solution. Next, 3 mg of Ni-Co LDH dielectric material was dispersed in 245 μL of nitrogen-methyl pyrrolidone solution. 19 μL of PVDF (20 mg / mL) binder and 38 μL of the prepared acetylene black solution (10 mg / mL) were added. Finally, the resulting mixed solution was dripped onto a pretreated nickel foam (10 × 10 mm) sheet. After drying at room temperature, the sheet was pressed with a pressure of 5 MPa to obtain a Ni-Co LDH redox dielectric electrode. The catalyst loading was 3 mg cm -2 .

[0061] Example 3

[0062] This embodiment provides a modular electrochemical synthesis system, which is constructed by the following steps:

[0063] (1) Preparation of Ni-Fe-MOF NSs-300 electrode: First, 74.4 mg of nickel acetate tetrahydrate (Ni(ac)2·4H2O), 24.9 mg of ferrous sulfate heptahydrate (FeSO4·7H2O), and 24.9 mg of terephthalic acid (PTA) were dispersed in a mixed solution of 6 mL of N,N-dimethylacetamide (DMAC) and 6 mL of deionized water. After ultrasonic homogenization, the mixture was transferred to a 30 mL Teflon-lined stainless steel autoclave and hydrothermally reacted at 150°C for 3 h and naturally cooled to room temperature. The substrate was removed by centrifugation and washed three times with anhydrous ethanol to remove other impurities. The obtained precipitate was dried in a vacuum drying oven at 70°C for 24 h. Finally, the dried precipitate was ground into fine powder. The temperature was increased to 300°C at a heating rate of 2°C / min in a tube furnace under argon atmosphere and kept at 300°C for 1 h. Ni-Fe-MOF NSs-300 was obtained after pyrolysis.

[0064] 2.5 mg of Ni-Fe-MOF NSs-300 material and 2 mg of carbon black were dispersed in 250 μl of isopropanol and 5 μl of Nafion (5 wt%) solution. The resulting mixture was sonicated for approximately 30 minutes to form a uniform ink. 100 μL of the ink was then dropped onto carbon paper (CP) (10 × 10 mm) and dried at room temperature to obtain a Ni-Fe-MOF NSs-300 electrode. The Ni-Fe-MOF NSs-300 loading was 1 mg cm -2 .

[0065] (2) Preparation of NiV-LDH / NF electrode: Weigh 192.52 mg of nickel chloride hexahydrate (NiCl2·6H2O) and 28.45 mg of vanadium chloride (VCl3) and place them in 30 mL of deionized water. After stirring to form a transparent solution, add 240.24 mg of urea. Then, after ultrasonic homogenization, transfer the mixture to a 50 mL Teflon-lined stainless steel autoclave and place a 1×3 cm 2 The pretreated nickel foam was hydrothermally reacted at 120°C for 12 hours and then naturally cooled to room temperature. After removal, the nickel foam was washed with copious amounts of water and ethanol and dried overnight at 60°C. This resulted in an in situ grown NiV-LDH on the nickel foam, i.e., a NiV-LDH / NF electrode.

[0066] (3) The modular electrochemical synthesis system includes a H2O2 electrolytic cell (Cell H2O2 ) and FDCA cells containing 10 mL of 1 M KOH + 10 mM HMF solution (Cell FDCA ). The Ni-Co LDH redox mediator electrode in Example 2 was used as the Cell H2O2 Take out the counter electrode in the Cell H2O2 The Ni-Co LDH redox medium electrode after oxidation in the electrolytic cell serves as the cell FDCA The counter electrode. H2O2 In the experiment, Ni-Fe-MOF NSs-300 electrode and Hg / HgO electrode were used as working electrode and reference electrode. O2 gas was continuously bubbled into the electrolyte to ensure O2 saturation. FDCA In the NiV-LDH / NF electrode (1 × 3 cm 2 ) and Hg / HgO electrodes were used as working and reference electrodes, respectively.

[0067] Test Example 1

[0068] In this test example, scanning electron microscopy and X-ray diffraction were used to characterize the Ni-Co LDH redox mediator of Example 1.

[0069] like Figure 3 Shown is the XRD pattern of the Ni-Co LDH redox mediator of Example 1. Figure 4 Shown is the SEM image of the Ni-Co LDH redox mediator of Example 1. Figure 3 It can be seen that the Ni-Co LDH redox mediator has a uniform porous nanosheet flower-like morphology. Figure 4It can be seen that the clear diffraction peaks observed at 2θ values ​​of 11.1, 22.2, 34.4, and 38.5° can be successfully indexed as the (003), (006), (009), and (015) plane reflections of the hydrotalcite-like LDH phase.

[0070] Test Example 2

[0071] This test example performs electrochemical testing on the Ni-Co LDH redox mediator electrode of Example 2, and the specific steps are as follows:

[0072] All electrochemical properties were measured using an electrochemical workstation (DH7006, Donghua, Jiangsu). A typical three-electrode system was assembled using a platinum sheet, Hg / HgO, and Ni-Co LDH redox mediator electrodes as the counter, reference, and working electrodes, respectively. The electrolyte was 1.0 M NaOH. Prior to other electrochemical measurements, the reversible redox mediator electrode was activated by performing 20 cyclic voltammetry (CV) tests at 20 mV.

[0073] Cyclic voltammetry (CV) curves of the prepared Ni-Co LDH reversible redox mediator electrode were measured at scan rates of 0.1 mV, 1 mV, 5 mV, and 10 mV. Galvanostatic charge-discharge (GCD) curves of the prepared Ni-Co LDH reversible redox mediator electrode were measured at current densities of 0.867 mA, 1.734 mA, 4.335 mA, 8.67 mA, 17.34 mA, and 43.35 mA. Electrochemical impedance spectroscopy (EIS) was recorded at open circuit voltage.

[0074] like Figure 5 The CV curves of the Ni-Co LDH redox mediator electrode of Example 2 at different scan rates in 1.0 M NaOH aqueous solution are shown. Figure 5 It can be seen that the Ni in the Ni-Co LDH redox electrode II / Ni III and Co II / Co III The redox couple produces excellent reversible redox chemistry with a formal potential of approximately 0.33 V vs. Hg / HgO.

[0075] like Figure 6 Shown is a representative galvanostatic discharge curve of the Ni-Co LDH redox mediator electrode of Example 2 in 1 M NaOH solution. Figure 7 Shown is the rate performance diagram of the Ni-Co LDH redox mediator electrode of Example 2. Figure 6It can be seen that the constant current discharge curves of the Ni-Co LDH redox electrode at different current densities produce a flat discharge platform at 0.275 V vs. Hg / HgO and provide stable energy output during the reduction process. Figure 7 It can be seen that the Ni-CoLDH redox mediator has a capacity of 203 mAhg at a rate of 1C (0.289 A / g). -1 Even at 50C (14.45 A / g), the capacity is still 101 mAhg -1 .

[0076] Test Example 3

[0077] In this test example, the Ni-Co LDH redox electrode was subjected to 100 charge and discharge cycles at charge and discharge rates of 2C (0.578 A / g) and 20C (5.78 A / g), respectively, to evaluate the cyclic stability of the Ni-Co LDH redox electrode.

[0078] like Figure 8 The graph shows the cycling stability performance of the Ni-Co LDH redox mediator electrode of Example 2. Figure 8 It can be seen that the Ni-Co LDH redox electrode has a capacity of 192 mAhg at a 2C rate. -1 The high capacity of the battery is 97% even at 20C, with a Coulombic efficiency (CE) higher than 94%. -1 .

[0079] Test Example 4

[0080] This experimental example investigated the oxidation and reduction performance of the Ni-Co LDH redox mediator electrode from Example 2 in different electrolytes during modular electrosynthesis. When the Ni-Co LDH redox mediator electrode was used in conjunction with the cathode to electrosynthesize H₂O₂, the Ni-Co LDH redox mediator was simultaneously oxidized and charged. The oxidized Ni-Co LDH redox mediator was then used in conjunction with the anode to electrosynthesize FDCA, resulting in a reduced discharge.

[0081] like Figure 9 The graph shows the constant current charge curve of the Ni-Co LDH redox mediator electrode in Example 2 of the present invention in a 1 M NaOH solution at the cathode and the constant current discharge curve in a 1 M KOH + 10 mM HMF solution at the anode, where the rate is 10 C (2.89 A / g). Figure 9As can be seen, the discharge capacity of the Ni-Co LDH redox mediator electrode in 1 M KOH + 10 mM HMF solution is only about 65% of the charge capacity in 1 M NaOH solution. This reduction in discharge capacity indicates a decrease in the amount of NiOOH and CoOOH formed by oxidation of the Ni-Co LDH redox mediator. This further supports the chemical interaction of the Ni-Co LDH redox mediator electrode in 1 M KOH + 10 mM HMF solution in spontaneously promoting the conversion of HMF to FDCA.

[0082] Figure 10 The graph shows 20 cycles of constant current charge and discharge of the Ni-Co LDH redox mediator electrode of Example 2. The Ni-Co LDH redox mediator electrode was charged in 1M NaOH solution and discharged in 1M KOH solution. + 10 mM HMF solution discharge. Figure 10 It can be seen that the Ni-Co LDH redox mediator electrode has good stability in different electrolytes.

[0083] Test Example 5

[0084] This experimental example investigates the performance of a modular electrochemical synthesis system. The modular electrochemical synthesis system was used to sustainably produce H2O2 and FDCA using two electrolytic cells. Both processes were performed in an undivided beaker-type cell with a three-electrode configuration. The modular electrochemical synthesis system consisted of a H2O2 electrolytic cell (Cell 1) containing 60 mL of 1 M NaOH solution. H2O2 ) and FDCA cells containing 10 mL of 1 M KOH + 10 mM HMF solution (Cell FDCA ). With the size of 2 × 3 cm 2 , Ni-Co LDH solid redox mediator electrode with an active material loading of 54 mg was used as a Cell H2O2 Take out the counter electrode in the Cell H2O2 The Ni-Co LDH redox medium electrode after oxidation in the electrolytic cell serves as the cell FDCA The counter electrode. H2O2 In the experiment, Ni-Fe-MOF NSs-300 electrode and Hg / HgO electrode were used as working electrode and reference electrode. O2 gas was continuously bubbled into the electrolyte to ensure O2 saturation. FDCA In the NiV-LDH / NF electrode (1 × 3 cm 2) and Hg / HgO electrodes were used as working and reference electrodes, respectively. A typical two-step cycling mode was studied by chronopotentiometry with an applied current of -35 mA for the cathodic HPR reaction and 15 mA for the anodic HMFOR reaction.

[0085] like Figure 11 The graphs show the chronopotentiometry curves of the electrodes in the H2O2 electrolytic cell and the FDCA electrolytic cell during the modular electrochemical synthesis process. Figure 11 As can be seen in the cathodic HMFOR reaction electrolysis cell, the HMFOR reaction at the Ni-Fe-MOF NSs-300 electrode exhibited an average potential of -0.48 V, while the Ni-Co LDH redox mediator was oxidized and charged to 0.38 V. After flushing with a 1 mM MKOH + 10 mM HMF anodic HMFOR reaction electrolyte solution, a model cycle was completed in the anodic HMFOR reaction electrolysis cell. The oxidized Ni-Co LDH redox mediator was reduced and discharged to the original Ni-Co LDH redox mediator starting at 0.24 V. The Ni-Co LDH redox mediator did not discharge and reduce starting at 0.38 V, indicating a material charge loss, further confirming the spontaneous chemical promotion of the Ni-Co LDH redox mediator on the anodic HMFOR reaction. The HMFOR reaction at the NiV-LDH / NF electrode exhibited an average potential of 0.54 V. The Faradaic efficiency and yield of HMFOR and HPR were calculated based on the H2O2 and FDCA produced in each electrolysis cell. During the co-production period, the average potential difference between the working catalytic electrode and the solid redox mediator electrode in the two electrolytic cells is defined as the average cell voltage (E cell ). In order to describe the energy utilization of the modular electrochemical production system, the voltage efficiency (VE) of the modular electrosynthesis system is defined by the following equation.

[0086]

[0087] Among them, E DIR are the potential differences between the HPR reaction potential on the Ni-Fe-MOF NSs-300 electrode and the HMFOR reaction potential on the NiV-LDH / NF electrode; ΔV is the potential difference between the average potentials of the oxidation and reduction processes of the solid redox mediator; E ModES is the sum of the applied voltages of the modular electrochemical production system. Specifically, E ModES The total VE is as high as 87.93% even at a large applied current.

[0088] like Figure 12Shown are the average potentials of the Ni-Co LDH redox mediator electrode and the corresponding average cell voltages of the H2O2 electrolysis cell and the FDCA electrolysis cell during 20 modular electrochemical syntheses. Figure 12 As can be seen, continuous production of H2O2 and FDCA was verified by cycling the same Ni-Co LDH redox mediator electrode (54 mg) with an applied current of -35 mA for the cathode HPR reaction and 15 mA for the anodic HMFOR reaction. The Ni-Co LDH redox mediator potential in the cathode HPR reaction electrolysis cell remained at 0.38 V with a fluctuation of ±0.03 V. The solid redox mediator potential in the anodic HMFOR reaction remained at 0.24 V with a variation of ±0.02 V. The corresponding average voltages for the cathode HPR reaction H2O2 electrolysis cell and the anodic HMFOR reaction FDCA were 0.97 and 1.02 V.

[0089] like Figure 13 The coulombic efficiency (CE) of the Ni-Co LDH redox mediator electrode during 20 modular electrochemical syntheses and the voltage efficiency (VE) of the modular electrosynthesis system are shown. Figure 13 It can be seen that during the 20-cycle production, the modular electrochemical synthesis system maintained a voltage efficiency of approximately 87%, and the Ni-Co LDH redox mediator maintained a coulombic efficiency of 65%. This is consistent with the charge-discharge tests of the Ni-Co LDH redox mediator in different electrolytes, further verifying that the Ni-Co LDH redox mediator has a spontaneous chemical effect in the anodic HMFOR reaction, promoting the conversion of HMF to FDCA, which leads to a decrease in coulombic efficiency.

[0090] like Figure 14 Shown are the H2O2 production and Faradaic efficiency (FE) diagrams during 20 modular electrochemical synthesis processes. Figure 15 The graph shows the yield of FDCA during 20 modular electrochemical syntheses and the amount of electricity applied in each cycle. Figure 14 and Figure 15 As can be seen, 20 cycles of continuous modular production of H2O2 and FDCA in their respective electrolytic cells (using a 54 mg Ni-Co LDH redox mediator electrode loading) were achieved. This modular electrochemical synthesis system can produce practically useful amounts of H2O2 and FDCA, with H2O2 concentrations as high as 162 ppm and FDCA yields maintained above 80%. This demonstrates the continuous electrochemical synthesis of the modular electrochemical synthesis system without sacrificing auxiliary reactions.

[0091] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

Claims

1. A method for constructing a modular electrochemical synthesis system, characterized in that: The modular electrochemical synthesis system includes an H2O2 electrolytic cell and a 2,5-furancarboxylic acid electrolytic cell, and comprises the following steps: S1. Dispersing a Ni-Co LDH redox medium in a nitrogen methyl pyrrolidone solution, then adding a polyvinylidene fluoride binder and an acetylene black solution to obtain a mixed solution, and finally dropping the mixed solution onto nickel foam, drying, and pressing to obtain a Ni-Co LDH redox medium electrode; wherein nickel nitrate hexahydrate and cobalt chloride hexahydrate are dissolved in a methanol-ultrapure water mixed solution and vigorously stirred for 15 to 25 minutes, and then cetyltrimethylammonium bromide is added and stirred for 50 to 70 minutes, and then subjected to a hydrothermal reaction, cooled, washed, and dried to obtain a Ni-Co LDH redox medium; S2. Nickel acetate tetrahydrate, ferrous sulfate heptahydrate, and terephthalic acid are dispersed in a mixed solution of N,N-dimethylacetamide and deionized water, subjected to ultrasonic treatment, and hydrothermally reacted at 140-160° C. for 2.5-3.5 h. Ni-Fe-MOF NSs-300 is obtained by cooling, washing, drying, grinding, and pyrolysis. The Ni-Fe-MOF NSs-300 and carbon black are then dispersed in isopropyl alcohol and Nafion solution, subjected to ultrasonic treatment for 25-35 min, to obtain ink. Finally, the ink is dropwise added onto carbon paper and dried to obtain a Ni-Fe-MOF NSs-300 electrode. S3, adding nickel chloride hexahydrate and vanadium chloride to deionized water and stirring, adding urea and then ultrasonically treating, then placing together with nickel foam in a stainless steel autoclave and hydrothermally reacting at 110-130° C. for 11-13 hours, cooling, washing, and drying to obtain a NiV-LDH / NF electrode; S4. Using the Ni-Co LDH redox medium electrode as a counter electrode, the Ni-Fe-MOF NSs-300 electrode as a working electrode, and a NaOH solution as an electrolyte, a H2O2 electrolytic cell is obtained; then taking out the Ni-Co LDH redox medium electrode that is charged and oxidized in the H2O2 electrolytic cell as a counter electrode, the NiV-LDH / NF electrode as a working electrode, and a mixed solution of KOH and 5-hydroxymethylfurfural as an electrolyte to obtain a 2,5-furancarboxylic acid electrolytic cell.

2. The method for constructing a modular electrochemical synthesis system according to claim 1, characterized in that: In the Ni-CoLDH redox mediator electrode, the loading amount of the Ni-Co LDH redox mediator is 3 to 9 mg cm -2 .

3. The method for constructing a modular electrochemical synthesis system according to claim 2, characterized in that: In step S2, the mass volume ratio of the nickel acetate tetrahydrate, the ferrous sulfate heptahydrate, the terephthalic acid, and the N,N-dimethylacetamide-deionized water mixed solution is 6-6.5:0.3-0.4:0.3-0.4:1 (mg / mg / mg / mL).

4. The method for constructing a modular electrochemical synthesis system according to claim 1, wherein: Step S2: In the Ni-Fe-MOF NSs-300 electrode, the loading amount of the Ni-Fe-MOF NSs-300 is 0.8-1.2 mg cm -2 .

5. The method for constructing a modular electrochemical synthesis system according to claim 1, wherein: In step S3, the mass volume ratio of the nickel chloride hexahydrate, the vanadium chloride, the deionized water, and the urea is 6.5-7:1:0.8-1.2:8-9 (mg / mg / mL / mg).

6. A modular electrochemical synthesis system, characterized in that Prepared according to the construction method according to any one of claims 1 to 5.

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