A cation-exchange high-entropy layered hydroxide bifunctional electrocatalyst, its preparation method, and its application.

Abstract

This invention belongs to the field of electrocatalytic materials technology, specifically relating to a cation-exchange type high-entropy layered hydroxide bifunctional electrocatalyst, its preparation method, and its applications. This invention synthesizes a high-entropy layered hydroxide bifunctional electrocatalyst via a hydrothermal method and an electric field-driven cation exchange strategy. The obtained catalyst exhibits excellent conversion rate, selectivity, and Faradaic efficiency in the electrocatalytic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid, and also shows high Faradaic efficiency in the electrocatalytic reduction of nitrate to ammonia. With its constructed oxidation-coupled reduction electrolysis system, both electrodes exhibit excellent Faradaic efficiency, enabling simultaneous and efficient production of biomass at the anode and pollutant resources at the cathode. This invention provides a new reference approach for the precise construction of high-entropy materials and the application of bifunctional electrocatalysis, and has broad application prospects in biomass conversion, environmental remediation, and green electrosynthesis.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic materials technology. More specifically, it relates to a cation-exchange type high-entropy layered hydroxide bifunctional electrocatalyst, its preparation method, and its application. Background Technology

[0002] 5-Hydroxymethylfurfural (HMF) is a key biomass platform molecule, and its electrocatalytic oxidation to produce high-value-added chemical 2,5-furandicarboxylic acid (FDCA) is of great significance. FDCA is a key monomer for the synthesis of biodegradable plastic poly(ethylene furandicarboxylate) (PEF), which is expected to replace petroleum-based polyethylene terephthalate (PET) plastic.

[0003] On the other hand, nitrate (NO3) - As a common nitrogenous pollutant in industrial wastewater and agricultural runoff, the electrocatalytic reduction of nitrate (HMF) to ammonia (NH3) not only achieves denitrification of water bodies but also provides a green alternative to the traditional high-energy-consuming and high-carbon-emission Haber-Bosch process for ammonia synthesis. Pairing the anode HMF oxidation with the cathode nitrate reduction via electrolysis allows for simultaneous biomass value-added and pollutant resource recovery within the same electrolysis system, significantly improving energy utilization efficiency and economic viability.

[0004] Layered double hydroxides (LDHs) have attracted much attention due to their unique two-dimensional layered structure, flexible tunability of metal composition, and excellent electrocatalytic performance. In recent years, high-entropy layered hydroxides (HELHs), through the introduction of five or more metal elements to form an atomically homogeneous dispersion structure, have exhibited a unique "cocktail" synergistic effect, showing great potential in the field of electrocatalysis. However, the preparation of existing high-entropy materials mostly employs one-step co-precipitation or hydrothermal methods, making it difficult to achieve precise post-synthetic control of the layer metal composition. In particular, there is a lack of selective substitution strategies for specific active sites (such as Fe sites), resulting in poor performance of the obtained high-entropy materials, which requires further improvement.

[0005] Therefore, developing a method for preparing high-entropy layered hydroxides that can precisely control the metal composition of the layers and optimize the electronic structure of the active centers, and exploring the application of the obtained high-entropy layered hydroxides in bifunctional electrocatalysis of HMF oxidation and nitrate reduction, has important scientific significance and industrial application prospects. Summary of the Invention

[0006] The technical problem to be solved by this invention is to overcome the shortcomings and deficiencies of existing high-entropy materials, which are mostly prepared by one-step co-precipitation or hydrothermal methods, making it difficult to achieve precise post-synthesis control of the metal composition of the layers, especially lacking a selective replacement strategy for specific active sites (such as Fe sites), resulting in poor performance of the high-entropy materials that need further improvement. The primary objective is to provide a method for preparing high-entropy layered hydroxide bifunctional electrocatalysts.

[0007] A second objective of this invention is to provide a high-entropy layered hydroxide bifunctional electrocatalyst prepared by the aforementioned preparation method.

[0008] A third objective of this invention is to provide applications of the aforementioned high-entropy layered hydroxide bifunctional electrocatalyst.

[0009] A fourth objective of this invention is to provide an electrocatalytic device.

[0010] A fifth objective of the present invention is to provide the application of the electrocatalytic device.

[0011] The above-mentioned objective of this invention is achieved through the following technical solution: This invention protects a method for preparing a high-entropy layered hydroxide bifunctional electrocatalyst, comprising the following steps: S1. Nickel salt, iron salt, ammonium fluoride and urea are mixed in water to obtain a mixed solution; a carbon-based support is placed in the obtained mixed solution and subjected to a hydrothermal reaction. After the reaction is complete, the solution is post-processed to obtain a catalyst precursor. S2. Electrochemical treatment was performed using a three-electrode system. A mixed solution containing copper, cobalt, and zinc salts was used as the anolyte, and an aqueous solution containing potassium chloride and trisodium citrate was used as the catholyte. The catalyst precursor obtained in step S1 was used as the working electrode and placed in the anolyte solution. Cyclic voltammetry was performed in the potential range of -0.9 to 1.2 V. After the scan was completed, post-processing was performed to obtain the high-entropy layered hydroxide bifunctional electrocatalyst. In step S1, the molar ratio of nickel in the nickel salt to iron in the iron salt is (2.5~3.5):1; In step S2, the molar ratio of copper in the copper salt, cobalt in the cobalt salt, and zinc in the zinc salt is 1:(0.8~1.2):(0.8~1.2).

[0012] This invention first utilizes a hydrothermal method to grow nickel-iron hydroxide in situ on the surface of a carbon-based support to obtain a catalyst precursor. Then, a high-entropy layered hydroxide bifunctional electrocatalyst is further synthesized using an electric field-driven cation exchange strategy. The resulting bifunctional catalyst exhibits excellent conversion, selectivity, and Faradaic efficiency in the electrocatalytic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid, and also shows high Faradaic efficiency in the electrocatalytic reduction of nitrate to ammonia.

[0013] Specifically, in step S1, the molar ratio of nickel in the nickel salt to iron in the iron salt can be 2.5:1, 2.8:1, 2.9:1, 3:1, 3.1:1, 3.2:1, 3.3:1, 3.4:1, 3.5:1, etc., or any specific ratio between the above ratios, or any range of these specific ratios. For the sake of simplicity, not all possible specific ratios or ranges are listed here.

[0014] Preferably, in step S1, the molar ratio of nickel in the nickel salt to iron in the iron salt is (2.8~3.2):1, more preferably (2.9~3.1).

[0015] Specifically, in step S2, the molar ratio of copper in the copper salt, cobalt in the cobalt salt, and zinc in the zinc salt can be 1:0.8:0.8, 1:0.8:0.9, 1:0.8:1.0, 1:0.8:1.1, 1:0.8:1.2, 1:0.9:0.8, 1:0.9:0.9, 1:0.9:1.0, 1:0.9:1.1, 1:0.9:1.2, 1:1:0.8, or 1:1:0.9. The ratios can be 1:1:1, 1:1:1.1, 1:1:1.2, 1:1.1:0.8, 1:1.1:0.9, 1:1.1:1, 1:1.1:1.1, 1:1.1:1.2, 1:1.2:0.8, 1:1.2:0.9, 1:1.2:1, 1:1.2:1.1, 1:1.2:1.2, etc., or any specific ratio between the above ratios, or any range of these specific ratios. For the sake of simplicity, not all possible specific ratios or ranges are listed here.

[0016] Preferably, in step S2, the molar ratio of copper in the copper salt, cobalt in the cobalt salt, and zinc in the zinc salt is 1:(0.9~1.1):(0.9~1.1), more preferably 1:1:1.

[0017] Further, in step S1, the mixing ratio of nickel element in the nickel salt with ammonium fluoride and urea is 1 mol: (50~70) g: (500~550) g.

[0018] Preferably, in step S1, the mixing ratio of nickel element in the nickel salt with ammonium fluoride and urea is 1 mol: (55~65) g: (520~540) g, more preferably 1 mol: (60~62) g: (530~535) g.

[0019] Furthermore, the preparation conditions of the preparation method include at least one of the following: (1) The mass-volume ratio of the urea and water is 1 g: (20~40) mL; (2) The nickel salt is a soluble nickel salt, which includes at least one of nickel nitrate or its hydrate, nickel acetate or its hydrate, nickel chloride or its hydrate, and nickel sulfate or its hydrate; (3) The iron salt is a soluble iron salt, which includes at least one of ferric nitrate or its hydrate, ferric acetate or its hydrate, ferric chloride or its hydrate, and ferric sulfate or its hydrate.

[0020] Preferably, the mass-volume ratio of the urea and water is 1 g: (25~35) mL, more preferably 1 g: (30~32) mL.

[0021] Preferably, the carbon-based support is selected from carbon paper or carbon cloth. The support used in this application must be a carbon-based support, such as carbon paper or carbon cloth, and metal-based supports such as nickel foam or copper foam cannot be used. If a metal-based support is used, during the first step of the hydrothermal synthesis, Fe ions from the iron salt will etch the surface of the metal-based support (Fe ions will replace the metal-based support). During the second step of the electric field-driven cation exchange, the metal-based support will dissolve metal ions, affecting the synthesis effect.

[0022] Furthermore, the carbon-based support is a pretreated carbon-based support.

[0023] Furthermore, the pretreatment includes cutting, washing, and drying.

[0024] Optionally, the cutting involves cutting the carbon-based carrier to a size of 2.5 cm × 2.5 cm.

[0025] Furthermore, the washing process involves washing in ethanol and water sequentially.

[0026] Furthermore, the washing process also includes ultrasonic treatment during the washing process.

[0027] Furthermore, the power of the ultrasonic treatment is 200~300 W, preferably 230~250 W.

[0028] Furthermore, the frequency of the ultrasonic treatment is 30~50 kHz, preferably 35~45 kHz.

[0029] Furthermore, the drying process is called baking.

[0030] Furthermore, the drying temperature is 50~80 ℃, preferably 60~70 ℃.

[0031] Preferably, the drying time is 8-15 hours, and more preferably 11-13 hours.

[0032] Preferably, the temperature of the hydrothermal reaction is 110~130 ℃, more preferably 115~125 ℃.

[0033] Preferably, the hydrothermal reaction time is 6-20 h, more preferably 15-17 h.

[0034] Furthermore, the hydrothermal reaction also includes the addition of hydrogen peroxide. The addition of hydrogen peroxide is to make the nickel-iron hydroxide nanosheets grown in situ on the carbon-based support surface thinner.

[0035] Further, the volume ratio of the hydrogen peroxide to the water in step S1 is 1:(50~60), preferably 1:(54~56).

[0036] Furthermore, in step S1, the post-processing includes cutting, washing, and drying.

[0037] Optionally, when the size of the pretreated carbon-based support is 2.5 cm × 2.5 cm, the cutting is to cut the carbon-based support on the obtained catalyst precursor to a size of 1.0 cm × 1.0 cm.

[0038] Furthermore, the washing process involves washing in ethanol and water sequentially.

[0039] Furthermore, the drying process is vacuum drying.

[0040] Furthermore, the vacuum drying temperature is 50~80 ℃, preferably 60~70 ℃.

[0041] Preferably, the vacuum drying time is 8-15 h, and more preferably 11-13 h.

[0042] Furthermore, the preparation conditions of the preparation method include at least one of the following: (1) The copper salt is a soluble copper salt, which includes at least one of copper nitrate or its hydrate, copper acetate or its hydrate, copper chloride or its hydrate, and copper sulfate or its hydrate; (2) The cobalt salt is a soluble cobalt salt, which includes at least one of cobalt nitrate or its hydrate, cobalt acetate or its hydrate, cobalt chloride or its hydrate, and cobalt sulfate or its hydrate; (3) The zinc salt is a soluble zinc salt, which is selected from at least one of zinc acetate or its hydrate, zinc nitrate or its hydrate, zinc chloride or its hydrate, and zinc sulfate or its hydrate.

[0043] Specifically, in the three-electrode system, the Hg / HgO electrode is used as the reference electrode, the platinum sheet electrode is used as the counter electrode, and the catalyst precursor obtained in step S1 is used as the working electrode.

[0044] Furthermore, the scanning rate of the cyclic voltammetric scan is 0.08~0.12 V / s, preferably 0.09~0.11 V / s.

[0045] Furthermore, the cyclic voltammetric scan is performed 45 to 55 times, preferably 50 times.

[0046] Furthermore, the solvent of the anolyte is water.

[0047] Furthermore, the anolyte also contains potassium chloride and trisodium citrate. Even further, the molar concentration of potassium chloride in the anolyte is 0.8~1.2 mol / L, preferably 0.9~1.1 mol / L.

[0048] Furthermore, the molar concentration of trisodium citrate in the anolyte is 0.8~1.2 mol / L, preferably 0.9~1.1 mol / L.

[0049] Furthermore, the molar concentration of potassium chloride in the cathode electrolyte is 0.8~1.2 mol / L, preferably 0.9~1.1 mol / L.

[0050] Furthermore, the molar concentration of trisodium citrate in the cathode electrolyte is 0.8~1.2 mol / L, preferably 0.9~1.1 mol / L.

[0051] Furthermore, in step S2, the post-processing includes washing and drying.

[0052] Furthermore, the washing is performed using water.

[0053] Furthermore, the drying process is vacuum drying.

[0054] Furthermore, the vacuum drying temperature is 50~80 ℃, preferably 60~70 ℃.

[0055] Preferably, the vacuum drying time is 8-15 h, and more preferably 11-13 h.

[0056] This invention also protects the high-entropy layered hydroxide bifunctional electrocatalyst prepared by the aforementioned preparation method.

[0057] This invention also protects the application of the high-entropy layered hydroxide bifunctional electrocatalyst in the electrocatalytic reduction of nitrate to ammonia and / or the electrocatalytic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid.

[0058] Furthermore, the nitrate ions are derived from nitrates.

[0059] Furthermore, the nitrate includes at least one of potassium nitrate and sodium nitrate.

[0060] As an optional implementation, the concentration of nitrate in the electrocatalytically reduced nitrate is ≥5 mM, preferably 5~200 mM, and more preferably 80~120 mM.

[0061] As an optional implementation, the concentration of 5-hydroxymethylfurfural in the electrocatalytic oxidation of 5-hydroxymethylfurfural is ≥5 mM, preferably 5~100 mM, and more preferably 8~12 mM.

[0062] This invention also protects an electrocatalytic device, comprising a power source, a membrane, an anode chamber, a cathode chamber, an anode, and a cathode; The electrolyte in the anode chamber contains 5-hydroxymethylfurfural; The electrolyte in the cathode chamber contains nitrate ions; Both the anode and cathode are made of the high-entropy layered hydroxide bifunctional electrocatalyst.

[0063] Furthermore, the diaphragm is a Nafion diaphragm.

[0064] Furthermore, the electrolyte in the anode chamber also contains potassium hydroxide.

[0065] Furthermore, the molar concentration of potassium hydroxide in the electrolyte in the anode chamber is 0.08~0.12 mol / L, preferably 0.09~0.11 mol / L.

[0066] Furthermore, the electrolyte in the cathode chamber also contains potassium hydroxide.

[0067] Furthermore, the molar concentration of potassium hydroxide in the electrolyte in the cathode chamber is 0.08~0.12 mol / L, preferably 0.09~0.11 mol / L.

[0068] As an optional implementation, the concentration of nitrate in the electrolyte in the cathode chamber is ≥5 mM, preferably 5~200 mM, and more preferably 80~120 mM.

[0069] As an optional implementation, the concentration of 5-hydroxymethylfurfural in the electrolyte in the anode chamber is ≥5 mM, preferably 5~100 mM, and more preferably 8~12 mM.

[0070] This invention also protects the application of the electrocatalytic device in the electrocatalytic reduction of nitrate to ammonia and the electrocatalytic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid.

[0071] Furthermore, the nitrate ions are derived from nitrates.

[0072] Furthermore, the nitrate includes at least one of potassium nitrate and sodium nitrate.

[0073] Compared with the prior art, the present invention has the following beneficial effects: This invention synthesizes a high-entropy layered hydroxide bifunctional electrocatalyst via a hydrothermal method and an electric field-driven cation exchange strategy. The resulting catalyst exhibits excellent conversion, selectivity, and Faradaic efficiency (all three values ​​approaching 100%) in the electrocatalytic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid, and also demonstrates high Faradaic efficiency (up to 90%) in the electrocatalytic reduction of nitrate to ammonia. The constructed oxidation-coupled reduction electrolysis system exhibits excellent Faradaic efficiency at both electrodes (the sum of the Faradaic efficiencies at both electrodes reaches nearly 200%), enabling simultaneous and efficient production of biomass at the anode and pollutant at the cathode. This invention provides a new reference approach for the precise construction of high-entropy materials and the application of bifunctional electrocatalysis, and has broad application prospects in biomass conversion, environmental remediation, and green electrosynthesis. Attached Figure Description

[0074] Figure 1 The X-ray diffraction (XRD) patterns of the final materials obtained in Example 1 and Comparative Examples 1 to 2 are shown; wherein, (a) is the XRD pattern at 10 to 60° and (b) is the XRD pattern at 10 to 12°.

[0075] Figure 2 The images show the scanning electron microscope (SEM) morphology of the final materials obtained in Example 1 and Comparative Examples 1 to 2; wherein, (a) to (c) are SEM morphology images of the final materials obtained in Comparative Example 1 at different magnifications, (d) to (f) are SEM morphology images of the final materials obtained in Example 1 at different magnifications, and (g) to (i) are SEM morphology images of the final materials obtained in Comparative Example 2 at different magnifications.

[0076] Figure 3 The images show transmission electron microscopy (TEM)-energy dispersive spectroscopy (EDS) images of the final materials obtained in Example 1 and Comparative Examples 1 to 2; wherein, (a) is the TEM-EDS image of the final material obtained in Comparative Example 1, (b) is the TEM-EDS image of the final material obtained in Example 1, and (c) is the TEM-EDS image of the final material obtained in Comparative Example 2.

[0077] Figure 4 The data statistics of inductively coupled plasma mass spectrometry tests of the final materials obtained in Example 1 and Comparative Examples 1 to 2 are shown in the figure.

[0078] Figure 5The figures are statistical graphs of the electrocatalytic oxidation test results of the final materials obtained in Example 1 and Comparative Examples 1 to 2 on 5-hydroxymethylfurfural; wherein, (a) is the LSV (linear sweep voltammetry) curve, (b) is the Tafel slope graph, (c) is the statistical graph of the electrochemical active area results, and (d) is the electrochemical impedance spectroscopy.

[0079] Figure 6 The following is a statistical chart showing the performance of the final material obtained in Example 1 in the electrocatalytic oxidation of 5-hydroxymethylfurfural; wherein, (a) is a statistical chart showing the conversion rate, selectivity and yield at different voltages, and (b) is a statistical chart showing the cycle stability test results.

[0080] Figure 7 The figures are statistical graphs of the final materials obtained in Example 1 and Comparative Examples 1 to 2 in nitrate reduction; wherein, (a) is the LSV curve, (b) is the statistical graph of the yield at different voltages, (c) is the statistical graph of the Faraday efficiency at different voltages, and (d) is the statistical graph of the cycle stability test results of the final material obtained in Example 1.

[0081] Figure 8 The figures are statistical graphs showing the performance of the bifunctional electrocatalytic system constructed from the final material obtained in Example 1; (a) is a schematic diagram of the bifunctional electrocatalytic device, (b) is an LSV curve, (c) is a statistical graph of the Faradaic efficiency of the oxidation reaction, (d) is a statistical graph of the Faradaic efficiency of the reduction reaction, and (e) is a statistical graph of the cycle stability test results of the oxidation and reduction reactions. Detailed Implementation

[0082] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0083] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0084] Example 1: Preparation of a cation-exchange type high-entropy layered hydroxide bifunctional electrocatalyst A method for preparing a cation-exchange type high-entropy layered hydroxide bifunctional electrocatalyst includes the following steps: S1. Pretreatment of carbon paper: The pre-cut carbon paper (size: 2.5 cm × 2.5 cm) is ultrasonically treated in ethanol and deionized water in sequence (ultrasonic power of 240 W, ultrasonic frequency of 40 KHz) for 30 minutes. Finally, the treated clean carbon paper is dried in an oven at 65 ℃ for 12 h for later use.

[0085] S2. Synthesis of NiFe-LDH: 880 mg (3 mmol) nickel nitrate hexahydrate, 404 mg (1 mmol) ferric nitrate nonahydrate, 185 mg ammonium fluoride, and 1.6 g urea were sequentially added to 50 mL of deionized water and stirred continuously for about 20 min until a transparent and homogeneous solution was formed. 900 µL of H2O2 was added and stirring was continued for 10 min. The above solution was transferred to a 100 mL hydrothermal reactor, and 2.5 cm × 2.5 cm carbon paper pretreated in step S1 was added. The reaction was carried out at 120 ℃ for 16 h. After natural cooling, the catalyst-supported side of the carbon paper was rinsed with ethanol and deionized water, and then dried under vacuum at 65 ℃ for 12 h to obtain the carbon paper supporting the nickel-iron hydroxide precursor. This paper was cut into 1.0 cm × 1.0 cm pieces, and the resulting material was named NiFe-LDH.

[0086] S3. Synthesis of HELH-EC: 5 mmol copper nitrate hydrate, 5 mmol cobalt nitrate hexahydrate, 5 mmol zinc acetate dihydrate, 0.05 mol potassium chloride, and 0.05 mol trisodium citrate were dissolved in deionized water and brought to a final volume of 50 mL to obtain the anolyte. 0.05 mol potassium chloride and 0.05 mol trisodium citrate were dissolved in deionized water and brought to a final volume of 50 mL to obtain the catholyte. Electrochemical treatment was performed using a three-electrode system, with Hg / HgO as the reference electrode, a platinum sheet electrode as the counter electrode, and the NiFe-LDH obtained in step S2 as the working electrode. NiFe-LDH was placed in the anolyte, and cyclic voltammetry was performed in the potential range of -0.9 to 1.2 V at a scan rate of 0.1 V / s for 50 cycles. After treatment, the catalyst surface was rinsed with deionized water to remove physically adsorbed ions, and then dried under vacuum at 65 °C for 12 h to obtain a cation exchange-type high-entropy layered hydroxide bifunctional electrocatalyst, which was named HELH-EC. The obtained HELH-EC was stored in a desiccator for later use.

[0087] Comparative Example 1: Preparation of NiFe-LDH Following steps S1-S2 of Example 1, NiFe-LDH was prepared.

[0088] Comparative Example 2: Preparation of Traditional High-Entropy Catalysts Following the procedures of steps S1-S2 in Example 1, the difference from Example 1 is that in step S2, 880 mg of nickel nitrate hexahydrate is replaced with 818.81 mg of nickel nitrate hexahydrate, 14.65 mg of copper nitrate hydrate, 19.38 mg of cobalt nitrate hexahydrate, and 14.42 mg of zinc acetate dihydrate. All other procedures are the same, and HELH-HT is prepared.

[0089] The specific preparation method includes the following steps: 818.81 mg of nickel nitrate hexahydrate, 404 mg of ferric nitrate nonahydrate, 14.65 mg of copper nitrate hydrate, 19.38 mg of cobalt nitrate hexahydrate, 14.42 mg of zinc acetate dihydrate, 185 mg of ammonium fluoride, and 1.6 g of urea were sequentially added to 50 mL of deionized water and stirred continuously for about 20 min until a transparent and homogeneous solution was formed. 900 µL of H₂O₂ was then added and stirring continued for 10 min. The solution was transferred to a 100 mL hydrothermal reactor, and pretreated carbon paper was added. The reaction was carried out at 120 °C for 16 h. After natural cooling, one side of the catalyst supported on the carbon paper was rinsed with ethanol and deionized water, and then vacuum dried overnight at 65 °C to obtain the conventional high-entropy catalyst, which was named HELH-HT.

[0090] Experiment Example 1 XRD Test XRD tests were performed on the final materials obtained in Example 1 and Comparative Examples 1 to 2, and the results are as follows: Figure 1 As shown in Figure (a), the three samples from Example 1 (HELH-EC), Comparative Example 2 (HELH-HT), and Comparative Example 1 (NiFe-LDH) all exhibit characteristic diffraction peaks of layered double hydroxides near 11~12°, 22~24°, and 34~36°, which are basically consistent with the standard card (PDF 40-0215), indicating that the electrochemical electric field strengthening substitution did not destroy the main layered structure. The normalized diffraction peaks of the (003) crystal plane were compared, and the results are as follows... Figure 1 As shown in Figure (b), the peak positions of HELH-EC in Example 1, NiFe-LDH in Comparative Example 1, and HELH-HT in Comparative Example 2 are 10.98°, 11.3°, and 11.5°, respectively, corresponding to a decreasing interlayer spacing. The significant expansion of the interlayer spacing in HELH-EC of Example 1 can be attributed to the large Co ionic radius during the electrochemical in-situ translocation process. 2+ (74.5 pm), Cu 2+ (73 pm), Zn 2+ (74 pm) partially replaced the smaller-radius Ni in the precursor. 2+ (69 pm) or Fe 3+ (64.5 pm), leading to lattice distortion and weakened interlayer forces. In contrast, HELH-HT of Comparative Example 2, synthesized in a high-temperature, high-pressure hydrothermal environment, exhibits lattice shrinkage, with its (003) peak shifting to a higher angle and exhibiting the smallest interlayer spacing. These results demonstrate that the cation exchange strategy successfully achieved precise reconstruction and high entropy of the lamination composition, providing a more open space for the exposure of active sites in subsequent electrocatalytic reactions.

[0091] Experimental Example 2: Morphology Test (1) Scanning electron microscopy (SEM) test The final materials obtained in Example 1 and Comparative Examples 1 to 2 were subjected to SEM morphology testing, and the results are as follows: Figure 2 As shown, the evolution of the microstructure of catalysts obtained by different synthetic strategies is illustrated. Comparative Example 1 ( Figure 2 The nickel-iron hydroxide precursors in Figures (a) to (c) formed a uniform and vertically grown nanosheet array on the surface of carbon paper fibers. The sheets were of uniform thickness and regularly arranged, exhibiting typical layered double hydroxide morphology. HELH-EC was obtained by electric field-driven cation exchange of NiFe-LDH. The HELH-EC obtained in Example 1 (… Figure 2 Figures (d) to (f) in the diagram fully inherit the nanosheet array structure of the precursor, but the sheet surface exhibits slight roughening and granulation characteristics, the sheet edges are clearer, and richer secondary nanostructures are visible. This is due to Co²⁺. + Cu² + Zn² + Partial displacement by plasma leads to laminar remodeling. In contrast, the HELH-HT synthesized in one step using the conventional hydrothermal method in Comparative Example 2... Figure 2 Figures (g) to (i) show a more typical and uniform two-dimensional nanosheet assembly, with larger sheet sizes and more dense and ordered stacking, reflecting the crystal evolution characteristics of uniform nucleation growth under high temperature and high pressure. The above morphological differences indicate that the electric field-driven exchange process, while achieving precise reconstruction of the lamellar composition, influences local crystallization kinetics through dynamic ion exchange, resulting in a more expansive and open nanosheet array and richer surface structures; while direct hydrothermal synthesis follows the traditional homogeneous nucleation growth path. The expanded interlamellar spacing and rich surface structures of the HELH-EC obtained in Example 1 are expected to provide more active sites and better mass transfer channels for electrocatalytic reactions.

[0092] (2) Transmission electron microscopy (TEM)-energy dispersive spectroscopy (EDS) test TEM-EDS tests were performed on the final materials obtained in Example 1 and Comparative Examples 1-2 to analyze the microstructure and elemental distribution characteristics of the three catalysts at the nanoscale. The results are as follows: Figure 3 As shown in the TEM image, the NiFe-LDH in Comparative Example 1 exhibits a typical nanosheet morphology with uniformly dispersed sheets. Its EDS image indicates that only Ni, Fe, and O elements are detected in a uniform distribution. Figure 3Figure (a) shows that it conforms to its binary composition design. NiFe-LDH was subjected to electric field-driven cation exchange to obtain HELH-EC. The resulting HELH-EC (Example 1) completely inherited the main structure of the nanosheets, with clearer edges. Its EDS diagram further confirmed that Co, Cu, and Zn elements were successfully introduced and achieved a highly uniform co-distribution with Ni, Fe, and O elements throughout the nanosheet region, indicating that the cation exchange reaction was sufficient and uniform. Figure 3 (Figure (b) in the figure). In contrast, the HELH-HT synthesized by the conventional hydrothermal method in Comparative Example 2 exhibits a thick layer nanosheet morphology with more uniform size and more regular stacking. Its EDS also shows a uniform distribution of six elements, Ni, Fe, Co, Cu, Zn, and O, and the signal intensity is relatively higher. Figure 3 (Figure (c) in the text), which is consistent with its growth mechanism of full precipitation under high temperature and high pressure.

[0093] Experiment Example 3: Inductively Coupled Plasma Mass Spectrometry Test The metal element content in the final materials obtained in Example 1, Comparative Example 1, and Comparative Example 2 was determined using inductively coupled plasma mass spectrometry (ICP-MS) on an Agilent 7700 ICP-MS instrument. Before testing, the samples were digested with a mixed solution of H₂SO₄, HNO₃, and HF using microwave, diluted to a fixed volume, and then tested.

[0094] The elemental composition of the sample was quantitatively analyzed using ICP-MS, and the results are as follows: Figure 4 As shown. The final material obtained in Comparative Example 1 ( Figure 4 In Figure (b), the atomic percentages of Ni and Fe are 53.3% and 46.7%, respectively, with a Ni / Fe atomic ratio of 1.14, consistent with the stoichiometric characteristics of typical layered bimetallic hydroxides. After cation exchange driven by an electric field, the final material obtained in Example 1 ( Figure 4 In Figure (a), the atomic percentages of Ni and Fe become 65.4% and 32.7%, respectively, significantly increasing the Ni / Fe atomic ratio to 2.00. Simultaneously, three metal elements, Co (0.8%), Cu (0.5%), and Zn (0.5%), were successfully introduced. This result clearly demonstrates that the cation substitution reaction preferentially occurs at Fe sites rather than Ni sites in traditional substitution under the influence of an electric field, achieving specific reconstruction of the laminate matrix and successfully constructing a high-entropy solid solution structure. In contrast, Comparative Example 2 (… Figure 4In Figure (c), the final material synthesized by the traditional hydrothermal method contains 52.6% Ni and 45.8% Fe atoms, with a Ni / Fe atomic ratio of 1.15, which is very close to the final material of Comparative Example 1. It also contains Co (0.7%), Cu (0.4%), and Zn (0.5%). This comparison confirms that the multi-metal composition of HELH-HT obtained in Comparative Example 2 mainly originates from simultaneous co-precipitation in the precursor solution, rather than in-situ replacement of existing layers.

[0095] Experiment Example 4: Electrochemical Performance Testing (1) Linear sweep voltammetry test – electrocatalytic oxidation of 5-hydroxymethylfurfural Linear sweep voltammetry (LSV) testing: The electrocatalytic performance of the catalyst was evaluated using LSV testing. Before testing, the catalyst was subjected to a linear sweep voltammetry (LSV) at a rate of 50 mV·s within the non-Radatian range (0–0.4 V vs. Hg / HgO). -1 Activation was performed using 20 cycles of cyclic voltammetry (CV) at a scan rate of 0–1.2 V vs. Hg / HgO. After activation, the voltammetry was applied at 10 mV·s⁻¹ within the potential range of 0–1.2 V vs. Hg / HgO. -1 LSV testing was performed at a constant scan rate, with magnetic stirring maintained throughout the test. All samples were repeatedly tested to obtain stable polarization curves before data recording. To eliminate the influence of solution resistance, 85% ohmic compensation was applied to the LSV data, calculated using the following formula: E = Evs.RHE-85%·iR (Formula 1) In Formula 1 above, E represents electromotive force in V; Evs.RHE represents the reversible hydrogen electrode electromotive force in V; i represents the current in mA; and R represents the resistance in Ω.

[0096] Tafel slope analysis: The reaction kinetics of the catalyst are evaluated using the slope of the Tafel curve. The Tafel curve is obtained from LSV data through the Tafel equation (Equation 2): E= blog(J)+a(Formula 2) In Formula 2 above, E represents the electric potential in V; blog represents the Tafel slope; and J represents the current density at the corresponding potential in mA·cm. -2 ; a is a constant.

[0097] The results are as follows Figure 5 As shown, HELH-EC in Example 1 exhibits significantly better overall performance than HELH-HT and NiFe-LDH in the electrocatalytic oxidation of HMF. (LSV curve) Figure 5Figure (a) shows that, in an electrolyte containing 50 mM 5-hydroxymethylfurfural (HMF), the HELH-EC of Example 1 exhibited the highest oxidation current density and the lowest onset potential, with a current density significantly higher than the final materials of Comparative Examples 1 and 2 at 1.50 V vs. RHE. Tafel slope analysis ( Figure 5 Figure (b) further confirms that the HELH-EC of Example 1 has the smallest Tafel slope (25.23 mV·dec). -1 The concentration was significantly lower than that of HELH-HT in Comparative Example 2 (50.13 mV·dec). -1 ) and Comparative Example 1 NiFe-LDH (134.7 mV·dec) -1 This indicates that it possesses the fastest interfacial reaction kinetics. Electrochemical active area measurement ( Figure 5 Figure (c) shows that the electric double-layer capacitance (Cdl) of HELH-EC in Example 1 is as high as 8.82 mF·cm. -2 The values ​​are HELH-HT (1.09 mF·cm⁻¹) from Comparative Example 2. -2 ) and Comparative Example 1 NiFe-LDH (0.25mF·cm) -2 The electrochemical impedance spectroscopy (EIS) was 8.1 times and 35.3 times higher than that of the standard EIS, confirming that it exposed the most abundant electrocatalytic active sites. Figure 5 Figure (d) further reveals that the charge transfer resistance (Rct) of HELH-EC in Example 1 is the lowest (14.82 Ω), significantly lower than that of HELH-HT in Comparative Example 2 (26.91 Ω) and NiFe-LDH in Comparative Example 1 (46.12 Ω), indicating that it has the lowest interfacial charge transport barrier and the fastest electron transfer rate. These results collectively confirm that the HELH-EC catalyst constructed using the electric field-driven cation exchange strategy has comprehensive advantages in terms of activity, kinetics, number of active sites, and charge transport efficiency.

[0098] (2) Constant potential electrolysis experiment - electrocatalytic oxidation of 5-hydroxymethylfurfural The conversion capacity, activity, and stability of the catalyst for 10 mL of 10 mM HMF were evaluated using the chronoamperometry (CA) method at different constant potentials. The charge passing through the system was calculated by integrating the it curve, and the Faraday efficiency of the reaction was determined by product analysis.

[0099] The catalytic performance and stability of HELH-EC from Example 1 were further evaluated through constant potential electrolysis experiments. Performance comparison at different operating potentials ( Figure 6Figure (a) shows that as the voltage increases from 1.40 V vs. RHE to 1.55 V vs. RHE, both the HMF conversion and the 2,5-furandicarboxylic acid (FDCA) selectivity exhibit a trend of first increasing and then stabilizing, reaching their optimal values ​​at 1.45 V vs. RHE, where both conversion and selectivity are close to 100%, indicating that the catalyst has good adaptability over a wide potential window. Cyclic stability testing ( Figure 6 Figure (b) shows that after 15 consecutive electrolysis cycles at 1.45 V vs. RHE, the HMF conversion, FDCA selectivity, and Faraday efficiency of HELH-EC in Example 1 did not show significant degradation, remaining above 95% of their initial values, confirming its excellent electrochemical durability. These results demonstrate that HELH-EC not only achieves efficient directional conversion of HMF at optimized potentials but also possesses excellent operational stability.

[0100] (3) Constant potential electrolysis experiment - electrocatalytic reduction of nitrate ions The effect of the catalyst on 10 mL of 100 mM NO3 was evaluated using chronoamperometry (CA) at different constant potentials. - The conversion capacity, activity, and stability of the reaction were determined. The charge passing through the system was calculated by integrating the it curve, and the Faraday efficiency of the reaction was determined by product analysis.

[0101] The catalytic performance of three catalysts in the nitrate reduction reaction was evaluated using a constant potential electrolysis experimental system. LVS curves ( Figure 7 Figure (a) shows that in a solution containing 0.1 M NO3 - In the electrolyte, the reduction current density of HELH-EC in Example 1 was significantly higher than that of the control sample, reaching -250 mA·cm at -0.4 V vs. RHE. -2 The above demonstrates optimal intrinsic catalytic activity. Comparison of ammonia yield at different operating voltages ( Figure 7 Figure (b) shows that the yield of HELH-EC in Example 1 increases continuously with a negative potential shift, reaching a maximum of 12 mg·h at -0.5V vs. RHE. -1 ·cm -2 The concentration was significantly higher than that of HELH-HT (7.2 mg / h) in control example 2. -1 ·cm -2 ) and Comparative Example 1 NiFe-LDH (3.5 mg·h) -1 ·cm -2 Comparison of Faraday efficiency at different voltages () Figure 7Figure (c) shows that the HELH-EC of Example 1 reaches a peak efficiency of approximately 90% at -0.4 V, significantly higher than HELH-HT (65%) in Comparative Example 2 and NiFe-LDH (42%) in Comparative Example 1, and maintains approximately 80% or higher over a wide potential window from -0.1 V vs. RHE to -0.4 V vs. RHE, demonstrating excellent electron utilization efficiency. Cyclic stability test ( Figure 7 Figure (d) shows that after seven consecutive cycles, the ammonia yield and Faraday efficiency of HELH-EC in Example 1 remained above 90% of their initial values. In contrast, HELH-HT in Comparative Example 2 and NiFe-LDH in Comparative Example 1 decreased to 85% and 76%, respectively, confirming that HELH-EC exhibits the best electrochemical durability. These results demonstrate that HELH-EC possesses high activity, high selectivity, and excellent stability in nitrate reduction, with significantly better overall performance than HELH-HT and NiFe-LDH. This is attributed to its optimized electronic states and abundant active sites due to its high-entropy structure.

[0102] (4) Construction and application of bifunctional electrocatalytic devices A dual-chamber H-type electrolytic cell (separated by a Nafion 117 membrane) was used. The anolyte was a mixed aqueous solution of 10 mM HMF and 1 M KOH, and the catholyte was a mixed aqueous solution of 0.1 M KNO3 and 1 M KOH. Linear sweep voltammetry (LSV, 10 mV·s) was performed in two-electrode mode. -1 The optimal coupling voltage was determined. Chronopotentiometric electrolysis or constant voltage electrolysis was performed at 1.50 V for an extended period, and current-time curves were recorded. The anolyte FDCA was quantified by high-performance liquid chromatography (HPLC), and the cathode product NH3 was determined by indophenol blue colorimetry. The total charge was calculated by integrating the it curve, and the Faradaic efficiency of the anolyte FDCA and cathode NH3 was calculated based on the product formation. The stability of the system was evaluated through multiple electrolysis cycles.

[0103] HMF OR||NO was constructed using HELH-EC from Example 1 as both an anode and cathode catalyst. 3- The RR (OR represents oxidation reaction, RR represents reduction reaction) full electrolysis system achieves simultaneous and efficient production of anode biomass value-added and cathode pollutant resource utilization. (Diagram of the device) Figure 8 Figure (a) shows the structure of a two-chamber electrolytic cell, with the anode chamber containing a 1 M KOH solution of 50 mM HMF and the cathode chamber containing a 1 M KOH solution of 0.1 M KNO3. LSV curve results ( Figure 8 Figure (b) shows that the initial voltage of this coupling system is approximately 1.2 V, and at 50 mA·cm⁻¹, the voltage is [missing information]. -2The required voltage at the current density is only 1.45 V, significantly lower than the traditional OER||HER system (>1.6 V), demonstrating its superior energy efficiency. At a tank voltage of 1.50 V, the Faraday efficiency of the anode FDCA (…) is… Figure 8 (c) Figure shows that the Faraday efficiency of the cathode NH3 reaches 92.3%. Figure 8 The (d) figure shows that the electrons flowing into the system were used efficiently and selectively to simultaneously produce two high-value-added chemicals, while side reactions such as oxygen evolution and hydrogen evolution were effectively suppressed. Cyclic stability testing ( Figure 8 Figure (e) shows that after seven consecutive cycles, the Faraday efficiency at both electrodes remained above 90% of the initial value, confirming the excellent operational stability of the total electrolysis system. These results demonstrate that the HMF OR||NO constructed by HELH-EC exhibits excellent performance. 3- The RR coupling system can synchronously, efficiently, and stably couple HMF and NO. 3- They are converted into FDCA and NH3 respectively, providing a new strategy for green electrochemical synthesis and resource utilization of pollutants.

[0104] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-entropy layered hydroxide bifunctional electrocatalyst, characterized in that, Includes the following steps: S1. Soluble nickel salt, soluble iron salt, ammonium fluoride and urea are mixed in water to obtain a mixed solution; a carbon-based support is placed in the obtained mixed solution and subjected to a hydrothermal reaction. After the reaction is complete, the catalyst precursor NiFe-LDH is obtained through post-treatment. S2. Electrochemical treatment was performed using a three-electrode system. A mixture containing soluble copper salt, soluble cobalt salt, and soluble zinc salt was used as the anolyte, and an aqueous solution containing potassium chloride and trisodium citrate was used as the catholyte. An Hg / HgO electrode was used as the reference electrode, and the catalyst precursor NiFe-LDH obtained in step S1 was used as the working electrode. The precursor was placed in the anolyte, and cyclic voltammetry was performed in the potential range of -0.9 to 1.2 V. After the scan was completed, post-processing was performed to obtain the high-entropy layered hydroxide bifunctional electrocatalyst. In step S1, the molar ratio of nickel in the soluble nickel salt to iron in the soluble iron salt is (2.5~3.5):1; In step S2, the molar ratio of copper in the soluble copper salt, cobalt in the soluble cobalt salt, and zinc in the soluble zinc salt is 1:(0.8~1.2):(0.8~1.2).

2. The preparation method according to claim 1, characterized in that, In step S1, the mixing ratio of nickel element in the soluble nickel salt with ammonium fluoride and urea is 1 mol: (50~70) g: (500~550) g.

3. The preparation method according to claim 1, characterized in that, The preparation conditions of the preparation method include at least one of the following: (1) The mass-to-volume ratio of urea to water is 1 g: (20~40) mL; (2) The soluble nickel salt includes at least one of nickel nitrate or its hydrate, nickel acetate or its hydrate, nickel chloride or its hydrate, and nickel sulfate or its hydrate; (3) The soluble iron salt includes at least one of ferric nitrate or its hydrate, ferric acetate or its hydrate, ferric chloride or its hydrate, and ferric sulfate or its hydrate.

4. The preparation method according to claim 1, characterized in that, The carbon-based carrier is selected from carbon paper or carbon cloth.

5. The preparation method according to claim 1, characterized in that, The temperature of the hydrothermal reaction is 110~130 ℃.

6. The preparation method according to claim 1, characterized in that, The preparation conditions of the preparation method include at least one of the following: (1) The soluble copper salt includes at least one of copper nitrate or its hydrate, copper acetate or its hydrate, copper chloride or its hydrate, and copper sulfate or its hydrate; (2) The soluble cobalt salt includes at least one of cobalt nitrate or its hydrate, cobalt acetate or its hydrate, cobalt chloride or its hydrate, and cobalt sulfate or its hydrate; (3) The soluble zinc salt is selected from at least one of zinc acetate or its hydrate, zinc nitrate or its hydrate, zinc chloride or its hydrate, and zinc sulfate or its hydrate.

7. The high-entropy layered hydroxide bifunctional electrocatalyst prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the high-entropy layered hydroxide bifunctional electrocatalyst of claim 7 in the electrocatalytic reduction of nitrate to ammonia and / or the electrocatalytic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid.

9. An electrocatalytic device, characterized in that, Includes power source, diaphragm, anode chamber, cathode chamber, anode, and cathode; The electrolyte in the anode chamber contains 5-hydroxymethylfurfural; The electrolyte in the cathode chamber contains nitrate ions; Both the anode and cathode are made of the high-entropy layered hydroxide bifunctional electrocatalyst described in claim 7.

10. The application of the electrocatalytic device according to claim 9 in the electrocatalytic reduction of nitrate to ammonia and the electrocatalytic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid.

Images