A composite material and its application in the electrocatalytic hydrogenation reduction of indigo.

Abstract

This invention discloses a composite material and its application in the electrocatalytic hydrogenation reduction of indigo. The composite material comprises hollow nanorods and an oxide layer; the oxide layer coats at least a portion of the surface of the hollow nanorods; the hollow nanorods consist of a shell and an internal cavity; the shell includes an inner shell and an outer shell; the inner shell includes nickel molybdate; the outer shell includes a Prussian blue analog and iron oxide; the oxide layer contains a metal element and oxygen; the metal element includes Ru, Gd, Cu, Co, Ce, and B. This invention uses hollow nanorods composed of nickel molybdate, a Prussian blue analog, and iron oxide as a substrate, and coats their surface with an oxide layer containing high-entropy oxides, greatly increasing the stability of the composite material. This composite material has advantages such as strong bonding, stable chemical interface, high catalytic activity, and high selectivity. Using this composite material, the electrocatalytic hydrogenation reduction of indigo can be promoted with high selectivity.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, and particularly relates to a composite material and its application in the electrocatalytic hydrogenation reduction of indigo. Background Technology

[0002] Natural indigo, as a natural dye, relies on the core process of reducing its insoluble form to a soluble leuco form. For a long time, both industrial and small-scale workshops have commonly used sodium dithionite as a reducing agent to convert insoluble indigo into its leuco form. However, this method has significant drawbacks. The most significant problem is severe environmental pollution. The sulfur-containing wastewater generated during the reduction process is difficult and costly to treat, contradicting the current advocacy of clean production. Secondly, this process requires extremely stringent control of reaction conditions. The alkalinity and reduction potential in the dye vat fluctuate continuously, necessitating frequent adjustments based on experience, resulting in poor process stability and difficulty in automation. Furthermore, the introduction of a strong reducing agent inevitably affects the unique color of natural indigo, potentially leading to over-reduction and a darker color, thus diminishing its value as a high-end natural dye. In addition, sodium dithionite itself is a high-cost and flammable hazardous chemical, adding extra safety burdens to its storage and transportation.

[0003] To find alternatives, electrochemical reduction technology has come into focus. However, existing electrochemical pathways all exhibit limitations when applied to the natural indigo system. Direct electrochemical reduction is limited by the extremely low water solubility of indigo molecules and the slow electrode reaction kinetics, resulting in low reduction efficiency. Against this backdrop, electrocatalytic hydrogenation reduction technology shows unique potential. This method utilizes highly reactive hydrogen atoms generated in situ by cathode electrolysis of water to directly attack and reduce indigo molecules. The hydrogen source is water, requiring no external chemical reducing agents, fundamentally eliminating the generation of sulfur-containing waste, making it an extremely green and economical reduction source. The entire process is mild, can be carried out at room temperature and pressure, and the reaction rate can be precisely controlled by adjusting external electrical parameters, providing possibilities for intelligent dyeing. However, the key challenge in successfully applying this technology to the reduction of natural indigo lies in how to effectively suppress the competing side reaction of electrochemical hydrogen evolution. Because the reduction potential range of natural indigo highly overlaps with the hydrogen evolution reaction range, most of the electrical energy is ineffectively consumed in hydrogen generation, resulting in a significantly low Faraday efficiency of the target reaction. The key to solving this problem lies in developing a dedicated cathode catalyst that can efficiently stabilize active hydrogen atoms and preferentially promote their combination with indigo molecules rather than another hydrogen atom.

[0004] High-entropy oxides (HEOs), as an emerging class of multi-component advanced functional materials, are composed of five or more metal elements in near equimolar ratios. Their unique "cocktail effect," severe lattice distortion, and slow diffusion make them highly promising in the field of catalysis. Compared to traditional single or binary oxide catalysts, HEOs can provide a large number of active sites with tunable electronic structures. Their complex surface chemistry is believed to exhibit unique adsorption behavior for various reaction intermediates, offering the possibility of finely controlling the competition between hydrogen evolution reaction and target hydrogenation reaction. However, the practical application of this conceptual material, HEOs, to electrocatalytic hydrogenation reduction systems, particularly for the complex and representative organic substrate of natural indigo, remains a technological gap. The challenges include designing specific element combinations to synergistically optimize activity and selectivity, and constructing stable large-scale preparation methods to obtain electrode structures suitable for industrial scale-up. Summary of the Invention

[0005] In order to overcome at least one of the problems existing in the prior art, one of the objectives of the present invention is to provide a composite material that combines high activity, high selectivity and excellent stability, which can effectively solve the core technical problems of poor selectivity and low Faraday efficiency in the electrocatalytic hydrogenation reduction of natural indigo. It not only has significant theoretical innovation value, but also has broad industrial application prospects.

[0006] The second objective of this invention is to provide a method for preparing the above-mentioned composite material.

[0007] A third objective of this invention is to provide a cathode for the electrocatalytic hydrogenation reduction of indigo.

[0008] The fourth objective of this invention is to provide a method for the electrocatalytic hydrogenation reduction of indigo.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A first aspect of the present invention provides a composite material comprising hollow nanorods and an oxide layer; the oxide layer covering at least a portion of the surface of the hollow nanorods; The hollow nanorods consist of a shell and an internal cavity; the shell includes an inner shell and an outer shell; the inner shell includes nickel molybdate; and the outer shell includes a Prussian blue analogue and iron oxide. The oxide layer contains metal elements and oxygen elements; the metal elements include Ru, Gd, Cu, Co, Ce and Ba.

[0010] This invention utilizes carefully selected Gd, Cu, Co, Ce, and Ba to form a high-entropy oxide, which is then doped with Ru. The resulting oxide layer exhibits a suitable adsorption energy for active hydrogen atoms, ensuring continuous generation while moderately delaying their desorption and binding processes. This provides a valuable time window for indigo molecules to contact and react, fundamentally improving reaction selectivity. The method combines low-noble metals with non-noble metals, offering advantages such as simplicity, mildness, safety, and low cost. The oxide layer is constructed based on the high-entropy oxide, and the Ru doping significantly enhances the electrocatalytic hydrogenation reduction activity of the composite material. Simultaneously, it ensures compatibility between the high-entropy oxide and the metal compounds within the hollow nanorods, resulting in a composite material with strong bonding, stable chemical interfaces, high catalytic activity, and high selectivity. This addresses the core technical challenges of poor selectivity and low Faraday efficiency in the electrocatalytic hydrogenation reduction of natural indigo, thus overcoming current technological bottlenecks and promoting efficient and green electrocatalytic reduction of natural indigo for dyeing.

[0011] In some embodiments of the invention, the Prussian blue analogue (PBA) comprises potassium nickel ferrocyanide (KNiFe(CN)6). In some embodiments of the invention, the composite material is used for the electrocatalytic hydrogenation reduction of indigo.

[0012] In some embodiments of the present invention, the application of the composite material in the electrocatalytic hydrogenation reduction of indigo is also provided.

[0013] In some embodiments of the present invention, each element in the metal element independently accounts for 10-25% of the total molar amount of the metal element; for example, it can be any value of 10%, 12%, 15%, 17%, 20%, 22% or 25% or a range between any two; in some specific embodiments of the present invention, each element in the metal element independently accounts for 15-17% of the total molar amount of the metal element.

[0014] In some embodiments of the present invention, the molar content of each element in the metal element is equal.

[0015] In some embodiments of the present invention, the iron oxide crystal morphology is cubic.

[0016] The surface of the hollow nanorods is coated with cubic iron oxide, and the electric field strength at the tip is stronger than that at other locations, which helps the oxide layer grow.

[0017] In some embodiments of the present invention, the composite material further includes nickel foam; the nickel foam serves as the growth substrate for the hollow nanorods.

[0018] A second aspect of the present invention provides a method for preparing a composite material as described in the first aspect of the present invention, comprising the following steps: using the hollow nanorod as a working electrode and an aqueous solution containing the metal element as an electrolyte, performing electrodeposition to obtain an electrodeposition product; and annealing the electrodeposition product to obtain the composite material.

[0019] The preparation process of this invention does not use dangerous chemical reagents (such as sodium borohydride, hydrazine hydrate, etc.) or toxic reagents. It has the advantages of being simple, mild, safe and efficient. The raw materials are simple, the process is concise and easy to operate, and it is suitable for large-scale preparation. The reaction process is green and safe.

[0020] In some embodiments of the present invention, the precursor of the metal element includes at least one of a nitrate, a chloride, or an acetate containing the metal element.

[0021] In some embodiments of the present invention, the precursors of the metal element include ruthenium chloride, gadolinium nitrate, copper nitrate, cobalt nitrate, cerium nitrate, and barium acetate; in some specific embodiments of the present invention, the precursors of the metal element include RuCl3, Gd(NO3)3·6H2O, Cu(NO3)2·3H2O, Co(NO3)2·6H2O, Ce(NO3)3·6H2O, and (CH3COO)2Ba.

[0022] In some embodiments of the present invention, in the precursors of the metal elements, the precursors of each element independently account for 10-25% of the total molar amount of the precursors of the metal elements; for example, it can be any value or a range between 10%, 12%, 15%, 17%, 20%, 22%, or 25%; in some specific embodiments of the present invention, in the precursors of the metal elements, the precursors of each element independently account for 15-17% of the total molar amount of the precursors of the metal elements.

[0023] In some embodiments of the present invention, the molar content of each element's precursor is equal in the precursor of the metal element.

[0024] In some embodiments of the present invention, the molar amounts of RuCl3, Gd(NO3)3·6H2O, Cu(NO3)2·3H2O, Co(NO3)2·6H2O, Ce(NO3)3·6H2O and (CH3COO)2Ba are equal in the precursors of the metal elements.

[0025] In some embodiments of the present invention, the total concentration of the precursor of the metal element in the electrolyte is 0.3~1.5 mol / L; in some embodiments of the present invention, the total concentration of the precursor of the metal element in the electrolyte is 0.5~1 mol / L.

[0026] In some embodiments of the present invention, the electrolyte also contains additives.

[0027] In some embodiments of the present invention, the additive includes at least one of ammonium chloride, sodium chloride, or sodium citrate; in some specific embodiments of the present invention, the additive includes ammonium chloride (NH4Cl), sodium chloride (NaCl), and sodium citrate (C6H5Na3O7).

[0028] In some embodiments of the present invention, the mass ratio of ammonium chloride, sodium chloride and sodium citrate in the additive is 1:(1~3):(0.5~2); in some specific embodiments of the present invention, the mass ratio of ammonium chloride, sodium chloride and sodium citrate in the additive is 1:(1.5~2.4):(1~1.7).

[0029] In some embodiments of the present invention, the total concentration of the additive in the electrolyte is 10-20 g / L; in some specific embodiments of the present invention, the total concentration of the additive in the electrolyte is 13-16 g / L.

[0030] In some embodiments of the present invention, the electrodeposition uses platinum as the counter electrode and a calomel electrode as the reference electrode.

[0031] In some embodiments of the present invention, the electrodeposition potential is -1.5 to -3V; in some specific embodiments of the present invention, the electrodeposition potential is -2 to -2.2V.

[0032] In some embodiments of the present invention, the electrodeposition time is 2 to 10 minutes; in some specific embodiments of the present invention, the electrodeposition time is 4 to 6 minutes.

[0033] In some embodiments of the present invention, the annealing temperature is 250~400℃; in some specific embodiments of the present invention, the annealing temperature is 300~350℃.

[0034] In some embodiments of the present invention, the annealing time is 100-150 min; in some specific embodiments of the present invention, the annealing time is 110-130 min.

[0035] In some embodiments of the present invention, the annealing process is performed in an oxygen-containing atmosphere; in some specific embodiments of the present invention, the oxygen-containing atmosphere includes air.

[0036] In some embodiments of the present invention, the hollow nanorods are prepared by a method comprising the following steps: mixing nickel foam with an aqueous solution containing a nickel source and a molybdenum source, performing a hydrothermal reaction, growing nickel molybdate nanorods on the nickel foam to obtain a precursor substrate; mixing the precursor substrate with an aqueous solution of potassium ferricyanide, performing an etching reaction to obtain the hollow nanorods.

[0037] In some embodiments of the present invention, the temperature of the hydrothermal reaction is 130~170°C; in some specific embodiments of the present invention, the temperature of the hydrothermal reaction is 140~160°C.

[0038] In some embodiments of the present invention, the holding time for the hydrothermal reaction is 4-8 hours; in some specific embodiments of the present invention, the holding time for the hydrothermal reaction is 5-7 hours.

[0039] In some embodiments of the present invention, the etching reaction temperature is 50~80°C; in some specific embodiments of the present invention, the etching reaction temperature is 60~70°C.

[0040] In some embodiments of the present invention, the nickel source includes at least one of nickel nitrate, nickel chloride, or nickel acetate; in some specific embodiments of the present invention, the nickel source is selected from nickel nitrate; more specifically, Ni(NO3)2·6H2O.

[0041] In some embodiments of the present invention, the molybdenum source includes at least one of ammonium molybdate, sodium molybdate, or ammonium molybdate; in some specific embodiments of the present invention, the molybdenum source is selected from ammonium molybdate; more specifically, it is (NH4)6Mo7O. 24 ·4H2O.

[0042] In some embodiments of the present invention, the concentration of the nickel source in the aqueous solution containing the nickel source and the molybdenum source is 0.1~0.5 mol / L; in some specific embodiments of the present invention, the concentration of the nickel source in the aqueous solution containing the nickel source and the molybdenum source is 0.3~0.4 mol / L.

[0043] In some embodiments of the present invention, the concentration of the molybdenum source in the aqueous solution containing the nickel source and the molybdenum source is 0.001~0.002 mol / L; in some specific embodiments of the present invention, the concentration of the molybdenum source in the aqueous solution containing the nickel source and the molybdenum source is 0.0013~0.0017 mol / L.

[0044] In some embodiments of the present invention, the concentration of the potassium ferricyanide aqueous solution is 3-10 g / L; in some specific embodiments of the present invention, the concentration of the potassium ferricyanide aqueous solution is 5-7 g / L.

[0045] In some embodiments of the present invention, the nickel foam is pretreated before undergoing the hydrothermal reaction. The pretreatment removes surface oxides.

[0046] In some embodiments of the present invention, the pretreatment of the nickel foam is as follows: ultrasonic treatment is performed sequentially with water, hydrochloric acid solution and ethanol; specifically, the water can be deionized water; the concentration of the hydrochloric acid solution can be 5~7 mol / L; the ethanol can be anhydrous ethanol; and the ultrasonic treatment time can be 4~6 min.

[0047] A third aspect of the present invention provides a cathode for the electrocatalytic hydrogenation reduction of indigo, the cathode comprising the composite material described in the first aspect of the present invention, or the composite material prepared by the preparation method described in the second aspect of the present invention.

[0048] The cathode made of the above-mentioned composite material has good stability. In addition, the doping of Ru element significantly improves the electrocatalytic hydrogenation reduction activity of the electrode, and it has good activity in the electrocatalytic hydrogenation reduction of indigo.

[0049] A fourth aspect of the present invention provides a method for electrocatalytic hydrogenation reduction of indigo, wherein the cathode described in the third aspect of the present invention is used to electrocatalytically hydrogenate and reduce an aqueous solution of indigo.

[0050] In some embodiments of the present invention, the indigo concentration of the indigo aqueous solution is 0.5~10 g / L; in some specific embodiments of the present invention, the indigo concentration of the indigo aqueous solution is 1~5 g / L.

[0051] In some embodiments of the present invention, the indigo in the indigo aqueous solution is natural indigo.

[0052] In some embodiments of the present invention, the indigo aqueous solution further contains sodium hydroxide; in some specific embodiments of the present invention, the concentration of sodium hydroxide in the indigo aqueous solution is 0.5~1.5 mol / L.

[0053] In some embodiments of the present invention, in the method of electrocatalytic hydrogenation reduction of indigo, a platinum sheet electrode clamp is used to fix the cathode as the working electrode, mercury / mercuric oxide is used as the reference electrode, platinum is used as the counter electrode, and an indigo aqueous solution is used as the electrolyte.

[0054] The beneficial effects of this invention are as follows: This invention uses hollow nanorods composed of nickel molybdate, Prussian blue analogues and iron oxide as a substrate, and coats its surface with an oxide layer containing high-entropy oxides, which greatly increases the stability of the composite material. In addition, due to the doping of Ru, the electrocatalytic hydrogenation reduction activity of the composite material is significantly improved. This composite material has the advantages of strong binding force, stable chemical interface, high catalytic activity and high selectivity. Using this composite material, the electrocatalytic hydrogenation reduction of indigo can be promoted with high selectivity. Attached Figure Description

[0055] Figure 1 These are scanning electron microscope images of Example 1 and Comparative Example 2.

[0056] Figure 2 The image shows the UV-Vis absorption spectra of natural indigo solutions of different concentrations.

[0057] Figure 3 The graph shows the electrocatalytic hydrogenation reduction test results of Example 1 and Comparative Examples 1-2 at a potential of -1V.

[0058] Figure 4 The cyclic voltammetry test results for Example 1 and Comparative Example 2 are shown in the potential range of -0.6V to -0.8V.

[0059] Figure 5 Images of indigo solutions before and after 1 hour of electrocatalytic hydrogenation reduction of indigo using the materials in Examples 1-3. Detailed Implementation

[0060] The following specific embodiments further illustrate the content of the present invention in detail. It should also be understood that the following embodiments are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by those skilled in the art based on the principles described herein are all within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make selections within a suitable range based on the description herein, and are not intended to be limited to the specific data in the examples below. Unless otherwise specified, the raw materials, reagents, or apparatus used in the following embodiments and comparative examples can be obtained from conventional commercial sources or by existing known methods.

[0061] Example 1 A composite material, designated Ru / HEOs / NiMoO4 / NF-PBA, is prepared as follows: S1. First, take a 2cm × 4cm piece of nickel foam (NF) and clean the surface oxides with deionized water, 6mol / L hydrochloric acid, and anhydrous ethanol for 5 minutes each. Then, use 10 mmol (NH4)6Mo7O 24·4H2O and 0.05mol Ni(NO3)2·6H2O were dissolved in 30mL of deionized water and stirred for 30min. The resulting solution and the cleaned nickel foam were placed in a 50mL high-pressure reactor and kept at 150℃ for 6h to grow NiMoO4 on the nickel foam to obtain NiMoO4 / NF. Then, it was placed in an oven to dry for later use. S2. Dissolve 200 mg of K3[Fe(CN)6] in 30 mL of deionized water and stir until clear. Then, add NiMoO4 / NF to the K3[Fe(CN)6] solution and place in an oven to etch at 60 °C for 2 h to form hollow NiMoO4 / NF-PBA nanorods, which are then dried for later use. Here, PBA refers to KNiFe(CN)6.

[0062] S3. Subsequently, 5 mmol of equimolar amounts of Gd(NO3)3·6H2O, RuCl3, Cu(NO3)2·3H2O, Co(NO3)2·6H2O, Ce(NO3)3·6H2O, and (CH3COO)2Ba, along with 150 mg of NH4Cl, 200 mg of C6H5Na3O7, and 300 mg of NaCl, were weighed and dissolved in 50 mL of deionized water. The solution was stirred for 15 min to prepare the electrolyte. Constant voltage electrodeposition was performed at -2 V for 5 min in a three-electrode system (working electrode: NiMoO4 / NF-PBA; counter electrode: platinum mesh; reference electrode: calomel electrode) to obtain Ru / HEOs / NiMoO4 / NF-PBA. The Ru / HEOs / NiMoO4 / NF-PBA was then dried and stored for later use. Finally, it was annealed in a tube furnace at 300 °C for 120 min in an air stream to obtain the Ru / HEOs / NiMoO4 / NF-PBA material.

[0063] Example 2 A composite material, denoted as Ru / HEOs / NiMoO4 / NF-PBA-3, differs from Example 1 in that the electrodeposition time in step S3 of this example is 3 minutes, while the other conditions are the same as in Example 1.

[0064] Example 3 A composite material, denoted as Ru / HEOs / NiMoO4 / NF-PBA-8, differs from Example 1 in that the electrodeposition time in step S3 of this example is 8 minutes, while the other conditions are the same as in Example 1.

[0065] Comparative Example 1 A composite material, denoted as HEOs / NiMoO4 / NF-PBA, differs from Example 1 in that the electrolyte used for electrodeposition in step S3 of this example does not contain Ru, while the other conditions are the same as in Example 1.

[0066] Comparative Example 2 A composite material, denoted as NiMoO4 / NF-PBA, differs from Example 1 in that step S3 is omitted in this example, while all other conditions are the same as in Example 1.

[0067] Comparative Example 2: No oxide layer was prepared.

[0068] Performance testing (1) Morphological and structural characterization of composite materials Figure 1 The images shown are scanning electron microscope (SEM) images of Example 1 and Comparative Example 2, where (a) is an SEM image of NiMoO4 / NF-PBA in Comparative Example 2, and (b) is an SEM image of Ru / HEOs / NiMoO4 / NF-PBA in Example 1. Figure 1 As can be observed in (a), NiMoO4 / NF-PBA has a hollow nanorod array morphology and is covered with Fe2O3 particles. Since the Fe2O3 particles are cubic, the electric field intensity is stronger at the tips compared to other locations, which facilitates the growth of the high-entropy oxide layer. Figure 1 As can be observed in (b), after electrodeposition in step S3, a high-entropy oxide layer is uniformly covered on the surface of NiMoO4 / NF-PBA, and its rough surface morphology provides a larger active area and active sites for subsequent electrocatalytic hydrogenation reduction.

[0069] Furthermore, if oxide layers are directly electrodeposited on nickel foam or NiMoO4 / NF, insufficient conductivity or excessive deposition potential can lead to uneven element distribution. In contrast, the hollow NiMoO4 / NF-PBA nanorods obtained in Example 1, after etching, have a Fe2O3 transition layer on their surface and possess sharp edges. This tip effect results in a more uniform surface element distribution and higher electrocatalytic activity.

[0070] (2) Electrocatalytic hydrogenation reduction performance test, the test steps are as follows: 1) The working electrode uses a platinum sheet electrode holder, which is just immersed in the electrolyte; 2) Prepare natural indigo solutions with concentrations of 1 g / L, 2 g / L, 3 g / L, 4 g / L, and 5 g / L respectively, then add excess sodium hydrosulfite to completely reduce it, and then measure the ultraviolet spectrum of the indigo leuco form to establish a standard curve; 3) Electrocatalytic hydrogenation reduction of natural indigo: The samples from each example and comparative example were fixed with platinum electrode clamps as working electrodes, mercury / mercuric oxide as reference electrodes, and a platinum mesh as the counter electrode. An aqueous solution containing 1M NaOH and 5g / L natural indigo was used as the electrolyte. Electrocatalytic hydrogenation reduction was performed for 1 hour on an electrochemical workstation. The absorbance of solutions sampled at different reduction times was measured using a UV-Vis spectrophotometer, and the conversion rate was calculated based on a standard curve. The conversion rate was measured at a visible wavelength of 485 nm.

[0071] Figure 2 The images show the UV-Vis absorption spectra of natural indigo solutions at different concentrations. (a) is the standard curve, and (b) is the UV-Vis absorption spectrum. The linear relationship obtained by fitting is A = 0.544 + 0.646C (where A is the absorbance and C is the concentration of the natural indigo solution).

[0072] Figure 3 The graph shows the electrocatalytic hydrogenation reduction test results of Example 1 and Comparative Examples 1-2 at a potential of -1V. Figure 3 As can be seen, when reduction was performed at a potential of -1V, the sample of Example 1 exhibited the highest conversion rate due to the effective increase in surface active sites caused by Ru doping, followed by Comparative Example 2, with Comparative Example 1 showing the lowest conversion rate. The specific conversion rates of the three are shown in Table 1.

[0073] Table 1 Conversion rate data for examples and comparative examples

[0074] In addition, cyclic voltammetry (CV) tests were performed on Example 1 and Comparative Example 2 within the potential range of -0.6V to 0.8V, and the reduction peaks were analyzed by integration. Figure 4 The figures show the cyclic voltammetry results for Example 1 and Comparative Example 2 in the potential range of -0.6V to 0.8V; where (a) is Example 1 and (b) is Comparative Example 2. The results show that the reduction peak area of ​​Example 1 is 0.00465, significantly larger than that of Comparative Example 2 (0.00192). The increased reduction peak area further explains the higher conversion rate of Example 1 during electrocatalysis.

[0075] To investigate the effect of different electrodeposition times on the reduction of indigo in solution, the composite materials of Examples 1-3 were subjected to electrocatalytic hydrogenation reduction of indigo, and the reaction system before and after the reaction was irradiated with a light source to test the change in its transmittance. Figure 5Images of indigo solutions from Examples 1-3 before and after 1 hour of electrocatalytic hydrogenation reduction of indigo. (a) shows the material from Example 1 before the reaction; (b) shows the material from Example 1 after 1 hour of reaction; (c) shows the material from Example 2 before the reaction; (d) shows the material from Example 2 after 1 hour of reaction; (e) shows the material from Example 3 before the reaction; and (f) shows the material from Example 3 after 1 hour of reaction. It is clearly observed that the sample obtained in Example 1 with an electrodeposition time of 5 min exhibits the highest transmittance of the indigo solution after the reaction. Since the transmittance gradually increases as indigo is reduced and dissolved in the solution, this indicates that more indigo is reduced and dissolved in the solvent. This phenomenon demonstrates that the sample synthesized in Example 1 with a 5-min electrodeposition time exhibits better reduction performance compared to Examples 2-3.

[0076] In summary, this invention uses hollow nanorods composed of nickel molybdate, Prussian blue analogues, and iron oxide as a substrate, and coats their surface with an oxide layer containing high-entropy oxides, which greatly increases the stability of the composite material. In addition, due to the doping of Ru, the electrocatalytic hydrogenation reduction activity of the composite material is significantly improved. This composite material has the advantages of strong binding force, stable chemical interface, high catalytic activity, and high selectivity. It can be used to promote the electrocatalytic hydrogenation reduction of indigo with high selectivity.

Claims

1. A composite material, characterized in that, It includes hollow nanorods and an oxide layer; the oxide layer covers at least a portion of the surface of the hollow nanorods; The hollow nanorods consist of a shell and an internal cavity; the shell includes an inner shell and an outer shell; the inner shell includes nickel molybdate; and the outer shell includes a Prussian blue analogue and iron oxide. The oxide layer contains metal elements and oxygen elements; the metal elements include Ru, Gd, Cu, Co, Ce and Ba.

2. The composite material according to claim 1, characterized in that, Each of the metal elements independently accounts for 10-25% of the total molar amount of the metal element; And / or, the iron oxide crystal morphology is cubic.

3. A method for preparing the composite material as described in claim 1 or 2, characterized in that, Includes the following steps: Using the hollow nanorods as the working electrode and the aqueous precursor containing the metal element as the electrolyte, electrodeposition was performed to obtain the electrodeposition product. The electrodeposited product is annealed to obtain the composite material.

4. The preparation method according to claim 3, characterized in that, The precursor of the metal element includes at least one of the nitrate, chloride, or acetate containing the metal element; And / or, the total concentration of the precursor of the metal element in the electrolyte is 0.3~1.5 mol / L; And / or, the electrolyte also contains additives; the additives include at least one of ammonium chloride, sodium chloride, or sodium citrate.

5. The preparation method according to claim 3, characterized in that, The electrodeposition potential is -1.5 ~ -3V; And / or, the electrodeposition time is 2 to 10 minutes; And / or, the annealing temperature is 250~400℃; And / or, the annealing process takes 100-150 minutes; And / or, the annealing process is performed in an oxygen-containing atmosphere.

6. The preparation method according to claim 3, characterized in that, The hollow nanorods are prepared by a method comprising the following steps: mixing nickel foam with an aqueous solution containing a nickel source and a molybdenum source, performing a hydrothermal reaction, growing nickel molybdate nanorods on the nickel foam to obtain a precursor substrate; mixing the precursor substrate with an aqueous solution of potassium ferricyanide, performing an etching reaction to obtain the hollow nanorods.

7. The preparation method according to claim 6, characterized in that, The temperature of the hydrothermal reaction is 130~170℃; And / or, the holding time for the hydrothermal reaction is 4~8 hours; And / or, the etching reaction temperature is 50~80℃.

8. The preparation method according to claim 6, characterized in that, The nickel source includes at least one of nickel nitrate, nickel chloride, or nickel acetate; And / or, the molybdenum source includes at least one of ammonium molybdate, sodium molybdate, or ammonium molybdate; And / or, in the aqueous solution containing the nickel source and the molybdenum source, the concentration of the nickel source is 0.1~0.5 mol / L; And / or, in the aqueous solution containing the nickel source and the molybdenum source, the concentration of the molybdenum source is 0.001~0.002 mol / L; And / or, the concentration of the potassium ferricyanide aqueous solution is 3~10 g / L.

9. A cathode for the electrocatalytic hydrogenation reduction of indigo, characterized in that, The cathode comprises the composite material according to claim 1 or 2, or the composite material prepared by any one of claims 3 to 8.

10. A method for electrocatalytic hydrogenation reduction of indigo, characterized in that, Electrocatalytic hydrogenation reduction of indigo aqueous solution was performed using the cathode described in claim 9.

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