Three-dimensional flower-shaped heteropolyacid-based composite material as well as preparation method and application thereof

Abstract

The invention provides a three-dimensional flower-shaped heteropolyacid-based composite material as well as a preparation method and application thereof, and belongs to the technical field of electro-catalytic materials. According to the preparation method, firstly, MXene is attached to the surface of foamed nickel by utilizing electrostatic attraction, then phosphomolybdic acid, NiCo-LDH and MXene are compounded by utilizing an electrochemical deposition method, and the PMo12-coated NiCo-LDH / MX / NF catalyst is successfully prepared. According to the invention, phosphomolybdic acid, NiCo-LDH and MXene are compounded to construct a synergistic heterostructure, so that the specific surface area of the electrode material is increased, the contact area between the electrode material and lignin is increased, and Caryl-O (C) bonds in lignin are subjected to efficient and mild electrocatalytic reduction cracking on lignin.

Description

Technical Field

[0001] This invention relates to the field of electrocatalytic materials technology, and in particular to a three-dimensional flower-like heteropolyacid-based composite material, its preparation method, and its application. Background Technology

[0002] Lignin is abundant, renewable, readily available, and inexpensive, showing great potential in the production of fuels and the value-added production of small-molecule aromatic compounds, thereby reducing dependence on fossil fuel resources. Therefore, developing new, efficient, selective, environmentally friendly, and mild-condition catalytic processes is crucial for biomass utilization and biometallurgical technology, and is also an important research topic in the field of sustainable environmental resource utilization.

[0003] Electrochemical catalysis has attracted widespread attention due to its advantages of low energy consumption, greenness, and convenience; therefore, the electrocatalytic depolymerization of lignin has aroused great interest. The cleavage of the phenoxy bond (Caryl-O(C)) in the β-O-4 bond of lignin holds promise for mitigating the condensation of degradation products and improving product value. Currently, common cleavage methods include thermochemical methods, biological methods, photocatalytic methods, and electrochemical reduction methods. Among these, electrochemical reduction offers strong controllability and avoids excessive bond breaking. However, due to its high dissociation energy (~409 kJ / mol), it requires further research and development. -1 Caryl-O(C) bonds are prone to over-reduction, and current methods have not yet achieved highly selective and high-yield electrochemical reduction of Caryl-O(C) bonds. Summary of the Invention

[0004] The purpose of this invention is to provide a three-dimensional flower-like heteropolyacid-based composite material, its preparation method and application, which can achieve precise cleavage of lignin Caryl-O(C) bonds and improve the selectivity and yield of electrochemical reduction of lignin.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing a three-dimensional flower-like heteropolyacid-based composite material, comprising the following steps:

[0007] Nickel foam was impregnated in a hexadecyltrimethylammonium bromide solution to perform surface modification, resulting in surface-modified nickel foam.

[0008] The surface-modified nickel foam was impregnated in an MXene dispersion for adsorption to obtain MX / NF;

[0009] Using the MX / NF as the working electrode and the cobalt salt solution as the electrolyte, the first electrodeposition was performed by cyclic voltammetry to obtain Co(OH)2 / MX / NF;

[0010] Using an aqueous solution of phosphomolybdic acid as the electrolyte and the Co(OH)₂ / MX / NF as the working electrode, a second electrodeposition was performed using cyclic voltammetry to obtain PMo. 12 / Co(OH)2 / MX / NF electrode;

[0011] The PMo 12 The / Co(OH)2 / MX / NF electrode underwent a coordination reaction in a 2-methylimidazole solution to obtain PMo. 12 @ZIF-67 / MX / NF;

[0012] The PMo 12 @ZIF-67 / MX / NF was impregnated in a nickel salt solution and subjected to an ion exchange reaction to obtain a three-dimensional flower-like heteropolyacid-based composite material.

[0013] Preferably, the concentration of the hexadecyltrimethylammonium bromide solution is 2–10 mg / mL; the surface modification time is 3–10 min; the concentration of the MXene dispersion is 4–10 mg / mL; and the adsorption time is 30–60 min.

[0014] Preferably, the potential range of the first electrodeposition is -0.4V to -1.6V, the scan rate is 0.01 to 0.10V / s, and the number of cycles is 4 to 10.

[0015] Preferably, the phosphomolybdic acid in the aqueous solution is a Keggin-type heteropolyacid H3PMo. 12 O 40 The concentration of the phosphomolybdic acid aqueous solution is 1.5–3.5 mg / mL.

[0016] Preferably, the voltage range for the second electrodeposition is -0.9 to 0.4 V, the scan rate is 0.01 to 0.10 V / s, and the number of cycles is 10 to 20.

[0017] Preferably, the concentration of the 2-methylimidazole solution is 1–2.5 mmol / mL; and the coordination reaction time is 1–3 h.

[0018] Preferably, the concentration of the nickel salt solution is 4–6 mg / mL; and the ion exchange reaction time is 12–24 h.

[0019] The present invention provides a three-dimensional flower-like heteropolyacid-based composite material prepared by the preparation method described in the above technical solution.

[0020] This invention provides the application of the three-dimensional flower-like heteropolyacid-based composite material described above in the electrocatalytic preparation of monobenzene ring compounds from lignin.

[0021] Preferably, the method for preparing monobenzene ring compounds by electrocatalysis of lignin includes the following steps:

[0022] A three-electrode structure is adopted, with a three-dimensional flower-like heteropolyacid-based composite material as the working electrode and a lignin-containing solution as the electrolyte for electrochemical depolymerization; the concentration of lignin in the electrolyte is 1-5 mmol / L.

[0023] This invention provides a method for preparing a three-dimensional flower-like heteropolyacid-based composite material. First, MXene is electrostatically attached to the surface of nickel foam. Then, phosphomolybdic acid, NiCo-LDH, and MXene are composited using electrodeposition to successfully prepare PMo. 12 @NiCo-LDH / MX / NF catalyst.

[0024] Single MXene materials have low specific capacity, and their surface functional groups are prone to irreversible oxidation in alkaline electrolytes, resulting in limited cycle stability. This invention combines phosphomolybdic acid, NiCo-LDH, and MXene to construct a synergistic heterostructure, successfully overcoming the performance bottleneck of MXene materials, increasing the specific surface area of ​​the electrode material, and enhancing its contact area with lignin. The addition of Ni and Co increases the active sites of the electrode material. H3PMo 12 O 40 The catalytic activity of the electrode material was enhanced, enabling efficient and mild electrocatalytic reduction and cleavage of the Caryl-O(C) bond in lignin.

[0025] The three-dimensional flower-like heteropolyacid-based composite material of the present invention was used for electrocatalytic reduction and cleavage of lignin, and the yield of monobenzene ring compound (phenol) reached 57.2%. Attached Figure Description

[0026] Figure 1 In the example, (a) represents PMo in Example 1. 12 (a) SEM images of the NiCo-LDH / MX / NF-25 composite material at different magnifications; (b) SEM images of NF, MXene, and PMo in Example 1. 12 (c) Cross-sectional SEM image of @NiCo-LDH / MX / NF-25; (d) PMo in Example 1 12 @NiCo-LDH / MX / NF-25 and PMo in Comparative Example 1 12 Nitrogen adsorption-desorption isotherms of @NiCo-LDH / NF;

[0027] Figure 2 For NF, MX / NF, PMo 12 / NF、PMo 12 @NiCo-LDH / NF, PMo 12@ZIF-67 / MX / NF-25 and PMo 12 (a) LSV curve, (b) Tafel curve, (c) Nyquist curve and (d) double-layer capacitance of @NiCo-LDH / MX / NF-25;

[0028] Figure 3 For different working electrodes (a) and different H3PMo 12 O 40 The effect of lignin content in composite material (b) on lignin depolymerization properties;

[0029] Figure 4 The effects of different reaction times and voltage conditions on the distribution of lignin depolymerization products: (a) -0.48V, (b) -0.38V and (c) -0.28V;

[0030] Figure 5 The conversion rate and yield of different lignins;

[0031] Figure 6 For PMo 12 @NiCo-LDH / MX / NF-25 (a) CV plot before and after 2000 cycles, (b) stability, (c) cyclic test and Faraday efficiency, and (d) SEM plot after recovery;

[0032] Figure 7 This represents a possible transformation path mechanism for PPE. Detailed Implementation

[0033] In this invention, unless otherwise specified, the raw materials or reagents required for preparation are all commercially available products well known to those skilled in the art.

[0034] This invention provides a method for preparing a three-dimensional flower-like heteropolyacid-based composite material, comprising the following steps:

[0035] Nickel foam was impregnated in a hexadecyltrimethylammonium bromide solution to perform surface modification, resulting in surface-modified nickel foam.

[0036] The surface-modified nickel foam was impregnated in an MXene dispersion for adsorption to obtain MX / NF;

[0037] Using the MX / NF as the working electrode and the cobalt salt solution as the electrolyte, the first electrodeposition was performed by cyclic voltammetry to obtain Co(OH)2 / MX / NF;

[0038] Using an aqueous solution of phosphomolybdic acid as the electrolyte and the Co(OH)₂ / MX / NF as the working electrode, a second electrodeposition was performed using cyclic voltammetry to obtain PMo. 12 / Co(OH)2 / MX / NF electrode;

[0039] The PMo 12 The / Co(OH)2 / MX / NF electrode underwent a coordination reaction in a 2-methylimidazole solution to obtain PMo. 12 @ZIF-67 / MX / NF;

[0040] The PMo 12 @ZIF-67 / MX / NF was impregnated in a nickel salt solution and subjected to an ion exchange reaction to obtain a three-dimensional flower-like heteropolyacid-based composite material.

[0041] In this invention, nickel foam (NF) is preferably cut into 2cm×2cm pieces and ultrasonically cleaned for 15 minutes each with acetone, hydrochloric acid, ethanol and deionized water to remove surface impurities. The cleaned NF sheets are then dried in a vacuum drying oven at 60°C for 8 hours and then immersed in a cetyltrimethylammonium bromide solution.

[0042] In this invention, the concentration of the hexadecyltrimethylammonium bromide solution is preferably 2–10 mg / mL, more preferably 2–5 mg / mL, and even more preferably 2 mg / mL; the solvent is preferably water; the surface modification time is preferably 3–10 min, more preferably 3–5 min. This invention utilizes the cationic properties of CTAB to make the NF surface positively charged.

[0043] The present invention does not limit the ratio of the nickel foam to hexadecyltrimethylammonium bromide; the nickel foam can be completely impregnated and impregnated for the time specified above.

[0044] In this invention, the concentration of the MXene dispersion is preferably 4–10 mg / mL, more preferably 4–6 mg / mL, and the dispersant is preferably water. This invention does not impose any particular limitation on the specific preparation process of MXene in the MXene dispersion; it can be prepared according to methods well known in the art.

[0045] In this invention, the adsorption time is preferably 30-60 min, more preferably 30-50 min; the adsorption is preferably carried out under static conditions; this invention utilizes electrostatic adsorption to uniformly load negatively charged MXene nanosheets onto a positively charged NF surface.

[0046] The present invention does not limit the ratio of the surface-modified nickel foam to the MXene dispersion; the surface-modified nickel foam can be completely impregnated and the adsorption time can be carried out as described above.

[0047] After the adsorption is completed, the product is preferably dried under vacuum at 40°C for 12 hours to obtain MX / NF.

[0048] In this invention, the cobalt salt in the cobalt salt solution is preferably cobalt nitrate, and the solvent is preferably water; the concentration of the cobalt salt solution is preferably 0.1 to 0.5 mol / L, more preferably 0.1 to 0.2 mol / L.

[0049] In this invention, in the three-electrode system used for the first electrodeposition, MX / NF is the working electrode, Ag / AgCl is the reference electrode, and the platinum sheet is the counter electrode.

[0050] In this invention, the potential range of the first electrodeposition is preferably -0.4V to -1.6V, the scan rate is preferably 0.01 to 0.10V / s, more preferably 0.01 to 0.03V / s, and the number of cycles is preferably 4 to 10, more preferably 4 to 6.

[0051] After electrodeposition, the present invention preferably uses deionized water to rinse the electrode surface to remove unreacted ions, and then dries it in a vacuum drying oven at 60°C to obtain Co(OH)2 / MX / NF.

[0052] In this invention, the phosphomolybdic acid in the aqueous solution is preferably a Keggin-type heteropoly acid H3PMo. 12 O 40 The concentration of the phosphomolybdic acid aqueous solution is preferably 1.5–3.5 mg / mL, more preferably 2.5 mg / mL. In this invention, 15–35 mg of phosphomolybdic acid is dissolved in 10 mL of water to obtain the phosphomolybdic acid aqueous solution.

[0053] In this invention, the preferred three-electrode system for the second electrodeposition is: Co(OH)2 / MX / NF as the working electrode, Ag / AgCl as the reference electrode, and a platinum sheet as the counter electrode.

[0054] In this invention, the voltage range of the second electrodeposition is preferably -0.9 to 0.4 V, the scanning speed is preferably 0.01 to 0.10 V / s, more preferably 0.04 V / s, and the number of cycles is preferably 10 to 20, more preferably 10 to 15.

[0055] This invention limits the loading and reaction degree of each component of the material after deposition by the number of electrodeposition cycles.

[0056] In this invention, the concentration of the 2-methylimidazole solution is preferably 1 to 2.5 mmol / mL, more preferably 1.6 mmol / mL, and the solvent is preferably methanol; in this invention, 30 to 50 mmol of 2-methylimidazole (2-MIM) is dissolved in 20 to 30 mL of methanol to obtain the 2-methylimidazole solution.

[0057] The present invention does not have a specific limitation on the amount of the 2-methylimidazole solution used, as long as the electrode is completely immersed and the coordination reaction is carried out according to the specified time.

[0058] In this invention, the coordination reaction time is preferably 1 to 3 hours, more preferably 1 to 2 hours.

[0059] During the coordination reaction, Co reacts with 2-methylimidazole to form ZIF-67, which grows in situ on the electrode surface.

[0060] This invention first deposits ZIF-67 in phosphomolybdic acid and then synthesizes it in situ, thus avoiding the degradation of adjacent PMo during the growth of ZIF-67 on the Co(OH)2 surface. 12 The particles are encapsulated within ZIF-67.

[0061] After the coordination reaction is completed, the product is preferably washed several times with methanol to remove unreacted 2-MIM, and then dried overnight at 50–70°C to obtain PMo. 12 @ZIF-67 / MX / NF.

[0062] In this invention, the nickel salt in the nickel salt solution is preferably nickel nitrate hexahydrate, and the solvent is preferably ethanol; the concentration of the nickel salt solution is preferably 4-6 mg / mL, more preferably 4.8 mg / mL; the present invention preferably dissolves 100-150 mg of nickel salt in 25 mL of anhydrous ethanol and stirs continuously for 0.5-2.0 h, more preferably 0.5-1 h, to obtain the nickel salt solution.

[0063] The present invention does not have a special limitation on the amount of nickel salt solution used, as long as the electrode is fully immersed and the ion exchange reaction is carried out according to the limited time.

[0064] In this invention, the preferred temperature for the ion exchange reaction is room temperature, and the preferred time is 12–24 hours, more preferably 12 hours. During the ion exchange reaction, Ni… 2+ Ions and Co in ZIF-67 2+ An ion exchange reaction occurs, generating a NiCo-LDH structure.

[0065] After the ion exchange reaction is completed, the electrode is preferably removed and washed several times with ethanol to remove unreacted Ni. 2+ Ions were vacuum dried overnight at 50–70 °C to obtain a three-dimensional flower-like heteropolyacid-based composite material, denoted as PMo. 12 @NiCo-LDH / MX / NF.

[0066] The present invention provides a three-dimensional flower-like heteropolyacid-based composite material prepared by the preparation method described in the above technical solution.

[0067] This invention provides the application of the three-dimensional flower-like heteropolyacid-based composite material described above in the electrocatalytic preparation of monobenzene ring compounds from lignin.

[0068] In this invention, the method for preparing monobenzene ring compounds by electrocatalysis of lignin preferably includes the following steps:

[0069] A three-electrode structure is adopted, with a three-dimensional flower-like heteropolyacid-based composite material as the working electrode and a lignin-containing solution as the electrolyte for electrochemical depolymerization.

[0070] In this invention, the three-electrode structure uses a composite material as the working electrode, an Hg / HgO electrode as the reference electrode, and a Pt electrode as the counter electrode.

[0071] In this invention, the solvent used in the electrolyte is preferably water and methanol, and the volume ratio of water to methanol in the electrolyte is preferably 9:1. The electrolyte also includes KOH, and the concentration of KOH in the electrolyte is preferably 1 mol / L.

[0072] In this invention, the concentration of lignin in the electrolyte is 1-5 mmol / L, more preferably 1-2 mmol / L.

[0073] In this invention, the electrochemical depolymerization temperature is preferably room temperature, and the time is preferably 30-90 min, more preferably 60 min; the electrochemical depolymerization is carried out under stirring conditions, and the stirring speed is preferably 400-600 rpm, more preferably 500 rpm; this invention preferably carries out the electrochemical depolymerization of lignin in a single electrolytic cell.

[0074] Electrochemical depolymerization is complete. This invention preferably uses ethyl acetate for extraction. The supernatant solution is then analyzed by HPLC. The HPLC conditions are: UV-Vis detector 210 nm, C18 column (4.6 mm × 150 mm, 5 μm), sample injection volume 20 μL, flow rate 1 mL / min, mobile phase H₂O / acetonitrile (40 / 60, v / v), flow rate 1.0 mL / min. -1 .

[0075] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods.

[0076] Unless otherwise specified, the experimental and testing methods described below are conventional methods; unless otherwise specified, the reagents and raw materials described below are commercially available.

[0077] In the following examples, MXene is prepared as follows:

[0078] Dissolve 2g LiF in a 100mL beaker, add 20mL of 12mol / L HCl solution, stir for 30min, add 2g Ti3AlC2 MAX (Eleventh Technology Co., Ltd.) to the resulting mixed solution, and heat and etch in a 35℃ water bath for 24h. Then wash the mixture with deionized water until the supernatant becomes neutral. Disperse the resulting multilayer MXene uniformly in 200mL of deionized water and stir for 10min. Sonicate in a nitrogen atmosphere and ice-water bath (0℃) for 60min to obtain an MXene aqueous dispersion.

[0079] Example 1

[0080] (1) Preparation of MX / NF

[0081] Nickel foam (NF) was cut into 2cm×2cm pieces and ultrasonically cleaned for 15min each with acetone, hydrochloric acid, ethanol and deionized water. The cleaned NF pieces were dried in a vacuum drying oven at 60℃ for 8h. The dried NF pieces were then immersed in a 2mg / mL hexadecyltrimethylammonium bromide (CTAB) aqueous solution for 3min. The treated NF pieces were then immersed in a 4mg / mL MXene aqueous dispersion, allowed to stand for 30min, and dried under vacuum at 40℃ for 12h to obtain MXene-loaded NF pieces, denoted as MX / NF.

[0082] (2) Preparation of Co(OH)2 / MX / NF

[0083] Co(OH)2 was loaded onto the MX / NF surface using electrochemical deposition.

[0084] A three-electrode system was constructed using MX / NF as the working electrode, Ag / AgCl as the reference electrode, and a platinum sheet as the counter electrode. Electrodeposition was performed using 0.1M cobalt nitrate (Co(NO3)2) aqueous solution as the electrolyte and cyclic voltammetry (CV) was employed. The potential range was -0.4V to -1.6V (vs. Ag / AgCl), the scan rate was 0.01V / s, and the cycle was 4 times. After electrodeposition, the electrode surface was rinsed with deionized water and then dried in a vacuum drying oven at 60℃ to obtain Co(OH)2 / MX / NF.

[0085] (3) Preparation of PMo@ZIF-67 / MX / NF

[0086] 25mg (1.2×10 -2 mmol) Keggin type heteropolyacid (H3PMo 12 O 40(Purchased from Shanghai Maclean Biochemical Co., Ltd.) was dissolved in 10 mL of deionized water to obtain a phosphomolybdic acid solution; using Co(OH)2 / MX / NF as the working electrode, Ag / AgCl as the reference electrode, and a platinum sheet as the counter electrode, electrochemical deposition was performed in the phosphomolybdic acid solution by cyclic voltammetry. The CV parameters were set to a potential range of -0.9 V to 0.4 V, a scan rate of 0.04 V / s, and 10 cycles.

[0087] 40 mmol of 2-methylimidazole (2-MIM) was dissolved in 25 mL of methanol. The PMo obtained after electrodeposition was... 12 The / Co(OH)2 / MX / NF electrode was immersed in a prepared methanol solution of 2-methylimidazole and allowed to stand for 1 hour. The electrode was then removed, washed several times with methanol, and dried overnight at 60°C to obtain PMo. 12 @ZIF-67 / MX / NF, referred to as PMo 12 @ZIF-67 / MX / NF-25.

[0088] (4) PMo 12 Preparation of @NiCo-LDH / MX / NF composite materials

[0089] Dissolve 120 mg (0.42 mmol) of nickel nitrate hexahydrate (Ni(NO3)2·6H2O) in 25 mL of anhydrous ethanol and stir continuously for 30 min until completely dissolved. 12 @ZIF-67 / MX / NF was immersed in the above nickel nitrate solution and stirred at room temperature for 12 hours. After the reaction was completed, the product was washed several times with anhydrous ethanol and dried under vacuum at 60°C overnight to obtain PMo. 12 @NiCo-LDH / MX / NF composite material, denoted as PMo 12 @NiCo-LDH / MX / NF-25.

[0090] Example 2

[0091] The only difference from Example 1 is:

[0092] In step (3), the Keggin-type heteropolyacid H3PMo 12 O 40 The mass was 15 mg, and PMo was obtained. 12 @ZIF-67 / MX / NF-15; The composite material prepared in step (4) is denoted as PMo. 12 @NiCo-LDH / MX / NF-15.

[0093] Example 3

[0094] The only difference from Example 1 is:

[0095] In step (3), the Keggin-type heteropolyacid H3PMo 12 O 40 The mass was 35 mg, and PMo was obtained. 12 @ZIF-67 / MX / NF-35; The composite material prepared in step (4) is denoted as PMo. 12 @NiCo-LDH / MX / NF-35.

[0096] Comparative Example 1

[0097] The only difference from Example 1 is that the step of loading MX in step (1) is removed according to the method of Example 1 to obtain PMo. 12 @NiCo-LDH / NF.

[0098] Characterization and performance testing

[0099] Figure 1 In the example, (a) represents PMo in Example 1. 12 SEM images of the @NiCo-LDH / MX / NF-25 composite material at different magnifications clearly show its hierarchical structure and surface morphology. Low-magnification SEM images reveal a uniform, continuous conductive network composed of laterally arranged MXene nanosheets covering the surface of the nickel foam three-dimensional framework. This unique two-dimensional / three-dimensional heterostructure not only provides a high specific surface area substrate for subsequent material growth, but the electron transport channels formed by the interlinked MXene nanosheets significantly enhance the overall conductivity of the composite material. High-resolution SEM images further show dense, nearly spherical three-dimensional flower-like structures formed on the MXene-modified NF substrate. MXene helps disperse the LDH sheets, reducing stacking and preventing the active sites from being masked. Notably, the smooth surface of the original ZIF-67 is transformed by NiCo-LDH / MX / NF-25. 2+ After ion hydrolysis etching, it transforms into a rough surface structure composed of ultrathin nanosheets, which is conducive to subsequent PMo etching. 12 Electrostatic recombination with LDH sheets provides abundant active sites. Figure 1 (b) shows NF, MXene, and PMo in Example 1. 12 Cross-sectional SEM image of @NiCo-LDH / MX / NF-25 (corresponding to Ni-Co-LDH), analyzed through cross-sectional SEM ( Figure 1 In (b) it was found that MXene nanosheets formed a tight interfacial bond with the NF substrate, and this strong interaction can effectively suppress the structural pulverization problem during cycling.

[0100] From the perspective of microstructure evolution, the material synthesis process produced three key structural features: (1) a three-dimensional conductive framework constructed from MXene nanosheets, whose surface roughness significantly increased the loading of active materials; (2) the branches and pores of the NiCo-LDH three-dimensional flower-like structure can affect PMo 12 The formation of a "cage-like" enclosure can effectively inhibit PMo 12 (3) The vertically grown LDH sheets form an open hierarchical porous structure, which is conducive to the rapid permeation and mass transfer of electrolytes. The nanosheet structure obtained by the ZIF-67 template conversion in this invention exhibits excellent stability, which is mainly attributed to the strong chemical bonding between the MXene substrate and the LDH sheets. These unique microstructural features work together to make PMo 12 The @NiCo-LDH / MX / NF-25 composite material shows broad application prospects in the field of electrochemistry.

[0101] Figure 1 (c) represents PMo in Example 1 12 @NiCo-LDH / MX / NF-25 and PMo in Comparative Example 1 12 The nitrogen adsorption-desorption isotherm of @NiCo-LDH / NF shows that PMo 12 The isotherms of @NiCo-LDH / MX / NF-25 exhibit Type IV characteristics, with a significant hysteresis loop appearing within the relative pressure (P / P0) range, indicating that the material possesses a mesoporous structure. The average pore size is 12.2 nm, and the BET specific surface area is as high as 99.3 m². 2 ·g -1 The hierarchical porous system not only significantly increases the exposure of active sites, but also constructs a three-dimensional, interconnected mass transport channel, providing an ideal material transport platform for electrocatalytic reactions.

[0102] Test Example 1

[0103] To evaluate PMo 12 The electrocatalytic reduction performance of @NiCo-LDH / MX / NF-25 on the lignin model compound 2-phenoxy-1-phenylethanol (PPE) was tested using linear sweep voltammetry (LSV) in a 1M KOH electrolyte with a PPE concentration of 1 mmol / L and an electrochemical depolymerization time of 60 min.

[0104] Figure 2 For NF, MX / NF, PMo 12 / NF、PMo 12 @NiCo-LDH / NF, PMo 12 @ZIF-67 / MX / NF-25 and PMo 12(a) LSV curve, (b) Tafel curve, (c) Nyquist curve, and (d) double-layer capacitance of @NiCo-LDH / MX / NF-25. Conditions: 1M KOH, 1mM PPE.

[0105] Among them, PMo 12 The preparation process of / NF is as follows: 25mg H3PMo 12 O 40 A phosphomolybdic acid solution was prepared by dissolving the compound in 10 mL of deionized water. Electrochemical deposition was performed in the phosphomolybdic acid solution using NF as the working electrode, Ag / AgCl as the reference electrode, and a platinum sheet as the counter electrode. CV parameters were set to a potential range of -0.9 V to 0.4 V, a scan rate of 0.04 V / s, and 10 cycles to obtain PMo. 12 / NF.

[0106] like Figure 2 As shown in (a), PMo 12 @NiCo-LDH / MX / NF-25 at a current density j = 90 mA·cm -2 The overpotential (η) at that time was only 320mV (vs. RHE), which was significantly lower than that of the control sample PMo. 12 @NiCo-LDH / NF-25(η=410mV), PMo 12 The results of / NF (η = 380 mV) and pure NF (η = 450 mV) indicate that the introduction of MXene significantly reduced the reaction energy barrier.

[0107] The LSV curve was further fitted using the Tafel equation (η = b·logj + a). Figure 2 (b) PMo 12 The Tafel slope of @NiCo-LDH / MX / NF-25 is 18.7 mV·dec. -1 Far lower than PMo 12 @NiCo-LDH / NF(96.7mV·dec -1 PMo 12 / NF(72.1mV·dec -1 ) and NF (96.7mV·dec -1 The smaller Tafel slope indicates that PMo 12 @NiCo-LDH / MX / NF-25 exhibits faster charge transfer rates and superior reaction kinetics.

[0108] Analysis of interfacial charge transport behavior using electrochemical impedance spectroscopy (EIS) Figure 2 (c)). In the Nyquist plot, the diameter of the semicircle in the high-frequency region corresponds to the charge transfer resistance (Rct), PMo. 12The Rct value of @NiCo-LDH / MX / NF-25 is only 4.51Ω, significantly lower than that of PMo. 12 @NiCo-LDH / NF (5.04Ω), MX / NF (14.58Ω), and NF (20.89Ω). This result confirms that the high conductivity of MXene and its interfacial coupling with NiCo-LDH effectively reduce electron transport resistance, thereby accelerating the reduction reaction process.

[0109] Introducing MXene can increase the specific surface area of ​​the active material to a certain extent, resulting in a significant difference between the area of ​​the electrochemically active region and the geometric area of ​​a conventional planar electrode. To further evaluate the electrocatalytic reduction performance of the electrode, cyclic voltammetry was used to measure the double-layer capacitance C0. dl Value testing, such as Figure 2 (d) According to the C of different materials dl The electrochemical active surface area (ECSA) was calculated to further evaluate the electrocatalytic performance of the sample. Calculations showed that PMo... 12 The NiCo-LDH / MX / NF-25 composite material has a height of up to 151cm. 2 The ECSA values ​​are PMo 12 @NiCo-LDH / NF(60cm 2 ), MX / NF (50cm) 2 ) and NF (29cm) 2 The ECSA values ​​were 2.5, 3.0, and 5.2 times higher than those of PMo. The high ECSA values ​​indicate that the three-dimensional flower-shaped structure of the composite material and the MXene conductive network synergistically promote the exposure of active sites and provide efficient channels for reactant diffusion. Therefore, PMo... 12 @NiCo-LDH / MX / NF exhibits optimal electrocatalytic performance.

[0110] Test Example 2

[0111] PMo 12 The activity of the NiCo-LDH / MX / NF-25 catalyst in the electrocatalytic reduction of lignin depolymerization:

[0112] The depolymerization tests of the lignin model compound 2-phenoxy-1-phenylethanol (PPE) were conducted on a Shanghai Huachen CHI760E electrochemical workstation using a three-electrode system. In this system, different materials served as working electrodes, with an Hg / HgO electrode as the reference electrode and a Pt electrode (10 mm × 10 mm) as the counter electrode. The electrolyte was a 1 M KOH solution with a PPE concentration of 1 mmol / L, and the operating voltage was -0.38 V.

[0113] (1) Effect of different electrode materials on lignin depolymerization performance

[0114] Figure 3 For different working electrodes (a) and different H3PMo 12 O 40 Effect of content of composite material (b) on lignin depolymerization properties; Test conditions: 1M KOH, 1mM PPE, -0.38V;

[0115] like Figure 3 As shown in (a), PMo 12 @NiCo-LDH / MX / NF-25 exhibits better current response than other electrodes. PMo electrodeposition on NF 12 Then, PPE was electrocatalytically reduced. Compared with NF, PMo 12 The conversion and yield of / NF were significantly improved because the introduction of Mo effectively promoted the adsorption of model compounds on the catalyst surface. While the introduction of MXene did not significantly improve the conversion, it did significantly enhance the current density and product selectivity. This phenomenon is attributed to the abundant oxygen-containing functional groups (-OH, -O) on the MXene surface, which can adsorb PPE molecules through hydrogen bonding, optimizing their orientation and promoting C… α –C β Directional bond breaking. Furthermore, the high conductivity of MXene accelerates interfacial electron transfer, causing the reaction current density to increase from PMo. 12 @NiCo-LDH / NF 45.8mA·cm -2 Increased to 54.8 mA·cm -2 This further verifies its promoting effect on reaction kinetics.

[0116] Figure 3 (b) represents different PMo 12 The effect of loading on depolymerization performance; such as Figure 3 As shown in (b), when PMo 12 When the loading dose is 25 mg (PMo) 12 @NiCo-LDH / MX / NF-25), the benzoic acid yield reached 64.1%, significantly higher than that of the low loading (15 mg, yield 52.3%) and high loading (35 mg, yield 58.9%) samples. Adequate H3PMo 12 O 40 The introduction of (25mg) can maximize the interaction between NiCo-LDH and PMo. 12 Electron interactions between them enhance the redox capabilities of active sites. Excess H3PMo 12 O 40 It may cause pore blockage in the three-dimensional flower-shaped structure, inhibiting the mass transfer process and reducing the utilization rate of active sites.

[0117] (2) Optimization of lignin depolymerization properties

[0118] Following the method in Test Example 2, the electrocatalytic depolymerization reaction was carried out for 60 min. The electrolyte was then extracted with ethyl acetate to obtain the supernatant. The supernatant was analyzed by high-performance liquid chromatography (HPLC) to calculate the yield of the monobenzene ring compound (phenol) and the conversion rate of lignin. The HPLC conditions were: UV-vis detector 210 nm, C18 column (4.6 mm × 150 mm, 5 μm), injection volume 20 μL, sample flow rate 1 mL / min, mobile phase H₂O / acetonitrile (40 / 60, v / v), and mobile phase flow rate 1.0 mL / min. -1 .

[0119] Figure 4 Effects of different reaction times and voltage conditions on the distribution of lignin depolymerization products: (a) -0.48V, (b) -0.38V and (c) -0.28V; test conditions: 1M KOH, 1mmol / L PPE, 30-150min.

[0120] like Figure 4 As shown, the PPE conversion (86.9%) and phenol yield (57.2%) reached their peak values ​​after 60 min at -0.38 V. Extending the reaction time further to 150 min resulted in a decrease in phenol yield to 16.8%. This phenomenon is related to the excessive accumulation of reactive oxygen species (such as ·OH) during the reaction, which may trigger excessive reduction or condensation side reactions of the target product, thereby reducing the product yield. Furthermore, while voltage changes (-0.38 V to -0.48 V) increased the conversion (86.9–87.4%), the phenol yield decreased from 57.2% to 46.8%. Higher current density indicated better electrocatalytic performance, suggesting an enhanced reduction potential. Based on the above experimental results, the optimal conditions for the electrocatalytic reduction of PPE are a reaction time of 60 min and a voltage of -0.38 V.

[0121] (3) Study on the electrocatalytic activity of real lignin

[0122] To verify the versatility of the catalysts, pine lignin, birch lignin, and alkaline lignin were selected for electrocatalytic reduction tests: the electrochemical experiments were conducted using a three-electrode setup on an electrochemical workstation CHI760E. PMo 12 @NiCo-LDH / MX / NF-25 is the working electrode, Pt electrode (10mm×10mm) is the counter electrode, and Hg / HgO electrode is the reference electrode; conditions: 1M KOH, 1mM lignin, -0.38V.

[0123] Figure 5 To determine the conversion rate and yield of different lignins; test conditions: 1M KOH, 1mmol / L lignin, -0.38V, 60min; Figure 5 As shown, under conditions of -0.38V and 60 min, alkaline lignin exhibited the highest conversion rate (95.2%), with yields of vanillin and guaiacol at 29.2% and 10.7%, respectively. In contrast, pine lignin showed a conversion rate of only 45.2%, but a guaiacol yield of 18.6%. This difference stems from the structural complexity of lignin: alkaline lignin is rich in β-O-4 ether bonds (65-75%), and its cleavage pathway for generating monophenolic products is well-defined. Pine lignin, however, has a high proportion of condensation structures (such as 5-5′ and β-5 bonds) (>40%), requiring higher energy for depolymerization and readily generating polysubstituted phenolic byproducts. The structural characteristics of pine may limit product selectivity and yield, while alkaline lignin exhibits higher conversion rates due to its unique structure or reactivity. These results indicate that PMo 12 @NiCo-LDH / MX / NF has a significant advantage in selectively breaking β-O-4 bonds, but its adaptability to real lignin still needs further optimization.

[0124] (4) PMo 12 @NiCo-LDH / MX / NF Stability Experiment

[0125] The working electrode PMo was evaluated by cyclic voltammetry (2000 cycles) and constant potential electrolysis (30 h). 12 Electrochemical stability of @NiCo-LDH / MX / NF:

[0126] Electrochemical experiments were conducted using a three-electrode setup on a CHI760E electrochemical workstation. PMo 12 The NiCo-LDH / MX / NF-25 electrode was used as the working electrode, the Pt electrode (10mm × 10mm) as the counter electrode, and the Hg / HgO electrode as the reference electrode. Cyclic voltammetry (CV) was used in a 1M KOH system at 10mV·s. -1 The scanning rate was 2000 scans within the range of -2 to 2V. The constant potential electrolysis (30h) voltage was -0.38V.

[0127] Figure 6 For PMo 12 @NiCo-LDH / MX / NF-25 (a) CV curves before and after 2000 cycles, (b) stability, (c) cycling test and Faraday efficiency, and (d) SEM images after recovery. Conditions: 1M KOH, 1mM PPE, -0.38V, 60min.

[0128] like Figure 6As shown in (a) and (b), the electrocatalytic performance of the working electrode did not show a significant decrease after 2000 CV cycles and constant potential electrolysis (30 h). Figure 6 As shown in (c), PMo 12 @NiCo-LDH / NF-25 can be recycled at least 5 times in electrocatalytic reduction without a significant decrease in PPE conversion and yield.

[0129] PMo after 5 cycles of electrocatalytic experiments 12 @NiCo-LDH / MX / NF was characterized by SEM, and the results are as follows: Figure 6 As shown in (d). From Figure 6 As can be seen in (d), the recovered PMo 12 The @NiCO-LDH / MX / NF nickel foam substrate retains its pre-reaction three-dimensional flower-like morphology and remains tightly bound to MXene, without significant dissolution or detachment. These results indicate that under optimal electrocatalytic conditions, PMo… 12 @NiCo-LDH / MX / NF exhibits excellent cycleability and stability.

[0130] (5) Mechanism Analysis

[0131] Experiments show that the synergistic effect of the MXene conductive substrate and the three-dimensional NiCo-LDH flower-like structure significantly improves the electron transport efficiency of the catalyst. Under the influence of the anodic potential, the Ni in NiCo-LDH... 2+ -OH groups generate highly active Ni via an electrochemically driven proton deintercalation / intercalation reaction. 3+ -O(reaction formula: Ni) 2+ -OH+OH-→Ni 3+ -O+H2O+e - Meanwhile, Co 2+ / Co 3+ with Mo 6+ / Mo 4+ Cooperative electron transfer from redox pairs significantly optimizes the stability of active sites. 2+ As an electron donor to accelerate Ni 3+ The formation of -O, and Mo 6+ As an electron acceptor, it is reduced to Mo 4+ A stable charge balance, together with the other two components, forms an efficient electron transport channel. The breaking of the CC / CO bond originates from Ni. 3+ The -O site activates the adsorption of PPE and attacks it with ·OH radicals, resulting in... Figure 7 The intermediate, then spontaneously dehydrogenated by a nucleophile (Ni). 3+ -O+XH=Ni 2+-OH+X*) generates phenol, benzyl alcohol, and benzaldehyde, as well as byproducts. During this process, Co 3+ / Co 2+ with Mo 6+ / Mo 4+ The cyclic regeneration ensures the continuous activity of the catalyst. The electron-rich nature of Mo induces C / C bond polarization, while the redox regulation of Co inhibits Ni. 3+ Excessive oxidation of -O maintains the stability of the catalytic interface.

[0132] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a three-dimensional flower-like heteropolyacid-based composite material, characterized in that, Includes the following steps: Nickel foam was impregnated in a hexadecyltrimethylammonium bromide solution to perform surface modification, resulting in surface-modified nickel foam. The surface-modified nickel foam was impregnated in an MXene dispersion for adsorption to obtain MX / NF; Using the MX / NF as the working electrode and the cobalt salt solution as the electrolyte, the first electrodeposition was performed by cyclic voltammetry to obtain Co(OH)2 / MX / NF; Using an aqueous solution of phosphomolybdic acid as the electrolyte and the Co(OH)₂ / MX / NF as the working electrode, a second electrodeposition was performed using cyclic voltammetry to obtain PMo. 12 / Co(OH)2 / MX / NF electrode; The PMo 12 The / Co(OH)2 / MX / NF electrode underwent a coordination reaction in a 2-methylimidazole solution to obtain PMo. 12 @ZIF-67 / MX / NF; The PMo 12 @ZIF-67 / MX / NF was impregnated in a nickel salt solution and subjected to an ion exchange reaction to obtain a three-dimensional flower-like heteropolyacid-based composite material.

2. The preparation method according to claim 1, characterized in that, The concentration of the hexadecyltrimethylammonium bromide solution is 2–10 mg / mL; the surface modification time is 3–10 min; the concentration of the MXene dispersion is 4–10 mg / mL; and the adsorption time is 30–60 min.

3. The preparation method according to claim 1, characterized in that, The potential range of the first electrodeposition is -0.4V to -1.6V, the scan rate is 0.01 to 0.10V / s, and the number of cycles is 4 to 10.

4. The preparation method according to claim 1, characterized in that, The phosphomolybdic acid in the aqueous solution is a Keggin-type heteropolyacid H3PMo. 12 O 40 The concentration of the phosphomolybdic acid aqueous solution is 1.5–3.5 mg / mL.

5. The preparation method according to claim 1 or 4, characterized in that, The voltage range for the second electrodeposition is -0.9 to 0.4 V, the scan rate is 0.01 to 0.10 V / s, and the number of cycles is 10 to 20.

6. The preparation method according to claim 1, characterized in that, The concentration of the 2-methylimidazole solution is 1–2.5 mmol / mL; the coordination reaction time is 1–3 h.

7. The preparation method according to claim 1, characterized in that, The concentration of the nickel salt solution is 4–6 mg / mL; the ion exchange reaction time is 12–24 h.

8. The three-dimensional flower-like heteropolyacid-based composite material prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the three-dimensional flower-like heteropolyacid-based composite material of claim 8 in the electrocatalytic preparation of monobenzene ring compounds from lignin.

10. The application according to claim 9, characterized in that, The method for preparing monobenzene ring compounds by electrocatalysis of lignin includes the following steps: A three-electrode structure is adopted, with a three-dimensional flower-like heteropolyacid-based composite material as the working electrode and a lignin-containing solution as the electrolyte for electrochemical depolymerization; the concentration of lignin in the electrolyte is 1-5 mmol / L.

Images