S-doped CoV-LDH electrode material and preparation method and application thereof

Abstract

The invention belongs to the technical field of electro-catalytic materials and biomass energy conversion, and particularly relates to an S-doped CoV-LDH electrode material and a preparation method and application thereof. The invention discloses an S-doped CoV-LDH electrode material. The electrode material comprises a conductive substrate and an S-doped CoV-LDH active layer which grows on the surface of the conductive substrate in situ, in the S-doped CoV-LDH active layer, an S element is doped in a lattice of CoV-LDH and partially replaces lattice oxygen. According to the material, lattice distortion is triggered through S anion doping, the electronic structure of CoV-LDH is effectively regulated and controlled, and competitive adsorption of a reaction substrate is balanced, so that the activity, selectivity and stability of HMF electrocatalytic oxidation are remarkably improved, and low-energy-consumption HMF oxidative coupling hydrogen production is successfully realized.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic materials and biomass energy conversion technology, specifically relating to an S-doped CoV-LDH electrode material and its preparation method, as well as the application of this material in the electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF) coupled with hydrogen evolution reaction. Background Technology

[0002] With the increasing depletion of fossil fuel resources, the development of renewable energy and high-value-added chemicals has become a global focus. Biomass resources, as an important alternative energy source, can be converted into a variety of fine chemicals. Among them, 5-hydroxymethylfurfural (HMF), as a key biomass platform molecule, can be selectively oxidized to generate high-value-added 2,5-furanic acid (FDCA). FDCA has a structure similar to petroleum-based terephthalic acid (PTA) and is considered an important precursor for the preparation of green biodegradable plastics.

[0003] Traditional HMF oxidation methods typically require high temperature and pressure conditions and use precious metal catalysts, resulting in high costs and poor environmental friendliness. In contrast, electrocatalytic oxidation of HMF (HMFOR) offers advantages such as mild reaction conditions and high controllability. In particular, coupling anodic HMFOR with cathodic hydrogen evolution reaction (HER) not only produces high-value FDCA but also simultaneously generates clean hydrogen energy at the cathode, significantly improving energy utilization efficiency.

[0004] Among numerous electrocatalysts, layered double hydroxides (LDHs) have attracted considerable attention due to their unique layered structure and tunable metal composition. However, pure LDH materials typically suffer from poor conductivity and insufficient exposure of active sites. More importantly, during HMFOR in alkaline media, the reaction involves organic molecules reacting with OH-. - The synergistic effect of HMF molecules and OH. - Intense competitive adsorption exists on the catalyst surface: if OH - Excessive adsorption can occupy active sites and hinder HMF adsorption; conversely, excessive HMF adsorption can lead to catalyst poisoning or sluggish reaction kinetics. Therefore, balancing the adsorption of HMF and OH groups is crucial. - The adsorption behavior on the catalyst surface, while simultaneously improving the intrinsic conductivity and active site density of the material, is the main technical bottleneck currently facing the development of highly efficient HMFOR electrocatalysts.

[0005] Existing modification strategies such as cation doping have some effect, but their ability to regulate electronic structure is limited. Although anion doping (such as S, Se, etc.) is considered to be able to effectively regulate electronic structure, there are few reports on the precise construction of S-doped CoV-LDH systems through a one-step hydrothermal method, and the use of its lattice distortion effect to solve the above-mentioned competitive adsorption problem and achieve efficient HMFOR coupling HER. Summary of the Invention

[0006] To address the aforementioned problems in the existing technology, the present invention aims to provide an S-doped CoV-LDH electrode material. This material effectively regulates the electronic structure of CoV-LDH by inducing lattice distortion through S anion doping, balances the competitive adsorption of reaction substrates, thereby significantly improving the activity, selectivity, and stability of HMF electrocatalytic oxidation, and successfully realizing low-energy HMF oxidation coupled hydrogen production.

[0007] The technical solution adopted by this invention to solve its technical problem is:

[0008] An S-doped CoV-LDH electrode material, the electrode material comprising a conductive substrate and an S-doped CoV-LDH active layer grown in situ on the surface of the conductive substrate; in the S-doped CoV-LDH active layer, S element is doped into the lattice of CoV-LDH and partially replaces lattice oxygen to form Co-S bonds.

[0009] Preferably, the S-doped CoV-LDH active layer has a multi-level flower-like microsphere structure, which is assembled from nanosheets and uniformly distributed on the framework of the conductive substrate.

[0010] Preferably, the conductive substrate is nickel foam; in the S-doped CoV-LDH active layer, the molar ratio of Co to V is 4:3 to 7:0.

[0011] Preferably, the molar ratio of Co to V is 5:2 to 6:1.

[0012] In this invention, the X-ray diffraction pattern of the S-doped CoV-LDH electrode material has characteristic diffraction peaks near 2 Theta of 11.6°, 23.4°, 34.1°, 38.7°, and 60.5°, and these characteristic diffraction peaks are shifted to higher angles compared to undoped CoV-LDH.

[0013] A method for preparing the S-doped CoV-LDH electrode material according to the present invention includes the following steps:

[0014] Step 1: Dissolve the cobalt source, vanadium source, urea and sulfur source in water to obtain a mixed precursor solution;

[0015] Step 2: Place the pretreated conductive substrate in the mixed precursor solution;

[0016] Step 3: The system obtained in Step 2 is subjected to a hydrothermal reaction under sealed conditions to allow S-doped CoV-LDH to grow in situ on the conductive substrate;

[0017] Step 4: After the reaction is complete, the conductive substrate is removed, washed, and dried to obtain the S-doped CoV-LDH electrode material.

[0018] Preferably, the cobalt source is cobalt nitrate hexahydrate, the vanadium source is vanadium chloride, and the sulfur source is thiourea; in the mixed precursor solution, the concentration of the cobalt source is 0.01-0.1 M, the concentration of the vanadium source is 0.01-0.05 M, the concentration of the urea is 0.1-0.5 M, and the concentration of the sulfur source is 0.01-0.05 M.

[0019] Preferably, the hydrothermal reaction temperature is 100-140℃ and the reaction time is 8-16 hours; more preferably, the hydrothermal reaction temperature is 120℃ and the reaction time is 12 hours.

[0020] Preferably, the concentration of the sulfur source in the mixed precursor solution is 0.0375 M.

[0021] Application of the S-doped CoV-LDH electrode material described in this invention in the electrocatalytic oxidation of 5-hydroxymethylfurfural.

[0022] Preferably, the application involves catalytic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid in an alkaline electrolyte using the S-doped CoV-LDH electrode material as the anode, while simultaneously coupling a hydrogen evolution reaction at the cathode. The optimal concentration of 5-hydroxymethylfurfural is 50 mM.

[0023] The beneficial effects of this invention are:

[0024] This invention introduces lower electronegativity and higher polarizability S atoms into the LDH lattice via a one-step hydrothermal method to partially replace O atoms, forming unique Co-S bonds and inducing lattice distortion. This structural modification effectively modulates the electron density of the active centers, reduces the interfacial charge transfer resistance, and thus significantly lowers the reaction energy barrier of HMFOR. Experiments show that at 100 mA cm⁻¹... -2 At the current density, the potential for this material to catalyze HMFOR is 263 mV lower than that of the oxygen evolution reaction (OER).

[0025] Thanks to the optimization of intermediate adsorption energy by S doping, the S-doped CoV-LDH electrode material of this invention can effectively balance HMF and OH. -Competitive adsorption on the surface promotes the reaction toward the target product. At a potential of 1.45 V relative to the reversible hydrogen electrode (RHE), the Faraday efficiency for the conversion of HMF to FDCA is as high as 99.6%, and the FDCA yield reaches 99.4%.

[0026] The multi-level flower-like microsphere structure formed by in-situ growth of S-doped CoV-LDH on nickel foam, as described in this invention, not only maximizes the exposure of active sites but also enhances the bonding force between the catalyst and the substrate. This material exhibits no significant decline in Faraday efficiency and product selectivity during 12 consecutive electrolysis cycles, demonstrating excellent potential for industrial applications.

[0027] This invention couples HMFOR with HER and uses S-doped CoV-LDH as a bifunctional or anodic catalyst to simultaneously obtain high-value-added FDCA and high-purity hydrogen at a lower cell voltage, providing a new energy-efficient and high-efficiency approach for biomass upgrading and green hydrogen production. Attached Figure Description

[0028] Figure 1 ac S 12.5 SEM images of CoV-LDH materials; dS 12.5 XRD patterns of CoV-LDH and CoV-LDH materials; ef S 12.5 S 2p and Co 2p XPS spectra of CoV-LDH and CoV-LDH materials;

[0029] Figure 2 S 12.5 EDS diagram of CoV-LDH material;

[0030] Figure 3 ag S with different metal ratios 12.5 LSV curves of HMFOR and OER for CoV-LDH materials; h-values ​​of S with different S contents in the reaction solution. x LSV curves of CoV-LDH-catalyzed HMFOR; i LSV curves of HMFOR at different concentrations of 5-hydroxymethylfurfural;

[0031] Figure 4 a. Tafel plots of CoV-LDH with different S content; b. Impedance plots of CoV-LDH with different S content; c. HMFOR in S 12.5 HPLC product detection chromatogram on CoV-LDH catalyst; d. Concentration change curve corresponding to HPLC; e. Conversion, selectivity and Faraday efficiency of catalyst at different potentials; f. S 12.5 Cyclic stability of CoV-LDH catalyst;

[0032] Figure 5Possible reaction pathways of HMFOR. Detailed Implementation

[0033] The technical solution of the present invention will be further described in detail below through specific embodiments. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any modifications and / or alterations made to the present invention will fall within the protection scope of the present invention.

[0034] In this invention, unless otherwise specified, all parts and percentages are by weight, and the equipment and raw materials used are commercially available or commonly used in the art. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0035] Unless otherwise specified, the reagents used in the following examples can be purchased from a regular biochemical reagent store.

[0036] Chemical reagents: Nickel foam (NF), cobalt nitrate hexahydrate (Co(NO3)2·6H2O), vanadium chloride (VCl3), urea (CH4N2O), thiourea (CH4N2S), potassium hydroxide (KOH), 5-hydroxymethylfurfural (HMF), 2,5-furandicarboxylic acid (FDCA), 5-hydroxymethyl-2-furancarboxylic acid (HMFCA), 5-formyl-2-furancarboxylic acid (FFCA), hydrochloric acid (HCl), anhydrous ethanol, acetone. All chemicals are analytical grade and require no further purification; they are to be used directly upon receipt.

[0037] Examples 1-4 and Comparative Example 1

[0038] 1. Preparation of catalyst

[0039] Pretreatment of the nickel foam substrate: First, cut the nickel foam (NF*1.5 mm) into 3×3 cm pieces. 2 Small pieces were ultrasonically treated for 15 minutes each in acetone, 3 M hydrochloric acid (HCl) solution, and deionized water to remove the surface oxide layer. Then, they were rinsed thoroughly with deionized water and anhydrous ethanol, respectively. Finally, they were dried in a vacuum drying oven at 60°C.

[0040] Comparative Example 1: Synthesis of CoV-LDH:

[0041] Measure 35 mL of deionized water into a beaker, and add cobalt source (Co(NO3)2·6H2O), vanadium source (VCl3), urea (CH4N2O), and sulfur source (thiourea CH4N2S) sequentially. Stir continuously for 15 minutes to mix thoroughly, obtaining a mixed precursor solution. The concentrations of Co(NO3)2·6H2O, VCl3, and CH4N2O in the mixed precursor solution are 0.05 M, 0.02 M, and 0.2 M, respectively. Transfer the mixed precursor solution to a polytetrafluoroethylene-lined hydrothermal reactor, then vertically place pretreated nickel foam into the reactor. Seal the reactor and transfer it to an oven for hydrothermal treatment at 120 °C for 12 hours. After the reaction was completed, the hydrothermal reactor was allowed to cool naturally to room temperature. The nickel foam with the material grown on the surface was removed from the reactor and washed repeatedly with ethanol and deionized water. Finally, the sample was transferred to a vacuum drying oven and dried at 60 °C for 12 hours to obtain CoV-LDH (Comparative Example 1).

[0042] Examples 1-4 S x Synthesis of CoV-LDH:

[0043] Step 1:

[0044] Measure 35 mL of deionized water into a beaker, and add cobalt source (Co(NO3)2·6H2O), vanadium source (VCl3), urea (CH4N2O), and sulfur source (thiourea CH4N2S) sequentially. Stir continuously for 15 minutes to mix thoroughly, obtaining a mixed precursor solution. In the mixed precursor solution, the concentrations of Co(NO3)2·6H2O are 0.05 M, VCl3 is 0.02 M, and CH4N2O is 0.2 M. Different S-doped CoV-LDH electrode materials (S...) are obtained by adding different concentrations of thiourea. x CoV-LDH). In the mixed precursor solutions, the thiourea concentrations were 0.0125 M, 0.025 M, 0.0375 M, and 0.05 M, corresponding to S 4.1 CoV-LDH (Example 1), S 8.3 CoV-LDH (Example 2), S 12.5 CoV-LDH (Example 3) and S 16.6 CoV-LDH (Example 4).

[0045] Step 2: Transfer the mixed precursor solution to a polytetrafluoroethylene-lined hydrothermal reactor, and then vertically place the pretreated nickel foam into the hydrothermal reactor.

[0046] Step 3: Seal the hydrothermal reactor and transfer it to an oven for hydrothermal treatment at 120 °C for 12 hours to allow S-doped CoV-LDH to grow in situ on a conductive substrate.

[0047] Step 4: After the reaction is complete, allow the reaction vessel to cool naturally to room temperature. Remove the nickel foam loaded with active material, rinse the surface repeatedly with deionized water and anhydrous ethanol to remove any residual reaction solution, and finally place it in a vacuum drying oven and dry at 60 °C for 12 hours to obtain the S-doped CoV-LDH electrode material.

[0048] 2. Characterization of the catalyst

[0049] The sample used to test the phase structure was a nickel foam substrate with the grown material cut into 0.5 × 0.5 cm pieces. 2 The samples were then placed in a sample holder for testing. The morphology of the samples was characterized using a Hitachi S-4800 field emission scanning electron microscope (SEM) equipped with an energy-scattering X-ray spectrometer. The crystal structure of the samples was examined using a Shimadzu XRD-7000 X-ray diffractometer.

[0050] 3. Electrochemical Testing

[0051] Electrochemical measurements were performed in an H-type electrolytic cell separated by an anion exchange membrane, consisting of a working electrode, a Pt counter electrode, and a mercury / mercury oxide reference electrode (1.0 M KOH). Cyclic voltammetry (CV), linear voltammetry (LSV), and constant voltage measurements were performed on an electrochemical workstation (Shanghai Chenhua CHI-660E). The electrolyte was a 1.0 M KOH solution (pH=13.99). All measured potentials were calibrated to the reversible hydrogen electrode (RHE) using the following equation:

[0052] E RHE = E Hg / HgO + 0.098 + 0.059×pH

[0053] Nickel foam with a catalyst sample was used as the working electrode, with a working area of ​​1 cm². 2 The potential used is corrected according to formula (1):

[0054] (1)

[0055] Where i refers to the current flowing through the battery, and R refers to the ohmic impedance of the battery.

[0056] In an electrolyte of 1 M KOH + 50 mM HMF, at a rate of 5 mV s -1Linear scan voltammetry curves for HMF oxidation were collected in an H-type electrolytic cell at the specified scan rate. 90% iR compensation was used for the ohmic voltage drop caused by solution resistance. Potentiostatic electrolysis (it) was performed in 40 mL of electrolyte containing 10 mM HMF. The electro-oxidation of HMF occurred on the prepared catalyst in the anolyte chamber. All experiments were conducted at room temperature.

[0057] In-situ electrochemical impedance spectroscopy (EIS) measurements were performed in 1 M KOH solution and 1 M KOH solution containing 50 mM HMF, covering a frequency range of 10. -1 -10 5 Hz, AC signal amplitude is 5 mV.

[0058] 4. Product Analysis

[0059] High-performance liquid chromatography (HPLC, Agilent Technologies 1260 Infinity II) with a 265 nm UV-Vis detector was used for quantitative analysis of HMF oxidation products. Mobile phase A was methanol, and mobile phase B was 5 mM ammonium formate aqueous solution, with a volume ratio of A:B of 2:8, and a flow rate of 0.5 mL / min. -1 The column temperature was 30℃, and the injection volume was 20 μL. For each analysis, 200 μL of the electrolyte after potentiostatic electrolysis was taken, 200 μL of dilute H2SO4 was added, and the solution was diluted to 8 mL with ultrapure water. The retention time for each injection was 12 minutes.

[0060] HMF and oxidation products were quantitatively determined based on the calibration curve of the standard solution. The performance parameters for the electrocatalytic oxidation of HMF were HMF conversion, FDCA yield, FDCA selectivity, and Faradaic efficiency (FE), calculated using the following formulas:

[0061]

[0062]

[0063]

[0064]

[0065] Where F is the Faraday constant (96485 C mol) -1 ), where n is the number of moles of reactants calculated based on the concentration measured by HPLC. The theoretical charge for complete conversion of HMF is 232 C.

[0066] 5 Results and Discussion

[0067] 5.1 S12.5 Characterization of CoV-LDH electrode materials

[0068] X-ray diffraction (XRD) was used to examine S 12.5 The bulk lattice structures of CoV-LDH and CoV-LDH were characterized. For example... Figure 1 As shown in d, S 12.5 The peak positions of CoV-LDH and CoV-LDH are basically the same. The diffraction peaks at 11.6°, 23.4°, 34.1°, 38.7°, and 60.5° correspond to the (003), (006), (012), (015), and (113) crystal planes of LDH (PDF#00-050-0235), respectively. In addition, the strong diffraction peaks at 44.5°, 51.8°, and 76.4° originate from the nickel foam substrate (NF, PDF#00-004-0850).

[0069] Figure 1 As shown in Figure d, the XRD diffraction peak positions of the S-doped sample shifted significantly (moving to higher angles), indicating that the introduction of S altered the lattice parameters of CoV-LDH, inducing lattice distortion. The absence of independent metal sulfide impurities confirms that S atoms were successfully doped into the LDH crystal structure, rather than through simple physical mixing.

[0070] Figure 1 The high-resolution XPS curve of S 2p in e shows two main peaks at 161.51 eV and 168.94 eV, respectively. The 161.51 eV peak is attributed to sulfide ions bonded to the metal ions, which in turn indicates that some M-OH groups have been replaced by MS bonds. The characteristic peak at 168.94 eV can be attributed to oxidized sulfate species present on the material surface. The high-resolution XPS curve of Co is shown below. Figure 1 As shown in f, for CoV-LDH, Co 3+ and Co 2+ The peak values ​​occurred at 780.82 and 782.78 eV, respectively, at S 12.5 After S doping, the binding energies shifted to 781.13 and 783.71 eV, respectively. The positive shift in binding energy (main peak shift of 0.31 eV) not only reflects the electron transfer effect induced by the high electronegativity of S atoms, but also directly proves that orbital hybridization occurs between Co and S atoms, forming a covalent Co-S bond. This bonding process removes valence electrons from Co atoms, reducing their electron cloud density and thus increasing the binding energy.

[0071] We used scanning electron microscopy (SEM) to study S 12.5 The basic morphology of the CoV-LDH material was characterized. Figure 1 (ac). Among them, the three-dimensional porous framework of the nickel foam substrate is completely preserved, and many nano-flower-like S 12.5 The CoV-LDH material grew uniformly on the Ni framework without obvious aggregation or delamination. Notably, S... 12.5 The CoV-LDH material is a hierarchical flower-like microsphere. This structure maximizes the accessible specific surface area, which is beneficial for providing abundant active sites for catalytic reactions. (Scanning electron microscopy EDS image) Figure 2 (ag) shows that S 12.5 The uniform distribution of all elements in the CoV-LDH catalyst further indicates the formation of a homogeneous S-phase. 12.5 CoV-LDH composite material. The average loading of the S-doped CoV-LDH catalyst on nickel foam was measured to be approximately 4.5 mg·cm³. -2 .

[0072] 5.2 S 12.5 Study on the electrocatalytic HMF oxidation performance of CoV-LDH

[0073] (1) S 12.5 Study on the basic properties of CoV-LDH electrode materials

[0074] Performance Comparison: Using nickel foam as a substrate and 5-hydroxymethylfurfural (HMF) as the substrate, we synthesized a series of S with different metal ratios. 12.5 Performance comparisons were conducted on CoV-LDH composite materials (Co:V ratios of 1:6, 2:5, 3:4, 4:3, 5:2, 6:1, and 7:0). Figure 3 (ag). We measured the onset potentials and current densities of 5-hydroxymethylfurfural oxidation (HMFOR) and OER in an H-type electrolytic cell using LSV with and without 50 mM HMF solution, comparing the onset potentials and current densities at 100 and 200 mA / cm². -2 The potential difference is as follows. Among them, S has a Co:V metal ratio of 6:1. 12.5 CoV-LDH exhibited optimal catalytic activity. Figure 3 f), whose HMFOR onset potential is approximately 1.22 V, achieving 100 mA·cm -2 At a current density of 200 mA / cm², the potential of HMFOR is 263 mV lower than that of OER. Further increasing the current density to 200 mA / cm²... -2 At that time, the potential of HMFOR was 264 mV lower than that of OER, which indicates that the reaction system can significantly reduce the voltage of the anodic reaction, increase the energy conversion efficiency, and at the same time, effectively suppress the concurrent OER.

[0075] S doping level: We further synthesized a series of S with different sulfur contents. x The effect of sulfur content on the properties of CoV-LDH composite materials was investigated. Figure 3 h). The LSV plots of the HMFOR reaction show that the electrochemical activities of all sulfur-doped samples are significantly higher than those of the undoped CoV-LDH, indicating that the introduction of sulfur can effectively enhance the HMFOR catalytic activity of the material. Meanwhile, with the synthesis of S... x The concentration of thiourea in the CoV-LDH reaction solution increased from 0 to 0.0375 M (S) 12.5 CoV-LDH), its electrochemical activity gradually increases, and when its amount increases to 0.05 M (S 16.6 When CoV-LDH is present, the electrochemical activity shows a downward trend. This indicates that moderate sulfur doping can enhance catalytic performance by regulating the electronic structure and surface active site distribution of the material. However, excessive sulfur content may lead to over-modification of active centers or increase in structural disorder, resulting in a weakening of the improvement in catalytic activity.

[0076] Substrate dosage: We are optimizing S x Based on CoV-LDH, we further explored the electrocatalytic synthesis conditions of HMFOR, and compared the LSV curves of 5-hydroxymethylfurfural HMFOR at different concentrations (10 mM-90 mM). Figure 3 (i) The results show that as the HMF concentration gradually increases from 0 mM to 50 mM, the voltage gradually decreases. However, when the HMF concentration is further increased to 70 mM and 90 mM, the voltage decrease trend is not obvious. This may be because excessively high HMF concentrations can easily induce competitive adsorption saturation of active sites or form local mass transfer resistance on the electrode surface, thus limiting the continued progress of the reaction. In summary, an HMF concentration of 50 mM can simultaneously take into account both effective substrate utilization and reaction kinetic efficiency, and is the optimal substrate concentration condition for the HMFOR reaction in this system.

[0077] (2) Electrocatalytic performance and product analysis of HMFOR

[0078] Electrochemical performance parameters: To investigate the reaction kinetics of CoV-LDH and its derivatives with different S contents in the 1 M KOH + 50 mM HMF system, we calculated the Tafel slope using polarization curves to evaluate its catalytic kinetics. The Tafel slope is a key parameter reflecting the kinetic rate of electrocatalytic reactions; a smaller slope indicates a lower kinetic energy barrier and a faster reaction rate. For example... Figure 4 As shown in figure a, the Tafel slope of pure CoV-LDH is 75.9 mV / dec. After S doping, S... 4.1 CoV-LDH, S 8.3CoV-LDH and S 16.6 The Tafel slopes for CoV-LDH were 106.2 mV / dec, 90.0 mV / dec, and 73.0 mV / dec, respectively. Among them, S... 12.5 The Tafel slope of CoV-LDH is as low as 60.6 mV / dec. This indicates that appropriate sulfur doping can effectively reduce the kinetic energy barrier of CoV-LDH in the electro-oxidation reaction of HMF, significantly improving its reaction kinetic rate. Furthermore, we verified this from the perspective of interfacial charge transfer. When the reaction at the electrode interface is mainly limited by charge transfer rather than mass transfer diffusion, electrochemical impedance spectroscopy (EIS) typically exhibits a semi-circular response. To investigate the interfacial charge transfer behavior of CoV-LDH and its sulfur-doped derivatives, we performed electrochemical impedance spectroscopy measurements in 1 M KOH electrolyte. As can be seen from the Nyquist plot (…), Figure 4 (b) All samples exhibit a distinct semi-circular arc characteristic in the high-frequency region. It is noteworthy that the semi-circular diameter (corresponding to the charge transfer resistance R)... t The variation with sulfur doping amount is significant: among which, S 12.5 The Nyquist plot of CoV-LDH shows a semicircle with the smallest diameter, much smaller than that of pure CoV-LDH and other sulfur-doped samples. Smaller R... t A value of S implies a faster charge transfer kinetic rate at the electrode-electrolyte interface. Therefore, S 12.5 The doping ratio of CoV-LDH can effectively regulate its electronic structure, reduce the interfacial charge transfer barrier, and accelerate the charge transport process, thereby significantly improving the electrocatalytic activity of the catalyst. This is consistent with the Tafel slope test results mentioned above, further verifying the optimizing effect of the doping ratio on electrocatalytic performance.

[0079] Potentially constant HMFOR reaction: High performance liquid chromatography (HPLC) was used to detect the oxidation products after electrocatalysis. For example... Figure 4 cd represents the peak positions of different oxidized substances and the relationship between substance concentration and charge. The content of HMF gradually decreases with increasing charge, while the concentration of the target product FDCA gradually increases with the progress of the reaction. The byproducts HMFCA and FFCA can be detected during the oxidation process, while the signal peak of 2,5-dicarboxyfuran (DFF) is almost undetectable. When the transferred charge reaches 232 C (theoretical charge), the HMF concentration drops to zero, and the FDCA concentration reaches its maximum value. The results indicate that the oxidation process of HMF may follow pathway I (…). Figure 5 That is, under alkaline catalysis, the ethyl group preferentially adsorbs onto the catalyst surface and adds to H₂O to form a geminal diol. Then, in OH⁻... -Electrocatalytic dehydrogenation of CH and OH bonds is initiated under activation to form the HMFCA intermediate (HMF→HMFCA→FFCA→FDCA), as shown in the reaction process. Figure 5 As shown.

[0080] In addition, we also measured S at different potentials. 12.5 HMF conversion rate, FDCA selectivity and Faraday efficiency (FE) of CoV-LDH Figure 4 e). The results showed that the catalyst exhibited better FDCA selectivity (99.4%) and FE (99.6%) at a potential of 1.45 V. Most importantly, in 12 consecutive cycles ( Figure 4 f), S 12.5 The HMF conversion, FDCA selectivity, and Faraday efficiency of the CoV-LDH electrode did not show a significant decrease, indicating that the catalyst has strong activity and stability, and is expected to realize the practical application of HMFOR.

[0081] in conclusion

[0082] This invention successfully prepared an S-doped CoV-LDH electrode material on a nickel foam substrate via a one-step hydrothermal synthesis method, and applied it to the electrocatalytic value-added oxidation coupled with cathode hydrogen evolution of the biomass platform molecule 5-hydroxymethylfurfural (HMF). We also systematically explored the regulatory mechanism of S doping on the catalyst's structural characteristics and catalytic performance, and proposed a new concept for designing high-performance electrocatalysts to construct a coupled system for biomass upgrading and integrated hydrogen production. Structural characterization and performance testing results show that the successful introduction of S element induces lattice distortion through the formation of unique Co-S bonds, effectively regulating the crystal structure and electronic configuration of CoV-LDH, increasing the number of exposed active sites on the catalyst surface, and optimizing the electron density distribution of the active centers, laying the structural and electronic foundation for improved catalytic reaction kinetics. Electrochemical testing confirmed that the S doping amount has a significant impact on catalytic performance, with S... 12.5 CoV-LDH exhibits optimal overall electrocatalytic performance. In a 1 M KOH + 50 mM HMF system, this catalyst can achieve highly efficient conversion of HMF to 2,5-furandicarboxylic acid (FDCA) at a potential of 1.45 V relative to the reversible hydrogen electrode (RHE), with a Faradaic efficiency (FE) as high as 99.6% and an FDCA yield of 99.4%. Furthermore, the catalyst possesses excellent structural and catalytic stability; after 12 consecutive electrocatalytic cycles, its Faradaic efficiency, product selectivity, and yield did not show significant decline, with the product yield consistently remaining above 94%. This invention not only provides an efficient strategy for the doping modification of transition metal LDH-based catalysts but also offers a reference for the development of low-energy-consumption, high-value-added biomass conversion technologies through the coupled design of biomass value-added oxidation and green hydrogen production.

[0083] The foregoing has provided a detailed description of the S-doped CoV-LDH electrode material, its preparation method, and its applications. Specific examples have been used to illustrate the principles and implementation methods of the invention. These examples are merely illustrative and are intended to aid in understanding the method and core concepts of the invention. It should be noted that those skilled in the art can make various improvements and modifications to the invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims.

Claims

1. An S-doped CoV-LDH electrode material, characterized in that, The electrode material includes a conductive substrate and an S-doped CoV-LDH active layer grown in situ on the surface of the conductive substrate; In the S-doped CoV-LDH active layer, the S element is doped into the CoV-LDH lattice and partially replaces the lattice oxygen.

2. The S-doped CoV-LDH electrode material according to claim 1, characterized in that, The S-doped CoV-LDH active layer has a multi-level flower-like microsphere structure, which is assembled from nanosheets and uniformly distributed on the framework of the conductive substrate.

3. The S-doped CoV-LDH electrode material according to claim 1, characterized in that, The conductive substrate is nickel foam; in the S-doped CoV-LDH active layer, the molar ratio of Co to V is 4:3 to 7:

0.

4. The S-doped CoV-LDH electrode material according to claim 2, characterized in that, The molar ratio of Co to V is 5:2 to 6:

1.

5. A method for preparing the S-doped CoV-LDH electrode material as described in any one of claims 1-4, characterized in that, The method includes the following steps: Step 1: Dissolve the cobalt source, vanadium source, urea and sulfur source in water to obtain a mixed precursor solution; Step 2: Place the pretreated conductive substrate in the mixed precursor solution; Step 3: The system obtained in Step 2 is subjected to a hydrothermal reaction under sealed conditions to allow S-doped CoV-LDH to grow in situ on the conductive substrate; Step 4: After the reaction is complete, the conductive substrate is removed, washed, and dried to obtain the S-doped CoV-LDH electrode material.

6. The preparation method according to claim 5, characterized in that, The cobalt source is cobalt nitrate hexahydrate, the vanadium source is vanadium chloride, and the sulfur source is thiourea; in the mixed precursor solution, the concentration of the cobalt source is 0.01-0.1 M, the concentration of the vanadium source is 0.01-0.05 M, the concentration of the urea is 0.1-0.5 M, and the concentration of the sulfur source is 0.01-0.05 M.

7. The preparation method according to claim 5, characterized in that, The hydrothermal reaction is carried out at a temperature of 100-140℃ for 8-16 hours.

8. The preparation method according to claim 5, characterized in that, The concentration of the sulfur source in the mixed precursor solution is 0.0375 M.

9. The application of the S-doped CoV-LDH electrode material as described in any one of claims 1-4 in the electrocatalytic oxidation of 5-hydroxymethylfurfural.

10. The application according to claim 9, characterized in that, The application involves using the S-doped CoV-LDH electrode material as the anode in an alkaline electrolyte to catalytically oxidize 5-hydroxymethylfurfural to generate 2,5-furandicarboxylic acid, while simultaneously coupling a hydrogen evolution reaction at the cathode.

Images