Nickel-cobalt sulfide catalyst for preparing FDCA through electrocatalytic oxidation and preparation and application of nickel-cobalt sulfide catalyst

Abstract

The invention relates to a nickel-cobalt sulfide catalyst for preparing 2, 5-furandicarboxylic acid (FDCA) through electrocatalytic oxidation as well as a preparation method and application of the nickel-cobalt sulfide catalyst. The catalyst is synthesized by adopting a one-step hydrothermal method, and the bimetallic synergistic effect and the precise regulation and control of sulfur vacancy are realized by optimizing the nickel-cobalt ratio and the sulfur element content. According to the unique structural design, the catalytic efficiency of oxidizing 5-hydroxymethylfurfural (HMF) into FDCA is remarkably improved, efficient conversion can be achieved under the low potential, and competition with the water electrolysis oxygen evolution reaction is avoided. The catalyst has excellent catalytic performance, the FDCA yield is close to the theoretical maximum value, and meanwhile, excessive oxidation of an intermediate product and decarboxylation side reaction can be effectively inhibited. The composite structure shows good corrosion resistance, and can still keep stable catalytic activity after being recycled in a strong alkaline electrolyte for a long time. The cobalt content is controlled to be lower than the nickel content, so that the raw material cost is reduced, the use of a noble metal catalyst is avoided, and the overall production cost is greatly reduced.

Description

Technical Field

[0001] The present application relates to the technical field of electrocatalytic oxidation catalysts and their preparation and application, and more specifically to a nickel-cobalt sulfide catalyst for electrocatalytic oxidation preparation of 2,5-furandicarboxylic acid (FDCA) and its preparation and application. Background Art

[0002] 2,5-Furandicarboxylic acid (FDCA) is one of the priority chemicals for future sustainable development. As the most promising compound to replace terephthalic acid, it can be used to produce furandicarboxylic acid ethylene glycol (PEF, polyethylene high foam insulation material) and is expected to replace the petroleum derivative polyethylene terephthalate (PET).

[0003] FDCA is primarily prepared by oxidizing HMF. The mainstream technical routes include chemical oxidation, biological oxidation, and electrocatalytic oxidation. Chemical oxidation, in particular, primarily uses precious metal catalysts (such as Pt and Au) to oxidize HMF under high temperature and high pressure. This is expensive, and the reaction time is long, separation and purification is complex, and energy consumption is high, making it difficult to scale up and unsuitable for industrial production. Biological oxidation, which primarily uses enzymes or engineered bacteria as catalysts, operates under mild conditions, but the enzymes are unstable (half-life <24 hours), have low reaction rates, and require stringent storage conditions. Furthermore, significant substrate inhibition also presents significant technical bottlenecks in the industrial scale-up of FDCA. Directed oxidation of HMF on an electrode surface driven by an external electric field offers advantages such as mild reaction conditions (ambient temperature and pressure), controllable pathways, and the absence of chemical oxidants. It is considered the greenest synthetic route with the greatest industrial potential. Therefore, the catalytic oxidation of 5-hydroxymethylfurfural (HMF) is often used in industry to prepare FDCA. However, catalytic oxidation technology still faces numerous challenges. Defects such as slow electron transfer rate of electrode materials, high oxidation overpotential, low Faradaic efficiency, low FDCA product conversion rate and low catalyst repetition number increase the energy consumption of the reaction system and the cost of FDCA production, thereby limiting the development of the industry.

[0004] Currently, there are no reports on the one-step synthesis of nickel cobalt sulfide for the preparation of catalysts and their application in the electrocatalytic oxidation of HMF to produce FDCA. Summary of the Invention

[0005] In view of the above problems, the present application provides a nickel-cobalt sulfide catalyst for the electrocatalytic oxidation preparation of FDCA, its preparation and application. The nickel-cobalt bimetallic sulfide catalyst is synthesized by a one-step method to overcome the defects of complex catalyst synthesis process, short catalyst service life, and environmental pollution in the process of electrocatalytic oxidation of 5-hydroxymethylfurfural HMF to 2,5-furandicarboxylic acid FDCA, thereby achieving the purpose of using the nickel-cobalt sulfide catalyst for the electrocatalytic oxidation preparation of FDCA with a simple synthesis step process, low cost, fast reaction speed, high selectivity, and long catalyst service life.

[0006] To achieve the above objectives, in the first aspect, the inventors provide a nickel-cobalt sulfide catalyst for the electrocatalytic oxidation preparation of 2,5-furandicarboxylic acid, comprising a pretreated nickel foam support and a nickel-cobalt sulfide active component loaded thereon, wherein the molar ratio of nickel to cobalt is (1.5-3.5):1, and the molar ratio of sulfur element to total metal is (0.5-1.5):1.

[0007] Nickel foam (NF) was pretreated by first ultrasonicating it in an acetone solution for 15 minutes, then repeatedly rinsing it with deionized water several times, ultrasonicating it in a 3M HCl solution for 15 minutes, repeatedly soaking it in ultrapure water, ultrasonicating it again in ultrapure water for 15 minutes, and then ultrasonicating it in an ethanol solution for 15 minutes. The foam was then vacuum-dried for 4 hours and sealed for storage, resulting in the pretreated nickel foam support. This removes organic contaminants from the nickel foam surface, ensuring a clean substrate and preventing impurities from interfering with catalyst loading. Ultrasonication with a 3M HCl solution dissolves the nickel oxide layer, exposing a fresh metal surface and increasing active sites. It also micro-etches the surface, increasing the specific surface area and roughness, promoting the diffusion of the reactants (HMF) and products (FDCA), and enhancing the adhesion and dispersibility of the catalyst. Subsequent rinsing with ultrapure water and ultrasonication thoroughly removes residual HCl and reaction products, preventing the negative effects of chloride ions on the subsequent catalytic process. Optimizing the physicochemical properties of the nickel foam paves the way for efficient loading and stable operation of the nickel-cobalt sulfide catalyst, significantly improving the performance of the electrocatalytic oxidation of HMF to FDCA.

[0008] The setting of nickel-cobalt molar ratio (1.5-3.5:1) and sulfur-to-metal molar ratio (0.5-1.5:1) is an innovative design based on scientific principles and experimental optimization goals. Nickel (Ni) has high redox activity and can provide abundant active sites (such as Ni 3+ / Ni 2+ The introduction of cobalt (Co) can adjust the electronic structure of the catalyst, enhance the adsorption capacity of reaction intermediates (such as aldehyde and hydroxyl groups of HMF), and stabilize the high-valent metal sites (such as Co 3+), inhibiting excessive oxidation and deactivation of active sites. A higher proportion of Ni than Co (1.5-3.5:1) can not only ensure sufficient Ni active sites to dominate the reaction, but also optimize electron transport and intermediate adsorption through appropriate amounts of Co, avoiding excessive Co leading to coverage of active sites or decreased structural stability. In addition, NiCo sulfide has better conductivity than single metal sulfide, but too high a Ni content may increase resistance due to lattice distortion; the inventors found that controlling the nickel-cobalt molar ratio at 1.5-3.5:1 can achieve a balance between high catalytic activity and conductivity. Appropriate doping of Co can inhibit the structural collapse of Ni sulfide during the electrocatalytic process and extend the life of the catalyst.

[0009] S atoms form a porous sulfide network by bridging the Ni-Co metal center, enhancing the adsorption and activation ability of the C=O and C-OH bonds in the HMF molecule. However, if the S ratio is too low (the molar ratio of S: metal is less than 0.5:1), the sulfide crystallinity will be insufficient, making it difficult to form a stable active phase; if the S ratio is too high (the molar ratio of S: metal is greater than 1.5:1), excessive S will be generated. 2- or S - When the S ratio is in the range of 0.5 to 1.5:1, the moderate introduction of sulfur vacancies can adjust the electron cloud density of the metal (such as promoting Ni 2+ →Ni 3+ oxidation), and improve the catalytic selectivity for HMF oxidation intermediates (such as 5-hydroxymethyl-2-furoic acid HMFCA and 5-formyl-2-furoic acid FFCA).

[0010] Different from the existing technology, the above technical solution adopts a one-step hydrothermal method to synthesize nickel-cobalt sulfide catalysts. The bimetallic synergy and sulfur vacancy regulation significantly improve the current density and Faradaic efficiency of HMF oxidation to FDCA. By optimizing the ratio to suppress excessive oxidation or decarboxylation side reactions of the intermediates, the yield of FDCA can be close to 100%. The composite structure of the nickel-cobalt sulfide catalyst has strong corrosion resistance. After circulating in an alkaline electrolyte for 100 hours, the activity decay is less than 10%. It can be reused more than ten times and has good stability. Controlling the Co content (lower than Ni) reduces the cost of raw materials and avoids the use of precious metal catalysts (such as Pt and Ru), which are inexpensive and economical, in line with the principles of green chemistry.

[0011] In some embodiments, the active component of the nickel-cobalt sulfide catalyst comprises a hexagonal Ni3S2 phase. In these embodiments, hexagonal Ni3S2 exhibits a metallic bond-dominated crystal structure with partial overlap between its conduction band and valence band, exhibiting high metal-like conductivity, significantly superior to other semiconductor-type sulfides. This crystal structure also provides efficient pathways for rapid electron transfer in the electrocatalytic oxidation reaction, reducing the reaction overpotential and increasing the number of active sites, enabling targeted catalytic oxidation of HMF to FDCA.

[0012] In some more preferred embodiments, the hexagonal Ni3S2 phase is a coexistence structure of 0.28nm interplanar spacing and 0.16nm interplanar spacing. The 0.28nm interplanar spacing corresponds to an open layered structure, and the surface of the nickel-cobalt sulfide catalyst exposes a large amount of Ni 3+ Active sites preferentially adsorb HMF's aldehyde groups (-CHO) and catalyze their oxidation to carboxylic acids (-COOH). The 0.16nm interplanar spacing corresponds to a dense atomic arrangement rich in sulfur vacancies. This strong adsorption stabilizes the intermediate, preventing its desorption and reaction interruption, while also promoting the gradual oxidation of the hydroxymethyl group. The alternating arrangement of different interplanar spacings disperses the mechanical stress caused by volume changes during electrocatalysis, preventing crack propagation and thus improving cycling stability (performance degradation <10% over >500 hours).

[0013] As a preferred embodiment of the present invention, the nickel-cobalt sulfide catalyst is prepared by a preparation method comprising the following steps:

[0014] S1: nickel salt, cobalt salt, sulfur-containing raw material, precipitant and corrosive agent are dissolved in deionized water at a molar ratio of Ni:Co:S:precipitant:corrosive agent = (2.5-3.5):(0.8-1.2):(2.5-3.5):(8-12):(7-9), and stirred to form a homogeneous solution;

[0015] S2: immersing the pretreated nickel foam support into the homogeneous solution described in step S1 to perform a hydrothermal reaction;

[0016] After the hydrothermal reaction in S3 is completed, the catalyst is cleaned and vacuum dried to obtain a nickel-cobalt sulfide catalyst.

[0017] The above-mentioned preparation method adopts a one-step hydrothermal synthesis method to prepare a nickel-cobalt sulfide catalyst, while achieving the coprecipitation of nickel-cobalt sulfide, the in-situ growth of active components on the nickel foam support, and the chemical bonding of the heterogeneous interface, avoiding the generation of heterogeneous phases in the target crystal form of the catalyst, and also avoiding the problem that the traditional step-by-step method (synthesis → loading → calcination) easily leads to the agglomeration of active components and weak carrier binding force. Since the one-step method eliminates the calcination link of the traditional method, energy consumption and time are greatly saved, and the reactants of the hydrothermal reaction are all efficiently converted in a closed system, reducing the treatment cost of the waste liquid. The airtightness and uniform heat transfer characteristics of the hydrothermal system can ensure that the morphology and component deviation of different batches of catalysts are within the minimum range. The synthesis step process of the nickel-cobalt sulfide catalyst of the present invention is simple, the cost of preparing the catalyst is low, and it is suitable for industrial promotion and application.

[0018] In a further preferred embodiment, the precipitant is urea or sodium carbonate, and the etchant is ammonium fluoride or sodium fluoride. More preferably, the precipitant is urea and the etchant is ammonium fluoride. The precipitant is preferably urea, which can slowly release the precipitate to ensure fine and uniform particles, without sodium ion contamination to avoid blocking of active sites. However, sodium carbonate precipitates too quickly and easily agglomerates, and the introduced sodium ions require additional cleaning to remove. The etchant is preferably ammonium fluoride, which has a dual role: F - Etching carrier surface, NH4 + Coordination regulates crystal surface growth to form a low resistance interface. However, sodium fluoride only has etching function and lacks coordination regulation, resulting in poor crystal surface control and high interface resistance. At the same time, the decomposition products of urea and ammonium fluoride (NH3, CO2) are non-toxic, the reaction system is closed and controllable, and nitrogen / fluorine co-modification improves electron transport to achieve chemical synergistic effects. NH4 + The coordination effect ensures the orderly assembly of the interplanar spacing gradient, which has excellent advantages in industrial implementation.

[0019] In a more preferred embodiment, the nickel salt is nickel nitrate, nickel chloride or nickel acetate; and / or the cobalt salt is cobalt nitrate, cobalt chloride or cobalt acetate; and / or the sulfur-containing raw material is thioacetamide or thiourea. In a further preferred embodiment, the nickel salt is nickel nitrate hexahydrate, the cobalt salt is cobalt nitrate hexahydrate, and the sulfur-containing raw material is thioacetamide. The hexahydrate nitrate of nickel / cobalt has high solubility, which can circumvent the problems of easy deliquesce of chloride and low solubility of acetate. Nitrate has no complexing effect and will not produce competitive coordination. The sulfur source uses thioacetamide, which can achieve the purpose of controllable sulfurization through moderate hydrolysis, promote the exposure of large-spacing crystal planes, realize the coexistence of gradient crystal planes and ensure the purity of the electronic structure of sulfide. The combined use of nickel nitrate hexahydrate, cobalt nitrate hexahydrate and thioacetamide can also achieve a synergistic effect of maintaining the temperature stability of the system by low-temperature decomposition of nitrate → medium-temperature hydrolysis of thioacetamide → simultaneous sulfidation of metal ions, avoiding waste of sulfur source or pre-oxidation of metal. The release of crystal water of hexahydrate balances the endothermic hydrolysis process of thioacetamide.

[0020] In some preferred embodiments, the hydrothermal reaction conditions are: a reaction temperature of 110-130°C and a reaction time of 10-14 hours, more preferably, a reaction temperature of 120±2°C and a reaction time of 12±0.5 hours. Compared with the traditional distributed method, the one-step hydrothermal reaction method of the present invention has mild reaction conditions, low energy consumption, and a short reaction time.

[0021] In a second aspect of the present invention, the inventors provide a method for preparing 2,5-furandicarboxylic acid by electrocatalytic oxidation, using an H-type double electrolytic cell as a reactor, in the anode chamber, the nickel-cobalt sulfide catalyst described in the first aspect of the present invention is used as a working electrode, and a 1 mol / L alkaline electrolyte containing 5 to 30 mmol / L 5-hydroxymethylfurfural is used as the anode liquid; in the cathode chamber, a platinum sheet electrode is used as a counter electrode, mercury or mercuric oxide is used as a reference electrode, and a 0.1 to 1 mol / L alkaline electrolyte is used as the cathode liquid. The cathode chamber and the anode chamber are separated by a Nafion-117 proton exchange membrane, and electrolysis is carried out using chronopotentiometry at a constant potential of 1.45 to 1.65 V vs. RHE. The reaction time is 15 to 180 min. During the reaction, samples are taken by acid quenching and the yield of 2,5-furandicarboxylic acid is monitored by HPLC.

[0022] Different from the existing technology, the present invention uses non-precious metal nickel cobalt sulfide catalyst with the same activity as the traditional precious metal catalyst, but the cost is reduced by about 90%. The precise potential window of 1.45–1.65V vs. RHE inhibits the oxidation side reaction in alkaline medium, improves the selectivity of FDCA by more than 95%, and improves the reaction stability and the cycle life of the catalyst. Nafion-117 membrane allows H + It migrates directionally to the cathode chamber, maintains the pH value of the anode chamber stable, prevents local acidity and alkalinity fluctuations from causing HMF hydrolysis side reactions, blocks the diffusion of FDCA anions to the cathode, and avoids product reduction at the cathode. The present invention increases the yield of FDCA to more than 95%, greatly improves the current efficiency, and greatly reduces the energy consumption index and catalyst cost. The present invention can electrocatalytically oxidize 5-hydroxymethylfurfural (HMF) to produce 2,5-furandicarboxylic acid (FDCA) at a lower potential, avoiding competition with the electrolysis reaction of water, and because no precious metal catalysts are used, the production cost is low and it is easy to promote and apply industrially, providing an efficient, economical and green solution for the supply of bio-based polyester (PEF) raw materials.

[0023] In a more preferred embodiment, the nickel cobalt sulfide catalyst is repeatedly used for the electrocatalytic oxidation of 5-hydroxymethylfurfural to prepare 2,5-furandicarboxylic acid 10-15 times, and the 5-hydroxymethylfurfural conversion rate, 2,5-furandicarboxylic acid productivity and Faraday efficiency are all higher than 95%.

[0024] Furthermore, the pH value of the anolyte is ≥13, the constant potential is 1.465±0.005Vvs.RHE, and the reaction time is 2±0.2h.

[0025] The above-mentioned records related to the content of the invention are only an overview of the technical solution of this application. In order to enable ordinary technicians in this field to understand the technical solution of this application more clearly, and then implement it according to the text of the specification and the contents recorded in the drawings, and to make the above-mentioned purposes and other purposes, features and advantages of this application easier to understand, the following is an explanation in combination with the specific implementation methods and drawings of this application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are only used to illustrate the principles, implementation methods, applications, characteristics and effects of the specific embodiments of the present invention and other related contents, and are not to be considered as limiting the present application.

[0027] In the drawings of the specification:

[0028] Figure 1 TEM image of the NiCo-S catalyst of Example 1;

[0029] Figure 2 is a STEM image of the NiCo-S catalyst of Example 1;

[0030] Figure 3 HRTEM image of the NiCo-S catalyst of Example 1;

[0031] Figure 4 HRTEM and EDX mapping images of Ni element in the NiCo-S catalyst of Example 1;

[0032] Figure 5 HRTEM and EDX mapping images of the Co element in the catalyst of Example 1;

[0033] Figure 6 HRTEM and EDX mapping images of the O element in the catalyst of Example 1;

[0034] Figure 7 HRTEM and EDX mapping images of the S element in the catalyst of Example 1;

[0035] Figure 8 LSV (Linear Sweep Voltammetry) diagrams of NiCo-O (Comparative Example 1) and NiCo-S (Example 1) in 1 M KOH solution with / without 0.02 M HMF;

[0036] Figure 9 LSV (linear sweep voltammetry) diagrams of NiCo-S (Example 1), Ni-S (Comparative Example 2), Co-S (Comparative Example 3) and NF-S (Comparative Example 4);

[0037] Figure 10Comparison of current density at different potentials for NiCo-S (Example 1), Ni-S (Comparative Example 2), Co-S (Comparative Example 3), and NF-S (Comparative Example 4);

[0038] Figure 11 This is a comparison chart of the LSV of catalyst materials prepared using different ratios of sulfur sources in Examples 1-4;

[0039] Figure 12 This is the graph of HPLC peak area changes during electrolysis;

[0040] Figure 13 is the concentration change curve of organic matter during electrolysis;

[0041] Figure 14 This is the electrochemical activity test diagram of nickel cobalt sulfide catalyst, specifically NiCo-S from 10mV s -1 to 100mVs -1 CV curve diagram under scanning speed;

[0042] Figure 15 For NiCo-O, the voltage is from 10mV s -1 to 100mVs -1 CV curve diagram under scanning speed;

[0043] Figure 16 C is calculated by fitting the capacitance current versus scan rate function at 0.56 V (vs. RHE) of the CV curve. dl ;

[0044] Figure 17 The yield of FDCA, HMF conversion and Faradaic efficiency of the electrocatalytic oxidation of HMF to FDCA over nickel cobalt sulfide catalyst were tested over ten cycles. DETAILED DESCRIPTION

[0045] In order to explain in detail the possible application scenarios, technical principles, specific solutions that can be implemented, and the purpose and effects of this application, the following is a detailed description of the specific embodiments listed in conjunction with the accompanying drawings. The embodiments described herein are only used to more clearly illustrate the technical solutions of this application and are therefore only examples and are not intended to limit the scope of protection of this application.

[0046] References to "embodiments" herein mean that the specific features, structures, or characteristics described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the word "embodiment" in various places in the specification does not necessarily refer to the same embodiment, nor does it particularly limit its independence or relevance to other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the various technical features mentioned in the embodiments can be combined in any manner to form a corresponding implementable technical solution.

[0047] Unless otherwise defined, the technical terms used herein have the same meanings as those generally understood by those skilled in the art to which this application belongs; the use of relevant terms herein is only for describing specific embodiments and is not intended to limit this application.

[0048] In the description of this application, the term "and / or" is used to describe a logical relationship between objects, indicating that three relationships can exist. For example, A and / or B means: A exists, B exists, and both A and B exist. In addition, the character " / " in this document generally indicates that the objects before and after are in a logical "or" relationship.

[0049] In this application, terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual quantity, priority or sequence relationship between these entities or operations.

[0050] Without further limitations, in this application, the words "include", "comprise", "have" or other similar open-ended expressions used in sentences are intended to cover non-exclusive inclusion. These expressions do not exclude the presence of additional elements in the process, method or product that includes the elements, so that the process, method or product that includes a series of elements may include not only those defined elements, but also other elements that are not explicitly listed, or also include elements inherent to such process, method or product.

[0051] Consistent with the understanding in the Examination Guidelines, in this application, expressions such as "greater than," "less than," and "exceed" are understood to exclude the number itself; expressions such as "above," "below," and "within" are understood to include the number itself. Furthermore, in the description of the embodiments of this application, "multiple" means more than two (including two), and similar expressions related to "multiple" are also understood in this manner, such as "multiple groups," "multiple times," etc., unless otherwise specifically defined.

[0052] In the description of the embodiments of the present application, the space-related expressions used, such as "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "vertical", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicate the orientation or position relationship based on the orientation or position relationship shown in the specific embodiments or drawings, and are only for the convenience of describing the specific embodiments of the present application or facilitating the reader's understanding, and do not indicate or imply that the device or component referred to must have a specific position, a specific orientation, or be constructed or operated in a specific orientation. Therefore, it should not be understood as a limitation on the embodiments of the present application.

[0053] 2,5-Furandicarboxylic acid (FDCA) is a key bio-based platform compound for replacing petroleum-based polyesters. However, its mainstream preparation process—the catalytic oxidation of HMF—faces significant challenges. Chemical methods rely on precious metals and suffer from poor enzyme stability. Electrocatalytic methods are limited by slow electron transport in electrode materials, high oxidation overpotentials, low product selectivity, and short catalyst lifetimes, hindering industrialization. To address these challenges, the development of efficient and stable non-precious metal electrocatalysts is crucial. Nickel- and cobalt-based compounds have shown great potential for the electrocatalytic oxidation of HMF due to their tunable electronic structures, abundant redox active sites, and cost advantages. Recent studies have demonstrated that bimetallic sulfides (such as NiCo2S4) can optimize OH adsorption energy and reduce the C-H bond activation barrier through synergistic effects, thereby enhancing FDCA selectivity. However, existing reports have primarily focused on step-by-step syntheses (e.g., preparing a hydroxide precursor followed by sulfidation), which are complex and lack sufficient exposure of active sites. To date, there has been no systematic report on the direct construction of nickel-cobalt sulfide catalysts for the efficient electrooxidation of HMF to FDCA. The technical solution of the present invention is expected to provide a new strategy for the low-cost manufacturing of FDCA by simplifying the synthesis process and regulating the microenvironment of the active site, thereby simultaneously solving the problems of activity, selectivity and stability.

[0054] Unless otherwise specified, all raw materials and reagents used in the present invention were commercially available chemically pure or analytically pure products and were used directly without further purification. Analytically pure nickel nitrate hexahydrate was purchased from Beijing No. 56701 Chemical Plant; analytically pure cobalt nitrate hexahydrate was purchased from Jingchun Biochemical Co., Ltd.; analytically pure ammonium fluoride was purchased from Jingchun Biochemical Co., Ltd.; analytically pure urea was purchased from Maclean Co., Ltd.; analytically pure thioacetamide was purchased from Jingchun Biochemical Co., Ltd.; potassium hydroxide was purchased from Tianjin Fine Chemicals; and 5-hydroxymethylfurfural was purchased from Aladdin Reagent.

[0055] The nickel salt is selected from nickel nitrate, nickel chloride, and nickel acetate; the cobalt salt is selected from cobalt nitrate, cobalt chloride, and cobalt acetate; the sulfur-containing raw material is selected from thioacetamide and thiourea; the precipitant is selected from urea and sodium carbonate; and the etchant is selected from one or more combinations of ammonium fluoride and sodium fluoride. Preferably, the nickel salt is nickel nitrate hexahydrate, the cobalt salt is cobalt nitrate hexahydrate, the sulfur-containing raw material is thioacetamide, the precipitant is urea, and the etchant is ammonium fluoride.

[0056] Deionized water or ultrapure water was prepared using a Milli-Q pure water system with a resistivity of ≥18 MΩ·cm.

[0057] The alkaline electrolyte is prepared by dissolving an alkali metal hydroxide (such as potassium hydroxide or sodium hydroxide) in deionized water or ultrapure water, with a concentration of 0.1 mol / L to 5 mol / L, preferably 1 mol / L.

[0058] Pretreatment method of nickel foam (NF) carrier: The nickel foam (NF) carrier needs to be pretreated before use. The specific steps include: first placing it in acetone solution for ultrasonication for 15 minutes, then repeatedly washing it with deionized water several times, then placing it in 3M HCl solution for ultrasonication for 15 minutes, repeatedly soaking it in ultrapure water, soaking it in ultrapure water and continuing to ultrasonicate for 15 minutes, then placing it in ethanol solution for ultrasonication for 15 minutes, and finally vacuum drying it at 60°C for 4 hours and sealing it for storage.

[0059] The synthesis equipment used in the embodiment of the present invention is described as follows:

[0060] The hydrothermal reaction is carried out in a polytetrafluoroethylene-lined autoclave with a volume of 50 mL to 200 mL, preferably 100 mL.

[0061] The stirring operation is performed using a magnetic stirrer or a mechanical stirrer, and the rotation speed is controlled at 200 rpm to 800 rpm, preferably 500 rpm.

[0062] The drying process is carried out in a vacuum drying oven with a set temperature of 50°C to 80°C, a vacuum degree maintained at -0.09MPa to -0.1MPa, and a drying time of 2h to 12h.

[0063] Ultrasonic cleaning is performed using an ultrasonic cleaning machine with an ultrasonic power of 100W to 500W and a frequency of 40kHz.

[0064] The following equipment was used for characterization:

[0065] The morphology and structure of the catalysts were observed using a scanning electron microscope (FEINova NanoSEM 450) and a transmission electron microscope (JEOL JEM-2100F).

[0066] The crystal structure of the catalyst was determined by X-ray diffractometer Bruker D8 Advance using Cu Kα radiation. The analysis was performed with a scanning range of 5° to 90° in the 2θ range and a scanning speed of 5° / min.

[0067] The elemental composition and chemical state of the catalysts were analyzed by X-ray photoelectron spectroscopy (XPS) on a ThermoScientific ESCALAB 250Xi instrument using an AlKα monochromatized X-ray source and a binding energy calibrated at C 1s = 284.8 eV.

[0068] The electrochemically active specific surface area (ECSA) of the catalyst is determined by the double layer capacitance C dl The instrument used is capable of performing cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), constant potential / constant current transient tests, etc. to directly extract C dl The Princeton VersaSTAT with the same parameters was used. The test method was cyclic voltammetry (CV), which scanned the voltage in the non-Faraday potential range (no redox reaction) and calculated C from the current response. dl .

[0069] Instrument settings: Scan rate (v): 10-100mV / s (multi-rate testing verifies double layer characteristics), potential window: select the range where non-Faradaic reaction occurs (e.g., 0.1-0.2V vs. RHE), calculation formula: Cdl = (1 / 2v)·(ΔI / ΔV), where ΔI is the non-Faradaic current difference and ΔV is the potential window. The electrochemical testing equipment is described below:

[0070] The electrocatalytic performance test was carried out in a standard three-electrode H-type electrolytic cell, using a CHI 760E to control the potential / current and collect data.

[0071] The working electrode is a nickel foam loaded with the catalyst of the present invention, with a geometric area of approximately 1 cm × 1 cm to 3 cm × 3 cm, preferably 1 cm × 1 cm. The counter electrode is a platinum electrode, and the reference electrode is a mercury / mercury oxide electrode (Hg / HgO). Before testing, all potentials are converted to potentials relative to the reversible hydrogen electrode (RHE) using the following conversion formula: E(vs.RHE) = E(vs.Ref) + E_ref + 0.059*pH, where E_ref is the potential of the reference electrode relative to the standard hydrogen electrode (NHE), and Hg / HgO is +0.098 V in 1 M KOH.

[0072] The anode and cathode chambers were separated by a Nafion 117 proton exchange membrane with an effective area of 4 cm 2 .

[0073] The electrolyte alkaline solution is one or two of potassium hydroxide, sodium hydroxide, and lithium hydroxide, preferably 1M KOH solution. The pH of the anode alkaline reaction solution is ≥13, and the anode alkaline solution includes an alkaline electrolyte 1M KOH solution and the reaction substrate 5-hydroxymethylfurfural. The concentration of the 5-hydroxymethylfurfural HMF substrate is 5 to 30 mmol / L, preferably 20 mmol / L. The electrocatalytic oxidation process of HMF is carried out at an anode potential of 1.45 to 1.5 V vs. RHE, and electrocatalytic oxidation is carried out using it (constant potential).

[0074] The product analysis was performed using the following method:

[0075] High performance liquid chromatography (HPLC) Agilent 1260 Infinity II was used to analyze the concentrations of HMF and its oxidation products (including HMFCA, FFCA, and FDCA) in the reaction solution samples.

[0076] HPLC conditions: Agilent ZORBAX Eclipse Plus C18 column (4.6×250 mm, 5 μm); mobile phase: acetonitrile: 0.1% formic acid in water (10:90 v / v); flow rate: 1.0 mL / min; column temperature: 30°C; detection wavelength: 268 nm; injection volume: 20 μL. Components were identified qualitatively by retention time, and quantified by external standard method (using a standard to generate a calibration curve).

[0077] The FDCA yield (%) was calculated according to the following formula: FDCA yield (%) = (n_FDCA / n_HMF, initial) * 100%, where n_FDCA is the number of moles of FDCA produced and n_HMF, initial is the number of moles of HMF initially added. The factor of 2 is because one molecule of HMF theoretically produces one molecule of FDCA (a molar ratio of 1:1).

[0078] The conversion rate (%) of HMF was calculated according to the following formula: HMF conversion rate (%) = [(n_HMF, initial - n_HMF) / n_HMF, initial] * 100%, where n_HMF is the number of moles of HMF remaining after the reaction.

[0079] The electrochemical performance is calculated as follows:

[0080] Faradaic efficiency (FE, %) was calculated according to the following formula: FE (%) = [(n_FDCA*n*F) / Q]*100%, where: n_FDCA: moles of FDCA generated (mol); n: number of electrons required to generate 1 mol of FDCA (FDCA is oxidized by HMF, usually n=6); F: Faraday constant (96485 C / mol); Q: total charge passed during electrolysis (C), calculated by Q=I*t, where I is the average current (A) and t is the electrolysis time (s).

[0081] The one-step hydrothermal method for synthesizing a nickel-cobalt sulfide bimetallic catalyst comprises the following specific steps: taking a nickel raw material, a cobalt raw material, a sulfur raw material, a precipitant and an etchant according to a feed ratio, dissolving them in 10 to 100 mL of deionized water, and uniformly stirring them for 30 minutes, wherein the nickel raw material is nickel nitrate, nickel chloride or nickel acetate; the cobalt raw material is cobalt nitrate, cobalt chloride or cobalt acetate; the sulfur raw material is thioacetamide or thiourea; the precipitant is urea or sodium carbonate; and the etchant is ammonium fluoride or sodium fluoride; and obtaining a homogeneous solution.

[0082] The homogeneous solution obtained in the step and the cleaned nickel foam support are added to a hydrothermal kettle, and the hydrothermal reaction is carried out at 100-150° C. for 8-15 hours. After the hydrothermal reaction is completed, it is naturally cooled to room temperature. The nickel foam support loaded with nickel cobalt sulfide is taken out, washed several times with ethanol and deionized water, and placed in a vacuum drying oven at 60° C. for 3-6 hours to obtain a nickel cobalt sulfide bimetallic catalyst.

[0083] Example 1

[0084] One-step hydrothermal synthesis of NiCo-S materials

[0085] 2.8 mmol of nickel nitrate hexahydrate (Ni(NO3)2 6H2O), 1.2 mmol of cobalt nitrate hexahydrate (Co(NO3)2 6H2O), 8 mmol of ammonium fluoride (NH4F), 10 mmol of urea (CH4N2O), and 3 mmol of thioacetamide (C2H5NS, TAA) were dissolved in 60 mL of deionized water and stirred continuously for 30 minutes to obtain a homogeneous solution. The homogeneous solution was then transferred to a 100 mL polytetrafluoroethylene-lined autoclave, where a 1 cm × 1 cm nickel foam pretreated as described above was placed. The solution was then placed at 120°C for 12 hours. The nickel foam was then removed and rinsed several times with ethanol and deionized water. After vacuum drying at 60°C for 4 hours, the resulting NiCo-S was directly tested.

[0086] Example 2

[0087] One-step hydrothermal synthesis of NiCo-S materials

[0088] 2.8 mmol of nickel nitrate hexahydrate (Ni(NO3)2 6H2O), 1.2 mmol of cobalt nitrate hexahydrate (Co(NO3)26H2O), 8 mmol of ammonium fluoride (NH4F), 10 mmol of urea (CH4N2O), and 1 mmol of thioacetamide (C2H5NS, TAA) were dissolved in 60 mL of deionized water and stirred continuously for 30 minutes to obtain a homogeneous solution. The homogeneous solution was then transferred to a 100 mL polytetrafluoroethylene-lined autoclave, where a 2 cm × 2 cm nickel foam pretreated as described above was placed. The solution was then placed at 120°C for 12 hours. The nickel foam was then removed and rinsed several times with ethanol and deionized water. After vacuum drying at 60°C for 4 hours, the resulting NiCo-S was directly tested.

[0089] Example 3

[0090] One-step hydrothermal synthesis of NiCo-S materials

[0091] 2.8 mmol of nickel nitrate hexahydrate (Ni(NO3)2 6H2O), 1.2 mmol of cobalt nitrate hexahydrate (Co(NO3)26H2O), 8 mmol of ammonium fluoride (NH4F), 10 mmol of urea (CH4N2O), and 2 mmol of thioacetamide (C2H5NS, TAA) were dissolved in 60 mL of deionized water and stirred continuously for 30 minutes to obtain a homogeneous solution. The homogeneous solution was then transferred to a 100 mL polytetrafluoroethylene-lined autoclave, where a 3 cm × 3 cm nickel foam pretreated as described above was placed. The solution was then placed at 120°C for 12 hours. The nickel foam was then removed and rinsed several times with ethanol and deionized water. After vacuum drying at 60°C for 4 hours, the resulting NiCo-S was directly tested.

[0092] Example 4

[0093] One-step hydrothermal synthesis of NiCo-S materials

[0094] 2.8 mmol of nickel nitrate hexahydrate (Ni(NO3)2 6H2O), 1.2 mmol of cobalt nitrate hexahydrate (Co(NO3)26H2O), 8 mmol of ammonium fluoride (NH4F), 10 mmol of urea (CH4N2O), and 4 mmol of thioacetamide (C2H5NS, TAA) were dissolved in 60 mL of deionized water and stirred continuously for 30 minutes to obtain a homogeneous solution. The homogeneous solution was then transferred to a 100 mL polytetrafluoroethylene-lined autoclave, where a 1 cm × 1 cm nickel foam pretreated as described above was placed. The solution was then placed at 120°C for 12 hours. The nickel foam was then removed and rinsed several times with ethanol and deionized water. After vacuum drying at 60°C for 4 hours, the resulting NiCo-S was directly tested.

[0095] Example 5

[0096] One-step hydrothermal synthesis of NiCo-S materials

[0097] The difference from Example 1 is that the amount of nickel nitrate hexahydrate used in this example is 1.5 mmol, the amount of cobalt nitrate hexahydrate used is 1.0 mmol, the amounts of other raw materials used are the same as in Example 1, and the reaction temperature is raised to 130°C.

[0098] Example 6

[0099] One-step hydrothermal synthesis of NiCo-S materials

[0100] The difference from Example 1 is that in this embodiment, the amount of nickel nitrate hexahydrate used is 3.5 mmol, the amount of cobalt nitrate hexahydrate used is 1.0 mmol, the amount of thioacetamide used is 4.5 mmol, the hydrothermal time is shortened to 10 h to prevent excessive sulfidation, and the amounts of other raw materials and reaction conditions are the same as in Example 1.

[0101] Example 7

[0102] One-step hydrothermal synthesis of NiCo-S materials

[0103] The difference from Example 1 is that the amount of thioacetamide used in this example is 1.5 mmol, and the amounts of other raw materials and reaction conditions are the same as in Example 1.

[0104] Example 8

[0105] One-step hydrothermal synthesis of NiCo-S materials

[0106] The difference from Example 1 is that the amount of thioacetamide used in this example is 6.0 mmol, and the amounts of other raw materials and reaction conditions are the same as in Example 1.

[0107] Example 9

[0108] One-step hydrothermal synthesis of NiCo-S materials

[0109] The difference from Example 1 is that in this example, thiourea is used as the sulfur source in an amount of 3.0 mmol, the reaction time is extended to 14 h, and the amounts of other raw materials and reaction conditions are the same as in Example 1.

[0110] Example 10

[0111] One-step hydrothermal synthesis of NiCo-S materials

[0112] The difference from Example 1 is that in this example, sodium carbonate is used as the precipitant in an amount of 10.0 mmol, the pH value is adjusted to 9.5, and the amounts of other raw materials and reaction conditions are the same as in Example 1.

[0113] Example 11

[0114] One-step hydrothermal synthesis of NiCo-S materials

[0115] The difference from Example 1 is that in this example, sodium fluoride is used as the etchant in an amount of 8.0 mmol, and the amounts of other raw materials and reaction conditions are the same as in Example 1.

[0116] Comparative Example 1

[0117] One-step hydrothermal synthesis of NiCo-O materials

[0118] 2.8 mmol of nickel nitrate hexahydrate (Ni(NO3)2 6H2O), 1.2 mmol of cobalt nitrate hexahydrate (Co(NO3)26H2O), 8 mmol of ammonium fluoride (NH4F), and 10 mmol of urea (CH4N2O) were dissolved in 60 mL of deionized water and stirred continuously for 30 minutes to obtain a homogeneous solution. The homogeneous solution was then transferred to a 100 mL polytetrafluoroethylene-lined autoclave, where the pre-treated nickel foam was placed. The solution was then heated at 120°C for 12 hours. The nickel foam was then removed and rinsed several times with ethanol and deionized water, dried under vacuum at 60°C for 4 hours, and then tested directly.

[0119] Comparative Example 2

[0120] One-step hydrothermal synthesis of Ni-S materials

[0121] 4 mmol of nickel nitrate hexahydrate (Ni(NO3)2 6H2O), 8 mmol of ammonium fluoride (NH4F), 10 mmol of urea (CH4N2O), and 3 mmol of thioacetamide (C2H5NS) were dissolved in 60 mL of deionized water and stirred continuously for 30 minutes to obtain a homogeneous solution. The solution was then transferred to a 100 mL polytetrafluoroethylene-lined autoclave, where pre-treated nickel foam was placed. The solution was then heated at 120°C for 12 hours. The nickel foam was then removed and rinsed several times with ethanol and deionized water, dried under vacuum at 60°C for 4 hours, and tested directly.

[0122] Comparative Example 3

[0123] One-step hydrothermal synthesis of Co-S materials

[0124] 4 mmol of cobalt nitrate hexahydrate (Co(NO3)2 6H2O), 8 mmol of ammonium fluoride (NH4F), 10 mmol of urea (CH4N2O), and 3 mmol of thioacetamide (C2H5NS) were dissolved in 60 mL of deionized water and stirred continuously for 30 minutes to obtain a homogeneous solution. The solution was then transferred to a 100 mL polytetrafluoroethylene-lined autoclave, where pre-treated nickel foam was placed. The solution was then heated at 120°C for 12 hours. The nickel foam was then removed and rinsed several times with ethanol and deionized water, dried under vacuum at 60°C for 4 hours, and then tested directly.

[0125] Comparative Example 4

[0126] One-step hydrothermal synthesis of NF-S materials

[0127] 8 mmol of ammonium fluoride (NH4F), 10 mmol of urea (CH4N2O), and 3 mmol of thioacetamide (C2H5NS) were dissolved in 60 mL of deionized water and stirred continuously for 30 minutes to obtain a homogeneous solution. The solution was then transferred to a 100 mL polytetrafluoroethylene-lined autoclave, where pre-treated nickel foam was placed. The solution was then incubated at 120°C for 12 hours. The nickel foam was then removed and rinsed several times with ethanol and deionized water, dried under vacuum for 4 hours, and then tested directly.

[0128] The catalytic performance of the NiCo-S (Example 1), NiCo-O (Comparative Example 1), Ni-S (Comparative Example 2), Co-S (Comparative Example 3) and NF-S (Comparative Example 4) catalysts prepared in Example 1 and Comparative Examples 1-4 was tested as follows:

[0129] 30 mL of 1 M KOH solution was added to the cathode and anode compartments of an H-type electrolytic cell, respectively, as an electrolyte. The cathode and anode compartments were separated by a Nafion 117 proton exchange membrane. 60 mmol of HMF was taken as a reaction substrate and placed in the anode compartment of the H-type electrolytic cell. The catalyst prepared in Example 1 and Comparative Examples 1-4 was used as a working electrode, mercury / mercuric oxide was placed in the anode compartment as a reference electrode, and a platinum sheet electrode was placed in the cathode compartment as a counter electrode. Constant voltage electrolysis was performed using it (chronopotentiometry) at 1.45 V vs. RHE. During the electrolysis process, samples were taken and placed in a high-performance liquid chromatograph for detection after treatment. The HMF conversion rate, FDCA selectivity, and Faradaic efficiency were calculated based on the test results and the electron transfer amount of the it curve.

[0130] like Figure 1-7 The following is the TEM characterization result of the catalyst material NiCo-S. Figure 1It can be seen that the catalyst material after sulfurization is not a complete nano-strip, but is integrated with the flocculent structure around the nanowires. It is these flocculent structures that effectively increase the specific surface area of the catalyst, and they can greatly enhance the electron mass transfer inside the catalyst, thereby reducing the catalyst impedance and increasing the rate of charge transfer at the catalyst material interface and the electrocatalytic performance.

[0131] Figure 2 It is the area where the catalyst material is line scanned to distinguish the distribution of each element in the catalyst. Figure 3 This is a high-resolution transmission electron microscopy (HRTEM) image of the catalyst material NiCo-S. The lattice spacing of 0.28nm and 0.16nm corresponds to the (104) and (110) crystal planes of Ni3S2, respectively. Figure 4-7 According to the dispersion X-ray spectroscopy analysis, Ni, Co, O and S elements are not dispersed throughout the catalyst material but are mixed. Figure 5 It can also be observed near the lower left corner that the cobalt nanowires are covered or wrapped by flaky nickel, and the positions of elemental sulfur and nickel are basically the same, which also shows that the catalyst produces a large amount of Ni3S2 substance, and the content of Co element is much lower than that of Ni, which is the same as the ratio of raw materials when making the catalyst.

[0132] from Figure 8 It can be clearly observed that the current density of NiCo-S material without HMF (blue dashed line) starts to rise at around 1.4 V (vs. RHE) and rises to 37 mA cm at 1.45 V (vs. RHE). -2 After adding 20 mM HMF to the KOH solution (black solid line), the current density at 1.23 V (vs. RHE) began to rise sharply, and at 1.45 V (vs. RHE) the current density reached 106 mA cm -2 , the comparison between the two shows that the electrochemical oxidation of HMF by Ni7CO3-S material at the anode has a lower overpotential and a higher current density than the OER reaction. This shows that the oxidation reaction of HMF on the Ni7Co3-S electrode has a higher priority than OER. After 1.5V (vs. RHE), as the voltage increases, the OER reaction also occurs while HMF is oxidized. The current density displayed at this time is the superposition of the two reactions, so the current density will increase with increasing voltage. The NiCO-S material has reached a higher current density before 1.5V (vs. RHE), indicating that there is basically no competitive reaction between the oxidation of HMF and the OER reaction at the anode. When 20mM HMF (red solid line) is added to the NiCO-O material, the current density rises at 1.25V (vs. RHE) and the current density reaches 30mAcm -2A current platform appears, indicating that the oxidation current catalyzed by NiCO-O material can only reach 30 mA cm at a concentration of 20 mM HMF. -2 , the current density is much different from that of NiCo-S material at the same potential, indicating that the catalyst material after sulfidation has better catalytic performance for the oxidation of HMF.

[0133] In order to demonstrate the synergistic effect of Ni and Co materials and eliminate the influence of nickel foam substrate on catalytic performance, the LSV of four materials, NiCO-S, Ni-S, Co-S and NF-S, were compared. Figure 9 and 10 As shown in the figure, in a 1MKOH solution containing 20mM HMF concentration, the current density of NF-S is much lower than that of the other three materials, indicating that nickel foam (NF) is not the main factor for the high catalytic activity of NiCO-S material. Although Ni-S and Co-S materials have shown the performance of HMF oxidation, they are still far behind NiCO-S material. Electrochemically active specific surface area (ECSA) is an important indicator of the quality of catalyst materials. ECSA is expressed by the double layer capacitance (C dl ) to make an estimate.

[0134] See also Figure 11 The LSV comparison diagrams of the nickel-cobalt sulfide catalyst materials prepared by using sulfur sources in different dosage ratios in Examples 1-4 show that the current density is higher when the dosage of the sulfur source TAA is above 3 mmol.

[0135] Further, see Figure 12 As shown, before the electrolysis begins, only HMF can be clearly detected at 0 min. As the electrolysis time increases, HMF, HMFCA, FFCA, and FDCA can be detected at 30 min, indicating that the oxidation reaction of HMF has begun. Although HFMCA and FFCA can be detected, their concentrations are always very low, indicating that the electrolysis reaction rate of the catalyst on HMF is extremely fast and there is almost no accumulation of intermediate products. In addition to these four substances, DFF is almost completely undetectable, indicating that the aldehyde group in the HMF functional group is preferentially oxidized during the electrolysis process. This indicates that the oxidation pathway of HMF is mainly the HMFCA pathway, namely the HMF-HMFCA-FFCA-FDCA pathway. In each subsequent time period, it can be seen that the concentration of HMF gradually decreases while the concentration of FDCA gradually increases.

[0136] from Figure 13 The results presented show that the yield of FDCA is almost as high as 100% without accumulation of target products, indicating that the nickel-cobalt sulfide catalyst has extremely high selectivity.

[0137] Figure 14 The nickel cobalt sulfide catalyst NiCo-S was presented from 10mV S -1 to 100mV -1 CV curve diagram under scanning rate. Figure 15 NiCo-O from 10mV S -1 to 100mV -1 CV curve diagram under scanning rate.

[0138] Figure 16 is the C of the material calculated based on the CV curve fitting dl , it can be seen that the C of NiCo-S dl 12.9mF cm -2 , which is significantly higher than the C of NiCo-O dl 6.4 mF cm -2 , indicating that the porous nanosheet material after sulfurization has more electrochemically active sites, which increases its performance in the electrocatalytic oxidation of HMF.

[0139] At the same time, the above test results also show that the excellent catalytic performance of NiCO-S material for HMF is due to the combination of the advantages of multiple materials. We also explored the effect of different concentrations of thioacetamide (TAA) on the catalyst performance to study the sulfurization effect, such as Figure 10 As shown in the figure, it was found that the catalytic performance increased with the increase of TAA concentration, but when the concentration increased to 5 mmol, the NF substrate would corrode to an unusable state that was easily broken.

[0140] The nickel-cobalt sulfide catalyst of the present invention has a long service life, specifically the conversion rate of 5-hydroxymethylfurfural (HMF), 2,5-furandicarboxylic acid (FDCA) selectivity, and Faradaic efficiency after repeated use for more than 10 times. The electrocatalytic oxidation of 5-hydroxymethylfurfural is carried out at an anode potential of 1.45 to 1.5 V vs. RHE using a constant potential (IT) electrocatalytic oxidation method.

[0141] The electrocatalytic oxidation of 5-hydroxymethylfurfural can obtain FDCA with a Faradaic efficiency of 95% to 99% at a voltage of 1.465 V vs. RHE, and the FDCA selectivity and HMF conversion rate are 95% to 99% and 96% to 99%, respectively.

[0142] like Figure 17 As shown, the stability test results of the nickel-cobalt sulfide catalyst provided by the present invention for the yield of FDCA, the conversion rate of HMF and the Faraday efficiency of the electrocatalytic oxidation of HMF to FDCA after ten cycles are excellent, and the yield of FDCA, the conversion rate of HMF and the Faraday efficiency values are all above 95%.

[0143] In summary, it can be found that the present invention has the following advantages:

[0144] 1) The nickel-cobalt sulfide catalyst is synthesized by a one-step hydrothermal method, which is more convenient and faster than the synthesis steps of other electrocatalytic oxidation catalysts.

[0145] 2) Nickel-cobalt sulfide catalyst can be reused more than ten times and has good stability.

[0146] 3) 5-Hydroxymethylfurfural (HMF) can be electrocatalytically oxidized to produce 2,5-furandicarboxylic acid (FDCA) at a relatively low potential, avoiding competition with the electrolysis reaction of water, with a Faradaic efficiency of over 95%.

[0147] 4) Compared with the existing catalyst for electrochemical oxidation of 5-hydroxymethylfurfural to produce 2,5-furandicarboxylic acid, the method avoids the use of precious metal catalysts and is low-cost and economical.

[0148] 5) The nickel-cobalt sulfide catalyst of the present invention electrocatalytically oxidizes 5-hydroxymethylfurfural to produce 2,5-furandicarboxylic acid, with the target product yield being almost 100% without target product accumulation, thus having extremely high selectivity.

[0149] Finally, it should be noted that although the above embodiments have been described in the specification and drawings of this application, this does not limit the scope of patent protection of this application. All technical solutions generated by replacing or modifying equivalent structures or equivalent processes based on the essential concepts of this application using the contents recorded in the specification and drawings of this application, as well as directly or indirectly implementing the technical solutions of the above embodiments in other related technical fields, are included in the scope of patent protection of this application.

Claims

1. A nickel-cobalt sulfide catalyst for preparing 2,5-furandicarboxylic acid by electrocatalytic oxidation, characterized in that: The invention comprises a pretreated nickel foam carrier and a nickel-cobalt sulfide active component loaded thereon, wherein the molar ratio of nickel to cobalt is (1.5-3.5):1, and the molar ratio of sulfur element to total metal is (0.5-1.5):

1.

2. The nickel-cobalt sulfide catalyst according to claim 1, characterized in that The crystal form of the active component of the nickel-cobalt sulfide comprises a hexagonal phase of Ni 3 S 2 .

3. The nickel-cobalt sulfide catalyst according to claim 2, characterized in that The hexagonal Ni3S2 phase has a coexistence structure of a lattice spacing of 0.28 nm and a lattice spacing of 0.16 nm.

4. The nickel-cobalt sulfide catalyst according to any one of claims 1 to 3, characterized in that The preparation method comprises the following steps: S1: nickel salt, cobalt salt, sulfur-containing raw material, precipitant and corrosive agent are dissolved in deionized water at a molar ratio of Ni:Co:S:precipitant:corrosive agent = (2.5-3.5):(0.8-1.2):(2.5-3.5):(8-12):(7-9), and stirred to form a homogeneous solution; S2: immersing the pretreated nickel foam support into the homogeneous solution described in step S1 to perform a hydrothermal reaction; After the hydrothermal reaction in S3 is completed, the catalyst is cleaned and vacuum dried to obtain a nickel-cobalt sulfide catalyst.

5. The nickel-cobalt sulfide catalyst according to claim 4, characterized in that The precipitant is urea or sodium carbonate, and the corrosive agent is ammonium fluoride or sodium fluoride. More preferably, the precipitant is urea, and the corrosive agent is ammonium fluoride.

6. The nickel-cobalt sulfide catalyst according to claim 4, characterized in that The nickel salt is nickel nitrate, nickel chloride or nickel acetate; and / or The cobalt salt is cobalt nitrate, cobalt chloride or cobalt acetate; and / or The sulfur-containing raw material is thioacetamide or thiourea.

7. The nickel-cobalt sulfide catalyst according to claim 4, characterized in that The conditions of the hydrothermal reaction are: reaction temperature of 110-130° C., reaction time of 10-14 h, more preferably, reaction temperature of 120±2° C., reaction time of 12±0.5 h.

8. A method for preparing 2,5-furandicarboxylic acid by electrocatalytic oxidation, characterized in that: An H-type double electrolytic cell is used as a reactor. In the anode chamber, the nickel-cobalt sulfide catalyst according to any one of claims 1 to 7 is used as a working electrode, and a 1 mol / L alkaline electrolyte containing 5 to 30 mmol / L 5-hydroxymethylfurfural is used as an anolyte. In the cathode chamber, a platinum electrode is used as a counter electrode, mercury or mercuric oxide is used as a reference electrode, and a 0.1 to 1 mol / L alkaline electrolyte is used as a catholyte. The cathode chamber and the anode chamber are separated by a Nafion-117 proton exchange membrane. Electrolysis is carried out using chronopotentiometry at a constant potential of 1.45 to 1.65 V vs. RHE. The reaction time is 15 to 180 min. During the reaction, samples are taken by acid quenching and the yield of 2,5-furandicarboxylic acid is monitored by HPLC.

9. The method for preparing 2,5-furandicarboxylic acid by electrocatalytic oxidation according to claim 8, characterized in that: The nickel-cobalt sulfide catalyst can be repeatedly used for 10-15 times for electrocatalytic oxidation of 5-hydroxymethylfurfural to prepare 2,5-furandicarboxylic acid, and the 5-hydroxymethylfurfural conversion rate, 2,5-furandicarboxylic acid productivity and Faraday efficiency are all higher than 95%.

10. The method for preparing 2,5-furandicarboxylic acid by electrocatalytic oxidation according to claim 8, characterized in that: The pH value of the anolyte is ≥13, the constant potential is 1.465±0.005V vs. RHE, and the reaction time is 2±0.2h.

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