Coal gasification wastewater electrolysis catalyst, preparation method and application thereof

Abstract

The application discloses a coal gasification wastewater electrolysis catalyst and a preparation method and application thereof, and belongs to the technical field of wastewater electrolysis treatment. The coal gasification wastewater electrolysis catalyst provided by the application comprises a foamed nickel substrate and a heterostructure catalytic layer loaded on the foamed nickel substrate; the heterostructure catalytic layer comprises a crystalline sulfide and an amorphous metal covering the surface of the crystalline sulfide; the crystalline sulfide comprises MoS2 and Ni3S2; and the amorphous metal comprises Co, Ni and Fe. The application constructs a heterostructure catalyst composed of crystalline Mo / Ni3S2 and amorphous CoNiFe on the surface of the foamed nickel. The catalyst exhibits excellent oxygen evolution reaction and hydrogen evolution reaction activity in the coal gasification wastewater, can realize the synergistic treatment of electrolysis hydrogen production and pollutant degradation, and maintains high stability in long-term operation.

Description

Technical Field

[0001] This invention relates to the field of wastewater electrolysis treatment technology, and in particular to a coal gasification wastewater electrolysis catalyst, its preparation method, and its application. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Hydrogen energy, due to its high energy density, clean combustion products, and wide availability, is considered an important component of the future energy system. Water electrolysis for hydrogen production has attracted widespread attention because it can be coupled with renewable energy sources to achieve zero-carbon emission hydrogen production. Among these technologies, anion exchange membrane (AEM) water electrolysis combines the advantages of alkaline and proton exchange membrane electrolysis, offering high efficiency and low cost potential, and is considered a promising hydrogen production technology route.

[0004] However, traditional water electrolysis for hydrogen production requires high-quality feed water and typically consumes large amounts of pure water, which poses a bottleneck for applications in water-scarce regions. To reduce dependence on freshwater resources, researchers have attempted to use seawater, domestic wastewater, or industrial wastewater to replace pure water in hydrogen electrolysis, but these studies are mostly focused on laboratory exploration, and stable operation under complex real-world water quality conditions still faces many challenges.

[0005] Coal gasification wastewater is a typical type of recalcitrant industrial wastewater generated during coal chemical processes. It is produced in large quantities and has a complex composition. This wastewater contains high concentrations of pollutants such as ammonia nitrogen, chemical oxygen demand (COD), and biochemical oxygen demand (BOD). In addition, it contains large amounts of cationic components such as sodium, calcium, and magnesium ions. These coexisting pollutants and ions can adversely affect the electrode materials used in the electrolysis process, for example, by occupying or blocking catalytic active sites and accelerating electrode surface corrosion, leading to a significant decrease in catalytic activity.

[0006] Combining ammonia nitrogen oxidation in coal gasification wastewater with electrolytic hydrogen production theoretically achieves the dual goals of pollutant degradation and energy recovery. However, ammonia oxidation is a multi-step reaction involving six-electron transfer, requiring the overcoming of high overpotentials in practical systems. When electrode materials are exposed to the complex environment of real coal gasification wastewater, their catalytic performance often declines significantly due to insufficient electrode stability and interference from wastewater components, making it difficult to effectively reduce the overpotential. Therefore, developing electrode materials that maintain high activity and long-term stability in coal gasification wastewater is crucial for promoting the practical application of this technology.

[0007] To improve the electrolysis efficiency of catalysts in complex wastewaters, researchers are dedicated to developing non-precious metal electrocatalysts with high tolerance and high current density. Transition metal-based materials, such as oxides, sulfides, phosphides, and layered double hydroxides of cobalt, iron, and nickel, are considered potential alternatives to precious metal catalysts due to their lower cost and certain catalytic activity. However, further enhancing the tolerance and catalytic stability of these materials in real coal gasification wastewater systems remains a key challenge in current research. Summary of the Invention

[0008] In view of this, the present invention provides a catalyst for the electrolysis of coal gasification wastewater, its preparation method, and its application. The present invention constructs a heterostructure catalyst composed of crystalline Mo / Ni3S2 and amorphous CoNiFe on the surface of nickel foam. This catalyst exhibits excellent oxygen evolution reaction and hydrogen evolution reaction activity in coal gasification wastewater, enabling synergistic treatment of hydrogen production by electrolysis and pollutant degradation, and maintains high stability during long-term operation.

[0009] In a first aspect, the present invention provides a coal gasification wastewater electrolysis catalyst, comprising: Nickel foam substrate; A heterostructured catalyst layer supported on the nickel foam substrate; the heterostructured catalyst layer includes crystalline sulfides and an amorphous metal covering the surface of the crystalline sulfides; the crystalline sulfides include MoS2 and Ni3S2; the amorphous metal includes Co, Ni and Fe.

[0010] Secondly, the present invention provides a method for preparing the above-mentioned coal gasification wastewater electrolysis catalyst, comprising the following steps: Pretreatment of the nickel foam substrate; Pretreated nickel foam was placed in an aqueous solution of molybdenum and sulfur sources for hydrothermal reaction to obtain nickel foam loaded with crystalline sulfides. The nickel foam loaded with crystalline sulfide is electrodeposited in an electrolyte containing cobalt salt, nickel salt and iron salt to obtain the coal gasification wastewater electrolysis catalyst.

[0011] Preferably, the molybdenum source is selected from one or more of molybdates, molybdenum oxides, or molybdenum halides; the sulfur source is selected from one or more of thiourea, thioacetamide, sulfides, or thiosulfates; and the molar ratio of Mo in the molybdenum source to S in the sulfur source is 1:(1~4).

[0012] Furthermore, the molybdenum source is sodium molybdate, and the sulfur source is thioacetamide.

[0013] Preferably, the hydrothermal reaction is carried out in a closed reactor at a temperature of 150-250°C for 6-24 hours.

[0014] Preferably, the cobalt salt is selected from one or more of cobalt nitrates, sulfates, chlorides, or acetates; the nickel salt is selected from one or more of nickel nitrates, sulfates, chlorides, or acetates; and the iron salt is selected from one or more of iron nitrates, sulfates, chlorides, or acetates.

[0015] Preferably, in the electrolyte, the molar ratio of cobalt salt, nickel salt and iron salt is (0.1~10):(0.1~10):(0.1~10); and the concentration of cobalt salt is 0.01~0.2M.

[0016] Preferably, the electrodeposition is performed using a constant potential method, the electrodeposition voltage is -2V to -1V, and the electrodeposition time is 50 to 300s.

[0017] Thirdly, the present invention provides the application of the above-mentioned coal gasification wastewater electrolysis catalyst or the coal gasification wastewater electrolysis catalyst prepared by the above-mentioned preparation method in the electrolytic treatment of organic wastewater containing ammonia nitrogen.

[0018] Preferably, the ammonia-nitrogen-containing organic wastewater is coal gasification wastewater.

[0019] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) This invention combines a nickel foam substrate with a heterostructured catalytic layer supported thereon. The catalytic layer comprises crystalline sulfides and an amorphous metal covering the surface of the crystalline sulfides. Specifically, the crystalline sulfides are MoS2 and Ni3S2, and the amorphous metals specifically include Co, Ni, and Fe. This heterostructure fully utilizes the interfacial synergistic effect between the crystalline sulfides and the amorphous metals. The framework structure provided by the crystalline sulfides helps to increase the specific surface area of ​​the catalytic layer, while the amorphous metals provide abundant active sites. The heterostructure formed between the two facilitates electron transfer, thereby endowing the catalyst with excellent bifunctional electrocatalytic activity of oxygen evolution and hydrogen evolution without the use of precious metals.

[0020] (2) This invention constructs a crystalline sulfide substrate on the surface of nickel foam through a hydrothermal reaction, and then introduces an amorphous metal component through electrodeposition. This stepwise construction method enables a good interfacial bond between the crystalline sulfide and the amorphous metal. This method can effectively control the microstructure and component distribution of the catalyst, allowing the crystalline sulfide to maintain its original array morphology, while the amorphous metal is uniformly covered on its surface, forming a stable core-shell heterostructure. This improves the structural stability of the catalyst during electrolysis and extends its service life.

[0021] (3) When the catalyst prepared by this invention is used for the electrolytic treatment of organic wastewater containing ammonia nitrogen, it can simultaneously oxidize and degrade ammonia nitrogen in the wastewater while realizing oxygen evolution and hydrogen evolution reactions. The catalyst exhibits good tolerance in complex wastewater environments and can effectively resist the interference of coexisting ions in the wastewater on catalytic activity. It can simultaneously realize hydrogen production and pollutant removal during electrolysis, combining energy recovery with wastewater purification and reducing the overall cost of wastewater treatment. Attached Figure Description

[0022] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0023] Figure 1 These are scanning electron microscope (SEM) images of the catalyst prepared in Example 1 of this invention; Figure 2 This is a transmission electron microscope (TEM) image of the catalyst prepared in Example 1 of the present invention; Figure 3 This is the X-ray diffraction (XRD) pattern of the catalyst prepared in Example 1 of this invention; Figure 4 These are scanning electron microscope (SEM) images of the catalyst prepared in Comparative Example 1 of this invention; Figure 5 These are the linear sweep voltammetric curves of Example 1, Comparative Example 1, Comparative Example 2, and the nickel foam substrate (NF) in 50% coal gasification wastewater. Figure 6 This is a stability test diagram of the catalyst prepared in Example 1 of the present invention; Figure 7 The catalyst prepared in Example 1 of this invention is used for electrolytic treatment of coal gasification wastewater for 0-72 hours, and the change in ammonia nitrogen concentration in the electrolyte is shown. Figure 8 The chemical oxygen demand (COD) of the electrolyte after 0-72 hours of electrolytic treatment of coal gasification wastewater using the catalyst prepared in Example 1 of this invention is shown. Detailed Implementation

[0024] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0025] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used in this invention, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such a composition, step, method, article, or apparatus.

[0026] In this invention, when a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1~5” is disclosed, the described range should be interpreted as including ranges “1~4”, “1~3”, “1~2”, “1~2 and 4~5”, “1~3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0027] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0028] As noted in the background section, existing catalysts, when used for the electrolysis of coal gasification wastewater, are prone to catalytic degradation due to the high concentrations of ammonia nitrogen, chemical oxygen demand (COD), and various cations in the wastewater. This leads to the blockage of active sites on the catalyst and corrosion of the electrode surface, making it difficult to achieve efficient and stable hydrogen production in actual wastewater, and even more difficult to simultaneously degrade pollutants. Therefore, this invention provides a coal gasification wastewater electrolysis catalyst, comprising: Nickel foam substrate; A heterostructured catalyst layer supported on the nickel foam substrate; the heterostructured catalyst layer includes crystalline sulfides and an amorphous metal covering the surface of the crystalline sulfides; the crystalline sulfides include MoS2 and Ni3S2; the amorphous metal includes Co, Ni and Fe.

[0029] This invention uses nickel foam as the substrate material, which has a three-dimensional porous network structure that can provide a large specific surface area, which is beneficial for the loading and dispersion of catalytic active substances. At the same time, its good conductivity helps the charge collection and transport during the electrocatalytic reaction process.

[0030] The core of this invention is a heterostructured catalytic layer supported on a nickel foam substrate. This catalytic layer comprises crystalline sulfides and an amorphous metal, forming a heterostructure. Specifically, the crystalline sulfides are a composite of MoS2 and Ni3S2, which grows in situ on the surface of the nickel foam during a hydrothermal reaction, forming a crystal structure with a specific morphology, preferably needle-like or nanoarray structures. This structure significantly increases the specific surface area of ​​the catalytic layer, exposing more active sites. The amorphous metal comprises Co, Ni, and Fe, which are deposited onto the surface of the crystalline sulfides via electrodeposition. Due to its long-range disorder and short-range order in atomic arrangement, the amorphous structure possesses numerous unsaturated coordination sites and defects on its surface, serving as highly active sites for electrocatalytic reactions. The heterostructure interface formed between the crystalline sulfides and the amorphous metal exhibits strong electronic interactions, facilitating charge transfer and redistribution at the interface, thereby optimizing the adsorption energy of intermediates and enhancing the catalytic reaction kinetics. In addition, the amorphous metal layer covering the surface of the crystalline sulfide can protect the crystalline sulfide from corrosion or structural collapse in complex electrolyte environments to a certain extent, thereby improving the long-term operational stability of the catalyst.

[0031] This invention constructs a heterostructure catalyst with synergistic effects by combining crystalline MoS2 / Ni3S2 with amorphous CoNiFe metal. Both MoS2 and Ni3S2 are typical transition metal sulfide electrocatalysts with good hydrogen evolution and oxygen evolution activities, and their crystalline structures provide a stable framework and electron conduction pathways. Amorphous CoNiFe metal provides abundant surface active sites, especially in complex wastewater systems containing ammonia nitrogen, exhibiting potential catalytic activity for ammonia oxidation. The heterostructure formed by these two compounds can simultaneously achieve efficient oxygen evolution, hydrogen evolution, and ammonia nitrogen oxidative degradation, realizing bifunctional or even multifunctional catalysis.

[0032] In this invention, the crystalline sulfide is loaded onto a nickel foam substrate, preferably in the form of a nanoneedle-like, nanorod-like, or nanosheet array. This array structure grows perpendicular to the substrate, maximizing the exposure of the active surface and facilitating electrolyte penetration and gas escape. The amorphous metal covers the surface of the crystalline sulfide, and the covering can be a continuous or discontinuous thin film, or a nanoparticle layer, preferably forming a core-shell structure, i.e., the crystalline sulfide is the core and the amorphous metal is the shell. This structure can fully utilize the synergistic effect of the two, while the amorphous shell can protect the core.

[0033] The present invention also provides a method for preparing the above-mentioned coal gasification wastewater electrolysis catalyst, comprising the following steps: Pretreatment of the nickel foam substrate; Pretreated nickel foam was placed in an aqueous solution of molybdenum and sulfur sources for hydrothermal reaction to obtain nickel foam loaded with crystalline sulfides. The nickel foam loaded with crystalline sulfide is electrodeposited in an electrolyte containing cobalt salt, nickel salt and iron salt to obtain the coal gasification wastewater electrolysis catalyst.

[0034] In this invention, the nickel foam substrate needs to be pretreated before use to remove surface oil, oxides, and other impurities, ensuring good adhesion between the subsequent catalyst layer and the substrate. Pretreatment methods typically include pickling, cleaning, and drying.

[0035] Pickling can be performed using an inorganic acid solution, such as one or more of hydrochloric acid, sulfuric acid, or nitric acid, with hydrochloric acid being preferred. The acid concentration can be adjusted according to the actual situation, for example, 1-3 M. The nickel foam is immersed in the acid solution, and ultrasonic treatment can be used to enhance the cleaning effect; the ultrasonic treatment time is usually 10-30 minutes. After pickling, it needs to be rinsed several times alternately with deionized water and / or organic solvents (such as anhydrous ethanol) to remove residual acid and dissolved impurities. The cleaned nickel foam is dried at an appropriate temperature, preferably 50-80°C, for example, 60°C, for a time usually of 6-12 hours, for example, 12 hours. Drying can be carried out under vacuum conditions to prevent oxidation.

[0036] In this invention, pretreated nickel foam is placed in an aqueous solution containing a molybdenum source and a sulfur source for a hydrothermal reaction, resulting in the in-situ growth of crystalline sulfides on the surface of the nickel foam, primarily forming a complex of MoS2 and Ni3S2. During this process, the nickel foam itself provides the nickel source, participating in the formation of Ni3S2.

[0037] In this invention, the molybdenum source is a compound capable of providing molybdenum, selected from one or more of molybdates, molybdenum oxides, or molybdenum halides. Examples of molybdates include sodium molybdate (Na₂MoO₄), potassium molybdate, and ammonium molybdate; examples of molybdenum oxides include molybdenum trioxide (MoO₃); and examples of molybdenum halides include molybdenum pentachloride (MoCl₅). Preferably, the molybdenum source is sodium molybdate, specifically sodium molybdate dihydrate (Na₂MoO₄·2H₂O). The concentration of the molybdenum source in the aqueous solution can be adjusted as needed, typically 5–50 mM, preferably 10–40 mM, more preferably 15–25 mM, for example, 10 mM, 15 mM, 20 mM, 25 mM, 30 mM, or 40 mM.

[0038] In this invention, the sulfur source is a compound capable of providing sulfur, selected from one or more of thiourea, thioacetamide, sulfides, or thiosulfates. Thiourea (CH4N2S) and thioacetamide (CH3CSNH2) are commonly used sulfur sources, which decompose to release sulfur ions under hydrothermal conditions; sulfides include, for example, sodium sulfide (Na2S); thiosulfates include, for example, sodium thiosulfate (Na2S2O3). Preferably, the sulfur source is thioacetamide. The concentration of the sulfur source in the aqueous solution is typically 20-100 mM, preferably 30-80 mM, more preferably 35-60 mM, for example, 30 mM, 40 mM, 50 mM, or 60 mM.

[0039] In this invention, the molar ratio of Mo in the molybdenum source to S in the sulfur source is 1:(1~4), preferably 1:2. The molar ratio affects the composition and morphology of the final product.

[0040] In this invention, the hydrothermal reaction is carried out in a closed reactor, utilizing a high-temperature and high-pressure environment to promote crystal growth. The reaction temperature has a significant impact on the crystal form and morphology of the product; too low a temperature may lead to incomplete reaction, while too high a temperature may cause overgrowth or phase transition. In this invention, the hydrothermal reaction temperature is controlled within the range of 150~250℃, preferably 180~220℃, more preferably 190~210℃, for example, 150℃, 180℃, 200℃, 220℃, and 250℃. The reaction time affects the degree of crystal growth; too short a time results in incomplete crystal development, while too long a time may lead to overgrowth. The reaction time is controlled within the range of 6~24 hours, preferably 10~20 hours, more preferably 12~18 hours, for example, 6 hours, 12 hours, 16 hours, 18 hours, and 24 hours.

[0041] After the hydrothermal reaction is complete, the reactor is allowed to cool naturally to room temperature. The nickel foam loaded with crystalline sulfides is then removed and rinsed repeatedly with deionized water and / or anhydrous ethanol to remove unreacted substances and byproducts adhering to the surface. Finally, it is dried at an appropriate temperature, such as vacuum drying at 50-80°C for 6-12 hours, to obtain the precursor material, denoted as nickel foam loaded with crystalline sulfides or Mo / Ni3S2-NF. The crystalline sulfides grown on the surface of the nickel foam loaded with crystalline sulfides prepared by the hydrothermal synthesis method are mainly a composite of MoS2 and Ni3S2, which may form a heterostructure or mixed phase. This material has a high specific surface area and good electrical conductivity, providing an ideal substrate for subsequent electrodeposition.

[0042] The foamed nickel loaded with crystalline sulfide was used as the working electrode and electrodeposited in an electrolyte containing cobalt salt, nickel salt and iron salt to introduce amorphous metal components onto the surface of the crystalline sulfide, thus obtaining the final coal gasification wastewater electrolysis catalyst.

[0043] In this invention, electrodeposition employs a three-electrode system, wherein foamed nickel loaded with crystalline sulfides serves as the working electrode, the counter electrode can be an inert conductive material such as a platinum mesh, platinum sheet, or carbon rod, and the reference electrode can be a saturated calomel electrode (SCE) or a silver / silver chloride electrode (Ag / AgCl). The electrolyte is an aqueous solution containing cobalt salt, nickel salt, and iron salt.

[0044] In this invention, the cobalt salt is a water-soluble salt capable of providing cobalt ions, selected from one or more of cobalt nitrates, sulfates, chlorides, or acetates, such as cobalt nitrate (Co(NO3)2), cobalt sulfate (CoSO4), cobalt chloride (CoCl2), cobalt acetate (Co(CH3COO)2), and their hydrates. Cobalt nitrate is preferred, for example, cobalt nitrate hexahydrate (Co(NO3)2·6H2O).

[0045] In this invention, the nickel salt is a water-soluble salt capable of providing nickel ions, selected from one or more of nickel nitrates, sulfates, chlorides, or acetates, such as nickel nitrate (Ni(NO3)2), nickel sulfate (NiSO4), nickel chloride (NiCl2), nickel acetate (Ni(CH3COO)2), and their hydrates. Nickel nitrate is preferred, for example, nickel nitrate hexahydrate (Ni(NO3)2·6H2O).

[0046] In this invention, the iron salt is a water-soluble salt capable of providing iron ions, selected from one or more of iron nitrates, sulfates, chlorides, or acetates, such as ferric nitrate (Fe(NO3)3), ferric sulfate (Fe2(SO4)3), ferric chloride (FeCl3), ferric acetate (Fe(CH3COO)3), and their hydrates. Ferric nitrate is preferred, for example, ferric nitrate nonahydrate (Fe(NO3)3·9H2O).

[0047] In this invention, the concentration and ratio of cobalt salt, nickel salt, and iron salt in the electrolyte affect the composition, morphology, and thickness of the electrodeposited layer. The molar ratio of the three can be adjusted within a wide range to optimize catalytic performance. In this invention, the molar ratio of cobalt salt, nickel salt, and iron salt is controlled as (0.1~10):(0.1~10):(0.1~10), preferably (0.5~5):(0.5~5):(0.5~5), and further preferably (1~2):(1~2):(0.5~1.5), for example, it can be 1:1:0.5, 1:1:1, 2:1:1, 1:2:1, etc. The concentration of cobalt salt is typically controlled within the range of 0.01 to 0.2 M, preferably 0.05 to 0.15 M, and more preferably 0.08 to 0.12 M. For example, it can be 0.01 M, 0.05 M, 0.1 M, 0.15 M, or 0.2 M. The concentrations of nickel salt and iron salt can be determined accordingly based on the selected molar ratio.

[0048] The electrodeposition method can be any of the following: potentiostatic method, galvanostatic method, or pulsed electrodeposition method, with potentiostatic method being preferred. When using the potentiostatic method, the applied potential must be sufficient to reduce the metal ions, but should not be too negative to avoid excessive hydrogen evolution that would affect the quality of the deposited layer. The electrodeposition voltage (relative to the Ag / AgCl reference electrode) is controlled within the range of -2V to -1V, for example, it can be -2.0V, -1.5V, -1.3V, -1.2V, or -1.0V, preferably -1.5V to -1.2V, and more preferably -1.4V to -1.3V.

[0049] The electrodeposition time affects the thickness and coverage of the amorphous metal layer. Too short a time may result in incomplete deposition and low coverage; too long a time may lead to an excessively thick layer, clogging the pores of the crystalline sulfide or masking its active sites. The electrodeposition time is controlled within the range of 50–300 seconds, for example, 50 seconds, 100 seconds, 150 seconds, 200 seconds, and 300 seconds, with 100–200 seconds being more preferred.

[0050] During electrodeposition, the electrolyte may or may not be stirred, and the temperature is usually room temperature. After electrodeposition, the electrode is removed and gently rinsed with deionized water to remove the electrolyte adhering to the surface. Then it is dried at an appropriate temperature, such as vacuum drying at 50~80℃ for 6~12 hours, to obtain the final coal gasification wastewater electrolysis catalyst, denoted as CoNiFe-Mo / Ni3S2 / NF.

[0051] An amorphous CoNiFe metal component was introduced onto the surface of crystalline Mo / Ni3S2 via electrodeposition. This amorphous layer formed a close-contact heterogeneous interface with the underlying crystalline sulfides. The electrodeposition process was conducted under mild conditions, effectively preserving the original morphology of the underlying crystalline sulfides while achieving uniform coverage of the amorphous layer. The resulting catalyst combines the structural stability of crystalline materials with the abundant active sites of amorphous materials.

[0052] The present invention also provides the application of the above-mentioned coal gasification wastewater electrolysis catalyst or the coal gasification wastewater electrolysis catalyst prepared by the above-mentioned preparation method in the electrolytic treatment of organic wastewater containing ammonia nitrogen.

[0053] In this invention, the ammonia-nitrogen-containing organic wastewater is preferably coal gasification wastewater. Coal gasification wastewater is a typical recalcitrant industrial wastewater generated during coal chemical processes. It has a complex composition, containing high concentrations of ammonia nitrogen, chemical oxygen demand (COD), phenols, cyanides, and various metal cations. Using the catalyst of this invention for the electrolytic treatment of this type of wastewater allows for the simultaneous realization of oxygen evolution reaction and ammonia nitrogen oxidation at the anode, and hydrogen evolution reaction at the cathode, under an applied voltage. Ammonia nitrogen in the wastewater is oxidized to nitrogen gas, and organic matter is oxidized and degraded, thereby purifying the wastewater; simultaneously, hydrogen gas is generated at the cathode, achieving energy recovery.

[0054] The catalyst of this invention exhibits excellent electrocatalytic performance and stability in coal gasification wastewater. At a current density of 50 mA·cm⁻¹, [the catalyst performs well]. -2 and 100 mA·cm -2 Under these conditions, the overpotentials of the oxygen evolution reaction can be as low as below 125 mV and 210 mV, respectively. After continuous operation at currents of 10 mA and 50 mA for 100 hours, the catalyst performance remained stable, with no significant increase in overpotential. After electrolytic treatment of coal gasification wastewater, the removal rate of ammonia nitrogen and chemical oxygen demand (COD) in the wastewater can reach over 92% and over 90%, respectively. This indicates that the catalyst of this invention can effectively resist the interference and poisoning effects of coexisting ions in wastewater, maintain high activity and high stability in complex environments, and achieve synergistic treatment of electrolytic hydrogen production and wastewater purification.

[0055] The technical solution of the present invention will be further described below with reference to specific embodiments. The present invention does not impose any special restrictions on the source of reagents used in the following embodiments; commercially available products well known to those skilled in the art can be used.

[0056] Example 1 This embodiment provides a coal gasification wastewater electrolysis catalyst and its preparation method.

[0057] (1) Pretreatment of nickel foam substrate Nickel foam was cut into 1 cm × 2 cm sheets and ultrasonically treated in 3 M HCl solution for 15 minutes to remove surface oil and oxides. After removal, it was ultrasonically cleaned alternately with deionized water and anhydrous ethanol for 10 minutes each, repeated 2-3 times. The cleaned nickel foam was then dried in a 60℃ vacuum drying oven for 12 hours to obtain pretreated nickel foam.

[0058] (2) Hydrothermal reaction to construct crystalline sulfides Dissolve 20 mmol Na2MoO4·2H2O in 20 mL of deionized water and stir magnetically for 10 minutes to obtain solution A. Immerse the pretreated nickel foam obtained in step (1) in solution A, sonicate for 15 minutes, and let it stand for 30 minutes. Dissolve 40 mmol CH3CSNH2 in 30 mL of deionized water and stir magnetically for 10 minutes to obtain solution B.

[0059] The soaked nickel foam, along with solutions A and B, was transferred to a 100 mL PTFE-lined stainless steel hydrothermal reactor and sealed. The molar ratio of Mo to S was 1:2. The reactor was placed in an oven and heated at 200°C for 16 hours for the hydrothermal reaction. After the reaction, the reactor was allowed to cool naturally to room temperature. The nickel foam was removed and rinsed alternately with anhydrous ethanol and deionized water 3-5 times to remove loose products adhering to the surface. The cleaned nickel foam was then dried in a vacuum drying oven at 60°C for 12 hours to obtain nickel foam loaded with crystalline sulfides, denoted as Mo / Ni3S2-NF.

[0060] (3) Electrodeposition to introduce amorphous metals Preparation of electrolyte: Dissolve Co(NO3)2·6H2O, Ni(NO3)2·6H2O and Fe(NO3)3·9H2O in deionized water to make their concentrations 0.1 M, 0.1 M and 0.05 M respectively, and stir until homogeneous.

[0061] Electrodeposition was performed using a three-electrode system: the Mo / Ni3S2-NF obtained in step (2) was used as the working electrode, the platinum mesh as the counter electrode, and the saturated Ag / AgCl electrode as the reference electrode. The three electrodes were placed in the electrolyte and electrodeposition was performed at a constant potential of -1.3 V (vs. Ag / AgCl) for 150 seconds.

[0062] After electrodeposition, the electrode was removed and the surface was gently rinsed with deionized water to remove residual electrolyte. The sample was then dried in a vacuum drying oven at 60℃ for 12 hours to obtain the coal gasification wastewater electrolysis catalyst, denoted as CoNiFe-Mo / Ni3S2 / NF.

[0063] Figure 1 The image shown is a scanning electron microscope (SEM) image of the catalyst prepared in this embodiment. It can be seen that its surface exhibits uniformly distributed nanospheres, demonstrating a high specific surface area.

[0064] Figure 2 This is a transmission electron microscope (TEM) image of the catalyst prepared in this embodiment. The black needle-like portion is crystalline Mo / Ni3S2, with amorphous CoNiFe attached to its exterior.

[0065] Figure 3 The X-ray diffraction (XRD) pattern of the catalyst prepared in this embodiment shows that there is a strong peak of Ni3S2 and a small amount of characteristic peaks of MoS2.

[0066] Example 2 The only difference between this embodiment and embodiment 1 is that in step (2) of this embodiment, the amount of Na2MoO4·2H2O added is 10 mmol, that is, the molar ratio of Mo to S is 1:4.

[0067] Example 3 The only difference between this embodiment and embodiment 1 is that in step (2) of this embodiment, the amount of Na2MoO4·2H2O added is 40 mmol, that is, the molar ratio of Mo to S is 1:1.

[0068] Example 4 The only difference between this embodiment and embodiment 1 is that in step (3) of this embodiment, electrodeposition is performed at a constant potential of -1 V (vs. Ag / AgCl) for 100 seconds.

[0069] Example 5 The only difference between this embodiment and embodiment 1 is that in step (3) of this embodiment, electrodeposition is performed at a constant potential of -1.5 V (vs. Ag / AgCl) for 150 seconds.

[0070] Comparative Example 1 The only difference between this comparative example and Example 1 is that this comparative example does not perform step (3) and directly uses the Mo / Ni3S2-NF obtained in step (2) as the catalyst.

[0071] Figure 4 This is a SEM image of the catalyst prepared in the comparative example. It can be seen that Mo / Ni3S2-NF exhibits a distinct needle-like structure.

[0072] Comparative Example 2 The only difference between this comparative example and Example 1 is that this comparative example does not perform step (2), but directly performs the electrodeposition of step (3) on the pretreated nickel foam. The resulting catalyst is denoted as CoNiFe-NF.

[0073] Comparative Example 3 The only difference between this comparative example and Example 1 is that the electrolyte in step (3) of this comparative example contains only Co(NO3)2·6H2O, and its concentration is 0.25 M.

[0074] Test case Electrochemical tests were conducted at room temperature using a three-electrode system: the prepared catalyst as the working electrode, a platinum sheet as the counter electrode, and a saturated Ag / AgCl electrode as the reference electrode. A 1M KOH solution was mixed with coal gasification wastewater at a 1:1 volume ratio to form the electrolyte (denoted as "50% coal gasification wastewater"). The main components of the coal gasification wastewater are shown in Table 1. High-purity oxygen or nitrogen was bubbled into the electrolyte until saturation before testing. All test potentials were converted to reversible hydrogen electrode potentials using formulas.

[0075] Table 1 Main components of coal gasification wastewater COD <![CDATA[BOD5]]> ammonia nitrogen <![CDATA[Ca 2+ ]]> <![CDATA[Na + ]]> <![CDATA[Mg 2+ ]]> Total Hardness 290 mg / L 126 mg / L 202 mg / L 151 mg / L 83.4 mg / L 12.9 mg / L 446 mg / L Note: In Table 1, COD is Chemical Oxygen Demand, and BOD5 is Biochemical Oxygen Demand for five days.

[0076] 1. Linear scanning voltammetry test: The scan rate is 5 mV / s, the polarization curve is recorded, and the current density is read at 50 mA·cm⁻¹. -2 and 100 mA·cm -2 The corresponding overpotentials are summarized in Table 2.

[0077] Table 2 Overpotential Data serial number <![CDATA[Overpotential @ 50 mA·cm -2 (mV)]]> <![CDATA[Overpotential @ 100 mA·cm -2 (mV)]]> Example 1 124 202 Example 2 152 240 Example 3 138 236 Example 4 130 210 Example 5 135 214 Comparative Example 1 201 469 Comparative Example 2 285 356 Comparative Example 3 184 386 Linear sweep voltammetric curves of Example 1, Comparative Example 1, Comparative Example 2, and nickel foam substrate (NF) in coal gasification wastewater are shown below. Figure 5 As shown.

[0078] From Table 2 and Figure 5 As can be seen, the catalysts in the examples exhibit lower overpotentials, which are much lower than those in the comparative examples, and the CoNiFe-Mo / Ni3S2 / NF catalyst in Example 1 has the best performance.

[0079] 2. Stability Test: The constant current method was used, with the catalyst from Example 1 as the working electrode, a platinum sheet as the counter electrode, and a saturated Ag / AgCl electrode as the reference electrode. Stability tests were conducted at 10 mA·cm⁻¹. -2 and 50 mA·cm -2 It was run continuously for 100 hours under the specified current, and the potential change curve over time was recorded.

[0080] Test results are as follows Figure 6 As shown, the catalyst CoNiFe-Mo / Ni3S2 in Example 1 can operate stably for 100 hours at currents of 10mA and 50mA with almost no degradation.

[0081] 3. Pollutant degradation performance test: Using the catalyst of Example 1 as the working electrode, the degradation performance was tested at 10 mA·cm⁻¹. -2 and 50mA·cm -2 Coal gasification wastewater was electrolyzed at various current densities for 0–72 hours. Water samples were taken before and after electrolysis to determine ammonia nitrogen concentration and chemical oxygen demand (COD), and the removal rate was calculated.

[0082] Test results are as follows Figure 7 and Figure 8 As shown. At 10 mA·cm -2 and 50mA·cm -2 After stable operation at a current density for 72 h, the ammonia nitrogen degradation rates reached 80.8% and 92.6%; respectively at 10 mA·cm⁻¹. -2 and 50mA·cm-2 After 72 hours of stable operation at the current density, the COD degradation rate reached 43.5% and 51.4%, demonstrating a good degradation effect.

[0083] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A catalyst for the electrolysis of coal gasification wastewater, characterized in that, include: Nickel foam substrate; A heterostructured catalyst layer supported on the nickel foam substrate; the heterostructured catalyst layer includes crystalline sulfides and an amorphous metal covering the surface of the crystalline sulfides; the crystalline sulfides include MoS2 and Ni3S2; the amorphous metal includes Co, Ni and Fe.

2. The preparation method of the coal gasification wastewater electrolysis catalyst as described in claim 1, characterized in that, Includes the following steps: Pretreatment of the nickel foam substrate; Pretreated nickel foam was placed in an aqueous solution of molybdenum and sulfur sources for hydrothermal reaction to obtain nickel foam loaded with crystalline sulfides. The nickel foam loaded with crystalline sulfide is electrodeposited in an electrolyte containing cobalt salt, nickel salt and iron salt to obtain the coal gasification wastewater electrolysis catalyst.

3. The preparation method according to claim 2, characterized in that, The molybdenum source is selected from one or more of molybdates, molybdenum oxides, or molybdenum halides; the sulfur source is selected from one or more of thiourea, thioacetamide, sulfides, or thiosulfates; the molar ratio of Mo in the molybdenum source to S in the sulfur source is 1:(1~4).

4. The preparation method according to claim 3, characterized in that, The molybdenum source is sodium molybdate, and the sulfur source is thioacetamide.

5. The preparation method according to claim 2, characterized in that, The hydrothermal reaction is carried out in a closed reactor at a temperature of 150-250°C for 6-24 hours.

6. The preparation method according to claim 2, characterized in that, The cobalt salt is selected from one or more of cobalt nitrates, sulfates, chlorides, or acetates; the nickel salt is selected from one or more of nickel nitrates, sulfates, chlorides, or acetates; and the iron salt is selected from one or more of iron nitrates, sulfates, chlorides, or acetates.

7. The preparation method according to claim 2, characterized in that, In the electrolyte, the molar ratio of cobalt salt, nickel salt and iron salt is (0.1~10): (0.1~10): (0.1~10); the concentration of cobalt salt is 0.01~0.2M.

8. The preparation method according to claim 2, characterized in that, The electrodeposition is performed using a constant potential method, with the electrodeposition voltage ranging from -2V to -1V and the electrodeposition time ranging from 50 to 300 seconds.

9. The application of the coal gasification wastewater electrolysis catalyst as described in claim 1 or the coal gasification wastewater electrolysis catalyst prepared by any one of claims 2 to 8 in the electrolytic treatment of organic wastewater containing ammonia nitrogen.

10. The application as described in claim 9, characterized in that, The ammonia-nitrogen-containing organic wastewater is coal gasification wastewater.

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