A coal gangue residual carbon-based substrate and ligand intercalation layered double hydroxide composite water electrolysis catalyst and a preparation method thereof

Abstract

The application discloses a coal gangue residual carbon-based substrate and ligand insertion layered double hydroxide composite water electrolysis catalyst and a preparation method thereof, and belongs to the technical field of electrocatalysis and new energy materials. The preparation method comprises the following steps: pretreatment and functionalization of coal gangue residual carbon, in-situ growth of LDH, and preparation of a composite bifunctional catalyst after ligand insertion. That is, the application utilizes waste-derived carbon to reduce the cost, effectively controls the electronic structure of LDH and increases the active specific surface area through the ligand insertion strategy, and meanwhile, the strong interface coupling ensures excellent charge transport capacity. The obtained composite material exhibits high catalytic activity, low overpotential and excellent stability for oxygen evolution reaction and hydrogen evolution reaction, and is a low-cost and high-performance bifunctional water electrolysis catalyst, and has a wide application prospect in the field of green hydrogen production.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalysis and new energy materials technology, and particularly relates to a composite water electrolysis catalyst based on coal gangue residual carbon substrate and ligand-intercalated layered double hydroxide and its preparation method. Background Technology

[0002] Hydrogen production via water electrolysis is a promising green energy conversion technology, but its efficiency and cost are highly dependent on the performance of the electrocatalyst used. Currently, the best-performing OER catalysts are oxides of iridium (Ir) and ruthenium (Ru), while HER catalysts are platinum (Pt)-based materials. However, their high cost and scarcity severely limit their large-scale application. Therefore, developing efficient, stable, and inexpensive non-precious metal catalysts is crucial.

[0003] Layered double hydroxides (LDHs) are a class of two-dimensional materials composed of divalent and trivalent metal cation hydroxide layers and interlayer anions. Due to their tunable chemical composition, large specific surface area, and abundant active sites, they have shown great potential in the field of electrocatalysis. However, intrinsic LDH materials suffer from inherent drawbacks such as poor conductivity, easy stacking of layers, and limited accessibility of active sites. To overcome these shortcomings, common strategies include: 1) compositing with conductive materials (such as carbon nanotubes and graphene) to enhance electron conduction; 2) introducing anions or molecular intercalations to expand the interlayer spacing and expose more active sites. However, conventional intercalation ions (such as CO32-) are limited in their effectiveness. 2- NO3 - The ability to modulate the electronic structure of LDH is limited, and the cost of high-performance carbon materials remains high. Coal gangue is a major solid waste generated by the coal industry, and its main components are aluminosilicates and residual carbon. With proper treatment, its carbonaceous components can be transformed into carbon materials with porous structures and certain electrical conductivity, providing an ideal raw material for the preparation of low-cost catalyst substrates. However, how to efficiently composite LDH with this amorphous, complex residual carbon and achieve deep modulation of the electronic structure of LDH remains a technical challenge. Summary of the Invention

[0004] To address the above technical problems: (1) high cost, relying on precious metals or high-purity carbon materials; (2) poor conductivity of LDH itself and insufficient utilization of active sites; (3) weak interaction between components in traditional composite catalysts and insignificant synergistic effect; this invention proposes a composite water electrolysis catalyst based on coal gangue residual carbon substrate and ligand-intercalated layered double hydroxide and its preparation method.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a composite water electrolysis catalyst based on a coal gangue residual carbon substrate and ligand-intercalated layered double hydroxides includes the following steps: (1) A functionalized coal gangue residual carbon substrate (C-Coal) with oxygen-containing functional groups on its surface was prepared by calcination, acid washing and oxidation treatment using coal gangue as raw material. (2) Layered double hydroxide (LDH) is grown in situ on the surface of the coal gangue residual carbon substrate by hydrothermal growth to obtain residual carbon substrate-LDH; (3) By inserting ligands into the LDH interlayer through a secondary hydrothermal reaction, a structurally stable and tightly bonded composite water electrolysis catalyst based on coal gangue residual carbon substrate and ligand-inserted layered double hydroxide is obtained.

[0006] Optionally, in step (1), the calcination conditions are: heating to 500-800°C at 5°C / min under nitrogen protection, and then calcining at this temperature for 1-4 hours.

[0007] Optionally, in step (1), the pickling conditions are as follows: the acid solution is stirred and washed at 60°C for 2 hours to remove some of the ash, and then washed with deionized water until neutral.

[0008] Optionally, in step (1), the oxidation treatment conditions are as follows: under conditions of 60℃-100℃, the mixture is stirred in a round-bottom flask with a reflux condenser for 1-4 hours using concentrated nitric acid. After cooling, the mixture in the flask is slowly poured into a beaker containing a large amount of ice water or cold distilled water to terminate the reaction. Then, the mixture is filtered and washed with water. The filter cake, which has been washed to neutrality, is placed in an oven and dried to constant weight at 80℃-105℃.

[0009] Optionally, in step (2), the specific process of in-situ hydrothermal growth of layered double hydroxides on the surface of the coal gangue residual carbon substrate is as follows: Metal ions, urea, and ammonium fluoride are dissolved in a solvent to obtain a mixture. The coal gangue residual carbon substrate is then added to the mixture and ultrasonically dispersed. The mixture is then subjected to a hydrothermal treatment to promote the in-situ growth of LDH crystal nuclei on the surface of the residual carbon substrate. After cooling, centrifugation, water washing, ethanol washing, and vacuum drying, the product residual carbon substrate-LDH, i.e., C-Coal-LDH, is obtained.

[0010] Furthermore, the metal ions are divalent metal ions and / or trivalent metal ions; The divalent metal ions are selected from Ni. 2+ Co 2+ and Fe 2+ At least one of them; The trivalent metal ions are selected from Fe. 3+ Al 3+ and Cr 3+ At least one of them.

[0011] Furthermore, when two metal ions are present simultaneously, the molar ratio of the two metal ions is (1∶4)-(4∶1).

[0012] Furthermore, the molar ratio of the metal ions, urea, and ammonium fluoride is 1 mmol : 3 mmol : 1 mmol.

[0013] Furthermore, the conditions for the first hydrothermal treatment are: hydrothermal reaction at 120-180℃ for 6-24 hours.

[0014] Optionally, in step (3), the ligand is selected from at least one of aminotrimethylenephosphonic acid (ATMP), ethylenediaminetetramethylenephosphonic acid (EDTMP), monosodium glutamate, sodium aspartate, p-aminobenzenesulfonic acid and sodium malate. Beneficial Effects: This invention uses bulk industrial solid waste coal gangue as raw material to prepare a porous conductive carbon substrate through a simple process, significantly reducing the cost of catalyst materials and achieving "waste-to-waste treatment". "Ligand Insertion" Strategy: Introducing ligands with specific functional groups into the LDH interlayer not only expands the interlayer spacing, increases specific surface area and active site exposure, but more importantly, optimizes the electronic structure of the metal centers of the LDH layers through coordination, lowering the adsorption energy barrier of reaction intermediates, thereby enhancing intrinsic catalytic activity. Strong Interfacial Coupling: By functionalizing the residual carbon substrate and achieving in-situ growth of LDH under mild hydrothermal conditions, a tight heterogeneous interface is ensured between the LDH nanosheets and the carbon substrate, promoting rapid interfacial charge transfer and synergistically improving conductivity and stability. Through the above steps, a high-performance, low-cost bifunctional catalyst for water electrolysis is constructed.

[0015] Optionally, in step (3), the conditions for the secondary hydrothermal reaction are: reacting at 120-180 °C for 6-24 hours.

[0016] A composite water electrolysis catalyst based on coal gangue residual carbon substrate and ligand-intercalated layered double hydroxide was prepared by the above preparation method.

[0017] A cathode or anode of a water electrolysis hydrogen production system uses the above-mentioned composite water electrolysis catalyst based on coal gangue residual carbon substrate and ligand-intercalated layered double hydroxide as the active material.

[0018] Compared with the prior art, the present invention has the following advantages and technical effects: 1. The composite catalyst prepared by this invention exhibits excellent bifunctional electrocatalytic performance, specifically high activity and low overpotential for both OER and HER. For example, in a 1.0 M KOH electrolyte, it achieves an overpotential of 10 mA cm⁻¹. -2The required OER overpotential for current density is below 250 mV, and the HER overpotential is below 100 mV. When used as a full hydrolysis catalyst, it can achieve efficient hydrogen and oxygen production at relatively low cell pressures.

[0019] 2. The composite catalyst prepared by this invention also has excellent stability: the tight interfacial bonding and stable ligand intercalation structure enable the composite catalyst to maintain structural and performance stability during long-term electrolysis tests (such as more than 50 hours), and the metal ion dissolution rate is low.

[0020] 3. Significant cost advantages: The raw materials used in this invention are mainly derived from waste, the preparation process is simple, and there is no need for expensive equipment or high-purity reagents. The overall cost is far lower than that of commercial precious metal catalysts and many reported nano-carbon-based composite materials. Attached Figure Description

[0021] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a SEM image of the composite catalyst prepared in Example 1 of the present invention. Detailed Implementation

[0022] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0023] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0024] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0025] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0026] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0027] This invention discloses a composite water electrolysis catalyst based on coal gangue residual carbon substrate and ligand-intercalated layered hydrogen hydroxide (LDH) and its preparation method. The catalyst uses calcined, acid-washed, and oxidized coal gangue residual carbon as a porous conductive substrate, and LDH nanosheets with specific functional group ligands (such as amino acids) intercalated in situ are grown on its surface via a hydrothermal method. The preparation method includes the following steps: pretreatment and functionalization of coal gangue residual carbon, in-situ growth of LDH, and preparation of the composite bifunctional catalyst after ligand insertion. In other words, this invention utilizes waste-derived carbon to reduce costs, effectively controls the electronic structure of LDH and increases the active specific surface area through a ligand insertion strategy, while strong interfacial coupling ensures excellent charge transport capabilities. The composite material (composite catalyst) obtained by this invention exhibits high catalytic activity, low overpotential, and excellent stability for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), making it a low-cost, high-performance bifunctional water electrolysis catalyst with broad application prospects in the field of green hydrogen production.

[0028] This invention discloses a composite catalyst for water electrolysis. The catalyst uses pretreated coal gangue residue as a three-dimensional conductive network and porous substrate, and layered double hydroxide nanosheets with ligand insertion are uniformly grown on its surface and in its pores. The ligand is a small molecule or anion containing functional groups (such as amino, phosphonic acid, sulfonic acid, etc.) that can coordinate with the metal center.

[0029] This invention also discloses a method for preparing the above-mentioned water electrolysis composite catalyst, comprising the following steps: Step 1: Pretreatment and functionalization of coal gangue residual carbon substrate Coal gangue is crushed, ground, and sieved to obtain coal gangue powder. The specific steps are as follows: the powder is calcined in an inert atmosphere (N2 or Ar) at 500-800℃ for 1-4 hours to remove volatiles, yielding crude residual carbon. The crude residual carbon is washed with acid solutions (such as HCl or HNO3) to remove most of the ash (metal oxides, silicates, etc.), then washed with deionized water until neutral, and dried to obtain purified residual carbon. The purified residual carbon is then oxidized (by reflux with concentrated HNO3 or by mild oxidation with air) to introduce oxygen-containing functional groups such as carboxyl and hydroxyl groups onto its surface, enhancing its hydrophilicity and binding force with LDH precursors, resulting in a functionalized coal gangue residual carbon substrate.

[0030] Step 2: In-situ growth of LDH on the surface of functionalized coal gangue residual carbon substrate Formulating a mixture containing divalent metal ions (M 2+ , such as Ni 2+ Co 2+ Fe 2+ ) and / or trivalent metal ions (M 3+ , such as Fe 3+ Al 3+ Cr 3+ A mixed metal aqueous solution of urea and ammonium fluoride, wherein M 2+ / M 3+ The molar ratio is 1:4 to 4:1, and the total metal ion concentration is 0.005-0.2 M. Under vigorous stirring, the mixed metal aqueous solution is mixed with the residual carbon substrate and then treated hydrothermally (120-180℃, 6-24 hours) to promote the in-situ growth of LDH crystal nuclei on the C-Coal surface, forming C-Coal-LDH.

[0031] Step 3: Ligand insertion modulates catalyst performance Prepare an alkaline solution containing the target intercalation ligand (L); the ligand L is selected from one or more of the following: at least one of aminotrimethylenephosphonic acid (ATMP), ethylenediaminetetramethylenephosphonic acid (EDTMP), monosodium glutamate, sodium aspartate, p-aminobenzenesulfonic acid, and sodium malate; the concentration of the ligand is 0.01-0.1 M.

[0032] The ligand solution and the C-Coal-LDH obtained in step two were uniformly dispersed in deionized water to form a suspension. The mixture was vigorously stirred at room temperature for 1-4 hours. The mixture was then transferred to a high-pressure reactor and subjected to hydrothermal reaction at 120-180℃ for 6-24 hours. During this process, the ligands were stably inserted and fixed between the LDH layers. Hydrothermal conditions favored the formation of a composite structure with moderate crystallinity and tight interfacial bonding. After the reaction, the mixture was naturally cooled to room temperature. The product was collected by centrifugation or filtration, repeatedly washed with deionized water and ethanol, and finally vacuum dried at 60-80℃ for 6-12 hours to obtain the coal gangue residual carbon-based ligand-intercalated LDH composite catalyst (C-Coal-LDH-ligand).

[0033] Unless otherwise specified, "room temperature" in this invention refers to 20-30℃.

[0034] All raw materials used in this invention were purchased from the market.

[0035] The technical solution of the present invention will be further illustrated by the following embodiments.

[0036] Example 1 A method for preparing a composite water electrolysis catalyst based on a coal gangue residual carbon substrate and ligand-intercalated layered double hydroxides includes the following steps: Step 1. Crush the coal gangue and grind it to approximately 100 mesh. Place the powder in a tube furnace and calcine it at 600°C under nitrogen protection at a rate of 5°C / min for 2 hours. Then, wash it with 1M hydrochloric acid solution at 60°C with stirring for 2 hours to remove some of the ash. Wash it with deionized water until neutral and dry it. React the dried product at 80°C in a round-bottom flask equipped with a reflux condenser using concentrated nitric acid for 3 hours with stirring. After cooling, slowly pour the mixture from the flask into a beaker containing a large amount of ice water or cold distilled water to terminate the reaction. Then, filter and wash with water simultaneously. Place the neutralized filter cake in an oven and dry it at 80°C to constant weight to obtain the coal gangue residual carbon matrix (C-Coal).

[0037] Step 2. Weigh 5 mmol Ni(CH3COO)2·4H2O, 5 mmol Co(CH3COO)2·4H2O, 30 mmol urea, and 10 mmol ammonium fluoride and dissolve them in a mixed solvent of 30 mL deionized water and 10 mL ethanol. Add 100 mg of coal gangue residual carbon matrix to the mixture and sonicate for 30 minutes. Transfer the suspension to a 50 mL polytetrafluoroethylene-lined high-pressure reactor and react at 140 °C for 10 hours. After the reaction is complete, allow it to cool naturally. After centrifugation, washing with water and ethanol, the product is dried under vacuum at 60 °C to obtain the product C-Coal-NiCoLDH. Step 3. Dissolve the above-mentioned residual carbon matrix-LDH in an aqueous solution, then add 2 mmol of sodium aspartate. After stirring for 1 hour, transfer the solution to a 50 mL polytetrafluoroethylene-lined high-pressure reactor and react at 150 °C for 8 hours. After the reaction is complete, allow it to cool naturally. The product is then centrifuged, washed with water and ethanol, and vacuum dried at 60 °C to obtain the composite catalyst C-Coal-NiCoLDH-sodium aspartate.

[0038] Figure 1 This is a SEM image of the composite catalyst prepared in Example 1 of the present invention. The image shows that the catalyst exhibits a standard nanoflower morphology composed of catalyst nanosheets.

[0039] Example 2 The only difference from Example 1 is that sodium aspartate is not added in step 3; instead, 2 mmol of sodium malate is added. The resulting catalyst is designated C-Coal-NiCoLDH-sodium malate.

[0040] Example 3 The only differences from Example 1 are: in step 2, instead of adding 5 mmol Co(CH3COO)2·4H2O, 5 mmol Fe(NO3)3 is added; and in step 3, instead of adding sodium aspartate, 2 mmol aminotrimethylenephosphonic acid is added. The resulting catalyst is denoted as C-Coal-NiFeLDH-aminotrimethylenephosphonic acid.

[0041] Example 4 The only difference from Example 1 is that sodium aspartate is not added in step 3; instead, 2 mmol of ethylenediaminetetramethylenephosphonic acid is added. The resulting catalyst is denoted as C-Coal-NiCoLDH-ethylenediaminetetramethylenephosphonic acid.

[0042] Comparative Example 1 Commercial OER catalyst RuO2 and HER catalyst Pt / C were used as comparisons.

[0043] Comparative Example 2 The pure coal gangue residual carbon substrate (C-Coal) prepared in step 1 of Example 1 was used as the catalyst only.

[0044] Comparative Example 3 Only the C-Coal-NiCoLDH prepared in step 2 of Example 1 was used as the catalyst.

[0045] Effect verification The products of Examples 1-4 and Comparative Examples 1-3 were used as water electrolysis catalysts to verify the corresponding OER and HER effects. The effect data are shown in Table 1.

[0046] Table 1 Comparing the data in Table 1, it can be seen that the four coal gangue-based composite catalysts prepared in the embodiments of this invention exhibit significantly better OER and HER activities than those on pure carbon substrates. In terms of OER performance, the composite catalysts in the embodiments are superior to commercial RuO2; in terms of HER performance, although they lag behind the top-performing Pt / C, they still demonstrate good bifunctional catalytic potential. The C-Coal-NiCoLDH without ligand insertion shown in Comparative Example 3 exhibits weaker OER and HER performance than the four composite catalysts with inserted ligands, illustrating the necessity of ligand insertion.

[0047] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a composite water electrolysis catalyst based on a coal gangue residual carbon substrate and ligand-intercalated layered double hydroxides, characterized in that, Includes the following steps: (1) Coal gangue residual carbon matrix is ​​prepared by calcination, acid washing and oxidation treatment using coal gangue as raw material; The calcination conditions are as follows: under nitrogen protection, the temperature is increased to 500-800℃ at a rate of 5℃ / min, and then calcined at this temperature for 1-4 hours; The pickling conditions are as follows: the acid solution is stirred and washed at 60°C for 2 hours, and then washed with water until neutral. The oxidation treatment conditions are as follows: stirring reaction in concentrated nitric acid at 60℃-100℃ for 1-4 hours, followed by washing and drying after the reaction is completed. (2) Layered double hydroxides are grown in situ on the surface of the coal gangue residual carbon substrate using hydrothermal methods to obtain residual carbon substrate-LDH; the specific process is as follows: Metal ions, urea, and ammonium fluoride are dissolved in a solvent to obtain a mixture. The coal gangue residual carbon matrix is ​​then added to the mixture, ultrasonically dispersed, subjected to a hydrothermal treatment, and then cooled, centrifuged, washed with water, washed with ethanol, and dried to obtain the product residual carbon matrix-LDH. The metal ions are divalent metal ions and / or trivalent metal ions; The divalent metal ions are selected from Ni 2+ Co 2+ and Fe 2+ At least one of them; The trivalent metal ions are selected from Fe. 3+ Al 3+ and Cr 3+ At least one of them; (3) The ligands are inserted into the LDH interlayer through a secondary hydrothermal reaction to obtain the composite water electrolysis catalyst based on coal gangue residual carbon substrate and ligand-intercalated layered double hydroxide; The ligand is selected from at least one of aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, glutamic acid, sodium aspartate, p-aminobenzenesulfonic acid, and sodium malate.

2. The preparation method of a composite water electrolysis catalyst based on a coal gangue residual carbon substrate and ligand-intercalated layered double hydroxides according to claim 1, characterized in that, When two metal ions are present, the molar ratio of the two metal ions is (1:4) - (4:1).

3. The preparation method of a composite water electrolysis catalyst based on a coal gangue residual carbon substrate and ligand-intercalated layered double hydroxides according to claim 1, characterized in that, The conditions for the first hydrothermal treatment are: hydrothermal reaction at 120-180℃ for 6-24 hours.

4. The preparation method of a composite water electrolysis catalyst based on a coal gangue residual carbon substrate and ligand-intercalated layered double hydroxides according to claim 1, characterized in that, In step (3), the conditions for the secondary hydrothermal reaction are: reaction at 120-180℃ for 6-24 hours.

5. A composite water electrolysis catalyst based on a coal gangue residual carbon substrate and ligand-intercalated layered double hydroxides, characterized in that, It is prepared by the preparation method according to any one of claims 1-4.

6. A cathode or anode of a water electrolysis hydrogen production system, characterized in that, The composite water electrolysis catalyst based on coal gangue residual carbon substrate and ligand-intercalated layered double hydroxide as described in claim 5 is used as the active material.

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