In-situ transformed feconimo fef nanosheet catalyst and preparation method and application thereof
By preparing FeCoNi MOF nanosheet catalysts through in-situ conversion on nickel foam, the problems of batch preparation and stability of two-dimensional MOF catalytic materials were solved, achieving high-efficiency oxygen evolution reaction performance and durability, making it suitable for water electrolysis devices.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANDONG JIANZHU UNIV
- Filing Date
- 2026-03-02
- Publication Date
- 2026-06-12
AI Technical Summary
Existing technologies make it difficult to prepare structurally stable two-dimensional MOF catalytic materials with highly exposed active sites in batches using simple and controllable methods. Furthermore, when powdered catalysts are loaded on current collectors, there are problems with active site masking and interfacial contact resistance, which affect the durability of the catalytic system.
Using nickel foam as the matrix and iron-cobalt basic carbonate as the sacrificial template, FeCoNi MOF nanosheet catalysts were prepared in situ through stepwise hydrothermal and solvothermal reactions, avoiding high-temperature calcination and directly growing ultrathin nanosheet structures on a conductive framework.
It achieves high catalytic activity and high stability, reduces production costs, is suitable for large-scale preparation, and the catalyst shows no significant activity decay during long-term operation in a strongly alkaline environment, meeting the requirements of industrial-grade water electrolysis devices.
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Figure CN121737753B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of electrocatalytic materials technology, and in particular to an in-situ conversion FeCoNi MOF nanosheet 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, as a clean energy carrier, relies on high-performance catalytic materials for its efficient production. Among these, the oxygen evolution reaction (OER), a key half-reaction in energy conversion processes such as water splitting, suffers from slow kinetics that severely limit overall efficiency. Therefore, developing highly active and stable OER catalysts is crucial.
[0004] Metal-organic frameworks (MOFs) exhibit great potential in catalysis due to their tunable structure, high specific surface area, and abundant active sites. Currently, a common material optimization strategy involves high-temperature calcination of MOFs to obtain derived materials. However, this process often destroys their original fine porous structure and regular morphology, leading to the loss of some intrinsic active sites or structural collapse. In contrast, directly utilizing two-dimensional MOF materials with nanometer-thickness as catalysts holds promise for preserving their structural advantages to the greatest extent, providing abundant active interfaces and efficient mass transfer pathways for catalytic reactions. However, how to prepare structurally stable two-dimensional MOF catalytic materials with highly exposed active sites in large quantities using simple and controllable methods remains a significant challenge.
[0005] Furthermore, in constructing practical catalytic systems, it is typically necessary to mix powdered catalysts with binders and then load them onto current collectors. This method may not only mask some active sites and introduce additional interfacial contact resistance, affecting charge transport efficiency, but the instability of the binder during long-term operation may also lead to catalyst detachment, affecting the durability of the catalytic system. Therefore, developing a method for directly growing two-dimensional MOF catalytic materials in situ on a conductive framework is of great value for obtaining catalytic systems with robust structures, excellent performance, and easy integration. Summary of the Invention
[0006] In view of this, the present invention provides an in-situ transformation FeCoNi MOF nanosheet catalyst, its preparation method, and its application. Using nickel foam as a matrix and iron-cobalt basic carbonate as a sacrificial template, the present invention successfully prepared a FeCoNi trimetallic MOF catalyst with an ultrathin nanosheet structure through in-situ transformation. This catalyst exhibits high catalytic activity and high stability in the oxygen evolution reaction.
[0007] In a first aspect, the present invention provides a method for preparing an in-situ transformed FeCoNi MOF nanosheet catalyst, comprising the following steps:
[0008] Cobalt salt, ferrous salt, urea and ammonium fluoride are dissolved in a first solvent and stirred to obtain a precursor solution; the molar ratio of cobalt salt, ferrous salt, urea and ammonium fluoride is (1~3): (0.1~0.5): (2~4): 1; the first solvent is a mixed solvent of water and low-carbon alcohols;
[0009] The nickel foam is immersed in the precursor solution and subjected to a hydrothermal reaction to obtain nickel foam loaded with iron-cobalt basic carbonates.
[0010] Terephthalic acid is dissolved in a second solvent to obtain a ligand solution; the second solvent is a mixture of water, lower alcohols and polar aprotic solvents.
[0011] The nickel foam loaded with iron-cobalt basic carbonate was immersed in the ligand solution and subjected to a solvothermal reaction to obtain the in-situ transformed FeCoNi MOF nanosheet catalyst.
[0012] Preferably, the cobalt salt is selected from at least one of cobalt nitrate, cobalt chloride, cobalt sulfate, or cobalt acetate; and the ferrous salt is selected from at least one of ferrous chloride, ferrous sulfate, or ferrous acetate.
[0013] Preferably, the lower alcohol in the first solvent and the second solvent is at least one of methanol, ethanol or isopropanol.
[0014] Preferably, in the first solvent, the volume ratio of water to lower alcohol is (3~8):1.
[0015] Preferably, the hydrothermal reaction temperature is 100~130℃ and the reaction time is 4~12 hours.
[0016] Preferably, the ratio of the total molar amount of the cobalt salt and ferrous salt to the molar amount of terephthalic acid is (15~25):1.
[0017] Preferably, in the second solvent, the polar aprotic solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, or dimethyl sulfoxide.
[0018] Preferably, the temperature of the solvothermal reaction is 100~130℃, and the reaction time is 4~10 hours.
[0019] Secondly, the present invention provides an in-situ transformed FeCoNi MOF nanosheet catalyst, which is prepared by the above-described preparation method.
[0020] Thirdly, the present invention provides the application of the above-mentioned in-situ transformed FeCoNi MOF nanosheet catalyst as an oxygen evolution reaction catalyst.
[0021] Compared with the prior art, the present invention has achieved the following beneficial effects:
[0022] (1) This invention uses cobalt salt and ferrous salt as raw materials and adopts a stepwise hydrothermal and solvothermal reaction to achieve in-situ conversion of iron-cobalt basic carbonates into FeCoNi MOF nanosheets using iron-cobalt basic carbonates as sacrificial templates. The preparation method has mild process conditions, simple steps and good reproducibility. It does not require subsequent high-temperature calcination, and the obtained catalyst can be used directly as an electrode without the need to add binders, which is beneficial to reducing production costs and is suitable for large-scale preparation.
[0023] (2) The present invention grows an ultrathin nanosheet structure in situ on a nickel foam substrate. The structure has a rich active interface and a large electrochemical active area, which effectively promotes charge transport and mass transfer kinetics in the reaction process, thereby significantly improving the intrinsic oxygen evolution reaction activity of the material, enabling it to achieve high current density output at a low overpotential.
[0024] (3) The FeCoNi MOF nanosheet catalyst obtained by the present invention exhibits excellent catalytic stability and structural durability in a strongly alkaline environment. It can operate for a long time under industrial-grade high current density without significant activity decay, thus meeting the requirements of actual water electrolysis devices for long-life operation of anode materials. Attached Figure Description
[0025] 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.
[0026] Figure 1 These are scanning electron microscope (SEM) images of the catalysts prepared in Examples 1, 2, 3 and Comparative Example 1 of the present invention; wherein, a~d are SEM images of Examples 1, 2, 3 and Comparative Example 1, respectively;
[0027] Figure 2 The linear sweep voltammetry curves and Tafel slopes of the catalysts prepared in Examples 1, 2, and 3 of this invention and Comparative Example 1, and the pretreated nickel foam (NF) in Comparative Example 2, in 1 M KOH solution are shown; where a is the linear sweep voltammetry curve and b is the Tafel slope graph.
[0028] Figure 3The double-layer capacitance (C) of the catalysts in Example 1 and Comparative Example 1 of this invention is... dl The curves and the electrochemical impedance spectroscopy of the catalysts of Example 1 and Comparative Example 1 and the nickel foam substrate (NF) of Comparative Example 2; where a is C dl Curve b, where b is the electrochemical impedance spectroscopy;
[0029] Figure 4 The catalyst of Example 1 of this invention is used as the anode of an AEM (anion exchange membrane) electrolyzer at 1 A·cm -2 The following is a graph showing the stability test results. Detailed Implementation
[0030] 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.
[0031] In this invention, the terms "comprising" or "including" mean that, in addition to the listed elements, other elements not explicitly listed may be included, which are inherent to the technical solution or are usually added to achieve the effect.
[0032] Unless otherwise stated, all numerical ranges mentioned in this invention, such as "4~10" and "100~130℃", include both end values and any sub-ranges or specific point values within that range. For example, "4~10" should be understood to disclose all possible combinations of numerical values such as "4~5", "5~8", "8~10", and "4, 5, 6, 7, 8, 9, 10".
[0033] In one embodiment of the present invention, a method for preparing an in-situ transformed FeCoNi MOF nanosheet catalyst is provided. The steps and their technical features are described in detail below:
[0034] Step 1, Preparation of precursor solution and growth of iron-cobalt basic carbonate: Cobalt salt, ferrous salt, urea and ammonium fluoride are dissolved in a first solvent and stirred to obtain a precursor solution; nickel foam is immersed in the precursor solution and subjected to a hydrothermal reaction to obtain nickel foam (FeCoCH / NF) loaded with iron-cobalt basic carbonate.
[0035] This step aims to grow a uniform iron-cobalt basic carbonate (FeCoCH) layer in situ on a nickel foam substrate, suitable as a conversion template.
[0036] In this invention, before immersing the nickel foam in the precursor solution, a pretreatment step is included for the nickel foam substrate. The pretreatment involves sequentially cleaning the nickel foam with an acidic solution, an organic solvent, and water, possibly supplemented by ultrasonic treatment, followed by drying. This step aims to thoroughly remove the oxide layer, organic contaminants, and dust impurities from the surface of the nickel foam, thereby obtaining a clean and activated substrate surface to ensure that the precursor layer in the subsequent hydrothermal growth process is uniform, dense, and firmly bonded.
[0037] In optional embodiments of the present invention, the cobalt salt may be selected from at least one of cobalt nitrate, cobalt chloride, cobalt sulfate, or cobalt acetate; or a hydrated salt of the above cobalt salts may be selected. The ferrous salt may be selected from at least one of ferrous chloride, ferrous sulfate, or ferrous acetate; or a hydrated salt of the above ferrous salts may be selected. These soluble salts are chosen because they can sufficiently ionize in water to provide Co. 2+ and Fe 2+ The ions, and their anions, do not produce interfering precipitation or strong complexation during subsequent hydrothermal processes, which is conducive to homogeneous nucleation. In one or more embodiments of the present invention, the cobalt salt is cobalt nitrate hexahydrate, and the ferrous salt is ferrous chloride tetrahydrate.
[0038] In step one of this invention, urea slowly decomposes under hydrothermal conditions to produce OH- - and CO3 2- It is crucial for providing alkalinity and a source of carbonate ions to form basic carbonates. The F in ammonium fluoride (NH4F) is essential. - Ions are a mild etchant and structure directing agent that can moderately etch the surface of nickel foam, enhance the adhesion between the substrate and the product, and regulate the growth rate of precursor crystal faces, which helps to form a uniform nanostructure layer.
[0039] In an optional embodiment of the present invention, the molar ratio of the cobalt salt, ferrous salt, urea, and ammonium fluoride is (1~3):(0.1~0.5):(2~4):1; more preferably (1.5~2.5):(0.2~0.4):(2.5~3.5):1; and even more preferably (1.8~2.2):(0.3~0.35):(2.8~3.3):1. Controlling the ratio of cobalt to iron in the precursor is fundamental to obtaining a specific crystal phase and electronic structure FeCoCH. A suitable amount of urea added ensures sufficient and continuous release of OH- in the hydrothermal environment. - and CO3 2- This drives the complete crystallization of FeCoCH. Insufficient urea leads to incomplete nucleation and growth; excessive urea results in overly alkaline conditions, potentially generating hydroxide impurities. Appropriate ammonium fluoride addition can ensure the complete crystallization of FeCoCH. - It effectively plays a guiding role in structure, avoiding substrate damage or loosening of the precursor layer due to excessive etching.
[0040] In an optional embodiment of the present invention, the first solvent is a mixed solvent of water and a lower alcohol, preferably at least one of methanol, ethanol, or isopropanol, and the volume ratio of water to the lower alcohol is (3~8):1. More preferably, it is (4~6):1; even more preferably, it is (5~6):1. The addition of the lower alcohol can reduce the surface tension of the solution, improve the wettability to the three-dimensional porous structure of nickel foam, and enable the precursor solution to contact all surfaces of the substrate more uniformly, achieving uniform growth. Ethanol is often preferred due to its moderate polarity and low toxicity.
[0041] In an optional embodiment of the present invention, the temperature of the hydrothermal reaction is 100~130℃, for example, 100℃, 110℃, 120℃, 130℃, etc., more preferably 115~130℃. A suitable temperature range provides sufficient reaction kinetic energy to allow for effective decomposition of urea and sufficient growth and firm anchoring of FeCoCH crystals onto the nickel foam. The hydrothermal reaction time is 4~12 hours, more preferably 6~10 hours, to ensure complete reaction.
[0042] After the hydrothermal reaction is completed, the present invention further includes a step of washing the foamed nickel loaded with iron-cobalt basic carbonate, preferably by washing with ethanol and water in sequence, so as to thoroughly remove unreacted raw materials and by-products adsorbed on its surface.
[0043] Step 2, preparation of ligand solution and in-situ conversion of MOF: terephthalic acid is dissolved in a second solvent to obtain a ligand solution; the nickel foam loaded with iron-cobalt basic carbonate is immersed in the ligand solution to carry out a solvothermal reaction, thereby obtaining the in-situ converted FeCoNi MOF nanosheet catalyst.
[0044] This step utilizes the nickel foam loaded with iron-cobalt basic carbonate obtained in step one as a sacrificial template. Through a solvothermal reaction, it reacts with organic ligands to transform in situ into the target FeCoNi MOF. The nickel foam (NF) acts as an indispensable nickel (Ni) source in this process. Under the combined action of terephthalic acid ligands and a mixed solvent, the surface of the nickel foam undergoes slight and continuous dynamic etching and dissolution, thereby providing Ni to the reaction system. 2+ Ions. These Ni 2+ Fe dissolved from FeCoCH precursor 2+ Co 2+ Ions coordinate and assemble with deprotonated terephthalate ligands near the reaction interface, ultimately growing a uniformly distributed MOF lattice of Fe, Co, and Ni on the substrate.
[0045] In this invention, the ratio of the total molar amount of the cobalt salt and ferrous salt to the molar amount of terephthalic acid is (15~25):1, more preferably (18~22):1. At the above ratio, the ligand terephthalic acid can react with Co released slowly from the sacrificial template. 2+ Fe 2+ and Ni replenished by etching from the nickel foam substrate 2+ Sufficient coordination is achieved without excessive amounts leading to homogeneous nucleation in the solution, which would affect in-situ growth on the substrate.
[0046] In an optional embodiment of the present invention, the second solvent is a mixed solvent of water, a lower alcohol, and a polar aprotic solvent. The lower alcohol is at least one of methanol, ethanol, or isopropanol, and the polar aprotic solvent is at least one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), or dimethyl sulfoxide (DMSO). Water provides the coordination environment and is the basic medium for ligand dissolution and metal ion coordination. The lower alcohol is used to adjust the polarity of the system and its wettability to the substrate. The polar aprotic solvent has a high boiling point and strong coordination ability; on the one hand, its high boiling point is suitable for the high-temperature conditions of solvothermal reactions; on the other hand, it can weakly coordinate with metal ions, regulating the coordination kinetics of the metal center, controlling the growth rate of MOF crystals, and playing a key regulatory role in the formation of ultrathin nanosheet structures. The volume ratio of water, lower alcohol, and polar aprotic solvent can be adjusted within a wide range, for example, (1~15):(1~15):(1~5).
[0047] In an optional embodiment of the present invention, the temperature of the solvothermal reaction is 100~130℃, for example, 100℃, 110℃, 120℃, 130℃, etc., more preferably 115~130℃. The solvothermal reaction time is 4~12 hours, more preferably 6~10 hours, to ensure complete reaction. The above conditions are used to drive the partial dissolution of the FeCoCH precursor, the release of metal ions, and coordination assembly with terephthalic acid ligands, completing the structural transformation to MOF. Temperature and time together determine the degree of completeness of transformation and the crystallinity quality of the nanosheets.
[0048] After the solvothermal reaction is completed, the present invention further includes a step of washing and drying the obtained FeCoNi MOF nanosheet catalyst, preferably by washing with ethanol and deionized water in sequence, followed by drying, to obtain a pure final product.
[0049] In this invention, "in-situ conversion" specifically refers to the process where a pre-formed iron-cobalt basic carbonate (FeCoCH) precursor on a nickel foam substrate is directly used as a metal source and structural template in the subsequent solvothermal reaction without separation, transforming into the target FeCoNi MOF material through a dissolution-recoordination mechanism. During this process, the nickel foam substrate not only serves as a conductive framework for supporting the catalyst, but its surface also undergoes slight etching in the solvothermal environment, continuously providing Ni. 2+ Ions, thus reacting with Fe from the precursor 2+ Co 2+ They jointly participate in coordination, ultimately forming FeCoNi MOF nanosheet catalysts.
[0050] In another embodiment of the present invention, an in-situ transformed FeCoNi MOF nanosheet catalyst is provided, which is prepared by the above-described preparation method. The FeCoNi MOF nanosheet catalyst is a Fe, Co, Ni trimetallic organic framework material with an ultrathin nanosheet morphology, typically with an average thickness in the range of 5–100 nm, preferably 20–50 nm. This morphology provides a large specific surface area and highly exposed active sites.
[0051] In another embodiment of the invention, the in-situ transformed FeCoNi MOF nanosheet catalyst is provided as an oxygen evolution reaction (OER) catalyst. Specifically, this catalyst is suitable for applications including, but not limited to, the following: as an anode catalyst in alkaline water electrolysis hydrogen production devices; as an auxiliary catalyst for the cathode oxygen reduction reaction (ORR) or anode small molecule oxidation reaction in fuel cells; and as an air electrode catalyst in metal-air batteries. Particularly in alkaline water electrolysis hydrogen production applications, this catalyst can be used directly as a self-supporting electrode in situ grown on nickel foam, avoiding the coating process required for traditional powder catalysts, thus combining excellent catalytic activity, good structural stability, and convenient device integration characteristics.
[0052] 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.
[0053] Example 1
[0054] This embodiment provides a method for preparing FeCoNi MOF nanosheet catalysts through in-situ transformation.
[0055] (1) Pretreatment of nickel foam: Take a piece of nickel foam (NF) of 2 cm × 3 cm and ultrasonically clean it for 15 minutes each in 3 mol / L HCl solution, anhydrous ethanol and deionized water to remove surface oxides and oil stains. Then dry it in an oven at 60℃.
[0056] (2) Preparation of FeCoCH / NF precursor: Weigh 873 mg (approximately 3 mmol) of cobalt nitrate hexahydrate (Co(NO3)2·6H2O), 95 mg (approximately 0.48 mmol) of ferrous chloride tetrahydrate (FeCl2·4H2O), 270 mg (approximately 4.5 mmol) of urea (CO(NH2)2), and 56 mg (approximately 1.5 mmol) of ammonium fluoride (NH4F). Dissolve the above solids together in a mixed solvent of 37 mL of deionized water and 17 mL of ethanol, and stir magnetically for 1 hour to form a homogeneous precursor solution. Immerse the pretreated nickel foam from step (1) into this solution, and transfer it to a 50 mL high-pressure reactor lined with polytetrafluoroethylene. After sealing, place it in an oven at 120°C for 8 hours. After the reaction is complete, allow it to cool naturally, remove the nickel foam, rinse it several times with ethanol and deionized water, and dry it at 60°C to obtain nickel foam (FeCoCH / NF) loaded with iron-cobalt basic carbonate. In this step, the molar ratio of cobalt nitrate hexahydrate, ferrous chloride tetrahydrate, urea, and NH4F is approximately 2:0.32:3:1.
[0057] (3) In-situ conversion to FeCoNi MOF: Weigh 30 mg of terephthalic acid (approximately 0.18 mmol), i.e., the molar ratio of the total molar amount of cobalt nitrate hexahydrate and ferrous chloride tetrahydrate to the molar amount of terephthalic acid is approximately 19.3:1. Dissolve the weighed terephthalic acid in a mixed solvent consisting of 10 mL of deionized water, 10 mL of anhydrous ethanol, and 3 mL of N,N-dimethylformamide (DMF), and stir until clear to obtain a ligand solution. Immerse the FeCoCH / NF obtained in step (2) into this solution, transfer it to a new 50 mL reaction vessel, and react in a 120 °C oven for 6 hours. After cooling, remove it, rinse with ethanol and water, and dry in a 60 °C vacuum drying oven for 12 hours to finally obtain the in-situ converted FeCoNi MOF nanosheet catalyst, denoted as FeCoNi MOF / FeCoCH / NF.
[0058] Example 2
[0059] The difference between this embodiment and Example 1 is that the amount of ferrous chloride tetrahydrate added in this embodiment is 38 mg (approximately 0.19 mmol), that is, the molar ratio of cobalt nitrate hexahydrate, ferrous chloride tetrahydrate, urea, and NH4F is approximately 2 : 0.13 : 3 : 1. The remaining steps and parameters remain unchanged.
[0060] Example 3
[0061] The difference between this embodiment and Example 1 is that the amount of ferrous chloride tetrahydrate added in this embodiment is 149 mg (approximately 0.75 mmol), that is, the molar ratio of cobalt nitrate hexahydrate, ferrous chloride tetrahydrate, urea, and NH4F is approximately 2:0.5:3:1. The remaining steps and parameters remain unchanged.
[0062] Comparative Example 1
[0063] This comparative example provides a method for preparing a comparative catalyst that grows FeCoNi MOF directly on nickel foam without using a FeCoCH sacrificial template.
[0064] The specific preparation method is as follows:
[0065] (1) Pretreatment of nickel foam: Take a piece of nickel foam with dimensions of 2 cm × 3 cm and ultrasonically clean it for 15 minutes each in 3 mol / L HCl solution, anhydrous ethanol and deionized water to remove surface oxides and oil stains. Then dry it in an oven at 60℃.
[0066] (2) Direct growth of FeCoNi MOF: Weigh 873 mg of cobalt nitrate hexahydrate (Co(NO3)2·6H2O), 95 mg of ferrous chloride tetrahydrate (FeCl2·4H2O), and 30 mg of terephthalic acid, and dissolve them together in a mixed solvent consisting of 10 mL of deionized water, 10 mL of anhydrous ethanol, and 3 mL of DMF. Stir magnetically for 2 hours to form a homogeneous solution. Immerse the pretreated bare nickel foam from step (1) into this solution, transfer it to a 50 mL reactor, and react in a 120℃ oven for 6 hours. After cooling, remove it, wash and dry it in the same manner to obtain the directly grown catalyst, denoted as FeCoNi MOF / NF.
[0067] Comparative Example 2
[0068] The difference between this comparative example and Example 1 is that this comparative example only performs the pretreatment step (1) on the nickel foam.
[0069] Test case
[0070] 1. Morphological and structural characterization
[0071] Figure 1 a, b, c, and d in the image are scanning electron microscope (SEM) images of the catalysts obtained in Examples 1, 2, 3, and Comparative Example 1, respectively. Figure 1 As shown in a, the catalyst prepared using FeCoCH as a sacrificial template has a typical ultrathin nanosheet morphology with uniform thickness and an average thickness of about 30 nm. The uniform nanosheet structure is beneficial to improving the electrochemical active area of the catalyst. Figure 1Figure b shows that reducing the iron source content causes the in-situ transformed MOF to tend towards nanoribbon morphology growth, and the thickness increases significantly. Figure 1 As shown in Figure 'c', with the increase of iron source content, the in-situ transformed MOF still retains a nanosheet structure. The nanosheets overlap, which easily leads to fewer contact sites with the electrolyte and makes them prone to detachment. The direct growth product of Comparative Example 1 has an irregular morphology and exhibits a bulk aggregated state, indicating that the FeCoCH precursor template is crucial for guiding the formation of the ideal two-dimensional nanostructure.
[0072] 2. Oxygen Evolution Reaction (OER) Performance Testing
[0073] The catalysts prepared in Examples 1, 2, 3 and Comparative Example 1, and the pretreated nickel foam (NF) of Comparative Example 2 were used directly as working electrodes. The oxygen evolution reaction (OER) performance was tested in a standard three-electrode system in 1 M KOH electrolyte.
[0074] Figure 2 These are linear sweep voltammetry curves and Tafel slope plots of the catalysts in Examples 1, 2, and 3, Comparative Example 1, and the nickel foam substrate (NF) in Comparative Example 2 in 1 M KOH solution. Figure 2 As can be seen from a in Figure 1, Example 1 has the smallest overpotential. At 50 mA·cm⁻¹ -2 At the given current density, the overpotentials of Examples 1, 2, 3, Comparative Example 1, and Comparative Example 2 were 231 mV, 257 mV, 263 mV, 243 mV, and 436 mV, respectively. Figure 2 As can be seen from Figure b, the Tafel slope of Example 1 is the smallest, indicating that it has a faster kinetic reaction process.
[0075] Figure 3 In this context, 'a' represents the double-layer capacitance (C) of the catalysts in Example 1 and Comparative Example 1. dl )curve, Figure 3 In Figure b, the electrochemical impedance spectroscopy of the catalysts of Example 1 and Comparative Example 1 and the nickel foam substrate (NF) of Comparative Example 2 in 1 M KOH solution is shown. As can be seen from the figure, Example 1 has the largest electrochemical active area and the fastest electron transfer rate.
[0076] 3. Stability Test
[0077] The catalyst prepared in Example 1 was used as the anode in an AEM (anion exchange membrane) electrolyzer, and commercial Pt / C was used as the cathode for long-term stability testing. Test conditions: ambient temperature and pressure, 1 M KOH solution as electrolyte, and 1 A·cm⁻¹ current density. -2 .
[0078] Test results are as follows Figure 4As shown, the in-situ transformed FeCoNi MOF nanosheets can be observed at 1 A·cm⁻¹. -2 The battery voltage showed no degradation after 500 hours of continuous operation at industrial-grade current density.
[0079] 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 method for preparing an in-situ transformed FeCoNi MOF nanosheet catalyst, characterized in that, Includes the following steps: Cobalt salt, ferrous salt, urea, and ammonium fluoride are dissolved in a first solvent and stirred to obtain a precursor solution; the molar ratio of the cobalt salt, ferrous salt, urea, and ammonium fluoride is (1.8~2.2): (0.3~0.35): (2.8~3.3):1; the first solvent is a mixed solvent of water and low-carbon alcohols; The nickel foam is immersed in the precursor solution and subjected to a hydrothermal reaction to obtain nickel foam loaded with iron-cobalt basic carbonates. Terephthalic acid is dissolved in a second solvent to obtain a ligand solution; the second solvent is a mixture of water, lower alcohols and polar aprotic solvents; the ratio of the total molar amount of the cobalt salt and ferrous salt to the molar amount of terephthalic acid is (15~25):1; The nickel foam loaded with iron-cobalt basic carbonate was immersed in the ligand solution and subjected to a solvothermal reaction to obtain the in-situ transformed FeCoNi MOF nanosheet catalyst. The FeCoNi MOF nanosheet catalyst is a trimetallic organic framework material of Fe, Co, and Ni with an ultrathin nanosheet morphology and an average thickness of 5~100 nm.
2. The preparation method according to claim 1, characterized in that, The cobalt salt is selected from at least one of cobalt nitrate, cobalt chloride, cobalt sulfate, or cobalt acetate; the ferrous salt is selected from at least one of ferrous chloride, ferrous sulfate, or ferrous acetate.
3. The preparation method according to claim 1, characterized in that, The lower alcohol in the first solvent and the second solvent is at least one of methanol, ethanol or isopropanol.
4. The preparation method according to claim 1, characterized in that, In the first solvent, the volume ratio of water to lower alcohol is (3~8):
1.
5. The preparation method according to claim 1, characterized in that, The hydrothermal reaction is carried out at a temperature of 100-130°C for 4-12 hours.
6. The preparation method according to claim 1, characterized in that, In the second solvent, the polar aprotic solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, or dimethyl sulfoxide.
7. The preparation method according to claim 1, characterized in that, The temperature of the solvothermal reaction is 100~130℃, and the reaction time is 4~10 hours.
8. An in-situ transformation FeCoNi MOF nanosheet catalyst, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 7.
9. The application of the FeCoNi MOF nanosheet catalyst of claim 8 as a catalyst for the oxygen evolution reaction.