A TiN / Sn composite carbon felt electrode material, its preparation method and application

Abstract

This invention provides a TiN / Sn composite carbon felt electrode material, its preparation method, and its application, belonging to the field of flow battery electrode technology. The preparation method of this electrode material includes the following steps: pre-complexing a tin source and a titanium source in an organic solvent to obtain a Ti-O-Sn mixed precursor solution; adding the Ti-O-Sn mixed precursor solution to an aqueous fluoride solution and mixing thoroughly to obtain a suspension; adding carbon felt to the suspension and then performing a hydrothermal reaction to obtain a Sn-TiO2@CF precursor; placing the Sn-TiO2@CF precursor in a nitrogen-containing environment and then performing segmented heat treatment under a protective atmosphere to obtain the target product. This invention utilizes the pre-anchoring of the Ti–O–Sn precursor and in-situ nucleation during the TiO2 to TiN conversion process, accompanied by lattice reconstruction, oxygen-nitrogen substitution, and defect generation. The resulting electrode is less prone to deactivation after cyclic rinsing and long-term electrochemical operation.

Description

Technical Field

[0001] This invention relates to the field of flow battery electrode technology, and in particular to a TiN / Sn composite carbon felt electrode material, its preparation method, and its application. Background Technology

[0002] A flow battery is a large-scale electrochemical energy storage device that stores electrochemically active materials in an external electrolyte tank and uses a circulating pump to drive the electrolyte through a fuel cell stack to complete the charging and discharging process. Compared with traditional energy storage technologies such as lithium-ion batteries and lead-acid batteries, flow batteries have advantages such as independent power and capacity design, easy expansion of energy storage scale, long cycle life, high safety, deep charge and discharge capability, and low operation and maintenance costs. They have broad application prospects in renewable energy, backup power, and large-scale energy storage power stations. Among them, alkaline zinc-iron flow batteries have received widespread attention in recent years due to their use of inexpensive and environmentally friendly active materials, resulting in advantages such as low cost, high theoretical energy density, and excellent safety performance. During the charging process, the Zn in the electrolyte... 2+ A reduction reaction occurs on the surface of the negative electrode, and Zn is deposited. During the discharge process, the deposited Zn is re-oxidized and enters the electrolyte, realizing the energy storage and release process.

[0003] However, during long-term charge-discharge cycles, the electrodeposition behavior of zinc is easily affected by factors such as electrode surface structure, current distribution, and local ion concentration, leading to uneven zinc deposition on the negative electrode surface. As the deposition layer thickens, the zinc deposits tend to form dendritic or needle-like structures, i.e., zinc dendrites. The continuous growth of zinc dendrites not only increases battery polarization, causing poor contact between some deposited zinc and the electrode substrate, forming "dead zinc" and reducing the utilization rate of active materials, but may also puncture the separator, causing short circuits between the positive and negative electrodes, severely affecting the battery's coulombic efficiency, energy efficiency, and cycle stability. In addition, the zinc negative electrode is also accompanied by problems such as hydrogen evolution, side reactions, and electrode surface passivation, further reducing the cycle life and operational reliability of alkaline zinc-iron flow batteries.

[0004] Currently, methods to improve the stability of zinc anodes mainly include optimizing electrolyte composition, regulating charge and discharge strategies, constructing a three-dimensional conductive framework, and functionalizing the anode surface. Among these, introducing functional materials with good conductivity and zinc affinity onto the conductive substrate surface can effectively regulate zinc nucleation and growth behavior, reduce the zinc deposition nucleation energy barrier, promote uniform zinc deposition, and inhibit zinc dendrite formation. Therefore, this has become an important research direction for anodes in alkaline zinc-iron flow batteries in recent years.

[0005] Carbon felts are widely used in flow batteries, electrocatalysis, and other electrochemical systems due to their good conductivity, chemical stability, three-dimensional porous structure, and low cost. However, existing anode modification materials still suffer from problems such as a limited number of active sites, insufficient interfacial bonding stability, easy deactivation or detachment of functional layers during long cycling, and limited effect on regulating zinc deposition behavior, making it difficult to simultaneously achieve uniform zinc deposition, dendrite suppression, and long-term cycling stability.

[0006] Therefore, there is an urgent need to provide a composite anode and its preparation method that can synergistically improve the conductivity of the anode, enhance the uniformity of zinc nucleation, and stabilize the zinc deposition interface, so as to effectively suppress zinc dendrite growth and hydrogen evolution side reaction, and improve the cycle stability and energy efficiency of alkaline zinc-iron flow batteries. Summary of the Invention

[0007] The purpose of this invention is to provide a TiN / Sn composite carbon felt electrode material, its preparation method, and its application. The method involves pre-complexing Sn and Ti precursors in an alcohol phase to form a Ti–O–Sn mixed precursor; then, a Sn–TiO2 precursor is constructed on the carbon felt surface via a hydrothermal process; finally, a segmented heat treatment is performed using a nitrogen-containing atmosphere generated from the thermal decomposition of urea to convert TiO2 into TiN, while simultaneously reducing and confining Sn species at phase transition-induced defect sites, resulting in the TiN / Sn composite carbon felt electrode material.

[0008] Compared with traditional TiN-loaded Sn or Sn-post-deposition methods, the core difference of this invention is that Sn is not externally loaded after TiN formation, but is pre-anchored by Ti–O–Sn precursors and nucleates in situ during the TiO2 to TiN conversion process, accompanied by lattice reconstruction, oxygen and nitrogen substitution and defect generation. This forms a strong TiN / Sn interface coupling structure, avoiding the problems of Sn agglomeration, detachment and weak interface interaction in traditional post-loading methods.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] One of the technical solutions of this invention is a method for preparing a TiN / Sn composite carbon felt electrode material, comprising the following steps:

[0011] A tin source and a titanium source were pre-complexed in an organic solvent to obtain a Ti-O-Sn mixed precursor solution.

[0012] The Ti-O-Sn mixed precursor solution was added to the aqueous phase solution of fluoride and mixed evenly to obtain a suspension.

[0013] Carbon felt was added to the suspension, followed by a hydrothermal reaction to obtain the Sn-TiO2@CF precursor;

[0014] The Sn-TiO2@CF precursor was placed in a nitrogen-containing environment and then subjected to segmented heat treatment under a protective atmosphere to obtain the TiN / Sn composite carbon felt electrode material.

[0015] The second technical solution of the present invention is a TiN / Sn composite carbon felt electrode material, wherein the TiN / Sn composite carbon felt electrode material is prepared by the preparation method of the aforementioned TiN / Sn composite carbon felt electrode material.

[0016] The third technical solution of the present invention is a TiN / Sn composite carbon felt electrode material, which is applied to an alkaline zinc-iron flow battery.

[0017] The present invention discloses the following beneficial technical effects

[0018] (1) The present invention uses Ti-O-Sn precursor pre-complexation to anchor Sn species in the titanium oxide precursor network before TiN is formed, thereby avoiding the problems of particle agglomeration, uneven dispersion and weak interfacial interaction that are prone to occur during Sn post-loading.

[0019] (2) The present invention utilizes the defect sites generated during the TiO2 to TiN phase transition process to induce Sn nucleation in a confined manner, so that Sn nanoparticles are preferentially distributed on the surface, edge and defect sites of TiN nanosheets, forming high-density, stable and usable zinc-loving active sites.

[0020] (3) The TiN framework has high conductivity and structural stability, which can reduce the charge transfer impedance at the electrode interface; the Sn active sites can reduce the nucleation barrier of zinc deposition. The two work together to promote uniform zinc deposition and suppress zinc dendrites.

[0021] (4) Compared with ordinary carbon felt, single TiN modified carbon felt or post-loaded Sn / TiN composite carbon felt, the functional layer of the electrode obtained by the present invention is more firmly bonded to the carbon felt, the Sn is more uniformly dispersed, and it is not easy to deactivate or fall off after cyclic rinsing and long-term electrochemical operation.

[0022] (5) When the electrode prepared by this invention is used as the negative electrode of an alkaline zinc-iron flow battery, it can reduce the uniform local current density, induce uniform zinc deposition, and suppress zinc dendrites and hydrogen evolution side reactions, thereby improving the coulombic efficiency and cycle life of the battery. This method can effectively suppress the growth of zinc dendrites, thereby improving the cycle life and energy efficiency of alkaline zinc-iron flow batteries.

[0023] (6) The preparation process of this invention is mainly based on hydrothermal reaction and segmented heat treatment in a tubular furnace. The raw materials are readily available and the steps are controllable. It is suitable for large-scale preparation and can be used in alkaline zinc-iron flow batteries. It can also be extended to other electrochemical systems containing zinc deposition / stripping processes. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 The image shows a SEM image of the TiN / Sn@CF composite carbon felt electrode prepared in Example 1.

[0026] Figure 2 This is a TEM image of the TiN / Sn@CF composite carbon felt electrode prepared in Example 1.

[0027] Figure 3 The image shows the XRD pattern of the TiN / Sn@CF composite carbon felt electrode prepared in Example 1.

[0028] Figure 4 The CV curves of the TiN / Sn@CF composite carbon felt electrode prepared in Example 1 and the original carbon felt (CF) under three-electrode testing are shown.

[0029] Figure 5 Cyclic curves of alkaline zinc-iron flow batteries assembled with the deposited Sn composite TiN@CF carbon felt electrode prepared in Comparative Example 1 and the TiN / Sn@CF composite carbon felt electrode prepared in Example 1, respectively.

[0030] Figure 6 Cyclic curves of alkaline zinc-iron flow batteries assembled with the TiN / Sn@CF composite carbon felt electrode prepared in Example 1 and the original carbon felt (CF), respectively.

[0031] Figure 7 The graphs show the rate test results of alkaline zinc-iron flow batteries assembled with the TiN / Sn@CF composite carbon felt electrode prepared in Example 1 and the original carbon felt (CF) at different current densities. Detailed Implementation

[0032] 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.

[0033] 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. Any stated value or intermediate value within a stated range, as well as each smaller range between 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] The first aspect of this invention provides a method for preparing a TiN / Sn composite carbon felt electrode material, comprising the following steps:

[0038] A tin source and a titanium source were pre-complexed in an organic solvent to obtain a Ti-O-Sn mixed precursor solution.

[0039] The Ti-O-Sn mixed precursor solution was added to the aqueous phase solution of fluoride and mixed evenly to obtain a suspension.

[0040] Carbon felt was added to the suspension, followed by a hydrothermal reaction to obtain the Sn-TiO2@CF precursor;

[0041] The Sn-TiO2@CF precursor was placed in a nitrogen-containing environment and then subjected to segmented heat treatment under a protective atmosphere to obtain the TiN / Sn composite carbon felt electrode material.

[0042] In a preferred embodiment of the present invention, the tin source is selected from at least one of tin acetylacetonate, stannous octoate, stannous chloride dihydrate and stannous oxalate, and the titanium source is selected from at least one of tetrabutyl titanate, isopropyl titanate and titanium tetrachloride; the molar ratio of tin in the tin source to titanium in the titanium source is (0.01–0.04):1.

[0043] More preferably, the molar ratio of tin in the tin source to titanium in the titanium source is 0.01:1, 0.02:1, 0.03:1 or 0.04:1.

[0044] In a preferred embodiment of the present invention, the organic solvent is an alcohol solvent; the alcohol solvent is selected from at least one of methanol, ethanol, isopropanol, n-butanol, and ethylene glycol. The present invention does not impose a special limitation on the amount of organic solvent used, as long as it is sufficient to dissolve the tin source and the titanium source. For example, after dissolving the tin source and the titanium source in the organic solvent, the concentration of the tin source is 0.005–0.08 mol / L.

[0045] In a preferred embodiment of the present invention, the temperature of the pre-complexation reaction is 20–65°C and the time is 0.5–3 h.

[0046] In this invention, when the tin source and titanium source are subjected to a pre-complexation reaction in an organic solvent, the tin source and titanium source are first dissolved in the organic solvent to obtain a tin precursor solution and a titanium precursor solution, respectively. Then, the tin precursor solution is added dropwise to the titanium precursor solution, and stirring is continued for 10–60 min to allow the tin precursor to pre-complex with the titanium alkoxide, forming a mixed precursor solution containing a Ti-O-Sn structure.

[0047] In this invention, there are no restrictions on the order in which the tin precursor solution is added to the titanium precursor solution or the titanium precursor solution is added to the tin precursor solution. The order of addition will not affect the structure of the product. There are no special restrictions on the method of addition. Drop addition or direct mixing can be selected.

[0048] In a preferred embodiment of the present invention, the concentration of the aqueous solution of the fluoride is 0.005–0.20 mol / L; the fluoride in the aqueous solution is selected from at least one of NaF, NH4F, KF, and LiF; and the molar ratio of fluorine in the fluoride to titanium in the titanium source is 0.05–0.25:1. The fluoride is added in this invention to regulate the growth of TiO2 crystals and induce the formation of plate-like or porous plate-like TiO2 precursors.

[0049] In a preferred embodiment of the present invention, before adding carbon felt to the suspension, a pretreatment step of the carbon felt is further included; the pretreatment is as follows: the carbon felt is washed sequentially with ethanol and water, then placed in an activating agent for activation treatment, followed by washing until neutral and drying; the activating agent is dilute nitric acid; the activation treatment temperature is 60–90℃, and the time is 1–3 h; the drying temperature is 50–80℃, and the time is 10–12 h. The present invention increases the oxygen-containing functional groups and nucleation anchoring sites on the surface of the carbon felt by activating it.

[0050] More preferably, the concentration of the dilute nitric acid is 0.05–2 mol / L.

[0051] In a preferred embodiment of the present invention, the temperature of the hydrothermal reaction is 120–200°C and the time is 12–18 h.

[0052] In a preferred embodiment of the present invention, the nitrogen source is urea; the segmented heat treatment is as follows: heating to 250–350°C at a heating rate of 1–5°C / min and holding for 0.5–2 hours, then heating to 500–700°C at a heating rate of 1–5°C / min and holding for 0.5–2 hours, and finally heating to 750–900°C at a heating rate of 1–5°C / min and holding for 1–4 hours.

[0053] In this invention, the heating rate has no effect on the material and structure obtained in the range of 1-5℃ / min; the holding time also has no effect on the material and structure. When the holding time is extended, it will only make the material reaction more complete, without affecting the structure of the material.

[0054] During the segmented heat treatment, urea is placed upstream of the heat treatment furnace, and the Sn-TiO2@CF precursor is placed downstream. During the heating process, urea thermally decomposes to generate a nitrogen-containing atmosphere, which is used to promote the transformation of TiO2 to TiN phase.

[0055] More preferably, the temperature is increased to 300–350°C at a heating rate of 2–3°C / min and held for 1–2 hours, then increased to 600–700°C at a heating rate of 2–3°C / min and held for 1–2 hours, and finally increased to 850–900°C at a heating rate of 2–3°C / min and held for 2–4 hours.

[0056] In a preferred embodiment of the present invention, the mass ratio of urea to Sn-TiO2@CF precursor is 5–80:1.

[0057] More preferably, the mass ratio of urea to Sn-TiO2@CF precursor is 5:1, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1 or 80:1.

[0058] In a preferred embodiment of the present invention, the protective atmosphere is nitrogen or argon; the flow rate of the protective atmosphere gas is 20–200 mL / min.

[0059] The second aspect of the present invention provides a TiN / Sn composite carbon felt electrode material, wherein the TiN / Sn composite carbon felt electrode material is prepared by the preparation method of the aforementioned TiN / Sn composite carbon felt electrode material.

[0060] The TiN / Sn composite carbon felt electrode material prepared by the present invention includes a carbon felt skeleton, TiN nanosheets or porous TiN nanosheets loaded on the surface of the carbon felt, and Sn nanoparticles confined and dispersed on the surface of the TiN nanosheets or at defect sites.

[0061] The Sn nanoparticles have a particle size of 5–50 nm; the Sn loading is 0.01–5 mg / cm² based on the geometric area of ​​the carbon felt; in the TiN / Sn composite carbon felt electrode material, Sn exists in the form of metallic Sn, low-valence Sn, or a combination thereof, and forms an interfacial electronic coupling structure with the TiN framework.

[0062] A third aspect of the present invention provides a TiN / Sn composite carbon felt electrode material, which is applied to an alkaline zinc-iron flow battery.

[0063] In a preferred embodiment of the present invention, the alkaline zinc-iron flow battery further includes a positive electrode, a separator, a positive electrolyte, and a negative electrolyte.

[0064] More preferably, the positive electrode is a carbon felt; the positive electrode electrolyte contains hexacyanoferrate and an alkali, and the negative electrode electrolyte contains zinc salt and an alkali; the hexacyanoferrate is ferrocyanide or ferricyanide; the alkali is selected from at least one of sodium hydroxide and potassium hydroxide; and the membrane is one of a cation exchange membrane, an anion exchange membrane, and a composite ion exchange membrane.

[0065] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0066] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0067] Example 1

[0068] (1) Carbon felt pretreatment: 2cm×2cm carbon felt was ultrasonically cleaned in ethanol and deionized water for 20min respectively to remove surface oil and impurities. Then, the carbon felt was placed in 1mol / L dilute nitric acid solution and treated at 80℃ for 2h to increase the oxygen-containing functional groups and nucleation anchoring sites on the carbon felt surface. After treatment, it was washed with deionized water and vacuum dried at 60℃ for 12h to obtain pretreated carbon felt.

[0069] (2) Preparation of Ti-Sn mixed precursor solution: 5 mL of tetrabutyl titanate was added to 20 mL of anhydrous ethanol and stirred at room temperature for 30 min to obtain a clear titanium-containing precursor solution A; 0.10 g of tin acetylacetone was added to 20 mL of anhydrous ethanol and stirred at 55 °C to dissolve, obtaining a tin-containing precursor solution B. Tin-containing precursor solution B was added to titanium-containing precursor solution A at a rate of 1 drop / s, and stirring was continued at 25 °C for 1 h to allow the tin precursor to pre-complex with the titanium alkoxide, forming a Ti-O-Sn mixed precursor solution.

[0070] (3) Preparation of Sn-TiO2@CF precursor: 0.10 g NaF was added to 25 mL of deionized water and stirred until completely dissolved to obtain solution C. The Ti-O-Sn mixed precursor solution obtained in step (2) was added dropwise to solution C under stirring. After the addition was complete, sonication was continued for 30 min to obtain a homogeneous milky white suspension. The pretreated carbon felt obtained in step (1) was immersed in the suspension and transferred as a whole to a 100 mL polytetrafluoroethylene-lined reactor. The reactor was hydrothermally reacted at 180 °C for 12 h. After the reaction was completed, the sample was naturally cooled to room temperature, removed, and washed alternately with deionized water and ethanol until no obvious free particles were found. Then, it was vacuum dried at 60 °C for 12 h to obtain the Sn-TiO2@CF precursor.

[0071] (4) Preparation of TiN / Sn@CF material: The Sn-TiO2@CF precursor obtained in step (3) was placed downstream of the ceramic boat, and 8g of urea was placed upstream of the ceramic boat; the ceramic boat was placed in a tube furnace and subjected to segmented heat treatment under an argon atmosphere with an argon flow rate of 80mL / min. The heat treatment procedure was as follows: the temperature was increased to 300℃ at 2℃ / min and held for 1h to decompose the organic ligands and further fix the Ti-O-Sn related structure; the temperature was further increased to 600℃ at 2℃ / min and held for 1h to gradually convert TiO2 into TiO2. x N y The intermediate phase generates oxygen vacancies, nitrogen introduction sites, and lattice defects. The temperature is further increased to 850℃ at 2℃ / min and held for 2 hours, allowing TiO2 to further transform into the TiN phase. Simultaneously, Sn species are reduced, nucleated, and confined at the phase transition-induced defect sites. After natural cooling to room temperature, the TiN / Sn@CF composite carbon felt electrode material is obtained.

[0072] The prepared TiN / Sn composite electrode was assembled into an alkaline zinc-iron flow battery, and the steps were as follows:

[0073] The TiN / Sn@CF composite carbon felt electrode prepared in this embodiment was used as the negative electrode in an alkaline zinc-iron flow cell, while a regular carbon felt of the same size and shape was used as the positive electrode. The end plate, insulating sheet, positive current collector, positive electrode, separator, negative electrode, negative current collector, insulating sheet, and end plate were installed sequentially. The positive electrolyte circulated from the storage tank to the positive electrode side via an electrolyte circulation pump, and the negative electrolyte circulated from the storage tank to the negative electrode side via the same electrolyte circulation pump. The negative electrolyte was a mixed solution of zinc oxide and potassium hydroxide, with a zinc oxide concentration of 0.4 mol / L and a potassium hydroxide concentration of 3.8 mol / L. The positive electrolyte was a mixed solution of potassium ferrocyanide and potassium hydroxide, with a potassium ferrocyanide concentration of 0.8 mol / L and a potassium hydroxide concentration of 3 mol / L. The battery separator was a Nafion 212 membrane. An alkaline zinc-iron flow cell with an untreated raw carbon felt (CF) negative electrode was assembled using the same method as a control.

[0074] The scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the TiN / Sn@CF composite carbon felt electrode obtained in Example 1 are shown below. Figure 1 and Figure 2 As shown, the formation of TiN nanosheets can be observed. The layered structure can improve conductivity and increase the reaction surface area. At the same time, Sn nanoparticles grow uniformly on TiN, increasing the active sites, which enables zinc to be deposited and exfoliated better, and inhibits the growth of zinc dendrites.

[0075] The XRD analysis of the TiN / Sn@CF composite carbon felt electrode obtained in Example 1 is as follows: Figure 3 As shown in the figure, both TiN and Sn materials are generated on the carbon felt.

[0076] Example 2

[0077] (1) Carbon felt pretreatment: 2cm×2cm carbon felt was ultrasonically cleaned in ethanol and deionized water for 20min respectively to remove surface oil and impurities. Then, the carbon felt was placed in 1mol / L dilute nitric acid solution and treated at 80℃ for 2h to increase the oxygen-containing functional groups and nucleation anchoring sites on the carbon felt surface. After treatment, it was washed with deionized water and vacuum dried at 60℃ for 12h to obtain pretreated carbon felt.

[0078] (2) Preparation of Ti-Sn mixed precursor solution: 5 mL of tetrabutyl titanate was added to 20 mL of anhydrous ethanol and stirred at room temperature for 30 min to obtain a clear titanium-containing precursor solution A; 0.15 g of tin acetylacetone was added to 20 mL of anhydrous ethanol and stirred at 55 °C to dissolve, obtaining a tin-containing precursor solution B. Tin-containing precursor solution B was slowly added to titanium-containing precursor solution A at a rate of 1 drop / s, and stirring was continued at 60 °C for 1 h to allow the tin precursor to pre-complex with the titanium alkoxide, forming a Ti-O-Sn mixed precursor solution.

[0079] (3) Preparation of Sn-TiO2@CF precursor: 0.15g NaF was added to 25mL of deionized water and stirred until completely dissolved to obtain solution C. The Ti-O-Sn mixed precursor solution obtained in step (2) was added dropwise to solution C under stirring. After the addition was complete, sonication was continued for 30min to obtain a homogeneous milky white suspension. The pretreated carbon felt obtained in step (1) was immersed in the suspension and transferred as a whole to a 100mL polytetrafluoroethylene-lined reactor. The reactor was hydrothermally reacted at 180℃ for 18h. After the reaction was completed, the sample was naturally cooled to room temperature, removed, and washed alternately with deionized water and ethanol until no obvious free particles were found. Then, it was vacuum dried at 60℃ for 12h to obtain the Sn-TiO2@CF precursor.

[0080] (4) Preparation of TiN / Sn@CF material: The Sn-TiO2@CF precursor obtained in step (3) was placed downstream of the ceramic boat, and 10g of urea was placed upstream of the ceramic boat; the ceramic boat was placed in a tube furnace and subjected to segmented heat treatment under an argon atmosphere with an argon flow rate of 80mL / min. The heat treatment procedure was as follows: the temperature was increased to 300℃ at 2℃ / min and held for 1h to decompose the organic ligands and further fix the Ti-O-Sn related structure; the temperature was further increased to 600℃ at 2℃ / min and held for 1h to gradually convert TiO2 into TiO2. x N y The intermediate phase generates oxygen vacancies, nitrogen introduction sites, and lattice defects. The temperature is further increased to 800℃ at 2℃ / min and held for 2 hours, allowing TiO2 to further transform into the TiN phase. Simultaneously, Sn species are reduced, nucleated, and confined at the phase transition-induced defect sites. After natural cooling to room temperature, the TiN / Sn@CF composite carbon felt electrode material is obtained.

[0081] The prepared TiN / Sn@CF composite carbon felt electrode was assembled into an alkaline zinc-iron flow battery. The steps are as follows:

[0082] The TiN / Sn@CF composite carbon felt electrode prepared in this embodiment was used as the negative electrode in an alkaline zinc-iron flow cell, while a regular carbon felt of the same size and shape was used as the positive electrode. The end plate, insulating sheet, positive current collector, positive electrode, separator, negative electrode, negative current collector, insulating sheet, and end plate were installed sequentially. The positive electrolyte circulated from the storage tank to the positive electrode side via an electrolyte circulation pump, and the negative electrolyte circulated from the storage tank to the negative electrode side via the same electrolyte circulation pump. The negative electrolyte was a mixed solution of zinc oxide and potassium hydroxide, with a zinc oxide concentration of 0.4 mol / L and a potassium hydroxide concentration of 3.8 mol / L. The positive electrolyte was a mixed solution of potassium ferrocyanide and potassium hydroxide, with a potassium ferrocyanide concentration of 0.8 mol / L and a potassium hydroxide concentration of 3 mol / L. The battery separator was a Nafion 212 membrane. An alkaline zinc-iron flow cell with an untreated raw carbon felt (CF) negative electrode was assembled using the same method as a control.

[0083] Example 3

[0084] (1) Carbon felt pretreatment: 2cm×2cm carbon felt was ultrasonically cleaned in ethanol and deionized water for 20min respectively to remove surface oil and impurities. Then, the carbon felt was placed in 1mol / L dilute nitric acid solution and treated at 80℃ for 2h to increase the oxygen-containing functional groups and nucleation anchoring sites on the carbon felt surface. After treatment, it was washed with deionized water and vacuum dried at 60℃ for 12h to obtain pretreated carbon felt.

[0085] (2) Preparation of Ti-Sn mixed precursor solution: 5 mL of tetrabutyl titanate was added to 20 mL of anhydrous ethanol and stirred at room temperature for 30 min to obtain a clear titanium-containing precursor solution A; 0.05 g of tin acetylacetone was added to 20 mL of anhydrous ethanol and stirred at 55 °C to dissolve, obtaining a tin-containing precursor solution B. Tin-containing precursor solution B was slowly added to titanium-containing precursor solution A at a rate of 1 drop / s, and stirred at 60 °C for 1 h to allow the tin precursor to pre-complex with the titanium alkoxide, forming a Ti-O-Sn mixed precursor solution.

[0086] (3) Preparation of Sn-TiO2@CF precursor: 0.05 g NaF was added to 25 mL of deionized water and stirred until completely dissolved to obtain solution C. The Ti-O-Sn mixed precursor solution obtained in step (2) was added dropwise to solution C under stirring. After the addition was complete, sonication was continued for 30 min to obtain a homogeneous milky white suspension. The pretreated carbon felt obtained in step (1) was immersed in the suspension and transferred as a whole to a 100 mL polytetrafluoroethylene-lined reactor. The reactor was hydrothermally reacted at 150 °C for 12 h. After the reaction was completed, the sample was naturally cooled to room temperature, removed, and washed alternately with deionized water and ethanol until no obvious free particles were found. Then, it was vacuum dried at 60 °C for 12 h to obtain the Sn-TiO2@CF precursor.

[0087] (4) Preparation of TiN / Sn@CF material: The Sn-TiO2@CF precursor obtained in step (3) was placed downstream of the ceramic boat, and 5g of urea was placed upstream of the ceramic boat; the ceramic boat was placed in a tube furnace and subjected to segmented heat treatment under an argon atmosphere with an argon flow rate of 80mL / min. The heat treatment procedure was as follows: the temperature was increased to 300℃ at 2℃ / min and held for 1h to decompose the organic ligands and further fix the Ti-O-Sn related structure; the temperature was further increased to 600℃ at 2℃ / min and held for 1h to gradually convert TiO2 into TiO2. x N y The intermediate phase generates oxygen vacancies, nitrogen introduction sites, and lattice defects. The temperature is further increased to 900℃ at 2℃ / min and held for 2 hours, allowing TiO2 to further transform into the TiN phase. Simultaneously, Sn species are reduced, nucleated, and confined at the phase transition-induced defect sites. After natural cooling to room temperature, the TiN / Sn@CF composite carbon felt electrode material is obtained.

[0088] The prepared TiN / Sn@CF composite carbon felt electrode was assembled into an alkaline zinc-iron flow battery, and the steps are as follows:

[0089] The TiN / Sn@CF composite electrode carbon felt prepared in this embodiment was used as the negative electrode in an alkaline zinc-iron flow cell, while ordinary carbon felt of the same size and shape was used as the positive electrode. The end plate, insulating sheet, positive current collector, positive electrode, separator, negative electrode, negative current collector, insulating sheet, and end plate were installed sequentially. The positive electrode electrolyte circulated from the storage tank to the positive electrode side via an electrolyte circulation pump, and the negative electrode electrolyte circulated from the storage tank to the negative electrode side via the same electrolyte circulation pump. The negative electrode electrolyte was a mixed solution of zinc oxide and potassium hydroxide, with a zinc oxide concentration of 0.4 mol / L and a potassium hydroxide concentration of 3.8 mol / L. The positive electrode electrolyte was a mixed solution of potassium ferrocyanide and potassium hydroxide, with a potassium ferrocyanide concentration of 0.8 mol / L and a potassium hydroxide concentration of 3 mol / L. The battery separator was a Nafion 212 membrane. An alkaline zinc-iron flow cell with an untreated raw carbon felt (CF) negative electrode was assembled using the same method as a control.

[0090] Comparative Example 1

[0091] The difference from Example 1 is that Sn is subsequently deposited onto the TiN electrode.

[0092] (1) Carbon felt pretreatment: 2cm×2cm carbon felt was ultrasonically cleaned in ethanol and deionized water for 20min respectively to remove surface oil and impurities. Then, the carbon felt was placed in 1mol / L dilute nitric acid solution and treated at 80℃ for 2h to increase the oxygen-containing functional groups and nucleation anchoring sites on the carbon felt surface. After treatment, it was washed with deionized water and vacuum dried at 60℃ for 12h to obtain pretreated carbon felt.

[0093] (2) Preparation of TiO2@CF precursor: Add 5 mL of tetrabutyl titanate to 20 mL of anhydrous ethanol and stir at room temperature for 30 min to obtain a clear titanium-containing precursor solution A; dissolve 0.5 g of NaF in 25 mL of deionized water and sonicate until clear to obtain solution B; slowly add solution A to solution B and stir for 30 min to obtain a white suspension; put the pretreated carbon felt from step (1) into the above solution and transfer it to a 100 mL reactor for hydrothermal treatment at 180 °C for 12 h. After the reaction is completed, cool naturally to room temperature, take out the sample, wash it alternately with deionized water and ethanol until there are no obvious free particles, and then vacuum dry at 60 °C for 12 h to obtain TiO2@CF precursor.

[0094] (3) Preparation of TiN@CF material: The TiO2@CF precursor obtained in step (2) was placed downstream of the ceramic boat, and 5g of urea was placed upstream of the ceramic boat; the ceramic boat was placed in a tube furnace and subjected to segmented heat treatment under an argon atmosphere with an argon flow rate of 80mL / min. The heat treatment procedure was as follows: the temperature was increased to 500℃ at 2℃ / min and held for 1h; then the temperature was increased to 850℃ at 5℃ / min and held for 3h. After natural cooling to room temperature, TiN@CF electrode material was obtained.

[0095] (4) Preparation of Sn deposition solution: 6.3 ml of hydrochloric acid was slowly added dropwise to 150 ml of deionized water, and then 0.1 mol / L of tin acetylacetone was added to the above solution and stirred evenly to obtain Sn deposition solution.

[0096] (5) Sn deposition: The deposition solution described in step (4) is placed in a three-electrode system. The working electrode is the TiN@CF electrode described in step (3), the reference electrode is a saturated calomel electrode, and the counter electrode is a platinum sheet. The deposition is carried out at a voltage of -0.6V for 30s using the constant potential deposition method to obtain a TiN modified carbon felt electrode with Sn deposited afterward.

[0097] The electrodes obtained in Comparative Example 1 were assembled into an alkaline zinc-iron flow battery. The steps were as follows:

[0098] The electrode obtained in Comparative Example 1 was used as the negative electrode in an alkaline zinc-iron flow cell, and a common carbon felt of the same size and shape was used as the positive electrode. The end plate, insulating sheet, positive current collector, positive electrode, separator, negative electrode, negative current collector, insulating sheet, and end plate were installed sequentially. The positive electrolyte circulated from the storage tank to the positive electrode side via an electrolyte circulation pump, and the negative electrolyte circulated from the storage tank to the negative electrode side via the same electrolyte circulation pump. The negative electrolyte was a mixed solution of zinc oxide and potassium hydroxide, with a zinc oxide concentration of 0.4 mol / L and a potassium hydroxide concentration of 3.8 mol / L. The positive electrolyte was a mixed solution of potassium ferrocyanide and potassium hydroxide, with a potassium ferrocyanide concentration of 0.8 mol / L and a potassium hydroxide concentration of 3 mol / L. The battery separator was a Nafion 212 membrane.

[0099] test:

[0100] The flow batteries assembled in Examples 1-3 were tested at a current density of 100 mA / cm². 2 Under the specified conditions, charge-discharge cycle tests were conducted, with the charging cutoff voltage controlled at 2.0V and the discharging cutoff voltage at 0.1V. Various electrochemical performance parameters were tested, and the results are shown in Table 1.

[0101] Table 1

[0102] Coulombic efficiency Energy efficiency Voltage efficiency Example 1 99.5% 81.4% 87.58% Example 2 98.7% 82.5% 87.38% Example 3 98.2% 80.7% 87.42% Comparative Example 1 96.3% 70.4% 82.8%

[0103] As shown in Table 1, compared with Comparative Example 1, Examples 1-3 can significantly improve the electrocatalytic activity and specific surface area of ​​carbon felt by loading titanium nitride conductive framework and metal active sites. At the same time, it can enable zinc ions to be deposited uniformly, effectively reducing redox reaction polarization, thus significantly improving coulombic efficiency. Meanwhile, the electrode reaction kinetics are accelerated and the ion transport resistance is reduced, ultimately effectively improving its energy efficiency.

[0104] The following tests were performed on Example 1 and Comparative Example 1:

[0105] (1) The CV curve of the TiN / Sn@CF composite carbon felt electrode is as follows Figure 4 As shown, compared with the basic carbon felt, the TiN / Sn@CF composite electrode exhibits a more pronounced redox peak response and a higher peak current density, indicating that the composite structure can effectively promote Zn... 2+ / Zn redox process. Meanwhile, TiN / Sn@CF exhibits a smaller interpeak potential difference, indicating faster electron transfer kinetics and a higher electrochemical active area.

[0106] The cyclic test results of the electrode obtained in Comparative Example 1 are as follows: Figure 5As shown, the capacity of the comparative electrode continued to decay after 150 cycles, indicating that the electrode obtained in Example 1 has better cycle stability and better energy efficiency.

[0107] (2) Cyclic testing and rate testing at different current densities of the alkaline zinc-iron flow battery are as follows: Figure 6 and Figure 7 As shown, compared to an alkaline zinc-iron flow cell with a pristine carbon felt negative electrode, at 100 mA cm⁻¹... -2 High current density and 50mAh cm -2 Under high areal capacity conditions, the TiN / Sn composite electrode exhibits excellent long-term cycling stability, maintaining a coulombic efficiency above 98% for an extended period and operating stably for over 900 cycles, while the bare carbon felt electrode only maintains a lower coulombic efficiency and fails rapidly. Further rate testing shows that as the current density increases from 20 mA / cm²... -2 Increased to 300 mA cm -2 TiN / Sn@CF consistently maintains a higher coulombic efficiency than bare carbon felt.

[0108] In summary, this demonstrates that the composite electrode can effectively alleviate Zn 2+ The problems of uneven electron transport, current concentration, and dendrite-induced growth are mainly attributed to the enhanced electron transport capability of the TiN conductive framework, while the Sn nanoparticles provide zinc-loving active sites to lower the Zn nucleation energy barrier, further improving stability and utilization. This enables a uniform and reversible zinc deposition / stripping process, with broad application prospects.

[0109] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a TiN / Sn composite carbon felt electrode material, characterized in that, Includes the following steps: A tin source and a titanium source were pre-complexed in an organic solvent to obtain a Ti-O-Sn mixed precursor solution. The Ti-O-Sn mixed precursor solution was added to the aqueous phase solution of fluoride and mixed evenly to obtain a suspension. Carbon felt was added to the suspension, followed by a hydrothermal reaction to obtain the Sn-TiO2@CF precursor; The Sn-TiO2@CF precursor was placed in a nitrogen-containing environment and then subjected to segmented heat treatment under a protective atmosphere to obtain the TiN / Sn composite carbon felt electrode material.

2. The preparation method according to claim 1, characterized in that, The tin source is selected from at least one of tin acetylacetonate, stannous octoate, stannous chloride dihydrate and stannous oxalate, and the titanium source is selected from at least one of tetrabutyl titanate, isopropyl titanate and titanium tetrachloride; the molar ratio of tin in the tin source to titanium in the titanium source is (0.01–0.04):

1.

3. The preparation method according to claim 1, characterized in that, The pre-complexation reaction is carried out at a temperature of 20–65°C for a time of 0.5–3 h.

4. The preparation method according to claim 1, characterized in that, The concentration of the aqueous solution of the fluoride is 0.005–0.20 mol / L; the fluoride in the aqueous solution of the fluoride is selected from at least one of NaF, NH4F, KF and LiF; the molar ratio of fluorine in the fluoride to titanium in the titanium source is 0.05–0.25:

1.

5. The preparation method according to claim 1, characterized in that, Before adding carbon felt to the suspension, a pretreatment step of carbon felt is also included; the pretreatment is as follows: the carbon felt is washed with ethanol and water in sequence, then placed in an activator for activation treatment, then washed until neutral, and dried; The activator is dilute nitric acid; the activation treatment temperature is 60–90℃ and the time is 1–3h; the drying temperature is 50–80℃ and the time is 10–12h.

6. The preparation method according to claim 1, characterized in that, The hydrothermal reaction is carried out at a temperature of 120–200°C for a duration of 12–18 hours.

7. The preparation method according to claim 1, characterized in that, The nitrogen source is urea; the segmented heat treatment is as follows: the temperature is increased to 250–350℃ at a heating rate of 1–5℃ / min and held for 0.5–2h, then increased to 500–700℃ at a heating rate of 1–5℃ / min and held for 0.5–2h, and finally increased to 750–900℃ at a heating rate of 1–5℃ / min and held for 1–4h.

8. A TiN / Sn composite carbon felt electrode material, characterized in that, The TiN / Sn composite carbon felt electrode material is prepared using the preparation method of TiN / Sn composite carbon felt electrode material as described in any one of claims 1-7.

9. A TiN / Sn composite carbon felt electrode material as described in claim 8, characterized in that, The TiN / Sn composite carbon felt electrode material was applied to an alkaline zinc-iron flow battery.

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