A method for topotactic transformation synthesis of high-entropy hydroxyl oxide nanosheets

Abstract

The application provides a method for topological transformation synthesis of high-entropy hydroxyl oxide nanosheets, and belongs to the technical field of inorganic materials, and comprises the following steps: 1) component design: Ca2Fe2O5 brown iron ore type oxide is used as a matrix material for element doping; 2) combustion synthesis of a precursor: a low-temperature solution combustion synthesis method is used to in-situ composite the raw material of step 1), and brown iron ore type oxide powder rich in ordered oxygen vacancies is prepared by burning the obtained powder; 3) structure reconstruction: the brown iron ore type oxide powder rich in ordered oxygen vacancies obtained in step 2) is subjected to high-energy ultrasonic activation to form a high-activity ultrathin structure nanosheet, and then an ion exchange reaction is carried out to obtain the high-entropy hydroxyl oxide nanosheet electrocatalyst. Compared with traditional NiFe and CoFe hydroxide / hydroxyl oxide, the nanosheet catalyst also shows higher anti-Fe leaching capacity in the OER process. The assembled zinc-air battery can stably operate for more than 225 hours at a low charging voltage.

Description

Technical Field

[0001] This invention belongs to the field of inorganic materials technology, and specifically relates to a method for synthesizing high-entropy hydroxyl oxide nanosheets through topological transformation. Background Technology

[0002] The oxygen evolution reaction (OER) plays a crucial role in green energy conversion and storage technologies, such as hydrogen production and water splitting in metal-air batteries, and has attracted widespread attention. This is a multi-electron proton transfer process involving various oxygen intermediates, requiring highly efficient catalysts. Transition metal hydroxides and hydroxyoxides, particularly those based on Fe, Co, and Ni, are widely considered effective electrocatalysts for OER in alkaline environments. However, current metal hydroxide and hydroxyoxide catalysts struggle to strike a balance between activity and stability, especially regarding iron. Iron-deficient catalysts typically exhibit poor intrinsic activity, and stability issues due to iron leaching are prevalent in iron-containing catalysts when exposed to the high acid and alkaline conditions of OER.

[0003] Studies have shown that polymetallic, and even high-entropy, compositions induce additional lattice distortions and vacancies, which may enhance intermediate evolution and charge transfer in OERs. However, achieving homogeneous polymetallic compositions using common synthetic strategies such as coprecipitation and hydrothermal methods has proven challenging. This is due to variations in the reaction barriers of different metal cations, as well as differences in the nucleation and growth rates of their hydroxides. This underscores the need to develop a universal method for synthesizing polymetallic hydroxyl oxides. Summary of the Invention

[0004] To address the problems of existing technologies, this invention provides a method for synthesizing high-entropy hydroxyl oxide nanosheets via topological transformation. The powder preparation process is divided into two steps: combustion synthesis of the precursor and structural reconstruction. The resulting product is measured at 10 mA. cm -2 It exhibits an overpotential below 267 mV, making it one of the best-performing non-nickel-based catalysts. Compared to conventional NiFe and CoFe hydroxides / hydroxyoxides, this catalyst also demonstrates higher resistance to Fe leaching during the OER process. The assembled zinc-air battery was able to operate stably for over 225 hours at low charging voltage.

[0005] The technical solution provided by this invention is as follows:

[0006] This invention provides a method for synthesizing high-entropy hydroxyl oxide nanosheets via topological transformation, comprising the following steps:

[0007] 1) Composition design: Element doping is carried out with Ca2Fe2O5 limonite-type oxide (A2B2O5) as the matrix material. The doping element at the A site is an alkaline earth metal or a lanthanide metal element, and the doping element at the B site is a transition metal element;

[0008] 2) Combustion synthesis precursor: The raw materials in step 1) are in-situ compounded by the low-temperature solution combustion synthesis method, and the obtained powder is calcined at 800 - 1200 °C for 18 - 36 hours to prepare a limonite-type oxide powder rich in ordered oxygen vacancies;

[0009] 3) Structure reconstruction: The limonite-type oxide powder rich in ordered oxygen vacancies obtained in step 2) is activated by high-energy ultrasonic waves to undergo topological transformation and lamellar exfoliation to form highly active ultrathin structure nanosheets, and then an ion exchange reaction is carried out to obtain the high-entropy hydroxyoxide nanosheets.

[0010] Furthermore, the raw materials for element doping in step 1) are metal soluble salts and glycine, and the molar ratio of metal soluble salts to glycine is 2:1. The detailed ratio calculation of metal salts is carried out based on the limonite oxide with the molecular formula A2B2O5. The dosage of various metal salts is calculated according to the ratio of the doping elements at the Ca site, A site, Fe site, and B site as x:2 - x:y:2 - y. The molecular formula of the doped limonite-type oxide is Ca x A 2-x Fe y B 2-y O5. The value ranges of x and y are 0 < x < 2 and 0 < y < 2 respectively. For example, Ca 1.8 La 0.2 Fe 1.8 Co 0.2 O5.

[0011] Furthermore, the doping element at the A site in step 1) is selected from at least one of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), magnesium (Mg), strontium (Sr), and barium (Ba).

[0012] Furthermore, the doping element at the B site in step 1) is selected from at least one of titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), and zinc (Zn). Due to the synthesis of perovskite materials, the ionic radii of doping at the A site and B site need to meet certain conditions, and are limited to the above elements after screening.

[0013] Further, in step 2), the low-temperature solution combustion synthesis method includes: preparing a mixed solution of metal salts containing the elements from step 1); complexing and evaporating the mixed solution to form a gel; and then subjecting it to a rapid, spontaneous combustion reaction at 200-500°C to obtain a powder. The metal salts are water-soluble salts of the aforementioned A-site and B-site doping elements, such as chlorides, nitrates, and sulfates.

[0014] Further, in step 3), the high-energy ultrasonic activation frequency is 20-50 kHz, the input power is 500-1000 W, and the ultrasonic activation time is 3-5 hours. During the ultrasonic activation process, due to the instability of Ca element at site A, it dissolves along the oxygen vacancy channel, causing the structure to collapse. The original octahedral point-shared structure becomes edge-shared, undergoing topological transformation and lamellar exfoliation, forming highly active ultrathin nanosheets.

[0015] Further, the ion exchange in step 3) is carried out in a metal salt solution with a solubility less than that of calcium hydroxide. The metal salt solution for ion exchange is selected from at least one of the following soluble metal salts: magnesium (Mg), cerium (Ce), praseodymium (Pr), samarium (Sm), rubidium (Ru), chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu), and zinc (Zn). The soluble metal salt is a water-soluble salt, such as chlorides, nitrates, or sulfates. The concentration of the metal salt solution is 0.01~0.03 mol / L. In this step, in a weakly acidic metal salt solution, due to the difference in solubility, the remaining Ca ions located within the ultrathin nanosheet layer undergo ion exchange to obtain a structurally reconstructed high-entropy hydroxyl oxide nanosheet electrocatalyst. The amount of solute used in the metal salt solution depends on whether the ion exchange is partial or complete. Specifically, the amount of metal salt used to completely or partially replace the calcium element in the nanosheets obtained by ultrasonic activation is determined based on the calcium content. If the calcium element in the nanosheet is completely replaced, an excess of solute is added to the metal salt solution; if the calcium element in the nanosheet is partially replaced, an insufficient amount of solute is added to the metal salt solution.

[0016] The present invention also provides high-entropy hydroxyl oxide nanosheets prepared by the method.

[0017] The present invention also provides the application of the high-entropy hydroxyl oxide nanosheets as an electrocatalyst in zinc-air batteries.

[0018] This invention proposes a general method for preparing multi-component transition metal hydroxyl oxide ultrathin nanosheets from limonite oxide for efficient and durable OER catalysis. First, a calcium-rich limonite oxide precursor can be rapidly synthesized via solution combustion and calcination, exhibiting a flexible structure and facilitating elemental adjustment. Subsequently, with high-energy ultrasonic input, Ca... 2+Significant dissolution occurs, and the point-shared structure of the metal-oxygen octahedron transforms into an edge-shared structure, leading to structural collapse and a topological transformation to the hydroxyl oxide phase. Finally, ion exchange is performed to achieve the synthesis of high-entropy hydroxyl oxide ultrathin nanosheets.

[0019] The beneficial effects of this invention include at least the following:

[0020] 1. Compared to traditional high-entropy hydroxide preparation methods such as co-precipitation and hydrothermal processes, this method involves a strong redox reaction, and combustion can proceed spontaneously once it occurs. 2. The synthesized high-entropy hydroxyoxides exhibit uniform elemental distribution without segregation, and due to their ultrathin nanosheet structure, active sites are fully exposed. 3. This method has a certain degree of versatility, allowing for the adjustment of elemental ratios to prepare electrocatalysts with different catalytic properties. The ultrathin nanosheets of the multi-component hydroxyoxides prepared in this invention provide an ultra-low overpotential of less than 300 mV, effectively reducing energy consumption. The enhanced iron leaching resistance significantly improves catalytic stability. The assembled zinc-air battery can operate stably for over 225 hours at low charging voltage. The preparation method provided by this invention offers valuable insights into the synthesis of multi-component hydroxyoxides and highlights the enormous potential of multi-component catalysts. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0022] Figure 1 These are the XRD patterns of the crystal form transformation before and after structural reconstruction in Example 1 of this invention.

[0023] Figure 2 This is a TEM electron microscope image of CoFeZn hydroxyoxide in Example 1 of the present invention.

[0024] Figure 3 This is an EDS surface scan of the CoFeZn hydroxy oxide in Example 1 of the present invention. Detailed Implementation

[0025] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0026] Example 1

[0027] Using Ca2CoFeO5 limonite oxide as a precursor, calcium nitrate, cobalt nitrate, ferric nitrate, and glycine were dissolved in water in a molar ratio of 2.0:1.0:1.0:2.0 to prepare a solution. The mixed solution was complexed and concentrated by evaporation to form a gel. The gel was heated at 200 °C, and after volatilization, concentration, and combustion reactions, oxide powder was obtained. This powder was then calcined at 1100 °C at a heating rate of 10 °C / min for 24 hours to obtain Ca2CoFeO5 limonite oxide. The prepared limonite powder was subjected to high-energy ultrasonic treatment in 1M KOH solution for 3 hours. The high-energy ultrasonic activation frequency was 20 kHz, and the input power was 500 W. The powder was then collected by centrifugation and washing. 400 mg of the ultrasonically activated powder was immersed in 40 ml of 0.01 M ZnCl2 solution for 2 hours for ion exchange to obtain CoFeZn hydroxyoxide. A 10 mA measurement was obtained. cm -2 With an overpotential of 267mV, the assembled zinc-air battery can operate stably for 242 hours.

[0028] Figure 1 This is the XRD pattern of the crystal form transformation before and after structural reconstruction in Example 1 of this invention. The lower part shows the spectrum before structural reconstruction, indicating that the oxide powder has a limonite crystal form and is well-crystallized; the upper part shows the spectrum after structural reconstruction, indicating that the limonite structure collapsed after ultrasonic activation, and spectral lines belonging to hydroxyl oxides appeared. The reason for this is that with the high energy input of ultrasound, Ca... 2+ Significant dissolution occurs, and the point-shared structure of the metal-oxygen octahedron transforms into an edge-shared structure, leading to structural collapse and a topological transformation to the hydroxyl oxide phase.

[0029] Figure 2 This is a TEM image of the CoFeZn hydroxyl oxide from Example 1 of this invention. It can be seen that the nanosheets are approximately 100 nm in size, exhibiting an ultrathin nanoscale sheet-like morphology.

[0030] Figure 3 These are EDS surface scans of the CoFeZn hydroxyl oxides in Example 1 of this invention. The top left image is a dark-field topography image, and the other three images are the EDS surface scan results of Co, Fe, and Zn at corresponding positions. Analysis of the high-magnification EDS surface scan results shows that Co, Fe, and Zn are uniformly distributed, with no elemental segregation, and that Zn has uniformly replaced all the remaining Ca after ultrasonic activation. 2+ .

[0031] Table 1 shows the energy dispersive spectroscopy (EDS) data of the CoFeZn hydroxyoxides in Example 1. It can be seen that the contents of Co, Fe, and Zn in the hydroxyoxides are similar.

[0032] Table 1

[0033]

[0034] Example 2

[0035] With Ca2Co 0.6 Fe 0.8 Mn 0.6 Using O5 limonite-type oxide as a precursor, calcium nitrate, cobalt nitrate, ferric nitrate, manganese nitrate, and glycine were dissolved in water in a molar ratio of 2.0:0.6:0.8:0.5:2.0 to prepare a solution. The mixed solution was then complexed and concentrated by evaporation to form a gel. The gel was heated at 200 °C, and after volatilization, concentration, and combustion reactions, oxide powder was obtained. Subsequently, it was calcined at 1200 °C at a heating rate of 10 °C / min for 24 hours to obtain Ca2Co. 0.6 Fe 0.8 Mn 0.6 O5 limonite oxide. The prepared limonite powder was subjected to high-energy ultrasonic treatment for 3 hours. The high-energy ultrasonic activation frequency was 20 kHz, the input power was 500 W, and the ultrasonic activation time was 3.5 hours. 400 mg of the ultrasonically activated powder was immersed in 40 ml of 0.01 M ZnCl2 solution for 2 hours for ion exchange. The powder was then collected by centrifugation and washing to obtain CoFeMnZn hydroxyoxide. A 10 mA value was measured. cm -2 With an overpotential of 290 mV, the assembled zinc-air battery can operate stably for 253 hours.

[0036] Example 3

[0037] With Ca2Co 0.4 Fe 0.8 Mn 0.4 Cu 0.4 Using O5 limonite-type oxide as a precursor, calcium nitrate, cobalt nitrate, ferric nitrate, manganese nitrate, and glycine were dissolved in water in a molar ratio of 2.0:0.4:0.8:0.4:0.4:2.0 to prepare a solution. The mixed solution was then complexed and concentrated by evaporation to form a gel. The gel was heated at 200 °C, and after volatilization, concentration, and combustion reactions, oxide powder was obtained. Subsequently, it was calcined at 1200 °C at a heating rate of 10 °C / min for 24 hours to obtain Ca2Co. 0.4 Fe 0.8 Mn 0.4 Cu 0.4O5 limonite oxide. The prepared limonite powder was subjected to high-energy ultrasonic treatment for 3 hours at a frequency of 30 kHz and an input power of 600 W. The powder was then collected by centrifugation and washing. 400 mg of the ultrasonically activated powder was immersed in 40 ml of 0.01 M NiCl2 solution for 2 hours for ion exchange to obtain CoFeMnCuNi hydroxyoxide. The measured value was 10 mA. cm -2 With an overpotential of 297 mV, the assembled zinc-air battery can operate stably for 236 hours.

[0038] Example 4

[0039] With Ca 1.0 La 1.0 Fe 1.8 Co 0.2 Using O5 limonite-type oxide as a precursor, calcium nitrate, lanthanum nitrate, ferric nitrate, cobalt nitrate, and glycine were dissolved in water in a molar ratio of 1.0:1.0:1.8:0.2:2.0 to prepare a solution. The mixed solution was then complexed and concentrated by evaporation to form a gel. The gel was heated at 200 °C, and after volatilization, concentration, and combustion reactions, oxide powder was obtained. This powder was then calcined at 1200 °C at a heating rate of 10 °C / min for 24 hours to obtain Ca. 1.0 La 1.0 Fe 1.8 Co 0.2 O5 limonite oxide. The prepared limonite powder was subjected to high-energy ultrasonic treatment for 3 hours at a frequency of 20 kHz and an input power of 500 W. The powder was then collected by centrifugation and washing. 400 mg of the ultrasonically activated powder was immersed in 40 ml of 0.01 M MnCl2 solution for 2 hours for ion exchange to obtain LaCoFeMn hydroxyoxide. The measured value was 10 mA. cm -2 With an overpotential of 299 mV, the assembled zinc-air battery can operate stably for 226 hours.

[0040] Comparative Example 1

[0041] Using Ca2Fe2O5 limonite oxide as a precursor, calcium nitrate, ferric nitrate, and glycine were dissolved in water at a molar ratio of 1.0:1.0:1.0 to prepare a solution. The mixed solution was then complexed and concentrated by evaporation to form a gel. The gel was heated at 200 °C, and after volatilization, concentration, and combustion reactions, oxide powder was obtained. This powder was then calcined at 1100 °C at a heating rate of 10 °C / min for 24 hours to obtain Ca2Fe2O5 limonite oxide. Subsequent high-energy ultrasound and ion exchange processes were performed as in Example 1 to obtain FeZn hydroxyoxides. A 10 mA measurement was obtained. cm -2 With an overpotential of 355 mV, the assembled zinc-air battery can operate stably for 77 hours.

[0042] Compared with Example 1, in Comparative Example 1, step 1) did not involve doping the AB site of Ca2Fe2O5 limonite oxide. The product overpotential increased and the battery running time decreased, indicating that the dopant element can interact with the matrix element, reduce the energy barrier in the OER reaction process, and promote the occurrence of the OER reaction process.

[0043] Comparative Example 2

[0044] Using Ca2CoFeO5 limonite-type oxide as a precursor, the powder was collected after high-energy ultrasonic activation. No ion exchange was performed; other steps were the same as in Example 1 to obtain CaCoFe hydroxy oxide. A 10 mA reading was measured. cm -2 With an overpotential of 330 mV, the assembled zinc-air battery can operate stably for 91 hours.

[0045] Compared with Example 1, in Comparative Example 2, no ion exchange was performed in step 3), the product overpotential increased and the battery running time decreased. This indicates that replacing the inert element Ca in the OER reaction process during ion exchange is beneficial to promoting the OER reaction, reducing the overpotential required for the reaction, and increasing the running time of the zinc-air battery.

[0046] The above description is merely a specific embodiment 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 technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for synthesizing high-entropy hydroxyl oxide nanosheets through topological transformation, characterized in that, Includes the following steps: 1) Composition design: Ca2Fe2O5 limonite-type oxide is used as the matrix material for element doping. The A-site doping element is an alkaline earth metal or a lanthanide metal element, and the B-site doping element is a transition metal element. 2) Combustion synthesis precursor: The raw materials in step 1) are synthesized in situ using a low-temperature solution combustion synthesis method. The resulting powder is calcined at 800~1200℃ and held for 18~36 hours to prepare limonite-type oxide powder rich in ordered oxygen vacancies. 3) Structural reconstruction: The goethite-type oxide powder rich in ordered oxygen vacancies obtained in step 2) is activated by high-energy ultrasonication to form highly active ultrathin nanosheets. Then, an ion exchange reaction is carried out to obtain the high-entropy hydroxyl oxide nanosheets. Step 1) The molecular formula of the doped limonite oxide is Ca x A 2-x Fe y B 2-y O5, the amount of each metal salt is calculated based on the ratio of Ca-site dopant, A-site dopant, Fe-site dopant, and B-site dopant as x:2-x:y:2-y, where 0 <x<2,0<y<2; The ion exchange described in step 3) is carried out in a metal salt solution with a solubility less than that of calcium hydroxide.

2. The method for synthesizing high-entropy hydroxyl oxide nanosheets by topological transformation according to claim 1, characterized in that, Step 1) The raw materials for element doping are metal soluble salt and glycine, with a molar ratio of metal soluble salt to glycine of 2:

1.

3. The method for synthesizing high-entropy hydroxyl oxide nanosheets by topological transformation according to claim 1, characterized in that, The A-site doping element mentioned in step 1) is selected from at least one of lanthanum, cerium, praseodymium, neodymium, samarium, magnesium, strontium, and barium; The B-site doping element is selected from at least one of titanium, vanadium, chromium, manganese, cobalt, nickel, copper, and zinc.

4. The method for synthesizing high-entropy hydroxyl oxide nanosheets by topological transformation according to claim 3, characterized in that, In step 2), the low-temperature solution combustion synthesis method includes: preparing a mixed solution of metal salts containing the elements of step 1), complexing and evaporating the mixed solution to form a gel, and then conducting a rapid spontaneous combustion reaction at 200~500℃ to obtain powder.

5. The method for synthesizing high-entropy hydroxyl oxide nanosheets by topological transformation according to claim 1, characterized in that, Step 3) The high-energy ultrasonic activation frequency is 20~50 KHz, the input power is 500~1000 W, and the ultrasonic activation time is 3~5 hours.

6. The method for synthesizing high-entropy hydroxyl oxide nanosheets by topological transformation according to claim 1, characterized in that, The metal salt solution for ion exchange is selected from at least one of the soluble metal salts of magnesium, cerium, praseodymium, samarium, rubidium, chromium, manganese, nickel, copper, and zinc, and the concentration of the metal salt solution is 0.01~0.03 mol / L.

7. High-entropy hydroxyl oxide nanosheets prepared by the method according to any one of claims 1 to 6.

8. The application of the high-entropy hydroxyl oxide nanosheets of claim 7 as an electrocatalyst in a zinc-air battery.

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