Hollow spherical nickel-iron oxide and preparation method and electrocatalyst thereof

Abstract

The application provides a hollow spherical nickel-iron oxide and a preparation method and an electrocatalyst thereof, and the preparation method comprises the following steps: mixing a nickel source, an iron source, a saccharide carbon source template agent and a solvent to obtain a precursor solution; performing spray atomization treatment on the precursor solution to obtain atomized droplets; performing pyrolysis treatment on the atomized droplets to obtain a pyrolysis product; and performing calcination treatment on the pyrolysis product to obtain the hollow spherical nickel-iron oxide. The amorphous nickel-iron oxide hollow microspherical catalyst is prepared by the method of saccharide carbon source template agent + spray pyrolysis, and through the synergistic effect of the amorphous structure and the hollow morphology, the specific surface area and the active site exposure are increased, the catalytic activity and stability are improved, the efficient and stable operation of the catalyst under medium and low temperature and high current density is realized, the actual demand of industrial hydrogen production is met, and the total cost of hydrogen energy production is reduced.

Description

Technical Field

[0001] This invention belongs to the field of catalyst materials technology, and relates to a hollow spherical nickel-iron oxide, its preparation method, and an electrocatalyst. Background Technology

[0002] Spray pyrolysis technology is a highly efficient, large-scale preparation process for functional metal oxides based on the principle of spray drying. This process shows great potential in the field of green hydrogen electrocatalysts, providing a new pathway to overcome the bottleneck of large-scale anion exchange membrane water electrolysis (AEMWE). As a low-cost green hydrogen solution, anion exchange membrane water electrolysis is crucial for the sustainable hydrogen economy transition, but due to the lack of efficient oxygen evolution reaction (OER) catalysts, it cannot be scaled up to industrial current densities (>1 A / cm²). 2 Stable operation is possible, but large-scale production is hindered.

[0003] NiFe-based catalysts are preferred for oxygen evolution reaction catalysts in anion exchange membrane water electrolysis systems due to their low cost and good initial activity. However, they suffer from structural instability and insufficient active sites under harsh operating conditions. Traditional modification strategies can optimize performance, but they rely on complex processes such as hydrothermal treatment, templates, and atomic layer deposition, making it difficult to balance scalability and structural precision, and thus failing to meet the needs of large-scale production.

[0004] In industrial production, additives with specific functions are typically added to the precursor solution to optimize process performance and product quality. These additives play multiple key regulatory roles: first, they adjust the physicochemical properties of the precursor solution, optimizing atomization and droplet distribution to facilitate the formation of hollow microspheres; second, they complex with Ni and Fe ions to improve the elemental uniformity of the product; third, they regulate the reaction temperature, inhibiting high-temperature crystallization to stabilize the amorphous phase; and fourth, they construct hollow structures using carbon-based intermediates, promoting the decomposition of organic components and improving product purity and yield. This process enables the large-scale synthesis of amorphous NiFe oxide hollow microspheres, providing an important solution for overcoming the bottleneck in the preparation of amorphous TMOs and promoting the industrialization of anion exchange membranes.

[0005] CN118996508A discloses a core-shell structured FeOOH / NiOOH electrocatalyst, prepared via a stepwise deposition method. NiOOH forms the shell and FeOOH the core, utilizing the shell structure to stabilize Fe sites for use in the OER process of water electrolysis to produce hydrogen. The core technical measures are: first, a NiOOH substrate is prepared; then, an FeOOH core layer is loaded via electrochemical deposition, controlling the deposition voltage at 1.2-1.5V and the deposition time at 30-60min, ultimately obtaining the core-shell structured catalyst. The catalyst operates at 10mA / cm². 2 The overpotential at the current density is 220mV.

[0006] CN113026045A discloses a Ni(OH)₂ / FeOOH nanoflower composite catalyst supported on nickel foam, prepared by hydrothermal synthesis, for use as a bifunctional catalytic catalyst for OER and HER in water electrolysis to produce hydrogen. The core technical measures are as follows: using nickel foam as a substrate, nickel nitrate, ferric nitrate, and urea are mixed in a certain proportion, and deionized water is added to form a precursor solution. The solution is then subjected to a hydrothermal reaction at 120-150℃ for 4-6 hours, allowing Ni(OH)₂ / FeOOH nanoflowers to grow in situ on the surface of the nickel foam. The product is a crystalline composite oxide, which can be obtained at 100 mA / cm². 2 The OER overpotential is 296mV and the HER process potential is 290mV at the current density, and hydrogen production by water electrolysis can be achieved by powering the system with solar cells.

[0007] The nickel-iron composite catalyst prepared by the above scheme has problems such as poor adaptability to high current conditions and insufficient stability. In addition, due to the limited specific surface area and the structure that easily causes bubble aggregation, the mass transfer resistance increases and the catalytic activity decreases. Furthermore, during long-term operation, phenomena such as loss of active sites, structural damage, or catalyst shedding are prone to occur, making it difficult to meet the industrial green hydrogen production requirements and restricting its industrial application. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a hollow spherical nickel-iron oxide catalyst, its preparation method, and an electrocatalyst. This invention prepares an amorphous hollow nickel-iron oxide microsphere catalyst using a sugar-based carbon source template agent and spray pyrolysis. Through the synergistic effect of the amorphous structure and hollow morphology, the specific surface area and active site exposure are increased, enhancing catalytic activity and stability. This enables the catalyst to operate efficiently and stably at medium and low temperatures and high current densities, meeting the actual needs of industrial hydrogen production and reducing the overall cost of hydrogen production.

[0009] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing hollow spherical nickel-iron oxide, the method comprising the following steps: A precursor solution is obtained by mixing a nickel source, an iron source, a sugar-based carbon source template agent, and a solvent. The precursor solution was spray-atomized to obtain atomized droplets; The atomized droplets are subjected to pyrolysis to obtain pyrolysis products, and the pyrolysis products are then calcined to obtain the hollow spherical nickel-iron oxide.

[0010] This invention uses a carbohydrate carbon source as a template agent to prepare a uniform precursor solution. The precursor solution is then atomized into independent droplets. The carbohydrate carbon source (taking glucose as an example) contains five hydroxyl groups and one aldehyde group, providing multiple oxygen atoms as electron donors. Its flexible carbon chain can adapt to Ni... 2+ Fe 2+ / Fe 3+ Different coordinations form stable five- / six-membered ring chelates, significantly enhancing the dispersion uniformity of metal ions within the precursor droplets. The multi-hydroxyl hydrophilic framework maintains the droplets in a "high boiling point-high viscosity" state within the high-temperature zone of spray pyrolysis, slowing the solvent evaporation rate and preventing instantaneous supersaturation and nucleation of metal salts. Simultaneously, glucose undergoes instantaneous pyrolysis at 400℃~600℃, releasing gases such as CO / CO2 / H2O and generating inward expansion forces, thus constructing a mesoporous shell (10nm~20nm) and internal cavity in one step, achieving a controllable balance between a "dense-hollow" structure. This not only solves the problems of easy breakage of hollow microspheres and loss of active components but also increases the specific surface area through in-situ pore formation, providing a high density of active sites for OER / HER and ensuring rapid debubbling and mass transfer at high current densities.

[0011] Spray atomization ensures that the composition and size of each atomized droplet are highly uniform, thus guaranteeing the uniformity of particle size and composition of the hollow spheres produced. Subsequent pyrolysis treatment involves solvent evaporation and metal salt decomposition of the atomized droplets, spontaneously forming hollow spheres through internal material diffusion. Finally, calcination removes residual carbon impurities to obtain hollow spherical nickel-iron oxide. The hollow spherical nickel-iron oxide, through the synergistic effect of its amorphous structure and hollow morphology, increases specific surface area and active site exposure, thereby exhibiting high catalytic activity and stability.

[0012] Preferably, the nickel source includes any one or a combination of at least two of nickel nitrate, nickel acetate, or nickel chloride. Typical but non-limiting combinations include combinations of nickel nitrate and nickel chloride, combinations of nickel acetate and nickel chloride, or combinations of nickel nitrate and nickel acetate.

[0013] Preferably, the iron source includes any one or a combination of at least two of ferric nitrate, ferric chloride, or ferric acetate. Typical but non-limiting combinations include combinations of ferric nitrate and ferric acetate, ferric chloride and ferric acetate, or ferric nitrate and ferric chloride, etc.

[0014] Preferably, the carbohydrate carbon source template agent includes any one or a combination of at least two of glucose, fructose, or sucrose.

[0015] Preferably, the solvent includes water and / or ethanol.

[0016] Preferably, the molar ratio of nickel in the nickel source to iron in the iron source is 1:(0.3~0.8), for example: 1:0.3, 1:0.4, 1:0.6, 1:0.7 or 1:0.8, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0017] Preferably, the total molar concentration of metal ions in the precursor solution is 0.05 mol / L to 0.2 mol / L, for example: 0.05 mol / L, 0.08 mol / L, 0.1 mol / L, 0.15 mol / L or 0.2 mol / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0018] Preferably, the mass concentration of the carbohydrate carbon source template agent in the precursor solution is 5 g / L to 20 g / L, for example: 5 g / L, 8 g / L, 10 g / L, 15 g / L or 20 g / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] Preferably, the atomizing gas used in the spray atomization process includes nitrogen and / or air.

[0020] Preferably, the gas flow rate of the spray atomization treatment is 0.5L / min to 6L / min, for example: 0.5L / min, 1L / min, 2L / min, 4L / min or 6L / min, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] Preferably, the feed rate of the precursor solution for the spray atomization treatment is 5L / h to 10L / h, for example: 5L / h, 6L / h, 8L / h, 9L / h or 10L / h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] Preferably, the diameter of the atomized droplets is 1μm to 5μm, for example: 1μm, 2μm, 3μm, 4μm or 5μm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] This invention controls the solution feed rate and gas flow rate of the spray atomization process to ensure that the atomized droplets are within a suitable range, thereby obtaining hollow spherical oxides with uniform particle size and stable structure. If the droplets are too large, the solvent evaporation rate from the surface will be much faster than the diffusion rate of the solute from the inside to the center. Although this is beneficial for forming hollow particles, the excessively thick shell layer is prone to cracking or collapse due to internal stress during subsequent calcination. If the droplets are too small, solid particles may be formed, or the resulting hollow spherical shell layer may be too thin and have poor mechanical strength.

[0024] Preferably, the temperature of the pyrolysis treatment is 400℃~800℃, for example: 400℃, 500℃, 600℃, 700℃ or 800℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] Preferably, the pyrolysis treatment time is 10s to 30s, for example: 10s, 15s, 20s, 25s or 30s, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] This invention precisely matches the temperature and time of the pyrolysis treatment, ensuring that the metal salt is completely converted into an amorphous oxide while avoiding crystallization and structural collapse.

[0027] Preferably, the calcination temperature is 200℃~400℃, for example: 200℃, 250℃, 300℃, 350℃ or 400℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] Preferably, the calcination time is 1h to 2h, for example: 1h, 1.2h, 1.5h, 1.8h or 2h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] In a second aspect, the present invention provides a hollow spherical nickel-iron oxide, which is prepared by the preparation method described in the first aspect.

[0030] Thirdly, the present invention provides an electrocatalyst comprising hollow spherical nickel-iron oxide as described in the second aspect.

[0031] The hollow spherical nickel-iron oxide catalyst described in this invention exhibits good OER and HER catalytic activity and can also be used for chemical chain hydrogen production.

[0032] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0033] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention prepares amorphous nickel-iron oxide hollow microsphere catalysts by using a sugar-based carbon source template agent + spray pyrolysis. Through the synergistic effect of the amorphous structure and hollow morphology, the specific surface area and the exposure of active sites are increased, thereby improving the catalytic activity and stability. The catalyst can achieve high performance at medium and low temperatures (200℃~500℃) and high current densities (≥1000mA / cm²). 2 It can operate efficiently and stably under the conditions of industrial hydrogen production, meet the actual needs of industrial hydrogen production, and reduce the total cost of hydrogen production.

[0034] (2) The BET of the hollow spherical nickel-iron oxide of the present invention can reach 133m. 2 / g or more, OER 10mA / cm2 Overpotentials can reach over 168mV, while HER's is 10mA / cm. 2 Overpotential can reach over 18mV, 500mA / cm 2 After running for 600 hours, the activity decay rate can be controlled within 4.6%, the CH4 conversion rate can reach over 95.6%, and the purity of the produced hydrogen can reach over 84.6%. Attached Figure Description

[0035] Figure 1 This is the XRD pattern of the hollow spherical nickel-iron oxide prepared in Example 1.

[0036] Figure 2 This is a SEM image of the hollow spherical nickel-iron oxide obtained in Example 1.

[0037] Figure 3 This is a TEM image of the hollow spherical nickel-iron oxide obtained in Example 1.

[0038] Figure 4 This is a SEM image of the hollow spherical nickel-iron oxide obtained in Example 2.

[0039] Figure 5 This is a SEM image of the hollow spherical nickel-iron oxide obtained in Example 3. Detailed Implementation

[0040] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0041] The scope of this invention can be defined by lower and upper limits. The selected lower and upper limits define the boundaries of a specific range. The range defined in this way can be defined by the inclusion or exclusion of endpoints. Any endpoint can be independently selected for inclusion or exclusion, and all lower and upper limits can be arbitrarily combined to form new ranges. That is, any lower limit can be combined with any upper limit to form an effective range. For example, if the ranges of 60~120 and 80~110 are listed for specific parameters, it should be understood that the ranges of 60~110 and 80~120 also fall within the scope of this invention. In addition, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are also listed, then all ranges of 1~3, 1~4, 1~5, 2~3, 2~4 and 2~5 fall within the scope of this invention. In this invention, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0~5" means that all real numbers between 0 and 5 have been fully listed in this document, and "0~5" is only a shortened representation of this set of numerical combinations. When a parameter is expressed as an integer ≥2, it is equivalent to listing positive integers that meet the requirements, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. When a parameter is expressed as an integer selected from "2~10", it is equivalent to listing any integer among 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0042] In this invention, "a combination of at least two" refers to a quantity greater than or equal to 2 unless otherwise specified. For example, "any one or a combination of at least two" means that any one of the listed items can be selected, or a combination of at least two of the listed items formed in a manner that does not conflict and enables the implementation of this invention. In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" cover any one of two or more related listed items, as well as any and all combinations of the related listed items. The arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" means a set consisting of A, B, and combinations of A and B, where "containing A and / or B" can be understood, depending on the context of the statement, as containing A, containing B, or simultaneously containing both A and B. In this invention, "optional" means that the corresponding feature, component, step or solution is not necessary, that is, it is selected from either "with" or "without". If there are multiple "optional" limitations in a technical solution, unless otherwise specified and there is no technical conflict or mutual constraint, each "optional" limitation is independent and does not affect the others.

[0043] In this invention, technical features or solutions described using open-ended terms such as "comprising" or "including" do not exclude additional non-conflicting elements beyond the listed elements unless otherwise specified. They are considered to disclose both closed-ended features or solutions consisting solely of the listed elements and open-ended features or solutions that may include additional non-conflicting elements beyond the listed elements. For example, if A includes a1, a2, and a3, unless otherwise specified, this means that A can consist only of a1, a2, and a3, or it can include other non-conflicting elements based on a1, a2, and a3. This corresponds to the disclosure of technical solutions such as "A consists of a1, a2, and a3," "A is selected from a1, a2, and a3," and "A not only includes a1, a2, and a3, but may also include other non-conflicting elements." All embodiments and optional embodiments of this invention, unless otherwise specified and without technical conflict, can be combined to form new technical solutions, and such combinations fall within the scope of this invention. The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various locations throughout the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this invention can be combined with other embodiments that do not conflict with the technology. The ordinal numbers "first," "second," "third," and "fourth," etc., used in the expressions "first aspect," "second aspect," "third aspect," and "fourth aspect" in this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly specifying the importance or quantity of the indicated technical features. They serve only as a non-exhaustive enumeration and do not constitute a closed limitation on quantity.

[0044] In this invention, the order in which the steps are written in the methods described in each embodiment does not imply a strict execution order. The actual execution order of each step should be determined according to its function and possible internal logic. Unless otherwise specified, all steps of this invention can be executed in the order in which they are written or in any order that does not conflict with the technology.

[0045] Example 1 This embodiment provides a hollow spherical nickel-iron oxide, which is prepared by the following method: Nickel nitrate, ferric nitrate, glucose, and deionized water were mixed and stirred at 40°C for 40 minutes until completely dissolved, yielding a precursor solution with a nickel ion molar concentration of 0.1 mol / L, an ferric ion molar concentration of 0.06 mol / L, and a glucose mass concentration of 12.5 g / L. The precursor solution was spray-atomized using nitrogen gas at a flow rate of 1 L / min and the feed rate of the precursor solution was 8 L / h, resulting in atomized droplets with a diameter of 2 μm. The atomized droplets were pyrolyzed at 500℃ for 20s, and the pyrolysis products were collected by a cyclone separator. The pyrolysis products were then calcined at 350℃ for 1.5h to obtain the hollow spherical nickel-iron oxide.

[0046] The XRD pattern of the hollow spherical nickel-iron oxide is as follows: Figure 1 As shown, by Figure 1 As can be seen, the hollow spherical nickel-iron oxide has no obvious crystallization diffraction peaks. The SEM image of the hollow spherical nickel-iron oxide is shown below. Figure 2 As shown, the TEM image of the hollow spherical nickel-iron oxide is as follows. Figure 3 As shown, by Figure 2-3 It can be seen that the hollow spherical nickel-iron oxide has a spherical hollow structure with an outer diameter of 0.7 μm and a shell thickness of 80 nm.

[0047] Example 2 This embodiment provides a hollow spherical nickel-iron oxide, which is prepared by the following method: Nickel nitrate, ferric nitrate, sucrose, and deionized water were mixed and stirred at 40°C for 40 min until completely dissolved to obtain a precursor solution with a nickel ion molar concentration of 0.1 mol / L, an ferric ion molar concentration of 0.04 mol / L, and a sucrose mass concentration of 10 g / L. The precursor solution was spray-atomized using air as the atomizing gas at a flow rate of 6 L / min and the feed rate of the precursor solution was 10 L / h, resulting in atomized droplets with a diameter of 1 μm. The atomized droplets were pyrolyzed at 450°C for 15 seconds, and the pyrolysis products were collected by a cyclone separator. The pyrolysis products were then calcined at 400°C for 1 hour to obtain the hollow spherical nickel-iron oxide.

[0048] The SEM image of the hollow spherical nickel-iron oxide is as follows: Figure 4 As shown, by Figure 4 It can be seen that the hollow spherical nickel-iron oxide has a spherical hollow structure with an outer diameter of 0.65 μm and a shell thickness of 70 nm.

[0049] Example 3 This embodiment provides a hollow spherical nickel-iron oxide, which is prepared by the following method: Nickel acetate, ferric acetate, glucose, and deionized water were mixed and stirred at 40°C for 40 minutes until completely dissolved to obtain a precursor solution with a nickel ion molar concentration of 0.1 mol / L, an ferric ion molar concentration of 0.08 mol / L, and a glucose mass concentration of 20 g / L. The precursor solution was spray-atomized using air as the atomizing gas at a flow rate of 0.5 L / min and the feed rate of the precursor solution was 5 L / h, resulting in atomized droplets with a diameter of 5 μm. The atomized droplets were pyrolyzed at 550℃ for 25s, and the pyrolysis products were collected by a cyclone separator. The pyrolysis products were then calcined at 200℃ for 1.5h to obtain the hollow spherical nickel-iron oxide.

[0050] The SEM image of the hollow spherical nickel-iron oxide is as follows: Figure 5 As shown, by Figure 5 It can be seen that the hollow spherical nickel-iron oxide has a spherical hollow structure with an outer diameter of 0.73 μm and a shell thickness of 90 nm.

[0051] Example 4 The only difference between this embodiment and Embodiment 1 is that the diameter of the atomized droplets is controlled to be 0.5 μm; all other conditions and parameters are exactly the same as in Embodiment 1.

[0052] Example 5 The only difference between this embodiment and Embodiment 1 is that the diameter of the atomized droplets is controlled to be 6 μm; all other conditions and parameters are exactly the same as in Embodiment 1.

[0053] Example 6 The only difference between this embodiment and Embodiment 1 is that the temperature of the pyrolysis treatment is controlled at 300°C, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0054] Example 7 The only difference between this embodiment and Embodiment 1 is that the temperature of the pyrolysis treatment is controlled at 900℃, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0055] Example 8 The only difference between this embodiment and Embodiment 1 is that the pyrolysis treatment time is controlled to be 5 seconds, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0056] Example 9 The only difference between this comparative example and Example 1 is that the pyrolysis treatment time is controlled at 40 seconds, while the other conditions and parameters are exactly the same as in Example 1.

[0057] Comparative Example 1 This comparative example provides a hollow spherical nickel-iron oxide using a template method, which is prepared by the following method: Glucose was mixed with deionized water to prepare a glucose concentration of 100 g / L. After stirring until completely dissolved, the solution was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and hydrothermally reacted at 180 °C for 8 h. After naturally cooling to room temperature, the product was collected by centrifugation and washed three times each with deionized water and anhydrous ethanol. The product was then dried at 60 °C for 12 h to obtain carbon sphere templates. The prepared carbon sphere template, nickel acetate tetrahydrate, ferric nitrate nonahydrate, urea, and deionized water were mixed and ultrasonically dispersed for 30 min to obtain a suspension. The suspension contained 2.0 g / L carbon spheres, 0.02 mol / L nickel ions, 0.04 mol / L ferric ions, and 0.2 mol / L urea. The suspension was transferred to a thermostatic magnetic stirrer and stirred at 90 °C for 3 h. After natural cooling, it was centrifuged and washed three times each with deionized water and anhydrous ethanol. The mixture was then dried in a 60 °C oven for 12 h to obtain the precursor complex. The precursor composite was spread in a ceramic boat and placed in a muffle furnace. The temperature was increased to 500 °C at a rate of 2 °C / min in air atmosphere and calcined at a constant temperature for 3 h. The furnace was then cooled to room temperature to obtain the hollow spherical nickel-iron oxide.

[0058] The hollow spherical nickel-iron oxide has a spherical hollow structure with an outer diameter of 0.32 μm and a shell thickness of 50 nm.

[0059] Performance testing: (1) HER performance test Electrochemical performance testing of the hydrogen evolution reaction was conducted using a three-electrode setup on an electrochemical workstation.

[0060] Cyclic voltammetry test: The electrode voltage test range was set to -1.6 to -1 V, and the scan rate was 30 mV / s. -1 The number of scans is 30.

[0061] Linear scanning voltammetry test: The electrode voltage test range is set to -1.9 to -1 V, and the scan speed is 10 mV / s. -1 Scan once.

[0062] Electrochemical impedance spectroscopy: Data were obtained from linear sweep voltammetry at a range of 10 mA cm⁻¹. -2 The electrode voltage value corresponding to the current density is set as the test electrode voltage value, and the frequency range is set to 0.01~150 kHz.

[0063] Double-layer capacitance test: The test electrode voltage range was set to -0.89 V to -0.89 V, and the scan speed was set from 20 to 100 mV / s. -1The speed gradually increases, with 20 scans at each scanning speed.

[0064] Stability testing: The stability of the catalyst was tested using the chronoamperometry method.

[0065] (2) The OER performance test is similar to the hydrogen evolution reaction performance test, except that the cyclic voltammetry test range is 0~0.6 V, the linear sweep voltammetry test range is 0~0.9 V, the double layer capacitance test range is -0.05~0.05 V, and the alkaline electrolyte solution needs to be saturated with a small amount of oxygen beforehand. Other operations are the same as the HER test. In the seawater environment, the test solution is replaced with an oxygen-saturated 1 M KOH + 0.5 M NaCl solution, and other operations are the same as the above process.

[0066] The test results are shown in Table 1: Table 1 As can be seen from Table 1, as obtained from Examples 1 to 9, the BET of the hollow spherical nickel-iron oxide described in this invention can reach 133m. 2 / g or more, OER 10mA / cm 2 Overpotentials can reach over 168mV, while HER's is 10mA / cm. 2 Overpotential can reach over 18mV, 500mA / cm 2 After running for 600 hours, the activity decay rate can be controlled within 4.6%, the CH4 conversion rate can reach over 95.6%, and the purity of the produced hydrogen can reach over 84.6%.

[0067] Comparing Examples 1 and 4-5, it can be seen that the diameter of the atomized droplets affects the performance of the hollow spherical nickel-iron oxide produced in this invention. Controlling the diameter of the atomized droplets to 1μm-5μm results in better performance of the hollow spherical nickel-iron oxide. If the diameter of the atomized droplets is too large, the solvent will evaporate from the surface much faster than the solute will diffuse from the center. An excessively thick shell is prone to cracking or collapse due to internal stress during subsequent calcination. If the diameter of the atomized droplets is too small, solid particles will be formed, or the hollow spherical shell will be too thin and have poor mechanical strength.

[0068] A comparison of Examples 1 and 6-7 shows that the pyrolysis temperature affects the performance of the hollow spherical nickel-iron oxide produced in this invention. Controlling the pyrolysis temperature between 400℃ and 800℃ yields hollow spherical nickel-iron oxide with better performance. If the pyrolysis temperature is too high, glucose decomposes rapidly and burns instantly, resulting in excessive instantaneous gas production that causes the hollow sphere shell to crack or collapse due to a surge in internal gas pressure. Simultaneously, the metal salt rapidly sinters at excessively high temperatures, leading to shell densification, mesopore closure, and amorphous nickel-iron oxide transforming into a highly crystalline form. This results in a sharp decrease in the density of active sites and specific surface area, significantly reducing catalytic performance. Conversely, if the pyrolysis temperature is too low, glucose pyrolysis is incomplete, leaving a large amount of carbonaceous skeleton that coats the active centers. Insufficient inward gas expansion force prevents the effective construction of a hollow structure. Furthermore, incomplete decomposition of the metal salt makes it difficult to form pure-phase nickel-iron oxide, resulting in products that are mostly solid or collapsed particles with low specific surface area and poor catalytic activity.

[0069] A comparison of Examples 1 and 8-9 shows that the pyrolysis time affects the performance of the hollow spherical nickel-iron oxide produced in this invention. Controlling the pyrolysis time to 10-30 seconds yields hollow spherical nickel-iron oxide with better performance. If the pyrolysis time is too long, the precursor droplets remain excessively in the high-temperature zone, causing the shell particles to sinter and shrink severely due to continuous heating. This leads to the collapse of the hollow structure into a dense solid body, the disappearance of mesopores, and exacerbated crystallization of the amorphous structure, resulting in a significant decrease in catalytic activity and stability. Conversely, if the pyrolysis time is too short, the droplet drying and pyrolysis are insufficient, the carbon source and metal salt fail to react and decompose completely, the hollow shell is underdeveloped, and the product contains a large amount of residual organic matter and solid particles. The active sites are masked, resulting in extremely low catalytic performance.

[0070] As can be seen from the comparison between Example 1 and Comparative Example 1, the present invention uses a carbon source as a template agent to prepare a uniform precursor solution. By spraying and atomizing the precursor solution into independent atomized droplets, the composition and size of each atomized droplet are highly uniform, thereby ensuring the uniformity of particle size and composition of the hollow spheres in the product. Then, pyrolysis is performed. During the pyrolysis process, the solvent of the atomized droplets evaporates and the metal salt decomposes, and hollow spheres are spontaneously formed through internal material diffusion. Finally, the residual carbon impurities are removed by calcination to obtain hollow spherical nickel-iron oxide. The hollow spherical nickel-iron oxide increases the specific surface area and the exposure of active sites through the synergistic effect of amorphous structure and hollow morphology, thus exhibiting high catalytic activity and stability.

[0071] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing hollow spherical nickel-iron oxide, characterized in that, The preparation method includes the following steps: A precursor solution is obtained by mixing a nickel source, an iron source, a sugar-based carbon source template agent, and a solvent. The precursor solution was spray-atomized to obtain atomized droplets; The atomized droplets are subjected to pyrolysis to obtain pyrolysis products, and the pyrolysis products are then calcined to obtain the hollow spherical nickel-iron oxide.

2. The preparation method according to claim 1, characterized in that, The nickel source includes any one or a combination of at least two of nickel nitrate, nickel acetate, or nickel chloride. Preferably, the iron source includes any one or a combination of at least two of ferric nitrate, ferric chloride, or ferric acetate; Preferably, the carbohydrate carbon source template agent includes any one or a combination of at least two of glucose, fructose, or sucrose; Preferably, the solvent includes water and / or ethanol.

3. The preparation method according to claim 1 or 2, characterized in that, The molar ratio of nickel in the nickel source to iron in the iron source is 1:(0.3~0.8).

4. The preparation method according to any one of claims 1-3, characterized in that, The total molar concentration of metal ions in the precursor solution is 0.05 mol / L to 0.2 mol / L; Preferably, the mass concentration of the carbohydrate carbon source template agent in the precursor solution is 5 g / L to 20 g / L.

5. The preparation method according to any one of claims 1-4, characterized in that, The atomizing gas used in the spray atomization process includes nitrogen and / or air; Preferably, the gas flow rate for the spray atomization treatment is 0.5 L / min to 6 L / min; Preferably, the feed rate of the precursor solution for the spray atomization treatment is 5L / h to 10L / h.

6. The preparation method according to any one of claims 1-5, characterized in that, The diameter of the atomized droplets is 1μm to 5μm.

7. The preparation method according to any one of claims 1-6, characterized in that, The temperature of the pyrolysis treatment is 400℃~800℃; Preferably, the pyrolysis treatment time is 10s to 30s.

8. The preparation method according to any one of claims 1-7, characterized in that, The calcination temperature is 200℃~400℃; Preferably, the roasting treatment time is 1h to 2h.

9. A hollow spherical nickel-iron oxide, characterized in that, The hollow spherical nickel-iron oxide is prepared by the preparation method according to any one of claims 1-8.

10. An electrocatalyst, characterized in that, The electrocatalyst comprises hollow spherical nickel-iron oxide as described in claim 9.

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