Self-supporting high-entropy oxide catalyst and preparation and application thereof

Abstract

The invention belongs to the field of catalyst preparation, and discloses a preparation and application method of a self-supporting high-entropy oxide catalyst. The preparation method comprises the following steps: taking a zinc oxide nanowire array as a template; firstly, a high-entropy metal organic framework grows in situ on the surface through a coprecipitation reaction; then, pyrolyzing the zinc oxide nanowire to realize the preparation of the zinc oxide nanowire loaded high-entropy oxide; the used reaction liquid is green and environment-friendly and does not contain toxic substances; the process is low in cost and easy for large-area preparation; the prepared self-supporting catalyst is firmly combined with the substrate, is convenient to put and place in the use process, and is easy to recycle after being used; the catalyst has excellent catalytic activity, can be used for various reduction reactions including nitrate ion reduction synthesis of ammonia, and has a wide application prospect in the fields of industrial sewage treatment and ammonia resource sustainability.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation, and specifically relates to a self-supporting high-entropy oxide catalyst and its preparation and application. Background Technology

[0002] High-entropy oxides (HOOs) have recently attracted widespread attention in the field of electrocatalysis due to their high configurational entropy, severe lattice distortion, slow atomic diffusion kinetics, unique "cocktail effect," and broad component tunability. For example, the multi-component synergistic effect of HOOs can form various active sites for adsorbing and activating catalytic reaction substrates and intermediates, thus exhibiting high catalytic activity and selectivity. Simultaneously, the thermodynamic stability and slow atomic diffusion behavior of HOOs contribute to their excellent stability during electrocatalytic reactions. To date, most reported HOOs exist in powder form. However, in practical applications, powdered electrocatalysts require coating the electrode surface with organic binders. This not only blocks the active sites of the HOOs but also affects their conductivity. Furthermore, vigorous electrochemical reactions and prolonged immersion in electrolytes can lead to the shedding of HOOs. Therefore, the electrocatalytic performance of existing powdered HOOs falls far short of expectations. In contrast, self-supporting electrocatalysts do not use binders and therefore possess superior activity and stability. What is particularly noteworthy is that the recovery and separation of self-supported catalysts are easier than those of powdered catalysts, thus exhibiting excellent recycling rates. Therefore, the development of self-supported high-entropy oxide catalysts is of great significance. Surprisingly, there are currently few reports on the synthesis methods of self-supported high-entropy oxides. Correspondingly, many directions regarding their application prospects in the field of electrocatalysis remain unexplored. Summary of the Invention

[0003] In order to overcome the shortcomings and deficiencies of the prior art, the primary objective of this invention is to provide a method for preparing a self-supporting high-entropy oxide catalyst.

[0004] Another object of the present invention is to provide a self-supporting high-entropy oxide catalyst prepared by the above method.

[0005] Another objective of this invention is to provide the application of the above-mentioned self-supporting high-entropy oxide catalyst in the electrocatalytic reduction of nitrate to ammonia.

[0006] The objective of this invention is achieved through the following solution: A method for preparing a self-supporting high-entropy oxide catalyst mainly includes the following steps: first, placing a zinc oxide nanowire array in a solution containing multiple metal salts, and then taking it out and pyrolyzing it in air to obtain zinc oxide nanowire-supported high-entropy oxide.

[0007] Preferably, the preparation method of the self-supporting high-entropy oxide catalyst specifically includes the following steps: (1) Preparation of reaction solution: Add metal salt and additives to water to form reaction solution; (2) The zinc oxide nanowire array was immersed in the reaction solution prepared in step (1) to obtain a zinc oxide nanowire loaded with a high-entropy metal-organic framework. (3) The zinc oxide nanowire loaded with high entropy metal-organic framework obtained in step (2) is washed with water and then placed in a muffle furnace for pyrolysis to obtain zinc oxide nanowire loaded with high entropy oxide.

[0008] The concentration of metal salt in the reaction solution described in step (1) is 1~100 g / L and the concentration of additive is 1~330 g / L; The metal ion salt mentioned in step (1) is at least three of the following: Co(NO3)2, Ni(NO3)2, Cu(NO3)2, Zn(NO3)2, Mn(NO3)2 and Al(NO3)3.

[0009] The additive mentioned in step (1) is potassium ferricyanide, and at least one of citric acid, tartaric acid, pyrophosphate, hypophosphoric acid, nitric acid, triacetic acid, oxalic acid, lactic acid, nicotinic acid, boric acid, aminosulfonic acid, fluoroboric acid, hydroxyethylidene diphosphate, 5,5′-dimethylhydantoin, sorbitol and their salts, that is, the additive must contain potassium ferricyanide, wherein the concentration of potassium ferricyanide in the reaction solution in step (1) is 1~100 g / L.

[0010] Preferably, the metal ion salts mentioned in step (1) are Co(NO3)2, Ni(NO3)2 and Cu(NO3)2, and the additives mentioned in step (2) are a mixture of potassium ferricyanide and sodium citrate, wherein the mass ratio of Co(NO3)2, Ni(NO3)2 and Cu(NO3)2, potassium ferricyanide and sodium citrate is (0.1~1): (0.1~1): (0.1~1): (0.1~5): (0.1~5), preferably 1:1:1:3.6:4.1.

[0011] The zinc oxide nanowire array mentioned in step (2) can be zinc oxide nanowires grown on the surface of any conductive substrate. The preparation of the zinc oxide nanowire array is described in reference to patent application (ZL201810834195.8 - A method for preparing zinc oxide nanowire thin films based on hydrothermal reaction of nanocrystalline zinc coating).

[0012] The amount of zinc oxide nanowire array used in step (2) satisfies the following condition: it can be completely immersed in the reaction solution of step (1); preferably, the amount of zinc oxide nanowire array used in step (2) satisfies the following condition: per 1×1 cm 2The zinc oxide nanowire array was immersed in 50 mL of a reaction solution containing 1~100 g / L of metal salt.

[0013] The soaking reaction mentioned in step (2) refers to soaking at 1~90 ℃ for 1~10 h, preferably soaking at room temperature for 1~10 h.

[0014] The pyrolysis described in step (3) refers to placing a high-entropy metal-organic framework loaded with zinc oxide nanowires into a muffle furnace, controlling the heating rate to be 1~10 ℃ / min, heating to 100~500 ℃, and holding at that temperature for 2~10 h.

[0015] A self-supporting high-entropy oxide catalyst prepared by the above method is grown on a zinc oxide nanowire array with a size of 200 nm to 2 μm and a porous surface.

[0016] The above-mentioned zinc oxide nanowire array supports a self-supporting high-entropy oxide catalyst for electrocatalytic reduction of nitrate ions to ammonia.

[0017] This invention develops a novel, economical, and efficient self-supporting high-entropy oxide catalyst, namely, an iron-cobalt-nickel-copper-zinc oxide supported on a zinc oxide nanowire array, and verifies its electrocatalytic ability to reduce nitrate ions. The preparation method of this self-supporting high-entropy oxide catalyst is characterized by its simple operation, abundant raw materials, and scalability, and it has certain reference value for the development of electrochemical ammonia synthesis and industrial wastewater treatment technologies.

[0018] The mechanism of this invention is as follows: Zinc oxide nanowire arrays release Zn in solutions containing potassium ferricyanide [K3Fe(CN)6]. 2+ And Zn 2+ It can also be combined with [Fe(CN)6] 3- and other metal ions in the solution (e.g., Co) 2+ Ni 2+ and Cu 2+ (etc.) co-precipitated into a high-entropy metal-organic framework and grown in situ on the surface of zinc oxide nanowires; after pyrolysis, the high-entropy metal-organic framework was oxidized into high-entropy oxide, and finally a self-supporting high-entropy oxide catalyst was obtained.

[0019] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. The method of the present invention is simple to operate, low in cost, and easy to prepare on a large scale. It is applicable to zinc oxide nanowire arrays grown on any substrate and is not limited by the aspect ratio of zinc oxide nanowires. 2. In the self-supporting high-entropy oxide catalyst of the present invention, the zinc oxide nanowire array serves as both a support for the high-entropy oxide and directly participates in the synthesis reaction of the high-entropy oxide. Therefore, the prepared zinc oxide nanowire-loaded high-entropy oxide is firmly bonded to the substrate, making it easy to place and install during use and easy to recycle after use. 3. The prepared self-supporting high-entropy oxide catalyst exhibits a nano-heterogeneous structure. There is a strong synergistic effect between the zinc oxide nanowire support and the high-entropy oxide it supports, thus exhibiting higher catalytic activity than the high-entropy oxide powder.

[0020] 4. The self-supporting high-entropy oxide catalyst prepared by this invention has strong electrocatalytic activity in the reduction of nitrate ions to ammonia, and has broad application prospects in the fields of environmental science and chemical engineering. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the synthesis method of the self-supporting high-entropy oxide catalyst in Example 1.

[0022] Figure 2 The images show SEM images of the zinc oxide nanowire array used in Example 1 (a), the prepared zinc oxide nanowire loaded high-entropy metal-organic framework (b), the zinc oxide nanowire loaded high-entropy oxide (c), and the zinc oxide nanowire loaded high-entropy oxide prepared in Example 4 (d).

[0023] Figure 3 TEM image and EDS distribution map of the high-entropy oxide prepared in Example 1.

[0024] Figure 4 A digital photograph of an H-type electrolytic cell.

[0025] Figure 5 The figures show the chronocurrent curves, UV-Vis absorption spectra, and corresponding ammonia yield and Faraday efficiency graphs under different voltage conditions in Example 9.

[0026] Figure 6 The images show the chronoamperometry curves, UV-Vis absorption spectra, and corresponding ammonia yield and Faraday efficiency plots of the high-entropy iron-cobalt-nickel-copper-zinc oxide powder loaded on zinc oxide nanowires in Example 9. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0028] The zinc oxide nanowire array described in the examples was prepared according to Example 1 of the patent application (ZL201810834195.8 - A method for preparing zinc oxide nanowire thin films based on hydrothermal reaction of nanocrystalline zinc coating).

[0029] Example 1: Preparation of self-supporting high-entropy oxide catalysts The preparation process of high-entropy oxide supported on zinc oxide nanowires is shown in the schematic diagram. Figure 1 As shown.

[0030] 1. Dissolve 6.6 g / L potassium ferricyanide and 7.4 g / L sodium citrate in 50 mL of deionized water, then add 1.82 g / L cobalt nitrate, 1.82 g / L nickel nitrate and 1.88 g / L copper nitrate respectively to obtain the reaction solution; 2. Then, add 1 cm of the solution prepared in step one to the reaction solution. 2 Zinc oxide nanowire arrays (such as) Figure 2 As shown in a), after standing at room temperature for 2 hours, the sample was removed, rinsed with deionized water, and then dried to obtain a zinc oxide nanowire-supported high-entropy iron-cobalt-nickel-copper-zinc organic framework (e.g., as shown in a diagram). Figure 2 (as shown in b). Thirdly, the zinc oxide nanowires loaded with a high-entropy metal-organic framework prepared in step two were placed in a muffle furnace and heated to 400 °C at a rate of 2 °C / min, and held at that temperature for 2 h. This completes the preparation of zinc oxide nanowires loaded with high-entropy iron-cobalt-nickel-copper-zinc oxide (e.g., Figure 2 (As shown in c). Additionally... Figure 3 TEM images and corresponding EDS distribution maps of oxide particles scraped from high-entropy iron-cobalt-nickel-copper-zinc oxide supported on zinc oxide nanowires are also presented. As shown in the figure, the oxide nanoparticles are composed of Fe, Co, Ni, Cu, Zn and O elements, which meets the definition of high-entropy oxides, proving the successful preparation of self-supporting high-entropy oxides.

[0031] Example 2: Preparation of self-supporting high-entropy oxide catalysts The difference between this embodiment and Example 1 is that the metal salts used in the reaction solution in step one are 1.82 g / L cobalt nitrate, 1.79 g / L manganese nitrate, and 2.13 g / L aluminum nitrate; the rest are the same as in Example 1. Scanning electron microscope (SEM) images of zinc oxide nanowires loaded with high-entropy aluminum-manganese-iron-cobalt-zinc oxide prepared in Example 2 and... Figure 2 The similarity to c indicates that replacing some metal ions can also yield a self-supporting high-entropy oxide catalyst.

[0032] Example 3: Preparation of self-supporting high-entropy oxide catalysts The difference between this embodiment and Example 1 is that the metal salts used in the reaction solution of step one are 1.82 g / L cobalt nitrate, 1.82 g / L nickel nitrate, 1.88 g / L copper nitrate, 1.79 g / L manganese nitrate, and 2.13 g / L aluminum nitrate. The rest is the same as in Example 1. Scanning electron microscope (SEM) images of zinc oxide nanowires loaded with high-entropy aluminum, manganese, iron, cobalt, nickel, copper, and zinc oxides prepared in Example 3 and... Figure 2 The similarity to c indicates that adding metal ions can also yield self-supporting high-entropy oxide catalysts.

[0033] Example 4: Preparation of self-supporting high-entropy oxide catalysts The difference between this embodiment and embodiment 1 is that sodium citrate used in step one is replaced with boric acid, while the rest is the same as in embodiment 1. Scanning electron microscope (SEM) images of the zinc oxide nanowires prepared in Example 4, which are loaded with high-entropy iron, cobalt, nickel, copper, and zinc oxides, are shown below. Figure 2 As shown in d, boric acid only plays a role in regulating the morphology of high-entropy oxides and is not the key to the successful synthesis of high-entropy metal-organic frameworks or oxides.

[0034] Therefore, the boric acid used can also be replaced by at least one of citric acid, tartaric acid, pyrophosphate, hypophosphoric acid, nitric acid, triacetic acid, oxalic acid, lactic acid, nicotinic acid, aminosulfonic acid, fluoroboric acid, hydroxyethylidene diphosphate, 5,5′-dimethylhydantoin, sorbitol and their salts.

[0035] Example 5: Preparation of self-supporting high-entropy oxide catalysts The difference between this embodiment and embodiment 1 is that the soaking temperature in step two is 60 ℃ and the soaking time is 2 h, while the rest is the same as in embodiment 1. Scanning electron microscope (SEM) images of zinc oxide nanowires loaded with high-entropy iron-cobalt-nickel-copper-zinc oxide prepared in Example 5 and... Figure 2 The similarity of c indicates that self-supporting high-entropy oxide catalysts can also be obtained from zinc oxide nanowires at different immersion temperatures.

[0036] Example 6: Preparation of self-supporting high-entropy oxide catalysts The difference between this embodiment and embodiment 1 is that the soaking temperature in step two is room temperature and the soaking time is 6 hours, while the rest is the same as in embodiment 1. Scanning electron microscope (SEM) images of zinc oxide nanowires loaded with high-entropy iron-cobalt-nickel-copper-zinc oxide prepared in Example 6 and... Figure 2 The similarity of c indicates that self-supporting high-entropy oxide catalysts can also be obtained from zinc oxide nanowires under different immersion times.

[0037] Example 7: Preparation of self-supporting high-entropy oxide catalysts The difference between this embodiment and embodiment 1 is that the heating rate in step 3 is 2 ℃ / min, the temperature is raised to 500 ℃, and the temperature is held for 2 h, while the rest is the same as in embodiment 1. Scanning electron microscope (SEM) images of zinc oxide nanowires loaded with high-entropy iron-cobalt-nickel-copper-zinc oxide prepared in Example 7 and... Figure 2 The similarity of c indicates that self-supporting high-entropy oxide catalysts can also be obtained under different pyrolysis temperature conditions.

[0038] Example 8: Preparation of self-supporting high-entropy oxide catalysts The difference between this embodiment and embodiment 1 is that the heating rate in step 3 is 2 ℃ / min, the temperature is raised to 400 ℃, and the temperature is held for 6 h, while the rest is the same as in embodiment 1. Scanning electron microscope (SEM) images of zinc oxide nanowires loaded with high-entropy iron-cobalt-nickel-copper-zinc oxide prepared in Example 8 and... Figure 2 The similarity of c indicates that self-supporting high-entropy oxide catalysts can also be obtained under different holding times during pyrolysis.

[0039] Example 9: Application Example The zinc oxide nanowire-supported high-entropy iron-cobalt-nickel-copper-zinc oxide prepared in Example 1 was used as a catalyst, and its electrocatalytic activity for the reduction of nitrate ions to ammonia was characterized. All experiments were conducted in a three-electrode system controlled by a CHI 760E electrochemical workstation (working electrode was 1 cm). 2 A self-supported high-entropy oxide catalyst with an auxiliary electrode of 1 cm. 2 Platinum sheet, with an Ag / AgCl reference electrode, such as Figure 4 As shown in the figure, the left chamber of cell H contained 0.5 M K₂SO₄ and 0.1 M KNO₃ aqueous solution, while the right chamber contained 0.5 M K₂SO₄ aqueous solution. Electrolysis was performed at different voltages (-0.5 to -0.9 V (compared to the standard hydrogen electrode)), and after a colorimetric reaction of the electrolyte, the solution was analyzed using a UV-Vis spectrophotometer. The obtained current-time curves and UV-Vis absorption spectra are shown below. Figure 5As shown, the absorption peaks of NH3 and K2SO4 solutions are at 650 nm. However, the current density of the catalyst varies under different voltages, resulting in different absorbances. A higher absorption peak at 650 nm indicates a greater amount of NH3 generated during the reaction. The colorimetric reagents were prepared as follows: Colorimetric reagent A: a 1 M sodium hydroxide solution containing 5 wt% sodium salicylate and 5 wt% potassium sodium tartrate. Colorimetric reagent B: 0.3725 g sodium hypochlorite dissolved in 100 mL of water. Colorimetric reagent C: 0.2 g sodium nitrosoferricyanide dissolved in 20 mL of water. The colorimetric reaction was performed as follows: 5 mL of the test solution was added to a beaker, followed by 5 mL of colorimetric reagent A, 2.5 mL of colorimetric reagent B, and 0.5 mL of colorimetric reagent C. The mixture was thoroughly shaken and allowed to stand at room temperature for 1 hour for complete color development. The absorption peak of NH3 in the solution (λ=655 nm) was measured using a UV spectrophotometer.

[0040] also, Figure 6 The following are given: zinc oxide nanowires loaded with high-entropy iron-cobalt-nickel-copper-zinc oxide (i.e., zinc oxide nanowires) under different voltages. Figure 6 ZnO-HEOs in the powder), and high-entropy iron-cobalt-nickel-copper-zinc oxide powder (i.e. Figure 6 Electrocatalytic NO3 in Powders — The Faradaic efficiency (FE) and ammonia yield (NH3 yield) of the →NH3 reaction show that the self-supported catalyst exhibits the optimal Faradaic efficiency and ammonia yield at -0.7 V, which are higher than those of the powdered catalyst under the same conditions. The powdered catalyst was prepared as follows: 6.6 g / L potassium ferricyanide and 7.4 g / L sodium citrate were dissolved in 50 mL of deionized water, followed by the addition of 1.89 g / L zinc nitrate, 1.82 g / L cobalt nitrate, 1.82 g / L nickel nitrate, and 1.88 g / L copper nitrate, respectively. After stirring at room temperature for 2 h, the mixture was dried in a vacuum drying oven at 60 °C for 5 h to obtain a high-entropy metal-organic framework powder. The powder was then pyrolyzed in a muffle furnace at 400 °C for 2 h to obtain a high-entropy alloy oxide. 10 mg of the high-entropy alloy oxide powder and 60 μL of Nafion were dissolved in 2 mL of isopropanol under ultrasonic conditions to obtain a homogeneous slurry. 400 μL of this slurry was then dropped onto a surface with an area of ​​1 cm². 2 On a stainless steel substrate. All catalysts were loaded with a loading of 2 mg / cm³. -2 .

[0041] The above results demonstrate that the prepared self-supporting high-entropy oxide catalyst has high electrocatalytic activity and has certain application prospects in the field of electrochemical ammonia synthesis and industrial wastewater treatment to remove excess nitrate ions.

[0042] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a self-supporting high-entropy oxide catalyst, characterized in that... The main steps include: First, the zinc oxide nanowire array is placed in a solution containing various metal salts, and then removed and pyrolyzed in air to obtain zinc oxide nanowires loaded with high entropy oxide.

2. The method for preparing a self-supporting high-entropy oxide catalyst according to claim 1, characterized in that... Specifically, the following steps are included: (1) Preparation of reaction solution: Add metal salt and additives to water to form reaction solution; (2) The zinc oxide nanowire array was immersed in the reaction solution prepared in step (1) to obtain a zinc oxide nanowire loaded with a high-entropy metal-organic framework. (3) The zinc oxide nanowire loaded with high entropy metal-organic framework obtained in step (2) is washed with water and then placed in a muffle furnace for pyrolysis to obtain zinc oxide nanowire loaded with high entropy oxide.

3. The method for preparing a self-supporting high-entropy oxide catalyst according to claim 2, characterized in that: The metal ion salt mentioned in step (1) is at least three of the following: Co(NO3)2, Ni(NO3)2, Cu(NO3)2, Zn(NO3)2, Mn(NO3)2, and Al(NO3)3; The additive mentioned in step (1) is potassium ferricyanide, and at least one of citric acid, tartaric acid, pyrophosphate, hypophosphoric acid, nitric acid, triacetic acid, oxalic acid, lactic acid, nicotinic acid, boric acid, aminosulfonic acid, fluoroboric acid, hydroxyethylidene diphosphate, 5,5′-dimethylhydantoin, sorbitol and their salts.

4. The method for preparing a self-supporting high-entropy oxide catalyst according to claim 3, characterized in that: The concentration of metal salt in the reaction solution in step (1) is 1~100 g / L and the concentration of additive is 1~330 g / L.

5. The method for preparing a self-supporting high-entropy oxide catalyst according to claim 2, characterized in that: The metal ion salts mentioned in step (1) are Co(NO3)2, Ni(NO3)2 and Cu(NO3)2, and the additives mentioned in step (2) are a mixture of potassium ferricyanide and sodium citrate, wherein the mass ratio of Co(NO3)2, Ni(NO3)2 and Cu(NO3)2, potassium ferricyanide and sodium citrate is (0.1~1): (0.1~1): (0.1~1): (0.1~5): (0.1~5), preferably 1:1:1:3.6:4.

1.

6. The method for preparing a self-supporting high-entropy oxide catalyst according to claim 2, characterized in that: The zinc oxide nanowire array mentioned in step (2) is zinc oxide nanowires grown on the surface of any conductive substrate; the preparation of the zinc oxide nanowire array mentioned in step (2) refers to patent application ZL201810834195.8 - A method for preparing zinc oxide nanowire thin films based on hydrothermal reaction of nanocrystalline zinc coating.

7. The method for preparing a self-supporting high-entropy oxide catalyst according to claim 2, characterized in that: The amount of zinc oxide nanowire array used in step (2) satisfies the following condition: it is completely immersed in the reaction solution of step (1); The soaking reaction mentioned in step (2) refers to soaking at 1~90 ℃ for 1~10 h.

8. The method for preparing a self-supporting high-entropy oxide catalyst according to claim 2, characterized in that: The pyrolysis described in step (3) refers to placing a high-entropy metal-organic framework loaded with zinc oxide nanowires into a muffle furnace, controlling the heating rate to be 1~10 ℃ / min, heating to 100~500 ℃, and holding at that temperature for 2~10 h.

9. A self-supporting high-entropy oxide catalyst prepared by the method according to any one of claims 1-8.

10. The application of the self-supporting high-entropy oxide catalyst according to claim 9 in the electrocatalytic reduction of nitrate ions to ammonia.

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