Nano flower structure Ni-Cu LDH electrocatalyst and preparation method and application thereof
阅读说明：本技术 一种纳米花结构Ni-Cu LDH电催化剂及其制备方法、应用 (Nano flower structure Ni-Cu LDH electrocatalyst and preparation method and application thereof ) 是由 叶伟 徐梦秋 于 2021-09-14 设计创作，主要内容包括：本发明涉及催化剂技术领域,公开了一种用于硝酸根还原的Ni-Cu LDH电催化剂及其制备方法。所述Ni-Cu LDH电催化剂原料包括六水合硝酸锌,尿素,三乙二醇和二水合氯化铜；所述Ni-Cu LDH电催化剂为纳米花结构,用于硝酸根还原。本发明制备的Ni-Cu LDH电催化剂具有片状结构,BET高,催化效率高,显示出了优异的结构和电化学耐久性；合成方法具有工艺简单、耗能少、条件温和及产品形貌好,适合大规模生产应用。(The invention relates to the technical field of catalysts, and discloses a Ni-Cu LDH electrocatalyst for nitrate radical reduction and a preparation method thereof. The raw materials of the Ni-Cu LDH electrocatalyst comprise zinc nitrate hexahydrate, urea, triethylene glycol and copper chloride dihydrate; the Ni-Cu LDH electrocatalyst is in a nanoflower structure and is used for nitrate radical reduction. The Ni-Cu LDH electrocatalyst prepared by the invention has a sheet structure, high BET (BET) and high catalytic efficiency, and shows excellent structure and electrochemical durability; the synthesis method has the advantages of simple process, low energy consumption, mild conditions and good product appearance, and is suitable for large-scale production and application.)
1. A Ni-Cu LDH electrocatalyst, characterized in that the electrocatalyst materials comprise zinc nitrate hexahydrate, urea, triethylene glycol and copper chloride dihydrate; the Ni-Cu LDH electrocatalyst has a nanoflower structure.
2. The electrocatalyst according to claim 1, wherein the nanoflower structure is formed from ni (oh)2Nanosheet composition, Ni (OH)2Cu particles are distributed on the nano-sheets.
3. A method of preparing an electrocatalyst according to claim 1 or 2, comprising the steps of:
(1) dissolving nickel nitrate hexahydrate in a mixed solution of ionized water and triethylene glycol to obtain a uniform solution A; the mass ratio of the ionized water to the triethylene glycol is 1: 4-7;
(2) adding urea and copper chloride dihydrate into the uniform solution A obtained in the step (1) to obtain a uniform solution B;
(3) carrying out hydrothermal synthesis on the uniform solution B at the temperature of 110-130 ℃ for 18-30h, and after the reaction is finished, separating, cleaning and drying to obtain the Ni-Cu LDH electrocatalyst.
4. The method of claim 3, wherein in step (1), the molar ratio of nickel nitrate hexahydrate to deionized water in solution A is 1: 4.5-5.5.
5. The method according to claim 3, wherein in the step (1), the uniform solution A is obtained by one or more of magnetic stirring, ultrasonic mixing and mechanical stirring.
6. The method according to claim 3, wherein in the step (2), the molar ratio of urea, copper chloride dihydrate and nickel nitrate hexahydrate is 2-5:5-10: 0.2-0.8.
7. The method according to claim 3, wherein in the step (2), the uniform solution A is obtained by one or more of magnetic stirring, ultrasonic mixing and mechanical stirring.
8. The method according to claim 3, wherein in the step (2), the separation is performed by centrifugation at 3000-4000 r/min for 60-120 min.
9. The method according to claim 3, wherein in the step (3), the cleaning manner is alternately cleaning with deionized water and ethanol; the drying mode is drying for 24-30h in vacuum at 60-70 ℃.
10. A Ni-Cu LDH electrocatalyst as claimed in claim 1 or 2 for nitrate reduction.
Technical Field
The invention relates to the technical field of catalysts, in particular to a Ni-Cu LDH electrocatalyst with a nanoflower structure and a preparation method and application thereof.
Background
Although it can pass electrochemical nitrogen (N) under ambient conditions2) The reduction reaction (NRR) produces ammonia, but the reaction rate and faradaic efficiency are generally low due to the large bond energy of the nitrogen-nitrogen triple bond (941 kJ/mol). In sharp contrast, the reduction of nitrate (nitrate) to ammonia requires only 204 kJ/mol, so the nitrate reduction reaction (NO)3RR) has attracted considerable attention as a more efficient and energy efficient ammonia production strategy. However, the ammonia production rate of NO3RR is still much lower than the Harbour route due to the lack of a powerful electrocatalyst to generate the high current density (4200 mA cm)-2) And well inhibits the competitive Hydrogen Evolution Reaction (HER). Low temperature electrified ammonia production powered by renewable energy as an alternative to the haber process may reduce fossil fuel usage and carbon dioxide emissions. Electrocatalytic conversion of nitrate nitrogen to ammoniaThe conversion involves 9 protons and 8 electrons (NO)3 −+ 9 H++ 8 e−→NH3+ 3H2O) is a slow kinetic eight electron transfer process with various by-products (i.e. nitrogen dioxide, N)2And N2H4). For this reason, there have been a great deal of effort to develop different metal-based electrocatalysts (i.e., Cu, Ru, Ag, Fe, Au, Ti) to promote the conversion of nitrates to ammonia. Therefore, rational design and development of high NO3RR activity, an electrocatalyst that inhibits HER well is highly urgent. The Ni-Cu LDH material has good catalytic effect, but is mostly sea urchin-shaped and has small BET.
Publication No. CN113184926A discloses a method for preparing Ni-Cu LDH material by using electroplating sludge and application thereof. Performing chlorination roasting treatment on the electroplating sludge to obtain chlorinated electroplating sludge, adding water, stirring to dissolve chloride, filtering to obtain filtrate, adding terephthalic acid and polyvinylpyrrolidone into a mixed solvent of N, N-dimethylformamide, ethanol and water for hydrothermal reaction, washing and drying a solid product to obtain a Ni-Cu MOF material, adding the Ni-Cu MOF material into a potassium hydroxide solution, stirring at room temperature, performing solid-liquid separation, washing and drying the obtained solid to obtain the Ni-Cu LDH material applicable to the supercapacitor electrode. However, the catalyst used in the present invention is hardly applicable to nitrate reduction electrocatalysis.
Disclosure of Invention
In order to solve the technical problems, the invention provides a Ni-Cu LDH electrocatalyst with a nanoflower structure and a preparation method and application thereof, and the Ni-Cu LDH electrocatalyst prepared by the invention has a sheet structure, high BET (BET surface area) and high catalytic efficiency, and shows excellent structure and electrochemical durability; the synthesis method has the advantages of simple process, low energy consumption, mild conditions and good product appearance, and is suitable for large-scale production and application.
The specific technical scheme of the invention is that the Ni-Cu LDH electrocatalyst is prepared by the following steps that raw materials of the electrocatalyst comprise zinc nitrate hexahydrate, urea, triethylene glycol and copper chloride dihydrate; the Ni-Cu LDH electrocatalyst has a nanoflower structure.
The catalyst is prepared from Ni (OH)2Nanosheets, and nano-Cu. The adjustability can change the adsorption configuration of nitrate radical in nitric acid reduction, because the high electron density of Cu hinders the competitive reaction of HER, the reduction energy barrier of nitrate radical is obviously reduced, and the orbit of Cu is similar to the energy level of LUMO Π of nitrate radical, the Ni-Cu LDH provided by the invention can reduce nitrate radical, and the synthesis method provided by the invention has the characteristics of simple process, less energy consumption, mild conditions, good product appearance and the like, and is suitable for large-scale production and application.
Preferably, the nanoflower structure is made of Ni (OH)2Nanosheet composition, Ni (OH)2Cu particles are distributed on the nano-sheets.
The invention also provides a preparation method of the electrocatalyst, which comprises the following steps:
(1) dissolving nickel nitrate hexahydrate in a mixed solution of ionized water and triethylene glycol to obtain a uniform solution A; the mass ratio of the ionized water to the triethylene glycol is 1: 4-7;
(2) adding urea and copper chloride dihydrate into the uniform solution A obtained in the step (1) to obtain a uniform solution B;
(3) carrying out hydrothermal synthesis on the uniform solution B at the temperature of 110-130 ℃ for 18-30h, and after the reaction is finished, separating, cleaning and drying to obtain the Ni-Cu LDH electrocatalyst.
When the amount of triethylene glycol added is less than 4 times of the amount of water, the reaction tends to generate echinoid substances, and when the amount of triethylene glycol is more than 4 times of the amount of water, a nanosheet structure is easier to form, the nanosheet structure is thin in shape, larger in BET (BET), more in surface-exposed active sites and more favorable for adsorption of nitric acid, and Ni (OH)2Nanosheet pair H2The O cracking is faster, and after Cu is added, the Ni-Cu bond causes potential difference, so that the nitric acid adsorption and the water cracking are more favorable, and the nitric acid reduction activity and the Faraday efficiency are higher. When the amount of triethylene glycol is more than 7 times the amount of water, the amount of dissolved nickel hydroxide is too small, and the reactants cannot be sufficiently combined into Ni — Cu LDH, thereby deteriorating the performance.
Preferably, in the step (1), the molar ratio of nickel nitrate hexahydrate to deionized water in the solution A is 1: 4.5-5.5.
Preferably, in step (1), the manner of obtaining the homogeneous solution a is one or more of magnetic stirring, ultrasonic mixing and mechanical stirring.
Preferably, in the step (2), the molar ratio of the urea, the copper chloride dihydrate and the nickel nitrate hexahydrate is 2-5:5-10: 0.2-0.8.
Preferably, in the step (2), the manner for obtaining the uniform solution a is one or more of magnetic stirring, ultrasonic mixing and mechanical stirring; the separation mode is centrifugal separation, the centrifugal rotating speed is 3000-4000 r/min, and the centrifugal time is 60-120 min.
Preferably, in the step (3), the cleaning mode is that deionized water and ethanol are used for cleaning alternately; the drying mode is drying for 24-30h in vacuum at 60-70 ℃.
The invention also discloses application of any one of the Ni-Cu LDH electro-catalysts in nitrate reduction.
Compared with the prior art, the invention has the beneficial effects that:
1. the Ni-Cu LDH electrocatalyst has a sheet structure, is high in BET (BET) and catalytic efficiency, and shows excellent structure and electrochemical durability;
2. the synthesis method has the advantages of simple process, low energy consumption, mild conditions and good product appearance, and is suitable for large-scale production and application.
Drawings
FIG. 1 is an SEM photograph of example 1 of the present invention;
FIG. 2 is a TEM image of example 1 of the present invention;
FIG. 3 is an XRD pattern for example 1 of the present invention;
FIG. 4 is a graph of ammonia production activity and Faraday efficiency for electrocatalysts prepared in examples 1-3 of the present invention and comparative examples 1-3.
Detailed Description
The present invention will be further described with reference to the following examples. The devices, reagents and methods referred to in the present invention are those known in the art unless otherwise specified.
Example 1
(1) Dissolving nickel nitrate hexahydrate in a mixed solution of ionized water and triethylene glycol, and mechanically stirring to obtain a uniform solution A; the mass ratio of the ionized water to the triethylene glycol is 1: 4; the molar ratio of nickel nitrate hexahydrate to deionized water is 1: 5;
(2) adding urea and copper chloride dihydrate into the uniform solution A obtained in the step (1) to obtain a uniform solution B; in the solution B, the molar ratio of urea, copper chloride dihydrate and nickel nitrate hexahydrate is 2:5: 0.5;
(3) hydrothermal synthesis of the uniform solution B is carried out for 18-30h at 120 ℃, after the reaction is finished, centrifugal separation is carried out for 100min at 4000r/min, deionized water and absolute ethyl alcohol are used for filtering and washing for a plurality of times, and the Ni-Cu LDH electrocatalyst is obtained after drying in vacuum at 60 ℃ for 24 h.
Example 2
(1) Dissolving nickel nitrate hexahydrate in a mixed solution of ionized water and triethylene glycol, and mechanically stirring to obtain a uniform solution A; the mass ratio of the ionized water to the triethylene glycol is 1: 5; the molar ratio of nickel nitrate hexahydrate to deionized water is 1: 5;
(2) adding urea and copper chloride dihydrate into the uniform solution A obtained in the step (1) to obtain a uniform solution B; in the solution B, the molar ratio of urea, copper chloride dihydrate and nickel nitrate hexahydrate is 2:5: 0.5;
(3) hydrothermal synthesis of the uniform solution B is carried out for 18-30h at 120 ℃, after the reaction is finished, centrifugal separation is carried out for 100min at 4000r/min, deionized water and absolute ethyl alcohol are used for filtering and washing for a plurality of times, and the Ni-Cu LDH electrocatalyst is obtained after drying in vacuum at 60 ℃ for 24 h.
Example 3
(1) Dissolving nickel nitrate hexahydrate in a mixed solution of ionized water and triethylene glycol, and mechanically stirring to obtain a uniform solution A; the mass ratio of the ionized water to the triethylene glycol is 1: 7; the molar ratio of nickel nitrate hexahydrate to deionized water is 1: 5;
(2) adding urea and copper chloride dihydrate into the uniform solution A obtained in the step (1) to obtain a uniform solution B; in the solution B, the molar ratio of urea, copper chloride dihydrate and nickel nitrate hexahydrate is 2:5: 0.5;
(3) hydrothermal synthesis of the uniform solution B is carried out for 18-30h at 120 ℃, after the reaction is finished, centrifugal separation is carried out for 100min at 4000r/min, deionized water and absolute ethyl alcohol are used for filtering and washing for a plurality of times, and the Ni-Cu LDH electrocatalyst is obtained after drying in vacuum at 60 ℃ for 24 h.
Comparative example 1
(1) Dissolving nickel nitrate hexahydrate in a mixed solution of ionized water and triethylene glycol, and mechanically stirring to obtain a uniform solution A; the mass ratio of the ionized water to the triethylene glycol is 1: 3; the molar ratio of nickel nitrate hexahydrate to deionized water is 1: 5;
(2) adding urea and copper chloride dihydrate into the uniform solution A obtained in the step (1) to obtain a uniform solution B; in the solution B, the molar ratio of urea, copper chloride dihydrate and nickel nitrate hexahydrate is 2:5: 0.5;
(3) hydrothermal synthesis of the uniform solution B is carried out for 18-30h at 120 ℃, after the reaction is finished, centrifugal separation is carried out for 100min at 4000r/min, deionized water and absolute ethyl alcohol are used for filtering and washing for a plurality of times, and the Ni-Cu LDH electrocatalyst is obtained after drying in vacuum at 60 ℃ for 24 h.
Comparative example 2
(1) Dissolving nickel nitrate hexahydrate in a mixed solution of ionized water and triethylene glycol, and mechanically stirring to obtain a uniform solution A; the mass ratio of the ionized water to the triethylene glycol is 1: 8; the molar ratio of nickel nitrate hexahydrate to deionized water is 1: 5;
(2) adding urea and copper chloride dihydrate into the uniform solution A obtained in the step (1) to obtain a uniform solution B; in the solution B, the molar ratio of urea, copper chloride dihydrate and nickel nitrate hexahydrate is 2:5: 0.5;
(3) hydrothermal synthesis of the uniform solution B is carried out for 18-30h at 120 ℃, after the reaction is finished, centrifugal separation is carried out for 100min at 4000r/min, deionized water and absolute ethyl alcohol are used for filtering and washing for a plurality of times, and the Ni-Cu LDH electrocatalyst is obtained after drying in vacuum at 60 ℃ for 24 h.
Comparative example 3
(1) Dissolving nickel nitrate hexahydrate in a mixed solution of ionized water and triethylene glycol to obtain a uniform solution A; the mass ratio of the ionized water to the triethylene glycol is 1: 4; the molar ratio of nickel nitrate hexahydrate to deionized water is 1: 5;
(2) adding urea into the uniform solution A obtained in the step (1) to obtain a uniform solution B;
(3) and carrying out hydrothermal synthesis on the uniform solution B for 18-30h at 120 ℃, and after the reaction is finished, separating, cleaning and drying to obtain the Ni-Cu LDH electrocatalyst.
Performance testing
The final products of examples 1-3 and comparative examples 1-2 were weighed to obtain 4mg, and 750. mu.L of deionized water, 200. mu.L of isopropyl alcohol and 50. mu.L of naphthol were added to prepare a catalyst solution, and 30. mu.L of the catalyst solution was dropped onto 1cm by 1cm carbon paper to measure the reducing activity.
The test method is as follows:
the test adopts a three-electrode system, carbon paper is clamped by an electrode clamp to be used as a working electrode, a silver/silver chloride electrode is used as a reference electrode, a platinum net is used as a counter electrode, 1mol/L potassium hydroxide and 1mol/L potassium nitrate mixed solution is used as an electrolyte solution, an electrochemical workstation is used for providing a power supply, the applied voltage range is-0.5 to-1 v, and the test duration is 1 hour. Testing
As can be seen from the SEM and TEM of fig. 1 and 2, the Ni-Cu LDH electrocatalyst prepared by example 1 of the present invention has a nanoflower structure.
As can be seen from FIG. 3, the XRD pattern of the Ni-Cu LDH electrocatalyst prepared in example 1 of the present invention is similar to that of Ni (OH)2The main peaks can be well matched.
As can be seen from fig. 4, the Ni — Cu LDH nanoflower structure electrocatalyst according to the present invention has the highest nitric acid reduction activity and faraday efficiency when the mass ratio of water to triethylene glycol is 1: 4. When the amount of triethylene glycol added is less than 4 times of the amount of water, the reaction tends to generate echinoid substances, and when the amount of triethylene glycol is more than 4 times of the amount of water, a nanosheet structure is easier to form, the nanosheet structure is thin in shape, larger in BET (BET), more in surface-exposed active sites and more favorable for adsorption of nitric acid, and Ni (OH)2Nanosheet pair H2The O cracking is faster, and after Cu is added, the NI-Cu bond causes potential difference, so that the nitric acid adsorption and the water cracking are more favorable, and the nitric acid reduction activity and the Faraday efficiency are higher. Thus, examples 1-3 performed better than comparative example 1. When the amount of triethylene glycol is more than 7 times the amount of water, the amount of dissolved nickel hydroxide is too small, and the reactants cannot be sufficiently combined into Ni — Cu LDH, thereby deteriorating the performance. Thus, examples 1-3 performed better than comparative example 2.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all simple modifications, alterations and equivalents of the above embodiments according to the technical spirit of the present invention are still within the protection scope of the technical solution of the present invention.