阅读说明：本技术 一种Ni-Cu LDH金属纳米层材料电催化剂的制备方法 (Preparation method of Ni-Cu LDH metal nano-layer material electrocatalyst ) 是由 叶伟 徐梦秋 于 2021-08-04 设计创作，主要内容包括：本发明涉及催化剂领域,针对缺乏使硝酸盐高效生成NH-(3)的催化剂的问题,提供一种Ni-Cu LDH金属纳米层材料电催化剂的制备方法,先将六水合硝酸镍、十二烷基硫酸钠SDS和六亚甲基四胺HMT溶解在去离子水中,搅拌,再加入二水合氯化铜,继续搅拌,然后将每个溶液都充入氮气,加热反应,产物过滤、洗涤、干燥得ML Ni-Cu LDH；将ML Ni-Cu LDH与甲酰胺混合,加热反应,反应液纯化、干燥,得SL Ni-Cu LDH。本方法工艺简单、耗能少、条件温和,制得的催化剂形貌好,具有较高的理论比电容和优良的氧化还原性,可以使硝酸盐高效生成NH-(3)。(The invention relates to the field of catalysts, and aims to overcome the defect of high-efficiency generation of NH from nitrate 3 Firstly, dissolving nickel nitrate hexahydrate, Sodium Dodecyl Sulfate (SDS) and Hexamethylenetetramine (HMT) in deionized water, stirring, then adding copper chloride dihydrate, continuously stirring, then filling nitrogen into each solution, heating for reaction, filtering, washing and drying the product to obtain ML Ni-Cu LDH; and mixing the ML Ni-Cu LDH with formamide, heating for reaction, purifying and drying reaction liquid to obtain the SL Ni-Cu LDH. The method has the advantages of simple process, low energy consumption, mild conditions, good appearance of the prepared catalyst, higher theoretical specific capacitance and excellent oxidation-reduction property, and can enable nitrate to efficiently generate NH 3 。)

1. A preparation method of an electrocatalyst made of Ni-Cu LDH metal nano-layer materials is characterized by comprising the following steps:

step one, preparing ML Ni-Cu LDH: firstly, dissolving nickel nitrate hexahydrate, Sodium Dodecyl Sulfate (SDS) and Hexamethylenetetramine (HMT) in deionized water, stirring, adding copper chloride dihydrate, continuously stirring, heating to react under the protection of inert gas, filtering, washing and drying a product to obtain MLNi-Cu LDH;

step two, preparing SLNi-Cu LDH: and (3) mixing the ML Ni-Cu LDH prepared in the step one with formamide, heating for reaction, and purifying and drying reaction liquid to obtain the SL Ni-Cu LDH.

2. The method for preparing the electrocatalyst of the Ni-Cu LDH metal nano-layer material, according to claim 1, wherein the mass ratio of the nickel nitrate hexahydrate and the copper chloride dihydrate in the first step is Ni: Cu ═ 1 (0.1-1).

3. The method for preparing the electrocatalyst for the Ni-Cu LDH metal nano-layer material according to claim 1 or 2, wherein the mass ratio of the nickel nitrate hexahydrate, the sodium dodecyl sulfate SDS and the hexamethylenetetramine HMT in the first step is (1-2): (1-2).

4. The method for preparing an electrocatalyst of Ni-Cu LDH metal nanolayer material as claimed in claim 1, wherein the heating reaction in step one is carried out at 110-130 ℃ for 10-12 h.

5. The method for preparing the electrocatalyst of Ni-Cu LDH metal nanolayer material as claimed in claim 1 or 4, wherein the drying condition in step one is air drying at room temperature to constant weight.

6. The method for preparing the electrocatalyst for the Ni-Cu LDH metal nanolayer material as claimed in claim 1, wherein the amount of formamide used in step two is 75-200ml formamide added per 1mmol nickel nitrate hexahydrate in step one.

7. The method for preparing the electrocatalyst of the Ni-Cu LDH metal nano-layer material as claimed in claim 1, wherein the heating reaction conditions in step two are 50-70 ℃ under inert gas protection and heating and stirring for 47-50 h.

8. The method for preparing the electrocatalyst of Ni-Cu LDH metal nanolayer material as claimed in claim 1, 6 or 7, wherein the step of purifying in step two is: the reaction solution is firstly subjected to ultrasonic treatment for 1-2h, then centrifuged at a low rotating speed for 3-5min to obtain an upper layer solution, then centrifuged at a high rotating speed for 10-12min to remove impurities, and filtered and washed with deionized water and absolute ethyl alcohol for several times.

9. The method for preparing the electrocatalyst made of Ni-Cu LDH metal nanolayer material as claimed in claim 8, wherein the centrifugation rotation speed at small rotation speed in step two is 3000-5000r/min, and the centrifugation rotation speed at large rotation speed is 8000-10000 r/min.

Technical Field

The invention relates to the field of catalysts, in particular to a preparation method of an electrocatalyst made of a Ni-Cu LDH metal nano-layer material.

Background

Electrochemical production of ammonia as an alternative to the haber-bosch process can reduce fossil fuel usage and carbon dioxide emissions. An attractive technique that has emerged in recent years is direct electroreduction of nitrogen, but to date, NH has been electrochemically synthesized₃Poor selectivity and large energy consumption become a great obstacle. The invention introduces an electrochemical strategy, and efficiently generates NH from nitrate by using a Ni-Cu LDH catalyst₃. Nitrate has long been recognized as a toxic pollutant in industrial and agricultural wastewater and is thereforeA valuable resource which can be recovered and used for the production of NH₃。

Ammonia is produced on a large scale by the Haber-Bosch process. Such an industry N₂The yield of the reduction reaction (NRR) is generally less than 200mmol g_cat ^-1h^-1The process is energy intensive because it is carried out at high temperatures of 400-. However, these reaction rates and partial current densities are generally less than 10mmol g, respectively_cat ^-1h^-1And 1mA cm^-2。N₂941kJ/mol was required to break the NN triple bonds, and the energy required for NO bond cleavage in nitrate was only 204 kJ/mol. From an energy perspective, it is very meaningful and feasible to explore the electrocatalytic nitric acid reduction reaction (NITRR) as a promising tool for low temperature ammonia synthesis, but the poor selectivity is also a big obstacle to nitric acid reduction, so the kinetics of NITRR can be optimized for the competing Hydrogen Evolution Reaction (HER). It is well known that nitrate in drinking water causes diseases such as methemoglobinemia and non-hodgkin's lymphoma. Converting nitrate to ammonia by electrocatalysis may provide a good solution to energy and environmental problems. In addition, due to the worldwide use of nitrogenous fertilizers and pesticides, nitrate is abundant in nature. The reduction of nitric acid to ammonia is promising from the point of view of feasibility and raw material abundance. For example, patent CN112354541A discloses a Co/CoO heterojunction electrocatalyst supported on a foamed nickel substrate and a preparation method thereof, which is mainly applied to nitrate radical hydrogenation reduction in water, and utilizes an electrode material with catalytic action to generate an electrocatalytic reduction reaction, so that nitrate radicals are changed into valuable substances and converted into ammonium radicals.

The electrocatalytic conversion of nitrate nitrogen to ammonia involves 9 protons and 8 electrons (NO)₃ ^-+9H⁺+8e^-→NH₃+3H₂O), in addition, complex products of NITRR, possibly including NO₂ ^-、N₂And NH₃Also, significant challenges are presented to the goal of highly selective synthesis. Nitrogen oxyanions and nitrogen are inevitably produced as unwanted by-products in this process. Accordingly, an ideal solution is needed.

Disclosure of Invention

The invention aims to overcome the defect of high-efficiency generation of NH from nitrate₃The method has simple process, less energy consumption and mild conditions, and the prepared catalyst has good appearance, a porous structure, higher theoretical specific capacitance and excellent oxidation-reduction property, and can enable nitrate to efficiently generate NH₃。

In order to achieve the purpose, the invention adopts the following technical scheme:

a preparation method of an electrocatalyst made of Ni-Cu LDH metal nano-layer materials comprises the following steps:

step one, preparing ML Ni-Cu LDH: firstly, dissolving nickel nitrate hexahydrate, Sodium Dodecyl Sulfate (SDS) and Hexamethylenetetramine (HMT) in deionized water, stirring, adding copper chloride dihydrate, continuously stirring, heating to react under the protection of inert gas, filtering, washing and drying a product to obtain MLNi-Cu LDH;

step two, preparing SLNi-Cu LDH: and (3) mixing the ML Ni-Cu LDH prepared in the step one with formamide, heating for reaction, and purifying and drying reaction liquid to obtain the SL Ni-Cu LDH.

In the first step and the second step of the invention, deionized water is used for dissolution, and zinc nitrate hexahydrate, Sodium Dodecyl Sulfate (SDS) and Hexamethylenetetramine (HMT) and copper chloride dihydrate form inorganic compounds containing specific Ni-Cu LDH. Ni (OH)₂Cu is loaded on the nano-chip, the high electron density of the Cu hinders the competitive reaction of HER, the reduction energy barrier of nitrate radical is obviously reduced, and the orbital of the Cu and the LUMO pi of the nitrate radical^*Have similar energy levels and therefore have high potential in nitrate reduction.

Preferably, in the first step, the mass ratio of the nickel nitrate hexahydrate to the copper chloride dihydrate is Ni to Cu 1 (0.1-1).

Preferably, the mass ratio of the nickel nitrate hexahydrate, the sodium dodecyl sulfate SDS and the hexamethylenetetramine HMT in the first step is (1-2) to (1-2).

Preferably, the heating reaction in the first step is carried out at 110-130 ℃ for 10-12 h.

Preferably, the drying condition in the first step is air drying to constant weight at room temperature.

Preferably, the amount of formamide used in the second step is 75-200ml of formamide added in every 1mmol of nickel nitrate hexahydrate in the first step.

Preferably, the heating reaction conditions in the second step are 50-70 ℃ and heating and stirring for 47-50h under the protection of inert gas.

Preferably, the purification step in step two is: the reaction solution is firstly subjected to ultrasonic treatment for 1-2h, then centrifuged at a low rotating speed for 3-5min to obtain an upper layer solution, then centrifuged at a high rotating speed for 10-12min to remove impurities, and filtered and washed with deionized water and absolute ethyl alcohol for several times.

Preferably, in the second step, the small-rotation-speed centrifugal rotation speed is 3000-5000r/min, and the large-rotation-speed centrifugal rotation speed is 8000-10000 r/min.

Therefore, the beneficial effects of the invention are as follows: the Ni-Cu LDH metal nano-layer material electrocatalyst prepared by the invention has a porous structure, has higher theoretical specific capacitance and excellent oxidation-reduction property, is an attractive supercapacitor candidate material, can generate higher electrocatalytic activity in an electrochemical workstation, and has wide application prospect in the field of electrocatalysis. The synthesis method provided by the invention has the characteristics of simple process, low energy consumption, mild conditions, good product appearance and the like, and is suitable for large-scale production and application.

Drawings

FIG. 1 is a TEM image of Ni-Cu LDH metal nano-layer material electrocatalyst prepared in example 5;

FIG. 2 is an XRD pattern of the electrocatalyst for Ni-Cu LDH metal nanolayer material prepared in example 5;

FIG. 3 is an activity diagram of the electrocatalyst for Ni-Cu LDH metal nanolayer material prepared in example 5 at different voltages;

FIG. 4 is a graph comparing the activity of electrocatalysts prepared in examples 1-7 and comparative example 1;

figure 5 is a graph of the cycling stability of the Ni-Cu LDH metal nano-layer material electrocatalyst prepared in example 5.

Detailed Description

The technical solution of the present invention is further illustrated by the following specific examples.

In the present invention, unless otherwise specified, all the raw materials and equipment used are commercially available or commonly used in the art, and the methods in the examples are conventional in the art unless otherwise specified.

Example 1

A preparation method of an electrocatalyst made of Ni-Cu LDH metal nano-layer materials comprises the following steps:

step one, preparing ML Ni-Cu LDH: dissolving 1mmol of nickel nitrate hexahydrate, 1mmol of Sodium Dodecyl Sulfate (SDS) and 1mmol of Hexamethylenetetramine (HMT) in 50mL of deionized water, fully stirring for 10min, adding 170.48mg of copper chloride dihydrate (namely the amount of substances of Ni: Cu is 1:1), stirring for 30min, heating to 120 ℃ under the protection of nitrogen, reacting for 12h, filtering and washing for 3 times by using deionized water and absolute ethyl alcohol after the reaction is finished, and finally air-drying at room temperature to constant weight to obtain MLNi-Cu LDH;

step two, preparing SL Ni-Cu LDH: mixing the prepared ML Ni-Cu LDH with 150mL of formamide, heating and stirring the mixture in a 60 ℃ oil bath for 48 hours under the protection of nitrogen, purifying the reaction solution, and specifically, carrying out ultrasonic treatment on the obtained reaction solution for 2 hours, centrifuging the reaction solution at a low rotating speed of 3000r/min for 3 minutes, taking the upper layer solution, centrifuging the reaction solution at a high rotating speed of 8000r/min for 10 minutes to remove impurities, filtering and washing the reaction solution for 3 times by using deionized water and absolute ethyl alcohol, and finally drying the reaction solution in a vacuum oven at 60 ℃ to constant weight to obtain the SL Ni-Cu LDH.

4mg of the prepared SL Ni-Cu LDH was added with 750. mu.L of deionized water, 200. mu.L of isopropyl alcohol and 50. mu.L of naphthol to prepare a catalyst solution, 30. mu.L of the catalyst solution was dropped on 1cm by 1cm carbon paper, and the reduction activity was measured.

Example 2

The difference from example 1 is that the mass of copper chloride dihydrate is 127.86mg, i.e. the amount of Ni to Cu species is 1: 0.75.

Example 3

The difference from example 1 is that the mass of copper chloride dihydrate is 85.24mg, i.e. the amount of Ni: Cu species is 1: 0.5.

Example 4

The difference from example 1 is that the mass of copper chloride dihydrate is 68.192mg, i.e. the amount of Ni to Cu species is 1: 0.4.

Example 5

The difference from example 1 is that the mass of copper chloride dihydrate is 51.144mg, i.e. the amount of Ni to Cu species is 1: 0.3.

Example 6

The difference from example 1 is that the mass of copper chloride dihydrate is 34.092mg, i.e. the amount of Ni: Cu species is 1: 0.2.

Example 7

The difference from example 1 is that the mass of copper chloride dihydrate is 17.048mg, i.e. the amount of Ni to Cu species is 1: 0.1.

Example 8

A preparation method of an electrocatalyst made of Ni-Cu LDH metal nano-layer materials comprises the following steps:

step one, preparing ML Ni-Cu LDH: dissolving 1mmol of nickel nitrate hexahydrate, 2mmol of Sodium Dodecyl Sulfate (SDS) and 1mmol of Hexamethylenetetramine (HMT) in 50mL of deionized water, fully stirring for 10min, adding 170.48mg of copper chloride dihydrate (namely the amount of substances of Ni: Cu is 1:1), stirring for 30min, heating to 110 ℃ under the protection of nitrogen, reacting for 12h, filtering and washing for 3 times by using deionized water and absolute ethyl alcohol after the reaction is finished, and finally air-drying at room temperature to constant weight to obtain MLNi-Cu LDH;

step two, preparing SL Ni-Cu LDH: mixing the prepared ML Ni-Cu LDH with 75mL of formamide, heating and stirring the mixture in a 50 ℃ oil bath for 50 hours under the protection of nitrogen, purifying the reaction solution, and specifically, carrying out ultrasonic treatment on the obtained reaction solution for 1 hour, centrifuging the reaction solution for 5 minutes at a small rotating speed of 4000r/min, taking the upper layer solution, centrifuging the reaction solution for 12 minutes at a large rotating speed of 9000r/min to remove impurities, filtering and washing the reaction solution for 3 times by using deionized water and absolute ethyl alcohol, and finally drying the reaction solution in a vacuum oven at 60 ℃ to constant weight to obtain the SLNi-Cu LDH.

Example 9

A preparation method of an electrocatalyst made of Ni-Cu LDH metal nano-layer materials comprises the following steps:

step one, preparing ML Ni-Cu LDH: dissolving 1mmol of nickel nitrate hexahydrate, 2mmol of Sodium Dodecyl Sulfate (SDS) and 2mmol of Hexamethylenetetramine (HMT) in 50mL of deionized water, fully stirring for 10min, adding 170.48mg of copper chloride dihydrate (namely the amount of substances of Ni: Cu is 1:1), stirring for 30min, heating to 130 ℃ under the protection of nitrogen, reacting for 10h, filtering and washing for 3 times by using deionized water and absolute ethyl alcohol after the reaction is finished, and finally air-drying at room temperature to constant weight to obtain MLNi-Cu LDH;

step two, preparing SL Ni-Cu LDH: mixing the prepared ML Ni-Cu LDH with 200mL of formamide, heating and stirring the mixture in a 70 ℃ oil bath for 47 hours under the protection of nitrogen, purifying the reaction solution, and specifically, carrying out ultrasonic treatment on the obtained reaction solution for 2 hours, centrifuging the reaction solution for 4 minutes at a low rotating speed of 5000r/min, taking the upper layer solution, centrifuging the reaction solution for 11 minutes at a high rotating speed of 10000r/min to remove impurities, filtering and washing the reaction solution for 3 times by using deionized water and absolute ethyl alcohol, and finally drying the reaction solution in a vacuum oven at 60 ℃ to constant weight to obtain the SL Ni-Cu LDH.

Comparative example 1

The difference from example 1 is that no copper chloride dihydrate was added in step one.

Performance testing

The electrocatalyst made from the Ni-Cu LDH metal nano-layer material prepared in example 5 of the present invention was subjected to TEM, XRD, and electrochemical tests for nitric acid reduction. The method for testing the catalytic activity of the nitric acid reduction comprises the following steps: a three-electrode system is adopted, carbon paper is clamped by an electrode clamp to serve as a working electrode, a silver/silver chloride electrode serves as a reference electrode, a platinum net serves as a counter electrode, a mixed solution of 1mol/L potassium hydroxide and 1mol/L potassium nitrate serves as an electrolyte solution, an electrochemical workstation is used for providing a power supply, the applied voltage range is-0.1 to-0.6 v, and the test duration is 1 hour.

The characterization results show in fig. 1 that the electrocatalyst made of the Ni-Cu LDH metal nano-layer material prepared in example 5 mostly has a nano flower-like structure. And tested via an electrochemical workstation at 1mol/L KOH and 1mol/L KNO₃In the electrolyte, the measured nitric acid reduction rate is best; as can be seen from FIG. 2, the electrocatalyst for Ni-Cu LDH metal nanolayer material prepared in example 5, Ni (OH)₂The main peaks can be well matched; as can be seen from FIG. 3, the electrocatalyst made from Ni-Cu LDH metal nano-layer material prepared in example 5 is applied at-0.6V voltageThe ammonia production activity is highest;

as can be seen from FIG. 4, the ammonia generating activity of each example of the present invention was greatly improved as compared with that of comparative example 1 in which copper chloride dihydrate was not used, since the present invention was applied to Ni (OH)₂Cu is loaded on the nano-chip, the high electron density of the Cu hinders the competitive reaction of HER, the reduction energy barrier of nitrate radical is obviously reduced, and the orbital of the Cu and the LUMO pi of the nitrate radical^*Have similar energy levels, so the catalyst has good catalytic effect in nitrate reduction. Compared with the examples, in example 5, the nitric acid reduction activity is the highest under the condition that Ni and Cu are 1:0.3, namely the ammonia generating activity is the highest; fig. 5 is a graph of the cycling stability of Ni-Cu LDH metal nano-layer material electrocatalyst prepared in example 5, and it can be seen that example 5 has good faradaic efficiency.

Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.