Application of amorphous copper quantum dot catalyst in preparation of ammonia by electro-catalytic reduction of nitrate

Abstract

The invention belongs to the technical field of electro-catalysis materials, and discloses application of an amorphous copper quantum dot catalyst in electro-catalysis of nitrate reduction to prepare ammonia, and a preparation method of amorphous copper quantum dots comprises the following steps: adding copper salt into an alcohol solvent, and stirring for dissolving; and then adding a reducing agent tannic acid, adding alkali, continuously stirring, transferring into a reaction kettle, carrying out hydrothermal reaction, centrifuging, separating, washing and drying to obtain the copper quantum dots. The amorphous Cu (QDs) catalytic material prepared by the invention ingeniously solves the problems of low activity, poor selectivity and weak stability in the process of electrocatalytic reduction of nitrate to prepare ammonia.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrocatalytic materials, and relates to application of an amorphous copper quantum dot catalyst in electrocatalytic reduction of nitrate to prepare ammonia. BACKGROUND

[0002] Ammonia is an important material for fertilizers, refrigerants and fibers, and is also a renewable energy and clean energy storage medium, which is widely used in the fields of agriculture / industry, distributed energy storage, power generation, etc., and the global demand for ammonia is also increasing. At present, the synthesis of ammonia includes nitrogenase, Haber-Bosch method, photocatalytic or electrocatalytic nitrogen to ammonia, and electrocatalytic nitrate. However, although the ammonia synthesis by nitrogenase has high efficiency, it is slow and difficult to recover. At present, the production of ammonia depends on the Haber-Bosch method, but it consumes a large amount of fossil fuels and emits a large amount of carbon dioxide. Therefore, it is urgent to develop green and sustainable ammonia synthesis technology.

[0003] Electrocatalytic ammonia synthesis not only can utilize renewable electricity, making electrons as reducing agents, but also has the advantages of environmental friendliness and high safety. In recent years, with the development of electrochemical nitrogen oxidation and plasma nitrogen oxidation methods, the strategy of first oxidizing nitrogen to NOx or NO3 - and then reducing it to ammonia is more feasible than the strategy of directly electrochemical nitrogen reduction to synthesize ammonia. In addition, from the environmental point of view, electrocatalytic reduction of nitrate to ammonia is considered to be a very promising green process. However, electrocatalytic reduction of nitrate is a complex reaction process involving multiple electron and proton transfer, and in the reaction process, multiple intermediates such as nitrite, nitric oxide and nitrous oxide are produced, so this method brings great challenges to the high selectivity of ammonia synthesis.

[0004] Many kinds of materials have been proposed as electrocatalysts for the reduction of nitrate to ammonia, including noble metals, transition non-noble metals and non-metallic electrocatalysts. The catalysts currently widely used are mainly transition metal catalysts, which are divided into noble metal and non-noble metal catalysts. However, due to the high price and scarcity of noble metal catalysts, they are difficult to be widely used. Therefore, non-noble metal catalysts in transition metals have become a research hotspot.

[0005] In recent years, many optimizations have been made to further improve the performance of transition metal catalysts, such as doping, alloying, exposing specific lattice planes, and introducing defects. The study of defect chemistry has attracted widespread attention as an effective way to regulate the physical / chemical properties of the surface of catalytic materials. The presence of defects will significantly change the structure and chemical properties, and promote the formation of new physical and chemical properties or strong synergistic effects, thereby optimizing the catalytic performance of electrocatalysts. Defects are divided into 0, 1, 2 and 3-dimensional defects. Currently, 3-dimensional defects, which are defects caused by atomic disorder degree to produce free volume regions of atoms, are rarely studied to improve the activity of catalysts in electrocatalytic reduction of nitrate to ammonia. Therefore, a new type of catalyst needs to be developed to solve the above problems and improve the practical application potential of electrocatalytic reduction of nitrate to ammonia. SUMMARY

[0006] The application provides an application of amorphous copper quantum dots in electrocatalytic reduction of nitrate to ammonia, which solves the problem of low selectivity in electrocatalytic reduction of nitrate to ammonia and has good stability under the premise of ensuring good high-activity and high-selectivity catalytic effect.

[0007] To achieve the above object, the application adopts the following technical scheme: The application provides an application of amorphous copper quantum dots in electrocatalytic reduction of nitrate to ammonia, and a preparation method of the amorphous copper quantum dots comprises the following steps: A copper salt is added to an alcohol solvent and stirred and dissolved, then a reducing agent tannic acid is added, alkali is added and stirring is continued, and then the mixture is transferred to a reaction kettle for hydrothermal reaction at 0-30 DEG C, centrifuged, separated, washed and dried to obtain copper quantum dots.

[0008] In the above technical scheme, the alcohol solvent is selected from ethanol, ethylene glycol, n-propanol or isopropanol.

[0009] In the above technical scheme, the mass ratio of the copper salt to the reducing agent tannic acid is 2.5:1.

[0010] In the above technical scheme, the copper salt is selected from one of copper chloride, copper sulfate and copper nitrate.

[0011] In the above technical scheme, the hydrothermal reaction time is 1-3 h.

[0012] In the above technical scheme, the alkali is selected from one of sodium hydroxide and potassium hydroxide.

[0013] In the above technical scheme, the dosage ratio of the alkali to the reducing agent tannic acid is 1 g:25 ml.

[0014] Compared with the prior art, the application has the beneficial technical effects that: Compared with the prior art, the application has the beneficial effects that: 1. The amorphous Cu (QDs) catalytic material prepared by the method has strong NO3 - adsorption capacity, electron structure regulation capacity, can reduce the reaction energy barrier and inhibit the competitive reaction, and more than 98% of the atoms on the surface are active sites, and the size effect of quantum dots also promotes the electron transfer efficiency, reduces the reaction energy barrier and increases the active sites, and the combination of the two cleverly solves the problems of low activity, poor selectivity and weak stability in the reduction of nitrate to ammonia by electrocatalysis.

[0015] 2. The method only uses one-step hydrothermal growth, uses tannic acid as a reducing agent, a complexing agent, a surface functional agent and a nucleation control agent to form amorphous quantum dots with uniform size in cooperation with an alcohol solvent, has low reaction temperature, simple process, ingenious idea, remarkable effect, uses green and inexpensive common materials as reagents, and has high raw material utilization rate. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is the XRD graph of Cu (QDs) catalysts obtained at different reaction temperatures.

[0017] Figure 2 is the TEM graph of Cu (QDs) catalysts obtained at different reaction temperatures.

[0018] Figure 3 is the Cu 2p XPS graph of Cu (QDs) catalysts obtained at different reaction temperatures.

[0019] Figure 4 is the LSV graph of Cu (QDs) catalysts obtained at different reaction temperatures.

[0020] Figure 5 is the FE and yield graph of NH3 of Cu (QDs) catalysts obtained at 0 ℃ (left), 30 ℃ (middle) and 60 ℃ (right).

[0021] Figure 6 is the stability of 30 ℃-Cu (QDs) catalyst under the constant potential test condition of-0.9V vs.RHE. DETAILED DESCRIPTION

[0022] The following examples are used to illustrate the present application, but are not used to limit the protection scope of the present application. If not specifically indicated, the technical means used in the examples is the conventional means known to those skilled in the art. The test methods in the following examples are conventional methods, unless otherwise specified.

[0023] Example 1 0.2 g of CuCl2•2H2O was dispersed in 40 ml of ethylene glycol and dissolved by ultrasonic stirring for 15 min. Then, 0.08 g of tannic acid was added and stirring continued to maintain a homogeneous solution. Next, 2 ml of 1 mol / L NaOH was added dropwise to adjust the pH, and stirring was continued for 5 min. The entire solution was then transferred to a 100 ml polytetrafluoroethylene (PTFE) reactor and reacted at 30 ℃ for 1 h. The reaction product was removed, centrifuged, and cooled to room temperature to obtain a brown precipitate. This precipitate was washed repeatedly by centrifugation with deionized water and anhydrous ethanol. Finally, it was dried in an oven at 60 ℃ for 12 h to obtain the amorphous Cu(QDs) catalyst, denoted as 30 ℃-Cu(QDs).

[0024] Example 2 This embodiment is basically the same as Example 1, except that the hydrothermal reaction temperature is changed from 30 ℃ to 0 ℃, and the product is denoted as 0 ℃-Cu(QDs).

[0025] Example 3 This embodiment is basically the same as Example 1, except that the hydrothermal reaction temperature is changed from 60 ℃ to 0 ℃, and the product is denoted as 60 ℃-Cu(QDs).

[0026] Example 4 This embodiment is basically the same as Example 1, except that the hydrothermal reaction temperature is changed from 90 ℃ to 0 ℃, and the product is denoted as 90 ℃-Cu(QDs).

[0027] Example 5 This embodiment is basically the same as Example 1, except that the hydrothermal reaction temperature is changed from 120 ℃ to 0 ℃, and the product is denoted as 120 ℃-Cu(QDs).

[0028] like Figure 1 As shown, the XRD diffraction peaks of the obtained materials correspond one-to-one with the standard cards. Among them, 0 ℃-Cu(QDs) and 30 ℃-Cu(QDs) are amorphous quantum dots, while 60 ℃-Cu(QDs), 90 ℃-Cu(QDs) and 30 ℃-Cu(QDs) are crystalline quantum dots.

[0029] like Figure 2 As shown, transmission of the catalyst at different reaction temperatures revealed a size of 20 nm, preliminarily proving the availability of Cu(QDs) catalyst material.

[0030] like Figure 3 The XPS results show that, through Cu 2+ The binding energies of 3 / 2p and Cu 1 / 2p shift downwards, causing the d-band center to move lower, thereby enhancing the binding of NO3. -adsorption, accelerate the proton coupled electron transfer and inhibit the competing hydrogen evolution reaction.

[0031] Example 6 A homogeneous suspension was obtained by mixing 1 mg of catalyst prepared in Example 1-6, 380 μL of ultrapure water, 100 μL of absolute ethanol and 20 μL of 5wt.% nafion 117 solution, and then ultrasonic treatment for 30 min. The conductive carbon paper was cut into 1×2 cm 2 in size, washed with ultrapure water and absolute ethanol in turn, and dried for standby use. An appropriate amount of prepared turbid liquid was taken by a pipette and drop-coated on the carbon paper, with a coating area of 1×1 cm 2 . After drying, repeated dropwise addition was performed until the catalyst loading reached 0.1 mg cm -2 . The carbon paper coated with catalyst was clamped to the platinum sheet electrode clamp, which was the working electrode. The reaction was controlled in a standard H-type electrolytic cell three-electrode system by an electrochemical workstation. The cathode and anode chambers were separated by a nafion 117 membrane, and a platinum mesh electrode (1×1 cm 2 ) was used as the counter electrode, and a Hg / HgO (1 M KOH) electrode was used as the reference electrode. The electrolyte was a mixture of 1 M KOH + 0.1 M KNO3, and 30 mL was added to the cathode and anode chambers, respectively. Before testing, high-purity Ar was introduced into the cathode chamber for 30 min to remove O2 and N2 and other pollutants in the solution, and Ar was continuously introduced during the test. The magnetic stirring was started when the Ar was introduced, and the magnetic stirring was maintained throughout the test.

[0032] (1) The Cu(QDs) series catalysts were electrochemically tested by linear sweep voltammetry (LSV).

[0033] As shown in Figure 4 , the results show that in the 1 M KOH + 0.1 M KNO3 electrolyte, the Cu(QDs) catalysts obtained at different reaction temperatures all show a significantly right-shifted onset potential (compared with the 1 M KOH system) and a significantly increased current density, which strongly proves that the prepared catalyst has the ability to electrocatalyze the reduction of nitrate to ammonia in this range. In addition, in the 1 M KOH + 0.1 M KNO3 electrolyte, the current density of the 30℃-Cu(QDs) catalyst is much larger than that of the Cu(QDs) catalysts at other reaction temperatures at the same potential, which indicates that the atomic disorder degree at this temperature effectively improves the catalytic performance of the reduction of nitrate to ammonia.

[0034] (2) The NO3 -NH3 performance of RR. The test was carried out in 1 M KOH + 0.1 M KNO3 mixed electrolyte system, with a step potential of -0.7 ~ -1.1 V vs. RHE (ΔV = 0.1 V) applied, and each electrolysis lasted for 1 h. After the reaction, the cathode chamber electrolyte was taken out, moderately diluted, and the NH3 concentration was determined by indophenol blue spectrophotometry, and quantitative analysis was carried out based on the standard curve.

[0035] As shown in Figure 5 , the NH3 FE of Cu (QDs) catalysts obtained at different reaction temperatures showed a volcano trend with the increase of overpotential, but the NH3 FE of 30℃-Cu (QDs) catalyst reached 96% at -0.9 V vs. RHE, and the yield was as high as 20 mg h - 1 cm -2 , which were higher than those of 0℃-Cu (QDs) and 60℃-Cu (QDs) catalysts. As shown in Figure 6 , after 6 cycles, the NH3 yield and FE of 30℃-Cu (QDs) catalyst did not decrease, indicating that 30℃-Cu (QDs) catalyst had good stability.

[0036] The above-described embodiments are only preferred embodiments of the present application, merely used to explain the present application, and are not intended to limit the scope of the present application. For those skilled in the art, of course, other embodiments can be easily made by substitution or change based on the technical content disclosed in the present specification, and therefore, any changes and improvements made on the principles of the present application shall be included in the scope of the present application.

Claims

1. Use of an amorphous copper quantum dot catalyst for the electrocatalytic reduction of nitrate to ammonia, characterized in that, The preparation method of the amorphous copper quantum dots comprises the following steps: A copper salt is added in an alcohol solvent and stirred and dissolved; then a reducing agent tannic acid is added, alkali is added and stirring is continued, and then the mixture is transferred to a reaction kettle to perform hydrothermal reaction at 0-30 DEG C, centrifuged, separated, washed and dried to obtain copper quantum dots.

2. Use according to claim 1, characterized in that, The alcohol solvent is selected from ethanol, ethylene glycol, n-propanol or isopropanol.

3. Use according to claim 1, characterized in that, The mass ratio of the copper salt to the reducing agent tannic acid is 2.5:

1.

4. Use according to claim 1, characterized in that, The copper salt is selected from one of copper chloride, copper sulfate and copper nitrate.

5. The use according to claim 1, characterized in that, The hydrothermal reaction time is 1-3 h.

6. Use according to claim 1, characterized in that, The alkali is selected from one of sodium hydroxide and potassium hydroxide.

7. The use according to claim 1, characterized in that, The dosage ratio of the alkali to the reducing agent tannic acid is 1 g:25 ml.

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