A copper tetrahedral electrocatalyst for carbon dioxide reduction and preparation method thereof

Abstract

The application discloses a copper tetrahedron electrocatalyst for carbon dioxide reduction and a preparation method thereof. The copper tetrahedron electrocatalyst is prepared by the following steps: mixing cuprous bromide and tri-n-octylphosphine oxide, dissolving the mixture in oleylamine, heating under vacuum, adding N,N-dimethylformamide for regulation, and then heating for reaction. The particle size of the copper tetrahedron electrocatalyst is 45 nm to 65 nm. The catalyst has excellent electrochemical activity and stability, and when the catalyst is applied to electrocatalytic reduction of carbon dioxide, the CO faradic efficiency can reach 67% at-0.83 V vs. RHE, so the catalyst has a good popularization prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of electrocatalysts, and particularly relates to a copper tetrahedron electrocatalyst for carbon dioxide reduction (e-CO2RR) and a preparation method thereof. BACKGROUND

[0002] With the overuse and consumption of fossil fuels, the rise in the content of carbon dioxide generated thereby is seriously damaging the environment, leading to climate deterioration. Therefore, it is urgent to convert carbon dioxide into high-value and sustainable energy. Among numerous strategies, electrocatalytic carbon dioxide reduction reaction (e-CO2RR) is considered as a very promising method. This method can utilize the surplus power generated by renewable energy to achieve green conversion of carbon dioxide under mild conditions. However, the e-CO2RR still has many shortcomings such as a variety of reduction products, high reduction overpotential, low energy utilization rate, high cost of catalysts, poor stability of catalysts and the like, which seriously limit the industrial application of the catalysts. At the same time, because the theoretical reduction potential of the hydrogen evolution reaction (HER) is generally lower than that of the CO2RR, the HER is still a very strong competitive reaction in the CO2RR, especially in the water system. Therefore, it is urgent to develop and design efficient electrocatalysts to solve the above problems as soon as possible.

[0003] Among the materials applied to the electrocatalytic carbon dioxide reduction system, copper-based catalysts are widely considered as the most efficient and inexpensive electrocatalytic materials, and single-crystal copper catalysts are more carefully studied and explored by researchers due to their regular structure. Peng Dongliang et al. first prepared copper nanocubes and nanospheres by disproportionation reaction of cuprous bromide under the protection of argon gas with the use of tri-n-octylphosphine oxide (TOPO) and tri-n-octylphosphine (TOP). On the basis of the experimental conditions, Raffaella Buonsanti et al. prepared a series of copper single-crystal materials with single crystal faces such as copper cubes, copper tetrahedrons and copper octahedrons by changing the proportion of raw materials and the reaction conditions such as protective gas (N2), and explored the e-CO2RR performance of the materials, and found that the copper (200) crystal face is more conducive to the production of C2H4, and the (111) crystal face is more conducive to the production of CO. This finding provides guidance for further research on the e-CO2RR mechanism of copper-based catalysts. However, the catalysts prepared by the above method have the shortcomings of low yield and low structural integrity of the prepared copper tetrahedrons, and further exploration and improvement are still needed. SUMMARY

[0004] In view of the above problems, the present application provides a copper tetrahedron material with high structural integrity and size effect and a preparation method thereof. The copper tetrahedron material has excellent electrochemical activity and stability, and can be used as an electrocatalyst for carbon dioxide reduction (e-CO2RR).

[0005] To achieve the above object, the present application adopts the following technical solutions:

[0006] One of the objects of the present application is to protect a copper tetrahedron electrocatalyst for carbon dioxide reduction, which has a particle size of 45-65 nm.

[0007] The second object of the present application is to protect a preparation method of the copper tetrahedron electrocatalyst, which comprises the following steps:

[0008] 1) Under N2 protection, uniformly mix cuprous bromide and tri-n-octylphosphine, then dissolve in oleylamine, uniformly stir at room temperature to obtain a light green mixed solution;

[0009] 2) The mixed solution obtained in step 1) is heated to 80 ℃ under vacuum for 60 min, then N,N-dimethylformamide (DMF) is added under N2 atmosphere, and the mixed solution is stirred for 10 min to obtain a light yellow-green mixed solution;

[0010] 3) The mixed solution obtained in step 2) is heated to 270 ℃ and kept for 60 min, then cooled to room temperature to obtain a brick red suspension;

[0011] 4) The suspension obtained in step 3) is washed by centrifugation with n-hexane and ethanol alternately, and the precipitate is collected, which is the copper tetrahedron electrocatalyst.

[0012] Further, the amount ratio of cuprous bromide, tri-n-octylphosphine and oleylamine used in step 1) is (0.5-1) g:9 g:150 mL.

[0013] Further, the amount of N,N-dimethylformamide added in step 2) is 1 mL per (0.5-1) g of cuprous bromide.

[0014] Further, the heating rate in step 3) is 10 ℃ ` min -1 .

[0015] The present application has at least the following beneficial effects:

[0016] (1) The present application uses tri-n-octylphosphine, oleylamine, cuprous bromide and N,N-dimethylformamide as raw materials, and different particle sizes of copper tetrahedron can be synthesized through disproportionation reaction under N2 atmosphere. The synthesis method is simple, the structure of the product is complete, and the product has excellent microcrystalline lattice arrangement.

[0017] (2) The synthesized 45 nm copper tetrahedron applied in e-CO2RR shows excellent electrochemical activity and stability. The copper tetrahedron can reach an excellent CO faradic efficiency of 67 % under the condition of low overpotential (-0.83 V vs. RHE). The result of the constant potential test for 12 hours shows that the copper tetrahedron current curve does not change obviously at the potential corresponding to the current density, indicating that the copper tetrahedron has excellent electrocatalytic stability. 2 The copper tetrahedron current curve does not change obviously at the potential corresponding to the current density, indicating that the copper tetrahedron has excellent electrocatalytic stability. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 Transmission electron microscopy images of the copper materials prepared for Examples 1-3 (a-c) and Comparative Example (d).

[0019] Figure 2 X-ray powder diffraction pattern of the copper tetrahedron prepared for Example 1.

[0020] Figure 3 High-resolution transmission electron microscopy image and selected area electron diffraction pattern of the copper tetrahedron prepared for Example 1.

[0021] Figure 4 High-resolution X-ray photoelectron spectroscopy pattern of copper and oxygen elements of the copper tetrahedron prepared for Example 1.

[0022] Figure 5 Faradic efficiency pattern of the copper tetrahedron prepared for Example 1 in e-CO2RR in carbon dioxide-saturated 1 M KOH solution.

[0023] Figure 6 Constant potential curve pattern of the copper tetrahedron prepared for Example 1 after 12 hours of reaction. DETAILED DESCRIPTION

[0024] In order to make the content of the present application more convenient to understand, the technical solutions of the present application will be further described below in combination with specific embodiments, but the present application is not limited thereto.

[0025] Example 1

[0026] 1) Under N2protection, 1 g of cuprous bromide and 9 g of tri-n-octylphosphine oxide were added into a three-necked bottle, uniformly mixed and dissolved in 150 mL of degassed oleylamine, uniformly stirred at room temperature to obtain a light green mixed solution;

[0027] 2) The mixed solution obtained in step 1) was heated to 80 ℃ under vacuum for 60 min, then 1 mL of DMF was added under N2atmosphere, and the solution was stirred for 10 min to obtain a light yellow-green mixed solution;

[0028] 3) The mixed solution obtained in step 2) is heated to 270 ℃ at a rate of 10 ℃ ` min -1 , and the reaction is terminated after 60 min, and the mixture is cooled to room temperature to obtain a brick red suspension;

[0029] 4) The suspension obtained in step 3) is washed by centrifugation with n-hexane and ethanol alternately, and the precipitate is collected to obtain copper tetrapods with a particle size of 45 nm.

[0030] Example 2

[0031] 1) Under the protection of N2, 0.7 g of cuprous bromide and 9 g of tri-n-octyl phosphine oxide are added into a three-necked flask, uniformly mixed, dissolved in 150 mL of degassed oleylamine, and uniformly stirred at room temperature to obtain a light green mixed solution;

[0032] 2) The mixed solution obtained in step 1) is heated to 80 ℃ under vacuum for 60 min, and then 1 mL of DMF is added under N2 atmosphere, and the mixture is stirred for 10 min to obtain a light yellow-green mixed solution;

[0033] 3) The mixed solution obtained in step 2) is heated to 270 ℃ at a rate of 10 ℃ ` min -1 , and the reaction is terminated after 60 min, and the mixture is cooled to room temperature to obtain a brick red suspension;

[0034] 4) The suspension obtained in step 3) is washed by centrifugation with n-hexane and ethanol alternately, and the precipitate is collected to obtain copper tetrapods with a particle size of 55 nm.

[0035] Example 3

[0036] 1) Under the protection of N2, 0.5 g of cuprous bromide and 9 g of tri-n-octyl phosphine oxide are added into a three-necked flask, uniformly mixed, dissolved in 150 mL of degassed oleylamine, and uniformly stirred at room temperature to obtain a light green mixed solution;

[0037] 2) The mixed solution obtained in step 1) is heated to 80 ℃ under vacuum for 60 min, and then 1 mL of DMF is added under N2 atmosphere, and the mixture is stirred for 10 min to obtain a light yellow-green mixed solution;

[0038] 3) The mixed solution obtained in step 2) is heated to 270 ℃ at a rate of 10 ℃ ` min -1 , and the reaction is terminated after 60 min, and the mixture is cooled to room temperature to obtain a brick red suspension;

[0039] 4) The suspension obtained in step 3) was washed by centrifugation with n-hexane and ethanol alternately, and the precipitate was collected to obtain copper tetrahedron with a particle size of 65 nm.

[0040] Comparative Example

[0041] 1) Under N2 protection, 1 g of cuprous bromide and 9 g of tri-n-octyl phosphine oxide were added into a three-necked flask, uniformly mixed, and dissolved in 150 mL of degassed oleylamine, and then uniformly stirred at room temperature to obtain a light green mixed solution;

[0042] 2) The mixed solution obtained in step 1) was heated to 80 °C under vacuum for 60 min, and then stirred under N2 atmosphere for 10 min, and then heated to 270 °C at a rate of 10 °C / min, and then kept for 60 min, and then cooled to room temperature to obtain a suspension; ` min -1

[0043] 3) The suspension obtained in step 2) was washed by centrifugation with n-hexane and ethanol alternately, and the precipitate was collected to obtain single-crystal copper material.

[0044] Figure 1 The transmission electron microscopy images of the copper materials prepared in Examples 1-3 (a-c) and Comparative Example (d). As can be seen from the figure, the use of DMF plays a regulating role in the morphology of copper particles, which realizes the successful preparation of copper tetrahedron.

[0045] Figure 2 The X-ray diffraction pattern of the copper tetrahedron prepared in Example 1. As can be seen from the figure, the copper tetrahedron has diffraction peak characteristics at 43.3°, 50.4° and 74.1°, which correspond to the (111), (200) and (220) faces of Cu, respectively, and the characteristic peak of the (111) face is obviously enhanced, indicating that the obtained copper tetrahedron is a single-crystal copper material with (111) face orientation advantage.

[0046] Figure 3 The high-resolution transmission electron microscopy image and selected area electron diffraction pattern of the copper tetrahedron prepared in Example 1. As can be seen from the figure, the lattice fringes attributed to the Cu (111) face are captured under the high-resolution transmission electron microscopy mode; at the same time, the diffraction ring of the Cu (111) face is also captured in the selected area electron diffraction pattern, which is consistent with the XRD data, proving that the copper tetrahedron material with (111) face orientation advantage is successfully prepared.

[0047] Figure 4 The high-resolution X-ray photoelectron spectroscopy of copper and oxygen elements of the copper tetrahedron prepared in Example 1. As shown in the figure, the copper tetrahedron mainly exists in the form of zero-valent copper, and there is a small amount of sub-oxidized monovalent copper on the surface.

[0048] ​Application Examples

[0049] The electrochemical performance of the copper tetrahedron prepared in Example 1 was tested. Specifically, a three-electrode system was used for e-CO2RR. The electrolyte was 1 M KOH saturated with carbon dioxide. The three electrodes used included a counter electrode (platinum mesh), a reference electrode (silver / silver chloride), and a working electrode (30T carbon paper with a catalyst loading of 0.5 mg cm). -2 The instrument used for the electrochemical performance test is Autolab, model PGSTAT302N, manufactured by Metrohm, Switzerland.

[0050] Figure 5 is the obtained Faraday efficiency diagram. Figure 5 It can be seen that the optimal performance point of copper tetrahedron is -0.83 V vs. RHE, and it can achieve a CO Faradaic efficiency of 67% under alkaline conditions, exceeding most of the copper single crystal catalysts reported so far.

[0051] Figure 6 This is the constant potential test curve for 12 hours. Figure 5 It can be seen that the copper tetrahedron exhibits good stability during the 12-hour electrolysis process.

[0052] The above results demonstrate that the copper tetrahedrons prepared in the present invention exhibit good e-CO2RR activity at low potential.

[0053] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing a copper tetrahedral electrocatalyst for carbon dioxide reduction, characterized in that: The following steps are involved: 1) Under nitrogen protection, cuprous bromide and tri-n-octylphosphine oxide were mixed and dissolved in oleylamine. The mixture was stirred magnetically at room temperature to obtain a light green mixed solution. 2) The mixed solution obtained in step 1) was heated to 80°C under vacuum conditions and maintained for 60 min. Then, N,N-dimethylformamide was added under a nitrogen atmosphere and stirred for 10 min to obtain a light yellow-green mixed solution. 3) heating the mixed solution obtained in step 2) to 270°C, maintaining the temperature for 60 minutes, and then cooling the mixture to room temperature to obtain a brick-red suspension; 4) washing the suspension obtained in step 3) by alternating centrifugation with n-hexane and ethanol, and collecting the precipitate to obtain the copper tetrahedron electrocatalyst; The ratio of cuprous bromide, tri-n-octylphosphine oxide, and oleylamine used in step 1) is (0.5-1) g:9 g:150 mL; The amount of N,N-dimethylformamide added in step 2) is calculated as 1 mL per (0.5-1) g of cuprous bromide; In step 3), the heating rate is 10 °C ` min -1 .

2. A copper tetrahedral electrocatalyst for carbon dioxide reduction prepared by the method of claim 1, characterized in that: Its particle size is 45~65nm.

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