Two-dimensional sheet structure CuO and preparation method and application thereof

Abstract

The application belongs to the technical field of electrocatalytic carbon dioxide reduction reaction, and discloses a two-dimensional sheet structure CuO and a preparation method and application thereof. The preparation method of the two-dimensional sheet structure CuO comprises the following steps: mixing terephthalic acid, a first organic solvent, a second organic solvent and Cu(NO3)2.3H2O, and performing a hydrothermal reaction to obtain Cu-MOF; and calcining the Cu-MOF to obtain the two-dimensional sheet structure CuO. The two-dimensional sheet structure Cu-MOF is prepared by using an in-situ synthesis method, the two-dimensional sheet structure Cu-MOF is used as a precursor, the crystal face of the two-dimensional sheet structure CuO material is regulated by a simple pyrolysis oxidation method, the pyrolysis temperature is controlled, the preferential selectivity of the CuO crystal face can be precisely regulated, and the high selectivity of CO2RR to ethylene can be realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrocatalytic carbon dioxide reduction reaction, and particularly relates to a two-dimensional sheet structure CuO and a preparation method and application thereof. BACKGROUND

[0002] Electrocatalytic conversion of carbon dioxide (CO2) into high-value chemicals and fuels is a promising technical approach that can convert waste into valuable resources and promote the development of a sustainable society. Among various CO2 emission reduction products, C 2+ products are of great interest due to their high value, and ethylene, as an important component of the chemical industry, has become the focus of this field. However, effectively converting CO2 into ethylene remains a formidable challenge. Notably, copper-based catalysts in the field of transition metal catalysts have attracted widespread attention due to their excellent C 2+ product selectivity. Generally, the electrocatalytic CO2 reduction reaction (CO2RR) on copper-based catalysts includes three key steps: efficient diffusion of CO2 to the catalyst interface, activation of CO2 molecules at the interface, and coordinated proton-electron transfer (CPET) steps to ultimately form CO intermediates. Finally, the catalyst must have high activity to promote C * -Coupling reactions to facilitate the formation of C 2+ products.

[0003] To overcome its limitations, researchers have developed some effective strategies, such as developing efficient electrocatalysts, adjusting the electrode-electrolyte interface, and optimizing the electrolytic cell design. However, C-C coupling is the most critical step in determining the selectivity and yield of various C 2+ products. In addition, there is still a lack of comprehensive consensus on the C-C coupling mechanism. In addition, to promote C-C coupling on the copper surface, strategies such as morphology tuning, crystal plane adjustment, chemical state manipulation, and surface modification have become hotspots for research, among which the crystal plane is considered a key parameter. From the crystal structure of copper, Cu(100) with a lower surface coordination number has higher CO dimerization reaction activity and C 2+ product selectivity. Theoretical calculations show that the C-C coupling of two * CO intermediates on Cu(100) is conducive to the generation of ethylene. Therefore, controlling the exposure of Cu(100) is considered a necessary condition to promote ethylene selectivity. However, the dynamic reconstruction of copper crystal planes during the CO2RR process is a challenge due to its low condensation energy driving, and CO2RR intermediates exacerbate this challenge. Therefore, it is necessary to ensure the stability of the Cu(100) crystal surface of the catalyst during the CO2RR reaction process while increasing the content of Cu(100) in the catalyst material.

[0004] Cu oxide (CuOx ), which is of great interest due to its broad chemical selectivity towards a variety of multi-carbon products. Studies have reported that copper oxide derived copper surfaces have more grain boundary-like defects, which are active sites for CO2RR, thus improving its activity; while some believe that the activity improvement may simply be due to the increased active sites from the rougher morphology. CuO x is reduced to copper in the reaction, and is more inclined to produce C 2+ products, and inhibits the generation of CH4. Compared with in-situ oxidation method, electrodeposition method and hydrothermal method, the copper oxide obtained by the hot oxidation method in air is thicker and rougher, and has high activity at low overpotential, while at high overpotential, the current density is too high to cause serious mass transfer limitation, resulting in C 2+ product selectivity is lower than that of other methods.

[0005] Therefore, how to improve the C 2+ product selectivity of Cu oxide in the process of electrocatalysis is a problem to be solved at present. SUMMARY

[0006] The purpose of the present application is to provide a two-dimensional sheet structure CuO and a preparation method and application thereof, and to solve the problem of low C 2+ product selectivity of existing Cu oxide in the process of electrocatalysis.

[0007] In order to achieve the above-mentioned purpose of the application, the present application provides the following technical solutions:

[0008] The present application provides a preparation method of a two-dimensional sheet structure CuO, comprising the following steps:

[0009] terephthalic acid, a first organic solvent, a second organic solvent and Cu(NO3)2·3H2O are mixed to perform a hydrothermal reaction, so as to obtain Cu-MOF;

[0010] The Cu-MOF is calcined to obtain the two-dimensional sheet structure CuO.

[0011] Preferably, in the above preparation method of the two-dimensional sheet structure CuO, the amount ratio of the terephthalic acid, the first organic solvent and the second organic solvent is 30-50 mg: 1-6 mL: 0.5-3 mL;

[0012] The first organic solvent is N,N-dimethylformamide or dimethyl sulfoxide;

[0013] The second organic solvent is ethanol, methanol, propanol or isopropanol.

[0014] Preferably, in the above preparation method of the two-dimensional sheet structure CuO, the mass ratio of the terephthalic acid and Cu(NO3)2·3H2O is 3-5: 2-4.

[0015] Preferably, in the preparation method of the two-dimensional sheet structure CuO, the temperature of the hydrothermal reaction is 100-200 DEG C, and the time of the hydrothermal reaction is 4-8h.

[0016] Preferably, in the preparation method of the two-dimensional sheet structure CuO, the calcination condition is that the initial temperature is 20-30 DEG C, the final temperature is 200-800 DEG C, the temperature rising rate to the final temperature is 1-5 DEG C / min, and the holding time at the final temperature is 1-5h.

[0017] The application further provides the two-dimensional sheet structure CuO prepared by the preparation method of the two-dimensional sheet structure CuO.

[0018] The application further provides application of the two-dimensional sheet structure CuO in electrocatalytic CO2 reduction to prepare ethylene.

[0019] Compared with the prior art, the application has the following beneficial effects:

[0020] The application is different from single CuO x Nanoparticle structure, the two-dimensional sheet stack nanostructure Cu-MOF is prepared by an in-situ synthesis method, it is found that in the direct pyrolysis process, the two-dimensional sheet stack nanostructure has a crystal face control effect, the two-dimensional (2D) sheet CuO material crystal face is regulated by a simple pyrolysis oxidation method using the two-dimensional sheet stack nanostructure Cu-MOF as a precursor, by controlling the pyrolysis temperature, the accurate regulation of the preferential selectivity of the CuO crystal face can be realized, which is different from one-dimensional nanoparticle / nanowire structure, and the high selectivity of CO2RR to ethylene is realized. Due to the 2D sheet structure, in the pyrolysis process, the CuO crystal has a preferential selectivity of the crystal face. Therefore, the crystal face of copper also has a preferential conversion characteristic in the conversion process of CuO to copper in the reaction, and the high selectivity of ethylene is realized. This is compared with the unstable and complex Cu + / Cu 0 Proportion / crystal face regulation strategy, the pyrolysis oxidation method for regulating the 2D sheet CuO crystal face has good stability and is easy to control, thereby enhancing the CO2RR activity, and providing a new way for the preparation of CuO x The electrode realizes the high selectivity of ethylene. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description.

[0022] Figure 1 The XRD patterns of the two-dimensional (2D) sheet structure CuO in examples 1-6 and the Cu-MOF in example 1.

[0023] Figure 2 SEM image of Cu-MOF in Example 1;

[0024] Figure 3 SEM image of two-dimensional (2D) sheet structure CuO in Examples 1-6;

[0025] Figure 4 CO2RR performance chart of two-dimensional (2D) sheet structure CuO in Examples 2-6. DETAILED DESCRIPTION

[0026] The present application provides a preparation method of two-dimensional sheet structure CuO, comprising the following steps:

[0027] terephthalic acid, a first organic solvent, a second organic solvent and Cu(NO3)2.3H2O are mixed to perform a hydrothermal reaction to obtain Cu-MOF;

[0028] The Cu-MOF is calcined to obtain two-dimensional sheet structure CuO.

[0029] In the present application, the amount ratio of terephthalic acid, the first organic solvent and the second organic solvent is preferably 30-50 mg: 1-6 mL: 0.5-3 mL, further preferably 35-45 mg: 2-5 mL: 0.8-2.5 mL, and more preferably 38-41.5 mg: 3-4.5 mL: 1-2 mL.

[0030] In the present application, the first organic solvent is preferably N,N-dimethylformamide or dimethyl sulfoxide, and further preferably N,N-dimethylformamide.

[0031] In the present application, the second organic solvent is preferably ethanol, methanol, propanol or isopropanol, further preferably ethanol, propanol or isopropanol, and more preferably ethanol.

[0032] In the present application, the mass ratio of terephthalic acid and Cu(NO3)2.3H2O is preferably 3-5: 2-4, further preferably 3.5-4.5: 2.5-3.5, and more preferably 3.8-4.15: 2.8-3.02.

[0033] In the present application, the specific process of mixing is as follows:

[0034] Terephthalic acid is added into a mixed solution of N,N-dimethylformamide and ethanol, and magnetic stirring is performed until terephthalic acid is dissolved, then Cu(NO3)2.3H2O is added, and after magnetic stirring for 10 min, ultrasonic is performed until Cu(NO3)2.3H2O is dissolved.

[0035] In the present application, the temperature of the hydrothermal reaction is preferably 100-200℃, further preferably 125-176℃, and more preferably 130-150℃; the time of the hydrothermal reaction is preferably 4-8h, further preferably 4.5-7.5h, and more preferably 5-6h.

[0036] In the present application, after the hydrothermal reaction, the obtained product is washed with ethanol, centrifuged, and the precipitate obtained by centrifugation is dried.

[0037] The temperature of the drying is preferably 50-70℃, further preferably 55-65℃, and more preferably 58-60℃; the time of the drying is preferably 6-12h, further preferably 7-10h, and more preferably 8-9h.

[0038] In the present application, the conditions of the calcination are as follows: the initial temperature is preferably 20-30℃, further preferably 21-27℃, and more preferably 23-25℃; the final temperature is preferably 200-800℃, further preferably 400-700℃, and more preferably 500-600℃; the temperature rising rate to the final temperature is preferably 1-5℃ / min, further preferably 1.5-4.5℃ / min, and more preferably 2-4℃ / min; the holding time at the final temperature is preferably 1-5h, further preferably 1.5-4.5h, and more preferably 2-3h.

[0039] In the present application, after the calcination, natural cooling to room temperature is further included.

[0040] The present application also provides a two-dimensional sheet structure CuO prepared by the preparation method of the two-dimensional sheet structure CuO.

[0041] The present application also provides an application of the two-dimensional sheet structure CuO in electrocatalytic CO2 reduction to prepare ethylene.

[0042] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0043] Embodiment 1

[0044] A preparation method of a two-dimensional sheet structure CuO, comprising the following steps:

[0045] 830mg terephthalic acid was added into a mixed solution of 45mL N,N-dimethylformamide and 20mL ethanol, and magnetically stirred until the terephthalic acid was dissolved; 604mg Cu(NO3)2·3H2O was added, and magnetically stirred for 10min, and then ultrasonically treated until the Cu(NO3)2·3H2O was dissolved; it was transferred into a hydrothermal reactor, and hydrothermally reacted at 150℃ for 6h; the obtained product was washed with ethanol, centrifuged, and the precipitate obtained by centrifugation was placed into a blast drying oven and dried at 60℃ for 8h to obtain Cu-MOF;

[0046] The Cu-MOF was placed in a muffle furnace, and heated from 25℃ to 200℃ at a heating rate of 2℃ / min, and kept at 200℃ for 2h, and then naturally cooled to room temperature to obtain two-dimensional sheet structure CuO.

[0047] Example 2

[0048] A method for preparing two-dimensional sheet structure CuO, comprising the following steps:

[0049] The Cu-MOF prepared in Example 1 was placed in a muffle furnace, and heated from 25℃ to 400℃ at a heating rate of 2℃ / min, and kept at 400℃ for 2h, and then naturally cooled to room temperature to obtain two-dimensional sheet structure CuO.

[0050] Example 3

[0051] A method for preparing two-dimensional sheet structure CuO, comprising the following steps:

[0052] The Cu-MOF prepared in Example 1 was placed in a muffle furnace, and heated from 25℃ to 500℃ at a heating rate of 2℃ / min, and kept at 500℃ for 2h, and then naturally cooled to room temperature to obtain two-dimensional sheet structure CuO.

[0053] Example 4

[0054] A method for preparing two-dimensional sheet structure CuO, comprising the following steps:

[0055] The Cu-MOF prepared in Example 1 was placed in a muffle furnace, and heated from 25℃ to 600℃ at a heating rate of 2℃ / min, and kept at 600℃ for 2h, and then naturally cooled to room temperature to obtain two-dimensional sheet structure CuO.

[0056] Example 5

[0057] A method for preparing two-dimensional sheet structure CuO, comprising the following steps:

[0058] The Cu-MOF prepared in Example 1 was placed in a muffle furnace and heated from 25℃ to 700℃ at a heating rate of 2℃ / min, and kept at 700℃ for 2h, and then naturally cooled to room temperature to obtain two-dimensional sheet structure CuO.

[0059] Example 6

[0060] A method for preparing two-dimensional sheet structure CuO, comprising the following steps:

[0061] The Cu-MOF prepared in Example 1 was placed in a muffle furnace and heated from 25℃ to 800℃ at a heating rate of 2℃ / min, and kept at 800℃ for 2h, and then naturally cooled to room temperature to obtain two-dimensional sheet structure CuO.

[0062] The XRD patterns of the two-dimensional (2D) sheet structure CuO prepared in Examples 1-6 and the Cu-MOF prepared in Example 1 are shown in Figure 1 It can be seen from Figure 1 that no oxidation occurs at 200℃ (the ligand decomposition temperature is not reached); as the oxidation temperature increases (400℃-800℃), the (111) crystal plane of CuO has a preferential growth trend. At temperatures of 700℃ and 800℃, the (111) crystal plane of CuO tends to be stable.

[0063] The SEM image of the Cu-MOF prepared in Example 1 is shown in Figure 2 It can be seen from Figure 2 that the Cu-MOF has a multi-layer stacked structure, and the surface is smooth without obvious particles, indicating that the Cu-MOF is successfully prepared.

[0064] The SEM images of the two-dimensional (2D) sheet structure CuO prepared in Examples 1-6 are shown in Figure 3 It can be seen from Figure 3 that as the oxidation temperature increases, the particles continue to grow, and the layered structure gradually disappears. However, the sheet structure is still retained, and the overall structure does not collapse, indicating that there is a strong interaction between the crystal planes (non-111 planes) of CuO.

[0065] Application Example

[0066] 5mg of the two-dimensional sheet structure CuO prepared in Examples 2-6 was dispersed in 970μL of acetone and 30μL of Naifion mixed solution, respectively, and cold water ultrasonic treatment was performed for 2h to obtain a mixed solution;

[0067] The mixed solution was added dropwise to a hydrophobic carbon paper (size 3cm×1.5cm), and the loading amount of CuO on the hydrophobic carbon paper was 1mg / cm 2 to obtain a working electrode;

[0068] Electrochemical reduction of CO2 was carried out in a gas diffusion electrolyzer, the detailed process is as follows:

[0069] The gas diffusion electrolyzer was composed of ion exchange membrane (Nafion 117 membrane), anode chamber, cathode chamber and flowing CO2 gas chamber.

[0070] The electrolyte (1M KOH) was recirculated by a peristaltic pump, in which the side of the working electrode loaded with CuO was in contact with the electrolyte, and the other side of the working electrode was in contact with the gas chamber. The flow rate of CO2 was 20 mL / min, and the flow rate of electrolyte was 7 mL / min. Ag / AgCl was used as the reference electrode, and platinum plate was used as the counter electrode.

[0071] After the catalyst (working electrode loaded with two-dimensional sheet structure CuO) was pretreated by linear sweep voltammetry (LSV) cycles 10 times (scan rate was 50 mV / s) in the voltage window of 0~ -2V, and the structure evolved stably, cyclic voltammetry (CV) test and impedance spectrum (EIS) test were carried out at different scan rates in the non-faradic potential window, in order to estimate the electrochemical active surface area ECSAs. The formula E RHE = E Ag / AgCl + 0.197V + 0.0591pH was used to convert all the potentials measured with Ag / AgCl as the reference to the reversible hydrogen electrode potential (RHE).

[0072] Gas product analysis: gas chromatograph (GC), flame ionization detector (FID) and thermal conductivity detector (TCD) were used for online detection of gas products.

[0073] FEgas= nvFN / VI;

[0074] Where n is the amount of gas measured by gas chromatography, v is the flow rate of CO2 gas of 20 sccm, F is the Faraday constant (96485 C / mol), N is the number of transferred electrons to produce gas product molecules, V is the volume of 1 mol of gas at 298.15 K and 101.325 kPa (24.45 L), and I is the average current mA.

[0075] Liquid product analysis: 0.5 mL of liquid product was mixed with 100 uL of D2O (containing 25 ppm of DMSO), and was analyzed by liquid nuclear magnetic resonance spectrometer. The Faraday efficiency of the liquid product can be calculated as:

[0076] FE liquid = nFN / Q;

[0077] wherein n is the molar mass of the liquid product, F is the Faraday constant (96485 C / mol), N is the number of transferred electrons per molecule of liquid product, and Q is the total input electric charge, which can be directly read from the electrochemical workstation.

[0078] The CO2RR performance of the two-dimensional (2D) sheet structure CuO prepared in Examples 2-6 is shown in FIG. 2. As can be seen from FIG. 2, the (111) crystal plane of CuO has a preferential growth trend as the temperature increases. The two-dimensional (2D) sheet structure CuO has the highest ethylene selectivity of ~65% at 600°C, which is likely due to the preferential selectivity of the CuO (111) crystal plane. At temperatures of 700°C and 800°C, although the (111) crystal plane of CuO is optimal, the specific surface area of the overall two-dimensional (2D) sheet structure of CuO decreases due to the continuous increase in the size of the CuO particles, which weakens the adsorption of carbon dioxide. This leads to a decrease in the ethylene selectivity. Figure 4 Figure 4 As can be seen from FIG. 2, the (111) crystal plane of CuO has a preferential growth trend as the temperature increases. The two-dimensional (2D) sheet structure CuO has the highest ethylene selectivity of ~65% at 600°C, which is likely due to the preferential selectivity of the CuO (111) crystal plane. At temperatures of 700°C and 800°C, although the (111) crystal plane of CuO is optimal, the specific surface area of the overall two-dimensional (2D) sheet structure of CuO decreases due to the continuous increase in the size of the CuO particles, which weakens the adsorption of carbon dioxide. This leads to a decrease in the ethylene selectivity.

[0079] The above description is merely preferred embodiments of the present application, and it should be noted that, for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, which should also be considered within the scope of the present application.​

Claims

1. The application of two-dimensional layered CuO in the electrocatalytic reduction of CO2 to ethylene, characterized in that, The method for preparing the two-dimensional sheet-like CuO includes the following steps: Terephthalic acid, a first organic solvent, a second organic solvent, and Cu(NO3)2·3H2O were mixed and subjected to a hydrothermal reaction to obtain Cu-MOF; Cu-MOF was calcined to obtain a two-dimensional layered CuO structure. The ratio of terephthalic acid, the first organic solvent, and the second organic solvent is 30-50 mg: 1-6 mL: 0.5-3 mL; The first organic solvent is N,N-dimethylformamide or dimethyl sulfoxide; The second organic solvent is ethanol, methanol, propanol, or isopropanol; The hydrothermal reaction temperature is 100~200℃, and the hydrothermal reaction time is 4~8h; The calcination conditions are as follows: initial temperature is 20~30℃, final temperature is 400~800℃, heating rate to the final temperature is 1~5℃ / min, and holding time at the final temperature is 1~5h.

2. The application of the two-dimensional layered CuO structure according to claim 1 in the electrocatalytic reduction of CO2 to ethylene, characterized in that, The mass ratio of terephthalic acid to Cu(NO3)2·3H2O is 3~5:2~4.

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