Preparation and application of r-Cu2 (OH) 3X electrocatalyst

Abstract

The invention discloses preparation and application of an r-Cu2 (OH) 3X electrocatalyst, and belongs to the technical field of electrocatalyst preparation. The preparation method adopts an improved sol-gel method, after washing and drying, carbon dioxide is introduced for electrolysis under an alkaline condition, and halogen is doped into a copper-based material to obtain the catalyst r-Cu2 (OH) 3X. Due to the fact that halogen doping has an electronic regulation effect on copper, the catalyst has high reaction activity and selectivity on multi-carbon products in alkaline electrolyte, and the catalyst can serve as a catalyst for the reaction of electro-catalyzing carbon dioxide reduction to produce multi-carbon in the alkaline environment. The catalyst for preparing the multi-carbon product by reducing the carbon dioxide through alkaline electro-catalysis is high in activity, has an obvious stability advantage and has a wide development prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalytic carbon dioxide reduction reaction under alkaline conditions, and specifically relates to a preparation method of a halogen-doped copper-based catalyst and its application in the direction of efficiently and stably electrocatalytically reducing carbon dioxide to produce multi-carbon products under alkaline conditions. Background Art

[0002] With the intensification of global climate change and the gradual depletion of fossil fuel resources, the development of sustainable clean energy technologies has become an important topic in current scientific research. Carbon dioxide (CO2) is an important component of greenhouse gases, and the continuous increase in its concentration has led to the rise of global temperature and the frequent occurrence of extreme climates. Therefore, effectively converting CO2 into valuable chemicals and fuels can not only reduce environmental pollution but also alleviate the energy crisis to a certain extent. It is crucial to find efficient and safe carbon dioxide conversion technologies. Electrochemical reduction of CO2 (CO2RR) is an effective method to convert greenhouse gases into valuable chemicals. However, current catalysts usually have problems such as poor selectivity for multi-carbon products, insufficient activity, and poor stability in the CO2 reduction reaction, which limits their industrial applications. Therefore, the research and development of new efficient catalysts have become a hot topic in current research.

[0003] In recent years, in order to improve catalytic activity and selectivity and reduce catalyst costs, the research on non-metal doped copper catalysts has increased. For example: copper clusters anchored by boron-doped graphene significantly improve the production efficiency of C2 products in the electrocatalytic reduction of carbon dioxide; nitrogen-doped carbon-confined copper-silver bimetallic catalysts efficiently produce high-value-added products in the electrocatalytic reduction of carbon dioxide; by using special proton transport and the electronic structure modification of phosphorus, a phosphorus-containing Cu catalyst (CuP-xV) is prepared by in-situ electrodeposition at different potentials, realizing high selectivity for multi-carbon products. Although these catalysts are significantly superior to elemental copper catalysts in terms of selectivity and activity for carbon dioxide reduction to produce multi-carbon, their selectivity still needs to be improved and the catalyst synthesis method is complex, still unable to meet the actual needs of carbon dioxide reduction. Summary of the Invention

[0004] The object of the present invention is to develop a preparation method of an r-Cu2(OH)3X catalyst that continuously works during the electrocatalytic reduction of carbon dioxide under alkaline conditions. The Faraday efficiency of this catalyst for producing multi-carbon products can reach about 78% at a total current density of -250 mA cm −2 which is 2.5 times that of copper hydroxide and 2 times that of metallic copper. A potentiostatic electrolysis stability test is carried out at a potential of -1.9 V vs. Ag / AgCl, and it can maintain -90 mA cm –2The local current density of multi-carbon production and nearly 45% ethylene selectivity can be achieved without obvious deactivation. And the catalyst synthesis method is simple and efficient.

[0005] To achieve the above object, the technical solution of the present invention is as follows: A preparation method of r-Cu2(OH)3X electrocatalyst, comprising the following steps: (1) Dissolve copper halide in propanol to obtain a solution with a concentration of 0.15 - 6 mol / L; add propylene oxide and deionized water under continuous stirring to obtain a mixed solution; (2) Seal and age the mixed solution for 1 - 5 days, centrifuge the aged solution to obtain a precipitate, wash and vacuum dry; (3) Electrochemical reconstruction: Make the dried product into an electrode sheet and electrolyze it in the electrolyte for 10 - 30 min.

[0006] Further, the copper halide is copper fluoride, copper chloride and copper bromide.

[0007] Further, the molar ratio of propylene oxide to copper halide is (8 - 12):1. Preferably, the molar ratio of propylene oxide to copper halide is 10:1 Further, the electrolyte is 1 M KOH solution.

[0008] An r-Cu2(OH)3X electrocatalyst is prepared by the above method.

[0009] Further, there are two crystal phases of copper and cuprous oxide in the electrocatalyst.

[0010] Further, the electrocatalyst is applied to electrocatalytic reduction of carbon dioxide under alkaline conditions.

[0011] Further, the electrocatalyst is applied to electrocatalytic preparation of multi-carbon products from carbon dioxide under alkaline conditions.

[0012] Preferably, bromine element is introduced into metallic copper to obtain a catalyst precursor first. The halogen-doped Cu2(OH)3X (X = F, Cl, Br) nanomaterial is used as the working electrode, the platinum sheet electrode is used as the counter electrode, the Ag / AgCl electrode is used as the reference electrode, and 1 M KOH solution is used as the electrolyte. The Cu-based electrocatalytic CO2RR catalyst r-Cu2(OH)3X is obtained by constant voltage activation. A rich Cu 0 / Cu + sites are formed on the surface of the electrochemically reconstructed r-Cu2(OH)3Br catalyst, and a small amount of Br ions remain, resulting in a significant increase in the lattice spacing, changing the surface electronic structure and local environment of the catalyst, thereby further improving the selectivity of electrocatalytic CO2RR to C 2+ products.

[0013] A Br-doped Cu-based electrocatalytic CO2RR catalyst is prepared by the above method.

[0014] Application of a Br-doped Cu-based electrocatalytic CO2RR catalyst, where the catalyst is used for electrocatalytic CO2RR to prepare C 2+ product.

[0015] For the above-mentioned bromine-doped copper catalyst precursor, the atomic ratio in the precursor, Br:Cu should be 1:1.

[0016] The preparation process of the above-mentioned bromine-doped copper catalyst (r-Cu2(OH)3Br) is as follows: Dissolve 0.3 - 3 mmol of copper bromide (CuBr2) in 0.2 - 2 mL of 2-propanol to form a dark green transparent solution A. Under continuous stirring, gradually add 0.2 - 2 mL of propylene oxide and 0.02 - 0.2 mL of deionized water to solution A, and finally obtain a blue-green solution B. Seal and age the obtained mixed solution B. Then wash the obtained precipitate clean to remove possible organic substances. After vacuum drying for 8 - 12 h, grind it evenly to obtain a bromine-doped copper precursor catalyst. Prepare the precursor powder into a working electrode and electrolyze for 10 - 30 min to obtain the catalyst.

[0017] For the preparation method of the above-mentioned catalyst r-Cu2(OH)3Br, the reactions are carried out under normal temperature conditions except for vacuum drying.

[0018] For the preparation method of the above-mentioned catalyst r-Cu2(OH)3Br, the aging process needs to be carried out for 1 - 3 days under airtight conditions.

[0019] For the preparation method of the above-mentioned catalyst r-Cu2(OH)3Br, the washing process uses the organic solvent acetone.

[0020] For the preparation method of the above-mentioned catalyst r-Cu2(OH)3Br, the drying temperature is 60 - 70 °C.

[0021] For the preparation method of the above-mentioned catalyst r-Cu2(OH)3Br, the electrolysis process is carried out in 1 M KOH solution and the atmosphere is CO2.

[0022] Compared with the prior art, the present invention has the following beneficial effects: 1. The synthesis process is simple, the yield is relatively high, and the experimental process can be regulated. The obtained catalyst r-Cu2(OH)3X has high crystallinity, presents a mixed structure of nanoparticles and dendrites, and has a higher active surface area.

[0023] 2. Copper is the only catalyst that can simultaneously catalyze carbon monoxide, formic acid and polycarbonate (C 2+ ) products, and has good application prospects. The present invention regulates the electronic properties of the copper catalyst by introducing halogen elements to improve its selectivity and stability, which is the key to achieving CO2 reduction. The electronic structure of the copper in the obtained catalyst r-Cu2(OH)3X is regulated by halogens, which optimizes the activity of the copper metal itself and the selectivity for multi-carbon products. Among them, the r-Cu2(OH)3Br catalyst shows the highest selectivity for multi-carbon products at -1.0 V, reaching 78%, of which the selectivity for ethylene reaches 53.2%. The material has excellent activity and stability in the carbon dioxide reduction reaction in alkaline media, which is significantly better than traditional copper hydroxide and metallic copper catalysts, and reduces the cost of the material to a certain extent, and can be used as an alternative.

[0024] 3. The obtained catalyst r-Cu2(OH)3X has very broad application prospects in the fields of electrocatalytic CO2RR, new energy, etc. The catalyst described in the present invention can successfully dope non-metallic halogen elements into copper catalysts, successfully adjust the lattice spacing and internal electronic structure of copper, significantly improve the reaction activity and high selectivity of copper, and perfectly improve the catalytic performance while reducing costs. The synthesis process of the present invention is simple, the experimental process is easy to control, and it has great potential in the field of electrocatalytic CO2RR. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 These are the relevant SEM images of catalysts Cu2(OH)3Br and r-Cu2(OH)3Br.

[0026] Figure 2 The relevant XRD patterns of catalysts Cu2(OH)3Br and r-Cu2(OH)3Br.

[0027] Figure 3 These are the relevant TEM and HRTEM images of the catalyst r-Cu2(OH)3Br.

[0028] Figure 4 Linear sweep voltammetry curve of catalyst r-Cu2(OH)3X in alkaline medium (1 M KOH).

[0029] Figure 5 This is a comparison chart of the selectivity of the electrocatalytic CO2RR of the catalyst r-Cu2(OH)3X and its control sample for multi-carbon products.

[0030] Figure 6 HRTEM images of the catalyst r-Cu2(OH)3X and the control samples (Implementation Cases 2~3 and commercial copper hydroxide). DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific examples. In the present invention, without special instructions, M representing concentration all refers to mol / L. For example, 1 M KOH represents a KOH solution of 1 mol / L.

[0032] (1) Preparation of the precursor: Dissolve 0.3 - 3 mmol of copper halide in 0.2 - 2 mL of 2-propanol to form a dark green transparent solution A. Under continuous stirring, gradually add 0.2 - 2 mL of propylene oxide and 0.02 - 0.2 mL of deionized water to solution A, and finally obtain a blue-green solution B. Seal and age the obtained mixed solution B for 1 - 3 days to obtain a blue-green precipitate. Then wash the obtained precipitate with the organic solvent acetone to remove possible organic substances. Place it in a vacuum oven and dry it at 60 °C overnight, and then grind it evenly to obtain a halogen-doped copper precursor catalyst (Cu2(OH)3X).

[0033] (2) Preparation of the catalyst r-Cu2(OH)3X: Prepare the precursor powder Cu2(OH)3X into a working electrode, use a platinum plate electrode as the counter electrode, an Ag / AgCl electrode as the reference electrode, and use a 1 M KOH solution as the electrolyte, and activate it at a constant voltage to obtain a Cu-based electrocatalytic CO2RR catalyst r-Cu2(OH)3X.

[0034] Example 1: r-Cu2(OH)3Br (1) Preparation of the precursor: Dissolve 3 mM of copper bromide (CuBr2) in mL of 2-propanol to form a dark green transparent solution A. Under continuous stirring, gradually add 2 mL of propylene oxide and 0.2 mL of deionized water to solution A, and finally obtain a blue-green solution B. Seal and age the obtained mixed solution B for 1 day to obtain a blue-green precipitate. Then wash the obtained precipitate with the organic solvent acetone to remove possible organic substances. Place it in a vacuum oven and dry it at 60 °C overnight, and then grind it evenly to obtain a bromine-doped copper precursor catalyst (Cu2(OH)3Br).

[0035] (2) Preparation of the catalyst r-Cu2(OH)3Br: Prepare the precursor powder Cu2(OH)3Br into a working electrode, use a platinum plate electrode as the counter electrode, an Ag / AgCl electrode as the reference electrode, and use a 1 M KOH solution as the electrolyte, and activate it at a constant voltage to obtain a Cu-based electrocatalytic CO2RR catalyst r-Cu2(OH)3Br.

[0036] Example 2: r-Cu2(OH)3Cl (1)Preparation of precursor Cu2(OH)3Cl: Dissolve 3 mM of copper chloride (CuCl2) in 2 mL of 2-propanol to form a dark green transparent solution A. Under continuous stirring, gradually add 2 mL of propylene oxide and 0.2 mL of deionized water to solution A, and finally obtain a blue-green solution B. Seal and age the obtained mixed solution B for 1 day to obtain a blue-green precipitate. Then wash the obtained precipitate with the organic solvent acetone to remove possible organic substances. Place it in a vacuum oven and dry it at 60 °C overnight, and then grind it evenly to obtain the bromine-doped copper precursor catalyst (Cu2(OH)3Cl).

[0037] (2)Preparation of catalyst r-Cu2(OH)3Cl: Prepare the precursor powder into a working electrode, use a platinum plate electrode as the counter electrode, an Ag / AgCl electrode as the reference electrode, and use 1 M KOH solution as the electrolyte, and activate it at a constant voltage to obtain the Cu-based electrocatalytic CO2RR catalyst r-Cu2(OH)3Cl.

[0038] Example 3: r-Cu2(OH)3F (1)Preparation of precursor Cu2(OH)3F: Dissolve 3 mM of copper fluoride (CuF2) in 2 mL of 2-propanol to form a dark green transparent solution A. Under continuous stirring, gradually add 2 mL of propylene oxide and 0.2 mL of deionized water to solution A, and finally obtain a blue-green solution B. Seal and age the obtained mixed solution B for 1 day to obtain a blue-green precipitate. Then wash the obtained precipitate with the organic solvent acetone to remove possible organic substances. Place it in a vacuum oven and dry it at 60 °C overnight, and then grind it evenly to obtain the bromine-doped copper precursor catalyst (Cu2(OH)3F).

[0039] (2)Preparation of catalyst r-Cu2(OH)3F: Prepare the precursor powder into a working electrode, use a platinum plate electrode as the counter electrode, an Ag / AgCl electrode as the reference electrode, and use 1 M KOH solution as the electrolyte, and activate it at a constant voltage to obtain the Cu-based electrocatalytic CO2RR catalyst r-Cu2(OH)3F.

[0040] Example 4: r-Cu(OH)2 Prepare the commercial copper hydroxide powder into a working electrode, use a platinum plate electrode as the counter electrode, an Ag / AgCl electrode as the reference electrode, and use 1 M KOH solution as the electrolyte, and activate it at a constant voltage to obtain the Cu-based electrocatalytic CO2RR catalyst r-Cu(OH)2.

[0041] Example 5: r-Cu

[0042] A commercial copper powder was prepared into a working electrode, a platinum sheet electrode was used as the counter electrode, and an Ag / AgCl electrode was used as the reference electrode. A 1 M KOH solution was used as the electrolyte, and the Cu-based electrocatalytic CO2RR catalyst r-Cu was obtained by constant voltage activation. Example 6

[0043] Structural characterization of Cu2(OH)3Br and r-Cu2(OH)3Br catalysts: The catalyst precursors Cu2(OH)3Br and r-Cu2(OH)3Br prepared in Example 1 were structurally characterized. The microscopic morphology of the catalyst surface was observed by field emission scanning electron microscopy (SEM). Preparation of test samples: Paste the conductive adhesive on the sample stage on the carrier plate, then cut the sample to be tested into an appropriate size and paste it on the conductive adhesive, and gently blow it with a nitrogen gun to remove the loosely adhered powder. Put the sample stage into the sputtering coater for sputtering treatment to enhance the conductivity of the sample. After the sputtering is completed, the sample can be injected for testing. It can be Figure 1 observed that the precursor catalyst prepared in Example 1 has a relatively smooth and regular nanosheet structure, while the r-Cu2(OH)3Br catalyst becomes sharper and has a greater roughness after electrochemical reconstruction, transforming into a mixed structure of nanoparticles and dendrites. This is beneficial to the contact between the electrode material and the electrolyte, providing a larger active surface area for the electrocatalytic CO2RR reaction.

[0044] The powder X-ray diffractometer (XRD) characterization method was used to analyze the crystal structure and phase of the catalyst precursors Cu2(OH)3Br and r-Cu2(OH)3Br in Example 1. Place the sample powder or carbon paper in the groove of the quartz plate, flatten the surface and then put it into the machine. The scanning range is 5° - 80°, and the scanning speed is 10° min -1 , and the diffraction pattern was collected. The diffraction peaks of the catalyst precursor can be clearly seen, corresponding to the standard card Cu2(OH)3Br (PDF#45-1309) ( Figure 2 in a), and the main crystal phases of the reconstructed catalyst are Cu (PDF#04-0836) and Cu2O (PDF#05-0667) ( Figure 2 in b). In summary, the XRD pattern shows that bromine elements are successfully introduced into the copper-based catalyst, and the configuration and electronic structure of the catalyst are changed after reconstruction.

[0045] The structural characteristics of the catalyst surface prepared in Example 1 were further observed by FEI TF300 transmission electron microscopy (TEM). Before testing, scrape a small amount of the catalyst loaded on the carbon paper with a file, grind it thoroughly and pour it into a small bottle filled with ethanol, and ultrasonicate it in an ultrasonic oscillator for more than 15 min to ensure that the catalyst is evenly dispersed in the solvent. Take a small amount of the solution and drop it on the molybdenum grid, and then the sample can be injected for testing. It can be seen fromFigure 3 The hybrid structure of nanoparticles and dendrites can be clearly observed ( Figure 3 in a)), which is consistent with the SEM test results. And the lattice fringes attributed to Cu(111) and Cu2O(111) can be measured ( Figure 3 in b)).

[0046] Electrochemical tests of r-Cu2(OH)3X catalysts: All electrochemical tests in this example were carried out using a CHI760E electrochemical workstation at room temperature (25 °C). The test used a gas diffusion flow cell device. In a 1 M KOH alkaline medium (pH = 13.6), the material electrode to be tested was used as the working electrode (the contact area of the catalyst with the electrolyte was 1 cm 2 ), a platinum sheet electrode was used as the counter electrode, and an Ag / AgCl electrode was used as the reference electrode (0.197 V vs . RHE, reversible hydrogen electrode) to conduct electrochemical performance tests on the prepared catalysts.

[0047] Linear sweep voltammetry curves (LSV) were performed on the catalysts r-Cu2(OH)3Br, r-Cu2(OH)3Cl, r-Cu2(OH)3F, r-Cu(OH)2, and r-Cu prepared in Examples 1-5: at a scan rate of 5 mV s -1 in the range from 0 to -2.0 V vs. vs. Ag / AgCl for linear sweep voltammetry tests. As Figure 4 shown, compared with r-Cu2(OH)3Cl, r-Cu2(OH)3F, r-Cu(OH)2, and r-Cu, r-Cu2(OH)3Br has an obvious advantage in current density, and at a voltage of -2.0 V vs vs. Ag / AgCl, the current density is as high as -280 mA cm -2 and has better catalytic activity.

[0048] Electrocatalytic CO2RR product performance tests were carried out on the catalysts r-Cu2(OH)3Br, r-Cu2(OH)3Cl, r-Cu2(OH)3F, r-Cu(OH)2, and r-Cu prepared in Examples 1-5 to prepare C 2+ The test voltage range was -0.8 V to -1.2 V vs. vs. RHE, the electrolyte was 1 M KOH solution, and the test time was 30 min each. From Figure 5As can be seen from Table 1, the r-Cu2(OH)3Br catalyst exhibits the highest selectivity for multi-carbon products under the condition of -1.0 V vs. reversible hydrogen electrode, reaching 78%. The Faraday efficiencies of ethylene and ethanol are 53.2% and 20% respectively. These results indicate that r-Cu2(OH)3Br can not only effectively catalyze the conversion process of CO2, but also achieve remarkable performance in the formation of multi-carbon products.

[0049] Table 1 shows the Faraday efficiencies of C2H4 and C2H5OH for the CO2RR of the catalyst r-Cu2(OH)3Br under different potential conditions.

[0050] <![CDATA[r-Cu2(OH)3Br for CO2RR at different voltages (V vs. RHE)]]> <![CDATA[FE C2H4(%)]]> <![CDATA[FE C2H5OH(%)]]> -1.4 45.81 21.14 -1.3 50.19 16.86 -1.2 47.45 20.00 -1.1 49.64 18.23 -1.0 53.21 20.06 -0.9 43.25 15.34 -0.8 30.30 14.95 -0.7 34.82 11.11 -0.6 20.11 7.68 -0.5 14.73 0.34 The catalysts r-Cu2(OH)3Br, r-Cu2(OH)3Cl, r-Cu2(OH)3F and r-Cu(OH)2 prepared in Examples 1-5 were subjected to HRTEM testing to obtain their more detailed crystal structure characteristics. The lattice spacings of Cu2O(111) for the four catalysts are the same, while the lattice spacings of Cu(111) are different. With the introduction of fluorine, chlorine and bromine, the spacing of d-Cu(111) gradually increases, indicating that the sample doped with Br has the largest interplanar spacing. This change may be due to the changes in the crystal structure and electronic structure caused by the introduction of Br ions, thereby exposing more active sites.

[0051] The above embodiments are only used to illustrate the present invention. Any equivalent transformation and improvement based on the technical solution of the present invention should not be excluded from the protection scope of the present invention.

Claims

1. A method for preparing an r-Cu2(OH)3X electrocatalyst, characterized in that: The steps include: (1) dissolving copper halide in propanol to prepare a solution with a concentration of 0.15-6 mol / L; adding propylene oxide and deionized water under continuous stirring to obtain a mixed solution; (2) sealing the mixed solution and aging it for 1-5 days, centrifuging the aged solution to obtain a precipitate, washing it, and vacuum drying it; (3) Electrical reconstruction: The dried product is made into an electrode sheet and electrolyzed in an electrolyte for 10 to 30 min.

2. The method for preparing a r-Cu2(OH)3X electrocatalyst according to claim 1, characterized in that: The copper halide is copper fluoride, copper chloride and copper bromide.

3. The method for preparing a r-Cu2(OH)3X electrocatalyst according to claim 1, characterized in that: The molar ratio of propylene oxide to copper halide is (8-12):

1.

4. The method for preparing a r-Cu2(OH)3X electrocatalyst according to claim 1, characterized in that: The electrolyte is 1 M KOH solution.

5. An r-Cu2(OH)3X electrocatalyst, characterized in that: The method is prepared by any one of claims 1 to 4.

6. The r-Cu2(OH)3X electrocatalyst according to claim 5, characterized in that: The electrocatalyst exists in two crystal phases: copper and cuprous oxide.

7. The use of an r-Cu2(OH)3X electrocatalyst according to claim 5, characterized in that: The electrocatalyst is used for electrocatalytic reduction of carbon dioxide under alkaline conditions.

8. The use of an r-Cu2(OH)3X electrocatalyst according to claim 7, characterized in that: The electrocatalyst is used for electrocatalyzing carbon dioxide to prepare multi-carbon products under alkaline conditions.

9. The use of an r-Cu2(OH)3X electrocatalyst according to claim 8, characterized in that: The alkaline condition is 1 M KOH as the electrolyte.

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