A pvp-coated cu-based electrocatalytic material, a preparation method thereof and an electrode for electrocatalytic carbon dioxide reduction

Abstract

This invention provides a PVP-coated Cu-based electrocatalytic material, its preparation method, an electrode for electrocatalytic carbon dioxide reduction, and its application. Copper chloride dihydrate, polyvinylpyrrolidone (PVP), and dimethylformamide are mixed to obtain a mixture. Under a protective atmosphere and with stirring, potassium borohydride solution is added dropwise to the mixture, generating a precipitate. The precipitate is then centrifuged and dried to obtain the PVP-coated Cu-based electrocatalytic material. This invention introduces PVP, which has the advantages of low cost and wide availability. Cross-linked nanosheet-like copper-based catalytic materials are successfully prepared by reducing divalent copper ions with potassium borohydride solution. During the reduction process, 0.18–0.22 g of PVP (based on 2 mmol of copper) is introduced to coat the copper nanosheet structure, effectively regulating the valence state change of divalent copper ions during the reduction process, controlling it between monovalent and divalent copper, thus making it more favorable for the formation of C2 products.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic materials technology, and particularly relates to a PVP-coated Cu-based electrocatalytic material, its preparation method, and an electrode for electrocatalytic carbon dioxide reduction. Background Technology

[0002] Currently, the world's energy relies on fossil fuels, and the scarcity of fossil fuels has triggered environmental problems and an energy crisis, thus sparking considerable controversy. The world's population is growing exponentially, leading to increased global energy consumption, with fossil fuels remaining the primary source of energy demand. However, the continued use of fossil fuels generates substantial amounts of anthropogenic greenhouse gases. Replacing fossil fuels with renewable energy can alleviate the environmental and energy crisis to some extent, but modern renewable energy sources, including hydropower, wind power, bioenergy, geothermal / ocean energy / solar energy, accounted for only 11.2% of global energy consumption in 2019. Today, mitigating carbon dioxide emissions into the atmosphere has become a key challenge facing the scientific community.

[0003] Electrocatalytic reduction of CO2 has attracted widespread attention as a highly efficient and convenient route for CO2 conversion. The products of electrocatalytic CO2 reduction are abundant, including carbon monoxide (CO), methane (CH4), formic acid (HCOOH), ethylene (C2H4), and ethanol (C2H5OH). C1 products, such as carbon monoxide, methane, and formic acid, require fewer electrons in their reduction process, resulting in a relatively simple reaction pathway and Faradaic efficiencies approaching 90%. However, the formation of C2 products requires further C-coupling on the catalytic material surface. This involves a longer reaction pathway, and the multi-electron process often requires a higher overpotential, resulting in lower Faradaic efficiencies and poorer product selectivity for C2 products. Among various catalytic materials, copper-based materials exhibit moderate adsorption strength for CO reaction intermediates, making C-coupling easier and more efficient. Therefore, copper has unparalleled advantages over other metal catalysts in the production of C2 products.

[0004] Using bulk polycrystalline copper directly as the working electrode in the electrocatalytic reduction of CO2 results in poor performance. The yield of competing hydrogen products is too high, and the carbon-containing products are mostly carbon monoxide, with fewer C2 products. Current research indicates that factors affecting the selectivity of CO2 reduction products in copper-based materials include material size, morphology, crystal form and grain boundaries, and elemental valence states. Among these, copper with a zero valence state (Cu) is particularly effective. 0 ), divalent (Cu) 2+ Intermediate valence state copper (Cu) + Copper oxide (CuO) is more conducive to the formation of C2 products, while copper oxide (CuO) is more conducive to the formation of methane. However, intermediate copper ions are difficult to prepare and are difficult to maintain a stable intermediate valence state during electrochemical reduction. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a PVP-coated Cu-based electrocatalytic material, a method for preparing the same, and an electrode for electrocatalytic carbon dioxide reduction. The PVP-coated Cu-based electrocatalytic material prepared by this method can improve the selectivity of C2 products and enhance the stability of the material.

[0006] This invention provides a method for preparing a PVP-coated Cu-based electrocatalytic material, comprising the following steps:

[0007] A mixture of copper chloride dihydrate, polyvinylpyrrolidone (PVP), and dimethylformamide was prepared to obtain a mixture.

[0008] Under a protective atmosphere and with stirring, potassium borohydride solution is added dropwise to the mixture to generate a precipitate. The precipitate is then centrifuged and dried to obtain a PVP-coated Cu-based electrocatalytic material.

[0009] This invention introduces PVP (polyvinylpyrrolidone), which has the advantages of low cost and wide availability. Cross-linked nanosheet-like copper-based catalytic materials were successfully prepared by reducing divalent copper ions with potassium borohydride solution. During the reduction process, a sufficient amount of the polymer PVP was introduced to coat the copper nanosheet structure, effectively regulating the valence state change of divalent copper ions during reduction and controlling it between monovalent and divalent copper, thus making it more favorable for the formation of C2 products.

[0010] In this invention, the mass ratio of copper chloride dihydrate, polyvinylpyrrolidone, and dimethylformamide is 0.34 g : (0.18–0.22) g : (14–16) mL. This invention improves the selectivity for C2 products by controlling the amount of PVP incorporated, thereby regulating the valence state of the copper-based catalyst.

[0011] In this invention, potassium borohydride solution is added dropwise to the mixture under ice-water bath conditions. The concentration of the potassium borohydride solution in this invention is 1 mol / L; the volume ratio of the potassium borohydride solution to the mass ratio of polyvinylpyrrolidone is 20 mL: (0.18–0.22) g.

[0012] In this invention, after a black precipitate is formed in the solution, the mixture is stirred continuously for 7 to 9 hours, preferably 7.5 to 8.5 hours.

[0013] This invention provides a PVP-coated Cu-based electrocatalytic material, which is prepared by the method described in the above technical solution.

[0014] The PVP-coated Cu-based electrocatalytic material provided by this invention effectively regulates the generation of Cu through PVP incorporation. x+ The intermediate valence state improves the selectivity of C2 products, while the outer PVP coating protects Cu. x+ Not oxidized to Cu 2+This effectively improves the stability of the material.

[0015] This invention provides a working electrode for electrocatalytic carbon dioxide reduction, the raw materials of which include PVP-coated Cu-based electrocatalytic materials prepared by the preparation method described above.

[0016] In this invention, the raw materials also include isopropanol and naphthol;

[0017] The mass ratio of the PVP-coated Cu-based electrocatalytic material to the volume ratio of isopropanol and Nafion is 0.005 g : (450–500) μL : (28–32) μL. In a specific embodiment, the mass ratio of the PVP-coated Cu-based electrocatalytic material to the volume ratio of isopropanol and Nafion is 0.005 g : 470 μL : 30 μL.

[0018] This invention uses the above-mentioned electrode for electrocatalytic carbon dioxide reduction, comprising the following steps:

[0019] A three-electrode system consisting of a working electrode, a reference electrode, and a counter electrode was used. 50 mL of 0.5 mol / L potassium hydroxide solution was used as the electrolyte, and CO2 was introduced at a flow rate of 15 mL / min. Electrolysis was performed at a constant potential with a voltage range of -1.6 V to -2.5 V and a time of 2 h. After the reaction started, the products such as ethylene, methane, carbon monoxide, and hydrogen generated were analyzed by gas chromatography. After the reaction was completed, the liquid in the cathode chamber was taken for nuclear magnetic resonance analysis to determine the liquid phase products.

[0020] The working electrode is the working electrode for electrocatalytic carbon dioxide reduction described in the above technical solution.

[0021] The electrocatalytic reduction of carbon dioxide method of the present invention can improve the selectivity of C2 products such as ethylene, ethanol, and n-propanol by using the Cu-based electrocatalytic material coated with PVP according to the above scheme.

[0022] This invention provides a method for preparing a PVP-coated Cu-based electrocatalytic material, comprising the following steps: mixing copper chloride dihydrate, polyvinylpyrrolidone (PVP), and dimethylformamide to obtain a mixture; adding potassium borohydride solution dropwise to the mixture under a protective atmosphere and with stirring to generate a precipitate; centrifuging and drying to obtain the PVP-coated Cu-based electrocatalytic material. This invention introduces PVP, which has the advantages of low cost and wide availability. Cross-linked nanosheet-like copper-based catalytic materials are successfully prepared by reducing divalent copper ions with potassium borohydride solution; 0.2 g of PVP (based on 2 mmol of copper) is introduced during the reduction process to coat the copper nanosheet structure, effectively regulating the valence state change of divalent copper ions during the reduction process, controlling it between monovalent and divalent copper, making it more favorable for the formation of C2 products. Attached Figure Description

[0023] Figure 1 The image shows a transmission electron microscope (TEM) image of the copper-based nanomaterials in Example 1 with 0.2 g of PVP incorporated.

[0024] Figure 2 X-ray diffraction pattern of the PVP-coated Cu-based electrocatalytic material prepared in Example 1;

[0025] Figure 3 (a) is the Faradaic efficiency diagram of the PVP-coated Cu-based electrocatalytic material prepared in Example 1, and (b) is the Faradaic efficiency diagram of the material prepared in Comparative Example 1.

[0026] Figure 4 This is the X-ray photoelectron spectrum of the electrocatalytic material. Detailed Implementation

[0027] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, provides a PVP-coated Cu-based electrocatalytic material, its preparation method, and an electrode for electrocatalytic carbon dioxide reduction, but these descriptions should not be construed as limiting the scope of protection of the present invention.

[0028] Example 1

[0029] 0.2 g of PVP was added to 15 ml of DMF solution and sonicated. After the PVP dissolved in the DMF solution, 0.324 g (0.2 mmol) of copper chloride dihydrate was added. The mixture was stirred in an ice-water bath and nitrogen gas was introduced as a protective gas. 20 ml of 1 mol / L potassium borohydride solution was slowly added dropwise. After a black precipitate was formed in the solution, the mixture was stirred for 8 hours. The black precipitate was separated by centrifugation and washed three times with deionized water and ethanol, respectively. The mixture was then dried in a vacuum oven for 6 hours to obtain the catalyst material.

[0030] 0.005 g of the prepared catalytic material was weighed and added to 470 μL of isopropanol and 30 μL of Nafion. The mixture was sonicated to ensure uniform dispersion in the solvent. The material was then uniformly coated onto the surface of a 0.5 × 1.5 cm carbon paper sheet and dried at room temperature. The dried carbon paper was then used as the working electrode.

[0031] The test system was a three-electrode system of a flow electrolytic cell, consisting of a working electrode, a reference electrode, and a counter electrode. The reference electrode was Ag / AgCl (saturated KCl solution), the counter electrode was a commercially available platinum sheet, and the working electrode was prepared carbon paper.

[0032] The electrolyte was 50 mL of 0.5 M / L potassium hydroxide solution, and CO2 was introduced at a flow rate of 15 mL / min. Linear sweep voltammetry (LSV) was performed on a CHI 660 electrochemical workstation with a scanning window of -0.6 to -2.5 V. Potentiostatic electrolysis was also performed on a CHI 660 electrochemical workstation with a voltage setting range of -1.6 V to -2.4 V and a duration of 2 h. After the reaction started, the solution was introduced into a gas chromatograph, and samples were taken every 9 min. After the reaction, the liquid in the cathode chamber was collected for NMR analysis to determine the liquid phase products.

[0033] Figure 1 The image shows a transmission electron microscope (TEM) image of the copper-based nanomaterial, specifically the TEM image of the material in Example 1 with 0.2 g of PVP incorporated; from Figure 1 It can be seen that anhydrous copper chloride is reduced to cross-linked Cu by potassium borohydride. + Nanosheets with a lattice spacing of 0.21 nm, and Figure 2 Cu 2 O phase compatibility. During the reaction, PVP coats the Cu surface with a thickness of 0.1–2.5 nm, forming PVP-coated Cu. 2 O-crosslinked sheet-like nanomaterials.

[0034] Example 2

[0035] Add 0.18g of PVP to 15ml of DMF solution and sonicate. After the PVP dissolves in the DMF solution, add 0.34g (0.2mmol) of copper chloride dihydrate; the rest is the same as in Example 1.

[0036] When 0.18g of PVP is added, it can achieve a relatively complete coating of copper-based materials, and its performance is close to the optimal ratio at 0.2g. The Faraday efficiency of the C2 product is 65.7%.

[0037] Example 3

[0038] 0.22 g of PVP was added to 15 ml of DMF solution and sonicated. After the PVP dissolved in the DMF solution, 0.34 g (0.2 mmol) of copper chloride dihydrate was added; the rest was the same as in Example 1.

[0039] When 0.22g of PVP was added, its performance was close to the optimal ratio at 0.2g, but with a slight decrease, and the Faraday efficiency of its C2 product was 70.8%.

[0040] Comparative Example 1

[0041] 0.1 g of PVP was added to 15 ml of DMF solution and sonicated. After the PVP dissolved in the DMF solution, 0.34 g (0.2 mmol) of copper chloride dihydrate was added; the rest was the same as in Example 1.

[0042] The addition of a small amount of PVP (0.1g) did not completely coat the copper-based material, making the valence state of the copper-based material closer to that of the material without PVP. It did not significantly improve the C2 product, and the Faraday efficiency of the C2 product was 43.3%.

[0043] Comparative Example 2

[0044] Add 0.3g of PVP to 15ml of DMF solution and sonicate. After the PVP dissolves in the DMF solution, add 0.34g (0.2mmol) of copper chloride dihydrate; the rest is the same as in Example 1.

[0045] The excessive incorporation of PVP (0.3g) resulted in an excessively thick coating layer, which hindered the catalytic efficiency of copper as a catalytic active site, leading to an increase in the hydrogen evolution competition reaction and a decrease in the selectivity of the C2 product. The Faraday efficiency of the C2 product decreased to 58.3%, while the Faraday efficiency of the competing product hydrogen increased to 21%.

[0046] Comparative Example 3

[0047] 0.324 g (0.2 mmol) of copper chloride dihydrate was added to 15 ml of DMF solution and then dissolved by sonication; all other steps were the same as in Example 1. The Faraday efficiency of the C2 product was 40.2%, see [link to example]. Figure 3 (b)

[0048] Figure 3 (a) shows the Faradaic efficiency of the PVP-coated Cu-based electrocatalyst material prepared in Example 1, and (b) shows the Faradaic efficiency of the material prepared in Comparative Example 1. Figure 3 It can be seen that the Faraday efficiency of ethylene nearly doubled from 40.2% without PVP to 73.2%, significantly improving the application of copper-based materials in the field of electrocatalytic carbon dioxide.

[0049] Figure 4 The images show the X-ray photoelectron spectra of the electrocatalytic materials, where (a) is the overall X-ray photoelectron spectrum of the material prepared in Example 1; (b) is the Cu2p X-ray photoelectron spectrum of the material prepared in Example 1; (c) is the CuLMN X-ray photoelectron spectrum of the material prepared in Example 1; (d) is the overall X-ray photoelectron spectrum of the material prepared in Comparative Example 1; (e) is the Cu2p X-ray photoelectron spectrum of the material prepared in Comparative Example 1; and (f) is the CuLMN X-ray photoelectron spectrum of the material prepared in Comparative Example 1. Figure 4 It can be seen that after adding PVP, the valence state of copper is mainly monovalent copper, such as... Figure 4 As shown in (b) and (c); while the copper without PVP is all divalent copper, such as Figure 4As shown in (e) and (f), the addition of PVP can effectively ensure that anhydrous copper chloride is reduced to an intermediate valence state that is more conducive to carbon-carbon coupling during the reduction process, thereby effectively improving the selectivity of C2 products.

[0050] As can be seen from the above embodiments, the present invention provides a method for preparing a PVP-coated Cu-based electrocatalytic material, comprising the following steps: mixing copper chloride dihydrate, polyvinylpyrrolidone (PVP), and dimethylformamide to obtain a mixture; adding potassium borohydride solution dropwise to the mixture under a protective atmosphere and stirring to generate a precipitate, centrifuging, and drying to obtain the PVP-coated Cu-based electrocatalytic material. The present invention introduces PVP (polyvinylpyrrolidone), which has the advantages of low price and wide availability. Cross-linked nanosheet-like copper-based catalytic materials were successfully prepared by reducing divalent copper ions with potassium borohydride solution; during the reduction process, (0.18–0.22 g) of the polymer PVP (based on 2 mmol of copper) was introduced to coat the nanosheet-like copper structure, effectively regulating the valence state change of divalent copper ions during the reduction process, controlling it between monovalent and divalent copper, making it more favorable for the formation of C2 products. Experimental results show that the Faraday efficiency of the Cu-based electrocatalytic material coated with PVP is 73.2%, which is nearly double that of the undoped PVP.

[0051] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a PVP-coated Cu-based electrocatalytic material, comprising the following steps: Copper chloride dihydrate, polyvinylpyrrolidone, and dimethylformamide were mixed to obtain a mixture; the mass ratio of copper chloride dihydrate, polyvinylpyrrolidone, and dimethylformamide was 0.34 g : (0.18~0.22) g : (14~16) mL. Under a protective atmosphere, potassium borohydride solution was added dropwise to the mixture while stirring to generate a precipitate. The precipitate was then centrifuged and dried to obtain a PVP-coated Cu-based electrocatalytic material.

2. The preparation method according to claim 1, characterized in that, Potassium borohydride solution was added dropwise to the mixture under ice-water bath conditions.

3. The preparation method according to claim 1, characterized in that, The concentration of the potassium borohydride solution is 1 mol / L; The volume ratio of the potassium borohydride solution to the mass ratio of polyvinylpyrrolidone is 20 mL: (0.18~0.22) g.

4. The preparation method according to claim 1, characterized in that, After the precipitate is formed, continue stirring for 7-9 hours to allow potassium borohydride to react completely with Cu and PVP.

5. A PVP-coated Cu-based electrocatalytic material, prepared by any one of the preparation methods of claims 1 to 4.

6. A working electrode for electrocatalytic carbon dioxide reduction, wherein the raw materials include Cu-based electrocatalytic material coated with PVP prepared by the preparation method according to any one of claims 1 to 4.

7. The electrode for electrocatalytic carbon dioxide reduction according to claim 6, characterized in that, The raw materials also include isopropanol and naphthol; The mass ratio of the Cu-based electrocatalytic material coated with PVP, the volume ratio of isopropanol to naphthol is 0.005 g: (450~500) μL: (28~32) μL.

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