A pvp-doped cu-mg binary metal electrocatalytic material, a preparation method and application thereof

Abstract

This invention provides a PVP-doped Cu-Mg binary metal electrocatalyst material, its preparation method, and its application. The method includes the following steps: dissolving copper chloride, polyvinylpyrrolidone, and magnesium chloride in N,N-dimethylformamide to obtain a mixed solution; the molar ratio of copper chloride to magnesium chloride is 1:0.98–1.02; stirring the mixed solution under ice-water bath conditions while introducing a protective gas, adding sodium borohydride solution dropwise to generate a precipitate, separating, washing, and drying the precipitate to obtain the PVP-doped Cu-Mg binary metal electrocatalyst material. This invention effectively regulates the formation of Cu by incorporating magnesium and controlling its doping amount, combined with PVP. + The valence state of Cu improves the selectivity of C2 products, while the outer PVP coating protects Cu. + Not oxidized to Cu 2+ This effectively improves the stability of the material.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic materials technology, and particularly relates to a PVP-doped Cu-Mg binary metal electrocatalytic material, its preparation method and application. 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 this invention is to provide a PVP-doped Cu-Mg binary metal electrocatalytic material, its preparation method, and its application. The electrocatalytic material prepared by this method is capable of being in a stable intermediate valence state (Cu). + Copper-based catalysts, when used as cathode materials for the electrocatalysis of carbon dioxide, can effectively improve the selectivity of CO2 reduction of C2 products while maintaining stable catalytic performance.

[0006] This invention provides a method for preparing PVP-doped Cu-Mg binary metal electrocatalytic materials, comprising the following steps:

[0007] Copper chloride, polyvinylpyrrolidone, and magnesium chloride were dissolved in N,N-dimethylformamide to obtain a mixed solution; the molar ratio of copper chloride to magnesium chloride was 1:0.98 to 1.02.

[0008] Under ice-water bath conditions, the mixture was stirred and a protective gas was introduced. Sodium borohydride solution was added dropwise to generate a precipitate, which was then separated, washed, and dried to obtain a PVP-doped Cu-Mg binary metal electrocatalytic material.

[0009] This invention effectively controls the valence state of copper-based materials by incorporating alkaline earth metal magnesium and PVP. Magnesium has a strong interaction with the CO reaction intermediate, which can effectively promote carbon-carbon coupling in the carbon dioxide reduction process and improve the selectivity of C2 products. PVP is introduced in the preparation process, which has the advantages of low price and wide availability. The high molecular weight polymer PVP introduced in the reduction process ensures uniform dispersion of Mg doping and avoids agglomeration and oxidation. Cross-linked nanosheet copper-based catalytic materials are successfully prepared by reducing divalent copper ions with potassium borohydride solution.

[0010] The copper chloride, polyvinylpyrrolidone, magnesium chloride, and N,N-dimethylformamide mentioned in this invention are all commercially available products.

[0011] This invention, through screening a series of alkaline earth metals Mg, Sr, and Ba, discovered that magnesium atoms have a strong interaction with the *CO reaction intermediate, effectively promoting carbon-carbon coupling in the carbon dioxide reduction process and improving the selectivity of C2 products. The molar ratio of copper chloride to magnesium chloride in this invention is 1:0.98–1.02, preferably 1:1. This invention improves the selectivity for C2 products by adjusting the type and amount of alkaline earth metals incorporated, thereby controlling the valence state of the copper-based catalyst. Specifically, the C2 product content increases from 40.2% without magnesium incorporation to 74.1% after magnesium incorporation (FE). C2H4 +FE C2H5OH +FE CH3CH2CH2OH The Faraday efficiency of ethylene and ethanol was nearly doubled, significantly improving the application of copper-based electrocatalysis in carbon dioxide.

[0012] The molar ratio of copper chloride and polyvinylpyrrolidone in this invention is 0.1 mmol: 0.2 g.

[0013] In this invention, the ratio of N,N-dimethylformamide to copper chloride is (14-16) mL:0.1 mmol, preferably 15 mL:0.1 mmol.

[0014] The concentration of the sodium borohydride solution in this invention is 0.95–1.05 mol / L. In a specific embodiment, the concentration of the sodium borohydride solution is 1 mol / L.

[0015] In this invention, the volume ratio of sodium borohydride solution to N,N-dimethylformamide is 4:3.

[0016] The present invention preferably uses deionized water and ethanol for washing in sequence; the washing is performed at least 3 times.

[0017] The present invention preferably involves drying in a vacuum oven; the drying time is 5.5 to 6.5 hours, preferably 6 hours.

[0018] This invention provides a cathode material for an electrocatalytic carbon dioxide battery, the raw materials of which include PVP-doped Cu-Mg binary metal electrocatalytic material prepared by the preparation method described above.

[0019] The raw materials for preparing the PVP-doped Cu-Mg binary metal electrocatalytic material described in this invention also include isopropanol and perfluorosulfonic acid resin.

[0020] The mass ratio of the PVP-doped Cu-Mg binary metal electrocatalyst material, the volume ratio of isopropanol to the volume ratio of perfluorosulfonic acid resin is 0.005 g:(460-480) μL:(28-32) μL. In a specific embodiment of the present invention, the mass ratio of the PVP-doped Cu-Mg binary metal electrocatalyst material, the volume ratio of isopropanol to the volume ratio of perfluorosulfonic acid resin is 0.005 g:470 μL:30 μL.

[0021] This invention provides a method for preparing a PVP-doped Cu-Mg binary metal electrocatalyst, comprising the following steps: dissolving copper chloride, polyvinylpyrrolidone, and magnesium chloride in N,N-dimethylformamide to obtain a mixed solution; wherein the molar ratio of copper chloride to magnesium chloride is 1:0.98–1.02; stirring the mixed solution under ice-water bath conditions and introducing a protective gas, then adding sodium borohydride solution dropwise to generate a precipitate, which is then separated, washed, and dried to obtain the PVP-doped Cu-Mg binary metal electrocatalyst. This invention effectively regulates the formation of Cu by incorporating magnesium and controlling its doping amount, combined with PVP. +The valence state of Cu improves the selectivity of C2 products, while the outer PVP coating protects Cu. + Not oxidized to Cu 2+ This effectively improves the stability of the material. Attached Figure Description

[0022] Figure 1 Transmission electron microscopy (TEM) images of the PVP-doped Cu-Mg binary metal electrocatalytic material prepared in Example 1 of this invention at 100 nm and 2 nm.

[0023] Figure 2 The energy dispersive spectroscopy (EDS) analysis diagram of the PVP-doped Cu-Mg binary metal electrocatalytic material prepared in Example 1 of this invention;

[0024] Figure 3 The X-ray diffraction pattern of the PVP-doped Cu-Mg binary metal electrocatalytic material prepared in Example 1 of this invention;

[0025] Figure 4 The results are the Faraday efficiency analysis results of the electrocatalytic materials prepared in Example 1 and Comparative Example 4 of this invention;

[0026] Figure 5 The X-ray photoelectron spectra of the electrocatalytic materials prepared in Example 1 and Comparative Example 3 of this invention are shown below. (a) is the overall X-ray photoelectron spectrum of the electrocatalytic material in Example 1, (b) is the Cu 2p X-ray photoelectron spectrum of the electrocatalytic material in Example 1, (c) is the Cu LMN X-ray photoelectron spectrum of the electrocatalytic material in Example 1, (d) is the Mg X-ray photoelectron spectrum of the electrocatalytic material in Example 1, (e) is the overall X-ray photoelectron spectrum of the electrocatalytic material in Comparative Example 3, (f) is the Cu 2p X-ray photoelectron spectrum of the electrocatalytic material in Comparative Example 3, and (g) is the Cu LMN X-ray photoelectron spectrum of the electrocatalytic material in Comparative Example 3. Detailed Implementation

[0027] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, of a PVP-doped Cu-Mg binary metal electrocatalytic material, its preparation method, and its application, is provided by the present invention, 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, 0.17 g (0.1 mmol) of copper chloride dihydrate and 0.095 g (0.1 mmol) of anhydrous magnesium chloride were added. The mixture was stirred in an ice-water bath with nitrogen gas as a protective gas, and 20 mL of 1 mol / L sodium borohydride solution was slowly added dropwise. After a black precipitate formed in the solution, the mixture was stirred for 8 h. The black precipitate was separated by centrifugation and washed three times with deionized water and ethanol, respectively. After drying in a vacuum oven for 6 h, the PVP-doped Cu-Mg binary metal electrocatalytic material was obtained.

[0030] Comparative Example 1

[0031] 0.2 g of PVP was added to 15 mL of DMF solution and sonicated. After the PVP dissolved, 0.17 g (0.1 mmol) of copper chloride dihydrate and 0.0475 g (0.05 mmol) of anhydrous magnesium chloride were added. The mixture was stirred in an ice-water bath with nitrogen gas as a protective gas, and 20 mL of 1 mol / L sodium borohydride solution was slowly added dropwise. After a black precipitate formed in the solution, the mixture was stirred for 8 h. 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 h to obtain the PVP-doped Cu-Mg binary metal electrocatalytic material.

[0032] Comparative Example 2

[0033] 0.2 g of PVP was added to 15 mL of DMF solution and sonicated. After the PVP dissolved, 0.17 g (0.1 mmol) of copper chloride dihydrate and 0.1425 g (0.15 mmol) of anhydrous magnesium chloride were added. The mixture was stirred in an ice-water bath with nitrogen gas as a protective gas, and 20 mL of 1 mol / L sodium borohydride solution was slowly added dropwise. After a black precipitate formed in the solution, the mixture was stirred for 8 h. 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 h to obtain the PVP-doped Cu-Mg binary metal electrocatalytic material.

[0034] Comparative Example 3

[0035] 0.17 g (0.1 mmol) of copper chloride dihydrate and 0.1425 g (0.15 mmol) of anhydrous magnesium chloride were added to 15 mL of DMF solution. The mixture was stirred in an ice-water bath with nitrogen gas as a protective gas, and 20 mL of 1 mol / L sodium borohydride solution was slowly added dropwise. After a black precipitate formed in the solution, the mixture was stirred for 8 h. 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 h to obtain Cu-Mg binary metal electrocatalytic material.

[0036] Comparative Example 4

[0037] 0.17 g (0.1 mmol) of copper chloride dihydrate was added to 15 mL of DMF solution. The mixture was stirred in an ice-water bath with nitrogen gas as a protective gas. 20 mL of 1 mol / L sodium borohydride solution was slowly added dropwise. After a black precipitate was formed in the solution, the mixture was stirred for 8 h. The black precipitate was separated by centrifugation and washed three times with deionized water and ethanol, respectively. The precipitate was then dried in a vacuum oven for 6 h to obtain Cu-based electrocatalytic material.

[0038] Comparative Example 5

[0039] 0.2 g of PVP was added to 15 mL of DMF solution and sonicated. After the PVP dissolved, 0.17 g (0.1 mmol) of copper chloride dihydrate and 0.16 g (0.1 mmol) of anhydrous strontium chloride were added. The mixture was stirred in an ice-water bath with nitrogen gas as a protective gas, and 20 mL of 1 mol / L sodium borohydride solution was slowly added dropwise. After a black precipitate formed in the solution, the mixture was stirred for 8 h. 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 h to obtain the PVP-doped Cu-Sr binary metal electrocatalytic material.

[0040] Comparative Example 6

[0041] 0.2 g of PVP was added to 15 mL of DMF solution and sonicated. After the PVP dissolved, 0.17 g (0.1 mmol) of copper chloride dihydrate and 0.21 g (0.1 mmol) of anhydrous barium chloride were added. The mixture was stirred in an ice-water bath with nitrogen gas as a protective gas, and 20 mL of 1 mol / L sodium borohydride solution was slowly added dropwise. After a black precipitate formed in the solution, the mixture was stirred for 8 h. 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 h to obtain the PVP-doped Cu-Ba binary metal electrocatalytic material.

[0042] Comparative Example 7

[0043] 0.2 g of PVP was added to 15 mL of DMF solution and sonicated. After the PVP dissolved, 0.17 g (0.1 mmol) of copper chloride dihydrate and 0.095 g (0.1 mmol) of anhydrous magnesium chloride were added. The mixture was stirred in an ice-water bath with nitrogen gas as a protective gas and stirred continuously for 8 h. After centrifugation to separate the black precipitate, it was washed three times with deionized water and ethanol, and then dried in a vacuum oven for 6 h. Due to the lack of sodium borohydride, the electrocatalytic material could not be synthesized.

[0044] Performance testing

[0045] (1) Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) analysis

[0046] The PVP-doped Cu-Mg binary metal electrocatalyst material prepared in Example 1 is shown in the transmission electron microscope (TEM) images at 100 nm and 2 nm. Figure 1 ,Depend on Figure 1 It can be seen that a two-dimensional nanosheet-like metal catalytic material was successfully prepared by the sodium borohydride reduction method, wherein the Cu lattice size is 0.213 nm. + Corresponding to its X-ray diffraction pattern ( Figure 3 Energy dispersive spectroscopy (EDS) analysis can be found in [link to EDS analysis]. Figure 2 ,Depend on Figure 2 It can be seen that the material contains elements C, N, O, Cu, and Mg, and each element is evenly distributed, indicating that C and Mg elements have been successfully dispersed and incorporated. The dispersed incorporation of Mg is more conducive to the occurrence of C-C coupling in the electrocatalytic CO2 reduction reaction.

[0047] (2) X-ray diffraction

[0048] The X-ray diffraction pattern of the PVP-doped Cu-Mg binary metal electrocatalyst material prepared in Example 1 is shown in Figure 1. Figure 3 It can be seen that the prepared Cu-based nanomaterials are mainly Cu₂O, while the materials without Mg and PVP are mainly divalent copper and monovalent Cu. + It is more conducive to the selectivity of C2 products.

[0049] (3) Faraday efficiency analysis

[0050] 0.005 g of the electrocatalytic materials prepared in Example 1 and Comparative Example 3 were weighed out, and then 470 μL of isopropanol and 30 μL of Nafion (perfluorosulfonic acid resin) were added. After ultrasonication and uniform dispersion, the mixture was uniformly coated onto the surface of 0.5 × 1.5 cm carbon paper and dried at room temperature. The dried carbon paper was used as the working electrode.

[0051] 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.

[0052] The electrolyte was 50 mL of 0.5 mol / L potassium hydroxide solution, with CO2 introduced at a flow rate of 15 mL / min. Linear sweep voltammetry (LSV) was performed on a CHI 660 electrochemical workstation with a scan 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 injected into a gas chromatograph, with samples taken every 9 min. After the reaction, the liquid in the cathode chamber was collected for NMR analysis to determine the liquid phase products.

[0053] The Faradaic efficiency analysis results of the electrocatalytic materials prepared in Example 1 and Comparative Example 4 are shown in the figure. Figure 4 In this paper, (a) shows the Faraday efficiency test results of the electrocatalytic material prepared in Example 1, and (b) shows the Faraday efficiency test results of the electrocatalytic material prepared in Comparative Example 4. Figure 4 It can be seen that the prepared PVP-doped Cu-Mg two-dimensional nanomaterials are more conducive to CC coupling in the electrocatalytic reduction of CO2, and can effectively improve the Faradaic efficiency of the products. Compared with metallic Cu, the Faradaic efficiency of the PVP-doped Cu-Mg C2 products increased from 40.2% to 74.1%, and the Faradaic efficiency of ethylene and ethanol nearly doubled.

[0054] In addition, the electrocatalytic materials prepared in Comparative Examples 1-3 and Comparative Examples 5-6 were analyzed for Faradaic efficiency using the same method described above. The results showed that:

[0055] Comparative Example 1: The addition of a small amount of Mg could not effectively promote C-C coupling, and its effect on the metal d-band center of Cu was not significant. The Faraday efficiency of the C2 product was 43.8%, which was not significantly improved.

[0056] Comparative Example 2: Excessive Mg incorporation intensified the hydrogen evolution competition reaction, and the Faraday efficiency of the C2 product was 56.2%, which was significantly lower than that of Example 1.

[0057] Comparative Example 3: The Cu-Mg binary metal material without PVP showed obvious agglomeration of Mg, which could not be effectively dispersed, thus failing to effectively control the valence state of Cu metal. The Faraday efficiency of its C2 product was 65.8%.

[0058] Comparative Example 5: The incorporation of metallic Sr improves the selectivity of C2 products to some extent, with a Faraday efficiency of 54.1%, which is relatively low compared to Mg.

[0059] Comparative Example 6: The incorporation of metallic Ba significantly improved the CH4 content, but had a limited effect on the C2 product. Its C2 product Faraday efficiency was 50.6%, which was lower than that of Mg.

[0060] (4) X-ray photoelectron spectroscopy analysis

[0061] The X-ray photoelectron spectra of the electrocatalytic materials prepared in Example 1 and Comparative Example 3 are shown below. Figure 5Among them, (a) is the overall X-ray photoelectron spectrum of the electrocatalytic material of Example 1, (b) is the Cu 2p X-ray photoelectron spectrum of the electrocatalytic material of Example 1, (c) is the Cu LMN X-ray photoelectron spectrum of the electrocatalytic material of Example 1, (d) is the X-ray photoelectron spectrum of Mg, (e) is the overall X-ray photoelectron spectrum of the electrocatalytic material of Comparative Example 3, (f) is the Cu 2p X-ray photoelectron spectrum of the electrocatalytic material of Comparative Example 3, and (g) is the Cu LMN X-ray photoelectron spectrum of the electrocatalytic material of Comparative Example 3. It can be seen that the valence state of Cu in the PVP-doped Cu-Mg metal catalyst is stable at Cu 2p. + Compared to Cu 0 or Cu 2+ Cu + This is more conducive to the occurrence of C-C coupling, thereby effectively improving the selectivity of C2 products.

[0062] As demonstrated by the above embodiments, this invention incorporates alkaline earth metals (Mg, Sr, Ba) into a copper-based catalyst via sodium borohydride reduction, proving their impact on the catalytic mechanism of the catalyst material during carbon dioxide reduction. Among these, magnesium showed the most significant improvement in C2 production. Furthermore, the incorporation of the polymer PVP effectively ensured the doping and dispersion of the alkaline earth metals, preventing their aggregation and oxidation during the doping process. The incorporated alkaline earth metals and PVP effectively controlled the formation of Cu. + The valence state was improved, the selectivity of C2 products was enhanced, and the outer PVP coating protected Cu. + Not oxidized to Cu 2 + This effectively improves the stability of the material.

[0063] 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-doped Cu-Mg binary metal electrocatalytic material, comprising the following steps: Copper chloride, polyvinylpyrrolidone, and magnesium chloride were dissolved in N,N-dimethylformamide to obtain a mixed solution; the molar ratio of copper chloride to magnesium chloride was 1:0.98~1.

02. The mixture was stirred and a protective gas was introduced under ice-water bath conditions. Sodium borohydride solution was added dropwise to generate a precipitate. The precipitate was separated, washed, and dried to obtain a PVP-doped Cu-Mg binary metal electrocatalytic material. The molar ratio of copper chloride to polyvinylpyrrolidone is 0.1 mmol: 0.2 g; The ratio of N,N-dimethylformamide to copper chloride is (14~16) mL: 0.1 mmol.

2. The production method according to claim 1, characterized by, The concentration of the sodium borohydride solution is 0.95~1.05 mol / L.

3. The preparation method according to claim 2, characterized in that, The volume ratio of the sodium borohydride solution to N,N-dimethylformamide is 4:

3.

4. A PVP-doped Cu-Mg binary metal electrocatalytic material, prepared by the preparation method according to any one of claims 1 to 3.

5. A cathode material for an electrocatalytic carbon dioxide battery, wherein the raw materials for preparation include the PVP-doped Cu-Mg binary metal electrocatalytic material prepared by the preparation method described in claim 1.

6. The electrocatalytic carbon dioxide battery cathode material according to claim 5, characterized in that, It also includes isopropanol and perfluorosulfonic acid resins; The mass ratio of the PVP-doped Cu-Mg binary metal electrocatalytic material, the volume ratio of isopropanol to the volume ratio of perfluorosulfonic acid resin is 0.005 g: (460~480) μL: (28~32) μL.

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