Copper-based catalyst for preparing propyl alcohol through electrocatalytic reduction of carbon dioxide and application of copper-based catalyst

Abstract

The invention discloses a copper-based catalyst for preparing propyl alcohol by electrocatalytic reduction of carbon dioxide and application of the copper-based catalyst. The preparation method of the copper-based catalyst comprises the following steps: adding a sodium hydroxide solution into an aqueous solution of a copper compound to obtain a turbid solution; adding a hydroxylamine hydrochloride aqueous solution into the turbid solution, carrying out a reaction, and carrying out centrifugal drying to obtain Cu (OH) 2 / CuO; cu (OH) 2 / CuO is prepared into a working electrode, and then the working electrode is reduced into the Cu / Cu2O nanosheet through an electrochemical reconstruction method. The Cu / Cu2O electrocatalyst with the bicontinuous nano-domain structure is obtained by using a two-step electrochemical reconstruction method, and the Cu / Cu2O electrocatalyst is used as a cathode for electrocatalytic reduction of carbon dioxide. The hydrogen evolution reaction is inhibited in a KOH or KHCO3 aqueous solution system, so that the activity of propyl alcohol preparation is remarkably improved. Experiments show that the Faraday efficiency of propyl alcohol exceeds 12.1% under the current density of 0.84 A cm <-2 >, and the Faraday efficiency of propyl alcohol is good. According to the analysis, the Cu / Cu2O catalyst obtained through the electrochemical reconstruction method serves as the cathode, and the propyl alcohol can be prepared through the carbon dioxide electrocatalytic reduction reaction.

Description

Technical Field

[0001] The present invention relates to a copper-based catalyst for electrocatalytic reduction of carbon dioxide to propanol and its application, belonging to the field of chemical engineering. Background Art

[0002] The increasingly serious energy crisis and environmental problems are gradually threatening the sustainable development of human society. The electrocatalytic reduction of CO2 reaction driven by renewable energy provides key energy storage for value-added carbon-based products to meet the growing energy demand. It can convert CO2 into high-value fuels and chemicals under ambient conditions using renewable energy such as photovoltaic, hydropower, and wind power. However, using an aqueous solution as the electrolyte, its conversion efficiency is usually limited by various competing reactions, such as the hydrogen evolution reaction and the C1 pathway. This is still the main obstacle to the development of highly efficient electrocatalytic reduction of CO2 catalysts. Therefore, the rational design and preparation of new electrocatalysts with high activity and high selectivity are the key to the large-scale practical application of electrocatalytic reduction of CO2.

[0003] Currently, the electrocatalytic reduction of CO2 reaction to produce carbon monoxide (CO) or formic acid (HCOOH) has initially met the fundamental needs of industrialization, with a Faraday efficiency (FE) > 95% and a partial current density > 200 mA cm -2 2. For other typical C1 and C2 products, the FE can reach values above 65%, such as methane (CH4), methanol (CH3OH), ethylene (C2H4), and ethanol (CH3CH2OH). In contrast, the electrocatalytic reduction of CO2 reaction to produce C3 products, especially n-propanol with a high energy mass density (30.91 KJ / g) and a high market value ($1,400 - $1,500 per ton), is still largely limited. According to literature research, in an H-type electrolytic cell, the highest FE for the electrocatalytic reduction of CO2 reaction to produce propanol is 17.2%, while the partial current density of propanol is 8.1 mA cm -2 2. However, in the case of replacing the H-type electrolytic cell with a commercial flow battery, the partial current density of propanol can be increased to 62.1 mA cm -2 2, and the FE of propanol drops to 6.9%. Due to the limited selectivity and low activity of current catalysts, the method of directly electrocatalytically reducing CO2 to produce propanol is still below the requirements of economic feasibility. Therefore, further improving the electrocatalytic reduction of CO2 performance of Cu-based catalysts and expanding the high selectivity and full-cell efficiency of propanol under industrial current density are still the urgent needs for its industrial application.

[0004] In summary, the key to the research is to prepare a robust catalyst with high selectivity for propanol products and high activity under industrial current density. Summary of the Invention

[0005] The object of the present invention is to provide a copper-based catalyst for electrocatalytic reduction of carbon dioxide to propanol. First, the present invention uses an oxidation etching method to obtain a sea urchin-like Cu(OH)2 / CuO nanomaterial, and then uses an electrochemical reconstruction method to convert the sea urchin-like into a nanosheet Cu / Cu2O catalyst, which is used as a cathode material to efficiently electrocatalytically reduce CO2 to propanol. This reaction has high activity, high selectivity for propanol, and maintains a high selectivity for propanol at high currents.

[0006] The preparation method of the copper-based catalyst for electrocatalytic reduction of carbon dioxide to propanol provided by the present invention includes the following steps:

[0007] S1. Add an aqueous sodium hydroxide solution to an aqueous solution of a copper compound to obtain a turbid solution;

[0008] S2. Add an aqueous hydroxylamine hydrochloride solution to the turbid solution, carry out a reaction, and obtain Cu(OH)2 / CuO by centrifugation and drying;

[0009] S3. Prepare the Cu(OH)2 / CuO into a working electrode, and then reduce it to Cu / Cu2O nanosheets by an electrochemical reconstruction method.

[0010] In the preparation method of the present invention, in step S1, the concentration of the aqueous sodium hydroxide solution is 0.5 mol / L to 2 mol / L;

[0011] The concentration of the aqueous solution of the copper compound is 5 mmol / L to 100 mmol / L;

[0012] The molar ratio of the copper compound to sodium hydroxide is 1:100 to 400;

[0013] Under the condition of stirring, the aqueous sodium hydroxide solution is added dropwise to the aqueous solution of the copper compound.

[0014] In the preparation method of the present invention, in step S1, the copper compound is one of copper nitrate (Cu(NO3)2), copper chloride (CuCl2), cuprous chloride (CuCl), copper sulfate (CuSO4), copper acetate (Cu(CH3COO)2), and copper acetylacetonate (Cu(C5H7O2)2).

[0015] In the preparation method of the present invention, in step S2, the concentration of the hydroxylamine hydrochloride is 50 mmol / L to 400 mmol / L;

[0016] The molar ratio of the copper compound to hydroxylamine hydrochloride is 1:10 to 80;

[0017] The temperature of the reaction is 20 °C to 50 °C, and the time is 0.5 to 24 h.

[0018] In the preparation method of the present invention, in step S3, the steps of preparing the working electrode are as follows:

[0019] Mix the Cu(OH)₂ / CuO with isopropanol and Nafion solution and disperse them by ultrasonic treatment to obtain a mixed solution, then uniformly coat the mixed solution on carbon paper, and then dry it in a N₂ atmosphere to form a Cu(OH)₂ / CuO working electrode;

[0020] The Nafion solution is preferably a 5wt% perfluorosulfonic acid resin Nafion solution.

[0021] Among them, the ratio of the Cu(OH)₂ / CuO, the isopropanol and the Nafion solution is preferably 10 mg: 3 mL: 0.03 mL.

[0022] In the preparation method of the present invention, in step S3, the steps of the electrochemical reconstruction method are as follows:

[0023] Using the working electrode as the cathode, perform potentiostatic electrolysis in a KHCO₃ solution;

[0024] The concentration of the KHCO₃ solution is 0.1 mol / L to 1 mol / L;

[0025] The conditions of the electrolysis are as follows:

[0026] The potential is -1.4 V to -1.5 V (vs. RHE);

[0027] The time is 10 min to 60 min.

[0028] The copper-based catalyst prepared by the method of the present invention can be used for electrocatalytic reduction of carbon dioxide to prepare propanol, wherein the copper-based catalyst serves as the cathode.

[0029] The present invention further provides a method for electrocatalytic reduction of carbon dioxide to prepare propanol, including the following steps:

[0030] Using the copper-based catalyst as the working electrode, under a three-electrode system in an H-type electrolytic cell, perform an electrocatalytic CO₂ reduction reaction to obtain it;

[0031] The specific steps may be:

[0032] Before the electrolysis experiment starts, introduce a KHCO₃ or KOH electrolyte solution into high-purity CO₂ for 20 to 40 minutes to make it fully saturated, and perform electrolysis in a constant current manner under a stable CO₂ gas flow of 20 to 50 sccm; collect the gas product with an air bag, analyze it with a gas chromatograph, and analyze the liquid product with a nuclear magnetic resonance hydrogen spectrum.

[0033] The present invention has the following beneficial effects:

[0034] The present invention uses a two-step electrochemical reconstruction method to obtain a Cu / Cu2O electrocatalyst with a bicontinuous nanodomain structure, and uses this as the cathode for electrocatalytic reduction of carbon dioxide. By suppressing the occurrence of hydrogen evolution reaction in an aqueous KOH or KHCO3 solution system, the activity for producing propanol is significantly improved. It has been experimentally found that at a current density of 0.84 A cm -2 , the Faraday efficiency of propanol exceeds 12.1%, and it has good stability. Based on the above analysis, the Cu / Cu2O catalyst obtained by the electrochemical reconstruction method in the present invention can electrocatalytically reduce carbon dioxide reaction to prepare propanol as the cathode. Brief Description of the Drawings

[0035] Figure 1 It is the SEM image of the copper-based material Cu(OH)2 / CuO obtained by the oxidation etching method in the present invention.

[0036] Figure 2 It is the SEM image of the copper-based electrode material Cu / Cu2O obtained by the electrochemical reconstruction method in the present invention.

[0037] Figure 3 It is the HRTEM image of the copper-based electrode material Cu / Cu2O obtained by the electrochemical reconstruction method in the present invention.

[0038] Figure 4 It is the EDS image of the copper-based electrode material Cu / Cu2O obtained by the electrochemical reconstruction method in the present invention.

[0039] Figure 5 It is the XRD image of the copper-based electrode material Cu / Cu2O obtained by the electrochemical reconstruction method in the present invention.

[0040] Figure 6 It is the XAFS spectrum of the copper-based electrode material Cu / Cu2O obtained by the electrochemical reconstruction method in the present invention.

[0041] Figure 7 It is the gas chromatogram of the gas products generated at an applied voltage of -1.4 V vs. RHE with the copper-based electrode material Cu / Cu2O obtained by the electrochemical reconstruction method in the present invention as the cathode and the 1H NMR spectrum of the electrolyte after the reaction.

[0042] Figure 8 It is the Faraday efficiency and current density diagram of the copper-based electrode materials Cu / Cu2O, Cu / Cu2O-1, and Cu / Cu2O-2 obtained by the electrochemical reconstruction method in the present invention for electrocatalytic reduction of carbon dioxide to propanol products. Detailed Embodiments

[0043] The experimental methods used in the following examples are all conventional methods unless otherwise specified.

[0044] The materials, reagents, etc. used in the following examples can be obtained from commercial sources without special instructions.

[0045] Example 1: Preparation of a copper-based catalyst for electrocatalytic reduction of carbon dioxide to propanol

[0046] Step (1): Dissolve 8 mM CuSO4 in 100 mL of deionized water to form Solution A. Separately, dissolve 1.5 M sodium hydroxide in 30 mL of deionized water to form Solution B. Dropwise add Solution B into Solution A under magnetic stirring. A blue-green precipitate will slowly form during the stirring process, turning into a turbid Solution C. Among them, the molar ratio of CuSO4 to sodium hydroxide is 1:187.5.

[0047] Step (2): Dissolve 100 mM hydroxylamine hydrochloride in 20 mL of deionized water, and after ultrasonic treatment for 10 min, a clear solution is formed and marked as Solution D.

[0048] Step (3): Dropwise add Solution D obtained in Step (2) into Solution C obtained in Step (1). Among them, the molar ratio of CuSO4 to hydroxylamine hydrochloride is 1:12.5. At a reaction temperature of 30 °C, react under magnetic stirring for 7 h. After the obtained product is separated by a centrifuge, vacuum dry it overnight at 60 °C to finally form a black-gray powder, which is the sample Cu(OH)2 / CuO.

[0049] Step (4): Mix the sample Cu(OH)2 / CuO, isopropanol, and Nafion solution in a ratio of 10 mg: 3 mL: 0.03 mL and ultrasonically disperse to obtain a mixed solution. Then evenly coat the mixed solution on carbon paper, and then dry it under a N2 atmosphere to form the Cu(OH)2 / CuO working electrode. Then, use the electrochemical reconstruction method to reduce the catalyst to Cu / Cu2O nanosheets (using the Cu(OH)2 / CuO working electrode as the cathode, in a 0.1 M KHCO3 solution, apply a constant potential of -1.4 V vs. RHE and electrolyze for 30 min) to obtain a Cu / Cu2O catalyst with a bicontinuous nanodomain structure. The molar proportion of Cu2O in Cu / Cu2O is 42.4% (see Table 1).

[0050] Figure 1 Figure 1 is the SEM image of the copper-based material Cu(OH)2 / CuO obtained by the oxidation etching method in Example 1. It can be seen that the material is a sea urchin structure self-assembled by nanosheets and nanoneedles.

[0051] Figure 2 Figure 2 is the SEM image of the copper-based electrode material Cu / Cu2O obtained by the electrochemical reconstruction method in Example 1. It can be seen that it becomes nanosheets after electrochemical reconstruction.

[0052] Figure 3Figure showing the HRTEM image of the copper-based electrode material Cu / Cu2O obtained by the electrochemical reconstruction method in Example 1. It can be seen that a bicontinuous nanodomain structure is formed on the nanosheets after electrochemical reconstruction.

[0053] Figure 4 Figure showing the EDS image of the copper-based electrode material Cu / Cu2O obtained by the electrochemical reconstruction method in Example 1. Cu atoms and O atoms are evenly distributed on the surface of the material.

[0054] Figure 5 Figure showing the XRD pattern of the copper-based electrode material Cu / Cu2O obtained by the electrochemical reconstruction method in Example 1. The diffraction peaks of Cu / Cu2O after reconstruction are consistent with those of metallic copper, cuprous oxide, and carbon paper.

[0055] Figure 6 Figure showing the XAFS spectrum of the copper-based electrode material Cu / Cu2O obtained by the electrochemical reconstruction method in Example 1. The molar ratio of Cu2O in Cu / Cu2O after reconstruction is 42.4%.

[0056] Example 2

[0057] Using the method of Example 1, the reaction time in step (3) was changed to 5 hours to obtain the Cu / Cu2O-1 catalyst. The molar ratio of Cu2O in Cu / Cu2O is 57.8%.

[0058] Example 3

[0059] Using the method of Example 1, the reaction time in step (3) was changed to 9 hours to obtain the Cu / Cu2O-2 catalyst. The molar ratio of Cu2O in Cu / Cu2O is 24.6%.

[0060] Table 1 Parameters for preparing the working electrode in Examples 1 - 3

[0061] Reaction time <![CDATA[Molar proportion of Cu2O (%)]]> Potential (V vs. RHE) <![CDATA[FE 丙醇 (%)]]> Example 1 7 42.4 -1.4 17.0 Example 2 5 57.8 -1.4 11.2 Example 3 9 24.6 -1.5 7.4

[0062] Application Example 1, electrocatalytic reduction of carbon dioxide (H-type electrolytic cell)

[0063] The electrolysis experiment was carried out in a commercial H-type electrolytic cell under a three-electrode system. The cathode and anode were separated by an ion-exchange membrane. The three electrodes included a working electrode, a platinum mesh counter electrode, and an Ag / AgCl reference electrode. The reference electrode was stabilized through a glass tube with a Luggin capillary. Before the experiment, the reference electrode was calibrated according to the method in the literature.

[0064] Before the electrolysis experiment, the electrolyte of 0.1 M KHCO3 was purged with high-purity CO2 for 30 minutes to make it fully saturated, and the electrolysis experiment was carried out at a constant current under a stable CO2 gas flow of 20 sccm. The gas products were collected with an airbag and analyzed by a gas chromatograph, and the liquid products were analyzed by 1H NMR.

[0065] Figure 7 When the copper-based electrode material (Cu / Cu2O) obtained by the electrochemical reconstruction method in Example 1 was used as the cathode, the analysis and determination of gas and liquid products were carried out. As can be seen from Figure 7 Figure a in [reference], the main product in the product is C2H4 gas. Figure 7 As can be seen from Figure b in [reference], propanol product was formed (about 0.8).

[0066] Figure 8 When the copper-based electrode materials (Cu / Cu2O, Cu / Cu2O-1, and Cu / Cu2O-2) obtained by the electrochemical reconstruction method in Examples 1-3 were used as the cathode, the Faraday efficiency and partial current density of propanol were calculated. It can be seen that the catalytic system of the present invention has high activity for reducing carbon dioxide to propanol. In this example, at an applied potential of -1.4 V vs. RHE, the Faraday efficiency of producing propanol exceeded 17%.

[0067] Application Example 2: Electrochemical Reduction of Carbon Dioxide (Flow Electrolytic Cell)

[0068] The electrolysis experiment was carried out in a commercial flow electrolytic cell under a three-electrode system. The cathode and anode were separated by an ion exchange membrane. The three electrodes included a working electrode, a nickel mesh counter electrode, and an Ag / AgCl reference electrode. The reference electrode was stabilized through a glass tube with a Luggin capillary. Before the experiment, the reference electrode was calibrated according to the method in the literature.

[0069] Before the electrolysis experiment, the electrolyte of 1 M KOH was purged with high-purity CO2 for 30 minutes to make it fully saturated, and the electrolysis experiment was carried out at a constant potential under a stable CO2 gas flow of 50 sccm. The gas products were collected with an airbag and analyzed by a gas chromatograph, and the liquid products were analyzed by 1H NMR.

[0070] Table 2 Faraday efficiency and partial current density of propanol products at different potentials when using the electrode material prepared in Example 1

[0071]

[0072] It can be seen that the catalytic system of the present invention has excellent selectivity and relatively high reaction activity for reducing carbon dioxide to propanol. In this example, within the applied potential range of -0.9 V to -1.3 V vs. RHE, it has a good Faraday efficiency for propanol (see Table 2). Among them, at -1.1 V vs. RHE, the Faraday efficiency for generating propanol is 12.1%, and the partial current density of propanol is 101.6 mA cm -2 .

[0073] The above results clearly demonstrate that the catalytic material of the present invention has a relatively high current density (at 840 mAcm -2 ) and excellent selectivity for propanol, proving that the present invention has certain industrial application value.

Claims

1. A preparation method of a copper-based catalyst for electrocatalytic reduction of carbon dioxide to propanol, comprising the following steps: S1. Add an aqueous sodium hydroxide solution to an aqueous solution of a copper compound to obtain a turbid solution; S2. Add an aqueous hydroxylamine hydrochloride solution to the turbid solution, carry out a reaction, and obtain Cu(OH)2 / CuO through centrifugation and drying; S3. Prepare the Cu(OH)2 / CuO into a working electrode, and then reduce it to Cu / Cu2O nanosheets by an electrochemical reconstruction method.

2. The preparation method according to claim 1, characterized in that: In step S1, the concentration of the aqueous sodium hydroxide solution is 0.5 mol / L to 2 mol / L; the concentration of the aqueous solution of the copper compound is 5 mmol / L to 100 mmol / L; the molar ratio of the copper compound to sodium hydroxide is 1:100 to 400; Under the condition of stirring, the aqueous sodium hydroxide solution is added dropwise to the aqueous solution of the copper compound.

3. The preparation method according to claim 1 or 2, characterized in that: In step S1, the copper compound is one of copper nitrate, copper chloride, cuprous chloride, copper sulfate, copper acetate and copper acetylacetonate.

4. The preparation method according to any one of claims 1-3, characterized in that: In step S2, the concentration of the hydroxylamine hydrochloride is 50 mmol / L to 400 mmol / L; the molar ratio of the copper compound to hydroxylamine hydrochloride is 1:10 to 80; the temperature of the reaction is 20 °C to 50 °C, and the time is 0.5 to 24 h.

5. The preparation method according to any one of claims 1-4, characterized in that: In step S3, the steps of preparing the working electrode are as follows: Mix the Cu(OH)2 / CuO with isopropanol and a Nafion solution and ultrasonically disperse to obtain a mixed solution, then uniformly coat the mixed solution on carbon paper, and then dry it in a N2 atmosphere to form a Cu(OH)2 / CuO working electrode.

6. The preparation method according to any one of claims 1-5, characterized in that: In step S3, the steps of the electrochemical reconstruction method are as follows: Using the working electrode as the cathode, carry out potentiostatic electrolysis in a KHCO3 solution.

7. The preparation method according to claim 6, characterized in that: The concentration of the KHCO3 solution is 0.1 mol / L to 1 mol / L; The conditions of the electrolysis are as follows: the potential is -1.4 V to -1.5 V (vs. RHE); the time is 10 min to 60 min.

8. A copper-based catalyst prepared by the method according to any one of claims 1-7.

9. Use of the copper-based catalyst according to claim 8 in the electrocatalytic reduction of carbon dioxide to prepare propanol.

10. A method for electrocatalytic reduction of carbon dioxide to prepare propanol, comprising the following steps: Using the copper-based catalyst according to claim 8 as the working electrode, under a three-electrode system in an H-type electrolytic cell, carry out an electrocatalytic CO2 reduction reaction to obtain.

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