A method for producing carbon monoxide by electrocatalytic reduction of carbon dioxide

Abstract

The present invention discloses a method for preparing carbon monoxide by electrocatalytic reduction of carbon dioxide. The electrocatalytic reduction system described in the method uses a cadmium-based catalyst in situ electrodeposited on carbon paper as an electrode material, and a solution composed of ionic liquid and acetonitrile as an electrolyte. The catalyst does not need to be prepared separately. It only needs to add a certain amount of cadmium-based metal salt to the electrolyte to prepare the cadmium-based catalyst at a suitable potential, and simultaneously reduce CO2 to CO. The present invention innovatively designs an in situ electrodeposited cadmium-based catalyst as a cathode material, and applies it to a three-electrode system with ionic liquid and acetonitrile as a mixed electrolyte, to efficiently electrocatalytically reduce CO2 to CO. The electrocatalytic system of the present invention is simple to operate, has mild reaction conditions, and a simple method for preparing the cathode catalyst. It has industrial development value and provides an important and practical approach for the fixation and resource utilization of CO2.

Description

Technical Field

[0001] The invention belongs to the field of chemistry and chemical engineering, and particularly relates to a method for preparing carbon monoxide by using an electrochemical method and carbon dioxide as a raw material. Background Art

[0002] Traditional fossil fuels still dominate the current energy mix, and this structure is unlikely to change in the foreseeable future. The use of traditional fossil fuels releases large amounts of CO₂, contributing to the annual increase in CO₂ levels in the air and causing a series of serious ecological and social problems. At the same time, as a cheap and readily available C₁ resource, CO₂'s efficient conversion into high-value-added chemicals and the development of related industries holds significant practical value. Extensive research has been conducted on CO₂ conversion using a variety of chemical methods, including thermochemical, photocatalytic, electrocatalytic, and biochemical approaches. In recent years, electrochemical CO₂ conversion has attracted widespread attention. These methods feature simple equipment, convenient operation, controllable reaction conditions, and can be performed at room temperature and pressure. The electrolyte can be recycled, reducing chemical consumption and waste generation. The reaction process does not require an external hydrogen source. The electricity required can be generated from renewable clean energy sources (including nuclear, wind, and tidal energy), or from excess electricity at specific times, meeting the requirements of sustainable development.

[0003] In recent years, numerous researchers have continuously explored and designed novel catalysts, electrolytes, and reaction devices, achieving significant progress in the electrocatalytic reduction of CO2. The electrocatalytic conversion of CO2 involves multiple electron / proton transfer processes, resulting in a variety of reduction products, primarily including CO, formic acid, methane, methanol, ethylene, ethane, and ethanol. Among these products, multi-carbon products have a higher market demand, but the process has slow reaction kinetics, and the current technological level falls far short of the requirements for industrial application. In the electrocatalytic reduction of CO2, considering the cost of electricity (as mentioned in Ref. 1 (JinS, HaoZ, ZhangK, et al. Advances and Challenges for Electrochemical Reduction ofCO2 to CO:From Fundamental to Industrialization[J]. Angewandte Chemie. 2021, 60: 20627–20648), CO and formic acid as the products of a two-electron reaction are more economically viable. Furthermore, the cost of gas separation is lower than that of liquid separation. At the same time, CO, as an important platform molecule, can be mixed with hydrogen (H2) to form syngas (a mixture of CO and H2) with varying ratios. This can then be used through methods such as Fischer-Tropsch synthesis to produce higher-value chemicals or fuels (such as methanol, ethanol, paraffin, diesel, gasoline, and naphtha), significantly boosting market demand for CO. Therefore, the electrocatalytic reduction of CO2 to CO is a promising area for industrial application.

[0004] Research on the electrochemical conversion of CO2 to CO dates back to the 1960s. To improve the Faradaic efficiency and current density of the CO reaction, a variety of catalysts have been designed, including metal catalysts, carbon-based catalysts, transition metal sulfides, molecular catalysts, and single-atom catalysts. Reference 2 (Clark EL, Ringe S, Tang M, et al. Influence of Atomic Surface Structure on the Activity of Ag for the Electrochemical Reduction of CO2 to CO[J]. Acs Catalysis, 2019. 9: 4006-4014) modulates the active centers and electronic structure of the catalyst at the nanoscale by manipulating crystal planes, grain boundaries, and defects, thereby affecting its binding ability to reaction intermediates and improving its catalytic activity. Reference 3 (Li Z, He D, Yan X, et al. Size-Dependent Nickel-Based Electrocatalysts for SelectiveCO2 Reduction[J].Angewandte Chemie International Edition, 2020, 59(42): 18572–18577) By changing the particle size, porosity, surface roughness, etc. of the catalyst, its electrochemically active surface area can be changed, affecting the mass transfer of the reaction and thus regulating the performance of the catalyst. However, these current systems for the electrocatalytic reduction of CO2 to CO are still imperfect, and their catalyst performance is difficult to achieve both high current density and high Faradaic efficiency at the same time. Therefore, the development of new and efficient catalysts to achieve high CO Faradaic efficiency at higher current density remains an urgent and challenging topic, and it is also a difficult problem that the current scientific research and industrial communities urgently need to solve.

[0005] Industrial-scale CO2 electrolysis requires high current densities (> 200 mA cm -2 ) and high selectivity and low applied voltage to achieve high energy efficiency. Currently, the main source of CO2 emissions is the combustion of fossil fuels, including waste gases from various industries and thermal power plants, with CO2 concentrations of approximately 5% to 15%. Directly converting industrial waste gases with low CO2 concentrations into high-value-added chemicals without the energy-consuming concentration process is a key technology for the industrialization of electrocatalytic CO2 reduction and a challenge that currently needs to be addressed by both scientific research and industry. Summary of the Invention

[0006] This invention proposes a method for the electrocatalytic reduction of CO2 to CO. This reaction, utilizing an in-situ electrodeposited cadmium-based catalyst / carbon paper and an ionic liquid-acetonitrile electrolyte, can efficiently electrocatalyze the conversion of CO2 to CO at relatively low CO2 concentrations. This represents a significant breakthrough in the electrocatalytic conversion of CO2, opening a practical path for the conversion of CO2 to CO and possessing significant economic and social benefits.

[0007] The technical solution adopted in the present invention is:

[0008] A method for efficiently converting carbon dioxide to carbon monoxide by electrocatalytic conversion uses carbon dioxide as a raw material, an in-situ electrodeposited cadmium-based catalyst / carbon paper as a cathode material, and an ionic liquid-acetonitrile mixed solution as an electrolyte to form an electrocatalytic system for reaction to produce carbon monoxide.

[0009] Furthermore, the method comprises the following steps:

[0010] (1) Prepare the required electrolyte: dissolve the cadmium salt in the ionic liquid-acetonitrile solution as the reaction electrolyte and catalyst precursor;

[0011] (2) The above solution is passed through CO2 gas and stirred for a certain period of time. The resulting carbon dioxide saturated solution is used as the cathode electrolyte, and the electrode sandwiched with carbon paper is used as the cathode;

[0012] (3) Electrolysis experiments were conducted under different applied voltages to electrocatalytically reduce CO2 to CO while forming a cadmium-based catalyst / carbon paper on the carbon paper substrate.

[0013] Furthermore, the cadmium compound in step (1) may be selected from cadmium compounds such as cadmium nitrate (Cd(NO3)2), cadmium chloride (CdCl2), cadmium sulfate (CdSO4), cadmium acetate (Cd(CH3COO)2), cadmium acetylacetonate (Cd(acac)2), cadmium perchlorate (Cd(ClO4)2), cadmium phosphate (Cd3(PO4)2), and cadmium bis(trifluoromethylsulfonyl)imide (Cd(NTf2)2).

[0014] Furthermore, the amount of cadmium salt used in step (1) is 0.1-10 mg / mL.

[0015] Furthermore, the ionic liquid in step (1) is 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4), 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([Bmim]TfO), 1-butyl-3-methylimidazolium perchlorate ([Bmim]ClO4), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Bmim]NTf2), 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim]PF6), 1-butyl-3-methylimidazolium hydrogen sulfate ([Bmim]HSO4), 1-ethyl-3-methylimidazolium hexafluorophosphate ([Emim]PF6), 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim]BF4), 1-ethyl-3-methylimidazolium acetate ([Emim]Ac), 1-ethyl-3-methylimidazolium dihydrogen phosphate ([Emim]H2PO4), 1-hexyl-3-methylimidazolium hexafluorophosphate ([Hmim]PF6), 1-hexyl-3-methylimidazolium tetrafluoroborate ([Hmim]BF4), preferably 1-butyl-3-methylimidazolium hexafluorophosphate ([Emim]PF6).

[0016] Furthermore, in the ionic liquid-acetonitrile solution of step (1), the mass percentage of the ionic liquid is 1% to 100%.

[0017] Furthermore, the concentration of CO2 gas in step (2) is 5% to 99.999%.

[0018] Furthermore, the applied voltage in step (3) is -1.7 to -2.7 V vs. Ag / Ag + .

[0019] The beneficial effects of the present invention are:

[0020] This invention utilizes in-situ electrodeposition to prepare a cadmium-based electrocatalyst while simultaneously performing CO2 electrochemical reduction. This method achieves high reactivity and selectivity in an ionic liquid-acetonitrile mixed electrolyte. Furthermore, it achieves high CO yields and CO2 conversion rates even at low CO2 concentrations. This represents a significant breakthrough in the electrochemical catalytic conversion of CO2, opening a practical path for the electrocatalytic conversion of CO2 to CO and possessing significant commercial value. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1a This is a SEM image of the cadmium-based material obtained by in-situ electrodeposition in the present invention;

[0022] Figure 1b for Figure 1a Magnified image of;

[0023] Figure 2 This is a TEM image of the cadmium-based material obtained by in-situ electrodeposition in the present invention;

[0024] Figure 3a In the present invention, the in-situ cadmium-based nanomaterial is used as the cathode at -2.0Vvs.Ag / Ag + Gas chromatogram of gas products produced under applied voltage;

[0025] Figure 3b In the present invention, the in-situ cadmium-based nanomaterial is used as the cathode at -2.0Vvs.Ag / Ag + H NMR spectrum of the electrolyte after the reaction is completed under the applied voltage;

[0026] Figure 4 The gas chromatogram of the gas products produced when the cadmium-based nanomaterial is used as the cathode to reduce low-concentration CO2 in the present invention. DETAILED DESCRIPTION

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0028] The electrolysis experiment was carried out in a commercial H-type electrolytic cell with a three-electrode system. The cathode and anode were separated by a proton exchange membrane. The three electrodes included a working electrode, a counter electrode (platinum mesh) and an Ag / Ag + Reference electrode, the reference electrode is stabilized by a glass tube with a Luggin capillary. Before the experiment, the reference electrode was calibrated according to the method in the literature.

[0029] Example 1

[0030] A method for efficiently converting carbon dioxide to carbon monoxide by electrocatalytic conversion comprises the following steps: using a [Bmim]PF6-acetonitrile solution containing 0.5 mg / mL CdCl2 as the cathode electrolyte, wherein the mass percentage of [Bmim]PF6 in the solution is 10%. Before the electrolysis experiment begins, the electrolyte is passed through high-purity CO2 for 30 minutes to fully saturate it. The electrolysis experiment is then conducted under a steady CO2 flow of 20 sccm and an applied voltage of -2.0 V vs. Ag / Ag. + The gaseous products were collected by air bags and analyzed by gas chromatography, and the liquid products were analyzed by nuclear magnetic resonance spectroscopy.

[0031] Figure 1a 、 Figure 1b The SEM image of the cadmium-based material obtained in Example 1 shows that the material is evenly covered on the carbon paper and has a cross-linked linear structure. Figure 2The TEM image of the cadmium-based material obtained in Example 1 shows that the size of the linear structure is about 6 nm. Figure 3 shows the analysis and determination of the gas products when the cadmium-based material is used as the cathode in Example 1. Figure 3a It can be seen that the product is mainly CO gas. Figure 3b It can be seen that no liquid product is generated (no signal around 8.2). The calculated Faradaic efficiency of CO is 94.2% (see Table 1).

[0032] Example 2

[0033] A method for efficiently converting carbon dioxide to carbon monoxide by electrocatalytic conversion comprises the following steps: using a [Bmim]PF6-acetonitrile solution containing 0.8 mg / mL Cd(NO3)2, wherein the mass percentage of [Bmim]PF6 is 30%, as the cathode electrolyte. Prior to the electrolysis experiment, the electrolyte was saturated with high-purity CO2 for 30 minutes. The electrolysis experiment was then conducted under a steady CO2 flow of 20 sccm and an applied voltage of -2.0 V vs. Ag / Ag. + The gaseous products were collected by air bags and analyzed by gas chromatography, and the liquid products were analyzed by nuclear magnetic resonance spectroscopy.

[0034] The catalytic system of the present invention has excellent selectivity and high reaction activity for reducing carbon dioxide to carbon monoxide. The Faradaic efficiency of producing CO in this embodiment is close to 100% (see Table 1 for the results).

[0035] Example 3

[0036] A method for efficiently converting carbon dioxide to carbon monoxide by electrocatalytic conversion comprises the following steps: using a [Bmim]PF6-acetonitrile solution containing 0.8 mg / mL Cd(NO3)2, with a mass percentage of [Bmim]PF6 of 30%, as the cathode electrolyte. Prior to the electrolysis experiment, the electrolyte was saturated with high-purity CO2 for 30 minutes. The electrolysis experiment was conducted under a steady CO2 flow of 20 sccm and an applied voltage of -2.4 V vs. Ag / Ag. + The gaseous products were collected by air bags and analyzed by gas chromatography, and the liquid products were analyzed by nuclear magnetic resonance spectroscopy.

[0037] The catalytic system of the present invention has high activity for reducing carbon dioxide to carbon monoxide. In this embodiment, no liquid product is generated, the Faradaic efficiency of CO generation is above 90%, and the current density is relatively high (greater than 200 mA cm -2 , see Table 1).

[0038] Example 4

[0039] A method for efficiently converting carbon dioxide to carbon monoxide by electrocatalytic conversion comprises the following steps: using a [Bmim]PF6-acetonitrile solution containing 3 mg / mL Cd(NO3)2 as the cathode electrolyte, with the mass percentage of [Bmim]PF6 being 30%. Before the electrolysis experiment begins, the electrolyte is passed through high-purity CO2 for 30 minutes to fully saturate it. The electrolysis experiment is then conducted under a stable CO2 flow of 20 sccm and an applied voltage of -2.0 V vs. Ag / Ag. + The gaseous products were collected by air bags and analyzed by gas chromatography, and the liquid products were analyzed by nuclear magnetic resonance spectroscopy.

[0040] The catalytic system of the present invention has high activity for reducing carbon dioxide to carbon monoxide (no liquid product). The Faradaic efficiency of CO production in this embodiment is about 85%, and the current density is relatively high, 188 mA cm -2 (See Table 1).

[0041]

[0042] Example 5

[0043] A method for efficiently converting carbon dioxide to carbon monoxide by electrocatalytic conversion comprises the following steps: using a [Bmim]PF6-acetonitrile solution containing 3 mg / mL Cd(NO3)2 as the cathode electrolyte, with the mass percentage of [Bmim]PF6 being 30%. Before the electrolysis experiment begins, the electrolyte is saturated with 5% CO2 for 30 minutes. The electrolysis experiment is then conducted under a steady CO2 flow of 20 sccm and an applied voltage of -2.0 V vs. Ag / Ag. + The gaseous products were collected by air bags and analyzed by gas chromatography, and the liquid products were analyzed by nuclear magnetic resonance spectroscopy.

[0044] In this embodiment, the conversion rate of low-concentration CO2 can reach 6.8%, and the CO production rate can reach 4.03 mL / (hcm -2 ) (see Table 2).

[0045] Example 6

[0046] A method for efficiently converting carbon dioxide to carbon monoxide by electrocatalytic conversion comprises the following steps: using a [Bmim]PF6-acetonitrile solution containing 3 mg / mL Cd(NO3)2 as the cathode electrolyte, with the mass percentage of [Bmim]PF6 being 30%. Before the electrolysis experiment begins, the electrolyte is saturated with 10% CO2 for 30 minutes. The electrolysis experiment is then conducted under a steady CO2 flow of 20 sccm and an applied voltage of -2.3 V vs. Ag / Ag. +The gaseous products were collected by air bags and analyzed by gas chromatography, and the liquid products were analyzed by nuclear magnetic resonance spectroscopy.

[0047] The conversion rate of low-concentration CO2 in this embodiment can reach more than 30%, and the CO production rate can reach 40.8 mL / (h cm -2 ) (see Table 2), which is higher than the data reported in existing literature.

[0048] Example 7

[0049] A method for efficiently converting carbon dioxide to carbon monoxide by electrocatalytic conversion comprises the following steps: using a [Bmim]PF6-acetonitrile solution containing 3 mg / mL Cd(NO3)2 as the cathode electrolyte, with a mass percentage of [Bmim]PF6 of 30%. Before the electrolysis experiment begins, the electrolyte is saturated with 20% CO2 for 30 minutes. The electrolysis experiment is then conducted under a steady CO2 flow of 20 sccm and an applied voltage of -2.0 V vs. Ag / Ag. + The gaseous products were collected by air bags and analyzed by gas chromatography, and the liquid products were analyzed by nuclear magnetic resonance spectroscopy.

[0050] The conversion rate of low-concentration CO2 in this embodiment can reach 15.1%, and the CO production rate can reach 36.3 mL / (h cm -2 ) (see Table 2), which is higher than the data reported in existing literature.

[0051]

[0052] The above results clearly demonstrate that the method of the present invention has a high current density (greater than 200 mA cm -2 ) and excellent CO selectivity, and a high conversion rate for low-concentration CO2 produced in simulated industrial processes. These results demonstrate that the method described in the present invention has certain industrial application value.

[0053] Although the embodiments of the present invention have been described above, it will be apparent to those skilled in the art that modifications and substitutions made without departing from the principles and spirit of the present invention are intended to fall within the scope of protection claimed by the present invention.

Claims

1. A method for producing carbon monoxide by electrocatalytic reduction of carbon dioxide, characterized in that: Carbon monoxide is produced by reacting carbon dioxide as a raw material, in-situ electrodeposited cadmium-based catalyst carbon paper as a cathode material, and an ionic liquid-acetonitrile mixed solution as an electrolyte. The electrocatalytic system comprises the following steps: (1) Prepare the required electrolyte: a certain amount of cadmium salt is dissolved in an ionic liquid-acetonitrile solution as the reaction electrolyte and also as a catalyst precursor; (2) The above solution is passed through CO2 gas and stirred for a certain period of time. The resulting carbon dioxide-saturated solution is used as the cathode electrolyte, and the electrode sandwiched with carbon paper is used as the cathode; (3) Electrolysis experiments were performed at different applied voltages to electrocatalytically reduce CO2 to CO while simultaneously depositing a cadmium-based catalyst on the carbon paper substrate.

2. The method according to claim 1, wherein: The cadmium salt is one of cadmium nitrate, cadmium chloride, cadmium sulfate, cadmium acetate, cadmium acetylacetonate, cadmium perchlorate, cadmium phosphate and cadmium bis(trifluoromethylsulfonyl)imide.

3. The method according to claim 1, wherein: The dosage of cadmium salt is 0.1-10 mg / mL.

4. The method according to claim 1, wherein: The ionic liquids are 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-3-methylimidazolium perchlorate, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium hydrogensulfate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium dihydrogenphosphate, 1-hexyl-3-methylimidazolium hexafluorophosphate, and 1-hexyl-3-methylimidazolium tetrafluoroborate.

5. The method according to claim 4, characterized in that: The ionic liquid is 1-butyl-3-methylimidazolium hexafluorophosphate.

6. The method according to claim 4, characterized in that: In the ionic liquid-acetonitrile solution, the mass percentage of the ionic liquid is 1% to 100%.

7. The method according to claim 1, wherein: The concentration of CO2 gas is 5% to 99.999%.

8. The method according to claim 1, wherein: The potential of the reaction is -1.7 to -2.7 V vs. Ag / Ag+.

9. The method according to claim 8, characterized in that: The potential of the reaction is -2.0 V vs. Ag / Ag+.

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