A method for electrocatalytic reduction of CO2 by ionic liquid-polymer-modified copper-based catalysts

Abstract

The application discloses a method for realizing electrocatalytic reduction of CO2 by using ion liquid cooperated with ionomer modified copper-based catalysts, and adopts a wet chemical synthesis method, selects copper sulfate, lactic acid, sodium hydroxide, ascorbic acid and hexadecyl trimethyl ammonium chloride as materials to synthesize Cu2O copper-based catalysts, introduces ion liquid cooperated with ionomer modified catalysts as high-efficiency electrocatalysts for electrocatalytic reduction of CO2, and effectively improves the CO2 reduction performance of the electrode in a neutral electrolyte. The ion liquid is introduced to optimize the electrode treatment, modify the surface of the electrocatalyst, enhance the mass transfer and activation of CO2, and the ion liquid cooperated with the ionomer shows excellent CO2 electro-reduction performance, improves the selectivity of multi-carbon products, suppresses the hydrogen evolution side reaction, and further reduces the cell voltage.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical catalysis and new energy materials, and particularly relates to a method for electrocatalytic reduction of CO2 by modifying copper-based catalysts with ionic liquids and ionomers. Background Technology

[0002] The challenges of global climate change are intensifying, with the development of renewable energy and the recycling of carbon resources being two key pillars. However, renewable energy sources such as wind and solar power are intermittent and volatile, and their large-scale grid connection poses a challenge to grid stability (i.e., the "absorption" problem). Meanwhile, as a major greenhouse gas, CO2 faces increasing pressure for emission reduction and utilization. Electrocatalytic CO2 reduction technology, as an important downstream pathway of CCUS (carbon capture, storage, and utilization), can convert CO2 into high-value-added chemicals such as C2H4 and C2H5OH at ambient temperature and pressure, achieving the absorption of renewable energy power and the high-value utilization of CO2. Current technologies still face challenges such as low selectivity of target products, poor reaction stability, and low system energy efficiency.

[0003] Research has shown that ionomers can play a role in the electrocatalytic reduction of CO2 (CO2RR) to produce multi-carbon products (C). 2+ In electrocatalytic reduction of CO2 to prepare multi-carbon products such as C2H4 and C2H5OH, ionic liquids primarily enhance selectivity and stability by regulating the microenvironment on the catalyst surface. Their core function is to create a localized reaction site around the catalytically active sites that is conducive to CO2 conversion, intermediate stabilization, and CC coupling. For this purpose, ionic liquids can directly interact with the catalytically active sites (e.g., through coordination and electron transfer), altering the adsorption energy of intermediates and the reaction energy barrier, thereby improving the selectivity of multi-carbon products and suppressing hydrogen evolution side reactions.

[0004] Based on this, the present invention designs a method for modifying copper-based catalysts with ionic liquids and ionomers, which can efficiently convert CO2 into multi-carbon products such as C2H4 and C2H5OH under mild conditions. Summary of the Invention

[0005] The purpose of this invention is to propose a method for achieving highly efficient electrocatalytic CO2 reduction by modifying copper-based catalysts with ionic liquids and ionomers, based on existing electrocatalytic CO2 conversion technologies. This method involves introducing ionic liquids and ionomers to functionally modify the surface of the copper-based catalyst, altering the hydrophilicity / hydrophobicity of the electrode surface, effectively suppressing competitive hydrogen evolution side reactions, stabilizing key reaction intermediates, and enabling specific interactions with intermediates such as *CO, thereby lowering the energy barrier for their dimerization (CC coupling) and promoting the formation of multi-carbon products. This solves the problems of low selectivity, poor stability, and high energy consumption in existing electrocatalytic CO2 conversion processes to multi-carbon products.

[0006] The objective of this invention is achieved through the following technical solution: a method for electrocatalytic reduction of CO2 by modifying a copper-based catalyst with an ionic liquid and ionomer, the method comprising the following steps: (1) Preparation of catalyst material: A wet chemical reduction method was adopted, and an appropriate amount of CTAC was introduced as a structure directing agent. First, 1.65 mL of lactic acid was dissolved in 25 mL of deionized water and stirred for 30 min. Then, 0.16 g of CTAC and 0.4 g of CuSO4 were added to the solution in sequence, and stirring was continued for 30 min to form a uniform light blue solution. Then, under stirring conditions, 4 M NaOH was slowly added to the above solution until the pH value of the suspension reached 12, and stirring was continued for 2 hours. Next, the mixture was sonicated for 30 min, and then 0.55 g of ascorbic acid was added and stirred for 2 h to obtain the target product precipitate. The sample was centrifuged at 8000 r / min for 5 min, washed 3 times with deionized water and ethanol, and finally dried in a vacuum oven at 60℃ for 12 h to obtain the product cuprous oxide (Cu2O), which was then ground. (2) Preparation of catalyst ink: 5 mg Cu2O, 30 uL perfluorosulfonic acid resin (NafionD-520), 20 uL tetraethylammonium hydroxide (TEAOH) prepared in step (1) are mixed with 600 uL isopropanol and ultrasonically treated for 30 min to prepare a uniform catalyst ink. (3) Cathode electrode preparation: The catalyst ink obtained in step (2) was sprayed onto the surface of carbon paper (SGL 28BC, 4 cm) using a spray gun. 2 After standing and drying, the cathode electrode is obtained.

[0007] Further, in step (1), the molar ratio of CuSO4 to CTAC is 5:1, and the mass fraction of the perfluorosulfonic acid resin (Nafion D-520) is 5%.

[0008] Furthermore, the amount of 4 M NaOH added in step (1) is 6.825 mL.

[0009] Further, the TEAOH aqueous solution in step (2) has a mass fraction of 25%. The addition order is: TEAOH is added after cuprous oxide, perfluorosulfonic acid resin and isopropanol are mixed evenly.

[0010] Furthermore, in step (3), the spraying needs to be carried out evenly, with each spray load being 1 mg / cm². 2 The static drying conditions are 60℃ for 12 h to remove solvent and enhance interfacial bonding strength.

[0011] This invention also provides an application of ionic liquid-polymer-modified electrode surface in neutral electrocatalytic carbon dioxide reduction, using 0.1 M KHCO3 as the electrolyte and a working current density of 60–100 mA cm⁻¹. -2 The Faraday efficiency of multi-carbon products is significantly improved compared to the synergistic effect of non-ionic liquids, while the tank pressure is significantly reduced.

[0012] The beneficial effects of this invention are: (1) This invention prepares a copper-based catalyst with high catalyst active sites by introducing the synergistic effect of ionic liquid and ionomer, and the performance is significantly improved.

[0013] (2) The method for modifying catalysts with ionic liquid synergistic ionomer provided by the present invention is simple to operate, easy to scale up and modify, and has broad application prospects.

[0014] (3) High versatility: This technology can be extended to other metal catalysts and ionomer systems. By adjusting the composition of the ionomer and introducing ionic liquids, it can be adapted to different electrolyte systems (alkaline, neutral, acidic) and different target products (C1~C3), providing a universal solution for the industrialization of electrocatalytic CO2 reduction. Attached Figure Description

[0015] Figure 1 This is a scanning electron microscope (SEM) of the ionomer-modified copper-based catalyst in Example 2. Figure 2 This is a scanning electron microscope image of the copper-based catalyst modified by ionic liquid synergistic ionomer in Example 3; Figure 3 This is a selectivity diagram of the electrode products of the copper-based catalyst modified with ionomers in Example 4; Figure 4 This is a product selectivity diagram of the copper-based catalyst modified with ionic liquid synergistic ionomer in Example 4; Figure 5 This is a comparison diagram of hydrogen selectivity of copper-based catalyst electrodes with and without ionic liquid synergistic ionomer modification in Example 4; Figure 6 This is a comparison diagram of the ethylene selectivity of copper-based catalyst electrodes with and without ionic liquid synergistic ionomer modification in Example 4; Figure 7 This is a comparison chart of electrode cell pressures of copper-based catalysts modified with and without ionic liquid synergistic ionomers in Example 4. Detailed Implementation

[0016] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0017] Example 1 A copper-based catalyst was prepared using a wet chemical reduction method, incorporating an appropriate amount of CTAC as a structure-directing agent. First, 1.65 mL of lactic acid was dissolved in 25 mL of deionized water and stirred for 30 min. Then, 0.16 g of CTAC and 0.4 g of CuSO4 were added sequentially to the solution, and stirring continued for 30 min to form a homogeneous light blue solution. Next, under stirring conditions, 6.825 mL of 4 M NaOH was slowly added to the solution, and stirring continued for 2 hours. The mixture was then sonicated for 30 min, followed by the addition of 0.55 g of ascorbic acid, and stirring for 2 h to obtain the target product precipitate. The sample was centrifuged at 8000 r / min for 5 min, washed three times with deionized water and ethanol, and finally dried in a vacuum oven at 60 °C for 12 h to obtain cuprous oxide (Cu₂O).

[0018] Example 2 5 mg of cuprous oxide powder (Cu2O) and 30 μL of perfluorosulfonic acid resin (Nafion D-520) were dispersed in 600 μL of isopropanol and ultrasonically treated in an ultrasonic cleaner for 30 minutes to form a uniform and stable catalyst ink. The ink was then uniformly sprayed onto hydrophobic carbon paper (SGL 28BC) (4 cm) using a spray gun (nozzle diameter 0.5 mm). 2 On the surface, the loading of cuprous oxide was controlled at 1.0 ± 0.2 mg cm⁻¹. 2 The sample was then placed in a vacuum drying oven at 60°C for 2 hours to remove the solvent and enhance the interfacial bonding strength between the catalyst and the substrate. The surface morphology of the sample was characterized using scanning electron microscopy. Figure 1 As shown, the copper-based catalyst is uniformly dispersed on the surface of the carbon paper substrate without obvious agglomeration.

[0019] Example 3 5 mg of cuprous oxide powder (Cu2O) and 30 μL of perfluorosulfonic acid resin (Nafion D-520) were dispersed in 600 μL of isopropanol and ultrasonically treated for 30 minutes in an ultrasonic cleaner. Then, 20 μL of tetraethylammonium hydroxide (TEAOH, 25%) was added, and ultrasonic treatment was carried out for another 30 minutes to form a uniform and stable catalyst ink (suspension). The ink was then uniformly sprayed onto hydrophobic carbon paper (SGL 28BC) (4 cm) using a spray gun (nozzle diameter 0.5 mm). 2 On the surface, the loading of cuprous oxide was controlled at 1.0 ± 0.2 mg / cm³. -2 The sample was then dried in a vacuum drying oven at 60°C for 12 hours to remove the solvent and enhance the interfacial bonding strength between the catalyst and the substrate. The surface morphology of the sample was characterized using scanning electron microscopy. Figure 2As shown, the copper-based catalyst is uniformly dispersed on the surface of the carbon paper substrate without obvious agglomeration. The surface morphology of the copper-based catalyst changes, with dendritic crystals generated, exposing more catalyst active sites, which is beneficial to the electrocatalytic reduction and conversion of CO2.

[0020] Example 4 The performance of the membrane electrode assembly system was evaluated. Under continuous carbon dioxide flow conditions of 0.1 M KHCO3 electrolyte and 30 sccm, different currents were applied to the copper-based catalyst electrode systems with and without ionic liquid-co-polymer modification, and the Faradaic efficiency (FE) of each product at the corresponding current density was measured. Figure 3 and Figure 4 As shown. The Faraday efficiency (FE) of hydrogen, as... Figure 5 As shown. The Faraday efficiency (FE) of ethylene, as... Figure 6 As shown. The results show that the copper-based catalyst electrode modified with ionic liquid synergistic ionomer exhibits performance at 60-100 mA cm⁻¹. -2 At various current densities, multi-carbon product selectivity >70% was achieved, with even higher ethylene selectivity. It also exhibited a certain degree of suppression of competitive hydrogen evolution reactions and lower cell voltage energy consumption. Figure 7 As shown.

[0021] Through performance comparison of the above embodiments, it was found that ionic liquid synergistically modified with ionomers on the surface of copper-based catalyst electrodes constructs a stable ion transport network, thereby improving the performance of neutral carbon dioxide electrocatalytic reduction. Compared with ordinary single ionomer catalyst electrodes, it exhibits better multi-carbon product selectivity and stability at 200 mA cm⁻¹. -2 At the specified current density, the average ethylene selectivity remained above 25% during 30 hours of continuous operation, exhibiting a more hydrophobic surface structure and improved salt-out resistance, demonstrating promising potential for widespread application. This significant performance improvement is primarily attributed to the optimization of the ionomer configuration using ionic liquids, thereby controlling the cation hydration state and surface concentration to achieve K... + Dehydration and enrichment on the Cu surface enhance the key reaction intermediates. * CO adsorption and CC coupling inhibit hydrogen evolution side reactions.

[0022] The above embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A method for electrocatalytic reduction of CO2 by modifying a copper-based catalyst with an ionic liquid and ionomer, characterized in that, The method includes the following steps: (1) Preparation of catalyst material: Wet chemical reduction method was adopted, and an appropriate amount of CTAC was introduced as a structure directing agent. First, lactic acid was dissolved in deionized water and stirred. CTAC and CuSO4 were added to the solution in sequence and stirred continuously to form a uniform light blue solution. Then, under stirring conditions, 4 M NaOH was slowly added to the above solution until the pH value of the suspension reached 12 and stirring was continued. Next, the mixture was ultrasonically treated, and ascorbic acid was added. The mixture was stirred and the target product precipitate was obtained. The target product precipitate was centrifuged, washed, and dried to obtain the product cuprous oxide Cu2O. (2) Preparation of catalyst ink: 5 mg Cu2O, 30 uL perfluorosulfonic acid resin Nafion D-520, 20 uL tetraethylammonium hydroxide TEAOH prepared in step (1) are mixed with 600 uL isopropanol and ultrasonically treated for 30 min to prepare a uniform catalyst ink. (3) Cathode electrode preparation: The catalyst ink obtained in step (2) is sprayed onto the surface of carbon paper (SGL 28BC, 4cm) using a spray gun. 2 After standing and drying, a cathode electrode is obtained, which is used for the electrocatalytic reduction of CO2.

2. The preparation method according to claim 1, characterized in that, In step (1), the centrifugation conditions are 8000 r / min and 5 min.

3. The preparation method according to claim 1, characterized in that, In step (1), the molar ratio of CuSO4 to CTAC is 5:1, and the molar ratio of CuSO4 to ascorbic acid is 5:

6.

4. The preparation method according to claim 1, characterized in that, The mass fraction of the perfluorosulfonic acid resin Nafion D-520 mentioned in step (2) is 5%.

5. The preparation method according to claim 1, characterized in that, The TEAOH aqueous solution in step (2) has a mass fraction of 25%. TEAOH is added after cuprous oxide, perfluorosulfonic acid resin and isopropanol are mixed evenly.

6. The preparation method according to claim 1, characterized in that, In step (3), the spraying needs to be carried out evenly, with a coating load of 1 mg / cm² per spray. 2 The static drying conditions are 60℃ for 12 hours.

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