A method for electrochemical reduction of co2 to produce c2h4

Abstract

The application discloses a method for preparing C2H4 by electrochemical reduction of CO2. The method comprises the following steps: using Cu-Ni alloy nanowires as a gas diffusion electrode, and electrochemically reducing CO2 to obtain C2H4; performing the electrochemical reduction in a flow electrolysis cell; the flow electrolysis cell is provided with a three-electrode system, an Ag / AgCl electrode is used as a reference electrode, an iridium oxide net is used as a counter electrode, and the Cu-Ni alloy nanowires are used as a working electrode. The method can electrochemically reduce CO2 to prepare C2H4 by using Cu-Ni alloy nanowires in-situ grown on carbon paper as a gas diffusion electrode, and the Faraday efficiency for producing C2H4 is obviously higher than that of bare copper nanowires. The Cu-Ni alloy nanowires are in-situ constructed on the carbon paper, and thus excellent stability is achieved.

Description

Technical Field

[0001] The present invention relates to a method for preparing C2H4 by electrochemical reduction of CO2, belonging to the technical field of electrocatalysis. Background Art

[0002] Converting CO₂ into valuable industrial products through electrocatalytic processes is a crucial approach for sustainable development. In particular, reducing CO₂ to fuels and industrial feedstocks not only alleviates energy challenges but also closes the carbon cycle and provides a viable solution for carbon neutrality. Therefore, the design and fabrication of high-performance electrocatalysts for specific high-value-added products is crucial. In recent years, researchers have made significant progress in developing electrocatalysts, ultimately achieving high conversion efficiencies for carbon monoxide (CO), formic acid (HCOOH), methane (CH₄), and other C₁ products. Despite this, converting CO₂ to multi-carbon products (C₂), such as ethylene (C₂H₄) and ethanol (C₂H₅OH), remains a daunting challenge. C₂H₄, renowned for its high energy density, is a key compound that holds a strategic position in industrial gases. Metal catalysts, including Au, Ag, Sn, Ni, and Pb, exhibit a propensity for generating C₁ products. Uniquely, copper-based catalysts have demonstrated the ability to convert CO₂ to C₂H₄ via a C₂-C coupling process. However, efficient C₂H₄ conversion is hampered by high kinetic barriers to the C₂-C coupling process and the stable adsorption of key intermediates on the Cu catalyst surface. There are many strategies, such as crystal surface regulation, single atoms, defect engineering, etc., to regulate the physical or chemical properties of catalysts to improve the adsorption and desorption processes. Researchers have designed a series of alloy catalysts such as Au-Cu and Ag-Cu, which enhance CC coupling through the CO spillover effect, thereby greatly improving the selectivity and efficiency of Cu metal in C2H4 production. Nevertheless, in order to reduce application costs, it is necessary to free ourselves from dependence on precious metals. Researchers have advanced the development of alloy materials such as Cu-Zn, Cu-Sn and Cu-Pd, but the catalytic results have not met high expectations. The present invention is specially proposed. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for preparing C2H4 by electrochemical reduction of CO2, which uses in-situ grown Cu-Ni alloy nanowires as gas diffusion electrodes and has excellent C2H4 selectivity and stability.

[0004] The present invention adopts a Cu-Ni alloy nanowire and a non-noble metal collaborative method to perform in-situ construction on a gas diffusion layer (GDL). Specifically, the construction method is as follows:

[0005] S1, immersing carbon paper in a mixed solution of CuSO4, NiCl2, and NiSO4 for electrodeposition to obtain a Cu-Ni film;

[0006] S2, reacting the Cu-Ni film under alkaline conditions to obtain Cu-Ni hydroxide nanowires;

[0007] S3, annealing the Cu-Ni hydroxide nanowires to obtain Cu-Ni oxide nanowires;

[0008] S4. The Cu-Ni oxide nanowires are electrochemically reduced to obtain in-situ grown Cu-Ni alloy nanowires.

[0009] In step S1, the mixed solution is prepared from 0.1 M citric acid buffer.

[0010] In step S1, in the mixed solution, the concentration of CuSO4 is 0.05M-0.15M, the concentration of NiCl2 is 0.03M-0.08M, and the concentration of NiSO4 is 0.03M-0.08M.

[0011] In step S1, the electrodeposition time is 1500-2000 s, and the obtained film is completely dried under a nitrogen atmosphere.

[0012] In step S2, the alkaline condition is an aqueous solution of NaOH and (NH4)2S2O8, the concentration of NaOH is 45-50 g / L, and the concentration of (NH4)2S2O8 is 20-25 g / L.

[0013] In step S2, the reaction temperature is 2-8°C and the reaction time is 0.3-0.6h.

[0014] In step S3, the annealing temperature is 150-200° C., the time is 0.5-2 h, and the annealing is performed in a muffle furnace.

[0015] In step S4 , the electrochemical reduction is performed in a flowing electrolytic cell using a 0.50 M sodium sulfate solution as an electrolyte, and a potential of −1.0 V (vs Ag / AgCl sat. KCl) is applied for the electrochemical reduction.

[0016] The method for preparing C2H4 by electrochemically reducing CO2 using the Cu-Ni oxide nanowires comprises the following steps:

[0017] The Cu-Ni alloy nanowires serve as gas diffusion electrodes to electrochemically reduce CO2 to obtain C2H4.

[0018] Preferably, the electrochemical reduction is performed in a flow electrolysis cell.

[0019] Preferably, a three-electrode system is provided in the flow electrolysis cell, wherein the Ag / AgCl electrode serves as a reference electrode, the iridium oxide mesh serves as a counter electrode, and the Cu-Ni alloy nanowire serves as a working electrode.

[0020] The method of the present invention uses in-situ grown Cu-Ni alloy nanowires as gas diffusion electrodes, which can electrochemically reduce C2H4 and CO. The Faradaic efficiency (FE) of producing C2H4 reaches 46.98%, and the current density reaches 231.81 mA / cm 2 , significantly exceeding bare copper nanowires (Cu NWs, 25.33%). The Cu-Ni alloy nanowires used in this invention, thanks to their in-situ construction on the gas diffusion electrode, exhibit excellent stability and can operate for over 8 hours at high currents. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is an electron microscope photograph of the Cu-Ni thin film prepared in Example 1 of the present invention.

[0022] Figure 2 1 is an electron microscope photograph of the cross-sectional thickness of the Cu-Ni film prepared in Example 1 of the present invention.

[0023] Figure 3 It is an enlarged cross-sectional view of the Cu-Ni film prepared in Example 1 of the present invention.

[0024] Figure 4 The Cu prepared in Example 1 of the present invention x Ni y Electron microscope image of (OH)2 nanowires.

[0025] Figure 5 The Cu prepared in Example 1 of the present invention x Ni y Enlarged image of (OH)2 nanowires.

[0026] Figure 6 The Cu prepared in Example 1 of the present invention x Ni y Electron microscope image of O nanowires.

[0027] Figure 7 3 is an electron microscope photograph of the Cu-Ni nanowires prepared in Example 1 of the present invention.

[0028] Figure 8 is a TEM image of the Cu-Ni nanowires prepared in Example 1 of the present invention.

[0029] Figure 9 is a HR-TEM image of the Cu-Ni nanowires prepared in Example 1 of the present invention.

[0030] Figure 10 This is a scanning electron microscope and EDS image of the cross section of the Cu-Ni nanowire prepared in Example 1 of the present invention.

[0031] Figure 11 is the XRD pattern of the Cu-Ni NWs prepared in Example 1 of the present invention.

[0032] Figure 12 is the XRD pattern of Cu (111) peak.

[0033] Figure 13 is the LSV diagram of Cu-Ni NWs prepared in Example 1 of the present invention.

[0034] Figure 14 is the Faradaic efficiency of Cu-Ni NWs.

[0035] Figure 15 is the Faradaic efficiency of Cu NWs.

[0036] Figure 16 is the current density of the Cu-Ni NWs and Cu NWs prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0037] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0038] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0039] In the following examples, all reagents were used as received without further purification. Copper sulfate (CuSO4, 99.99%), nickel sulfate (NiSO4, 99.99%), nickel chloride (NiCl2, 99.99%), potassium bicarbonate (KHCO3, 99.7%), and boric acid (H3BO3, 99.8%) were provided by Sinopharm Chemical Reagent Co., Ltd. Sodium sulfate (NaSO, 99%), sodium hydroxide (NaOH, 99%), citric acid (CHO, 99%), ammonium persulfate (NH₄)S₂O₂, 98%), hydrochloric acid (HCl, AR), and anhydrous ethanol (CHO₂H₅OH) were obtained from Aladdin reagent. Carbon dioxide (CO₂, 99.999%), nitrogen (N₂, 99.999%), and argon (Ar, 99.999%) were used as received. Gas diffusion layers (GDLs, hydrophobic carbon paper, Sigracet 22 BB) and anion exchange membranes (3PK-130) were purchased from Gauss Associates. Ultrapure water with a resistivity of 18.45 MΩ cm was homemade in the laboratory.

[0040] In the following examples, the electrochemical test method is as follows:

[0041] Electrochemical tests were conducted at ambient temperature in a flow electrolysis cell. The flow electrolysis cell is a three-electrode cell with three compartments. A 3PK-130 anion exchange membrane separated the anode and cathode. An Ag / AgCl electrode (KCl saturated, salt bridge) served as the reference electrode. 1 M KOH was used as the electrolyte. An iridium oxide mesh (3 × 1 cm) served as the counter electrode. The working electrode was fixed with a spacer to a size of 2 × 0.5 cm. CO2 flowed into the gas chamber at a rate of 30 sccm and diffused through the gas diffusion layer into the cathode, where electroreduction occurred at the gas-liquid-solid three-phase interface. The effluent gaseous products were sampled at regular intervals (15 min) and quantitatively analyzed using GC. A peristaltic pump facilitated the circulation of the catholyte (10 mL / min) and anolyte (40 mL / min). Electrochemical reaction data were collected using a CHI760E electrochemical workstation, and the Faradaic efficiencies of the liquid and gaseous products were calculated based on the collected charge information (see the Supporting Information for test details). All electrochemical measurements were performed using solution resistance to compensate for IR drops and converting all potentials to RHE values. Linear sweep voltammetry was performed at a scan rate of 20 mV / s.

[0042] Example 1. Preparation of Cu-Ni NWs

[0043] A hydrophobic carbon paper (1 x 3 cm) was cleaned with anhydrous ethanol and then a 0.5 M HCl solution. The clean carbon paper was rinsed with ultrapure water and the support layer of the carbon paper was protected with cover tape. The carbon paper was then immersed in a mixture of 0.1 M CuSO₄, 0.07 M NiCl₂, and 0.03 M NiSO₄ (buffered in 0.1 M citric acid) and electrodeposited for 1500 s. The resulting Cu-Ni film-coated carbon paper was thoroughly dried under a nitrogen atmosphere.

[0044] Carbon paper covered with a Cu-Ni film was placed in a 100 mL aqueous solution containing 4.8 g of NaOH and 2.282 g of (NH₄)₂S₂O₄. The mixture was then allowed to react at 5°C for 30 minutes. After thorough washing and drying, a blue hydroxide was obtained. Subsequently, the sample was annealed in a muffle furnace at 200°C for 2 hours to form a black oxide. Electrochemical reduction was performed in a flowing electrolytic cell using a 0.50 M sodium sulfate solution as the electrolyte and a potential of -1.0 V (vs. Ag / AgCl sat. KCl) to produce an in situ grown Cu-Ni alloy nanowire gas diffusion electrode.

[0045] Example 2. Characterization of Cu-Ni NWs

[0046] GDEs fabricated using catalyst ink coatings struggle to capitalize on their inherent advantages, suffering from impeded CO2 mass transfer, slow electron transport, and insufficient exposure of catalytic active sites, leading to suboptimal CO2RR results. In contrast, nanoarray electrodes fabricated in situ on GDLs can promote rapid CO2 and charge transport, significantly enhancing reaction kinetics.

[0047] In Example 1 of the present invention, a Cu-Ni alloy film is constructed on the GDL by electrodeposition as a precursor of the nanowire structure ( Figure 1 The cross-sectional view shows that the deposited alloy film is distributed on the outer surface of the GDL with a thickness of approximately 6.95 μm ( Figure 2 and Figure 3 ). The continuous and uniform films ensure their electrical connection with the carbon paper substrate. Under alkaline conditions, the Cu-Ni alloy film is converted into Cu x Ni y (OH)2 nanowires ( Figure 4 and Figure 5 ). By annealing Cu in a muffle furnace x Ni y (OH)2 to obtain Cu x Ni y O nanowires ( Figure 6 Subsequently, CuO was in situ electrochemically reduced to Cu-Ni alloy nanowires (Cu-Ni NWs) in a flow electrochemical cell ( Figure 7 ).

[0048] The one-dimensional linear structure of Cu-Ni NW was confirmed by transmission electron microscopy, and its width was about 65 nm ( Figure 8 In addition, HR-TEM showed that Cu NW is composed of nanocrystals with different crystal orientations, and the abundant grain boundaries within the structure indicate that the surface is full of defects, and the rich microporous structure promotes the mass transfer process of CO2 ( Figure 9 ). Cross-sectional SEM image ( Figure 10 ) shows that after nanoscale processing, the Cu-Ni NWs are uniformly distributed on the GDL surface without noticeable gaps or cracks, demonstrating good adhesion to the GDL substrate. EDS images also support this result. Compared to nanowire / GDL electrodes prepared by catalyst ink coating, the abundant open spaces between the nanowires in situ constructed on the GDL facilitate the diffusion and adsorption of reactants onto the catalyst surface and promote rapid charge transfer, significantly enhancing the CO2RR reaction kinetics.

[0049] The crystal composition of Cu-Ni NWs samples was determined by X-ray diffraction (XRD) patterns ( Figure 11). Cu-Ni NWs exhibit diffraction peaks similar to those of standard copper (ICDD No. 98-000-0172), corresponding to the (111), (200), and (220) planes of copper. Compared to pristine Cu NWs, the peaks corresponding to air-oxidized CuO and Cu2O in Cu NWs disappear due to Ni doping. The more chemically active nickel prevents oxidation of Cu NWs, a phenomenon consistent with the behavior observed in Cu-Ni corrosion-resistant alloys.

[0050] In addition, due to the low loading of Ni and relatively weak crystallinity, no diffraction data of nickel phase were shown. Figure 12 In the scattering of Cu-Ni NWs, the Cu(111) peak shifted slightly to a higher diffraction angle and was located between the standard peaks of Cu(111) and Ni(111). This was attributed to the incorporation of Ni atoms into the Cu crystal phase, which resulted in lattice strain and confirmed the formation of an alloy.

[0051] Example 3: Cu-Ni NWs electrocatalysis of CO2

[0052] The Cu-Ni NWs were loaded onto a flow cell and 1 M KOH was used as the electrolyte for the electroreduction of CO2.

[0053] Before testing, all samples underwent an activation process consisting of 20 cyclic voltammetry (CVs) from 0 to -1 V (vs. RHE). Cu NWs in situ loaded onto GDLs under the same conditions served as a control for consistent experimental evaluation. Initially, each catalyst was subjected to linear sweep voltammetry, performed in an Ar and CO2 atmosphere to ensure a comprehensive analysis.

[0054] like Figure 13 As shown in the Figure 3, it is observed that the reaction initiation time of Cu-Ni NWs is earlier than that of Cu NWs, and the current density is significantly greater than that of Cu NWs, which indicates that the Cu-Ni NWs of the present invention have faster adsorption and electrochemical reaction of CO2 and promote the accelerated kinetics of CC coupling.

[0055] The CO2RR performance was evaluated by applying electrode potentials ranging from -0.7 V to 1.2 V (vs. RHE). The gas phase products were analyzed by online gas chromatography (GC). The distribution of the main product FE for different catalysts is shown in Figure 2. Figure 14 and Figure 15 Cu-Ni NW achieved the highest C2H4 selectivity (46.98%) at -1 V, and the current density reached 231.81 mA / cm 2 ( Figure 16Cu NWs achieved a carbon product Faradaic efficiency of 56.11% at an applied potential of -1.0 V. However, Cu NWs exhibited poor selectivity, with relatively uniform distribution of CO (25.62%), CH4 (14.88%), and C2H4 (16.99%), with no obvious dominant product and poor selectivity.

[0056] Compared with bare Cu NWs, Cu-Ni NWs exhibit significantly enhanced C2H4 selectivity, demonstrating the catalytic advantage of alloy nanowires.

[0057] In contrast, the Cu-Ni interface material in thin film form produced only ~18% formate product.

[0058] The Cu-Ni NW three-dimensional nanoarray structure adopted in the present invention provides abundant active sites, greatly enhances the mass transfer process, and promotes CC coupling kinetics, which is attributed to the synergistic interaction between Cu and Ni atoms, creating a favorable environment for accelerating chemical transformations.

Claims

1. A method for preparing C2H4 by electrochemical reduction of CO2, comprising the following steps: Cu-Ni alloy nanowires serve as gas diffusion electrodes for electrochemical reduction of CO2 to C2H4; performing said electrochemical reduction in a flow electrolytic cell; The flow electrolytic cell is provided with a three-electrode system, wherein the Ag / AgCl electrode serves as a reference electrode, the iridium oxide mesh serves as a counter electrode, and the Cu-Ni alloy nanowire serves as a working electrode; The Cu-Ni alloy nanowires are prepared according to a method comprising the following steps: S1, immersing carbon paper in a mixed solution of CuSO4, NiCl2, and NiSO4 for electrodeposition to obtain a Cu-Ni film; S2, reacting the Cu-Ni film under alkaline conditions to obtain Cu-Ni hydroxide nanowires; S3, annealing the Cu-Ni hydroxide nanowires to obtain Cu-Ni oxide nanowires; S4. The Cu-Ni oxide nanowires are electrochemically reduced to obtain in-situ grown Cu-Ni alloy nanowires.

2. The method according to claim 1, wherein: In step S1, the mixed solution is prepared by citric acid buffer; In step S1, in the mixed solution, the concentration of CuSO4 is 0.05M-0.15M, the concentration of NiCl2 is 0.03M-0.08M, and the concentration of NiSO4 is 0.03M-0.08M.

3. The method according to claim 1 or 2, characterized in that: In step S1, the electrodeposition time is 1500-2000s.

4. The method according to claim 1 or 2, characterized in that: In step S2, the alkaline condition is an aqueous solution of NaOH and (NH4)2S2O8, the concentration of NaOH is 45-50 g / L, and the concentration of (NH4)2S2O8 is 20-25 g / L.

5. The method according to claim 1 or 2, characterized in that: In step S2, the reaction temperature is 2-8°C and the reaction time is 0.3-0.6h.

6. The method according to claim 1 or 2, characterized in that: In step S3, the annealing temperature is 150-200° C. and the time is 0.5-2 h.

7. The method according to claim 1 or 2, characterized in that: In step S4, the electrochemical reduction is performed in a flowing electrolytic cell using a sodium sulfate solution as an electrolyte.

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