Preparation method of copper-nickel alloy electrode and method for preparing wide-proportion synthesis gas by driving CO2 electrocatalytic reduction through copper-nickel alloy electrode

Abstract

The invention discloses a preparation method of a copper-nickel alloy electrode and a method for preparing wide-proportion synthesis gas by driving CO2 electrocatalytic reduction through the copper-nickel alloy electrode. Belongs to the field of CO2 electrocatalytic reduction. According to the invention, the molar ratio of copper ions to nickel ions in the precursor is controlled to regulate and control the ratio of copper to nickel elements in the alloy, so that the regulation and control of catalytic active sites and CO2 catalytic performance of the alloy are realized. After copper and nickel form an alloy, as the electronegativity of nickel is stronger than that of copper, electron transfer from copper to nickel exists at an alloy interface. The electron rearrangement effect causes downward movement of the d-band center of copper, so that the adsorption strength of the copper on a key reaction intermediate is regulated and controlled. According to the invention, the adsorption energy of the COOH intermediate is moderately weakened, and the energy barrier for activating and converting CO2 into CO is reduced (embodied as reduction of the initial potential); meanwhile, the adsorption energy of the CO intermediate is also optimized, so that the CO intermediate can be stably generated and is easy to desorb, further hydrogenation reduction of * CO is effectively inhibited, and the selectivity of a CO product is remarkably improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of CO2 electrocatalytic reduction, and particularly relates to a preparation method of a copper-nickel alloy electrode and a method for driving CO2 electrocatalytic reduction to prepare a wide-ratio synthetic gas. BACKGROUND

[0002] At present, the continuous increase of CO2 emission promotes the in-depth research on the resource utilization of CO2. The electrocatalytic reduction (ECO2RR) technology can convert CO2 into high-value-added chemicals and fuels. Among them, the synthetic gas (H2 / CO) as a kind of key chemical raw material is widely used in the preparation of methanol, synthetic ammonia and many other bulk chemicals. Compared with the traditional preparation process relying on fossil raw materials, the electrocatalytic route has potential advantages such as clean process and mild operating conditions, and has important significance for the development of low-cost and efficient synthetic gas preparation technology.

[0003] Under the background of the "double carbon" target, the preparation of synthetic gas by ECO2RR has become a research hotspot and an important path. However, the reaction process involves multi-electron transfer, and the product is complex and the selectivity of the target product is low, therefore, the development of high-performance catalytic electrode materials is a core challenge.

[0004] At present, the technology for preparing synthetic gas (H2 / CO) by electrocatalysis of CO2 faces the core challenge that the selectivity of the target product is difficult to effectively control and improve. This "selectivity limitation" problem specifically manifests as follows: first, the CO2 reduction process itself has multiple parallel reaction paths, and the final product is complex, in addition to the target carbon monoxide (CO), it often generates formic acid, methanol, methane and even ethylene, ethanol and other hydrocarbons, which seriously disperses the selectivity of the reaction to synthetic gas; second, even if synthetic gas is generated, the key H2 / CO ratio is extremely difficult to accurately control, because the hydrogen evolution reaction (HER) in the water electrolysis inevitably produces a large amount of hydrogen byproduct, and the adsorption strength of the catalytic material surface to the key intermediate (such as *CO) directly affects the generation efficiency and subsequent conversion of CO, making it extremely difficult to achieve a wide range of predictable synthetic gas ratio output. The purpose of the present application is to provide a bimetallic catalytic electrode material, which can efficiently and stably reduce CO2 to synthetic gas by precisely controlling the types, proportions and microstructures of the two metal components and utilizing the electronic effect and synergistic catalytic effect between them. The key innovation is that by reasonable design of the copper-nickel bimetallic catalyst, the H2 / CO ratio can be adjusted in a wide range, thereby meeting the specific needs of different downstream chemical processes for raw gas. This adjustability significantly improves the energy utilization efficiency and process economy of CO2, providing a novel and efficient solution for the electrocatalytic preparation of synthetic gas.

[0005] The method of the present application prepares a copper-nickel alloy catalyst by a hydrogen reduction method, utilizes alloy structure and crystal face to regulate the reduction performance of the catalyst, studies the reduction product by applying electrolytic voltage to the above-mentioned catalyst, and improves the Faraday efficiency and selectivity of the CO gas phase product. In an electrolyte solution, the prepared copper-nickel alloy catalyst is smeared on a carbon cloth as a working electrode, CO2 is subjected to electrocatalytic reduction to obtain CO and H2 products, and a specific application case is provided for preparing synthesis gas (H2 / CO) by electrocatalytic reduction of CO2.

[0006] In order to achieve the above technical problems, the present application adopts the following technical solutions: I. The present application aims to provide preparation of a bimetallic copper-nickel alloy In the copper-nickel alloy catalyst prepared by the present application, the molar ratio of copper element to nickel element is 1:1, 1:2 or 2:1.

[0007] 1. Configuration of copper-nickel precursor 0.15~0.52 g Ni(NO3)2·6H2O and 0.11~0.52 g Cu(NO3)2·3H2O are dissolved in 20~70 ml H2O at room temperature to form a uniform A solution, and 0.20~0.82 g citric acid (excess) is dissolved in 10~50 mL H2O at room temperature to form a uniform B solution. After mixing A and B solutions and ultrasonic treatment for 10~50 min, they are placed in a vacuum drying box at 50~200 ℃ and vacuum dried at-0.05 MPa~-0.15 MPa for 8~20 h to obtain Cu / Ni alloy precursor powders with different proportions.

[0008] Reduction of copper-nickel catalyst The Cu / Ni precursor powders prepared in different proportions are placed in a muffle furnace and heated at 300~500 ℃ for 1~7 h; then, under the protection of H2 atmosphere, the reduction treatment is carried out at a temperature of 200~700 ℃ for 1~5 h to obtain black powder, which is the copper-nickel alloy catalyst II. Preparation of copper-nickel alloy electrode 2~8 mg of catalyst powder is placed in 200~500 μL of isopropanol and 10~50 μL of 5 wt% Nafion solution to prepare a catalyst solution. Then, the catalyst solution is ultrasonically treated in an ultrasonic cleaner for 10~50 min, and the catalyst solution is uniformly coated on the treated carbon cloth with a pipette. The prepared electrode is dried at 10~80 ℃ for 2~8 h for standby use.

[0009] III. Test of electrocatalytic reduction of CO2 by copper-nickel alloy catalyst The prepared copper-nickel alloy electrode is used as a working electrode, an Ag / AgCl electrode is used as a reference electrode, a double-chamber electrolysis cell system is assembled, and CO2 catalytic reduction tests are carried out in the system. The specific implementation steps are as follows: 1. Preparation of electrolyte The cathode solution is a 0.5 M KHCO3 solution of 30 mL. The anode solution is a 0.1 M dilute sulfuric acid solution of 30 mL.

[0010] 2. Electro-catalytic reduction of CO2 electrolysis test The CO2 electrolysis reaction is carried out in an H-type double-chamber electrolysis cell, and the cathode and anode of the electrolysis cell are separated by a Nafion 117 proton exchange membrane, which only allows protons to pass through, providing protons for the reaction in the cathode area. The dried alloy catalyst electrode is directly used as the working electrode, the Pt electrode is the auxiliary electrode, and the reference electrode is the Ag / AgCl electrode. Before electrolysis, the cathode is first purged with a certain amount of N2 to remove air, and then CO2 is continuously introduced for 30 min to saturate the electrolyte. During the electrolysis process, the gas inlet is stopped to prevent disturbance caused by gas bubbles in the cathode chamber. After constant potential electrolysis for 60 min, the gas phase product is collected for detection.

[0011] The copper-nickel alloy catalyst with different proportions prepared by the application is further used for electro-catalytic reduction of CO2 to prepare synthesis gas (H2 / CO). The copper-nickel alloy material is used in the ECO2RR reduction system to evaluate the reduction current density and the Faraday efficiency and selectivity of the reduction product synthesis gas (H2 / CO).

[0012] Compared with the prior art, the application has the following beneficial effects: The proportion of the bimetallic copper-nickel alloy catalyst provided by the application is easy to control. Specifically, the proportion of copper ions and nickel ions in the precursor can be controlled to adjust the proportion of copper and nickel elements in the alloy, thereby realizing the control of the catalytic active sites and the CO2 catalytic performance. After copper and nickel form an alloy, due to the stronger electronegativity of nickel than copper, there is an electron transfer from copper to nickel at the alloy interface. This electron rearrangement effect causes the d-band center of copper to move down, thereby adjusting the adsorption strength of the key reaction intermediate. Specifically, the adsorption energy of the COOH intermediate is moderately weakened, and the energy barrier for the activation of CO2 to CO is reduced (reflected as a decrease in the initial potential); at the same time, the adsorption energy of the CO intermediate is also optimized, making it stable and easy to desorb, effectively inhibiting the further hydrogenation reduction of CO, thereby significantly improving the selectivity of the CO product (the Faraday efficiency can reach more than 78%).

[0013] The scheme process of the bimetallic copper-nickel alloy provided by the application is simple and efficient, the water is used as a safe and environmentally friendly solvent, the high-activity copper-nickel alloy catalyst is accurately prepared through citric acid complexing and segmented heat treatment, and the application prospect is excellent.

[0014] The application obtains a catalyst (Cu1Ni1) with high selectivity and stability by regulating the proportion of copper and nickel elements, and the initial potential of the catalyst for electrocatalytic reduction of CO2 is only-0.08( vs. RHE), the Faraday efficiency of CO can reach 78.13% at most when electrolysis is performed at-0.08( vs. RHE) for 1 h, and the catalyst can maintain a high current density (0.168 mA / cm 2 ) under the condition that the Faraday efficiency is greater than 50% at a voltage of-0.38( vs. RHE).

[0015] The proportion of the synthesis gas (H2 / CO) prepared in the copper-nickel alloy material ECO2RR reduction system is about 0.25-47.52, the range is wide, and the controllability is high.

[0016] For a further understanding of the features and technical contents of the application, reference can be made to the detailed description and the accompanying drawings. It should be noted that the accompanying drawings are provided for illustrative purposes only, and are not used to limit the application. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is an X-ray powder diffraction pattern of three copper-nickel alloy catalysts prepared; Figure 2 is an SEM spectrum of the Cu1Ni1 catalyst prepared; Figure 3 is a cyclic voltammetry curve of a copper-nickel alloy electrode saturated with N2 or CO2; Figure 4 is a linear sweep voltammetry (LSV) scan curve of a copper-nickel alloy electrode saturated with N2 or CO2; Figure 5 is an electrochemical impedance spectroscopy (EIS) test curve of a copper-nickel alloy electrode saturated with N2 or CO2; Figure 6 is an i-t curve of the electrocatalytic reduction of CO2 reaction when the Cu1Ni1 alloy is used as a working electrode in an H-type double-chamber electrochemical electrolysis cell; Figure 7 is a product Faraday efficiency and current density diagram of the Cu1Ni1 catalyst under different potentials; Figure 8 is a comparison diagram of the synthesis gas range of the three copper-nickel alloy catalysts prepared. DETAILED DESCRIPTION

[0018] The application will be described in detail below with reference to specific examples. These examples are helpful for those skilled in the art to further understand the application, but should not be regarded as limiting the application. It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the application. These all belong to the protection scope of the application.

[0019] Example 1 (1) Preparation of Cu / Ni alloy precursor powder: 0.291 g of Ni(NO3)2·6H2O and 0.242 g of Cu(NO3)2·3H2O were dissolved in 40 ml of H2O at room temperature to form a uniform A solution, and 0.576 g of citric acid (excess) was dissolved in 20 mL of H2O at room temperature to form a uniform B solution. After mixing the A and B solutions and ultrasonicating for 20 min, the mixture was placed in a vacuum drying oven at 120 ℃ and vacuum dried at -0.09 MPa for 12 h to obtain a Cu / Ni alloy precursor powder.

[0020] (2) Reduction of copper-nickel catalyst: The Cu / Ni precursor powder was placed in a muffle furnace and heated at 400 ℃ for 4 h; then, under the protection of H2 atmosphere, the powder was reduced at a temperature of 500 ℃ for 2 h to obtain a black powder, which was a copper-nickel alloy catalyst.

[0021] The copper-nickel alloy electrode was used for electrocatalytic reduction of CO2, and the specific implementation steps were as follows:

[0022] Preparation of electrolyte: I. Cathode electrolyte: 1.5 g of KHCO3 was dissolved in 30 ml of H2O to obtain an electrolyte, which was the cathode solution. The concentration of KHCO3 in the solution was 0.5 M.

[0023] II. Anode electrolyte: 28.641 mL of deionized water and 1.359 mL of concentrated sulfuric acid were stirred and mixed to obtain a 0.1 M dilute sulfuric acid solution, which was the anode solution, with a volume of 30 mL. 2. Copper-nickel alloy catalyst was loaded on carbon cloth to prepare an electrode: I. Preparation of catalyst slurry: 5-6 mg of catalyst powder was placed in 350 μL of isopropyl alcohol and 30 μL of 5 wt% Nafion solution and ultrasonicated in an ultrasonic cleaner for 30 min. The dispersed slurry could be used for loading of the electrode.

[0024] II. Loading and drying of the catalyst 10 μL of catalyst solution was taken with a pipette and evenly coated on the treated carbon cloth (geometric area = 1 cm 2 ​(1cm×1cm) of catalyst carrier) for 10 times. The carbon cloth coated with catalyst was dried at 60 o C to obtain the copper-nickel alloy catalyst electrode.

[0025] The carbon cloth was treated by two-step acid treatment method: first, immerse in H2SO4 / HNO3 (volume ratio 1:3) mixed acid at room temperature for 10 h, then dry after washing with water, and then reflux in concentrated HNO3 at 100℃ for 2 h, dry after washing with water.

[0026] 3. Electro-catalytic reduction of CO2 by copper-nickel alloy catalyst The CO2 electrolysis reaction was carried out in a H-type double-chamber electrolysis cell, and the cathode and anode of the electrolysis cell were separated by Nafion117 proton exchange membrane, which only allowed protons to pass through, providing protons for the reaction in the cathode area. The dried alloy catalyst electrode was directly used as the working electrode, the Pt electrode was the auxiliary electrode, and the reference electrode was the Ag / AgCl electrode. Before electrolysis, N2 was introduced into the cathode to exhaust the air, and then CO2 was continuously introduced for 30 min to saturate the electrolyte. During the electrolysis process, the gas was stopped to prevent the disturbance caused by the gas bubbles in the cathode chamber. After constant potential electrolysis for 60 min, the liquid and gas products were collected for detection. The gas products after the reaction were CO and H2, and there was no liquid product. The Faraday efficiency of the gas product CO was 2.14%~78.13%, and the ratio of synthesis gas (H2 / CO) was the largest at 47.52 and the smallest at 0.25.

[0027] According to the molar ratio of copper element to nickel element of 1:1, 1:2 and 2:1, three kinds of alloy powders Cu1Ni1, Cu1Ni2 and Cu2Ni1 were obtained by the method of Example 1.

[0028] The three kinds of alloy powders Cu1Ni1, Cu1Ni2 and Cu2Ni1 were detected by X-ray powder diffraction, and the detection results are shown in Figure 1 Cu1Ni1, Cu1Ni2 and Cu2Ni1 samples all formed alloy solid solution. Among them, the diffraction peak intensity of Cu1Ni1 was obviously higher, indicating that its crystallinity was better or the phase purity was higher. At the same time, due to the change of alloy composition causing the change of lattice constant, the diffraction peak positions of Cu1Ni2 and Cu2Ni1 all shifted clearly relative to Cu1Ni1, which directly confirmed the successful synthesis of alloys with different Cu / Ni ratios.

[0029] Figure 2 is the SEM morphology of the freshly prepared Cu1Ni1 powder alloy catalyst, and the catalyst before the reaction presents a typical irregular porous structure with uniform pore distribution and good connectivity. This high porosity feature effectively increases the contact area between the electrolyte and the catalyst surface, providing abundant active site contact channels for the reactant molecules.

[0030] The cyclic voltammograms of the three copper-nickel alloys with different proportions are shown in FIG. 3, where FIG. 3A shows the cyclic voltammogram of Cu1Ni1, FIG. 3B shows the cyclic voltammogram of Cu1Ni2, and FIG. 3C shows the cyclic voltammogram of Cu2Ni1. As can be seen from FIG. 3, the copper-nickel alloys with different proportions have good electrochemical activity, and by comparing the current density in N2 and CO2 atmosphere, it can be found that the current density of the three alloy catalysts in CO2 atmosphere is higher than that in N2 atmosphere, which shows that the three synthesized alloys can effectively promote CO2 reduction. It can also be found that the current density of Cu1Ni1 is the largest, which shows that it is better in catalyst activity, electrode structure optimization and electrolyte synergistic effect. This advantage not only improves the electrochemical reaction rate and stability, but also shows the application potential in ECO2RR.

[0031] Linear sweep voltammetry (LSV) tests were performed on the three copper-nickel alloys as working electrodes, as shown in FIG. 4, Figure 4A which shows the cyclic voltammogram of Cu1Ni1, Figure 4B which shows the cyclic voltammogram of Cu1Ni2, Figure 4C which shows the cyclic voltammogram of Cu2Ni1. As can be seen from FIG. 4, LSV scanning tests were performed in CO2-saturated Na2SO4 solution with a voltage range of -0.58~1.1 V(RHE). vs. By comparing the LSV curves in different atmospheres, it can be found that the current density of these catalyst materials in CO2-saturated electrolyte is higher than that in N2-saturated electrolyte, which shows that these three materials have better catalytic performance.

[0032] EIS tests were performed on the three copper-nickel alloys as working electrodes, as shown in FIG. 4, where FIG. 5A shows the EIS curve of Cu1Ni1, FIG. 5B shows the EIS curve of Cu1Ni2, FIG. 5C shows the EIS curve of Cu2Ni1, and FIG. 5D shows the EIS curves of the three catalysts prepared in Example 1 in CO2 atmosphere. The EIS test shows that the CO2 atmosphere significantly reduces the charge transfer resistance of the catalyst, which confirms its strong promotion effect on ECO2RR. Among them, the Cu1Ni1 catalyst shows the smallest charge transfer resistance, has the optimal interface transmission performance and reaction kinetics, and is the key reason for its high catalytic activity.

[0033] In the H-type double-chamber electrolytic cell, Cu1Ni1 alloy electrode was used as the working electrode, a series of constant voltages were applied to the system, and potentiostatic electrolysis was performed to obtain I-t curves. As Figure 6As shown, the Cu1Ni1 catalyst showed good stability in a certain voltage range, and the current density did not fluctuate significantly over time after 1 h constant potential electrolysis.

[0034] As shown, the figure shows the faradic efficiency of CO2 and H2 and the current density of the Cu1Ni1 alloy electrode as the working electrode at different potentials. Figure 7

[0035] Figure 8 The above is a comparison chart of the ratio of synthesis gas at different potentials when the three copper-nickel alloys prepared in Example 1 are used as working electrodes. It can be seen that Cu1Ni1 has the widest ratio of synthesis gas.

[0036] The specific embodiments of the present application are described in detail above. It should be noted that the present application is not limited to the above specific embodiments. Those skilled in the art can make various modifications or changes without departing from the scope of the protection defined by the claims, and these modifications or changes all belong to the technical scheme of the present application.​

Claims

1. A method of producing a copper-nickel alloy electrode, characterized by, The method comprises the following steps: Step 1, dissolving Ni(NO3)2·6H2O and Cu(NO3)2·3H2O in H2O to form a uniform A solution, dissolving citric acid in H2O to form a uniform B solution; mixing A and B solutions and then ultrasonic treatment, drying to obtain Cu / Ni alloy precursor powder; Step 2, then 300 ℃~500 ℃ for 1h~7 h; then, reducing treatment at 200 ℃~700 ℃ under H2 atmosphere for 1~5 h to obtain a catalyst; Step 3, placing the catalyst in isopropanol and Nafion solution, ultrasonic treatment for 10min~50min, uniformly coating on the acid-treated carbon cloth, drying to obtain the copper-nickel alloy electrode; The molar ratio of copper element to nickel element is 1:2-2:

1.

2. The method of claim 1, wherein, 0.15g~0.52 g Ni(NO3)2·6H2O and 0.11g~0.52 g Cu(NO3)2·3H2O are dissolved in 20 ml~70 ml H2O.

3. The method of claim 1, wherein, 0.20 g~0.82 g citric acid is dissolved in 10mL~50 mL H2O.

4. The method of claim 1, wherein, 2mg~8 mg catalyst is placed in 200μL~500 μL isopropanol and 10μL~50 μL 5 wt% Nafion solution.

5. The method of claim 1, wherein, In step 1, vacuum drying at 50 ℃~200 ℃, -0.08MPa~-0.1MPa.

6. The method of claim 1, wherein, Acid treatment: first, room temperature immersion in H2SO4 / HNO3 (1:3) mixed acid for 5h~15h, sufficient water washing and drying, then 100 ℃ reflux in concentrated HNO3 for 2h, sufficient water washing and drying.

7. The method of claim 1 wherein, In step 3, drying at 10 ℃~80 ℃.

8. A method for driving the electrocatalytic reduction of CO2 to synthesize wide-ratio syngas by a copper-nickel alloy electrode, characterized in that, In a H-type double-chamber electrolytic cell, the copper-nickel alloy electrode prepared by the method of claim 1 is used as a working electrode, an Ag / AgCl electrode is used as a reference electrode, a Pt electrode is used as an auxiliary electrode, a Nafion117 proton exchange membrane is used to separate the cathode and the anode, a KHCO3 solution is used as a catholyte, a dilute sulfuric acid solution is used as an anolyte, before electrolysis, N2 is introduced into the cathode to exhaust air, then CO2 is continuously introduced to saturate the electrolyte, gas introduction is stopped during electrolysis, and constant potential electrolysis is carried out.

9. The method of claim 8, wherein, The concentration of the KHCO3 solution is 0.5 M.

10. The method of claim 8, wherein, The concentration of the dilute sulfuric acid solution is 0.1 M.

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