Anion ionomer modified porous copper catalyst as well as preparation method and application thereof

Abstract

The invention discloses an anion ionomer modified porous copper catalyst and a preparation method thereof.The prepared porous copper catalyst electrocatalyzes carbon dioxide reduction in an industrial galvanic pile, under the same current density, the cell pressure of the prepared porous copper catalyst is obviously lower than that of a commercial copper catalyst, meanwhile, the Faraday efficiency of a multi-carbon product of the prepared porous copper catalyst is higher and can reach 82% or above, and the prepared porous copper catalyst has a good application prospect. And the reduction of the stability of the electrolysis system caused by the separation of bicarbonate can be obviously avoided.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to an anion ionomer-modified porous copper catalyst, a method for preparing the anion ionomer-modified porous copper catalyst, and the application of the anion ionomer-modified porous copper catalyst. Background Technology

[0002] With the acceleration of globalization and industrialization, carbon dioxide (CO2) emissions continue to increase, exacerbating the greenhouse effect and making climate change an increasingly serious problem. As an abundant C1 resource, CO2 plays a crucial role in addressing current environmental issues by utilizing renewable energy-driven technologies to produce clean fuels and high-value-added chemical products. Electrocatalytic CO2 reduction reaction (CO2RR) uses electrical energy to convert CO2 into various reduction products under mild conditions. Compared to C1 products, multi-carbon products such as ethylene, ethanol, acetic acid, and propanol have higher energy density and added value, attracting widespread attention from researchers. However, the formation of multi-carbon products is a coupled process involving multiple electrons and protons, and the complexity of intermediates can severely affect the formation rate and selectivity of multi-carbon products. Effectively improving the selectivity of multi-carbon products at high current densities is scientifically challenging. Catalyst design is a crucial step in improving the formation rate of multi-carbon products at industrial-grade current densities. Compared to neutral or acidic electrolytes, alkaline electrolytes yield higher reactivity for CO2RR, but CO2 readily reacts with alkaline solutions, causing bicarbonate precipitation, which severely affects the stability and lifespan of the electrolysis equipment.

[0003] Replacing high-concentration alkaline solutions with dilute electrolytes for CO2 precipitation reduction (CORR) is an effective strategy to mitigate salting out and improve the stability of electrolysis equipment. However, the high proton concentration in dilute electrolytes and the excessively low CO2 concentration in the local reaction zone can severely lead to the evolution of hydrogen byproducts. Therefore, improving the local pH and local CO2 concentration of the reaction microenvironment is crucial. Although traditional copper-based catalysts can achieve high multi-carbon product Faradaic efficiencies (FE) at certain current densities, they still suffer from problems such as excessively high cell voltage and easy catalyst remodeling leading to decreased stability of the electrolysis system, making them unsuitable for current commercial applications.

[0004] Therefore, developing efficient and stable electrocatalysts suitable for industrial fuel cell stacks is a key step in ensuring that CO2 production moves from laboratory scale to industrial scale. Summary of the Invention

[0005] The primary objective of this invention is to provide a method for preparing porous copper catalysts modified with anionic ionomers, thereby addressing the shortcomings of existing technologies, such as the low Faraday efficiency of industrial electrocatalysts in reducing carbon dioxide to produce multi-carbon products and the tendency for salting out in strongly alkaline electrolytes, which leads to decreased stability of the electrolysis system.

[0006] A second objective of this invention is to provide a porous copper catalyst modified with anionic ionomers.

[0007] To achieve the above objectives, the following technical solution is adopted: A method for preparing an anionic ionomer-modified porous copper catalyst includes the following steps: (1) Dissolve the copper salt precursor in deionized water, slowly add ammonia solution, stir, and obtain a blue complex; add alkali solution, stir, and obtain a blue solid; (2) The blue solid was washed with water and centrifuged, collected and freeze-dried to obtain copper salt precursor; then calcined in air and cooled naturally to obtain porous copper oxide powder. (3) Disperse porous copper oxide powder with anionic ionomer in a solvent in a certain proportion and perform ultrasonic dispersion to obtain anionic ionomer / copper oxide catalyst dispersion; spray the anionic ionomer / copper oxide catalyst dispersion onto a gas diffusion electrode to obtain a cathode catalytic electrode / gas diffusion electrode composite electrode. (4) The cathode catalytic electrode / gas diffusion electrode composite electrode is electrochemically activated in situ to obtain a porous copper catalyst modified with anion ionomer.

[0008] In this invention, the copper salt precursor is one or more of copper chloride, copper nitrate, copper sulfate, and copper acetate.

[0009] Furthermore, the copper salt precursor is copper nitrate.

[0010] In this invention, the alkaline solution is one or more of lithium hydroxide, sodium hydroxide, and potassium hydroxide solutions.

[0011] In this invention, the molar ratio of the copper salt precursor, ammonia, and alkali solution is 1:0.9-1.2:1.8-3.

[0012] Preferably, the molar ratio of the copper salt precursor, ammonia, and alkali solution is 1:1.08:2.4.

[0013] In this invention, the centrifugation conditions for washing in step (2) are a centrifugation speed of 8000~12000 rpm and a centrifugation time of 3~5 minutes.

[0014] In this invention, the freeze-drying temperature is -80 to -50°C, the freeze-drying pressure is 5 to 20 Pa, and the freeze-drying time is 12 to 36 hours.

[0015] Furthermore, the freeze-drying temperature is -70℃, the freeze-drying pressure is 10 Pa, and the freeze-drying time is 12~36h.

[0016] In this invention, the calcination temperature in step (2) is 300~600℃, the heating rate is 5℃ / minute, and the calcination time is 1~3h.

[0017] In this invention, the anionic ionomer is PiperION A-5; the mass ratio of the anionic ionomer to the porous copper oxide powder is 0.05~0.2.

[0018] In this invention, the dispersing solvent in step (3) is one or more of deionized water, anhydrous ethanol, isopropanol, and acetone.

[0019] In this invention, the ultrasonic dispersion conditions in step (3) are ultrasonication in an ice bath environment for 10 to 40 minutes.

[0020] In this invention, the gas diffusion electrode is one of carbon paper, carbon cloth, carbon felt, and PTFE film.

[0021] In this invention, the loading of the anionic ionomer / copper oxide catalyst in the gas diffusion electrode is 0.3~1 mg / cm³. 2 .

[0022] In this invention, the in-situ electrochemical activation of the cathode catalytic electrode / gas diffusion electrode composite electrode in step (4) is carried out in an MEA electrolysis system. The electrolyte is one or more of potassium bicarbonate, potassium hydroxide, potassium sulfate, and potassium chloride aqueous solution; the electrolyte concentration is 0.01~10M; and the in-situ activation current density is 50~300 mA / cm². 2 The restoration time is 30~120 minutes.

[0023] A porous copper catalyst modified with anionic ionomer was prepared by the above method.

[0024] Application of a porous copper catalyst modified with the above-mentioned anionic ionomer in the electrocatalytic reduction of carbon dioxide in industrial fuel cell stacks.

[0025] Furthermore, the electrocatalytic reduction of carbon dioxide is carried out in an MEA industrial fuel cell stack, using iridium dioxide / titanium felt as the anode; the electrolyte is one or more of potassium bicarbonate, potassium hydroxide, potassium sulfate, and potassium chloride aqueous solution; the electrolyte concentration is 0.01~10M; the multi-carbon products obtained from the electrocatalytic reduction of carbon dioxide are ethylene, ethanol, acetic acid, and propanol.

[0026] The present invention has the following beneficial effects: (1) The porous copper catalyst prepared by the anion ionomer modified porous copper catalyst of the present invention can be used for the electrocatalytic reduction of carbon dioxide into multi-carbon chemicals in industrial stacks. It can be mass-produced on a large scale, the production steps are simple, the raw materials are readily available, the introduction of precious metals is avoided, and the cost is lower than that of commercial copper catalysts.

[0027] (2) The porous copper catalyst prepared in this invention exhibits significantly lower cell voltage than commercial copper catalysts in the electrocatalytic reduction of carbon dioxide in industrial fuel cell stacks at the same current density, particularly at a current density of 200 mA / cm². 2 Under these conditions, its cell voltage is more than 0.3V lower than that of commercial copper catalysts; at the same time, the Faradaic efficiency of its multi-carbon products can reach more than 82%. In particular, in 0.1M KHCO3 aqueous electrolyte, it can significantly avoid the decrease in the stability of the electrolysis system caused by the precipitation of bicarbonate, and its stability can be maintained for at least 100 hours, showing strong application potential.

[0028] (3) The method for preparing the cathode catalytic electrode / gas diffusion electrode composite electrode proposed in this invention has a certain degree of universality and can be extended to other electrocatalyst systems, such as Ag, Sn, Bi, etc., and is suitable for industrial electrocatalytic carbon dioxide reduction to produce carbon monoxide and formate systems.

[0029] (4) The porous copper composite electrode modified with anion ionomer proposed in this invention can also be used in cathodic reduction reactions such as urea electrosynthesis, nitrate reduction and electrochemical hydrogenation of small organic molecules. Attached Figure Description

[0030] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0031] Figure 1 This is an X-ray diffraction image of the porous copper catalyst modified with anionic ionomer in this invention; Figure 2 This is a transmission electron microscope (TEM) image of the anion ionomer-modified porous copper catalyst in Example 3 of the present invention. Figure 3 This is an elemental distribution diagram of the anion ionomer-modified porous copper catalyst in Example 3 of the present invention; Figure 4 Linear voltammetry (LSV) curves of the anionic ionomer-modified porous copper catalysts prepared in Examples 1-4 and Comparative Example 1 of this invention in 0.1 M KHCO3; Figure 5 This is a distribution diagram of the reduction products of the anionic ionomer-modified porous copper catalyst in 0.1M KHCO3 electrolyte as a function of current density in Example 3 of the present invention. Figure 6 This is a distribution diagram of reduction products of the commercial copper catalyst modified with anionic ionomer in Comparative Example 1 of the present invention in 0.1 M KHCO3 electrolyte as a function of current density; Figure 7To test the stability of the anion-modified porous copper catalyst in Example 3 of this invention for the electrocatalytic conversion of carbon dioxide to multi-carbon products, a current density of 200 mA / cm² was used. 2 The X-axis represents the test time, the left Y-axis represents the cell voltage of the fuel cell stack, and the right Y-axis represents the Faraday efficiency of the multi-carbon products. Figure 8 This is a TEM image of the porous copper catalyst modified with anionic ionomer in Example 3 of the present invention after stability testing. Figure 9 This is an elemental distribution diagram of the porous copper catalyst modified with anionic ionomer in Example 3 of the present invention after stability testing; Figure 10 This is the chemical structural formula of the anionic ionomer PiperION A-5 in this invention. Detailed Implementation

[0032] Example 1: A method for preparing an anionic ionomer-modified porous copper catalyst includes the following steps: (1) Dissolve 20 g of copper nitrate trihydrate in 2 L of deionized water and stir for 30 min to generate a blue solution. Then slowly add 600 ml of 0.15 M ammonia solution to the blue solution at a rate of 10 ml / min and continue stirring at room temperature to obtain a blue complex. Slowly add 200 ml of 1 M sodium hydroxide solution to the blue complex at a rate of 10 ml / min and continue stirring at room temperature to obtain a blue solid.

[0033] (2) The above blue solid was washed with water and centrifuged several times to remove unreacted raw materials and impurities. After collection, it was placed in a freeze dryer and freeze-dried at 10 Pa and -70℃ for 24 h. After freeze-drying, the copper salt precursor was ground and calcined in an air atmosphere in a muffle furnace. The heating rate was 5℃ / min, the calcination temperature was 500℃, and the calcination time was 2 h. After natural cooling to room temperature, porous copper oxide powder was obtained for use. (3) Take 720 mg of the above porous copper oxide powder and disperse it in 100 ml of isopropanol. Disperse it ultrasonically for 30 min under ice bath conditions. Then add 10 wt% PiperION A-5 (chemical structure formula is shown in the figure). Figure 10 After sonicating for 30 minutes, 360 mg of the solution was applied to a conductive carbon paper substrate using a spray gun, ensuring a catalyst loading of 0.5 mg / cm³. 2 A composite electrode of cathode catalytic electrode / gas diffusion electrode was obtained.

[0034] (4) Assemble the above-mentioned cathode catalytic electrode / gas diffusion electrode into the MEA electrolysis system, and perform in-situ electrochemical activation in 0.1 M KHCO3 solution at a carbon dioxide flow rate of 30 sccm. The in-situ activation current density is 100 mA / cm. 2 An activation time of 1 h yielded an anion-modified porous copper catalyst with a mass ratio of 0.05:1 (anion ionomer:copper oxide). Its X-ray diffraction pattern is shown below. Figure 1 This catalyst was then used in industrial fuel cell stacks for CO2RR to produce multicarbon chemicals.

[0035] This invention also provides a novel electrolytic stack with high current density and high multi-carbon Faraday efficiency, comprising cathode-side and anode-side components separated by an anion exchange membrane. The cathode side includes a cathode end plate, a cathode insulating plate, a cathode current collector plate, a cathode flow field plate, and the aforementioned prepared cathode gas diffusion electrode, ensuring conductivity and gas permeability. The anode-side components correspond to the cathode side and include an anode end plate, an anode insulating plate, an anode current collector plate, an anode flow field plate, and a commercially available IrO2 / Ti counter electrode. The electrolyte is one or more of potassium bicarbonate, potassium hydroxide, potassium sulfate, and potassium chloride aqueous solutions; the electrolyte concentration is 0.01~10M.

[0036] The gas diffusion electrodes at the cathode and anode are located on opposite sides of the anion exchange membrane, with the catalyst layer closely attached to the membrane, together forming the membrane electrode assembly. To enhance the stability of the stack structure, a polytetrafluoroethylene (PTFE) border layer can be added to the outside of the cathode and anode gas diffusion layers. Furthermore, all components are assembled sequentially from the outside in, thereby optimizing the gas transport channels and electron transfer paths to achieve high CO2RR performance.

[0037] Example 2 The same preparation method as in Example 1 was used, with the only difference being: Add 10 wt% PiperION A-5 solution (720 mg total) and follow the same procedure as in Example 1 to prepare an anionic ionomer-modified porous copper catalyst with a mass ratio of 0.1:1 (anionic ionomer: copper oxide).

[0038] Example 3 The same preparation method as in Example 1 was used, with the only difference being: Add 10 wt% PiperION A-5 solution (1080 mg total) and follow the same procedure as in Example 1 to prepare an anionic ionomer-modified porous copper catalyst with a mass ratio of 0.15:1 (anionic ionomer: copper oxide).

[0039] Example 4: The same preparation method as in Example 1 was used, with the only difference being: Add 10 wt% PiperION A-5 solution (1440 mg), and follow the same procedure as in Example 1 to prepare an anionic ionomer-modified porous copper catalyst with a mass ratio of 0.2:1 (anionic ionomer: copper oxide).

[0040] Compare with Example 1 The same preparation method as in Example 1 was used, with the only difference being: Copper oxide was a commercially available source, purchased from Sigma Biotechnology Co., Ltd. (Sigma, CuO). The rest of the preparation was the same as in Example 1, resulting in a copper catalyst without anionic ionomer modification.

[0041] Taking the anion-modified porous copper catalyst in Example 3 as an example, its structural composition and elemental distribution can be determined by TEM and EDS-mapping; from Figure 2 The TEM images show that the catalyst particle size is 100-200 nanometers; from Figure 3 The elemental distribution shows that the copper, fluorine, and nitrogen elements are uniformly distributed in the porous copper catalyst modified with anion ionomer; in addition, the composition and elemental distribution of the catalysts in Examples 1, 2, and 4 are similar to those in Example 3.

[0042] Figure 4 The linear voltammetry (LSV) curves of the anionic ionomer-modified porous copper catalysts prepared in Examples 1-4 and Comparative Example 1 in 0.1 MKHCO3 are shown. The results indicate that the CO2RR activity of the anionic ionomer-modified porous copper catalysts prepared in this invention is significantly higher than that of commercial copper catalysts, and there is an optimal value between the CO2RR activity response current and the amount of ionomer added. The ratio in Example 3 of this invention has the highest CO2RR activity.

[0043] The catalysts from Example 3 and Comparative Example 1 were applied to CO2RR, and their effects were observed at different reaction current densities (100~300 mA / cm²). 2 The reduction products include hydrogen, carbon monoxide, methane, formic acid, ethylene, ethanol, acetic acid, and propanol; from Figure 5 It can be seen that, after condition optimization, the electrocatalyst in Example 3, applied to CO2RR, at 200 mA / cm², achieved optimal performance. 2 At the given current density, the Faradaic efficiency of the multi-carbon products (ethylene, ethanol, acetic acid, propanol) reached a maximum of 82%; while in Control Example 1 ( Figure 6 The optimal current density is 150 mA / cm². 2Furthermore, the Faraday efficiency of the multi-carbon product was only 30.3%; this result indicates that the intrinsic activity of the copper catalyst in Example 3 is significantly higher than that of commercial copper catalysts, which increases the reactive current density and reduces the cell voltage of the stack.

[0044] Figure 7 The catalyst in Example 3 was used in a 0.1 M KHCO3 solution at 200 mA / cm². 2 The electrochemical stability was tested over 100 hours. During the operating time, there were no significant changes in the applied cell pressure and the Faraday efficiency of the multi-carbon products. This result indicates that the anion-modified porous copper catalyst in Example 3 has excellent electrochemical stability. After a 100-hour stability test, the TEM image of the anion-modified porous copper catalyst in Example 3 is visible. Figure 8 The results showed that its structure and composition did not change significantly after the stability test.

[0045] After a 100-hour stability test, the elemental distribution of the anion-modified porous copper catalyst in Example 3 was observed. Figure 9 The results showed that copper, fluorine, and nitrogen elements were evenly distributed in the catalyst, and the anionic ionomers did not degrade, maintaining relative stability in the actual CO2RR process.

[0046] In summary, the porous copper catalyst proposed in this invention for the electrocatalytic reduction of carbon dioxide into multi-carbon chemicals in industrial fuel cell stacks is not only simple in synthesis and low in cost, but also exhibits excellent electrocatalytic activity for the synthesis of multi-carbon chemicals from carbon dioxide, significantly higher than that of commercial copper catalysts.

[0047] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for preparing a porous copper catalyst modified with anionic ionomers, characterized in that, Includes the following steps: (1) Dissolve the copper salt precursor in deionized water, slowly add ammonia solution, stir, and obtain a blue complex; add alkali solution, stir, and obtain a blue solid; (2) The blue solid was washed with water and centrifuged, collected and freeze-dried to obtain copper salt precursor; then calcined in air and cooled naturally to obtain porous copper oxide powder. (3) Disperse porous copper oxide powder and anionic ionomer in a solvent in a certain proportion and perform ultrasonic dispersion to obtain anionic ionomer / copper oxide catalyst dispersion. An anionic ionomer / copper oxide catalyst dispersion was sprayed onto a gas diffusion electrode to obtain a cathode catalytic electrode / gas diffusion electrode composite electrode. (4) The cathode catalytic electrode / gas diffusion electrode composite electrode is electrochemically activated in situ to obtain a porous copper catalyst modified with anion ionomer.

2. The method for preparing anionic ionomer-modified porous copper catalyst according to claim 1, characterized in that, The molar ratio of the copper salt precursor, ammonia, and alkali solution is 1:0.9-1.2:1.8-3.

3. The method for preparing anionic ionomer-modified porous copper catalyst according to claim 2, characterized in that, The freeze-drying temperature is -80~-50℃, the freeze-drying pressure is 5~20Pa, and the freeze-drying time is 12~36h.

4. The method for preparing anionic ionomer-modified porous copper catalyst according to claim 3, characterized in that, In step (2), the calcination temperature is 300~600℃, the heating rate is 5℃ / minute, and the calcination time is 1~3h.

5. The method for preparing anionic ionomer-modified porous copper catalyst according to any one of claims 1-4, characterized in that, The anionic ionomer is PiperION A-5; the mass ratio of the anionic ionomer to the porous copper oxide powder is 0.05~0.

2.

6. The method for preparing anionic ionomer-modified porous copper catalyst according to claim 5, characterized in that, The loading of the anionic ionomer / copper oxide catalyst in the gas diffusion electrode is 0.3~1 mg / cm³. 2 .

7. The method for preparing anionic ionomer-modified porous copper catalyst according to claim 5, characterized in that, In step (4), the in-situ electrochemical activation of the cathode catalytic electrode / gas diffusion electrode composite electrode is carried out in an MEA electrolysis system. The electrolyte is one or more of the following: potassium bicarbonate, potassium hydroxide, potassium sulfate, and potassium chloride aqueous solution; the electrolyte concentration is 0.01~10M; and the in-situ activation current density is 50~300 mA / cm². 2 The restoration time is 30~120 minutes.

8. The method for preparing anionic ionomer-modified porous copper catalyst according to claim 1, characterized in that, The copper salt precursor is one or more of copper chloride, copper nitrate, copper sulfate, and copper acetate; the dispersing solvent in step (3) is one or more of deionized water, anhydrous ethanol, isopropanol, and acetone; the gas diffusion electrode is one of carbon paper, carbon cloth, carbon felt, and PTFE membrane.

9. A porous copper catalyst modified with anionic ionomer, prepared by the method described in any one of claims 1-8.

10. The application of the anion ionomer-modified porous copper catalyst of claim 9 in the electrocatalytic reduction of carbon dioxide in an industrial fuel cell stack.

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