A bismuth-europium bimetallic catalyst, a preparation method thereof and an application thereof

Abstract

The present invention discloses a bismuth-europium bimetallic catalyst, a preparation method thereof and an application thereof. The bismuth-europium bimetallic catalyst of the present invention can efficiently electroreduce carbon dioxide to formic acid. By using the sol-gel method and the calcination method, a bismuth-europium bimetallic oxide precursor is prepared, and then the bismuth-europium bimetallic catalyst is prepared by an electrochemical reduction method. The present invention prepares a bismuth-europium bimetallic as an efficient and stable catalyst, and the preparation method is simple and easy to operate and has no pollution to the environment. Against the background that the global carbon dioxide concentration increases year by year due to human industrial activities, it can efficiently and continuously convert carbon dioxide, which may cause the global greenhouse effect, into formic acid, a chemical product required for human life, which is beneficial to the global carbon cycle and can be applied to industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of electroreduction of carbon dioxide, and particularly relates to a bismuth-based bimetallic catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Since the 18th century, due to the influence of human industrial activities, the carbon balance on the earth has been disrupted, the global carbon dioxide concentration has increased year by year, and the greenhouse effect has become increasingly serious [Adv Mater, 2016, 28, 3423 - 52]. Due to the increasingly obvious phenomena such as extreme climate change, sea - level rise, and reduction of polar glacier area brought about by the greenhouse effect, the rise in global temperature has had an increasingly greater impact on human social activities. Therefore, carbon dioxide, as a major greenhouse gas, has also received more and more extensive attention [ACS Catalysis, 2019, 10, 358 - 364]. In recent years, electro - reduction of carbon dioxide has become an effective means to promote the global carbon cycle, which can convert carbon dioxide into chemical products beneficial to human life and has great economic prospects. Electro - catalytic reduction is an effective way to convert electrical energy into high - energy - density fuels for storage and standby. However, there are still many problems to be solved, such as improving the reaction rate, enhancing the selectivity of product conversion, and reducing the over - potential of the reaction to make the reaction more likely to occur. Formic acid is considered to be one of the most attractive products of electro - reduction of carbon dioxide because it is a huge hydrogen storage medium and is easier to store and transport than gas products. As a basic chemical raw material, formic acid is widely used in industries such as pesticides, leather, and rubber. Moreover, as a liquid product of carbon dioxide reduction, formic acid can be directly used as a fuel for fuel cells without separation, showing more potential application prospects than methanol fuel [Nature Communications, 2020, 11, 3633]. In recent years, the demand for formic acid has increased year by year, and it is expected that the global formic acid market size will grow to about 1 million tons by 2030. Compared with the current energy - intensive methanol carbonylation process for producing formic acid, electro - catalytic reduction of carbon dioxide to formic acid simultaneously realizes the resource utilization of carbon dioxide and the effective conversion of clean and low - grade electrical energy. Therefore, it is expected to become one of the technologies for large - scale utilization of carbon dioxide. Although various metals such as Pb, In, and Hg can efficiently produce formic acid, they cannot be used on a large scale due to their high toxicity and environmental unfriendliness. In addition, under high - potential conditions, the competition between the hydrogen evolution reaction and the carbon dioxide reduction reaction will be more intense, resulting in a decrease in the Faraday efficiency of formic acid. Metal bismuth has been widely used in the field of electro - reduction of carbon dioxide due to its low toxicity and high cost - effectiveness. However, due to the low melting point and easy oxidation of metal bismuth, there are still many challenges in directly preparing bismuth - based catalysts. Currently, bismuth oxides, sulfides, oxohalides, etc. are mostly used as precursors to prepare bismuth - based catalysts by in - situ reduction methods. Bismuth - metal catalysts have received extensive attention due to their excellent performance. However, the single - metal bismuth catalysts reported so far often require relatively high potentials, and the current density or Faraday efficiency is not ideal. In order to reduce costs and change the activity and selectivity of bismuth - based catalysts, introducing other metals to make them bimetallic catalysts has become the first choice, and the interaction between their components has also become a research hotspot.[NanoEnergy, 2017, 42, 51 - 57]. In addition, in addition to some common preparation methods of bimetals, according to previous reports, the electrochemical reduction of bimetal oxides to obtain bimetal catalysts is an effective strategy, which can not only give the catalyst a unique local environment, but also construct a unique surface structure, thus promoting the reduction of carbon dioxide [Angew Chem Int Ed Engl, 2019, 58, 14197 - 14201]. The change in the activity and selectivity of bismuth catalysts caused by the introduction of other metals is mainly attributed to the beneficial synergistic effect and electronic effect between metals. The introduced metals can further affect the binding strength of intermediates by changing the electronic structure and geometric effect of bismuth. Different from some common transition metals, rare earth elements are widely used to regulate the electronic and geometric structures of various metals to obtain better catalytic performance due to their unique electronic structures [Nano Energy, 2017, 38, 290 - 296]. However, there are few reports on the electroreduction of carbon dioxide using rare earth metals on bismuth - based bimetal electrocatalysts. Therefore, it is of great significance to prepare catalysts containing these two metal elements through certain chemical methods. Summary of the Invention

[0003] In order to solve the problems of the existing technology, the purpose of the present invention is to overcome the deficiencies of the existing technology and provide a bismuth - europium bimetal catalyst, its preparation method and its application. The bismuth - europium bimetal catalyst of the present invention uses low - cost and low - toxicity metal bismuth and rare earth metal europium, and is suitable for the efficient electroreduction of carbon dioxide to formic acid. The preparation method is simple, pollution - free to the environment, and can be applied to industrial production.

[0004] To achieve the above - mentioned purpose of the invention, the present invention adopts the following technical solutions:

[0005] A bismuth - europium bimetal catalyst uses metal bismuth and europium as catalyst active materials, and the molar ratio of bismuth to europium is 4:1 - 12:1.

[0006] Preferably, the bismuth - europium bimetal catalyst uses carbon paper as the catalyst carrier, and bismuth and europium are loaded on the carbon paper, and the catalyst loading of bismuth and europium on the carbon paper is not less than 1 mg / cm 2 .

[0007] Preferably, the molar ratio of bismuth to europium is 8:1 - 12:1.

[0008] A preparation method of the bismuth - europium bimetal catalyst of the present invention includes the following steps:

[0009] Step 1): Dissolve bismuth nitrate pentahydrate and europium acetate hydrate in deionized water, add nitric acid dropwise, put it into a water bath, and stir until it is completely dissolved to form a uniform and transparent solution, obtaining a first solution;

[0010] Step 2): Dissolve ethylenediaminetetraacetic acid in deionized water, add ammonia water dropwise, and stir at room temperature until the solution becomes clear to obtain a second solution;

[0011] Step 3): Mix the first solution in Step 1) and the second solution in Step 2), place it in a water bath, add ethylene glycol, continuously stir, then dry it to form a dry gel, then put the dry gel into a muffle furnace, and then calcine and grind it to obtain a bismuth-europium bimetallic oxide precursor;

[0012] Step 4): Mix the bismuth-europium bimetallic oxide precursor with isopropanol and a 5% by mass Nafion solution, ultrasonically mix it until it is uniformly mixed, and then uniformly coat it on carbon paper, and use it as a working electrode for electroreduction to prepare a bismuth-europium bimetallic catalyst.

[0013] Preferably, in the said Step 1), the molar ratios of bismuth nitrate pentahydrate and europium acetate hydrate are respectively 4:1 to 12:1;

[0014] Preferably, in the said Step 1), the mass percentage concentration of the nitric acid used is 65 - 68%, and the deionized water is at least 10 mL;

[0015] Preferably, in the said Step 1), control the temperature of the water bath to be not lower than 60 °C.

[0016] Further preferably, in the said Step 1), the molar ratios of bismuth nitrate pentahydrate and europium acetate hydrate are respectively 8:1 to 12:1.

[0017] Preferably, in the said Step 2), the ammonia water used is an aqueous solution with a mass percentage of ammonia not lower than 25%.

[0018] Preferably, in the said Step 3), when mixing the first solution in Step 1) and the second solution in Step 2), the molar ratio of ethylenediaminetetraacetic acid to the sum of the molar amounts of bismuth nitrate pentahydrate and europium acetate hydrate is 1:1;

[0019] Preferably, in the said Step 3), the temperature of the water bath is not lower than 60 °C, and the dosage of ethylene glycol is not lower than 20 mL;

[0020] Preferably, in the said Step 3), in the muffle furnace, calcine at not lower than 400 °C for at least 5 hours.

[0021] Preferably, in the said Step 4), the mass of the bismuth-europium bimetallic oxide precursor weighed is 4 mg, the dosage of isopropanol is not lower than 1 mL, and the dosage of the 5% by mass Nafion solution is not lower than 40 μL.

[0022] Preferably, in step 4), the ultrasonic dispersion time is at least 0.5 h, and the length and width dimensions of the carbon paper used are not less than 2 cm;

[0023] Preferably, in step 4), the electroreduction is carried out at a potential of -1.09 V, and the electroreduction time is not less than 2 h;

[0024] Preferably, in step 4), when the electroreduction is carried out, an H-type electrolytic cell with a KHCO3 electrolyte concentration of not less than 0.1 M is used.

[0025] An application of the bismuth-europium bimetallic catalyst described in the present invention, using the bismuth-europium bimetallic catalyst to prepare formic acid by electroreduction of carbon dioxide.

[0026] Preferably, in the application of the bismuth-europium bimetallic catalyst described in the present invention, the Faraday efficiency of the bismuth-europium bimetallic catalyst is not less than 91.6% at -0.79 V; in the wide potential window of -0.89 V to -1.19 V, the Faraday efficiency of the bismuth-europium bimetallic catalyst is not less than 97%; and the bismuth-europium bimetallic catalyst still does not deactivate after 400 h of stability test, and the bismuth-europium bimetallic catalyst always maintains a high Faraday efficiency of not less than 93%.

[0027] Compared with the prior art, the present invention has the following obvious outstanding substantive features and remarkable advantages:

[0028] 1. The catalyst of the present invention is a bismuth-europium bimetallic catalyst, which can be applied in the field of electrochemically reducing carbon dioxide to formic acid; it can maintain a high Faraday efficiency of >97% at low potential and wide potential window, has strong stability, and still does not deactivate after 400 hours of stability test. The preparation method is simple and environmentally friendly, and it is an excellent electrode catalyst that can be applied to electrochemically reduce carbon dioxide to formic acid;

[0029] 2. The bimetallic catalyst of the present invention not only exhibits excellent electrochemical performance but also has excellent stability; especially when the molar ratio of bismuth to europium is 8:1 and the catalyst loading on the carbon paper is 1 mg / cm 2 , its Faraday efficiency can reach 91.6% at -0.79 V, and in the wide potential window of -0.89 V to -1.19 V, its Faraday efficiency is higher than 97%; using the catalyst of the present invention to prepare a working electrode and applying it to an H-type electrolytic cell has a high stability of up to 400 hours;

[0030] 3. The method of the present invention is not only green and environmentally friendly, with easily available raw materials, low cost, mild reaction conditions, and short reaction time, but also has the advantages of simple process, practicality, and strong controllability, and is easy to scale up production. It is an excellent electrode catalyst that can be applied to electrochemically reduce carbon dioxide to formic acid;

[0031] 4. The working electrode prepared with the catalyst of the present invention is applied to a flow cell, and the current density in 0.1 M KOH solution can reach 250 mA / cm 2 , meeting the standards for industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Cyclic voltammogram of the bismuth-europium bimetallic catalyst with a molar ratio of bismuth to europium of 8:1 in an argon-saturated 0.1 M KHCO3 solution, which is a preferred embodiment of the present invention.

[0033] Figure 2 Linear voltammogram of the bismuth-europium bimetallic catalyst with a molar ratio of bismuth to europium of 8:1 in an argon-saturated 0.1 M KHCO3 solution, which is a preferred embodiment of the present invention.

[0034] Figure 3 Cyclic voltammogram of the bismuth-europium bimetallic catalyst with a molar ratio of bismuth to europium of 8:1 in a carbon dioxide-saturated 0.1 M KHCO3 solution, which is a preferred embodiment of the present invention.

[0035] Figure 4 Linear voltammogram of the bismuth-europium bimetallic catalyst with a molar ratio of bismuth to europium of 8:1 in a carbon dioxide-saturated 0.1 M KHCO3 solution, which is a preferred embodiment of the present invention.

[0036] Figure 5 Linear voltammograms of bismuth-europium bimetallic catalysts with different ratios in an argon-saturated 0.1 M KHCO3 solution, which are preferred embodiments of the present invention.

[0037] Figure 6 Linear voltammograms of bismuth-europium bimetallic catalysts with different ratios in a carbon dioxide-saturated 0.1 M KHCO3 solution, which are preferred embodiments of the present invention.

[0038] Figure 7 Faraday efficiency diagrams of bismuth-europium bimetallic catalysts with different ratios for the electroreduction of carbon dioxide to formic acid, which are preferred embodiments of the present invention.

[0039] Figure 8 Cyclic voltammogram of the bismuth-europium bimetallic catalyst with a molar ratio of bismuth to europium of 8:1 in a carbon dioxide-saturated 1 M KOH solution, which is a preferred embodiment of the present invention.

[0040] Figure 9 Linear voltammogram of the bismuth-europium bimetallic catalyst with a molar ratio of bismuth to europium of 8:1 in a carbon dioxide-saturated 1 M KOH solution, which is a preferred embodiment of the present invention.

[0041] Figure 10Stability test chart of the bismuth-europium bimetallic catalyst with a molar ratio of bismuth to europium of 8:1 in a 0.1 M KHCO3 solution saturated with carbon dioxide at a potential of -1.09 V for a preferred embodiment of the present invention.

[0042] Figure 11 Electron micrograph of the bismuth-europium bimetallic catalyst obtained in Example 1 of the present invention. Detailed description of the specific implementation

[0043] To make the invention more clearly understandable, preferred embodiments are described in detail below in conjunction with the accompanying drawings.

[0044] In Examples 1-7, bismuth nitrate pentahydrate was purchased from Shanghai Titan Scientific Co., Ltd., analytical grade, with a molecular weight of about 485.07 g; europium acetate hydrate was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., analytical grade, with a molecular weight of about 329.1 g; ethylenediaminetetraacetic acid was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., analytical grade, with a molecular weight of about 292.24 g.

[0045] The above scheme is further described below in conjunction with specific implementation examples. The preferred embodiments of the present invention are described in detail as follows:

[0046] Example 1

[0047] In this example, a bismuth-europium bimetallic catalyst uses metallic bismuth and europium as catalyst active materials, and the molar ratio of bismuth to europium is 8:1. The bismuth-europium bimetallic catalyst uses carbon paper as the catalyst carrier, and bismuth and europium are loaded on the carbon paper. The catalyst loading of bismuth and europium on the carbon paper is 1 mg / cm 2 . The bimetallic catalyst in this example includes low-cost and low-toxic metallic bismuth and rare earth metal europium.

[0048] In this example, the preparation method of the bismuth-europium bimetallic catalyst includes the following steps:

[0049] Step 1): Weigh bismuth nitrate pentahydrate and europium acetate hydrate with a molar ratio of 8:1 in a 50 mL small beaker, add 10 mL of deionized water thereto, and drop a small amount of nitric acid. Place it in a water bath, adjust the temperature to 60 °C, and stir until it is completely dissolved to form a uniform and transparent solution, obtaining a first solution; the mass percentage concentration of the nitric acid used is 65-68%, and the added nitric acid is 1 mL;

[0050] Step 2): weigh ethylenediaminetetraacetic acid in a 50mL beaker, the ratio of the molar amount of ethylenediaminetetraacetic acid to the molar amount of bismuth nitrate pentahydrate and europium acetate hydrate being 1:1, add 10mL of deionized water, and dropwise add a small amount of ammonia water, stir at room temperature until completely dissolved, and make the solution clear to obtain a second solution; the ammonia water used is an aqueous solution containing 25% ammonia by mass; 4mL of ammonia water is added;

[0051] Step 3): the first solution in step 1) and the second solution in step 2) are mixed, placed in a water bath, 20 mL of ethylene glycol is added, stirred continuously, and then dried to form a dry gel, and then the dry gel is placed in a muffle furnace, and then calcined at 400° C. for 5 hours, and the obtained powder product is ground to obtain a bismuth-europium bimetallic oxide precursor; the temperature of the water bath is controlled to be 60° C.;

[0052] Step 4): Weigh 4 mg of bismuth-europium bimetallic oxide precursor into a small glass bottle, add 1 mL of isopropanol and 40 μL of a 5% mass percent Nafion solution, and ultrasonicate for 30 minutes until mixed evenly to obtain a slurry; then use a pipette to evenly coat the slurry on a carbon paper with a length and width of 2 cm × 2 cm, and after drying, use it as a working electrode and place it in an H-type electrolytic cell with an electrolyte of 0.1 M KHCO3, and continue electroreduction for 2 hours at a potential of -1.09 V to obtain a bismuth-europium bimetallic catalyst.

[0053] Experimental test analysis:

[0054] The cyclic voltammetry curve and linear voltammetry curve of the catalyst were measured by an electrochemical workstation. Argon was introduced into a 0.1M KHCO3 solution for 30 minutes, and the carbon paper coated with the bismuth-europium bimetallic catalyst of this embodiment was used as the working electrode, the Ag / AgCl electrode was used as the reference electrode, and the Pt electrode was used as the counter electrode, and the cyclic voltammetry curve and linear voltammetry curve were measured in turn.

[0055] The experimental results are as follows Figure 1 , Figure 2 As shown, the results show that under the condition of passing argon, the current density presented by the catalyst is very small, indicating that the catalyst can suppress the hydrogen evolution reaction that may compete with the electroreduction reaction of carbon dioxide.

[0056] The bismuth-europium bimetallic catalyst prepared in this example was observed microscopically. Figure 11 As shown, the microstructure of the bismuth-europium bimetallic catalyst is a loose and porous sheet structure.

[0057] Example 2

[0058] This embodiment is basically the same as the first embodiment, except that:

[0059] In this embodiment, a bismuth-europium bimetallic catalyst uses metallic bismuth and europium as catalyst active materials, and the molar ratio of bismuth to europium is 8:1. The bismuth-europium bimetallic catalyst uses carbon paper as a catalyst carrier, and bismuth and europium are loaded on the carbon paper. The catalyst loading of bismuth and europium on the carbon paper is 1 mg / cm 2 . The bimetallic catalyst of this embodiment includes low-cost and low-toxic metallic bismuth and rare-earth metal europium.

[0060] In this embodiment, a bismuth-europium bimetallic catalyst uses metallic bismuth and europium as catalyst active materials, and the molar ratio of bismuth to europium is 8:1. The bismuth-europium bimetallic catalyst uses carbon paper as a catalyst carrier, and bismuth and europium are loaded on the carbon paper. The catalyst loading of bismuth and europium on the carbon paper is 1 mg / cm 2 .

[0061] In this embodiment, the preparation method of the bismuth-europium bimetallic catalyst includes the following steps:

[0062] Step 1): Weigh bismuth nitrate pentahydrate and europium acetate hydrate with a molar ratio of 8:1 in a 50 mL small beaker, add 10 mL of deionized water thereto, and dropwise add a small amount of nitric acid. Place it in a water bath, adjust the temperature to 60 °C, and stir until it is completely dissolved to form a uniform and transparent solution to obtain a first solution; the mass percentage concentration of the nitric acid used is 65-68%, and the added nitric acid is 1 mL;

[0063] Step 2): Weigh ethylenediaminetetraacetic acid in a 50 mL small beaker. The molar amount of ethylenediaminetetraacetic acid is in a ratio of 1:1 to the sum of the molar amounts of bismuth nitrate pentahydrate and europium acetate hydrate. Add 10 mL of deionized water and dropwise add a small amount of ammonia water. Stir at room temperature until it is completely dissolved to make the solution clear to obtain a second solution; the ammonia water used is an aqueous solution with a mass percentage of ammonia of 25%; the added ammonia water is 4 mL;

[0064] Step 3): Mix the first solution in Step 1) and the second solution in Step 2), place it in a water bath, add 20 mL of ethylene glycol, stir continuously, then dry it to form a dry gel, then put the dry gel into a muffle furnace, and then calcine it at 400 °C for 5 h. Then grind the obtained powder product to obtain a bismuth-europium bimetallic oxide precursor; control the temperature of the water bath to be 60 °C;

[0065] Step 4): Weigh 4 mg of the bismuth-europium bimetallic oxide precursor into a small glass bottle, add 1 mL of isopropanol and 40 μL of a 5% by mass Nafion solution, and ultrasonicate for 30 minutes until evenly mixed to obtain a slurry; then use a pipette to evenly coat the slurry on a carbon paper with a length and width of 2 cm × 2 cm. After drying, it is used as a working electrode and placed in an H-type electrolytic cell with an electrolyte of 0.1 M KHCO3. At a potential of -1.09 V, continuously electro-reduce for 2 h to prepare the bismuth-europium bimetallic catalyst.

[0066] Experimental test analysis:

[0067] Use an electrochemical workstation to measure the cyclic voltammetry curve and linear voltammetry scan curve of the catalyst. Pass carbon dioxide into a 0.1 M KHCO3 solution for 30 minutes. Use the carbon paper coated with the bismuth-europium bimetallic catalyst as the working electrode, the Ag / AgCl electrode as the reference electrode, and the Pt electrode as the counter electrode, and successively measure its cyclic voltammetry curve and linear voltammetry curve.

[0068] The experimental results are as Figure 3 、 Figure 4 shown. The results show that compared with introducing argon in Example 1, after introducing carbon dioxide, the trend of the current density decreasing is very large, indicating that the catalyst has good performance in electro-reducing carbon dioxide.

[0069] Example 3

[0070] This example is basically the same as the above example, with the special feature that:

[0071] In this example, a bismuth-europium bimetallic catalyst uses metallic bismuth and europium as catalyst active materials, and the molar ratios of bismuth and europium are 12:1, 8:1, and 4:1 respectively. The bismuth-europium bimetallic catalyst uses carbon paper as the catalyst carrier, and bismuth and europium are loaded on the carbon paper. The catalyst loading of bismuth and europium on the carbon paper is 1 mg / cm 2 . The bimetallic catalyst in this example includes low-cost and low-toxicity metallic bismuth and rare earth metal europium.

[0072] In this example, the preparation method of the bismuth-europium bimetallic catalyst includes the following steps:

[0073] Step 1): Weigh bismuth nitrate pentahydrate and europium acetate hydrate with molar ratios of 12:1, 8:1, and 4:1 respectively into a 50 mL small beaker, add 10 mL of deionized water thereto, and drop a small amount of nitric acid. Place it in a water bath and adjust the temperature to 60 °C, and stir until it is completely dissolved to form a uniform and transparent solution to obtain a first solution; the mass percentage concentration of the nitric acid used is 65-68%, and the added nitric acid is 1 mL;

[0074] Step 2): Weigh ethylenediaminetetraacetic acid in a 50 mL small beaker. The molar ratio of ethylenediaminetetraacetic acid to the sum of the molar amounts of bismuth nitrate pentahydrate and europium acetate hydrate is 1:1. Add 10 mL of deionized water and dropwise add a small amount of ammonia water. Stir at room temperature until completely dissolved to make the solution clear, obtaining a second solution. The ammonia water used is an aqueous solution with a mass percentage of ammonia of 25%. The added ammonia water is 4 mL.

[0075] Step 3): Mix the first solution in Step 1) and the second solution in Step 2), place it in a water bath, add 20 mL of ethylene glycol, continuously stir, then dry it to form a dry gel. Then put the dry gel into a muffle furnace, and after calcining at 400 °C for 5 h, grind the obtained powder product to obtain a bismuth-europium bimetallic oxide precursor. Control the temperature of the water bath to be 60 °C.

[0076] Step 4): Weigh 4 mg of bismuth-europium bimetallic oxide precursors with three different ratios in small glass bottles, respectively add 1 mL of isopropanol and 40 μL of a 5% mass percentage concentration Nafion solution, and ultrasonicate for 30 minutes until evenly mixed to obtain a slurry. Then use a pipette to evenly coat the slurry on carbon paper with a length and width of 2 cm × 2 cm, and after drying, use it as a working electrode and set it in an H-type electrolytic cell with an electrolyte of 0.1 M KHCO3. At a potential of -1.09 V, continuously electroreduce for 2 h to prepare different bismuth-europium bimetallic catalysts.

[0077] Experimental test and analysis:

[0078] Use an electrochemical workstation to measure the linear voltammetry scanning curve of the catalyst. Bubble argon into a 0.1 M KHCO3 solution for 30 minutes. Use the carbon paper coated with the bismuth-europium bimetallic catalyst as the working electrode, the Ag / AgCl electrode as the reference electrode, and the Pt electrode as the counter electrode to measure its linear voltammogram.

[0079] The experimental results are as Figure 5 shown. The results show that under the condition of bubbling argon, the bismuth-europium bimetallic catalyst with a bismuth to europium molar ratio of 8:1 exhibits the smallest current density, indicating that this catalyst is most capable of inhibiting the hydrogen evolution reaction that may compete with the electroreduction of carbon dioxide reaction.

[0080] Example 4

[0081] This example is basically the same as the above example, with the special feature being:

[0082] In this embodiment, a bismuth-europium bimetallic catalyst uses metallic bismuth and europium as catalyst active materials, and the molar ratios of bismuth to europium are 12:1, 8:1, and 4:1 respectively. The bismuth-europium bimetallic catalyst uses carbon paper as the catalyst carrier, and bismuth and europium are loaded on the carbon paper. The catalyst loading of bismuth and europium on the carbon paper is 1 mg / cm 2 . The bismuth-europium bimetallic catalysts with three different metal ratios are the same as those in Example 3. The bimetallic catalyst in this embodiment includes low-cost and low-toxicity metallic bismuth and rare-earth metal europium.

[0083] Experimental test and analysis:

[0084] The linear voltammetric scanning curve of the catalyst was measured using an electrochemical workstation. After introducing carbon dioxide into a 0.1 M KHCO3 solution for 30 minutes, the carbon paper coated with the bismuth-europium bimetallic catalyst was used as the working electrode, the Ag / AgCl electrode was used as the reference electrode, and the Pt electrode was used as the counter electrode to sequentially measure its linear voltammetric curve.

[0085] The experimental results are as Figure 6 shown. The results indicate that after introducing carbon dioxide, the bismuth-europium bimetallic catalyst with a bismuth-to-europium molar ratio of 8:1 has the largest decreasing trend in current density, indicating that this catalyst has the best performance for electro-reducing carbon dioxide.

[0086] Example 5

[0087] This embodiment is basically the same as the above embodiments, with the special feature that:

[0088] In this embodiment, a bismuth-europium bimetallic catalyst uses metallic bismuth and europium as catalyst active materials, and the molar ratios of bismuth to europium are 12:1, 8:1, and 4:1 respectively. The bismuth-europium bimetallic catalyst uses carbon paper as the catalyst carrier, and bismuth and europium are loaded on the carbon paper. The catalyst loading of bismuth and europium on the carbon paper is 1 mg / cm 2 . The bismuth-europium bimetallic catalysts with three different metal ratios are the same as those in Example 3. The bimetallic catalyst in this embodiment includes low-cost and low-toxicity metallic bismuth and rare-earth metal europium.

[0089] Experimental test and analysis:

[0090] The products of electro-reducing carbon dioxide by the bismuth-europium bimetallic catalyst were detected using ion chromatography. After introducing carbon dioxide into a 0.1 M KHCO3 solution for 30 minutes, the carbon paper coated with the bismuth-europium bimetallic catalyst was used as the working electrode, the Ag / AgCl electrode was used as the reference electrode, and the Pt electrode was used as the counter electrode. Electrolysis was carried out for the same time at potentials of -0.79 V, -0.89 V, -0.99 V, -1.09 V, and -1.19 V respectively, and the liquid products were detected using ion chromatography.

[0091] The experimental results are asFigure 7 As shown in the figure, the Faraday efficiency of the bismuth-europium bimetallic catalyst with a bismuth-to-europium molar ratio of 8:1 can reach 91.6% at -0.79V, and its Faraday efficiency is higher than 97% in the wide potential window from -0.89V to -1.19V. The bismuth-europium bimetallic catalyst with a bismuth-to-europium molar ratio of 8:1 has very good catalytic performance for the electroreduction of carbon dioxide to formic acid.

[0092] Example 6

[0093] This example is basically the same as Example 2, with the special feature that:

[0094] In this example, a bismuth-europium bimetallic catalyst uses metallic bismuth and europium as catalyst active materials, and the molar ratio of bismuth to europium is 8:1. The bismuth-europium bimetallic catalyst uses carbon paper as the catalyst carrier, and bismuth and europium are loaded on the carbon paper, and the catalyst loading of bismuth and europium on the carbon paper is 1mg / cm 2 . The bismuth-europium bimetallic catalyst is the same as that in Example 2. The bimetallic catalyst in this example includes low-cost and low-toxicity metallic bismuth and rare-earth metal europium.

[0095] Experimental test analysis:

[0096] Since the dissolution of carbon dioxide in the aqueous solution is limited, which will in turn hinder the operation of the entire catalytic system. In order to overcome the drawbacks of using traditional cathode electrodes and H-type electrolytic cells, a flow-type electrolytic cell is studied to improve the catalytic effect, and the cyclic voltammetry curve and linear voltammetry sweep curve of the catalyst are measured using an electrochemical workstation. Using 1M KOH solution as the electrolyte, the carbon paper coated with the bismuth-europium bimetallic catalyst is used as the working electrode, the Ag / AgCl electrode is used as the reference electrode, and the Pt electrode is used as the counter electrode to measure its cyclic voltammetry curve and linear voltammetry curve.

[0097] The experimental results are as Figure 8 、 Figure 9 shown, and it can be found that in the flow electrolytic cell, the catalyst shows a higher electroreduction carbon dioxide current density, and the current density can reach 250mA / cm 2 . The special structure of the flow cell can directly and quickly introduce gaseous carbon dioxide without passing through the solution, directly contact the catalyst through the gas diffusion layer, and the catalytic reaction occurs at the solid-liquid-gas three-phase interface, improving the catalytic performance.

[0098] Example 7

[0099] This example is basically the same as Example 2, with the special feature that:

[0100] In this embodiment, a bismuth-europium bimetallic catalyst uses metallic bismuth and europium as catalyst active materials, and the molar ratio of bismuth to europium is 8:1. The bismuth-europium bimetallic catalyst uses carbon paper as the catalyst carrier, and bismuth and europium are loaded on the carbon paper. The catalyst loading of bismuth and europium on the carbon paper is 1 mg / cm 2 . The bismuth-europium bimetallic catalyst is the same as that in Example 2. The bimetallic catalyst of this embodiment includes low-cost and low-toxic metallic bismuth and rare-earth metal europium.

[0101] Experimental test analysis:

[0102] The stability of the catalyst was measured using an electrochemical workstation. The stability of the catalyst was tested in an H-type electrolytic cell with 0.1 M KHCO3 solution as the electrolyte. The carbon dioxide gas flow rate was always kept consistent. The electrolysis was continued at a potential of -1.09 V, and the content of the liquid product was measured every 10 hours. The carbon paper coated with the bismuth-europium bimetallic catalyst was used as the working electrode, the Ag / AgCl electrode was used as the reference electrode, and the Pt electrode was used as the counter electrode.

[0103] The experimental results are as Figure 10 shown. The results show that the stability of the catalyst is very good. The catalyst did not deactivate after a stability test of up to 400 hours, and the Faraday efficiency always remained above 93%. It is a high-quality electrode catalyst that can be applied to the field of electrochemical reduction of carbon dioxide to formic acid and has high selectivity and high Faraday efficiency.

[0104] In summary, the bismuth-europium bimetallic catalyst of the above embodiment can efficiently electroreduce carbon dioxide to formic acid. The bismuth-europium bimetallic oxide precursor is prepared by the sol-gel method and the calcination method, and then the bismuth-europium bimetallic catalyst is prepared by the electrochemical reduction method. The above embodiments of the present invention prepared bismuth-europium bimetal as an efficient and stable catalyst. Its preparation method is simple and easy to operate, and it is environmentally friendly. Against the background that the global carbon dioxide concentration increases year by year due to human industrial activities, it can efficiently and continuously convert carbon dioxide, which may cause the global greenhouse effect, into formic acid, a chemical product required for human life. It is beneficial to the global carbon cycle and can be applied to industrial production.

[0105] The above describes the embodiments of the present invention in conjunction with the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made according to the purpose of the invention of the present invention. Any changes, modifications, substitutions, combinations, or simplifications made based on the spirit and principle of the technical solution of the present invention shall be equivalent replacement methods. As long as they meet the invention purpose of the present invention and do not deviate from the technical principle and invention concept of the present invention, they all belong to the protection scope of the present invention.

Claims

1. A bismuth-europium bimetallic catalyst, characterized in that: Using bismuth metal and europium as catalyst active materials, with the molar ratio of bismuth to europium being 4:1 to 12:1, a bismuth-europium bimetallic oxide precursor is prepared by using the sol-gel method and the calcination method, and then the bismuth-europium bimetallic catalyst is prepared by an electrochemical reduction method.

2. The bismuth-europium bimetallic catalyst according to claim 1, wherein: Using carbon paper as a catalyst support, bismuth and europium are loaded on the carbon paper, and the catalyst loading of bismuth and europium on the carbon paper is not less than 1 mg / cm 2 .

3. The preparation method of the bismuth-europium bimetallic catalyst according to claim 1, characterized in that, It includes the following steps: Step 1): Dissolve bismuth nitrate pentahydrate and europium acetate hydrate in deionized water, add nitric acid dropwise, place it in a water bath, and stir until it is completely dissolved to form a uniform and transparent solution to obtain the first solution; Step 2): Dissolve ethylenediaminetetraacetic acid in deionized water, add ammonia water dropwise, and stir at room temperature until the solution is clear to obtain the second solution; Step 3): Mix the first solution in Step 1) and the second solution in Step 2), place it in a water bath, add ethylene glycol, continuously stir, then dry it to form a dry gel, then put the dry gel into a muffle furnace, and then calcine and grind it to obtain the bismuth-europium bimetallic oxide precursor; Step 4): Mix the bismuth-europium bimetallic oxide precursor with isopropyl alcohol and a 5% by mass Nafion solution, ultrasonically mix it until it is uniformly mixed, and then uniformly coat it on carbon paper, and use it as a working electrode for electroreduction to prepare the bismuth-europium bimetallic catalyst.

4. The preparation method of the bismuth-europium bimetallic catalyst according to claim 3, wherein: In the said Step 1), the molar ratios of bismuth nitrate pentahydrate and europium acetate hydrate are respectively 4:1 to 12:1; Or, the mass percentage concentration of the nitric acid used is 65-68%, and the deionized water is at least 10 mL; Or, control the temperature of the water bath to be not lower than 60 °C.

5. The preparation method of the bismuth-europium bimetallic catalyst according to claim 3, characterized in that: In the said Step 2), the ammonia water used is an aqueous solution with a mass percentage of ammonia not lower than 25%.

6. The preparation method of the bismuth-europium bimetallic catalyst according to claim 3, characterized in that: In the said Step 3), when mixing the first solution in Step 1) and the second solution in Step 2), the molar ratio of ethylenediaminetetraacetic acid to the sum of the molar amounts of bismuth nitrate pentahydrate and europium acetate hydrate is 1:1; Or, the temperature of the water bath is not lower than 60 °C, and the dosage of ethylene glycol is not lower than 20 mL; Or, in the muffle furnace, calcine at not lower than 400 °C for at least 5 hours.

7. The preparation method of the bismuth-europium bimetallic catalyst according to claim 3, characterized in that: In the said Step 4), the mass of the bismuth-europium bimetallic oxide precursor weighed is 4 mg, the dosage of isopropyl alcohol is not lower than 1 mL, and the dosage of the 5% by mass Nafion solution is not lower than 40 μL.

8. The preparation method of the bismuth-europium bimetallic catalyst according to claim 3, wherein: In the said Step 4), the ultrasonic dispersion time is at least 0.5 h, and the length and width dimensions of the carbon paper used are both not lower than 2 cm; Or, perform electroreduction at a potential of -1.09 V, and the electroreduction time is not lower than 2 h; Or, when performing electroreduction, use an H-type electrolytic cell with an electrolyte concentration of not lower than 0.1 M KHCO3.

9. Use of the bismuth-europium bimetallic catalyst according to claim 1, characterized in that: Using the bismuth-europium bimetallic catalyst, formic acid is prepared by electroreducing carbon dioxide.

10. Use of the bismuth-europium bimetallic catalyst according to claim 9, characterized in that: The Faraday efficiency of the bismuth-europium bimetallic catalyst is not lower than 91.6% at -0.79 V; in the wide potential window from -0.89 V to -1.19 V, the Faraday efficiency of the bismuth-europium bimetallic catalyst is not lower than 97%; and the bismuth-europium bimetallic catalyst does not deactivate after 400 h of stability testing, and the bismuth-europium bimetallic catalyst always maintains a high Faraday efficiency of not lower than 93%.

Images