Silver metal nanoclusters and application thereof in electrocatalytic reduction of carbon dioxide

Abstract

The application discloses silver metal nanoclusters and application thereof in electrocatalytic reduction of carbon dioxide, and belongs to the technical field of electrocatalysis. 10 The silver metal nanoclusters are nanoclusters containing 10 silver cores, and the molecular formula is Ag (SR)6(DPPP)3(CF3COO)4.The silver metal nanoclusters are loaded on carbon paper to obtain a supported catalyst, and the supported catalyst is used as a catalyst in the process of electrocatalytic reduction of carbon dioxide into carbon monoxide.The method is simple, the synthesis condition is mild, the operation is simple, the method has excellent catalytic performance, and has high Faraday efficiency and reaction selectivity.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrocatalysis, and particularly relates to a silver metal nanocluster and application thereof in electrocatalytic reduction of carbon dioxide. BACKGROUND

[0002] With the intensification of global warming and energy crisis, carbon dioxide (CO2) emission reduction and resource utilization have become the focus of global attention. Electrochemical CO2 reduction (ECO2R) technology is a new technology that uses electrical energy to convert carbon dioxide into high-value chemicals and fuels (such as carbon monoxide, methane, ethylene, etc.), which not only helps to alleviate carbon emission problems, but also provides a new way for clean energy production. This technology takes the catalyst on the electrode surface as the core, and through the transfer of electrons and protons, it activates stable carbon dioxide molecules and realizes their selective reduction. However, the carbon dioxide reduction process is complex, involving multiple reaction pathways and multiple products, and its efficiency and selectivity are constrained by the performance of the catalyst. In addition, the competition of hydrogen evolution reaction (HER) can significantly reduce the faradic efficiency, further increasing the difficulty of industrialization. Therefore, developing efficient, stable and highly selective catalysts, and optimizing reaction conditions and electrochemical systems, are the core directions of current research in this field.

[0003] In recent years, in response to the challenges of electrochemical CO2 reduction, important progress has been made in catalyst design and system optimization. For example, single-metal and double-metal catalysts significantly improve the selectivity of target products by adjusting the electronic structure and surface geometry; nanostructured catalysts reduce the reaction overpotential and improve the conversion efficiency due to their high specific surface area and abundant active sites. In addition, heteroatom doping and surface functionalization technologies further optimize the performance of the catalyst, while molecular catalysts have become a new research hotspot due to their highly adjustable structure and high selectivity. At the same time, by improving the design of electrolytic cells, adjusting the pH and temperature of the electrolyte, etc., researchers have successfully reduced the influence of hydrogen evolution reaction and improved the reaction efficiency. Looking to the future, electrochemical CO2 reduction technology combined with renewable energy (such as solar and wind energy) is expected to achieve carbon neutrality and energy sustainable development goals, but it still needs to overcome technical bottlenecks through interdisciplinary collaborative research to find low-cost catalysts with high conversion rate and high selectivity in electrocatalytic hydrogenation reaction, and to promote the transition from laboratory research to industrial application. SUMMARY

[0004] Therefore, the present application provides a silver metal nanocluster and application thereof in electrocatalytic reduction of carbon dioxide. The present application has mild synthesis conditions, simple operation, high yield of silver metal nanocluster, and excellent catalytic performance.

[0005] The silver metal nanocluster of the present application is a nanocluster containing 10 silver cores, and the molecular formula is Ag 10 (SR)6(DPPP)3(CF3COO)4, and there is a free CF3COO counter ion around the cluster structure.

[0006] The preparation method of the silver metal nanocluster of the present application comprises the following steps:

[0007] CF3COOAg (88 mg, 0.4 mmol) was poured into a 100 mL round-bottom flask, 20 mL of methanol was added, and stirring was performed on a magnetic stirrer until complete dissolution. Then DPPP (41 mg, 0.1 mmol) was added to the above CF3COOAg methanol solution, and stirring was performed again for about 10 minutes to make it fully dissolved, at which time the solution was colorless and transparent. Then adamantane thiol (Adm-SH, 34 mg, 0.2 mmol) was added, and the colorless and transparent solution turned milky white. After 30 minutes, 100 mg of NaBH4 (2.64 mmol) was dissolved in 5 mL of methanol, and then quickly added to the above mixture, and the color of the solution gradually changed from milky white to brown black. The reaction was continued at room temperature for 5 hours. After 5 hours, the crude product was centrifuged at 10000 rpm for 3 minutes to remove the large particles that were not dissolved in methanol during the reaction. The supernatant was spin-dried using a rotary evaporator, and the crude product was repeatedly washed with a large amount of n-hexane, then extracted with dichloromethane solvent for two to three times, and finally the product was purified with toluene, diffused with toluene / n-hexane solvent at room temperature, and a small amount of ethanol was used as a buffer layer, and after about a week, transparent sheet-shaped crystals were obtained at the bottom of the single crystal bottle. In order to obtain single crystals of higher quality, the sheet-shaped crystals were collected and recrystallized with dichloromethane.

[0008] The application of the silver metal nanocluster in the electrocatalytic reduction of carbon dioxide.

[0009] The silver metal nanocluster is loaded on carbon paper to obtain a supported catalyst. The carbon paper electrode loaded with the silver metal nanocluster is used as a working electrode, and an Ag / AgCl reference electrode and a platinum sheet electrode are used for electrochemical reduction. The electrochemical reduction is carried out in an H-type three-electrode system electrolytic cell.

[0010] The cathode chamber electrolyte is composed of an alkaline electrolyte and water, and 30 minutes of carbon dioxide is required before testing to make the electrolyte saturated.

[0011] The alkaline electrolyte is one or more of potassium bicarbonate and potassium hydroxide, and the concentration of the alkaline electrolyte in the electrolyte is 0.5-1 mol / L.

[0012] The anode chamber electrolyte is an aqueous solution of an alkaline electrolyte. Preferably, the alkaline electrolyte is potassium bicarbonate.

[0013] In the catalytic hydrogenation reaction of electrocatalytic reduction of carbon dioxide to carbon monoxide, the reaction conditions can be conventional in the art.

[0014] Further, the voltage of the electrocatalytic hydrogenation reaction is -0.5 V vs. RHE to -1.3 V vs. RHE, preferably -0.7 V vs. RHE to -1.3 V vs. RHE. The time of the electrocatalytic hydrogenation reaction is 5-30 minutes, preferably 10 minutes. The temperature of the electrocatalytic hydrogenation reaction can be room temperature, for example 20-25℃.

[0015] The supported catalyst is prepared by the following method:

[0016] The silver metal nanoclusters are dissolved in DMF and drop-coated on a 1 cm x 2 cm carbon paper, and dried. The cluster solution is prepared at a concentration of 0.1-2 mg / mL, and 5 wt% nafion content of 20-50 μL per mL.

[0017] More preferably, the cluster solution is prepared at a concentration of 2 mg / mL, and 5 wt% nafion content of 40 μL per mL.

[0018] The carbon paper is commercially available in the art. The technical parameters of the carbon paper are as follows: resistivity 5.5 mΩ·cm 2 , density 0.83 g / cm 3 , thickness 0.21 mm ± 0.01 mm; for example, HCP 120 series. The size of the carbon paper can be cut according to experimental needs, for example (1 cm x 1 cm) to (3 cm x 3 cm), preferably 1 cm x 2 cm.

[0019] Compared with the prior art, the present application has the following beneficial effects:

[0020] 1. The preparation method of silver metal nanoclusters provided by the present application has mild synthesis conditions, simple and controllable operation, high yield, easy to repeat and enlarge, and is suitable for mass production.

[0021] 2. The silver metal nanoclusters prepared by the present application have small size, high stability and good catalytic performance, which provides a broad prospect for subsequent application.

[0022] 3. The silver metal nanocluster catalyst prepared by the present application has low cost in the electrocatalytic hydrogenation reaction, and has good conversion rate and selectivity.

[0023] 4、In the preferred embodiment of the present application, the silver metal nanocluster catalyst of the present application can still maintain high catalytic efficiency and high stability after 10 cycles of single group in the electrocatalytic hydrogenation reaction. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 UV spectrum of silver metal nanocluster.

[0025] Figure 2 Mass spectrum of silver metal nanocluster.

[0026] Figure 3 Single crystal structure diagram of silver metal nanocluster (Ag: blue; S: red; P: purple).

[0027] Figure 4 Thermogravimetric analysis diagram of silver metal nanocluster.

[0028] Figure 5 Transmission electron microscopy (TEM) diagrams of silver metal nanocluster catalysts of Examples 2 and 3 before and after reaction.

[0029] Figure 6 Linear sweep voltammetry (LSV) curve diagrams of Examples 3 and Comparative Example 1 in electrochemical reduction reaction.

[0030] Figure 7 Comparison diagram of catalytic results of different catalysts of Examples 4 and Comparative Example 2 in electro-reduction at -0.8 V vs. RHE voltage.

[0031] Figure 8 Catalytic result diagram of silver metal nanocluster catalyst of Example 4 in electro-reduction at different potentials.

[0032] Figure 9 Gas phase detection diagram of silver metal nanocluster catalyst of Example 4 in electro-reduction of carbon dioxide product.

[0033] Figure 10 Stability test diagram of silver metal nanocluster catalyst of Example 5. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantages of the present application more clear and explicit, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0035] The experimental methods in the present application are all conventional methods unless otherwise specified. The experimental materials used in the present application are all obtained by market purchase unless otherwise specified.

[0036] Example 1: Preparation of silver metal nanocluster

[0037] A method for preparing silver metal nanoclusters, comprising the following steps:

[0038] CF3COOAg (88 mg, 0.4 mmol) was poured into a 100 mL round bottom flask, 20 mL of methanol was added, and stirred on a magnetic stirrer until fully dissolved. Then DPPP (41 mg, 0.1 mmol) was added to the above CF3COOAg methanol solution, and stirred again for about 10 minutes to fully dissolve, at which time the solution was colorless and transparent. Adamantane thiol (Adm-SH, 34 mg, 0.2 mmol) was then added, and the colorless and transparent solution turned milky white. After 30 minutes, 100 mg of NaBH4 (2.64 mmol) was dissolved in 5 mL of methanol, and then quickly added to the above mixture, and the color of the solution gradually changed from milky white to brown black. The reaction was continued at room temperature for 5 hours. After 5 hours, the crude product was centrifuged at 10,000 rpm for 3 minutes to remove large particles that were not dissolved in methanol during the reaction. The supernatant was spin-dried using a rotary evaporator, and the crude product was repeatedly washed with a large amount of n-hexane, then extracted with dichloromethane solvent for two to three times, and finally the product was purified with toluene, which was diffused with toluene / n-hexane solvent at room temperature, with a small amount of ethanol as a buffer layer, and after about a week, transparent sheet crystals were obtained at the bottom of the single crystal bottle. To obtain single crystals of higher quality, the sheet crystals were collected and recrystallized with dichloromethane. The UV spectrum is shown in Figure 1 , the mass spectrum is shown in Figure 2 , the single crystal structure is shown in Figure 3 , and the thermal gravimetric analysis is shown in Figure 4 .

[0039] Example 2: Preparation of silver metal nanocluster catalyst

[0040] Carbon paper was cut into small pieces of 1 cm x 2 cm, 2 mg of silver metal nanoclusters were dissolved in 1 mL of DMF containing 40 μl of 5 wt% nafion, and were drop-cast on the carbon paper with a drop-cast area of 1 cm x 1 cm, and then dried for use.

[0041] Example 3: Detection of the electro-reduction performance of the silver metal nanocluster catalyst

[0042] A Chenhua 760 electrochemical workstation was used to perform the test under a standard three-electrode system. The silver metal nanocluster catalyst prepared in Example 2 was used as the working electrode, Ag / AgCl was used as the reference electrode, and a platinum sheet was used as the counter electrode. An H-type electrolytic cell was used for the reaction, and the room was separated from the room by a DuPont 117 cation exchange membrane. The anode chamber electrolyte was 0.5 mol / L potassium bicarbonate solution, and the cathode chamber was 0.5 mol / L potassium bicarbonate solution saturated with carbon dioxide for 30 minutes.

[0043] The parameters were set as follows: initial potential of 0.2 V vs. RHE, end potential of -1.3 V vs. RHE, scan rate of -0.1 mV / s, and the results are shown in Figure 6 Before and after electrolysis, the clusters were dispersed relatively uniformly on the carbon paper carrier, and no agglomeration was found, as shown in Figure 5

[0044] Example 4: Detection of carbon dioxide electro-reduction of silver metal nanocluster catalyst

[0045] A CHI 760 electrochemical workstation was used to perform the test under a standard three-electrode system. The silver metal nanocluster catalyst prepared in Example 2 was used as the working electrode, Ag / AgCl was used as the reference electrode, and a platinum plate was used as the counter electrode. An H-type electrolytic cell was used for the reaction, and the chambers were separated by a DuPont 117 cation exchange membrane. The anode chamber electrolyte was a 0.5 mol / L potassium bicarbonate solution, and the cathode chamber was a 0.5 mol / L potassium bicarbonate solution saturated with carbon dioxide for 30 minutes.

[0046] The catalytic effect obtained after electrocatalytic hydrogenation for 10 minutes at -0.7, -0.8, -0.9, -1, -1.1, -1.2, and -1.3 V vs. RHE is shown in the figure. As can be seen from Figure 8 , at -0.8 V vs. RHE, the carbon monoxide reached a maximum Faraday efficiency of 94.8%, and remained above 90% Faraday efficiency at a wide potential of -0.8 V vs. RHE ~ -1.1 V vs. RHE. As the potential gradually increased, the Faraday efficiency of carbon monoxide decreased slightly but remained above 80%. The gas-phase products were detected by gas chromatography, as shown in Figure 9 .

[0047] Example 5: Carbon dioxide electro-reduction cycle stability test of silver metal nanocluster catalyst

[0048] A CHI 760 electrochemical workstation was used to perform the test under a standard three-electrode system. The silver metal nanocluster catalyst prepared in Example 2 was used as the working electrode, Ag / AgCl was used as the reference electrode, and a platinum plate was used as the counter electrode. An H-type electrolytic cell was used for the reaction, and the chambers were separated by a DuPont 117 cation exchange membrane. The anode chamber electrolyte was a 0.5 mol / L potassium bicarbonate solution, and the cathode chamber was a 0.5 mol / L potassium bicarbonate solution saturated with carbon dioxide for 30 minutes.

[0049] ​The experimental conditions were the same as the best selectivity conditions in Example 4, and ten experiments were performed using the same working electrode to ensure that the experimental conditions were the same each time. After each experiment, the electrolytic cell was cleaned to ensure that no product remained. The experimental results are shown in Table 1. Figure 10 As shown in Table 1, the faradaic efficiency of carbon monoxide was essentially unchanged, and the catalyst was relatively stable.

[0050] Comparative Example 1: Preparation of carbon paper catalyst

[0051] The carbon paper was cut into small pieces of 1 cm x 2 cm for use.

[0052] Comparative Example 2: Electrochemical reduction of carbon dioxide using carbon paper catalyst

[0053] The carbon paper catalyst prepared in Comparative Example 1 was used as the working electrode, Ag / AgCl was used as the reference electrode, and platinum was used as the counter electrode. The reaction was performed using an H-type electrolytic cell, and the chambers were separated by a DuPont 117 cation exchange membrane. The electrolyte in the anode chamber was 0.5 mol / L potassium bicarbonate solution, and the electrolyte in the cathode chamber was 0.5 mol / L potassium bicarbonate solution saturated with carbon dioxide for 30 minutes.

[0054] LSV detection was performed under the optimal conditions of Example 3, and the results are shown in Table 2. Figure 6

[0055] The results obtained after electrocatalytic hydrogenation for 10 minutes under the optimal conditions of Example 3 are shown in Table 3. Figure 7 Figure 7 As shown in Table 3, at -0.8 V vs. RHE, the carbon paper catalyst had low catalytic efficiency, and the faradaic efficiency of carbon monoxide was only 4.5%.

[0056] The specific embodiments of the application described above do not constitute a limitation on the scope of the application. Any other corresponding changes and modifications made in accordance with the technical concept of the application should be included within the scope of the claims of the application.​​

Claims

1. The application of silver metal nanoclusters in the electrocatalytic reduction of carbon dioxide, characterized by: A carbon paper electrode loaded with silver metal nanoclusters was used as the working electrode, and electrochemical reduction was performed using a reference electrode and a counter electrode; the reference electrode was an Ag / AgCl reference electrode; and the counter electrode was a platinum sheet electrode. The silver metal nanoclusters are nanoclusters containing 10 silver cores, with the molecular formula Ag. 10 (SR)6(DPPP)3(CF3COO)4; The silver metal nanoclusters were dissolved in DMF to prepare a cluster solution with a concentration of 0.1-2 mg / mL, wherein the content of 5 wt% nafion in the cluster solution was 20-50 μL per milliliter; the above mixed solution was drop-coated onto 1 cm × 2 cm carbon paper, dried, and used as a working electrode; The voltage for the electrocatalytic hydrogenation reaction ranges from -0.5V vs. RHE to -1.3V vs. RHE, and the reaction time is 5 to 30 minutes.

2. The application according to claim 1, characterized in that: Prepare a cluster solution with a concentration of 2 mg / mL, wherein the cluster solution contains 40 μL of 5 wt% nafion per milliliter.

3. The application according to claim 1, characterized in that: The technical parameters of the carbon paper are: resistivity 5.5 mΩ / cm. 2 Density 0.83 g / cm³ 3 Thickness 0.21mm±0.01mm.

4. The application according to claim 1, characterized in that: The voltage for the electrocatalytic hydrogenation reaction ranged from -0.7V vs. RHE to -1.3V vs. RHE, and the reaction time was 10 minutes.

5. The application according to claim 1, characterized in that: The cathode electrolyte consists of alkaline electrolyte and water. Carbon dioxide is introduced into it before the reaction to saturate it. The anode electrolyte is an aqueous solution of alkaline electrolyte.

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