A ternary copper-based catalyst, a preparation method and application thereof

Abstract

The application relates to a ternary copper-based catalyst and a preparation method thereof, and the catalyst is prepared by the following steps: dissolving sodium hydroxide / potassium hydroxide / rubidium hydroxide in water, then adding copper chloride, sodium sulfide nine hydrate and hydrazine hydrate in sequence and fully stirring, and drying after centrifugal washing with deionized water and anhydrous ethanol to obtain NaCu5S3, KCu7S4 and RbCu7S4 respectively. Compared with copper-based catalysts such as copper oxide and copper sulfide, the ternary copper-based catalyst can well maintain its components and structure in the process of CO2 electro-reduction, avoids the C-C coupling step in the process of CO2 electrochemical reduction reaction, and realizes the purpose of high selectivity, large current and stable preparation of formic acid. The catalyst preparation process provided by the application is simple, the process is mild, and the raw materials are widely sourced, so that a potential way is provided for the large-scale production of formic acid by CO2 electrochemical reduction.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic CO2 reduction technology, specifically relating to a ternary copper-based catalyst for the electrochemical reduction of CO2 to formic acid and its preparation method. Background Technology

[0002] Electrochemical reduction of CO2 to produce high-value fuels or chemicals is considered an effective way to alleviate the energy crisis and address the greenhouse effect. Among the various products obtained from CO2 reduction reactions, formic acid (formate salts) has attracted much attention due to its wide application in industries such as leather, dyes, pharmaceuticals, and rubber. Furthermore, formic acid can serve as a good carrier for hydrogen energy, potentially solving problems such as low energy density and poor safety in hydrogen storage and transportation. Currently, the consumption and price of formic acid are continuously increasing worldwide, with global production capacity reaching 1.317 million tons in 2022. Therefore, achieving efficient formic acid production based on CO2 electrochemical reduction methods has significant environmental and economic benefits.

[0003] Currently, copper is the only metal catalyst capable of catalyzing the reduction of CO2 to multiple carbon products. Copper-based catalysts can reduce CO2 to various carbon oxides, hydrocarbons, and alcohols, such as CO, HCOOH, CH4, C2H4, and C2H5OH. However, they also face problems such as low product selectivity and poor stability. To address these issues, numerous strategies, including morphology control, surface and interface modification, defect engineering, and alloying, have been employed to improve the selectivity of copper-based catalysts for the reduction products. However, existing copper-based catalysts still exhibit low formate Faradaic efficiencies (typically below 60%), and the partial current density of the formate product remains difficult to reach industrial current levels (>200 mA cm⁻¹). -2 Related studies have shown that existing copper-based catalysts (such as copper oxide and copper sulfide) are reduced to copper metal in situ during CO2 reduction, leading to CC coupling.

[0004] Therefore, developing a novel copper-based catalyst to achieve efficient and stable preparation of formate is of great significance. Summary of the Invention

[0005] In view of this, the present invention provides a ternary copper-based catalyst and its preparation method. The catalyst is a NaCu5S3 / KCu7S4 / RbCu7S4 catalyst for the electroreduction of CO2 to formate. The addition of alkali metal elements enables this type of ternary copper-based catalyst to maintain its composition and structure well during the CO2 electroreduction process, avoiding the C-C coupling step in the CO2 electrochemical reduction reaction. Furthermore, the presence of sulfur activates the reaction of H2O and CO2 to generate *HCOO. - The intermediate exhibits excellent selectivity and reactivity towards formate.

[0006] This invention enables the large-scale preparation of catalysts using a low-temperature solution method, and also features short reaction time and low cost.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] The first technical objective of this invention is to provide a ternary copper-based catalyst, wherein the chemical formula of the catalyst is NaCu5S3, KCu7S4, or RbCu7S4.

[0009] The second technical objective of this invention is to provide a method for preparing the above-mentioned ternary copper-based catalyst, comprising the following steps:

[0010] S1. Dissolve sodium hydroxide, potassium hydroxide, and rubidium hydroxide separately in ultrapure water and form a mixed solution by magnetic stirring.

[0011] S2. Add copper chloride, sodium sulfide nonahydrate and hydrazine hydrate to the container in sequence and stir thoroughly.

[0012] S3. Seal the container and keep it in a water bath for 1 hour. Then collect the grayish-brown product by centrifugation. After washing and drying, the NaCu5S3 / KCu7S4 / RbCu7S4 catalyst can be obtained.

[0013] Optionally, the amount of sodium hydroxide used is 1-5g, the amount of potassium hydroxide is 1-10g, the amount of rubidium hydroxide is 1-20g, and the amount of ultrapure water is 5-30mL.

[0014] Optionally, the amount of copper chloride used is 1-10 mmol, the amount of sodium sulfide nonahydrate is 1-20 mmol, and the amount of hydrazine hydrate is 1-5 mmol.

[0015] Optionally, the magnetic stirring speed is 400-1000 r / min, and the stirring time is 10-60 min.

[0016] Optionally, the temperature of the water bath insulation is 50–90°C.

[0017] Optionally, the centrifugation speed is 5000-8000 r / min.

[0018] Optionally, the washing and drying process involves washing the grayish-brown spongy product collected by centrifugation with deionized water and anhydrous ethanol 1-2 times, and then vacuum drying it at 40-60°C for 4-8 hours.

[0019] The third technical objective of this invention is to provide an application of the above-mentioned NaCu5S3 / KCu7S4 / RbCu7S4 catalyst in the CO2 electroreduction reaction to produce formate, specifically:

[0020] Electrodes were prepared using the NaCu5S3 / KCu7S4 / RbCu7S4 catalyst obtained by the above method, and then the electrochemical reduction performance of the electrodes was tested.

[0021] Electrochemical performance was tested using an electrochemical workstation in an H-type electrolytic cell (0.1M KHCO3 as electrolyte, platinum mesh as counter electrode) or a flow electrolytic cell (1.0M KOH as electrolyte, nickel mesh as counter electrode); both used a saturated silver / silver chloride electrode as reference electrode, and gas phase and liquid phase products were detected by gas chromatography and nuclear magnetic resonance, respectively.

[0022] The preparation of the electrode includes the following steps:

[0023] (1) Preparation of electrode paste: 10 mg of NaCu5S3 / KCu7S4 / RbCu7S4 catalyst was dispersed in 1 mL of ethanol solution (containing 50 μL Nafion) and the catalyst ink was obtained by sonication for 30 min.

[0024] (2) Preparation of the working electrode: If it is an H-type electrolytic cell, take 60 μL of the catalyst ink obtained in step (1) and drop it onto the glassy carbon electrode. After drying, it serves as the working electrode. If it is a flow electrolytic cell, take a certain amount of the catalyst ink obtained in step (1) and load it onto carbon paper by drop coating or spraying. After drying, the working electrode of the electrolytic cell is obtained, wherein the catalyst ink loading on the carbon paper is 1 mg cm³. -2 .

[0025] As can be seen from the above technical solutions, compared with the prior art, the ternary copper-based catalyst, its preparation method, and its application provided by the present invention have the following superior effects:

[0026] (1) The ternary copper-based catalyst (M-Cu-S, M=Na,K,Rb) provided by the present invention has a mild preparation process, simple process steps, wide availability of raw materials, and the ability to be produced on a large scale.

[0027] (2) The NaCu5S3 / KCu7S4 / RbCu7S4 catalyst provided by this invention exhibits high selectivity for formate. Compared with copper oxides and copper sulfides, the introduction of alkali metal cations enhances the stability of the Cu-S bond. Based on this, the NaCu5S3 / KCu7S4 / RbCu7S4 catalyst shows a lower overpotential and a higher current density when electrocatalyzing the reduction of CO2 to formate.

[0028] (3) The NaCu5S3 / KCu7S4 / RbCu7S4 catalyst provided by this invention maintains its structure well during CO2 electroreduction and operates stably in a flow electrolyzer for over 72 hours, with a formate partial current density reaching 272.1 mA / cm². -2 4688 μmol cm -2 h -1 The formate yield is significantly improved. Compared with most copper-based catalysts currently studied, it exhibits superior formate selectivity and activity. The method for preparing the NaCu5S3 / KCu7S4 / RbCu7S4 catalyst provided by this invention has promising application prospects in the field of CO2 electroreduction formate production, offering a good solution for green formic acid production. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0030] Figure 1 Scanning electron microscope (SEM) images of the NaCu5S3 / KCu7S4 / RbCu7S4 catalysts prepared in Examples 1-9 and the Cu2S catalyst prepared in Comparative Example 1 are shown; where a represents Cu2S, b represents NaCu5S3, c represents KCu7S4, and d represents RbCu7S4. Both the comparative example and the ternary copper-based catalyst with added alkali metal elements exhibit rod-like structures with lengths of approximately tens of micrometers.

[0031] Figure 2 The Faradaic efficiency of formate prepared in H-type electrolytic cells under different applied potentials for the NaCu5S3 / KCu7S4 / RbCu7S4 catalysts prepared in Examples 1-9 and the Cu2S catalyst prepared in Comparative Example 1.

[0032] Figure 3 The Faradaic efficiency of formate under different applied potentials in a flow electrolytic cell was measured for the NaCu5S3 / KCu7S4 / RbCu7S4 catalysts prepared in Examples 1-9 and the Cu2S catalyst prepared in Comparative Example 1.

[0033] Figure 4 The partial current density of formate at different potentials was measured in a flow electrolytic cell for the NaCu5S3 / KCu7S4 / RbCu7S4 catalyst prepared in Examples 1-9 and the Cu2S catalyst prepared in Comparative Example 1.

[0034] Figure 5The current density curves and corresponding formate Faraday efficiencies of the RbCu7S4 catalyst prepared in Example 7 and the Cu2S catalyst prepared in Comparative Example 1, when operated in a flow electrolyzer at -1.0V (relative to the reversible hydrogen electrode) for 72 hours are shown. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] This invention discloses a method for preparing a ternary copper-based catalyst.

[0037] To better understand the present invention, the following embodiments are provided for further detailed description of the present invention, but they should not be construed as limiting the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above-described invention are also considered to fall within the protection scope of the present invention.

[0038] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0039] Example 1

[0040] A method for preparing a NaCu5S3 catalyst for the electroreduction of CO2 to formate comprises the following steps:

[0041] 3g of sodium hydroxide was dissolved in 10mL of ultrapure water, and then stirred at 500r / min for 10 minutes to form a mixed solution. Then, 1mmol of copper chloride, 4mmol of sodium sulfide nonahydrate and 1mL of hydrazine hydrate were added to the solution in sequence, and the mixture was placed in an 80℃ water bath and stirred at 500r / min for 1 hour. The suspension obtained by water bath stirring was centrifuged at 6000r / min for 10 minutes. The precipitate after centrifugation was collected and washed twice with deionized water and anhydrous ethanol, respectively. Then, it was vacuum dried in an oven at 60℃ for 6 hours. The dried sample is the NaCu5S3 catalyst.

[0042] Example 2

[0043] A method for preparing a NaCu5S3 catalyst for the electroreduction of CO2 to formate comprises the following steps:

[0044] 3g of sodium hydroxide was dissolved in 10mL of ultrapure water, and then stirred at 500r / min magnetically for 10 minutes to form a mixed solution. Then, 1mmol of copper chloride, 4mmol of sodium sulfide nonahydrate and 1mL of hydrazine hydrate were added to the solution in sequence, and the mixture was placed in a 70℃ water bath and stirred at 500r / min magnetically for 50 minutes. The suspension obtained by water bath stirring was centrifuged at 6000r / min for 10 minutes. The precipitate after centrifugation was collected and washed twice with deionized water and anhydrous ethanol, respectively. Then, it was vacuum dried in an oven at 60℃ for 6 hours. The dried sample is the NaCu5S3 catalyst.

[0045] Example 3

[0046] A method for preparing a NaCu5S3 catalyst for the electroreduction of CO2 to formate comprises the following steps:

[0047] 3g of sodium hydroxide was dissolved in 10mL of ultrapure water, and then stirred at 500r / min magnetically for 10 minutes to form a mixed solution. Then, 1mmol of copper chloride, 4mmol of sodium sulfide nonahydrate and 1mL of hydrazine hydrate were added to the solution in sequence, and the mixture was placed in a 60℃ water bath and stirred at 500r / min magnetically for 40 minutes. The suspension obtained by water bath stirring was centrifuged at 6000r / min for 10 minutes. The precipitate after centrifugation was collected and washed twice with deionized water and anhydrous ethanol, respectively. Then, it was vacuum dried in an oven at 60℃ for 6 hours. The dried sample is the NaCu5S3 catalyst.

[0048] Example 4

[0049] A method for preparing a KCu7S4 catalyst for the electroreduction of CO2 to formate comprises the following steps:

[0050] 3.52 g of potassium hydroxide was dissolved in 10 mL of ultrapure water and mixed evenly. The mixture was stirred at 500 rpm for 10 minutes to form a solution. Then, 1 mmol of copper chloride, 4 mmol of sodium sulfide nonahydrate, and 1 mL of hydrazine hydrate were added to the container sequentially. The container was then placed in an 80 °C water bath and stirred at 500 rpm for 1 hour. The suspension obtained by water bath stirring was centrifuged at 6000 rpm for 10 minutes. The precipitate was collected and washed twice with deionized water and anhydrous ethanol, respectively. Then, it was vacuum dried in an oven at 60 °C for 6 hours. The dried sample was the KCu7S4 catalyst.

[0051] Example 5

[0052] A method for preparing a KCu7S4 catalyst for the electroreduction of CO2 to formate comprises the following steps:

[0053] 3.52 g of potassium hydroxide was dissolved in 10 mL of ultrapure water and mixed evenly. The mixture was stirred at 500 rpm for 10 minutes to form a solution. Then, 1 mmol of copper chloride, 4 mmol of sodium sulfide nonahydrate, and 1 mL of hydrazine hydrate were added to the container sequentially. The container was then placed in a 70 °C water bath and stirred at 500 rpm for 50 minutes. The suspension obtained by water bath stirring was centrifuged at 6000 rpm for 10 minutes. The precipitate was collected and washed twice with deionized water and anhydrous ethanol, respectively. Then, it was vacuum dried in an oven at 60 °C for 6 hours. The dried sample is the KCu7S4 catalyst.

[0054] Example 6

[0055] A method for preparing a KCu7S4 catalyst for the electroreduction of CO2 to formate comprises the following steps:

[0056] 3.52 g of potassium hydroxide was dissolved in 10 mL of ultrapure water and mixed evenly. The mixture was stirred at 500 rpm for 10 minutes to form a solution. Then, 1 mmol of copper chloride, 4 mmol of sodium sulfide nonahydrate, and 1 mL of hydrazine hydrate were added to the container sequentially. The container was then placed in a 60 °C water bath and stirred at 500 rpm for 40 minutes. The suspension obtained by water bath stirring was centrifuged at 6000 rpm for 10 minutes. The precipitate was collected and washed twice with deionized water and anhydrous ethanol, respectively. Then, it was vacuum dried in an oven at 60 °C for 6 hours. The dried sample was the KCu7S4 catalyst.

[0057] Example 7

[0058] A method for preparing an RbCu7S4 catalyst for the electroreduction of CO2 to formate comprises the following steps:

[0059] 4 g of rubidium hydroxide was dissolved in 10 mL of ultrapure water and mixed evenly. The mixture was stirred at 500 r / min for 10 minutes to form a solution. Then, 2 mmol of copper chloride, 8 mmol of sodium sulfide nonahydrate and 2 mL of hydrazine hydrate were added to the container in sequence. The container was then placed in an 80 °C water bath and stirred at 500 r / min for 1 hour. The suspension obtained by water bath stirring was centrifuged at 6000 r / min for 10 minutes. The spongy precipitate after centrifugation was washed twice with deionized water and anhydrous ethanol, and then vacuum dried in an oven at 60 °C for 6 hours. The dried sample is the RbCu7S4 catalyst.

[0060] Example 8

[0061] A method for preparing an RbCu7S4 catalyst for the electroreduction of CO2 to formate comprises the following steps:

[0062] 4 g of rubidium hydroxide was dissolved in 10 mL of ultrapure water and mixed evenly. The mixture was stirred at 500 r / min for 10 minutes to form a solution. Then, 2 mmol of copper chloride, 8 mmol of sodium sulfide nonahydrate and 2 mL of hydrazine hydrate were added to the container in sequence. The container was then placed in a 70 °C water bath and stirred at 500 r / min for 50 minutes. The suspension obtained by water bath stirring was centrifuged at 6000 r / min for 10 minutes. The spongy precipitate after centrifugation was taken and washed twice with deionized water and anhydrous ethanol, respectively. Then, it was vacuum dried in an oven at 60 °C for 6 hours. The dried sample is the RbCu7S4 catalyst.

[0063] Example 9

[0064] A method for preparing an RbCu7S4 catalyst for the electroreduction of CO2 to formate comprises the following steps:

[0065] 4 g of rubidium hydroxide was dissolved in 10 mL of ultrapure water and mixed evenly. The mixture was stirred at 500 r / min for 10 minutes to form a solution. Then, 2 mmol of copper chloride, 8 mmol of sodium sulfide nonahydrate and 2 mL of hydrazine hydrate were added to the container in sequence. The container was then placed in a 60 °C water bath and stirred at 500 r / min for 40 minutes. The suspension obtained by water bath stirring was centrifuged at 6000 r / min for 10 minutes. The spongy precipitate after centrifugation was washed twice with deionized water and anhydrous ethanol, and then vacuum dried in an oven at 60 °C for 6 hours. The dried sample is the RbCu7S4 catalyst.

[0066] Comparative Example 1

[0067] A method for preparing a Cu2S catalyst for the electroreduction of CO2 to formate comprises the following steps:

[0068] 0.3 mmol copper nanowires, 0.9 mmol 2-mercaptoethanol, and 10 mL anhydrous ethanol were stirred at 500 rpm for 5 minutes to mix evenly. 0.3 mmol sulfur powder was added to the mixture, and the mixture was stirred at 500 rpm for 24 hours. The black suspension was then centrifuged at 6000 rpm for 10 minutes. The black precipitate was collected, washed twice with deionized water and anhydrous ethanol, and then vacuum dried in an oven at 60 °C for 4 hours. The dried sample was the Cu2S catalyst.

[0069] Application Example 1

[0070] To further illustrate the performance of the NaCu5S3 / KCu7S4 / RbCu7S4 catalysts provided in Examples 1-9 for the electrocatalytic reduction of CO2 to formate, the CO2 electroreduction performance of the NaCu5S3 / KCu7S4 / RbCu7S4 catalysts obtained in Examples 1-9 and the Cu2S catalyst obtained in Comparative Example 1 was tested in an H-type electrolytic cell, including the following steps:

[0071] 1. Preparation of working electrode

[0072] 10 mg of each of the NaCu5S3 / KCu7S4 / RbCu7S4 catalysts prepared in Examples 1-9 and the Cu2S catalyst prepared in Comparative Example 1 were weighed and dispersed in 1 mL of ethanol solution (containing 50 μL Nafion), and the catalyst ink was obtained by sonication for 30 min. 60 μL of the ink was drop-coated onto a glassy carbon electrode and dried to serve as the working electrode.

[0073] 2. Electrochemical performance testing and product detection

[0074] The working electrode prepared in step 1 was placed in an H-type electrolytic cell (0.1M KHCO3 as electrolyte). A platinum sheet was used as the counter electrode of the H-type electrolytic cell, and a saturated silver / silver chloride electrode was used as the reference electrode. The electrochemical performance of the electrode was tested using an electrochemical workstation. Before the test, CO2 gas (30 sccm) was introduced for 1 hour to saturate the solution. Electrolysis was performed for 1 hour in a potential range of -0.6V to -1.4V (relative to the reversible hydrogen electrode). The gas phase products were detected by gas chromatography, and the Faraday efficiency of the gas phase products was calculated using formula (1). The liquid phase products were detected by nuclear magnetic resonance, and the Faraday efficiency of the liquid phase products was calculated using formula (2).

[0075] from Figure 1 It can be seen that both the comparative and the ternary copper-based catalysts with added alkali metal elements have rod-shaped structures with a length of about ten micrometers.

[0076] and from Figure 2 It is evident that the ternary copper-based catalyst with added alkali metal elements exhibits higher formic acid Faraday efficiency and higher selectivity for formic acid compared to the Cu2S catalyst.

[0077] Application Example 2

[0078] To further illustrate the performance of the NaCu5S3 / KCu7S4 / RbCu7S4 catalysts provided in Examples 1-9 for the electrocatalytic reduction of CO2 to formate, the CO2 electroreduction performance of the NaCu5S3 / KCu7S4 / RbCu7S4 catalysts obtained in Examples 1-9 and the Cu2S catalyst obtained in Comparative Example 1 was tested in a flow electrolyzer, including the following steps:

[0079] 1. Preparation of working electrode

[0080] 10 mg of the NaCu5S3 / KCu7S4 / RbCu7S4 catalyst prepared in Examples 1-9 and the Cu2S catalyst prepared in Comparative Example 1 were dispersed in 1 mL of ethanol solution (containing 50 μL Nafion), and the catalyst ink was obtained by sonication for 30 min. This ink was then drop-coated or spray-coated onto carbon paper and dried to obtain the working electrode of the electrolytic cell. The catalyst ink loading on the carbon paper was 1 mg cm³. -2 .

[0081] 2. Electrochemical performance testing and product detection

[0082] The carbon paper working electrode prepared in step 1 was placed in a flow electrolytic cell, and the electrochemical performance of the catalyst was tested using an electrochemical workstation. 1M KOH solution was used as the electrolyte, a nickel mesh as the counter electrode, and a saturated silver / silver chloride electrode as the reference electrode. The CO2 gas flow rate was constant at 30 sccm. Electrolysis was performed for 1 hour in the potential range of -0.6V to -1.4V (relative to the reversible hydrogen electrode). The gas phase products were detected by gas chromatography, and the Faraday efficiency of the gas phase products was calculated using formula (1). The liquid phase products were detected by nuclear magnetic resonance, and the Faraday efficiency of the liquid phase products was calculated using formula (2).

[0083] from Figure 3 As shown in Figure 4, the ternary copper-based catalyst with added alkali metal elements exhibits a higher formic acid Faradaic efficiency and greater selectivity compared to Cu₂S. Furthermore, the Faradaic efficiency of RbCu₇S₄ for formic acid exceeds 90% at -1.0V (relative to the reversible hydrogen electrode). Simultaneously, the ternary copper-based catalyst with added alkali metal elements demonstrates a higher formic acid partial current density compared to the Cu₂S catalyst, making it more suitable for industrial applications.

[0084] Application Example 3

[0085] To further illustrate the excellent stability of the NaCu5S3 / KCu7S4 / RbCu7S4 catalyst for CO2 reduction provided by this invention, given that the RbCu7S4 catalyst exhibits the highest selectivity for formate at -1.0V (relative to the reversible hydrogen electrode), the stability of the CO2 reduction reaction is tested at -1.0V (relative to the reversible hydrogen electrode) using the RbCu7S4 catalyst provided in Example 7 and the Cu2S catalyst obtained in Comparative Example 1 as examples.

[0086] The Faraday efficiency of the formate product was calculated using formula (2) based on the current density recorded by the electrochemical workstation and the formate concentration obtained by nuclear magnetic resonance. Figure 5As can be seen, during the 72-hour test, the Faradaic efficiency of RbCu7S4 for formate remained at around 90% with no significant degradation, which is far longer than the stable operating time of most reported catalysts in a flowing electrolyzer. In contrast, the Faradaic efficiency of Cu2S for formate rapidly declined within 4 hours.

[0087] The formula for calculating Faraday efficiency in application examples 1-3 is as follows:

[0088] FE=(z·v·V·F·P0) / (I·R·T0) (1)

[0089] FE=z·n·F / Q (2)

[0090] Where z is the charge transfer per mole of gaseous product; v (Vol%) is the volume concentration of gaseous product in the gas chromatographic tail gas; V (mL min⁻¹) is the gas flow rate; and F is a constant 96485 Cmol. -1 I(A) is the total current density; Q(C) is the amount of charge accumulated during the reaction; R, P0, and T0 are constants, where R = 8.314 J mol -1 K -1 ;P0=1.01×105Pa; T0=298.15K.

[0091] It is worth noting that the current density of Cu2S dropped abruptly after 4 hours of electrolysis due to severe flooding. The main reason for this was that the KHCO3 crystal salt generated by the reaction of CO2 and KOH blocked the flow channel, causing the catalytic reaction to be unable to continue.

[0092] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. The application of a ternary copper-based catalyst in the electroreduction of CO2 to produce formate, characterized in that, The chemical formula of the catalyst is NaCu5S3 or RbCu7S4. The preparation method of the catalyst specifically includes the following steps: sodium hydroxide is dissolved in ultrapure water and mixed evenly; copper chloride, sodium sulfide nonahydrate and hydrazine hydrate are added sequentially under magnetic stirring and stirred thoroughly until dissolved; then the mixture is kept warm under water bath conditions, the product is collected by centrifugation, and then washed and dried to obtain the ternary copper-based catalyst, namely NaCu5S3 catalyst. Alternatively, dissolve rubidium hydroxide in ultrapure water and mix thoroughly. Then, add copper chloride, sodium sulfide nonahydrate, and hydrazine hydrate in sequence under magnetic stirring, and stir thoroughly until dissolved. The product was then kept in a water bath for 1 hour, collected by centrifugation, and then washed and dried to obtain the ternary copper-based catalyst, namely RbCu7S4 catalyst.

2. The application of the ternary copper-based catalyst according to claim 1 in the CO2 electroreduction formate production reaction, characterized in that, The molar ratio of sodium hydroxide / rubidium hydroxide to copper chloride, sodium sulfide nonahydrate, and hydrazine hydrate is 1~10:1~10:1~20:1~5.

3. The application of the ternary copper-based catalyst according to claim 1 in the electroreduction of CO2 to produce formate, characterized in that, The water bath temperature is 50~90℃, and the holding time is 1 hour.

4. The application of the ternary copper-based catalyst according to claim 1 in the electroreduction of CO2 to produce formate, characterized in that, The specific washing and drying operations are as follows: the product collected by centrifugation is washed 1-2 times with deionized water and anhydrous ethanol, and then vacuum dried at 40-60°C for 4-8 hours.

5. The application of the ternary copper-based catalyst according to claim 1 in the electroreduction of CO2 to produce formate, characterized in that, An electrode was prepared using the aforementioned ternary copper-based catalyst, and then the electrochemical reduction performance of the electrode was tested. The preparation of the electrode included the following steps: The ternary copper-based catalyst was weighed and dispersed in an ethanol solution containing Nafion to obtain catalyst ink; then the catalyst ink was drop-coated / sprayed onto the electrode / carbon paper and dried.

6. The application of the ternary copper-based catalyst according to claim 5 in the electroreduction of CO2 to produce formate, characterized in that, If it is an H-type electrolytic cell, the catalyst ink is drop-coated onto a glassy carbon electrode and dried to obtain the working electrode; If it is a flowing electrolytic cell, the catalyst ink is drop-coated or sprayed onto carbon paper and dried to obtain the working electrode.

7. The application of the ternary copper-based catalyst according to claim 6 in the electroreduction of CO2 to produce formate, characterized in that, The mass / volume ratio of the ternary copper-based catalyst, Nafion solution, and ethanol solution is 10 mg: 50 μL: 1 mL. Furthermore, the catalyst ink loading on the glassy carbon electrode is 0.5~1 mg / cm³. -2 The catalyst ink loading on the carbon paper is 1~3 mg / cm³. -2 .

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