Catalyst and catalytic electrode for electrochemical reduction of CO2 and preparation method of catalyst and catalytic electrode

Abstract

The preparation method comprises the following steps: in a three-electrode working system comprising a working electrode, an auxiliary electrode and a reference electrode, mixing graphene oxide slurry and a metal salt solution to serve as an electroplating solution, and scanning by adopting constant voltage to obtain an electroplating solution; and performing electrochemical deposition on a working electrode to obtain the catalyst formed by metal-supported reduced graphene oxide. The graphene oxide and the high-valence metal ions are reduced and deposited on the working electrode plate in one step by utilizing an electrochemical deposition method, the preparation method is simple, and the obtained catalyst and the catalytic electrode covered by the catalyst have good electrocatalytic activity.

Description

Technical Field

[0001] The present invention relates to the technical field of CO2 electrocatalysis, and in particular to a catalyst for CO2 electrochemical reduction, a catalytic electrode and a preparation method thereof. Background Art

[0002] The electrochemical catalytic reduction of CO2 can be achieved under mild conditions to produce high-value-added chemical products or small molecule fuels such as carbon monoxide and formic acid. At the same time, this process can be directly and effectively combined with renewable energy sources (such as wind energy, tidal energy, and solar energy) without the need for other auxiliary energy sources, achieving true recycling of carbon resources, and is considered to be the most promising CO2 conversion method. However, the development of CO2 electrocatalytic reduction technology is still facing a series of challenges: slow kinetics, high overpotential of the reaction, competitive participation of the hydrogen evolution reaction leading to low selectivity and conversion efficiency, and easy deactivation of electrode materials. In order to solve the above problems, the development of efficient and stable electrochemical catalysts has become the key to research in this field.

[0003] Metal catalysts based on graphene have excellent catalytic performance due to their large surface area, easy contact with reactants, and high surface atomic utilization, and have shown great potential in heterogeneous catalytic reactions. At present, graphene-based CO2 electrocatalyst materials are usually prepared by thermochemical methods, such as Bi-rGO catalysts and SnP-rGO catalysts, which have defects such as complex processes, high costs, and many precursors that may be toxic and harmful. For example, the strong reducing agent NaBH4 needs to be added during the preparation of SnP-rGO catalysts, which has the defect of being explosive; the precursor Bi(NO3)·3.5H2O(DCDA) in the preparation of Bi-rGO catalysts is a toxic substance. Summary of the invention

[0004] In view of this, the main purpose of the present invention is to provide a catalyst, a catalytic electrode and a preparation method thereof for the electrochemical reduction of CO2. The electrochemical deposition method is used to reduce graphene oxide and high-valent metal ions and deposit them on a working electrode plate in one step. The method is simple, and the obtained catalyst and the catalytic electrode covered by the catalyst have good electrocatalytic activity. The catalyst preparation process does not require heating, calcination or addition of a strong reducing agent, and the process is non-toxic and harmless.

[0005] To achieve the above-mentioned object of the invention, the first aspect of the present invention provides a method for preparing a catalyst for electrochemical reduction of CO2, comprising:

[0006] In a three-electrode working system including a working electrode, an auxiliary electrode and a reference electrode, graphene oxide slurry is mixed with a metal salt solution as an electroplating solution, and a constant voltage scan is adopted to electrochemically deposit a catalyst formed by metal-supported reduced graphene oxide on the working electrode.

[0007] Furthermore, the working electrode is a carbon-based material electrode, the auxiliary electrode is a platinum sheet, and the reference electrode is a reference electrode suitable for use under neutral or acidic conditions.

[0008] Furthermore, the concentrations of the graphene oxide slurry and the metal salt solution are 0.05-0.1 mg / ml and 0.01-0.05 mol / L, respectively.

[0009] Furthermore, the constant voltage scanning includes: when silver / silver chloride is used as a reference electrode, the constant voltage range is -0.1V to -0.3V, preferably -0.1V to -0.2V, and the scanning time is 60s to 240s, preferably 60s to 120s.

[0010] Furthermore, the mixing of the graphene oxide slurry with the metal salt solution comprises: adding the metal salt solution dropwise into the graphene oxide slurry; preferably, adding an acid solution into the graphene oxide slurry to a pH value of 1.

[0011] Furthermore, the metal salt solution is selected from one or more of a silver nitrate solution, a copper sulfate solution, a nickel nitrate solution, a cobalt sulfate solution, and a copper chloride solution.

[0012] Furthermore, the method further comprises: activating the working electrode before use, wherein the activation comprises: cleaning the working electrode, activating it in dilute sulfuric acid by electrochemical cyclic voltammetry, and cleaning it again.

[0013] Furthermore, the method further comprises: after the electrochemical deposition is completed, cleaning and drying the working electrode to obtain a catalyst formed by metal-supported reduced graphene oxide.

[0014] The second aspect of the present invention provides a catalyst for electrochemical reduction of CO2 prepared by the above preparation method.

[0015] The third aspect of the present invention provides a catalytic electrode formed by covering a working electrode with a catalyst for electrochemical reduction of CO2 obtained by the above preparation method.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] In the present invention, in a three-electrode working system, graphene oxide slurry and metal salt solution are mixed as electroplating solution, constant voltage scanning is adopted, and electrochemical deposition is performed on the working electrode to obtain a catalyst-covered catalytic electrode formed by metal-supported reduced graphene oxide. The present invention adopts graphene oxide as an electro-deposition precursor. Graphene oxide is obviously fragmented relative to graphene, and has many defect sites, which is conducive to the embedding of nanoparticles; in the formed catalyst, nano-metal active sites are embedded in the defect sites of reduced graphene oxide as active sites, and the surrounding reduced graphene oxide provides a large number of electrons, which is conducive to the generation of multi-carbon products; electrons can be quickly introduced into the nano-metal catalyst through reduced graphene oxide, so that the prepared catalyst has good electrocatalytic activity. At the same time, the present invention adopts constant voltage scanning, which can reduce the agglomeration of active components (after metal particles are deposited at a specific voltage, it is not conducive to re-deposition at the same voltage), thereby improving the dispersibility of active metal nanoparticles, which is conducive to catalytic reactions.

[0018] The electrochemical deposition method of the present invention can prepare the catalyst as a catalytic electrode in situ on the surface of the working electrode, providing a catalyst and catalytic electrode preparation and regeneration method with potential large-scale application value for CO2 electrocatalytic technology. Therefore, the present invention utilizes the electrochemical deposition method to reduce and deposit graphene oxide and high-valent metal ions on the working electrode plate in one step, which is simple to operate, does not require heating and roasting during the preparation process, does not require the addition of a strong reducing agent, and is non-toxic and harmless, energy-saving and environmentally friendly.

[0019] Other features and advantages of the present invention will be described in detail through the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention but do not constitute a limitation of the present invention. In the accompanying drawings:

[0021] Figure 1 This is a transmission electron microscope image of the catalyst material (copper metal-supported reduced graphene oxide) on the surface of the catalytic electrode prepared in Example 1 of the present invention.

[0022] Figure 2 Schematic diagram of the distribution of reduction products and current density under a specific reduction voltage in Example 1 of the present invention.

[0023] Figure 3 Schematic diagram of the distribution of reduction products and current density under a specific reduction voltage in Example 2 of the present invention.

[0024] Figure 4 Schematic diagram of the distribution of reduction products and current density of Example 3 of the present invention at a specific reduction voltage.

[0025] Figure 5 Schematic diagram of the distribution of reduction products and current density of Example 4 of the present invention at a specific reduction voltage.

[0026] Figure 6 Schematic diagram of the distribution of reduction products and current density of Example 5 of the present invention at a specific reduction voltage.

[0027] Figure 7 Schematic diagram of the reduction product distribution and current density of Comparative Example 1 at a specific reduction voltage.

[0028] Figure 8 Schematic diagram of the reduction product distribution and current density of Comparative Example 2 at a specific reduction voltage.

[0029] Fig. 9 Schematic diagram of the reduction product distribution and current density of Comparative Example 3 at a specific reduction voltage. DETAILED DESCRIPTION

[0030] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0031] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0032] Furthermore, the terms “first”, “second”, etc. are used for descriptive purposes only and are not to be understood as indicating or implying relative importance.

[0033] Unless otherwise specified, the materials used in the embodiments of the present invention can be obtained from commercial channels.

[0034] The first aspect of the present invention provides a method for preparing a catalyst for electrochemical reduction of CO2, comprising:

[0035] In a three-electrode working system including a working electrode, an auxiliary electrode and a reference electrode, graphene oxide slurry is mixed with a metal salt solution as an electroplating solution, and a constant voltage scan is adopted to electrochemically deposit a catalyst formed by metal-supported reduced graphene oxide on the working electrode.

[0036] The reaction process in the electrochemical deposition process of the present invention includes metal electrodeposition (Formula 1) and graphene oxide reduction (Formula 2)

[0037] Me n+ +ne - =Me (1)

[0038]

[0039] In some embodiments, the working electrode is selected from a carbon-based material electrode, such as glassy carbon sheet, carbon paper, carbon cloth, etc., the auxiliary electrode is a platinum sheet, and the reference electrode can be selected from a reference electrode under neutral or acidic conditions, such as saturated calomel, silver / silver chloride, mercuric sulfate, etc.

[0040] In some embodiments, the graphene oxide slurry is prepared by using an existing Hummer method or an improved Hummer method, or is obtained by external purchase.

[0041] In some embodiments, the concentrations of the graphene oxide slurry and the metal salt solution are 0.05-0.1 mg / ml and 0.01-0.05 mol / L, respectively. For example, the concentration of the graphene oxide slurry is 0.05 mg / ml, 0.06 mg / ml, 0.07 mg / ml, 0.08 mg / ml, 0.09 mg / ml, 0.1 mg / ml, etc., and the concentration of the metal salt solution is 0.01 mol / L, 0.015 mol / L, 0.02 mol / L, 0.025 mol / L, 0.03 mol / L, 0.035 mol / L, 0.04 mol / L, 0.045 mol / L, 0.05 mol / L, etc.

[0042] Further, the constant voltage scanning includes: when silver / silver chloride is used as a reference electrode, the constant voltage range is -0.1V to -0.3V, such as -0.1V, -0.15V, -0.2V, -0.25V, -0.3V, etc., and the scanning time is 60s to 240s, such as 60s, 80s, 100s, 120s, 140s, 160s, 180s, 200s, 220s, 240s, etc. Depending on the electrolyte, the present invention can adopt different scanning voltages and scanning times, and the constant voltage range is preferably -0.1V to -0.2V, and the scanning time is preferably 60s to 120s.

[0043] In the present invention, by setting different concentration ratios of graphene oxide and metal salt within the above range, and applying the reduction voltage for a certain period of time, the composition and loading amount of the catalyst are controlled, and the physical properties of the synthesized catalyst are characterized to ensure uniform dispersion of metal nanoparticles and reduction of defect sites of graphene oxide.

[0044] In the present invention, the mixing of the graphene oxide slurry with the metal salt solution specifically includes, in some embodiments, adding the metal salt solution dropwise to the graphene oxide slurry, preferably, adding an acid solution (such as sulfuric acid, nitric acid, hydrochloric acid, etc.) at the same time to pH = 1, so as to increase the ionic strength of the electroplating solution and promote catalyst formation.

[0045] In some embodiments, the metal salt solution is selected from one or more of copper sulfate solution, silver nitrate solution, nickel nitrate solution, copper chloride solution, cobalt sulfate solution, etc. The "metal salt" herein can be a single metal salt or a mixture of multiple metal salts.

[0046] Preferably, the method further comprises: activating the working electrode before use, the purpose of the activation being to remove impurities and dirt on the surface of the electrode through repeated activation so that the electrode reaches an optimal working state.

[0047] In some embodiments, the activation comprises: cleaning the working electrode, activating it in dilute sulfuric acid by electrochemical cyclic voltammetry, and cleaning it again.

[0048] In other embodiments, the activation includes: polishing the working electrode, followed by cleaning and drying; for example, polishing may be performed using aluminum oxide powder, cleaning may be performed using an organic solvent such as water and acetone, and preferably drying under a nitrogen atmosphere.

[0049] Preferably, the method further comprises: after the electrochemical deposition is completed, cleaning and drying the working electrode to obtain a catalyst formed by metal-supported reduced graphene oxide. In some embodiments, the cleaning comprises placing the working electrode in deionized water and ethanol for a period of time under ultrasound. Preferably, the working electrode is dried under a nitrogen atmosphere.

[0050] The second aspect of the present invention provides a catalyst for electrochemical reduction of CO2 prepared by the above preparation method.

[0051] The third aspect of the present invention provides a catalytic electrode formed by covering a working electrode with a catalyst for electrochemical reduction of CO2 obtained by the above preparation method.

[0052] The present invention is further described below with detailed exemplary embodiments, but these embodiments do not constitute any limitation to the present invention.

[0053] Example 1

[0054] The method for preparing a catalytic electrode for electrochemical reduction of CO2 in this embodiment comprises:

[0055] 1) The glassy carbon electrode was polished with 1 μm and 0.05 μm alumina powder.

[0056] 2) The polished electrode sheet was cleaned with deionized water and acetone, respectively, and dried in a nitrogen atmosphere to serve as a working electrode.

[0057] 3) Build a three-electrode system: the working electrode is a glassy carbon electrode, the auxiliary electrode is a platinum sheet, and the reference electrode is silver / silver chloride.

[0058] 4) In 100 mL of 0.1 mg / mL graphene oxide solution (Gt01221, Angxing New Carbon Material Co., Ltd.), copper sulfate solution was added dropwise until the concentration of copper sulfate was 0.01 M, and sulfuric acid solution was added dropwise until the pH of the system was 1.

[0059] 5) Scan with constant voltage, the scanning parameters are: -0.2V, 120s.

[0060] 6) The working electrode was taken out, ultrasonicated in 100 mL of deionized water and ethanol for 5 minutes respectively, and dried in a nitrogen atmosphere to obtain a working electrode covered with a copper / graphene catalyst. Figure 1 The transmission electron microscope image of copper metal-supported reduced graphene oxide shows that the copper-supported reduced graphene oxide prepared by the present invention has copper nanoparticles embedded in the defect edges of graphene fragments, which not only realizes the nanoscale of the copper particles, but also ensures the contact between the graphene fragments and the copper particles, which is beneficial to the flow of electrons and the release of active sites, thereby kinetically providing sufficient electrons, which is beneficial to the improvement of current density and the generation of multi-carbon products (for example, 12 electrons are required to generate 1 C2H5OH, and 20 electrons are required to generate 1 C3H8).

[0061] Example 2

[0062] The difference from Example 1 is that the type of metal salt is changed to silver nitrate, a silver nitrate solution is added dropwise until the concentration of the silver nitrate is 0.015 M, and a nitric acid solution is added dropwise until the pH is 1.

[0063] Example 3

[0064] The difference from Example 1 is that the scanning voltage is changed to -0.3V, and the scanning time is changed to 180s.

[0065] Example 4

[0066] The difference from Example 1 is that: in 100 mL of 0.05 mg / mL graphene oxide solution, copper sulfate solution is added dropwise to a concentration of 0.05 M copper sulfate, and sulfuric acid solution is added dropwise to a pH value of 1.

[0067] Example 5

[0068] The difference from Example 1 is that the scanning voltage is changed to -0.1V, and the scanning time is changed to 60s.

[0069] Comparative Example 1

[0070] The difference from Example 1 is that cyclic voltammetry electrodeposition is adopted, and the specific parameters are 0.0 to -1.2 V (vs. Ag / AgCl), a scan rate of 20 mV / s, and 5 cycles.

[0071] Comparative Example 2

[0072] The difference from Example 2 is that linear voltammetry electrodeposition is adopted, with specific parameters of 0.0 to -1.2 V (vs. Ag / AgCl), scan rate of 20 mV / s, and 5 cycles.

[0073] Comparative Example 3

[0074] The difference from Example 1 is that the concentrations of the graphene oxide solution and the copper sulfate solution are 0.1 mg / ml and 0.2 mol / L, respectively.

[0075] The catalytic performance characterization method in the above Examples 1-5 and Comparative Examples 1-3 is:

[0076] The electrocatalytic performance of CO2 was characterized in a three-electrode H-type electrolytic cell. The prepared glassy carbon electrode was 1cm×1cm and used as the working electrode. The platinum electrode was 2cm×2cm and used as the reference electrode. Nafion117 was used as a proton exchange membrane to separate the cathode chamber and the anode chamber. 50 ml of 1.0M potassium bicarbonate solution saturated with CO2 was added to the cathode chamber and the anode chamber respectively. During the experiment, CO2 gas was introduced in real time to maintain the saturated state at a flow rate of 10 mL / min. The product was analyzed by gas chromatography. The gas was sampled every 15 minutes to determine the gas product. Every 30 minutes, 5 ml of the cathode chamber solution was extracted, placed in a headspace device, and then passed through a gas chromatograph for analysis. All experiments were carried out at room temperature and pressure. The characterization results are shown in Figure 2-Figure 9 .

[0077] Specifically, Figure 2 and Figure 3 The reduction product distribution and current density of Example 1 and Example 2 at a specific reduction voltage are shown respectively. The difference lies in the different metal catalysts used. The use of copper-based catalysts can generate C2+ hydrocarbons, while the use of silver-based catalysts only generates CO products.

[0078] Specifically, Figure 4It is the distribution of reduction products and current density of Example 3 at a specific reduction voltage. Compared with Example 1, the difference is that the scanning voltage is lower and the scanning time is longer, but it can be seen that the current density and Faraday efficiency are reduced, and the propylene product can be measured in Example 1, but not in Example 3. It can be seen that there is an optimized scanning voltage and scanning time. Taking the glassy carbon electrode in the present invention as the electrode substrate, the more optimized voltage is -0.1V to -0.2V, and the scanning time is 60s-120s. The better scanning voltage and scanning time can generate evenly dispersed copper nanoparticles inlaid with reduced graphene oxide defect edges. For different electrode substrates, the corresponding scanning voltage and scanning time should be determined.

[0079] Specifically, Figure 5 and Figure 6 The reduction product distribution and current density of Example 4 and Example 5 at a specific reduction voltage are shown in Figure 4 and Figure 5, respectively. Within the preferred implementation range of the present invention, the current density of carbon dioxide reduction can be greater than 50 mA / cm under certain conditions. 2 , and the Faradaic efficiency of valuable electrochemical products is higher than 50%.

[0080] Specifically, Figure 7 The reduction product distribution and current density at a specific reduction voltage of Comparative Example 1 are shown. Compared with Example 1, due to the different electrodeposition methods, the agglomeration of the active groups of the catalyst in the comparative example is more obvious, resulting in a larger copper particle size at the active site, which is not conducive to the catalytic reaction to generate C2+ products, and greatly reduces the Faraday efficiency and current density.

[0081] Specifically, Figure 8 The reduction product distribution and current density of Comparative Example 2 at a specific reduction voltage are shown. Compared with Example 2, both use a silver-based catalyst. Although the reduction product is the same and the Faraday efficiency is not significantly reduced, the current density is greatly reduced, indicating that the catalyst preparation method of the present invention is more conducive to improving the catalyst activity. By comparison, it can also be seen that due to the different catalytic metal salts, the distribution of the reduction product will be different, but the preparation method of the present invention is helpful to improve the activity of the same metal-based catalyst.

[0082] Specifically, Fig. 9 It is the distribution of reduction products and current density of Example 3 at a specific reduction voltage. Due to the inappropriate concentration ratio of graphene oxide and copper salt, graphene oxide has agglomeration and precipitation phenomenon during implementation, and a large amount of copper is deposited on the electrode surface without corresponding reduced graphene oxide loading, resulting in the carbon dioxide electrocatalytic characterization result being close to that of copper alone, and the product is mainly relatively low-value methane, supplemented by ethylene.

[0083] Obviously, the above embodiments of the present invention are merely examples for clearly explaining the present invention, and are not intended to limit the implementation methods of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to list all implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are within the spirit scope of the present invention.

Claims

1. A method for preparing a catalyst for electrochemical reduction of CO2, characterized in that: include: In a three-electrode working system including a working electrode, an auxiliary electrode and a reference electrode, graphene oxide slurry is mixed with a metal salt solution as an electroplating solution, and a constant voltage scan is adopted to electrochemically deposit a catalyst formed by metal-supported reduced graphene oxide on the working electrode.

2. The method for preparing the catalyst according to claim 1, characterized in that: The working electrode is a carbon-based material electrode, the auxiliary electrode is a platinum sheet, and the reference electrode is a reference electrode suitable for use under neutral or acidic conditions.

3. The method for preparing the catalyst according to claim 1, characterized in that: The concentration of the graphene oxide slurry is 0.05-0.1 mg / ml, and the concentration of the metal salt solution is 0.01-0.05 mol / L.

4. The method for preparing the catalyst according to claim 1, characterized in that: The constant voltage scanning includes: when silver / silver chloride is used as a reference electrode, the constant voltage range is -0.1V to -0.3V, preferably -0.1V to -0.2V, and the scanning time is 60s to 240s, preferably 60s to 120s.

5. The method for preparing the catalyst according to claim 1, characterized in that: The mixing of the graphene oxide slurry and the metal salt solution comprises: dripping the metal salt solution into the graphene oxide slurry; preferably, adding an acid solution into the graphene oxide slurry.

6. The method for preparing the catalyst according to claim 1, characterized in that: The metal salt solution is selected from one or more of a silver nitrate solution, a copper sulfate solution, a nickel nitrate solution, a cobalt sulfate solution, and a copper chloride solution.

7. The method for preparing the catalyst according to any one of claims 1 to 6, characterized in that: The method further comprises: activating the working electrode before use, wherein the activation comprises: cleaning the working electrode, activating it in dilute sulfuric acid by electrochemical cyclic voltammetry, and cleaning it again.

8. The method for preparing the catalyst according to claims 1-7, characterized in that: The method further comprises: after the electrochemical deposition is completed, cleaning and drying the working electrode to obtain a catalyst formed by metal-supported reduced graphene oxide.

9. A catalyst for electrochemical reduction of CO2 prepared by the preparation method according to any one of claims 1 to 8.

10. A catalytic electrode formed by coating a working electrode with a catalyst for electrochemical reduction of CO2 obtained by the preparation method according to any one of claims 1 to 8.

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