A copper-based nanocatalyst and its preparation method and application

Abstract

The present invention belongs to the technical field of electrocatalytic carbon dioxide reduction, and specifically relates to a copper-based nanocatalyst and a manufacturing method thereof and an application thereof in electrocatalytic CO2 production of ethanol. The present invention reconstructs an alkali metal copper-based halide perovskite material under in-situ CO2 reduction conditions to form a copper-based nanocatalyst with halogen anions and alkali metal cations co-modified on the surface of a Cu(200) or Cu(111) substrate. The co-modification of halogen anions and alkali metal cations can effectively inhibit hydrogen and one-carbon products (mainly including carbon monoxide and methane) at industrial current density, and can highly selectively promote the generation of ethanol products among two-carbon products. The raw materials of the present invention are widely available and inexpensive; and the preparation method is simple. The prepared highly active electrocatalyst can efficiently convert greenhouse gas CO2 into high-value-added ethanol products at industrial current density, and has broad application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of electrocatalytic carbon dioxide reduction, and specifically relates to a copper-based nanocatalyst and a preparation method thereof, and application thereof in electrocatalytic CO2 reduction to produce ethanol. Background Art

[0002] Since the Industrial Revolution, fossil fuels have been used in large quantities, and the emission of carbon dioxide (CO2) greenhouse gases has accelerated the process of global warming. Using clean electricity, under the action of copper-based catalysts, CO2 molecules and water can be effectively converted into small molecular chemicals or fuels at room temperature and pressure, such as carbon monoxide, formic acid, methane, methanol and other one-carbon products, ethylene, ethanol, acetic acid, propanol and other two-carbon and above products. At present, carbon monoxide, formic acid and ethylene have a selectivity (Faraday efficiency of more than 70%) and activity (current density of more than 1 A cm −2 ) have reached relatively high values. However, due to the competition between hydrogen, methane and ethylene at a higher overpotential, the activity of ethanol is currently less than 200 mA cm −2 .

[0003] It is reported that surface modification of halogen anions can effectively inhibit the formation of hydrogen and methane at high current density and promote carbon-carbon coupling. Adding alkali metal cations to the electrolyte has been reported to effectively improve the activity of CO2 reduction, but this method cannot effectively chemically adsorb the intermediates of CO2 reduction in the inner Helmholtz layer, so the effect is limited. The present invention screens alkali copper-based halide perovskite materials, reconstructs the metal Cu (200) or Cu (111) substrate surface to co-modify halogen anions and alkali metal cations under in-situ CO2 reduction conditions, and can simultaneously achieve selective exposure of the metal copper substrate crystal surface and modification of alkali metal cations anchored by halogen anions on the surface with chemical bonds, and can produce ethanol as the main product by highly selective electrocatalytic CO2 reduction at industrial current density, and the production steps are simple, which is convenient for large-scale utilization. Summary of the invention

[0004] The purpose of the present invention is to provide a copper-based nanocatalyst with simple process and convenient use, a method for preparing the same, and an application of the same in electrocatalytic CO2 reduction to produce ethanol.

[0005] The method for preparing the copper-based nanocatalyst provided by the present invention is to select a suitable alkali metal copper-based halide perovskite material, reconstruct it under in-situ CO2 reduction conditions, and form a catalyst in which the surface of the metal Cu (200) or Cu (111) substrate is co-modified with halogen anions and alkali metal cations. The specific steps are:

[0006] (1) Making an alkali copper-based halide perovskite material into a working electrode;

[0007] (2) According to the structure of different copper-based halide perovskite electrocatalysts, the valence bond strength between atoms and the ion reduction potential, in a flow cell electrolytic cell system, at room temperature (e.g., 25 °C) and atmospheric pressure (one standard atmosphere), appropriate in situ CO2 reduction conditions are selected, for example, at −0.6 to −6 A cm −2 Electrolysis is performed at a current density of 30 seconds or more, such as 30 seconds to 30 minutes, to obtain a reconstructed substrate with the (200) or (111) crystal plane of the metallic copper exposed as the main surface, and the surface is exposed by halogen anions (such as Cl − or F − ) chemically anchored alkali metal cations (such as Cs + or K + ) modified catalyst.

[0008] In the present invention, the alkali copper-based halide perovskite material is selected from Cs3Cu2Cl5, Cs2CuCl4, and KCuF3.

[0009] In the present invention, the exposed crystal surface of the metal Cu on the reconstructed copper substrate includes one or more of Cu(200) and Cu(111), and the halogen anions and alkali metal cations co-modified on the crystal surface are Cl − , F − , Cs + , K + One or more of .

[0010] In the present invention, the in-situ CO2 reduction condition preferably has a current density of −0.6 to −1 A cm −2 The preferred electrolysis time is 30 to 90 seconds.

[0011] The copper-based nanocatalyst prepared by the method of the present invention has excellent characteristics: compared with common polycrystalline copper, the highly exposed Cu (200) or Cu (111) crystal surface is more conducive to the adsorption of ethanol *C2 intermediates; compared with ordinary anion modification and adding alkali metal cations in the electrolyte, the surface anions formed by in-situ reconstruction are modified by chemically bonded alkali metal cations, which can react with various CO2 reduction intermediates, especially with negatively charged end groups such as O through electrostatic interaction in the inner Helmholtz layer. ẟ− , C ẟ− A strong chemical adsorption is formed, thereby increasing the concentration of key intermediates in the ethanol pathway. Therefore, it can be used for electrocatalytic CO2 reduction to ethanol at industrial current density.

[0012] The copper-based electrocatalyst prepared by the method is used for electrocatalytic CO2 reduction reaction to obtain ethanol as the main product. The preparation method under in-situ CO2 reduction conditions at industrial current density can not only obtain highly exposed Cu(200) or Cu(111) crystal faces, but also stably modify alkali metal cations anchored by halogen anions on the surface. The alkali metal cations anchored by chemical bonds on the catalyst surface can react with various CO2 reduction intermediates in the inner Helmholtz layer through electrostatic interactions, especially with negatively charged end groups such as O ẟ− , C ẟ− A strong chemical adsorption is formed, thereby increasing the concentration of key intermediates in the ethanol pathway. In the flow-type electrolytic cell, the partial current density of ethanol products can reach 400 mA cm −2 The corresponding Faraday efficiency is above 45%, which is one of the best values ​​currently reported internationally.

[0013] For the electrocatalytic CO2 reduction system, a KOH-based electrolyte is used.

[0014] In the present invention, a copper-based catalyst with metal Cu(200) or Cu(111) exposed as the main part and halogen anions and alkali metal cations co-modified on the surface formed by reconstructing alkali copper-based halide perovskite under in-situ CO2 reduction conditions can be effectively electrocatalyzed to reduce CO2 to produce ethanol. The manufacturing method of the electrocatalyst is simple to operate, stable and controllable. The electrocatalytic reduction of CO2 to high-value-added ethanol products has the characteristics of high selectivity and activity, is suitable for large-scale production, is of great significance in the research of electrocatalytic CO2 reduction, and also has good application prospects in the field of new energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The present invention is a flow chart showing the reconstruction of Cs3Cu2Cl5 in Example 1 under in-situ CO2 reduction conditions to obtain a copper-based nanocatalyst Cu(200)-Cl-Cs), and its use in electrocatalytic CO2 reduction to produce an ethanol product.

[0016] Figure 2 The total current of Cs3Cu2Cl5 in Example 1 is −1 A cm −2 X-ray diffraction patterns (a) and morphology and high-resolution transmission electron microscopy images (b) of Cu(200)-Cl-Cs obtained under different electrolysis times.

[0017] Figure 3 is the relative ratio of Cu(200) to Cu(111) of Cu(200)-Cl-Cs obtained from Cs3Cu2Cl5 at different total current densities in Example 1.

[0018] Figure 4The total current of Cs3Cu2Cl5 in Example 1 is −1 A cm −2 Photoelectron spectrum of Cu(200)-Cl-Cs obtained under.

[0019] Figure 5 The total current of Cs3Cu2Cl5 in Example 1 is −1 A cm −2 Faradaic efficiency of different products of the Cu(200)-Cl-Cs electrocatalyst obtained under the conditions of KOH as electrolyte in a flow-type electrolytic cell.

[0020] Figure 6 Schematic diagram of the process of reconstructing KCuF3 under in-situ CO2 reduction conditions in Example 2 to obtain the copper-based nanocatalyst Cu(111)-FK.

[0021] Figure 7 For KCuF3 in Example 2, the total current is −800 mA cm −2 X-ray diffraction pattern of Cu(111)-FK obtained under (a), spherical aberration-corrected high-angle annular dark-field scanning transmission electron microscopy image (b) and the intensity of the corresponding line position (c).

[0022] Figure 8 This is the photoelectron spectrum of Cu(111)-FK in Example 2.

[0023] Fig. 9 is the Faraday efficiency of different products of the Cu(111)-FK electrocatalyst in the flow-type electrolytic cell (KOH as the electrolyte) in Example 2. DETAILED DESCRIPTION

[0024] The present invention is further described below through specific embodiments and drawings.

[0025] Example 1

[0026] The alkali copper-based halide perovskite material Cs3Cu2Cl5 was reconstructed under in situ CO2 reduction conditions to obtain a copper-based catalyst. The metal Cu substrate was mainly exposed to Cu(200), and the surface was co-modified with chloride anions and cesium cations. The copper-based catalyst was recorded as Cu(200)-Cl-Cs. It was then used for electrocatalytic CO2 reduction to produce ethanol products. Figure 1 .

[0027] First, using wet chemical method, CuCl and CsCl were used as copper source and cesium source respectively, in a mixed solvent of formic acid and dimethyl sulfoxide, under argon protection at 120℃ to obtain Cs3Cu2Cl5. After X-ray diffraction analysis, its phase corresponds to the standard Cs3Cu2Cl5 card (JCPDS#00-024-0247) ( Figure 2(a)). When the total current is −1 A cm −2 After 10 seconds of CO2 electrolysis, the diffraction peaks of Cs3Cu2Cl5 disappeared, and a strong peak appeared at 50.4°, corresponding to the (200) crystal plane of metallic copper (JCPDS#03-065-9026). ° , 30.6 ° and 28.3 ° Three weak diffraction peaks were observed, corresponding to the (111) crystal plane of metallic copper, and the (212) and (230) crystal planes of Cs2CuCl4 (JCPDS#01-071-0901). When the electrolysis time was greater than 30 seconds, the diffraction peaks of Cs2CuCl4 disappeared, indicating that it was completely converted into metallic copper (denoted as Cu(200)-Cl-Cs). Transmission electron microscopy and high-resolution transmission electron microscopy at different electrolysis times also showed that the initial Cs3Cu2Cl5 nanospheres gradually transitioned to metallic copper nanocubes ( Figure 2 (b)). In addition, when a larger electrolysis current is applied, the Cu(200) / Cu(111) ratio in Cu(200)-Cl-Cs reconstructed by Cs3Cu2Cl5 also increases ( Figure 3 ) Cu(200)-Cl-Cs Cs 3 d and Cl 2 p The photoelectron spectrum observed two main peaks at 723.4 and 196.7 eV respectively ( Figure 4 ), corresponding to Cs 3 d 5 / 2 and Cl 2 p 3 / 2 , suggesting the existence of Cu−Cl and Cs−Cl chemical bonds on the surface.

[0028] Finally, the Cu(200)-Cl-Cs material was used as an electrocatalyst and 1M KOH was used as the electrolyte to test the CO2 reduction performance in a flow-type electrolytic cell. −2 Cu(200)-Cl-Cs exhibited a Faradaic efficiency of 35.7 ± 1.6% for ethanol ( Figure 5 ), which is the highest among all the reduction products, and the corresponding partial current density is 357 ± 16 mA cm −2 .

[0029] Example 2

[0030] The alkali copper-based halide perovskite material KCuF3 was reconstructed under in-situ CO2 reduction conditions. The metal Cu substrate was mainly exposed to Cu(111), and the surface was co-modified with fluoride anions and potassium cations. The copper-based catalyst was recorded as Cu(111)-FK. It was then used for electrocatalytic CO2 reduction to produce ethanol products ( Figure 6 ).

[0031] First, a wet chemical method was used to directly react CuCl2·2H2O and KF as copper source and fluorine source respectively in anhydrous methanol solvent to obtain KCuF3 after washing and filtration. After X-ray diffraction analysis, its phase corresponded to the standard KCuF3 card (JCPDS#01-073-0232) ( Figure 7 (a)). At a total current of −800 mA cm −2 After 100 coulombs (125 seconds) of CO2 electrolysis under the condition of 43.4 ° A weak diffraction peak appeared, corresponding to the (111) crystal plane of metallic copper (JCPDS#03-065-9026). Spherical aberration-corrected high-angle annular dark-field scanning transmission electron microscopy showed a typical hexagonal lattice of Cu(111) ( Figure 7 (b)). The average Cu-Cu distance shown on lines 1 and 2 is 0.240 nm, which corresponds to the Cu(111) lattice spacing. times ( Figure 7 (c)) further illustrates the formation of Cu(111) crystal plane (denoted as Cu(111)-FK). K2 p and F1 s The photoelectron spectrum observed a main peak and two weak peaks at 292.5, 686.4 and 683.8 eV, respectively ( Figure 8 ), corresponding to K2 p 3 / 2 , Cu−F and K−F chemical bonds.

[0032] Finally, the performance of CO2 reduction was tested in a flow-type electrolytic cell using Cu(111)-FK as an electrocatalyst and 1M KOH as an electrolyte. −2 Cu(111)-FK exhibited a Faradaic efficiency of 52.9 ± 3.7% for ethanol ( Fig. 9 ), which is the highest among all the reduction products, and the corresponding partial current density is 423 ± 30 mA cm −2 .

Claims

1. A method for producing a copper-based nanocatalyst, characterized in that: The alkali copper-based halide perovskite material is reconstructed under in-situ CO2 reduction conditions to form a copper-based nanocatalyst with halogen anions and alkali metal cations co-modified on the surface of a metal Cu(200) or Cu(111) substrate. The specific steps are as follows: (1) Making an alkali copper-based halide perovskite material into a working electrode; (2) According to the structure, bond strength and ion reduction potential of different copper-based halide perovskite electrocatalysts, in situ CO2 reduction conditions were selected in a flow cell electrolytic cell system at room temperature and atmospheric pressure: −0.6 to −6 A cm -2 Electrolysis is performed at a current density of 30 seconds or more to obtain a reconstructed substrate with the (200) or (111) crystal plane of metallic copper exposed as the main surface, and a copper-based nanocatalyst modified with alkali metal cations chemically anchored by halogen anions on the surface; The alkali copper-based halide perovskite material is selected from Cs3Cu2Cl5, Cs2CuCl4, and KCuF3.

2. The method for producing a copper-based nanocatalyst according to claim 1, characterized in that: The copper substrate obtained by the reconstruction has an exposed crystal face of metal Cu, including one or more of Cu(200) and Cu(111), and the halogen anions and alkali metal cations co-modified on the crystal face are Cl − , F − , Cs + , K + One or more of .

3. The copper-based nanocatalyst obtained by the production method according to claim 1 or 2.

4. Use of the copper-based nanocatalyst as claimed in claim 3 in electrocatalytic CO2 reduction to produce ethanol.

5. The use according to claim 4, characterized in that: The electrocatalytic CO2 reduction system uses a KOH-based electrolyte.

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