A method for preparing a single-atom catalyst based on a cathodic corrosion phenomenon

Abstract

The application discloses a method for preparing a single-atom catalyst based on a cathode corrosion phenomenon, and comprises the following steps: S1, constructing an electrochemical two-electrode or three-electrode system, wherein a metal nanoparticle is loaded on a working electrode; an electrolyte is an alkali or salt solution of an alkali metal; S2, adding a carrier powder; S3, applying a constant negative potential to the working electrode; S4, filtering the carrier powder material and cleaning and drying, so as to obtain a metal single-atom catalyst. The metal particles on the electrode surface are induced to undergo cathode corrosion by the constant negative potential, and the metal single atoms falling off can be captured by the carrier and anchored on a suitable site, so that the metal single-atom catalyst is prepared. The application does not involve harsh conditions such as high temperature and vacuum, has the advantages of simple operation, easy scale-up, low energy consumption and short time consumption, is suitable for the preparation of a single-atom electrocatalyst, provides a good pre-basic foundation for the application of the single-atom catalyst in the fields of water electrolysis and fuel cells, and is very suitable for popularization and application.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of single-atom catalysts, and particularly relates to a method for preparing a single-atom catalyst based on a cathode corrosion phenomenon. BACKGROUND

[0002] The statements in this section merely provide background information related to the present disclosure and can not constitute the prior art.

[0003] In recent years, single-atom catalysts (SACs) have become an important research direction in the fields of catalysis and material science due to their high atomic utilization efficiency and unique coordination structure, and exhibit high catalytic activity in catalytic reactions such as hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reaction. However, the controllable preparation of metal single atoms is extremely challenging due to their high surface energy and poor stability. Existing preparation methods can be generally divided into "bottom-up" and "top-down" strategies. The "top-down" strategy is based on the dissociation of metal-metal bonds in metal bulk or metal nanoparticles, and then dispersing the metal atoms on a suitable support. This strategy has the advantages of easy availability of raw materials and easy large-scale preparation. At present, the "top-down" strategy mainly relies on the migration of metal atoms in metal nanoparticles supported on the carrier at high temperature, which has the problems of high energy consumption, the need for a large amount of inert gas, and high requirements for the thermal stability of the carrier. Therefore, it is necessary to develop other "top-down" preparation methods under mild conditions.

[0004] The cathode corrosion phenomenon refers to the phenomenon that metal atoms on the surface of a metal obtain electrons under a high negative potential, and generate stable metastable metal anions (Zintl phase) near the electrode. Based on this phenomenon, there are currently methods for using alternating current to etch pure metals or alloys into a solution in a water system or an ionic liquid system, and using polymers or carbon materials to stabilize them, thereby preparing corresponding metal or alloy nanoparticles. However, this method is only suitable for preparing nanoparticles and is difficult to be used for preparing metal single atoms with high surface energy. We previously reported a method for converting metal nanoparticles on the surface of a carbon electrode into single-atom catalysts. However, this conversion only occurs on the surface of the cathode, has high requirements for the mechanical strength of the electrode, and is difficult to prepare powder catalysts that are more commonly used, and is also difficult to be prepared on a large scale. Therefore, it is of great significance to develop a "top-down" preparation method for single-atom catalysts based on the cathode corrosion phenomenon, which can etch and convert metal nanoparticles on the surface of an electrode into a solution. SUMMARY

[0005] The present application aims to solve the problems that single-atom catalysts cannot be prepared by the current cathode corrosion technology, or the single-atom catalysts obtained by corrosion can only exist on the surface of the original electrode, and it is difficult to prepare powder single-atom catalysts on a large scale. The present application provides a method for preparing a single-atom catalyst based on a cathode corrosion phenomenon, which has the advantages of mild preparation conditions, short time, low energy consumption, and easy large-scale preparation.

[0006] The technical solution of the present application is as follows:

[0007] A method for preparing a single-atom catalyst based on cathodic corrosion phenomenon, comprising the following steps:

[0008] S1: Constructing an electrochemical two-electrode or three-electrode system, wherein the working electrode carries metal nanoparticles; the electrolyte is an alkali or salt solution of an alkali metal;

[0009] S2: Adding carrier powder to the electrolyte and stirring uniformly;

[0010] S3: Applying a constant negative potential to the working electrode and continuously stirring;

[0011] S4: Filtering the carrier powder material and washing and drying to obtain a metal single-atom catalyst.

[0012] According to a preferred embodiment, in step S1, the metal nanoparticles are nanoparticles of platinum, palladium, gold, silver, iridium or copper.

[0013] Preferably, the duration in step S3 is at least 10 min.

[0014] According to a preferred embodiment, in step S1, the electrolyte can be any one of hydroxide, sulfate or carbonate of an alkali metal (lithium, sodium, potassium).

[0015] According to a preferred embodiment, in step S2, the carrier powder material is any one of nitrogen-doped carbon powder, sulfur-doped carbon powder, nitrogen-doped carbon nanotube or molybdenum disulfide powder.

[0016] According to a preferred embodiment, in step S2, the amount of carrier powder material added is 1-20 mg / mL.

[0017] According to a preferred embodiment, in step S3, the constant negative potential applied is between -2 and -8 V.

[0018] Preferably, the constant negative potential applied is between -5 and -8 V.

[0019] Compared with the existing technology, the present application has the following beneficial effects:

[0020] 1. A method for preparing a single-atom catalyst based on cathodic corrosion phenomenon, compared with the common high-temperature migration method for preparing a single-atom catalyst, the preparation process is carried out in an aqueous system at room temperature, does not involve high-temperature treatment and special atmosphere, has a short treatment time and lower energy consumption. Moreover, since many metals can undergo cathodic corrosion phenomenon, the present application has good universality and can be used for the preparation of single-atom catalysts of high-melting-point metals.

[0021] 2. A method for preparing a single-atom catalyst based on cathodic corrosion phenomenon, wherein, compared with a cathodic corrosion method based on alternating current, the method of the present application realizes slow etching and release of metal atoms by using a mild direct current treatment with a relatively low negative potential, so that a metal single-atom catalyst can be obtained in a controllable manner; compared with a method for preparing a single-atom catalyst electrode by cathodic corrosion, the method of the present application introduces carrier powder into an electrolyte to capture and anchor metal atoms produced by etching, so that the amount of metal loss during the preparation process is lower, and the metal loading density is more controllable, and large-scale preparation can be easily realized by adjusting the amount of powder added. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is a flowchart of the present application.

[0023] Figure 2 It is (a) a scanning electron microscope image of a platinum particle-carbon cloth precursor before electrochemical treatment, (b) a scanning electron microscope image of a platinum particle-carbon cloth precursor after electrochemical treatment for 30 minutes, (c) a transmission electron microscope image of nitrogen-doped carbon powder before electrochemical treatment, and (d) a spherical aberration-corrected transmission electron microscope image of a platinum single-atom catalyst / nitrogen-doped carbon powder after electrochemical treatment in Example 1 of the present application.

[0024] Figure 3 It is (a) a polarization curve graph, (b) a mass specific activity curve graph, (c) a Tafel curve graph, and (d) an accelerated degradation test result of a platinum single-atom catalyst / nitrogen-doped carbon powder catalytic hydrogen evolution reaction in Example 1 of the present application.

[0025] Figure 4 It is (a) a spherical aberration-corrected transmission electron microscope image of a platinum single-atom catalyst / nitrogen-doped carbon powder after electrochemical treatment in Example 2 of the present application, (b) a spherical aberration-corrected transmission electron microscope image of a palladium single-atom catalyst / nitrogen-doped carbon powder after electrochemical treatment in Example 3 of the present application, (c) a spherical aberration-corrected transmission electron microscope image of an iridium single-atom catalyst / nitrogen-doped carbon powder after electrochemical treatment in Example 4 of the present application, and (d) a spherical aberration-corrected transmission electron microscope image of a platinum single-atom catalyst / nitrogen-doped carbon nanotube after electrochemical treatment in Example 5 of the present application. DETAILED DESCRIPTION

[0026] The features and properties of the present application will be further described in detail below in conjunction with examples. In the following examples, the test methods are conventional methods unless otherwise specified. The test materials used in the following examples are commercially available unless otherwise specified.

[0027] The application provides a method for preparing a single-atom catalyst based on a cathodic corrosion phenomenon. By applying a high negative potential, atoms in metal particles on the surface of an electrode are etched and migrated to a solution, and are captured and anchored by a suitable carrier powder. The method has the advantages of simple operation, low energy consumption and being applicable to large-scale preparation. The process of the application mainly includes constructing an electrolysis system and inducing cathodic corrosion of metal particles under a high negative potential, as shown in Figure 1 .

[0028] First, an electrolytic cell system is constructed. An electrode loaded with metal particles is used as a working electrode to construct a three-electrode system or a two-electrode system. An alkali or salt solution of an alkali metal is selected as an electrolyte, and a suitable amount of carrier powder is added and stirred uniformly. The electrode loaded with metal particles can be selected from various carbon-loaded metal particle electrodes. The requirement for the electrode substrate is to remain stable under a high negative potential. The loading of metal particles can be selected from chemical reduction, electrodeposition and the like, and the types can be nanoparticles of platinum, palladium, gold, silver, iridium, copper, nickel, iron, cobalt and the like. The alkali or salt solution of an alkali metal can be a solution of hydroxide, sulfate, carbonate and the like of an alkali metal such as lithium, sodium, potassium and the like. The carrier powder should provide the required defect sites for anchoring the metal single atoms to be loaded, and materials such as nitrogen-doped carbon powder, sulfur-doped carbon powder, nitrogen-doped carbon nanotubes, molybdenum disulfide powder and the like can be selected. Considering the product uniformity and work efficiency requirements, the amount of carrier powder added can be 1-20 mg / mL.

[0029] Then, cathodic corrosion of the metal is induced under a negative potential, so that the metal atoms migrate to the solution area and are captured and anchored by the carrier. After a period of time, the metal particles on the surface of the electrode are basically eliminated, and metal single atom sites appear on the surface of the carrier in the solution. The applied negative potential is direct current, and the potential range is relatively mild to ensure slow release of the metal atoms and avoid the generation of metal nanoparticle impurities in the product. During the electrochemical treatment process, the solution is kept in a stirred state to ensure that the carrier powder can well access the area near the surface of the electrode and capture the etched and migrated metal atoms.

[0030] Example 1

[0031] The single-atom catalyst is prepared according to the following method:

[0032] S1: Carbon paper (4×2.5 cm 2 ) is electrodeposited in a 0.01 mol / L chloroplatinic acid solution using -0.3 V (vs. silver / silver chloride electrode), and a carbon paper loaded with platinum nanoparticles self-supporting electrode is obtained. A three-electrode system is composed of the electrode as a working electrode, a graphite rod as a counter electrode and mercury / mercury oxide as a reference electrode. A 5 mol / L potassium hydroxide solution is used as an electrolyte.

[0033] S2: Nitrogen-doped carbon powder is added to 20 mL of electrolyte at 10 mg / mL and stirred uniformly;

[0034] S3: Apply a constant negative potential of -5V to the working electrode and maintain it for 30 minutes while continuously stirring;

[0035] S4: Filter the nitrogen-doped carbon powder material, clean and dry it to obtain the platinum single-atom / nitrogen-doped carbon powder catalyst.

[0036] Depend on Figure 2 As can be seen, in the platinum nanoparticle-carbon paper electrode, the platinum particle size is around 500 nm, and the size distribution is uneven. After electrochemical treatment for 30 min, the platinum size significantly decreased to around 30 nm, indicating the occurrence of cathodic corrosion. Figure 2 b). By Figure 2 As can be seen from c, the surface of the nitrogen-doped carbon powder support does not contain metal particles or atoms. After 30 min of electrochemical treatment, the platinum single atoms detached from the electrode surface are captured and anchored by the nitrogen-doped carbon powder, producing a large number of uniformly distributed platinum single atoms. Figure 2 d).

[0037] The prepared platinum single-atom / nitrogen-doped carbon powder catalyst was then supported on the surface of a glassy carbon electrode and used for hydrogen evolution reaction catalysis. The results are as follows: Figure 3 As shown, it can be observed that this catalyst at 10 mA cm⁻¹ -2 At a current density of [value missing], the overpotential is only 0.024V, which is superior to that of platinum-carbon catalyst (0.051V) and nitrogen-doped carbon powder support (0.365V). Figure 3 a) Its specific activity at –0.05V reaches 5.89 A mg. Pt -1 It is superior to platinum-carbon catalyst (0.21 mg). Pt -1 ()( Figure 3 b). The Tafel slope of the platinum single-atom / nitrogen-doped carbon powder catalyst is 29.7 mV dec. -1 It is also superior to platinum-carbon catalysts (31.3 mV dec). -1 ) and nitrogen-doped carbon powder support (165mV dec -1 ()( Figure 3 c). Furthermore, the polarization curves of the platinum single-atom / nitrogen-doped carbon powder catalyst remained essentially unchanged before and after 5000 accelerated degradation cycles, indicating its good stability. Figure 3 d).

[0038] Example 2

[0039] S1: Place the carbon paper (10×5cm) 2) in 0.01 mol / L chloroplatinic acid solution using -0.3 V (vs. silver / silver chloride electrode) to obtain a carbon paper supported platinum nanoparticle self-supported electrode, and a three-electrode system was formed with the electrode as the working electrode, a graphite rod as the counter electrode, and mercury / mercury oxide as the reference electrode. A 5 mol / L potassium hydroxide solution was used as the electrolyte.

[0040] S2: Nitrogen-doped carbon powder was added to 200 mL of electrolyte at 10 mg / mL and stirred uniformly;

[0041] S3: A constant negative potential of -5 V was applied to the working electrode for 30 min, and stirring was continued;

[0042] S4: The nitrogen-doped carbon powder material was filtered, washed, and dried to obtain a platinum monatomic / nitrogen-doped carbon powder catalyst.

[0043] As Figure 4 a can be seen, after the carrier amount is increased, the prepared platinum catalyst is still monatomic dispersion, and electrochemical tests also show that the performance of the gram-level prepared monatomic catalyst is basically consistent with that of the milligram-level product.

[0044] Example 3

[0045] S1: Carbon paper (4 x 2.5 cm 2 ) in 0.01 mol / L chloroplatinic acid solution using -0.3 V (vs. silver / silver chloride electrode) to obtain a carbon paper supported platinum nanoparticle self-supported electrode, and a three-electrode system was formed with the electrode as the working electrode, a graphite rod as the counter electrode, and mercury / mercury oxide as the reference electrode. A 5 mol / L potassium hydroxide solution was used as the electrolyte.

[0046] S2: Nitrogen-doped carbon powder was added to 200 mL of electrolyte at 10 mg / mL and stirred uniformly;

[0047] S3: A constant negative potential of -5 V was applied to the working electrode for 30 min, and stirring was continued;

[0048] S4: The nitrogen-doped carbon powder material was filtered, washed, and dried to obtain a platinum monatomic / nitrogen-doped carbon powder catalyst.

[0049] As Figure 4 b can be seen, the prepared palladium catalyst is still monatomic dispersion.

[0050] Example 4

[0051] S1: Carbon paper (4 x 2.5 cm 2)A carbon paper supported iridium nanoparticle self-supported electrode was obtained by electrodeposition in 0.01 mol / L chloro iridic acid solution using -0.3 V (vs. silver / silver chloride electrode). A three-electrode system was formed with the electrode as the working electrode, a graphite rod as the counter electrode, and mercury / mercury oxide as the reference electrode. A 5 mol / L potassium hydroxide solution was used as the electrolyte.

[0052] S2: Nitrogen-doped carbon powder was added to 200 mL of electrolyte at 10 mg / mL and stirred uniformly;

[0053] S3: A constant negative potential of -5 V was applied to the working electrode for 30 min, and stirring was continued;

[0054] S4: The nitrogen-doped carbon powder material was filtered, washed, and dried to obtain an iridium monatomic / nitrogen-doped carbon powder catalyst.

[0055] As Figure 4 cIt can be seen that the prepared iridium catalyst is still monatomic dispersion.

[0056] As can be seen from Examples 3 and 4, the cathodic corrosion method can also be used to prepare palladium, iridium, and other noble metal monatomic catalysts.

[0057] Example 5

[0058] S1: Carbon paper (4 x 2.5 cm 2 ) was electrodeposited in 0.01 mol / L chloro platinum acid solution using -0.3 V (vs. silver / silver chloride electrode) to obtain a carbon paper supported platinum nanoparticle self-supported electrode. A three-electrode system was formed with the electrode as the working electrode, a graphite rod as the counter electrode, and mercury / mercury oxide as the reference electrode. A 5 mol / L potassium hydroxide solution was used as the electrolyte.

[0059] S2: Nitrogen-doped nanotubes were added to 20 mL of electrolyte at 10 mg / mL and stirred uniformly;

[0060] S3: A constant negative potential of -5 V was applied to the working electrode for 30 min, and stirring was continued;

[0061] S4: The nitrogen-doped nanotube material was filtered, washed, and dried to obtain a platinum monatomic / nitrogen-doped carbon powder catalyst.

[0062] As Figure 4 dIt can be seen that the use of nitrogen-doped carbon nanotube carriers can also obtain monodispersed platinum monatomic catalysts. This indicates that powder carriers with suitable anchor sites can be used in the cathodic corrosion method for preparing monatomic catalysts.

[0063] The above embodiments only express the specific implementation of the present application, which is described in more detail and specifically, but cannot be understood as a limitation to the protection scope of the present application. It should be noted that for those skilled in the art, without departing from the technical concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application.

Claims

1. A method for preparing a single-atom catalyst based on a cathodic corrosion phenomenon, characterized by, The method comprises the following steps: S1: constructing an electrochemical two-electrode or three-electrode system, wherein the working electrode carries metal nanoparticles; the electrolyte is an alkali or salt solution of an alkali metal; the metal nanoparticles are nanoparticles of platinum, palladium, gold, silver, iridium, copper, nickel, iron or cobalt; S2: adding carrier powder to the electrolyte and stirring uniformly; the carrier powder material is nitrogen-doped carbon powder, sulfur-doped carbon powder, nitrogen-doped carbon nanotube or molybdenum disulfide powder; the amount of the carrier powder material added is 1-20 mg / mL; S3: applying a constant negative potential to the working electrode and continuously stirring; the constant negative potential applied is between -2 and -8 V; S4: filtering the carrier powder material and washing and drying, to obtain a metal monatomic catalyst.

2. The method of claim 1, wherein the single-atom catalyst is prepared based on a cathodic corrosion phenomenon. In step S1, the electrolyte is one of hydroxide, sulfate and carbonate of an alkali metal.

3. The method of claim 2, wherein the single-atom catalyst is prepared based on a cathodic corrosion phenomenon. The alkali metal is any one of lithium, sodium and potassium.

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