CN110015721B

CN110015721B - Method for producing electrocatalytic coatings using plasma

Info

Publication number: CN110015721B
Application number: CN201910334198.XA
Authority: CN
Inventors: 辛煜; 马晓萍; 王柯童; 何奕
Original assignee: Wuxi Little Swan Electric Co Ltd
Current assignee: Wuxi Little Swan Electric Co Ltd
Priority date: 2019-04-24
Filing date: 2019-04-24
Publication date: 2021-12-21
Anticipated expiration: 2039-04-24
Also published as: CN110015721A

Abstract

The invention relates to a method for preparing an electrocatalytic coating by using plasma, which comprises the following steps: forming a precursor coating on the surface of a substrate by using a precursor solution of an electrocatalytic material, and then baking the precursor coating by adopting plasma jet, wherein the baking temperature is 100-400 ℃; repeating the steps for multiple times to form a composite coating with the thickness of 5-20 mu m on the surface of the substrate; and then sintering the composite coating by adopting plasma jet, wherein the sintering temperature is 400-600 ℃, and the electrocatalytic coating is formed on the surface of the substrate. The invention not only obviously reduces the cracking behavior of the coating surface and lightens the electrochemical oxidation process of the substrate, but also enhances the catalytic activity of the electrocatalytic material.

Description

Method for producing electrocatalytic coatings using plasma

Technical Field

The invention relates to the field of electrochemistry, in particular to a method for preparing an electrocatalytic coating by using plasma.

Background

In the electrochemical field, hydroxyl radicals have a very strong oxidizing power, which is inferior to fluorine gas in its ability to acquire electrons. The hydroxyl free radical reacts with organic matters such as microorganism and bacteria, and can be oxidized into inorganic substances such as CO harmless to human body₂，H₂O, inorganic salts, and the like. Therefore, the hydroxyl free radical can be used for degrading organic polluted wastewater, purifying, disinfecting and sterilizing tap water and the like.

Among these electrocatalytic materials with promising application prospects, iridium-based oxide electrocatalytic materials are receiving much attention due to the characteristics of long operation time and high oxygen evolution reactivity. In these anode materials, other oxides, such as tantalum pentoxide, tin dioxide, cobalt dioxide, etc., are often incorporated as stabilizers to promote the electrocatalytic effect. It is well known that the active surface of an electrocatalytic material is determined by the surface topography of the oxide, which provides the surface activation sites for oxygen evolution reactions, as are the iridium oxide and the inactive oxide stabilizers.

Although the iridium-based oxide has the characteristics of high activity, corrosion resistance and long-lasting operation, the continuous operation of industrial production is restricted by some unstable factors and abnormal failure conditions in industrial application. The conventional preparation method of the electrocatalytic material is that after sand blasting treatment is carried out on the surface of a titanium substrate, a specific precursor solution is coated on the surface of the titanium substrate and baked in an oven for many times, and finally sintering treatment is carried out, so that the required coating performance is obtained. The conventional iridium-based oxide coating is prepared by high-temperature pyrolysis reaction after repeated painting and baking drying. Due to the pyrolysis of the halides, the recrystallization of the oxides and the difference in thermal expansion coefficient between the obtained oxides and the substrate, the surface of the prepared oxides usually exhibits a chap-like surface morphology with cracks of up to several microns in width. With this type of surface morphology, not only the titanium substrate is oxidized by the high temperature treatment, but also the electrolyte is easily penetrated through cracks during the electrochemical process to cause the electrochemical oxidation of the titanium substrate, which in turn causes the shedding and deactivation of the iridium-based oxide.

Disclosure of Invention

In order to solve the technical problems, the invention aims to provide a method for preparing an electrocatalytic coating by using plasma, which adopts plasma jet to replace the conventional thermal decomposition process and directly carries out thermal annealing and activation treatment on an electrocatalytic material precursor coating by using radio frequency plasma jet, thereby greatly reducing the cracking degree of the coating surface and enhancing the catalytic activity of an anode coating.

In order to achieve the purpose, the invention adopts the technical scheme that:

the invention provides a method for preparing an electrocatalytic coating by using plasma, which comprises the following steps:

(1) forming a precursor coating on the surface of the substrate by using a precursor solution of an electrocatalytic material, and then baking the precursor coating by using plasma jet, wherein the baking temperature is 100-;

(2) repeating the steps for multiple times to form a composite coating with the thickness of 5-20 mu m on the surface of the substrate; then sintering the composite coating by adopting the plasma jet, wherein the sintering temperature is 400-600 ℃ (preferably 500-600 ℃), and the sintering time is 1-30min (preferably 10-30min), namely forming the electrocatalytic coating on the surface of the substrate;

wherein, in the step (1) and the step (2), the gas for generating the plasma jet comprises oxygen.

Further, in step (1), the electrocatalytic material is iridium-based oxide, cobalt oxide, tantalum oxide, or ruthenium oxide. Preferably, the electrocatalytic material is an iridium-based oxide. More preferably, the electrocatalytic material is iridium cobalt oxide.

Further, in the step (1), the electrocatalytic material is iridium cobalt oxide, iridium tantalum oxide or iridium ruthenium oxide, and a precursor solution of the electrocatalytic material comprises chloroiridic acid, metal halide, citric acid and ethylene glycol; the metal halide is cobalt chloride, tantalum chloride or ruthenium chloride. The chloroiridic acid and the metal halide in the precursor solution are oxidized after being treated by the method of the invention to obtain an oxide which plays a role of a stabilizer.

Further, the mol ratio of the chloroiridic acid, the metal halide, the citric acid and the glycol is as follows: (0.1-0.5): (0.01-0.2): (0.3-0.7): (12-20).

Further, in the step (1), the substrate is made of titanium.

Further, repeating the step (1)6-20 times.

Further, in the step (1) and the step (2), the plasma jet is a plasma torch generated by a direct-current high-voltage arc, a plasma jet excited by radio frequency, a plasma generated by hollow cathode discharge or a plasma generated by dielectric barrier discharge. According to the actual situation, the proper plasma can be flexibly applied to the surface of the coating.

Further, in the step (1) and the step (2), the plasma jet is a radio-frequency excited plasma jet.

Further, the excitation frequency of the plasma jet is 1-13.56 MHz. Preferably, the excitation frequency of the plasma jet is 2-5 MHz.

Further, the plasma jet is generated under the condition that the vacuum degree is atmospheric pressure.

Further, in the step (1) and the step (2), the gas for generating the plasma jet is a mixed gas of oxygen and argon or compressed air.

Further, in step (1) and step (2), the frequency of the plasma jet can range from direct current to radio frequency, depending on whether the plasma jet has unique high temperature characteristics and highly chemically active characteristics of the plasma.

The invention uses an efficient plasma jet preparation method to carry out high-temperature annealing and activation on the surface of the electrocatalytic coating, thereby realizing the compact electrocatalytic coating surface, the efficient electrocatalytic property and the service life of the anode. On one hand, the high-temperature characteristic of the plasma is utilized to replace the traditional annealing process, electrons in the plasma jet can obtain enough energy from a strong electric field and elastically or inelastically collide with background gas molecules, so that the temperature of the plasma jet is generally high and the plasma jet can be used as a high-temperature rapid annealing tool. On the other hand, the catalytic performance of the material is promoted by active species in the plasma, such as oxygen radicals. The plasma jet has a large number of energetic reactive particles, such as oxygen atoms, hydroxyl radicals, etc., which are transported to the surface to promote chemical reactions at the surface of the material. The radio frequency plasma jet is acted on the surface of the precursor catalytic coating, the synergistic effect caused by the high-temperature quick annealing characteristic of the radio frequency plasma jet and the quick chemical reaction characteristic of the surface greatly shortens the surface treatment time of the catalytic oxide synthetic material, saves the time cost obviously, and enhances the electrocatalysis performance of the coating.

By the scheme, the invention at least has the following advantages:

the invention carries out plasma annealing and surface activation on the surface of the substrate coated with the precursor, and finally directly adopts plasma jet flow to carry out rapid sintering treatment, thereby replacing the conventional thermal baking and sintering process. The invention not only obviously reduces the cracking behavior of the surface of the coating and lightens the electrochemical oxidation process of the substrate, but also enhances the catalytic activity of the electrocatalytic material, thus being a novel preparation method with development potential and suitable for the processing of the electrocatalytic material.

The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical solutions of the present invention more clearly understood and to implement them in accordance with the contents of the description, the following detailed description is given with reference to the preferred embodiments of the present invention and the accompanying drawings.

Drawings

FIG. 1 is a schematic of a 2.0MHz excited RF plasma jet of the present invention;

FIG. 2 is a surface topography of different titanium sheet anode coatings selected by an electron microscope;

fig. 3 is the electrochemical performance test results of the anode coating prepared by the process.

Detailed Description

The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.

Example 1

As a preferred example, the invention takes the preparation of iridium cobalt oxide coating as an example, 2MHz excited radio frequency plasma jet is taken as a preparation tool to illustrate the preparation method of the electrocatalytic anode coating, and a series of experimental tests are carried out on the prepared anode coating to verify the effectiveness of the preparation method. The preparation of the iridium cobalt oxide coating by using the radio frequency plasma jet shown in figure 1 comprises the following main experimental steps:

1. processing the cut titanium sheet by using a conventional cleaning and surface treatment method, and air-drying for later use;

2. the plasma jet device excited by radio frequency is connected, the input gas is argon, the temperature of the argon plasma jet is higher, and the thermal annealing effect acting on the surface is more obvious; in order to enhance the high chemical activity of the plasma jet, a certain amount of oxygen is introduced into argon; or directly using compressed air as the reaction gas of the plasma. FIG. 1 is a schematic representation of a radio frequency excited plasma jet.

3. The precursor solution for preparing the iridium-cobalt oxide coating is a mixed solution formed by mixing chloroiridic acid, cobalt chloride, citric acid and ethylene glycol according to a certain molar ratio, wherein the molar ratio is as follows: (0.1-0.5): (0.01-0.2): (0.3-0.7): (12-20).

4. Manually coating the precursor solution of the iridium cobalt oxide coating on the surface of the titanium sheet, and baking the coated titanium sheet at a place with a temperature of about 200 ℃ below the plasma jet for about 1 minute.

5. Repeat step 4 6-20 times depending on the final desired coating thickness to be prepared.

6. And moving the baked titanium sheet to a place with the temperature about 500 ℃ below the plasma jet flow again for high-temperature sintering, wherein the time can be set to be 10-30 minutes. After high-temperature rapid sintering at 500 ℃, a nano composite coating with higher adhesive force and a thickness of about a few microns is formed on the surface of the titanium sheet. Citric acid and ethylene glycol in the coating are used as solvents to be volatilized in the atmosphere with high temperature and high chemical activity, chloroiridic acid and cobalt chloride form an oxide ceramic composite material tightly combined with a base material under the condition of high-temperature sintering, and the surface appearance is quite different from the surface characteristics of conventional high-temperature sintering.

The plasma jet can be a plasma torch generated by a direct-current high-voltage electric arc, can also be a plasma jet excited by radio frequency, can carry out plasma annealing and activation treatment on the surface of the catalytic coating by other devices such as hollow cathode discharge and dielectric barrier discharge, and can flexibly apply proper plasma to act on the surface of the coating according to actual conditions.

FIGS. 2a and 2 a' show the surface morphology of the iridium cobalt oxide coating after conventional high temperature sintering; it can be seen that the coating has a chapped surface, the length and width of the chapped slit exceed the size of a few microns, and the surface structure easily causes the electrolyte to penetrate into the surface of the titanium substrate, and an oxidized titanium oxide layer is formed under the electrochemical action, thereby causing the failure and even the peeling of the surface functional coating. Fig. 2b and 2 b' show the surface appearance of the iridium cobalt oxide coating after the plasma jet effect. As can be seen from the figure, the coating surface has only a few micro-crack structures, and obviously, the surface topography greatly prevents the penetration of electrolyte, thereby greatly reducing the electrochemical oxidation effect on the surface of the titanium sheet.

Testing at the electrochemical workstation will help understand the electrochemical performance of the coating in both annealing modes. FIG. 3(a) shows two different annealing methodsAnodic coating at 1mol/L H₂SO₄Cyclic voltammogram in solution. It is clear that the plasma jet annealed coated anode has a higher current density at the same voltage, which means that the plasma jet treated coated anode has better electrochemical properties. Fig. 3(b) is a result of a degradation rate test of a congo red solution under two different annealing modes, and the result shows that the anode subjected to plasma jet annealing treatment has better organic matter degradation capability.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, it should be noted that, for those skilled in the art, many modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.

Claims

1. A method of preparing an electrocatalytic coating using a plasma, comprising the steps of:

(1) forming a precursor coating on the surface of a substrate by using a precursor solution of an electrocatalytic material, and then baking the precursor coating by adopting plasma jet, wherein the baking temperature is 100-400 ℃, and the baking time is 60-180 s;

(2) repeating the steps for multiple times to form a composite coating with the thickness of 5-20 mu m on the surface of the substrate; then sintering the composite coating by adopting the plasma jet, wherein the sintering temperature is 400-600 ℃, and the sintering time is 1-30min, namely forming the electrocatalytic coating on the surface of the substrate;

2. The method of claim 1, wherein: in step (1), the electrocatalytic material is iridium-based oxide, cobalt oxide, tantalum oxide, or ruthenium oxide.

3. The method of claim 1, wherein: in the step (1), the electrocatalytic material is iridium cobalt oxide, iridium tantalum oxide or iridium ruthenium oxide, and a precursor solution of the electrocatalytic material comprises chloroiridic acid, metal halide, citric acid and ethylene glycol; the metal halide is cobalt chloride, tantalum chloride or ruthenium chloride.

4. The method of claim 3, wherein: the mol ratio of the chloroiridic acid to the metal halide to the citric acid to the ethylene glycol is as follows: (0.1-0.5): (0.01-0.2): (0.3-0.7): (12-20).

5. The method of claim 1, wherein: in the step (1), the substrate is made of titanium.

6. The method of claim 1, wherein: in the step (1) and the step (2), the plasma jet is a plasma torch generated by a direct-current high-voltage arc, a plasma jet excited by radio frequency, a plasma generated by hollow cathode discharge or a plasma generated by dielectric barrier discharge.

7. The method of claim 1, wherein: in the step (1) and the step (2), the plasma jet is a radio-frequency excited plasma jet.

8. The method of claim 7, wherein: the excitation frequency of the plasma jet is 1MHz-13.56 MHz.

9. The method of claim 1, wherein: the plasma jet is generated under atmospheric pressure conditions.

10. The method of claim 1, wherein: in the step (1) and the step (2), the gas for generating the plasma jet is a mixed gas of oxygen and argon or compressed air.