CN118878022A - A highly robust self-supporting three-dimensional porous anode and its preparation method and application - Google Patents

Abstract

The present invention relates to a highly robust self-supporting three-dimensional porous anode and a preparation method and application thereof. The anode is prepared by pressing and heat treatment processes based on electrocatalytic active substances and using engineering fibers as pore-forming agents. The highly robust self-supporting three-dimensional porous anode is obtained by a simple process, and can efficiently, quickly and stably electrocatalytically oxidize and remove organic pollutants, which is conducive to large-scale production and application in the industry.

Description

A highly robust self-supporting three-dimensional porous anode and its preparation method and application

Technical Field

The invention relates to an anode and a preparation method and application thereof, and belongs to the field of electrocatalytic oxidation.

Background Art

In the process of electrocatalytic oxidation to remove persistent organic pollutants, the performance of the anode catalytic electrode determines the oxidation removal effect of pollutants. At present, there are two preparation methods based on electrocatalytic active material powder anode: a planar structure anode coated with a flat substrate powder catalyst and a self-supporting three-dimensional structure anode sintered by pressing the powder into a tablet. Compared with the planar structure anode, the self-supporting three-dimensional anode has the advantages of simple composition, uniform structure, and rich porosity, which is more conducive to the rapid and stable electrochemical oxidation reaction. In the preparation process of the self-supporting three-dimensional anode, the use of pore-forming agents can form pores inside and on the surface of the self-supporting three-dimensional anode, increase the specific surface area of the self-supporting three-dimensional anode and the number of exposed active sites, thereby accelerating the migration and oxidative degradation of pollutants in the pores. The pyrolysis temperature not only affects the presence of pore-forming agents and binders in the final material, but also affects the sintering effect between the particles of the electrocatalytic active material. Therefore, the selection of pore-forming agents and pyrolysis temperature has an important influence on the structure and performance of the self-supporting three-dimensional anode finally formed.

Currently, commonly used pore-forming agents include ammonium carbonate, ammonium bicarbonate, carbon fiber, starch, etc. However, the composition of ammonium carbonate and ammonium bicarbonate is relatively complex; the decomposition temperature of carbon fiber is high, and it is difficult to completely remove it in the low-temperature pyrolysis process; such pore-forming agents are prone to residual elements to form impurities that affect electrode performance. Starch is prone to swelling, resulting in poor pressing and molding effects, and the electrode sheets obtained by pyrolysis are incomplete or even broken, which is not conducive to large-scale promotion and application.

Engineering fiber is a micron-sized synthetic fiber with polypropylene as the main component. It is often used in construction projects. It is low-cost, widely available, and easy to obtain. It only contains carbon and hydrogen elements, has a low thermal decomposition temperature, and does not react with water. There are no reports on its application in the field of fine synthesis.

Summary of the invention

The purpose of the present invention is to provide a highly robust self-supporting three-dimensional porous anode with high mechanical strength and degradation performance, and a preparation method and application thereof. Low-cost and easily available engineering fibers are selected as new pore-forming agents, and a porous anode with high mechanical strength and high robustness is obtained through a simple synthesis process, which solves the problems of low mechanical strength, low degradation efficiency and poor stability of existing three-dimensional porous anodes, and is more conducive to wide application in actual production.

According to a first aspect of the present invention, the present invention provides a highly robust self-supporting three-dimensional porous anode, characterized in that it comprises the following steps:

Step 1: uniformly mixing the electrocatalytic active material, the pore-forming agent and the binder to obtain a mixed powder;

Step 2: Extruding the mixed powder obtained in step 1 into a desired shape to obtain a three-dimensional anode precursor;

Step 3: Pyrolyze the anode precursor obtained in step 2 to obtain a highly robust self-supporting three-dimensional porous anode.

Wherein, the pore-forming agent in step 1 is engineering fiber or a combination of engineering fiber and other pore-forming agents.

Preferably, the electrocatalytically active material is one or a combination of titanium oxide, tin oxide, lead oxide and C, N, B, F, Ni, Fe, La, Cu, Ce, Nb dopants thereof.

Preferably, the binder is one or a combination of paraffin, cyclodextrin, chitosan, polyvinylidene fluoride, methyl cellulose, and sodium alginate.

Preferably, in step 1, the mass ratio of the electrocatalytic active material to the pore-forming agent is 1:0.01 to 1:0.1.

Preferably, the pressure required for the pressing and forming in step 2 is 10 to 25 bar, and the action time is 5 to 30 minutes.

Preferably, the pyrolysis atmosphere in step three is air, the pyrolysis temperature is 400 to 1800° C., and the pyrolysis time is 1 to 12 hours.

According to a second aspect of the invention, the invention provides a highly robust self-supporting three-dimensional porous anode, characterized in that it has high mechanical strength, with typical values of hardness and toughness greater than 150N, elasticity greater than 0.7, and cohesion greater than 0.9.

According to a third aspect of the present invention, the present invention provides a highly robust self-supporting three-dimensional porous anode for use in electrocatalytic oxidation degradation of pollutants.

The beneficial effects of the present invention are embodied in:

(1) Pore-forming agents are low-cost and easy to obtain, and the synthesis process is simple, which is conducive to large-scale production. Compared with pore-forming agents such as carbon fiber, fructose, and starch, the amount of engineering fiber used is small, only 1% to 10% of the weight of the electrocatalytic active material used; and the price of engineering fiber is low, only one-tenth of the price of the same weight of carbon fiber pore-forming agent and one-half of fructose, so it is more conducive to promotion and application.

(2) By utilizing the characteristics of engineering fibers to replace existing pore-forming agents, a highly robust self-supporting three-dimensional porous anode with high mechanical strength and degradation performance can be obtained. It does not absorb moisture at room temperature and pressure, and can form a random support system in the three-dimensional anode precursor, which effectively promotes the integrity of the electrode obtained by pyrolysis. In contrast, fructose and starch are prone to hygroscopicity, and it is difficult to avoid broken electrodes when prepared in ordinary air, which is not conducive to promotion and application. In addition, the pyrolysis temperature of engineering fibers is relatively low (typical value is not higher than 200°C), and no residue will remain even when pyrolyzed at a relatively low temperature (typical value is 500-1000°C); while carbon fibers with a high pyrolysis temperature (1100-1350oC) will leave more carbon impurities after pyrolysis at the same low temperature, resulting in an increase in the energy consumption of the anode material obtained by this method in electrocatalytic oxidation applications, which is not conducive to promotion and application. In addition, the N element contained in ammonium carbonate and ammonium bicarbonate not only causes nitrogen-containing gas to pollute the atmosphere during the pyrolysis process, but may also form doping on the shallow surface of the electrocatalytic active material particles, and is easily dissolved and detached in subsequent electrocatalytic oxidation applications. Therefore, the anode material obtained by this method is insufficiently stable in electrocatalytic oxidation applications, which is not conducive to its promotion and application.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a physical picture of the highly robust self-supporting three-dimensional porous anode prepared in Example 1

Figure 2 is a scanning electron microscope photo of the highly robust self-supporting three-dimensional porous anode prepared in Example 1

Figure 3 is a pore size distribution diagram of the self-supporting three-dimensional porous anode prepared in Example 1

FIG. 4 is a graph showing the mechanical strength index of the highly robust three-dimensional porous anode prepared in Example 1

FIG5 is a cycle stability test result of the highly robust three-dimensional porous anode prepared in Example 1

Figure 6 is a scanning electron microscope photo of the three-dimensional porous anode prepared in Comparative Example 2

DETAILED DESCRIPTION

In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings. The following content is only an example and explanation of the concept of the present invention. The technicians in the field may make various modifications or supplements to the specific implementation cases described, or replace them with similar methods, as long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

Example 1

The preparation process of the three-dimensional porous electrocatalytic anode includes the following steps:

Step 1: Under normal temperature, pressure and air conditions, 1.2 g SnO ₂ -Sb nanopowder, 0.01 g engineering fiber and 0.06 g chitosan powder were mixed evenly using a vortex mixer to obtain a mixed powder;

Step 2: evenly distribute the mixed powder obtained in step 1 in the mold, place the mold in a tablet press, apply a vertical pressure of 20 bar for 10 minutes, and obtain a formed three-dimensional anode precursor;

Step 3: The anode precursor obtained in step 2 is pyrolyzed at 1000°C in air for 12 hours to remove the engineering fiber and chitosan, thereby obtaining a highly robust self-supporting three-dimensional porous anode, as shown in FIG1 .

The scanning electron microscope photo of the highly robust self-supporting three-dimensional porous anode obtained in this embodiment is shown in Figure 2, its pore size distribution is shown in Figure 3, and the mechanical strength index is shown in Figure 4. The electrocatalytic anode is dark blue, with a complete disc morphology, a diameter of 2.5 cm, and a thickness of about 1 mm. The electrode has abundant mesopores and macropores, with an average pore size of about 57 nm. In addition, the electrode also has high hardness, toughness, elasticity and cohesion, and the data corresponding to each index are 172.82, 162.97, 0.82 and 0.95, respectively, which is suitable for large-scale production.

Application of the three-dimensional porous electrocatalytic anode in pollutant degradation:

The self-supporting three-dimensional porous electrode in this embodiment is used as the anode, the platinum sheet is used as the cathode, the silver/silver chloride electrode is used as the reference electrode, and 0.1 mol L ^-1 _{Na2SO4 is} used as the electrolyte to degrade atrazine in a single-chamber electrolytic cell. FIG5 is the test result of the cyclic stability of atrazine degradation. It can be seen from the figure that the highly robust self-supporting three-dimensional porous anode can efficiently and quickly degrade atrazine, and has high long-term stability, which is conducive to practical promotion and application.

Comparative Example 1

Compared with Example 1, ammonium bicarbonate is used as a pore-forming agent, and other conditions are the same. During the pyrolysis process, the ammonium bicarbonate pore-forming agent generates ammonia gas that escapes and easily causes air pollution. In addition, the nitrogen element in the ammonium bicarbonate is very easy to form doping on the shallow surface of the electrocatalytic active material particles during the pyrolysis process, and is easily dissolved and separated in subsequent electrocatalytic oxidation applications. Therefore, the stability of the obtained anode material in electrocatalytic oxidation applications is insufficient.

Comparative Example 2

Compared with Example 1, carbon fiber is used as a pore former, and other conditions are the same. The pyrolysis temperature required for preparing the electrode needs to be higher than 1200°C to completely remove the carbon fiber. Figure 6 is a SEM image of the electrode obtained at a pyrolysis temperature of 800oC using a carbon fiber pore former. Moreover, the mechanical strength of the electrode prepared by this method is relatively low, and its brittleness is so poor that it cannot be measured by a texture analyzer, and the hardness, elasticity and cohesion indicators are 140.36, 0.74 and 0.95, respectively, which are much lower than the electrocatalytic anode prepared with engineering fiber as a pore former. In addition, its price is more than ten times that of engineering fiber of the same weight. Therefore, the use of engineering fiber has cost and mechanical strength advantages over using carbon fiber as a pore former.

Comparative Example 3

Compared with Example 1, starch is used as a pore former, and other conditions are the same. In the mixing process of step 1, starch prepared directly in the air is prone to moisture absorption and agglomeration, which is not conducive to the uniform dispersion of the pore former and the electrocatalytic active powder material and the binder, and is not conducive to the stable molding of the electrode precursor. Therefore, the use of engineered fiber has the advantage of lower manufacturing conditions than using starch as a pore former.

Example 2

The preparation process of the three-dimensional porous electrocatalytic anode includes the following steps:

Step 1: Mix 1.2 g of _PbO2 nanopowder, 0.1 g of engineering fiber and 0.08 g of paraffin wax to obtain a mixed powder;

Step 2: evenly distribute the mixed powder obtained in step 1 in the mold, place the mold in a tablet press, apply a vertical pressure of 10 bar for 30 minutes, and obtain a formed three-dimensional anode precursor;

Step 3: The anode precursor obtained in step 2 is pyrolyzed at 800° C. in air for 12 hours to obtain a highly robust self-supporting three-dimensional porous anode.

Example 3

The preparation process of the three-dimensional porous electrocatalytic anode includes the following steps:

Step 1: Mix 1.2 g _TiO2 powder, 0.08 g engineering fiber and 0.08 g methyl cellulose to obtain a mixed powder;

Step 2: evenly distribute the mixed powder obtained in step 1 in the mold, place the mold in a tablet press, apply a vertical pressure of 25 bar for 5 minutes, and obtain a formed three-dimensional anode precursor;

Step 3: The anode precursor obtained in step 2 is pyrolyzed at 1800° C. in air for 3 hours to obtain a highly robust self-supporting three-dimensional porous anode.

Example 4

The preparation process of the three-dimensional porous electrocatalytic anode includes the following steps:

Step 1: Under normal temperature, pressure and air conditions, 1.2 g SnO ₂ -F nanopowder, 0.12 g engineering fiber and 0.03 g cyclodextrin were mixed evenly to obtain a mixed powder;

Step 2: evenly distribute the mixed powder obtained in step 1 in the mold, place the mold in a tablet press, apply a vertical pressure of 25 bar for 5 minutes, and obtain a formed three-dimensional anode precursor;

Step 3: Pyrolyze the anode precursor obtained in step 2 at 400°C in air for 6 hours to obtain a highly robust self-supporting three-dimensional porous anode.

Example 5

Compared with Example 1, the active material is B and N doped _TiO2 nanopowder, and the pyrolysis temperature is 1600°C. The three-dimensional porous electrocatalytic anode can rapidly degrade 99.95% of levofloxacin in the electrolyte within 60 minutes in a single-chamber electrolytic cell.

Example 6

Compared with Example 1, the active material is La-doped _TiO2 nanopowder, the binder is 0.12 g cyclodextrin, and the pyrolysis temperature is 1300° C. The three-dimensional porous electrocatalytic anode can rapidly degrade 99.95% of bisphenol A in the electrolyte within 60 minutes in a single-chamber electrolytic cell.

The above are only exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims (11)

1. A self-supporting porous anode with high robustness, characterized by: a specific surface area of 12-70 ^m2 g ^-1 , a particle size of electrocatalytically active material of 20-500 nm, an electrode hardness and toughness higher than 150 N, an elasticity greater than 0.7, and a cohesion greater than 0.9. 2. A method for preparing a highly robust self-supporting three-dimensional porous anode according to claim 1, characterized in that it comprises the following steps: Step 1: Under normal temperature, pressure and air conditions, the electrocatalytic active material and the pore-forming agent binder are mixed uniformly to obtain a mixed powder; Step 2: Pressing the mixed powder obtained in step 1 into a shape to obtain a self-supporting three-dimensional anode precursor; Step three: pyrolyze the anode precursor in step two to obtain a highly robust self-supporting three-dimensional porous anode; the pore-forming agent is an engineering fiber or a combination of engineering fibers and other pore-forming agents. 3. The method for preparing a highly robust self-supporting three-dimensional porous anode according to claim 2 is characterized in that the electrocatalytically active substance is titanium oxide, tin oxide, lead oxide, or one or a combination of the above oxides doped with N, B, F, Ni, Fe, La, Cu, Ce, Nb. 4. The method for preparing a highly robust self-supporting three-dimensional porous anode according to claim 3, characterized in that the binder is one or a combination of paraffin, cyclodextrin, chitosan, polyvinylidene fluoride, methyl cellulose, and sodium alginate. 5. The method for preparing a highly robust self-supporting three-dimensional porous anode according to claim 4, characterized in that the mass ratio of the electrocatalytic active substance to the pore-forming agent in step 1 is 1:0.01 to 1:0.1. 6. The method for preparing a highly robust self-supporting three-dimensional porous anode according to claim 5, characterized in that the pressure required for pressing and forming in step 2 is 10 to 25 bar, and the action time is 5 to 30 minutes. 7. The method for preparing a highly robust self-supporting three-dimensional porous anode according to claim 6 is characterized in that the pyrolysis atmosphere in step three is air, the pyrolysis temperature is 400 to 1800°C, and the pyrolysis time is 1 to 12 hours. 8. A highly robust self-supporting three-dimensional porous anode prepared according to the preparation method of any one of claims 1 to 7, characterized in that its hardness and toughness are higher than 150N, its elasticity is greater than 0.7, and its cohesion is greater than 0.9. 9. Use of the highly robust three-dimensional porous anode according to claim 8 in electrocatalytic oxidation. 10. The use according to claim 9, characterized in that the use is for oxidative degradation of pollutants. 11. The use according to claim 10, characterized in that the pollutant is one or a mixture of levofloxacin, sulfadiazine, tetracycline, amoxicillin, bisphenol A, atrazine, rhodamine B, and phenol.