EP2937449A1

EP2937449A1 - Gas diffusion electrode and preparation method thereof

Info

Publication number: EP2937449A1
Application number: EP12891307.6A
Authority: EP
Inventors: Feng Wang; Yinliang CAO; Jingjun Liu; Zhilin Li
Original assignee: Beijing University of Chemical Technology
Current assignee: Beijing University of Chemical Technology
Priority date: 2012-12-24
Filing date: 2012-12-24
Publication date: 2015-10-28
Anticipated expiration: 2032-12-24
Also published as: CN104603331A; CN104603331B; EP2937449A4; JP2016505716A; JP6128709B2; WO2014100912A1; EP2937449B1

Abstract

Provided are a gas diffusion electrode and a preparation method thereof. The gas diffusion electrode comprises a current collector 1, a gas diffusion layer 2, a gas catalysis layer 3 coated on the gas diffusion layer, and a liquid guide layer 4 located on the gas catalysis layer. The gas diffusion layer comprises highly-graphitized carbon black and polytetrafluoroethylene, and the gas catalysis layer comprises a catalyst, acidified highly-graphitized carbon black and polytetrafluoroethylene; the highly-graphitized carbon black has a peak intensity ratio I_D/I_G between 0.3 and 1.0 in the Raman spectrum, and the degrees of graphitization in the gas diffusion layer and the gas catalysis layer may be the same or different. The gas diffusion electrode has good corrosion resistance and excellent and stable electrochemical performance in alkali solutions, thus it is suitable for electrolytic reactions in the chlor-alkali industry.

Description

Technical Field

The present invention relates to the field of chemical engineering, particularly to a gas diffusion electrode suitable for the chlor-alkali industry and a preparation method thereof.

Background

As a basic chemical industry, chlor-alkali industry plays an important role in promoting national economic development. Meanwhile, chlor-alkali industry is an industry with high energy consumption, so how to reduce the energy consumption of chlor-alkali industry to a minimum has always been an issue focused by many countries.
Recently, the ion-exchange membrane brine electrolytic process with an oxygen diffusion cathode (substituting for a hydrogen evolution cathode), the nature of which is a hydrogen evolution reaction is replaced by an oxygen reduction reaction, receives more attention increasingly. The reaction equations of the traditional ion-exchange membrane brine electrolytic process with a hydrogen evolution electrode as the cathode are as follows:

2Cl^-→Cl₂+2e (1.36V)

2H₂O+2e→2OH^-+H₂ (-0.83V)

2NaCl+2H₂O→Cl₂+2NaOH+H₂ (2.19V),
In contrast, the electrochemical reaction equations of the ion-exchange membrane brine electrolytic process with an oxygen diffusion electrode as the cathode are as follows:

2Cl^-→Cl₂+2e (1.36V)

O₂+2H₂O+4e→4OH^- (0.4V)

2NaCl+H₂O+1/2O₂→ Cl₂+2NaOH (0.96V).
It can be seen that, as for the ion-exchange membrane brine electrolytic process with an oxygen diffusion cathode substituting for a hydrogen evolution cathode, the theoretic decomposition voltage thereof can be reduced by 1.23 V, the theoretic energy thereof can be saved up to 40%, and the electric energy saved will be 700KWh per ton of alkali, which make the process have very considerable application value.
However, the original gas diffusion electrode begins in the development of fuel cell and zinc-air battery, which is relatively less applied to the chlor-alkali industry mainly because of the following aspects of difficulties:

1) the practical conditions of the electrolysis in chlor-alkali industry are relatively critical, usually under an alkali concentration of 30% or more and a temperature of 80-90°C, thus demanding relatively high requirement to the material and the preparation of the electrode;
2) during the electrochemical reaction of the oxygen diffusion cathode, influenced by the electro-catalysis mechanism of catalysts, two-electron side reaction will occur in some degree and produce a certain amount of HO₂ ^-, which is corrosive to carbon material and thus bring negative effects to the structure, lifetime and electrochemical properties of the electrode;
3) the electrochemical reaction of the oxygen diffusion cathode is actually a process of gas-liquid-solid multiphase catalytic reaction, the balance of which is difficult to control, thus affecting the catalytic efficiency of the oxygen diffusion cathode;
4) the oxygen diffusion cathode cannot satisfy the requirements of large-scale industrial production for its low mechanical strength and high difficulty of installation; and
5) for the oxygen diffusion cathode, it is difficult to obtain an electrode having good surface condition without cracks, because the processes of dispersion and film formation of its slurry are complex and the requirement of its drying is high.

At present, to solve the aforesaid problems, a lot of research has been carried out in each country. For example, Japanese Patent Publication 2007-327092 discloses a gas diffusion electrode having high resistance of water-pressure but low speed of deterioration, which is prepared using AB-6 carbon black as hydrophobic carbon black, AB-12 carbon black as hydrophilic carbon black, and Ag powder as a catalyst. Japanese Patent Publication 2004-300451 discloses a gas diffusion electrode having stable performance, which is prepared with AB-6 carbon black as hydrophobic carbon black and Ag-plated metal web as a catalyst layer through the steps of dispersing the hydrophobic carbon black and an adhesive, filtering and drying, followed by hot-press molding the Ag-plated metal web, however such electrode is difficult to satisfy the requirement of large-scale industrial production of large electrode. Chinese Patent CN101736360A discloses a gas diffusion electrode having a structure that a Ni web plated with Ag as a support is disposed between a gas diffusion layer and a catalyst layer, however such electrode involves problems such as low mechanical strength, being liable to form cracks on the surface of the electrode during the production thereof and difficult to release during the hot pressing process, and thus cannot satisfy the requirement of industrial production.

Summary

An object of the present invention is to provide a gas diffusion electrode which is simple and efficient as well as suitable for chlor-alkali industry, and a preparation method thereof so as to overcome the defects existed in prior art. Such object was achieved by the following technical solutions. In one aspect, the present invention relates to a gas diffusion electrode comprising a current collector, a gas diffusion layer, a gas catalysis layer coated on the gas diffusion layer, and a liquid guide layer located on the gas catalysis layer; wherein the gas diffusion layer comprises highly-graphitized carbon black and polytetrafluoroethylene (PTFE), and the gas catalysis layer comprises a catalyst, acidified highly-graphitized carbon black and polytetrafluoroethylene; the highly-graphitized carbon black is the carbon black having a peak intensity ratio I_D/I_G between 0.3 and 1.0 in the Raman spectrum, and the degrees of graphitization in the gas diffusion layer and the gas catalysis layer may be the same or different; the current collector and the liquid guide layer are both silver-plated metal foam having a thickness of 0.1-20 µm, and the silver-plated metal foam thereof may be the same or different.
In a preferred embodiment of the present invention, the mass ratio of the highly-graphitized carbon black to polytetrafluoroethylene in the gas diffusion layer is (0.01-1): (0.01-0.1).
In a preferred embodiment of the present invention, the mass ratio of the catalyst, the acidified highly-graphitized carbon black and polytetrafluoroethylene in the gas catalysis layer is (0.1-1): (0.1-1): (0.1-1).
In a preferred embodiment of the present invention, the metal of the silver-plated metal foam is selected from nickel, titanium, tungsten, cobalt, or alloys thereof.
In a preferred embodiment of the present invention, the catalyst in the gas catalysis layer is selected from silver powder or Ag/C composite catalyst; preferably, the catalyst has a particle size between 0.01 and 5 µm.
In a preferred embodiment of the present invention, the diffusion electrode is applied as a gas diffusion electrode in chlor-alkali industry.
In a preferred embodiment of the present invention, during the preparation of the gas diffusion electrode, the gas diffusion layer is prepared from raw materials comprising highly-graphitized carbon black, water, Triton, polytetrafluoroethylene emulsion and isopropanol in a mass ratio of (0.01-1): (0.1-1): (0.01-0.1): (0.01-0.1): 1, wherein the aqueous isopropanol solution of Triton is used as a dispersion medium.
In a preferred embodiment of the present invention, during the preparation of the gas diffusion electrode, the gas catalysis layer is prepared from raw materials comprising a catalyst, acidified highly-graphitized carbon black, water, Triton, polytetrafluoroethylene solution and isopropanol in a mass ratio of (0.1-1): (0.1-1): (1-10): (0.1-1): (0.1-1) : 1, wherein the aqueous solution of Triton is used as a dispersion medium.
In a preferred embodiment of the preparation method of the gas diffusion electrode according to the present invention, the preparation method of the gas diffusion layer comprises the following steps: (1) dispersing the highly-graphitized carbon black in the aqueous isopropanol solution comprising surfactant Triton, so as to obtain the slurry of the gas diffusion layer; dispersing this slurry by ultrasonic shear for 10 to 200 min; then adding 40 to 80 mass% of polytetrafluoroethylene emulsion, further dispersing by shear for 10 to 150 min; controlling the temperature during the dispersion of the gas diffusion layer slurry between 10 and 100°C, and the powder in the gas diffusion layer slurry having an average particle size between 0.2 and 10 µm after dispersion; setting the gas diffusion layer slurry for 5 to 100 h after dispersion; and controlling the solid content of the gas diffusion layer slurry between 5 and 40 wt%; and (2) coating the gas diffusion layer slurry evenly on the silver-plated metal foam of the current collector; after coating of the gas diffusion layer slurry, drying it at 40 to 120°C for 5-10 h; after coating and drying of the gas diffusion layer slurry, performing a primary cold-press molding treatment with a pressure between 0.1 and 2 MPa at a temperature between -10 and 50°C for a holding time between 10 and 300 s, so as to obtain an assembly of the current collector 1 and the gas diffusion layer 2.
In a preferred embodiment of the preparation method of the gas diffusion electrode according to the present invention, the preparation method of the gas catalysis layer comprises the following steps: (1) dispersing the catalyst, the acidified graphitized carbon black in the aqueous isopropanol solution comprising surfactant Triton, so as to obtain the catalysis layer slurry; dispersing this slurry by ultrasonic shear for 10-200 min; then adding 40-80 mass% of polytetrafluoroethylene emulsion, further dispersing by shear for 10-150 min; and controlling the temperature during the dispersion of the catalysis layer slurry between 10-100°C and the powder in the catalysis layer slurry having an average particle size between 0.2-10 µm after dispersion; and (2) coating the catalysis layer slurry evenly on the gas diffusion layer of the assembly of the gas diffusion layer and the current collector; drying it at 40-120°C for 0.5-1 h after coating of the catalysis layer slurry; after the coating and drying of the catalysis layer slurry, performing a secondary cold-press molding treatment to the assembly under a pressure between 0.1 and 2 MPa at a temperature between -10 and 50°C for a holding time between 10 and 300 s, so as to obtain a pre-molded gas diffusion electrode; baking the pre-molded gas diffusion electrode at high temperature between 270 and 290°C for 1 to 20 h; disposing the silver-plated metal foam of the liquid guide layer on the pre-molded gas diffusion electrode after baking, and performing hot-press molding thereto under a pressure between 2 and 12 MPa at a hot-press temperature between 330 and 450°C for a holding time between 10 and 300 s, thereby obtaining the gas diffusion electrode.
In a preferred embodiment of the above preparation method of the gas diffusion electrode, the silver-plated metal foam is prepared by plating Ag on the metal foam using electroplating, chemical plating, and replacement plating methods.
The catalyst used in the present invention includes Ag powder and Ag/C composite catalyst (the preparation thereof please refer to CN 101745390A ), and the Ag/C composite catalysts mentioned in the context are all those prepared according to patent publication CN 101745390A .
The present invention has the following advantageous effects.
In the present invention, a gas diffusion layer, which has not only good electrical conductivity and gas permeability capability but also excellent resistance to water pressure, can be prepared by the processes of dispersing highly-graphitized carbon black in the aqueous isopropanol solution comprising a certain surfactant using ultrasonic shear and standing, so as to obtain a uniformly dispersed gas diffusion layer slurry; coating the gas diffusion layer slurry evenly on the silver-plated metal foam; and performing cold-pressing after drying the slurry. A pre-molded gas diffusion electrode can be prepared by dispersing the catalyst and the acidified highly-graphitized carbon black in the aqueous isopropanol solution comprising a certain surfactant using ultrasonic shear so as to obtain a uniformly dispersed catalysis layer slurry; coating the catalysis layer slurry evenly on the gas diffusion layer; and performing cold-pressing after drying the slurry. The catalysis layer obtained in this way not only has suitable hydrophilic and hydrophobic capacity which is beneficial to the gas-liquid-solid three-phase reaction, but also has anti-etching capacity and the capacity of preventing the occurrence of side reaction producing hydrogen peroxide, thus facilitating the long-term and stable operation of the electrode. The pre-molded gas diffusion electrode is subjected to high-temperature baking in order to thoroughly remove the residual surfactant in the interior of the electrode, thereby facilitating the uniform of the pore structure during the hot-press molding process. A gas diffusion electrode having a sandwich structure is formed by hot-pressing the silver-plated metal foam on the surface of the catalysis layer during the hot-pressing process, thus not only being beneficial to the progression of the three-phase reaction in the catalysis process, but also being capable of improving the electro-catalysis capacity of the electrode in a basic solution and the mechanical strength of the electrode itself due to the silver-plated metal foam. Therefore, the gas diffusion electrode provided by the present invention has good corrosion resistance and good electrical conductivity, and runs stably in a basic solution; thus it is suitable for the electrolysis reaction in chlor-alkali industry.

Brief Description of the Drawings

Figure 1 is a schematic view showing the structure of the gas diffusion electrode provided by the present invention, wherein:
- 1 - current collector, 2 - diffusion layer, 3 - catalysis layer, 4 - liquid guide layer;
Figure 2 is a Raman Spectrogram of the highly-graphitized carbon black in the gas diffusion layer provided by the present invention;
Figure 3 is the results of the rotating ring-disk test of the Ag powder catalyst in a basic solution; and
Figure 4 is the test data of the actual electrolysis of the gas diffusion electrodes prepared in Example 1 and Comparative Example 1. (Test conditions: in 30% NaOH solution, current density of 3KA/m²)

Detailed Description of Certain Embodiments

Example 1

The highly-graphitized carbon black used in this example is prepared by graphitizing carbon black (Vulcan XC-72) in a high-temperature graphitization furnace at 2700°C for 6-10 h, and a Raman Spectrogram for measuring the graphitization degree thereof is shown in Figure 2 with I_D/I_G of 0.67. The silver-plated nickel foam is prepared by electroplating, wherein the nickel foam is commercially available from Heze Tianyu Technical Developing Lt. Corp. The acidified highly-graphitized carbon black is prepared by refluxing the graphitized carbon black in nitric acid solution (68 mass%) at 120°C for 6 to 10 h. Specifically,

1) weighing 0.4-2 g highly-graphitized carbon black and dispersing it in an aqueous isopropanol solution comprising 0.4-1 g Triton, wherein the amount of isopropanol is 40 mL and the amount of water is 10-25 mL; then dispersing thus-obtained slurry by ultrasonic shear for 60 min, followed by adding 1-2 g of PTFE emulsion (D-110, 60 mass%); continuing performing shear dispersion for 10 min, and then coating the gas diffusion layer slurry evenly on silver-plated nickel foam with a size of 90 mm×90 mm after dispersion completed, after drying it in an oven at 60°C for 30 min, performing the primary cold-press molding with a pressure of 0.1-2 MPa at room temperature for 60 s, so as to obtain the assembly of the current collector 1 and the gas diffusion layer 2;
2) dispersing 1-2 g Ag powder catalyst and 2-3 g acidified graphitized carbon black in 2.5-3 g/L aqueous isopropanol solution of Triton so as to make the oxygen-containing functional group on the surface of the acidified graphitized carbon black in a concentration of 0.5-2 mmol/g, wherein the amount of isopropanol is 3 mL, and the amount of water is 15-30 mL; dispersing the slurry by ultrasonic shear for 60 min and then adding 2.5-3 g 60 mass% of PTFE emulsion; further dispersing by ultrasonic shear for 10 min; after the dispersion completed, coating the catalysis layer slurry on the gas diffusion layer of the assembly of the current collector 1 and the gas diffusion 2; after drying the slurry, performing the secondary cold-press molding treatment with a cold pressure of 0.1-2 MPa at room temperature for a holding time of 30 s, so as to obtain the pre-molded gas diffusion electrode, wherein the results of the rotating ring-disk test of the Ag powder catalyst in a basic solution are shown in Figure 3. It can be seen that the electro-catalysis mechanism is almost four-electron reaction;
3) baking the pre-molded gas diffusion electrode obtained by the above steps at high temperature which is controlled to 290°C for 2 h; and
4) disposing the silver-plated nickel foam of the guide layer on the pre-molded gas diffusion electrode subjected to baking, and performing hot-press molding to it with a pressure of 5-8 MPa at a hot-press temperature of 360°C for 60 s holding time, so as to obtain the gas diffusion electrode. The test data of the actual electrolysis of the gas diffusion electrode prepared is shown in Figure 4, which indicates that the gas diffusion electrode has good corrosion resistance and excellent and stable electrochemical performance in alkali solutions, and therefore, is suitable for electrolytic reactions in the chlorine alkali industry.

Example 2

The highly-graphitized carbon black used in this example is prepared by graphitizing carbon black (Vulcan XC-72) at 2600°C for 2-15 h, and has a Raman Spectrogram with I_D/I_G of 0.7-1.0. The silver-plated nickel foam is prepared by electroplating, wherein the nickel foam is commercially available from Heze Tianyu Technical Developing Lt. Corp. The acidified highly-graphitized carbon black is prepared by refluxing the graphitized carbon black in nitric acid solution (68 mass%) at 140°C for 6 to 10 h. Specifically,

1) weighing 1-3 g highly-graphitized carbon black and dispersing it in an aqueous isopropanol solution comprising 0.4-3 g Triton, wherein the amount of isopropanol is 40 mL and the amount of water is 4-16 mL; then dispersing thus-obtained slurry by ultrasonic shear for 60 min, followed by adding 0.4-1.5 g of PTFE emulsion (D-110, 60 mass%); continuing performing shear dispersion for 10 min, and then coating the gas diffusion layer slurry evenly on silver-plated nickel foam with a size of 90 mm×90 mm after dispersion completed; after drying it in an oven at 60°C for 30 min, performing the primary cold-press molding with a cold pressure of 0.1-2 MPa at room temperature for 60 s, so as to obtain the assembly of the current collector 1 and the gas diffusion layer 2;
2) dispersing 0.3-1.5 g Ag powder catalyst orAg/Carbon composite catalyst and 0.5-2 g acidified graphitized carbon black in 0.3-1.8 g/L aqueous isopropanol solution of Triton so as to make the oxygen-containing functional group on the surface of the acidified graphitized carbon black in a concentration of 1.5-4 mmol/g, wherein the amount of isopropanol is 3 mL, and the amount of water is 3-8 mL; dispersing the slurry by ultrasonic shear for 60 min and then adding 0.3-1.5 g of PTFE emulsion (60 mass%); further dispersing by ultrasonic shear for 10 min; after the dispersion completed, coating the catalysis layer slurry on the gas diffusion layer of the assembly of the current collector 1 and the gas diffusion 2; after drying the slurry, performing the secondary cold-press molding treatment with a cold pressure of 0.1-2 MPa at room temperature for a holding time of 30 s, so as to obtain the pre-molded gas diffusion electrode;
3) baking the pre-molded gas diffusion electrode obtained by the above steps at high temperature which is controlled to 280°C for 4 h; and
4) disposing the silver-plated nickel foam of the guide layer on the pre-molded gas diffusion electrode subjected to baking, and performing hot-press molding to it with a pressure of 2-5 MPa at a hot-press temperature of 370°C for a holding time of 180 s, so as to obtain the gas diffusion electrode.

Example 3

The highly-graphitized carbon black used in this example is prepared by graphitizing carbon black (Vulcan XC-72) in a high-temperature graphitization furnace at 2900°C for 2-15 h, and has a Raman Spectrogram with I_D/I_G of 0.3-0.6. The silver-plated nickel foam is prepared by electroplating, wherein the nickel foam is commercially available from Heze Tianyu Technical Developing Lt. Corp. The acidified highly-graphitized carbon black is prepared by refluxing the graphitized carbon black in nitric acid solution (68 mass%) at 160°C for 6 to 10 h. Specifically,

1) weighing 2-4 g highly-graphitized carbon black and dispersing it in an aqueous isopropanol solution comprising 2.5-4 g Triton, wherein the amount of isopropanol is 40 mL and the amount of water is 20-40 mL; then dispersing thus-obtained slurry by ultrasonic shear for 60 min, followed by adding 1.8-4 g of PTFE emulsion (D-110, 60 mass%); continuing performing shear dispersion for 10 min, and then coating the gas diffusion layer slurry evenly on silver-plated nickel foam with a size of 90 mm×90 mm after dispersion completed; after drying it at 60°C for 30 min, performing the primary cold-press molding in a cold press machine with a cold pressure of 1.5-2 MPa at room temperature for 60 s, so as to obtain the assembly of the current collector 1 and the gas diffusion layer 2;
2) dispersing 2-3 g Ag powder catalyst or Ag/Carbon composite catalyst and 0.3-1 g acidified graphitized carbon black in 1.5-2.8 g/L aqueous isopropanol solution of Triton so as to make the oxygen-containing functional group on the surface of the acidified graphitized carbon black in a concentration of 3.5-5 mmol/g, wherein the amount of isopropanol is 3 mL, and the amount of water is 5-15mL; dispersing the slurry by ultrasonic shear for 60 min and then adding 1.4-2.8 g of PTFE emulsion (60 mass%); further dispersing by ultrasonic shear for 10 min; after the dispersion completed, coating the catalysis layer slurry on the gas diffusion layer of the assembly of the current collector 1 and the gas diffusion 2; after drying the slurry, performing the secondary cold-press molding treatment with a cold pressure of 1.5-2 MPa at room temperature for a holding time of 30 s, so as to obtain the pre-molded gas diffusion electrode;
3) baking the pre-molded gas diffusion electrode obtained by the above steps at high temperature which is controlled to 270°C for 6 h; and
4) disposing the silver-plated nickel foam of the guide layer on the pre-molded gas diffusion electrode subjected to baking, and performing hot-press molding to it with a pressure of 8-12 MPa at a hot-press temperature of 350°C for a holding time of 30 s, so as to obtain the gas diffusion electrode.

Comparative Example 1

The highly-graphitized carbon black used herein is prepared by graphitizing carbon black (Vulcan XC-72) in a high-temperature graphitization furnace at 2700°C for 6-10 h, and a Raman Spectrogram for measuring the graphitization degree thereof is shown in Figure 2 with I_D/I_G of 0.67. The silver-plated nickel foam is prepared by electroplating, wherein the nickel foam is commercially available from Heze Tianyu Technical Developing Lt. Corp. The acidified highly-graphitized carbon black is prepared by refluxing the graphitized carbon black in nitric acid solution (68 mass%) at 120°C for 6 to 10 h. Specifically,

1) weighing 0.4-2 g highly-graphitized carbon black and dispersing it in an aqueous isopropanol solution comprising 0.4-1 g Triton, wherein the amount of isopropanol is 40 mL and the amount of water is 10-25 mL; then dispersing thus-obtained slurry by ultrasonic shear for 60 min, followed by adding 1-2 g of PTFE emulsion (D-110, 60 mass%); continuing performing shear dispersion for 10 min, and then coating the gas diffusion layer slurry evenly on silver-plated nickel foam with a size of 90 mm×90 mm after dispersion completed, after drying it in an oven at 60°C for 30 min, performing the primary cold-press molding with a cold pressure of 0.1-2 MPa at room temperature for 60 s, so as to obtain the assembly of the current collector 1 and the gas diffusion layer 2;
2) dispersing 1-2 g Ag powder catalyst and 2-3 g acidified graphitized carbon black in 2.5-3 g/L aqueous isopropanol solution of Triton so as to make the oxygen-containing functional group on the surface of the acidified graphitized carbon black in a concentration of 0.5-2 mmol/g, wherein the amount of isopropanol is 3 mL, and the amount of water is 15-30 mL; dispersing the slurry by ultrasonic shear for 60 min and then adding 2.5-3 g 60 mass% of PTFE emulsion; further dispersing by ultrasonic shear for 10 min; after the dispersion completed, coating the catalysis layer slurry on the gas diffusion layer of the assembly of the current collector 1 and the gas diffusion 2; after drying the slurry, performing the secondary cold-press molding treatment with a cold pressure of 0.1-2 MPa at room temperature for a holding time of 30 s, so as to obtain the pre-molded gas diffusion electrode;
3) baking the pre-molded gas diffusion electrode obtained by the above steps at high temperature which is controlled to 290°C for 2 h; and
4) disposing the pre-molded gas diffusion electrode after baking directly on a hot press machine and performing hot-press molding to it with a hot pressure of 5-8 MPa at a hot-press temperature of 360°C for a holding time of 60 s, so as to obtain the gas diffusion electrode. The test data of the actual electrolysis of the gas diffusion electrode prepared is shown in Figure 4, which indicates that the electrolysis properties thereof show degradation in a basic solution with the elapse of time, thus the electrode is not suitable for the long-term electrolysis reaction in chlor-alkali industry.

It should be understood that, for a person skilled in the art, the embodiments would be modified or varied in accordance with the above description, and all such modifications and variations are within the scope of the invention as specifically set forth in the claims appended hereto.

Claims

A gas diffusion electrode comprising a current collector, a gas diffusion layer, a gas catalysis layer coated on the gas diffusion layer, and a liquid guide layer located on the gas catalysis layer; wherein the gas diffusion layer comprises highly-graphitized carbon black and polytetrafluoroethylene, and the gas catalysis layer comprises a catalyst, acidified highly-graphitized carbon black and polytetrafluoroethylene; the highly-graphitized carbon black is the carbon black having a peak intensity ratio I_D/I_G between 0.3 and 1.0 in the Raman spectrum, and preferably the concentration of the oxygen-containing functional group on the surface of the acidified graphitized carbon black is 0.5-2 mmol/g; the degrees of graphitization in the gas diffusion layer and the gas catalysis layer may be the same or different; the current collector and the liquid guide layer are both silver-plated metal foam having a thickness of 0.1-20 µm, and the silver-plated metal foam thereof may be the same or different.
The gas diffusion electrode according to claim 1, wherein the mass ratio of the highly-graphitized carbon black to polytetrafluoroethylene in the gas diffusion layer is (0.01-1): (0.01-0.1).
The gas diffusion electrode according to claim 1, wherein the mass ratio of the catalyst, the acidified highly-graphitized carbon black and polytetrafluoroethylene in the gas catalysis layer is (0.1-1): (0.1-1): (0.1-1).
The gas diffusion electrode according to any one of claims 1-3, wherein the metal of the silver-plated metal foam is selected from nickel, titanium, tungsten, cobalt, or alloys thereof.
The gas diffusion electrode according to claim 1, wherein the catalyst in the gas catalysis layer is selected from silver powder or Ag/C composite catalyst; preferably, the catalyst has a particle size between 0.01 and 5 µm.
The gas diffusion electrode according to any one of claims 1-5, wherein the diffusion electrode is a gas diffusion electrode applied in chlor-alkali industry.
A method for preparing the gas diffusion electrode according to claim 6, wherein the gas diffusion layer is prepared from raw materials comprising highly-graphitized carbon black, water, Triton, polytetrafluoroethylene emulsion and isopropanol in a mass ratio of (0.01-1) : (0.1-1) : (0.01-0.1) : (0.01-0.1) : 1, wherein the aqueous isopropanol solution of Triton is used as a dispersion medium.
A method for preparing the gas diffusion electrode according to claim 6, wherein the gas catalysis layer is prepared from raw materials comprising a catalyst, acidified highly-graphitized carbon black, water, Triton, polytetrafluoroethylene solution and isopropanol in a mass ratio of (0.1-1) : (0.1-1) : (1-10) : (0.1-1) : (0.1-1) : 1, wherein the aqueous isopropanol solution of Triton is used as a dispersion medium.
The method for preparing the gas diffusion electrode according to claim 7, wherein the preparation method of the gas diffusion layer comprises the following steps:
(1) dispersing the highly-graphitized carbon black in the aqueous isopropanol solution comprising surfactant Triton, so as to obtain a slurry of the gas diffusion layer; dispersing this slurry by ultrasonic shear for 10 to 200 min; then adding 40 to 80 mass% of polytetrafluoroethylene emulsion, further dispersing by shear for 10 to 150 min; controlling the temperature during the dispersion of the gas diffusion layer slurry between 10 and 100°C and after dispersion the powder in the gas diffusion layer slurry having an average particle size between 0.2 and 10 µm; setting the gas diffusion layer slurry for 5 to 100 h after dispersion; and controlling the solid content of the gas diffusion layer slurry between 5 and 40 wt%; and

(2) coating the gas diffusion layer slurry evenly on the silver-plated metal foam of the current collector; after coating of the gas diffusion layer slurry, drying it at 40 to 120°C for 5-10 h; after coating and drying of the gas diffusion layer slurry, performing a primary cold-press molding treatment at a cold pressure between 0.1 and 2 MPa, a temperature between -10 and 50°C and a holding time between 10 and 300 s, so as to obtain an assembly of the current collector and the gas diffusion layer.
The method for preparing the gas diffusion electrode according to claim 8, wherein the preparation method of the gas catalysis layer comprises the following steps:
(1) dispersing the catalyst, the acidified graphitized carbon black in the aqueous isopropanol solution comprising surfactant Triton, so as to obtain a catalysis layer slurry; dispersing this slurry by ultrasonic shear for 10-200 min; then adding 40-80 mass% of polytetrafluoroethylene emulsion, further dispersing by shear for 10-150 min; and controlling the temperature during the dispersion of the catalysis layer slurry between 10-100°C and the powder in the catalysis layer slurry having an average particle size between 0.2-10 µm after dispersion; and

(2) coating the catalysis layer slurry evenly on the gas diffusion layer of the assembly of the gas diffusion layer and the current collector; drying it at 40-120°C for 0.5-1 h after coating of the catalysis layer slurry; after the coating and drying of the catalysis layer slurry, performing a secondary cold-press molding treatment to the assembly under a cold pressure between 0.1 and 2 MPa at a temperature between -10 and 50°C for a holding time between 10 and 300 s, so as to obtain a pre-molded gas diffusion electrode; baking the pre-molded gas diffusion electrode at high temperature between 270 and 290°C for 1 to 20 h; disposing the silver-plated metal foam of the liquid guide layer on the pre-molded gas diffusion electrode after baking, and performing hot-press molding thereto under a hot pressure between 2 and 12 MPa at a hot-press temperature between 330 and 450°C for a holding time between 10 and 300 s, thereby obtaining the gas diffusion electrode.