CN113437319A

CN113437319A - Anode self-humidifying gas diffusion layer

Info

Publication number: CN113437319A
Application number: CN202110703819.4A
Authority: CN
Inventors: 刘勇; 李天涯; 朱蔡翰
Original assignee: Beijing University of Chemical Technology
Current assignee: Beijing University of Chemical Technology
Priority date: 2021-06-24
Filing date: 2021-06-24
Publication date: 2021-09-24

Abstract

The invention discloses an anode self-humidifying gas diffusion layer, and belongs to the technical field of fuel cells. The anode self-humidifying gas diffusion layer is a gradient anode self-humidifying gas diffusion layer, two microporous layers are formed in total, the ratio of the microporous layers is from the carbon paper side to the catalyst layer side, and the ratio of polytetrafluoroethylene to carbon black is 3:7 and 1: 9. The preparation method is a spraying method, wherein after ethanol solution of polytetrafluoroethylene and carbon black is sprayed on carbon paper in a spraying mode, the thickness of the carbon paper is controlled to be 240 mu m in a rolling mode. Compared with the commercial gas diffusion layer on the market at present, the anode self-humidifying gas diffusion layer has the advantages of higher power, lower impedance and high hydrophobicity under the condition of low humidity, can generate a synergistic effect with the cathode gas diffusion layer under the condition of high humidity, can realize better water management capability, effectively solves the problem of performance reduction of a battery due to a water flooding phenomenon under the condition of high humidity, and has great application prospect in the field of future hydrogen fuel cells.

Description

Anode self-humidifying gas diffusion layer

Technical Field

The invention belongs to the preparation of a gas diffusion layer, relates to the technical field of fuel cells, and particularly relates to an anode gas diffusion layer with a good self-humidifying effect, which is particularly suitable for fuel cell automobiles.

Background

The fuel cell is a battery which converts chemical energy into electric energy through electrochemical reaction, wherein the hydrogen fuel cell takes hydrogen and oxygen as fuel and water as a product, and zero emission and low pollution can be really realized from the viewpoints of energy consumption and environmental pollution, so that the fuel cell has a very good application prospect. Compared with the traditional automobile engine, the fuel cell has higher energy conversion rate due to electrochemical reaction without the limitation of Carnot cycle, so the fuel cell has great application prospect in the fields of automobiles, ships, airplanes and the like in the future.

The fuel cell gas diffusion layer is positioned between the catalyst layer and the bipolar plate, and plays the roles of supporting the catalyst layer, conveying gas and draining water in the fuel cell. Under low humidity, the anode gas diffusion layer needs to ensure that certain moisture exists on the anode catalyst layer side; under high humidity, it is also necessary to drain part of the water transferred from the cathode to the anode due to permeation to prevent flooding of the catalyst layer.

The gas diffusion layer is composed of carbon paper and a microporous layer. Currently, there are three main methods for preparing the microporous layer, spraying, blade coating, and electrospinning. The major disadvantages of the knife coating process for making microporous layers are: the micro-porous layer prepared by the blade coating method has uneven surface, obvious defects and low production efficiency, and the micro-porous layer prepared by the blade coating method has low repeatability, so that the consistency of the micro-porous layer prepared each time is difficult to ensure. The microporous layer prepared by the electrostatic spinning method has good performance, but the cost for preparing the microporous layer by the electrostatic spinning method is high, and the operation for preparing the microporous layer by the method is complicated, long-time stirring is needed, and the temperature and speed conditions of electrostatic spinning need to be controlled. In contrast, the spraying method for preparing the microporous layer has the advantages of cheap materials, high repeatability, simple method and the like, and is more suitable for preparing the microporous layer.

At present, most studies on gas diffusion layers relate to the gradient of cathode gas diffusion layers, and chinese patent CN111146467A discloses a cathode gradient gas diffusion layer with gradient effect obtained by preparing solution, spraying, drying, sintering, and spraying solutions with different contents, however, the gas diffusion layer prepared by the method has many steps and is complicated; US patent US8,945,790 discloses a method for preparing a gas diffusion layer with gradient by compounding multiple microporous layers, but the anode gas diffusion layer in this patent is the same as the cathode gas diffusion layer, and lacks a separate design for the anode; US6,821,661 discloses an anode gas diffusion layer with hydrophilicity by adding carbon fibers with water contact angle less than 140 ° to the anode gas diffusion layer side, while the cathode is more hydrophobic than the anode, achieving anode hydrophilicity by synergy, but in this patent only the carbon paper is modified without modifying the microporous layer. They have simply improved the structure of the cathode-side gas diffusion layer or simply changed the anode gas diffusion layer, but have lacked improvements to the anode side and a gradient design to the anode side. The improvement of the gas diffusion layer on the anode side can also effectively improve the performance of the fuel cell, so that the gas diffusion layer on the anode side with good performance under different temperatures and humidities is prepared for the gas diffusion layer on the anode side of the fuel cell according to the characteristics of the anode, so that the water management effect can be better played, and the fuel cell is ensured to have higher efficiency.

Disclosure of Invention

The present invention provides a gradient anode gas diffusion layer and a preparation method thereof by using a spray coating method to solve the problems, so as to improve the water management capability of the anode side gas diffusion layer.

The raw materials used by the gradient anode gas diffusion layer provided by the invention comprise carbon paper, carbon black, polytetrafluoroethylene and absolute ethyl alcohol. The preparation equipment comprises a spray gun, a tube furnace, a roller press and an air pump. By using spraying and rolling methods, ethanol solutions of carbon black and polytetrafluoroethylene in different proportions are sprayed on the carbon paper and rolled, so that the effect of hydrophilic and hydrophobic gradient under a certain thickness is achieved.

In order to achieve the purpose, the microporous layer in the gas diffusion layer is prepared by uniformly dispersing ethanol suspension solution of polytetrafluoroethylene and carbon black through a spraying method; the preparation process of the gradient anode gas diffusion layer comprises the steps of arranging a microporous layer close to the carbon paper side, Polytetrafluoroethylene (PTFE): carbon Black (CB) mass ratio of 3:7 (solvent 100ml ethanol); the microporous layer at the side far from the carbon paper, polytetrafluoroethylene: carbon black mass ratio is 1:9 (solvent 100ml ethanol).

The preparation process of the suspension solution comprises the following steps: adding 7g of carbon black into 100ml of absolute ethyl alcohol, magnetically stirring for 30 minutes, performing ultrasonic treatment for 30 minutes, repeating the steps for four times to obtain a uniform dispersion liquid, adding 3g of polytetrafluoroethylene, and performing magnetic stirring for 30 minutes and ultrasonic treatment for 30 minutes to obtain a uniformly dispersed suspension solution of the polytetrafluoroethylene and the carbon black; uniformly spraying the suspension solution onto carbon paper by using a spray gun, and heating and volatilizing ethanol by using a heating plate to obtain a microporous layer, wherein the devices required for the operation mainly comprise the spray gun, an air pump, a tubular furnace and a roller press; the nozzle is vertical to the carbon paper; the pressure of the air pump is 5 kPa; the carbon paper is directly placed on a tube furnace, and the temperature of the tube furnace is 200 ℃.

The steps for preparing the gas diffusion layer are as follows:

A. adding the suspension solution into a spray gun, and adjusting the mouth shape of the spray gun;

B. opening the tube furnace, placing the carbon paper in the tube furnace, heating the tube furnace to 200 ℃, opening the air pump, and adjusting the pressure to 5 kPa;

C. start the air pump, suspension solution spouts to carbon paper in the spray gun on, the slow movement spray gun for carbon black and polytetrafluoroethylene can evenly spout to carbon paper in the suspension solution on, at first use PTFE: the mass ratio of CB is 3:7, after the first layer spraying finishes, the spraying of the second layer is carried out, and PTFE is changed: the mass ratio of CB is 1:9, wherein the thickness of the carbon paper used is 200 μm, and the thickness of each of the two sprayed microporous layers is 35 μm;

D. the rolling operation was performed 2 to 3 times using a rolling device to compress the total thickness of the gas diffusion layer to 240 d, and an anode self-moisture-increasing gas diffusion layer was finally obtained.

Compared with the prior art, the gas diffusion layer can be obtained only by preparing the suspension solution, spraying and rolling, the required raw materials are less, and the method is simple. In addition, the anode gas diffusion layer with gradient can ensure certain water content of the catalyst layer due to certain hydrophobicity under low humidity; under high humidity, water is drained from the gradient hydrophobic microporous layer by capillary pressure, and a flooding phenomenon is prevented.

Drawings

FIG. 1 is a schematic view showing the structure of an anode-side gas diffusion layer according to the present invention

FIG. 2 is a SEM surface view of a gas diffusion layer according to the present invention

FIG. 3 is a flow chart of the present invention

FIG. 4 shows the results of the water contact angle test of the present invention (in comparison with commercial GDL29 BC)

FIG. 5 is a test chart of the polarization curve of the present invention (in contrast to commercial GDL29 BC)

FIG. 6 is a graph of the power density test of the present invention (compare with commercial GDL29 BC)

FIG. 7 shows a test chart of electrochemical impedance spectroscopy according to the present invention (in comparison with commercially available GDL29 BC)

In the figure: 1. carbon paper; 2. a microporous layer adjacent to the carbon paper side; 3. a microporous layer on the side far away from the carbon paper; 4. carbon paper; 5. carbon black; 6. polytetrafluoroethylene; 7. absolute ethyl alcohol; 8. a spray gun; 9. a tube furnace; 10. a rolling device; 11. a homogeneous dispersion of carbon black; 12. a homogeneous dispersion of carbon black and tetrafluoroethylene; 13. polytetrafluoroethylene (PTFE): carbon black 3g/(100ml absolute ethanol): 7g/(100ml absolute ethyl alcohol) of a homogeneous dispersion; 14. polytetrafluoroethylene (PTFE): carbon black ratio 1g/(100ml absolute ethanol): 9g/(100ml absolute ethyl alcohol) of a homogeneous dispersion; 15. an air pump.

Detailed Description

The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited thereto.

An anode self-moisture-increasing gas diffusion layer is shown in figure 1 and consists of carbon paper 1, a microporous layer 2 close to the carbon paper side and a microporous layer 3 far from the carbon paper side.

The microporous layer 2 close to the carbon paper side is made of Polytetrafluoroethylene (PTFE): carbon Black (CB) ═ 3g/(100ml absolute ethanol): 7g/(100ml of absolute ethyl alcohol), and the material composition ratio of the microporous layer 3 away from the carbon paper side is PTFE: CB ═ 1g/(100ml absolute ethanol): 9g/(100ml of absolute ethyl alcohol), and the purity of the absolute ethyl alcohol is more than or equal to 99.7 percent.

The preparation process of the anode self-humidifying gas diffusion layer provided by the invention is shown in fig. 3, and the operation steps of the embodiment are as follows: firstly, 7g of carbon black 5 is added into 100ml of absolute ethyl alcohol 7, magnetic stirring is carried out for 30 minutes, then ultrasonic treatment is carried out for 30 minutes, and circulation is carried out for four times. After obtaining the uniform dispersion liquid 11, 3g of polytetrafluoroethylene 6 was added and magnetic stirring was performed for 30 minutes again, and ultrasonic processing was performed for 30 minutes again to finally obtain a uniform dispersion suspension solution 12 of polytetrafluoroethylene and carbon black.

The anode self-humidifying gas diffusion layer provided by the invention is prepared by a spraying method, and the process comprises the following steps:

A. adding the prepared suspension solution 13 into the spray gun 8, and adjusting the mouth shape of the spray gun 8;

B. the tube furnace 9 was opened, the carbon paper 4 was placed on the tube furnace 9, the tube furnace 9 was heated to 200 ℃, the air pump was turned on, and the pressure was adjusted to 5 kpa.

C. Starting the air pump 15, spraying the suspension solution 13 in the spray gun 8 onto the carbon paper 4, and slowly moving the spray gun 8 so that the ratio of CB: the PTFE mass ratio is 7: the carbon black 5 and the polytetrafluoroethylene 6 in the suspension solution 13 of the carbon paper 3 can be uniformly sprayed on the carbon paper 4. After the first layer spraying finishes, carry out the spraying on second floor, change for CB: the PTFE mass ratio is 9: 1, the same procedure was carried out.

D. The rolling operation is performed 2 to 3 times using a roller press 10.

The temperature of the tube furnace 9 is controlled at 200 ℃, and the ethanol 7 in the suspension solution 13 and the suspension solution 14 is quickly evaporated without damaging the gas diffusion layer due to overhigh temperature. The carbon paper 4 of the graded anode-side gas diffusion layer prepared using the spray coating method had a thickness of 200 μm. Before rolling, the thickness of the gas diffusion layer near the carbon paper layer was 35 μm, and the thickness of the gas diffusion layer far from the carbon paper side was 35 μm. After the roll pressing, the total thickness of the gas diffusion layer was reduced to 240 μm. The gas diffusion layers prepared as described above were subjected to performance tests, and the results are shown in fig. 2, 4, 5, 6, and 7. The gas diffusion layer prepared by the spraying method is porous, and can effectively reduce the retention of water near the catalyst layer under high humidity, prevent the catalyst layer from being covered by water and reduce the efficiency of the battery.

Claims

1. An anode self-moisture-increasing gas diffusion layer is characterized in that a microporous layer in the gas diffusion layer is prepared by spraying a uniformly dispersed ethanol suspension solution of polytetrafluoroethylene and carbon black; the suspension solution is prepared from the following materials: proximal to the carbon paper side microporous layer, Polytetrafluoroethylene (PTFE): carbon Black (CB) mass ratio of 3:7 (solvent is 100ml ethanol), microporous layer on the side away from the carbon paper, polytetrafluoroethylene: carbon black mass ratio is 1:9 (100ml ethanol as solvent); the preparation process of the suspension solution comprises the following steps: adding 7g of carbon black into 100ml of absolute ethyl alcohol, magnetically stirring for 30 minutes, performing ultrasonic treatment for 30 minutes, repeating the steps for four times to obtain a uniform dispersion liquid, adding 3g of polytetrafluoroethylene, and performing magnetic stirring for 30 minutes and ultrasonic treatment for 30 minutes to obtain a uniformly dispersed suspension solution of the polytetrafluoroethylene and the carbon black; uniformly spraying the suspension solution onto carbon paper by using a spray gun, and heating and volatilizing ethanol by using a heating plate to obtain a microporous layer, wherein the devices required for the operation mainly comprise the spray gun, an air pump, a tubular furnace and a roller press; the nozzle is vertical to the carbon paper; the pressure of the air pump is 5 kPa; directly placing the carbon paper on a tubular furnace, wherein the temperature of the tubular furnace is 200 ℃; the steps for preparing the gas diffusion layer are as follows:

C. starting an air pump, spraying the suspension solution in the spray gun onto the carbon paper, and slowly moving the spray gun to enable the carbon black and the polytetrafluoroethylene in the suspension solution to be uniformly sprayed onto the carbon paper; first, PTFE was used: the mass ratio of CB is 3:7, after the first layer spraying finishes, the spraying of the second layer is carried out, and PTFE is changed: the mass ratio of CB is 1:9, carrying out the same operation, wherein the thickness of the used carbon paper is 200 μm, and the thicknesses of the sprayed two layers of microporous layers are 35 μm respectively;