CN115377448A - Application of gas diffusion layer with hydrophilic and hydrophobic structure in fuel cell - Google Patents

Abstract

The invention relates to the application of a gas diffusion layer with a hydrophilic and hydrophobic structure in a fuel cell, wherein the gas diffusion layer with a hydrophilic and hydrophobic structure is used as a cathode gas diffusion layer and an anode gas diffusion layer in a fuel cell, and the gas diffusion layer with a hydrophilic and hydrophobic structure The gas diffusion layer includes a hydrophilic area and a hydrophobic area; the hydrophilic area is a local area of the gas diffusion layer treated only by a hydrophilic agent, and the hydrophobic area is a local area of the gas diffusion layer treated successively by a hydrophilic agent and a hydrophobic agent; Adjacent hydrophilic regions are separated by hydrophobic regions; the hydrophilic agent is an oxidizing solution, and the hydrophobic agent includes any of polytetrafluoroethylene emulsion, fluorinated ethylene propylene copolymer, polyvinylidene fluoride emulsion or polyhexafluoropropylene emulsion One or a combination of at least two. Applying a gas diffusion layer with a hydrophilic-hydrophobic structure to a fuel cell can effectively improve the mass transfer efficiency of the fuel cell, reduce the voltage loss caused by mass transfer, and further improve the performance of the fuel cell.

Description

Application of a Gas Diffusion Layer with Hydrophilic and Hydrophobic Structure in Fuel Cells

technical field

The invention relates to the application of a gas diffusion layer with a hydrophilic and hydrophobic structure in a fuel cell, belonging to the technical field of the fuel cell.

Background technique

In a fuel cell, the transport of ionic charge is far more difficult than that of electrons, and the resistance of charge transport results in a loss of cell voltage, ie, loss of ohmic resistance. Mass transfer loss is one of the three major losses that cause the output voltage loss of proton exchange membrane fuel cells. In fuel cells, the main component responsible for transporting fuel gas and product water is the porous gas diffusion layer. Inside the pores of the gas diffusion layer used to transport substances, two-phase coupling often occurs or the pores are blocked due to excessive accumulation of the liquid phase in the capillary, resulting in a decrease in the concentration of the gas phase reaching the catalytic site and reducing the electrochemical reaction rate. Or excessive accumulation of liquid phase cannot be discharged in time, causing in-plane flooding, reducing catalyst activity and causing mass transfer loss.

As one of the indicators for evaluating the performance of fuel cells, mass transfer efficiency not only determines the rate of electrochemical reactions on the catalyst layer (CL), but also determines the internal mass transfer resistance of proton exchange membrane fuel (Proton Exchange Membrane Fuel Cell, PEMFC) cells. The main characterization formula has a non-negligible impact on the output voltage and efficiency of PEMFC. The gas diffusion layer (GDL) is the carrier of the main transmission medium inside the PEMFC, and its complex porosity and tortuosity have great disturbances in the transmission of gas or liquid. Therefore, it is of great significance to develop a gas diffusion layer that can effectively reduce the voltage loss caused by mass transfer and improve battery performance and apply it to fuel cells to promote the technical development of the fuel cell field.

Contents of the invention

Therefore, it is necessary to provide an application of a gas diffusion layer with a hydrophilic-hydrophobic structure in a fuel cell. The gas diffusion layer with a hydrophilic and hydrophobic structure is applied to a fuel cell, so that the transmission of the gas phase and the liquid phase in the fuel cell can be distinguished, the accumulation and discharge of water are promoted, and the ohmic resistance is lower at high current density, And it can effectively reduce the gas phase starvation problem caused by the accumulation or repulsion of the liquid phase by the single wettability of the wall surface, thereby increasing the limiting current density, and more effectively reducing the voltage loss caused by mass transfer, thereby improving the performance of the fuel cell.

To achieve the above object, the present invention provides an application of a gas diffusion layer with a hydrophilic and hydrophobic structure in a fuel cell, wherein the gas diffusion layer with a hydrophilic and hydrophobic structure is used as a cathode gas diffusion layer and an anode gas diffusion layer in a fuel cell. In the battery, the gas diffusion layer having a hydrophilic and hydrophobic structure includes a hydrophilic region and a hydrophobic region, the hydrophilic region is only a local area of the gas diffusion layer treated with a hydrophilic agent, and the hydrophobic region is formed by a hydrophilic agent 1. Partial areas of the gas diffusion layer treated successively with hydrophobic agents; adjacent hydrophilic areas are separated by hydrophobic areas;

The hydrophilic agent is an oxidizing solution, and the hydrophobic agent includes any one or at least two of polytetrafluoroethylene emulsion, fluorinated ethylene propylene copolymer, polyvinylidene fluoride emulsion or polyhexafluoropropylene emulsion The combination.

Different from the prior art, the above technical solution provides an application of a gas diffusion layer with a hydrophilic and hydrophobic structure in a fuel cell. The gas diffusion layer with a hydrophilic and hydrophobic structure has good mass transfer efficiency, can more effectively reduce the voltage loss caused by mass transfer, and is applied to a fuel cell, so that the gas phase and liquid phase transmission in the fuel cell can be distinguished , promote the accumulation and discharge of water, have lower ohmic resistance at high current density, and can effectively reduce the gas phase starvation problem caused by the single wettability of the wall surface to the accumulation or repulsion of the liquid phase, thereby increasing the limiting current density, And more effectively reduce the voltage loss caused by mass transfer, thereby improving the performance of the fuel cell.

Description of drawings

Fig. 1 is a schematic structural view of the in-plane infiltration device (air pump) described in the specific embodiment, wherein Fig. 1a is a three-dimensional diagram, and Fig. 1b is a physical diagram;

Fig. 2 is the SEM figure of embodiment 1～3 and comparative example 1 sample, wherein, Fig. 2a is the SEM figure of comparative example 1 sample, Fig. 2b is the SEM figure of embodiment 1 sample, Fig. 2c is the SEM of embodiment 2 sample Fig. 2d is the SEM figure of the sample of embodiment 3;

Fig. 3 is the surface static contact angle test result figure of embodiment 1～3 and comparative example 1 sample, wherein, Fig. 3 a is the test result figure of comparative example 1 sample, and Fig. 3 b is the test result figure of embodiment 1 sample, Fig. 3c is the test result figure of the sample of Example 2, and Fig. 3d is the test result figure of the sample of Example 3;

Figure 4 is the single-cell electrochemical impedance test spectrum of the samples of Examples 1-3 and Comparative Example 1, wherein Figures 4a-4c and Figures 4d-4f are Nyrnquist diagrams, The corresponding phase angle frequency diagram and the maximum phase angle frequency diagram;

Fig. 5 is the test graph of the fuel cell of Examples 1-3 and Comparative Example 1, wherein Fig. 5a is a linear volt-ampere characteristic graph, and Fig. 5b is a discharge energy graph;

Fig. 6 is a schematic structural view of the fuel cell described in the specific embodiment;

Explanation of reference signs:

1. Anode gas diffusion layer;

2. Cathode gas diffusion layer;

3. Anode catalytic layer;

4. Cathode catalytic layer;

5. Proton exchange membrane;

6. Anode plate;

7. Cathode plate.

Detailed ways

In order to explain in detail the technical content, structural features, achieved goals and effects of the technical solution, the following will be described in detail in conjunction with specific embodiments and accompanying drawings.

In order to describe in detail the technical content, structural features, achieved goals and effects of the technical solution, the following will be described in detail in conjunction with specific embodiments. This embodiment is carried out on the premise of the technical solution of the present invention, and the detailed implementation and specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

In the description of the present application, the numerical range represented by "numerical value A to numerical value B" refers to the range including the endpoint numerical value A, B and all numerical values within the range.

First, the application of the gas diffusion layer with a hydrophilic and hydrophobic structure provided in a specific embodiment of the present invention in a fuel cell will be described.

An application of a gas diffusion layer with a hydrophilic and hydrophobic structure in a fuel cell, wherein the gas diffusion layer with a hydrophilic and hydrophobic structure is used in a fuel cell as a cathode gas diffusion layer and an anode gas diffusion layer, and the gas diffusion layer with a hydrophilic and hydrophobic structure The gas diffusion layer includes a hydrophilic area and a hydrophobic area, the hydrophilic area is only a local area of the gas diffusion layer treated by a hydrophilic agent, and the hydrophobic area is a gas diffusion area treated successively by a hydrophilic agent and a hydrophobic agent. layer local area; adjacent hydrophilic areas are separated by hydrophobic areas;

The hydrophilic agent is an oxidizing solution, and the hydrophobic agent includes any one or at least two of polytetrafluoroethylene emulsion, fluorinated ethylene propylene copolymer, polyvinylidene fluoride emulsion or polyhexafluoropropylene emulsion The combination.

In the application provided by the above technical solution, the gas diffusion layer with a hydrophilic and hydrophobic structure has good mass transfer efficiency and can more effectively reduce the voltage loss caused by mass transfer. It is applied to a fuel cell, so that the gas phase and liquid phase in the fuel cell The transport of phases can be distinguished, promote the accumulation and discharge of water, have lower ohmic resistance at high current density, and can effectively reduce the gas phase starvation problem caused by the accumulation or repulsion of the liquid phase by the single wettability of the wall , so as to increase the limiting current density, and more effectively reduce the voltage loss caused by mass transfer, thereby improving the performance of the fuel cell.

In some embodiments of the present invention, the fuel cell includes: a membrane electrode assembly including the anode gas diffusion layer, the cathode gas diffusion layer, the anode catalyst layer, the cathode catalyst layer and a proton exchange membrane, the proton The exchange membrane is sandwiched between the anode catalyst layer and the cathode catalyst layer, the outer surface of the anode catalyst layer is pressed against the anode gas diffusion layer, and the outer surface of the cathode catalyst layer is bonded to the cathode gas diffusion layer. Diffusion layer lamination;

an anode plate on the outer surface of the anode gas diffusion layer of the membrane electrode assembly; and

The cathode plate is located on the outer surface of the cathode gas diffusion layer of the membrane electrode assembly.

In some embodiments of the present invention, there are multiple hydrophobic regions, and the size of each hydrophobic region changes in the following manner: sequentially increasing or decreasing sequentially in a predetermined direction. For example, the area size of each hydrophobic region may increase sequentially in a gradient from left to right in the length direction of the gas diffusion layer, or decrease sequentially in a gradient. Alternatively, the size of each hydrophobic area is as follows: it is large in the middle and small in the surrounding area, or small in the surrounding area and large in the middle. Compared with a gas diffusion layer with a single hydrophilic wettability or a gas diffusion layer with a hydrophilic and hydrophobic structure without gradient changes, the gas diffusion layer with a gradient hydrophilic and hydrophobic structure shows better mass transfer efficiency and can be more effective The voltage drop caused by mass transfer loss is reduced.

In some embodiments of the present invention, the hydrophilic agent is hydrogen peroxide, potassium permanganate or potassium dichromate. Preferably, the hydrophilic agent is a hydrogen peroxide solution with a mass concentration of 30%.

In some embodiments of the present invention, the hydrophobic agent is a polytetrafluoroethylene emulsion, and the polytetrafluoroethylene emulsion is a mixture of polytetrafluoroethylene, isopropanol, and glycerol in a ratio of 10:85:5 Post-dilute the resulting emulsion. Preferably, the mass fraction of the polytetrafluoroethylene emulsion is 20wt%.

In some embodiments of the present invention, the difference in contact angle of the gas diffusion layer having a hydrophilic-hydrophobic structure is >30°. When the gradient difference is lower than 30°, the liquid phase at the boundary of the wettability gradient is easily affected by the gas phase flow rate, and gathers together at the end of the gas phase transport direction, which reduces the specific surface area of the three-phase contact of the catalytic site and affects the electrochemical rate and battery performance. performance. When the gradient difference is greater than 30°, there is an obvious boundary at the wettability boundary of the gas diffusion layer, and there is an obvious liquid phase tendency on the surface.

In some embodiments of the present invention, the preparation method of the gas diffusion layer having a hydrophilic-hydrophobic structure comprises the following steps:

S1. Pretreatment: immerse the gas diffusion layer to be treated in deionized water, and then dry it naturally after ultrasonic oscillation;

S2. Hydrophilic treatment: immerse the dried gas diffusion layer to be treated in a hydrophilic agent, heat it to 75°C-85°C, keep it warm for 1.5-2.5 hours, wash it with deionized water for 2-4 times, and then rinse it with deionized water. Ultrasonic vibration in water and drying; then, calcining the dried gas diffusion layer at 400°C to 500°C for 1.5 to 2.5 hours, deionized cleaning, and drying to obtain a hydrophilic gas diffusion layer for later use;

S3. Hydrophobic treatment: divide the hydrophilic gas diffusion layer into hydrophilic and hydrophobic regions according to preset regions, apply a hydrophobic agent on the hydrophobic region, and pump the hydrophilic gas diffusion layer along the thickness direction of the hydrophilic gas diffusion layer. Gas drying, repeated coating and drying 2 to 4 times; then, the dried gas diffusion layer was kept at 115 ℃ to 125 ℃ for 0.5 to 1.5 hours, rinsed with deionized water 2 to 4 times, and dried; then, the The dried gas diffusion layer is calcined at 350° C. to 400° C. for 1.5 to 2.5 hours to obtain a gas diffusion layer with a hydrophilic and hydrophobic structure.

In the above technical solution, a gas diffusion layer with a hydrophilic-hydrophobic structure can be prepared through hydrophilic treatment and hydrophobic treatment in a local area, which is simple and easy to implement and has a good application prospect.

In some embodiments of the present invention, the gas diffusion layer to be treated is carbon paper or carbon cloth.

In some embodiments of the present invention, in step S3, the coating method of the hydrophobic agent includes scraping method, screen printing method, coating method or spraying method.

The above is the core technical solution of the present invention, and the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

The raw materials and reagents used in the following examples can be obtained from commercial sources unless otherwise specified. The experimental methods in the following examples are conventional methods unless otherwise specified.

In the following specific examples, the hydrophilic agent adopts 30% hydrogen peroxide solution, and the hydrophobic agent adopts the polytetrafluoroethylene emulsion (by polytetrafluoroethylene, isopropanol, glycerol by 10: 85:5 ratio mixed and then diluted to obtain the emulsion), the gas diffusion layer to be treated adopts the coating method of the carbon cloth hydrophobic agent and adopts the spraying method, which is illustrated as an example, but it is not used to limit the implementation and protection scope of the present invention .

Examples 1-3 Application of a gas diffusion layer with a hydrophilic and hydrophobic structure in a gas battery

(1) Preparation of gas diffusion layer with hydrophilic and hydrophobic structure

S1. Pretreatment: Cut the raw carbon cloth (Taiwan Carbon Energy, WOS1002) into a size of 50×50mm ² , soak it in deionized water, and ultrasonically vibrate (KQ3200E, working frequency 40KHz) to remove the raw carbon cloth during production and Auxiliaries and various types of dust attached to the surface during transportation should be dried naturally for 30 minutes.

S2. Hydrophilic treatment: immerse the dried raw carbon cloth in 30% hydrogen peroxide solution, heat it to 80°C, and keep it warm for 2 hours, and use the oxidation of hydrogen peroxide solution to remove the weak boundary layer and graphite on the surface. The crystallites are oxidized, increasing their oxygen-containing functional groups. Then, rinse with deionized water for 3 times, then place the green carbon cloth in deionized water and vibrate ultrasonically for 20 minutes to fully remove the hydrogen peroxide solution remaining on the carbon cloth, and dry it. Next, place the dried raw carbon in air at 450°C for calcination for 2 hours, the specific surface area increases sharply, deionized cleaning, and drying to obtain a hydrophilic gas diffusion layer for future use.

S3. Hydrophobic treatment: the hydrophilic gas diffusion layer is divided into hydrophilic and hydrophobic areas according to the preset area, and 20wt% polytetrafluoroethylene emulsion is coated on the hydrophobic area, and along the thickness of the hydrophilic gas diffusion layer Pump air in the direction to make it dry, and repeat the coating and dry for 3 times to ensure that the inner wall of the aperture of the gas diffusion layer contains a hydrophobic agent. Next, the dried gas diffusion layer was placed in an oven and heated to 120°C for 1 hour, rinsed repeatedly with deionized water for 3 times to remove excess hydrophobic agent on the surface of the carbon cloth, and dried in the air. Next, place the dried gas diffusion layer in an oven, heat it to 380° C., and calcinate it for 2 hours to obtain a gas diffusion layer with a hydrophilic-hydrophobic structure.

In step S3, before coating, after the hydrophilic gas diffusion layer (hydrophilized carbon cloth) is fixed with a clamp, the hydrophobic agent is sprayed on the hydrophobic area according to the pre-divided area (outside leakage of the clamp) materials section). The use of fixtures can better adapt to the subsequent infiltration in the surface and the wettability gradient is clearer. At the same time, the contact surface area of the hydrophilic-hydrophobic gradient can be gradually increased according to the needs, and the three-phase contact rate of the catalytic site can be increased.

When the hydrophobic agent is directly sprayed on the required area, more hydrophobic agent molecules will be suspended on the surface of the carbon cloth. Therefore, in order to achieve hydrophobic modification of the inner wall of the mass transfer channel, it is necessary to design an in-plane infiltration device to introduce the hydrophobic agent molecules into the pore size. inside, and ensure that the hydrophobic agent molecules will not be excessively aggregated to block the pores. The in-plane infiltration device is shown in Figure 1a and 1b, which is used to cooperate with the area coating fixture to suck the hydrophobic agent sprayed on the gas diffusion layer into the aperture, and let the gas diffusion layer dry.

The gas diffusion layers with hydrophilic and hydrophobic structures prepared in Examples 1-3 are respectively named as sample b, sample c and sample d. Wherein, the coating areas of sample b, sample c and sample d are 40×40mm ² , 50×20mm ² , and 4×15×15mm ² +20×20mm ² , respectively.

(2) Preparation of fuel cell

The gas diffusion layers (samples b to d) with hydrophilic and hydrophobic structures prepared in Examples 1 to 3 were used as the anode gas diffusion layer and the cathode gas diffusion layer to prepare fuel cells respectively, which were respectively denoted as fuel cell b and fuel cell c and fuel cells d.

Specifically, as shown in Figure 6, the fuel cell includes:

Membrane electrode assembly, including anode gas diffusion layer 1, cathode gas diffusion layer 2, anode catalyst layer 3, cathode catalyst layer 4 and proton exchange membrane 5, proton exchange membrane 5 is sandwiched between anode catalyst layer 3 and cathode catalyst layer 4 Between, the outer surface of the anode catalytic layer 3 is pressed with the anode gas diffusion layer 1, and the outer surface of the cathode catalytic layer 4 is pressed with the cathode gas diffusion layer 2;

an anode plate 6 located on the outer surface of the anode gas diffusion layer 1 of the membrane electrode assembly; and

The cathode plate 7 is located on the outer surface of the cathode gas diffusion layer 2 of the membrane electrode assembly.

Comparative Example 1 Application of Hydrophilic Gas Diffusion Layer in Gas Batteries

(1) Preparation of hydrophilic gas diffusion layer

S1. Pretreatment: Cut the raw carbon cloth (Taiwan Carbon Energy, WOS1002) into a size of 50×50mm ² , soak it in deionized water, and ultrasonically vibrate (KQ3200E, working frequency 40KHz) to remove the raw carbon cloth during production and Auxiliaries and various types of dust attached to the surface during transportation should be dried naturally for 30 minutes.

S2. Hydrophilic treatment: immerse the dried raw carbon cloth in 30% hydrogen peroxide solution, heat it to 80°C, and keep it warm for 2 hours, and use the oxidation of hydrogen peroxide solution to remove the weak boundary layer and graphite on the surface. The crystallites are oxidized, increasing their oxygen-containing functional groups. Then, rinse with deionized water for 3 times, then place the green carbon cloth in deionized water and vibrate ultrasonically for 20 minutes to fully remove the hydrogen peroxide solution remaining on the carbon cloth, and dry it. Next, after the dried carbon was placed in the air at 450°C for calcination for 2 hours, the specific surface area increased sharply, deionized cleaning, and drying to obtain a hydrophilic gas diffusion layer, which was named sample a.

(2) Preparation of fuel cell

The gas diffusion layer (sample a) with a hydrophilic and hydrophobic structure prepared in Comparative Example 1 was used as an anode gas diffusion layer and a cathode gas diffusion layer to prepare fuel cells, respectively. The specific structure of the fuel cell (referred to as fuel cell a) is the same as that of the fuel cell in Examples 1 to 3, except that the anode gas diffusion layer and the cathode gas diffusion layer are both gas diffusion layers prepared in Comparative Example 1 .

Experimental example 1 wettability characterization

The wettability was characterized by measuring contact angle and scanning electron microscope (scanning electron microscope, SEM) picture, using HITACHI UHR FE-SEM SU8000 Series to measure SEM scanning electron microscope picture and POWEREACH-JC2000C1 to measure contact angle. The single-cell test mainly measures the polarization curve and electrochemical impedance spectrum. The measurement of the polarization curve adopts the potentiostatic measurement method, controls the output voltage of the battery, and records the current response under the corresponding voltage. The electrochemical impedance spectroscopy was used to measure the current density as 0 and 1.5A*cm ² .

Fig. 2 shows the SEM pictures of the samples of Examples 1-3 and Comparative Example 1. It can be seen from Figure 2a that after the hydrophilization treatment of the raw carbon cloth, the surface of a single carbon fiber contains grooves corroded by hydrogen peroxide solution, and the grooves are basically distributed along the carbon fiber axis, which increases the contact with oxygen. The specific surface area and surface chemical energy, after high temperature treatment, the structure of carbon fiber is formed, which greatly improves the hydrophilicity of carbon fiber and raw carbon cloth. It can be seen from Figures 2b to 2c that after the regional hydrophobization treatment, the hydrophobic agent component is well attached to the single carbon fiber, which increases the roughness of the carbon fiber surface, and the attached hydrophobic agent particles and the bonding agent The binder reduces the surface energy of the carbon fiber surface very well, and secondly, the hydrophobic properties of the hydrophobic agent particles make the regionally treated carbon cloth have stable hydrophobic properties. The number of hydrophobic agent particles attached to the carbon fibers of samples b, c, and d increased sequentially while the surface hydrophobic agent content decreased. From a microscopic perspective, the attachment sites of the hydrophobic agent on the carbon fiber were not continuous, often accompanied by changes in the hydrophilic and hydrophobic intervals. However, after synthesis, with the increase of the content of the hydrophobic agent, its hydrophobicity is enhanced. Macroscopically speaking, the hydrophobicity on the carbon cloth surface decreases sequentially, while the hydrophobicity on the inner wall of the pore increases sequentially.

Fig. 3 shows the static contact angle test results of the samples of Examples 1-3 and Comparative Example 1. Among them, Fig. 3a shows sample a after hydrophilization treatment, and its contact angle is 34.3°, showing good hydrophilicity, which also shows that the wettability of the carbon cloth obtained by hydrophilization treatment has been changed; Fig. 3b The contact angle of sample b coated with a 40×40mm ² hydrophobized area after hydrophilization treatment reached 134.47°; Figure 3c and 3d are the contact angles of sample c and sample d respectively, which are 124.42°, 49.93° and 105.51°, 34.76°. In practice, it shows a good gradient of hydrophilicity and hydrophobicity. Since the wettability of samples a and b shows a single hydrophilicity or hydrophobicity, no wettability gradient comparison is made; the wettability of samples c and d are in contact with each other. The angular differences are 74.49° and 70.75°, respectively. There is an obvious boundary at the wettability boundary, and there is an obvious liquid phase tendency on the surface.

The hydrophobicity of samples c and d are both weaker than that of sample b. This is because the air pump (in-plane infiltration device) continues to work during the air-drying process after the hydrophobic agent is coated, and the hydrophobic agent coated on the surface The components are introduced into the pores of the carbon cloth by air flow and bonded to the carbon fibers. With the reduction of the regional coating area, under the same condition of the working power of the air pump and the mass fraction of the hydrophobic agent emulsion, the content of the hydrophobic agent entering the pore increases, and the content of the hydrophobic agent remaining on the surface decreases, that is, samples b, The hydrophobicity of c and d is weakened. The difference between the hydrophilic and hydrophobic contact angles of samples c and d is similar, indicating that the hydrophobic agent particles are hardly dispersed in the plane when they are pumped into the pore, but are distributed along the axis of the carbon fiber with the direction of the airflow velocity, which means that when the regional coating When coating, the smaller the coating area, the more hydrophobic agent content enters the inside of the pore, and the stronger the hydrophobicity of the inner wall of the pore.

When there are hydrophilic and hydrophobic wettability intervals on a single carbon fiber in the micro-scale range (approximate to the carbon fiber diameter scale), the macroscopic performance of the overall wettability is similar to the superposition effect in the wave propagation process. When the number of hydrophilic intervals in the area accounts for a large proportion and contains hydrophobic intervals, the macroscopic performance is wettability with relatively weakened hydrophilicity; when the number of hydrophobic intervals in the area accounts for a large proportion and contains hydrophilic intervals , the macroscopic performance is wettability with weakened hydrophobicity, which is the reason why the hydrophobicity of samples b, c, and d are weakened in turn, and the hydrophilicity is also weakened.

Experimental example 2 Electrochemical and battery performance test

The measurement results of electrochemical impedance spectroscopy are often drawn as impedance spectroscopy in the form of Nyquist diagrams, which can intuitively see the real and imaginary parts of the impedance at different frequencies, and the mass transfer loss characterizes the molecular Transmission resistance, the main causes of which are gas starvation and motor flooding. The expression of the finite layer diffusion resistance is:

In the formula, σ is the Warburg coefficient of the substance, which represents the effectiveness of the substance to reach or leave the effective reaction interface, defined as

In the formula, n is the number of transported electrons; F is the Faraday constant, C·mol ^-1 ; A is the electrode area, cm ² ; C is the total concentration of the substance, mol·m ^-3 ; D is the diffusion coefficient of the substance, cm ² · s ^-1 . δ is the thickness of the diffusion layer, cm; ω is the disturbance frequency. If the concentration of the substance is high and the diffusion speed is fast, the impedance caused by mass transfer can be ignored if σ is small; on the contrary, the impedance caused by mass transfer will be obvious if σ is large.

FIG. 4 shows the electrochemical impedance spectra of the samples of Examples 1-3 and Comparative Example 1. The ohmic losses caused by the four samples at 0 current density are basically similar, and the capacitive arcs of samples b, c, and d are also basically similar, and the diameter of the capacitive arc of sample a is significantly larger. In the case of high current density, the ohmic loss caused by sample c is the smallest, the capacitive arc of sample a is the smallest, and the ohmic loss and capacitive arc caused by sample b are the largest. The details are shown in Table 1.

Table 1 Embodiment 1～3 and comparative example 1 sample electrochemical impedance test result table

Among them, the modulus values of samples c and d are always higher than those of a and b, and the performance of sample d is particularly prominent. The biggest difference is that the frequency of the maximum value of the modulus is different, and that of sample d is 5082Hz. In the high and middle range of frequency, it shows charge transfer impedance. The smaller the diameter of the arc, the lower the charge transfer impedance. Samples c and d have better performance at low current density. The oblique line in the low frequency region is the Warbug impedance of ions on the electrode, that is, the diffusion resistance of ions when they diffuse to the electrode surface. At low frequencies, the slant line of sample c is almost parallel to the imaginary part, while at high frequencies, sample a shows the characteristics of pure resistance, and sample c shows the characteristics of series resistance and capacitance, which is capacitive ion diffusion. For samples c, b, In the order of d, the electrochemical capacitance decreases gradually.

In the case of high current density, due to the purely resistive characteristics of sample a, no detailed comparison is made. The order of ohmic loss is sample b, d, c from high to low, and the fitting radius R _P of the semi-circle is sample b, c, d from high to low in order, and the intercept value of the slope line in the real part in the low frequency area is from From large to small, they are b, d, and c in sequence. Combining with formula 2, it can be known that the diffusion coefficients of samples c and d are greater than those of sample b, and with the increase of frequency, sample b shows an obvious relaxation process, while at low frequency, the sample a also has a more obvious relaxation process. In summary, the overall performance of samples c and d is better than that of samples a and b, that is, the battery performance after the hydrophilic-hydrophobic gradient treatment of GDL is better than that of the single wettability treatment, especially at high current In case of density.

FIG. 5 shows test curves of the fuel cells of Examples 1-3 and Comparative Example 1. In the linear volt-ampere characteristic curve of Figure 5a, the open circuit voltages of the four fuel cells are basically equal, and as the current density increases, the voltage of fuel cell b drops the fastest, while the decline trends of fuel cells c and d are similar. However, in the concentration polarization part, the voltage drop of fuel cell d is relatively gentle, and its final limiting current density is also larger than that of fuel cell c. In the discharge energy curve, the discharge energy of fuel cell d is the largest, and is always higher than the values of other fuel cells. With the increase of current density, the difference between the discharge energy of fuel cells c and d is almost constant, and the curve is Parallel changes. In the discharge energy curve of Figure 5b, the reason why the performance of fuel cell d is better than that of fuel cell c is that the specific surface area of its hydrophilic and hydrophobic gradient increases during the wettability gradient treatment, which effectively increases the gas-liquid two-phase differential transport. occur, and make the liquid phase less prone to excessive aggregation at a certain level to reduce the utilization of catalytic sites. Combining with electrochemical impedance spectroscopy, the ohmic loss of fuel cell d is higher than that of fuel cell c, which is also reflected in the polarization curve, that is, the rate of decline in the middle half of the curve of fuel cell d is relatively fast, but the latter curve is relatively stable , which means that the GDL after the pro-hydrophobic gradient treatment shows a relatively good mass transfer efficiency, which effectively reduces the voltage drop caused by the mass transfer loss. Gradient combination modes (Examples 2 and 3) can effectively improve battery performance.

It should be noted that although the above-mentioned embodiments have been described herein, the scope of patent protection of the present invention is not limited thereby, and when the technical parameters not described in detail are changed within the parameter range listed in the present invention, they can still be obtained. The same or similar technical effects as those of the above embodiments still belong to the protection scope of the present invention. Therefore, based on the innovative concept of the present invention, the changes and modifications made to the embodiments described herein, or the equivalent structure or equivalent process conversion made by using the description of the present invention and the contents of the accompanying drawings, directly or indirectly apply the above technical solutions In other related technical fields, all are included in the patent protection scope of the present invention.

Claims (10)

1. The application of the gas diffusion layer with the hydrophilic and hydrophobic structure in the fuel cell is characterized in that the gas diffusion layer with the hydrophilic and hydrophobic structure is applied to the fuel cell as a cathode gas diffusion layer and an anode gas diffusion layer, the gas diffusion layer with the hydrophilic and hydrophobic structure comprises a hydrophilic area and a hydrophobic area, the hydrophilic area is a local area of the gas diffusion layer which is only treated by a hydrophilic agent, and the hydrophobic area is a local area of the gas diffusion layer which is sequentially treated by the hydrophilic agent and the hydrophobic agent; adjacent hydrophilic regions are separated by hydrophobic regions;

the hydrophilic agent is a solution with oxidizing property, and the hydrophobic agent comprises any one of or the combination of at least two of polytetrafluoroethylene emulsion, fluorinated ethylene-propylene copolymer, polyvinylidene fluoride emulsion or polyhexafluoropropylene emulsion.

2. Use according to claim 1, wherein the fuel cell comprises:

the membrane electrode assembly comprises the anode gas diffusion layer, the cathode gas diffusion layer, an anode catalyst layer, a cathode catalyst layer and a proton exchange membrane, wherein the proton exchange membrane is clamped between the anode catalyst layer and the cathode catalyst layer, the outer side surface of the anode catalyst layer is pressed with the anode gas diffusion layer, and the outer side surface of the cathode catalyst layer is pressed with the cathode gas diffusion layer;

an anode plate positioned on the outer side surface of the anode gas diffusion layer of the membrane electrode assembly; and

and the cathode plate is positioned on the outer side surface of the cathode gas diffusion layer of the membrane electrode assembly.

3. The use of claim 1, wherein the hydrophobic region is a plurality of hydrophobic regions, and the size of the area of each hydrophobic region varies as follows:

the gradient of the material is increased in sequence in a preset direction, or the gradient of the material is decreased in sequence; or,

the middle is big, the periphery is small, or the periphery is small and the middle is big.

4. Use according to claim 1, characterized in that the hydrophilic agent is hydrogen peroxide, potassium permanganate or potassium dichromate.

5. The use according to claim 1, wherein the hydrophilic agent is a 30% by mass hydrogen peroxide solution.

6. The use according to claim 1, wherein the hydrophobic agent is a polytetrafluoroethylene emulsion prepared from polytetrafluoroethylene emulsion, isopropanol, glycerol, in a ratio of 10:85:5, and diluting to obtain 20% emulsion.

7. Use according to claim 6, wherein the polytetrafluoroethylene emulsion is present in a mass fraction of 20 wt.%.

8. The use according to claim 1, wherein the difference in contact angle of the gas diffusion layer with an amphiphilic structure is >30 °.

9. Use according to any one of claims 1 to 8, wherein the method for preparing a gas diffusion layer having a hydrophobic-hydrophilic structure comprises the steps of:

s1, pretreatment: immersing a gas diffusion layer to be treated in deionized water, and naturally drying after ultrasonic oscillation;

s2, hydrophilization treatment: immersing the air-dried gas diffusion layer to be treated into a hydrophilic agent, heating to 75-85 ℃, preserving heat for 1.5-2.5 h, washing with deionized water for 2-4 times, ultrasonically oscillating in the deionized water, and drying; then, calcining the dried gas diffusion layer for 1.5-2.5 h at 400-500 ℃, and then carrying out deionization cleaning and drying to obtain a hydrophilic gas diffusion layer for later use;

s3, hydrophobization treatment: dividing hydrophilic and hydrophobic areas of the hydrophilic gas diffusion layer according to a preset area, coating a hydrophobic agent on the hydrophobic area, performing air suction drying along the thickness direction of the hydrophilic gas diffusion layer, and repeatedly coating and drying for 2-4 times; then, preserving the heat of the dried gas diffusion layer for 0.5-1.5 h at the temperature of 115-125 ℃, washing the gas diffusion layer for 2-4 times by using deionized water, and airing; and then calcining the air-dried gas diffusion layer at 350-400 ℃ for 1.5-2.5 h to obtain the gas diffusion layer with the hydrophilic-hydrophobic structure.

10. The use according to claim 9, wherein in step S3, the water repellent agent is applied by a blade coating method, a screen printing method, a coating method or a spray coating method.

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