CN110600749B

CN110600749B - Integrated diffusion layer of fuel cell and preparation method and application thereof

Info

Publication number: CN110600749B
Application number: CN201910866681.2A
Authority: CN
Inventors: 赵红; 舒清柱; 王素力; 魏伟
Original assignee: Dalian Jiaotong University
Current assignee: Dalian Jiaotong University
Priority date: 2019-09-12
Filing date: 2019-09-12
Publication date: 2022-05-24
Anticipated expiration: 2039-09-12
Also published as: CN110600749A

Abstract

The invention relates to a gas diffusion layer of a fuel cell, in particular to an integrated diffusion layer and a preparation method and application thereof. The preparation method takes carbon fiber as a framework, compounds a multi-walled carbon nanotube, takes N-methyl pyrrolidone as a dispersing agent for high-speed dispersion, takes Polytetrafluoroethylene (PTFE) as a bonding agent and a water repellent, and prepares the novel integrated diffusion layer by one step through a decompression suction filtration forming method. The integrated diffusion layer replaces the traditional diffusion layer consisting of carbon paper and a microporous layer, and the maximum power density of a single cell when the integrated diffusion layer is applied to the cathode of a direct methanol fuel cell or simultaneously used as a cathode diffusion layer and an anode diffusion layer is respectively improved by 20 percent and 35 percent compared with that of a commercial diffusion layer. The integrated diffusion layer is applied to the oxygen electrode of the zinc-air battery, and the maximum power density is up to 200mA cm^‑2This also provides a potential direction for the search for new diffusion layer processes and materials for fuel cells with high performance and low cost.

Description

Integrated diffusion layer of fuel cell and preparation method and application thereof

Technical Field

The invention relates to a gas diffusion layer of a fuel cell, in particular to an integrated diffusion layer and a preparation method and application thereof.

Background

Proton Exchange Membrane Fuel Cells (PEMFCs), Direct Methanol Fuel Cells (DMFCs), metal air cells, and the like have been the focus of research in recent years due to their advantages of high power density, high energy conversion efficiency, low-temperature start-up, no pollution, and light weight^[1-3]. A Membrane Electrode Assembly (MEA), which is a core component of a fuel cell, is generally prepared from a gas diffusion layer, a catalyst layer, and a proton exchange membrane by a hot-pressing process. The gas diffusion Layer is located between the catalyst Layer and the flow field plate, and generally comprises a support Layer (BL) and a Microporous Layer (MPL)^[4]. Supporting layer mainTo support the microporous layer and the catalytic layer, collect current, conduct gas, and discharge water, etc., it is made of an electrically conductive porous material having a thickness of about 100-; the microporous layer is contacted with the catalyst layer, usually a carbon powder layer is coated on the surface of the microporous layer in order to improve the pore structure of the support layer, the thickness of the microporous layer is about 10-100 mu m, the microporous layer has the functions of reducing the contact resistance of the support layer and the catalyst layer, performing secondary distribution on materials, and particularly performing water management on the membrane electrode, such as preventing the electrode catalyst layer from being flooded with water, preventing the catalyst layer from leaking to a substrate layer in the preparation process, and the like. The ideal diffusion layer should therefore have good gas permeability, water permeability, electron conductivity and a certain mechanical strength and good electrochemical stability^[5]。

Carbon Fiber Papers (CFPs) are widely used for gas diffusion layer substrate materials because of their advantages such as high electrical conductivity, excellent corrosion resistance, gas permeability, and high mechanical strength. CFPs are typically made by combining Carbon Fibers (CFs) with thermosetting resins (e.g., phenolic resins) and then carbonizing the combined product at high temperatures^[6]。Mathur^[7]And soaking the carbon fibers in thermosetting resin, and graphitizing at 2500 deg.c to obtain the composite paper. And the influence of the process parameters such as mould pressing, resin content, carbonization temperature and the like on the performance of the carbon paper is studied in detail, and a basis is provided for the preparation and improvement of the probe paper. However, CFs are difficult to disperse uniformly in a slurry form, and their bulk density is not easy to control. Therefore, CFPs are easily broken during the assembly of the fuel cell stack, and the CFPs preparation process is complicated, and the high temperature carbonization process undoubtedly increases the production cost. To overcome these problems, bitumen-based diffusion layers are often employed to reduce the fragility and cost of the diffusion layer^[8]. However, the asphalt-based CFs have relatively low electrical conductivity, which limits their wide application, and in recent years, researchers have proposed several methods for improving asphalt-based electrical conductivity by adding various nano-fillers, and adding nano-porous carbon materials into composite materials not only improves the porosity of the materials, but also positively affects the physical and chemical properties of CFs due to the porosity of the carbon materials themselves and the network structure formed between two or more materials^[9]. Among them, multi-walled carbon nanotubes (MWCNTs) have received much attention. MWCNT toolHas the advantages of large surface area, low density, heat resistance, good electrical conductivity, large mechanical strength and the like, and is a promising composite material filler^[10]。

Disclosure of Invention

In order to overcome the defects in the prior art, the invention provides an integrated diffusion layer and a preparation method and application thereof.

In order to realize the purpose, the invention adopts the following technical scheme:

the invention provides a preparation method of an integrated gas diffusion layer of a fuel cell, which is characterized in that asphalt-based Carbon Fiber (CF) is used as a framework, a composite multi-walled carbon nanotube (MWCNT) is used as a dispersing agent, N-methyl pyrrolidone (NMP) is used as a dispersing agent, Polytetrafluoroethylene (PTFE) is used as a bonding agent and a water repellent agent, and the integrated gas diffusion layer is prepared by combining high-speed stirring and dispersing and performing a decompression suction filtration molding method.

In the above technical solution, specifically, the preparation method comprises the following steps:

(1) solution A: adding dispersant N-methyl pyrrolidone (NMP) into a multi-walled carbon nano tube, and dispersing at the rotating speed of 15000-20000 rmp after ultrasonic treatment to obtain solution A;

(2) solution B: adding dispersant N-methyl pyrrolidone (NMP) into carbon fibers, and performing ultrasonic treatment to obtain a solution B;

(3) mixing the solution A obtained in the step (1) and the solution B obtained in the step (2), adding PTFE slurry, performing ultrasonic agitation, performing high-speed stirring at 15000-20000 rmp, performing suction filtration to form a film, and drying to obtain a preformed diffusion layer;

(4) and (3) treating the preformed diffusion layer at 300-350 ℃ for 2-3h to obtain the integrated diffusion layer.

In the technical scheme, the length of the carbon fiber is 5-10 mm.

In the technical scheme, the mass ratio of the carbon fiber carbon nano tube is 1: 1-5: 1.

In the above technical solution, further, the mass ratio of the carbon nanotubes to the carbon fibers is 3: 1.

In the technical scheme, specifically, the dispersion concentration of the carbon nano tubes in the NMP dispersant in the step (1) is 30-50 wt%; the dispersion concentration of the carbon fiber in the NMP dispersant in the step (2) is 30-50 wt%.

In the technical scheme, specifically, the ultrasonic dispersion time of the MWCNT in the step (1) is 1-2h, the ultrasonic dispersion time of the CF in the step (2) is 20-40 min, and the ultrasonic dispersion time in the step (3) is 30 min-1 h.

In the above technical solution, specifically, the concentration of the PTFE slurry in step (3) is 10 wt% to 20 wt%.

In another aspect, the invention provides an integrated gas diffusion layer, which is prepared by the above preparation method.

The invention provides the application of the integrated gas diffusion layer in the cathode and the anode of a proton exchange membrane fuel cell, the cathode and the anode of a direct methanol fuel cell and the cathode of a metal-air cell.

The invention has the beneficial effects that: according to the preparation method, N-methyl pyrrolidone (NMP) is used as a dispersing agent, and the carbon nano tubes are dispersed more uniformly and combined with carbon fibers more fully through high-speed stirring, so that a novel micron-nano porous diffusion layer is constructed. The carbon nano tubes with high conductivity are distributed in the carbon fibers in a gradient manner, so that electron transmission is facilitated, a formed multistage pore structure is beneficial to material distribution, the PTFE which is uniformly distributed is beneficial to water removal, the carbon nano tubes are distributed in multistage pore sizes in the suction filtration film forming process, and the surface with more enrichment can be directly used as a microporous layer, so that the novel diffusion layer prepared by the method disclosed by the invention is an integrated diffusion layer, and no additional microporous layer is needed, so that the traditional diffusion layer consisting of carbon paper and the microporous layer is replaced, the preparation process is simple, and the preparation cost is reduced.

The integrated diffusion layer prepared by the method has flexibility, and overcomes the defects of high brittleness and easy damage of the existing carbon paper or carbon cloth.

The thickness of the integrated diffusion layer prepared by the method can reach 120nm, and the integrated diffusion layer is thinner than the traditional diffusion layer and has strong mass transfer capability.

The integrated diffusion layer prepared by the method is applied to a DMFC cathode or simultaneously used as a cathode and anode diffusion layer, the maximum power density of a single cell is respectively improved by 20 percent and 35 percent compared with that of a commodity diffusion layer, the mass transfer polarization control area is obviously improved, and the integrated diffusion layer can also be used as a diffusion layer of an oxygen electrode of a zinc-air cell and has higher performance than that of the commodity diffusion layer.

The preparation method has low requirements on raw materials, and the used carbon fibers and carbon nanotubes are made of the most common and cheap materials, so that the raw materials and the preparation cost are greatly reduced.

Drawings

FIG. 1 is a schematic diagram of a preparation process of the present invention;

FIG. 2 optical photographic image of the integrated diffuser layer prepared in example 1; a. unfolding and placing, and b, bending for 180 degrees;

FIG. 3 SEM morphology comparison of GDL/CNT-CF with GDL/Toray-060H: (a) (b) is the front side of GDL/CNT-CF, (c) and (d) are the back side and cross section of GDL/CNT-CF, respectively; (e) (f) the front side of GDL/Toray-060H, and (g) the back side and the cross section of GDL/Toray-060H, respectively;

FIG. 4 pore size and distribution plot for the integral diffusion layer prepared in example 1;

FIG. 5 shows the results of single cell performance tests of different ratios of DGL/CNT-CF applied to DMFC cathodes;

FIG. 6 is a graph comparing the performance of assembled cells when GDL/CNT-CF (3:1) and GDL/Toray-060H are used as the cathode diffusion layer of DMFC, respectively; (a) is an alternating current impedance spectrum when a single cell discharges at a constant current of 100mA cm & lt-2 & gt; (b) is a polarization curve;

FIG. 7 results of single cell testing of the integrated diffusion layer prepared in example 1 applied simultaneously to the cathode and anode of DMFC;

FIG. 8 is a polarization diagram of the performance of a zinc-air cell assembled with GDL/CNT-CF (3:1) as the cathode diffusion layer and a commercial cell.

Detailed Description

The invention is further illustrated but is not in any way limited by the following specific examples.

Carbon Fiber (CF), nanjing latitude composite limited, 5mm in length; a multi-walled Carbon Nanotube (CNT), New energy Material Ltd, outer diameter 15-30 nm, length 100-200 μm; n-methyl pyrrolidone (NMP), national pharmaceutical group chemical Co., Ltd; polytetrafluoroethylene slurry (PTFE) at a concentration of 60 wt%, shanghai sanai rich new materials, inc.

Example 1 preparation of an integral diffusion layer

Weighing 45mg of multi-walled carbon nanotubes in a 100mL beaker, 45mL of N-methylpyrrolidone (NMP) was added as a dispersant (about 1mg mL)^-1) Performing ultrasonic treatment for 1h, and dispersing for 3min at a rotating speed of 20000rmp by using a high-speed disperser to obtain a solution A; 15mg of carbon fiber was weighed and 45mL of NMP (1/3mg mL) was added^-1) Performing ultrasonic treatment for 30min to obtain solution B; pouring A into the solution B, adding 6mg of PTFE slurry (10%), performing ultrasonic treatment in an ultrasonic cleaner for 1h, stirring at 20000rpm for 3min, and rapidly filtering with a prepared suction filtration device to obtain PTFE membrane (45 μm). Then drying at 130 ℃ in vacuum, and finally placing the preformed diffusion layer in a high-temperature tube furnace for processing for 3h at 350 ℃ to obtain the novel integrated diffusion layer (GDL/CNT-CF). The preparation method is schematically shown in figure 1; the photo of the cut entity of the prepared integrated diffusion layer is shown in fig. 2, and it can be seen from fig. 2 that the diffusion layer prepared by the invention is a thin film with certain mechanical strength, can be bent by 180 degrees without damage, and has very good flexibility.

Example 2

Preparing GDL/Toray-060H, namely, taking commercial Toray-060H carbon paper as a cathode and anode diffusion layer substrate, taking a proper amount of Polytetrafluoroethylene (PTFE) and carbon powder (XC-72), uniformly stirring to form mixed slurry, and coating the mixed slurry on the substrate by a coating method to prepare a microporous layer. The loading amounts of XC-72R and PTFE in the anode/cathode microporous layer are respectively 2mg cm ^-210 wt% and 2mg cm^-2、40wt％。

Example 3

The structure and microstructure of the diffusion layer prepared in example 1 were characterized by JOEL JSM-6360LV field emission Scanning Electron Microscope (SEM) and compared with the commercial diffusion layer of example 2, and the comparison results are shown in FIG. 3.

From the microscopic morphology of the front surface, the carbon nano tubes are dispersed very uniformly and are well dispersed, and PTFE small balls are also uniformly embedded on the carbon nano tubes; the carbon fibers and the carbon nanotubes are interwoven together from the reverse side topography, and a plurality of larger holes are formed among the carbon fibers; the novel GDL has the thickness of only 120nm, which is about 1/2 of a commercial diffusion layer, the content of the carbon nano tubes is distributed in a gradient manner from the front to the back, more carbon nano tubes are enriched on the front, the carbon nano tubes can directly serve as a microporous layer and are in contact with a catalytic layer, carbon fibers are more at the bottom, the pore structure is gradually increased, the large pores are beneficial to water transportation, small hydrophobic pores are kept free distribution of gas, the novel diffusion layer can be integrated, no additional microporous layer is needed, and the novel GDL is simpler and more convenient to prepare in the process.

Example 4

The cathode diffusion layer with a proper pore structure is vital to effective transfer of gas and discharge of water, and the pore size and distribution of the diffusion layer are represented by a PoreMaster-60 mercury intrusion instrument. As shown in fig. 4, GDL/Toray-060H has a certain small pore structure, while GDL/CNT-CF has a distribution in both large and small pores, and more of the large pore structure is more favorable for material transportation, which is corresponding to the result of example 3.

Example 5

Adopting JC2000C1 contact angle tester manufactured by Shanghai Zhongchen company, SZ-82 four-probe tester manufactured by Suzhou telecommunication instruments ltd, and self-made sealing device^[11]And respectively representing the hydrophilicity and the hydrophobicity, the conductivity and the porosity of the diffusion layer by a suspension impregnation method.

The test results are shown in table 1, and the homemade novel GDL/CNT-CF shows good performance no matter in thickness, facing resistance, porosity, density and flexibility, which lays a foundation for excellent battery performance.

TABLE 1 structural parameters of novel diffusion layers

Example 5

Diffusion layers of CNT and CF in different mass ratios were prepared as in example 1, with the CNT to CF ratio in the diffusion layer directly affecting the physical parameters of the diffusion layer and also affecting the cell performance differently. Fig. 5 shows the results of single cell tests performed with 5 GDL/CNT-CF electrodes in different ratios under oxygen atmosphere for DMFC cathodes, test conditions: temperature 90 ℃, anode 1M CH₃OH feed at a flow rate of 1mL min^-1Cathode O₂Flow rate of 200mL min^-1As can be seen from fig. 5, the polarization curve of the cell shows a trend of increasing first and then decreasing, and the performance difference of the cell is mainly reflected in the high current density region, i.e., the mass transfer polarization control region. The GDL/CNT-CF (1:1) has the lowest peak power density, and the GDL/CNT-CF (5:1), the GDL/CNT-CF (2:1) and the GDL/CNT-CF (4:1) are followed, while the GDL/CNT-CF (3:1) assembled single cell has the optimal performance, and the maximum output power density of air and oxygen is 90mW cm^-2And 110mWcm^-2。

Example 6

The diffusion layer GDL/CNT-CF (3:1) prepared in example 1 was compared to the cell performance of the commercial diffusion layer GDL/Toray-060H assembly of example 2; and (3) testing conditions are as follows: the temperature was 90 ℃ and the anode was fed with 1M CH3OH at a flow rate of 1ml min^-1Cathode O₂At a flow rate of 200ml min^-1. The comparison result is shown in fig. 6, the intersection point of the high-frequency arc and the real axis of the impedance spectrum is generally marked as the internal resistance of the cell, as shown in fig. 6(a), the internal resistance of the cell assembled by GDL/CNT-CF (3:1) is slightly smaller than that of the cell assembled by GDL/Toray-060H, and the radius of the low-frequency arc of the former is far smaller than that of the latter, which proves that the introduction of the carbon nanotube enables the novel diffusion layer to have more excellent conductivity and mass transfer performance. In the performance curve of FIG. 6(b), the peak power density of the GDL/CNT-CF (3:1) assembled cell is as high as 196mW cm^-2164mW cm compared to commercial electrodes^-2The improvement is about 20 percent, and the novel integrated diffusion layer has great application potential in DMFC cathodes.

Example 7

The diffusion layer GDL/CNT-CF (3:1) prepared in example 1 was simultaneously applied to the cathode and anode of DMFC, and the single cell was assembled for testing under the test conditions: the temperature was 80 ℃ and the anode was fed with 0.5M methanol at a flow rate of 1mL min^-1Introducing oxygen to the cathode at a gas flow rate of 100ml min^-1. As shown in FIG. 7, it can be seen that the performance of the single cell assembled by GDL/CNT-CF is significantly higher than that of the cell assembled by GDL/Toray-060H, especially in the high current density region, the limiting current density is as high as 500mA cm^-2About 1.8 times that of a Toray-060H assembled cell (its limiting current density is 278mA cm)^-2) Meanwhile, the maximum power density of the former is 126mW cm^-2Also, compared with the latter (93mW cm)^-2) The improvement is about 35%.

Example 8

The integral diffusion layer prepared in example 1 was applied to a zinc air battery cathode. FIG. 8 is a polarization curve diagram of the cell performance of the new GDL/CNT-CF (3:1) assembled zinc-air cell and commercial cathode diffusion layer assembled cell, with specification of 2X 2cm²The electrolyte is 7M KOH solution at open room temperature. As can be seen from the figure, the common working point of the zinc-air battery is 50mA cm^-2When the cell is used, the output voltage of the zinc-air cell assembled by adopting the GDL/CNT-CF (3:1) is 1.14V, which is higher than that of a single cell assembled by a traditional commercial diffusion layer (1.05V). And as the current density increases, the difference in performance between the two further increases. The maximum power density of the zinc-air battery assembled by GDL/CNT-CF (3:1) is as high as 200mA cm^-2Single cell (152mA cm) assembled with respect to a commercial diffusion layer^-2) The improvement is 32%, which shows that the discharge performance in the high current density area, namely the mass transfer polarization control area is superior to that of a single cell assembled by a commodity diffusion layer.

It will be apparent to those skilled in the art from this disclosure that many changes and modifications can be made, or equivalents modified, in the embodiments of the invention without departing from the scope of the invention. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention shall still fall within the protection scope of the technical solution of the present invention, unless the contents of the technical solution of the present invention are departed.

Example 9

Several main raw materials of the diffusion layer of the inventionThe cost of (2) is about 6.134 rmb/m as shown in Table 2²Even with the added cost of post-production of materials and labor costs, the total cost is much lower than that of the commodity diffusion layer, indicating that it is of great commercial value.

TABLE 2 cost chart of novel diffusion layer raw material

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Claims

1. the preparation method of the fuel cell integrated gas diffusion layer is characterized in that the method takes asphalt-based carbon fiber as a framework, compounds a multi-walled carbon nanotube, takes N-methyl pyrrolidone as a dispersing agent, takes polytetrafluoroethylene as a binding agent and a water repellent agent, combines high-speed stirring and dispersion, and is prepared by a decompression suction filtration forming method in one step; the preparation method comprises the following steps:

(1) preparation of solution A: adding dispersant azomethine pyrrolidone into a multi-walled carbon nano tube, and dispersing at the rotating speed of 15000-20000 rmp after ultrasonic treatment to obtain a solution A;

(2) preparing a solution B: taking carbon fibers, adding dispersant N-methyl pyrrolidone, and performing ultrasonic treatment to obtain a solution B;

(4) treating the preformed diffusion layer at 300-350 ℃ for 2-3h to obtain an integrated diffusion layer;

the content of the multi-wall carbon nano-tube is distributed in a gradient way from the front to the back, and the pore structure at the bottom is gradually increased.

2. The production method according to claim 1, wherein the carbon fiber has a length of 5 to 10 mm.

3. The production method according to claim 1, wherein the mass ratio of the carbon nanotube/carbon fiber is 3: 1.

4. The preparation method according to claim 1, wherein the dispersion concentration of the carbon nanotubes in the dispersant N-methylpyrrolidone in the step (1) is 30 to 50 wt%; the dispersion concentration of the carbon fiber in the dispersant N-methyl pyrrolidone in the step (2) is 30-50 wt%.

5. The preparation method of claim 1, wherein the ultrasonic dispersion time of the multi-walled carbon nanotubes in the step (1) is 1-2h, the ultrasonic dispersion time of the carbon fibers in the step (2) is 20-40 min, and the ultrasonic dispersion time in the step (3) is 30 min-1 h.

6. The production method according to claim 1, wherein the concentration of the PTFE slurry in the step (3) is 10 to 20% by weight.

7. An integrated gas diffusion layer, wherein the diffusion layer is prepared by the method of any one of claims 1 to 6.

8. Use of the integrated gas diffusion layer of claim 7 in a proton exchange membrane fuel cell cathode and anode, a direct methanol fuel cell cathode and anode, or a metal air cell cathode.