A microporous layer for a gas diffusion layer and a method for manufacturing the same
By preparing a carbon black-free microporous layer and employing fiber materials and heat treatment technology, the problems of microporous layer durability and pore structure control were solved, achieving efficient water-gas transport and large-scale production, which is suitable for proton exchange membrane fuel cells.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SOUTH CHINA UNIV OF TECH
- Filing Date
- 2023-02-01
- Publication Date
- 2026-05-29
AI Technical Summary
In existing technologies, microporous layers have poor durability, are prone to cracking, have difficult-to-control pore structure, and traditional methods are not conducive to large-scale production.
Microporous layers are prepared using high molecular weight polyethylene fiber, polyimide fiber, polyacrylonitrile fiber, poly(p-phenylenebenzodioxazole) fiber or aramid fiber as raw materials through fibrillation, sieving, wet molding, heat treatment and hydrophobic treatment, avoiding the use of carbon black and controlling the pore size to be between 100 nm and 10000 nm.
It provides a durable, crack-free microporous layer, improves the water-gas transport channel, reduces concentration loss, and is suitable for proton exchange membrane fuel cells under different operating conditions. The preparation method is simple and suitable for large-scale production.
Smart Images
Figure CN116314860B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of proton exchange membrane fuel cells, and particularly to a microporous layer for gas diffusion layer and its preparation method. Background Technology
[0002] The gas diffusion layer (GDL) is a crucial component in a proton exchange membrane fuel cell (PEMFC) and is central to maintaining the cell's operating efficiency. When a PEMFC operates at high current density, a significant amount of water is generated within the cell, making the GDL susceptible to flooding and resulting in substantial concentration losses. Conversely, low water content in the proton exchange membrane increases ohmic losses, necessitating excellent moisture retention properties in the GDL to maintain adequate water content. Therefore, the GDL requires superior water management performance to mitigate both ohmic and concentration losses.
[0003] GDL (Gas Difference Layer) consists of a microporous layer and a substrate layer. Traditional microporous layers are composed of carbon black and a hydrophobic agent. However, traditional microporous layers suffer from problems such as easy cracking, carbon black shedding during use, and water vapor transport. The microporous layer needs to possess good air permeability, hydrophobicity, and a suitable pore size to solve these problems. Chinese Patent 114709435 provides a method for preparing a microporous layer that solves the problem of surface cracking, but it still uses carbon black, and problems such as carbon black shedding and difficulty in controlling pore size persist. Chinese Patent CN115020736 prepares a gas diffusion layer based on a fiber-arranged microporous layer. This microporous layer improves battery performance, but it still uses carbon black and a large amount of organic solvent. Chinese Patent CN114824298 obtains a gas diffusion layer by pre-oxidizing, heat-treating, and carbonizing electrospun polyacrylonitrile fibers to obtain a membrane, which is then composited with carbon paper. Although this method produces a microporous layer without carbon black, it cannot control the pore structure of the microporous layer, the process is cumbersome, and it is not conducive to large-scale preparation.
[0004] Currently, the coating method is still the primary method for large-scale preparation of microporous layers. However, this method is prone to cracking, carbon black easily detaches during operation, and it is not conducive to controlling the pore structure of the microporous layer. Electrospinning can improve the durability of microporous layers and eliminate crack formation, but it is costly and not suitable for large-scale production. Therefore, preparing low-cost, highly durable microporous layers with easily controllable pore structures is of great significance for PEMFCs. Summary of the Invention
[0005] To address the shortcomings of existing technologies, the present invention aims to provide a novel microporous layer for gas diffusion layers and its preparation method, thereby solving the problems of poor durability, crack and pore structure control in existing microporous layers.
[0006] To address the aforementioned problems, this invention proposes a novel microporous layer for gas diffusion layers, characterized by comprising the following steps:
[0007] Step A, Preparation of microporous layer precursor: The synthetic fiber is fibrillated, then the treated fiber is sieved to obtain nanofibers, and finally the nanofibers are wet-formed to obtain microporous layer precursor.
[0008] Step B, Preparation of the microporous layer: The microporous layer precursor obtained in step A is subjected to high-temperature heat treatment, followed by hydrophobic treatment, and finally sintering and cooling to obtain the microporous layer.
[0009] Preferably, the synthetic fiber in step A is at least one selected from high molecular weight polyethylene fiber, polyimide fiber, polyacrylonitrile fiber, poly(p-phenylenebenzodioxazole) fiber, and aramid fiber; the freeness of the fibrillation treatment is 10–95°SR; the sieve mesh size is 100–1000 mesh; and the basis weight of the microporous layer precursor is 1–200 g / m³. 2 .
[0010] Preferably, the beating degree is 20–60°SR; the sieve mesh size is 200–600 mesh; and the quantitative amount of the microporous layer precursor is 10–100 g / m³. 2 The fibrillation process involves obtaining fibrillated fibers through mechanical pulping.
[0011] Preferably, the heat treatment temperature in step B is 900–3000℃, the heating rate is 1–100℃ / min, and the holding time is 0.5–5h; the sintering temperature is 300–400℃, and the sintering time is 0.2–4h.
[0012] Preferably, the heat treatment temperature is 1000-2000℃, the heating rate is 5-50℃ / min, and the holding time is 0.5-2h; the sintering temperature is 330-350℃, and the sintering time is 0.5-2h.
[0013] Preferably, the hydrophobic treatment in step B involves immersing the microporous layer precursor in a hydrophobic solution for 1 to 10 minutes; the hydrophobic solution is an aqueous solution of at least one fluoride; and the concentration of the hydrophobic solution is 5 wt.% to 30 wt.%.
[0014] Preferably, the fluoride is at least one of polytetrafluoroethylene and fluorinated ethylene propylene copolymer, with a concentration of 10 wt.% to 20 wt.%; and the impregnation time is 1 to 5 min.
[0015] Preferably, the wet forming steps in step A are fiber decomposition, forming, pressing, and drying.
[0016] A microporous layer for gas diffusion layer prepared by the above preparation method.
[0017] Compared with other methods, the beneficial technical effects of this invention are:
[0018] 1. The microporous layer for gas diffusion provided by the present invention does not contain carbon black as in traditional microporous layers, thus solving the problems of carbon black shedding and poor durability in traditional microporous layers.
[0019] 2. The microporous layer for gas diffusion provided by the present invention has no cracks on its surface and has abundant micro- and nano-pores, which can provide abundant water vapor transport channels, thereby improving the concentration loss problem under high current density.
[0020] The method for preparing the microporous layer for gas diffusion provided by this invention is simple, environmentally friendly, and conducive to large-scale production. It facilitates the preparation and control of the pore structure of the microporous layer, with the average pore size controllable between 100 nm and 10000 nm, enabling its application in proton exchange membrane fuel cells under different operating conditions. Attached Figure Description
[0021] Figure 1 (A)(B)(C)(D) are SEM images of Example 1, Example 2, Example 3 and Comparative Example 1, respectively.
[0022] Figure 2 These are pore size distribution diagrams of the gas diffusion layers prepared in Examples 1-3 and Comparative Example 1 of the present invention.
[0023] Figure 3 These are average pore size diagrams of the gas diffusion layers obtained in Examples 1-3 and Comparative Example 1 of the present invention.
[0024] Figure 4 These are battery performance curves of the gas diffusion layers prepared in Examples 1-4 and Comparative Example 1 of this invention. Detailed Implementation
[0025] The following describes some specific embodiments of the present invention. It should be noted that the described embodiments are only some embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention.
[0026] Example 1
[0027] 500g of poly(p-phenylenebenzodioxazole) fiber (PBO fiber) was weighed and mechanically beaten using a beater to obtain PBO fibrillated fibers with a freeness of 10°SR. The PBO fibrillated fibers were then placed in a grading sieve and passed through a 100-mesh sieve to obtain PBO nanofibers with a mesh size >100. A wet-forming process was used to prepare PBO nanofiber paper to obtain a microporous layer precursor with a basis weight of 20 g / cm³. 2 The microporous layer precursor was then placed in an atmosphere furnace for high-temperature heat treatment at a heating rate of 5℃ / min, a temperature of 900℃, and a holding time of 2h. After being allowed to cool to room temperature, the obtained sample was immersed in a 5wt.% polytetrafluoroethylene (PTFE) solution for 5min for hydrophobic treatment. The treated sample was then placed in a drying oven for sintering at 350℃ for 2h. After cooling, the microporous layer was obtained. Finally, the microporous layer and carbon paper (TGP-H-060, Toray) were placed together to form the gas diffusion layer.
[0028] Example 2
[0029] 500g of PBO fibers were weighed and mechanically beaten using a beater to obtain PBO fibrillated fibers with a freeness of 10°SR. The PBO fibrillated fibers were then placed in a grading sieve and passed through a 200-mesh sieve to obtain PBO nanofibers with a mesh size >200. A wet-forming process was used to prepare PBO nanofiber paper to obtain a microporous layer precursor, with a basis weight of 20 g / cm³. 2 The microporous layer precursor was then placed in an atmosphere furnace for high-temperature heat treatment at a heating rate of 5℃ / min, a temperature of 900℃, and a holding time of 2h. After being allowed to cool to room temperature, the obtained sample was immersed in a 5wt.% PTFE solution for 5min for hydrophobic treatment. The treated sample was then placed in a drying oven for sintering at 350℃ for 2h. After cooling, a microporous layer was obtained. Finally, the microporous layer and carbon paper (TGP-H-060, Toray) were placed together to form the gas diffusion layer.
[0030] Example 3
[0031] 500g of PBO fibers were weighed and mechanically beaten using a beater to obtain PBO fibrillated fibers with a freeness of 10°SR. The PBO fibrillated fibers were then placed in a grading sieve and passed through a 200-mesh sieve to obtain PBO nanofibers with a mesh size >200. A wet-forming process was used to prepare PBO nanofiber paper to obtain a microporous layer precursor, with a basis weight of 40 g / cm³. 2The microporous layer precursor was then placed in an atmosphere furnace for high-temperature heat treatment at a heating rate of 5℃ / min, a temperature of 900℃, and a holding time of 2h. After being allowed to cool to room temperature, the obtained sample was immersed in a 5wt.% PTFE solution for 5min for hydrophobic treatment. The treated sample was then placed in a drying oven for sintering at 350℃ for 2h. After cooling, a microporous layer was obtained. Finally, the microporous layer and carbon paper (TGP-H-060, Toray) were placed together to form the gas diffusion layer.
[0032] Example 4
[0033] 500g of polyacrylonitrile (PAN) fiber was weighed and mechanically beaten using a beater to obtain PBO fibrillated fibers with a freeness of 10°SR. The PAN fibrillated fibers were then placed in a grading sieve and passed through a 200-mesh sieve to obtain PAN nanofibers with a mesh size >200. A wet-forming process was used to prepare PAN nanofiber paper to obtain a microporous layer precursor with a basis weight of 20 g / cm³. 2 The microporous layer precursor was then placed in an atmosphere furnace for high-temperature heat treatment at a heating rate of 5℃ / min, a temperature of 900℃, and a holding time of 2h. After being allowed to cool to room temperature, the obtained sample was immersed in a 5wt.% PTFE solution for 5min for hydrophobic treatment. The treated sample was then placed in a drying oven for sintering at 350℃ for 2h. After cooling, a microporous layer was obtained. Finally, the microporous layer and carbon paper (TGP-H-060, Toray) were placed together to form the gas diffusion layer.
[0034] Example 5
[0035] 500g of aramid fiber was weighed and mechanically beaten using a beater to obtain aramid fibrillated fibers with a freeness of 10°SR. The aramid fibrillated fibers were then placed in a grading sieve and passed through a 200-mesh sieve to obtain aramid nanofibers with a mesh size >200. A wet-forming process was used to prepare aramid nanofiber paper to obtain a microporous layer precursor with a basis weight of 20g / cm³. 2 The microporous layer precursor was then placed in an atmosphere furnace for high-temperature heat treatment at a heating rate of 5℃ / min, a temperature of 900℃, and a holding time of 2h. After being allowed to cool to room temperature, the obtained sample was immersed in a 5wt.% PTFE solution for 5min for hydrophobic treatment. The treated sample was then placed in a drying oven for sintering at 350℃ for 2h. After cooling, a microporous layer was obtained. Finally, the microporous layer and carbon paper (TGP-H-060, Toray) were placed together to form the gas diffusion layer.
[0036] Example 6
[0037] 500g of aramid fiber was weighed and mechanically beaten using a beater to obtain aramid fibrillated fibers with a freeness of 10°SR. The aramid fibrillated fibers were then placed in a grading sieve and passed through a 200-mesh sieve to obtain aramid nanofibers with a mesh size >200. A wet-forming process was used to prepare aramid nanofiber paper to obtain a microporous layer precursor with a basis weight of 40g / cm³. 2 The microporous layer precursor was then placed in an atmosphere furnace for high-temperature heat treatment at a heating rate of 5℃ / min, a temperature of 900℃, and a holding time of 2h. After being allowed to cool to room temperature, the obtained sample was immersed in a 5wt.% PTFE solution for 5min for hydrophobic treatment. The treated sample was then placed in a drying oven for sintering at 350℃ for 2h. After cooling, a microporous layer was obtained. Finally, the microporous layer and carbon paper (TGP-H-060, Toray) were placed together to form the gas diffusion layer.
[0038] Example 7
[0039] 500g of aramid fiber was weighed and mechanically beaten using a beater to obtain aramid fibrillated fibers with a freeness of 10°SR. The aramid fibrillated fibers were then placed in a grading sieve and passed through a 200-mesh sieve to obtain aramid nanofibers with a mesh size >200. A wet-forming process was used to prepare aramid nanofiber paper to obtain a microporous layer precursor with a basis weight of 20g / cm³. 2 The microporous layer precursor was then placed in an atmosphere furnace for high-temperature heat treatment at a heating rate of 5℃ / min, a temperature of 1400℃, and a holding time of 2h. After being allowed to cool to room temperature, the resulting sample was immersed in a 5wt.% PTFE solution for 5min for hydrophobic treatment. The treated sample was then placed in a drying oven for sintering at 350℃ for 2h. After cooling, a microporous layer was obtained. Finally, the microporous layer and carbon paper (TGP-H-060, Toray) were placed together to form the gas diffusion layer.
[0040] Comparative Example 1
[0041] Conductive carbon black and PTFE dispersion were dispersed in isopropanol solution by ultrasonic stirring to obtain a uniformly mixed slurry. The slurry was then coated onto the surface of hydrophobically treated carbon paper and sintered in an oven at 350°C to obtain the final gas diffusion layer.
[0042] The experimental results of the above embodiments and comparative examples are as follows:
[0043] Figure 1 (A)(B)(C)(D) are SEM images of Example 1, Example 2, Example 3 and Comparative Example 1, respectively. As can be seen from the images, compared with Comparative Example 1, the microporous layer prepared by the present invention has no cracks on the surface due to solvent evaporation.
[0044] Figure 2 These are pore size distribution diagrams for Examples 1, 2, 3 and Comparative Example 1. It can be seen that the pore size distribution trends of Examples 1 and Comparative Example 1 are consistent. In Example 1, there are more pores >2μm compared to other samples. The pore size distributions of Examples 2 and Comparative Example 1 are quite similar.
[0045] Figure 3 The diagram shows the average pore size of Examples 1, 2, 3 and Comparative Example 1. It can be seen that the average pore size of Example 1 is slightly larger than that of the Comparative Example, the average pore size of Example 3 is slightly smaller than that of the Comparative Example, and the average pore size of Examples 2 and Comparative Example 1 is close to 2.42 μm. This shows that the method provided by the present invention can adjust the pore size of the microporous layer with a simple process.
[0046] Figure 4 These are battery performance curves for Examples 1, 2, 3, 4, and Comparative Example 1. Experimental results show that Example 1, with its larger average pore size, has a slightly lower limiting current density than Comparative Example 1; Example 2, with an average pore size similar to Comparative Example 1, exhibits superior battery performance; Example 3, with its smaller average pore size, has a higher limiting current density than Comparative Example 1; while Example 4, with an average pore size slightly larger than Comparative Example 1, has a limiting current density not significantly different from Comparative Example 1.
Claims
1. A method for preparing a microporous layer for a gas diffusion layer, characterized in that, Includes the following steps: Step A, Preparation of microporous layer precursor: The synthetic fiber is fibrillated, then the treated fiber is sieved to obtain nanofibers, and finally the nanofibers are wet-formed to obtain microporous layer precursor. The freeness of the fibrillation treatment is 20-60°SR; the sieve mesh size is 200-600 mesh; and the quantitative amount of the microporous layer precursor is 10-100 g / m³. 2 ; Step B, Preparation of microporous layer: The microporous layer precursor obtained in step A is subjected to high temperature heat treatment, then hydrophobic treatment, and finally sintering. After cooling, the microporous layer is obtained. The hydrophobic treatment in step B involves immersing the microporous layer precursor in a hydrophobic solution for 1-10 minutes; the concentration of the hydrophobic solution is 5 wt.% to 30 wt.%. The heat treatment temperature in step B is 900 ℃, the heating rate is 5 ℃ / min, and the holding time is 2h; the sintering temperature is 300~400 ℃, and the sintering time is 0.2~4h.
2. The preparation method according to claim 1, characterized in that, The synthetic fiber mentioned in step A is at least one of high molecular weight polyethylene fiber, polyimide fiber, polyacrylonitrile fiber, poly(p-phenylenebenzodioxazole) fiber, and aramid fiber.
3. The preparation method according to claim 2, characterized in that, The fibrillation process involves obtaining fibrillated fibers through mechanical pulping.
4. The preparation method according to claim 1, characterized in that, The sintering temperature is 330~350 ℃, and the sintering time is 0.5~2 h.
5. The preparation method according to claim 4, characterized in that, The hydrophobic aqueous solution mentioned in step B is an aqueous solution of at least one fluoride.
6. The preparation method according to claim 5, characterized in that, The fluoride is at least one of polytetrafluoroethylene and fluorinated ethylene propylene copolymer, with a concentration of 10 wt.% to 20 wt.%; the impregnation time is 1 to 5 min.
7. The preparation method according to claim 1, characterized in that, The wet forming steps described in step A are fiber decomposition, forming, pressing and drying.
8. The microporous layer for gas diffusion layer prepared by the preparation method according to any one of claims 1 to 7.