CN116264288A

CN116264288A - Fuel cell gas diffusion layer and preparation method and application thereof

Info

Publication number: CN116264288A
Application number: CN202111536868.XA
Authority: CN
Inventors: 侯明; 王曼丽; 齐满满; 刘志成; 邵志刚; 衣宝廉
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2021-12-14
Filing date: 2021-12-14
Publication date: 2023-06-16

Abstract

The invention relates to a fuel cell gas diffusion layer and a preparation method and application thereof, wherein the gas diffusion layer is prepared from a carbon material and a hydrophobic binder through dry compression molding and laser drilling, has good hydrophobicity, gas permeability and conductivity, and can reduce the resistance of water discharge, thereby relieving cathode flooding. The dry preparation avoids the defect that cracks are generated on the surface of the solvent volatilized by the wet method, thereby avoiding flooding caused by water collection at the cracks. The thickness and the porosity of the prepared gas diffusion layer with the ordered pore structure of the carbon-free paper are controllable; the preparation process is simple, the condition is mild, and the requirement on equipment is low. The single-layer ordered gas diffusion layer prepared by the invention has better electrochemical performance when being used as a gas diffusion layer of a fuel cell. The invention has wide application value in the field of fuel cells.

Description

Fuel cell gas diffusion layer and preparation method and application thereof

Technical Field

The invention relates to a single-layer and ordered pore structure gas diffusion layer for a fuel cell, and a preparation method and application thereof, and belongs to the technical field of fuel cells.

Background

The proton exchange membrane fuel cell (proton exchange membrane fuel cells, PEMFC) is an energy conversion device for converting chemical energy into electric energy, and the product is only water, so that the proton exchange membrane fuel cell is environment-friendly, has the advantages of high energy conversion rate, low-temperature rapid start and the like, has good application prospects in the fields of transportation, household power sources, fixed power stations and the like, and is a current research hotspot. However, commercialization has also faced serious challenges, and there is a need for improvement in terms of cost, lifetime, specific power, etc.

When the proton exchange membrane fuel cell is operated at high current density, if the produced water cannot be timely discharged from the PEMFC, the Membrane Electrode (MEA) is flooded, and the hydrogen and the oxygen are prevented from reaching the active site of the catalyst to react, so that the performance of the PEMFC is drastically reduced. And when the water content in the battery is low, the membrane is easy to dry, and the conduction of protons is not facilitated. Therefore, effective water management to maintain water balance within the cell is a key to improving the output performance of the fuel cell, and the gas diffusion layer serves as a core component of the MEA, and has important research significance in carrying the roles of water drainage, gas guide, electrical conduction, catalyst support, and the like in the fuel cell.

The current commercialized gas diffusion layer consists of two layers, one layer is hydrophobic treated carbon paper or carbon cloth, also called substrate layer (GDB); the other layer is a microporous layer (MPL), typically composed of conductive carbon black and a hydrophobic binder. Because the preparation of the carbon paper needs graphitization at 2000 ℃, a large amount of organic solvents are used in the preparation process of the microporous layer, and the traditional GDL preparation has the problems of excessively complex process, high energy consumption, high equipment cost, environmental pollution and the like. And the conventional double-layer gas diffusion layer is applied to the fuel cell, so that flooding is easy to occur under high current density, and the performance of the cell is unstable. In view of the above, there is an urgent need to develop new GDL technologies that have simple processes, low manufacturing temperatures, low energy consumption, and simple equipment costs, so as to manufacture novel, low-cost, high-performance GDLs.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide a single-layer and ordered pore structure gas diffusion layer for a fuel cell, a preparation method and application thereof, wherein the gas diffusion layer can be applied to different humidity conditions in order to reduce cost, improve performance and adapt to mass production.

The technical scheme of the invention is as follows:

in one aspect, the invention provides a proton exchange membrane fuel cell gas diffusion layer, wherein the gas diffusion layer is of a single-layer structure and only comprises carbon-free paper and a self-supporting microporous layer, the microporous layer is of a porous structure, and the porous structure comprises micropores and ordered macropores; the micropores are pores with the pore diameter smaller than 1 mu m, and the pore diameter of the macropores is 20-70 mu m.

Further, in the above technical scheme, the pore diameter of the micropores is 100-1000nm, the pore diameter of the macropores is 30-50 μm, and the porosity of the microporous layer is more than 70%, wherein the ratio of macropores is 30% -35%.

In another aspect, the present invention provides a method for preparing the gas diffusion layer, wherein the microporous layer is prepared by dry molding and laser perforation technology, and the method comprises the following steps:

step one, mechanically grinding and uniformly mixing raw materials, and sequentially carrying out hot pressing and cooling to obtain the self-supporting layer; the raw materials comprise conductive carbon materials and hydrophobic polymer binders;

and secondly, preparing ordered macropores on the self-supporting layer by utilizing a laser perforation technology to obtain the microporous layer.

Further, in the above technical scheme, the mass ratio of the conductive carbon material to the hydrophobic polymer binder is 1:0.075-0.2, preferably 9:1.

Further, in the above technical solution, the conductive material is one or more of conductive carbon powder, carbon fiber, and carbon nanotube.

Further, in the above technical solution, the hydrophobic polymer binder is one or more of Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and perfluoroethylene propylene copolymer (FEP).

Further, in the above technical solution, the dry molding in the first step specifically includes the following steps:

1) Mechanically grinding a certain proportion of carbon material and a hydrophobic agent to form a uniformly mixed microporous layer mixture;

2) Spreading the uniformly mixed mixture in a self-made mold, and keeping the surface flat;

3) Putting the die into a hot press, firstly applying a certain pressure at room temperature to enable the raw materials to be in a sheet shape, then releasing pressure and carrying out heat treatment, keeping for a certain time after the temperature reaches a target temperature to enable the binder to be uniformly dispersed, finally closing and heating to enable the binder to be naturally cooled to the room temperature, and demoulding to obtain the carbon-free paper and the self-supporting layer.

Further, in the above technical solution, the mechanical grinding time is 5-60min, preferably 30min.

Further, in the above technical scheme, the pressure is 0.1-1.0MPa, preferably 0.5MPa, and the pressing time is 1-60min, preferably 30min.

Further, in the above technical scheme, the heat treatment temperature is 150-350 ℃, preferably 150 ℃, and the heat treatment time is 20-60min, preferably 20min.

The invention also provides application of the single-layer and ordered pore structure gas diffusion layer for the proton exchange membrane fuel cell.

In the technical scheme, the cathode fuel and the anode fuel of the proton exchange membrane fuel cell are respectively air and hydrogen which are subjected to the same humidification treatment, and the humidification treatment is 40% -100% RH.

The beneficial effects are that:

1. the surface of the single-layer gas diffusion layer provided by the invention has no crack, an ordered porous structure and a porosity of more than 70%. Ordered macropores within a certain range are beneficial to gas-liquid mass transfer, so that flooding and mass transfer polarization of the battery under large electric density can be reduced.

2. According to the preparation method of the single-layer gas diffusion layer, ordered macropores are prepared on the microporous layer through a laser perforation technology, and the ordered pore structure forms a continuous mass transfer channel, so that a mass transfer path is reduced, the discharge of liquid water is facilitated, and the mass transfer resistance is reduced.

3. According to the invention, the microporous layer is prepared by a dry method, an organic solvent is not introduced in the preparation process, high-temperature treatment is not needed, and the preparation method is healthy, green, cheap and concise and easy for industrial production; meanwhile, the defect that cracks are generated on the surface of the solvent volatilized by the wet method is avoided, so that flooding caused by water collection at the cracks is avoided.

4. Compared with the traditional double-layer gas diffusion layer, the single-layer gas diffusion layer with the ordered pore structure provided by the invention has better mass transfer capacity and electrochemical performance. The reason is that the holes of the traditional gas diffusion layer are randomly distributed, mostly are discontinuous holes, the mass transfer path is tortuous and lengthy, and flooding is easy to cause in dead hole areas. Under the condition of 40% humidification, the mass transfer resistance of the single-layer and ordered pore structure gas diffusion layer sGDL is lower than that of the traditional gas diffusion layer C-GDL, which shows that the sGDL has better gas-liquid mass transfer capability; the cell performance assembled by using the single-layer and ordered pore structure gas diffusion layer as the cathode gas diffusion layer under the 100% humidification condition is superior to that of the traditional gas diffusion layer, wherein the cell performance of sGDL-2 is improved by 60mWcm compared with that of C-GDL ^-2 。

Drawings

Fig. 1 is a schematic diagram of the structure of a single cell. The sGDL is a single-layer and ordered pore structure gas diffusion layer prepared by the method; CCM is a catalyst coated membrane; the C-GDL is a traditional double-layer gas diffusion layer and consists of a microporous layer MPL and a substrate layer GDB.

FIG. 2 (A) is an SEM image of a conventional gas diffusion layer of comparative example 1 of the present invention; fig. 2 (B) and (C) are SEM images of the single-layer and ordered pore structure gas diffusion layer obtained in example 3.

FIG. 3 is a graph showing a comparison of the performance of a full cell under 40% humidification conditions of the single layer, ordered pore structure gas diffusion layers obtained in examples 1-3 of the present invention and the conventional gas diffusion layer of comparative example 1.

FIG. 4 is a graph showing a comparison of the performance of a full cell under 100% humidification conditions of the single layer, ordered pore structure gas diffusion layers obtained in examples 1-3 of the present invention with the conventional gas diffusion layer of comparative example 1.

Detailed Description

The following non-limiting examples will enable those of ordinary skill in the art to more fully understand the invention and are not intended to limit the invention in any way.

Example 1

0.72g of carbon fiber and 0.08g of hydrophobic binder PVDF are weighed, mechanically mixed for 30min by a pulverizer, and after fully grinding and mixing, the uniformly mixed mixture is flatly paved in a self-made stainless steel mold, so that the surface is smooth. The mold was then placed in a hot press and was first pressed at room temperature under a pressure of 0.5MPa for 30min to make the mixture into a tablet. Then releasing pressure and heating to raise the temperature to 150 ℃, and heat treating for 20min at 150 ℃ to uniformly distribute PVDF in the carbon-free paper and self-supporting microporous layer. And closing and heating to naturally cool the die to room temperature, and demolding to obtain the carbon-free paper and the self-supporting microporous layer. Holes with the diameter of 20 mu m are processed on the microporous layer by utilizing a laser drilling technology and named as sGDL-1, wherein the carbon powder loading capacity is 28mg cm ^-2 。

Example 2

0.72g of carbon fiber and 0.08g of hydrophobic binder PVDF are weighed, mechanically mixed for 30min by a pulverizer, and after fully grinding and mixing, the uniformly mixed mixture is flatly paved in a self-made stainless steel mold, so that the surface is smooth. The mold was then placed in a hot press and was first pressed at room temperature under a pressure of 0.5MPa for 30min to make the mixture into a tablet. Then releasing pressure and heating to raise the temperature to 150 ℃, and heat treating for 20min at 150 ℃ to uniformly distribute PVDF in the carbon-free paper and self-supporting microporous layer. And closing and heating to naturally cool the die to room temperature, and demolding to obtain the carbon-free paper and the self-supporting microporous layer. Holes with the diameter of 50 mu m are processed on the microporous layer by utilizing a laser drilling technology and named sGDL-2, wherein the carbon powder loading capacity is 28mg cm ^-2 。

Example 3

0.72g of carbon fiber and 0.08g of hydrophobic binder PVDF are weighed, mechanically mixed for 30min by a pulverizer, and after fully grinding and mixing, the uniformly mixed mixture is flatly paved in a self-made stainless steel mold, so that the surface is smooth. The mold was then placed in a hot press and was first pressed at room temperature under a pressure of 0.5MPa for 30min to make the mixture into a tablet. Then releasing pressure and heating to raise the temperature to 150 ℃, and heat treating for 20min at 150 ℃ to uniformly distribute PVDF in the carbon-free paper and self-supporting microporous layer. Closing and heating to naturally cool the die to room temperature, demolding to obtain a carbon-free paper and self-supporting microporous layer, and processing holes with the diameter of 70 μm on the microporous layer by using a laser drilling technology, which is named sGDL-3, wherein the carbon powder loading amount is 28mg cm ^-2 。

Comparative example 1

The traditional double-layer gas diffusion layer is characterized in that a substrate layer of the traditional double-layer gas diffusion layer is made of PTFE treated carbon paper, a microporous layer is made of carbon powder and PTFE, the specific preparation steps are that carbon powder and PTFE dispersion liquid are uniformly dispersed in isopropanol solvent through ultrasonic and stirring, then uniformly dispersed microporous layer slurry is scraped and coated on the surface of the carbon paper after hydrophobic treatment, and then heat treatment is carried out for 1h at 350 ℃ to remove organic solvent in the diffusion layer, wherein the carbon powder loading of the microporous layer is 1.0mg cm ^-2 The mass fraction of PTFE was 40wt.%, and the conventional double gas diffusion layer was designated C-GDL. The traditional double-layer gas diffusion layer is used as a comparison sample of the carbon-free paper and the self-supporting microporous layer prepared by the preparation method.

The above examples and comparative examples are characterized and experimental results are as follows:

FIG. 2 (A) is an SEM image of the C-GDL obtained in comparative example 1. FIGS. 2 (B) and (C) are SEM images of sGDL-3 obtained in example 3. It can be seen that compared with the gas diffusion layer prepared by the traditional wet method of comparative example 1, the single-layer and ordered pore structure gas diffusion layer prepared by the preparation method of the application has relatively flat surface, no cracks generated by solvent volatilization and ordered arrangement of macropores.

FIG. 3 is a graph showing the full cell performance of sGDL-1 obtained in example 1, sGDL-2 obtained in example 2, sGDL-3 obtained in example 3, and C-GDL obtained in comparative example 1 of the present invention under 40% humidified conditions. Comparing mass transfer polarization areas of the assembled batteries with 4 gas diffusion layers, the mass transfer polarization of the single-layer and ordered pore structure gas diffusion layers sGDL is lower than that of the traditional gas diffusion layer C-GDL, which shows that the sGDL has better gas-liquid mass transfer capability.

FIG. 4 is a graph showing the full cell performance of sGDL-1 obtained in example 1, sGDL-2 obtained in example 2, sGDL-3 obtained in example 3, and C-GDL obtained in comparative example 1 of the present invention under 100% humidified conditions. Comparing the maximum power densities of the assembled cells of the 4 gas diffusion layers, it can be seen that the single-layer, ordered pore structure gas diffusion layer sGDL has cell performance superior to that of the commercial gas diffusion layer (C-GDL), wherein the cell performance of sGDL-2 is improved by 60mW cm compared with that of the C-GDL ^-2 。

Claims

1. The proton exchange membrane fuel cell gas diffusion layer is characterized by having a single-layer structure and only comprising carbon-free paper and a self-supporting microporous layer, wherein the microporous layer has a porous structure, and the porous structure comprises micropores and ordered macropores; the pore diameter of the micropores is smaller than 1 mu m, and the pore diameter of the macropores is 20-70 mu m.

2. The gas diffusion layer according to claim 1, wherein the micropores have a pore size of 100-1000nm, the macropores have a pore size of 30-50 μm, and the microporous layer has a porosity of more than 70%, wherein the macropores have a ratio of 30% -35%.

3. A method of producing a gas diffusion layer according to any one of claims 1 to 2, wherein the microporous layer is produced by dry molding and laser perforation techniques, the method comprising the steps of:

step one, mechanically grinding and uniformly mixing raw materials, and sequentially carrying out hot pressing and cooling to obtain a self-supporting layer; the raw materials comprise conductive carbon materials and hydrophobic polymer binders;

4. A method of preparing according to claim 3, wherein the mass ratio of the conductive carbon material to the hydrophobic polymer binder is 1:0.075-0.2.

5. The method according to claim 3, wherein the conductive material is one or a mixture of more than one of conductive carbon powder, carbon fiber and carbon nanotube; the hydrophobic polymer binder is one or more than one of polytetrafluoroethylene, polyvinylidene fluoride and perfluoroethylene propylene copolymer.

6. A method according to claim 3, wherein said step one specifically comprises the steps of:

1) Mechanically grinding the carbon material and the hydrophobic agent to form a uniformly mixed microporous layer mixture;

2) Spreading the uniformly mixed mixture in a mould, and keeping the surface flat;

3) And (3) putting the die into a hot press, firstly applying pressure at room temperature to enable the raw materials to be in a sheet shape, then releasing pressure, carrying out heat treatment, keeping for a period of time after the temperature reaches a target temperature, uniformly dispersing the binder, finally closing heating, naturally cooling to the room temperature, and demoulding to obtain the self-supporting layer.

7. The method according to claim 6, wherein in the step (1), the mechanical grinding time is 5 to 60 minutes, and in the step (3), the pressure is 0.1 to 1.0MPa, the pressing time is 1 to 60 minutes, the heat treatment temperature is 150 to 350 ℃, and the heat treatment time is 20 to 60 minutes.

8. Use of a gas diffusion layer according to any one of claims 1-2 in a proton exchange membrane fuel cell.

9. The use according to claim 8, wherein the anode and cathode fuels of the pem fuel cell are air and hydrogen, respectively, which are subjected to the same humidification treatment, said humidification treatment being between 40% and 100% relative humidity.