TWI395365B - A method to manufacture the membrane electrode assembly in air breathing fuel cell - Google Patents

Description

Self-calling fuel cell membrane electrode group manufacturing method

The invention belongs to the technical field of material production of chemistry and chemical industry, and relates to a membrane electrode group required for simple preparation of a fuel cell stack, which mainly increases the hydrophobic treatment of the gas diffusion layer and adjusts the size of the nanopore of the nanocarbon gas diffusion layer, and utilizes The inert gas multi-pass spray gun spraying method can uniformly disperse the catalyst slurry on the surface of the carbon gas diffusion layer until the required catalyst content, and then combine with the proton exchange membrane to form a membrane electrode group, etc., and can be used for self-calling. The fuel cell.

For a Proton exchange membrane fuel cell (PEMFC), a single element that combines an anode, a proton exchange membrane, and a cathode into a sandwich structure is called a membrane electrode assembly (MEA). MEA is the core part of PEMFC and is the main place of electrochemical reaction. The performance of MEA directly determines the performance of PEMFC. In a proton exchange membrane fuel cell, a proton conducting polymer is usually used as a binder. The most commonly used Nafion (trade name), the sulfonate functional group responsible for ion conduction in Nafion is hydrophilic. The polytetrafluoroethylene (PTFE) backbone is hydrophobic, and the hydrophobic chain is the main gas channel in the electrode catalyst layer. The MEA produced must balance the hydrophilic ion conduction. Channels and hydrophobic gas channels are used for maximum efficiency.

The anode is mainly composed of carbon cloth (or carbon paper) and a catalyst. It is usually made of carbon cloth (or carbon paper) coated with a catalyst mixed with platinum and carbon powder. According to the mechanism, it can be divided into two regions: a diffusion layer and an active layer. The material of the gas diffusion layer is usually a porous material such as carbon cloth (or carbon paper), and in addition to supporting the catalyst, and expanding the area and area of action of the catalyst, electrons can be introduced or exported, and hydrogen molecules can be supplied. The passage of the reaction zone. When hydrogen passes through the electrode to reach the vicinity of the catalyst, it is necessary to Diffusion moves, so this area is called a gas diffusion layer. The active layer refers to the place where the electrochemical reaction occurs in the MEA, that is, the catalyst portion in the electrode. In order to increase the reaction area and reduce the platinum content, PEMFC generally uses carbon black as a catalyst carrier to improve electrocatalytic activity. cut costs. In the active layer on the hydrogen side, hydrogen is catalyzed by the platinum catalyst to release electrons into hydrogen ions, which are guided away by carbon cloth or carbon paper, and the hydrogen ions pass through the proton exchange membrane to react with oxygen ions.

The cathode structure is the same as the anode, and is also composed of a gas diffusion layer and an active layer. The gas diffusion layer of the cathode is composed of carbon cloth (or carbon paper), and the oxygen molecules are also moved to the vicinity of the catalyst by diffusion, and the carbon cloth (or carbon paper) in the cathode is The electrons involved in the reaction are introduced, and the generated water is also required to be exported. In the active layer of the cathode, the oxygen molecules combine with the hydrogen ions passing through the proton exchange membrane to form water after absorbing the electrons introduced by the carbon cloth (or carbon paper). This reaction process is slower than the anode, so the catalyst content of the cathode is usually Will be higher.

The carbon gas diffusion layer is an important component material of the fuel cell, and the carbon gas diffusion layer functions as an electron channel, a gas channel, and a drainage channel for supporting the catalytic catalyst layer, collecting current, and providing an electrochemical reaction. Generally, the carbon gas diffusion layer is made of carbon paper or carbon cloth as a supporting layer, the carbon paper has a low resistivity, and the carbon cloth has a relatively high resistivity, but the mechanical strength is strong. Carbon paper or carbon cloth has holes and uneven surface, so the surface of carbon paper or carbon cloth needs to be filled with carbon black/fluorocarbon polymer to be leveled and leveled. The leveling treatment has (1) avoiding the catalyst from being trapped in the void and causing waste of the catalyst. (2) Since the carbon paper or the carbon cloth is subjected to hydrophobic treatment, the electric resistance is increased, and if the flattening treatment can enhance the hydrophobic carbon paper or carbon cloth The conductivity, reducing the ohmic loss of the battery (3) adjusting the pore size and distribution of the gas diffusion layer to produce a suitable gas and water channel.

In the carbon gas diffusion layer, the foreign carbon gas diffusion layer has two supporting layers of carbon paper and carbon cloth, such as Electrochem, ion power, Mitsbishi and Ballard (US Pat. No. 5, 863, 673) to develop carbon paper and porous carbon support. The body is a support layer, generally carbon paper is thin and the resistivity is low, the carbon cloth is thick and the resistivity is small. Higher, but not easy to break and easier to mass production. SGL and E-Tek have been developing carbon gas diffusion layers for many years. The gas diffusion layer produced by E-Tek is widely used by academic units. Its products have been commercialized, but the price is expensive. The company is in the gas diffusion layer. There have been many achievements in research, and many papers and patents (USPat.No. 4,647,359) were published. From the literature, it was found that SGL developed gas diffusion layers of different thicknesses and porosity according to the operating conditions of fuel cells.

Catalyst coating method, Susan G. Yan et al., US Pat. No. 2005/0163920 A1, discloses spraying with a light and spraying the catalyst directly onto the film. The disadvantage is that it is difficult to control the uniformity of lamp heating and It is necessary to consider the problem that the film does not deform or wrinkle after spraying, and mass production and automatic production are difficult.

Fuel cells can be classified into active fuel cells and passive fuel cells according to the way oxygen fuel is supplied. Active fuel cells require external power to provide air, such as air pumps, passive fuel cells (such as self-injecting fuel cells). Air fuels provide air by convection of the cathode itself, because passive fuel cells have no external power. The system is more active than simple, but because the air fuel supply rate is slow and it is less able to exclude water (product) by the strong convection of air, it is easy to cause flooding of the fuel cell activation layer, resulting in electrical degradation, so the self-calling type Fuel cell membrane electrodes differ from active fuel cell membrane electrodes in that they require better air fuel delivery channels and better hydrophobic function.

When the invention develops a self-injection fuel cell membrane electrode, the hydrocarbon diffusion layer is subjected to hydrophobic treatment and the nanopore size of the nanocarbon gas diffusion layer is adjusted, and the catalyst is coated by an inert gas spray gun (as shown in FIG. 1). The cloth is disposed on the gas diffusion layer, and the heating temperature at the bottom of the gas diffusion layer is uniformly controlled, and the catalyst is effectively and quickly and evenly distributed in the catalyst layer. The advantage is that the catalyst has uniform distribution, good reproducibility, and multi-pass film coating application. Good, large-area coating, easy to manufacture and automated mass production.

Nano microporous carbon gas diffusion layer technology can improve fuel power Cell membrane electrode set power density. The function of the nanocarbon gas diffusion layer is to support the catalytic catalyst layer, collect current, provide electron channels, gas channels and drainage channels required for electrochemical reaction. The nano carbon gas diffusion layer is generally made of carbon paper or carbon cloth. The carbon paper has a low resistivity, and the carbon cloth has the disadvantages of thicker and higher resistivity, but its mechanical strength is strong and mass production is easy. The carbon cloth has voids and uneven surface, and needs to be leveled to adjust the nanopore size, pore distribution, conductivity and hydrophobic properties of the nanocarbon gas diffusion layer, so as to have suitable gas channels, electron channels and water. aisle. The invention mainly uses a carbon cloth to form a carbon gas diffusion layer, and uses the high conductivity particle size, the slurry solid content, the pre-dip process times and the rolling conditions to control the size, distribution and hydrophobicity of the carbon gas diffusion layer. . The production process is shown in Figure 2A and Figure 2B.

The specifications of the carbon cloth used in the present invention are as shown in Table 1. The carbon cloth is first subjected to hydrophobic treatment, and the carbon cloth is immersed in the diluted fluorinated propylene polymer (FEP) emulsion (FEP120J product of Dupont Company), and taken out and dried in the air. After the heat treatment at 280 to 360 ° C, the prepreg FEP and the heat treatment can be repeated, so that the surfactant contained in the fluorocarbon polymer emulsion impregnated in the carbon cloth is removed, and the fluorocarbon polymer is thermally sintered and uniformly sintered. Dispersed on carbon cloth.

Since the surface of the carbon cloth is uneven and has a hole, it has an influence on the catalytic catalyst layer, so it needs to be leveled. The polytetrafluoroethylene emulsion (PTFE) and the conductive powder were formulated to a fixed ratio, and the polytetrafluoroethylene emulsion was a product of Dupont PTFE 30B. The conductive powder may be carbon black, graphite powder, activated carbon or inert metal powder. The preparation of the conductive powder slurry is the key technology for the production of the gas diffusion layer. The distilled water is selected, and the conductive powder, the polytetrafluoroethylene emulsion and the dispersing agent are mixed. Adjust the slurry solid content to about 5~40wt%. In order to increase the viscosity of the slurry, about 0.5 to 2% by weight of methyl cellulose is added. Mix the slurry with ultrasonic vibration or mechanically. The mixed slurry is applied to the hydrophobically treated carbon cloth by a prepreg process, subjected to rolling, repeated prepreg and rolling steps one to five times until the desired conductive carbon solid content and nanopore size and distribution are required. To make the surface flat, each time the prepreg process is removed from 60 to 120 ° C, then cold-rolled or hot-rolled by 60 to 180 ° C, and finally heat treated at 280 to 360 ° C to make the PTFE hot-melt sintered bond. With hydrophobicity, a carbon gas diffusion layer is produced.

The membrane electrode assembly process is shown in Figure 3. The process is a catalyst slurry preparation. The catalyst slurry is uniformly dispersed on the surface of the carbon gas diffusion layer by a multi-pass nitrogen spray gun spray method until the required catalyst content is dried. Pressing, and then combining with the proton exchange membrane by hot pressing to form a membrane electrode set. 20 wt% Pt/C catalyst, 5 wt% Nafion solution and isopropanol were used in the catalyst slurry configuration. The weight ratio of Pt/C to Nafion solid content was 1.75:1, and the catalyst slurry was uniformly dispersed by spray gun spraying method. On the surface of the carbon gas diffusion layer, the surface temperature of the carbon gas diffusion layer must reach 45-85 ° C, of which 65 ° C is preferred, the anode platinum dosage is controlled at 0.1-0.3 mg/cm ² , and the cathode platinum dosage is 0.3-1 mg/cm. ^{2. The} surface is then sprayed once with a 1 to 5 wt% Nafion solution. The electrode and the proton exchange membrane are hot pressed, and the proton exchange membrane is placed in the middle of the anode and the cathode, and the three sheets are combined into one body by hot pressing. The hot pressing conditions are heated to 120 to 150 ° C for 60 to 90 seconds and then hot pressed for 60 to 100 seconds, and the pressure is 70 to 85 kg / cm ² to obtain a membrane electrode assembly.

The membrane electrode group testing process is as follows. In order to optimize the performance of the self-invoking unit cell, after the unit cell assembly is completed, activation treatment is required. First, the unit cell is connected to the testing machine, and the chemical equivalent ratio is estimated. The hydrogen flow passes through the single cell at no back pressure (1 atm). The initial cell temperature is set at 30 °C, the discharge mode is constant voltage, and its initial set voltage mode, when the open circuit voltage rises to 0.8~1.0V, the voltage is set at 0.5V for 3~5 hours (depending on the current density) Depending on the trend), observe the current change. Then, the temperature of the single cell is raised to 50 ° C ~ 60 ° C, the hydrogen condition is the same as above, after the temperature reaches, set 0.5V, time 0.5 hours, and observe the current change situation, when the current is stable, no longer rise, ie It can be tested, fixed voltage discharge and other experiments. The test system I-V test conditions are: temperature: hydrogen extreme humidification bottle temperature is 25 ° C (room temperature), single cell (or battery) temperature is 40 ° C ~ 60 ° C, gas flow is variable. Back pressure: 1 atmosphere (without back pressure), discharge: with constant voltage. The pore distribution test of the gas diffusion layer was measured using a PMI company's Liquid intrusion porosimeter, with a water injection test, a maximum test pressure of 3000 psi and a micropore minimum of 10 nm.

Example 1

The carbon cloth is first subjected to hydrophobic treatment, and the carbon cloth is immersed in the diluted 5 wt% FEP emulsion (FEP120J product of Dupont Co., Ltd.), taken out in the air and dried, and then dried at 100 ° C for 10 minutes, and then subjected to 350 ° C for 20 minutes. The heat treatment causes the fluorocarbon polymer to be thermally melted and uniformly dispersed on the carbon cloth.

The prepreg was prepared by taking 1039.5 g of distilled water, adding 3.7 g of Triton, and uniformly mixing, and then adding 57.5 g of carbon black (ENSACO 250 Power, average particle size 40 nm, BET 62 m ² /g), and ball milling in a ball mill for 2 hours. After further adding a polytetrafluoroethylene emulsion (PTFE) 30B, it was ball milled for 5 minutes. 1071 g of the mixture was taken out and placed in a PP beaker, 0.8 wt% or 8.57 g of methyl cellulose was added, and the beaker was placed in a hot water bath at 80 ° C for 2 hours, and then continuously stirred for 12 hours without heating, and finally allowed to stand 6 hour. The solid content of the obtained prepreg is 7 to 8 wt%.

The carbon gas diffusion layer is prepared, and the mixed prepreg is coated on the hydrophobically treated carbon cloth by a pre-dip process, and the pre-impregnated carbon cloth is dried at 90 ° C for 30 minutes, and then subjected to hot rolling at 120 ° C. The roller gap is 0.35mm, and the pre-dip process and the rolling step are repeated once until the required conductive carbon solid content and the size and distribution of the nanopores are made to make the surface flat, and then heat-treated at 350 ° C for 30 minutes to make the PTFE hot-melt sintered Bonding and hydrophobicity, that is, a carbon gas diffusion layer is obtained.

The membrane electrode assembly process is shown in Figure 3. In the catalyst slurry configuration, 24 g of 5 wt% Nafion solution and 30 g of isopropyl alcohol were placed in a glass bottle and placed on an electromagnetic heating stirrer for 1 hour. An inert gas such as nitrogen was introduced into the bottle, and 2.4 g of a 20 wt% Pt/C catalyst was slowly poured into the glass bottle, and stirring was continued for 6 hours. At this time, the weight ratio of 20 wt% Pt/C to Nafion solid content was 1.75:1, and the above three components were mechanically mixed uniformly to prepare a catalyst slurry. Place the heating iron plate on the electromagnetic heating stirrer, set the required temperature, and put the carbon gas diffusion layer. When the surface temperature of the carbon gas diffusion layer reaches 65 ° C, spray the gun with an inert gas such as nitrogen. The catalyst slurry is uniformly dispersed on the surface of the carbon gas diffusion layer in multiple passes, and the surface solvent is evaporated and dried once after each pass, and the spraying operation is repeated once until the required catalyst content (the anode platinum amount is controlled at 0.2 mg/ Cm ² , cathode platinum dosage 0.4~1.0mg/cm ² ), the catalyst electrode sheet is placed in a vacuum oven, vacuumed at 70 ° C for 60 minutes, the catalyst electrode sheet is cold rolled by 0.25 mm thickness, the surface is further 2.5 wt The % Nafion solution is sprayed once and thinly. Next, the catalyst electrode 5 cm x 5 cm and the 7 cm x 7 cm Dupont 212 proton exchange membrane product were hot pressed, and the proton exchange membrane was placed in the middle of the anode and cathode, and the three sheets were combined into one body by hot pressing. The hot pressing conditions were as follows: heating to 140 ° C for 1 minute and 10 seconds, pressure 80 kg / cm ² , that is, a 5 cm x 5 cm membrane electrode group, the power of the membrane electrode group in the self-calling air, as shown in FIG.

Example 2

The same as the process of the first embodiment, wherein the carbon cloth is first subjected to a hydrophobic treatment process, and the pre-dip and heat treatment are once, twice, three times and a gas diffusion layer such as a commercial E-Tek model LT 1400-W (hydrophobic treatment of the gas diffusion layer of the secondary process) The pore distribution is shown in Fig. 5). The membrane electrode group was prepared by controlling the catalyst content (the anode platinum dosage was controlled at 0.2 mg/cm ² and the cathode platinum dosage was 0.4 mg/cm ² ), and the membrane electrode group was compared in the self-calling air. The power conductivity, pre-dip and heat-treated secondary and tertiary membrane electrode sets are better than the commercial E-Tek model LT 1400-W. The power of the pre-dip and heat-treated secondary membrane electrode group in the self-calling air can be stably measured continuously for 500 minutes, as shown in FIG. 6 and FIG.

Example 3

In the same manner as in the second embodiment, the carbon gas diffusion layer is formed, the solid content of different conductive carbons and the size and distribution of the nanopores are changed, and the mixed prepreg is coated on the hydrophobically treated carbon cloth by a prepreg process. The carbon cloth after dipping is dried at 90 ° C for 30 minutes, and then hot rolled at 120 ° C. The prepreg process and the rolling step are repeated to control the solid content of different conductive carbons and the size and distribution of the pores of the nanometer to prepare a membrane electrode. Group, the power of the membrane electrode group in self-calling air, as shown in Figure 8.

1‧‧‧Inert gas

2‧‧‧With heating temperature control and microbalance

3‧‧‧ gas diffusion layer

4‧‧‧appropriate spout

5‧‧‧ spray gun

6‧‧‧catalyst paste

Figure 1. Photograph of the membrane electrode assembly.

Figure 2A, the carbon gas diffusion layer hydrophobic treatment production process.

Figure 2B, the production process of the microporous layer of the carbon gas diffusion layer.

Figure 3. Process of making a membrane electrode assembly.

Figure 4. Polarization curves of MEA made from different cathode catalyst contents in self-calling air.

Figure 5. Pore distribution of the gas diffusion layer in the secondary process of hydrophobic treatment.

Figure 6. The MED and the commercial E-Tek gas diffusion layer made by one-time, two-times and three times hydrophobic treatment of the gas diffusion layer, and the polarization curve of the membrane electrode group of the process in self-calling air.

Figure 7. The MEA produced by two hydrophobic treatments of the gas diffusion layer is in self-calling air. Tested for 500 consecutive minutes.

Figure 8. After the two diffusion treatments of the gas diffusion layer, the solid content of different conductive carbons and the size and distribution of the nanopores were controlled to obtain the polarization curve of the MEA made by the membrane electrode group in self-calling air.

Claims (4)

The invention discloses a method for manufacturing a fuel cell membrane electrode assembly, wherein the process is a carbon cloth hydrophobic treatment, a repeated prepreg process and a rolling method for producing a microporous carbon gas diffusion layer, a catalyst slurry preparation, and a multi-pass spray gun spraying method. The slurry is dispersed on the surface of the carbon gas diffusion layer, the catalyst electrode sheet is dried, and finally combined with the proton exchange membrane by hot pressing to form a membrane electrode group. The production method according to claim 1, wherein the carbon cloth is subjected to hydrophobic treatment for one to five times. The manufacturing method according to claim 1, wherein the microporous carbon gas diffusion layer is formed by repeating the prepreg process and the rolling step one to five times until the required conductive carbon solid content and the size and distribution of the nanopores are required. . The production method according to the first aspect of the patent application, wherein the multi-pass spray gun spraying method disperses the catalyst slurry on the surface of the carbon gas diffusion layer, and the gas required for the spray gun is an inert gas, such as nitrogen; The dosage is controlled at 0.1~0.3mg/cm ² and the cathode dosage is 0.3~0.6mg/cm ² .