JP2007164993A - Method of manufacturing electrode catalyst layer for solid polymer fuel cell, solid polymer fuel cell electrode catalyst layer, and solid polymer fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an electrode catalyst layer for solid polymer fuel cell in which condensation of catalyst carrying carbon particles is few, carbon particles with small particle size are uniformly dispersed, and a catalyst layer with high effective utilization rate of platinum catalyst is produced by forming a configuration of high porosity and increasing three-phase interface area in the method of manufacturing a solid polymer fuel cell electrode catalyst layer which includes a process in which catalyst carrying carbons, proton conductive polymer, ink consisting of dispersant are atomized and sprayed on a proton conductive solid polymer film or a porous carbon sheet by ultrasonic. <P>SOLUTION: Wet pressurizing dispersion treatment in which agitation and crushing are carried out by making a high pressure stream pass through a nozzle with small diameter is performed to an ink. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrode catalyst layer for a solid polymer electrolyte fuel cell, which is easy to produce, has high gas diffusibility, and has a high effective catalyst utilization rate, and a method for producing the same.

  A fuel cell is a power generation system that generates electricity by using hydrogen and oxygen as fuel and causing reverse reaction of water electrolysis. This has features such as high efficiency, low environmental load and low noise compared with the conventional power generation method, and is attracting attention as a clean energy source in the future. Among these, polymer electrolyte fuel cells that can be used near room temperature are expected to be used for in-vehicle power supplies, home-use power supplies, etc., and various research and development have been conducted in recent years. Issues for the practical application of fuel cells include improvements in power density and durability, but the biggest issue is cost reduction. What is most demanded for cost reduction is a reduction in the amount of platinum used as a catalyst for the electrode.

  A polymer electrolyte fuel cell is generally formed by laminating a large number of single cells. FIG. 1 is a partial explanatory view showing in cross section an example of a membrane / electrode assembly for a polymer electrolyte fuel cell. The single cell has a structure in which a membrane / electrode assembly 10 joined by sandwiching a proton conductive solid polymer membrane 3 between two electrodes (an oxidation electrode and a reduction electrode) is sandwiched by a separator having a gas flow path. . Oxidation of hydrogen gas occurs at the oxidation electrode, and reduction of hydrogen ions occurs at the reduction electrode. This oxidation-reduction reaction occurs only on the surface of the platinum catalyst that is in contact with both the carbon particles, which are electron conductors, and the proton conductor inside the electrode and can adsorb the introduced gas. This part where the redox reaction occurs is called a three-phase interface, and the area of this interface greatly affects the performance of the fuel cell. The platinum particles that are not at the three-phase interface do not contribute to the oxidation-reduction reaction of the electrode, and therefore do not function at all. In order to reduce the amount of platinum used, it is necessary to reduce the amount of platinum that does not function as much as possible and increase the effective utilization rate of the platinum used. The electrode has a two-layer configuration of catalyst layers 1 and 2 composed of carbon particles, proton conductors, and catalysts, and a gas diffusion layer 4 through which gas such as carbon paper permeates and conducts electricity. 2 is configured to contact the solid polymer film 3.

  At present, the platinum utilization rate is low because the platinum catalyst supported on the carbon particles is not in contact with the proton conductor or because the catalyst is covered with the proton conductor and the gas does not reach. It is a value. For this reason, optimizing the fine structure of the catalyst layer and increasing the effective utilization rate of platinum are very important issues.

  Until now, the catalyst layer has often been coated on a substrate by a coating method or a screen printing method. In this case, agglomeration of the catalyst-carrying carbon is likely to occur when the coated ink is dried, and as a result, the porosity in the catalyst layer is lowered and the fuel gas path is blocked, which makes contact with the proton conductor. There was a tendency to increase the number of non-existing catalysts. In such a case, it is expected that the area of the three-phase interface is reduced and the utilization rate of platinum is reduced. In order to increase the utilization rate, it is necessary to have a form in which the platinum-supporting carbon particles are not aggregated, the carbon particles having a small particle diameter are uniformly dispersed, and the porosity is high.

Therefore, it has been proposed to form a catalyst layer using a pressure spray (see, for example, Patent Document 1). In the case of using the pressure spray, the drying speed of the catalyst ink is increased, so that the aggregation of the catalyst hardly occurs, and as a result, the power generation characteristics are improved. However, in the conventional pressure spray, there are secondary agglomeration between spraying from the nozzle and coating, scattering of particles after coating, variation in the particle size of fog, etc., and these are the three-phase interface. It was a factor of decrease.

Known documents are described below.
JP-A-8-115726

  In view of the above problems, the present invention provides a solid oxide fuel cell electrode catalyst layer in which a catalyst-supporting carbon particle is less aggregated, carbon particles having a small particle diameter are uniformly dispersed, and a high porosity is formed. An object of the present invention is to provide a production method for producing a catalyst layer having a high effective utilization rate of a platinum catalyst by increasing the area of the three-phase interface.

  The present invention has been made in view of the above problems, and the invention of claim 1 is characterized in that an ink comprising catalyst-supported carbon, a proton conductive polymer, and a dispersion medium is atomized by ultrasonic to produce a proton conductive solid polymer film or In the method for producing an electrode catalyst layer for a polymer electrolyte fuel cell comprising a step of producing by spraying on a porous carbon sheet, a high pressure flow is stirred and crushed by passing through a nozzle having a small diameter hole. This is a method for producing an electrode catalyst layer for a polymer electrolyte fuel cell, characterized in that the treatment by pressure dispersion is performed on the ink.

  The invention according to claim 2 of the present invention is the polymer electrolyte fuel cell according to claim 1, wherein in the wet pressure dispersion treatment, the pressure of the liquid when passing through the nozzle is 30 MPa to 200 MPa. This is a manufacturing method of the electrode catalyst layer for use.

  According to a third aspect of the present invention, in the wet pressure dispersion treatment, the number of times the ink passes through the nozzle is 1 to 50 times, and the solid polymer type according to claim 1 or 2 This is a method for producing an electrode catalyst layer for a fuel cell.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the particle size of the particles comprising the catalyst-carrying carbon and the proton conductive particles present in the ink is 10 to 800 nm. The production method of the electrode catalyst layer for a polymer electrolyte fuel cell described above is used.

  According to a fifth aspect of the present invention, in the polymer electrolyte fuel cell electrode catalyst layer produced by the manufacturing method according to the first to fourth aspects, the porosity of the layer is 70 to 90%. This is an electrode catalyst layer for a solid polymer type fuel cell.

  Invention of Claim 6 of this invention is the electrode catalyst layer manufactured by the manufacturing method of the electrode catalyst layer for polymer electrolyte fuel cells of any one of Claims 1-4, or the electrode catalyst of Claim 5. A solid polymer fuel cell is characterized in that a proton conductive solid polymer membrane is sandwiched between layers.

As described above, the present invention stirs and crushes a mixed liquid composed of catalyst-carrying carbon, proton conductive polymer, and dispersion medium by wet pressure dispersion treatment, and atomizes the produced ink with ultrasonic waves to produce proton conduction. The polymer electrolyte fuel cell produced through the process of forming an electrode catalyst layer by spraying on a porous solid polymer membrane or a porous carbon sheet, and a method for producing the same. Particles composed of catalyst-carrying carbon and proton-conducting polymer in ink by using wet pressure dispersion that stirs and crushes the mixture by passing it through a nozzle having a small diameter hole at high pressure when dispersing ink Since the catalyst layer is made by ultrasonic spray so that the particles in the ink do not re-agglomerate during coating, the catalyst layer has a small particle size and a high porosity. it can. The catalyst layer thus produced has a high catalyst utilization rate, and a fuel cell produced using this catalyst layer has excellent performance with a small amount of catalyst.

  Details of the present invention will be described below. In the present invention, a treatment by wet pressure dispersion is performed in which a mixed liquid comprising catalyst-carrying carbon, proton conductive polymer, and dispersion medium is passed through a nozzle having a small-diameter hole of several hundred microns at high pressure to stir and crush. Thus, the catalyst-carrying carbon particles in the ink are refined, the produced ink is atomized by ultrasonic waves, and sprayed onto the substrate to produce an electrode catalyst layer for a polymer electrolyte fuel cell.

The catalyst particles used in the present invention include platinum, palladium, ruthenium, iridium, rhodium, osmium, platinum group elements, iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, and the like. A metal or an alloy thereof, or an oxide or a double oxide can be used. Moreover, since the activity of a catalyst will fall when the particle size of these catalysts is too large, and stability of a catalyst will fall when too small, 0.5-20 nm is preferable. More preferably, 1-5 nm is good.
Carbon powder is generally used as the electron conductive powder supporting these catalysts. Any kind of carbon may be used as long as it is in the form of fine powder, has conductivity and is not violated by the catalyst, but carbon black, graphite, graphite, activated carbon, carbon nanotubes, and fullerenes can be used. If the particle size of the carbon is too small, it becomes difficult to form an electron conduction path, and if it is too large, the gas diffusibility of the catalyst layer is lowered or the utilization factor of the catalyst is lowered. More preferably, 10-100 nm is good.

  Various proton conductive polymers are used in the catalyst ink, and it is necessary to select the proton conductive polymer in the ink depending on the components of the electrolyte membrane to be used. When commercially available Nafion is used as the electrolyte membrane, Nafion is preferably used. When materials other than Nafion are used for the electrolyte membrane, it is necessary to optimize such as dissolving the same components as the electrolyte membrane in the ink.

  The solvent used as the dispersion medium for the catalyst ink is not particularly limited as long as it does not erode the catalyst particles or the hydrogen ion conductive resin, and can dissolve or disperse the proton conductive polymer in a highly fluid state as a fine gel. Although there is no limitation, it is desirable that at least a volatile liquid organic solvent is contained, and although not particularly limited, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, Alcohols such as 2-butanol, isobutyl alcohol, tert-butyl alcohol, pentaanol, and ketones such as acetone, methyl ethyl ketone, pentanone, methyl isobutyl ketone, heptanone, cyclohexanone, methyl cyclohexanone, acetonyl acetone, diisobutyl ketone Solvent, tetrahydrofuran, dioxane, di Ether solvents such as tylene glycol dimethyl ether, anisole, methoxytoluene, dibutyl ether, and other polar solvents such as dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, diethylene glycol, diacetone alcohol, 1-methoxy-2-propanol A solvent or the like is used. Moreover, what mixed 2 or more types of these solvents can also be used. In addition, those using lower alcohol as a solvent have a high risk of ignition, and when using such a solvent, it is preferable to use a mixed solvent with water. Water that is compatible with the hydrogen ion conductive resin may be contained. The amount of water added is not particularly limited as long as the proton conductive polymer is separated to cause white turbidity or does not gel. In addition, glycerin can be added or a surfactant can be used to control the porosity of the catalyst layer after film formation.

  If the solid content in the catalyst ink is too high, the viscosity of the ink will increase, making it difficult to atomize with ultrasonic waves, and if it is too low, the film formation rate will be very slow and productivity will be reduced. 1 to 50 wt% is preferable. The solid content is composed of a catalyst-supporting carbon and a proton conductive polymer. When the content of the catalyst-supporting carbon is increased, the viscosity is increased even at the same solid content, and when the content is decreased, the viscosity is decreased. The proportion of the catalyst-supporting carbon in the solid content is preferably 10 to 80%. Further, the viscosity of the catalyst ink at this time is preferably about 0.1 to 500 cP in consideration of atomization by ultrasonic waves. More preferably, 5-100 cP is good. Further, the viscosity can be controlled by adding a dispersing agent when the ink is dispersed.

  The particles composed of the catalyst-supporting carbon and the proton conductive polymer in the catalyst ink are considered to be in a form in which several particles are aggregated. If the size of the agglomerated particles is too small, it is difficult to form an electron conduction path. If the size is too large, the gas diffusibility of the catalyst layer decreases or the utilization factor of the catalyst decreases. More preferably, the thickness is 10 to 800 nm.

  The viscosity of the catalyst ink and the size of the particles in the ink can be controlled by the conditions of the ink dispersion treatment. Distributed processing can be performed using various apparatuses. For example, a ball mill, ultrasonic treatment, a homogenizer, a kneader, a wet pressure dispersion treatment, and the like can be given. Among these, the wet pressure dispersion treatment not only enables the particle size to be made finer and uniform, but also increases the contact area between the catalyst-carrying carbon and the proton conducting polymer by the collision force generated by the collision of the jet stream, It can also be expected to increase the effective utilization rate. Further, there is an advantage that no medium is used unlike a ball mill, so that impurities are not mixed. Among wet pressure dispersion treatment devices, those that stir and crush by passing a high-pressure flow through a nozzle having a small-diameter hole of several hundred microns are commercially available under the name of nanomizer. This apparatus can be designed in various particle sizes by changing the pressurizing conditions and has a small variation in particle size, and therefore is a suitable method for dispersing the catalyst ink.

  Nanomizers are used in various applications depending on the processing pressure. When the processing pressure is 0 to 1 MPa, it is used for kneading of liquid and powder, when 1 to 50 MPa, emulsification of water and oil, uniform dispersion when 30 to 120 MPa, and crushing hard substances when it is 100 to 150 MPa. ing. When the catalyst ink is processed with a nanomizer, uniform dispersion and finer particles are required, so that the processing pressure is preferably between 30 and 200 MPa. More preferably, it is between 80 and 150 MPa.

  The pressure dispersion treatment in the nanomizer can be repeated once again after being performed once. There are no particular restrictions on the number of times of this treatment, but there are some that are sufficient in one use depending on the material used and the purpose of use, and some that need to be treated many times. When the catalyst ink is dispersed, it is preferable that the number of treatments is large because finer particles are required. Specifically, about 1 to 50 times is preferable.

  As a method for forming the catalyst layer, a coating method such as a dipping method, a screen printing method, a roll coating method, or a spray method is generally used. Among them, the spray method is preferable because the catalyst-supporting carbon hardly aggregates when the coated ink is dried, and a homogeneous catalyst layer having a high porosity can be obtained. Among the spray methods, those that atomize by ultrasonic waves do not have secondary agglomeration of ink between spraying from the nozzle and application, scattering of particles after application, and variation in mist particle size. Is also preferable. Hereinafter, this spray method will be described.

The ultrasonic spray using ultrasonic vibration is a spray that transmits ultrasonic waves having a frequency of 10 kHz to 200 kHz generated by a piezoceramic or the like to a nozzle portion to vibrate a liquid film to form and spray fine particles. Ultrasonic spraying does not require pressure during spraying, so spraying by natural fall can be realized. Therefore, the catalyst ink sprayed by the ultrasonic spray hardly causes overspray and secondary scattering in which particles are blown off from the work. Therefore, the ink utilization efficiency is increased. Compared with the conventional high-pressure spray, the ultrasonic spray has a fine mist particle size and a small variation in particle size, so that a homogeneous film can be produced. The particle size of the mist is about 10 to 90 μm. Further, the spray mist is easily affected by the air flow, and it is necessary to cap the whole from the nozzle to the work and control the mist progression pattern by flowing auxiliary air. The pressure of the auxiliary air may be about 0.005 to 0.02 MPa, and this does not prevent spontaneous fall spray.

  The spraying speed in the ultrasonic spraying is about 50 liters / hour maximum flow rate. However, uniform spraying is possible regardless of the flow rate, and natural falling spraying is also maintained.

  When the catalyst ink is sprayed using ultrasonic spray, the time from spraying to coating is long because it falls naturally, and the particle size of the mist is small. Aggregation of subsequent particles is unlikely to occur. Therefore, it is possible to form a catalyst layer having a high porosity. As the catalyst porosity increases, the gas diffusivity increases, but the electron and proton conduction paths decrease and the mechanical strength also decreases. Considering this, the porosity is preferably 50% or more. More preferably, 70 to 90% is good.

  In this way, by spraying ink using ultrasonic spray, it is possible to create a catalyst layer having a uniform and fine particle size composed of catalyst-carrying carbon and proton conductive polymer and a high porosity. . Further, by treating the ink with a wet jet mill, the particle size can be further refined and the catalyst utilization rate can be improved.

  As a process for producing a membrane / electrode assembly using a catalyst layer produced by ultrasonic spraying, generally, ink is sprayed on a gas diffusion layer and dried to form a proton conductive polymer membrane. A method of joining the catalyst layers by thermocompression bonding is used. In addition to this, the ink is directly sprayed on both sides of the proton conductive polymer membrane, and this is sandwiched between the gas diffusion layers, or the ink is sprayed on the releasable base material, and the proton conductive high There is no problem even if a method in which a film transferred on both sides of the molecular film is sandwiched between gas diffusion layers is used.

  The temperature of the substrate when spraying by ultrasonic spraying may be any value as long as it is between room temperature and the glass transition point of the proton conducting polymer, but the faster the evaporation rate of the solvent, 50-120 ° C. is preferable because there is little aggregation of particles due to flow and a homogeneous film can be produced.

  The gas diffusion layer may be anything as long as it has electron conductivity, high gas diffusibility, and high corrosion resistance. Generally, carbon-based porous materials such as carbon paper and carbon cloth are used. Is used. Also, in order to prevent the ink after coating from penetrating into the gas diffusion layer and reducing the gas diffusibility, a carbon layer that does not carry a catalyst as a sealing layer is provided on the gas diffusion layer Can also be used.

  Hereinafter, the solid polymer fuel cell and the production method thereof according to the present invention will be described with reference to specific examples, but the present invention is not limited to the examples.

<Example 1>
A platinum-supported carbon catalyst having a platinum loading of 45 wt% and a commercially available proton conductive polymer (Nafion) solution were mixed in a solvent and subjected to dispersion treatment with Nanomizer (TL-1500 manufactured by Tokai Corporation). The composition ratio of the starting materials was platinum catalyst-supporting carbon and Nafion at a weight ratio of 2: 1, and the solvent was water, 1-propanol, and 2-propanol at a volume ratio of 1: 1: 1. The solid content was 5 wt%. Nanomizer treatment was performed at a pressure of 50 MPa and a treatment frequency of 10 times. The viscosity of the ink after the treatment was about 50 cP. The average particle size of particles comprising platinum-supported carbon and proton conductive polymer in the ink was measured with a particle size distribution meter, and was about 500 nm. The catalyst layer was produced by spraying the produced ink on carbon paper by ultrasonic spray (Ultrasonic atomizer manufactured by LECHLER). At this time, the temperature of the carbon paper was set to 80 ° C. The thickness of the catalyst layer was adjusted so that the platinum loading of the catalyst layer was 0.5 mg / cm ² . The frequency of ultrasonic waves for atomization was 100 kHz, the flow rate was 50 L / h, and the distance between the substrate and the nozzle was 20 cm. Further, the entire pattern from the nozzle to the workpiece was capped, and the auxiliary air was allowed to flow at a pressure of 0.01 MPa to control the mist progression pattern. With respect to the obtained catalyst layer, the porosity of only the catalyst layer was measured with a pore distribution measuring apparatus, whereby the porosity was 80%.

<Example 2>
A starting material mixture similar to that in Example 1 was prepared and subjected to dispersion treatment with a nanomizer. The nanomizer treatment was performed at a pressure of 150 MPa and a treatment frequency of 10 times. The viscosity of the ink after the treatment was about 30 cP. The average particle diameter of the particles comprising platinum-supported carbon and proton conductive polymer in the ink was measured with a particle size distribution meter and found to be about 150 nm. A catalyst layer was produced by spraying the produced ink under the same conditions as in Example 1. The thickness of the catalyst layer was adjusted so that the platinum loading of the catalyst layer was 0.5 mg / cm ² . With respect to the obtained catalyst layer, the porosity of only the catalyst layer was measured with a pore distribution measuring apparatus, whereby the porosity was 90%.

<Comparative Example 1>
A starting material mixture similar to that in Example 1 was prepared and subjected to dispersion treatment using a planetary ball mill (Pulversette 7 manufactured by FRITSCH). The material of the pot and ball was zirconia. The viscosity of the ink after the treatment was about 60 cP. The average particle diameter of the particles comprising platinum-supporting carbon and proton conductive polymer in the ink was measured with a particle size distribution meter, and was about 700 nm. A catalyst layer was produced by spraying the produced ink under the same conditions as in Example 1. The thickness of the catalyst layer was adjusted so that the platinum loading of the catalyst layer was 0.5 mg / cm ² . With respect to the obtained catalyst layer, the porosity of only the catalyst layer was measured with a pore distribution measuring apparatus, whereby the porosity was 70%.

<Membrane / electrode assembly production>
A membrane / electrode assembly 10 was produced using the catalyst layer produced on the carbon paper 4 in Examples 1 and 2 and Comparative Example 1. The produced electrode was punched into a 5 cm ² square to obtain an oxidation electrode 1 and a reduction electrode 2. With the two electrodes sandwiching the proton conductive polymer membrane 3, hot pressing was performed at 130 ° C., 588 × 10 ⁴ Pa, for 30 minutes to obtain a membrane / electrode assembly. FIG. 1 shows a schematic diagram of a membrane / electrode assembly. Nafion 112 manufactured by DuPont was used as the proton conductive polymer membrane.

<Power generation performance measurement results>
The power generation performance of the produced membrane / electrode assembly was measured. As the measurement cell, a membrane / electrode assembly was sandwiched between separators having gas flow paths, and both electrodes were tightened with bolts. The evaluation conditions were a cell temperature of 80 ° C., gas was hydrogen at the oxidation electrode, and oxygen was at the reduction electrode. The flow rate is 1 L / min. It was. The relative humidity of the gas was 100%. The performance was compared at the current density when the voltage was 0.7V. Table 1 shows the results.

  Table 1 shows the evaluation results of the catalyst inks produced in Examples 1 and 2 and Comparative Example 1, the catalyst layer produced using the same, and the membrane / electrode assembly produced using the same.

It is the partial explanatory view which showed the example of the membrane electrode assembly for polymer electrolyte fuel cells in the section.

Explanation of symbols

1 ... Electrode catalyst layer (oxidation electrode)
2 ... Electrocatalyst layer (reducing electrode)
3 ... Proton conductive polymer membrane 4 ... Gas diffusion layer (carbon paper)
10. Membrane / electrode assembly

Claims (6)

  Solid polymer type including the process of atomizing ink consisting of catalyst-supported carbon, proton conductive polymer, and dispersion medium with ultrasonic waves and spraying it onto the proton conductive solid polymer membrane or porous carbon sheet A solid polymer characterized in that in a method for producing an electrode catalyst layer for a fuel cell, a high-pressure flow is stirred and crushed by passing through a nozzle having small-diameter holes, and a process by wet pressure dispersion is performed on ink. For producing an electrode catalyst layer for a flat fuel cell.   2. The method for producing an electrode catalyst layer for a polymer electrolyte fuel cell according to claim 1, wherein in the wet pressure dispersion treatment, the pressure of the liquid when passing through the nozzle is 30 MPa to 200 MPa.   The method for producing an electrode catalyst layer for a polymer electrolyte fuel cell according to claim 1 or 2, wherein, in the wet pressure dispersion treatment, the number of times the ink passes through the nozzle is 1 to 50 times.   The electrode for a solid polymer fuel cell according to any one of claims 1 to 3, wherein the particle size of the catalyst-supporting carbon and the proton conductive particles present in the ink is 10 to 800 nm. A method for producing a catalyst layer.   5. The polymer electrolyte fuel cell electrode catalyst layer produced by the production method according to claim 1, wherein the layer has a porosity of 70 to 90%. Electrocatalyst layer.   A proton conductive solid polymer membrane is produced by the electrode catalyst layer produced by the method for producing an electrode catalyst layer for a polymer electrolyte fuel cell according to any one of claims 1 to 4, or by the electrode catalyst layer of claim 5. A solid polymer fuel cell characterized by being sandwiched.

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