JP5003076B2 - Electrode catalyst layer for polymer electrolyte fuel cell, method for producing the same, and polymer electrolyte fuel cell - Google Patents

Description

  The present invention relates to an electrode catalyst layer for a polymer electrolyte fuel cell, a method for producing the electrode catalyst layer, and a polymer electrolyte fuel cell. The present invention relates to an electrode catalyst layer for a polymer electrolyte fuel cell having an electrode catalyst layer having a high effective utilization rate of a catalyst, a method for producing the same, and a polymer electrolyte fuel cell.

  A fuel cell is a power generation system that generates electricity simultaneously with heat by causing a hydrogen gas-containing fuel gas and oxygen-containing oxidant gas to undergo reverse reaction of water electrolysis at an electrode including a catalyst. This power generation system has features such as high efficiency, low environmental load, and low noise compared to conventional power generation methods, and is attracting attention as a clean energy source in the future. There are several types depending on the type of ion conductor used, and those using proton conductive polymer membranes are called solid polymer fuel cells.

  Among polymer fuel cells, polymer electrolyte fuel cells can be used near room temperature, so they are considered promising for use in in-vehicle power sources and household stationary power sources. In recent years, various research and development have been conducted. Yes. A polymer electrolyte fuel cell is a MEA (electrolyte membrane electrode assembly) assembly in which a pair of electrodes are arranged on both sides of a polymer electrolyte membrane, and a fuel gas containing hydrogen is supplied to one of the electrodes. The battery is sandwiched between a pair of separator plates formed with a gas flow path for supplying an oxidant gas containing oxygen to the other electrode. Here, the electrode for supplying the fuel gas is called a fuel electrode, and the electrode for supplying the oxidant is called an air electrode.

  The above-mentioned electrode is a joined body composed of an electrode catalyst layer formed by laminating carbon particles supporting a catalyst material such as a platinum-based noble metal and a polymer electrolyte, and a gas diffusion layer having both gas permeability and conductivity. . Issues for the practical application of polymer electrolyte fuel cells include improvement of power density and durability, but the biggest issue is cost reduction, and the use of platinum used as a catalyst for the electrode The amount is reduced.

  Hydrogen gas oxidation occurs at the fuel electrode, and proton reduction occurs at the air electrode. This oxidation-reduction reaction occurs only on the surface of the catalyst that is in contact with both the carbon particles that are electron conductors and the proton-conducting polymer inside the electrode and that can be contacted with the fuel gas or the oxidant gas. This part where the oxidation-reduction reaction occurs is called a three-phase interface, and this area greatly affects the performance of the fuel cell. Platinum present at a location other than the three-phase interface does not contribute to the oxidation-reduction reaction of the electrode and therefore does not function as a catalyst at all. At present, the gas diffusibility of the electrode catalyst layer is poor, the catalyst supported on the carbon particles is not in contact with the proton conductive polymer, the catalyst is covered with the proton conductive polymer, and as a result As a result, the utilization rate of platinum is low. In order to reduce the amount of platinum used, it is necessary to optimize the microstructure of the electrode catalyst layer, reduce the amount of platinum that does not contribute to the oxidation-reduction reaction as much as possible, and increase the effective utilization rate of the platinum used.

  The pores in the electrode catalyst layer are located in front of the separator through the gas diffusion layer and serve as a passage for transporting a plurality of substances. The fuel electrode functions not only to smoothly supply the fuel gas to the three-phase interface, which is a redox reaction field, but also to supply water for smoothly conducting the generated protons in the polymer electrolyte membrane. On the other hand, the air electrode performs the function of smoothly removing water generated by the electrode reaction together with the supply of the oxidant gas in the same manner as the fuel electrode. However, if the amount of pores is increased too much, it is considered that the number of carbon particles or proton conductive polymer is relatively decreased, and cell resistance and reaction resistance are increased. Therefore, ensuring the gas diffusibility of the electrode catalyst layer is a very important issue, and it is necessary to form pores in the electrode catalyst layer with an arbitrary gradient distribution in order to optimize the microstructure of the electrode catalyst layer. .

  So far, in order to improve the gas diffusibility of the electrode catalyst layer, a method has been devised to improve the gas diffusibility of the electrode catalyst layer by dispersing a pore former that can be removed after electrode formation in the catalyst ink. . Patent Document 1 (Japanese Patent Application Laid-Open No. 6-36771) discloses a method of using a powder of an inorganic salt such as a metal such as zinc, aluminum or chromium or a metal salt thereof as a pore-forming agent. A method has been devised in which a catalyst ink containing these pore forming agents is applied in a sheet form, the formed electrode is immersed in an acidic solution to remove the pore forming agent, and pores are formed in the electrode catalyst layer.

  Patent Document 2 (Japanese Patent Laid-Open No. 10-189012) discloses a method of using acicular iron or the like having a predetermined orientation in the longitudinal direction as a pore-forming agent. By applying or drying the catalyst ink in an environment in which a magnetic field is applied in a direction perpendicular to the electrode, the electrode is formed with the easy axis of magnetization of the pore forming agent and the magnetic flux arranged in parallel. A method of forming a plurality of pores having vertical orientation has been devised.

  In Patent Document 3 (Japanese Patent Application Laid-Open No. 2003-109606), a plurality of catalyst inks using pore formers having different particle diameters are prepared, and these are coated on a base sheet in order from the largest particle diameter. And a method for removing the transfer / pore-forming agent from the polymer electrolyte membrane is disclosed. A method has been devised to improve the gas diffusibility in the electrode catalyst layer thickness method by forming the pore size in the electrode catalyst layer larger from the side in contact with the polymer electrolyte membrane to the gas diffusion layer side. Yes.

  Patent Document 4 (Japanese Patent Laid-Open No. 2005-267981) discloses a method for forming a gradient distribution of a pore-forming agent using gravity. Using a sheet consisting of a gas diffusion layer and a pore-forming agent that can be dissolved in a solvent, the solvent in contact with the sheet is made to flow down using gravity, and an electrode catalyst layer with different gas diffusivity in the direction of gravity is formed. Has been devised.

In addition, as a device for using mass transfer using magnetic force, Patent Document 5 (Japanese Patent Laid-Open No. 2005-317930) discloses that a fluid substance is moved by applying a magnetic field to the fluid substance. A method of forming a desired shape pattern by solidifying the fluid substance after forming a desired shape is disclosed.
JP-A-6-36771 JP-A-10-189012 JP 2003-109606 A Japanese Patent Laid-Open No. 2005-267981 JP 2005-317930 A

  The fuel gas and the oxidant gas are transported from the separator through the gas diffusion layer, and finally to the three-phase interface that is a redox reaction field through the pores in the electrode catalyst layer. When viewed from the electrode catalyst layer, the transport of the fuel gas and the oxidant gas is from the gas diffusion layer side and is not performed from the opposite polymer electrolyte membrane side. From this, when the pores in the electrode catalyst layer are uniformly formed, it is considered that the gas diffusibility is inferior on the polymer electrolyte membrane side than on the gas diffusion layer side. That is, the catalyst existing on the polymer electrolyte membrane side does not contribute to the oxidation-reduction reaction of the electrode, and therefore does not function as a catalyst at all. Therefore, the method of using a powder of an inorganic salt such as a metal or a metal salt thereof disclosed in Patent Document 1 as a pore-forming agent has a problem that the effective utilization rate of platinum used is not sufficiently increased. is there.

  In addition, the method of orienting a ferromagnetic pore former in a magnetic field to form anisotropic pores in the electrode catalyst layer has a problem in maintaining the dispersibility of the pore former. If the ferromagnetic pore former is dispersed in the catalyst ink, the magnetic orientation is performed so that the easy magnetization axis and the magnetic flux of each pore former are parallel to each other. However, each of the ferromagnetic pore-forming agents is magnetized in a magnetic field, so that each becomes a small magnet. In particular, in the case of a needle-shaped ferromagnetic material, there is a problem in that the pore-forming agent has a poor dispersibility due to attractive or repulsive action like a bar magnet, and the pore diameter of the electrode catalyst layer becomes random. In addition, since the pore-forming agent is aggregated, there is a problem that it is difficult to form anisotropic pores by orienting the magnetic fields so that the easy axis magnetic fluxes of the individual aggregates are parallel to each other. Therefore, the method of using acicular iron or the like having a predetermined orientation in the longitudinal direction as disclosed in Patent Document 2 has a problem in maintaining the dispersibility of the pore-forming agent in a magnetic field, The effective utilization rate of platinum used is not sufficiently increased.

  Furthermore, in the method of forming pores uniformly large in the electrode catalyst layer near the interface with the polymer electrolyte membrane or the gas diffusion layer, there is a problem in the mechanical strength of the electrode catalyst layer itself. Since the pores in the electrode catalyst layer in contact with the interface are uniformly large, the electrode catalyst layer near the pores is brittle. In the fuel cell, the MEA is sandwiched between a pair of separators at a constant pressure so that the fuel gas and the oxidant gas do not leak out of the separator flow path, and in order to reduce the influence of contact resistance between the battery members. Is done. When the electrode catalyst layer is brittle, it is conceivable that the gas diffusibility decreases due to crushing due to the clamping pressure, and the effective utilization rate of platinum decreases.

  In view of the above-mentioned problems, the present invention has an electrode catalyst layer for a polymer electrolyte fuel cell, in which the gas diffusivity has a gradient distribution in the thickness direction or the membrane surface direction with respect to the polymer electrolyte membrane while maintaining mechanical strength. An object of the present invention is to provide an electrode catalyst layer for a polymer electrolyte fuel cell having a high effective utilization rate of a catalyst, a method for producing the electrode catalyst layer, and a polymer electrolyte fuel cell.

  As a result of intensive studies, the present inventor has been able to solve the above-mentioned problems and has completed the present invention.

In other words, the invention according to claim 1 is directed to a polymer electrolyte fuel cell in which a proton conductive polymer electrolyte membrane sandwiched between a pair of electrode catalyst layers is sandwiched between a pair of gas diffusion layers. A manufacturing method , wherein at least one substance having a magnetic susceptibility different from that of the pore forming agent is dissolved in a catalyst ink in which carbon particles carrying a catalyst substance, a polymer electrolyte, and a pore forming agent are dispersed in a dispersion solvent. Or it was selected from the step of dispersing and increasing the magnetic susceptibility difference between the pore former and the dispersion solvent on a planar substrate and the step of evaporating the dispersion solvent in the catalyst ink. At least one step is performed in a magnetic field having a non-uniform magnetic flux density distribution, and the pores in the electrode catalyst layer are gas diffusible in the thickness direction or the film surface direction with respect to the polymer electrolyte membrane by a magnetic force . Becomes higher A method for producing an electrode catalyst layer for a polymer electrolyte fuel cell, characterized by having a gradient distribution of porosity .

  According to a second aspect of the present invention, the maximum magnetic flux density of the permanent magnet or magnetic field generator that forms the magnetic field having the magnetic flux density distribution is 0.1 Tesla or higher. It is a manufacturing method of the electrode catalyst layer for molecular fuel cells.

  According to a third aspect of the present invention, a magnetic field is applied to a base material composed of two kinds of substances having different magnetic susceptibility, the magnetic force is concentrated on the substance having the highest magnetic susceptibility in the base material, and a desired magnetic flux 3. The method for producing an electrode catalyst layer for a polymer electrolyte fuel cell according to claim 1, wherein a magnetic field having a density distribution is used.

  The invention according to claim 4 is characterized in that at least one pore former having a magnetic susceptibility different from that of the dispersion solvent of the catalyst ink is dispersed in the dispersion solvent. It is a manufacturing method of the electrode catalyst layer for solid polymer type fuel cells of description.

According to a fifth aspect of the present invention, the pore forming agent dispersed in the dispersion solvent is removed by the solvent of the pore forming agent after forming the electrode catalyst layer, so that the pores of the electrode catalyst layer are the polymer. 5. The method for producing an electrode catalyst layer for a polymer electrolyte fuel cell according to claim 4, wherein the electrolyte membrane has a gradient distribution of porosity that increases gas diffusivity in a thickness direction or a membrane surface direction with respect to the electrolyte membrane. It is.

The invention described in claim 6 is such that the pore-forming agent dispersed in the dispersion solvent is removed by water generated by power generation so that the pores of the electrode catalyst layer are thicker than the polymer electrolyte membrane. 5. The method for producing an electrode catalyst layer for a polymer electrolyte fuel cell according to claim 4, wherein the method has a gradient distribution of porosity that increases gas diffusivity in a vertical direction or a film surface direction.

  The invention according to claim 8 is the production of an electrode catalyst layer for a polymer electrolyte fuel cell according to any one of claims 1 to 7, wherein the temperature of the base material is 20 ° C to 120 ° C. Is the method.

  According to the present invention, a solid polymer fuel cell with a high effective utilization rate of a catalyst having a gradient distribution of gas diffusivity in a thickness direction or a membrane surface direction with respect to a polymer electrolyte membrane while maintaining mechanical strength. An electrode catalyst layer, a production method thereof, and a polymer electrolyte fuel cell are provided.

Hereinafter, the present invention will be described in more detail.
The present invention is a method of generating different magnetic forces in the pore forming agent and the catalyst ink dispersion solvent by applying or drying the catalyst ink in a magnetic field having a magnetic flux density distribution, and moving the pore forming agent by the magnetic force. Is used to provide a method for producing an electrode catalyst layer for a polymer electrolyte fuel cell in which gas diffusivity is increased in the thickness direction or the membrane surface direction in a pattern with respect to the polymer electrolyte membrane.

  Since the pore-forming agent and the catalyst ink dispersion solvent are diamagnetic materials and weak in magnetism and have very little magnetic interaction, it is difficult to cause mass transfer using magnetic force. The difference in magnetic susceptibility from the pore-forming agent is increased by dissolving or dispersing the substance that increases the magnetic susceptibility in the catalyst ink dispersion solvent. As a result, in the present invention, mass transfer using magnetic force can be used. Become. Specifically, the catalyst ink dispersion solvent becomes a paramagnetic substance by adding a paramagnetic transition element compound that is dissolved or dispersed in the catalyst ink dispersion solvent.

  However, if the magnetic flux density distribution is uniform, mass transfer does not occur even if the magnetic susceptibility difference between the pore former and the catalyst ink dispersion solvent is increased, and the formation of a non-uniform magnetic flux density distribution is also an important point. Forming a magnetic field having a magnetic flux density distribution is obtained by applying a magnetic field to a substrate composed of two substances having different magnetic susceptibility, for example, a substrate composed of a ferromagnetic material and a weak magnetic material. The magnetic field lines that pass through the substance are effective in increasing the magnetic flux density with a ferromagnetic material such as Fe, Ni, or Co that has a large interaction with the magnet. However, the weak magnetic material has very little interaction with the magnetic field, so that the lines of magnetic force pass through as it is. Therefore, a magnetic field having a magnetic flux density distribution corresponding to the pattern of the ferromagnetic material and the weak magnetic material is formed on the substrate surface in the surface direction of the electrode catalyst layer. Further, since the magnetic flux density distribution becomes uniform as the distance from the substrate increases, the magnetic flux density distribution is also formed in the thickness direction of the electrode catalyst layer. That is, since the magnetic flux density is high on the surface of the ferromagnetic material such as Fe, the catalyst ink dispersion solvent of the paramagnetic material moves, and the magnetic flux density is low on the surface of the weak magnetic material such as Al. The pore-forming agent moves in a pattern in the surface direction or the thickness direction with respect to the polymer electrolyte membrane, and as a result, the pores in the electrode catalyst layer are in the thickness direction or the membrane surface with respect to the polymer electrolyte membrane. It has a gradient distribution in the direction, and the gas diffusivity increases in the thickness direction or the film surface direction of the electrode catalyst layer. As a result, the electrode catalyst layer produced in the present invention has high gas diffusibility in the thickness direction or the film surface direction of the electrode catalyst layer while maintaining the mechanical strength, and the effective utilization rate of the catalyst is high.

As described above, a preferred embodiment of the present invention is a conventional catalyst ink in which carbon particles supporting catalyst material (hereinafter referred to as catalyst-supporting carbon), polymer electrolyte, and pore former are dispersed in a dispersion solvent. _{2 · 4H 2 O, FeCl 2} · 4H 2 O, is to dissolve or disperse the paramagnetic transition element compound such as MnPO ₄ · _{H 2} O. That is, by dissolving at least one substance having a magnetic susceptibility different from that of the pore forming agent in the catalyst ink, the difference in magnetic susceptibility is increased, and the pore forming agent is moved by the magnetic force, so that the pattern is formed with respect to the polymer electrolyte membrane. Furthermore, gas diffusivity can be increased in the thickness direction or the film surface direction.

  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 particles are 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 particles, has conductivity and is not affected by the catalyst, but carbon black, graphite, graphite, activated carbon, carbon fiber, carbon nanotube, fullerene 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 polymer electrolytes (proton conductive polymers) contained in the catalyst ink are used, and it is necessary to select the proton conductive polymer in the catalyst 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 a material other than Nafion is used for the electrolyte membrane, it is necessary to optimize such as dissolving the same components as the polymer electrolyte membrane in the catalyst ink.

  The solvent used as a dispersion medium for the catalyst ink is not particularly limited as long as it does not erode the catalyst particles and the proton conductive polymer and can dissolve or disperse the polymer electrolyte in a highly fluid state as a fine gel. However, it is desirable to include at least a volatile liquid organic solvent, and is not particularly limited, but includes methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2- Alcohols such as butanol, isobutyl alcohol, tert-butyl alcohol, pentanole, ketone solvents such as acetone, methyl ethyl ketone, pentanone, methyl isobutyl ketone, heptanone, cyclohexanone, methylcyclohexanone, acetonyl acetone, diisobutyl ketone, Tetrahydrofuran, dioxane, diethylene Ether solvents such as recall 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 Etc. are 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 proton-conducting polymer may be contained. The amount of water added is not particularly limited as long as the polymer electrolyte is not separated to cause white turbidity or gelation.

  Moreover, in order to control the porosity of an electrode catalyst layer, glycerin and surfactant can also be used.

  As the pore-forming agent, any substance that is soluble in acid, alkali, and water may be used, but calcium carbonate, lithium carbonate, ammonium carbonate, lithium fluoride, polyvinyl alcohol, and polyethylene oxide are used.

  The substance for increasing the magnetic susceptibility difference between the pore former and the catalyst ink dispersion solvent is not particularly limited as long as it dissolves or disperses in the dispersion solvent, but the dispersion solvent increases the magnetic susceptibility difference with a small amount of addition. It is preferable that the magnetism is significantly different from that of the magnetic field. Addition of a large amount reduces the mechanical strength of the formed electrode catalyst layer, and is preferably 1 to 30 wt% in the dispersion solvent. Paramagnetic transition element compounds are used as substances that increase the magnetic susceptibility of the dispersion solvent. it can. In addition, ferromagnetic materials such as Fe, Ni, and Co can also be added. At this time, only the ferromagnetic material is dissolved and added so as not to interact with the magnetic field and separate from the dispersion solvent, or 100 nm. The following fine particles are preferably added. In the latter case, the particle diameter is more preferably in the range of 10 to 20 nm. Further, the magnetic susceptibility difference between the pore forming agent and the catalyst ink dispersion solvent may be increased by adding these substances to the pore forming agent.

  The substance added to the catalyst ink dispersion solvent to increase the difference in magnetic susceptibility with the pore former may be removed with a solvent after the electrode catalyst layer is formed. In this case, the porosity and pore diameter of the electrode catalyst layer are growing. Further, it may be removed by water generated by power generation.

  If the solid content in the catalyst ink is too high, the viscosity of the catalyst ink will be high, so that mass transfer by the magnetic force in the present invention will be difficult, and if it is too low, the film formation rate will be very slow and productivity will be low. Since it will fall, it is preferable that it is 1-50 wt%. 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%. In addition, the viscosity of the catalyst ink at this time is preferably about 0.1 to 500 cP in consideration of performing mass transfer by magnetic force. More preferably, 5-100 cP is good. Further, the viscosity can be controlled by adding a dispersing agent when the catalyst ink is dispersed.

  The viscosity and particle size of the catalyst ink can be controlled by the conditions for the dispersion treatment of the catalyst ink. Distributed processing can be performed using various apparatuses. Examples thereof include a ball mill, a roll mill, a shear mill, a wet mill, and an ultrasonic dispersion treatment. Moreover, you may use the homogenizer etc. which stir with centrifugal force.

  The present invention is characterized in that at least one of the step of applying the catalyst ink and the step of evaporating the dispersion solvent is performed in a magnetic field having a magnetic flux density distribution.

FIG. 1 is a schematic view showing an example of a production apparatus for producing an electrode catalyst layer of the present invention. The magnetic field is formed from the lower direction to the upper direction in FIG. A non-uniform magnetic flux density distribution is formed by applying a magnetic field to the substrate 3 configured in a pattern by a ferromagnetic material and a weak magnetic material. The gas diffusion layer 2 or the proton conductive polymer electrolyte membrane is disposed on the planar substrate 3 and the catalyst ink is directly applied to form the electrode catalyst layer 1. The magnetic field generator can be a permanent magnet, but preferably has a strong magnetic field strength and a wide magnetic field generation space in order to form a large electrode catalyst layer. For example, an electromagnet, a superconducting magnet, etc. are mentioned. In addition, the magnetic field generator includes an N ₂ gas introduction pipe and a water introduction pipe having an inlet portion and an outlet portion for controlling the temperature around the substrate. In the form of FIG. 1, the catalyst ink is spray-coated on the gas diffusion layer 2 by pressure spray. The maximum magnetic flux density of the magnetic field generator is preferably 0.1 Tesla or more, more preferably 2 Tesla or more. In particular, when a superconducting magnet is used, the temperature of the magnetic field generation space is not stabilized due to the influence of cooling of the superconducting coil. Therefore, for example, it is preferable to circulate water from a thermostatic chamber in a glass double tube.

  As a method for forming the electrode 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.

  As described above, in a preferred embodiment of the present invention, a gas diffusion layer or a proton conductive polymer electrolyte membrane is disposed on a substrate configured in a pattern by a ferromagnetic material and a weak magnetic material, and a catalyst ink is provided. Apply directly. Alternatively, after an electrode catalyst layer is formed on a transfer sheet disposed on a substrate, it may be transferred to a gas diffusion layer or a proton conductive polymer electrolyte membrane.

  A base material that enhances mass transfer using magnetic force is composed of a ferromagnetic material and a weak magnetic material. Ferromagnetic materials that increase the magnetic flux density are preferable for materials having stronger magnetism because they maintain a non-uniform magnetic flux density distribution even when they are separated from the substrate surface, and examples thereof include Fe, Ni, and Co. The weak magnetic material is preferably a substance that does not interact with the magnetic field at all, and examples thereof include aluminum, glass, paper, and plastic.

  The substrate is preferably configured in a pattern by a ferromagnetic material and a weak magnetic material. For example, a base material in which ferromagnetic materials are regularly embedded in a weak magnetic base material, a base material in which ferromagnetic materials and weak magnetic materials are arranged in a checkered pattern, or a weak magnetic material in a ferromagnetic base material The pattern can be designed to form any magnetic flux density distribution, such as a substrate with regularly embedded. An example of the substrate used in the production of the electrode catalyst layer according to the present invention is shown in FIG. The ferromagnetic bodies 11 and the weak magnetic bodies 12 are alternately formed, and portions where the magnetic lines of force are dense and portions where the lines of magnetic force are sparse are formed. If the thickness of the substrate is thin, the effect of increasing the magnetic flux density with a ferromagnetic material is low, so the magnetic flux density distribution becomes uniform immediately from the substrate surface, preferably 100 nm or more, more preferably 1 mm or more. . Further, if the width of the pattern is too wide, the effect of the inclined arrangement of the electrode catalyst layer is lost, and if it is too narrow, the magnetic flux density distribution immediately becomes uniform from the substrate surface.

  The gas diffusion layer is generally made of a material having gas diffusibility and conductivity. For example, carbon paper or carbon cloth can be used. Before applying the catalyst ink, an eye layer may be formed on the gas diffusion layer in advance. The eye-catching layer is a layer that prevents the catalyst ink from penetrating into the gas diffusion layer, and even if the coating amount is small, it does not penetrate into the electrode and deposits on the electrode to form a three-phase interface. To do. Such a sealing layer can be formed, for example, by kneading carbon and a fluororesin and sintering at a temperature equal to or higher than the melting point of the fluororesin. As the fluororesin, polytetrafluoroethylene (PTFE) or the like can be used.

  The transfer sheet is preferably a sheet such as PTFE or polyethylene terephthalate (PET).

  In the process of applying the catalyst ink or evaporating the dispersion solvent of the catalyst ink in a magnetic field with magnetic flux density distribution, hold for a certain period of time until the mass transfer due to magnetic force is stabilized after application, and then evaporate Is preferred. If it is too short, the mass transfer will be insufficient or unstable, and if it is too long, the film forming rate will be slow, so a holding time of 0.1 second to 1 minute is preferred.

  Further, it is preferable to apply the catalyst ink or evaporate the dispersion solvent in a state where the temperature of the substrate is heated to 20 ° C. to 120 ° C. By forming an electrode catalyst layer on a substrate heated to 20 to 120 ° C., the solvent in the catalyst ink is instantly dried to prevent aggregation of the catalyst-supported carbon after coating, and the porosity of the catalyst layer Can be improved. If the electrode surface is less than 20 ° C., the effect of instantly drying the solvent is low. Further, when the electrode surface exceeds 120 ° C., drying unevenness may occur.

  A solution containing a proton conductive polymer is preferably applied as a binder between the electrode catalyst layer and the proton conductive polymer electrolyte membrane, and the same substance as the proton conductive polymer electrolyte membrane is more preferable.

  The electrode catalyst layer for a polymer electrolyte fuel cell and the production method thereof according to the present invention will be described below with reference to specific examples, but the present invention is not limited to the following examples.

"Example"
[Adjustment of catalyst ink]
A platinum-supported carbon catalyst with a platinum loading of 45 wt%, a commercially available proton conductive polymer (Nafion) solution and a pore former are mixed in a solvent and dispersed with a planetary ball mill (Pulversette 7 manufactured by FRITSCH). went. Ball mill pots and balls made of zirconia were used. The composition ratio of the starting materials was platinum-supporting carbon, Nafion, and calcium carbonate as a pore-forming agent in a weight ratio of 4: 2: 1. The volume ratio was 1: 1: 1. The solid content was 10% by weight.
〔Base material〕
The flat base material that forms a non-uniform magnetic flux density distribution has aluminum (weak magnetic material) with a thickness of 10 mm as a base material, and cylindrical iron (ferromagnetic material) with a diameter of 1 mm penetrates the base material. I used what I have.
[Method for producing electrode catalyst layer]
A superconducting magnet that generates a magnetic field strength of 10 Tesla was used in the magnetic field generator, and a glass double tube in which water at 25 ° C. was circulated was fixed in the magnetic field generation space. With the carbon paper placed on the substrate and a magnetic field strength of 10 Tesla applied, the prepared catalyst ink was applied onto the carbon paper by a pressure spray and dried to prepare an electrode catalyst layer. The thickness of the electrode catalyst layer was adjusted so that the amount of platinum supported was 0.3 mg / cm ² . The pore former was removed with 1N nitric acid.

《Comparative example》
[Adjustment of catalyst ink]
A catalyst ink was prepared by the same starting material composition and dispersion method as described in the examples.
〔Base material〕
The same substrate as described in the examples was used.
[Method for producing electrode catalyst layer]
The electrode catalyst layer was prepared in the same manner as described in the examples except that the superconducting magnet was not operated.

<Preparation of electrolyte membrane electrode assembly>
The electrodes produced in the examples and comparative examples were punched into a 5.2 cm ² square to form a fuel electrode and an air electrode. Nafion 112 manufactured by DuPont Co., Ltd. was used as the proton conductive polymer membrane. A 5% Nafion solution was dropped onto the electrode as a binder, and the proton conductive polymer membrane was sandwiched between two electrodes formed on carbon paper. 125 ° C., 6.0 × 10 ⁶ Pa, 30 minutes Hot pressing was performed under conditions to obtain an electrolyte membrane electrode assembly.

<Evaluation>
[Hydrogen adsorption area]
Various membrane electrode assemblies were bonded with a separator, and this was subjected to cyclic voltammetry with a fuel cell measurement device (GFT-SG1 manufactured by Toyo Technica Co., Ltd.) at a cell temperature of 80 ° C., and the area was determined from the hydrogen desorption wave. The effective utilization rate of platinum was calculated by dividing this area by the theoretical area when the platinum catalyst was used 100% effectively.
[Power generation characteristics]
A separator is attached to various membrane electrode assemblies, and this is measured with a fuel cell measurement device (GFT-SG1 manufactured by Toyo Technica Co., Ltd.) under conditions of a cell temperature of 80 ° C., an anode of 100% RH, and a cathode of 26% RH. The maximum output (mW / cm ² ) was measured. The power generation characteristics were evaluated by flowing hydrogen as a fuel gas at a constant rate of 200 ml / min and oxygen as an oxidant gas at a constant rate of 100 ml / min.

"Measurement result"
The electrocatalyst layer produced in a state where a magnetic field strength of 10 Tesla was applied had an effective utilization rate of 36% determined from the hydrogen adsorption area, and the maximum output was as high as 1.4 W / cm ² (Example). . On the other hand, the electrocatalyst layer produced without operating the superconducting magnet had an effective utilization rate of 26% determined from the hydrogen adsorption area, and the maximum output was as high as 1.2 W / cm ² ( Comparative example). Therefore, it was speculated that the electrode catalyst layer obtained in the example had a high effective utilization rate of platinum, and the three-phase interface as an electrochemical reaction field was increased as compared with the comparative example. In addition, since the maximum output is increased as compared with the comparative example, it is presumed that the material is transported smoothly even under high load operation.

  Before removing the pore-forming agent with 1N nitric acid, the cross-section of the electrode catalyst layer produced with a magnetic field strength of 10 Tesla applied was examined. As shown in FIG. 3, the pore-forming agent was formed in a pattern. It was. Reference numeral 21 is a proton conductive polymer electrolyte, 22 is a catalyst-supporting carbon, 23 is a pore former, 24 is a ferromagnetic material made of iron, and 25 is a weak magnetic material made of aluminum. Therefore, it seems that the structure with high gas diffusivity in the thickness direction of the electrode catalyst layer contributes to the improvement of the effective utilization rate of platinum and the improvement of power generation characteristics.

  Also, after measuring the power generation characteristics, the membrane electrode assembly was removed from the power generation cell, and when the cross section of the electrode catalyst layer after power generation was examined, the occurrence of cracks in the electrode catalyst layer of the example was suppressed compared to the comparative example. I confirmed. Therefore, it seems that the structure of the patterned electrode catalyst layer contributes to maintaining the mechanical strength as compared with the uniform electrode catalyst layer.

It is an apparatus schematic diagram of electrode catalyst layer manufacture by this invention. It is typical sectional drawing which shows the form which a magnetic force line concentrates on the ferromagnetic material of a base material. It is typical sectional drawing of the electrode catalyst layer by this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electrode catalyst layer, 2 ... Gas diffusion layer, 3 ...... Base material comprised with a ferromagnetic material and a weak magnetic material, 11 ... Ferromagnetic material, 12 ... Weak magnetic material, 21 ... Proton Conductive polymer electrolyte, 22 ... catalyst-supported carbon, 23 ... pore former, 24 ... ferromagnetic material, 25 ... weak magnetic material.

Claims (6)

A method for producing an electrode catalyst layer in a polymer electrolyte fuel cell in which a proton conductive polymer electrolyte membrane sandwiched between a pair of electrode catalyst layers is sandwiched between a pair of gas diffusion layers. At least one substance having a magnetic susceptibility different from that of the pore forming agent is dissolved or dispersed in a catalyst ink in which carbon particles, a polymer electrolyte, and a pore forming agent are dispersed in a dispersion solvent, and the pore forming agent and the dispersion are dispersed. An at least one step selected from a step of applying a magnetic susceptibility difference with a solvent on a planar substrate and a step of evaporating the dispersed solvent in the catalyst ink is a non-uniform magnetic flux density distribution. The pores in the electrocatalyst layer have a gradient distribution of porosity that increases gas diffusivity in the thickness direction or the membrane surface direction with respect to the polymer electrolyte membrane due to the magnetic force. With features Method for producing that polymer electrolyte fuel cell electrode catalyst layer.   2. The electrode catalyst layer for a polymer electrolyte fuel cell according to claim 1, wherein a maximum magnetic flux density of a permanent magnet or a magnetic field generator that forms a magnetic field having a magnetic flux density distribution is 0.1 Tesla or more. Production method.   Applying a magnetic field to a base material composed of two kinds of materials having different magnetic susceptibility, concentrating the magnetic force on the material having the highest magnetic susceptibility in the base material, and using a magnetic field having a desired magnetic flux density distribution The method for producing an electrode catalyst layer for a polymer electrolyte fuel cell according to claim 1 or 2.   4. The polymer electrolyte fuel cell according to claim 1, wherein at least one pore former having a magnetic susceptibility different from that of the catalyst ink dispersion solvent is dispersed in the dispersion solvent. A method for producing an electrode catalyst layer. The pore-forming agent dispersed in the dispersion solvent is removed by the solvent of the pore-forming agent after forming the electrode catalyst layer, so that the pores of the electrode catalyst layer are in the thickness direction or with respect to the polymer electrolyte membrane. 5. The method for producing an electrode catalyst layer for a polymer electrolyte fuel cell according to claim 4, wherein the gas catalyst has a gradient distribution of porosity that increases gas diffusivity in the film surface direction. The pore-forming agent dispersed in the dispersion solvent is removed by water generated by power generation, so that the pores of the electrode catalyst layer are diffused in the thickness direction or the membrane surface direction with respect to the polymer electrolyte membrane. 5. The method for producing an electrode catalyst layer for a polymer electrolyte fuel cell according to claim 4, wherein the method has a gradient distribution of porosity that increases the property .

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