JP3549241B2 - Electrode for polymer solid electrolyte fuel cell and joined body thereof with polymer solid electrolyte - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an electrode for a polymer solid electrolyte fuel cell and a joined body of the electrode and the polymer solid electrolyte.
[0002]
[Prior art]
Due to its operation principle, the polymer electrolyte fuel cell has a possibility that its output density can be increased about four times as compared with a fuel cell using a conventional electrolyte (for example, a phosphoric acid type fuel cell), and its power generation efficiency is high. For this reason, in recent years, it has attracted attention as a small-sized mobile power supply and a distributed power supply. By the way, the electrochemical reaction of a solid polymer electrolyte fuel cell is a three-phase interface reaction of a catalyst, a solid polymer electrolyte, and a reaction gas, and its power generation characteristics are greatly affected by how many such three-phase interfaces are formed. . It is also important for the output characteristics that more catalyst be present at the reaction interface.
[0003]
Conventionally, the following method has been proposed as a gas diffusion electrode for this polymer solid electrolyte.
(1) An electrode formed by hot-pressing a catalytic substance on a polymer solid electrolyte membrane using PTFE or a polymer solid electrolyte as a binder.
(2) A paste or ink-like liquid obtained by mixing a PTFE dispersion and a catalyst substance, or a solution of a polymer solid electrolyte and a catalyst substance or a precursor thereof, is applied to a polymer solid electrolyte membrane, and dried and heated to form. Alternatively, the solvent is removed from the paste or ink-like liquid to form a film, which is transferred to a polymer solid electrolyte membrane and hot-pressed.
[0004]
(3) A catalyst layer is formed in the shape of a current collector, and this is hot-pressed to a polymer solid electrolyte membrane.
(4) A sheet-shaped electrode is formed from PTFE and a catalyst substance and hot-pressed on a polymer solid electrolyte membrane, or a polymer solid electrolyte solution is applied on the surface, and then this is used as a binder to form a polymer solid electrolyte membrane. Hot press.
[0005]
[Problems to be solved by the invention]
Although the above methods have been proposed, however, these methods have a two-dimensional reaction interface and do not ensure a sufficient reaction field, cannot provide a sufficient supply of the reaction gas because the entire surface is hydrophilic, and the amount of the catalyst is low. There was a problem that it could not secure enough.
Further, the present applicant discloses in Japanese Patent Application Laid-Open No. 2-85387 that an ion exchange resin or a metal and an ion exchange resin are introduced from one surface of a continuous porous body comprising a fluorine-containing polymer binder and an electrochemically functional material powder into pores. Disclosed a sheet-like electrode material containing an ion-exchange resin in which a mixture of the above is distributed, but the performance is not sufficient for fuel electricity.
[0006]
Therefore, the present invention solves these problems, and proposes an electrode in which the three-phase interface reaction zone is sufficiently secured three-dimensionally and the amount of catalyst is secured, and an electrode / polymer solid electrolyte joined body is proposed. Things.
[0007]
[Means for Solving the Problems]
According to the present invention, a first layer comprising conductive particles and polytetrafluoroethylene, and a second layer comprising catalyst-carrying particles and a solid polymer electrolyte on the first layer, An electrode material having a multilayer structure in which the catalyst-supporting particles of the second layer and the solid polymer electrolyte penetrate at least partially into the thickness direction of the first layer ; and a material provided on the first layer side of the electrode material. An electrode for a polymer solid electrolyte fuel cell, comprising: an electrode substrate; and an electrode-polymer in which a layer comprising only a polymer solid electrolyte is further provided on the surface of the second layer of the electrode. Provided is a solid electrolyte joined body and an electrode-polymer solid electrolyte joined body provided with a counter electrode in a layer made of only the polymer solid electrolyte of the joined body.
[0008]
The first layer is composed of polytetrafluoroethylene (PTFE) and conductive particles.
PTFE is usually used in the form of a dispersion.
As the conductive particles, carbon-based particles such as carbon black, graphite particles, activated carbon particles, and the like, or platinum-based metal particles such as metal particles can be used. Further, fibrous particles, for example, fine fibers of carbon fibers, graphite whiskers, and the like are also included. Further, a mixture thereof may be used. Further, catalyst particles may be supported on the particles. Preferably, carbon black alone or carbon black carrying a platinum-based catalyst is used.
[0009]
As a method for producing the first layer, after dispersing the conductive particles in water, an aqueous dispersion of PTFE is added, and if necessary, a pore-forming agent or the like is further added, followed by mixing well to form a paste, It may be prepared by coating a substrate such as carbon paper or metal mesh, drying and heating to remove moisture, solvent, pore-forming agent and the like.
Preferably, conductive particles and PTFE are co-aggregated from a mixed dispersion of conductive particles and PTFE, and the mixed particles obtained by filtration and drying are mixed with a solvent having a low surface tension such as petroleum ether or solvent naphtha as a liquid lubricant. In addition, after forming into a sheet by paste extrusion and / or rolling, the liquid lubricant is extracted or removed by heating to obtain a self-supporting sheet.
[0010]
Further, by adjusting the amount, viscosity, etc. of the liquid lubricant, or by stretching the sheet after the presence or removal of the liquid lubricant after forming the sheet, the material is made of a number of PTFE resins containing conductive particles. It is possible to obtain a sheet-like material composed of micro nodules and a number of PTFE resin fine fibers which do not include conductive particles extending from each of the micro nodules and connecting the micro nodules three-dimensionally. The latter production method is disclosed in detail in Japanese Patent Publication No. 63-19799. Such a film has a high porosity and a high water repellency, and furthermore, the ink-like solution described later easily penetrates into the pores. Therefore, the film is formed from the fine nodules and the ink-like solution penetrating the pores. The polymer solid electrolyte or the catalyst / polymer solid electrolyte mixture thus obtained is particularly preferable in the present invention because the mixture is finely distributed and a so-called three-dimensional reaction zone is easily formed.
[0011]
Further, in this manufacturing method, it is possible to integrally form the sheet by rolling in the presence of a liquid lubricant together with another sheet prepared in the same manner, thereby forming two layers having different compositions. It is also possible to obtain a sheet having two or more layers having different physical properties such as pore diameters, or a sheet having a plurality of layers. The same applies to the sheet obtained by the above stretching or the like. Therefore, for example, the first layer contains a large amount of conductive particles, is relatively hydrophilic, has large pores, and easily penetrates an ink component described later. It is possible to have a multilayer structure in which a layer having a strong aqueous property and a small pore size is formed. Further, a large number of fine holes may be mechanically formed in the sheet obtained as described above, if necessary.
[0012]
Naturally, the sheet may be bonded to a base such as carbon paper or metal mesh. In this case, it may be conveniently performed by a means such as bonding with a hot press using a fluororesin such as PTFE, FEP, ETFE or a mixture of the same and a conductive powder as a binder.
The mixing ratio of the PTFE and the conductive powder can be appropriately selected from the range of 5:95 to 70:30. If PTFE is less than this, required strength and durability cannot be obtained, and if it is more than 70%, sufficient conductivity cannot be obtained. A particularly preferred ratio is between 20% and 50% PTFE.
[0013]
In addition, a sheet having self-supporting properties is such that it does not break under the weight of the sheet itself. Has a strength of about 30 g / mm ² or more, preferably 90 g / mm ² or more. In such a product, the film-forming property of the ink-like solution applied to the surface is improved, and the formed film is excellent in reinforcement effect and protection effect. Such a sheet can be easily produced by a process including extrusion or rolling or both after the co-agglomeration. The same applies to a product prepared by adding a stretching step.
[0014]
The first layer needs holes for the catalyst-supporting particles of the second layer and the solid polymer electrolyte to penetrate, but is naturally formed according to the above-described production method. This is because (1) a gap is formed between the conductive particles. (2) In the case of carbon black, particularly, there is a series of particles called a structure, and thus the porosity is higher. Of course, (3) when the film is stretched, a fine structure having a higher porosity is formed as described above. The preferred porosity is 40 to 90%, and it is preferable to adjust the porosity to this range. The thickness of the first layer is preferably 30 to 300 μm. If it is less than 30 μm, the necessary strength and cushioning property (to improve the electrical contact with the current collector) cannot be obtained, and the formation of the three-dimensional reaction zone is also insufficient. On the other hand, when the thickness is 300 μm or more, the electric conductivity is hindered, and the reactant gas supply is deteriorated.
[0015]
Next, the second layer can be formed by applying, drying, and heating a mixed ink-like solution comprising at least catalyst-carrying particles and a solid polymer electrolyte component on the first layer. The ink-like solution component can be completely impregnated in the thickness direction in the first layer, or can be partially impregnated on the application surface side by side.
As the catalyst-supporting particles that are components of the mixed ink-like solution, a platinum group metal or a catalyst comprising a plurality of these components or a catalyst obtained by alloying a metal of another genus with these metals, preferably carbon black, graphite powder, activated carbon, or the like A material supported on a corrosion-resistant conductive substrate can be used.
[0016]
On the other hand, the polymer solid electrolyte component may be a solution of a hydrocarbon-based or fluorine-based ion exchange resin, but a fluorine-based material is preferred in terms of corrosion resistance and heat resistance. Such a product is a perfluorosulfonic acid resin. This resin is generally obtained as a solvent solution, for example as an alcohol solution. Therefore, the mixed ink-like solution can be obtained, for example, by dispersing catalyst-carrying particles in water or alcohol in advance, adding an ion-exchange resin solution, and further mixing and dispersing the mixture by ultrasonic waves or the like. Further, a PTFE dispersion may be further added to the mixture, and a mixture may be added. If necessary, a pore-forming agent such as ammonium bicarbonate or salt may be mixed.
[0017]
In the present invention, a catalyst-containing layer (second layer) to be brought into contact with a layer consisting only of a polymer solid electrolyte is a mixed layer of catalyst-supported particles in which a catalyst is supported on a corrosion-resistant conductive substrate and a polymer solid electrolyte. Form as Thus, there is an advantage that the conductivity in the second layer is improved and a three-phase interface is easily formed between the polymer solid electrolyte and the catalyst and the reaction gas. In particular, since the catalyst supported on the carrier has a relatively large particle size, the catalyst is easily exposed to the surface of pores formed in the second layer, and thus a three-phase interface is easily formed. Thus, it is preferable that the second layer contains a certain amount of holes. Since pores are formed between the catalyst-supporting particles as in the case of the conductive particles in the first layer, both the size and the ratio of the pores vary depending on the catalyst carrier, and also depending on the amount of the solid polymer electrolyte. change. Therefore, it is difficult to quantify the porosity, but it is preferably 40% or more.
[0018]
The catalyst-supporting particles and the solid polymer electrolyte (4) used for forming the second layer 2 partially penetrate into the pores of the first layer 1 as shown in FIG. 3 has a wavy (uneven surface) surface, which has an effect of forming a good three-phase interface between the uneven surface and the holes in the first layer. In addition, in FIG. 1, 5 is a micro nodule made of polytetrafluoroethylene containing conductive particles, and 6 is a microfiber made of polytetrafluoroethylene.
[0019]
The depth of penetration of the catalyst-carrying particles and the solid polymer electrolyte (4) into the first layer is not limited, but in particular in a fuel cell used at room temperature, it is hydrophilic to leave the first layer hydrophobic. It is desirable that certain polymer solid electrolytes do not penetrate the entire thickness of the first layer. This can be adjusted by the viscosity of the mixed ink-like solution forming the second layer, the particle size of the catalyst-carrying particles in the solution, and the like. However, it is generally preferable that the penetration depth is at least 10 μm or more.
[0020]
The mixing ratio between the catalyst-carrying particles and the polymer solid electrolyte may be appropriately determined depending on the catalyst used. For example, in the case of 30% platinum-carrying carbon black (PtC), the ratio (weight ratio) of PtC to the polymer solid electrolyte is It is about 9 to 1 from 1 to 9. If the PtC is less than this, the catalytic activity is insufficient, and if it is more than this, the film-forming property is impaired.
The thickness of the second layer (the thickness of the portion penetrating into the first layer is not taken into consideration) is appropriately changed depending on the required amount of the catalyst, but is generally between 3 μm and 100 μm.
[0021]
Thus, the composite membrane obtained by forming the second layer on the first layer can be suitably used as an electrode material for a polymer solid electrolyte fuel cell.
In order to construct a polymer solid electrolyte fuel cell using this electrode material, as shown in FIG. 2, a polymer solid electrolyte membrane 11 is sandwiched between gas diffusive electrodes 12 and 13, and a current collector (electrode substrate) 14 is formed. , 15. The electrode material of the present invention is used as at least one of the gas diffusive electrodes 12 and 13. In FIG. 2, reference numerals 21A and 21B denote a second layer made of catalyst-carrying particles and a polymer solid electrolyte, 22A and 22B denote first layers made of conductive particles and polytetrafluoroethylene, and 23A and 23B denote oxygen supply grooves 4A. And a separator plate having hydrogen supply grooves 4B, 24A and 24B are oxygen or hydrogen gas supply grooves.
[0022]
As the solid polymer electrolyte membrane 11, a perfluorosulfonic acid resin membrane is suitably used, and such a membrane has been announced by Dupont Corporation and Dow Chemical Company in the United States. Dupont's membrane is a trademark of "Nafion". It is sold, and "Nafion # 117" is particularly suitable for use here, but is not limited to this. It is preferable that the film thickness is as thin as possible from the viewpoint of electrical resistance. The lower limit is determined by mechanical strength and durability, but is generally 50 μm ^t . However, in the present invention, there is an advantage that the electrode sheet itself can be made thinner due to the reinforcement and protection effects due to its strength.
[0023]
It is preferable to use the electrode material of the present invention for both of the gas diffusing electrodes 12 and 13, but for one of them, other known gas diffusing electrodes may be used.
According to the present invention, in order to facilitate the manufacture of such a battery, an electrode in which a layer composed of only a polymer solid electrolyte is further joined to the surface of the second layer of the electrode material of the present invention in advance is used. An electrode-polymer solid electrolyte joined body in which another electrode is joined to the other surface side of the molecular solid electrolyte joined body, and a layer made of only the polymer solid electrolyte of the joined body can be prepared.
[0024]
As the current collectors (electrode bases) 14 and 15 in FIG. 2, a metal mesh, a metal expanded band mesh, a metal nonwoven fabric, a sintered plate of a metal sensor, carbon paper, a porous carbon plate, or the like is used.
In the solid polymer electrolyte fuel cell thus configured, referring to FIG. 2, when O ₂ and H ₂ are supplied to the gas supply groove 4A and O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O in the electrode 12, A reaction of 2H ₂ → 4H ⁺ + 4e ⁻ occurs in 13, 4H ⁺ flows from 13 to 12 through the solid polymer electrolyte membrane 11, and 4e ⁻ becomes electric energy by passing through an external load. The operating temperature ranges from 60 ° C to about 100 ° C, preferably about 80 ° C.
[0025]
In addition, the electrode and the electrode / solid electrolyte integrated molded article according to the present invention can be used not only for a solid polymer electrolyte fuel cell, but also for a water electrolyzer, an ozone generator, and the like.
[0026]
【Example】
Example 1
A PTFE dispersion and a dispersion of 25% platinum-supported carbon black in water are mixed, coagulated, filtered and dried. Solvent naphtha is added, and the mixture is extruded and rolled. Sheet 1 having 70% carbon black and a film thickness of 60 μm and a density of 0.54 g / cm ³ was prepared.
[0027]
Separately, 50% platinum-supported carbon black was dispersed in water by ultrasonic waves, and a perfluorosulfonic acid resin solution was further added to further disperse the ink, whereby an ink-like mixed solution A was prepared. This solution was a solution in which platinum-supported carbon black contained 10% of a mixture of 6 perfluorosulfonic acid resin to 6 parts.
[0028]
Next, the sheet 1 is placed on a vacuum table and fixed on the table by vacuuming from the back, then the ink mixture solution A is applied and impregnated by a screen printing method, air-dried, and then dried at 120 ° C. for 24 hours. By heating for a time, a sheet electrode was obtained. The thickness of the coating layer at this time was 20 μm.
[0029]
Example 2
A PTFE dispersion is applied to carbon paper having a thickness of 100 μm, heated and dried to adhere PTFE, and then a sword mountain-shaped jig having a large number of needles at the end of the plate is attached to the same sheet 1 used in Example 1. Then, a large number of fine holes were mechanically made, hot-pressed at 120 ° C., and then heated to 340 ° C. for bonding.
[0030]
Next, the same mixed solution A also used in Example 1 was applied and impregnated on the surface of the sheet 1 with a brush, and then completely dried. After repeating this three times, a step of applying a solution of only the perfluorosulfonic acid resin to the surface and drying the solution is repeated five times to form a 40 μm film of the perfluorosulfonic acid resin on the surface, A film integrated molded product was obtained.
[0031]
Example 3
Except that acetylene black was used in place of the platinum-supported carbon black, a 200 μm thick rolled liquid lubricant (solvent naphtha) consisting of 55% PTFE and 45% acetylene black was used in the same manner as in Example 1. Sheets were prepared. Similarly, a sheet having a thickness of 100 μm and comprising 25% of PTFE and 75% of carbon black supporting 20% of platinum was prepared. Next, these sheets were overlaid and further rolled to a thickness of 120 μm, and then the liquid lubricant was removed to obtain a two-layer structure integrated sheet.
[0032]
Next, the sheet was stretched 1.5 times while being heated at 150 ° C., and then heated to 320 ° C. along the surface of the stainless steel drum as it was to have dimensional stability. The thickness of this sheet was 100 μm.
Thereafter, Example 1 was fixed to a vacuum table similarly, to obtain an electrode material of the present invention is applied impregnated with still Example 1 The same mixed solution A screen printing method as that used in.
[0033]
Further, a perfluorosulfonic acid resin solution was applied thereon to obtain an electrode / solid electrolyte membrane integrated molded product.
After preparing two pieces of this integrally molded product, superposing the perfluorosulfonic acid resin surfaces together, temporarily bonding them through a roll, and then heating them at 130 ° C. for 24 hours under a load to integrate them, the FIG. As described above, a fuel cell was formed by sandwiching the current collector (electrode substrate) as an expanded mesh.
[0034]
When hydrogen and oxygen were supplied to each electrode of this fuel cell, an output of 0.42 V was obtained at 1 A / cm ² .
[0035]
Comparative Example 1
On the other hand, for comparison, a fuel cell was constructed in the same manner as in Example 3 except that the perfluorosulfonic acid resin was directly applied and impregnated without applying the mixed solution A, and the output was measured. As a result, 1 A / cm ^{2 was obtained.} At that time was 0.34V.
[0036]
Comparative Example 2 (corresponding to JP-A-2-85387)
Instead of the mixed solution A, an aqueous solution of chloropentaammineplatinum (platinum concentration: 2 mg / ml) was mixed with an alcohol solution of perfluorosulfonic acid resin, and the ion exchange resin concentration was 3% by weight and the platinum concentration was 0.5% by weight. % Solution was used. This was similarly applied to the sheet obtained in Example 3 , impregnated, air-dried, and subsequently subjected to a hydrogen reduction treatment at a temperature of 150 ° C. to reduce the platinum ammine complex to platinum, thereby forming a sheet electrode. Obtained. Hereinafter, a fuel cell was constructed in the same manner as in Example 3, and the output was measured. The voltage at 1 A / cm ² was 0.38 V.
[0037]
【The invention's effect】
The polymer solid electrolyte fuel cell electrode of the present invention or the joined body thereof and the polymer solid electrolyte can form a three-dimensional interface of a solid polymer electrolyte / catalyst / reaction gas three-dimensional interface, and have a small amount of catalyst. It is an electrode that can be sufficiently provided and has good properties such as gas permeability, water repellency, and film strength.
[Brief description of the drawings]
FIG. 1 is a schematic cross section of an electrode for a solid polymer electrolyte fuel cell of the present invention.
FIG. 2 shows an example of a polymer solid electrolyte fuel cell.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... 1st layer 2 ... 2nd layer 3 ... Penetration part of catalyst carrying particle and polymer solid electrolyte 4 ... Catalyst carrying particle and polymer solid electrolyte 5 ... PTFE micro nodule 6 ... PTFE micro fiber 11 ... high Molecular solid electrolyte membranes 12, 13 Gas permeable electrodes 14, 15 Current collectors 21A, 21B Second layers 22A, 22B First layers 23A, 23B Separator plates 24A, 24B Oxygen or hydrogen gas supply groove

Claims (7)

A first layer comprising conductive particles and polytetrafluoroethylene; and a second layer comprising catalyst-carrying particles on the first layer and a polymer solid electrolyte, wherein the second layer comprises a catalyst. From an electrode material having a multilayer structure in which the carrier particles and the solid polymer electrolyte penetrate at least partially into the thickness direction of the first layer, and an electrode substrate provided on the first layer side of the electrode material. solid polymer electrolyte fuel cell electrode, characterized in that it is configured. The electrode according to claim 1, wherein the catalyst-supporting particles are platinum-supporting carbon black powder. 3. The electrode according to claim 1, wherein the conductive particles are carbon black or carbon black powder carrying a catalyst powder. The polytetrafluoroethylene forms a flesh consisting of a number of micronodules and a number of microfibers extending from the micronodules and interconnecting the micronodules three-dimensionally, and the micronodules are formed in the micronodules. The electrode according to claim 1, 2 or 3, which contains conductive particles. The electrode according to claim 1, 2, 3, or 4, wherein the electrode substrate is a metal mesh, a metal expanded mesh, a metal nonwoven fabric, a fired plate of metal fiber, carbon paper or a porous carbon plate. An electrode-polymer solid electrolyte joined body, further comprising a layer comprising only a polymer solid electrolyte provided on the surface of the second layer of the electrode according to any one of claims 1 to 5 . An electrode-polymer solid electrolyte assembly, comprising a counter electrode on a side opposite to the electrode of the layer comprising only the polymer solid electrolyte according to claim 6 .

Images