JPH07326363A - Ion conductivity imparting electrode and jointing material for electrode and electrolyte and cell using the ion conductivity imparting electrode - Google Patents

Abstract

PURPOSE:To provide a highly functional electrode or jointing material for an electrode and a high molecular electrolytic film by covering the external surface of a porous electrode substrate and the internal surface thereof with high polymer for forming an ion exchange material layer and, then, attaching an electrode catalyst to the surface of the layer. CONSTITUTION:Porous carbon paper made of carbon fiber 3 is used as an electrode substrate. The porous carbon paper is immersed in a Nafion solution and, then, vacuum dried, thereby forming an ion exchange material layer 4 made of ion exchange high polymer on the surface of the carbon fiber 3. Also, the porous carbon paper is structured to have narrow holes continuous from one side to the other thereof. In addition, a catalyst 5 is vacuum deposited on the carbon paper having the layer 4, thereby preparing an ion conductivity imparting electrode 1. In this case, the electrode substrate preferably has a porosity between 35 and 50%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode for performing an electrochemical reaction, an electrode / polymer electrolyte joined body and a cell, and more specifically to various kinds of fuel cells, oxygen and / or hydrogen generators, oxygen or hydrogen sensors, etc. The present invention relates to an electrode that can be used in an electrode reaction, and an electrode / polymer electrolyte conjugate.

[0002]

2. Description of the Related Art Conventionally, in an electrode / polymer electrolyte membrane assembly for polymer electrolyte membrane fuel cells, a method of adding an ion exchanger or an active catalyst to the electrode has been adopted for the purpose of enhancing electrode performance. ing. When this method is used, a so-called three-phase interface is formed in the electrode structure and the electrode reaction area increases, so that an electrode with high power generation capability can be obtained.

By the way, such an electrode / polymer electrolyte membrane assembly has been conventionally manufactured by the following method. Metal particles having a catalytic function and electronic conductivity, or those having such metal particles supported on a carrier as an electrode catalyst,
This electrode catalyst, PTFE (polytetrafluoroethylene), and an ion exchanger are mixed, and the mixture is applied or sprayed on the surface of the polymer electrolyte membrane, and then hot pressed to separate the electrode and the polymer electrolyte membrane. A method for forming a joined electrode / polymer electrolyte membrane assembly.

Alternatively, after the mixture is formed into a sheet by a rolling roller to form an electrode, the sheet is superposed on a polymer electrolyte membrane and hot-pressed to form an electrode / polymer electrolyte membrane assembly.

[0005]

However, the conventional electrode prepared by the above method contains both the electrode catalyst and the ion exchanger, which are indispensable for the formation of the three-phase interface. Is not in a sufficiently suitable state in the electrode. That is, the catalyst particles and the ion exchanger are not evenly and uniformly mixed in the electrode, and in the electrode fine structure, there are catalyst particles (isolated catalyst particle region) existing separately from the ion exchanger, and colonies. In general, there is an ion exchanger region (discontinuous region) that is separated from other ion exchanger regions. In the isolated catalyst particle region, the catalyst does not contribute to the electrode reaction at all, and in the discontinuous region, the ion conductive path is not connected to the electrolyte membrane, so that the catalyst does not substantially contribute to the electrode reaction.

That is, in the conventional electrode, since the utilization rate of the catalyst is poor, the power generation capacity cannot be sufficiently enhanced. In particular, in polymer electrolyte fuel cells that use fuel gas or oxidant gas as the electrode reactant, the catalyst plays an important role in enhancing the electrode performance. It was an important issue in raising the level.

The present invention has been made in view of the above problems, and devised an electrode structure capable of increasing the utilization rate of a catalyst added to an electrode, thereby providing a high-performance electrode or electrode / polymer electrolyte membrane. It is intended to provide a zygote.

[0008]

The electrode of the present invention is, in order to solve the above-mentioned problems, an invention according to claim 1, wherein an electrode base material having continuous pores from one surface to the other surface, An ion-conductivity imparting electrode having an ion-exchange layer composed of an ion-exchange polymer covering the outer surface and the inner surface of pores of an electrode substrate, and an electrode catalyst attached to the surface of the ion-exchange layer. It is characterized by being.

According to a second aspect of the invention, in the ionic conductivity imparting electrode according to the first aspect, the electrode base material is mainly composed of a fibrous material having electronic conductivity or a porous material having electronic conductivity. It is characterized by being configured. A third aspect of the present invention is the ionic conductivity imparting electrode according to the first or second aspect, wherein the electrode base material is 3
It is characterized by having a porosity of 5% to 50%.

According to a fourth aspect of the invention, in the electrode according to the first to third aspects, the electrocatalyst is formed by supporting active catalyst metal particles on a conductive substance. The invention according to claim 5 is an ion exchange comprising an electrode base material having pores continuous from one surface to the other surface, and an ion-exchangeable polymer coating the outer surface and the inner surface of the pores of the electrode base material. A body layer, an ion-conductivity imparting electrode having an electrode catalyst attached to the surface of the ion-exchanger layer, and a polymer electrolyte membrane bonded to one surface of the electrode, and an electrode polymer-electrolyte assembly. It is characterized by being.

According to a sixth aspect of the present invention, there is provided an electrode base material having pores continuous from one surface to the other surface, and an ion-exchangeable polymer coating an outer surface and an inner surface of the pores of the electrode base material. An ion-exchanger layer having the following, and an ion-conductivity imparting electrode having an electrode catalyst attached to the surface of the ion-exchanger layer,
The cell is characterized by being arranged on both sides of the polymer electrolyte membrane so as to sandwich the polymer electrolyte membrane.

[0012]

In the structure of the first aspect of the invention, since the electrode base material has continuous pores from one surface to the other surface, the reaction gas and the like can easily diffuse. Further, since the ion exchange layer is formed on the outer surface and the inner surface of the pores of the electrode base material, the ion exchange layer can surely transfer the ions generated at the so-called three-phase interface to the electrolyte. Furthermore, since the electrode catalyst is attached to the surface of such an ion exchanger layer,
The utilization rate of the catalyst added to the electrode is extremely high. That is, the electrode catalyst effectively contributes to the expansion of the electrode reaction area. As described above, according to the invention of claim 1, an electrode having a high power generation capacity can be obtained.

According to the second aspect of the invention, in the ionic conductivity imparting electrode according to the first aspect, a fibrous material having electronic conductivity or a porous material having electronic conductivity is used as the electrode base material. When the electrode base material has conductivity as described above, the base material itself acts as an electron conductive path,
Electrode performance does not deteriorate due to disconnection of the electronic conductive path. Further, when the conductive base material is made of a fibrous or porous material, the reaction gas and the like can be easily diffused, and an ion exchanger layer can be easily formed on the entire surface of the electrode base material. It can have a good ion exchanger layer. Therefore, it is possible to obtain an electrode having excellent power generation capability and little performance deterioration.

Further, according to the invention of claim 3 above, claim 1
In the ion conductivity imparting electrode according to 1 to 3,
The electrode base material had a porosity of 0%. When the electrode base material having such a porosity is used, it is possible to secure a three-phase interface in which the electrode catalyst and the ion-exchange layer are mixed in the pores, and the electrode resistance can be kept within a suitable range where it does not become excessive. it can. Therefore, a well-balanced and high-performance electrode can be obtained.

When the porosity is high, the reaction gas can be easily diffused and the area where the electrode catalyst and the ion exchanger layer are mixed can be increased, so that the electrode reaction area is expanded. However, when the porosity is high, the electrode resistance value becomes large. Therefore, it is necessary to define the porosity in consideration of the balance between the two, but according to the invention of claim 3, since the electrode substrate having an appropriate porosity is used, the electrode performance is improved as a whole.

According to the invention of claim 4, the inventions of claims 1 to 3
In the described ion-conductivity imparting electrode, an electrocatalyst having metal catalyst particles supported on a conductive carrier was used as the electrode catalyst. When the catalyst particles are supported on the conductive carrier as described above, the electronic conductivity between the catalyst particles and the electrode base material is improved, and the catalyst effectively contributes to the electrode reaction. In the invention of claim 5, an electrode similar to the electrode for imparting ionic conductivity according to claim 1 is joined to a polymer electrolyte membrane to form an electrode / electrolyte membrane assembly. With such an electrode / electrolyte membrane assembly, the ion-conductivity imparting electrode exhibits the above-mentioned effects and effects, so that the electrode / electrolyte membrane assembly has a high electrochemical reaction ability as a whole. Therefore, an excellent electrode / electrolyte membrane assembly member that can be used in a fuel cell, an oxygen or hydrogen sensor, or the like can be obtained.

According to a sixth aspect of the present invention, there is provided the ionic conductivity imparting electrode which is excellent in the power generation ability described in the first aspect of the invention.
A cell was constructed by arranging the electrolyte membrane on both sides of the polymer electrolyte membrane so as to sandwich it. In such a cell, the ion-conductivity imparting electrodes arranged on both sides of the polymer electrolyte membrane respectively act as an anode or a cathode to exhibit the above-mentioned excellent performance. Therefore, according to the invention of claim 6, a high performance fuel cell, an oxygen and hydrogen generator or a sensor can be formed.

[0018]

EXAMPLES The present invention will be described in detail with reference to an electrode polymer electrolyte membrane assembly which is an example of the present invention. (Example) As the electrode base material, a rectangular porous carbon paper (porosity: about 50%) having a thickness of 0.1 mm and a size of 5 cm x 5 cm and made of carbon fiber was used. The porous carbon paper was dipped in a 5 ^w / _v % Nafion solution (Aldrich Chemical Co.) and vacuum dried to form a 20 wt% perfluorocarbon sulfonic acid polymer coating layer on the surface of the carbon fiber. It was Hereinafter, the layer in which the surface (outer surface and porous inner surface) of the porous electrode substrate is coated with the ion exchanger in this manner is referred to as an ion exchanger layer. This porous carbon paper is
Since it is made of carbon fiber, it has a structure in which continuous pores are formed from one surface of the paper to the other surface.

The 5 ^w / _v % Nafion solution was prepared by dissolving a perfluorocarbon sulfonic acid polymer in a mixed solution of 90: water of 10 lower alcohols. On the carbon paper on which the ion exchanger layer is formed, platinum as a catalyst is deposited by a vacuum deposition method to 0.5.
It was deposited until the mg / cm ² Pt. Hereinafter, the one in which the catalyst is attached to the ion exchanger layer in this manner is referred to as an ion-conductivity imparting electrode.

Next, two electrodes were prepared by applying a 5 ^w / _v % solution of Nafion to one surface of the ion-conductivity imparting electrode, and drying the two electrodes, each of which had a solid polymer electrolyte membrane (Nafion 117; DuPont). Company) side and stack 3
It was bonded to both sides of the polymer electrolyte membrane by hot pressing at 0 kg / cm ² and 125 ° C. Hereinafter, this is referred to as Inventive Example Electrolyte Membrane Assembly A.

Here, the structure of the electrode / electrolyte membrane assembly thus constructed will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view of an electrode / electrolyte membrane assembly a of the present invention. Reference numeral 1 is an ion conductivity imparting electrode using carbon paper as an electrode base material, and 2 is a polymer electrolyte membrane. In the carbon paper as the electrode base material, the carbon fibers 3 are intertwined with each other, and the voids 6 are formed between the fibers.
It has a basic structure with (pores) formed. In addition to the basic structure, a coating layer of Nafion (ion exchanger layer 4) is formed on the surface of the carbon fiber 3, and platinum particles (electrode catalyst 5) are attached to the surface of the ion exchanger layer 4. It has a micro structure.

Comparative Example A catalyst carrier was prepared by using carbon black as a catalyst carrier and supporting 20 wt% of platinum on the catalyst carrier. This catalyst carrier, PTFE (polytetrafluoroethylene), and the 5 ^w / _v % Nafion solution were mixed at a ratio such that the PTFE content was 20 wt% and the Nafion content was 20 wt%, and the mixture was obtained. Should be rolled with a rolling roller, and platinum should be 0.5 mg / c
It is made into a sheet so as to have m ² Pt. The sheet and the carbon paper that is the electrode base material are overlaid, and 30 kg
A pressure was applied at / cm ² to prepare a reference electrode in which the ionic conductor was superposed on the surface of the electrode base material.

Next, on one surface of the reference electrode, the 5 ^w
/ _v % Nafion solution was applied and dried to prepare two, each of which has a polymer electrolyte membrane (Nafion 11
7) and were hot-pressed at 30 kg / cm ² and 125 ° C. to bond them to both sides of the polymer electrolyte membrane. The thus-produced one is hereinafter referred to as Comparative Example Electrolyte Membrane Assembly X. [Experiment 1] Inventive Example Electrolyte Electrolyte Assembly a Produced Above
Was used as a cell, and a fuel cell was configured by using other known cell constituent members. This battery is referred to as a battery A _{cell according} to the invention.
On the other hand, a comparative battery X _cell was assembled in the same manner as the battery A _{cell according} to the present invention _except that the comparative electrode electrolyte membrane assembly X was used as a _cell . Then, these cells were operated using H ₂ gas as the fuel gas and air as the oxidant gas, and the relationship between the cell voltage and the current density was examined.

The results are shown in FIG. As is apparent from FIG. 2, the battery A _cell according to the present invention had a higher current density than the comparative battery X _cell at any battery voltage. Then, a battery voltage 70 that allows this type of battery to be used efficiently
Comparing the two at 0 mV, the current density of the comparative battery X is 260 mA / cm ² , whereas the current density of the battery A of the present invention is 260 mA / cm ^2.
_{The cell} was 500 mA / cm ² , and the battery of the present invention exhibited a current density about twice as high as that of the comparative battery.

Since the battery A _{cell according} to the present invention and the comparative battery X _cell have the same components except for the electrodes, the above experimental results can be analyzed as follows. That is, in the ion-conductivity imparting electrode according to the present invention, the ion-exchanger layer is formed on the surface of the carbon fibers that are intricately crossed, so that the ion-conducting path formed by this ion-exchanger layer is completely formed on the way. There is no break. Further, since the electrode catalyst is attached to the surface of the ion exchanger layer on which such a good conductive path is formed, the platinum catalyst is inevitably in contact with the ion exchanger and is dissociated on the platinum catalyst. The generated hydrogen ions are transferred to the electrolyte through an uninterrupted ionic conductive path. Further, the air is transferred to the platinum catalyst on the electrode side through which the air flows, through an uninterrupted ionic conductive path.

That is, in the ion-conductivity imparting electrode according to the present invention, the catalyst particles that exist independently are not present, and the ion-conducting path is not cut midway, so the utilization rate of the added catalyst is extremely high. high. Therefore, the effective electrode reaction area is increased. Further, the ionic conductivity imparting electrode according to the present invention is formed on the pore wall surface of the electron conductive porous electrode base material (carbon paper), and the pores allow the fuel gas and the like to pass through the base material. The electrode conducts electrons smoothly, and the electrode reaction proceeds smoothly. For these reasons, it is considered that the electrode performance of the battery A _cell according to the present invention is remarkably improved. Practically, the phenomenon that the catalyst cannot exert its effect does not occur.

On the other hand, the comparative battery X _cell uses the comparative electrode X prepared by simply mixing the ion exchanger with the catalyst particles and other materials. In the electrode of this comparative example electrode X, an ion conductive path is not well formed, and a region (continuous region) where the catalyst particle and the ion conductor are in contact with each other and connected to the electrolyte membrane, the catalyst particle and the ion A region in which the conductors are in contact with each other but not indirectly connected to the electrolyte membrane (a discontinuous region), and a region in which the catalyst particles are not in contact with the ionic conductor (called an isolated catalyst region), Three regions are formed. The reason is that, even when the electrode components are sufficiently mixed during electrode production, the ion exchangers aggregate to some extent in the process of drying and forming into a sheet, but at this time, the ion exchanger and the catalyst particles are separated. Further, since the ion exchanger region is formed in a colony in the electrode, it becomes discontinuous.
This is schematically shown in FIG. In FIG. 4, the catalyst particles 10
In the isolated catalyst region 12 in which is isolated, the catalyst particles do not contribute to the electrode reaction at all because the ionic conductor does not exist. Further, although there is an ion exchanger around the catalyst particles 10, the catalyst ion exchanger is isolated in the electrode and is discontinuous with other catalyst ion exchangers and electrolyte membranes 1
No. 3 cannot substantially contribute to the electrode reaction because ions cannot be transferred to the electrolyte membrane. Therefore, only the continuous region 14 in contact with the electrolyte membrane can substantially contribute to the electrode reaction. That is, the comparative electrode has a lower catalyst utilization rate than the electrode of the present invention. Since had therefore low power generation capacity of the entire electrode, comparative battery X _cell in the present invention applies the battery A
battery characteristics compared to the _cell is considered to be a bad thing.

From the above results, it was confirmed that according to the present invention, the electrode performance can be remarkably improved. [Experiment 2] In Experiment 2, in order to clarify the conditions of the electrode base material, a plurality of thicknesses of 0.
Using 1 mm of carbon paper, a 20 wt% ion-exchanger layer was formed on this substrate in the same manner as in the example, and various electrodes were prepared by adhering a platinum catalyst at a rate of 0.5 mg / cm ² , and each electrode was prepared. Porosity% (pore) of base material, electric resistance (μΩ · cm), and electrode reaction area (m ² -Pt / c)
m ² -electrode).

The porosity was measured by mercury porosimetry and the electrode reaction area was defined as the area of the platinum catalyst present in the unit area of the electrode. The experimental results are shown in FIG. From FIG. 3, the relationship between the porosity and the electrical resistance of the electrode is shown by the solid line in the figure. As the porosity (%) increases, the resistance value increases almost linearly, while the porosity ( %) And the electrode reaction area, the electrode reaction area was maximized when the porosity% was in the range of 40 to 80%.

From these results, it was found that it is preferable to use a porous electrode base material having a porosity of 40 to 80%. However, when the porosity is increased, the strength of the electrode structure as a structure is reduced and the electric resistance is increased. Therefore, when the electric resistance, the electrode reaction area, and the electrode strength are comprehensively judged in view of the past experience of the present inventors, it can be judged that the porosity of about 35% to 50% is more preferable. (Other Matters) In the above examples, porous carbon paper made of carbon fiber was used as the electrode base material, but the electrode base material usable in the present invention is not limited to this.
That is, in the present invention, a material having pores (pores) continuous from one surface to the other surface can be used as the electrode base material, and examples thereof include a fibrous material and a porous material. Examples of the fibrous material include the above-mentioned carbon, metal, conductive polymer resin. Examples include cloth and felt made of fibrous throat. As the porous material, there is a substrate made of a substance similar to the above, which is made porous, and specifically, a porous carbon plate, a foam metal plate, an expanded metal, or a porous sintered body obtained by sintering metal particles. Examples include bonded metal bodies. In the present invention, it is possible to use an electrode substrate in which a non-conductive substrate is coated with a conductive substance to impart electronic conductivity, but it is preferable to use a material itself having conductivity as the electrode substrate. Is good.

In the above examples, the method of attaching platinum to the ion exchanger layer by vacuum deposition was used. However, an electron conductive substance such as carbon black was used as a carrier, and platinum was supported on such carrier. It may be attached to the ion exchanger layer by a method such as coating or dipping. Supporting the catalyst on the electron conductive carrier in this manner is preferable in that the electron conductivity between the catalyst and the electrode base material can be improved. Incidentally, it goes without saying that a catalyst other than platinum can be used in the present invention.

The ion exchanger layer formed on the electrode substrate is preferably formed to such an extent that the pores of the electrode substrate can be secured and a continuous ion exchanger layer can be formed on the substrate. Thus, in the ion exchanger layer, for example, the coating layer can be formed thin by decreasing the concentration of the Nafion solution in the above example, and the layer thickness can be increased by repeating the operation of dipping and drying in the Nafion solution. Can be made.

[0033]

As described above, the outer surface and the inner surface of the porous electrode base material are coated with a polymer having an ion-exchange ability to form a continuous ion-exchanger layer, and then the surface is formed. In the ion-conductivity imparting electrode according to the present invention having an electrode catalyst attached thereto, the catalyst utilization rate is remarkably improved as compared with the conventional electrode, and the catalyst added to the electrode effectively contributes to the electrode reaction, so that it has excellent power generation capability. Can be used as an electrode.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an electrode / electrolyte membrane assembly according to the present invention.

FIG. 2 is a graph showing battery characteristics of a fuel cell A _cell configured by using an electrode / electrolyte membrane assembly according to the present invention and a comparative battery X _cell configured by using an electrode / electrolyte membrane assembly of a comparative example. is there.

FIG. 3 shows the relationship between the electrode porosity and the electric resistance value (solid line),
3 is a graph showing the relationship between electrode porosity and electrode reaction area (broken line).

FIG. 4 is a schematic sectional view showing a microstructure of a comparative example electrode (conventional electrode).

[Explanation of symbols]

 1 Electrode 2 Polymer Electrolyte Membrane 3 Carbon Fiber 4 Ion Exchanger Layer 5 Platinum Catalyst 6 Pore

Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication H01M 8/10 9444-4K (72) Inventor Toshihiko Saito 2-5-5 Keihanhondori, Moriguchi-shi Sanyo Electric Co., Ltd. In the company

Claims (6)

[Claims] 1. An ion exchange layer comprising an electrode base material having pores continuous from one surface to the other surface, and an ion exchange polymer coating the outer surface and the inner surface of the pores of the electrode base material. And an electrode catalyst attached to the surface of the ion exchanger layer. 2. The electrode substrate according to claim 1, wherein the electrode base material is mainly composed of a fibrous material having electronic conductivity or a porous material having electronic conductivity. Ion conductivity imparting electrode. 3. The ionic conductivity imparting electrode according to claim 1 or 2, wherein the electrode base material has a porosity of 35% to 50%. 4. The electrode for imparting ionic conductivity according to claim 1, wherein the electrode catalyst is a conductive substance carrying active catalyst metal particles. 5. An ion exchange layer comprising an electrode base material having pores continuous from one surface to the other surface, and an ion exchange polymer coating the outer surface and the inner surface of the pores of the electrode base material. And an electrode catalyst attached to the surface of the ion-exchanger layer, and a polymer electrolyte membrane bonded to one surface of the electrode, and an electrode-polymer electrolyte electrolyte bonded body. 6. An ion exchange layer comprising an electrode base material having pores continuous from one surface to the other surface, and an ion exchange polymer coating the outer surface and the inner surface of the pores of the electrode base material. A cell comprising ion-conductivity-imparting electrodes having an electrode catalyst attached to the surface of the ion-exchanger layer on both sides of the polymer electrolyte membrane so as to sandwich the polymer electrolyte membrane.