JPH03184266A - Fuel cell with solid electrolyte - Google Patents

Abstract

PURPOSE:To enhance the operating performance by allowing a porous catalyst layer to contain fine particles for attaching ion exchange resin to the surface, and thereby securing a sufficient path for material transfer without decreasing the effective reaction area. CONSTITUTION:Catalyst electrodes 2, 3 are formed from a porous substance in which electroconductive fine particles, for ex. carbon fine particles, bearing the catalyst such as Pt, Pd, or alloy thereof are held by a hydrophobic resin binder such as polytetrafluoroethylene. Further, fine particles 21 which bear attached ion exchange resin 22, for ex. perfluorocarbonsulphonic acid resin- Naffion-, is included as an electrode constituent element. Thus a path for material transfer in a gas diffusion electrode can be secured sufficiently without dropping the three-dimensional reaction region, and now it is practicable to move stably the reaction gas to interfere with electrode reaction or reactive products to lead to easy enhancement of the electrode characteristic (reduction of polarization voltage).

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a fuel cell having an ion-conducting solid electrolyte layer.

(Prior Art) In recent years, fuel cells have attracted attention as highly efficient energy conversion devices. In general, fuel cells have an electrolyte layer containing ionic species that contribute to electrode reactions, which can exchange electrons without being altered by electrode reactions, and which can transfer reactants into positive and negative two-layer electrolyte layers.
It is constructed by sandwiching between different types of electrodes to form an elementary battery, and stacking a plurality of these unit cells via a current collector plate. Since the above-mentioned electrode provides a place where an electromotive reaction occurs, it is usually made of a porous material and is used as a catalytic electrode containing a catalyst that contributes to the electromotive reaction.

The flow of the reaction system in such a fuel cell differs depending on whether the ion species is acidic or alkaline. For example, in the case of acidity, the reaction proceeds according to the flow shown below, and the product (water) is produced on the (+) pole side. arise.

Load e -1〆 ゝ, (+) pole (-) pole (H+) Ox → ← ←Re (e.g. knee, 01 +2H" +2e-4H20)l
I (Example: 82-+2) 1''+2e-) By the way, among the above-mentioned fuel cells, the electrolyte layer is made of a proton-conducting solid polymer electrolyte (S).

-1id Polymer Electrolyte)
Fuel cells (hereinafter referred to as SPE fuel cells) have a compact structure, high output density, and can be operated with a simple system, so they are attracting attention as a mobile power source for space applications and vehicles. There is.

In order to improve the performance of such SPE fuel cells, (
The following improvements have been made to the gas diffusion electrodes used for the +) and (-) side catalyst electrodes.

For example, by applying a solution of an ion exchange resin such as perfluorocarbon sulfonic acid resin, which is a proton conductor, to a gas diffusion electrode and incorporating the ion exchange resin into the gas diffusion electrode, the reaction region is separated from the electrolyte layer and the electrode. Attempts have been made to increase the electrode performance three-dimensionally only from the interface with the electrode. In addition, a catalyst electrode is formed by containing a catalyst metal in an ion exchange resin solution and applying a mixed acid of this and a fluororesin suspension to an electrolyte membrane, and similarly increasing the reaction area three-dimensionally. Attempts have been made (see Japanese Unexamined Patent Publications Nos. 61-295387 and 61-295388).

(Problems to be Solved by the Invention) As mentioned above, by using a gas diffusion electrode containing a proton-conducting ion exchange resin, the three-dimensional reaction area can be increased, which increases the effective reaction area. As a result, it is possible to improve the electrode performance of SPE fuel cells.

However, since the reaction sites are coated with an ion exchange resin that does not have electron conductivity, it has the disadvantage that internal resistance increases. In addition, this coating of reaction sites narrows the pore structure of the electrode and inhibits the mass transfer of reaction gases such as hydrogen and oxygen, as well as reaction products such as water, which are involved in electrode reactions, and is a contributing factor to the deterioration of characteristics. It became.

The present invention was made to address these issues, and is a solid oxide fuel that improves performance by ensuring sufficient mass transfer paths without reducing the effective reaction area. The purpose is to provide batteries.

[Structure of the Invention] (Means for Solving the Problems) That is, the solid oxide fuel cell of the present invention comprises a pair of gaseous catalyst layers having a porous catalyst layer in which conductive fine particles supporting a catalyst are held by a hydrophobic binder. In a solid electrolyte fuel cell comprising a diffusion electrode and an ion-conducting solid electrolyte layer sandwiched between the pair of gas diffusion electrodes, the porous catalyst layer contains fine particles having an ion exchange resin adhered to the surface. It is characterized by

The porous catalyst layer in the present invention is composed of fine particles to which an ion exchange resin is attached and supported, and the fine particles and conductive fine particles carrying a catalyst are held in a porous state by a hydrophobic binder.

The ion exchange resin used in the present invention is usually alkali-resistant, acid-resistant, such as those used as ion exchange resin membranes in various electrochemical devices (fuel cells, water electrolyzers, salt electrolyzers, etc.). Those with high heat resistance are preferred. Among these, ion exchange resins having a skeleton of fluorine-containing polymers, such as perfluorocarbon sulfonic acid resins, are particularly suitable.

Furthermore, the material of the fine particles that serve as a support for the ion exchange resin is not particularly limited, and both organic and inorganic materials can be used; for example, nylon 12 (trade name) Particles having a particle size of about 1 to 100 μm are preferably made of an organic resin having chemical resistance such as a styrene resin or a styrene resin.

As a method for attaching the ion exchange resin to the above-mentioned fine particles, it is possible to make the ion exchange resin into a solution and use a general coating method such as a dipping method or a filtration method. I can do it.

It is preferable that such fine particles carrying an ion exchange resin be contained in the porous catalyst layer in an amount of 1 to 10% by weight. If the content of the fine particles supporting this ion exchange resin is less than (wt%), the reaction area cannot be sufficiently increased, and if it exceeds 10 wt%, the internal resistance will increase and the electrode properties will deteriorate. It ends up.

(Function) In the solid oxide fuel cell of the present invention, fine particles to which an ion exchange resin is attached are contained in the porous catalyst layer as a constituent component. This makes it possible to secure sufficient passages for mass transfer within the gas diffusion electrode without reducing the three-dimensional reaction area, allowing stable movement of reaction gases and reaction products involved in electrode reactions. It becomes possible to do so. Therefore, improvement in electrode characteristics (reduction in polarization voltage) can be easily achieved.

(Example) Hereinafter, an example in which the solid oxide fuel cell of the present invention is applied to an SPE fuel cell will be described with reference to the drawings.

FIG. 1 is a sectional view showing essential parts of an SPE fuel cell according to an embodiment of the present invention. In the figure, 1 is a solid electrolyte membrane having ion conductivity, such as perfluorocarbon sulfonic acid resin Nafion (trade name, manufactured by DuPont).
It is composed of a solid polymer membrane with proton conductivity such as.

On both surfaces of this electrolyte membrane 1, a (=) sub-catalyst electrode 2 and a (+) sub-catalyst electrode 3 are integrally formed, and a unit cell 4 is constituted by these.

These catalyst electrodes 2.3 are gas diffusion electrodes in a porous state, and have the functions of both a porous catalyst layer and a gas diffusion layer. These catalyst electrodes 2.3 are composed of a porous body in which conductive fine particles, such as carbon fine particles, carrying a catalyst such as platinum, palladium, or an alloy thereof are held by a hydrophobic resin binder such as polytetrafluoroethylene. The electrode further contains fine particles to which an ion exchange resin, such as perfluorocarbon sulfonic acid resin Nafion, is attached and supported as an electrode component.

Further, on the other surface of the (-) sub-catalyst electrode 2, a current collector made of a conductive material such as carbon is formed with grooves 6a, which serve as passages for fuel gas such as hydrogen gas, through a porous carbon support 5. A plate 6 is arranged. Further, on the other surface of the (+) sub-catalyst electrode 3, a groove 8a that serves as a passage for an oxidant gas, such as oxygen gas, is provided through a porous conductive water-repellent layer 7.
A current collector plate 8 made of a conductive material such as carbon is arranged.

Furthermore, when the oxidant gas is supplied to the (+) side catalyst electrode 3, a reaction product such as water is generated on the (+) side catalyst electrode 3, so that the wick 9, which serves as a movement path for the electrolyte and liquid reaction products, is , is formed in a groove 8a provided in the current collector plate 8 on the (+) side catalyst electrode 3 side.

The electrolyte layer 1, the (+) and (-) side catalyst electrodes 2.3, the current collector plate 6.8, and the like constitute a fuel cell unit 10.

In the figure, reference numeral 11 indicates a cooling water passage for controlling the operating temperature of the fuel cell when the fuel cell units 10 are stacked in series to form a stack.

Next, a specific example of the SPE fuel cell having the above configuration will be described.

Example 1 First, the surface of organic resin fine particles made of nylon i2 and having an average particle size of 5 to 6 μm was coated with Nafion as an ion exchange resin by a dip method. As shown in FIG. 2, the obtained fine particles were ion exchange resin-attached particles 23 in which an ion exchange resin film 22 was uniformly adhered (coated) to the surface of organic resin fine particles 21.

Next, 10 parts by weight of the above ion-exchange resin-attached fine particles, 50 parts by weight of carbon black to which 10% by weight of platinum as a catalyst was added, and 40 parts by weight of a dispersion of polytetrafluoroethylene resin as a hydrophobic resin binder. About 10 times as much water as this dispersion was added, mixed thoroughly, filtered and dried, and the hydrophobic resin binder, ion exchange resin-attached fine particles, and catalyst-supported carbon fine particles were uniformly mixed. A blended mixture was obtained.

Next, the above mixture was further sufficiently kneaded to fiberize the polytetrafluoroethylene resin to obtain a rice cake-like product having a rice cake-like shape as a whole. Next, this cake-like material was formed into a sheet using a roller to produce a porous catalyst layer sheet. Thereafter, this catalyst layer sheet was heat treated in nitrogen gas at 320°C to obtain a gas diffusion electrode.

The gas diffusion electrode obtained in this way is placed on the (+) side and (=
) side as the catalyst electrode 2.3, the Nafion membrane that will become the electrolyte membrane 1 is sandwiched between these two catalyst electrodes 2.3, and hot pressed at a temperature of 120°C to 130°C and a pressure of 100kg/e1 to integrate them. By doing so, electrode/electrolyte membrane composite A was obtained.

Next, the electrode/electrolyte membrane composite A thus obtained was used as a unit cell 4 to assemble an SPE fuel cell having the above configuration.

In addition, as a comparison with the present invention, an electrode/electrolyte membrane composite B (Comparative Example 1) prepared in the same manner as in Example 1 above except that fine particles coated with Nafion were not used, and a gas diffusion electrode of Comparative Example 1 above. An SPE fuel cell was assembled in the same manner as in Example 1 using the electrode/electrolyte membrane composite C (Comparative Example 2) prepared by applying the Nafion solution to the electrode and electrolyte membrane composite C (Comparative Example 2).

In order to evaluate the current/voltage characteristics of the SPE fuel cells of these Examples and Comparative Examples, operational tests were conducted for each.

The test conditions were a temperature of 80°C, a pressure of 3aLls, fuel gas/hydrogen, and oxidant gas/oxygen.

The results are shown in FIG.

As is clear from FIG. 3, the SPE fuel cell according to Example 1 has a
It can be seen that the current and voltage characteristics are excellent. This is because the method of making the ion exchange resin exist in the electrode includes containing fine particles coated with an ion exchange resin membrane as an electrode component, so that a sufficient path for the transferred substances is ensured.

Example 2 60 parts by weight of ammonium hydrogen carbonate as a pore-forming agent was added to the homogeneous mixture of the hydrophobic resin binder, ion exchange resin-attached fine particles, and catalyst-supported carbon fine particles prepared in Example 1. Mixed evenly. Next, a catalyst layer sheet was prepared using this mixture in the same manner as in Example 1, and this catalyst layer sheet was once heat-treated at 100°C to vaporize the pore-forming agent, and then heated in nitrogen gas at 320°C. A gas diffusion electrode was obtained by heat treatment.

Then, using the gas diffusion electrode thus obtained, an electrode/electrolyte membrane composite was produced under the same conditions as in Example 1, and an SPE fuel cell was assembled in the same manner.

When the current/voltage characteristics of the SPE fuel cell thus prepared were evaluated under the same conditions as in Example 1, it was found that
Almost the same excellent characteristics as the SPE fuel cell were obtained.

Although platinum was used as the catalyst in each of the above Examples, similar effects were obtained with systems using palladium or an alloy of platinum and palladium.

Further, in the above embodiment, an example in which the present invention is applied to an SPE fuel cell has been described, but the present invention is not limited thereto, and can be applied to various fuel cells using an ion-conductive solid electrolyte layer.

[Effects of the Invention] As explained above, according to the solid oxide fuel cell of the present invention, the reaction area can be increased three-dimensionally while ensuring sufficient passages for mass transfer in the gas diffusion electrode. This makes it possible to reliably improve electrode characteristics.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing essential parts of an SPE fuel cell according to an embodiment of the present invention, FIG. 2 is a diagram for explaining fine particles attached to an ion exchange resin membrane used in the fuel cell of FIG. FIG. 3 is a diagram showing current/voltage characteristics in SPE fuel cells of Examples and Comparative Examples of the present invention. 1... Electrolyte membrane, 2... (-) side catalyst electrode, 3... (+) side catalyst electrode, 4...
- Unit cell, 5...Porous carbon support, 6.
8... Current collector plate, 7... Porous conductive water repellent layer, 21... Organic resin fine particles, 22...
...Ion exchange resin membrane, 23...Ion exchange resin membrane attached fine particles.

Claims (1)

[Claims] (1) A pair of gas diffusion electrodes having a porous catalyst layer in which conductive fine particles supporting a catalyst are held by a hydrophobic binder, and an ion conductive solid electrolyte layer sandwiched between the pair of gas diffusion electrodes. A solid oxide fuel cell comprising: The porous catalyst layer contains fine particles having an ion exchange resin adhered to the surface thereof.