JPH0471164A - Fuel cell - Google Patents

Abstract

PURPOSE:To eliminate the need for carton paper so as to decrease the internal resistance of a cell while improving the output power of the cell by mixing a specified amount of fiber or grain, inactive upon an electrolyte, with the material of a reaction layer, and increasing the bore diameter and void ratio of porous structure being formed in the reaction layer specified times over those of porous structure in a matrix layer. CONSTITUTION:Each of a cathode 1 and an anode 2 includes a basic member 4 made of a conductive porous-material, and is composed by monolithically laminating a reaction layer 5 on the inside of the basic member 4. And air is fed to the cathode 1 while hydrogen is fed to the anode 2, so that both the reaction gases react upon each other respectively in the two reaction layers 5 via an electrolyte in a matrix layer 3 to generate water and electric energy. Each of the reaction layers 5 forms such structure as having its bore diameter increased by 10 to 100 times and its void ratio increased by 1.2 to 1.4 times through the process of mixing 50 to 70wt.% of fiber or grain, inactive upon the electrolyte, besides a catalyst support conductive-grain with the material of the reaction layer. Since the reaction layer itself may have the ability to transmit the electrolyte so as to eliminate the need for interposing carbon paper, the internal resistance of a fuel battery cell may be decreased to improve the output power of the cell.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a fuel cell with reduced internal resistance and improved output.

[Prior art]

A fuel cell has a structure in which a matrix layer for holding an electrolyte such as phosphoric acid is interposed between an anode electrode base material and a cathode electrode base material via a reaction layer (catalyst layer). .

Among these constituent materials, the matrix layer needs to have properties such as electrical insulation, gas leak prevention, and electrolyte transfer ability.

On the other hand, fuel cells can be used in two ways, depending on the purpose: those that operate continuously, and those that operate intermittently, constantly repeating power generation, stopping, and storage. However, in the latter case of intermittent operation, the electrolyte (phosphoric acid, etc.) in the matrix layer
However, because the electrolyte is carried out of the cell system due to its own volumetric expansion and contraction and moisture absorption during storage, the rate of disappearance of the electrolyte tends to be faster than in the former case of continuous operation. If the fuel cell continues to operate with insufficient electrolyte in the cell, at some point the reactant gas will pass through the cell, resulting in a decrease in output and an inability to generate electricity. become.

To prevent such a phenomenon, it is necessary to replenish the insufficient electrolyte from outside the system, and it is necessary to distribute the replenished electrolyte within the cell surface in as short a time as possible. As a countermeasure against this problem, conventionally, carbon paper having a large porosity is sandwiched between the two electrodes of the fuel cell together with the matrix layer. However, the presence of conocarbon vapor increases the internal resistance of the fuel cell, causing a reduction in output.

[Problem to be solved by the invention]

The purpose of the present invention is to eliminate the need for conventional carbon paper by providing the reaction layer itself with the function of distributing the electrolyte within the cell surface in a short time, thereby reducing the internal resistance of the cell and improving the output. The purpose of the present invention is to provide a fuel cell that has the following characteristics.

[Means to solve the problem]

The present invention, which achieves the above object, is a fuel having a structure in which an electrolyte holding matrix layer is sandwiched between an anode electrode base material and a cathode electrode base material with a reaction layer made of catalyst-supported conductive particles interposed therebetween. In the battery cell, 50 to 70% by weight of fibers or particles inert to the electrolyte are mixed in the reaction layer, and the porous structure formed in the reaction layer has a bore diameter smaller than that of the matrix layer. 10 to 100 times, porosity 1.2 to
It is characterized by being 1.4 times larger.

Because the reaction layer has such a porous structure, it has the function of transmitting the electrolyte, and the replenished electrolyte can be diffused and distributed within the cell surface in a short time. It becomes like this. This eliminates the need for carbon paper, which is required for electrolyte transfer in conventional fuel cells.

Although the catalyst-supporting conductive particles constituting the reaction layer in the present invention are not particularly limited, carbon black supporting platinum is preferably used. Further, the inert fibers or particles to be mixed in the reaction layer are not particularly limited as long as they are inert to the electrolytic solution, but carbon fibers, phenol fibers, carbon black, etc. can be preferably used. In the case of fibers, it is desirable to cut or crush them into small short fibers and mix them. These catalyst-supported conductive particles and inert fibers or particles are uniformly mixed and bound together by a binder to form a porous body. The binder is polytetrafluoroethylene (PT), which has water repellency.
FE) is most preferred, and fluororesins such as fluorinated alkoxyethylene (PFA) and fluorinated ethylene propylene ether (FEP), which are also water repellent, can also be used.

In the present invention, the porous structure of the reaction layer formed by mixing fibers or particles inert to the electrolytic solution has a bore diameter and porosity larger than that of the porous structure of the matrix layer. It has become. Moreover, the porous structure of the reaction layer has a bore diameter of 10 to 10 mm compared to the porous structure of the matrix layer.
100 times, and the porosity is 1.2 to 1.4 times. If the bore diameter of the reaction layer is smaller than 10 times that of the matrix layer and the porosity is smaller than 1.2 times that of the matrix layer, the reaction layer itself cannot have electrolyte transfer ability. First, the purpose of the present invention is not achieved. However, if the bore diameter of the reaction layer is larger than 100 times that of the matrix layer or the porosity is larger than 1.4 times that of the matrix layer, the reaction layer absorbs the electrolyte. This is not preferable because it causes performance degradation due to reaction gas diffusion law.

In order to form a reaction layer with such a porous structure, it is necessary that the amount of the inert fibers or particles mixed is at least 50% by weight, preferably 60% by weight or more. However, the upper limit of this mixing amount should be 70% by weight; if it exceeds 70%, the amount of catalyst-supported conductive particles in the reaction layer will be insufficient and the original function of the reaction layer will deteriorate, so it is preferable. do not have.

Any known matrix layer can be used, but in particular silicon carbide (SiC), zirconia (ZrO□) particles and tetrafluoroethylene (P) can be used.
It is preferable to use a porous body formed by binding and molding a binder such as TFE), fluorinated alkoxyethylene (PFA), or fluorinated ethylene propylene ether (FEP). The bore diameter of this matrix layer is 0.1"1.Oam,
The porosity is generally 50 to 60%.

FIG. 1 shows an example of a fuel cell according to the present invention made of the above-mentioned constituent materials.

In the figure, 1 is an anode, 2 is a cathode, and 3 is a matrix layer for holding an electrolyte. The anode 1 and the cathode 2 each have a base material 4 made of a conductive porous material, and a reaction layer 5 is integrally provided inside the base material 4. Then, by supplying air to the anode 1 and hydrogen to the cathode 2, both reaction gases react in each reaction layer via the electrolyte in the matrix layer 3, generating water and electrical energy. do. The reaction layer 5 has the above-described bore diameter and porosity by mixing 50 to 70% by weight of fibers or particles that are inert to the electrolytic solution in addition to the catalyst-supported conductive particles. It has a structure.

With such a structure, the thick layer itself has an electrolyte transfer ability, and the intervention of carbon vapor can be made unnecessary. Therefore, the internal resistance of the fuel cell can be reduced and the output can be improved.

〔Example〕

Example 1 consisting of the following configuration. Example 2. Four types of reaction layers were prototyped: a conventional example and a comparative example.

Example 1 Platinum/carbon black 2.0 g (33% by weight) Carbon fiber 3.0 g (50% by weight) PT
FE (Pi7da) 1.0 g (17% by weight
) Example 2 Platinum/carbon black 3.0 g (26% by weight) Carbon fiber 7.0 g (60% by weight) PT
FE (binder) 1.5 g (13% by weight
) Comparative example Platinum/carbon black 2.0 g (40% by weight) Carbon fiber 2.0 g (40% by weight) PT
FE (binder) L, Og (20%
) Conventional example Platinum/carbon black 3.0 g (80% by weight) Carbon fiber PTFE (binder) 0.75 g (20% by weight) Regarding these four types of reaction layers, the electrolyte transfer ability test method described below was conducted. Transmission capacity D (cn+/h
), the results shown in the table below were obtained.

As shown in Fig. 2, the reaction layer sample S was placed on the carbon plate 100 heated by the heater 101, and after heating the reaction layer sample S to 150°C, one end of the reaction layer sample S was placed on the carbon plate 100 heated by the heater 101. A fixed amount of 1.5 cc of phosphoric acid E is added dropwise as an electrolyte to the phosphoric acid E.
The distance (ca+/h) traveled per hour in the direction of arrow A within the surface of the reaction layer sample S was measured, and this was taken as the electrolyte transfer ability.

From the results shown in the table, it can be seen that the reaction layer according to the present invention itself has a large electrolyte transfer ability.

In addition, when the reaction layer of the conventional example and the reaction layer of Example 2 were assembled into a fuel cell and the cell resistance of each fuel cell was measured, the cell resistance of the former conventional fuel cell was 5 m
Ω, but the cell resistance value of the latter fuel cell of Example 2 had decreased to 3 mΩ. Due to this decrease in internal resistance, the cell voltage becomes 610 m at 150 a+A-cs-"
It improved from V to 640 V.

〔Effect of the invention〕

As described above, according to the fuel cell of the present invention, the electrolyte is applied to the reaction layer itself within the cell surface for a short time. FIG. 3 is an explanatory diagram of a test method for electrolyte transfer ability of a reaction layer.

l... Anode, 2... Cathode, 3... Matrix layer,
4... Base material, 5... Reaction layer.

Agent: Patent Attorney Nobuo Kogawa -

Claims (1)

[Claims] In a fuel cell having a structure in which an electrolyte holding matrix layer is sandwiched between an anode electrode base material and a cathode electrode base material with a reaction layer made of catalyst-supported conductive particles interposed therebetween, the reaction layer is electrolyzed. 50~50% of fibers or particles that are inert to the liquid
70% by weight of the mixture, and the porous structure formed in the reaction layer has a bore diameter of 10 to 10% compared to the porous structure of the matrix layer.
A fuel cell with a porosity of 1.2 to 1.4 times.