JPH10340728A - Fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell in which resin particles and catalyst particles are uniformly dispersed, wetting of an electrolyte is uniformly maintained, superior power-generating characteristics are developed, and production cost is reduced by forming an electrode catalyst layer with a mixture of non- fibrillated fluororesin particles which do not elongate in a fibrous state, even if shearing force is applied and catalyst particles. SOLUTION: By using a mixture of catalyst particles and non-fibrillated fluororesin particles, since obstruction of reach of an electrolyte to the catalyst particles and uneven distribution of the fluororesin particles are avoided, power- generating characteristics of a fuel cell are enhanced, and long time operation is made possible. Since the mixture is obtained by dispersing and mixing in water, impurity removing work which is necessary when a surfactant is used is lightened. In addition, by previously wetting the resin particles with alcohol, highly uniform dispersion can be obtained, use of the surfactant is made unnecessary, and production cost is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell for obtaining electric energy by an electrochemical reaction by using, for example, phosphoric acid as an electrolyte and introducing a fuel gas and an oxidizing gas, and more particularly to a structure of an electrode layer thereof.

[0002]

2. Description of the Related Art FIG. 6 is a partial sectional view schematically showing the basic structure of a unit cell of a conventional fuel cell of this type. A single cell is constituted by sandwiching an electrolyte layer 1 holding an electrolyte, for example, phosphoric acid, between two electrode layers 4 in which an electrode catalyst layer 2 is bonded to a porous carbon substrate 3. Among them, the electrolyte layer 1 is configured by impregnating and holding phosphoric acid in a matrix formed using silicon carbide fine particles. Further, the electrode catalyst layer 2 is formed by binding catalyst particles having noble metal fine particles supported on the surface of a catalyst carrier with fluororesin particles.

In this configuration, when a fuel gas and an oxidizing gas flow through the outer surfaces of the two electrode layers 4, these reaction gases diffuse inside the porous carbon substrate 3 and are guided to the electrode catalyst layer 2. Then, it comes into contact with phosphoric acid (liquid phase) from the electrolyte layer 1 and a three-phase interface between the catalyst particles (solid phase) and the reaction gas (gas phase) is formed, so that the electrochemical reaction proceeds. In order for this electrochemical reaction to proceed efficiently, the catalyst particles and fluororesin particles should be as fine as possible, and the catalyst particles and fluororesin particles that are easily wettable by the phosphoric acid in the electrolyte should be dispersed as uniformly as possible. It is necessary to increase the interface. Therefore, in a conventional fuel cell, in order to effectively disperse the catalyst particles, the catalyst particles are dispersed in water containing a surfactant using an ultrasonic homogenizer, and the surfactant is added to the dispersion. The catalyst particles and the fluororesin particles are mixed by adding a dispersion in which the fluororesin particles are dispersed in water, and the mixture is roll-formed to form the electrode catalyst layer 2. Note that, in order to facilitate film-like molding by a roll, fibrillated fluororesin particles that fibrillate when a shearing force is applied are used as the fluororesin particles.

[0004]

As described above, in this type of conventional fuel cell, the catalyst particles and the fluororesin particles are dispersed uniformly in water containing a surfactant, and the fibril is dispersed. The film is formed by using fluorocarbon resin particles. However, when the fibrillated fluororesin particles are used as described above, in the electrode manufacturing process, the fluororesin is often excessively fibrillated by a shearing force, and the fluororesin often grows in a network. When such a situation occurs, a layer of a fluororesin that is hardly wetted by the electrolytic solution is formed in the electrode catalyst layer,
It becomes difficult for the electrolyte solution to reach the catalyst particles, and the three-phase interface where an electrochemical reaction occurs is drastically reduced, resulting in a significant decrease in power generation performance. Further, when the fluororesin is fibrillated in the production process, aggregation of the fluororesin particles occurs, and the uniformity of dispersion and mixing of the catalyst particles and the fluororesin particles is reduced. Along with this, a portion that is easily wetted by the electrolyte and a portion that is hardly wetted are unevenly distributed, and the amount of the electrolyte is insufficient in the portion that is hardly wetted, and the arrival of the reaction gas is easily hindered in the easily wetted portion, Electrochemical reaction is less likely to occur, which causes a reduction in power generation characteristics. further,
If the operation is continued for a long time, corrosion and erosion due to the electrolytic solution progress in a portion which is easily wetted by the electrolytic solution, and the catalyst performance is deteriorated and the power generation characteristics are reduced.

Further, as described above, when a surfactant is used in preparing a mixture of catalyst particles and fluororesin particles, if a surfactant is used to remove the surfactant which is a factor inhibiting the electrochemical reaction of the fuel cell, the electrode is removed. It is necessary to provide a process such as heat treatment in the manufacturing process, and there is a problem that the number of steps of the manufacturing process increases and the manufacturing cost increases. In addition, it is difficult to completely remove the surfactant even if a step such as heat treatment is provided to remove the surfactant, and a trace amount of the surfactant or impurities generated by the decomposition of the surfactant may be present in the electrode. When the surfactant is decomposed in the treatment step, the surface of the carrier of the catalyst particles is reduced or reacted with the surface of the carrier when the surfactant is decomposed, and the surface of the carrier has a hydrophilic functional group such as a carbonyl group or a hydroxyl group. Is very likely to occur. When such a state occurs, the entire electrode is more likely to be wet with the electrolytic solution, and the electrolytic solution hinders the reaction gas from reaching the three-phase interface, thereby lowering the power generation characteristics of the battery. Corrosion and erosion of the catalyst particles occur, and the life characteristics deteriorate.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned disadvantages of the prior art, to provide excellent power generation by uniformly dispersing catalyst particles and fluororesin particles of an electrode catalyst layer and maintaining uniform wetting by an electrolytic solution. It is another object of the present invention to provide a fuel cell which exhibits characteristics and can be manufactured at low cost with a small number of manufacturing steps.

[0007]

In order to achieve the above object, the present invention provides a single cell comprising an electrolyte layer sandwiched between two electrode layers each having an electrode catalyst layer formed on a porous carbon substrate. And a plurality of unit cells are stacked to form a fuel cell stack, and a fuel gas and an oxidizing gas are supplied to obtain electric energy. (1) The electrode catalyst layer is sheared It is formed using a mixture of non-fibrillated fluororesin particles and catalyst particles which do not expand into a fibrous form even when a force is applied.

(2) Further, the mixture of the non-fibrillated fluororesin particles and the catalyst particles is, for example, a mixture obtained by dispersing and mixing the non-fibrillated fluororesin particles and the catalyst particles in water. (3) Further, the non-fibrillated fluororesin particles are wetted with an alcohol or a mixture of alcohol and water, and then dispersed and mixed with the catalyst particles in water to obtain a mixture obtained.

In the case of the above (1), it is possible to prevent the electrolyte solution from reaching the catalyst particles and the distribution of the fluororesin particles to be uneven, which has conventionally been caused by fibrillation of the fluororesin particles. Since it is avoided, the power generation characteristics of the fuel cell are improved, and stable operation can be performed for a long time. Also,
As described in (2) above, if a mixture of non-fibrillated fluororesin particles and catalyst particles is obtained by dispersing and mixing in water, the work of removing impurities required when using a surfactant is reduced. .

Further, in the case of the above (3), the water-repellent fluororesin particles are wetted in advance with an alcohol having a small contact angle or a mixed solution of alcohol and water, whereby the particles are more highly uniformly dispersed. In addition, if this method is used, no surfactant is used in all the working steps, so that the impurity removal step by using a surfactant, which has been conventionally performed, becomes unnecessary, and the manufacturing cost of the fuel cell is reduced. It is effective in reducing the amount

[0011]

FIG. 1 is a partial cross-sectional view schematically showing a basic structure of a single cell according to an embodiment of the present invention, wherein 1 is an electrolyte layer in which phosphoric acid of an electrolytic solution is held in a matrix, and 2A is an electrode. The catalyst layer 3, 3 is a substrate made of a porous carbon material, and 4A is an electrode. The difference between this configuration and the configuration of the conventional example shown in FIG. 6 lies in the configuration of the electrode catalyst layer. The feature of this configuration is that the electrode catalyst layer 2A is formed using a mixture of non-fibrillated fluororesin particles and catalyst particles. It is in the point of forming. That is, the electrode catalyst layer 2A of the present configuration includes: (1) 50 g of a catalyst composed of catalyst particles having noble metal fine particles supported on the surface of a catalyst carrier is added to 500 g of pure water, and dispersed using an ultrasonic homogenizer; Is prepared.

(2) Separately, 40 g of non-fibrillated fluororesin (trade name: Lubron L5 manufactured by Daikin Co., Ltd.) is added to a mixed solution of 25 g of isopropyl alcohol and 75 g of pure water, and dispersed using an ultrasonic homogenizer. A solution of resin particles is prepared. (3) Next, the two obtained solutions are mixed, and an ultrasonic homogenizer is applied to obtain a uniform and fine mixed solution of catalyst particles and fluororesin particles.

(4) This mixed solution is subjected to centrifugal separation using a centrifugal separator to produce a paste material containing catalyst particles and fluororesin particles in high concentrations. (5) This paste material is applied to a substrate made of a porous carbon material. It is formed by the following procedure. A single cell is formed using the electrode 4A provided with the electrode catalyst layer 2A formed in this manner. At 190 ° C. and normal pressure, air is supplied as an oxidizing gas to one electrode, and fuel is supplied to the other electrode. The results of a fuel cell power generation experiment conducted by supplying a mixed gas of hydrogen and carbon dioxide as the gas are as follows.

FIG. 2 is a characteristic diagram showing an output voltage characteristic of the fuel cell according to the present embodiment in comparison with a conventional example. As can be seen from the figure, under the same power generation condition, that is, the same output current, the output voltage is improved by 2 to 3 mV as compared with the conventional example. FIG. 3 is a characteristic diagram showing the measurement results of the amount of phosphoric acid in the electrolyte remaining in the electrode after the operation for a certain period of time, in comparison with the case of a conventional fuel cell. The horizontal axis shows the operation time expressed on a logarithmic scale. The vertical axis represents the relative value of the measured amount of residual phosphoric acid. Although the amount of phosphoric acid in the electrode tends to decrease with the progress of the operation time, the amount of phosphoric acid varies greatly depending on the measurement sample in the case of the conventional fuel cell. In the case of (1), the variation due to the sample is small. By using non-fibrillated fluororesin for the fluororesin particles mixed with the catalyst particles, the uneven distribution of the fluororesin particles was reduced, indicating that the uneven distribution of the portions easily wettable by phosphoric acid and the portions hardly wetted was reduced. .

FIG. 4 shows a change with time of the generated voltage, that is,
FIG. 9 is a characteristic diagram showing life characteristics in comparison with the case of a conventional fuel cell. Comparing the degradation rate of the output voltage of the present embodiment with the degradation rate of the output voltage of the conventional example, it can be seen that the degradation rate of the present embodiment is about 9% lower than that of the conventional example, and the characteristics are improved. Instead of the electrode catalyst layer 2A used in the fuel cell of the present embodiment, the same procedure for preparing the solution of the fluororesin particles in (2) of the above-described procedure for preparing the electrode catalyst layer 2A was carried out. Also in the case where a method of preparing a solution of fluororesin particles by adding 40 g of fluororesin to 75 g of isopropyl alcohol and dispersing using an ultrasonic homogenizer is used, the characteristics of the fuel cell including the formed electrode catalyst layer are as described above. 2 to 4 of FIG.

FIG. 5 is a characteristic diagram showing the particle size distribution of a mixture of catalyst particles and fluororesin particles obtained according to the present invention in comparison with a conventional example. In the figure, characteristic A shows the particle size distribution of a mixture obtained by a method of preparing a mixture of catalyst particles and fluororesin particles by using a non-fibrillated fluororesin added to isopropyl alcohol to wet the mixture, and using this dispersion, and characteristic B. The non-fibrillated fluororesin is added to a mixed solution of isopropyl alcohol and pure water and wetted, and the particle size distribution of the mixture obtained by the method of preparing a mixture of the catalyst particles and the fluororesin particles using this dispersion, Characteristic C is the particle size distribution of the mixture prepared by the conventional method, in which the horizontal axis represents the particle size expressed on a logarithmic scale, and the vertical axis represents the relative frequency. As shown in the figure, when the fluororesin particles were wetted in advance with isopropyl alcohol or a mixed solution of isopropyl alcohol and pure water, the average particle size was small and the distribution was sharp, and the catalyst particles and It can be seen that the mixture of fluororesin particles has a finer and more uniform particle size distribution. Therefore, if the electrode catalyst layer is formed by using such a mixture, the catalyst particles and the fluororesin particles are uniformly dispersed, and the wetting by the phosphoric acid occurs uniformly, so that stable characteristics are maintained for a long time. It will be.

In the above embodiment, a paste material is prepared by centrifuging the mixed liquid of the obtained catalyst particles and fluororesin particles, and the paste material is applied on the substrate. After that, or after filtration by suction filtration and drying, to produce an electrode material powder in which catalyst particles and fluororesin particles are uniformly mixed, and to form an electrode by a method of spraying this electrode material powder on a substrate, the same applies. Was obtained.

Further, in the above embodiment, Lubron L5 manufactured by Daikin Co., Ltd. is used as the non-fibrillated fluororesin used for the fluororesin particles, but it is also manufactured by using Lubron L2 manufactured by Daikin Co., Ltd. At
Equivalent characteristics were obtained.

[0019]

As described above, according to the present invention, a single cell is constructed by sandwiching an electrolyte layer holding an electrolyte between two electrode layers each having an electrode catalyst layer formed on a porous carbon substrate. Then, a plurality of unit cells are stacked to form a fuel cell stack, and a fuel gas and an oxidizing gas are supplied to obtain electric energy. (1) The above electrode catalyst layer is made non-fibrillated. Since it was decided to use a mixture of the fluororesin particles and the catalyst particles, the catalyst particles and the fluororesin particles of the electrode catalyst layer were uniformly dispersed, and the wetting by the electrolyte was maintained in an appropriate amount and uniformly. Thus, a fuel cell having excellent power generation characteristics and stable operation for a long time can be obtained.

(2) Further, if the mixture of the non-fibrillated fluororesin particles and the catalyst particles is, for example, a mixture obtained by dispersing and mixing the non-fibrillated fluororesin particles and the catalyst particles in water, Since the operation of removing impurities necessary when using a surfactant is reduced, a fuel cell having excellent power generation characteristics and being manufactured inexpensively with a small number of manufacturing steps can be obtained.

(3) Further, if the non-fibrillated fluororesin particles are wetted with an alcohol or a mixture of alcohol and water and then dispersed and mixed with the catalyst particles in water to obtain a mixture obtained, the uniformity is further improved. It has an excellent electrode catalyst layer, and the operation of removing impurities when using a surfactant is completely unnecessary.
It is suitable as a fuel cell that can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view schematically showing a basic configuration of a single cell according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing output voltage characteristics of a fuel cell according to an embodiment of the present invention in comparison with a conventional example.

FIG. 3 is a characteristic diagram showing the amount of phosphoric acid inside an electrode measured after a fuel cell according to an embodiment of the present invention has been operated for a certain period of time in comparison with a conventional example.

FIG. 4 is a characteristic diagram showing a change over time of a generated voltage of a fuel cell according to an embodiment of the present invention, as compared with a conventional example.

FIG. 5 is a characteristic diagram showing a particle size distribution of a mixture of catalyst particles and fluororesin particles obtained according to an example of the present invention in comparison with a conventional example.

FIG. 6 is a partial cross-sectional view schematically showing a basic configuration of a single cell of a conventional phosphoric acid fuel cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrolyte layer 2 Electrode catalyst layer 2A Electrode catalyst layer 3 Base material 4 Electrode 4A electrode

Claims (3)

[Claims] An electrolyte layer is sandwiched between two electrode layers each having an electrode catalyst layer formed on a porous carbon substrate to form a single cell, and a plurality of single cells are stacked to form a fuel cell stack. In a fuel cell configured to obtain electric energy by supplying a fuel gas and an oxidizing gas, the electrode catalyst layer includes non-fibrillated fluororesin particles that do not expand in a fibrous form even when a shear force is applied. A fuel cell formed using a mixture with catalyst particles. 2. The method according to claim 1, wherein the mixture of the non-fibrillated fluororesin particles and the catalyst particles is a mixture obtained by dispersing and mixing the non-fibrillated fluororesin particles and the catalyst particles in water. 2. The fuel cell according to 1. 3. A mixture of the non-fibrillated fluororesin particles and the catalyst particles is obtained by wetting the non-fibrillated fluororesin particles with an alcohol or a mixture of alcohol and water, and then mixing the catalyst particles in water. The fuel cell according to claim 1, wherein the fuel cell is a mixture obtained by dispersion mixing.