JPS59224067A - Fuel cell - Google Patents

Abstract

PURPOSE:To improve affinity between electrolyte and catalyst bearing layer by forming the catalyst bearing layer to be provided between a matrix and gas diffusion electrode such that conductive micro particles and phosphoric acid particles are mixed and binded with hydrophobic polymer. CONSTITUTION:Catalyst bearing layers 2, 5 are arranged between a matrix 3 impregnated with phosphoric acid in unit cell for fuel cell and the gas diffusion electrodes or anode and cathode side electrodes 1, 4. Said catalyst bearing layers 2, 5 are formed by mixing 80-97.5vol% of conductive micro particles 8 such as carbon black and 2.5-20vol% of phosphoric acid particles 9 such as silicon carbide then adding 20-45wt% of hydrophobic polymer for 50-80wt% of said compound and binding. Consequently the affinity between the catalyst bearing layers 2, 5 and electrolyte is increased considerably to reduce the inner resistance of cell resulting in improvement of cell performance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a fuel cell, and particularly to a fuel cell C2 in which the composition of a catalyst support layer is improved.

[Technical background of the invention and its problems]

A fuel cell single cell is formed by providing a catalyst support layer between a conductive base material such as porous carbon paper or porous carbon sintered plate that forms a gas diffusion electrode and a matrix that forms an electrolyte layer. has been done.

The catalyst supporting layer is usually formed of conductive fine particles and a hydrophobic polymer.

The configuration of a single cell of a conventional fuel cell will be explained with reference to FIG. 1 is a fuel electrode base material, that is, an anode side electrode;
2 is a catalyst support layer, 3 is a matrix, 4 is an air electrode base material, that is, a cathode side electrode, and 5 is a catalyst support layer. FIG. 1(b) is a modification of FIG. 1(a), in which a fuel supply groove 6 and an air supply groove 7 are provided on the back surfaces of the anode side electrode (1) and the cathode side electrode 4, respectively, and are perpendicular to each other. .

However, as a result of the inventors' study of the configurations of these conventional single cells, the following problems became clear.

(1) Although it is the same carbon material as the catalyst support layer, it is required to use a material with improved corrosion resistance, such as carbon black or graphite fine particles, but the material with improved corrosion resistance itself has water repellency. For,
The water repellency of the catalyst supporting layer increases abnormally and repels the electrolyte, resulting in insufficient contact between the catalyst and the electrolyte, resulting in a small reaction area, which is the contact interface between the electrolyte, the catalyst, and the reaction gas, and thus increasing the internal resistance of the battery. , battery performance deteriorates significantly.

(2) Changes in the operating temperature, operating pressure, load, humidity in the reaction gas, etc. of the fuel cell are inevitably accompanied by changes in the volume of the electrolyte.

That is, phosphoric acid, which is an electrolyte, is a reaction product of water and phosphorus pentoxide as shown in the following reaction formula, and is also a highly hygroscopic desiccant. Therefore, 3H,O+1/2P at high temperature
2O,. ';j 2H,PO4 Under dry conditions, the reaction proceeds to the left; under low temperature and humid conditions, the reaction proceeds to the right. Although omitted here for the sake of explanation, many complex condensates of phosphoric acid are produced as the intermediate products. However, the progress of these reactions has the same tendency as explained above.

On the other hand, when a load is applied, water is produced as an electrochemical reaction product. Furthermore, since humidity is determined by the ratio of water vapor partial pressure to total pressure, the equilibrium of the reaction will vary depending on the operating pressure.

Due to such fluctuations, the volume of the electrolyte changes from time to time.

By the way, if the water repellency of the catalyst support layer is too large, the electrolyte overflowing from the matrix, which is the electrolyte layer, will interfere with the water repellency of the catalyst and be pushed out through the catalyst support layer and reach the electrode. However, when the amount of electrolyte in the matrix decreases, the overflowing electrolyte a supplies electrolyte to the matrix again, and as a result, a constant amount of electrolyte is always retained in the matrix, a so-called "reservoir function". Therefore, once the electrolyte overflows, it remains isolated in the electrode base material due to the strong water repellency of the catalyst support layer.

As a result, the electrolyte in the matrix gradually decreases, the void area increases accordingly, the separator function to prevent the reaction gas of the fuel cell, that is, the fuel gas, and air from mixing is lost, and the mixing of the re-reactant gas is eliminated. A so-called crossover phenomenon occurs, which significantly reduces battery performance and may even cause an explosion.

(3) In order to improve battery performance, the catalyst carrier is required to be fine particles of several tens of microns or less, and the finer the particles, the more the phenomena (1) and (2) above are promoted.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a fuel cell in which the composition of the catalyst support layer is improved and the reservoir function of the electrode for the electrolyte is effectively utilized to improve the cell performance.

[Summary of the invention]

In order to achieve such an object, the present invention provides a fuel cell comprising a plurality of stacked single cells each having a pair of gas diffusion electrodes arranged opposite to each other with a matrix forming an electrolyte layer interposed therebetween. The catalyst supporting layer disposed between the diffusion electrodes is characterized in that it is formed by binding a mixture of conductive fine particles and phosphoric acidic particles with a hydrophobic polymer.

[Embodiments of the invention]

Hereinafter, embodiments of the present invention will be described with reference to FIG.

The present invention improves the composition of the catalyst support layer 2, and includes conductive fine particles 8 (e.g. carbon black) and phosphoric acid particles 9.
(for example, silicon carbide) bound by a hydrophobic polymer 10.

[Example 1] The amount of platinum supported was 14% by weight and the average particle size was 0.0
Conductive fine particles of 3 μm, acetylene black particles, and silicon carbide particles having an average particle diameter of 5 μm, which are phosphoric acid particles, were mixed at different volume ratios, centering on a volume ratio of 1 silicon carbide particle to 10 acetylene black particles.

Next, a mixture of these volume ratios was mixed with water as a solvent and kneaded, and then a dispersion of polytetrafluoroethylene was added in an amount of 40% by weight as a solid content and kneaded with a mixer. The porous carbon paper forming the 41111 electrode was applied by suction spraying. After drying at 80°C for 2 hours, it was fired at 320°C for 1 hour. The amount of catalyst is approximately 25 μ/d. The thickness of the catalyst supporting layer on the carbon paper was about 8011 m. A single cell was formed using these electrodes as shown in FIG. 1(a), and the internal resistance of the battery and the load voltage of 220 mA/CrI were measured, and the results are shown in FIG. As shown in the figure, when the ratio of [silicon carbide particle volume]/[carbon particle volume] is smaller than 2.5% or larger than 20%, the internal resistance of the battery increases rapidly and the battery performance deteriorates significantly. I understand that. Therefore, the above volume ratio is 25-20%
It is preferably within the range of 33% to 10%. The weight ratio to the volume ratio (2.5-20Q'o) was approximately (30-240%).

In addition, in order to confirm the reservoir function, a cycle test of battery operation = - stop was repeated for the battery prepared under the conditions of point A in Figure 3, and as a result, the battery without silicon carbide particles was In contrast, in the battery according to the present invention, no crossover phenomenon was observed even after 100 cycle tests, and the battery performance was stable. That is,
This shows that the porous carbon paper has a sufficient effect of absorbing changes in the volume I of phosphoric acid, which is an electrolyte.

The reason for this is thought to be as follows. The catalyst supporting layer is in good contact with the electrolyte and has enough water repellency to prevent the catalyst from being immersed in the electrolyte, and has a passage through which the electrolyte can freely pass, and the electrode base material has a reservoir for the electrolyte. This is because the functions can be fully demonstrated. In addition, when the phosphoric acidic particles account for 2.5% or more by volume of the conductive fine particles, the phosphoric acidic part of the catalyst supporting layer communicates in the thickness direction of the catalyst supporting layer, and the electrolyte supports the highly water-repellent catalyst. can pass freely through the layers. By the way, if the hydrophobic polymer is less than 20% at 1 fflit percent, the contact force between the conductive particles becomes small, and the water repellency of the catalyst supporting layer decreases, causing the catalyst to become wet with the electrolyte. On the other hand, when the value exceeds 45%, the conductivity of the catalyst supporting layer decreases, the internal resistance of the battery increases, and the performance of the battery decreases.

Phosphorophilic acid particles are required to be stable at high temperatures and in phosphoric acid and air, and ZrO2゜Ta20B
, SiC, (zno), p, o□, etc., which can be used as a matrix material are desirable. These are electronically non-conducting materials. Furthermore, if the phosphoric acidic particles have a capacity ratio of 20% or more to the conductive fine particles, the conductivity of the catalyst layer will decrease, which is not preferable.

[Example 2] The average particle size with a supported amount of platinum of 10% by weight is 0.3
Microcarbon black particles (2. Silicon carbide particles with an average particle size of 5 microns, which are phosphoric acidophilic) were mixed.The volume ratios were 92.3% and 7.7%, respectively.Next, water was added as a solvent and kneaded. Then, 40% by weight of a dispersion solution of polytetrafluoroethylene was added as a solid content and kneaded.The mixture was applied by suction spraying onto a porous carbon paper with a porosity of 75% and a thickness of Q, 4 my.
After drying for an hour, it was fired at 320°C for 2 hours. The catalyst layer is about 5 zaq/cl.

The catalyst supporting layer is the surface of the carbon paper (: about 0.05~
A layer was formed with a thickness of 0.1 mm. A single cell was constructed, and a battery was created in the same manner as in Example 1, and the operation/stop cycle test was repeated 100 times. As a result, no crossover phenomenon was observed as in Example 1, and stable battery performance was verified.

Similar results were obtained when dill unilum oxide powder was used instead of silicon carbide particles.

〔Effect of the invention〕

As explained in detail above, according to the present invention, whereas the conventional catalyst supporting layer did not have good affinity with the electrolyte,
The catalyst support layer according to the present invention has good affinity with the electrolyte, the interfacial three-phase zone of electrolyte-catalyst-reactant gas increases throughout the catalyst support layer, and the internal resistance of the battery decreases.
As battery performance improves, it becomes possible to attract excess electrolyte to the electrodes as the electrolyte volume increases or decreases depending on operating conditions, and to supply it from the electrodes when the amount of electrolyte in the matrix decreases, increasing the amount of electrolyte in the matrix. can be maintained constant.

[Brief explanation of the drawing]

Figures 1 (a) and (b) are cross-sectional diagrams of a single cell;
Figure≠Rin is an embodiment of the present invention! - A sectional view of a main part of the catalyst support layer, and FIGS. 3(a) and 3(b) are diagrams showing the relationship between the volume ratio of the material forming the catalyst support layer and the battery characteristics. 1... Anode side electrode 4... Cathode side electrode 2
．． 5...Catalyst support layer 6...Fuel supply groove 3...
・Matrix 7...Air supply groove 8...Conductive fine particles 9...Phosphorophilic particles 10...Hydrophobic polymer Representative Patent attorney Noriyuki Chika (1 idiot) Figure 1 (Hisashi) <-b) Figure 2 Figure 3 (0-)

Claims (1)

[Claims] A catalyst support layer provided between the matrix and the gas diffusion electrode in a fuel cell formed by laminating a plurality of unit cells each having a pair of gas diffusion electrodes facing each other with a matrix impregnated with phosphoric acid interposed therebetween. , conductive fine particles 80-97.5Vo1% and parent phosphoric acid particles 2.5-20%
A mixture of 100Vo1% is formed with 1% Vo1%, and 2% of the hydrophobic polymer is added to 50 to 80wt% of this mixture.
A fuel cell characterized in that it is formed by adding and binding 0 to 45 wt%.