JPH06196187A - Activation of solid high polymer type fuel cell - Google Patents

Abstract

(57) [Summary] [Purpose] A method of shortening the activation treatment time of a fuel cell and a method of equalizing the discharge characteristics of each cell by applying a rapid hydrous treatment method to the whole laminated cell or each cell The purpose is to provide. [Structure] In a fuel cell in which an ion exchange membrane made of a solid polymer and a unit cell made of a positive electrode and a negative electrode having electrode catalyst layers on both sides in contact with the ion exchange membrane are laminated via a separator plate, the cells are humidified. It is an activation method in which electrolysis is performed in a state where gas is introduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell using pure hydrogen or methanol as a fuel, a reducing agent such as reformed hydrogen from a fossil fuel, and air or oxygen as an oxidant, and more particularly to a solid-state fuel cell. The present invention relates to a method for activating a molecular fuel cell.

[0002]

2. Description of the Related Art For example, in a polymer electrolyte fuel cell, when a cation exchange membrane which is a proton conductor is used as a polymer electrolyte and hydrogen is introduced as a fuel and oxygen is introduced as an oxidant, the following reaction occurs. Known to happen.

(Chemical formula 1) Negative electrode H ₂ → 2H ⁺ + 2e ⁻ (Chemical formula ₂ ) Positive electrode 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂
At the O 2 negative electrode, hydrogen dissociates into protons and electrons. Protons move in the cation exchange membrane toward the positive electrode, and electrons move in the cell laminated in series with the conductive separator plate and an external circuit to reach the positive electrode. At this time, power is generated. On the other hand, in the positive electrode, the protons that have moved in the cation exchange membrane, the electrons that have moved in the external circuit, and oxygen introduced from the outside react to generate water. Since this reaction is accompanied by heat generation, it is generally expressed by the following equation, and hydrogen, oxygen generate electricity, water, and heat.

(Chemical Formula 3) H ₂ + 1 / 2O ₂ → H ₂ O The solid polymer fuel cell is greatly different from other fuel cells in that the electrolyte is composed of an ion exchange membrane which is a solid polymer. Is. Perfluorocarbon sulfonic acid membrane (Dupont, USA, trade name Nafion) is used for this ion exchange membrane, but it is necessary for the membrane to have sufficient water content in order to show sufficient proton conductivity. There is. As a method of containing water in the ion exchange membrane, for example, J. Electrochem. Soc. 135 (198
8) As described in 2209, a method is adopted in which water vapor is introduced into the cell by passing the reaction gas through a humidifier and the ion exchange membrane is hydrated. The water content of the ion exchange membrane depends on the dew point temperature of the humidified gas. Electr
ochem. Soc. Moisture content increases with increasing temperature as described in 139 (1992) 2530. It takes a long time for the membrane to reach saturated water content,
Since the water once absorbed in the membrane is taken up by the polymer and retained, the dependence of the water content on the temperature change below the treatment temperature becomes small. Therefore, the Journal of P
power Sources. As described in 37 (1992) 181, it becomes possible to operate the fuel cell quickly from room temperature. As a method of joining the membrane and the electrode, for example, J. Electroanal. Chem. Two
51 (1988) 272.
A method of pressing at a temperature of 0 to 130 ° C. and a pressure of about 50 atm is used, but the water content of the membrane is significantly reduced in this step. Thus, after assembling each cell, a humidified gas is introduced into the cell to cause the membrane to hydrate and become activated.

[0005]

However, in the above-mentioned conventional method, in order for the water content of the ion exchange membrane of each cell immediately after assembly to reach a sufficient value, it is necessary to perform a humidification treatment for 24 to 72 hours or more. It has a drawback that it takes a long time for the battery to exhibit its original characteristics. Further, when the water content of the ion exchange membrane of each cell varied, the discharge characteristics of each cell also varied. Furthermore, in the fuel cell stack after the hydrous treatment, when the defective cell is replaced with a new cell or a new cell is added, the ion exchange membrane of the new cell has a remarkably low water content. The characteristics of the cells varied. Therefore, in order to make the characteristics uniform, it was necessary to re-hydrate the entire laminated battery.

The present invention solves the above-mentioned conventional problems. A method of shortening the activation treatment time of a fuel cell and a discharge of each cell by applying a rapid hydrous treatment method to the whole laminated cell or each cell. It is an object to provide a method for uniformizing characteristics.

[0007]

In order to achieve this object, according to the present invention, a positive electrode and a negative electrode having an ion exchange membrane made of a solid polymer and an electrode catalyst layer in contact with both sides of the ion exchange membrane. In the fuel cell in which the unit cells made of (1) are stacked via the separator plate, the activation method is performed by performing the electrolytic treatment in the state where the humidified gas is introduced.

[0008]

In this structure, by applying an electrolytic voltage to each cell, the water in the H ₂ O → H ₂ + 1 / 2O ₂ film is forcibly decomposed into hydrogen and oxygen by the following formula. To be done. Along with this, the concentration gradient of water molecules in the membrane is significantly increased as compared with that before electrolysis. Therefore, the diffusion rate of water in the membrane is increased, and as a result, the water in the humidified gas is transferred into the membrane and the water content can be rapidly increased. However, long-term electrolytic treatment causes depletion of water in the membrane. On the other hand, if the electrolysis voltage is too high, the catalyst used in the electrode and the carbon carrier are dissolved. Therefore, there are optimum electrolysis conditions.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 is an external view of a laminated cell of a general polymer electrolyte fuel cell. Separator plates 2 made of a conductive material such as glassy carbon and insulating gaskets 1 are alternately stacked, and a copper current collector plate 3 is adhered to the outermost separator plate. Insulation plate 4
The end plates 5 made of stainless steel are sandwiched between the end plates, and the end plates are fastened with bolts and nuts. Of course, the material of each part is conductive, insulating,
The materials are not limited to the above materials as long as conditions such as heat resistance and gas permeability do not adversely affect the battery performance.

FIG. 5 is a view showing a cross-sectional view of a general laminated battery internal cell. Electrodes 12 are bonded to both surfaces of the central ion exchange membrane 11, and grooved separator plates 2 are located above and below the bonded body. The area of the ion exchange membrane is larger than that of the electrode, and the periphery is sandwiched by gaskets to insulate the seal between each cell and the separator plate. As shown in the figure, the gas passage 1 may be provided inside the laminated body if necessary.
When 3 is installed (internal manifold type), the gasket also seals this gas passage. The grooved separator plate may have various structures such as a case where a porous grooved plate is fitted in the groove portion or a mesh is used, and this structure does not limit the present invention.

Example 1 FIG. 1 shows a total discharge time and a current density of 0.1 A of a polymer electrolyte fuel cell in which 10 cells are stacked.
The terminal voltage in / cm ² is shown. The cell has a dew point of 80 ℃
A humidified gas consisting of hydrogen and oxygen was introduced. The discharge curve of this example is curve A, and an electrolytic voltage of 18 V was applied to the entire 10 cell stack for 30 seconds 1 hour after the start of discharge with the humidified gas introduced into the cell. By this treatment, the electrolysis voltage of each unit cell is 1.7 to 1.9V.
showed that. Immediately after the treatment, the terminal voltage is 5.
It showed 6V and gradually increased. Two hours after the start of discharge, when the same electrolytic treatment was performed again, the terminal voltage was further increased to 7.
It increased to 2V and became almost stable thereafter. On the other hand, as a comparative example, the discharge curve of the battery not subjected to the electrolytic treatment was set to curve B. In the comparative example, 0.1 A /
The current density of cm ² could not be extracted. Therefore, discharge was performed at a current density of 0.1 A / cm ² or less.
The terminal voltage begins to increase gradually after about 10 hours, and 6
After a lapse of 0 hours, a constant voltage of 7.1V was shown.

As described above, conventionally, it took 60 hours or more for the discharge characteristics of the polymer electrolyte fuel cell to reach a stable value, but according to the activation method of the present invention, it takes about 2 hours. It is now possible to bring out the original characteristics of the battery. In the present embodiment, the activation treatment was performed twice every hour, but the present invention is not limited to this execution condition, and the electrolytic voltage, time, and It is possible to select the optimum conditions such as the number of times of addition. However, also in this example, when electrolytic treatment was performed for 2 minutes or more at an electrolytic voltage of 20 V or more, the characteristics of the battery were significantly deteriorated.

As a result of investigating the cause, the deterioration of the battery was not observed under the electrolytic treatment conditions in which the carbon carrier of the electrode and the platinum catalyst were dissolved and the electrodes were not dissolved.

That is, care must be taken because the electrolytic treatment in which the electrode catalyst is dissolved may deteriorate the characteristics of the battery.

On the contrary, when the electrolysis treatment is carried out for a long time at about 1.3 V or less which is the theoretical electrolysis voltage of the fuel cell (about 1.23 V in the atmosphere of 25 ° C.) plus the overvoltage due to resistance, concentration and the like. However, the reaction of the chemical formula 4 is not generated and the diffusion of water in the film is not generated, so that there is almost no effect.

On the other hand, when hydrogen gas and oxygen gas are introduced into the cell, and as the degree of humidification increases, activation by diffusion of water becomes more active, and the discharge characteristics become stable in a short time. Therefore, it is desirable that the humidification condition be such that the entire surface of the film is condensed.

It is more preferable to increase the concentration gradient of water between the membrane and the electrode, such as introduction of humidified gas having a higher dew point temperature and lowering of the cell temperature.

(Embodiment 2) FIGS. 2 and 3 show the discharge characteristics of each cell before and after the activation treatment of Embodiment 2 of the present invention. FIG. 2 shows the discharge characteristics of each unit cell of a battery in which 5 cells are stacked. The characteristics of two of the five cells were significantly lower than the others, and the voltage of each unit cell at a current density of 0.15 A / cm ² showed a large variation of 0.63 to 0.18 V. FIG. 3 shows the discharge characteristics of each unit cell after applying an electrolytic voltage of 9 V for 1 minute while introducing a humidified gas of hydrogen and oxygen having a dew point temperature of 85 ° C. into this laminated battery. As a result of the activation treatment of the present invention, the characteristics of cells exhibiting low characteristics are improved, and the variation range of each unit cell voltage at a current density of 0.15 A / cm ² is 0.64 to 0.59.
Improved to V.

As described above, by carrying out the activation treatment of this embodiment, the dispersion of the discharge characteristics of each unit cell of the laminated battery was reduced and the discharge was stabilized at a particularly high level. It was found that the dispersion of the discharge characteristics of each unit cell of the laminated battery depends largely on the dispersion of the water content of the ion exchange membrane of each unit cell. Therefore, the effect of the activation treatment of the present invention is
As described in Example 1, it is considered that this was caused by the increase in the water content of the membrane of each unit cell, which had low characteristics due to the electrolytic treatment, to the water content of each of the other unit cells. In this example, the activation treatment was performed under the condition of electrolysis voltage of 9 V for 1 minute, but the present invention is not limited to this execution condition, and the electrolysis may be performed according to the conditions such as the electrodes of the fuel cell. Optimal conditions such as voltage, time, and number of times of addition are selected. Further, an electrolytic voltage was applied to the stacked batteries in order to improve the characteristics of each of the two unit cells, but it is also possible to perform activation treatment only on the unit cells having low characteristics or on a module unit consisting of several unit cells. It is more desirable to prevent the above-mentioned excessive electrolytic treatment of the unit cell. Furthermore, the activation treatment of the present invention, when a new unit cell is added to the laminated battery, or when it is replaced with an old unit cell, the moisture content of the added unit cell is adjusted to the conventional cell,
It is very effective in homogenizing the characteristics at a high level.

[0021]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, a unit cell composed of an ion exchange membrane made of a solid polymer and a positive electrode and a negative electrode having an electrode catalyst layer in contact with both sides of the ion exchange membrane is interposed via a separator plate. In a stacked fuel cell, unit cell or a cell formed by stacking a plurality of unit cells is electrolyzed in a state where a humidifying gas is introduced, whereby the original characteristics of the cell can be obtained in a short time.
Furthermore, it becomes possible to make the discharge characteristics of the unit cells of the laminated battery uniform at a high level efficiently in a short time.

Due to the above effects, it is possible to provide a highly reliable solid polymer electrolyte fuel cell in which the activation process and the repair process of the fuel cell can be speeded up and the unit cell characteristics have little variation.

[Brief description of drawings]

FIG. 1 is a discharge characteristic diagram in Example 1 of the present invention and a comparative example.

FIG. 2 is a discharge characteristic diagram of each unit cell before implementation of the present invention.

FIG. 3 is a discharge characteristic diagram of each unit cell after implementation of Example 2 of the present invention.

FIG. 4 is an external view of a general polymer electrolyte fuel cell.

FIG. 5 is a sectional view of a general cell.

[Explanation of symbols]

 1 Gasket 2 Separator Plate 3 Current Collector Plate 4 Insulating Plate 5 End Plate 6 Hydrogen Inlet 7 Hydrogen Outlet 8 Oxygen Inlet 9 Oxygen Outlet 11 Ion Exchange Membrane 12 Electrode 13 Gas Passage

Claims (3)

[Claims] 1. A fuel cell comprising an ion exchange membrane made of a solid polymer and a unit cell made of a positive electrode and a negative electrode having electrode catalyst layers on both surfaces in contact with the ion exchange membrane, or a separator plate, which are laminated together. A method for activating a polymer electrolyte fuel cell, in which electrolytic processing is performed in a state where a humidified gas is introduced into. 2. A fuel cell comprising an ion exchange membrane made of a solid polymer and a unit cell or separator plate made of a positive electrode and a negative electrode having electrode catalyst layers on both sides in contact with the ion exchange membrane, which are stacked together. Alternatively, a method for activating a polymer electrolyte fuel cell in which the characteristics of each cell are made uniform by performing electrolytic treatment in a state where a humidified gas is introduced into the added unit cell or a cell of a module including the unit cell. 3. The method for activating a polymer electrolyte fuel cell according to claim 1, wherein the electrolysis voltage applied in the electrolysis treatment is 1.3 V or more and the potential at which the electrode catalyst is dissolved or less.