JP2001135324A - High molecular electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent local stop of gas supply caused by a gas supply route clogged by water, which could deteriorate functions of a separator board, as a construction element of a solid high molecular fuel cell which has usually been a carbon plate with the surface area cut for forming a gas flow route. SOLUTION: A gas flow route of a separator is made movable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a portable power supply,
The present invention relates to a fuel cell using a solid polymer electrolyte used for an electric vehicle power supply, a home cogeneration system, and the like.

[0002]

2. Description of the Related Art A fuel cell using a solid polymer electrolyte is
Electric power and heat are simultaneously generated by electrochemically reacting a fuel gas containing hydrogen and a fuel gas containing oxygen such as air. First, its structure
On both surfaces of a polymer electrolyte membrane that selectively transports hydrogen ions, a catalyst reaction layer mainly composed of carbon powder carrying a platinum-based metal catalyst is formed. Next, a diffusion layer having both gas permeability and electronic conductivity is formed on the outer surface of the catalyst reaction layer, and the diffusion layer and the catalyst reaction layer are combined to form an electrode.

Next, a gas seal material or a gasket is arranged around the electrodes with a polymer electrolyte membrane interposed therebetween so that the supplied fuel gas does not leak outside or the two types of fuel gas do not mix with each other. This sealing material and gasket are integrated with the electrode and polymer electrolyte membrane beforehand,
This is referred to as MEA (electrode electrolyte membrane assembly). MEA
A conductive separator plate for mechanically fixing the MEA and electrically connecting adjacent MEAs in series with each other is arranged outside the. A gas flow path for supplying a reaction gas to the electrode surface and carrying away generated gas and surplus gas is formed in a portion of the separator plate that contacts the MEA. Although the gas flow path can be provided separately from the separator plate, a method of providing a gas flow path by providing a groove on the surface of the separator is general.

In order to supply the fuel gas into the groove, a pipe jig for branching the pipe for supplying the fuel gas into the number of separators to be used and connecting the branch directly to the separator-shaped groove is required. . This jig is called a manifold, and the type directly connected from the fuel gas supply pipe as described above is called an external manifold. There is a type of this manifold called an internal manifold which has a simpler structure. In the internal manifold, a through hole is provided in a separator plate in which a gas flow path is formed, an inlet / outlet for gas flow is passed to the hole, and fuel gas is supplied directly from the hole.

[0005] Since the fuel cell generates heat during operation, it is necessary to cool the fuel cell with cooling water or the like in order to maintain the cell in a good temperature state. Usually, a cooling unit for flowing cooling water every 1 to 3 cells is inserted between the separators. In many cases, a cooling water flow path is provided on the back surface of the separator to serve as a cooling unit. The MEA, the separator and the cooling section are alternately stacked, and after stacking 10 to 200 cells, it is common to sandwich this with an end plate via a current collector plate and an insulating plate and fix it from both ends with fastening bolts. It is a structure of a simple stacked battery.

In such a polymer electrolyte fuel cell,
The separator needs to have high conductivity, high gas tightness with respect to the fuel gas, and high corrosion resistance to the reaction when redoxing hydrogen / oxygen. For this reason, the conventional separator is usually made of a carbon material such as glassy carbon or expanded graphite, and the gas flow path is formed by cutting the surface of the separator or, in the case of expanded graphite, by molding using a mold.

The polymer electrolyte fuel cell described above is
Since the electrolyte membrane functions as an electrolyte while containing water, it is necessary to humidify and supply the supplied fuel gas and oxidizing gas. Further, the polymer electrolyte membrane has at least 10
In the temperature range up to 0 ° C., the higher the water content, the higher the ionic conductivity, which has the effect of reducing the internal resistance of the battery and improving its performance. Therefore, in order to increase the water content in the electrolyte membrane, it is necessary to supply the supply gas with high humidification.

[0008] However, when a highly humidified gas at a temperature higher than the battery operating temperature is supplied, dew water is generated inside the battery, and water drops hinder the smooth gas supply. In addition, on the side of the air electrode supplying the oxidizing gas, water is generated by power generation, so that the efficiency of removing the generated water is reduced, which causes a problem of lowering the battery performance. Therefore, usually, the gas is supplied by humidifying the dew point slightly lower than the battery operating temperature.

As a method of humidifying the supply gas, a bubbler humidification method in which the supply gas is bubbled and humidified in deionized water maintained at a predetermined temperature, or a method for humidifying the water, such as an electrolyte membrane, on one surface of a film in which water can easily move. A membrane humidification system in which deionized water maintained at a predetermined temperature is flowed and a supply gas is flowed to the other surface to humidify the water is used. When a gas obtained by steam reforming a fossil fuel such as methanol or methane is used as the fuel gas, humidification may not be necessary because the reformed gas contains steam.

[0010] The humidified fuel gas and oxidizing gas are supplied to a polymer electrolyte fuel cell and used for power generation. At this time, a current density distribution occurs in a single plane of any single cell in the battery stack. That is, the fuel gas is supplied after being humidified by a predetermined amount at the gas supply inlet, but the hydrogen in the fuel gas is consumed by power generation. The phenomenon that the partial pressure of hydrogen is lower and the partial pressure of water vapor is higher in the downstream portion occurs.
The oxidizing gas is also supplied with a predetermined humidification at the gas supply inlet, but oxygen in the oxidizing gas is consumed by power generation and water generated by the power generation is generated. And the partial pressure of steam is low, and the partial pressure of oxygen is low and the partial pressure of water vapor is high in the downstream part of the gas.

Further, the temperature of the cooling water for cooling the battery is lower at the entrance and higher at the exit, so that a temperature distribution occurs in a single plane of the battery. For the above reasons,
A current density distribution (performance distribution) occurs in a single plane of the battery.

In addition, the partial pressures of hydrogen and water vapor in the fuel gas and the partial pressures of oxygen and water vapor in the oxidizing gas are non-uniform in a single plane of the battery, which are generated for the reasons described above. If the temperature distribution becomes extremely large and deviates from the optimal state, it will lead to an extremely over-dried (over-dry) state or an extremely over-wet (over-flooded) state. In some cases, it will not function as a battery.

In addition, the partial pressures of hydrogen and water vapor in the fuel gas and the partial pressures of oxygen and water vapor in the oxidizing gas are non-uniform in a single plane of the battery, which are generated for the reasons described above. Due to the temperature distribution and the like, a phenomenon in which overdrying and overflooding coexist in a single plane of the battery also occurs.

When the above-mentioned problem occurs in some of a large number of stacked batteries when the batteries are highly stacked, the operation of the entire stacked battery is hindered due to the partially degraded batteries. Come. That is, when some of the stacked batteries are overflooded, the overflooded batteries have an increased pressure loss for gas supply. Since the gas supply manifold is common in the stacked battery, gas does not easily flow through the battery that has been overflooded, resulting in more and more overflooding. Conversely, when a part of the stacked battery is overdried, the overdried battery has reduced pressure loss for gas supply. Therefore, gas easily flows into the battery that has fallen into overdry, and as a result, overdrying is caused more and more.

[0015] The above-mentioned problem is that the partial pressure of water vapor in the gas is higher on the gas outlet side than on the gas inlet side on both the fuel electrode side for supplying the fuel gas and the air electrode side for supplying the oxidizing gas. It is often due to the increase. Therefore, as shown in JP-A-9-511356, the flow direction of the oxidizing gas and the flow direction of the cooling water are set to the same direction, and the temperature of the downstream portion of the oxidizing gas is set to the upstream by the temperature distribution of the cooling water. Attempts have also been made to reduce over-flooding in the downstream portion of the air electrode by reducing the current density distribution in a single plane of the battery by increasing the height of the battery.

[0016]

However, when gas is supplied to the battery, there is always a pressure loss at the gas inlet, so the pressure distribution of the supplied gas also exists inside the battery, and the inlet side always becomes high in pressure. . On the air electrode side, water is generated, so the partial pressure of water vapor increases toward the outlet,
Due to the influence of the pressure distribution, the relative humidity does not always increase on the outlet side depending on the battery operating conditions. for that reason,
The battery is generated under operating conditions in which the relative humidity increases toward the entrance, the flow direction of the oxidizing gas and the flow direction of the cooling water are set to the same direction, and the temperature of the downstream portion of the oxidizing gas is increased by the temperature distribution of the cooling water. If it is higher than, the overflooding at the gas inlet side is accelerated, which has the opposite effect.

That is, in the polymer electrolyte fuel cell, it is necessary to humidify the fuel gas. However, in combination with the water generated by the reaction, the flow path of the oxidizing gas and the fuel gas is blocked by the water. However, there is a problem that the output is reduced.

[0018]

In order to prevent the gas flow path from being clogged with water, the polymer electrolyte fuel cell of the present invention comprises:
A pair of electrodes disposed with a hydrogen ion conductive polymer electrolyte membrane interposed therebetween, and a pair of conductive members having a gas flow path for supplying and discharging a fuel containing hydrogen to one of the electrodes and supplying and discharging an oxidizing gas to the other. And a conductive separator plate, wherein at least one of the conductive separator and the gas flow path has a movable structure.

[0019]

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

[0020]

Example 1 An acetylene black-based carbon powder carrying 25% by weight of platinum particles having an average particle diameter of about 30 ° was used as a catalyst for an electrode. A dispersion solution of the perfluorocarbon sulfonic acid powder shown in Chemical Formula 1 in ethyl alcohol was mixed with a solution of this catalyst powder dispersed in isopropanol to form a paste. Using this paste as a raw material, an electrode catalyst layer was formed on one surface of a carbon nonwoven fabric having a thickness of 250 μm using a screen printing method. The amount of platinum contained in the reaction electrode after the formation was adjusted to 0.5 mg / cm2, and the amount of perfluorocarbon sulfonic acid was adjusted to 1.2 mg / cm2.

[0021]

Embedded image

These electrodes have the same structure for both the positive electrode and the negative electrode, and the catalyst layers printed on both sides of the center portion of the hydrogen ion conductive polymer electrolyte membrane having an area slightly larger than the electrodes are in contact with the electrolyte membrane side. And an electrode / electrolyte assembly (MEA). Here, as the hydrogen ion conductive polymer electrolyte,
The perfluorocarbon sulfonic acid shown in (1) was thinned to a thickness of 25 μm.

[0023]

Embedded image

The structure of each component of the polymer electrolyte fuel cell manufactured in this embodiment is shown in FIGS. 1, 2 and 3.
First, FIG. 1 shows a basic configuration of a conductive separator. FIG.
As shown in the figure, the central part 1 of the carbon plate 1 having a thickness of 3 mm
1mm depth in the area of 0cm x 9cm by cutting
(A groove width of about 2.8 mm) was formed. When the gas pressure exceeds a certain value (0.5 kgf / cm ² ), the carbon thin plate 4 (with a plate width of about 2.
8 mm) was attached to the rib portion 5 having a 5.6 mm pitch. The height of the peak was about 1 mm, and the thickness of the movable carbon thin plate 4 was 0.95 mm, so that it was not fixed between the diffusion layer of the electrode and the separator when the battery was fastened. As shown in FIG. 1, a manifold 6 for hydrogen gas, a manifold 7 for cooling water, and a manifold 8 for air are provided on two opposing sides to supply and discharge gas.

During the operation of the battery, if the gas flow path is closed due to excessive humidification water or generated water, the pressure difference increases before and after the gas passage. As a result, when the pressure difference becomes larger than the set value of the spring, the air 10 flowing through each gas flow path moves the movable carbon thin plate as shown in FIG. Gas will not stagnate over the entire flow path.

FIG. 2A is a cross-sectional view of another embodiment of the present invention in a gas flow path portion of a conductive carbon separator. The ribs 5 of the severator 1 having the catalyst layer 12, the gas diffusion layer 13, and the gas flow path 2 are partially notched 1
4 as an organic sheet having flexibility and elasticity.
An ET (polyethylene terephthalate) sheet 15 is selected. In a normal state, the PET sheet closes the convex portion (rib portion), and when the differential pressure of the gas flow tube exceeds a certain value (whether it becomes large or small). The PET sheet was deformed to form a bypass channel. One side 16 of the L-shaped cross section of the PET sheet 15 is joined to the separator 1, and the PET sheet 15 is configured to be deformed left and right according to a differential pressure. FIG.
(B) shows another method. That is, the PET film is configured in a bridge shape, and when the pressure difference between the left and right gas flow paths becomes equal to or more than a certain value, the PET film is deformed, and a bypass flow path is formed between the PET film and the diffusion layer.

The change in the differential pressure due to the blockage of the gas flow path becomes more remarkable as the number of gas flow paths decreases when the gas supply amount of the single cell or the stacked cell is the same. It can be said that the effect of the present invention for preventing a significant decrease in performance and irreversible damage is greater for a separator having a smaller number of gas flow paths.

However, if the configuration is such that the elastic constant of the spring of the movable portion is made small so that it can be operated even with a slight differential pressure, it is also effective for a separator having a large number of gas flow paths. Also,
If a pressure difference is generated between the gas flow paths even if the water flow is not blocked, a bypass is formed between the gas flow paths, which is effective in making the gas flow uniform.

Although the above is an example using a cut separator made of sintered carbon, a metal may be used as a separator material. The separator on the hydrogen side formed uneven grooves and rib portions by press working, and provided a groove for guiding gas by the convex portion 5 made of phenol resin from the manifold hole to the gas flow groove by press working. In addition, convex portions made of a phenol resin were overlapped so that the two grooves were adjacent to each other and curved and connected. The projection made of phenolic resin had a thickness of about 1 mm and was the same as the height of the groove of the separator plate. A gasket corresponding to the shape of the metal plate is formed in the same manner on the outer peripheral portion of the separator plate and around the manifold hole.

In the separator on the air side, six adjacent grooves are curved to form a continuous gas flow groove. The structure is changed between the air side and the hydrogen gas side because the gas flow rate differs between the air side and the hydrogen gas side by about 25 times. Conversely, in such a structure, it is possible to obtain an optimum gas flow rate and gas pressure loss by changing the shape of the resin gas flow groove in accordance with the gas flow rate. As an embodiment of the present invention, the grooves and ribs of the separator are movable,
In order to prevent the gas from being clogged or to improve the gas distribution, the parts to be ribs and grooves during the pressing of the metal plate are kept flat, and a PET sheet as shown in FIG. 2 is used. Thus, a bypass portion was configured.

Next, as shown in FIG. 3, the MEA 8 is formed by these two types of separators 19 and gaskets 20.
Was used as a constituent unit of the scissor battery. Gas flow groove 1 on the hydrogen side
7 and the position of the gas flow groove 18 on the air side were configured to correspond to each other so that excessive sending force was not applied to the electrode. A cooling unit for flowing cooling water was provided for every two cells stacked in a unit cell. A metal mesh made of SUS316 was used for the cooling unit to ensure conductivity and cooling water flow, and a gasket made of phenol resin was provided on the outer peripheral portion and the gas manifold portion to form a seal portion. Grease is applied thinly to portions such as the gasket and the MEA, the separator plate and the separator plate, the gasket and the separator plate, and the like, so that the sealing property is secured without significantly lowering the conductivity.

After 50 cells of the above MEA were stacked, they were fastened with a stainless steel plate and a fastening rod at a pressure of 20 kgf / cm 2 via a current collector and an insulating plate. If the fastening pressure is too small, gas leaks and the contact resistance is large, so the battery performance will be reduced.On the contrary, if it is too large, the electrode will be damaged or the separator plate will be deformed. It was important to change the fastening pressure.

As the battery of the comparative example, a battery having a conductive separator made of a carbon plate having no spring as in the batteries of the above-described examples was manufactured. In the battery of the comparative example, the configuration was the same as that of the above example except for the conductive separator.

The thus-prepared polymer electrolyte fuel cells of this example and the comparative example were maintained at 85 ° C., and humidified and heated to a dew point of 83 ° C. on one electrode side. Humidified and heated air was supplied to the other electrode side so as to have a dew point of 78 ° C. As a result, a battery open-circuit voltage of 50 V was obtained when there was no load in which no current was output to the outside.

The battery was subjected to a continuous power generation test under the conditions of a fuel utilization of 80% and a current density of 0.5 A / cm 2, and the dependence of the output characteristics on the oxygen utilization was shown in FIG. As a result, in the battery of the present invention, high performance is maintained as compared with the battery of the comparative example even in a region where the oxygen utilization rate is 60% or more, that is, in a region where the supplied air is small and the generated water is flooded.
When the generated water is blocked in the gas flow path, the bypass movable portion of the rib portion is opened to allow gas to flow, thereby suppressing a rapid decrease in battery performance due to water clogging. Further, the performance was improved even in the dry-up region where the oxygen utilization was low. Also, it was confirmed that the output of the battery of the comparative example decreased with the driving time, whereas the battery of the present example maintained the battery output of 1000 W (22 V-45 A) for 8000 hours or more.

In this embodiment, the case where the gas flow groove is a plurality of parallel straight lines is tried. However, a structure in which the gas discharge manifold hole is connected to the gas discharge manifold hole by the gas flow groove via the twice curved portion 14, Various structures such as a structure in which a central manifold hole and an outer manifold hole are connected by a gas flow groove like a snail shell are also possible.

Further, in the present invention, a movable section is also provided for a manifold for supplying and distributing a reaction gas to each cell, collecting off-gas and discharging the off-gas to the outside of the battery system, thereby improving gas distribution. That is, the stack of 50 cells is divided into 5 parts every 10 cells, and the thickness between the parts is 8 mm.
Was inserted. Gas distribution can be controlled by inserting an open / close rod from the outside of the battery into a carbon connector plate in the air-side manifold penetrating these 50 cells. For example, in a state in which the cells from the gas supply side of the stack to 10 cells are blocked by the generated water and the performance is degraded, the open / close rod between the 10 cells and the 11 cells is closed, and the gas is given priority to the 10 cells. I was led to. The operation of the opening / closing rod may be performed manually, or the opening / closing operation may be automatically performed when the battery performance decreases while monitoring the average voltage of the battery. In contrast to the configuration in which the five parts of the manifold are connected in series, each of the manifolds is connected in parallel to the gas supply / exhaust pipe of the entire battery, and an opening / closing rod is provided at the entrance / exit portion of the manifold. The formed structure allows more effective gas distribution.

[0038]

According to the present invention, the supply of gas due to water clogging in the gas flow grooves is locally stopped by replacing the conventional gas flow grooves with fixed ones and replacing them with movable ones as separator plates. This makes it possible to prevent deterioration due to concentration of power in the electrodes and to supply a highly reliable fuel cell.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a conductive separator used in a fuel cell of the present invention.

FIG. 2 is a diagram showing another configuration of the present invention.

FIG. 3 is a diagram showing a configuration of a stacked cell of the fuel cell of the present invention.

FIG. 4 is a diagram showing the performance of the fuel cell of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Carbon plate 2 Gas flow path 3 Spring 4 Carbon thin plate 5 Rib part 6 Manifold of hydrogen gas 7 Manifold of cooling water 8 Manifold of air 9 Blockage part of gas flow path 10 Air flowing through gas flow path 11 Bypass flow Road flow 12 Catalyst layer 13 Gas diffusion layer 14 Notch 15 PET sheet 16 One side of joined L-shaped section 17 Hydrogen-side gas flow groove 18 Air-side gas flow groove

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Eiichi Yasumoto 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor: Osamu Sakai 1006, Kazuma, Kadoma, Osaka Prefecture, Matsushita Electric Industrial Co., Ltd. 1006, Kadoma, Kadoma, Futoma, Matsushita Electric Industrial Co., Ltd. (72) Inventor Junji Morita, 1006, Kadoma, Kadoma, Kadoma, Osaka Pref. Matsushita Electric Industrial Co., Ltd. F term (reference) 5H026 AA06 CC03 CC08 CX08

Claims (1)

[Claims] 1. A pair of electrodes arranged with a hydrogen ion conductive polymer electrolyte membrane interposed therebetween, and a gas flow path for supplying and discharging hydrogen-containing fuel to one of the electrodes and supplying and discharging an oxidizing gas to the other. A polymer electrolyte fuel cell, comprising: a pair of conductive separator plates having the following structure: at least one of the conductive separator and the gas flow path has a movable structure.