JP2002141090A - Operation method of solid polymer fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent fall of cell voltage in continuous operation under conditions to maintain high efficiency of the system and stability of fuel cells. SOLUTION: Operation conditions are switched over for a certain period of time, when output voltage of the fuel cell goes below the predetermined threshold.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of operating a polymer electrolyte fuel cell system for generating electric power using a polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art In a fuel cell using a solid polymer, a fuel gas containing hydrogen and an oxidizing gas containing oxygen, such as air, are electrochemically reacted to simultaneously generate electric power and heat. To be generated.

Conventionally, a catalytic reaction layer mainly composed of carbon powder carrying a platinum-based metal catalyst is formed on both sides of a polymer electrolyte membrane for selectively transporting hydrogen ions, and the outer surface of the catalytic reaction layer is formed. In addition, a diffusion layer having both gas permeability and electronic conductivity is formed, and the diffusion layer and the catalytic reaction layer are combined to form an electrode. Further, a gas sealing material or a gasket is arranged around the electrode 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. The sealing material and the gasket are integrated with the electrode and the polymer electrolyte membrane in advance and assembled, and this is called an MEA (electrode electrolyte membrane assembly). On the outside of the MEA, a conductive separator plate for mechanically fixing the MEA and electrically connecting adjacent MEAs in series with each other is disposed. A gas flow path for supplying a reaction gas to the surface and carrying away generated gas and surplus gas is formed. Although the gas flow path can be provided separately from the separator plate, a method of forming a gas flow path by providing a groove on the surface of the separator is general.

In order to supply a reaction gas to the groove, a through hole is provided in a separator plate having a gas flow path formed therein.
It is necessary to pass the inlet / outlet of the gas flow path to this hole, and supply the reaction gas directly from this hole while branching to each flow path.
Here, the through holes for supplying the reaction gas to the respective flow paths are called manifold holes. Since a fuel cell generates heat during operation, it is necessary to cool the fuel cell with a cooling medium or the like in order to maintain the cell in a favorable temperature state. Usually 1-3
A cooling section for flowing a cooling medium for each cell is inserted between the separators. In many cases, a cooling medium flow path is provided on the back of the separator to serve as a cooling section. In this case, the separator also needs a manifold hole for distributing the cooling medium to each cooling medium flow path. 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. This is the structure of a simple stacked battery.

[0005]

In order to maintain the performance of a conventional polymer electrolyte fuel cell, it is necessary to keep the ion conductivity constant by moistening the polymer membrane. Therefore, it is desirable to operate the fuel cell by supplying a highly humidified fuel gas and an oxidizing gas to the fuel cell. However, in order to make each gas highly humidified on the system, enormous energy is required when evaporating water, thereby reducing the efficiency of the entire system. In addition, in the operation in which the supply gas is humidified, the supply of the fuel gas and the oxidizing gas to the electrodes becomes insufficient due to the blockage of the separator channel and the MEA diffusion layer with water, so that the fuel cell system operates stably. There is a problem that it will not be possible.

Accordingly, the amount of humidification is reduced in order to suppress the heat of vaporization of water and operate the battery stably, and the flow rate of the fuel gas and the oxidizing gas is increased in order to prevent clogging of the water, thereby increasing the gas flow rate. Driving while physically discharging water. As a result, the battery performance has deteriorated due to drying over time in the MEA.

[0007] As described above, in the conventional polymer electrolyte fuel cell system, the battery voltage may drop when the continuous operation is performed under the operating conditions for improving the efficiency of the system and maintaining the stability of the battery. It was an issue.

[0008]

SUMMARY OF THE INVENTION A method of operating a polymer electrolyte fuel cell according to the present invention is directed to a fuel cell for generating electric power with a fuel gas and an oxidizing gas, and a fuel generation for generating the fuel gas from a power generation raw material gas. A fuel cell system comprising a fuel cell and a cooling medium means for cooling the inside of the fuel cell so as to keep the heat generated by the operation of the fuel cell at a constant temperature. The voltage is maintained at an initial value.

At this time, the temperature of the cooling medium decreases, the flow rate of the fuel gas decreases, the flow rate of the oxidizing gas decreases, the amount of humidification to the fuel gas increases, the amount of humidification to the oxidizing gas increases, or the It is effective to combine one or a plurality of conditions while increasing the amount of load that consumes the generated power.

[0010] As an operating condition, it is effective to stop the fuel gas and the oxidizing gas, the cooling medium, and the load supplied to the fuel cell for a predetermined time.

Further, the fuel cell has a structure in which the inside of the stacked fuel cells is divided into a plurality of cell groups, and the flow rates of the fuel gas and the oxidizing gas can be arbitrarily changed for each cell group. It is effective to change the flow rates of the fuel gas and the oxidizing gas.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A feature of the present invention is to find an operation method for easily recovering deteriorated cell performance by switching operation conditions when the output voltage of a fuel cell drops.

The term “threshold” used in the embodiment of the present invention is a value of the total output voltage of the fuel cell stack when the output voltage of the fuel cell system drops below an initial value.

[0014]

(Example 1) First, platinum having an average particle size of about 30 ° was obtained using Ketjen Black EC (AKZO Chemie, the Netherlands) which is a conductive carbon particle having an average primary particle diameter of 30 nm. The catalyst supporting 50% by weight of the particles was used as a catalyst on the air electrode side. The Ketjen Black EC was loaded with platinum particles and ruthenium particles having an average particle diameter of about 30 ° by 25% by weight, respectively, to obtain a catalyst on the fuel electrode side. A dispersion solution in which a powder of perfluorocarbon sulfonic acid was dispersed in ethyl alcohol was mixed with a solution in which this catalyst powder was 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 formation was 0.5 mg / cm
2. The amount of perfluorocarbon sulfonic acid is 1.2mg
/ Cm2.

The fuel electrode side and the oxidation electrode side are
The printed catalyst layer was joined to both surfaces at the center of the proton conductive polymer electrolyte membrane having an area slightly larger than the electrode by hot pressing so that the printed catalyst layer was in contact with the electrolyte membrane side. Here, a thin film of perfluorocarbon sulfonic acid (manufactured by DuPont, USA: Nafion 112) was used as the proton conductive polymer electrolyte. Further, a gasket punched in the same shape as the separator was joined to both sides of the electrolyte membrane on both sides of the electrolyte membrane by hot pressing, thereby forming an electrode / electrolyte assembly (MEA).

The MEA was sandwiched between separator plates to form a unit cell. The separator plate was prepared by cold pressing a carbon powder material into a carbon plate, impregnating and curing a phenolic resin, and then impregnating the resin with improved gas sealing properties. . The size of the separator is 10 cm × 20 cm, the thickness is 4 mm, and the groove is a recess having a width of 2 mm and a depth of 1.5 mm, through which gas flows. The ribs between the gas flow paths are projections having a width of 1 mm. Further, a manifold hole for the oxidizing gas, a manifold hole for the fuel gas, and a manifold hole for the cooling medium were formed in the separator. Further, a gas seal portion was formed around the gas flow passage and the manifold hole with a conductive gas sealant in which conductive carbon was dispersed in polyisobutylene.

On both sides of the MEA prepared as described above, the fuel gas flow side on the front surface of the conductive separator and the oxidizing gas flow side on the back surface of the conductive separator are joined to form a single cell A.
And In addition, on both sides of the MEA, the fuel gas flow side on the front surface of the conductive separator and the cooling medium flow side on the back surface of the conductive separator were joined to form a cell B. Next, the unit cells A and the unit cells B are alternately stacked one by one, for a total of 50 cells.
The cells were stacked.

The present invention will be described using the polymer electrolyte fuel cell stack prepared in this embodiment.

The operating conditions are simulated reformed gas (80% by volume of hydrogen, 20% by volume of carbon dioxide, 50 ppm of carbon monoxide).
Using air as an oxidant gas, hydrogen utilization rate 80%, oxygen utilization rate 30%, hydrogen humidifier bubbler temperature 75 ° C, air humidifier bubbler temperature 50 ° C, battery temperature 75 ° C, current density 0.3
A continuous operation was performed at A / cm ² . Assuming that the threshold value of the total output voltage of the fuel cell stack is 34V, the cell temperature is reduced to 70 ° C, the oxygen utilization rate is changed to 60%, and the air humidification bubbler temperature is changed to 60 ° C every time the value falls below the value during the continuous test. 1
Driven for hours. After the operation, the continuous test was restarted by returning to the initial operating conditions. The result is shown in FIG. 1 (practice). The figure also shows the result of continuous operation as a conventional example (dotted line). As is clear from the figure, in the conventional operation method, the average cell voltage decreased with time, but in the operation method of the present example, it was confirmed that the battery performance was maintained within an arbitrary voltage range. Was.

(Embodiment 2) Next, a second embodiment of the present invention will be described. In this example, the batteries used for the test,
The continuous operation conditions and the threshold value of the total voltage of the fuel cell stack were all the same as in Example 1. However, each time the voltage fell below the threshold value, the load from the battery, the supply of the fuel gas and the oxidizing gas, and the circulation of the cooling medium were completely stopped for 3 hours. Thereafter, the continuous test was restarted under the above-mentioned continuous operation conditions. The result is shown in FIG. As in Example 1, it was confirmed that the battery performance was maintained within an arbitrary voltage range. In the present embodiment, the same effect was easily obtained by stopping the operation with respect to the change of the operating condition of the first embodiment.

(Embodiment 3) Next, a third embodiment of the present invention will be described. FIG. 3 shows the structure of the fuel cell manufactured in this example. In the present embodiment, the same fuel cell stack 1 as the battery described in the first embodiment is used, and the external manifolds 2 and 3 are arranged evenly on six sides of the fuel cell stack 1 by an external manifold method. Further, a battery capable of dividing the supply of the oxidizing gas into two cell groups was used. That is, the oxidizing gas whose flow rate has been adjusted by the flow rate adjusting valve 4 is introduced into the upper and lower fuel cell stacks 1 from the oxidizing split external manifold 2 through the oxidizing gas supply pipe 5. Can be. In this embodiment,
The continuous operation conditions of both the upper and lower stages of the fuel cell stack 1 and the threshold value of the total voltage of the fuel cell stack were the same as those in Example 1. Each time the threshold value was dropped during the continuous test, the air humidification bubbler temperature was changed to 65 ° C., the oxygen utilization of the upper fuel cell stack was changed to 30%, the oxygen utilization of the lower fuel cell was changed to 70%, and The operation was performed for 2 hours as a continuous operation condition. Thereafter, the operation of the upper and lower stages was reversed, and the operation was continued for another 2 hours. Then, the continuous test was restarted by returning to the initial continuous operation condition. FIG. 4 shows the results. In this example, it was confirmed that the output voltage of the fuel cell stack at the time of operation switching was minimized as compared with Examples 1 and 2. The same effect was obtained when a plurality of stacked batteries were combined.

[0022]

According to the present invention, since the performance of a fuel cell stack whose cell performance has deteriorated can be restored by changing the operating conditions, the life of the fuel cell system can be extended.

[Brief description of the drawings]

FIG. 1 is a graph showing durability characteristics of a fuel cell according to a first embodiment of the present invention.

FIG. 2 is a graph showing durability characteristics of the fuel cell according to the second embodiment of the present invention.

FIG. 3 is a perspective view showing a fuel cell according to a third embodiment of the present invention.

FIG. 4 is a graph showing durability characteristics of the fuel cell according to the third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fuel cell stack 2 Oxidant division external manifold 3 External manifold 4 Flow control valve 5 Oxidant gas supply piping

Continued on the front page (72) Inventor Hideo Ohara 1006 Kadoma Kadoma, Osaka Pref.Matsushita Electric Industrial Co., Ltd. Person Nobuhiro Hase 1006 Kadoma Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd. (72) Inventor Yoshiaki Yamamoto 1006 Kadoma Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd. BA01 CC06 KK22 KK25 KK46 KK48 KK52 MM04 MM09

Claims (4)

[Claims] A fuel cell configured to generate power from a fuel gas and an oxidizing gas; a fuel generator configured to generate the fuel gas from a power generation raw material gas; In a fuel cell system provided with a cooling medium means for cooling the inside of the fuel cell, the operating conditions of the fuel cell system are switched, and the output voltage of the fuel cell is maintained at an initial value. Driving method. 2. The operating conditions include: a decrease in the temperature of a cooling medium that cools the inside of the fuel cell; a decrease in the flow rate of the fuel gas; a decrease in the flow rate of the oxidizing gas; 2. The solid height according to claim 1, wherein the solid height is at least one of an increase, an increase in the amount of humidification to the oxidizing gas, and an increase in a load that consumes electric power generated by the fuel cell. 3. A method for operating a molecular fuel cell system. 3. The operating condition is that the fuel gas and the oxidizing gas, a cooling medium that cools the inside of the fuel cell, and a load that consumes a power generation amount of the fuel cell are stopped for a certain period of time. An operation method of the polymer electrolyte fuel cell system according to claim 1. 4. A fuel cell in which the inside of a fuel cell is composed of a plurality of cells, wherein the flow rates of fuel gas and oxidizing gas can be arbitrarily changed for each of the cells. An operation method of a polymer electrolyte fuel cell system, wherein the operation is performed by changing the flow rate of the fuel cell.