JPS6112347B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a phosphoric acid type electrolyte that prevents a highly hygroscopic electrolyte, such as a highly concentrated phosphoric acid, from absorbing moisture in a reaction gas and being diluted during an operational shutdown. This article relates to a method for stopping a fuel cell.

In general, fuel cells that use phosphoric acid as an electrolyte use a circulating or non-circulating method for supplying the oxidizing gas, a non-circulating method for the fuel gas, and a non-circulating method for supplying the reactant gas, while the electrolyte is impregnated into a porous thin film called a matrix. A fixed method is used. A major feature of this type of fuel cell is that the electrolyte maintains a stable liquid state even at high temperatures (e.g. 240°C) and high concentration states (e.g. 100wt% or more). °C), and at this operating temperature, reaction product water generated during power generation and moisture contained in the supply system are all removed by the reaction gas, and the electrolyte concentration is maintained at 100 to 105 wt%. Therefore, when making a battery, it is
If a predetermined amount of phosphoric acid with a concentration of 100 to 105 wt% is impregnated in advance, there is no need to control the amount or concentration of the electrolyte during operation of the battery. Therefore, under normal operating conditions, for example,
It is not necessary to provide a moisture regulating device as described in 40369. However, when a phosphoric acid fuel cell is to be shut down, it is necessary to prevent the phosphoric acid electrolyte, which has extremely high hygroscopicity, from absorbing moisture in the reaction gas and swelling.

Traditionally, the method of shutting down this type of fuel cell is to turn off the load on the cell, cut off the air and hydrogen supply, and start cooling the cell at the same time.
One method is to supply an inert gas, such as dry nitrogen, to the fuel gas compartment, which is supplied with hydrogen, and the oxidizer compartment, which is supplied with air. This method requires an inert gas supply system such as nitrogen in addition to the air and hydrogen supply systems, which makes the equipment complicated and has the disadvantages that dry inert gas such as nitrogen must be kept on hand. It was hot. Alternatively, the fuel gas compartment and oxidizer compartment can be sealed with hydrogen and air, respectively, until the cell load is turned off and cell cooling begins and the cell temperature drops to near room temperature. There are ways to keep it that way. This method has the disadvantage that the consumption of the reactant gas by the internal discharge of the cell creates a negative pressure in each gas compartment, which causes the electrolyte to leak into the gas compartment, reducing the electrolyte volume. Ta. Therefore, when the fuel cell is taken out of operation, the load on the cell is turned off and a small amount of hydrogen and air are pumped into the fuel gas compartment, respectively, until the cell begins to cool down and the cell temperature drops to around room temperature. There is a way to keep the flow flowing into the oxidizer compartment. In this method, the hydrogen supplied to the fuel gas compartment may be a dry gas or a gas containing some moisture, while the air supplied to the oxidizer compartment contains a significant amount of moisture. For example, the temperature is 20℃ and the humidity is 50%.
The water vapor pressure in the air at 80% to 80% is approximately 9 mm.
Hg to 14mmHg. In contrast, highly concentrated phosphoric acid exhibits extremely high hygroscopicity at low temperatures, and the water vapor pressure of 100% concentrated phosphoric acid is approximately 0.37 mm.
It is Hg. Therefore, for example, if a fuel cell with an electrolyte concentration of 100% is cooled from an operating temperature of 150°C to 20°C by the method described above, the electrolyte absorbs moisture in the air and is successively diluted until it reaches 60°C. ，40℃，
The concentration of electrolyte at each temperature of 20℃ is 92
%, 80.1%, and 59%, and the increase rates of the electrolyte volume at this time are 0.5%, 8.1%, and 26.9%, respectively. In this way, when moisture in the air is absorbed into the electrolyte through the electrodes, the concentration of the electrolyte becomes diluted. As a result, the volume of the electrolyte increases, and the diluted electrolyte leaks into the reaction gas compartment through the electrodes, causing the balance of the electrolyte maintained during operation to collapse, and when operation is restarted. , the electrolyte becomes insufficient, leading to deterioration of battery characteristics, and furthermore, inducing the danger of explosion due to mixing of reactive gases.

In view of the above-mentioned points, the present invention eliminates the drawbacks of the prior art and provides a method for suspending phosphoric acid fuel cells in which the concentration of the electrolyte is not diluted during suspension of operation and the characteristics of the cell are maintained for a long period of time. The purpose is to provide a method.

According to the present invention, such an object is achieved by providing a dehumidifier in at least the main reaction gas supply pipe of the oxidizer supply system in a reaction gas supply system of a phosphoric acid fuel cell consisting of an oxidizer supply system and a reducing agent supply system. By connecting the reaction gas sub-supply pipes in parallel, when the operation is stopped,
This is achieved by closing the reaction gas main supply pipe, opening the reaction gas sub-supply pipe, and supplying the reaction gas dehumidified by the dehumidifier.

Next, one embodiment of the present invention will be described in detail based on the drawings.

FIG. 1 shows a schematic configuration diagram of an embodiment of the present invention. In the figure, a fuel cell 1 has a fuel electrode (hydrogen electrode) 2, an oxidizer electrode (air electrode) 3, and a 95%
an electrolyte compartment 19 consisting of a porous matrix impregnated with a certain amount of phosphoric acid; a fuel gas compartment 4 which contacts the electrolyte compartment 19 via a hydrogen electrode 2; The oxidant compartment 5 is in contact with the oxidizer compartment 5. A hydrogen supply pipe 6 for supplying hydrogen and a hydrogen discharge pipe 7 for discharging hydrogen are connected to the fuel gas compartment 4 as a reducing agent supply system, and the respective pipes 6 and 7 are provided with valves 8 and 9, respectively. The oxidizer compartment 5 has a main supply pipe 10 that supplies air as an oxidizer supply system, and a main supply pipe 1.
A sub-supply pipe 12 and an air exhaust pipe 13 for discharging air are connected to each other. The sub supply pipe 12 has a dehumidifier 11 and a three-way valve 14,1
5 to the main supply pipe 10. Note that the main supply pipe 10 is provided with a valve 16, and the air discharge pipe 13 is provided with a valve 17. 8 is a load connected to the electrodes 2 and 3.

Functions of the embodiment of the present invention having the above-described configuration will be explained. When operating the fuel cell 1, the valves 8,
9 is opened to supply hydrogen to the fuel gas compartment 4, valves 16 and 17 are opened, and the three-way valve 1 is opened.
4 and 15 on the main supply pipe 10 side, air is supplied to the oxidizer compartment 5. In this case, since the operating temperature of battery 1 is about 130°C to 190°C, the water contained in the reaction gas hydrogen or air and the water generated by the reaction evaporate due to the high operating temperature, and the electrolyte The electrolyte concentration is almost 100% as it is all carried out without being absorbed by the
Since a high concentration is maintained nearby, there is no need to specially dehumidify and supply the reactant gas.

When stopping the operation of the fuel cell 1, the load 18
and start cooling battery 1.
Close the discharge valves 9 and 17, and close the three-way valve 14,
15 from the main supply pipe 10 side to the sub supply pipe 12 side. Since the valves 8 and 16 remain open, hydrogen is supplied from the hydrogen supply pipe 6 by natural diffusion, and air is supplied as dehumidified air by natural diffusion via the sub-supply pipe 12 having the dehumidifier 11. . Therefore, the operation of the battery 1 is stopped while the electrolyte solution is maintained at the concentration during operation of the battery 1 without directly supplying air containing moisture.

FIG. 2 is a graph illustrating the effects obtained by the present invention by comparing the effects obtained with the prior art and the changes in battery life test characteristics. In the figure, A is the present invention,
B is a characteristic of the prior art, in which battery operation is temporarily stopped at arrows a to c and then restarted. As is clear from the graph results,
In invention A, where air is supplied via a dehumidifier when the operation is stopped, the current value remains approximately 740 to 750mv despite long-term operation of 10,000 hours, whereas air is supplied directly when the operation is stopped. Conventional technology B
In this case, the current value decreased every time the operation was stopped, and after 10,000 hours of operation, it decreased to approximately 600mv.

As explained above, according to the present invention, at least the oxidizer supply system of the phosphoric acid fuel cell is made of two systems, a reaction gas main supply pipe and a reaction gas sub-supply pipe,
When the battery is stopped, the reactant gas is supplied through the sub-supply pipe equipped with a dehumidifier, so the reactant gas containing moisture is not directly supplied to the fuel cell, and the concentration of the electrolyte is lower than that of the battery. This has the effect that the concentration during operation can be maintained and the characteristics of the battery can be maintained over a long period of time.

Note that the present invention is not limited to installing a dehumidifier on the air supply side to dehumidify the air, but when dehumidifying the fuel gas is required, a dehumidifier can also be installed on the fuel gas supply side.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention, and FIG.
The figure is a graph showing the life test characteristics of a battery obtained according to the present invention. 1: fuel cell, 2: hydrogen electrode, 3: air electrode,
4: Fuel gas compartment, 5: Oxidizer compartment, 6: Hydrogen supply pipe, 7: Hydrogen discharge pipe, 8, 9, 16, 1
7: Valve, 10: Main supply pipe, 11: Dehumidifier, 1
2: Sub supply pipe, 13: Air discharge pipe.

Claims (1)

[Claims] 1. In the reaction gas supply system of a phosphoric acid fuel cell consisting of an oxidizing agent supply system and a reducing agent supply system,
A reactive gas sub-supply pipe having a dehumidifier is connected in parallel to at least the reactive gas main supply pipe of the oxidizing agent supply system, and when the operation is stopped, the reactive gas main supply pipe is closed and the reactive gas sub-supply pipe is opened. and supplying a reaction gas dehumidified by the dehumidifier.