JPS6210874A - Liquid fuel cell - Google Patents

Abstract

PURPOSE:To prevent the temperature runaway of a liquid fuel cell in intermittent use by simple constitution by operating an auxiliary fuel electrode arranged in an air electrode liquid chamber in starting to consume methanol in the air electrode liquid chamber. CONSTITUTION:Dilute sulfuric acid is filled in an air electrode liquid chamber 7, and a mixture solution of dilute sulfuric acid and methanol is filled in a fuel electrode liquid chamber 6. In intermittent use, after several days methanol in the chamber 6 diffuses into the chamber 7 to make equilibrium condition. A switch 11 is operated by a command of a controller 10, and is connected to a contact 11b is starting to operate an auxiliary fuel electrode 2. Thereby, methanol in the chamber 7 is quickly consumed by chemical reaction in the electrode 2, and catalystic combustion of methanol on an air electrode is retarded to prevent temperature runaway. When a specified time elapsed after starting, power generation is switched to that with a main fuel electrode 1 by a command of the controller 10.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a liquid fuel cell that has a simple structure and prevents runaway cell temperature during intermittent use.

(Prior Art) Fuel cells have been known for a long time, but recently it has been considered that liquid fuel cells using methanol or the like as a fuel can be used instead of or in combination with conventional batteries as a power source for automobiles.

A liquid fuel cell has a fuel electrode and an air electrode (also called M cumulative) placed in a battery containing an electrolyte with a diaphragm separating them.
Electromotive force is extracted by the electrochemical reaction described below.

Fuel electrode: CH30H+lI20 →Co2+6H+6
e Air electrode: 3/2 o2+6H+6e →3■20
If we consider the case where this liquid fuel cell is used as a small power source in a vehicle, there are times when the vehicle is not being driven, so the liquid fuel cell is not used during this period. However, when a liquid fuel cell is used intermittently in this way, the following problems occur.

That is, during the rest period during intermittent use, some methanol diffuses and permeates from the anode fluid chamber to the air cathode fluid chamber through minute pinholes on the diaphragm. If this pause period is longer than several days, the concentration diffusion of methanol will reach an equilibrium state and the same concentration will be reached in both chambers.

In such a state, when air is supplied to the battery and the battery is activated, the methanol in the air cathode liquid chamber on the air electrode rapidly undergoes catalytic combustion (CH30H+3
．． /20. →CO2+2H20〉. Unlike the electrochemical reaction described above, this combustion is a thermochemical reaction and is accompanied by heat generation, which increases the battery temperature.

On the other hand, as the battery temperature rises, the diffusion permeation rate of methanol also increases, which promotes the diffusion of methanol into the air cathode chamber and accelerates catalytic combustion on the air electrode. This vicious cycle causes the battery temperature to run out of control, and the efficiency of converting methanol fuel into electrical energy gradually decreases.

To solve this problem, several temperature control methods for liquid fuel cells have been proposed (Utility Model Application No. 59-1155).
74 and Utility Model Publication No. 59-117067).

These control methods either circulate the electrolyte externally to radiate heat and lower its temperature, or use a blower installed on the air electrode to blow air into the air electrode to cool it and lower the temperature of the electrolyte.

However, in such conventional temperature control methods, the system becomes larger or more complex due to the use of auxiliary equipment such as pumps and blowers, and as a result, the proportion of electrical energy generated by the fuel cell consumed by the auxiliary equipment is reduced. The problem was that the efficiency of fuel use was low.

(Purpose and Structure of the Invention) The present invention has been made in view of the above points, and an object of the present invention is to prevent temperature runaway of a liquid battery during intermittent use with a simple structure. At startup, the auxiliary fuel electrode is activated to consume methanol in the air electrode liquid chamber, reduce its concentration, and suppress the catalytic combustion of methanol on the air electrode, and then the main fuel electrode is activated. It was configured as follows.

(Example) Hereinafter, the present invention will be explained based on the drawings.

FIG. 1 is a schematic diagram of an embodiment of a liquid fuel cell according to the present invention, in which 1 is a main fuel electrode, 2 is an auxiliary fuel electrode, 3 is an air electrode, 4 is a diaphragm, 5 is a fuel cell container, 6 is the fuel electrode liquid chamber, 7
is the catholyte chamber. Dilute sulfuric acid (10~
30wt%), but the fuel electrode liquid chamber 6 contains dilute sulfuric acid (10~30wt%).
Contains a mixed solution of (wt%) and methanol (5 to 20 wt%).

However, during intermittent use, if left for several days or more, methanol in the fuel electrode chamber 6 will be concentrated and diffused, and methanol will be in a diffusion equilibrium state in the fuel electrode chamber 6 and the air electrode chamber 7.

8 is a plastic filter for preventing contact between the auxiliary methanol electrode 2 and the air electrode 3, and 9 is an inlet for methanol as fuel. 11 are contacts 11a and 11b connected to the main fuel electrode 1 and the auxiliary fuel electrode 2, respectively.
10 is a controller that detects the electromotive force between the main fuel electrode 1 or the auxiliary fuel electrode 2 and the air electrode 3 and controls the changeover switch 11 according to the output thereof.

With the above configuration, when the battery is connected to the load and the start switch (not shown) is turned on, a start command is output.) The changeover switch 11 is connected to the contact 11b, and the following chemical A reaction occurs.

CH30H+H20→CO2+6H+6e- Due to this chemical reaction, the methanol in the air catholyte chamber 7 is rapidly consumed, and the methanol concentration decreases.

As a result, catalytic combustion of methanol on the air electrode 3 is suppressed and temperature runaway is prevented.

Next, the output voltage between the auxiliary fuel electrode 2 and the air electrode 3 rapidly decreased due to the decrease in the methanol concentration in the air electrode liquid chamber 7, and this voltage drop rate was 80 to 90% of the starting voltage. At this time, the changeover switch 11 is switched from the contact 11b to the contact 11a by a command from the controller 10, and from then on, the main fuel electrode 1 is used.

In the above embodiment, switching from the auxiliary fuel electrode to the main fuel electrode was performed based on the voltage drop rate, but the switching may be performed automatically after a certain period of time has passed since startup. Further, the switching may be performed manually without using the controller.

(Effects of the Invention) As explained above, in the present invention, the auxiliary fuel electrode provided in the catholyte chamber is used to start the battery, thereby consuming methanol in the catholyte chamber and rapidly increasing its concentration. This makes it possible to prevent temperature runaway due to catalytic combustion of methanol on the air electrode when the fuel cell is started up during intermittent use, with a simple configuration that does not require auxiliary equipment such as pumps or blowers. Effects can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the structure of a liquid fuel cell according to the present invention.

Claims (1)

[Claims] A main fuel electrode is provided in the fuel electrode liquid chamber, and an air electrode and an auxiliary fuel electrode are provided in the air cathode liquid chamber, and the auxiliary fuel electrode is operated at startup, and thereafter the main fuel electrode is operated using a switching means. A liquid fuel cell characterized by comprising: