JPS61269865A - Operation method of fuel cell - Google Patents

Abstract

PURPOSE:To quickly increase temperature by supplying higher concentration fuel than stationary operation at starting. CONSTITUTION:A fuel cell consists of unit cells each of which is comprised of a fuel electrode which electrochemically oxidizes fuel, and an oxidizing agent electrode with electrochemically reduces an oxidizing agent, and an electrolyte which holds ion conductivity between them, and supply and exhaust parts of fuel and oxidizing agent to and from the unit cell respectively. In this fuel cell, higher concentration fuel than stationary operation is supplied at starting. The temperature increasing time at starting of a low temperature type fuel cell which used liquid fuel can be shortened without the help of equipment other than fuel cell.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method of operating a fuel cell, and particularly to short circuiting of the heating time during startup from room temperature.

[Background of the invention]

In the invention system using a fuel cell, the operating temperature is generally set at a temperature higher than room temperature. For this reason, for molten carbonate fuel cells and phosphoric acid fuel cells that operate at temperatures much higher than room temperature, such as 650°C or 200°C, some kind of external heating method must be employed when cold starting them from room temperature. Even for fuel cells that operate at low temperatures of 100° C. or lower, there is a problem with the temperature rising to the steady operating temperature during cold startup. In other words, the output of a fuel cell is generally greatly affected by the cell temperature;
The higher the temperature, the higher the output tends to be. Therefore, being able to raise the temperature to the steady-state operating temperature in a short period of time means that it is possible to operate in a high-output steady-state operating state in a short time, and the success or failure of this greatly influences the value of the fuel cell as a practical power source.

A commonly considered method for accelerating the temperature rise of a low-temperature fuel cell is to insert a heater into the electrolyte (or anolite) and electrically heat it from the outside. However, this method requires a power source to heat the heater,
There is a problem in that another power source is required in addition to the fuel cell, which complicates the system. A method simpler than this method is the method disclosed in JP-A-57-80673 and JP-A-56-114284. All of these aim to generate heat by directly burning the oxidizing agent and reducing agent, which are isolated at the anode and cathode and are to be electrochemically reacted. Fever caused by these methods is
Generally, it is difficult to control and it is impossible to make it moderate. Furthermore, if heat generation on the catalyst is intense, there is a concern that the activity of the catalyst may be reduced. Furthermore, there is also the problem that a new flow path, disconnection valve, etc. must be newly installed to carry out such a method, which complicates the system.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for starting and increasing the temperature of a fuel cell, which is easy to control and can quickly raise the temperature.

[Summary of the invention]

The main point of the present invention is to focus on the fact that the amount of fuel diffused through an ion exchange membrane or an immobilized electrolyte such as a matrix is proportional to the fuel concentration in the fuel chamber. The aim is to control the heat generation and temperature rise caused by direct combustion in the fuel cell, thereby shortening the time it takes to heat up the fuel cell.

The contents of the present invention will be explained in more detail with reference to the drawings. Fourth
The figure is a schematic cross-sectional view of a stacked fuel cell.

This stacked fuel cell has a unit cell consisting of a fuel electrode 1, an oxidizer electrode 2, and an ionic conductive electrolyte 3 located between them.
By repeating the steps, a stacked battery is formed.

A reducing substance, which is a fuel, is supplied to the fuel electrode 1 through the groove 5 of the separator 4, and an oxidizer, which is an oxidizing substance, is supplied to the oxidizer electrode 2 through the groove 6 of the separator 4. An electrochemical reaction proceeds on top of the fuel cell, and the fuel cell generates electricity. Further, the electrolyte 3 may be either liquid or solid as long as it has the function of connecting the fuel electrode 1 and the oxidizer electrode 2 by ionic conduction. Generally, an aqueous solution of an electrolyte substance, a porous substance containing an aqueous electrolyte solution, a matrix that is a pasty substance, an ion exchange membrane, etc. are used. When both the fuel and the oxidizer are gases, it does not matter whether the electrolyte is in any of these three forms, but when at least one of the fuel and the oxidizer is a liquid, the fuel and the oxidizer At the very least, it is not preferable to use only an aqueous solution of an electrolyte substance as an electrolyte, since this may cause a problem of direct contact with the electrolyte substance and a short-circuit reaction. However, with the other two methods, it is impossible to completely prevent the movement of liquid substances 100%, and it is necessary to clarify for each fuel cell system what range is practically acceptable. There is.

Air or oxygen is generally used as the oxidizing agent for low temperature fuel cells that operate at low temperatures of 100° C. or lower. Thus, a fuel cell system with a liquid reactant is a fuel cell that uses liquid fuel material. Liquid fuels include methanol, formalin, formic acid, hydrazine, and ethylene glycol.

When using either a matrix or an ion exchange membrane as an electrolyte using these fuels, the fuel diffuses to the air electrode (i.e., oxidizer electrode) according to Frick's law, where it directly reacts with oxygen in the air. In other words, the fuel reacts and generates heat. For example, methanol is used as the fuel, an ion exchange membrane is used as the electrolyte, and the methanol concentration is 1. mo
Q/Q, methanol permeability coefficient of ion exchange membrane I X 1
The calorific value at 00-3a/min is 0.17caQ/
m, "min value is 60 mA/cn" methanol oxidation reaction (CH,○H+H20→6H"10CO
, +68), which is an amount that cannot be ignored. Furthermore, since the amount of methanol permeation is proportional to the methanol concentration, the amount of heat generated can be controlled by controlling the methanol concentration. This is true not only for fuel cell systems using methanol as fuel, but also for fuel cell systems using other liquid fuels. The inventors have discovered that the ability to control the calorific value through concentration control has a more important practical meaning than just the issue of heat balance during steady operation of the fuel cell. In other words, it can be used to shorten startup time, which is one of the problems in practical operation of fuel cells.

The above will be explained more specifically using an example.

The fuel cell used was an acidic electrolyte methanol air fuel cell. The rated output of this fuel cell is 100W and the weight is 20kg. Additionally, there is a methanol permeability coefficient I
/min (60°C) is interposed with a cation exchange membrane. The operating conditions of the battery were an anorite amount of 212, an air flow rate of 50 Q/win, and a discharge current density of 60 mA/d. Moreover, the sulfuric acid concentration in the anolyte is 3moQ/Q. Using the methanol concentration in the anolyte as a variable, the time required for the battery temperature to rise from room temperature to 50°C was measured. Note that 50''C is a temperature at which 90% of the output at the steady operating temperature of 60''C can be output. 5th result
As shown in the figure. As is clear from the figure, by increasing the methanol concentration, the rate of temperature rise of the battery can be shortened. The basic value obtained from Figure 5.

Based on the findings, embodiments of the present invention in a more practical form are shown below.

[Embodiments of the invention]

<Example 1> FIG. 1 shows the configuration of an apparatus embodying the present invention.

11 is an acidic electrolyte type methanol-1-air fuel cell with a rated output of 1oow, and a cation exchange membrane is interposed between the methanol electrode and the air electrode, and its methanol permeability coefficient is I x 10-"c++ /min.

Air, which is an oxidizing agent, is supplied to 5 by an air pump 15.
0 Q /win is fed, and methanol as fuel is fed as anolite from an anolite tank 12 to 11 by an anolite pump 16 and circulated. The anolyte is an aqueous solution of: 242 containing 3+ol/Q sulfuric acid and 3n+ol/A methanol.

It was started from room temperature at a constant current density of 60 mA/cn+'' and reached 50°C after 32 minutes. The time to raise the temperature to 50°C was 2/3 of that when operating at a methanol concentration of 1 moQ/fl. In this operation, the methanol supply valve 22 that supplies methanol from the methanol tank 13 to the anolyte tank 12 has a methanol concentration of 1.
It was set to 0moQ/ffi and did not open during 32 minutes of operation. In addition, the water retention valve 21 that retains water from the water tank 14 to the anorite tank 12 is opened three times during the 32-minute operation, and about 80 mQ of water is added to keep the water level in 12 constant. Ta.

<Example 2> Fig. 2 shows the apparatus of this example. The components other than the anolyte auxiliary tank 12' and the anolyte supply valve 23 are exactly the same as in the first embodiment. The amount of anolite in the anolite tank is 5
3monIQ at 00mΩ 3mon/fi with sulfuric acid
It contains methanol, and is fed and circulated to the stacked battery 11 by an anolyte pump 16. 60m A/c
It took 14 minutes for the temperature to reach 50°C after discharging at a constant current of 1.0 m''.This time was reduced to approximately 1/3 of the time required when operating at a methanol concentration of 1n+o12/Q. The methanol concentration and the amount of anolyte in the medium anolyte tank 12 were kept constant by retaining methanol and water through valves 22 and 21.The same conditions were maintained until the battery temperature rose from 50°C to 60°C. Operate, and when the temperature reaches 60°C, open the 7norite supply valve 23.

1,5Q 7nolite containing 3monIQ sulfuric acid and 1moQ/Q methanol was added to the anolyte tank.

Immediately after supplying the anolyte to the anolyte tank, the temperature dropped to about 51°C, but then rose slowly. After 24 minutes, the methanol concentration in the 7norite reached the steady-state operating concentration of 1 mo12/ρ.

<Embodiment 3> FIG. 3 shows the apparatus of this embodiment. Everything is the same as Example 2 and FIG. 2 showing the apparatus, except that a methanol supply bypass and a bypass valve 24 are provided. There are 3 in the anorite tank 12! IOQ/Q sulfuric acid and 3moQ/J
There is 500 m0 of anolyte containing methanol, and in the anolyte supply tank 12', 3 mon/u sulfuric acid and 1
Contains 1500m 12 anolytes containing rrroQ/Q methanol.

At the same time as starting the anolyte pump 16, open the bypass valve 24, inject an amount of methanol such that the methanol concentration of the anolite in the laminated cell becomes 5n+oQ/12, open the valve 24, and stop the anolyte pump 16 after 15 seconds. , a constant current discharge of 60 mA/c♂ was started. After 5 minutes, the anolyte pump was started again to continue discharging the battery. The battery temperature reached 50℃ 11 minutes after the start of discharge.
Became. During this time, methanol concentration is 1 mojl/Ω
This shows that the time has been shortened to about 1/4 of that under steady operating conditions.

Thereafter, when the battery temperature reached 60° C., the anolyte replenishment valve 23 was opened and 1.5Q of anolyte having a methanol concentration of 1taoQ/Q was replenished. Immediately after that the temperature was about 50
The temperature dropped to ℃.

〔Effect of the invention〕

According to the present invention, it is possible to shorten the temperature rise time during cold startup of a low-temperature fuel cell using liquid fuel without the aid of any other device other than the fuel cell.

In Examples 1, 2.3, an acidic electrolyte methanol-air fuel cell using methanol as fuel was used. However, the scope of application of the present invention is not limited to this example,
It is equally applicable to fuel cells using other liquid fuels such as formalin, formic acid, hydrazine, and ethylene glycol. As for the electrolyte, it is possible to use not only acidic substances but also alkaline substances. Furthermore, in fuel cells that use gaseous active substances, if we consider the concentration of gas, that is, the pressure, the gas pressure balance of the plane electrode is intentionally destroyed during cold startup, causing the glass to cross through the electrolyte, causing heat generation and temperature rise. It is also possible.

[Brief explanation of the drawing]

Figures 1 to 3 are system diagrams of one embodiment of the present invention;
The figure is a schematic cross-sectional view of a fuel cell, and FIG. 5 is a diagram showing the results of basic experiments that form the principle of the present invention. 11... Methanol-air fuel cell, 12... Anolyte tank, 13... Methanol tank, 14...
- Water tank, 15... Air pump, 16... Anorite pump, 21... Water supply valve.

Claims (1)

[Claims] 1. A unit cell consisting of a fuel electrode that electrochemically oxidizes a fuel substance, an oxidizer electrode that electrochemically reduces an oxidizer, and an electrolyte that maintains ionic conductivity between them. A fuel cell is characterized in that it supplies a higher concentration of fuel during startup than during steady operation, in a fuel cell consisting of a section that supplies and discharges the fuel and oxidizer consumed in that section. how to drive. 2. Claim 1 is characterized in that the amount and concentration of fuel at startup are set such that the fuel concentration applied at startup decreases to the concentration during steady operation when the fuel concentration reaches a predetermined temperature. How to operate a fuel cell. 3. The method of operating a fuel cell according to claim 1, characterized in that after reaching a predetermined temperature, the concentration is adjusted to a steady operating concentration by adding fuel with a low concentration. 4. The method of operating a fuel cell according to claim 1, wherein the fuel of the fuel cell is at least one liquid substance selected from methanol, formalin, formic acid, and hydrazine.