JPS6376264A - Ordinary temperature type acid methanol fuel cell - Google Patents

Abstract

PURPOSE:To secure such an ordinary temperature type acid methanol fuel cell that is large in discharge capacity, by attaching a cell element to the bottom of a fuel tank or in and around this bottom part, and making a negative electrode so as not to be exposed on a fuel level even if fuel goes down. CONSTITUTION:A cell element 10 is attached to a bottom part 20a of a fuel tank 20, while a positive electrode 11 contacts with air at the outside of this fuel tank 20, and a negative electrode 13 comes into contact with fuel 30 inside the fuel tank 20. This fuel tank 20 is one that is, for example, molded by polypropropylene, and the fuel 30 is made up of a mixture of methanol and water. A filling plug 21 for fuel combines a role as a discharge plug for carbon dioxide to be formed by the negative electrode 13, and a gas-liquid separate film is stuck to a hole part of the plug, whereby gas is passed through but liquid drops are designed so as not be discharge to the outside of the tank. If the fuel goes down due to discharge, the negative electrode 13 is made so as not to be exposed on a fuel level, so that self-consumption of methanol at the exposed art of the negative electrode and methanol by direct reaction of oxygen is thus preventable, and in consequence, any drop in the utilization factor of the methanol is prevented from occurring, thus a large capacity methanol fuel cell is securable.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a room temperature acid methanol fuel cell.

[Conventional technology]

In a room-temperature acid methanol fuel cell that uses an acidic electrolyte, a platinum-based catalyst is generally used for both the positive and negative electrodes. is called the air electrode, and the negative electrode is called the methanol electrode. The discharge reaction is 3/202 + 6 H'' + 6 e--3H20 at the positive electrode, CH30'H + H20-CO2 + 6H'' + 5 e- at the negative electrode, and the reaction for the entire battery is as shown below.

2CH30H+302-2CO2+4H20 As a result of the above discharge reaction, water is generated at the positive electrode and carbon dioxide gas is generated at the positive electrode.

By the way, in fuel cells, research has mainly focused on large-sized continuous replenishment batteries, taking advantage of their ability to continuously replenish fuel and oxidizer, and in line with this trend, methanol fuel cells have traditionally For example, JP-A-59-20927 and JP-A-60-165062.
As shown in the above publications, research has been conducted on large continuous Vt rechargeable batteries, but recently there has been a demand for small, portable methanol fuel cells that take advantage of their ability to achieve high capacity. It has become.

Therefore, in order to meet such demands, the present inventors
We have started developing a small, portable methanol fuel cell, but the limitation of a portable battery is that the necessary methanol fuel must be placed in a portable fuel tank. Therefore, as shown in FIG. 11, the fuel 30 is placed in a portable, one-portion fuel tank 20, and the battery element 10, which includes a positive electrode, a negative electrode, an electrolyte, etc., is initially easy to install. The positive electrode was attached to the side of the fuel tank 20 because it easily came into contact with the air outside the fuel tank 20 and also because it could increase volumetric efficiency.

However, when the battery element 10 is attached to the side surface of the fuel tank 20 as described above, as the discharge progresses, the amount of fuel decreases, and the liquid level of the fuel 30 decreases as shown in FIG. The upper part of the element 10 is exposed above the fuel liquid level, that is, the electrode upper part is exposed above the fuel liquid level.

In particular, when the catalyst surface of the negative electrode, that is, the methanol electrode, is exposed above the liquid surface of the fuel, methanol and oxygen in the air that has entered from outside the fuel tank (a Air enters the upper space inside the fuel tank from outside the fuel tank through the gas discharge plug and reacts directly with the methanol, causing self-depletion of methanol and making it unavailable for electrochemical reactions. As a result, the amount of methanol that can be discharged becomes smaller than the amount of methanol injected into the fuel tank, the discharge utilization rate of methanol decreases, and the discharge capacity of the battery decreases.

[Problem that the invention seeks to solve]

This invention solves the problem of the above-mentioned conventional products in that the negative electrode was exposed above the fuel liquid level, causing a decrease in discharge utilization rate, and provides a room-temperature acid methanol fuel cell with a large discharge capacity. The purpose is to

[Means for solving problems]

The present invention achieves the above object by mounting the battery element at or near the bottom of the fuel tank so that the negative electrode is not exposed above the fuel liquid level even if the fuel decreases.

In other words, the reason why the methanol discharge utilization rate decreases is
Oxygen in the air that has entered from outside the fuel tank reacts directly with methanol on the platinum-based catalyst of the negative electrode exposed above the fuel liquid surface, and the methanol is self-depleted and used for an electrochemical reaction, that is, a discharge reaction. This is because it will no longer be done. Therefore,
In the present invention, electric/l! By attaching one element to the bottom of the fuel tank or near the bottom, the negative electrode is prevented from being exposed above the fuel liquid level even if the fuel decreases.

In particular, when installing the battery element at the bottom of the fuel tank,
It is preferable to install the battery element at the bottom of the fuel tank because the negative electrode is not exposed above the fuel liquid level until the fuel is used up, and it is also possible to easily discharge carbon dioxide and water generated by the discharge reaction. It is preferable that the bottom of the fuel tank is made oblique as shown in the third and fourth embodiments to be described later, so that the battery element can be mounted obliquely at the bottom of the fuel tank.

〔Example〕

Next, embodiments of the present invention will be described based on the drawings.

Figure 1 shows the first diagram of the room-temperature acid methanol fuel cell of the present invention.
FIG. 2 is a schematic partial sectional view showing a cell element of a room temperature acid methanol fuel cell;
FIG. 3 is a perspective view of the current collector on the negative electrode side of the battery element shown in FIG. 2 above.

First, the battery element will be explained based on Fig. 2.
1 is a positive electrode as an air electrode, and this positive electrode 11 has an activated carbon fiber nonwoven fabric as a base, and platinum black as a catalyst is mixed with carbon and kneaded with Teflon (trade name) dispersion and applied, and after drying, It is made by sintering Teflon dispersion. 12 is an electrolyte layer, and this electrolyte N12 consists of a cation exchange membrane with polystyrene sulfonic acid graft polymer membranes formed on both sides, and the cation exchange membrane also serves as a separator.

Reference numeral 13 denotes a negative electrode. This negative electrode 13 has an activated carbon fiber nonwoven fabric as a base, and platinum-ruthenium black as a catalyst is mixed with carbon and applied by kneading with Teflon dispersion. After drying, the Teflon dispersion is sintered. It was made by Reference numeral 14 denotes a current collector on the positive electrode side. This current collector 14 on the positive electrode side is made of a carbon plate, and the portion in contact with the positive ill is hollowed out to allow for current collection and strength.
4a so that the positive electrode 11 can come into contact with air over as wide an area as possible. 15 is a current collector on the negative electrode side;
The current collector 15 on the negative electrode side is made of a carbon plate, and has many parallel grooves 15a as shown in FIG.
The side is pressed against the negative electrode 13. This negative electrode side current collector 1
The grooves 15a at 5 are for supplying fuel to the reaction surface of the negative electrode 13 and for facilitating removal of carbon dioxide gas generated at the negative electrode 13 due to discharge. Further, 16 is a conducting wire on the positive electrode side, and 17 is a conducting wire on the fish type side.

Next, the battery will be explained. FIG. 1 is a schematic cross-sectional view showing a first embodiment of the battery of the present invention. In FIG. 1, 10 is the battery element described above. For the sake of simplicity, the details are not shown and the whole is shown schematically. 20 is a fuel tank, and the battery element 10 is attached to the bottom 20a of this fuel tank 20. In the above installation, the positive electrode 11 of the battery element 10 comes into contact with the air outside the fuel tank 20, and the negative electrode 13 contacts the fuel 30 inside the fuel tank 20, although this is not shown for the sake of schematic illustration. It is attached to the fuel tank 20 so that it can make contact with it. The fuel tank 20 is made of polypropylene, for example, and the fuel 30 is made of a mixture of methanol and water. Reference numeral 21 denotes a fuel injection plug. This injection plug 21 also serves as a discharge plug for carbon dioxide gas generated at the negative electrode 13. A gas-liquid separation membrane is attached to the hole in the plug, allowing gas to pass through but not allowing liquid to flow through. Droplets are not discharged outside the tank. 22 is a leg of the fuel tank 20, and 40 is an upper space.This space 40 is thought to be mainly filled with methanol vapor, water vapor, and carbon dioxide gas generated by the battery reaction, but due to changes in ambient temperature, etc. Air enters from the outside of the fuel tank 20 through the pillar 21 and accumulates in the upper space, causing methanol to self-deplete as described above.

FIG. 4 is a diagram showing the discharge characteristics of the battery according to the first embodiment of the present invention shown in FIG. be. The battery elements 10 in both batteries have the same configuration with an area of 10 d, and the fuel tank 20 of both batteries has a methanol aqueous solution with a methanol concentration of 10% by volume as fuel and has a capacity of 500 mJ! Injected. The internal volume of the fuel tank 20 is 10,100 O, so in the battery of the control example, the upper part of the battery element 10, that is, the upper part of the negative electrode, is exposed above the fuel liquid level, and the state when the fuel liquid level is intentionally lowered, that is, the The state is shown in Figure 12.

Curve d in Figure 4 shows the control battery at 20°C and 150mA.
As shown by curve d, in the control battery with the battery element attached to the side of the fuel tank, the voltage drops as the battery discharges, and the discharge time increases. A large voltage drop occurred after 400 hours. This is thought to be due to self-depletion of methanol on the exposed negative electrode.Curve 6 shows the discharge characteristics when the battery of the first example of the present invention was continuously discharged at 20°C and 150 mA. As shown by curve a, the battery of the first embodiment of the present invention did not experience a large drop in discharge voltage even after the discharge time exceeded 1000 hours, and the battery maintained a stable discharge voltage until the fuel ran out. It was revealed that a larger capacity battery could be obtained by increasing the size of the fuel tank.

FIG. 5 shows the second diagram of the room-temperature acid methanol fuel cell of the present invention.
It is a schematic sectional view showing an example. In this second embodiment, the bottom 20a of the fuel tank 20 is flat (but
The battery element 10 is attached to the bottom of the battery element 10 (no notches), so that the negative electrode is not exposed above the fuel surface until the fuel is completely exhausted, resulting in stable discharge. voltage is maintained.

Figure 6 shows the third example of the room-temperature acid methanol fuel cell of the present invention.
It is a schematic sectional view of an example. In this third embodiment, the bottom 20a of the fuel tank 20 is immersed in the horizontal plane by about 15 mm, and the battery element 10 is immersed in the slanted bottom 20a.
is attached to.

In the third embodiment, as in the first embodiment, even if the fuel 30 in the fuel tank 20 decreases due to discharge, the negative electrode remains at the fuel level until the fuel 30 is almost completely exhausted. There is no exposure and self-combustion of methanol can be prevented, but in addition, there are also the following advantages. In other words, since the battery element 10 is installed diagonally, the carbon dioxide gas generated at the negative electrode 13 easily escapes along the groove 15a (see FIG. 3) of the current collector 15 on the negative electrode side. The movement of the bubbles causes convection of the fuel, promoting diffusion of the fuel near the negative electrode 13 and reducing polarization. Further, as in the case of the first embodiment described above, the water generated at the positive electrode is well removed, the amount of wetting the surface of the positive electrode is reduced, and the discharge reaction proceeds smoothly. In other words, as a result of the discharge reaction, water is generated at the positive electrode, but this water does not turn into steam if the humidity is high. , water droplets fall along the positive electrode surface. At this time, it accumulates on slight irregularities on the surface of the positive electrode and wets and covers the catalyst surface of the positive electrode, resulting in a decrease in the effective electrode area and a drop in voltage. However, when the battery element 10 is attached to the bottom 20a of the fuel tank 20, as in the third embodiment and the first and second embodiments, water droplets fall directly, wetting the positive electrode surface and reducing the electrode area. There is no such thing as causing a decrease in

In this way, the bottom part 20a of the fuel tank 20 is tilted, and the battery element 1
0, the smaller the angle of inclination of the fuel tank bottom 20a, the more fuel can be used until the negative electrode is exposed above the fuel liquid level, and the larger the angle of inclination, the more carbon dioxide gas will escape. As a result, the diffusion effect due to fuel convection increases.In view of the balance between the two, it is preferable that the inclination angle is 10 to 30 degrees.

FIG. 7 shows a battery according to the third embodiment of the present invention and a comparative battery in which the battery element 10 is attached to the side of the fuel tank 20 as shown in FIG. (Due to the relationship of 500ml for both batteries, the upper part of the battery element 10, that is, the upper part of the negative electrode is exposed above the fuel liquid level as shown in FIG. 12) was heated at 20°C for 15 minutes.
It is a figure which shows the discharge characteristic when it discharges continuously at 0 mA. In FIG. 7, the curve d shows the discharge characteristics of the battery of the third embodiment of the present invention, and the curve d shows the discharge characteristics of the battery of the control example, similar to FIG.

As already shown in the curve, the battery of this third embodiment also
Similar to the battery of the example, even if the discharge time exceeded 1000 hours, no large drop in discharge voltage occurred, and a stable discharge voltage could be maintained.

FIG. 8 is a schematic sectional view showing a fourth embodiment of the room temperature acidic methanol battery of the present invention, and the battery of this fourth embodiment is a partially modified version of the battery of the third embodiment. That is, in the fourth embodiment, the attachment part of the battery element 10 to the fuel tank 20 is the attachment part of the battery element 10 to the fuel tank 20, whereas in the battery of the third embodiment, the attachment part of the battery element 10 is attached to the bottom part 20 of the fuel tank 20.
a is uniformly inclined, whereas in the cell of this fourth embodiment, a part of the bottom 20a of the fuel tank 20 is inclined,
The battery element 10 is attached to the inclined portion. In the battery of this fourth embodiment, the same effects as those of the battery of the third embodiment described above are of course achieved, but the negative electrode remains in the fuel liquid until the amount of fuel becomes smaller than in the battery of the third embodiment. Since it is not exposed on the surface, a stable discharge voltage can be maintained for a longer period of time. FIG. 9 is a schematic perspective view of a fifth embodiment of the room temperature acid methanol fuel cell of the present invention. In the battery of this fifth embodiment, the battery element 10 is made into a rectangular shape with a low height, and the bottom 20a of the fuel tank 20
attached to the nearby side. The highest mounting position of the battery element 10 is at the height 173 of the fuel tank 20. As described above, in this fifth embodiment, the shape of the battery element 10 and the mounting position of the battery element 10 are different from those in the first embodiment.
As in the embodiments, even if the fuel level drops due to discharge, the negative electrode of the cell element 10 is rarely exposed above the fuel level (self-consumption of methanol is prevented. This is because even if the fuel is consumed, the amount of water alone is higher than 1/3 of the height of the fuel tank, so the liquid level rarely falls below 1/3 of the height of the fuel tank.

It will be explained with reference to FIG. 10 that the battery of the fifth embodiment of the present invention also exhibits the effect of preventing self-combustion of methanol.

FIG. 10 shows the battery of the fifth embodiment of the present invention shown in FIG. 9 above and the control example shown in FIG. FIG. 3 is a diagram showing the discharge characteristics when the upper part of the battery element 10 (in other words, the upper part of the negative electrode is exposed above the fuel liquid level) is continuously discharged at 20° C. and 10 mA/-.

Curve C shows the discharge characteristics of the battery of the fifth embodiment of the present invention,
Curve d shows the discharge characteristics of the battery of the control example, similar to FIG. There is no large drop in discharge voltage even when the discharge voltage is exceeded, a stable discharge voltage is maintained, self-consumption of methanol is prevented, and a battery with a large capacity can be obtained compared to the control example battery shown by curve d. It shows.

〔Effect of the invention〕

As explained above, in the present invention, by attaching the battery element to the bottom of the fuel tank or near the bottom, even if the fuel decreases due to discharge, the negative electrode is not exposed above the fuel liquid level, and the exposed part of the negative electrode is It was possible to prevent the self-depletion of methanol due to the direct reaction between methanol and oxygen. As a result, a decrease in the discharge utilization rate of methanol is prevented, making it possible to obtain a large-capacity methanol fuel cell.

[Brief explanation of the drawing]

Figure 1 shows the first diagram of the room-temperature acid methanol fuel cell of the present invention.
It is a schematic sectional view showing an example. FIG. 2 is a schematic partial sectional view showing a cell element of a room temperature acidic methanol fuel cell, and FIG. 3 is a perspective view of a current collector on the negative electrode side of the cell element shown in FIG. 2. FIG. 4 is a diagram showing the discharge characteristics of the battery of the first example of the present invention and the battery of the comparative example. FIG. 5 is a schematic sectional view showing a second embodiment of the room temperature acidic methanol fuel cell of the present invention, and FIG. 6 is a schematic sectional view showing a third embodiment of the room temperature acidic methanol fuel cell of the present invention. It is. FIG. 7 is a diagram showing the discharge characteristics of the battery of the third example of the present invention and the battery of the comparative example. FIG. 8 is a schematic sectional view showing a fourth embodiment of the room temperature acid methanol fuel cell of the present invention, and FIG. 9 is a schematic perspective view showing a fifth embodiment of the room temperature acid methanol fuel cell of the present invention. be. FIG. 10 is a diagram showing the discharge characteristics of the battery of the fifth example of the present invention and the battery of the comparative example. FIG. 11 is a schematic cross-sectional view showing a room temperature acid methanol fuel cell as a control example. FIG. 12 is a schematic cross-sectional view showing a state in which the fuel of the comparative example cell shown in FIG. 11 is reduced. 10...Battery element, 11...Positive electrode, 12...
Electrolyte layer, 13... negative electrode, 20... fuel tank, 2
0a...Bottom, 30...Fuel Fig. 1 Fig. 3 Fig. 4 Time (h) Fig. 5 Fig. 7 Time (h) Fig. 8 Fig. 9 Time (h) Fig. 1I Figure 12

Claims (1)

[Claims] (1) A battery element comprising a positive electrode as an air electrode, a negative electrode as a methanol electrode, and an acidic electrolyte is placed at or near the bottom of a fuel tank, with the positive electrode in contact with the air outside the fuel tank, and the negative electrode in contact with the fuel tank. A room-temperature acid methanol fuel cell, characterized in that it is installed in such a way that it can come into contact with the fuel inside the tank.