JP2003157880A - Liquid fuel direct supply type fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid fuel direct supply type fuel cell suitable for a portable small electronic apparatus. SOLUTION: As a construction for supplying oxidizing agent gas to a positive electrode in an electricity generator unit 10, an outside surface of the positive electrode in no contact with electrolysis is provided with a flow passage for making the oxidizing gas flow. The flow passage is provided with a holder 3 for holding a reaction product produced by electrochemical reaction at the positive electrode. The reaction product produced by electrochemical reaction at least at the positive electrode is vapored from an end portion of the holder 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid fuel direct supply type fuel cell, and more specifically, to a positive electrode suitable for use in a portable small electronic device such as a mobile phone. The present invention relates to a liquid fuel direct supply type fuel cell configured to supply oxygen as a chemical gas by natural diffusion or natural convection of the atmosphere.

[0002]

Conventionally, a secondary battery such as a nickel-cadmium battery, a nickel-hydrogen battery or a lithium ion battery has been used as a power source for a mobile phone, a portable computer and the like. These devices are often used with the power always on, and it cannot be said that the secondary battery has a sufficiently high energy density.
There was a problem in terms of continuous use time.

On the other hand, attempts have been made to use a fuel cell as a power source for such equipment, and a direct methanol fuel capable of generating power by directly supplying a liquid fuel such as methanol containing water. Liquid fuel direct-supply type fuel cells such as batteries are regarded as promising alternatives to hydrogen-fueled solid polymer fuel cells, which have complicated supply method of hydrogen as fuel and water content control of electrolyte membrane. .

That is, since it is possible to generate electricity by directly supplying a liquid fuel such as methanol containing water, it is not necessary to manage the water content of the electrolyte membrane, which is required in the polymer electrolyte fuel cell. The structure of the structure that supplies oxygen as an oxidant gas by natural diffusion or natural convection of the atmosphere does not require a driving power source such as a pump, and has the characteristic that it can be simplified. This was because it had the characteristic of being quiet and quiet without driving the pump.

However, in such a liquid fuel direct supply type fuel cell, a negative electrode and a positive electrode are arranged via an electrolyte made of a proton conductive polymer electrolyte, and the liquid fuel is supplied to the negative electrode to supply the positive electrode to the positive electrode. A single battery cell configured to be supplied with an oxidant gas or a power generation unit composed of a cell stack in which a plurality of single battery cells are stacked is provided, and as a reaction product generated by an electrochemical reaction of the power generation unit, Water is discharged as a liquid, so when using it as a power source for the above-mentioned portable small electronic devices, make sure that the water does not come into contact with the device, thereby causing corrosion, electric leakage, and malfunction. In particular, in the case of a direct methanol fuel cell, in addition to this, in addition to this, the reaction product contains methanol and a trace amount of by-products that do not contribute to power generation. Because formaldehyde and formic acid Te comes mixed, was important in the practical application may be processed how such waste.

[0006]

The present invention solves the above-mentioned problems and, in a liquid fuel direct supply type fuel cell such as a direct methanol type fuel cell, the above-mentioned water is produced and is not smoothly removed. Focusing on the fact that the reaction interface of the positive electrode becomes covered, the polarization becomes large and the reaction at the positive electrode becomes difficult to proceed. It was made in view of the situation that it cannot be solved by flowing a large amount of air as gas. Further, in particular, in the direct methanol fuel cell, another object is to accurately treat the waste liquid mixed with methanol and the by-products described above so that the discharge voltage does not decrease.

That is, according to the first aspect of the invention, a negative electrode and a positive electrode are arranged through an electrolyte composed of a proton conductive polymer electrolyte, a liquid fuel is supplied to the negative electrode, and an oxidant gas is supplied to the positive electrode. A liquid fuel direct supply type fuel cell comprising a power generation unit composed of a single battery cell configured to be supplied or a cell stack in which a plurality of the single battery cells are stacked, wherein an oxidant gas is supplied to the positive electrode. In this configuration, a flow path for flowing an oxidant gas is provided on the outer surface of the positive electrode that does not come into contact with the electrolyte, and a capillary body having at least one end suspended in the direction of gravity is arranged in the flow path. It is characterized in that at least the reaction product generated by the electrochemical reaction in the positive electrode is dropped from the suspended tip. As a result, it is possible to prevent the surface of the positive electrode from being covered with the generated water, and it is possible to prevent the discharge voltage from decreasing.

According to a second aspect of the present invention, in the liquid fuel direct supply type fuel cell according to the first aspect, the capillary body is partially a reaction product produced by an electrochemical reaction in the positive electrode or mixed therein. An adsorbent for adsorbing unreacted liquid fuel or a catalyst for decomposing these is carried. As a result, the unreacted liquid fuel and by-products in the reaction product described above can be adsorbed on the adsorbent or can be made harmless by reacting with the catalyst.

The invention according to claim 3 is characterized in that, in the liquid fuel direct supply type fuel cell according to claim 1 or 2, the capillary body has a water repellent substance held at a suspended tip. There is. This makes it possible to smoothly drop the unreacted liquid fuel and by-products described above.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below based on its embodiments.

As shown in FIG. 1, a liquid fuel direct supply type fuel cell according to an embodiment of the present invention is provided with a negative electrode 12 and a positive electrode 13 on both sides of an electrolyte 11, and the negative electrode 12 does not come into contact with the electrolyte 11. Is sandwiched between the negative electrode side separator 14 provided on the outer side surface of the positive electrode 13 and the positive electrode side separator 15 provided on the outer side surface of the positive electrode 13 that does not contact the electrolyte 11.
A power generation unit 1 having a structure in which a negative electrode terminal plate 16 and a positive electrode terminal plate 17 are arranged on the outer surfaces of these separators 14 and 15.
0, which is fastened by the end plate 18 and the fastening bolt 19. The liquid fuel supply port 1 for supplying the liquid fuel to the end plate 18
And a reaction product discharge port 2 for discharging the reaction product from the negative electrode generated by the electrochemical reaction of the power generation unit 10. Air as the oxidant gas is provided with a flow path groove on the positive electrode side of the positive electrode side separator 15,
It is supplied by natural diffusion or natural convection through this channel.

The power generation unit 10 shown in FIG. 1 has a negative electrode and a positive electrode arranged via an electrolyte made of a proton conductive polymer electrolyte, liquid fuel is supplied to the negative electrode, and oxidant gas is supplied to the positive electrode. Although the single battery cell is configured to be supplied, a cell stack in which a plurality of the single battery cells are stacked may be used.

As shown in FIGS. 2 (a) and 2 (b), the flow path groove for flowing the oxidant gas provided in the positive electrode side separator 15 facilitates the natural diffusion of air as the oxidant gas. It is preferable that the flowing shape is a straight line parallel to the direction of gravity and has a width of 1 to 5 mm and a depth of 1 to 5 mm. The flow channel groove is shown in FIGS. 3 (a) and 3 (b). In this way, the capillary body 3 having at least one end suspended in the direction of gravity is arranged,
At least the reaction product generated by the electrochemical reaction in the positive electrode is dropped from the suspended tip and is appropriately collected.

The capillary body 3 is preferably made of a hydrophilic material such as cotton or paper and has a shape such as a thread shape or a hollow fiber shape that does not obstruct the flow of the liquid.

Further, an adsorbent for adsorbing a reaction product generated by an electrochemical reaction in the positive electrode or an unreacted liquid fuel mixed with the reaction product or a catalyst for decomposing the reaction product is partially supported on the capillary body. Well, specifically, adsorbents such as activated carbon and zeolite, precious metal catalysts such as platinum and silver for decomposing these harmful substances, microbial catalysts for detoxifying these substances with inorganic catalysts or microorganisms. Alternatively, they may be carried alone or in combination as appropriate. As a result, some of the unreacted liquid fuel and by-products described above can be adsorbed on the adsorbent or reacted with the catalyst to render the reaction products to be added harmless. That is, when the liquid fuel direct supply type fuel cell is a direct methanol type fuel cell, a part of the methanol of the fuel is discharged unreacted from the reaction product discharge port 2 or a by-product of the electrochemical reaction. As a result, harmful substances such as formaldehyde and formic acid may be mixed in the water of the reaction product and discharged, and it is effective when treating the reaction product containing such a harmful substance.

Further, the capillary body 3 may be made to hold a water-repellent substance at the suspended tip. This water-repellent substance can be held by immersing the tip of the capillary body 3 in a suspension such as Teflon (registered trademark) for several cm. As a result, the above-mentioned unreacted liquid fuel and byproducts can be smoothly dropped together with water.

On the other hand, in the negative electrode side separator 14 provided on the outer surface of the negative electrode 12, the flow channel for flowing the liquid fuel is provided only on the contact surface with the negative electrode 12, and below the flow channel. From above, liquid fuel flows upward, and carbon dioxide as a reaction product is discharged from above. The flow channel groove has a meandering shape and has a width of 1 to 3 mm and a depth of 0.5. It is good to be ~ 2 mm.

In the above-described embodiment, the negative electrode 12 and the positive electrode 13 are provided on both surfaces of the electrolyte 11, the positive electrode side separator 15 having the flow channel groove on the positive electrode 13 side is arranged, and the flow channel groove is provided on the negative electrode side. Although the negative electrode side separator 14 is arranged, a cylindrical positive electrode may be formed inside a cylindrical electrolyte, and the above-mentioned capillary body may be inserted inside this positive electrode.

[0019]

EXAMPLE A negative electrode and a positive electrode are provided on both sides of the electrolyte, and the negative electrode side separator (the width of the flow channel groove is 3 mm and the groove depth is 1 mm) provided on the outer surface of the negative electrode which is not in contact with the electrolyte is in contact with the electrolyte. A conventional battery having an effective area of 25 cm ² consisting of a single battery cell sandwiched by a positive electrode side separator (channel groove width 3 mm, groove depth 3 mm) provided on the outer surface of the positive electrode, and the positive electrode side. A kite thread having a thickness of 1 mm as a capillary body was placed in the flow path groove of the separator, and a battery of the present invention having the same effective area in which both ends were hung was prepared, and air as an oxidant gas was supplied by natural diffusion. , Methanol having a concentration of 3% as a liquid fuel was supplied at 4 ml / min and discharged at a discharge current of 500 mA at a temperature of 25 ° C. The result is shown in FIG.

It can be seen from FIG. 4 that in the conventional battery, the output voltage decreased 4 hours after the start of discharge and the discharge was not possible, whereas in the battery of the present invention, the output voltage of Although there was a slight decrease, it was found that the discharge could be continued. Then, when a conventional battery in which discharge could not be performed was investigated, it was found that water as a reaction product was accumulated in the channel groove of the positive electrode side separator. On the other hand, it was found that such water was not accumulated in the battery of the present invention.

In the above-mentioned embodiment, a kite string having a thickness of 1 mm as a capillary body is arranged in the flow path groove of the positive electrode side separator, and both ends are suspended so that air as an oxidant gas is supplied by natural diffusion. However, as shown in FIG.
A fan may be provided above the power generation unit to facilitate the supply of air as an oxidant gas and the removal of water as a reaction product.

In the above embodiment, the groove width is 3 m.
m, a kite string with a thickness of 1 mm as a capillary body was placed in the flow path groove of the positive electrode side separator with a groove depth of 3 mm, but in order not to hinder the supply of air as the oxidant gas. It is better to be thin.

Further, the above-mentioned embodiment is a direct methanol fuel cell using methanol having a concentration of 3% as the liquid fuel, but ethanol, butanol and dimethyl ether were used as the liquid fuel instead of the aqueous methanol solution. It may be one.

[0024]

As described above, according to the present invention, when a liquid fuel direct supply type fuel cell is used for a portable small electronic device, water as a reaction product produced by an electrochemical reaction on the positive electrode side of a power generation unit is used. Can be removed smoothly and safely by using a capillary body, and therefore, it greatly contributes to popularization of the liquid fuel direct supply type fuel cell for such an application.

[Brief description of drawings]

FIG. 1 is a perspective view of a power generation unit of a liquid fuel direct supply type fuel cell according to an embodiment of the present invention.

FIG. 2 is a perspective view of a flow channel groove provided in a positive electrode side separator used for the liquid fuel direct supply type fuel cell according to the embodiment of the present invention for flowing an oxidant gas.

FIG. 3 is a perspective view of a main part of a liquid fuel direct supply type fuel cell according to an embodiment of the present invention.

FIG. 4 is a diagram comparing characteristics of a liquid fuel direct supply type fuel cell according to an embodiment of the present invention and a conventional liquid fuel direct supply type fuel cell.

FIG. 5 is a sectional view of a liquid fuel direct supply type fuel cell according to another embodiment of the present invention.

[Explanation of symbols]

1 Liquid fuel supply port 2 Reaction product outlet 3 Capillaries 10 power generation unit 15 Positive electrode side separator

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Claims (3)

[Claims] 1. A negative electrode and a positive electrode are arranged via an electrolyte made of a proton conductive polymer electrolyte, and a liquid fuel is supplied to the negative electrode and an oxidant gas is supplied to the positive electrode. A liquid fuel direct supply type fuel cell comprising a power generation unit composed of a single battery cell or a cell stack in which a plurality of the single battery cells are laminated, and a structure for supplying an oxidant gas to the positive electrode does not come into contact with an electrolyte. A flow path for flowing an oxidant gas is provided on the outer surface of the positive electrode, and a capillary body having at least one end suspended in the direction of gravity is arranged in the flow path, and an electrochemical reaction at least in the positive electrode. A liquid fuel direct supply type fuel cell, characterized in that the reaction product produced by the method is dripped from the suspended tip. 2. The liquid fuel direct supply type fuel cell according to claim 1, wherein a part of the capillary body adsorbs a reaction product generated by an electrochemical reaction in the positive electrode or an unreacted liquid fuel mixed therein. A liquid fuel direct supply type fuel cell, characterized in that it carries an adsorbing material or a catalyst for decomposing them. 3. The liquid fuel direct supply type fuel cell according to claim 1 or 2, wherein the capillary body has a water repellent substance held at a suspended tip thereof. .