JP2005129261A - Direct liquid supply type fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell of excellent storage stability and a high output of which the sub-products generated from an air pole are easy to be treated, and fuel is prevented from being wasted when no power generation is required. <P>SOLUTION: Liquid fuel is supplied to the fuel pole side of an electrode/film junction where a pair of air pole and fuel pole are jointed through an electrolyte film of proton conductivity, while an air is supplied to an air pole side. A plurality of electrode/film junctions are formed on the same plane. The adjoining air pole and the fuel pole of the plurality of electrode-film junctions are connected in series or parallel. Fuel is supplied to the plurality of fuel poles formed on the same plane from the same fuel storage through a capillary tube. An air pole chamber is so constituted as to cover the plurality of air poles formed on the same plane. The air pole chamber is applied with air using a fan or a blower. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a direct liquid supply type fuel cell capable of generating electricity by directly supplying an organic solvent and water. More specifically, the present invention relates to the structure of such a portable type such as a mobile phone and a notebook computer. The present invention relates to a small direct liquid supply type fuel cell optimal for electronic equipment.

  In recent years, countermeasures against environmental problems and resource problems have become important, and as one of the countermeasures, development of direct liquid supply type fuel cells has been actively carried out. In particular, a direct methanol fuel cell that uses an aqueous methanol solution as a fuel and generates electricity directly without reforming or gasification is simple in structure, small and lightweight, and is a small consumer such as a mobile phone or computer. It is a promising power source.

  In a direct methanol fuel cell, when a methanol aqueous solution having a concentration of about 3% is supplied to the fuel supply side, carbon dioxide is generated by the cell reaction, and this carbon dioxide is discharged from the fuel discharge side together with unreacted fuel. On the other hand, when air is supplied as an oxidant to the air supply side, water is generated by a battery reaction, and this water is discharged from the air discharge side together with unreacted air.

  In order to adapt the direct methanol fuel cell as described above to small consumer applications, it has the same or better characteristics as the secondary batteries such as lithium ion batteries and nickel metal hydride batteries that have been used for this purpose. It was indispensable to compete with these batteries.

  For example, in terms of characteristics, it is essential to improve energy density. In direct methanol fuel cells, cell stacks, fuel tanks, fuel pumps, air pumps, etc., are used to separate carbon dioxide emitted from the fuel discharge side. Many peripheral parts such as a gas-liquid separator and a water tank for storing the water discharged from the air discharge side are required, and it is an important issue to reduce these to a simple structure (Patent Document) 1 and 2).

JP 2003-100315 A JP-A 64-17379

  Patent Document 1 states that “a plurality of unit cells each having one or more vent holes on the wall surface of the fuel container and having an electrolyte membrane, an anode, and a cathode are mounted on the wall surface of the fuel container. (Claim 1) A fuel cell, that is, a fuel cell in which a plurality of monolithic cells are attached to the wall of a fuel container is described. However, this fuel cell has sufficient diffusion to supply air. This is a structure (paragraphs [0027] and [0028]) in which electricity is generated by directly opening a cathode (air electrode) having holes into the atmosphere.

  Patent Document 2 states that “the opening of the discharge path of the generated carbon dioxide gas generated at the fuel electrode and discharged from the fuel chamber into the fuel tank is positioned below the required height from the fuel level in the fuel tank. In addition, by positioning an intermediate portion of the air transport path of the air supplied to the oxidation electrode so as to be able to exchange heat with the fuel tank, the fuel tank is cooled with the air, and the fuel in the fuel chamber and the fuel in the fuel tank (Claim 4) A methanol fuel cell is described. Air supplied to the cathode (oxidation electrode, air electrode) is sucked from the outside with a blower, and the fuel tank is cooled and supplied to the air chamber. It is also shown that the temperature difference is increased (from the bottom left column to the bottom right column, the second row on page 3). What is a battery? Large is different.

In order to make a direct liquid supply type fuel cell such as a direct methanol type fuel cell inferior to a secondary battery such as a lithium ion battery or a nickel metal hydride battery, the number of peripheral parts described above is reduced, One of the problems was to improve the energy density.
In addition, in the fuel cell of Patent Document 1 developed as a countermeasure against this, the fuel cell of Patent Document 1 in which a plurality of monolithic cells are attached to the wall surface of the fuel container can be expected to greatly improve the energy density compared to conventional fuel cells, Since it is structured to generate electricity by opening the air electrode directly to the atmosphere, it is difficult to extract the output, and water or water vapor generated from the air electrode is in direct contact with the outside air. There are problems such as being unable to cope with the effects of failure, and causing by-products that may be generated from the air electrode side to be released to the outside as they are.
On the other hand, the fuel cell of Patent Document 2 supplies air to the air chamber by a blower, but the above air supply means is inevitably adopted because of the structure of the cell in which the air electrode enters. However, the improvement of output, the treatment of by-products, and the like are not particularly caused by forced supply of air.
Furthermore, since the current fuel cell has a problem that the electrolyte membrane permeates methanol, once the power generation is started, the fuel is consumed even when the power generation is not necessary, and the substantial energy efficiency is reduced. There was a problem.
The present invention is intended to solve the above-described problems, and has a large output, can easily handle by-products generated from the air electrode, and can prevent waste of fuel when power generation is not required. An object of the present invention is to provide a fuel cell excellent in storage stability.

In order to solve the above problems, the present invention employs the following means.
(1) A direct liquid that supplies liquid fuel to the fuel electrode side of the electrode-membrane assembly in which a pair of air electrode and fuel electrode are joined via a proton conductive electrolyte membrane, and supplies air to the air electrode side. In the feed type fuel cell, a plurality of electrode-membrane assemblies are formed on the same plane, and adjacent air electrodes and fuel electrodes of the plurality of electrode-membrane assemblies are connected in series or in parallel. Fuel is supplied to the plurality of fuel electrodes configured on the plane by the capillary body from the same fuel storage portion, and the air electrode chamber is configured to cover the plurality of air electrodes configured on the same plane, In the direct liquid supply type fuel cell, air is supplied to the air electrode chamber by a fan or a blower.
(2) The direct liquid supply fuel cell according to (1), wherein the electrolyte membrane is a polymer membrane.
(3) The direct liquid supply type fuel cell according to (1) or (2), wherein the air electrode chamber wall constituting the air electrode chamber does not have conductivity.
(4) The direct liquid supply fuel cell according to any one of (1) to (3), wherein an inlet and an outlet of the air electrode chamber have a valve structure.
(5) The above (1) to (4), characterized in that an adsorption filter for adsorbing by-products from the battery or a decomposition treatment filter for decomposing the by-products is provided at the outlet of the air electrode chamber. The direct liquid supply type fuel cell according to any one of the above.
(6) In any one of (1) to (5), an adsorption layer for adsorbing by-products or a decomposition treatment layer for decomposing by-products is provided in the air electrode chamber. It is a direct liquid supply type fuel cell of description.
(7) The fuel storage unit is provided with a porous membrane part for releasing carbon dioxide generated by a cell reaction to the outside of the system, and a fuel supply port for replenishing the fuel. 6) The direct liquid supply fuel cell according to any one of 6).
(8) The direct liquid supply fuel cell according to any one of (1) to (7), wherein the capillary body has a plate shape and has a portion protruding to the fuel storage unit. .
(9) The direct liquid supply fuel cell according to (8), wherein the capillary body has a T-shaped cross section having a portion protruding to the fuel storage section.
(10) The direct liquid supply according to any one of (1) to (9), wherein the plurality of electrode-membrane assemblies and air electrode chambers are provided on both sides of the same fuel storage unit, respectively. This is a fuel cell.
(11) The direct liquid according to (10) above, wherein the capillaries on both sides of the same fuel storage section project from the fuel storage section and are crossed over the fuel storage section. It is a supply type fuel cell.
(12) The direct liquid supply fuel cell according to (11), wherein the capillary body has an H-shaped cross section having a portion that crosses the fuel storage section.
(13) The direct liquid supply fuel cell according to any one of (10) to (12), wherein the plurality of direct liquid supply fuel cells are stacked in contact with an air electrode chamber.

  Since the direct liquid supply type fuel cell according to the present invention has a structure for forcibly supplying air, the output is large, and the part where water and water vapor come out is specified. It is possible to deal with harmful by-products that may be generated from the extreme side. In addition, fuel can be prevented from being wasted when power generation is not required, and the membrane can be prevented from drying out during long-term storage. Therefore, it is possible to obtain an optimal fuel cell as a power source for portable electronic devices.

Hereinafter, the present invention will be described based on the embodiments.
FIG. 1 shows the structure of a conventional direct liquid supply fuel cell.
In this figure, an MEA (Membrane Electrode Assembly) 1 in which three electrode-membrane assemblies are connected in series is provided on the surface of the fuel storage unit 2 for holding the fuel, and there are many holes for taking in air. The fuel cell is configured by being suppressed by the air introduction plate 3.
Further, the cross section is as shown in FIG. 2, and the fuel supplied / supplemented from the fuel supply port 4 is supplied from the fuel storage unit 2 to the fuel electrode 6 through the capillary body 5 and the air is supplied through the air introduction plate 3. It is supplied to the air electrode 7.
The fuel is oxidized at the fuel electrode 6 to generate carbon dioxide and protons, and the generated protons move through the electrolyte membrane 8 to reduce oxygen at the air electrode 7 to generate water or water vapor.
The carbon dioxide produced at the fuel electrode 6 is accumulated on the upper part of the fuel storage part 2 and released outside the system through the porous membrane part 9.
Water or water vapor generated at the air electrode 7 is released to the outside air as it is through the air introduction plate 3.

  In the present invention, the method for producing the MEA is not limited, but it can be produced by a method similar to the conventional method in which the air electrode and the fuel electrode are joined to both surfaces of the electrolyte membrane by hot pressing.

As the proton conductive electrolyte membrane, a polymer membrane is preferably used, and a fluororesin electrolyte membrane having a sulfonic acid group such as a perfluorosulfonic acid electrolyte membrane can be used.
In the fluororesin electrolyte membrane having a sulfonic acid group, a material having low methanol permeability is a preferable material because it can take a high fuel utilization rate and there is no decrease in battery voltage due to fuel crossover. The fuel cell can be operated at a temperature of 90 ° C. or lower. Further, by using a composite electrolyte membrane or the like in which proton conductive inorganic substance is micro-dispersed in a heat resistant resin, a fuel cell that can be operated to a higher temperature range can be obtained.

The air electrode and the fuel electrode can be prepared by applying a catalyst paste containing a catalyst supported on a carrier made of acetylene black and the like and a binder such as PTFE resin and drying the gas diffusion layer.
The gas diffusion layer is preferably made of carbon paper subjected to water repellent treatment.
Any air electrode catalyst can be used, but platinum is preferred, and the supported amount of platinum fine particles can be appropriately selected within the range of 10 to 70% by weight.
Any fuel electrode catalyst can be used, but platinum-ruthenium is preferable, and the supported amount of platinum-ruthenium fine particles can be appropriately selected within the range of 10 to 70% by weight. The weight ratio of platinum: ruthenium is 5: It can select suitably in the range of 1-1: 2.

An example of a method for manufacturing the MEA is shown below.
A Nafion membrane (trade name: Nafion 117) manufactured by DuPont, which is a perfluorosulfonic acid electrolyte membrane, is used as the proton conductive polymer electrolyte membrane. In addition, an air electrode catalyst in which platinum fine particles are supported on a carbon powder made of acetylene black in a gas diffusion layer made of carbon paper impregnated with a PTFE solution and subjected to water repellency treatment (the content of platinum fine particles is 40% by weight). ), A catalyst paste obtained by mixing PTFE resin and Nafion solution (isopropanol solvent) and dried to obtain an air electrode. A fuel electrode catalyst in which platinum-ruthenium fine particles are supported on carbon powder made of acetylene black in the same gas diffusion layer (content of platinum-ruthenium fine particles is 40 wt%, platinum: ruthenium weight ratio is 2: 1), A fuel electrode is obtained by applying and drying a catalyst paste obtained by mixing PTFE resin and Nafion solution (isopropanol solvent). The air electrode 7 and the fuel electrode 6 thus produced are joined to both surfaces of the electrolyte membrane 8 by hot pressing to produce an MEA. Three MEAs are bonded using the bonding film 10, and three MEAs are connected in series using the bonding member 11.

An example of the structure of the fuel cell of the present invention incorporating the three MEAs (electrode-membrane assemblies) produced as described above is shown in FIG.
Three electrode-membrane assemblies 1 (fuel electrode 6, air electrode 7-electrolyte membrane 8 assembly) are formed on the same plane. The adjacent fuel electrode 6 and air electrode 7 of these three electrode-membrane assemblies 1 are joined using a joining membrane 10 and a joining member 11 and are connected in series. Fuel is supplied to the three fuel electrodes 6 configured on the same plane by the capillary body 5 from the same fuel storage unit 2 and covers the three air electrodes 7 configured on the same plane. 12, and air is supplied to the air electrode chamber 12 by a fan or blower 13.

A feature of the present invention is that an air electrode chamber 12 is formed so as to cover a plurality of air electrodes 7, and air is supplied to the air electrode chamber 12 from the outside using a fan or a blower 13.
As a result, the air electrode can be forced to introduce outside air by the fan or the blower 13, and a large output can be obtained as compared with the conventional example in which air is supplied by natural diffusion.
According to JIS (B0132), the fan has a pressure ratio of less than 1.1 or a discharge pressure of less than 10 kPa, and the blower has a pressure ratio of 1.1 to less than 2.0 or a discharge pressure of 10 kPa to less than 0.1 MPa. However, in the present invention, a fan is preferably used because it is mainly intended for small fuel cells.

  In addition, the air electrode chamber wall 14 for forming the air chamber can be made of an insulating material having no electrical conductivity. This is because the air is discharged by the conductive separator plate provided with the conventional flow path. It is very different from the supplied type.

FIG. 4 shows a structure in which valves 15 are provided at the inlet and outlet of the air electrode chamber 12.
With such a structure, when the fuel cell is not used, it is possible to prevent oxidation of methanol that has permeated the electrolyte membrane 8 by air by closing the valve 15 and prevent waste of fuel. can do. In addition, since there is no air circulation, the film can be prevented from drying when stored for a long period of time.

FIG. 5 shows a structure when the adsorption / decomposition processing filter 16 is provided at the outlet portion of the air electrode chamber 12, and FIG. 6 shows a structure when the adsorption / decomposition processing layer 17 is provided in the air electrode chamber 12.
In the present invention, such a structure can be adopted by configuring the air electrode chamber 12 and supplying air with a fan or blower 13, thereby removing harmful by-products generated from the air electrode 7. can do.
The removal method is not limited, and examples thereof include a method of adsorption using activated carbon, zeolite, etc., a method of oxidative decomposition using a noble metal catalyst, and a method of photolysis using a titanium oxide catalyst. .
However, in the photodecomposing method, the fuel cell is used in a place where light hits, and the case and the air electrode chamber must be translucent so that the catalyst portion is in direct contact with light.
In particular, among the above methods, the method of adsorption using activated carbon is a simple method and is preferable.

The carbon dioxide discharged from the fuel electrode 6 becomes bubbles in the liquid fuel and accumulates in the upper part of the fuel storage unit 2. Further, an exhaust port may be provided in the upper part of the fuel storage unit 2 to exhaust the carbon dioxide. . Further, if a water-repellent porous film such as Teflon (registered trademark) is provided at the exhaust port, there is an effect of preventing liquid fuel from leaking from the porous film part (exhaust port) 9.
The fuel storage unit 2 is provided with a fuel supply port 4 for replenishing fuel. Fuel can be replenished at low cost and safely by using a syringe-like syringe in the fuel supply port 4 made of a rubber member.

FIG. 7 shows the fuel cell of the present invention when placed horizontally.
In this case, the capillary body 5 is plate-shaped and has a portion protruding to the fuel storage unit 2. In particular, it is preferable to have a T-shaped cross section having a portion protruding to the fuel storage unit 2. If the cross section is T-shaped, the protruding portion does not need to be continuous, the central portion is separated and left and right connected, and carbon dioxide from the right to the left in FIG. It is more preferable to improve the circulation of the mouth 4 and the position of the porous membrane portion 9 that discharges carbon dioxide). As a result, even if the installation direction of the fuel cell is horizontal, fuel can be supplied to the plurality of fuel electrodes 6 from the same fuel storage unit 2 by the same capillary body 5.
The capillary body 5 may be any material that has a small contact angle with an aqueous methanol solution, is electrochemically inactive, and is corrosion-resistant, such as powder or fiber in the form of a plate (sheet, mat, or felt). It is molded into For example, fibers such as glass, alumina, silica-alumina, silica, non-graphitic carbon, and cellulose, and molded articles such as water-absorbing polymer fibers are preferable because they have a low filling density and are excellent in aqueous methanol retention.

In the present invention, as shown in FIG. 3, the plurality of electrode-membrane assemblies 1 (6, 7, 8) and the air electrode chambers 12 may be provided on both sides of the same fuel storage unit 2, respectively. In this case, it is preferable that the protruding portions of the capillary bodies 5 on both sides of the same fuel storage unit 2 are connected to each other and cross the fuel storage unit 2. In particular, it is preferable that the capillary body 5 has an H-shaped cross section having a portion that crosses the fuel storage portion 2. In this case, if the cross section is H-shaped, the protruding portion does not need to be continuous, and the vicinity of the center is separated and communicated vertically so that the flow of carbon dioxide from the bottom to the top is improved. Is more preferable. As a result, even if the installation direction of the fuel cell is horizontal, fuel can be supplied to the plurality of fuel electrodes 6 from the same fuel storage unit 2 by the same capillary body 5.
It should be noted that the portion of the capillary body 5 that protrudes into the fuel storage section 2 is preferably provided at a position where fuel can be supplied most effectively to the fuel electrode 6 and does not hinder the discharge of carbon dioxide. The shape is not limited.

FIG. 8 shows a structure when the fuel cell of the present invention is stacked in contact with the air electrode chamber 12.
A conventional fuel cell has a structure in which a plurality of monolithic cells (electrode-membrane assemblies) are attached to the wall surface of a fuel container (fuel storage unit), and power is generated by directly opening the air electrode to the atmosphere. For this reason, the laminated structure could not be adopted, but the fuel cell of the present invention can employ the laminated structure as described above, and therefore can effectively utilize the three-dimensional structure.
In this figure, although the fuel storage part 2 is comprised separately, it is also possible to join these and integrate a fuel storage part.

  FIG. 9 shows the appearance of the fuel cell according to the present invention, which is the most simplified structure.

  The structure of the direct liquid supply type fuel cell of the present invention is not limited to a direct methanol type fuel cell using methanol as a liquid fuel, but also to a fuel cell using an organic solvent such as ethyl alcohol, isopropyl alcohol, butanol, dimethyl ether and water. Can be applied.

It is a figure which shows the structure of the conventional direct liquid supply type fuel cell. It is sectional drawing of the conventional direct liquid supply type fuel cell. It is sectional drawing of the direct liquid supply type fuel cell of this invention. It is sectional drawing of the fuel cell of this invention which has a valve structure. It is sectional drawing of the fuel cell of this invention which provided the adsorption / decomposition process filter in the exit part of the air electrode chamber. It is sectional drawing of the fuel cell of this invention which provided the adsorption / decomposition process layer in the air electrode chamber. It is sectional drawing at the time of placing the fuel cell of this invention horizontally. It is sectional drawing at the time of laminating | stacking the fuel cell of this invention. It is an external view of the fuel cell of the present invention.

Explanation of symbols

1 MEA in which three electrode-membrane assemblies are connected in series
2 Fuel storage part 3 Air introduction plate 4 Fuel supply port 5 Capillary body 6 Fuel electrode 7 Air electrode 8 Electrolyte membrane 9 Porous film part 10 Joining film 11 Joining member 12 Air electrode chamber 13 Fan or blower 14 Air electrode chamber wall 15 Valve 16 Adsorption / decomposition filter 17 Adsorption / decomposition layer

Claims (13)

Direct liquid supply type fuel that supplies liquid fuel to the fuel electrode side of the electrode-membrane assembly in which a pair of air electrode and fuel electrode are joined via a proton conductive electrolyte membrane and supplies air to the air electrode side In batteries,
A plurality of electrode-membrane assemblies are configured on the same plane, and adjacent air electrodes and fuel electrodes of the plurality of electrode-membrane assemblies are connected in series or in parallel.
Fuel is supplied to the plurality of fuel electrodes configured on the same plane by the capillary body from the same fuel storage unit, and
A direct liquid supply type fuel cell, wherein an air electrode chamber is configured to cover a plurality of air electrodes configured on the same plane, and air is supplied to the air electrode chamber by a fan or a blower.   2. The direct liquid supply fuel cell according to claim 1, wherein the electrolyte membrane is a polymer membrane.   The direct liquid supply fuel cell according to claim 1 or 2, wherein the air electrode chamber wall constituting the air electrode chamber does not have conductivity.   The direct liquid supply type fuel cell according to any one of claims 1 to 3, wherein an inlet and an outlet of the air electrode chamber have a valve structure.   The adsorption | suction filter for adsorb | sucking the by-product from a battery or the decomposition process filter for decomposing | disassembling a by-product is provided in the exit part of the said air electrode chamber, The any one of Claims 1-4 characterized by the above-mentioned. A direct liquid supply fuel cell as described in 1.   The direct liquid supply according to any one of claims 1 to 5, wherein an adsorption layer for adsorbing a by-product or a decomposition treatment layer for decomposing the by-product is provided in the air electrode chamber. Fuel cell.   The fuel storage part is provided with a porous membrane part for allowing carbon dioxide generated by a cell reaction to escape outside the system, and a fuel supply port for replenishing fuel. The direct liquid supply fuel cell according to the item.   The direct liquid supply fuel cell according to any one of claims 1 to 7, wherein the capillary body has a plate-like shape and has a portion protruding to the fuel storage section.   9. The direct liquid supply fuel cell according to claim 8, wherein the capillary body has a T-shaped cross section having a portion protruding to the fuel storage section.   The direct liquid supply type fuel cell according to any one of claims 1 to 9, wherein the plurality of electrode-membrane assemblies and the air electrode chamber are respectively provided on both sides of the same fuel storage unit.   11. The direct liquid supply fuel cell according to claim 10, wherein portions of the capillary body on both sides of the same fuel storage portion projecting from the fuel storage portion are connected to each other so as to cross the fuel storage portion. .   12. The direct liquid supply type fuel cell according to claim 11, wherein the capillary body has an H-shaped cross section having a portion crossing the fuel storage portion. The direct liquid supply type fuel cell according to any one of claims 10 to 12, wherein the plurality of direct liquid supply type fuel cells are stacked in contact with an air electrode chamber.