JP2004206885A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell capable of suppressing a crossover. <P>SOLUTION: A fuel electrode 12 and an oxidant electrode 13 are provided through an electrolyte 11, with a fuel chamber 15 adjacent to the fuel electrode 12. The fuel chamber 15 contains a liquid fuel 15A such as methanol solution of water. On the fuel electrode 12 side of the fuel chamber 15, a holding body 15B of film-like polymer compound or porous substance is provided. The polymer compound dissolves or swells to be gelatinous in the liquid fuel 15A to hold the liquid fuel 15A. Thus, the liquid fuel 15A is suppressed from excessively supplied to the fuel electrode 12, resulting in preventing crossover. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel cell using a liquid fuel.
[0002]
[Prior art]
2. Description of the Related Art In recent years, fuel cells have attracted attention as an energy supply source that has high power generation efficiency, has a reaction product of only water (H ₂ O) in principle, and has excellent environmental properties. Depending on the type of electrolyte used, such fuel cells are broadly classified into low-temperature operating fuel cells such as alkaline type, solid polymer type, and phosphoric acid type, and high-temperature operating fuel cells of molten carbonate type and solid oxide type. . Above all, polymer electrolyte fuel cells (PEFCs) using solid polymer as the electrolyte have a compact structure, high density and high output, and can be operated with a simple system. It has been widely studied not only as a stationary power source but also as a power source for vehicles and the like, and is expected to be put to practical use.
[0003]
In addition, a direct methanol fuel cell (DMFC) that generates power by directly supplying a liquid such as an aqueous methanol solution to the fuel electrode as fuel for the fuel cell and supplying an oxidant gas (air) to the oxidant electrode (air electrode). : Direct Methanol Fuel Cells) is known (for example, see Patent Document 1). This direct methanol fuel cell has a structure in which an aqueous methanol solution reacts with water to obtain hydrogen ions, and the hydrogen ions move inside the proton-conducting ion exchange membrane, so that electric energy can be obtained outside. . In addition, direct methanol fuel cells can be used for direct power generation without reforming or gasifying fuel alcohol.Since the structure is simple and small and lightweight, it is easy to use for distributed power sources and portable power sources. It is attracting attention.
[0004]
[Patent Document 1]
JP 2000-502205 A [Patent Document 2]
JP 10-40936 A
[Problems to be solved by the invention]
However, in a direct methanol fuel cell, a phenomenon of crossover in which a fuel such as methanol permeates an electrolyte and moves to an oxidant electrode has been known, and there has been a problem that power generation efficiency is reduced due to this. In order to prevent this crossover, a method of providing an oxidation catalyst layer between the electrolytes for oxidizing methanol has been reported (for example, see Patent Document 2). It was difficult to prevent this, and further improvement was required.
[0006]
The present invention has been made in view of such a problem, and an object of the present invention is to provide a fuel cell capable of suppressing crossover.
[0007]
[Means for Solving the Problems]
A first fuel cell according to the present invention is provided with a fuel electrode and an oxidizer electrode via an electrolyte. The first fuel cell includes a fuel chamber adjacent to the fuel electrode. And a compound.
[0008]
In the first fuel cell according to the present invention, the liquid fuel is held by the polymer compound, and crossover is suppressed. The fuel chamber may have the polymer compound in the form of a film on the side of the fuel electrode, or may have the polymer compound as a whole. The liquid fuel preferably contains at least one of methanol, ethanol and dimethyl ether, or contains a polyhydric alcohol and an aqueous alkali solution. Further, the fuel chamber may be removable.
[0009]
A second fuel cell according to the present invention is provided with a fuel electrode and an oxidizer electrode via an electrolyte, and includes a fuel chamber adjacent to the fuel electrode, and the fuel chamber includes a liquid fuel, And a porous body entirely housed in the fuel chamber.
[0010]
In the second fuel cell according to the present invention, the liquid fuel is held by the porous body, and crossover is suppressed. The porous body may be provided on the fuel electrode side, or may be provided entirely. The liquid fuel preferably contains at least one of methanol, ethanol and dimethyl ether, or contains a polyhydric alcohol and an aqueous alkali solution. Further, the fuel chamber may be removable.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0012]
(First Embodiment)
FIG. 1 shows a configuration of a fuel cell according to a first embodiment of the present invention. This fuel cell has a fuel electrode 12 and an oxidant electrode 13 provided via an electrolyte 11. These electrolyte 11, fuel electrode 12 and oxidizer electrode 13 are housed inside an exterior member 14. Inside the exterior member 14, a fuel chamber 15 is provided adjacent to the fuel electrode 12, and an oxidant chamber 16 is provided adjacent to the oxidant electrode 13.
[0013]
The electrolyte 11 is composed of, for example, a proton conductive polymer membrane. Examples of the proton conductive polymer membrane include a perfluorocarbon polymer membrane having a sulfonic acid group (—SO ₃ H), a composite membrane in which proton conductive powder is dispersed in a resin, and a proton conductive inorganic membrane. A hybrid membrane obtained by synthesizing a material and a polymer material is exemplified. It is also possible to use a room temperature molten salt composite film in which a room temperature molten salt is dispersed in a polymer material.
[0014]
The fuel electrode 12 and the oxidant electrode 13 have a configuration in which, for example, a catalyst layer containing a catalyst such as platinum (Pt) or ruthenium (Ru) is formed on a current collector made of carbon paper or the like. The catalyst layer is made of, for example, a material in which carbon black supporting a catalyst is dispersed in a proton conductive material.
[0015]
The fuel chamber 15 is sealed and has a liquid fuel 15A. The liquid fuel 15A is injected into the fuel chamber 15 from an injection hole 14A provided in the exterior member 14, and a plug 14B is provided in the injection hole 14A. The injection hole 14A also has a function as an exhaust hole for discharging carbon dioxide (CO ₂ ) generated by the reaction from the fuel chamber 15 when the liquid fuel 15A is injected. The liquid fuel 15A preferably contains at least one of methanol, ethanol and dimethyl ether and water, or contains a polyhydric alcohol and an aqueous alkali solution. Examples of the polyhydric alcohol include ethylene glycol, glycerol, erythritol and xylitol, and ethylene glycol is particularly preferable. Examples of the alkaline aqueous solution include a potassium hydroxide aqueous solution and a potassium carbonate aqueous solution, and potassium hydroxide is particularly preferred.
[0016]
The fuel chamber 15 also has a holder 15B made of a film-like polymer compound or a porous body on the side of the fuel electrode 12. The holder 15B is for suppressing crossover by holding the liquid fuel 15A. It is preferable that the holder 15B be entirely housed in the fuel chamber 15 adjacent to the fuel electrode 12. The term “adjacent” in this case is not limited to the case where the liquid fuel 15A is completely in contact with the fuel electrode 12, but may be a gap where the movement of the liquid fuel 15A to the fuel electrode 12 can be controlled. The holder 15B is preferably provided corresponding to the entire surface of the fuel electrode 12, but may be provided corresponding to a part.
[0017]
The high molecular compound forming the support 15B is preferably a compound that dissolves or swells in the liquid fuel and has high stability in a liquid absorbing state due to affinity with the liquid fuel. Dissolution or swelling in liquid fuel may be in water, in organic compounds, or both. Thereby, the polymer compound is in a so-called gel state while holding the liquid fuel. The polymer compound may or may not be crosslinked, and has a molecular weight of 10,000 or more, particularly preferably 100,000 or more. If the molecular weight is small, sufficient viscosity cannot be obtained, and crossover cannot be sufficiently suppressed.
[0018]
Further, the polymer compound may be any of nonionic, cationic or anionic, but nonionic is preferred. In the case of an anionic polymer compound, an ion of the anionic polymer compound, for example, a sodium ion (Na ⁺ ) is bonded to a proton conductive polymer material, for example, a perfluorocarbon polymer having a sulfonic acid group, and the proton conductive polymer This is because the properties may be reduced. Also, in the case of a cationic polymer compound, for example, halide ions such as chloride ions (Cl ⁻ ) may react with protons (H ⁺ ) and elute, thereby lowering power generation efficiency. is there.
[0019]
Specific examples of such a polymer compound include, for example, polyvinyl alcohol, poly-2-hydroxyethyl methacrylate, poly-2-hydroxyethyl acrylate, polyethylene glycol, polyvinyl methyl ether, polyvinyl pyrrolidone, polyacrylamide, polydimethylacrylamide, Examples thereof include poly-N-vinyl acedamide and a copolymer thereof. However, when the liquid fuel contains a polyhydric alcohol and an aqueous alkali solution, a polymer compound having no alkali resistance, for example, poly-2-hydroxyethyl methacrylate, poly-2-hydroxyethyl acrylate, polyacrylamide, polydimethylacrylamide Are excluded.
[0020]
As the porous body, for example, a resin microporous member or a sponge-like member, or a synthetic resin nonwoven fabric is preferable. The constituent material is not particularly limited as long as it has solvent resistance, water resistance, chemical resistance, and heat resistance for satisfying the operating temperature and conditions of the fuel cell. Preferred materials include, for example, fluororesins such as polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polysulfone, and polyetheretherketone. However, when the liquid fuel contains a polyhydric alcohol and an aqueous alkali solution, a resin having no alkali resistance, for example, polyimide is excluded.
[0021]
The oxidizing agent chamber 16 communicates with the outside through a flow hole 14C provided in the exterior member 14, so that air can be supplied to the oxidizing electrode 13 by natural ventilation.
[0022]
In this fuel cell, the liquid fuel 15A in the fuel chamber 15 is supplied to the fuel electrode 12 through the holder 15B, and generates carbon dioxide, protons, and electrons by a reaction. Protons move to the oxidant electrode 13 through the electrolyte 11 and react with electrons and oxygen (O ₂ ) in the air supplied from the oxidant chamber 16 to generate water. At this time, in the fuel chamber 15, the liquid fuel 15A is held by the holder 15B, so that the supply of the liquid fuel 15A to the fuel electrode 12 more than necessary is suppressed, and crossover is suppressed.
[0023]
As described above, according to the present embodiment, since the fuel chamber 15 has the holder 15B made of a polymer compound or a porous body, the liquid fuel 15A can be held by the holder 15B, and the fuel electrode 12 can be prevented from being excessively supplied with the liquid fuel 15A. Therefore, crossover can be suppressed, power generation efficiency can be improved, and stability can be improved.
[0024]
Further, according to this fuel cell, the structure for suppressing crossover is simple, the size and weight can be easily reduced, and the fuel chamber 15 can be easily refilled with the liquid fuel 15A. It can be used as a power source.
[0025]
(Second embodiment)
FIG. 2 shows a configuration of a fuel cell according to a second embodiment of the present invention. This fuel cell has the same configuration as that of the first embodiment except that the holder 25B is provided in the entire fuel chamber 15. Therefore, the same components as those of the first embodiment are denoted by the same reference numerals, and the detailed description is omitted.
[0026]
This fuel cell operates in the same manner as the first embodiment and has the same effect. Furthermore, according to this fuel cell, since the holder 25B is provided in the entire fuel chamber 15, leakage of the liquid fuel 15A can be prevented.
[0027]
(Third embodiment)
FIG. 3 shows a configuration of a fuel cell according to a third embodiment of the present invention. This fuel cell has the same configuration, operation and effect as the first embodiment, except that the fuel chamber 35 is not sealed. Therefore, the same components as those of the first embodiment are denoted by the same reference numerals, and the detailed description is omitted.
[0028]
The exterior member 34 is provided with a flow hole 34A for supplying the liquid fuel 15A to the fuel chamber 35 and discharging generated carbon dioxide, instead of the injection hole 14A. The flow hole 34A is connected to a fuel storage unit (not shown) provided separately from the fuel chamber 35, and the liquid fuel 15A is supplied from the fuel storage unit to the fuel chamber 35 by a pump (not shown). .
[0029]
In the fuel cell according to the second embodiment, as shown in FIG. 4, a fuel storage unit (not shown) is connected to the fuel chamber 35, and the liquid fuel 15A is transferred from the fuel storage unit by a pump (not shown). You may make it supply. At this time, when a polymer compound is used for the holder 25B, the liquid fuel 15A may be supplied from the fuel storage unit. However, a gel-like liquid containing the polymer compound holder 25B and the liquid fuel 15A may be used. A fuel mixture may be supplied.
[0030]
(Fourth embodiment)
FIG. 5 shows a configuration of a fuel cell according to a fourth embodiment of the present invention. This fuel cell has the same configuration, operation, and effect as the second embodiment except that the fuel chamber 45 is detachable from the fuel electrode 12. Therefore, the same components as those of the second embodiment are denoted by the same reference numerals, and the detailed description will be omitted.
[0031]
In this fuel cell, the exterior member 44 can be divided into a main body 44A and a cartridge portion 44B. An engaging portion 44C is provided at a joint between the main body 44A and the cartridge portion 44B, and the main body 44A and the cartridge portion 44B can be integrated by fitting them. The fuel electrode 12, the electrolyte 11, the oxidant electrode 13, and the oxidant chamber 16 are provided inside the main body 44A, and the fuel electrode 12 is exposed at the junction of the main body 44A with the cartridge portion 44B.
[0032]
A fuel chamber 45 is provided inside the cartridge portion 44B, and a support film 47 for supporting the holder 25B is provided at a joint portion of the cartridge portion 44B with the main body 44A. The support film 47 is provided with an opening 47A for bringing the holder 25B into contact with the fuel electrode 12 and supplying the liquid fuel 15A to the fuel electrode 12. The support film 47 is preferably made of a mesh body made of, for example, a resin or metal, and particularly preferably made of a fluorine-based resin having excellent acid resistance, alkali resistance, and solvent resistance. The holding body 25B is prepared so as to have a holding force that does not allow the liquid fuel 15A to leak from the fuel chamber 45. This is to prevent the liquid fuel 15A from leaking when the cartridge section 44B is removed.
[0033]
As described above, according to the present embodiment, the cartridge portion 44B having the fuel chamber 45 is separated from the main body 44A so as to be removable, so that the cartridge portion 44B is replaced or removed to remove the liquid fuel 15A. The liquid fuel 15A can be easily refilled simply by injection, and can be used as a portable power source.
[0034]
【Example】
Further, specific examples of the present invention will be described.
[0035]
(Example 1)
A fuel cell as shown in FIG. 2 was manufactured. First, 5% by mass of a resin of a nonionic water-absorbing agent as a support 15B was dissolved in a 1 mol / l aqueous methanol solution as a liquid fuel 15A to prepare a gel fuel mixture. Next, a perfluorocarbon polymer having a sulfonic acid group was dissolved in an ethanol solution at a content of 20% by mass, and a mixture of platinum and ruthenium in a mass ratio of Pt / Ru = 56/44 was added to this mixed solution. The fuel electrode 12 having a catalyst layer was produced by carrying 33% by mass of carbon black and dispersing it, applying it on carbon paper having a thickness of 200 μm, and drying it. Subsequently, carbon black carrying 50% by mass of platinum is dispersed in a mixed solution similar to that of the fuel electrode 12, which is coated on a 200 μm-thick carbon paper and dried to form an oxidant electrode having a catalyst layer. 13 was produced.
[0036]
Next, a 50 μm-thick perfluorocarbon polymer film having a sulfonic acid group is used as the electrolyte 11, and the fuel electrode 12, the electrolyte 11, and the oxidizer electrode 13 are stacked so that the catalyst layer is in contact with the electrolyte 11, It was incorporated into a cell for battery performance measurement. After that, the above gel-like fuel mixture was introduced into the fuel chamber 15 at room temperature to produce a fuel cell. When the open circuit voltage was measured for the manufactured fuel cell, the open circuit voltage was 0.49 V and was stable thereafter.
[0037]
(Example 2)
A fuel cell was obtained in the same manner as in Example 1, except that a porous body made of polyvinylidene fluoride was used as the support 15B. When the open circuit voltage of the fuel cell of Example 2 was measured, the open circuit voltage was 0.49 V and was stable thereafter.
[0038]
(Comparative example)
A fuel cell was obtained in the same manner as in Example 1, except that only the 1 mol / l aqueous methanol solution was injected into the fuel chamber without using the holder 15B. When the open circuit voltage of the fuel cell of Comparative Example 1 was also measured, the open circuit voltage was 0.49 V, and the voltage gradually decreased thereafter.
[0039]
Comparing the above results, the current and voltage characteristics of Examples 1 and 2 and the comparative example are almost the same, and there is no difference in the output characteristics. However, in Examples 1 and 2, the open circuit voltage is stable. On the other hand, in the comparative example, a decrease in the open circuit voltage was observed. This is probably due to crossover. That is, it was found that if the polymer chamber or the porous body holding the liquid fuel 15A is provided in the fuel chamber 15, the crossover can be suppressed and the stability can be improved.
[0040]
Note that, in the above-described example, the result using the aqueous methanol solution as the liquid fuel 15A was shown, but similar results were obtained when ethanol and dimethyl ether were used. Similar results were obtained when a liquid fuel 15A containing 1 mol / l ethylene glycol and 1 mol / l aqueous potassium hydroxide was used. Here, when a liquid fuel 15A containing a polyhydric alcohol and an aqueous alkali solution is used, a hydrocarbon-based anion exchange membrane can be used as the electrolyte 11 in addition to the perfluorocarbon polymer membrane.
[0041]
As described above, the present invention has been described with reference to the embodiment and the example. However, the present invention is not limited to the above-described embodiment and example, and can be variously modified. For example, in the above-described embodiments and examples, the configurations of the electrolyte 11, the fuel electrode 12, and the oxidizer electrode 13 have been specifically described. However, the configuration may be made of another structure or another material.
[0042]
Further, in the above-described embodiment and examples, the supply of air to the oxidant electrode 13 is performed by natural ventilation. However, the supply may be forcibly supplied using a pump or the like. In that case, an oxidizing gas containing oxygen other than air may be supplied.
[0043]
Furthermore, in the above embodiments and examples, a single-cell fuel cell has been described, but the present invention can also be applied to a stacked fuel cell in which a plurality of cells are stacked.
[0044]
【The invention's effect】
As described above, according to the fuel cell of the present invention, since the polymer chamber or the porous body is provided in the fuel chamber, the liquid fuel can be held by these, and the liquid fuel becomes excessive in the fuel electrode. Can be suppressed. Therefore, crossover can be suppressed, power generation efficiency can be improved, and stability can be improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a configuration of a fuel cell according to a first embodiment of the present invention.
FIG. 2 is a sectional view illustrating a configuration of a fuel cell according to a second embodiment of the present invention.
FIG. 3 is a cross-sectional view illustrating a configuration of a fuel cell according to a third embodiment of the present invention.
FIG. 4 is a cross-sectional view illustrating a configuration of another fuel cell according to a third embodiment of the present invention.
FIG. 5 is a sectional view illustrating a configuration of a fuel cell according to a fourth embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Electrolyte, 12 ... Fuel electrode, 13 ... Oxidizer electrode, 14, 34, 44 ... Exterior member, 14A ... Injection hole, 14B ... Plug, 14C, 34A ... Flow hole, 15, 35, 45 ... Fuel chamber, 15A ... liquid fuel, 15B, 25B ... holder, 16 ... oxidant chamber, 44A ... main body, 44B ... cartridge part, 44C ... locking part, 47 ... support film, 47A ... opening.

Claims (9)

A fuel cell provided with a fuel electrode and an oxidizer electrode via an electrolyte,
A fuel chamber is provided adjacent to the fuel electrode,
A fuel cell comprising a liquid fuel and a polymer compound in the fuel chamber. The fuel cell according to claim 1, further comprising a film-like polymer compound on the fuel electrode side of the fuel chamber. 2. The fuel cell according to claim 1, wherein the entire fuel chamber contains a polymer compound. A fuel cell provided with a fuel electrode and an oxidizer electrode via an electrolyte,
A fuel chamber is provided adjacent to the fuel electrode,
A fuel cell comprising: a liquid fuel in the fuel chamber; and a porous body entirely housed in the fuel chamber. The fuel cell according to claim 4, wherein a porous body is provided on the fuel electrode side of the fuel chamber. The fuel cell according to claim 4, wherein a porous body is provided in the entire fuel chamber. 7. The fuel cell according to claim 1, wherein the liquid fuel contains at least one of methanol, ethanol, and dimethyl ether. 7. The fuel cell according to claim 1, wherein the liquid fuel includes a polyhydric alcohol and an aqueous alkaline solution. The fuel cell according to any one of claims 1 to 8, wherein the fuel chamber is removable.

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