JP2008097985A - Direct methanol type fuel battery system and portable electronic equipment using this - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a direct methanol type fuel battery system supplying methanol capable of adjusting supply speed of methanol as gas, with the use of solid methanol extremely safe in a fuel cartridge state. <P>SOLUTION: The direct methanol type fuel battery system is provided with a carrier gas source 1 equipped with a compressed-air cylinder of nitrogen gas (N<SB>2</SB>), a solid methanol fuel cartridge 3, and a fuel battery cell 5. The carrier gas source 1 and the solid methanol fuel cartridge 3 are communicated with each other through a carrier gas supply channel 2, and at the same time, the solid methanol fuel cartridge 3 and the fuel battery cell 5 are communicated with each other through a fuel gas circulation channel 4. The fuel battery cell 5 consists of a fuel electrode 6, a solid polymer electrolyte film 7, and an air electrode 8, and the fuel electrode 6 is tightly sealed in a cover 5A where the fuel gas circulation channel 4 and an exhaust gas circulation channel 9 are communicated with each other. The solid methanol fuel cartridge 3 is made by filling a film-forming solid methanol inside. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a direct methanol fuel cell system using solid methanol as a fuel, and more particularly to a direct methanol fuel cell system suitable for small portable electronic devices.

  A solid polymer electrolyte fuel cell has a solid electrolyte membrane such as a perfluorosulfonic acid membrane as an electrolyte, and a fuel electrode (anode) and an oxidant electrode (cathode) are joined to both sides of the membrane, and hydrogen is connected to the anode. It is a device that generates electricity through an electrochemical reaction by supplying oxygen to methanol and cathode. Among these, a solid polymer electrolyte fuel cell using methanol as a fuel is called a “direct methanol fuel cell (DMFC)”, and power is generated by the following reaction formula.

Anode: CH ₃ OH + H ₂ O → 6H ⁺ + CO ₂ + 6e ⁻ ... [1]
Cathode: 3/2 O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O [2]
In order to cause this reaction, both electrodes are composed of a mixture of carbon fine particles carrying a catalyst material and a solid polymer electrolyte.

  In such a direct methanol fuel cell, the methanol supplied to the anode passes through the pores in the electrode and reaches the catalyst. The methanol is decomposed by this catalyst, and the electrons in the reaction of the above reaction formula [1]. And hydrogen ions. The hydrogen ions reach the cathode through the electrolyte in the anode and the solid electrolyte membrane between the two electrodes, react with oxygen supplied to the cathode and electrons flowing from the external circuit, and water as shown in the above reaction formula [2]. Produce. On the other hand, electrons emitted from methanol are led to the external circuit through the catalyst carrier in the anode, and flow into the cathode from the external circuit. As a result, in the external circuit, electrons flow from the anode to the cathode and electric power is taken out.

  The direct methanol fuel cell using methanol as a fuel is useful as a small power source for portable electronic devices because it has a low operating temperature and does not require a large auxiliary machine. Development has been activated as a next-generation power source.

  On the other hand, since methanol used for fuel is liquid, it easily leaks, and there are concerns about the flammability and toxicity of methanol itself, and measures for safe use have become issues. Furthermore, the disadvantages of using liquid fuel are the degradation of fuel cell performance due to the impurities dissolved in the liquid fuel being supplied to the fuel cell, and methanol, which is a liquid fuel component, permeates the electrolyte membrane of the fuel cell. And a crossover phenomenon that reaches the air electrode. In particular, when crossover occurs, not only the power generation efficiency per unit volume of the fuel decreases, but also the generation of harmful substances such as formaldehyde, formic acid, methyl formate, etc. generated in the oxidation process at the air electrode, this is solved. This is a major issue in the practical application of direct methanol fuel cells.

  As a direct methanol fuel cell system that has been developed in recent years, in order to improve the volume density of the fuel, a method of applying a higher concentration of methanol is the mainstream, but the problem of crossover becomes higher as the fuel concentration becomes higher. Becomes more serious. Therefore, it has been studied to reduce the crossover by improving the materials such as the electrolyte membrane used in the cell, but it has not yet reached a sufficient level, and this is a direct methanol fuel cell. It is a big barrier to commercialization.

Therefore, in order to solve such problems such as the safety of methanol, the present applicant has variously reported about "solid methanol fuel" which solidifies methanol by forming a molecular compound, makes it difficult to leak and greatly reduces flammability. Proposed (see Patent Documents 1 to 3). When this solid methanol comes into contact with water, the methanol in the solid is released to the water side. The aqueous methanol solution thus produced can be used directly as a fuel for a methanol fuel cell.
JP 2006-040629 A JP 2005-325254 A International Publication No. 2005/0624210 Pamphlet

  However, the method of use proposed in Patent Documents 1 to 3 is to extract methanol by bringing solid methanol into contact with water to produce an aqueous methanol solution, which is supplied to the fuel cell. . Therefore, the fuel cell system has problems such as leakage of methanol aqueous solution and crossover as in liquid fuel. In addition, this water supply system requires a water supply mechanism such as a water tank and a pump, but it is preferable that the apparatus has a simple device structure that does not require these to be applied to a portable electronic device or the like.

  On the other hand, low output of direct methanol fuel cells is an issue, and at present, secondary methanol batteries that can be charged with direct methanol fuel cells are not operated directly with direct methanol fuel cells. However, there is a demand for a function that directly operates a methanol fuel cell under the most efficient conditions and charges the secondary battery stably.

  Therefore, there is a demand for a direct methanol fuel cell system in which methanol is extracted from solid methanol as a gas and supplied. However, this method tends to lack sufficient water equivalent to methanol at the anode. There has been a demand for a direct methanol fuel cell capable of continuing the above.

  In order to realize the functions described above, it is required to supply methanol so that the direct methanol fuel cell can generate power most efficiently, that is, to maintain the methanol supply rate appropriately. Conventionally, however, it has been very difficult to optimize the methanol release rate.

  The present invention has been made in view of the above problems, and uses solid methanol, which is very safe in the state of a fuel cartridge, and solves the problems of liquid leakage and crossover when using liquid fuel as a system. In addition, an object of the present invention is to provide a direct methanol fuel cell system that supplies methanol as a gas capable of adjusting the supply rate of methanol. Another object of the present invention is to provide a portable electronic device using the direct methanol fuel cell system.

  In order to solve the above-described problems, the present invention provides a fuel containing portion containing solid methanol obtained by solidifying methanol, a fuel cell, and a fuel containing methanol vaporized from the solid methanol by circulation of a carrier gas. There is provided a direct methanol fuel cell system comprising a fuel gas supply means for supplying gas to the fuel cell, wherein a coating is formed on the surface of the solid methanol.

  According to the above invention (invention 1), when gas is supplied to the solid methanol in the fuel storage portion by the fuel gas supply means, in the solid methanol having a film formed, the methanol is a molecule such as an inclusion phenomenon inside the material. Since it is gently restrained by the interstitial force, it does not vaporize at once, gradually vaporizes at a vaporization rate according to the performance of the coating, and the fuel gas containing this is supplied to the fuel electrode of the fuel cell, The vaporized methanol is decomposed on the fuel electrode catalyst to generate power.

  At this time, in order to generate power in the fuel cell, it is necessary to supply the same amount of water as methanol to the fuel electrode, but the reaction proceeds by utilizing the water originally retained in the electrolyte membrane at the start of power generation. However, as the reaction proceeds, water generated at the air electrode reversely osmosis through the electrolyte membrane and is supplied to the fuel electrode. Therefore, power generation occurs without supplying water. And by continuing supply of this carrier gas, methanol is replenished to a fuel electrode, and electric power generation is continued.

  The vaporization rate of methanol from the solid methanol on which the film is formed can be controlled by changing the type and thickness of the film formed on the surface of the solid methanol, and thereby the methanol to the fuel cell. It becomes possible to control the supply conditions of the optimal.

  That is, as the film thickness increases, not only the methanol vaporization rate is suppressed, but also the methanol vaporization rate can be suppressed by the material forming the film. Therefore, a film that optimizes the methanol vaporization rate may be formed in consideration of the use environment and output. This coating must be easily soluble in methanol.

  In the above invention (invention 1), the fuel accommodating portion is provided with a carrier gas supply passage communicating with the carrier gas supply means and a fuel gas flow passage communicating with the fuel electrode side of the fuel cell. The fuel battery cell is provided with an exhaust gas flow path in communication with the fuel electrode side. When a carrier gas is supplied to the fuel storage portion, the fuel cell is vaporized from the solid methanol having a film formed thereon. It is preferable that the fuel gas containing methanol is discharged from the exhaust gas passage after being supplied to the fuel electrode of the fuel cell.

  According to the above invention (invention 2), when the carrier gas is supplied to the fuel storage portion by a blower such as a gas cylinder, a pump, or a blower, the solid methanol having a film (hereinafter referred to as a film-forming solid methanol) Methanol is gently constrained by intermolecular forces such as clathrate inside the material, so it does not vaporize at once, but gradually vaporizes at a vaporization rate according to the performance of the coating, and a fuel gas containing this Is supplied to the fuel electrode of the fuel cell, and the vaporized methanol is decomposed on the catalyst of the fuel electrode, thereby generating electric power.

  And by continuing supply of this carrier gas, while a fuel electrode is replenished with methanol and electric power generation is continued, excess methanol is discharged | emitted from an exhaust gas flow path. Thus, since excess methanol is not supplied to a fuel electrode, it can be set as the direct methanol fuel cell system by which problems, such as crossover and a liquid leak, were solved.

  In the said invention (invention 2), the said carrier gas supply means may be a ventilation means (invention 3), and may be a compressed gas cylinder (invention 4). Furthermore, the carrier gas supply means may include a heating device and a substance that generates gas by heating. As described above, various carrier gas supply means can be adopted according to the situation of the equipment that employs the system.

  Moreover, in the said invention (invention 1), the said fuel accommodating part has the carrier gas supply path connected to the said carrier gas circulation means, and the fuel gas flow path connected to the fuel electrode side of the said fuel cell. The fuel battery cell is provided with a circulation flow path that communicates with the fuel electrode side and communicates with the carrier gas circulation means, and passes through the carrier gas supply path from the carrier gas circulation means. When a carrier gas is supplied to the fuel storage portion, a fuel gas containing methanol vaporized from the solid methanol having a film is supplied to the fuel electrode of the fuel cell, and then the carrier gas is supplied from the circulation channel. It is preferable to recirculate to the circulation means (claim 6).

  According to the above invention (invention 6), when the carrier gas is introduced into the circulation flow path, and the carrier gas is circulated by the carrier gas circulation means such as a pump and supplied to the fuel storage unit, Is gently restrained by intermolecular forces such as the inclusion phenomenon within the material, so it will not vaporize at once, but will gradually vaporize at a vaporization rate according to the performance of the coating, and the fuel gas containing this will be The fuel cell is supplied to the fuel electrode, and the vaporized methanol is decomposed on the catalyst of the fuel electrode to generate power.

  Then, by continuing the supply of the carrier gas, the fuel electrode is replenished with methanol and power generation is continued. On the other hand, excess methanol is recirculated from the circulation flow path to the carrier gas circulation means and reused. . Thus, since excess methanol is not supplied to a fuel electrode, it can be set as the direct methanol fuel cell system by which problems, such as crossover and a liquid leak, were solved. In addition, since the carrier gas is circulated and used, it is not necessary to separately provide a gas cylinder or the like, and it is possible to effectively use methanol contained in the film-forming solid methanol.

  In the said invention (invention 1-6), it is preferable that the said fuel accommodating part is a detachable cartridge (invention 7). According to this invention (invention 7), when the amount of methanol contained in solid methanol decreases, the methanol concentration in the fuel gas decreases, and the output of the fuel cell decreases, the cartridge can be replaced. Can be used again in good condition.

  In the said invention (invention 1-7), it is preferable that the carrier gas supplied to the fuel electrode of the said fuel cell does not contain oxygen substantially (invention 8). According to this invention (invention 8), it is possible to prevent the generation of harmful substances such as formaldehyde, formic acid and methyl formate due to the oxidation of methanol, and also prevent the generation of heat and the consumption of methanol due to the oxidation of methanol. Can do.

  In the said invention (invention 1-8), it is preferable that the said solid methanol is what solidified methanol aqueous solution (invention 9). Moreover, in the said invention (invention 1-8), the said fuel accommodating part shall contain a water-containing solid material with the said solid methanol (invention 10). Furthermore, in the said invention (invention 1-8), it is preferable to provide the rehydration container containing a water-containing solid material between the said fuel accommodating part and the said fuel cell (invention 11).

  As described above, the reaction proceeds by using the water originally retained in the electrolyte membrane at the start of power generation, and as the reaction proceeds, the water generated at the air electrode reversely permeates the electrolyte membrane and supplies it to the fuel electrode. Therefore, power generation occurs even if water is not supplied, but when water consumption is high, that is, when the output of the fuel cell is increased, if the operation is continued in such a state, the electrolyte membrane is removed from the air electrode. Moisture is insufficient with only the moisture that is reverse osmosis and supplied to the fuel electrode or the humidity in the air, and the output may decrease over time. This is considered to be caused by the fact that when the water in the fuel electrode is insufficient, not only the water necessary for the reaction cannot be supplied, but also the electrical conductivity of the electrolyte membrane decreases.

  Then, according to the said invention (Claims 9-11), since water is also made into solid state with methanol, even if water as a liquid does not exist in a system, methanol and water evaporate, electrolyte can be obtained. Moisture required for the wetting and reaction can be supplied, and stable power generation can be performed.

  Moreover, this invention provides the portable electronic device characterized by including the direct methanol fuel cell system of the said invention (Invention 1-11) (Invention 12). According to this invention (Claim 12), problems such as crossover and liquid leakage are improved, power can be generated efficiently, and stable operation can be achieved by using a compact direct methanol fuel cell system. Portable electronic devices.

  ADVANTAGE OF THE INVENTION According to this invention, problems, such as a crossover and a liquid leak, are improved, the supply rate of methanol can be adjusted, and the direct methanol fuel cell system which can produce electric power efficiently can be provided. In addition, since it is not necessary to provide a device such as a water supply means, the direct methanol fuel cell system can be made compact.

Hereinafter, a direct methanol fuel cell system according to an embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a flowchart showing a direct methanol fuel cell system according to this embodiment, and FIG. 2 is a cross-sectional view showing a solid methanol container in the direct methanol fuel cell system according to this embodiment.

As shown in FIGS. 1 and 2, the direct methanol fuel cell system of the present embodiment includes a carrier having a compressed gas cylinder of nitrogen gas (N ₂ ) serving as carrier gas supply means so that oxygen is not supplied to the fuel electrode. A gas source 1, a solid methanol fuel cartridge 3 serving as a fuel storage unit, and a fuel cell 5 are provided. The carrier gas source 1 and the solid methanol fuel cartridge 3 communicate with each other through a carrier gas supply path 2. The solid methanol fuel cartridge 3 and the fuel battery cell 5 communicate with each other through a fuel gas flow passage 4.

  The fuel cell 5 includes a fuel electrode 6, a solid polymer electrolyte membrane 7, and an air electrode 8. The fuel electrode 6 is disposed in a cover 5A in which the fuel gas flow path 4 and the exhaust gas flow path 9 communicate with each other. While being sealed, the air electrode 8 is open to the atmosphere.

  In such a direct methanol fuel cell system, the solid methanol fuel cartridge 3 is provided with a partition wall 3B so as to form a bent channel in the box-shaped casing 3A as shown in FIG. A film-forming solid methanol S is filled. Then, one side (the upper side in the figure) partitioned by the partition wall 3B is connected to the carrier gas supply path 2, and the other side (the lower side in the figure) is connected to the fuel gas flow path 4, so that the carrier gas is The film-forming solid methanol S passes while being in sufficient contact.

In the direct methanol fuel cell system as described above, nitrogen gas (N ₂ ) is used as a carrier gas in the present embodiment. However, the present invention is not limited to this, and an inert gas such as Ar, CO ₂ or the like is supplied. May be.

  The film-forming solid methanol S is formed by coating the surface of solid methanol to form a film and adjusting the vaporization temperature of methanol. This solid methanol includes methanol molecular compounds including methanol clathrate, methanol solidified with a polymer or gelled with dibenzylidene-D-sorbitol, etc., and methanol by adsorption on a porous material. It is possible to use solids obtained by holding methanol on various base materials, such as those made solid by holding.

  A molecular compound is a compound in which two or more kinds of compounds that can exist stably alone are bonded by a relatively weak interaction other than a covalent bond, such as a hydrogen bond or van der Waals force. Hydrates, solvates, addition compounds, inclusion compounds and the like.

  Such a molecular compound can be formed by a contact reaction between a compound that forms the molecular compound and methanol, can convert methanol into a solid compound, and can store methanol in a relatively lightweight and stable manner. Can do. In particular, an inclusion compound in which methanol is included by a reaction between a host compound and methanol is preferable.

  In these, since it is easy to form a film, what solidified by hold | maintaining methanol by adsorption | suction etc. to an inorganic porous material is preferable. The porous material can take in methanol by contact with methanol, and can mold this into a desired shape.

  The porous material has irregularities in the surface shape, and has pores in which the depth of the recesses is larger than the pore diameter. The pore diameter of the pores of the porous material is not particularly limited as long as the methanol component can enter the pores and can be retained in the pores. The porous material has a pore diameter of 0.5 nm. As long as it has pores that are classified into ultra-micro pores having a pore diameter of 0.5 nm or more and less than 2 nm, mesopores having a pore diameter of 2 nm or more and less than 50 nm, or macropores having a pore diameter of 50 nm or more. If it has a pore with such a pore size, methanol can be effectively retained. Moreover, it is preferable that the specific surface area of a porous material is 100-1500 m <2> / g, and it is preferable that the bulk specific volume (tap) of a porous material is 2.0-20 mL / g.

  Examples of the shape of the porous material include powder, particles, fibers, films, and pellets. As the raw material that forms the basis for forming the porous material, an organic substance, an inorganic substance, or a composite thereof can be used.

  Examples of such porous materials include silica gel, powder silica, zeolite, activated alumina, magnesium metasilicate aluminate, activated carbon, molecular sieve, carbon, carbon fiber, activated clay, bone charcoal, porous glass; anodized aluminum material Fine powders composed of inorganic oxides such as calcium oxide, titanium oxide and calcium oxide; Perovsky type oxide minerals such as calcium titanate and sodium niobate; Clay minerals such as sepiolite, kaolinite, montmorillonite and saponite; Synthetic adsorption of ion exchange resins Examples thereof include resins. These porous materials may be used individually by 1 type, and 2 or more types may be mixed and used for them. These porous materials can also be used as a host for an inclusion compound.

  Of these porous materials, it is preferable to use magnesium aluminate metasilicate. Magnesium aluminate metasilicate is suitable for use in products that require compactness, such as direct methanol fuel cells, because the bulk specific volume can be reduced depending on the production method. In addition, since magnesium aluminate metasilicate is a material that is also used as a raw material for gastrointestinal preparations, it can be suitably used from the viewpoint of safety to the human body.

  As the porous material, a material in which water is taken together with methanol may be used as solid methanol. Solid methanol obtained by incorporating water and methanol into the porous material is methanol as a binary component of water and methanol, so methanol is porous as a single component system of methanol only. The vapor pressure is lower than when taken into the material, and the flash point and ignition point rise. On the other hand, since water is vaporized together with methanol, both methanol and water are supplied to the fuel electrode 2.

  The amount of water used for incorporating methanol and water into the porous material may be small, specifically, 0.01 to 1 part by mass of water may be added to 1 part by mass of methanol. . When water is taken into the porous material together with methanol, water may be taken into the porous material into which methanol has been taken in, or an aqueous solution of methanol may be taken into the porous material.

  The method for incorporating methanol into the porous material is not particularly limited. For example, methanol is incorporated into the porous material by adding the porous material to methanol (including an aqueous solution) and stirring sufficiently. Solid methanol can be produced. In this case, it is preferable that the compounding quantity of a porous material is 0.2-1 mass part with respect to 1 mass part of methanol. If the blending amount of the porous material is within the above range, methanol can be taken up effectively, and solid methanol obtained by taking methanol into the porous material can be effectively molded.

  The temperature conditions and pressure conditions for incorporating methanol into the porous material are not particularly limited, and methanol may be incorporated into the porous material at room temperature and normal pressure. By mixing methanol and a porous material under normal temperature and normal pressure, and sufficiently stirring, solid methanol in which methanol is taken into the porous material can be produced. In addition, when using gaseous fuel as methanol, it is preferable to make methanol take in a porous material under pressure.

  The obtained solid methanol is formed into a certain shape. Thereby, a molded body of solid methanol can be obtained. The shape may be any shape that is suitable for a fuel cell using methanol. For example, it may be a solid shape such as a spherical shape, a square shape, or a cylindrical shape, or may be a thin film shape or a fibrous shape. . Of these, a spherical shape is preferable. The method for forming the obtained solid methanol is not particularly limited, and examples thereof include a method for forming the solid methanol into a spherical shape using a binder or the like.

  Examples of the binder include starch, corn starch, molasses, lactose, cellulose, cellulose derivatives, gelatin, dextrin, gum arabic, alginic acid, polyacrylic acid, glycerin, polyethylene glycol, polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), Water, methanol, ethanol and the like can be mentioned. These may be used individually by 1 type, and 2 or more types may be mixed and used for them.

  In view of the fact that the fuel used in the direct methanol fuel cell is methanol, the binder used is preferably methanol, and more specifically, it has the property of thickening when it comes into contact with methanol. It is preferable to use together a substance that contributes to the bonding and methanol. Considering this point, it is preferable to use methanol and a cellulose derivative or PVP or the like as a binder. In addition, when using methanol as a binder, you may abbreviate | omit the process of taking in methanol which is methanol into a porous material. In this case, by adding methanol as a binder to the porous material and molding, a solid methanol molded body can be obtained while taking methanol as methanol into the porous material.

  When methanol and a cellulose derivative or PVP are used in combination as a binder, the blending ratio (mass basis) of methanol and the cellulose derivative or PVP in the binder is preferably 1000: 1 to 10: 1. If the blending ratio is within this range, solid methanol can be effectively molded.

  Examples of a method for obtaining a solid methanol molded body using a binder include, for example, a method of granulating and forming a viscous fluid obtained by bringing methanol into contact with a cellulose derivative or the like to solid methanol or a porous material, a cellulose derivative or the like. The powder is mixed with solid methanol or a porous material in a powder form, and granulated and molded while adding methanol.

  Specifically, rolling granulation method using drum granulator, dish granulator, etc .; mixed stirring granulation method using flexo-mix, vertical granulator, etc .; screw-type extrusion granulator, roll Extrusion granulation using a mold extrusion granulator, blade extrusion granulator, self-molding extrusion granulator, etc .; compression granulation using a tablet-type granulator, briquette granulator, etc .; Examples include fluidized bed granulation, which involves granulating by spraying a binder while keeping solid methanol suspended and suspended in a fluid to be blown up (mainly air). In consideration of the use of a class (methanol), the rolling granulation method or the mixed stirring granulation method is preferable.

  The compounding quantity of a binder is not specifically limited, It is preferable that it is 0.001-5 mass parts with respect to 1 mass part of solid methanol or a porous material. If the blending amount of the binder is within the above range, solid methanol can be effectively formed.

  As solid methanol as mentioned above, various forms, such as a sheet form, a block form (lump form), and a granular form, can be used. Among these, the particulate form is preferable. By using particulate methanol as the solid methanol, it is easy to form a film, the vaporization rate can be controlled by adjusting the particle size, and the generated methanol vapor can be easily moved.

  The particle size of the solid methanol is preferably in the range of 1 μm to 10 mm, particularly 100 μm to 5 mm in consideration of handling properties, filling properties, gas mobility and the like. The permeable material such as the synthetic resin mesh 12A may be appropriately selected and used so that it does not spill depending on the form of the solid methanol.

  In the present embodiment, a film is formed on the surface of such solid methanol. This makes it possible to control the vaporization of methanol held on a substrate such as a porous material or gel confined inside the formed coating. Examples of the method for forming a film on the surface of solid methanol include a method of bringing solid methanol into contact with a coating agent.

  As the coating agent, a polymer material having a film forming action is preferable, for example, a cellulose type such as methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, carboxymethylcellulose, hydroxypropylmethylcellulose acetate succinate, etc. Materials: Water-soluble polymer (polyvinyl alcohol) -based materials such as polyvinyl alcohol (PVA); water / alcohol-compatible polymers such as polyvinyl pyrrolidone (PVP), and polyacrylic acid-based materials. These may be used individually by 1 type, and 2 or more types may be mixed and used for them.

  Of these coating agents, cellulose derivatives and / or PVA are preferably used, and cellulose derivatives are particularly preferably used. Most cellulose derivatives are used as binders for tablets and granules, matrix bases for sustained-release tablets, jelly agents, etc. in the medical field. Thickening / gelling agents and health food film coating agents are used in the food field. It is used as an anti-deformation agent contained in capsules, frying pancakes, etc., and it is recognized as safe for the human body. It is suitable.

  Examples of the method for forming a film on the surface of solid methanol by bringing solid methanol into contact with the coating agent include a fluidized bed coating method, a rolling fluidized composite coating method, a drum coating method, and a pan coating method. However, it is not limited to these. In addition, examples of the coating method include film coating, sugar coating, and the like. From the viewpoint of increasing the methanol content in solid methanol by reducing the film thickness of the formed film as much as possible, preferable.

  It is preferable that the compounding quantity of a coating agent is 0.0001-0.1 mass part with respect to 1 mass part of solid methanol molded objects. When the blending amount of the coating agent is within the above range, a film having a desired film thickness can be effectively formed on the surface of the solid methanol molded body.

  The solid methanol (film-forming solid methanol) having a film formed in this manner is preferably one in which 1 to 3 parts by mass of methanol is incorporated with respect to 1 part by mass of the base material. Further, in the case of a film-forming solid methanol in which water and methanol are incorporated into a porous material, 1 to 3 parts by mass of methanol and water are incorporated in total for 1 part by mass of the base material. Is preferred.

The operation of the direct methanol fuel cell system of the first embodiment having such a configuration will be described.
In FIG. 1, when N 2 gas is supplied from the carrier gas source 1, the N 2 gas flows into the solid methanol fuel cartridge 3 through the carrier gas supply path 2.

The film-forming solid methanol S in the fuel cartridge 3 does not vaporize at a stroke because methanol is gently restrained by the intermolecular force including the inclusion phenomenon inside the material. Vaporizes gradually at a suitable vaporization rate. At this time, the vaporization rate of methanol is adjusted to a desired value by appropriately setting the material and thickness of the coating in advance. Methanol molecules gradually vaporized from the surface of the film-forming solid methanol S are mixed with N ₂ gas and supplied as fuel gas from the fuel gas flow passage 4 to the fuel electrode 6 of the fuel cell 5.

As a result, power generation is performed according to the following reaction formula.
Anode: CH ₃ OH + H ₂ O → 6H ⁺ + CO ₂ + 6e ⁻ ... [1]
Cathode: 3/2 O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O [2]

  At this time, the methanol concentration in the vicinity of the fuel electrode 6 is considerably dilute compared with the method of directly supplying liquid methanol (aqueous solution), but not all of the methanol in the fuel electrode 6 reacts even in the liquid supply method. Only partly decomposed due to the limit of activity. Moreover, the more methanol is, the more methanol is crossed over to the air electrode 8 side.

Therefore, the high concentration of methanol in the fuel electrode 6 is not necessarily a merit, and even with methanol having a concentration obtained by vaporizing N ₂ gas from solid methanol as a carrier gas, an output almost equivalent to that of the liquid supply method is obtained. Is obtained.

Then, while the methanol is reduced is decomposed in the fuel electrode 6, by continuous supply of N ₂ gas from the carrier gas source 1, the methanol gas from the film forming solid methanol S is also supplied, the The power generation reaction will continue.

  In order to reliably perform initial power generation, the fuel electrode 6 may contain water in advance. The reaction between methanol and water produces carbon dioxide gas that is equimolar with methanol, and this carbon dioxide gas is released from the exhaust gas passage 9 to the external environment.

  And since the methanol content contained in the film-forming solid methanol S is reduced by supplying methanol to the fuel cell along with power generation, power generation is performed for a predetermined time or the output voltage is lower than a predetermined level. Then, the power generation can be continued by replacing the fuel cartridge 3 together.

  In the reaction formula [1], water equivalent to methanol is required, but in the present embodiment, water is not an essential requirement. This is considered due to the following reasons.

  That is, when the power generation is started, the reaction is started by utilizing the water originally held in the solid polymer electrolyte membrane 7 in the fuel electrode 6, and as the reaction proceeds, the air electrode 8 as shown in the reaction formula [2]. This is because the water generated in the above process reversely osmosis the solid polymer electrolyte membrane 7 and is supplied to the fuel electrode 6. However, in order to reliably perform initial power generation, water may be included in the fuel electrode 6 in advance.

Next, a second embodiment of the present invention will be described in detail based on FIG.
FIG. 3 is a flowchart showing a direct methanol fuel cell system according to the second embodiment of the present invention.

  As shown in FIG. 3, the direct methanol fuel cell system according to the present embodiment is a pump 11 serving as a carrier gas circulation means that takes in normal air as a carrier gas, and serves as a fuel storage unit for film-forming solid methanol. The solid methanol fuel cartridge 13 and the fuel cell 15 are provided. The exhaust side of the pump 11 and the solid methanol fuel cartridge 13 are communicated with each other by a carrier gas supply path 12. The fuel cell 15 communicates with the fuel gas flow passage 14.

  The fuel cell 15 includes a fuel electrode 16, a solid polymer electrolyte membrane 17, and an air electrode 18, and the fuel electrode 16 is connected to the fuel gas flow passage 14 and the circulation channel 19 connected to the intake side of the pump 11. The air electrode 18 is open to the atmosphere. The circulation channel 19 is provided with a pressure regulating valve (not shown).

In such a direct methanol fuel cell system, normal air (air) is used as a carrier gas in the present embodiment, but not limited thereto, an inert gas such as nitrogen gas (N ₂ ) or Ar is used. You may supply. Note that when air is used as a carrier gas, oxygen is contained, so that oxidation of methanol generates harmful substances such as formaldehyde, formic acid, and methyl formate in addition to water. However, in this embodiment, since the carrier gas is recycled, oxygen is consumed immediately, and this oxidation reaction occurs only in the initial stage. Therefore, the harmful substance has substantially no problem, and moisture generated in the initial state is supplied to the fuel electrode.

  Further, as the solid methanol fuel cartridge 13, the same one as in the first embodiment described above can be used. Moreover, the same thing as 1st Embodiment mentioned above can also be used as film formation solid-state methanol.

The operation of the direct methanol fuel cell system of the second embodiment having such a configuration will be described.
In FIG. 3, when air is supplied from the pump 11, the air flows into the solid methanol fuel cartridge 13 through the carrier gas supply path 12.

  The solid methanol S in the fuel cartridge 13 is not vaporized all at once because the methanol is gently restrained by the intermolecular force including the inclusion phenomenon inside the material, but depending on the performance of the coating. It gradually vaporizes at the vaporization rate. At this time, the vaporization rate of methanol is adjusted to a desired value by appropriately setting the material and thickness of the coating in advance. The methanol molecules gradually vaporized from the surface of the film-forming solid methanol S are mixed with air and supplied as fuel gas from the fuel gas flow passage 14 to the fuel electrode 16 of the fuel cell 15.

As a result, power generation is performed according to the following reaction formula.
Anode: CH ₃ OH + H ₂ O → 6H ⁺ + CO ₂ + 6e ⁻ ... [1]
Cathode: 3/2 O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O [2]

  At this time, the methanol concentration in the vicinity of the fuel electrode 16 is considerably dilute compared with the method of supplying liquid methanol (aqueous solution) directly, but even in the liquid supply method, not all of the methanol in the fuel electrode 16 reacts, and the catalyst Only partly decomposed due to the limit of activity. Moreover, the more methanol is, the more methanol is crossed over to the air electrode 18 side.

Therefore, a high concentration of methanol in the fuel electrode 16 is not necessarily a merit, and even with methanol having a concentration obtained by vaporizing N ₂ gas from a solid methanol as a carrier gas, an output almost equivalent to that of the liquid supply method is obtained. Is obtained.

  And while methanol is decomposed | disassembled and reduced by the fuel electrode 16, since the methanol gas from solid methanol is also supplied by continuing supply of carrier gas by the pump 11, the said electric power generation reaction will continue. Become.

  At this time, in the above reaction formula [1], water equivalent to methanol is required, but in this embodiment, air is circulated as a carrier gas. As a result, the reaction is started by the moisture resulting from the oxidation of methanol and the moisture originally retained in the solid polymer electrolyte membrane 17.

  In order to reliably perform initial power generation, the fuel electrode 16 may contain water in advance.

  The reaction between methanol and water produces carbon dioxide gas in an equimolar amount with methanol. This carbon dioxide gas is circulated from the circulation flow path 19 to the pump 11. Further, methanol (gas) remaining without reacting at the fuel electrode 16 is also circulated from the circulation flow path 19 to the pump 11. Thereby, since the methanol contained in the film-forming solid methanol S does not diffuse into the external environment, the methanol can be effectively used and the life of the fuel cartridge 13 can be extended. Furthermore, it is not necessary to prepare a carrier gas cylinder or the like separately.

  When the pressure in the circulation path exceeds a predetermined pressure due to carbon dioxide gas generated by the anode reaction, an appropriate amount of carrier gas can be released from a pressure regulating valve (not shown) provided in the circulation channel 19. That's fine.

  And since the methanol content contained in the film-forming solid methanol S is reduced by supplying methanol to the fuel cell along with power generation, power generation is performed for a predetermined time or the output voltage is lower than a predetermined level. Then, the power generation can be continued by replacing the fuel cartridge 13 together.

  As mentioned above, although this invention has been demonstrated based on embodiment, this invention is not limited to the said embodiment, A various deformation | transformation implementation is possible.

  For example, the film-forming solid methanol S does not have to be 100% pure methanol in solid form, but water added to methanol to obtain a methanol solution with a desired concentration is used as a solid solution. May be. Furthermore, you may use together film-forming solid methanol and the water (film-forming solid water) made into the solid state by the same method. In this case, the film-forming solid methanol S and the film-forming solid water may be mixed in the fuel cartridge 3 (13), or the water-containing solid material cartridge separately from the solid methanol fuel cartridge 3 (13). A (water replenishment container) may be provided between the fuel cartridge 3 (13) and the fuel cell 5 (15), that is, in the fuel gas flow path 4 (14).

  The direct methanol fuel cell system of the present invention as described above does not have a liquid inside the system, can be made compact, and as long as the solid methanol has a predetermined amount of methanol, there is no decrease in output, etc. It is particularly suitable as a required power source for portable electronic devices.

The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.

[Example 1]
[Fuel battery cell]
The following fuel cell was used for the test.
MEA: MEA for DMFC manufactured by Chemix
・ Electrolyte membrane: Nafion117 (DuPont, film thickness 50μm)
・ Anode (fuel electrode) catalyst; Pt-Ru / C
・ Cathode (air electrode) catalyst; Pt / C
-Effective membrane area: 40 x 40 mm
Current collecting material: SUS mesh (Au plating)
Fuel electrode: sealed structure Air electrode: open structure

[Preparation of film-forming solid methanol]
After blending hydroxypropyl cellulose (2 g) and methanol (300 g) with magnesium aluminate metasilicate powder (100 g), the mixture was granulated into spherical particles having a diameter of about 3 mm using a granulator to obtain solid methanol particles. .

  After introducing the solid methanol particles into the coating apparatus, a 0.5% methanol aqueous solution of ethyl cellulose, which is a film forming material, is sprayed at a flow rate of 10 mL / min for 5 minutes and dried to form a film of ethyl cellulose having a thickness of about 30 μm on the surface. The film-forming solid methanol particles were formed. The methanol content of the film-forming solid methanol particles was about 65%.

[Direct methanol fuel cell system]
2 g of the film-forming solid methanol particles were filled in the cartridge 3 shown in FIG. 2 having a size of 40 × 40 × 10 (mm) and mounted on the system shown in FIG. 1 to prepare a system. At this time, as the fuel electrode 6 of the fuel cell 5, pure water was previously stretched and wetted, pure water was removed before the test, and water droplets were removed with a nitrogen gas flow.

[Comparative Example 1]
A direct methanol fuel cell system (Comparative Example 1) was produced in the same manner as in Example 1, except that a 3% methanol aqueous solution was supplied to the fuel electrode 6 of the fuel cell 5.

[Reference example]
A direct methanol fuel cell system (reference example) was produced in the same manner as in Example 1 except that solid methanol particles were filled as they were without forming a film.

[Example 2]
2 g of the film-forming solid methanol produced in Example 1 was filled in the cartridge 3 shown in FIG. 2 having a size of 40 × 40 × 10 (mm) and mounted on the system shown in FIG. At this time, as the fuel electrode 6 of the fuel cell 5, pure water was previously stretched and wetted, pure water was removed before the test, and water droplets were removed with a nitrogen gas flow.

[Power generation test]
For the direct methanol fuel cell systems of Example 1, Example 2, Comparative Example 1 and Reference Example, an electric current was passed by the electronic load device, and the characteristics of the fuel cell, that is, the cell voltage (V) at the maximum output, The load current density (mA / cm ² ) at the maximum output, the maximum output (mW / cm ² ), and the fuel cell temperature (° C.) were measured.

As is clear from Table 1, the fuel cell system of Example 1 has a maximum output of 17.43 mW / cm ² and a fuel cell temperature of 34.6 ° C., and the fuel cell system of Example 2 has a maximum output of The fuel cell temperature was 34.9 ° C. at 18.13 mW / cm ² . In contrast, the fuel cell system of the reference example had a maximum output of 11.75 mW / cm ² , but the fuel cell temperature was as high as 44.6 ° C. The cause of the heat generation of the fuel cell is thought to be that the methanol crossover occurred due to the supply of high-concentration methanol vapor, and heat was generated by the oxidation reaction of the air electrode.

Further, the fuel cell system of Comparative Example 1 had a maximum output of 13.86 mW / cm ² and a fuel cell temperature of 29.9 ° C. The difference in the maximum output between each Example and Comparative Example 1 is considered because methanol is supplied as a gas in the fuel cell system of each Example.

1 is a flowchart showing a direct methanol fuel cell system according to a first embodiment of the present invention. It is sectional drawing which shows the fuel cartridge of the direct methanol fuel cell system which concerns on the 1st Embodiment of this invention. It is a flowchart which shows the direct methanol fuel cell system which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

1 ... Carrier gas source (carrier gas supply means)
2, 12 ... Carrier gas supply path 3, 13 ... Solid methanol fuel cartridge (fuel storage part)
4, 14 ... Fuel gas flow passages 5, 15 ... Fuel cells 6, 16 ... Fuel electrodes 7, 17 ... Solid polymer electrolyte membranes 8, 18 ... Air electrode 9 ... Exhaust gas passage 11 ... Pump (carrier gas circulation means) )
19: Circulating flow path S: Film-forming solid methanol

Claims (12)

A fuel storage section for storing solid methanol obtained by solidifying methanol;
A fuel cell;
Fuel gas supply means for supplying a fuel gas containing methanol vaporized from the solid methanol by circulation of a carrier gas to the fuel cell,
A direct methanol fuel cell system, wherein a film is formed on the surface of the solid methanol. The fuel storage portion is provided with a carrier gas supply path that communicates with the carrier gas supply means, and a fuel gas flow path that communicates with the fuel electrode side of the fuel cell,
The fuel battery cell is provided with an exhaust gas passage in communication with the fuel electrode side,
When the carrier gas is supplied to the fuel storage portion, the fuel gas containing methanol vaporized from the solid methanol having a film is supplied to the fuel electrode of the fuel cell and then discharged from the exhaust gas flow path. The fuel cell system according to claim 1.   3. The direct methanol fuel cell system according to claim 2, wherein the carrier gas supply means is an air blowing means.   The direct methanol fuel cell system according to claim 2, wherein the carrier gas supply means is a compressed gas cylinder.   2. The direct methanol fuel cell system according to claim 1, wherein the carrier gas supply means includes a heating device and a substance that generates gas by heating. The fuel storage portion is provided with a carrier gas supply path that communicates with the carrier gas circulation means, and a fuel gas flow path that communicates with the fuel electrode side of the fuel cell,
The fuel battery cell is provided with a circulation flow path that communicates with the fuel electrode side and communicates with the carrier gas circulation means.
When a carrier gas is supplied from the carrier gas circulation means to the fuel storage portion via the carrier gas supply path, a fuel gas containing methanol vaporized from the solid methanol having a film formed on the fuel electrode of the fuel cell. 2. The fuel cell system according to claim 1, wherein after being supplied, the fuel cell system recirculates from the circulation flow path to the carrier gas circulation means.   The direct methanol fuel cell system according to claim 1, wherein the fuel storage unit is a detachable cartridge.   The direct methanol fuel cell system according to any one of claims 1 to 7, wherein the carrier gas supplied to the fuel electrode of the fuel cell substantially does not contain oxygen.   The direct methanol fuel cell system according to any one of claims 1 to 8, wherein the solid methanol is a solidified methanol aqueous solution.   The direct methanol fuel cell system according to any one of claims 1 to 8, wherein the fuel storage unit contains a water-containing solid material together with the solid methanol.   The direct methanol fuel cell system according to any one of claims 1 to 8, further comprising a water refill container containing a water-containing solid material between the fuel storage unit and the fuel cell.   A portable electronic device comprising the direct methanol fuel cell system according to claim 1.

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