JP5284657B2 - Direct alcohol fuel cell - Google Patents

Description

  The present invention relates to a fuel cell that can be used as a power source for various electric devices ranging from small devices such as notebook computers, mobile phones, and small video cameras to large devices such as automobiles and homes.

  Direct alcohol type fuel cells can generate electricity at relatively low temperatures, use liquid fuels compared to fuel cells that use flammable gases, and have a high energy density. As a result, the fuel container can be reduced in size, and furthermore, since hydrogen gas that is difficult to store is not used as fuel, the overall configuration of the fuel cell can be reduced. Therefore, the fuel cell is expected to be a promising power source for small portable devices such as notebook computers, mobile phones, and small video cameras.

  On the other hand, the conventional direct alcohol type fuel cell has a problem that the generated electric power is small as compared with the fuel cell using hydrogen gas as a fuel, and improvement of the generated electric power is an issue.

  A direct methanol fuel cell using methanol as a liquid fuel is divided into a liquid supply type that supplies liquid fuel directly to the battery body, and a vaporization supply type that supplies vaporized methanol to the battery body, depending on the fuel supply method to the battery body. It is divided roughly into.

In the former liquid supply type methanol fuel cell, when methanol is supplied to the fuel side of the cell main body, the methanol permeates through an electrode made of a mesh-like metal and further forms a porous gas diffusion layer. Permeate to reach the catalyst layer. When methanol and water of the same amount or more reach or exist in the catalyst layer composed of a platinum / ruthenium mixture, the methanol is decomposed into carbon dioxide, protons, and electrons.
CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ (1)
The carbon dioxide generated at this time is released to the outside through the gas diffusion layer and the electrode through which the fuel has permeated. The generated protons pass through the electrolyte membrane and move to the air supply side. Furthermore, the generated electrons pass through the porous gas diffusion layer, which is a conductor, and are captured by the electrodes, and move through the circuit formed between the electrodes on the opposite side (air supply side) to generate electricity. To do.

  The structure of the electrode is desirably a mesh shape so that liquid and gas can be easily transmitted and electricity can be easily captured. The electrode material is preferably a metal such as iron or copper plated with a noble metal such as platinum or gold so as not to be subject to electrical corrosion.

  The gas diffusion layer is preferably made of carbon fiber or carbon paper which is easy to permeate liquid and gas like the electrode and is a good electrical conductor. More preferably, the material constituting the gas diffusion layer may be subjected to a hydration treatment so that the liquid can easily pass therethrough. In the hydration treatment, carbon fiber or the like is generally impregnated with tin oxide or the like.

On the air supply side, oxygen contained in the air sucked by the standard atmospheric pressure reaches the catalyst layer via the electrode and gas diffusion layer on the air supply side, and in the proton and electrolyte membrane that has moved from the fuel supply side, together with electrons Reaction produces water.
3/2 O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O (2)

  However, in the above-described general methanol fuel cell, it is necessary to supply methanol in a liquid state under standard atmospheric pressure without using external power in order to stably extract necessary power. In order to stably extract the power to be used, it is insufficient. Therefore, conventionally, a small pump is used to forcibly supply the fuel electrode while controlling the flow rate of methanol.

  By the way, when a similar fuel cell is used in a portable small electronic device such as a mobile phone, the fuel supply pump as described above cannot be adopted from the viewpoint of its size. In general, electric power is required to control the pump, and when a part of the electric power generated by the fuel cell is used for driving the pump, the output power of the entire fuel cell is reduced.

  On the other hand, for the latter vaporization supply type methanol fuel cell, a method of vaporizing methanol fed by a conventional pump and supplying it by a blower is known. The electrode reaction performance is higher than that of the liquid supply type, but this method also requires an auxiliary device such as a vaporizer, which leads to an increase in the size of the apparatus.

  Conventionally, it has been proposed to use a fuel supply medium having a wick structure that causes capillary action instead of a pump. By using the wick structure, a passive structure can be adopted instead of an active structure like a conventional fuel cell. In addition, since the energy supply related to the fuel supply can be suppressed as much as possible and the fuel supply structure can be suppressed to be small, the possibility of the power supply for small portable devices described above can be further increased.

  An example in which a fuel supply medium having a wick structure is proposed is described in the following patent document. In Patent Document 1, in a liquid fuel supply type alcohol fuel cell, the liquid fuel is introduced into a single cell by using a capillary phenomenon, and the liquid fuel is vaporized by the reaction heat of the power generation unit, thereby increasing the electrode reactivity. The output power is improved. Further, since the gaseous fuel in the fuel vaporization layer is kept almost saturated, the liquid fuel is vaporized by the amount of fuel consumed by the cell reaction, and the liquid fuel is further introduced into the unit cell by capillary force by the vaporized amount. It is comprised so that.

  As a peripheral technology of such a liquid supply type fuel cell, Patent Document 2 discloses that in a liquid fuel supply type alcohol fuel cell, a surfactant is added to a liquid fuel composed of an alcohol aqueous solution when supplying fuel by capillary action. The liquid fuel composed of an aqueous alcohol solution and the capillary are improved in wettability.

  Patent Document 3 describes a configuration in which a pressure adjustment mechanism is provided in a fuel storage container for a liquid fuel supply type fuel cell. In this configuration, the pressure reduction in the liquid fuel storage container due to consumption of the liquid fuel is stored in the container. Adjust pressure by taking in external air. Further, the pressure in the liquid fuel container is discharged by the gas pressure of the inert gas sealed in the liquid fuel container due to the vaporization of the liquid fuel due to the temperature rise caused by the reaction heat of the electrode. Is kept constant, and the liquid fuel is stably supplied.

Japanese Patent No. 3442688 Japanese Patent No. 3563648 Japanese Patent No. 3668069

  However, in the configuration described in Patent Document 1, methanol is heated and evaporated by the heat generated by the power generation, so that the evaporation of methanol and the supply of the vapor to the fuel power are delayed with respect to the power generation. Therefore, the response to the power generation request may be lowered. In addition, since the amount of heat for heating methanol is ultimately limited by the amount of power generation, it cannot be said that the controllability of the amount of heat supplied is necessarily good. Furthermore, the reaction efficiency (usage efficiency) of the supplied methanol is hardly 100%, and in order to maintain a constant output, the fuel is continuously supplied. The methanol of the reaction may be discharged.

  The fuel composition for a fuel cell described in Patent Document 2 as a peripheral technology of a liquid supply type fuel cell is for improving the wettability between a liquid fuel composed of an aqueous alcohol solution and a capillary when supplying the fuel by a capillary phenomenon. In addition, it is said that a surfactant is added to a liquid fuel composed of an aqueous alcohol solution. However, it is effective at the time of start-up at a low temperature at which the liquid fuel can be frozen or at a low temperature where the viscosity of the liquid fuel is large and affects the power generation. When the battery reaction is performed in the power generation unit, the fuel is efficiently transported when the ratio of the vaporized liquid fuel is small, but when the ratio of the vaporized liquid fuel is large, the appropriate fuel transport is performed. There is a risk that it will not be done. Depending on the use conditions of the liquid fuel supply type alcohol fuel cell, the liquid fuel once vaporized may be recondensed and liquefied. In this case, it is necessary to reduce the partial pressure of the vaporized liquid fuel.

  Further, the fuel container for a liquid fuel supply type fuel cell described in Patent Document 3 adjusts the pressure decrease in the fuel container when liquid fuel is consumed by taking in air from the outside of the container, and contains fuel by reaction heat. It is said that the pressure rise in the container is discharged by the gas pressure of the inert gas sealed at the same time. However, when the liquid fuel is vaporized by reaction heat, the fuel is supplied to the power generation unit by the pressure of the vaporized liquid fuel. In addition, by applying a heat insulation structure to the fuel container, it is possible to avoid an increase in pressure in the fuel container due to vaporization of the liquid fuel due to reaction heat from the cell reaction or reaction heat between the catalyst and unreacted methanol (off methanol). can do.

  The present invention has been made by paying attention to the above technical problem, and an object of the present invention is to provide a direct alcohol fuel cell that has good power generation efficiency and can be miniaturized.

In order to achieve the above object, the invention of claim 1 is characterized in that a fuel chamber is formed on one side of a membrane / electrode assembly in which electrodes are provided on both the front and back surfaces of the electrolyte membrane, and an air chamber on the other side. In the direct alcohol fuel cell in which alcohol is supplied to the fuel chamber, an alcohol vapor source that supplies heated and vaporized alcohol fuel to the membrane-electrode assembly, and from the alcohol vapor source e Bei a noncondensable gas mixing unit for mixing the non-condensable gases consisting of oxygen to the alcohol vapor supplied to the membrane electrode assembly, the non-condensable gas mixing unit stores the hydrogen peroxide A hydrogen peroxide tank, a non-condensable gas supply path communicating with the alcohol vapor flow path and the hydrogen peroxide tank, and provided in the middle of the non-condensable gas supply path. It is a direct alcohol fuel cell, characterized in that a catalyst for generating oxygen by decomposing hydrogen.

According to the second aspect of the present invention , a fuel chamber is formed on one side of a membrane / electrode assembly in which electrodes are provided on both the front and back surfaces of the electrolyte membrane, and an air chamber is formed on the other side. In a direct alcohol fuel cell, an alcohol vapor source that supplies heated and vaporized alcohol fuel to the membrane / electrode assembly, and from the alcohol vapor source to the membrane / electrode assembly and a non-condensable gas mixing unit for mixing the non-condensable gases consisting of oxygen to alcohol vapors fed, prior Symbol noncondensable gas mixing unit, the membrane-liquid mixture of an alcohol fuel and hydrogen peroxide A fuel supply path that circulates toward the electrode assembly, and a catalyst that is interposed in the middle of the fuel supply path and generates oxygen by decomposing the hydrogen peroxide. It is a direct alcohol fuel cell that.

A third aspect of the invention is a direct alcohol fuel cell according to the second aspect of the invention, wherein the concentration of hydrogen peroxide in the alcohol is within 10 weight percent.

A fourth aspect of the invention is a direct alcohol fuel cell according to any one of the first to third aspects, wherein the alcohol is methanol.

  Therefore, according to the first aspect of the present invention, alcohol vapor is sent to the fuel chamber through the supply pipe, generates electric power with an oxidation reaction through the electrolyte membrane, and electric power is taken out from each electrode. In this case, since the pressure of the alcohol is increased by evaporating, a sufficient amount of alcohol can be supplied to the fuel chamber without the need for a mechanical pump, and the alcohol is vaporized. Since it diffuses widely throughout the fuel chamber, that is, it diffuses uniformly throughout the surface of the membrane / electrode assembly, the entire electrolyte membrane functions effectively and power generation efficiency can be improved. In particular, even when a plurality of membrane / electrode assemblies are laminated, alcohol vapor can be supplied quickly and efficiently to the fuel electrode side of each layer, so that a reduction in power generation efficiency due to lamination can be prevented or suppressed. . And since it is not necessary to provide movable parts, such as a pump, the structure as a whole can be reduced in size. Further, since alcohol is supplied as vapor to the membrane / electrode assembly, the surface of the membrane / electrode assembly is suppressed from being covered with liquid, and this prevents the flow of carbon dioxide gas generated by the power generation reaction. As a result, carbon dioxide can be efficiently removed from the surface of the fuel chamber or the membrane / electrode assembly, and the power generation efficiency can also be improved in this respect. In addition, alcohol vapor can be supplied to the membrane-electrode assembly even without heat generation due to power generation, so that the so-called start time for starting power generation can be shortened, particularly in cold conditions. Can be improved.

In addition, by mixing non- condensable gas consisting of oxygen with alcohol vapor, the partial pressure of alcohol vapor is reduced, so that alcohol vapor can be supplied to the fuel electrode side quickly and efficiently together with non-condensable gas. Condensation can be prevented or suppressed. As a result, alcohol is supplied as a vapor to the membrane-electrode assembly, so that the surface of the membrane-electrode assembly is suppressed from being covered with liquid, and therefore, the flow of carbon dioxide gas generated by the power generation reaction is suppressed. It is difficult to inhibit, and carbon dioxide can be efficiently removed from the surface of the fuel chamber or the membrane / electrode assembly. In this respect as well, power generation efficiency can be improved.

Furthermore, according to the invention billed to claim 1, by providing a site carrying a catalyst which decomposes the hydrogen peroxide to generate oxygen in the middle of the non-condensable gas supply passage, hydrogen peroxide in the supply channel It can be decomposed to generate oxygen, a non-condensable gas. Accordingly, the hydrogen peroxide is stored in the hydrogen peroxide tank as a liquid, and there is no need to provide a portion for storing a large volume of non-condensable gas, thereby saving space.

According to the invention of claim 2, the fuel supply path in which alcohol fuel and hydrogen peroxide are mixed and supplied to the membrane-electrode assembly is provided with a catalyst that decomposes hydrogen peroxide to generate oxygen. Since the portion is provided, hydrogen peroxide is stored in the hydrogen peroxide tank in a liquid state, and it is not necessary to provide a portion for storing a non-condensable gas having a large volume, thereby saving space.

According to the invention of claim 3, when the concentration of hydrogen peroxide in the alcohol fuel is within 10 weight percent, an excessive supply of oxygen, which is a non-condensable gas, is suppressed, and an excessive supply of oxygen is reduced. Can be suppressed.

According to the invention of claim 4, by using methanol with high reactivity and high energy density as the fuel, the fuel storage container can be kept small and handled as compared with the case where gaseous fuel such as hydrogen is used. Is easy.

  Next, a direct alcohol fuel cell according to the present invention will be described based on a specific example. The main configuration of the direct alcohol fuel cell according to the present invention is as shown in the block diagram of FIG. 1 and includes a fuel tank 1 for storing liquid alcohol. The fuel tank 1 is connected to a power generation unit 2 through a supply line 3. It is communicated through. In the middle of the supply pipe 3, a vaporizing section 4 for heating and evaporating the liquid alcohol is provided. The vaporization unit 4 is a part that heats and evaporates the alcohol in the supply pipe 3, and the heat source is an electric heater using an external power source or heat generated by burning alcohol as needed. Can be used as appropriate. FIG. 1 shows a configuration using the oxidation heat of alcohol.

  In addition, a non-condensable gas tank 5 for storing hydrogen peroxide is provided, and the non-condensable gas tank 5 is communicated with the vaporization unit 4 via a non-condensable gas supply path 6. The non-condensable gas tank 5 is configured to store non-condensable gas. For example, hydrogen peroxide solution is stored and manganese dioxide or platinum provided in the non-condensable gas supply path 6 is used as a catalyst. Alternatively, oxygen that is a non-condensable gas can be generated from the hydrogen peroxide solution. When platinum is used as a catalyst, platinum decomposes not only hydrogen peroxide solution but also methanol. Therefore, it is necessary to have a configuration that avoids contact between platinum and methanol. Further, a backflow prevention mechanism such as a valve for preventing the decomposition product such as carbon dioxide generated by the contact of platinum with methanol and the decomposition of methanol from flowing back to the fuel tank 1 or the non-condensable gas tank 5 is provided. There is a need. Therefore, in a configuration in which methanol is used as the fuel and hydrogen peroxide is used as a generation source of oxygen, which is a non-condensable gas, it is desirable to use manganese dioxide as a catalyst for decomposing the hydrogen peroxide.

Between the fuel tank 1 and the vaporization unit 4, a flow rate adjusting mechanism 7 for adjusting the flow rate of the liquid alcohol is provided. As the flow rate adjustment mechanism 7, but the flow rate adjustment valve is the most common, can you to use a suitable structure, such as an orifice is not limited thereto. In addition, a valve 8 is provided between the vaporization unit 4 and the power generation unit 2 to adjust the flow rate including the flow / blocking of alcohol vapor.

  FIG. 2 shows a main configuration for generating oxygen, which is a non-condensable gas, from hydrogen peroxide when hydrogen peroxide is stored in the non-condensable gas tank 5 described above. In the vaporization section 4, the non-condensable gas supply path 6 communicates with the alcohol supply pipe 3, and a catalyst 9 that decomposes hydrogen peroxide and generates oxygen in the middle of the non-condensable gas supply path 6. Is provided. The non-condensable gas mixing unit 10 is an intersection (connecting portion) between the non-condensable gas supply path 6 and the supply pipeline 3. As the catalyst 9, for example, manganese dioxide or platinum can be used.

  The power generation unit 2 is a portion corresponding to a substantial fuel cell, and is mainly composed of a membrane / electrode assembly (MEA) 11 that includes a polymer electrolyte membrane as an electrolyte and integrates the electrolyte membrane and electrodes. ing. FIG. 3 is a sectional view showing the structure, and catalyst layers 13 and 14 are provided on both the front and back surfaces of the electrolyte membrane 12.

The electrolyte membrane 12 is an electrolyte membrane made of a perfluorosulfonic acid polymer membrane (for example, Nafion 117 (registered trademark)) or polybenzimidazole (hereinafter sometimes referred to as PBI), and in particular, an electrolyte made of PBI. If it is a film | membrane, the crossover phenomenon of a fuel can be prevented or suppressed. Furthermore, an electrolyte membrane made of PBI is suitable for improving power generation efficiency in a high temperature region as compared with a perfluorosulfonic acid polymer membrane. Note that the cross-over phenomenon, without Oite alcohol fuel to the electrolyte membrane 12 of the power generation unit 2, which contributes chemical reaction generating a (cell reaction), it from the fuel supply side of the phenomena which passes through the air supply side Say.

  Further, as an example, the fuel-side catalyst layer 13 is composed mainly of a platinum / ruthenium mixture, and the air-side catalyst layer 14 is composed mainly of platinum. Gas diffusion layers 15 and 16 are formed on the surface sides of the catalyst layers 13 and 14, respectively. The gas diffusion layers 15 and 16 are for securing a space in which fuel and air circulate on the surface side of the catalyst layers 13 and 14 and have a conductive porous structure. Specifically, carbon fibers are knitted into a mesh structure, and are hydrated as necessary. Electrodes 17 and 18 are provided on the surface sides of these gas diffusion layers 15 and 16. The electrodes 17 and 18 are made of a good conductor, and in addition to this, a ventilation structure is used to allow fuel and air to reach the catalyst layers 13 and 14. As an example, it is a mesh structure made of stainless steel plated with platinum. An electric circuit 20 is formed by connecting a load 19 to these electrodes 17 and 18.

  In the example shown in FIG. 1, a catalytic combustion chamber 21 is attached to the vaporization unit 4. The catalytic combustion chamber 21 is used to oxidize alcohol by an oxidation catalyst such as platinum, and is configured to transmit heat generated by the oxidation to the alcohol in the vaporizing section 4 to evaporate it. . For example, the vaporization unit 4 and the catalytic combustion chamber 21 are isolated by a material having good thermal conductivity such as an aluminum plate, and the heat generated in the catalytic combustion chamber 21 is efficiently transferred to the alcohol in the vaporization unit 4. Is configured to do. Therefore, the catalytic combustion chamber 21 communicates with the power generation unit 2 and is configured to guide exhaust gas containing unburned alcohol discharged from the power generation unit 2 to the catalytic combustion chamber 21.

  A more specific example of the direct alcohol fuel cell according to the present invention described above is shown in FIG. In FIG. 4, the interior of the hollow package 22 is divided into two by a partition wall 23, and the fuel tank 1, the non-condensable gas tank 5, the flow rate adjusting mechanism 7, the vaporization unit 4, and the catalytic combustion chamber 21 are on the upper side in FIG. 4. The valve 8 is provided, and the power generation unit 2 is provided in the lower part of FIG. In the power generation unit 2, a membrane / electrode assembly 11 is provided in a lower region partitioned by the partition wall 23 in the package 22 so as to bisect the region, and the membrane / electrode assembly 11 and the partition wall 23 are separated from each other. A space is formed between the fuel chambers 24, and an air chamber 25 is formed on the side opposite to the fuel chambers 24. Although the fuel chamber 24 is configured as a sealed space, the air chamber 25 may be configured as a released space because it is only necessary to introduce outside air.

  The fuel tank 1 and the non-condensable gas tank 5 are configured as a sealed container provided with an inlet (not shown), and the vaporization unit 4 is formed as a sealed chamber in the vicinity of the fuel tank 1 and the non-condensable gas tank 5, A flow rate adjusting mechanism 7 is provided between the fuel tank 1 and the vaporizing unit 4. A heat insulating material 26 is interposed between the pipeline including the flow rate adjusting mechanism 7 and the power generation unit 2. A catalytic combustion chamber 21 is provided between the vaporization section 4 and the partition wall 23 (below the vaporization section 4 in FIG. 4). The vaporizing section 4 and the catalytic combustion chamber 21 are configured so as to be able to exchange heat with each other. For example, the vaporizing section 4 and the catalytic combustion chamber 21 are partitioned by a partition plate having good thermal conductivity such as aluminum.

  The inside of the vaporization part 4 is filled with a wick material that performs a capillary action made of a porous material that can be impregnated with liquid alcohol (specifically methanol), such as carbon fiber. On the other hand, the catalyst combustion chamber 21 is filled with a catalyst in which catalyst particles such as platinum are supported on a metal wick material. The catalytic combustion chamber 21 is provided with an intake port 27 that passes through the partition wall 23 and opens to the fuel chamber 24, and an exhaust pipe 28 that opens to the outer surface of the package 22 communicates with the catalytic combustion chamber 21. ing. Further, the vaporizing unit 4 is communicated with the fuel chamber 24 via the valve 8. The valve 8 is covered with a heat insulating material 26. In FIG. 4, reference numerals 29 and 30 denote lead wires, which are connected to the electrodes 17 and 18, respectively.

  Also in the fuel cell shown in FIG. 4, electric power is generated along with the oxidation reaction (power generation reaction) via the membrane / electrode assembly 11 as in the case of a normal alcohol fuel cell. That is, methanol, which is the fuel supplied to the fuel chamber 24, is divided into carbon dioxide and protons by the reaction shown in the above-described equation (1), and emits electrons. The proton passes through the electrolyte membrane and moves to the air chamber 25 side, and the electrons are taken out to the outside through the electrode 17 and become electricity. On the air chamber 25 side, protons and oxygen in the air perform the reaction represented by the above-described equation (2) to generate water.

  Such a reaction does not occur for all of the methanol supplied to the fuel chamber 24, and unburned methanol also remains, which is discharged from the intake port 27 to the catalytic combustion chamber before being discharged outside the package 22. 21 is led. That is, exhaust gas from the fuel chamber 24 is introduced into the catalytic combustion chamber 21, and methanol contained in the exhaust gas is oxidized by the catalyst. A part of the heat generated in this way is discharged from the exhaust pipe 28 to the outside of the package 22 together with the exhaust gas, and the other part is transmitted to the vaporization unit 4 provided adjacent to the catalytic combustion chamber 21. Is done.

  Liquid methanol is supplied from the fuel tank 1 with the flow rate adjusted to the evaporating section 4, and the liquid alcohol is heated by the heat transmitted from the catalytic combustion chamber 21 and evaporates. Note that an electric heater may be provided as an auxiliary heat source for quick start-up in cold weather. The hydrogen peroxide supplied from the non-condensable gas tank 5 is decomposed by the catalyst 9 provided in the non-condensable gas supply path 6 to generate oxygen, and the non-condensable gas mixing part in the vaporization part 4 At 10, it is mixed with alcohol vapor. Since the alcohol vapor mixed with the non-condensable gas is supplied to the fuel chamber 24 via the valve 8, the methanol as the fuel is supplied to the fuel chamber 24 with its partial pressure lowered. . Therefore, recondensation of alcohol vapor can be prevented and a sufficient amount of fuel can be supplied to the power generation unit 2.

  Since the mixed vapor fuel is a gas, it diffuses rapidly throughout the fuel chamber 24 and is diffused over the entire surface of the electrolyte membrane 12 by the gas diffusion layer 15 described above, and then the reaction described above in the catalyst layer 13. Occurs. Therefore, a power generation reaction occurs in the entire electrolyte membrane 12, and efficient power generation is performed.

  As shown by the above-described equation (1), carbon dioxide gas is generated by decomposition of methanol in the catalyst layer 13, but the methanol supplied to the catalyst layer 13 and the gas diffusion layer 15 is a gas evaporated by heating, and non- Since it is mixed with condensable gas and the partial pressure of methanol is lowered, recondensation is suppressed, and no liquid film is formed in the catalyst layer 13 or the gas diffusion layer 15, or the liquid film is suppressed. Carbon dioxide gas generated by the reaction is quickly discharged, and methanol is replaced. As a result, since methanol is always newly supplied to the catalyst layer 13 or the electrolyte membrane 12, power generation occurs efficiently.

  The carbon dioxide gas generated by the reaction is discharged together with oxygen, which is a non-condensable gas, from the intake port 27 described above to the catalytic combustion chamber 21, and is discharged from the package 22 to the outside via the exhaust pipe 28. Therefore, carbon dioxide gas also functions to transport unburned methanol to the catalytic combustion chamber 21. The unburned methanol is oxidized in the catalytic combustion chamber 21 to become carbon dioxide gas and water, so that no or little methanol is released from the package 22. Therefore, with the above-described configuration, safety is improved. A high alcohol fuel cell can be obtained. Since no power device such as a pump is required, downsizing is easy and there is no power consumption, so that the power generation efficiency can be improved in this respect as well.

  Next, another specific example of the direct alcohol fuel cell according to the present invention will be shown. In the above-described specific example, hydrogen peroxide is stored in the non-condensable gas tank 5 as a non-condensable gas generation source, and oxygen generated by decomposition by the catalyst 9 provided in the supply path 6 is supplied to the supply pipe line. In the non-condensable gas mixing unit 10, which is an intersection with 3, the alcohol vapor is mixed and supplied. In short, the present invention suffices if the non-condensable gas is mixed with the alcohol vapor and the mixed fuel vapor is supplied to the power generation unit 2. The liquid alcohol and hydrogen peroxide are mixed in advance. A configuration may be adopted in which oxygen, which is a non-condensable gas, is generated in the mixed fuel supply path and the mixed fuel vapor is supplied to the power generation unit 2.

  FIG. 5 shows an example of this, and a mixed fuel supply pipe provided by mixing methanol and hydrogen peroxide water in the fuel tank 1 and communicating between the mixed fuel tank 31 and the power generation unit 2. 32, and the catalyst 9 is arranged between the vaporizing section 4 provided in the middle of the supply pipe 32 and the mixed fuel tank 31. Since the power generation unit 2 and other configurations are the same as those shown in FIGS. 3 and 4 described above, the same reference numerals as those in FIGS. 3 and 4 are given to FIG.

  The mixed fuel tank 31 is formed with a mixed fuel supply line 32 that allows the power generation unit 2 to communicate. The supply pipe 32 is filled with a wick material (not shown) made of a structure in which fine wires such as carbon fibers are bundled or a porous material. This wick material is for causing methanol as a fuel to permeate and causing capillary action. The mixed fuel supplied from the mixed fuel tank 31 generates oxygen, which is a non-condensable gas, by the hydrogen peroxide solution in the mixed fuel being decomposed by the catalyst 9 provided in the middle of the vaporization unit 4. . Next, the methanol permeating the wick material in the vaporizing section 4 is heated and evaporated.

  Due to the evaporation of methanol, the meniscus of the wick material in the supply pipe line 32 is lowered, and the mixed fuel in the mixed fuel tank 31 is sucked by the capillary pressure associated therewith. Further, since the partial pressure of methanol vapor is lowered by the non-condensable gas, the mixed fuel vapor can be supplied to the power generation unit 2 quickly and efficiently. A valve for selectively stopping methanol flowing from the mixed fuel tank 31 to the power generation unit 2 may be provided.

  Therefore, in the alcohol fuel cell having the configuration shown in FIG. 5, oxygen is generated by the catalyst 9 provided in the mixed fuel supply pipe 32, and the mixed fuel gas is supplied by evaporating methanol in the vaporizing section 4. The The mixed fuel vapor is supplied to the membrane-electrode assembly 11 for a power generation reaction as in the alcohol fuel cell having the configuration shown in FIG. In the fuel chamber 24, the methanol vapor is supplied with its partial pressure lowered, so that a sufficient amount of methanol can be supplied quickly, and it can be uniformly diffused for efficient power generation. Further, the carbon dioxide generated by the power generation reaction can be quickly discharged together with oxygen, which is a non-condensable gas, to improve the power generation efficiency, as in the example shown in FIG. 4 described above. In particular, in the configuration shown in FIG. 5, methanol evaporates from a wick material (not shown), and the meniscus changes accordingly, so that the wick material sucks liquid methanol, so that the flow rate of methanol can be automatically adjusted. It is to be noted that, by not requiring a power device such as a pump, the miniaturization is easy and the power generation efficiency can be improved as in the example shown in FIG.

  The experimental machine shown in FIG. 4 was produced, and a 50% methanol solution diluted with water was used as the fuel. The hydrogen peroxide solution was diluted with water so that the concentration was 3%. Manganese dioxide was used as a catalyst for decomposing hydrogen peroxide. The vaporization part and the catalyst combustion chamber were 10 × 10 × 5 mm sealed chambers, each part had a thickness of 1 mm, and the vaporization part was filled with a wick material obtained by hydrating carbon fibers. The catalyst combustion chamber was filled with a catalyst in which platinum was supported on a metal wick material.

A 0.1 mm Nafion 117 (registered trademark) was used as the electrolyte membrane, an equivalent mixture of platinum and ruthenium was used as the catalyst on the fuel chamber side, and platinum was used as the catalyst on the air chamber side. The thickness of each catalyst layer was adjusted to 20 μm. The production method of the catalyst layer will be described. An alcohol is used as a solvent and a powdered catalyst is mixed therein to make an ink, and a catalyst film is produced on a Teflon sheet by a screen printer. This was superposed on the electrolyte membrane, heated and pressurized with a hot press machine (140 ° C. × 5 minutes), then cooled in a pressurized state, and the catalyst membrane was transferred to the electrolyte membrane.
In addition, a bonnet fiber with a thickness of 1 mm, which has been hydrated as a gas permeable layer, is arranged on the fuel chamber side and the air chamber side, and the electrode has a mesh structure with an opening diameter of 2 mm. The material is platinum plated. Stainless steel was used.
The above materials were heated and pressed with a hot press machine to produce an MEA as an integral structure. The electrode area at this time was 25 cm ² (5 × 5 cm).

  When the temperature of the partition between the vaporization section and the catalytic combustion chamber was measured after the power generation amount of the fuel cell was stabilized, a heat generation of about 200 ° C. was confirmed. The boiling point of methanol is about 65 ° C. under standard atmospheric pressure, and it has been confirmed that a sufficient amount of heat can be obtained to vaporize methanol.

  Moreover, the measured electromotive force is shown in FIG. In FIG. 6, the solid line represents the power generation characteristics of the direct methanol fuel cell according to the present invention, and the broken line represents the power generation characteristics of a comparative example of a conventional type that supplies liquid methanol directly to the power generation section. When the non-condensable gas is not mixed in the direct methanol fuel cell according to the present invention, the amount of power generation is higher than that when liquid methanol is supplied to the power generation unit, and stable power generation characteristics are obtained. It was confirmed that

  Although not shown, when the amount of methanol vapor transported by oxygen generated from hydrogen peroxide was evaluated in advance, it was confirmed that 20 g of methanol vapor per hour could be transported.

  By the way, in the direct alcohol fuel cell according to the present invention, in order to use high-temperature vaporized alcohol as a fuel, when a perfluorosulfonic acid polymer membrane which is a general electrolyte membrane material is used, Crossover phenomenon occurs. When the crossover phenomenon occurs, the vaporized methanol reaches the air chamber side electrode (cathode) from the fuel chamber side electrode (anode), and the vaporized methanol on the cathode and oxygen supplied from outside React to cause methanol oxidation reaction. As a result, the electrode potential shifts in the negative direction, and so-called electromotive force (generated power) decreases.

  This crossover phenomenon is more likely to occur as the electrolyte membrane is hotter and the alcohol concentration is higher. In the direct alcohol fuel cell according to the present invention, alcohol such as methanol, which is fuel, is heated and vaporized, so that the electrolyte membrane becomes high temperature, and the alcohol tends to have a high concentration because of the vapor pressure of the alcohol. As a result, a crossover phenomenon is likely to occur.

  Therefore, in this embodiment, in order to prevent or suppress the crossover phenomenon, it is preferable to use PBI having a high glass transition point as the electrolyte membrane. PBI exists stably even under a heat load of about 200 ° C. generated from the catalytic combustion chamber in the steady state of the direct alcohol fuel cell according to the present invention described above, that is, in a state where the power generation amount is stable. It is difficult to cause the aforementioned crossover phenomenon. FIG. 7 shows the power generation characteristics of a fuel cell produced by changing only the electrolyte membrane of the direct alcohol fuel cell according to the present invention to PBI. In FIG. 7, the solid line indicates the power generation characteristics when a perfluorosulfonic acid polymer membrane is used as the electrolyte membrane, and the broken line indicates the power generation characteristics when PBI is used as the electrolyte membrane. When PBI was used for the electrolyte membrane, it was recognized that the output power value was improved by about 50% compared to the case where a perfluorosulfonic acid polymer membrane was used for the electrolyte membrane.

  In the present invention, the wick material used in the fuel supply path is most suitable because the glass fiber having a wick structure is thermally stable and is most suitable, but depending on the use conditions, cotton, ceramics or aluminum fine wires are used. Also good. Furthermore, since the vaporization section and the catalytic combustion chamber described above are at a high temperature, it is desirable to have a heat insulating structure from the viewpoint of safety and long-term reliability of the entire fuel cell.

  On the other hand, when the fuel cell is used in an environment with a low external temperature, such as in a cold region, the time required to start power generation may increase because the temperature of the power generation unit is low. As a countermeasure, it is also effective to heat the power generation unit by transferring the heat generated from the catalyst combustion chamber described above to the power generation unit. As a heat transfer means in this case, a general member such as a metal plate or a heat pipe may be used.

  Manganese dioxide as a catalyst was supported on glass fiber by the method described below. Glass fibers that had been washed in advance were immersed in manganese nitrate (hexahydrate) diluted with ethanol to a concentration of 10%, and heated at 400 ° C. for 1 hour to be supported. As a catalyst for decomposing hydrogen peroxide, platinum may be used other than manganese dioxide. However, when alcohols, particularly methanol, are used as the fuel to be used, since methanol is decomposed by the catalytic action of platinum, it is necessary to take a structure in which methanol and platinum do not contact.

  The platinum catalyst in the catalytic combustion chamber was supported on glass fibers by the method described below. After immersing the pre-washed glass fiber in hexachloroplatinic acid (hexahydrate) diluted with water to a concentration of 10%, it is taken out of the solution, heated to 300 ° C., and then It was supported by carrying out a hydrogen reduction treatment at room temperature.

  Hydrogen peroxide, which is a non-condensable gas generation source, may be mixed in advance with alcohol, which is a fuel. In this case, in order to decompose the hydrogen peroxide solution, the mixed solution of hydrogen peroxide and alcohol is passed through a supply path in which the catalyst is arranged. However, when manganese dioxide is used as the catalyst, Only the alcohol is decomposed, so the alcohol is not affected by the catalyst.

In addition, the following example is given as a method of generating non-condensable gas. In the case of hydrogen peroxide, nitrogen gas can be generated by contacting with hydrazine.
H ₂ O ₂ + N ₂ H ₄ → N ₂ + 4H ₂ O

  In addition, the non-condensable gas can also be obtained by bringing the oxidizer, the fuel component, and, if necessary, the component constituting the additive into contact with each other.

  Examples of the oxidizing agent include nitric acids, nitrous acids, basic nitric acids, oxohalogenates, and the like.

  Examples of nitric acids include nitric acid, ammonium nitrate, sodium nitrate, potassium nitrate, barium nitrate, and strontium nitrate.

  Examples of nitrites include sodium nitrite, potassium nitrite, barium nitrite, and strontium nitrite.

  Examples of the basic nitric acid include basic copper nitrate, basic manganese nitrate, basic iron nitrate, basic molybdenum nitrate, basic bismuth nitrate, and basic cerium nitrate.

  Examples of oxohalogenates include halogen salts and perhalogenate salts.

  Examples of the halogen salts include alkali metal halide salts such as potassium chlorate and sodium chlorate, alkaline earth metal salts such as barium chlorate and calcium chlorate, and ammonium halide salts such as ammonium chlorate. . Examples of perhalogenates include alkali metal perhalogenates such as potassium perchlorate and sodium perchlorate, alkaline earth metal perchlorates such as barium perchlorate and calcium perchlorate, and ammonium perchlorate. And ammonium perhalogenate.

  Examples of the fuel component include nitrogen-containing compounds, organic acids, salts of organic acids, powdered microcrystalline carbon, and the like.

  Nitrogen-containing compounds include nitramine compounds, guanidine derivatives, tetrazole derivatives, triazole derivatives, hydrazine derivatives, azodicarbonamide derivatives, and the like.

  Examples of the nitramine compound include trimethylenetrinitroamine (RDX) and tetramethylenetetranitroamine (HMX).

  Examples of guanidine derivatives include nitroguanidine and triaminoguanidine nitrate (TAGM).

  Examples of tetrazole derivatives include aminotetrazole, tetrazole, azotetrazole, bitetrazole and the like.

  Examples of triazole derivatives include triazole and urazole.

  Examples of the hydrazine derivative include hydrazine nitrate (HN).

  Examples of the azodicarbonamide derivative include azodicarbonamide and hydrazodicarbonamide.

  Examples of the powdered microcrystalline carbon include activated carbon, charcoal, coke, animal charcoal, bone charcoal, bituminous coal, and carbon black.

  As other additives, a aging stabilizer can be blended in order to improve the aging stability. As such a aging stabilizer, any one that can improve aging stability can be used.

  For example, a diphenylurea derivative, a diphenylamine derivative, a phenylurethane derivative, a diphenylurethane derivative, etc. are mentioned as a time stabilizer.

  Examples of diphenylurea derivatives include diphenylurea, methyldiphenylurea, ethyldiphenylurea, diethyldiphenylurea, dimethyldiphenylurea, and methylethyldiphenylurea.

  Examples of diphenylamine derivatives include diphenylamine and 2-nitrodiphenylamine.

  Examples of the phenylurethane derivative include ethylphenylurethane and methylphenylurethane.

  Examples of the diphenylurethane derivative include diphenylurethane. Other examples include resorcinol.

  In order to suppress the release of the alkali metal or alkaline earth metal oxide generated by the decomposition of the oxidizing agent or the like as mist to the outside, a slag forming agent can be blended as another additive.

  For example, examples of the slag forming agent include slag forming agents selected from at least one of silica, alumina, acid clay, talc, mica, molybdenum disulfide, and the like. Among these, silica, alumina, or acid clay is preferable as the slag forming agent.

  In addition, when water is brought into contact with an amphoteric metal such as an alkali metal, alkaline earth metal, or metal aluminum, hydrogen that is a non-condensable gas is generated.

  Since these chemical reactions may proceed explosively, from the viewpoint of safety, either the oxidizing agent or the fuel component is molded into a shape such as a tablet, and the chemical reaction surface area is increased. It is desirable to take measures such as reducing or precisely controlling the flow rate, and using a low-concentration material.

As still another method, nitrogen, which is a non-condensable gas, can be generated by heating azo compounds. The chemical reaction formula is described below.
2NaN ₃ → 2Na + 3N ₂

It is a block diagram which shows the main structures of the direct alcohol type fuel cell which concerns on this invention. It is the figure which showed typically the supply pipeline of the mixed fuel of the liquid and liquid alcohol which generate | occur | produce noncondensable gas. It is sectional drawing which shows typically the electric power generation part of the direct alcohol type fuel cell which concerns on this invention. 1 is a cross-sectional view schematically showing a direct alcohol fuel cell according to the present invention. It is the figure which showed typically the other example of the supply line of the mixed fuel of the liquid and liquid alcohol which generate | occur | produce noncondensable gas. It is a figure which shows the power generation characteristic of the direct alcohol type fuel cell concerning this invention, and the power generation characteristic of the comparative example which supplies liquid methanol directly to a power generation part. It is a figure which shows the electric power generation characteristic at the time of using PBI for an electrolyte membrane in this invention, and the electric power generation characteristic at the time of using a perfluorosulfonic acid type polymer film for an electrolyte membrane.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Fuel tank, 2 ... Power generation part, 4 ... Evaporation part, 5 ... Non-condensable gas tank, 10 ... Non-condensable gas mixing part, 11 ... Membrane electrode assembly (MEA), 12 ... Electrolyte membrane, 23 ... Bulkhead, 24 ... Fuel chamber, 27 ... Intake port, 28 ... Exhaust pipe, 31 ... Mixed fuel tank.

Claims (4)

Direct alcohol type in which a fuel chamber is formed on one side of the membrane / electrode assembly with electrodes provided on both the front and back surfaces of the electrolyte membrane, and an air chamber is formed on the other side, and alcohol is supplied to the fuel chamber In fuel cells,
An alcohol vapor source that supplies heated and vaporized alcohol fuel to the membrane / electrode assembly, and a non- condensation composed of oxygen into the alcohol vapor supplied from the alcohol vapor source to the membrane / electrode assembly. e Bei a noncondensable gas mixing unit for mixing the sex gas,
The non-condensable gas mixing unit includes a hydrogen peroxide tank that stores hydrogen peroxide, a non-condensable gas supply path that connects the alcohol vapor channel and the hydrogen peroxide tank, and a non-condensable gas thereof. A direct alcohol fuel cell comprising: a catalyst provided in the middle of a supply path and generating oxygen by decomposing the hydrogen peroxide . Direct alcohol type in which a fuel chamber is formed on one side of the membrane / electrode assembly with electrodes provided on both the front and back surfaces of the electrolyte membrane, and an air chamber is formed on the other side, and alcohol is supplied to the fuel chamber In fuel cells,
An alcohol vapor source that supplies heated and vaporized alcohol fuel to the membrane / electrode assembly, and a non-condensation composed of oxygen into the alcohol vapor supplied from the alcohol vapor source to the membrane / electrode assembly. A non-condensable gas mixing part for mixing a functional gas,
The non-condensable gas mixing section includes a fuel supply path for allowing a mixture of alcohol fuel and hydrogen peroxide to flow toward the membrane-electrode assembly, and is interposed in the middle of the fuel supply path, and the peroxidation features and to holder Electricity alcohol fuel cell that has a catalyst for generating oxygen by decomposing hydrogen.   The direct alcohol fuel cell according to claim 2, wherein the concentration of hydrogen peroxide in alcohol is within 10 weight percent.   4. The direct alcohol fuel cell according to claim 1, wherein the alcohol is methanol.

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