Patent Application
20060008693
The present application claims priority from Japanese application JP 2004-201281 filed on Jul. 8, 2004, the content of which is hereby incorporated by reference into this application.
The present invention relates to a fuel cell in which liquid fuel is oxidized in the anode of a membrane electrode assembly (MEA) composed of an anode, an electrolyte membrane, a cathode and a diffusion layer, and oxygen is reduced in the cathode of the same MEA.
A fuel cell is an electric power generator which is composed of at least a solid or liquid electrolyte and two electrodes (an anode and a cathode) inducing a desired electrochemical reaction, and converts the chemical energy carried by the fuel in the cell directly into electrical energy with a high efficiency.
A polymer electrolyte membrane fuel cell (PEM-FC) system is generally composed of a battery, a fuel container, a fuel feeder, and an air or oxygen feeder; in this system, the battery is formed of unit cells connected in series or in parallel according to need, and each of the unit cells is composed of a polymer electrolyte membrane, and a porous anode and a porous cathode respectively arranged on both sides of the electrolyte membrane.
Among PEM-FCs, direct methanol fuel cells (DMFCs), metal hydride fuel cells, and hydrazine fuel cells have attracted attention as small effective transportable or portable electric power supplies because these fuel cells use liquid fuel and hence the energy density per volume of the fuel is high; among these fuel cells, DMFCs using methanol as fuel can be said to be ideal electric power supply systems because methanol is expected to be produced from biomass in the near future.
For the purpose of using fuel cells such as DMFCs using liquid fuel as electric power supplies for use in portable appliances, efforts have been made to achieve high performance of electrode catalysts, high performance of electrode structure, and development of solid polymer membranes small in fuel crossover (penetration) in a manner aiming at a battery having a higher output power density. Also for the same purpose, there have been pursued ultimate technique for downsizing of fuel pumps and air blowers, and systems requiring no auxiliary driving devices such as fuel feeding pumps and air feeding blowers.
JP-A-2003-100315 (Patent Document 1) discloses a fuel cell which needs no auxiliary driving devices; in this fuel cell, a gas-liquid separation membrane is arranged on the wall of a container holding liquid fuel, for the purpose of discharging outside the container carbon dioxide (CO2) generated in the anode, so that the generated carbon dioxide is discharged without leaking the liquid fuel outside the container.
However, now that recent advances in techniques involving MEA used in DMFCs have improved the battery performance of DMFCs, on the basis of the above disclosed cell structure with a gas-liquid separation membrane arranged therein, it comes to be difficult to bring out a large cell output power, because the above disclosed cell structure cannot discharge to a sufficient extent the carbon dioxide gas generated by the oxidation of the liquid fuel in the anode while electric power is generated in such a way that the generated carbon dioxide gas bubbles stick to the surface of the anode to impede the diffusion of the fuel.
An object of the present invention is to provide a fuel cell from which a large cell output power can be brought out.
According to the present invention, there is provided a fuel cell composed of an anode for oxidizing liquid fuel, a cathode for reducing oxygen, an electrolyte membrane provided between the above described anode and the above described cathode, a fuel chamber to hold liquid fuel to be fed to the anode, and an exhaust gas module having a function of gas-liquid separation installed so as to permit ventilation between the inside and the outside of the fuel chamber.
Thus, there can be obtained a fuel cell in which the carbon oxide generated in the anode is discharged from the fuel chamber, and a large electric output power can be generated.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.
FIGS. 10(a), 10(b) and 10(c) each illustrate an example of an anode current collector structure according to the present invention.
FIGS. 11(a), 11(b) and 11(c) each illustrate an example involving an MEA structure and diffusion layer structures according to the present invention.
Now, description will be made below on an embodiment related to the present invention, but the present invention is not limited by the embodiment to be described below.
A fuel cell 1, using methanol as fuel, to be used in the present embodiment generates electric power by directly converting the chemical energy contained in methanol into electric energy through the following electrochemical reaction. In the anode, a fed methanol aqueous solution undergoes a reaction according to formula (1) to be dissociated into carbon dioxide gas, hydrogen ions and electrons (oxidation reaction of methanol).
CH3OH+H2O→CO2+6H++6e− (1)
The generated hydrogen ions moves in an electrolyte membrane from the anode to the cathode, and react with the oxygen gas from the air reaching the electrode by diffusion and electrons on the electrode according to formula (2) to produce water (the reduction reaction of oxygen).
6H++3/2O2+6e−→3H2O (2)
Consequently, as shown by formula (3), the total chemical reaction associated with the electric power generation produces carbon dioxide gas and water by oxidizing methanol with oxygen to have the same chemical reaction formula as that in the flame combustion of methanol.
CH3OH+3/2O2→CO2+3H2O (3)
The open-circuit voltage of a unit cell is approximately 1.2 V, but the substantial voltage is 0.85 to 1.0 V owing to the effect of the penetration of the fuel into the electrolyte membrane; under practical load operation, the voltage is selected to range approximately from 0.2 to 0.6 V although no particular constraint is imposed on the voltage range. Accordingly, when unit cells are practically used as an electric power supply, the unit cells are connected in series so as to generate a predetermined voltage in conformity with the requirement from a load device. The output current density of a unit cell is affected and thereby varied by the electrode catalyst, the electrode structure and other factors; thus, a unit cell is designed so that a predetermined current may be effectively obtained by selecting the area of the electric power generation section of the unit cell. Additionally, appropriate parallel connection of unit cells makes it possible to adjust battery capacity. In the present embodiment, the rated voltage of a unit cell is set at 0.3 V.
An example of a fuel cell related to the present embodiment will be described below in detail.
In
Although the slits 22a to distribute fluids such as fuel and oxidant gas are formed as parallel grooves in
Additionally, because the respective gas-liquid separation tubes 31 in the exhaust gas module 30 are fixed so as to pass through the holes 24 in the rib supporting plates 23 arranged in the fuel chamber 12, the gas-liquid separation tubes 31 are separated from each other at an identical distance, and thus non-uniform gas discharge can be avoided.
Now, the slits 22 arranged in the anode terminal plate 13a will be described. In the case of spherical bubbles where the diameter of the detaching gas bubbles comes to be maximum, with the hole diameter D, the surface tension T, the density of the methanol aqueous solution ρ, the gravitational acceleration g, and the radius of the detaching gas bubbles γ, the following relation holds:
D=2γcos θ
where the contact angle of the gas bubble θ is determined by the following expression:
(πρgD2/24 cos2θ)(1−3 cos 2θ+sin 3θ−3 sin θ)−2πT cos2θ=0
The aperture of the slits 22 is generally selected to be 25 to 50% in view of the current collecting property and the rigidity compatible with the fixing of MEAs; additionally, in consideration of the thickness deformation of the MEAs caused by tightening and fixing, the slit width is selected to be 1 to 2 mm, the pitch of the slits is selected to be 2 to 4 mm. Consequently, with the diameter of 2 mm for the circular holes and a 10 wt % methanol aqueous solution, the contact angle of the gas bubble 0 comes to be about 60°, and the diameter 27 of the detaching gas bubbles comes to be about 4 mm. Accordingly, the separation between the gas-liquid separation module 30 and the anode terminal plate 13a facing the module is preferably set at 4 mm or less; thus, the generated and grown gas bubbles get into contact with the surface of the gas-liquid separation module 30 to be broken before the bubbles detach owing to the ascending force, and hence the gas bubbles are effectively removed, so that the gas does not block the surface of the anode, and the more stable and higher output power performance can thereby be maintained.
More specifically, the exhaust gas module 30 is not located on the wall surface of the fuel chamber as a conventional gas-liquid separation membrane formed on the wall surface of the fuel chamber, but located in the fuel chamber close to the anode surface, so that the exhaust gas module 30 makes it possible to discharge the carbon dioxide gas more efficiently.
In the above case, there is shown an example in which the module is formed by using water-repellent porous hollow fibers as the gas-liquid separation tubes 31; however, the formation of the exhaust gas module is not limited to this example, but can take any shape as long as the exhaust gas module is an exhaust gas module, having a function of gas-liquid separation, arranged in the fuel chamber 12 so as to face the anode surface. For example, as shown in
Additionally, the example disclosed in
Additionally, no particular constraint is imposed on the insulating sheet 41 constituting the anode terminal plate 13a as long as the insulating sheet is a material with which the current collectors 42 arranged in the surface of the sheet can be integrated and bonded in a manner ensuring insulating property and planarity of the sheet. It is recommended to use high density vinyl chloride, high density polyethylene, high density polypropylene, epoxy resin, polyetheretherketones, polyethersulfones, polycarbonate, polyimide resin, and glass fiber reinforced materials derived from these materials. Additionally, steel, nickel, alloy materials made of light weight metals such as aluminum and magnesium, intermetallic compounds represented by copper-aluminum, and various stainless steels are used; there are applied a method in which the surface of a sheet made of these materials is made nonconductive and a method in which the surface of the sheet is made to be insulating by applying resins onto the surface; and thus, the sheet can be bonded to the current collectors 42.
The prominent feature of the present invention is that the above described anode terminal plates 13a can achieve electric contact with the current collectors 42 and MEAs without need of large rigidity of the terminal plates because the present invention adopts a method of fixing the MEAs with the ribs 21 of the fuel chamber 12, so that the anode terminal plates can be made thinner to be 0.05 to 1.0 cm in thickness. Consequently, the carbon dioxide gas, generated in the anode when electric power is generated, moves away from the electrode without growth of the gas bubbles to be large in size in the vicinity of the electrode surface, so that the bubble growth of the carbon dioxide gas on the electrode surface can be suppressed, and hence a high electric power generation performance can be maintained.
Additionally, either by chemically introducing hydrophilic groups onto the surface of the anode terminal plate 13a or by making the anode terminal plate 13a hydrophilic by dispersing to support hydrophilic substances represented by titanium oxide on the surface thereof, there is obtained a prominent effect of removing the carbon dioxide gas in the vicinity of the anode because the carbon dioxide gas generated by electric power generation does not stick to and stay on the anode terminal plate 13a, and rapidly migrates.
The anode catalyst constituting the electric power generation section is a catalyst in which fine particles of a mixed metal of platinum and ruthenium or a platinum/ruthenium alloy are dispersed in and supported by a carbon powder carrier, and the cathode catalyst constituting the electric power generation section is a catalyst in which fine particles of platinum are dispersed in and supported by a carbon carrier; these catalyst materials are able to be easily prepared and utilized. It is generally preferable that the loading amount of platinum as the main component in relation to the carbon powder is 50 wt % or less; even when the loading amount is 30 wt % or less, a high performance electrode can be formed by using a highly active catalyst or by improving the dispersion condition on the carbon carrier. The amount of platinum in the anode 45 is preferably 0.5 to 5 mg/cm2 and that in the cathode 46 is preferably 0.1 to 2 mg/cm2.
However, the catalysts for the anode and cathode of the fuel cell according to the present example are not limited to particular catalyst compositions; those catalysts to be used in usual direct methanol fuel cells can be used; as the performance of a catalyst is increased, the catalyst amount can be reduced to be effective for reducing the cost of the electric power supply system.
When a proton conducting material is used for the electrolyte membrane, there can be actualized a stable fuel cell because such a cell is free from the effect of the carbon dioxide in the air. As such a material, there can be used materials of sulfonated or alkylsuofonated hydrocarbon polymers such as sulfonated fluoropolymers and polystyrene suflonic acid represented by polyperfluorostyrene sulfonic acid and perfluorocarbon sulfonic acid; and sulfonated polyethersulfones and sulfonated polyetheretherketones. When these materials are used as electrolyte membrane, fuel cells can be operated generally at a temperature of 80° C. or lower. Additionally, there can be actualized a fuel cell operatable up to higher temperatures by use of composite electrolyte membranes in which proton conducting inorganic substances such as tungsten oxide hydrate, zirconium oxide hydrate and tin oxide hydrate are microdispersed in a heat resistant resin or a sulfonated resin. In particular, composite electrolytes in which sulfonated polyethersulfones and polyetherethersulfones, or proton conducting inorganic substances are used are preferable as electrolyte membranes having a lower permeability of methanol to be used as fuel than polyperfluorocarbon sulfonic acids. In any rate, because the use of an electrolyte membrane high in proton conductivity and low in methanol permeability results in a high conversion rate of fuel into electricity, the use of such a membrane makes it possible to realize, at a high level of achievement, the effect of the present invention such that the electric supply system is made compact and long-time electric power generation is actualized.
FIGS. 11(b) and 11(c) show the structure of a cathode diffusion layer 70c and that of an anode diffusion layer 70a used in the present invention. The cathode diffusion layer 70c is composed of a water repellent layer 72 which strengthens the water repellency, elevates the water vapor pressure in the vicinity of the cathode, and prevents the diffusive discharge of the generated water vapor and the condensation of water, and a porous carbon substrate 71c; the water repellent layer 72 is laminated so as to be in contact with a cathode electrode 62c; no particular, constraint is imposed on the surface contact between the anode diffusion layer 70a and an anode electrode 62a; and porous carbon substrate 71a is used. For the porous carbon substrate 71c of the cathode diffusion layer 70c, a conductive porous material is used. In general, there is used carbon fiber woven or nonwoven cloth such as carbon fiber woven cloth including a carbon cloth (Torayca cloth, manufactured by Toray Industries, Inc.) and a carbon paper (TGP-H-060, manufactured by Toray Industries, Inc.); the water repellent layer 72 is formed by mixing carbon powder with water repellent fine particles, water repellent fibril or water repellent fiber such as poloytetrafluoroethylene.
In more detail, a sheet of carbon paper (TGP-H-060, manufactured by Toray Industries, Inc.) is cut to a predetermined size, the absorbed amount of water of the carbon paper piece thus obtained is measured; thereafter, the carbon paper piece is immersed into a polytetrafluorocarbon/water dispersion liquid (D-1, manufactured by Daikin Kogyo Co., Ltd.) diluted so that the weight ratio after baking the carbon paper piece may be 20 to 60 wt %, and dried at 120° C. for 1 hour; and moreover, the baking operation is conducted in the air at temperatures between 270 and 360° C. for 0.5 to 1 hour. Then, to a carbon powder (XC-72R, manufactured by Cabot Co., Ltd.), the polytetrafluorocarbon/water dispersion liquid is added so as for the ratio of the liquid to be 20 to 60 wt % in relation to the carbon powder, and the mixture thus obtained is kneaded. The kneaded mixture in paste form is applied onto the one side of the carbon paper piece made water repellent as described above so as for the thickness of the kneaded mixture to be 10 to 30 μm. The carbon paper piece thus treated is dried at 120° C. for about 1 hour, and then calcined in the air at temperatures between 270 and 360° C. for 0.5 to 1 hour to yield a cathode diffusion layer 70c. The air permeability and the moisture permeability of the cathode diffusion layer 70c, namely, the diffusion properties of the fed oxygen and the generated water are largely dependent on the addition amount, the dispersibility and the baking temperature of polytetrafluoroethylene, and accordingly, these conditions for polytetrafluoroethylene are properly selected after considering the design performance and the usage environment of the fuel cell.
For the anode diffusion layer 70a, suitable materials are woven and nonwoven carbon fiber cloth to meet the required conditions involving the electric conductivity and porosity, such as carbon fiber woven cloth including a carbon cloth (Torayca cloth, manufactured by Toray Industries, Inc.) and a carbon paper (TGP-H-060, manufactured by Toray Industries, Inc.). The function of the anode diffusion layer 70a is the acceleration of the feeding of an aqueous solution fuel and the rapid dissipation of the generated carbon dioxide gas, and hence the following methods are effective for the purpose of suppressing the growth of bubbles, in the carbon porous substrate 71a, of the gas generated in the anode and increasing the output power density of the fuel cell: a method in which the surface of the above described carbon porous substrate 71a is made hydrophilic by slow oxidation or ultraviolet irradiation, a method in which a hydrophilic resin is dispersed in the carbon porous substrate 71a and a method in which a strongly hydrophilic substance represented by titanium oxide are dispersed and supported in the carbon porous substrate 71a. Additionally, the material for the anode diffusion layer 70a is not limited to the above described materials, but there can also be used porous materials such as substantially electrochemically inactive metal materials (for example, stainless steel fiber nonwoven cloth, porous bodies, porous titanium, and porous tantalum).
A fuel feeding pipe 115 is arranged at the tip of the cylinder 111 through the intermediary of an open-close mechanism 114. FIGS. 20(A) and 20(B) show the conditions, respectively before and after mounting, of the sectional structures of the open-close mechanism 114 and the socket 26 for the cartridge, used in the fuel cartridge tank 2. The cartridge open-close mechanism 114 is constituted with the hollow fuel feeding pipe 115 having a liquid passage opening 123, an open-close valve 121, and a spring 122 to be used for pushing the fuel feeding pipe 115 for the purpose of closing the liquid passage opening 123 by use of the open-close valve 121 when the system is shut down. On the other hand, the socket 26 for the cartridge is fixed with the spring 122 so that a socket valve 131 having the liquid passage opening 123 may close the liquid passage opening 123 with seal rings 132 when the operation of the system is shut down. When the fuel cartridge tank 2 is fixed to the socket 26 for cartridge, the respective valves are opened as shown in
As long as the materials used for the liquid fuel cartridge 110, the open-close mechanism 114, the cylinder 111 and the socket 26 for cartridge are durable against the liquid fuel, no particular constraint is imposed on the materials; the materials are selected to be used from high density vinyl chloride, high density polyethylene, high density polypropylene, epoxy resin, polyetheretherketones, polyethersulfones, polycarbonate, polyimide resin and ethylene-propylene rubber and the like, in conformity with the compositions related to rigidity and flexibility required for the respective components. As the high pressure gas charged in the cartridge, one or more are selected to be used from the group consisting of pressurized gases such as carbon dioxide, nitrogen, argon and air, and pressurized liquefied gases such as butane and chlorofluorocarbon. Additionally, the charging pressure of the high pressure gas is varied depending on the volume ratio between the volume of the cylinder 111 and the volume of the high pressure gas charging part and the sliding resistance exerted to the piston 112 for use in feeding the liquid fuel; as the charging pressure of the high pressure gas is increased, the cylinder can be easily driven.
However, in consideration of the pressure proof property of the sealing in the fuel cell and the safety in handling the cartridge, the initial pressure is preferably 0.3 MPa or less (gauge pressure). Here is disclosed a method in which a high pressure gas is used as the force to transport the liquid fuel from the fuel cartridge to the fuel cell; however, no constraint is imposed on the method for transporting the liquid fuel, a method in which the piston is driven by use of force exerted by a spring is also effective.
A specific example of a DMFC for use in a portable information terminal will be described below.
A sheet of 0.3 mm thick titanium plate was used as the material for the current collectors, and the current collector surface contacting with the electrodes was beforehand cleaned and then the surface was deposited with gold with a thickness of about 0.1 μm.
The size of the electric power supply thus fabricated is 115 mm×90 mm×9 mm. A 30 wt % methanol aqueous solution was injected into the fuel chamber 12 of the fuel cell thus fabricated, an electric power generation test was carried out at room temperature, and the resulting output power was represented by 4.2 V and 1.2 W.
The present example is a fuel cell electric power generation apparatus in which the anode to oxidize the fuel and the cathode for reducing oxygen are bonded through the intermediary of an electrolyte membrane, and liquid fuel is used, wherein in the electrically insulating fuel chamber provided with a plurality of groove structures, an exhaust gas module made of a plurality of combined water-repellent porous hollow fibers is arranged in the above described grooves so as to face the anode surface, and a plurality of fuel cells are electrically connected onto the outer surface of the fuel chamber provided with a function to discharge gas. The fuel cell electric power generation apparatus, having a structure in which a plurality of fuel cells are arranged on the outer surface of the anode chamber and are electrically connected, is suitable as an electric power supply for use in a portable appliance comparatively small in load current and requiring a high voltage as compared to the unit cell voltage of the fuel cell, and the fuel cell electric power generation apparatus can be made to be a compact electric power supply. The growth of the bubbles of the carbon dioxide gas generated by oxidation of methanol in the vicinity of the anode surface can be suppressed to increase the gas discharge ability, and the electric power generation is made possible for any orientation of the fuel cell and the ability of discharging carbon dioxide can be further enhanced by providing a function to discharge gas by use of a fluid pressure in the fuel chamber, through arranging in the groove parts of the fuel chamber the exhaust gas module provided with a plurality of combined water-repellent porous hollow fibers. Additionally, by incorporating a gas-liquid separation mechanism in the fuel chamber, the area contributing to the gas-liquid separation can be made larger, and accordingly it is possible to adopt a gas-liquid separation material with a smaller pore diameter, so that gas-liquid separation is made possible even for a higher concentration of methanol aqueous solution. Moreover, the arrangement of the exhaust gas module in the fuel chamber leads to a method to be claimed effective for preventing the liquid short circuiting caused by impurities having electrolyte character, generated between the facing electric power generation sections particularly when the electric power generation sections are arranged on both sides of the fuel chamber.
As an injection-type liquid fuel cartridge 110 for feeding methanol fuel, a cartridge having a structure shown in
The present example is a fuel cell electric power generation apparatus in which an anode to oxidize the fuel and a cathode for reducing oxygen are bonded to each other through the intermediary of an electrolyte membrane, and a liquid is used as fuel, wherein a fuel chamber with a plurality of groove structures is electrically insulating, to the fuel chamber is connected a fuel cartridge to extrude the liquid fuel by use of the force exerted by a liquefied high pressure gas or a high pressure gas, or the reaction force of a spring, and the liquid fuel is fed under the condition that the pressure of the fuel chamber is higher than the atmospheric pressure. The fuel cell electric power generation apparatus, having a structure in which a plurality of fuel cells are arranged on the outer surface of the anode chamber and are electrically connected, is suitable as an electric power supply for use in a portable appliance comparatively small in load current and requiring a high voltage as compared to the unit cell voltage of the fuel cell, and the fuel cell electric power generation apparatus can be a compact electric power supply.
Additionally, an exhaust gas module made of a plurality of combined water-repellent porous hollow fibers and the like is arranged in the grooves of the fuel chamber; the carbon dioxide gas, generated from the anode surface when the electric power is generated, can be discharged by use of the fluid pressure in the inside of the fuel chamber; and moreover, the carbon dioxide gas can be discharged without being accompanied by liquid fuel leakage even when the fuel cell is operated at any orientation thereof. Additionally, the adoption of the fuel resupply using a fuel cartridge makes it possible to easily carry out the fuel resupply, so that there can be actualized an electric power supply requiring no charging time in contrast to secondary batteries and most suitable for portable appliances.
When the pressure inside the fuel chamber is not made positive (larger than the atmospheric pressure), the carbon dioxide gas generated in the anode is accumulated inside the anode chamber, and is discharged into the atmosphere through the gas-liquid separation membrane when the pressure of the carbon dioxide gas reaches a predetermined value (for example, 0.05 atm) related to the gas permeation rate of the gas-liquid separation membrane. Consequently, there is created a space accumulating the carbon dioxide gas. However, the pressure inside the fuel chamber is maintained to be positive, and the liquid fuel is thereby compressed, so that the generated carbon dioxide gas is completely discharged into the atmosphere when the positive pressure of, for example, 0.05 atm is applied, and hence in principle no space for accumulating the carbon dioxide gas is needed in the anode chamber. As a result, the contact efficiency with the anode comes to be high, which is effective for making the cell compact.
A partition wall 105 divides the power supply mounting section, in such a way that the main board 102 and the lithium ion secondary battery 106 are placed in the lower section and the fuel cells 1 are arranged in the upper section. The upper wall and side wall of the chassis are provided with slits 22c for diffusion of air and cell exhaust gas. The surface of the portions of the slits 22c inside the chassis are provided with an air filter 107, and the surface of the partition wall is provided with a water-absorbing quick-drying material 108. No particular constraint is imposed on the air filter, as long as the air filter is a material high in gas diffusivity and capable of preventing the penetration of powder dust; a mesh-like material or a woven cloth made of single threads of a synthetic resin is suitable, because no clogging is caused. The present example used a single thread mesh made of polytetrafluoroethylene high in water repellency.
There is provided a fuel cell electric power generation apparatus in which the anode to oxidize the fuel and the cathode for reducing oxygen are bonded to each other through the intermediary of an electrolyte membrane, and a liquid is used as fuel, wherein a fuel chamber with a plurality of groove structures is electrically insulating, an exhaust gas module made of a plurality of combined water-repellent porous hollow fibers is arranged in the above described grooves so as to face the anode surface, and a plurality of fuel cells are electrically connected to the outer surface of the fuel chamber having a function of gas discharge. Additionally, there is included a method in which to the fuel chamber is connected a fuel cartridge to extrude the liquid fuel by use of the force exerted by a liquefied high pressure gas or a high pressure gas, or the reaction force of a spring, and the liquid fuel is fed under the condition that the pressure of the fuel chamber is higher than the atmospheric pressure.
The fuel cell electric power generation apparatus, having a structure in which a plurality of fuel cells are arranged on the outer surface of the anode chamber and are electrically connected, is suitable as an electric power supply for use in a portable appliance comparatively small in load current and requiring a high voltage as compared to the unit cell voltage of the fuel cell, and the fuel cell electric power generation apparatus can be made to be a compact electric power supply. Additionally, provision of a plurality of grooves in the fuel chamber makes it possible to omit or to make thinner an anode side end plate for use in tightening the cell; thus, the growth of the bubbles of the carbon dioxide gas generated by oxidation of methanol in the vicinity of the anode surface can be suppressed to increase the gas discharge ability. The electric power generation is made possible for any orientation of the fuel cell and the ability of discharging carbon dioxide can be further enhanced by providing a function to discharge gas by use of a fluid pressure in the fuel chamber, through arranging in the groove parts of the fuel chamber the exhaust gas module provided with a plurality of combined water-repellent porous hollow fibers.
Moreover, the use of the fuel cartridge to extrude the liquid fuel by use of the force exerted by a liquefied high pressure gas or a high pressure gas, or the reaction force of a spring makes it possible to actualize an electric power supply requiring no driving force for feeding fuel. Additionally, by incorporating the gas-liquid separation mechanism in the fuel chamber, the area contributing to the gas-liquid separation can be made larger, and accordingly it is possible to adopt a gas-liquid separation membrane with a smaller pore diameter, so that gas-liquid separation is made possible even for a higher concentration of methanol aqueous solution.
Additionally, a liquid fuel is high in volume energy density and can be easily resupplied by use of a fuel cartridge, so that there can be actualize an electric power supply requiring no charging time in contrast to secondary batteries and most suitable for portable appliances.
It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-201281 | Jul 2004 | JP | national |
