Patent Application
20070238000
The present invention will be illustrated in further detail with reference to several examples below, which by no means limit the scope of the present invention.
A 500-ml four-necked round-bottom flask used herein was equipped with a reflux condenser connected with a stirrer, a thermometer, and a calcium chloride tube. After replacing the inner atmosphere of the flask with nitrogen, 30 g of a poly(ether sulfone) (PES) and 250 ml of carbon disulfide were placed in the flask, and chloromethyl methyl ether in the amounts shown in Table 1, a mixture of 1 ml of anhydrous tin(IV) chloride and 20 ml of carbon disulfide was added dropwise thereto, and the resulting mixture was heated and stirred at 46° C. for the reaction time periods in Table 1. Next, the reaction mixture was poured into 1 liter of methanol to precipitate polymers. The precipitates were pulverized using a mixer, were washed with methanol, and thereby yielded chloromethylated polyether sulfones represented by Formula (1):
Each of the chloromethylated poly (ether sulfone) s of Formula (1) was immersed in triethyl ester of phosphonic acid and heated under ref lux for twelve hours. The reaction mixtures were poured into ethanol to precipitate polymers. The precipitates were pulverized in a mixer, were washed with ethanol, and thereby yielded 35 g each of chloromethylated diethylphosphomethylated poly(ether sulfone)s represented by Formula (2). The resulting polymers contain phosphomethyl groups in amounts of 0.54 to 1.3 milliequivalents per gram of dried resin, as shown in Table 1.
Each of the above-prepared chloromethylated diethylphosphomethylated polyether sulfones of Formula (2) was placed in a 1000-ml four-necked round-bottom flask equipped with a ref lux condenser connected with a stirrer, a thermometer, and a calcium chloride tube, and 600 ml of N-methylpyrrolidone was added. A solution of 9 g of potassium thioacetate in 50 ml of N-methylpyrrolidone (NMP) was added thereto, and the mixture was heated with stirring at 80° C. for three hours. Next, the reaction mixture was poured into 1 liter of water to precipitate polymers. The precipitates were pulverized in a mixer, were washed with water, were dried by heating, and thereby yielded acetylthiodiethylphosphomethylated polyether sulfones.
Each 20 g of the above-prepared acetylthiodiethylphosphomethylated polyether sulfones was placed in a 500-ml four-necked round-bottom flask equipped with a ref lux condenser connected with a stirrer, a thermometer, and a calcium chloride tube, and 300 ml of acetic acid was added thereto. The mixture was combined with 20 ml of an aqueous hydrogen peroxide solution and was heated at 45° C. with stirring for four hours. Next, the reaction mixture was added to 1 liter of 6 N aqueous sodium hydroxide solution with cooling, and the mixture was stirred for a while.
The resulting polymers were filtered and were washed with water until no basic component was contained. The polymers were added to 300 ml of 1 N hydrochloric acid, and the mixture was stirred for a while. The polymers were then filtered, were washed with water until no acidic component was contained, were dried under reduced pressure, and thereby quantitatively yielded each 20 g of sulfomethylated diethylphosphomethylated polyether sulfones of Formula (3). These polymers were verified to contain sulfomethyl groups, because their NMR spectra show a chemical shift of methylene proton to 3.78 ppm. The polymers contain sulfomethyl groups in amounts of 0.7 to 1.5 milliequivalents per gram of dried resin, as shown in Table 1.
Each of the sulfomethyldiethylphosphomethylated polyether sulfones prepared according to the step (3) was dissolved to a concentration of 5 percent by weight in a 1:1 solvent mixture of dimethylacetamide and methoxyethanol. The solution was applied to glass by spin coating, was air-dried, was dried at 80° C. in vacuo, and thereby yielded a series of electrolyte membranes of sulfomethyldiethylphosphomethylated poly(ether sulfone)s each having a thickness of 45 μm.
The polymer electrolyte membranes have ionic conductivities at room temperature of 0.03 to 0.1 S/cm as shown in Table 1. The polymer electrolyte membranes show an increasing ionic conductivity with an increasing amount of sulfomethyl groups. In contrast, the amount of phosphomethyl groups in the membranes does not substantially affect the ionic conductivity.
In addition, the polymer electrolyte membranes were weighed (initial dry weights), were immersed in a 40 percent by weight aqueous methanol solution at 60° C. for twenty-four hours, were dried under reduced pressure, and were weighed. Differences in weight between before and after immersion were determined, and resistance (insolubility) of the polymer electrolyte membranes against an aqueous methanol solution was evaluated. The results are shown in Table 1.
The polymer electrolyte membranes according to Examples 1 to 12 showed substantially no difference in weight before and after immersion to find that they are insoluble in the aqueous methanol solution. These polymer electrolyte membranes contain phosphomethyl groups in amounts of 0.54 to 1.3 milliequivalents per gram of dried resin, and sulfomethyl groups in amounts of 0.7 to 1.5 milliequivalents per gram of dried resin. The polymer electrolyte membranes were immersed in a 3 percent by weight aqueous solution of hydrogen peroxide containing 20 ppm of ferric chloride at 80° C. for twenty-four hours, were washed with water, were dried under reduced pressure, and weights and ionic conductivities of the membranes were measured.
The oxidation resistances of the membranes were evaluated based on retentions in weight and ionic conductivity between before and after immersion, to find that they have good oxidation resistance. Specifically, the electrolyte membranes containing sulfomethyl groups and phosphomethyl groups have ionic conductivities of 0.03 S/cm or more, are highly resistant to methanol and to oxidation, and are advantageously used typically in direct-methanol fuel cells (DMFCs).
A slurry was prepared by mixing a catalyst powder, 30 percent by weight of a binder, and a solvent mixture of 1-propanol, 2-propanol, and methoxyethanol. The catalyst powder contained a carbon carrier and 50 percent by weight of fine particles of a 1:1 (by atomic ratio) platinum/ruthenium alloy dispersed and supported on the carbon carrier. The binder was the polymer electrolyte (sulfomethylated diethylphosphomethylated poly(ether sulfone)) prepared according to Example 12. The slurry was applied to a polyimide film by screen printing and thereby yielded an anode having a thickness of about 125 μm, a width of 30 mm, and a length of 30 mm. Next, another slurry was prepared by mixing a catalyst powder, a binder, and a solvent mixture of water and alcohols. The catalyst powder contained a carbon carrier and 30 percent by weight of platinum fine particles supported on the carbon carrier.
The binder was a solution of a poly(perfluorosulfonic acid) in a solvent mixture of 1-propanol, 2-propanol, and methoxyethanol. The slurry was applied to a polyimide film by screen printing and thereby yielded a cathode having a thickness of about 20 μm, a width of 30 mm, and a length of 30 mm. Next, about 0.5 ml of a 5 percent by weight solution of the polymer electrolyte prepared according to Example 12 in a solvent mixture of 1-propanol, 2-propanol, and methoxyethanol was allowed to permeate the surface of the anode, and the anode was then bonded with each of the sulfomethylated poly(ether sulfone) electrolyte membranes prepared in the step (4) in Examples 1 to 12.
The resulting articles were dried at 80° C. under a load of about 1 kg for three hours. Next, about 0.5 ml of a 5 percent by weight solution of the polymer electrolyte prepared according to Example 12 in a solvent mixture of 1-propanol, 2-propanol, and methoxyethanol was allowed to permeate the surface of the cathode, and the cathode was bonded with the other side of the polymer electrolyte membranes according to Examples 1 to 12 opposite to the anode layer, so that the cathode layer overlay the anode layer with the interposition of the membrane. The resulting articles were dried at 80° C. under a load of about 1 kg for three hours and thereby yielded a series of membrane/electrode assemblies (MEAs) (1).
Anode and cathode diffusion layers were prepared in the following manner. A paste was prepared by adding 40 percent by weight in terms of weight after firing of an aqueous dispersion of polytetrafluoroethylene (PTFE) fine particles (Dispersion D-1: Daikin Industries, Ltd.) as a water repellant to carbon powder particles, and kneading the mixture. The paste was applied to one side of a carbon cloth having a thickness of about 350 μm and a porosity of 87%, was dried at room temperature, was fired at 270° C. for three hours, and thereby yielded a carbon sheet.
The amounts of the polytetrafluoroethylene (PTFE) were set to 5 to 20 percent by weight relative to the weight of the carbon cloth. The sheet was cut to the same size as the electrodes of the membrane/electrode assembly (MEA) and thereby yielded a cathode diffusion layer. A carbon cloth having a thickness of about 350 μm and a porosity of 87% was immersed in fuming sulfuric acid (concentration: 60%) in a flask and was held at a temperature of 60° C. in an atmosphere of nitrogen gas flow for two days. Next, the flask was cooled to room temperature. After removing fuming sulfuric acid, the carbon cloth was fully washed until the distilled water became neutral.
Next, the carbon cloth was immersed in methanol and was dried. The resulting carbon cloth had an infrared absorption spectrum showing absorptions derived from —OSO3H group at 1225 cm−1 and 1413 cm−1, and an absorption derived from —OH group at 1049 cm−1. This demonstrates that the surface of the carbon cloth bears —OSO3H groups and —OH groups introduced thereto. In this connection, a carbon cloth not treated with fuming sulfuric acid has a contact angle with an aqueous methanol solution of 81°. The treated carbon cloth, however, had a contact angle with an aqueous methanol solution less than 81° to find to be hydrophilic. In addition, the carbon cloth was excellent in electroconductivity. The carbon cloth was cut to a piece having the same size as the electrodes of the membrane/electrode assemblies (MEAs) (1) and thereby yielded an anode diffusion layer.
Each of the membrane/electrode assemblies (MEAs) (1) bearing the diffusion layers was mounted to a single cell of solid polymer fuel cell generator shown in
A fuel cell was prepared and a test was conducted by the procedure of Example 1, except for using a poly(perfluorosulfonic acid) as the binder of electrodes and as the adhesive between the electrodes and the electrolyte membrane, instead of the electrolyte according to Example 12. The cell showed an output of 0.34 V after operating under a load of 50 mA/cm2 at 30° C. for 4,000 hours and was found to work stably.
A slurry was prepared by mixing a catalyst powder, 30 percent by weight of a poly(perfluorosulfonic acid) electrolyte as a binder, and a solvent mixture of water and alcohols (a 20:40:40 (by weight) solvent mixture of water, isopropyl alcohol, and n-propanol). The catalyst powder used herein included 50 percent by weight of fine particles of a 1:1 (by atomic ratio) platinum/ruthenium alloy dispersed on and supported by a carbon carrier. The slurry was applied to a polyimide film by screen printing and thereby yielded an anode having a thickness of about 125 μm, a width of 30 mm, and a length of 30 mm. Next, another slurry was prepared by mixing a catalyst powder, 30 percent by weight of a binder, and a solvent mixture of water and alcohols.
The catalyst powder contained a carbon carrier and 30 percent by weight of platinum fine particles supported on the carbon carrier. The binder was a poly(perfluorosulfonic acid). The slurry was applied to a polyimide film by screen printing and thereby yielded a cathode having a thickness of about 20 μm, a width of 30 mm, and a length of 30 mm. About 0.5 ml of a 5 percent by weight solution of a poly(perfluorosulfonic acid) in a solvent mixture (a 20:40:40 (by weight) solvent mixture of water, isopropyl alcohol, and n-propanol) was allowed to permeate the surface of the anode, and the anode was bonded with an electrolyte membrane, and was dried at 80° C. under a load of 1 kg for three hours.
The electrolyte membrane contained a sulfonated poly(ether sulfone) having a sulfonic acid equivalent of 1.1 milliequivalents per gram of dried resin. Next, about 0.5 ml of a 5 percent by weight solution of a poly(perfluorosulfonic acid) in a solvent mixture of 1-propanol, 2-propanol, and methoxyethanol was allowed to permeate the surface of the cathode. The cathode was then bonded with the other side of the polymer electrolyte membrane opposite to the anode layer, so that the cathode layer overlay the anode layer with the interposition of the membrane.
The resulting article was dried at 80° C. under a load of about 1 kg for three hours and thereby yielded a membrane/electrode assembly (MEA) (2).
The membrane/electrode assembly (MEA) (2) was combined with the hydrophilized carbon cloth as an anode diffusion layer, and the water-repellent carbon cloth as a cathode diffusion layer. The hydrophilized carbon cloth and the water-repellent carbon cloth were prepared in Example 1.
The membrane/electrode assembly (MEA) (2) bearing the diffusion layers was mounted to a single cell of solid polymer fuel cell generator shown in
These results demonstrate that fuel cells using hydrocarbon electrolyte membranes containing sulfoalkyl groups and phosphoalkyl groups can stably yield satisfactory outputs over extended periods of time, in contrast to a fuel cell using a polymer electrolyte membrane having sulfonic groups. The results also demonstrate that fuel cells using a hydrocarbon electrolyte having sulfoalkyl groups and phosphoalkyl groups as a binder in electrodes can exhibit durability equal to or higher than that of a fuel cell using a fluorine-containing electrolyte as the binder.
A fuel cell was prepared and a test was conducted by the procedure of Comparative Example 1, except for using an electrolyte membrane of a sulfomethylated poly(ether sulfone) having a sulfonic acid equivalent of 1.2 milliequivalents per gram of dried resin, instead of the sulfonated poly(ether sulfone) electrolyte membrane. A 20 percent by weight aqueous methanol solution as the fuel was circulated to the anode, and air was fed to the cathode. The cell was continuously operated under a load of 50 mA/cm2 at 30° C.
These results demonstrate that fuel cells using hydrocarbon electrolyte membranes containing both sulfoalkyl groups and phosphoalkyl groups can stably yield satisfactory outputs over extended periods of time, in contrast to a fuel cell using a polymer electrolyte membrane having sulfoalkyl groups alone. They also demonstrate that fuel cells using a hydrocarbon electrolyte having sulfoalkyl groups and phosphoalkyl groups as a binder in electrodes can exhibit durability equal to or higher than that of a fuel cell using a fluorine-containing electrolyte as the binder.
A fuel cell was prepared and a test was conducted by the procedure of Comparative Example 1, except for using an electrolyte membrane of a sulfonated phosphonated poly(ether sulfone) having a sulfonic acid equivalent of 1.2 milliequivalents per gram of dried resin, instead of the sulfonated poly(ether sulfone) electrolyte membrane. A 20 percent by weight aqueous methanol solution as the fuel was circulated to the anode, and air was fed to the cathode. The fuel cell was continuously operated under a load of 50 mA/cm2 at 30° C.
These results demonstrate that fuel cell using hydrocarbon electrolyte membranes containing both sulfoalkyl groups and phosphoalkyl groups can stably yield satisfactory outputs over extended periods of time, in contrast to a fuel cell using a polymer electrolyte membrane having sulfonic groups and phosphonic groups. They also demonstrate that a fuel cell using a hydrocarbon electrolyte having sulfoalkyl groups and phosphoalkyl groups as a binder in electrodes can exhibit durability equal to or higher than that of a fuel cell using a fluorine-containing electrolyte.
A 500-ml four-necked round-bottom flask used herein was equipped with a reflux condenser connected with a stirrer, a thermometer, and a calcium chloride tube. After replacing the inner atmosphere of the flask with nitrogen, 30 g of each sulfonated poly(ether sulfone)s having sulfonic acid equivalents of 0.9, 1.1, and 1.25 milliequivalents per gram of dried resin, respectively, and 250 ml of carbon disulfide were placed in the flask. After adding chloromethyl methyl ether in amounts shown in Table 1, a solution containing 1 ml of anhydrous tin(IV) chloride in 20 ml of carbon disulfide was added dropwise, and the mixture was heated at 46° C. with stirring for the reaction time periods shown in Table 1. Next, the reaction mixtures were poured into 1 liter of methanol to precipitate polymers. The precipitates were pulverized in a mixer, were washed with methanol, and thereby yielded sulfonated chloromethylated poly(ether sulfone)s.
Each of the sulfonated chloromethylated poly(ether sulfone)s was immersed in triethyl ester of phosphonic acid and was subjected to heating under reflux for twelve hours. The reaction mixtures were poured into ethanol to precipitate polymers. The precipitates were pulverized in a mixer, were washed with ethanol, and thereby yielded sulfonated diethylphosphomethylated poly(ether sulfone)s. These polymers contained phosphomethyl groups in amounts of 0.6 to 0.9 milliequivalents per gram of dried resin, as shown in Table 1.
Each of the sulfonated diethylphosphomethylated poly(ether sulfone) s prepared in the step (2) was dissolved to a concentration of 5 percent by weight in a 1:1 solvent mixture of dimethylacetamide and methoxyethanol. The solution was applied to glass by spin coating, was air-dried, was dried in vacuo at 80° C., and thereby yielded a series of electrolyte membranes of sulfonated diethylphosphomethylated poly(ether sulfone) shaving a thickness of 45 μm. The polymer electrolyte membranes have ionic conductivities at room temperature of 0.03 to 0.07 S/cm as shown in Table 1. They show an increasing ionic conductivity with an increasing amount of sulfonic groups. In contrast, the amount of phosphomethyl groups in the membranes does not substantially affect the ionic conductivity.
In addition, the polymer electrolyte membranes were weighed (initial dry weights), were immersed in a 40 percent by weight aqueous methanol solution at 60° C. for twenty-four hours, were dried under reduced pressure, and were weighed. Differences in weight between before and after immersion were determined, and resistance (insolubility) of the polymer electrolyte membranes against an aqueous methanol solution was evaluated. The results are shown in Table 1. The polymer electrolyte membranes according to Examples 14 and 15 showed weight loss after immersion of 10% to 15% to find that they are substantially insoluble in the aqueous methanol solution. These polymer electrolyte membranes have phosphomethyl groups in amounts of 0.6 to 0.9 milliequivalents per gram of dried resin, and sulfonic groups in amounts of 0.9 to 1.25 milliequivalents per gram of dried resin. The polymer electrolyte membranes were immersed in a 3 percent by weight aqueous solution of hydrogen peroxide containing 20 ppm of ferric chloride at 0° C. for twenty-four hours, were washed with water, were dried under reduced pressure, and weights and ionic conductivities of the membranes were measured. The oxidation resistances of the membranes were evaluated based on retentions in weight and ionic conductivity. The polymer electrolyte membranes each show good oxidation resistance. Superficially, the electrolyte membranes containing sulfonic groups and phosphomethyl groups retain ionic conductivities of 0.03 S/cm or more and are highly resistant to oxidation. They, however, show resistance to (insolubility in) methanol somewhat inferior to that of the electrolyte membranes having sulfoalkyl groups and phosphoalkyl groups (sulfomethyl groups and phosphomethyl groups).
A slurry was prepared by mixing a catalyst powder, 30 percent by weight of a binder, and a solvent mixture of 1-propanol, 2-propanol, and methoxyethanol. The catalyst powder contained 50 percent by weight of fine particles of a 1:1 (by atomic ratio) platinum/ruthenium alloy dispersed on and supported by a carbon carrier. The binder was the polymer electrolyte (sulfomethylated diethylphosphomethylated poly(ether sulfone)) prepared according to Example 12. The slurry was applied to a polyimide film by screen printing and thereby yielded an anode having a thickness of about 125 μm, a width of 30 mm, and a length of 30 mm. Next, another slurry was prepared by mixing a catalyst powder, a binder, and a solvent mixture of water and alcohols. The catalyst powder contained a carbon carrier and 30 percent by weight of platinum fine particles supported on the carbon carrier. The binder was a solution of a poly(perfluorosulfonic acid) in a solvent mixture of 1-propanol, 2-propanol, and methoxyethanol. The slurry was applied to a polyimide film by screen printing and thereby yielded a cathode having a thickness of about 20 μm, a width of 30 mm, and a length of 30 mm. Next, about 0.5 ml of a 5 percent by weight solution of the polymer electrolyte prepared according to Example 12 in a solvent mixture of 1-propanol, 2-propanol, and methoxyethanol was allowed to permeate the surface of the anode, and the anode was then bonded with each of the sulfonated diethylphosphomethylated poly(ether sulfone) electrolyte membranes prepared in the step (3) in Examples 14 to 16. The resulting articles were dried at 80° C. under a load of about 1 kg for three hours. Next, about 0.5 ml of a 5 percent by weight solution of the polymer electrolyte prepared according to Example 12 in a solvent mixture of 1-propanol, 2-propanol, and methoxyethanol was allowed to permeate the surface of the cathode, and the cathode was bonded with the other side of the sulfonated diethylphosphomethylated poly(ether sulfone) electrolyte membranes opposite to the anode layer, so that the cathode layer overlay the anode layer with the interposition of the membrane. The resulting articles were dried at 80° C. under a load of about 1 kg for three hours and thereby yielded a series of membrane/electrode assemblies (MEAs) (3).
Anode and cathode diffusion layers were prepared in the following manner. A paste was prepared by adding 40 percent by weight in terms of weight after firing of an aqueous dispersion of polytetrafluoroethylene (PTFE) fine particles (Dispersion D-1: Daikin Industries, Ltd.) as a water repellant to carbon powder particles, and kneading the mixture. The paste was applied to one side of a carbon cloth having a thickness of about 350 μm and a porosity of 87%, was dried at room temperature, was fired at 270° C. for three hours, and thereby yielded a carbon sheet. The amounts of the polytetrafluoroethylene (PTFE) were set to 5 to 20 percent by weight relative to the weight of the carbon cloth. The sheet was cut to the same size with the electrodes of the membrane/electrode assemblies (MEAs) (3) and thereby yielded a cathode diffusion layer.
A carbon cloth having a thickness of about 350 μ, and a porosity of 87% was immersed in fuming sulfuric acid (concentration: 60%) in a flask and held at a temperature of 60° C. in an atmosphere of nitrogen gas flow for two days. Next, the flask was cooled to room temperature. After removing fuming sulfuric acid, the carbon cloth was fully washed until the distilled water became neutral. Next, the carbon cloth was immersed in methanol and was dried. The resulting carbon cloth had an infrared absorption spectrum showing absorptions derived from —OSO3H group at 1225 cm−1 and 1413 cm−1, and an absorption derived from —OH group at 1049 cm−1. This demonstrates that the surface of the carbon cloth bears —OSO3H groups and —OH groups introduced thereto. In this connection, a carbon cloth not treated with fuming sulfuric acid has a contact angle with an aqueous methanol solution of 81°.
The treated carbon cloth, however, had a contact angle with an aqueous methanol solution less than 81° to find to be hydrophilic. In addition, the carbon cloth was excellent in electroconductivity. The carbon cloth was cut to a piece having the same size as the electrodes of the membrane/electrode assembly (MEA) (1) and thereby yielded an anode diffusion layer.
Each of the membrane/electrode assemblies (MEAs) (3) bearing the diffusion layers was mounted to a single cell of solid polymer fuel cell generator shown in
A 20 percent by weight aqueous methanol solution as the fuel was circulated to the anode, and air was fed to the cathode. The cells were continuously operated under a load of 50 mA/cm2 at 30° C.
The membrane/electrode assembly (MEA) (1) bearing the diffusion layers according to Example 1 was mounted to a compact single cell shown in
The compact single cell was placed in a thermostatic bath, and the temperature of the thermostat bath was controlled so that a temperature measured by a thermocouple (not shown) placed in the separator stood at 70° C. The anode and cathode were humidified using an external humidifier, and the temperature of the humidifier was controlled within a range of 70° C. to 73° C. so that a dew point in the vicinity of an outlet of the humidifier stood at 70° C. The dew point was determined using a dew-point temperature sensor. In addition, the consumption of the humidifying water was continuously measured so as to verify that a dew point as determined from the flow rate, temperature, and pressure of reaction gas was a predetermined value.
The fuel cell was allowed to generate electricity for about eight hours a day under a load at a current density of 250 mA/cm2, a hydrogen utilization of 70%, and an air utilization of 40% and to operate while keeping it hot during the remainder periods of time. Even after 7,000 hours, the fuel cell had an output voltage of 94% or more of the initial voltage. This demonstrates that a membrane/electrode assembly according to an embodiment of the present invention is highly durable when used in a fuel cell using hydrogen as a fuel.
The fuel cell 101 generates electricity, and the electric double layer capacitor 110 temporarily stores the electricity. The sensor/controller 112 determines the electricity in the electric double layer capacitor and allows the load rejection switch 113 to turn ON when a predetermined quantity of electricity is stored in the capacitor. The electricity is increased to a predetermined voltage by the action of the DC to DC converter and is then fed to an electronic device.
The motherboard 202 includes electronic elements and electronic circuits such as processors, volatile and nonvolatile memories, an electric power controller, a hybrid controller for the fuel cell and the secondary battery, and a fuel monitor. In this example, an auxiliary power source for the fuel cell is a lithium ion secondary battery 206. The auxiliary power source can also be, for example, a nickel hydrogen cell or an electric double layer capacitor.
The section housing the power source is partitioned by a partitioning plate 205 into a lower part and an upper part. The lower part houses the motherboard 202 and the lithium ion secondary battery 206, and the upper part houses the fuel cell power source 101. The upper and side walls of the cabinet have slits 122c for diffusing air and fuel exhaust gas. An air filter 207 is arranged on surface of the slits 122c in the cabinet, and a water-absorptive quick-drying material 208 is arranged on surface of the partitioning plate 205.
The air filter may include any material that is capable of satisfactorily diffusing gases and capable of preventing entry of dust. The air filter is preferably a mesh or woven fabric containing a single yarn of a synthetic resin, because such a filter is resistant to clogging. A single yarn mesh of a water-repellent polytetrafluoroethylene, for example, may be used. The personal digital assistant stably operated over 2,000 hours or longer.
Direct-methanol fuel cells (DMFCs) using hydrocarbon electrolyte membranes in related art undergo reduction in thickness and breakage in the cathode of electrolyte membrane, show reduced cell performance and become incapable of generating electricity after several hundreds of hours from the beginning of fuel supply. The present inventors found that this can be effectively avoided by introducing a sulfonic group and a phosphonic acid group into a hydrocarbon polymer electrolyte membrane for imparting proton conductivity and oxidation resistance, respectively.
However, they also found that such a hydrocarbon electrolyte membrane becomes more soluble in a fuel aqueous methanol solution with an increasing amount of phosphonic acid groups, and that the resulting hydrocarbon electrolyte membrane may not be suitably used in direct-methanol fuel cells (DMFCs). Accordingly, they made intensive investigations. According to an embodiment of the present invention, a sulfoalkyl group or sulfonic group as a proton-conductive group, and a phosphoalkyl group as an oxidation-resistance imparting group are introduced into a hydrocarbon electrolyte membrane. Thus, there is provided a fuel cell that is resistant to dissolution in an aqueous methanol solution as a fuel and can stably generate electricity over extended periods of time.
According to another embodiment, a sulfoalkyl group or sulfonic group as a proton-conductive group, and a phosphoalkyl group as an oxidation-resistance imparting group are introduced into a hydrocarbon electrolyte, and the resulting hydrocarbon electrolyte is used as an electrolyte of an electrode. Thus, there is provided a direct-methanol fuel cell (DMFC) that is inexpensive and can operate stably over extended periods of time.
A direct-methanol fuel cell power source using a membrane/electrode assembly according to an embodiment of the present invention may be used as a battery charger for electronic devices having secondary batteries, or as an integrated power source for electronic devices using no secondary battery. Such electronic devices include, for example, mobile phones, mobile personal computers, mobile audio/visual devices, and other personal digital assistants. The resulting electronic devices can be used over extended periods of time and can be continuously used by refueling. A solid polymer fuel cell using hydrogen as a fuel and including a membrane/electrode assembly according to an embodiment of the present invention can be used as a household or business cogeneration dispersed power source or a fuel cell power source for mobile use. The resulting apparatuses can be used over extended periods of time, and can be continuously used by refueling.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-104808 | Apr 2006 | JP | national |
