BRIEF DESCRIPTION OF THE DRAWINGS
The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:
FIG. 1 is a schematic diagram showing a cross section of a fuel cell system according to an embodiment of the invention;
FIG. 2 is a schematic diagram showing a cross section of a fuel cell system according to another embodiment of the invention;
FIG. 3 is a schematic diagram showing a cross section of a fuel cell system according to yet another embodiment of the invention; and
FIG. 4 is a schematic diagram showing a cross section of a fuel cell system according to still yet another embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.
FIG. 1 is a schematic diagram showing a cross section of a fuel cell system 100 according to an exemplary embodiment of the invention. As shown in FIG. 1, the fuel cell system 100 comprises a cell unit 20, a fuel supply unit 10 and an air supply unit 80.
In FIG. 1, the cell unit 20 comprises an anode current collector 22, a cathode current collector 34, a membrane electrode assembly (MEA) 40 interposed between the anode current collector 22 and the cathode collector 34, and a frame 36 surrounding the MEA 40, the anode current collector 22 and the cathode collector 34. In addition, the cell unit 20 further comprises a hydrophilic gas-blocking layer 50 thereunder and a hydrophobic gas-penetrating layer 60 disposed under the hydrophilic gas-blocking layer 50. In this embodiment the MEA 40 is formed as a stacked structure comprising a plurality of sequentially stacked layers formed over the anode current collector 22, such as an anode gas diffusion layer 24, an anode catalyst layer 26, an electrolyte membrane 28, a cathode catalyst layer 30 and a cathode gas diffusion layer 32. Additionally, a gas exhaust 70 is embedded in the frame 36 and the gas exhaust 70 exposes a part of the hydrophilic gas-blocking layer 50 and connects the surrounding area adjacent to the cell unit 20. Numbers, diameters and configurations of the gas exhaust 70 are not restricted to that illustrated in FIG. 1 and can be modified according to the design requirements. The hydrophilic gas-blocking layer 50 in the cell unit 20 may comprise hydrophilic porous materials such as woven cloth, non-woven cloth, paper, foam, and PU foams, capable of absorbing moisture, thereby still providing gas-blocking performance after being wetted by moisture or liquid such as water. The diameter of the hydrophilic gas-blocking layer 50 should be as small as possible and typically should be less than twice a thickness thereof for forming a water film thereon, thus blocking penetration of CO2 gases formed at the anode. Thus, the diameter of the hydrophilic gas-blocking layer 50 must be small enough or formed of non-direct penetration holes. In one embodiment, the hydrophilic gas-blocking layer 50 may have a thickness of about 100 μm and a pore size of about 0.1 μm. The hydrophobic gas-penetrating layer 60 may comprise materials durable under high-temperatures and corrosive environments and non-reactive in the fuel cell system, such as polytetrafluoroethylene (PTPE). The hydrophobic gas-penetrating layer 60 must also be capable of withstanding a water pressure of about 10 kPa or greater. In some embodiments, the hydrophobic gas-penetrating layer 60 can be a commercial product “Poreflon® Membrane FP-010-60” produced by SUMITOMO ELECTRIC FINE POLYMER INC. with a pore size of 0.1 μm capable of withstanding water pressure of about 220 kPa.
Still referring to FIG. 1, the fuel supply unit 10 is now disposed at a side adjacent to the hydrophobic gas-penetrating layer 60 of the cell unit 20 to thereby provide gaseous fuel to an anode side of the cell unit 20. The air supply unit 80 is now disposed at a side away from the hydrophobic gas-penetrating layer 60 of the cell unit 20 to thereby provide oxygen or oxygen elements in the air to a cathode of the cell unit 20. The fuel supply unit 10 here comprises a tank 12 with liquid fuel 14 and vaporized gases 18 therein, the vaporized gases 18 are directly vaporized from the liquid fuel 14. In addition, the air supply unit 80 comprises a moisture plate 82 formed with a plurality of air introducing inlets 86.
Operation of the fuel cell system 100 in FIG. 1 is described as follows. The vaporized gases of the fuel, such as vaporized methanol gases, penetrate the hydrophobic gas-penetrating layer 60 and arrive at the hydrophilic gas-blocking layer 50. Because the hydrophilic gas-blocking layer 50 is a moist membrane such as a water-wetted moist membrane, the fuel gases 18 are thus dissolved into the hydrophilic gas-blocking layer 50 again, thereby contacting the anode current collector layer 22 and the anode gas diffusion layer 50 as a liquid formation, and reacting with the anode catalyst layer 26. Oxygen gases or oxygen elements in the air can be introduced through the air inlets 86 of the air supply unit 80 and react with the cathode catalyst layer 30 after passing through the cathode current collector 34 and the cathode gas diffusion layer 32. Through the described reactions, the fuel cell system 100 generates electric power and the gases reacted at the anode, for example CO2 when using methanol as fuel, may move along an interface between the anode current collector 22 and the hydrophilic gas-blocking layer 50 and arrives the gas exhaust 70 embedded in the frame 36. Gases are thus exhausted to the surroundings of the fuel cell system 100 without diffusing into the lower compartment of the fuel supply unit 10. The fuel supply unit 10 has a higher vaporized gaseous fuel concentration and a lower ratio of gaseous fuel in the gases exhausted to the surroundings. Because a hydrophobic gas-penetrating layer 60 is disposed under the hydrophilic gas-blocking layer 50, moisture in the hydrophilic gas-blocking layer 50 will be blocked by the hydrophobic gas-penetrating layer 60 after the hydrophilic gas-blocking layer 50 is wetted. Dilution of the concentration of the liquid fuel 14 in the tank 12 is therefore avoided. Thus, by the described operation, the fuel cell system 100 is capable of maintaining resistance under certain conditions (in one embodiment, resistance increases 0% after 6 hours operation) after long term operation. The fuel cell system 100 is thus capable of serving as a non-active fuel cell system, such as a non-active direct methanol fuel cell battery, for as long as the liquid fuel 14 can be provided, and will generate electric power without issues of electricity breakdown or cell change.
FIGS. 2 and 3 are schematic diagrams respectively showing a cross section of a fuel cell system according another exemplary embodiment of the invention. As shown in FIGS. 2 and 3, the fuel cell systems 100′ and 100″ are modifications of the fuel cell systems illustrated in FIG. 1. In FIGS. 2 and 3, same reference numbers represent the same components, difference between the fuel cell systems are described in the following.
FIG. 2 shows a gas-liquid separation membrane 16 optionally disposed in the fuel supply system 10 of the fuel cell system 100′ for separating liquid fuel 14 and the vaporized gases 18 of the liquid fuel 14. As shown in FIG. 2, the gas-liquid separation membrane 16 is partially embedded in the tank 12, thereby defining the tank 12 into two compartments 12a and 12b. Compartment 12a of tank 12 stores the liquid fuel 14. Compartment 12b stores vaporized gases 18. Additionally, a gas exhaust 70′ of a modified configuration is disposed in the frame 36 of the cell unit 12. The gas exhaust 70′ is disposed at an edge of the frame 36 and the hydrophilic gas-blocking layer 50 and extends horizontally in the frame 36. A multi-hole plate 65 can be optionally disposed between a top surface of the fuel cell supply unit 10 and the cell unit 20 to control transportation of the vaporized fuel gases and function as a support structure of the cell unit 20 and the gas supply unit 80. The multi-hole plate 65 has a porosity of about 0.1˜20% and the porosity therein is decided according to the electrical currents of the MEA. The multi-hole plate 65 may comprise materials are that are gas-blocking, corrosive resistant and chemically inert, such as polyesters or polyolefin. In some embodiments, the multi-hole plate 65 may comprise materials such as polyethylene terephthalate (PET), polyacrylonitrile (PAN), polyethylene (PE), or polypropylene (PP).
FIG. 4 is a schematic diagram showing a cross section of an embodiment of a fuel cell system 100′″ modified from that illustrated in FIG. 2. In FIG. 4, the same reference numbers represent the same components illustrated in FIG. 2 and differences are described in the following.
FIG. 4 shows that a liquid storage tank 90 can be further provided in the fuel cell system 100′″. The liquid storage tank 90 is structurally independent from the fuel supply system 10 and the cell unit 20. A water collector layer 92 can further be embedded in the moisture-keeping plate 82 of the air supply unit 80. The water collector layer 92 may comprise porous and hydrophilic porous materials such as woven cloths, non-woven cloths, paper, foam, and PU foam, and are physically connected with the liquid storage tank 90. Additionally, as shown in FIG. 4, the hydrophilic gas-blocking layer 50 protrudes over a side of the frame 36 and is partially embedded in the liquid storage tank 90. An amount of liquid such as water can thus be manually introduced to the liquid storage tank 90, or condensed moisture can reflow back to the liquid storage tank 90 through the water collector layer 92 partially embedded in the liquid storage tank 90. Moisture can thus be supplied to the hydrophilic gas-blocking layer 50 disposed between the MEA 40 and the hydrophobic gas-penetrating layer 60. The amount of reflowed water will thus not be affected by environmental conditions and will not cause water-loss issues in the hydrophilic gas-blocking layer 50. Operating life and performance of the fuel cell unit 100′″ can thus be improved. The water supply system illustrated in FIG. 4 can be also adopted in the fuel cell system in FIGS. 1 and 3 and is not restricted to that disclosed in FIG. 4.
While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
Patent Application
20080096092
