Abstract:
A fuel cell which can utilize the fuel in its fuel reservoir to the fullest possible extent. The fuel cell includes: an electrolyte layer; a first electrode which is provided on one surface of the electrolyte layer and to which a liquid fuel is supplied; and a second electrode which is provided on the other surface of the electrolyte layer and to which an oxidant is supplied. The fuel cell further includes: a fuel chamber which is provided next to the first electrode and stores the liquid fuel; a fuel reservoir which is provided next to the fuel chamber and stores the liquid fuel to be refilled into the fuel chamber; a selectively permeable unit which is provided between the fuel chamber and the fuel reservoir and is permeable to the liquid fuel; and an osmotic pressure generating source which dissolves in a liquid stored in the fuel chamber and does not permeate the selectively permeable unit.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a fuel cell, and in particular to a fuel cell which runs on a liquid fuel and is capable of making full use of the fuel in a fuel reservoir. 
     2. Description of the Related Art 
     Fuel cells are devices for generating electric energy from hydrogen and oxygen, and are capable of providing high power generation efficiency. One of the main features of a fuel cell is that electrical power is generated through direct power generation, which is in contrast to conventional power generation methods where electrical power is generated via thermal or kinetic energy processes. Therefore, in a fuel cell, high efficiency power generation can be expected even in small-scale systems. Furthermore, a fuel cell is considered to be very environmentally friendly as it emits lesser amounts of nitrogen compounds and the like and generates less noise and vibration than conventional power generation methods. Since fuel cells can thus make effective use of the chemical energy of fuel, and have environmentally friendly characteristics, they are expected to serve as the energy supply systems of the 21st century. Fuel cells are attracting considerable attention as promising novel generation systems in a variety of applications ranging from large-scale power generation to small-scale power generation, including space technologies, automobiles, and portable devices. Thus, the technological development of the fuel cell for practical use is well under way. 
     Above all, polymer electrolyte fuel cells are characterized by lower operating temperatures and higher output densities as compared to the other types of fuel cells. Among various types of polymer electrolyte fuel cells, direct methanol fuel cells (DMFCs) have recently been gaining attention in particular. In DMFCs, an aqueous methanol solution (or pure methanol) serving as the fuel is supplied directly to the anode without any modification so that electrical power is generated through an electrochemical reaction between the aqueous methanol solution and oxygen. During this electrochemical reaction, carbon dioxide is discharged from the anode, and water is produced at the cathode as a reaction product. In comparison to hydrogen, aqueous methanol solution provides higher energy per unit volume, and has a lower risk of explosion or the like and is also suitable for storage. Thus, a DMFC is expected to be employed as a power source for automobiles, portable devices (cellular phones, notebook PCs, PDAs, MP3 players, digital cameras, and electronic dictionaries (books)), and the like. 
     In conventional fuel cells such as that disclosed in Japanese Patent Laid-Open Publication No. 2004-039293, the aqueous methanol solution to be supplied to the anode is delivered using a fuel supply unit such as a liquid pump. In the case of a so-called passive fuel cell where pumps and other driving sources are omitted as much as possible, however, the main body of the fuel cell has no driving source for delivering the fuel from a replaceable fuel reservoir (such as fuel cartridge) to a fuel chamber. In this instance, the fuel cartridge is removably connected to the fuel cell body. The fuel chamber is arranged next to the anode, and temporarily retains the fuel to be supplied to the anode by the action of natural convection, capillary force, or the like. The problem with this arrangement is that the fuel cartridge must be replaced when the fuel in the fuel cartridge and the fuel in the fuel chamber reach an equal concentration level, or when the fuel must be delivered from the fuel cartridge to the fuel chamber by the application of a spring force, gravity, or a squeezing force or the like imparted by the user. 
     SUMMARY OF THE INVENTION 
     The present invention has been developed in view of the foregoing problem, and a general purpose thereof is to provide a fuel cell which runs on a liquid fuel and is capable of making full use of the fuel in a fuel reservoir. 
     To achieve the foregoing purpose, a fuel cell according to the present invention comprises: an electrolyte layer; a first electrode which is provided on one surface of the electrolyte layer and to which a liquid fuel is supplied; a second electrode which is provided on the other surface of the electrolyte layer and to which an oxidant is supplied; a fuel chamber which is provided next to the first electrode and stores the liquid fuel; a fuel reservoir which is provided next to the fuel chamber and stores the liquid fuel to be refilled into the fuel chamber; a selectively permeable unit which is provided between the fuel chamber and the fuel reservoir and is permeable to the liquid fuel; and an osmotic pressure generating source which dissolves in a liquid stored in the fuel chamber and does not permeate the selectively permeable unit. If an osmotic pressure generating source having large molecules, such as glucose, is dissolved in the fuel-chamber side, and a semipermeable membrane or other member that is selectively permeable to the liquid fuel (such as methanol molecules) is interposed between the fuel chamber and the fuel reservoir, an osmotic pressure occurs between the fuel chamber and the fuel reservoir. This pressure makes it possible to refill the fuel chamber with the liquid fuel from the fuel reservoir. Consequently, the fuel in the fuel reservoir can be utilized to the fullest possible extent even when passive fuel cells and the like that have no driving source are used. 
     It should be appreciated that in preferred embodiments the fuel reservoir may be removable from the fuel cell. Then, even when the fuel in the fuel reservoir is consumed to a point where it can no longer be supplied into the fuel chamber, it is therefore possible to remove the fuel reservoir from the fuel cell and replace it with a new fuel reservoir. 
     It is to be noted that any arbitrary combination or rearrangement of the above-described structural components and so forth are all effective as and encompassed by the present embodiments. Moreover, this summary of the invention does not necessarily describe all necessary features so that the invention may also be sub-combination of these described features. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will now be described, by way of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures, in which: 
         FIG. 1  is a perspective view schematically showing the appearance of a fuel cell according to the embodiment; 
         FIG. 2  is a sectional view schematically showing the internal structure of the fuel cell according to the embodiment; 
         FIG. 3  is an enlarged view schematically showing the connecting structure of the fuel cell according to the embodiment; and 
         FIG. 4  is a perspective view schematically showing the appearance of a cellular phone which is equipped with the fuel cell according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will now be described by reference to the preferred embodiments. This does not intend to limit the scope of the present invention, but to exemplify the invention. 
     The basic configuration of a fuel cell  100  according to the embodiment will now be described with reference to the drawings.  FIG. 1  is a perspective view schematically showing the appearance of the fuel cell  100  according to the embodiment.  FIG. 2  is a sectional view schematically showing the internal structure of the fuel cell  100  according to the embodiment as taken along the line A-A′ of  FIG. 1 . In the present embodiment, the fuel  100  is a DMFC in which an aqueous methanol solution or pure methanol (hereinafter, referred to as “methanol fuel”) is supplied to its anodes  10 . Membrane electrode assemblies (MEAs)  12 , or power-generating parts, are formed by sandwiching an electrolyte membrane  14  between the anodes  10  and cathodes  16 . As shown in  FIG. 2 , the fuel cell  100  according to the embodiment has three cells. Referring to  FIG. 2 , anodes  10   a ,  10   b  and  10   c , and cathodes  16   a ,  16   c  and  16   c  mark distinction between cells. The term “anodes  10 ” is a generic reference to the anodes  10   a ,  10   b  and  10   c , and the term “cathodes  16 ” is a generic reference to the cathodes  16   a ,  16   b  and  16   c.    
     The methanol fuel to be supplied to the anodes  10  is delivered from outside a fuel cell body  50  to a fuel chamber  22  through a methanol fuel supply hole  20 . The methanol fuel stored in the fuel chamber  22  is supplied to the anodes  10 . The anodes  10  cause a methanol reaction as shown in formula (1) to take place, so that H +  move to the cathodes  16  through the electrolyte membrane  14  and electrical power is output.
 
CH 3 OH+H 2 O→CO 2 +6H + +6 e   −   (1)
 
As is evident from formula (1), the anodes  10  produce carbon dioxide as a byproduct of this reaction. Then, a gas-liquid separation filter  30  is placed between the fuel chamber  22  and anode-side product discharge holes  26  formed in an anode-side case  24   a  of the fuel cell  100 .
 
     This gas-liquid separation filter  30  is a flat filter having microscopic holes that selectively allow gaseous components to pass through but not liquid components. Examples of materials suitable for this gas-liquid separation filter  30  are fluorinated synthetic resins that are resistant to methanol (alcohol), including: polychlorotrifluoroethylene, polyfluorovinylidene, polyfluorovinyl, polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer (E/TFE), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), chlorotrifluoroethylene-ethylene copolymer (E/CTFE), perfluoro cyclic polymer, and polyvinyl fluoride (PVF). 
     Cases  24  (including the anode-side case  24   a  and cathode-side case  24   c ) are suitably made of materials that have light weight, high rigidity, and corrosion resistance. Specific examples of the materials include: synthetic resins such as acryl resins, epoxy resins, glass epoxy resins, silicon resins, cellulose, nylon, polyamideimide, polyarylamide, polyaryletherketone, polyimide, polyurethane, polyetherimide, polyetheretherketone, polyetherketoneetherketoneketone, polyetherketoneketone, polyethersulfone, polyethylene, polyethylene glycol, polyethylene terephthalate, polyvinyl chloride, polyoxymethylene, polycarbonate, polyglycolic acid, polydimethylsiloxane, polystyrene, polysulfone, polyvinyl alcohol, polyvinylpyrrolidone, polyphenylene sulfide, polyphthalamide, polybutylene terephthalate, polypropylene, polyvinyl chloride, polytetrafluoroethylene, and rigid polyvinyl chloride; and metals such as aluminum alloys, titanium alloys, and stainless steel. Tempered glass and skeleton resins may also be used. Like the gas-liquid separation filter  30 , the cases  24  also have areas that make contact with the methanol fuel. The areas that are to make contact with the methanol fuel are thus particularly preferably made of the foregoing synthetic resins or composite materials formed by covering metals with fluorinated synthetic resins. The reference numeral  32  designates a supporting member which forms the fuel chamber  22  and fastens the MEAs  12 . The supporting member  32  is also preferably made of the same material as that of the cases  24  where to make contact with the methanol fuel. 
     In the present embodiment, the electrolyte membrane  14  of the MEAs  12  is made of Nafion 115 (from DuPont). An anode catalyst paste made of a mixture of Pt—Ru black and 5 wt % of Nafion solution (from DuPont) is applied to one surface of this electrolyte membrane  14  to form the anodes  10 . A cathode catalyst paste made of a mixture of Pt black and 5 wt % of Nafion solution (from DuPont) is applied to the other surface to form the cathodes  16 . While the electrolyte membrane  14  of the present embodiment is made of Nafion 115, the electrolyte membrane  14  may be made of any electrolyte membrane as long as it is ion-conductive and has a thickness in the range of 50 to 200 μm. In the case of DMFCs that run on a methanol fuel as detailed in the present embodiment, it is even more preferable that the electrolyte membrane  14  is capable of suppressing a so-called cross over phenomenon in which methanol permeates through the electrolyte membrane  14  to reach the cathode side. Moreover, while the anodes  10  and the cathodes  16  are formed on the electrolyte membrane  14 , the fabrication method and configuration may be such that the catalyst layers are formed on electrode bases made of carbon paper or the like. Furthermore, the catalysts are not limited to Pt—Ru or other catalysts based on Pt-based particles (such as Pt—Ru black and Pt black) but may be carbon-based materials that carry catalysts, or catalyst-carrying carbons, as long as they have the catalytic function of generating H +  from methanol, or generating water from H +  and oxygen. 
     Air is supplied to the cathodes  16  through cathode-side product discharge holes  28 . H +  that reach the cathodes  16  through the electrolyte membrane  14  and oxygen in the air cause a reaction to produce water, as shown in formula (2).
 
3/2O 2 +6H + +6 e   − →3H 2 O  (2)
 
The inner walls of the cathode-side product discharge holes  28 , and the surfaces of the cathode-side case  24   c  where the cathode-side product discharge holes  28  are formed, are coated with a functional coating material that contains a photocatalyst such as titanium oxide. The product water discharged from the cathodes  16  is prevented from dripping by provision of a large number of small holes. Furthermore, by coating the inner wall with the functional coating material, the product water spreads thinly over the surface of the inner wall without clogging the holes. Thus, the evaporation of the product water is facilitated, and breeding of microorganisms or the like can be prevented. Preferably, this functional coating material contains a metal such as silver, copper, or zinc in order to provide an organic material decomposition function and an antimicrobial function that are activated even when the fuel cell  100  is not irradiated with light that includes photocatalyst-activating wavelengths, as sunlight. Furthermore, when a user of the fuel cell  100  touches the fuel cell  100 , organic materials may adhere to the fuel cell  100 . When the entire surface of the cases  24  is coated with the functional coating material, any organic materials adhered to the cell can be decomposed. In this manner, a soil resistance function or the antimicrobial function can be imparted to the fuel cell  100 .
 
     In order to prevent the methanol fuel from flowing from the anodes  10  to the cathodes  16 , O-rings  34  (an anode-side O-ring  34   a  and a cathode-side O-ring  34   c ) are placed so as to surround and enclose the plurality of MEAs  12 . In this Example, the O-rings  34  are pressed by the cathode-side case  24   c  and the support member  32  to prevent the methanol fuel from flowing from the anodes  10  to the cathodes  16  and to prevent oxygen from flowing into the anodes  10  as well. Desirably, the O-rings  34  are made of a material having both flexibility and corrosion resistance. Suitable materials include: natural rubber, nitrile rubber, acrylic rubber, urethane rubber, silicon rubber, butadiene rubber, styrene rubber, butyl rubber, ethylene-propylene rubber, fluorine rubber, chloroprene rubber, isobutylene rubber, acrylonitrile rubber, and acrylonitrile-butadiene rubber. 
     Aside from the foregoing configuration, a porous Teflon™ sheet or the like capable of circulating the air and the water produced at the cathodes  16  is preferably interposed between the cathodes  16  and the cathode-side case  24   c  so that the cathodes  16  will not be touched by users, although this is not shown in the diagram. Furthermore, the diameters of the cathode-side product discharge holes  28  and the thickness of the cathode-side case  24   c  where the cathode-side product discharge holes  28  are formed may be adjusted (to increase the thickness dimension of the cathode-side case  24   c  with respect to the diametric dimension of the cathode-side product discharge holes  28 ). Such a case design can prevent users from making contact with the cathodes  16  even when they touch the surface of the cathode-side case  24   c  of the fuel cell  100 . Moreover, the areas where the cathode-side product discharge holes  28  are formed may be provided with a covering lid. This makes it possible to prevent the MEAs  12 , or the electrode membrane  14  in particular, from drying while the fuel cell  100  is at rest. The entry of dust, bacteria (mold), and other organics into the side of the cathodes  16  can also be avoided. This lid may be formed as a slide lid to save on installation space. 
     While the present embodiment has dealt with the case where the fuel chamber  22  is a space which is filled with the methanol fuel, a three-dimensional porous body which absorbs the methanol fuel (being a fuel absorber), like a sponge, may be put in the fuel chamber  22 . Examples of such a fuel absorber include woven fabrics, unwoven cloths, and felts of fibers made of polyolefins (such as polyethylene and polypropylene), nylon, polyester, rayon, cotton, polyester/rayon, polyester/acryl, rayon/polychlal, and the like. The fuel absorber put in the fuel chamber  22  causes a capillary action, thereby supplying the methanol fuel to the anodes  10  evenly irrespective of the installed position (orientation) of the fuel cell  100 . The present embodiment has also dealt with the case where the cases  24  are coated with a functional coating material that contains a photocatalyst. Nevertheless, the antibacterial function at least can be ensured by coating the surfaces of the cases  24  with metals such as silver, copper, and zinc, or by making the cases  24  out of a material that contains metals such as silver, copper, and zinc. 
     The fuel cell body  50  (fuel chamber  22 ) of the fuel cell  100  according to the embodiment is supplied with the methanol fuel which is delivered from a fuel cartridge  80 , removable from the fuel cell body  50 , to the fuel chamber  22  through the methanol fuel supply hole  20 . The fuel cartridge  80  is composed of an outer case  60  which maintains a predetermined shape, and a fuel bag  62  which is loaded inside with the methanol fuel and changes its shape depending on the amount of methanol fuel loaded. The outer case  60  is preferably made of a material or materials that have light weight and high rigidity, or are made of the same material as that of the cases  24  of the fuel cell body  50  if taking design into consideration. The fuel bag  62 , which stores the methanol fuel inside, is preferably made of a synthetic resin that is highly resistant to methanol (corrosion resistance), and exhibits good plasticity, elasticity, or flexibility. Suitable materials thereof include: acrylic resins, epoxy resins, glass epoxy resins, silicon resins, cellulose, nylon, polyamideimide, polyarylamide, polyaryletherketone, polyimide, polyurethane, polyetherimide, polyetheretherketone, polyetherketoneetherketoneketone, polyetherketoneketone, polyethersulfone, polyethylene, polyethylene glycol, polyethylene terephthalate, polyvinyl chloride, polyoxymethylene, polycarbonate, polyglycolic acid, polydimethylsiloxane, polystyrene, polysulfone, polyvinyl alcohol, polyvinylpyrrolidone, polyphenylene sulfide, polyphthalamide, polybutylene terephthalate, polypropylene, polyvinyl chloride, polytetrafluoroethylene, and rigid polyvinyl chloride. 
       FIG. 3  is an enlarged view of the part P shown in  FIG. 2 , schematically showing the connecting structure between the fuel cell body  50  and the fuel cartridge  80  of the fuel cell  100  according to the embodiment. The anode-side case  24   a  of the fuel cell body  50  includes the methanol fuel supply hole  20 . This methanol supply hole  20  is configured to close when the fuel cartridge  80  is not connected, so that the methanol fuel inside the fuel chamber  22  does not leak out. An insert protrusion  64  of the fuel cartridge  80 , to be inserted into the methanol fuel supply hole  20 , is tapered in the outer periphery so that it fits into the methanol fuel supply hole  20  (with fitting tolerances in the range of 0 to 20 μm) for easy connection. The methanol fuel supply hole  20  is configured to be opened when pushed on by this insert protrusion  64 . The insert protrusion  64  is cylindrical (hollow) in shape, and a semipermeable membrane (serving as the selectively permeable unit)  66  is arranged inside. The semipermeable membrane  66  is supported by a tab  68  and a retaining ring  70 . The tab  68  is formed on the inner wall of the insert protrusion  64 . The retaining ring  70  fastens the inlet of the fuel bag  62  to the outer case  60  (insert protrusion  64 ). For the sake of safety, the extremity of the insert protrusion  64  may be sealed with a sticker before the use with the fuel cartridge  80 . This sticker shall be removed and the insert protrusion  64  shall be inserted into the methanol fuel supply hole  20  immediately prior to use of the fuel cartridge  80  (before inserting the insert protrusion  64  into the methanol fuel supply hole  20 ), so as to avoid leakage of any methanol fuel from the fuel cartridge  80 . 
     Since the connecting area between the fuel cell body  50  and the fuel cartridge  80  include a semipermeable membrane  66 , the fuel chamber  22  of the fuel cell  100  according to the embodiment is loaded with glucose in advance. This makes it possible to supply the methanol fuel from the fuel bag  62  to the fuel chamber  22  through the semipermeable membrane  66  by means of osmotic pressure. That is, the fuel chamber  22  is prepared to contain methanol (being the hydrogen atom source), glucose (being the osmotic pressure generating source), and water (medium). 
     Alternatively, the fuel chamber  22  may be prepared to contain glucose (the osmotic pressure generating source) and water (the medium) at the time of shipment of the fuel cell  100 . The fuel cartridge  80  is then connected to the fuel cell body  50 , whereby methanol in the fuel bag  62  is supplied to the fuel chamber  22  through the semipermeable membrane  66  by osmotic pressure so that the fuel chamber  22  contains methanol (the hydrogen atom source), glucose (the osmotic pressure generating source), and water (the medium). It therefore follows that the fuel cell body  50  (including the fuel chamber  22 ) is filled with an aqueous glucose solution, and the cathodes  16  will not react with any oxygen that leaks in. Moreover, at the time of shipment of the fuel cell  100 , the fuel chamber  22  may be prepared to contain glucose (the osmotic pressure generating source) and methanol (the hydrogen atom source and medium) so that the anode reaction (as detailed in formula (1)) occurs due to water produced at the cathodes  16  that diffuses back from such. In this case, the glucose loaded in the fuel chamber  22  in advance facilitates the back diffusion as the electrolyte membrane  14 , being a solid polymer membrane, also exhibits the properties of a semipermeable membrane. Glucose is less soluble in methanol than in an aqueous methanol solution. The fuel chamber  22  may therefore be loaded with glucose to a point where as some of the glucose remains undissolved, so that this remaining glucose dissolves when water produced at the cathodes  16  diffuses back to lower the concentration of the methanol fuel in the fuel chamber  22 . This makes it possible to start using the fuel cell body  50  (immediately after purchase) without connecting the fuel cartridge  80  to supply the methanol fuel. When glucose or other substances that cannot permeate the electrolyte membrane are used as the osmotic pressure generating source, the electrolyte membrane functions as a semipermeable membrane. Then, the water produced at the cathodes  16  diffuses back toward the anodes  10 . The back diffusion of the produced water can lower the methanol concentration near the anodes  10  (locally), thereby reducing cross over. Moreover, the back diffusion of the water produced at the cathodes  16  precludes any water shortage at the anode and allows continuous power generation even when an aqueous methanol solution (or pure methanol) beyond the stoichiometric ratio (methanol:water=1:1, or a methanol concentration of 64% by weight) is used as the fuel. 
     The semipermeable membrane  66  may be made of a membrane that has microscopic holes of such dimensions that allow methanol molecules to pass through, but not glucose or other substances contributing to the generation of osmotic pressure, or may be made of a membrane that has an equivalent function (methanol permeability and glucose impermeability). Specifically, suitable materials include: celluloses such as cellophane, regenerated cellophane, and acetate; and synthetic polymers such as polysulfone, polyacrylonitrile, polymethyl methacrylate, ethylene vinyl alcohol copolymer, and polyester polymer alloys. In addition to this, Nafion™ and other ion exchange membranes may also be used as solid polymer membranes as long as they exhibit the properties of semipermeable membranes, as mentioned previously. 
     Meanwhile, the osmotic pressure generating source to be loaded into the fuel chamber  22  is preferably made of materials that are stable in the operating conditions (environment) of the fuel cell  100 , i.e., in the range of −10° C. to 60° C., and are resistant to methanol and acid. The materials preferably cause neither ionization nor electrode reaction so as not to affect the electrolyte membrane  14 , and must also have an impermeable property against the semipermeable membrane  66  described above. Further, the osmotic pressure generating source loaded into the fuel chamber  22  needs to be made of materials that are impermeable to the electrolyte membrane  14 . At present, glucose is easily available and is thus considered to be an optimum material, though not restrictive. 
     A description will now be given in detail, with reference to the drawings, of how the fuel cell  100  of the present embodiment as described above is applied to a cellular phone  200 .  FIG. 4  is a perspective view schematically showing the appearance of the cellular phone  200  which is equipped with the fuel cell  100 . As shown in  FIG. 4 , the fuel cell  100  is mounted on an operating part  202  of the cellular phone  200 , and the cathode-side product discharge holes  28 , though not shown, are formed in the surface not in contact with the cellular phone  200  (being the rear surface thereof). The fuel cell  100  is arranged on the operating part  202  of the cellular phone  200  so that the fuel cartridge  80  lies near a hinge part  204  of the cellular phone  200  as shown in  FIG. 4 . In this position, the fuel cartridge  80  is positioned above the fuel cell body  50  when in use, in situations such as where the power consumption of the cellular phone  200  is higher, such as during calling, emailing, texting or making a video phone call. This makes it possible to supply the methanol fuel from the fuel cartridge  80  to the fuel cell body  50  not only using osmotic pressure but also using gravity, so that with even a small osmotic pressure the methanol fuel (with a small amount of glucose) is supplied to the fuel cell body  50 . Conversely, when the anode-side product discharge holes  26  are positioned near the hinge part  204 , the supply of the methanol fuel from the fuel cartridge  80  to the fuel cell body  50  relies on the osmotic pressure, whereas carbon dioxide produced by the anodes  10  can be discharged smoothly. 
     The present invention has dealt with a fuel cell in which a semipermeable membrane is formed in the connecting area between the fuel cell body and the fuel cartridge. However, the present invention is not limited thereto. The semipermeable membrane may also be formed between the fuel chamber and the anodes. Moreover, despite the use of the fuel cartridge which is removable from the fuel cell body, the present invention is also applicable to a fuel cell in which the fuel cartridge is turned into a fuel tank that is fixed to the fuel cell body, and the methanol fuel is refilled into the fuel tank accordingly. 
     Furthermore, while the cellular phone has been provided as an example of the application for the fuel cell to be mounted on, it should be understood that the fuel cell may also be applied to other various portable devices, including personal computers, PDAs, MP3 players, digital cameras, and electronic dictionaries (books).