JPWO2008032449A1 - Electrolyte membrane and fuel cell - Google Patents

Abstract

The electrolyte membrane 10 includes a support substrate 20 made of a porous body having pores 21, and a plurality of porous thin films 40 having through holes 41 in the thickness direction on one surface of the support substrate 20 with a predetermined gap. And a porous thin film layer 45 formed by being divided. The pores 21 of the support substrate 20 are filled with a first electrolyte 22 having proton conductivity, and the through holes 41 of the porous thin film 40 are filled with a second electrolyte 42 having proton conductivity. Is filled.

Description

  The present invention relates to an electrolyte membrane and a small fuel cell including the same.

  2. Description of the Related Art In recent years, electronic devices have been reduced in size, performance, and portability due to advances in electronic technology. In portable electronic devices, there is an increasing demand for higher energy density of batteries used. For this reason, there is a demand for a secondary battery having a high capacity while being lightweight and small.

  In response to the demand for such secondary batteries, for example, lithium ion secondary batteries have been developed. In addition, the operation time of portable electronic devices tends to increase further, and in lithium ion secondary batteries, the improvement in energy density is almost limited from the viewpoints of materials and structure, which is further demanded. It is becoming impossible to respond.

  Under such circumstances, small fuel cells are attracting attention instead of lithium ion secondary batteries. In particular, direct methanol fuel cells (DMFC) using methanol as fuel require more difficult handling of hydrogen gas and devices that produce hydrogen by reforming organic fuel, compared to fuel cells using hydrogen gas. It is thought that it is excellent in miniaturization.

  In DMFC, methanol is oxidatively decomposed at the fuel electrode to generate carbon dioxide, protons and electrons. On the other hand, in the air electrode, water is generated by oxygen obtained from air, protons supplied from the fuel electrode through the electrolyte membrane, and electrons supplied from the fuel electrode through an external circuit. In addition, power is supplied by electrons passing through the external circuit. However, in the fuel cell having such a configuration, methanol permeates from the fuel electrode to the air electrode through the electrolyte membrane, and as a result, the power generation potential is lowered.

  Such permeation of methanol is further promoted when the electrolyte membrane swells with water or methanol. Therefore, a technique for preventing electrolyte crossover by filling the porous membrane with electrolyte and preventing methanol crossover is disclosed. ing.

  However, in the porous membrane filled with the above-described conventional electrolyte, the electrolyte is unevenly distributed in the pores, so that the impedance of the entire membrane increases. In order to suppress this increase in impedance, it is necessary to form a thin film. However, if the film is formed thin, the strength of the porous film is lowered, and there is a problem that the swelling of the electrolyte itself cannot be suppressed. In this case, if the membrane is broken, operation as a fuel cell becomes impossible.

Even if a thin film is formed by sputtering or vapor deposition, the film is processed into a porous film and filled with an electrolyte, and an electrolyte-filled film with low impedance is obtained, the proton conductivity A support substrate having the above is required. As this support substrate, for example, an organic porous body having high rigidity, such as porous polyimide, which is infiltrated with an electrolyte can be considered. This organic porous body has large surface irregularities. For this reason, when an inorganic thin film is formed uniformly on the surface by sputtering, vapor deposition or the like, there is a problem that stress is concentrated in the film and deformation is likely to occur.
JP 2004-171844 A JP 2002-83612 A

  Accordingly, an object of the present invention is to provide an electrolyte membrane having low impedance, sufficient mechanical strength, and capable of suppressing methanol crossover, and a fuel cell that is small and can maintain stable output characteristics. Is to provide.

  An electrolyte membrane according to an aspect of the present invention has a thickness on a support substrate made of a porous body, a first electrolyte having proton conductivity filled in the support substrate, and one surface of the support substrate. A porous thin film layer formed by dividing a plurality of porous thin films having through holes in a direction with a predetermined gap, and a second electrolyte having proton conductivity filled in the through holes of the porous thin film It is characterized by comprising.

  The fuel cell according to one aspect of the present invention is a fuel cell including a fuel electrode, an air electrode, and an electrolyte membrane sandwiched between the fuel electrode and the air electrode, wherein the electrolyte membrane is A fuel cell comprising the electrolyte membrane according to one embodiment of the present invention.

It is a perspective view showing typically the electrolyte membrane of one embodiment concerning the present invention. It is the figure which showed typically the cross section of the membrane electrode assembly provided with the electrolyte membrane of one Embodiment which concerns on this invention. It is the figure which showed typically the cross section of the fuel cell provided with the membrane electrode assembly which concerns on this invention. It is the figure which showed typically the cross section of the fuel cell provided with the electrolyte membrane of one Embodiment which concerns on this invention. It is a perspective view which shows the structure of a fuel distribution mechanism typically.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Electrolyte membrane, 20 ... Support substrate, 21 ... Pore, 22 ... 1st electrolyte, 40 ... Porous thin film, 41 ... Through-hole, 42 ... 2nd electrolyte, 45 ... Porous thin film layer.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a perspective view schematically showing an electrolyte membrane 10 according to an embodiment of the present invention. As shown in FIG. 1, the electrolyte membrane 10 includes a support substrate 20 made of a porous body having pores 21, and a plurality of pores having through holes 41 in the thickness direction on one surface of the support substrate 20. The thin film 40 includes a porous thin film layer 45 formed by dividing the thin film 40 with a predetermined gap. The pores 21 of the support substrate 20 are filled with a first electrolyte 22 having proton conductivity, and proton conduction is provided in the through holes 41 of the porous thin film 40 and in the gaps between the porous thin films 40. The 2nd electrolyte 42 which has property is filled.

  The support substrate 20 that supports the porous thin film layer 45 is composed of a porous body made of an organic material. As the organic porous body, it is preferable to use a synthetic resin having high rigidity (mechanical strength) and in which the pores 21 are less likely to be expanded by swelling of the filled first electrolyte 22. Specific examples of the organic porous material include polyimide, polyamide, polyethylene, polystyrene, polypropylene, polyetherimide, polyetheretherketone, polytetrafluoroethylene, tetrafluoroethylene-ethylene copolymer, and tetrafluoroethylene-propylene. Porous made of copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyvinylidene fluoride, tetrafluoroethylene-perfluoroalkoxyethylene copolymer, polysulfone, polyphenylene sulfide, polyarylate, polyethersulfone, polysilazane, etc. There is a mass.

  Moreover, the thickness of the support substrate 20 is 10-50 micrometers, More preferably, it is 20-30 micrometers. Here, the reason why the thickness of the support substrate 20 is in the range of 10 to 50 μm is that the strength is insufficient when the thickness is less than 10 μm, and the electrical impedance is increased when the thickness is greater than 50 μm. Moreover, the porosity of the support substrate 20 is 30 to 80%, more preferably 40 to 60%. Here, the reason why the porosity of the support substrate 20 is in the range of 30 to 80% is that proton conductivity decreases when the porosity is less than 30%, and shape deformation occurs when the porosity is greater than 80%. Because it grows.

  Further, as the first electrolyte 22 filled in the support substrate 20, for example, a fluororesin such as a perfluorosulfonic acid polymer having a sulfonic acid group (Nafion manufactured by Dupont, Flemion manufactured by Asahi Glass Co., etc.), Examples thereof include organic polymer electrolytes such as hydrocarbon resins having a sulfonic acid group (polystyrene sulfonic acid, poly (α-methylstyrene) sulfonic acid, polyvinyl sulfonic acid, polyether ketone sulfonic acid, etc.). Further, phosphate glass that is inorganic glass or the like may be used as the first electrolyte 22. The first electrolyte 22 is not limited to the above-described material, and any electrolyte having proton conductivity can be used.

The porous thin film layer 45 is configured by dividing and forming a plurality of porous thin films 40 on the support substrate 20 with a predetermined gap. The porous thin film 40 constituting the porous thin film layer 45 is made of an inorganic material and has a large number of through holes 41 penetrating in the thickness direction. Examples of the inorganic material constituting the porous thin film 40 include oxide ceramics such as alumina, silica (SiO ₂ ) and zirconia, nitride ceramics such as silicon nitride, and carbide ceramics such as silicon carbide. Further, ceramics such as sialon, quartz glass, or the like may be used as the inorganic material.

  Alternatively, an electrolyte may be applied on the support substrate 20 and the porous thin film layer 45 may be formed via this electrolyte. In this case, the electrolyte interposed between the porous thin film layer 45 and the support substrate 20 is formed so that the unevenness on the surface of the support substrate 20 is filled and the surface on which the porous thin film 40 is formed is flat. . It is preferable that the thickness of the electrolyte is configured so as to fill the unevenness on the surface of the support substrate 20. Thus, by filling the unevenness on the surface of the support substrate 20, it is possible to form the porous thin film 40 having no defect, and to suppress the permeation of methanol. The electrolyte is formed by applying a Nafion solution manufactured by Dupont on the surface of the support substrate 20, for example, an electrolyte having proton conductivity. Note that the electrolyte material applied to the surface of the support substrate 20 is not limited to this, and any electrolyte material having proton conductivity may be used as in the case of the first electrolyte 22. Further, when the electrolyte is laminated on the support substrate 20, if the electrolyte is formed so as to fill the irregularities on the surface of the support substrate 20 and the surface on which the porous thin film 40 is formed is flat, You may form by methods other than application | coating.

  Further, the porous thin film 40 may be formed on the support substrate 20 by being equally divided. That is, a plurality of porous thin films 40 having the same size may be formed on the support substrate 20. Further, the porous thin film 40 may be formed on the support substrate 20 by being divided non-uniformly. That is, a plurality of types of porous thin films 40 having different aspect ratios may be formed on the support substrate 20. The cross-sectional shape of the porous thin film 40 facing the support substrate 20 is not limited to a rectangle, and may be, for example, a circle, a triangle, a polygon, or an ellipse. The porous thin film layer 45 may be configured by combining porous thin films 40 having different cross-sectional shapes. Moreover, it is preferable that the gap | interval with each porous thin film 40 is 10-100 micrometers, More preferably, it is 10-50 micrometers. Here, the reason why the gap with each porous thin film 40 is in the range of 10 to 100 μm is that when it is smaller than 10 μm, there is no allowance for the fluctuation range when the film is deformed, and when it is larger than 100 μm. This is because methanol crossover increases.

  Moreover, the thickness of the porous thin film 40 is 0.2-2000 micrometers, More preferably, it is 0.5-50 micrometers. Here, the reason why the thickness of the porous thin film 40 is in the range of 0.2 to 2000 μm is that when it is thinner than 0.2 μm, it becomes difficult to suppress the swelling of the electrolyte to be filled. This is because when the thickness is thick, the increase in electrical internal impedance becomes large. Moreover, the diameter of the through-hole 41 of the porous thin film 40 is 0.1-1000 micrometers, More preferably, it is 1-100 micrometers, More preferably, it is 5-30 micrometers. Here, the reason why the diameter of the through hole 41 is in the range of 0.1 to 1000 μm is that it is difficult to fill the electrolyte when the diameter is smaller than 0.1 μm, and when the diameter is larger than 1000 μm, This is because swelling cannot be suppressed.

  Moreover, the through-hole 41 of the porous thin film 40 should just be formed in the thickness direction, ie, the direction perpendicular | vertical with respect to a main surface, and cross-sectional shape is not specifically limited. For example, the through hole 41 may have a cross-sectional shape such as a circle, a triangle, a rectangle, or a polygon. Moreover, the through-hole 41 may be comprised combining the through-hole of a different cross-sectional area, and the through-hole of a different shape. Further, the aspect ratio (depth of the through hole 41 in the vertical direction / diameter of the through hole 41) is preferably 1 or more. Here, when the aspect ratio is 1 or more, the effect of suppressing the permeation of methanol by suppressing the swelling of the filled second electrolyte 42 is great. On the other hand, when the aspect ratio is smaller than 1, the filled second electrolyte 42 swells greatly when it contains water, so that the effect of suppressing the permeation of methanol is reduced.

The division of the porous thin film 40 and the formation of the through holes 41 of the porous thin film 40 are precisely performed by photolithography at predetermined positions of the thin film made of an inorganic material. First, the plurality of porous thin films 40 described above are formed on the surface of the support substrate 20 made of an organic porous material by, for example, a sputtering method such as a vacuum sputtering method or a reactive sputtering method, or a vapor deposition method such as a CVD method or a PVD method. A thin film of an inorganic material such as silica (SiO ₂ ) is formed. Subsequently, a photoresist is applied on the inorganic thin film, exposed using a mask having a predetermined pattern, baked, the inorganic thin film is etched, and finally the photoresist is peeled off. In this manner, a plurality of porous thin films 40 each having a large number of through holes 41 that are divided with a predetermined gap and precisely arranged in a predetermined pattern are formed on the surface of the support substrate 20. The second electrolyte 42 filled in the through holes 41 of the porous thin film 40 and the gaps between the porous thin films 40 is made of the same electrolyte material as that of the first electrolyte 22.

  Here, the thickness of the electrolyte membrane 10 configured by laminating the porous thin film layer 45 on one surface of the support substrate 20 is not particularly limited, but is preferably 20 to 200 μm, more preferably Preferably it is 30-80 micrometers. The thickness of 20 to 200 μm is preferable because when it is thinner than 20 μm, mechanical strength as an electrolyte membrane cannot be obtained, and when it is thicker than 200 μm, proton conductivity decreases and internal impedance increases. It is. In addition, the thickness of the electrolyte membrane 10 can be appropriately set in accordance with the specification application, the constituent material, and the like within the above-described range.

  According to the electrolyte membrane 10 of the above-described embodiment, the stress concentration in the porous thin film layer 45 is reduced by forming the plurality of porous thin films 40 on the surface of the support substrate 20 by dividing them with a predetermined gap. It is possible to relax, and deformation of the porous thin film layer 45 can be prevented. Thereby, permeation of methanol can be suppressed. In addition, by configuring the support substrate 20 with an organic porous body having high mechanical strength, sufficient mechanical strength can be obtained, and further thinning can be achieved and low impedance can be obtained.

  Next, a membrane electrode assembly (MEA) 50 including the above-described electrolyte membrane 10 will be described.

  FIG. 2 is a diagram schematically showing a cross section of a membrane electrode assembly 50 including the above-described electrolyte membrane 10.

  As shown in FIG. 2, the membrane electrode assembly 50 includes a fuel electrode composed of a fuel electrode catalyst layer 111 and a fuel electrode gas diffusion layer 112, an air electrode composed of an air electrode catalyst layer 113 and an air electrode gas diffusion layer 114, The electrolyte membrane 10 is sandwiched between the fuel electrode catalyst layer 111 and the air electrode catalyst layer 113.

  Examples of the catalyst contained in the fuel electrode catalyst layer 111 and the air electrode catalyst layer 113 include platinum group elements, such as single metals such as Pt, Ru, Rh, Ir, Os, and Pd, and alloys containing platinum group elements. And so on. Specifically, Pt—Ru or Pt—Mo having strong resistance to methanol or carbon monoxide is used as the fuel electrode catalyst layer 111, and platinum or Pt—Ni is used as the air electrode catalyst layer 13. Although preferable, it is not necessarily limited to these. Further, a supported catalyst using a conductive support such as a carbon material or an unsupported catalyst may be used.

  The fuel electrode gas diffusion layer 112 stacked on the fuel electrode catalyst layer 111 serves to uniformly supply fuel to the fuel electrode catalyst layer 111 and also has a function as a current collector of the fuel electrode catalyst layer 111. . On the other hand, the air electrode gas diffusion layer 114 laminated on the air electrode catalyst layer 113 serves to uniformly supply the oxidant to the air electrode catalyst layer 113, and also functions as a current collector of the air electrode catalyst layer 113. Have both. The fuel electrode gas diffusion layer 112 and the air electrode gas diffusion layer 114 are made of a known conductive material made of a porous material in order to allow gas to pass therethrough. The fuel electrode gas diffusion layer 112 and the air electrode gas diffusion layer 114 are made of, for example, carbon paper, carbon woven fabric, or the like, but are not limited thereto.

  The electrolyte membrane 10 sandwiched between the fuel electrode catalyst layer 111 and the air electrode catalyst layer 113 is disposed with the porous thin film layer 45 side facing the fuel electrode side.

  The membrane electrode assembly 50 configured as described above is installed in a fuel cell and generates electric power by supplying fuel and air. Fuel cells are roughly classified into active fuel cells and passive fuel cells. In the active type fuel cell, the amount of fuel composed of an aqueous methanol solution is adjusted by a pump so as to be constant, and is supplied to the fuel electrode of the membrane electrode assembly 50, and air is also supplied to the air electrode by a pump. The method is adopted. On the other hand, in the passive type fuel cell, the methanol vaporized to the fuel electrode of the membrane electrode assembly 50 is sent by natural supply, and external air is also naturally supplied to the air electrode, thereby extra equipment such as a pump. The method that does not equip is adopted. The electrolyte membrane 10 according to an embodiment of the present invention can be used for a fuel cell using any of the methods, and the use thereof is not limited.

  Next, a direct methanol fuel cell 100 including the above-described membrane electrode assembly (MEA) 50 will be described.

  FIG. 3 is a diagram schematically showing a cross section of a direct methanol fuel cell 100 including the membrane electrode assembly 50.

  As shown in FIG. 3, the fuel cell 100 includes the membrane electrode assembly 50 described above as an electromotive unit. A fuel electrode conductive layer 117 is stacked on the fuel electrode gas diffusion layer 112, and an air electrode conductive layer 118 is stacked on the air electrode gas diffusion layer 114. As the fuel electrode conductive layer 117 and the air electrode conductive layer 118, for example, a porous layer (for example, a mesh) or a foil body made of a metal material such as gold or nickel, or a conductive metal material such as stainless steel (SUS) is used. A composite material coated with a highly conductive metal such as gold can be used.

  A fuel electrode sealing material 119 having a rectangular frame shape is disposed between the fuel electrode conductive layer 117 and the electrolyte membrane 10 and surrounds the fuel electrode catalyst layer 111 and the fuel electrode gas diffusion layer 112. Yes. On the other hand, an air electrode sealing material 120 having a rectangular frame shape is disposed between the air electrode conductive layer 118 and the electrolyte membrane 10 and surrounds the air electrode catalyst layer 113 and the air electrode gas diffusion layer 114. Yes. The fuel electrode sealing material 119 and the air electrode sealing material 120 are made of, for example, a rubber O-ring, and prevent fuel leakage and oxidant leakage from the membrane electrode assembly 50. The shapes of the fuel electrode sealing material 119 and the air electrode sealing material 120 are not limited to the rectangular frame shape, and are appropriately configured to correspond to the outer edge shape of the fuel cell 100.

  Further, as shown in FIG. 3, a gas-liquid separation membrane 122 is disposed so as to cover the opening of the liquid fuel tank 121 that stores the liquid fuel F. On the gas-liquid separation membrane 122, a frame 123 (here, a rectangular frame) configured in a shape corresponding to the outer edge shape of the fuel cell 100 is disposed. On the frame 123, the membrane electrode assembly 50 including the fuel electrode conductive layer 117 and the air electrode conductive layer 118 is stacked.

  Here, the frame 123 is made of an electrically insulating material, and is specifically formed of a thermoplastic polyester resin such as polyethylene terephthalate (PET). The gas-liquid separation membrane 122 is configured so that fuel or the like does not leak from the periphery. The liquid fuel F stored in the liquid fuel tank 121 is a methanol aqueous solution having a concentration exceeding 50 mol% or pure methanol. The purity of pure methanol is preferably 95% by weight or more and 100% by weight or less. The vaporized component of the liquid fuel F means vaporized methanol when liquid methanol is used as the liquid fuel F, and the vaporized component of methanol when an aqueous methanol solution is used as the liquid fuel F. It means an air-fuel mixture consisting of water vaporization components.

  The vaporized fuel storage chamber 124, which is a space surrounded by the gas-liquid separation membrane 122, the fuel electrode conductive layer 117, and the frame 123, temporarily stores the vaporized component of the liquid fuel F that has permeated the gas-liquid separation membrane 122. Furthermore, it functions as a space for making the fuel concentration distribution in the vaporized component uniform.

  The gas-liquid separation membrane 122 described above separates the vaporized component of the liquid fuel F and the liquid fuel F, and allows the vaporized component to permeate the fuel electrode catalyst layer 11 side. The gas-liquid separation membrane 122 is formed into a sheet shape with a material that is inert to the liquid fuel F and does not dissolve, and specifically, silicone rubber, low-density polyethylene (LDPE) thin film, polyvinyl chloride (PVC) thin film. , Polyethylene terephthalate (PET) thin film, fluororesin (for example, polytetrafluoroethylene (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), etc.), etc.

  On the other hand, a moisturizing layer 126 is laminated on the air electrode conductive layer 118 via a frame 125 (here, a rectangular frame) configured in a shape corresponding to the outer edge shape of the fuel cell 100. On the moisturizing layer 126, a surface cover layer 127 in which a plurality of air inlets 128 for taking in air as an oxidant is formed is laminated. The surface cover layer 127 is also made of a metal such as SUS304, for example, because it also serves to pressurize the laminated body including the membrane electrode assembly 50 and enhance its adhesion. In addition, the frame 125 is made of an electrically insulating material like the above-described frame 123, and is specifically formed of, for example, a thermoplastic polyester resin such as polyethylene terephthalate (PET).

  In addition, the moisture retention layer 126 impregnates part of the water generated in the air electrode catalyst layer 113 to suppress water evaporation and uniformly introduces an oxidant into the air electrode gas diffusion layer 114. Therefore, it also has a function as an auxiliary diffusion layer that promotes uniform diffusion of the oxidizing agent to the air electrode catalyst layer 113. The moisturizing layer 126 is made of, for example, a material such as a polyethylene porous film. The movement of water from the air electrode catalyst layer 113 side to the fuel electrode catalyst layer 111 side due to the osmotic pressure phenomenon is performed by changing the number and size of the air inlets 128 in the surface cover layer 127 installed on the moisturizing layer 126. It can be controlled by adjusting the area of the opening.

  Next, the operation of the fuel cell 100 described above will be described.

The liquid fuel F (for example, methanol aqueous solution) in the liquid fuel tank 121 is vaporized, and the vaporized mixture of methanol and water vapor passes through the gas-liquid separation membrane 122 and is temporarily stored in the vaporized fuel storage chamber 124, and the concentration distribution. Is made uniform. The air-fuel mixture once stored in the vaporized fuel storage chamber 124 passes through the fuel electrode conductive layer 117 together with water vapor, is further diffused in the fuel electrode gas diffusion layer 112, and is supplied to the fuel electrode catalyst layer 111. The air-fuel mixture supplied to the fuel electrode catalyst layer 111 causes an internal reforming reaction of methanol represented by the following formula (1).
CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ Formula (1)

  In addition, when pure methanol is used as the liquid fuel F, since water vapor is not supplied from the liquid fuel tank 121, water generated in the air electrode catalyst layer 113, water in the electrolyte membrane 10 and the like are methanol and the above. The internal reforming reaction of formula (1) is generated, or the internal reforming reaction is generated by another reaction mechanism that does not require water, regardless of the internal reforming reaction of formula (1).

Protons (H ⁺ ) generated by the internal reforming reaction are conducted through the electrolyte membrane 10 and reach the air electrode catalyst layer 113. The air taken from the air inlet 128 of the surface cover layer 127 diffuses through the moisture retention layer 126, the air electrode conductive layer 118, and the air electrode gas diffusion layer 114 and is supplied to the air electrode catalyst layer 113. The air supplied to the air electrode catalyst layer 113 causes the reaction shown in the following formula (2). By this reaction, water is generated and a power generation reaction occurs.
(3/2) O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O Formula (2)

  The water produced in the air electrode catalyst layer 113 by this reaction diffuses through the air electrode gas diffusion layer 114 and reaches the moisture retention layer 126, and a part of the water covers the surface cover layer 127 provided on the moisture retention layer 126. However, the remaining water adheres to the surface cover layer 127. In particular, when the reaction of Formula (2) proceeds, the amount of water whose transpiration is inhibited by the surface cover layer 127 increases, and the amount of water stored in the air electrode catalyst layer 113 increases. In this case, the water storage amount of the air electrode catalyst layer 113 becomes larger than the water storage amount of the fuel electrode catalyst layer 111 as the reaction of the formula (2) proceeds. As a result, a reaction in which water generated in the air electrode catalyst layer 113 moves to the fuel electrode catalyst layer 111 through the electrolyte membrane 10 is promoted by the osmotic pressure phenomenon. Therefore, as compared with the case where the supply of moisture to the fuel electrode catalyst layer 111 depends only on the vapor vaporized from the liquid fuel tank 121, the supply of moisture is promoted, and the internal reforming reaction of methanol in the above-described equation (1) is performed. Can be promoted. As a result, the output density can be increased and the high output density can be maintained for a long period of time.

  Even when a methanol aqueous solution having a methanol concentration exceeding 50 mol% or pure methanol is used as the liquid fuel, the water that has moved from the air electrode catalyst layer 113 to the fuel electrode catalyst layer 111 is used for the internal reforming reaction. Therefore, it is possible to stably supply water to the fuel electrode catalyst layer 111. Thereby, the reaction resistance of the internal reforming reaction of methanol can be further reduced, and the long-term output characteristics and load current characteristics can be further improved.

  As described above, according to the fuel cell 100 of one embodiment of the present invention, it is possible to supply a small, high performance, stable and high output.

  In the above-described embodiment, a direct methanol fuel cell using a methanol aqueous solution or pure methanol as the liquid fuel F has been described. However, the liquid fuel F is not limited thereto. For example, ethanol fuel such as ethanol aqueous solution and pure ethanol, propanol fuel such as propanol aqueous solution and pure propanol, glycol fuel such as glycol aqueous solution and pure glycol, dimethyl ether, formic acid, and other liquid fuels may be used. In any case, the liquid fuel F corresponding to the fuel cell 100 is accommodated in the liquid fuel tank 121.

  Further, in order to obtain a predetermined battery output, a plurality of fuel cells 100 shown in FIG. 3 can be arranged in parallel, and the fuel cells 100 can be electrically connected in series to constitute a fuel cell. At this time, for example, one liquid fuel tank 121 can be shared.

  Next, the configuration of the fuel cell 200 having another configuration including the above-described electrolyte membrane 10 will be described with reference to FIGS. 4 and 5.

  FIG. 4 is a diagram schematically showing a cross section of a fuel cell 200 including the above-described electrolyte membrane 10. FIG. 5 is a perspective view schematically showing the configuration of the fuel distribution mechanism 230.

  As shown in FIG. 4, the membrane electrode assembly 210 includes an anode (fuel electrode) 222 having an anode catalyst layer 220 and an anode gas diffusion layer 221, and a cathode having a cathode catalyst layer 223 and a cathode gas diffusion layer 224 ( Air electrode) 225, and the electrolyte membrane 10 sandwiched between the anode catalyst layer 220 and the cathode catalyst layer 223.

  Rubber O-rings 227 are interposed between the electrolyte membrane 10 and a fuel distribution mechanism 230 and a surface cover layer 226, which will be described later, thereby preventing fuel leakage and oxidant leakage from the membrane electrode assembly 210. It is preventing. The surface cover layer 226 has an opening (not shown) for taking in air as an oxidant. Between the surface cover layer 226 and the cathode (air electrode) 225, a moisturizing layer and a surface layer are disposed as necessary. The moisturizing layer is impregnated with a part of the water generated in the cathode catalyst layer 223 to suppress the transpiration of water and promote uniform diffusion of air to the cathode catalyst layer 223. The surface layer adjusts the amount of air taken in, and has a plurality of air inlets whose number, size, etc. are adjusted according to the amount of air taken in.

  The materials constituting the anode catalyst layer 220, the anode gas diffusion layer 221, the cathode catalyst layer 223, the cathode gas diffusion layer 224, the surface cover layer 226, etc. constituting the membrane electrode assembly 210 described above are the membrane electrodes described above. It is the same as the material which comprises the corresponding layer in the joined_body | zygote 50. FIG.

  A fuel distribution mechanism 230 is arranged on the anode (fuel electrode) side of the membrane electrode assembly 210. A fuel storage unit 232 is connected to the fuel distribution mechanism 230 via a fuel flow path 231 such as a pipe.

  The fuel storage portion 232 stores the liquid fuel F corresponding to the membrane electrode assembly 210. Examples of the liquid fuel F include methanol fuels such as methanol aqueous solutions having various concentrations and pure methanol. The liquid fuel F is not necessarily limited to methanol fuel. The liquid fuel F may be, for example, an ethanol fuel such as an ethanol aqueous solution or pure ethanol, a propanol fuel such as a propanol aqueous solution or pure propanol, a glycol fuel such as a glycol aqueous solution or pure glycol, dimethyl ether, formic acid, or other liquid fuel. In any case, fuel corresponding to the fuel cell 200 is stored in the fuel storage portion 232.

  Liquid fuel F is introduced into the fuel distribution mechanism 230 from the fuel storage portion 232 via the flow path 231. The flow path 231 is not limited to piping independent of the fuel distribution mechanism 230 and the fuel storage unit 232. For example, when the fuel distribution mechanism 230 and the fuel storage portion 232 are stacked and integrated, a liquid fuel flow path connecting them may be used. The fuel distribution mechanism 230 only needs to be connected to the fuel storage portion 232 via the flow path 231.

  Here, as shown in FIG. 5, the fuel distribution mechanism 230 includes at least one fuel inlet 233 into which the liquid fuel F flows through the flow path 231, and a plurality of liquid fuel F and a plurality of components that discharge the vaporized components thereof. A fuel distribution plate 235 having a fuel discharge port 234 is provided. As shown in FIG. 4, a gap 236 serving as a passage for the liquid fuel F guided from the fuel injection port 233 is provided inside the fuel distribution plate 235. The plurality of fuel discharge ports 234 are directly connected to the gaps 236 that function as fuel passages.

  The liquid fuel F introduced into the fuel distribution mechanism 230 from the fuel injection port 233 enters the gap portion 236, and is guided to the plurality of fuel discharge ports 234 via the gap portion 236 functioning as the fuel passage. For example, a gas-liquid separator (not shown) that transmits only the vaporized component of the fuel and does not transmit the liquid component may be disposed in the plurality of fuel discharge ports 234. As a result, the vaporized component of the fuel is supplied to the anode (fuel electrode) 222 of the membrane electrode assembly 210. The gas-liquid separator may be installed as a gas-liquid separation film or the like between the fuel distribution mechanism 230 and the anode (fuel electrode) 222. The vaporized component of the liquid fuel F is discharged from a plurality of fuel discharge ports 234 toward a plurality of locations of the anode (fuel electrode) 222.

A plurality of fuel discharge ports 234 are provided on the surface of the fuel distribution plate 235 that contacts the anode (fuel electrode) 222 so that fuel can be supplied to the entire membrane electrode assembly 210. The number of the fuel discharge ports 234 may be two or more. However, in order to equalize the fuel supply amount in the surface of the membrane electrode assembly 210, 0.1 to 10 / cm ² fuel discharge ports 234 are provided. It is preferable to form it so that it exists.

  A pump 237 is inserted into the flow path 231 connecting the fuel distribution mechanism 230 and the fuel storage unit 232. The pump 237 is not a circulation pump through which the liquid fuel F is circulated, but is a fuel supply pump that transfers the liquid fuel F from the fuel storage unit 232 to the fuel distribution mechanism 230 to the last. By supplying the liquid fuel F with such a pump 237 when necessary, the controllability of the fuel supply amount is improved. In this case, as the pump 237, a rotary vane pump, an electroosmotic pump, a diaphragm pump, a squeezing pump, etc. are used from the viewpoint that a small amount of liquid fuel F can be fed with good controllability and can be reduced in size and weight. It is preferable to do. The rotary vane pump feeds liquid by rotating wings with a motor. The electroosmotic flow pump uses a sintered porous body such as silica that causes an electroosmotic flow phenomenon. A diaphragm pump drives a diaphragm with an electromagnet or piezoelectric ceramics to send liquid. The ironing pump presses a part of the flexible fuel flow path and irons the liquid fuel F. Among these, it is more preferable to use an electroosmotic pump or a diaphragm pump having piezoelectric ceramics from the viewpoint of driving power, size, and the like.

  In such a configuration, the liquid fuel F stored in the fuel storage portion 232 is transferred through the flow path 231 by the pump 237 and supplied to the fuel distribution mechanism 230. The fuel discharged from the fuel distribution mechanism 230 is supplied to the anode (fuel electrode) 222 of the membrane electrode assembly 210. The subsequent operation is the same as that of the fuel cell 100 described above.

  In addition, as long as the fuel is supplied from the fuel distribution mechanism 230 to the membrane electrode assembly 210, a fuel cutoff valve may be arranged instead of the pump 237. In this case, the fuel cutoff valve is provided to control the supply of the liquid fuel F through the flow path.

  Next, in the fuel cell provided with the electrolyte membrane 10 of the present invention, it will be described in the following examples that excellent output characteristics can be obtained.

Example 1
The electrolyte membrane in the present invention was produced as follows.
On one surface of a porous polyimide substrate (Ube Industries, Upilex PT) having a thickness of 25 μm and a porosity of 45% that functions as a support substrate, RF (radio frequency) sputtering (ULVAC, CS-200 RF400W Ar30sccm 40 ° C. ), A film made of SiO ₂ having a thickness of 0.5 μm that functions as the porous thin film 40 was formed. Subsequently, this porous polyimide substrate was attached to a Si substrate with Kapton tape, and hydrophilic treatment was performed with hexamethyldisilazane (manufactured by Tokyo Ohka Kogyo Co., Ltd., OAP). Thereafter, a positive type photosensitizer (OFPR-800C LB manufactured by Tokyo Ohka Kogyo Co., Ltd.) composed of ethyl lactate and normal butyl acetate was spin-coated, and then heated on a hot plate at 100 ° C. for 1 minute. Using an exposure machine (PLA501FA manufactured by Canon) using a Cr mask that is uniformly opened with a hole size of 10 μm, a hole area ratio of 63% on the film formed by sputtering, and is divided into 9 parts as a whole. Exposure (Mercury Lamp5A Supply3 0gap exposure time 15 seconds). Thereafter, development is performed with an aqueous tetramethylammonium hydroxide solution (NMD-3, manufactured by Tokyo Ohka Kogyo Co., Ltd.) having a concentration of 2.38 w% for 60 seconds, rinsed with water, and post-baked at 100 ° C. for 1 minute on a hot plate. It was. Thereafter, an etching process of 1 μm was performed with buffered hydrofluoric acid (manufactured by Daikin, BHF63U), and the resist was removed with a stripping solution (manufactured by Tokyo Ohka Kogyo Co., Ltd.). The membrane thus obtained was vacuum impregnated with a Nafion solution and filled with electrolytes functioning as the first electrolyte and the second electrolyte. This operation was repeated several times, and Nafion was filled in the entire membrane to produce an electrolyte membrane.

  Further, platinum-supported graphite particles were mixed with DE2020 (manufactured by Dupont) with a homogenizer to prepare a slurry, which was applied to carbon paper which is an air electrode gas diffusion layer. And this was dried at normal temperature and the air electrode was produced.

  Further, carbon particles carrying platinum ruthenium alloy fine particles were mixed with DE2020 (manufactured by Dupont) with a homogenizer to prepare a slurry, which was applied to carbon paper as a fuel electrode gas diffusion layer. And this was dried at normal temperature and the fuel electrode was produced.

The produced electrolyte membrane 10 was sandwiched between the produced air electrode and fuel electrode, and pressed under conditions of a temperature of 120 ° C. and a pressure of 10 kgf / cm ² to produce a membrane electrode assembly (MEA). The electrode area was 12 cm ² for both the air electrode and the fuel electrode.

  Subsequently, the membrane electrode assembly was sandwiched between gold foils having a plurality of holes for taking in air and vaporized methanol to form a fuel electrode conductive layer and an air electrode conductive layer.

  The laminate in which the membrane electrode assembly (MEA), the fuel electrode conductive layer, and the air electrode conductive layer described above were stacked was sandwiched between two resin-made frames. In addition, a rubber O-ring was sandwiched between the air electrode side of the membrane electrode assembly and one frame, and between the fuel electrode side of the membrane electrode assembly and the other frame, respectively. .

  Also, the fuel electrode side frame was fixed to the liquid fuel tank by screwing through a gas-liquid separation membrane. A silicone sheet having a thickness of 0.1 mm was used for the gas-liquid separation membrane. On the other hand, a porous plate was disposed on the air electrode side frame to form a moisture retention layer. On this moisturizing layer, a stainless steel plate (SUS304) with a thickness of 2 mm in which air inlets for intake of air (diameter 3 mm, number of ports 56) are formed is arranged to form a surface cover layer and screwed Fixed by.

  5 ml of pure methanol is injected into the liquid fuel tank of the fuel cell formed as described above, and the output of the voltage, current value and voltage value in the open circuit state in an environment of temperature 25 ° C. and relative humidity 50% is output. The maximum value was measured. Further, the maximum value of the surface temperature of the fuel cell was measured by a thermocouple attached to the surface of the surface cover layer.

As a result of the measurement, the voltage in the open circuit state was 0.58 V, the maximum value of the output was 22.3 mW / cm ² , and the maximum value of the surface temperature of the fuel cell was 42.5 ° C.

(Comparative Example 1)
The electrolyte membrane used in Comparative Example 1 was prepared by applying a film made of SiO ₂ by RF sputtering on the surface of a porous polyimide substrate (Ube Industries, Upilex PT) having a thickness of 25 μm and a porosity of 45%. The method is the same as that for the electrolyte membrane of Example 1, except that the pattern is formed using a Cr mask that is exposed without being divided, and is integrally exposed. Note that the measurement method and measurement conditions for the maximum value of output and the maximum value of the surface temperature of the fuel cell from the voltage, current value and voltage value in the open circuit state are the same as the measurement method and measurement conditions in Example 1. .

As a result of the measurement, the voltage in the open circuit state was 0.51 V, the maximum value of the output was 12.6 mW / cm ² , and the maximum value of the surface temperature of the fuel cell was 45.2 ° C.

(Comparative Example 2)
In Comparative Example 2, a Nafion 112 membrane manufactured by DuPont having a thickness of 50 μm was used as the electrolyte membrane. Other configurations are the same as the configuration of the fuel cell of the first embodiment. Note that the measurement method and measurement conditions for the maximum value of output and the maximum value of the surface temperature of the fuel cell from the voltage, current value and voltage value in the open circuit state are the same as the measurement method and measurement conditions in Example 1. .

As a result of the measurement, the voltage in the open circuit state was 0.48 V, the maximum value of the output was 11.8 mW / cm ² , and the maximum value of the surface temperature of the fuel cell was 47.5 ° C.

(Examination of measurement results of Examples and Comparative Examples)
Table 1 shows the measurement results of Example 1 and Comparative Examples 1 and 2 described above.

  From the measurement results shown in Table 1, the maximum value of the output of Example 1 was higher than that of Comparative Examples 1 and 2. Moreover, the maximum value of the surface temperature of the fuel cell was lower in Example 1 than in Comparative Examples 1 and 2.

  Here, when the methanol crossover occurs, the methanol that has moved to the air electrode catalyst layer directly reacts with oxygen present in the vicinity of the air electrode catalyst layer to generate water and carbon dioxide. Since this reaction is an exothermic reaction, the temperature rises. Furthermore, since oxygen is used for the exothermic reaction, the oxygen concentration in the air electrode catalyst layer is lowered, the potential is lowered, and the output is lowered.

  Considering the above phenomenon, it is presumed that methanol crossover (MCO) occurred in Comparative Examples 1 and 2. Further, in Comparative Example 1, deformation or a crack with a through hole formed in the film as a fracture source occurred in the film made of SiO 2 formed on one surface of the porous polyimide substrate. Thereby, it is considered that methanol crossover could not be suppressed. In Comparative Example 2, when a Nafion 112 membrane was used as the electrolyte membrane, the electrolyte membrane swelled, and it was considered that methanol crossover could not be suppressed.

  From the above results, in Example 1, a plurality of porous thin films are divided and formed on the surface of the support substrate with a predetermined gap, thereby reducing the stress concentration in the porous thin film layer. It is considered that the permeation of methanol could be suppressed because the deformation of the layer could be prevented. It was also found that excellent output characteristics can be obtained in the fuel cell including the electrolyte membrane 10 of the present invention.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  In addition, even in the liquid fuel vapor supplied to the membrane electrode assembly (MEA), all the liquid fuel vapor may be supplied, but the present invention can be applied even when a part of the liquid fuel vapor is supplied in a liquid state. Can be applied.

  According to the electrolyte membrane according to the aspect of the present invention, stress concentration in the porous thin film layer can be alleviated by forming a plurality of porous thin films on the surface of the support substrate by providing predetermined gaps. And deformation of the porous thin film layer can be prevented. Thereby, permeation of methanol can be suppressed. In addition, by configuring the support substrate with an organic porous body having high mechanical strength, sufficient mechanical strength can be obtained, and further, the thickness can be reduced and low impedance can be obtained. The electrolyte membrane according to the embodiment of the present invention is effectively used as an electrolyte membrane in a liquid fuel direct supply type fuel cell, for example. In addition, according to the fuel cell including the electrolyte membrane according to the aspect of the present invention, it is possible to supply a small, high-performance, stable and high output, for example, effective in a liquid fuel direct supply type fuel cell. Is done.

Claims (8)

A support substrate made of a porous material;
A first electrolyte having proton conductivity filled in the support substrate;
A porous thin film layer formed by dividing a plurality of porous thin films having through holes in a thickness direction on one surface of the support substrate by providing a predetermined gap;
An electrolyte membrane comprising: a proton-conducting second electrolyte filled in a through-hole of the porous thin film. The electrolyte membrane according to claim 1,
The electrolyte membrane, wherein the second electrolyte is further filled in a gap between each porous thin film and the porous thin film. The electrolyte membrane according to claim 1,
An electrolyte membrane, wherein the porous body constituting the support substrate is made of an organic substance. The electrolyte membrane according to claim 1,
The electrolyte membrane, wherein the porous thin film is made of an inorganic material. The electrolyte membrane according to claim 1,
The electrolyte membrane, wherein the plurality of porous thin films have the same cross-sectional shape facing one surface of the support substrate. The electrolyte membrane according to claim 1,
The electrolyte membrane, wherein the plurality of porous thin films have two or more different cross-sectional shapes opposed to one surface of the support substrate. A fuel cell comprising a fuel electrode, an air electrode, and an electrolyte membrane sandwiched between the fuel electrode and the air electrode,
The fuel cell, wherein the electrolyte membrane is the electrolyte membrane according to any one of claims 1 to 6. The fuel cell according to claim 7, wherein
The fuel cell, wherein the electrolyte membrane is disposed with the porous thin film layer facing the fuel electrode.

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