JP2007128908A - Cell unit of solid polymer electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost cell unit of a solid polymer electrolyte fuel cell incorporating a metallic separator having a structure capable of demonstrating high corrosion resistance and durability. <P>SOLUTION: The cell unit of a solid polymer electrolyte fuel cell includes: (a) a polymer electrolyte membrane; (b) a pair of electrodes fixed on either side of the polymer electrolyte membrane and capable of gas diffusion; (c) a pair of porous/conductive graphite current collectors fixed on the outside of the electrodes in close contact and capable of gas diffusion; (d) a pair of metallic separators separately introducing fuel gas and oxygen-contained gas into the electrodes; and (e) a porous conductive buffer layer each provided between the metallic separator and the graphite current collector and having flexibility and ventilating performance. The metallic separator has a conductive membrane made of at least one kind of metal selected from a group of Au, Pt, Ag, Pd, Ir, Ni, and Cr, or an alloy made of above formed at least on a contacting surface with the buffer layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a cell unit of a solid polymer electrolyte fuel cell used as an in-vehicle fuel cell, and more particularly to a cell unit of a solid polymer electrolyte fuel cell in which power generation performance does not deteriorate even when a metal separator is used.

Fuel cells are attracting attention as next-generation power generation devices because they have high energy conversion efficiency from fuel to electricity and do not emit harmful substances such as SOx and NOx and CO ₂ gas that causes global warming. Widely developed. Among these, fuel cells called polymer ion exchange membrane fuel cells or solid polymer electrolyte fuel cells that operate in a temperature range of 150 ° C. or less have the feature that they can be miniaturized due to their high output density, so that It is suitable as a power source or a vehicle-mounted power source. Therefore, solid polymer electrolyte fuel cells are currently being actively researched and are expected to be put into practical use several years later.

  A solid polymer electrolyte fuel cell usually uses a fluororesin-based ion exchange membrane having a sulfonic acid group (for example, Nafion) as a solid polymer electrolyte membrane, and a fuel electrode and an oxygen (air) electrode on both sides of the electrolyte membrane. It is fixed and used as a single battery (cell). Each electrode is usually composed of carbon black dispersed with water-repellent PTFE particles and noble metal fine particles as a catalyst. The unit cells are stacked via a plate-like separator provided with a ventilation groove for uniformly supplying fuel gas and air on both sides to form a fuel cell stack (see FIG. 1).

When the solid polymer electrolyte fuel cell having such a configuration is operated, the hydrogen gas is oxidized to emit electrons and become protons. Protons enter the polymer electrolyte, combine with water molecules to become H ₃ O ⁺ , and move to the anode electrode side. Electrons generated by the oxidation reaction of hydrogen gas flow to the anode electrode side through an external circuit. Therefore, oxygen at the anode electrode obtains the above electrons and becomes O ²⁻ ions, and combines with H ₃ O ⁺ to become water. Since this reaction process proceeds continuously, electric energy can be continuously extracted.

  The cell unit battery has a theoretical electromotive force of 1.2 V, but electrode polarization, reaction gas close-over (a phenomenon in which fuel gas permeates the polymer electrolyte and reaches the air electrode), and electrode material and current collector material. The actual output voltage is about 0.6 to 0.8 V due to the voltage drop due to the ohmic resistance. For this reason, it is necessary to laminate several tens of cells in series via a separator so that a practical output can be obtained.

As can be seen from the above power generation principle, since a large amount of H ⁺ ions are present in the polymer electrolyte membrane, the inside of the polymer electrolyte membrane and the vicinity of the electrode are strongly acidic. In addition, oxygen undergoes a reduction reaction on the anode electrode side and combines with H ⁺ to generate water, but hydrogen peroxide may be generated depending on the operating state of the battery. Since the separator is incorporated in such an environment, electrochemical stability (corrosion resistance) is required in addition to conductivity and airtightness regarding the characteristics of the separator.

  Conventional separators for fuel cells are almost made of graphite material and are manufactured by machining. While graphite has the advantage of low electrical resistance and high corrosion resistance, it has the disadvantages of poor mechanical strength and high processing costs. In particular, in the case of an on-vehicle fuel cell, there is a problem that it is difficult to use a graphite separator because a material constituting the fuel cell is required to have high mechanical strength.

  Recently, a method for producing a graphite separator by forming a uniform mixture of graphite powder and resin into a separator shape and firing at a high temperature has been proposed. In addition, a molded body of a mixture of graphite powder and resin may be used as a separator without firing. In any case, such a graphite separator has problems in electrical resistance, gas tightness, mechanical strength, and thermal conductivity.

  In addition to separators made of carbon material, metal separators are also being studied. Metals are very advantageous over carbon materials in terms of electrical resistance, hermeticity and mechanical strength. In addition, when a metal is used, the separator can be thinned, so that the weight can be easily reduced. However, metals are more susceptible to corrosion than carbon materials, and when metal ions generated by corrosion enter the polymer electrolyte membrane, the ionic conductivity of the polymer electrolyte membrane decreases, affecting the power generation performance of the fuel cell. There is also a risk of giving.

  In order to solve this problem, for example, Japanese Patent Laid-Open No. 11-162478 (Patent Document 1) proposes a method for improving the corrosion resistance of a metallic separator by plating a precious metal on the entire surface of the separator. However, this method has no problem in terms of performance, but is not practical because the manufacturing cost of the separator is increased due to the anticorrosion film.

  In order to reduce costs, the use of a corrosion-resistant metal such as stainless steel or nickel alloy for the separator has also been studied. This kind of metal is passive because a very thin oxide film is formed on the surface, so that corrosion is suppressed. However, the formation of an oxide film increases the contact electrical resistance of the surface, which reduces the power generation performance of the fuel cell.

  In order to solve this problem, a method of forming a noble metal film or a metal or resin film containing carbon particles on a contact surface with a separator electrode produced by processing a corrosion-resistant material to reduce the contact electric resistance. Has been proposed (for example, JP-A-10-308226 (Patent Document 2)). In order to reduce the weight of the fuel cell, a separator using aluminum has also been studied (for example, JP-A-10-255823 (Patent Document 3)).

  However, since aluminum is poor in corrosion resistance, in the case of an aluminum separator, a corrosion-resistant metal film must be formed on the surface to provide corrosion resistance. The metal used for this film is almost noble metal (for example, Au) so far. However, since noble metals such as Au are very expensive, a noble metal-coated aluminum separator is extremely expensive. In order to reduce the cost of the separator, it is necessary to coat the noble metal as thin as possible. However, as the noble metal film becomes thinner, the corrosion resistance decreases and practical durability cannot be obtained.

  Even if a metal film having sufficient corrosion resistance is formed on a metal separator, the film may be damaged during the assembly of the fuel cell, resulting in corrosion of the base metal of the separator and an increase in contact resistance. There is also.

As described above, in the cell unit of a fuel cell incorporating a metal separator, particularly in the case of an aluminum alloy separator, the power generation performance deteriorates due to low corrosion resistance. Therefore, it has not been possible to construct a low-cost and practical fuel cell using a metal separator.
JP-A-11-162478 JP-A-10-308226 JP 10-255823 A

  Accordingly, an object of the present invention is to provide a cell unit of a low-cost solid polymer electrolyte fuel cell incorporating a metal separator and having a structure capable of exhibiting high corrosion resistance and durability. It is.

  As a result of diligent research in view of the above-mentioned object, the present inventors have found that the conductive film of the metal separator is destroyed by the pressing of the graphite current collector, and corrosion occurs therefrom, resulting in deterioration of the performance of the fuel cell. (1) Rather than bringing the current collector of the gas diffusion electrode into direct contact with the surface of the metal separator, the corrosion resistance, flexibility, conductivity and gas between the current collector and the metal separator The conductive film on the surface of the metal separator is protected by mounting a fibrous or foam-like buffer layer having permeability or forming a buffer film having corrosion resistance and conductivity on the current collector. Therefore, it is possible to significantly reduce the corrosion of the metal separator and maintain the power generation performance of the fuel cell, particularly when (2) the metal separator is made of relatively low hardness aluminum or aluminum alloy, or the metal separator If the conductive coating is very thin Au film and the like, when installing the buffer layer, dramatically it discovered that can suppress performance degradation of the fuel cell, thereby completing the present invention.

  That is, the cell unit of the solid polymer electrolyte fuel cell of the present invention comprises: (a) a polymer electrolyte membrane; (b) a pair of electrodes capable of gas diffusion fixed to both surfaces of the polymer electrolyte membrane, c) a pair of gas-diffusible porous and conductive graphite current collectors fixed in contact with the outside of the electrode; and (d) a pair of metals for separately introducing a fuel gas and an oxygen-containing gas into the electrode. And (e) a cell unit of a solid polymer electrolyte fuel cell having a flexible and air-permeable porous conductive buffer layer disposed between the metal separator and the graphite current collector The metal separator is made of at least one metal selected from the group consisting of Au, Pt, Ag, Pd, Ir, Ni, and Cr, or an alloy thereof, at least on the surface in contact with the buffer layer. A conductive film is formed And

  The buffer layer is preferably made of a woven or non-woven fabric of conductive fibers made of metal, carbon, or a conductive resin, or a foamed sheet having pores communicating to the extent that it has air permeability.

  It is preferable that at least the surface of the buffer layer in contact with the metal separator is coated with a metal or a conductive resin so as not to impair the porosity. Moreover, it is preferable that the conductive fiber which comprises the said buffer layer is coat | covered with the metal or conductive resin.

  The metal coated on the surface of the buffer layer or the conductive fibers constituting the buffer layer is made of Au, Pt, Pd, Ru, Rh, Ir, Ag, Ti, Cu, Pb, Ni, Cr, Co, and Fe. It is preferably at least one selected metal or an alloy thereof. The buffer layer preferably has a porosity of 20 to 90%. The thickness of the buffer layer is preferably 0.01 to 1.0 mm, and more preferably 0.05 to 0.2 mm.

  The conductive film formed on the surface of the metallic separator preferably has a thickness of 0.01 to 20 μm. The metal separator is preferably made of aluminum or an aluminum alloy.

  A cell unit of a preferred solid polymer electrolyte fuel cell of the present invention comprises: (a) a polymer electrolyte membrane; and (b) a pair of electrodes capable of gas diffusion fixed to both surfaces of the polymer electrolyte membrane, (c) a pair of gas-diffusible porous and conductive graphite current collectors fixed so as to be in contact with the outside of the electrode, and (d) a pair of fuel gas and oxygen-containing gas separately introduced into the electrode A separator made of aluminum or aluminum alloy, and (e) a porous conductive buffer layer having flexibility and air permeability disposed between the separator and the current collector made of graphite, and the buffer layer A conductive film having a thickness of 0.01 to 20 μm is formed on the surface of the separator in contact with the substrate.

  Another solid polymer electrolyte fuel cell unit of the present invention includes: (a) a polymer electrolyte membrane; and (b) a pair of electrodes capable of gas diffusion fixed to both surfaces of the polymer electrolyte membrane. And (c) a pair of gas diffusible porous bodies fixed so as to be in contact with the outside of the electrode, and (d) a pair of metal separators that separately introduce fuel gas and oxygen-containing gas into the electrode. And a conductive buffer film made of a corrosion-resistant metal, a conductive resin, or a conductive ceramic is formed on at least the porous body in contact with the metal separator.

  The porous body is preferably made of a porous / conductive graphite current collector, and more preferably made of a carbon fiber woven or non-woven fabric or carbon paper. The porous body is preferably made of resin fibers or woven or non-woven fabric of natural fibers, or a porous resin sheet.

  The conductive buffer film formed on the porous body preferably has a film thickness of 0.5 to 50 μm, Au, Pt, Pd, Ru, Rh, Ir, Ag, Ti, Cu, Pb, Ni, Cr, Co And at least one metal selected from the group consisting of Fe and an alloy thereof. The conductive buffer film is preferably formed by sputtering, vacuum deposition, electroplating or electroless plating.

  As described above, in the cell unit of the solid polymer electrolyte fuel cell of the present invention in which the buffer layer having conductivity, air permeability, and flexibility is mounted between the metal separator and the current collector, the metal separator Therefore, the power generation performance of the fuel cell can be maintained for a long time. Moreover, corrosion of a metal separator can also be effectively suppressed by forming a conductive buffer film on a porous body such as a current collector.

  FIG. 1 shows a configuration example of a cell unit of a solid polymer electrolyte fuel cell according to an embodiment of the present invention, and FIG. 3 shows a configuration example of a cell unit of a conventional solid polymer electrolyte fuel cell. A cell unit 1 of the conventional solid polymer electrolyte fuel cell shown in FIG. 3 includes a polymer electrolyte membrane (solid polymer electrolyte) 2, a cathode electrode 3 and an anode electrode 4 formed on both sides thereof, and both electrodes 3. , 4 and current separators 5, 5 and metal separators 7, 7 in contact with the current collectors 5, 5. On the other hand, the cell unit 1 of the solid polymer electrolyte fuel cell shown in FIG. 1 includes a solid polymer electrolyte 2, a cathode electrode 3 and an anode electrode 4 formed on both sides thereof, and both electrodes 3 and 4. Current collectors 5, 5 provided respectively, buffer layers 6, 6 disposed outside the current collectors 5, 5, and metal separators 7, 7 in contact with the buffer layers 6, 6. Thus, the cell unit of the present invention is equipped with a fibrous or foamed sheet-like buffer layer having excellent flexibility, conductivity, and gas permeability between each current collector 5 and each metal separator 7. It is characterized by that. Because of this structure, the conductive film of the metallic separator is not damaged by contact with the current collector 5, and the corrosion resistance is maintained.

  FIG. 2 shows a configuration example of a cell unit of a solid polymer electrolyte fuel cell according to another embodiment of the present invention. This cell unit 1 includes a solid polymer electrolyte 2, cathode electrodes 3 and anode electrodes 4 formed on both sides thereof, current collectors 5, 5 provided on both electrodes 3, 4, and current collectors 5, respectively. , 5 and conductive buffer films 8 and 8 formed on the outer side of the metal buffer 7 and metal separators 7 and 7 in contact with the conductive buffer films 8 and 8. In this manner, since the conductive buffer film 8 is formed on the surface of each current collector 5 in contact with each metal separator 7, the metal separator is connected to the current collector 5 in the cell unit 1 shown in FIG. 2. It will not be corroded by contact.

  Among the constituent elements of the solid polymer electrolyte fuel cell, the solid polymer electrolyte 2, the cathode electrode 3, and the anode electrode 4 may be the same as those in the prior art, and thus detailed description thereof is omitted here. Therefore, only the buffer layer, the separator, the porous / conductive graphite current collector and other porous bodies will be described in detail below.

[1] Buffer layer The buffer layer must not only have excellent conductivity in order to conduct the metal separator 7 and the graphite current collector 5, but the graphite current collector 5 is a metal separator. In order to mitigate the impact and the like when coming into contact with 7, it must also have excellent flexibility. In addition, since it is used in fuel cells, it must also have excellent thermal conductivity and corrosion resistance.

  The buffer layer 6 that requires such characteristics is preferably composed of a woven or non-woven fabric made of metal fibers, carbon fibers or conductive resin fibers, or a foamed sheet made of these conductive materials. As the metal fiber, a fiber such as stainless steel or nickel can be used. Carbon fibers are preferred because they have electrical conductivity and corrosion resistance. Commercially available carbon fibers can be used as the carbon fibers. Examples of the conductive resin fibers include fibers such as metal-dispersed polyolefin resins, polyester resins, and fluorine resins. The average diameter of these fibers may be about 0.5 to 20 μm.

  When the fiber or the foamed sheet constituting the buffer layer 6 is made of a non-conductive material such as resin, the surface of the fiber or foamed sheet may be covered with a conductive material such as metal or conductive resin.

  As apparent from FIG. 1, the fuel cell gas must pass through each buffer layer 6 in order to reach the interface between each electrode 3, 4 and the polymer electrolyte 2 from the ventilation groove 7 a of each separator 7. Therefore, the buffer layer 6 is required to have excellent air permeability. If the resistance of the gas passing through the buffer layer 6 is large, it affects the large current output characteristics of the fuel cell. Therefore, it is preferable that the resistance of the buffer layer 6 is small with respect to the passage of gas. Therefore, the porosity of the buffer layer 6 is preferably 20 to 90%, more preferably 30 to 80%. When the porosity of the buffer layer 6 is less than 20%, not only the air permeability of the buffer layer 6 is insufficient, but also the flexibility (buffer property) that reduces the impact between the graphite current collector and the metal separator. ) Is also lacking. If the porosity of the buffer layer 6 is more than 90%, the mechanical strength of the buffer layer 6 is insufficient, and the buffer layer 6 becomes thin due to the pressing force when the cell units are stacked.

  Although the thickness of the buffer layer 6 varies depending on the porosity, it is generally preferably 0.01 to 1.0 mm, and more preferably 0.05 to 0.2 mm. When the thickness of the buffer layer 6 is less than 0.01 mm, the flexibility (buffer property) is insufficient. If the thickness of the buffer layer 6 exceeds 1.0 mm, not only the electric resistance value between the metal separator 7 and the graphite current collector 5 becomes too large, but the cell unit becomes too thick, and the fuel cell It becomes difficult to reduce the size of the stack.

  In order to further increase the conductivity of the buffer layer 6, Au, Pt, Pd, Ru, Rh, Ir, and the like are formed on the surface of the buffer layer 6 (at least on the side in contact with the separator 7) or on the surface of the conductive fiber constituting the buffer layer 6. It is preferable to coat at least one metal selected from the group consisting of Ag, Ti, Cu, Pb, Ni, Cr, Co and Fe, or an alloy thereof. Particularly preferred from the viewpoint of conductivity and corrosion resistance is at least one metal selected from the group consisting of Au, Pt, Ir, Ag, Pb and Co, or an alloy thereof.

  The thickness of the conductive film of the buffer layer 6 is preferably 0.05 to 10 μm. When the thickness of the conductive film is less than 0.05 μm, sufficient conductivity is not imparted. Moreover, even if the thickness of the conductive film exceeds 10 μm, the corresponding conductivity improvement effect cannot be obtained, and only the cost is increased. Note that the conductive film of the buffer layer 6 can be formed by sputtering, physical vapor deposition, plating, or the like.

  If the graphite current collector 5 and the buffer layer 6 are combined, the structure of the fuel cell unit is simplified and the electrical resistance of the current collector 5 can be reduced. In this case, the current collector 5 may have the above structure without providing the buffer layer 6 in addition to the current collector 5.

[2] Separator When the metallic separator 7 is formed of aluminum or an aluminum alloy, the conduction with the buffer layer 6 is good, and the output density / weight, mechanical strength, etc. of the fuel cell unit are improved.

  However, since aluminum or aluminum alloy is inferior in corrosion resistance, at least the surface of the separator 7 in contact with the buffer layer 6 is at least selected from the group consisting of Au, Pt, Ag, Pd, Ir, Ni and Cr. It is preferable to form a conductive film made of one kind of metal or an alloy thereof. In particular, it is preferable to form a conductive film from Au, Ag, Pt or an alloy thereof because excellent conductivity and corrosion resistance can be obtained.

  The thickness of the conductive film of the metallic separator 7 is preferably 0.01 to 20 μm in view of the manufacturing cost and the film functionality. If the film thickness of the conductive film is less than 0.01 μm, sufficient conductivity cannot be obtained. Further, even if the film thickness of the conductive film exceeds 20 μm, the conductivity improvement effect corresponding to the film cannot be obtained, and only the cost is increased. A more preferable thickness of the conductive film is 0.1 to 1.0 μm. The conductive film having such a film thickness can be formed by sputtering, physical vapor deposition, plating, or the like.

  The metal separator 7 having the above structure is not only lightweight, but also has excellent mechanical strength, conductivity, electrothermal property, and the like.

[3] Porous / conductive graphite current collector and other porous bodies When the cell unit is not provided with a buffer layer, a conductive buffer film may be formed on the graphite current collector and other porous bodies. is necessary. Similarly to the buffer layer, the conductive buffer film also reduces electrical resistance and prevents corrosion of the metal separator. The porous body is preferably (a) a porous / conductive graphite current collector, or (b) a resin fiber or a woven or non-woven fabric of natural fiber, or a porous resin sheet.

  (a) When the porous body is a graphite current collector, the current collector is preferably made of carbon fiber woven or non-woven fabric or carbon paper. Carbon fibers are preferred because they have electrical conductivity and corrosion resistance. Commercially available carbon fibers can be used as the carbon fibers. As the carbon paper, a paper produced by a papermaking-graphitization method or the like can be suitably used. According to an example of the papermaking-graphitization method, paper made of cellulose fibers using pulp waste liquid, polyvinyl alcohol, etc. as a binder, or commercially available cellulose-based captive paper with controlled pore size is baked at 1000-1800 ° C., carbon paper Can be obtained.

  (b) When the porous body is made of a woven or non-woven fabric of resin fibers or natural fibers, or a porous resin sheet, these porous body materials may be conductive or non-conductive. Since the conductive buffer film is formed on the porous body, the porous body can function as a porous / conductive current collector regardless of whether the material is conductive or not. Examples of the conductive resin include metal-dispersed polyolefin resin, polyester resin or fluorine resin, and carbon fiber. Examples of the nonconductive resin include nylon, polypropylene, and polyester resin. Specific examples of natural fibers include cellulose. The average diameter of these fibers may be about 0.5 to 20 μm.

  The porous body needs to have excellent air permeability so that the fuel cell gas can pass through the porous body. In particular, when the cell unit is not provided with a buffer layer, excellent flexibility is also required so as not to corrode the separator. Specifically, the porosity of the porous body is preferably 20 to 90%, more preferably 30 to 80%. The thickness of the porous body is preferably 0.01 to 1.0 mm, and more preferably 0.05 to 0.2 mm.

  The conductive buffer film is formed on at least a porous body in contact with the metal separator to such an extent that the porosity is not hindered, and is made of a corrosion-resistant metal, conductive resin, or conductive ceramic. When the conductive buffer film is made of metal, at least one metal selected from the group consisting of Au, Pt, Pd, Ru, Rh, Ir, Ag, Ti, Cu, Pb, Ni, Cr, Co, and Fe, or Those alloys are preferred. Particularly preferred from the viewpoint of conductivity and corrosion resistance is at least one metal selected from the group consisting of Au, Pt, Ir, Ag, Pb and Co, or an alloy thereof. Examples of the conductive resin that forms the conductive buffer film include a polyolefin resin, a polyester resin, or a fluorine resin in which a metal is dispersed. Specific examples of conductive ceramics include indium tin oxide (ITO).

  The thickness of the conductive buffer film is preferably 0.5 to 50 μm. When the thickness of the conductive buffer film is less than 0.5 μm, sufficient conductivity and corrosion resistance are not imparted. Moreover, even if the film thickness of the conductive buffer film exceeds 50 μm, the improvement effect of the conductivity and corrosion resistance corresponding to that cannot be obtained. As a method for forming the conductive buffer film, a sputtering method, a vacuum deposition method, an electroplating method or an electroless plating method is preferable.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Example 1
An aluminum plate having a thickness of 5 mm was pressed into the shape of a fuel cell separator. After etching and cleaning the surface of the obtained aluminum separator, a zinc replacement treatment, Ni electroless plating, and Au electroless plating were sequentially performed, and a 1 μm thick Ni film and a 0.4 μm thick Au film were formed on the separator surface. Were formed in order. As shown in FIG. 1, a pair of aluminum separators from outside, a pair of carbon layers for a buffer layer having a thickness of 0.2 mm and a porosity of about 80%, a pair of carbon papers for a current collector, and a Pt catalyst, respectively. A cell unit was constructed by assembling a polymer electrolyte membrane made of Nafion having a thickness of 170 μm, on which both the hydrogen electrode and the air electrode were formed, and fastening the separator with bolts.

  The output current of this fuel cell unit was measured under the conditions of a temperature of 60 ° C. and a voltage of 0.65 V. Next, after generating power for 100 hours, the output current at a voltage of 0.65 V was measured again. The results are shown in FIG. From the results of this example, it was found that there was almost no change in output current before and after power generation for 100 hours.

Example 2
An aluminum plate having a thickness of 5 mm was pressed into the shape of a fuel cell separator. After etching and cleaning the surface of the obtained aluminum separator, a zinc replacement treatment, Ni electroless plating, and Au electroless plating were sequentially performed, and a 1 μm thick Ni film and a 0.4 μm thick Au film were formed on the separator surface. Were formed in order. Further, a carbon cloth having a thickness of 0.2 mm and a porosity of about 80% was coated with Au to a thickness of about 0.1 μm by a sputtering method to obtain a current collector buffer material. A cell unit for a fuel cell was assembled in the same manner as in Example 1 except that this was mounted between the separator and the current collector as shown in FIG.

  The output current of this fuel cell unit was measured under the conditions of a temperature of 60 ° C. and a voltage of 0.65 V. Next, after generating power for 100 hours, the output current at a voltage of 0.65 V was measured again. The results are shown in FIG. From the results of this example, the change in the output current was very small before and after power generation for 100 hours, and the contact electrical resistance of the current collector / buffer layer and buffer layer / separator was reduced, compared to Example 1, It was found that the output current increased somewhat.

Example 3
In the same manner as in Example 1, a fuel cell separator was prepared using an aluminum plate having a thickness of 5 mm, and a Ni coating and an Au coating were formed on the separator surface. Further, a non-woven fabric (cotton-like sheet) made of stainless steel fibers having a thickness of about 0.2 mm and a porosity of about 70% is coated with Au having a thickness of about 0.05 μm by a sputtering method. did. As shown in FIG. 1, a fuel cell unit was assembled in the same manner as in Example 1 except that it was mounted between the separator and current collector of the fuel cell.

  The output current of this fuel cell unit was measured under the conditions of a temperature of 60 ° C. and a voltage of 0.65 V. Next, after generating power for 100 hours, the output current at a voltage of 0.65 V was measured again. The results are shown in FIG. From the results of this example, it was found that the current change was very small before and after power generation for 100 hours.

Comparative Example 1
In the same manner as in Example 1, a fuel cell separator was prepared using an aluminum plate having a thickness of 5 mm, and a Ni film and an Au film were formed on the surface of the separator. As shown in FIG. 3, this separator was directly brought into contact with carbon paper as a current collector for a hydrogen electrode and an air electrode to assemble a fuel cell unit.

  The output current of this fuel cell unit was measured under the conditions of a temperature of 60 ° C. and a voltage of 0.65 V. Next, after generating power for 100 hours, the output current at a voltage of 0.65 V was measured again. The results are shown in FIG. In this comparative example, the output current significantly decreased after 100 hours of power generation.

Example 4
A separator for a fuel cell was manufactured by pressing an aluminum plate having a thickness of 5 mm. The surface of the obtained aluminum separator that contacts the current collector is plated with a Ni film to a thickness of 5 μm, and an alloy film composed of 95% by weight of Ag and 5% by weight of Au is formed thereon with a thickness of about 2 μm. Plated. Further, carbon cloth having a thickness of about 0.15 mm was immersed in a PTFE solution and then treated at a temperature of 280 ° C. to impart water repellency. A cell unit for a fuel cell was assembled in the same manner as in Example 1 except that the carbon cloth treated in this way was used as a current collector buffer and mounted between the separator and the current collector of the fuel cell shown in FIG.

  The output current of this fuel cell unit was measured under the conditions of a temperature of 60 ° C. and a voltage of 0.65 V. Next, after generating power for 100 hours, the output current at a voltage of 0.65 V was measured again. The results are shown in FIG. From the results of this example, it was found that the change in the output current was very small before and after power generation for 100 hours, and that there was no influence due to the corrosion of the separator.

Comparative Example 2
Similarly to Example 4 , a fuel cell separator was produced using an aluminum plate having a thickness of 5 mm, and an Au film having a thickness of 1 μm was formed on the surface. As shown in FIG. 3, this separator was directly brought into contact with carbon paper, which is a current collector for the hydrogen electrode and air electrode of the fuel cell, to assemble a cell unit for the fuel cell.

  The output current of this fuel cell unit was measured under the conditions of a temperature of 60 ° C. and a voltage of 0.65 V. Next, after generating power for 100 hours, the output current at a voltage of 0.65 V was measured again. The results are shown in FIG. From the results of the present example, it was found that the output current significantly decreased before and after power generation for 100 hours.

Example 5
An aluminum plate having a thickness of 5 mm was pressed into the shape of a fuel cell separator. After etching and cleaning the surface of the obtained aluminum separator, a zinc replacement treatment, Ni electroless plating, and Au electroless plating were sequentially performed, and a 1 μm thick Ni film and a 0.4 μm thick Au film were formed on the separator surface. Were formed in order. Also, an Ag film having a thickness of 1 μm was formed as a conductive buffer film only on the surface in contact with the separator of the collector carbon paper having a thickness of 180 μm and a porosity of about 60% by sputtering. This current collector and separator were assembled in a cell unit of a fuel cell having the configuration shown in FIG.

  The output current of this fuel cell unit was measured under the conditions of a temperature of 60 ° C. and a voltage of 0.65 V. Next, after generating power for 100 hours, the output current at a voltage of 0.65 V was measured again. The results are shown in FIG. From the results of this example, it was found that the output current did not decrease before and after power generation for 100 hours.

Example 6
An aluminum plate having a thickness of 5 mm was pressed into the shape of a fuel cell separator. After etching and cleaning the surface of the obtained aluminum separator, a zinc replacement treatment, Ni electroless plating, and Au electroless plating were sequentially performed, and a 1 μm thick Ni film and a 0.4 μm thick Au film were formed on the separator surface. Were formed in order. Moreover, an Ag film having a thickness of 2 μm is formed as a conductive buffer film on both surfaces of nylon cloth having an average fiber diameter of about 5 μm, a thickness of 100 μm and a porosity of 50% by sputtering. A current collector was prepared. This current collector and separator were assembled in a cell unit of a fuel cell having the configuration shown in FIG.

  The output current of this fuel cell unit was measured under the conditions of a temperature of 60 ° C. and a voltage of 0.65 V. Next, after generating power for 100 hours, the output current at a voltage of 0.65 V was measured again. The results are shown in FIG. From the results of this example, it was found that the output current did not decrease before and after power generation for 100 hours.

It is a schematic sectional drawing which shows the layer structural example of the cell unit of the fuel cell by one Embodiment of this invention. It is a schematic sectional drawing which shows the layer structural example of the cell unit of the fuel cell by another embodiment of this invention. It is a schematic sectional drawing which shows the layer structural example of the cell unit of the conventional fuel cell. 6 is a graph comparing power generation performance before and after 100 hours of power generation in Examples 1 to 3 and Comparative Example 1. 6 is a graph comparing power generation performance before and after power generation for 100 hours in Example 4 and Comparative Example 2. It is a graph which compares the power generation performance before and behind power generation for 100 hours in Examples 5 and 6.

Explanation of symbols

1 ... cell unit 2 ... solid polymer electrolyte (polymer electrolyte membrane)
DESCRIPTION OF SYMBOLS 3 ... Cathode electrode 4 ... Anode electrode 5 ... Current collector 6 ... Buffer layer 7 ... Separator 8 ... Conductive buffer film

Claims (2)

(a) a polymer electrolyte membrane, (b) a pair of electrodes capable of gas diffusion fixed to both surfaces of the polymer electrolyte membrane, and (c) a gas diffusion capable of being fixed so as to contact the outside of the electrodes A pair of porous and conductive graphite current collectors, (d) a pair of metal separators that separately introduce fuel gas and oxygen-containing gas into the electrodes, and (e) the metal separator and the graphite current collector A cell unit of a polymer electrolyte fuel cell having a porous conductive buffer layer having flexibility and breathability placed between the body and the metal separator, at least a surface in contact with the buffer layer And a conductive film made of at least one metal selected from the group consisting of Au, Pt, Ag, Pd, Ir, Ni and Cr, or an alloy thereof. Type fuel cell unit. 2. The cell unit of a solid polymer electrolyte fuel cell according to claim 1, wherein the buffer layer is a woven fabric made of conductive fibers containing at least one of metal, carbon, and conductive resin, or metal and conductive resin. A cell unit of a solid polymer electrolyte fuel cell, comprising a non-woven fabric made of conductive fibers containing at least one of the above, or a foamed sheet having pores communicating to such an extent that it has air permeability.

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